General & Performance Related
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12/18/02 AILERON FLUTTER TESTING
01/02/03 AEROBATIC WEIGHT
08/28/02 FUSELAGE &WINGS: HP vs. PLANS
05/10/02 AEROBATIC RANKING
05/09/02 AILERON DESIGN
12/06/01 FAA REFERENCE MATERIAL FOR HOMEBUILDERS
12/05/01 TEST FLIGHTS IN PHASE 1
11/12/01 INSURANCE, TEST PERIOD
10/01/01 PILOT REPORT FROM JOHN ROSS - N80JR
06/29/01 CURTIS' ORIGINAL 3-VIEW, HISTORY
06/21/01 ROUND ENGINES IN SKYBOLTS, PITTS vs. SKYBOLT
06/10/01 FAA INSPECTIONS
04/21/01 360 HP vs. 400 HP, M14P vs. M14PF
04/14/01 PITTS vs. SKYBOLT,COMPARISON
03/26/01 PLANS, S1S,S1T, S1C, SUPER STINKER
02/26/01 AIRPLANES FLOWN SO FAR
02/24/01 HORSEPOWER
11/19/00 KIMBALL CHANGES, HISTORY
11/19/00 PITTS vs. CULP, COMPARISON, CULP, PERFORMANCE, STALL SPEED, COST
10/18/00 MAGAZINE ARTICLES
09/07/00 RUDDER SIZE,AEROBATIC CAPABILITIES
09/03/00 PITTS vs.SKYBOLT, COMPARISON, CULP
06/22/00 INSURANCE
04/27/00 SPORT AVIATION ARTICLE, HISTORY
01/10/03 PLANS vs. HP WINGS
Kevin, I plan on working on the wings components first. In reviewing the price
list, the wing wood kit is listed under the HP wing section. I would like to
clarify that this kit is interchangeable between the HP and the stock version.
Regards, Remi
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Remi, The HP wigs can be used on a stock fuselage. Same is true the other way
around. Attach points are the same. HP wing require HP struts, wires and
ailerons. Stock wings all the same in stock form. So, when considering one set
of wings or the other, keep in mind that these are wing "systems" and
have to use all the parts of the system. Both styles of wings can be installed
on either fuselage without adjustment. We have airplanes flying and being built
with various combinations of HP and stock parts.
If you want the HP wing wood kit yet want to make as much of the wing metal as
possible, you can do that. Much of the wing metal is the same as stock. There
are some parts that are different like drag wires, and pushrods but for the most
part, builders are able to figure these out with a bit of guidance from us.
We sell some wing metal parts to scratch builders. Items like cabane fittings
and top wing compression members are popular.
As I mentioned to you earlier, you can mix and match between purchased items and
scratch built items. We do not force you to make an all or nothing choice. As
you get into the project and find a component that seems tough to build, call
and get a price on it and see if the trade off of price to labor is worth it to
you.
We do offer some stock version specific items for those who are building stock
airframes. Items like spar blanks, engine mounts, fitting sets, flying wires,
etc are all available. In addition to these items, we offer the items that are
common to both versions such as gear, wheels and wheel pants, engine
installation components, cowling, etc. KK

12/18/02 AILERON FLUTTER TESTING
What is a safe way to perform flutter tests? Someone once told me to
"slap" the stick to the side during cruise flight, but what's the
difference between induced flutter and un-expected flutter? - Doug
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To perform flutter tests, start at the lower speeds and check all 3 axis.
Increase 5 mph at a time until you have checked to Vne + 5. The drill is to trim
the airplane for a lower speed, dive thru the check speed then release the
pitch. When the aircraft noses up thru the desired speed, excite the control to
be checked with a brisk input. The idea is that the airplane is moving towards a
slower speed which has already been checked. It is best to do this in smooth
air. Also, flutter is a function of True Airspeed, so it is more valid to
perform these tests at lower altitudes. Make sure you have a fresh packed 'chute
on and aren't afraid to use it. - Monty B
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Here's a scan from AC 23.629-1A. Flutter
Curves These are flutter curves for a control surface, and
should help you understand what you're trying to do (or avoid) when you flight
test for flutter. You hope your airplane behaves like curves (1) or (2). Curve
(3) would be scary, but would probably damp merely by taking a firm grip on the
stick. Curve (4) may require a parachute.
When you nose up thru the desired speed and excite the control to be checked,
allow the stick to be quite loose in your hand. Note curve (3). Let's suppose
the test speed is just past the zero crossing on the velocity line. With the
stick loose in your hand you'll feel it nibble, which is your warning that you
are reaching possible flutter speeds. If you hold the stick tight and thus damp
the surface at this just-barely-into-instablity speed, you may miss the warning.
So you preceed to the next faster speed (farther to the right on the velocity
line), and when it flutters it will be more violent.
Consider the mass damping effect of control linkages and your hands, and you can
see why slack (freeplay) in control linkages and trim surfaces is a Bad Thing.
The steep upslope of curve (4) is what makes it dangerous. No warning at a
slower speed, explosive flutter at the next higher speed. - Dan H

01/02/03 AEROBATIC WEIGHT
Sorry for all the confusion on the weight limits for the Pitts Model 12. Here is
the run down on how all these puzzle pieces fit together....
The airplane, both stock and HP have the same ultimate and limit G ratings. This
is the case even though the HP airplane is stronger than the stock version which
gives the HP wings, for example, greater margins of safety. The airplane was
designed at a gross weight of 2300lb. All ultimate and limit load calcs were
done at this 2300lb gross weight. Curtis lowered the published weight to 2250lb
for an added 50lb fudge factor knowing that many people will fly the airplane at
slightly over gross. This is where the 2250lb number comes from.
The ultimate G loads for the model 12 are +9, -7.5g at 2300lb(2250lb published).
The limit G loads for the model 12 are +6, -4.5g at 2300lb(2250lb published).
The acro G loads are the same as the limit loads at the same weight of
2300lb(2250 published).
So, this means the airplane is designed to break at +9 and -7.5g at 2300lb. The
airplane is designed to see unlimited number of cycles at +6 and -4.5g at 2300lb
without and structural over stress.
Mid America, the previous plans holders, placed the 1900lb figure into the mix.
This was intended to be noted as a typical acro weight not a max acro gross
weight. Typically, 1 person, fuel, smoke oil, chute etc will weigh in at about
1900lb. Typical for competition or airshow work. 1900lb is not a max acro gross.
You can fly the Pitts model 12 at full gross weight to +6, -4.5 g and not damage
the structure. This is the big leap this airplane has over others such as the
skybolt or S2B. Acro at full gross weight is not allowed. You must be under the
acro gross which in the case of these other aircraft presents the issues you
raised of not being able to have 2 people, chutes and gas and be legal.
It is interesting to note that you can place higher than +6, -4.5 gs on the
model 12 if you fly at weights of less than 2300lb(2250 published) without
hurting the airframe. However, these higher loads are not listed as it may
encourage pilots to fly at high Gs while at standard G weights.
The model 12 was designed and flight tested to fly as advertised at the weights
above by Curtis Pitts. A skybolt, on the other hand, was originally designed by
a high school shop teacher for a max gross of 1650lb and an empty weight of
around 850-900lb. It soon was bumped up 1800lb gross and then again to 2000lb
gross while maintaining the same non structure. Most 540 skybolts weigh over
1300lb and some as much as 1550lb leaving very little room for people and gas at
gross weight. Even if you use the 2000lb currently spec'd gross, the acro gross
is still 1650lb as before resulting in 100lb acro useful for many skybolts out
there. How do guys fly them if this is the case? Simple. Over gross. A 540 lyc
and constant speed prop on a skybolt is like hanging an R985 450hp PW and
Hamilton standard prop on a model 12. Too heavy for the airplane.
I hope all of this has eased your concerns on the weights and loads for the
Pitts Model 12. When I ran my computer analysis of the structure, I found that
the fuselage was a +/-10g structure. The wings were just a tick better than +9
and -7.5.
When I designed the HP wings, I increased strength in them in the areas of
designed failure at ultimate loads. This increased the max load capacity of the
wings to more closely match the fuselage and tail. The HP wings are +9.8, -8.7
wings at 2300lb. KK

08/28/02 FUSELAGE & WINGS: HP vs. PLANS
What are the differences between the Kimball HP fuselage & wings versus the
plans versions, and how did the changes evolve?
----------
First, let's clear up what it takes to be able to make the changes I will be
discussing here. If you are an engineer with design experience in
Tube/Wood/Fabric structures, you are qualified to develop and make the type
changes we are discussing here. If you do not have these qualifications, you are
shooting from the hip without proper knowledge and that can be dangerous. This
is why most airplane plans state in them or the related agreements that builders
are to follow the plans precisely or use the approved components available for
purchase. It keeps the builder from making tragic errors. So, in the case of the
model 12, Dad and I were qualified to make the engineering changes in the
airplane and went back to Curtis Pitts to have him double check what we did.
Pretty safe.
What brought on the changes? In 1995. Curtis gave Dad and I a 3-view of the
Model 12. This was before the first part was made and all the design work was
not yet completed. At that point, the 3-view was of a short nosed
"Cocky" looking biplane and we loved it. As a matter of fact, that
original 3-view had the airplane shorter than what we now produce as the HP
version. Anyway, we got a picture in our head of what the airplane would look
like. In the end, the engine mount had to be quite a bit longer than Curtis had
thought in order to get the CG correct. Not that this was a major error on his
part, but as the final drawings were being done, he stretched the fuselage,
rearranged a few things etc and knew the mount would be longer than the original
3-view. The result was a fine looking, very strong, great flying airplane that
all plans holders can build with the data as it is printed. But, for Dad and I,
it was NOT the look we had in our heads. This lead us to determine how to get
the look the way we wanted and make some creature comfort changes along the way.
The result is the HP version of the fuselage and engine mount.
Now the wings are a different story. Ben Morphew test flew the model 12 in acro
test for Curtis. He loved the airplane and wanted one RIGHT THEN. We did not
know him at the time but later Ben told me that he would have bought the
prototype from Curtis if it rolled faster. So, Ben decided to build a model 12
but wanted better wings and ailerons. I designed them to meet his requirements
and also be stronger and lighter. Again, I had Curtis as a mentor during this
process. The resulting model 12, N69BM, was built by Ben and had the first set
of HP wings. It was the first customer 12 to fly and 2nd overall. The wings
worked perfectly so, we kitted them. Ben's fuselage was built to full long plans
length, engine mount too. Take a look at the photos of the 2 model 12 together
in Budd Davisson's EAA
article. It is hard to see the difference isn't it?
As for performance between the 2 versions, yes, the HP wings roll faster and
work better in hover type figures. Yes, the larger rudder is better in acro than
the plans rudder. But, the fuselage/engine mount changes result in such small
differences in how the airplane works, that it would take an acro pilot with
lots of time in one version to sense the difference when flying the other
assuming the wings were the same on both versions. N69BM and N360KJ were flown
together quite a bit by two of the world's best pitts drivers, Ben Morphew and
Steve Wolf. Both will tell you that the fuse length change does not affect how
the airplane flies. I take that as a compliment to me, it means I didn't screw
it up!
Now, I agree it ain't rocket science here and that the stuff we did is not
special or really tough to do. But, the simple things can add up to bigger
problems down the road. Most do-it-yourselfers or first timers do not see the
big picture in a project like this. A change to the fuselage in one plane may
seem simple enough and not a big deal either way. But, later you find out that a
control component will not work or the specified bearing won't work now because
the rod runs into something else. Maybe, you can't get full aileron deflection
because the pushrod binds up. These are the little things that can become HUGE
whe you shoot from the hip.
There are 2 or 3 model 12 builders out there creating their own version of the
short fuselage. In the case of Darin's
changes, he asked me what we did. I told him it was about 5" in the
fuselage and about 5" in the engine mount for a total of about 10"
shorter fuselage/mount. He created his fuselage layout on his own but I gave him
a few hints of what not to do. Darin's fuselage is not the same as the HP frame
we sell and obviously not the same as on the model 12 plans. I don't think he
had an analysis done on the fuselage to see if the changes he made resulted in
satisfactory load paths but chances are the paths are OK. When we did our
changes, we not only changed the length of the fuselage but rearranged some of
the controls, changed some tubing sizes etc to create a complete engineered
package. This is what we sell.
So what do we recommend to builders? Simple. If you are gonna scratch build,
follow the plans as they are drawn. Buy our fitting package for the fuse and
tail which will allow you to make a either a small tailed, rounded version of
the long fuselage or a lean looking version with the big tail as Ben's was. It
gets you the lean look without the guess work. If you want to buy parts, you
will get the HP version as we do not kit the plans version.
Up until now, we have not given out specific dimensions for the HP version parts
other than a weight and balance diagram for both versions of the model 12. We
have a few reasons why we hold the HP data to ourselves and why we freely sell
the stock version of the plans. When we entered into the model 12 biz, we had no
intention to sell plans. Curtis told us NOT to do it as the never ending phone
calls would drive us crazy with questions like, "can I use these bass boat
seats" or " I've got a set of luscombe tail feathers I want to
use", etc. He said the backyard "in-guh-nears" can really make a
mess of things. So, we went the route of developing tooling and prefab parts.
At that time, we did not own the rights to the model 12. Mid America Aircraft
did. They decided to sell plans and maybe supplement that later with parts
sales. They looked at several sources for parts manufacture in the US and abroad
but never really got that going. We made a deal with them to sell parts only to
those who had a serial number and plans from them. This way, they sold plans, we
sold parts, the desired activity for both parties. Later, the priciples of Mid
America decided to sell the rights to the design and plans. We bought it from
them. We thought about what to do with the plans sales and after considering
halting the sale of plans, decided to continue selling the Mid Am plans as they
had already sold around 100 sets. The plans "horse" was already out of
the stable so why not continue selling them. After all, even scratch builders
have to buy some parts like gear, wires, canopy etc. We did not want to have 2
sets of data out there for builders to confuse, mix and match. We also wanted to
protect the investment we had in both time and money developing the HP versions
of the model 12. So, we opted not to distribute plans for the HP version which
would minimize the danger of someone mixing and matching the wrong parts. Heck,
we made all our tooling so we could build both version of the model 12, stock
and HP but have yet to sell a stock fuselage as those who decided to buy a
fuselage wanted the HP version anyway. We have built stock tail parts, stock
engine mounts etc and sold those to plans builders.
To sum it up, we know there are scratch builders who will copy the HP parts,
even directly by copying some from a kit buyer. That is to be expected in this
biz. Heck there are those who would rather copy a set of plans from another
person instead of spending $300 for a lifetime of support. Silly really. Just
keep in mind that YOU need to know what you are doing if you choose to change a
design not simply THINK you know. If developing a sound design were easy, the
email groups we take part in would all have 1 member........... the designer/biulder/owner/pilot
of one of the ump-teen jillion airplanes that would be out there. I know I have
spent a lot of time here on this but I felt it was needed to make sure we are
all on the same page. Enjoy building, have fun, make the airplane in your style
and flair but don't make changes for change sake without proper backup. Smile,
build something everyday and always fly safe. KK

05/10/02 AEROBATIC RANKING
If considering aerobatic competition with the Model 12, up to what class would
it be effective?
----------
We tried to get the Model 12 accepted as AWAC legal. AWAC is the Advanced World
Aerobatic Championships. So, when evaluated by the numbers, the model 12 came
out too good for AWAC legal. It ranked as WAC legal. This was determined in 1999
I have the full reports with each of the approximate dozen points that were
compared to the other designs. The HP/weight ratio, thrust to weight ratio, Vne
speed, etc. etc.
Obviously, the Model 12 is not on par with a Sukhoi or Edge 540. But, it is
capable of far more than some of the other sport bipes in the same size class.
Keep in mind that there is world class unlimited flying and there is local IAC
unlimited flying. I have seen S2As and other smaller or older designs compete in
Unlimited. You can complete in whatever you want but that doesn't mean you are
competitive. The model 12 is capable of competing and winning locally in
unlimited but would not be truly competitive with world class pilots in world
class monoplanes. The model 12 is capable of winning in Advanced yet it is too
powerful for world level advanced competition at this time. Its Rock >>
<< Hardplace. KK

05/09/02 AILERON DESIGN
Guys, Beware this got long!! I have seen the posts on the subject of the
"SS" ailerons. I would like to take this chance to clear up a few
details on this subject.
First, the name. These are not actually called "SS" ailerons. That
name had come from the Late Hale Wallace and his version of these ailerons for
the S1 wing mods he came up with a few years ago. Hale got the rights to the S1C
Pitts from Curtis and this may have been a trade for wires or something. I don't
know really. But, Hale and now the new guys, have the S1C design rights only.
Not all of the S1 versions as it was hinted in one of your posts. The S1S and
S1T are still held by the pitts factory, now Aviat Aircraft or its holding
company. Hale come up with the SS title to indicate Super Stinker style ailerons
and not use a single "S" like the Aviat owned design. He put together
a set of drawings for symetrical airfoil wings with the new style ailerons and
offered these as an update to the "C" model plans he had for sale. I
think he went on to stretch the fuse of the "C" to meet that of the
"S" and "T" versions. Not sure on that one though. Oh yeah,
back to the name thing............These ailerons are actually,
"Aerodynamically Boosted Ailerons". The first design Curtis used them
on was the Super Stinker model 11-260. The second design was the Model 12. The
3rd design Curtis used these ailerons on was the new S2C wings for Aviat. I have
have used them on 7 designs so far. The redesign of the model 12 wings and
ailerons, Steve Wolf's WolfHawk wings, a super cub like bush plane for a friend,
Frank Ryder's Cyclone, Sean Tucker's Challenger, Jim LeRoy's Bulldog, and The Mc
Cullocoupe. I will use them on other designs as well. As a point of interest in
the time line, I designed the alum ailerons for the model 12. Following that,
Curtis did the same for the S2C.
Curtis has often done contract design work for others. Doing the design of the
ailerons for Aviat, Steen or whoever is no big deal. I too have done work for
others in the same industry. It only makes sense to go to the best source for
the technology vs. hacking your way through it on your own. When I do design or
engineering work for others, a full endorsement of their products is not
automatic. I can like what I do for them without liking the entire project. I am
sure this is true for some of you and most likely Curtis as well.
I think Randy brought up the old style Fat ailerons from the mid 80's. This
design is NOT the same as the ailerons being discussed here. That FAT ailerons
were over thickness by 16% at the hinge line, had thick trailing edges and had
extra chord length aded to increase total aileron area. This design did improve
the roll rate of the airplane but, all the features had to be used as well as
good size spades to reduce forces to the point that the pilot liked them. Yes,
the over thickness was there to keep the air attached. That was the first step
in Symetrical aileron, or round nose aileron design and is exactly what is on
the S2B, Husky etc. Over think and round nose. The wing cove is constant gap to
the nose of the aileron. When this was first done to the S1S moving away from
the freise style ailerons, the stick forces were so high that at speed, the
airplane was not fun to fly (I get this info directly from Curtis and others who
were in the know at the time). So, the spades were added copying what the Chechs
had done on the 526 Zlins for aileron boost(yes spades were someone elses idea).
Ben Morphew, a good friend of mine was the person who pointed Herb Anderson of
the pitts factory toward the spade idea. So, stick force problem fixed but the
ailerons lost center feel which is important for precise acro. This is where the
fat trailing edges came into the game. These added some center feel by keeping
the 'bleed' from the bottom high pressure side of the wing up and around the
trailing edge making the center position of the aileron feel mushy. The added
length to the chord simply adds affective area.
Now, back the the aerodynamically boosted aileron as used in the super stinker
and model 12, as well as others. This is a system not just an aileron that can
be bolted to a given wing as a replacement part. There is a set of formulas to
define the thickness, leading edge radius, leading edge camber, hinge location
all as a function of the chord length of the aileron and the thickness of the
wing airfoil at the chordwise point where the aileron hinges. The upper ailerons
are different than the lowers. Another huge key point is the cove shape in the
aileron bay. The cove is the area where the aileron fits in the wing and there
are critical gaps required between the cove and the leading edge of the aileron.
One gap and full deflection. Another at neutral. There is a required radius of
curvature of the cove as well as radius of the edges of the cove where it meets
the upper and lower wing airfoil surfaces. This is only the requirements. Not
the design. With all this in mind, the structure has to be designed to meet all
these factors and be strong enough for the required flight loads. My point in
writing all this is that the new style ailerons cannot be hap-hazzardly
installed in a given wing structure. Rather, the wing structure must be designed
to accept the ailerons.
Do I have all the data and formulas to design such aileron systems? Yep. Can I
use it on whatever I want? Yep. Can I give it out to everyone who wants it?
Nope. Curtis asked me not to. He can but I won't.
This style of aileron with its deep hinge line, airfoil shape, etc is not new.
It is on the tail feathers of most jets, on other acro airplanes like sukhois,
extras, cap's etc. The big difference is the cove. The cove is the key to what
makes Curtis' version work the way it does. I hope you guys have enjoyed this
little Aileron 101 course. KK

12/06/01 FAA REFERENCE MATERIAL FOR HOMEBUILDERS
See http://av-info.faa.gov/dst/amateur/
AC20-27E, Certification and Operation of Amateur-Built Aircraft, This AC
provides information and guidance in the building, certification and operation
of amateur-built aircraft.
AC20-139, Commercial Assistance During Construction of Amateur-Built Aircraft,
Explains FAA regulations and policy regarding commercial assistance during the
fabrication and assembly of amateur-built aircraft.
AC21-12B Application for U.S. Airworthiness Certificate, Form 8130-6 (11/2001)
word version
AC90-89A, Amateur-Built Aircraft & Ultralight Flight Testing Handbook , This
AC sets forth suggestions and safety related recommendations to assist amateur
and ultralight builders in developing individualized aircraft flight test plans.
AC65-23A, Certification of Repairpersons (Experimental Aircraft Builders), This
AC provides guidance to builders of amateur-built aircraft concerning their
certification as repairmen.
AC39-7C, Airworthiness Directives, This AC provides guidance and information to
owners and operators of aircraft concerning their responsibility for complying
with airworthiness directives (AD) and recording AD compliance in the
appropriate maintenance records.
AC103-7 The Ultralight Vehicle, This advisory circular provides guidance to the
operators of ultralights in the United States. It discusses the elements which
make up the definition of ultralight vehicles for the purposes of operating
under Federal Aviation Regulation (14 CFR part 103). It also discusses when an
ultralight must be operated as an aircraft under the regulations applicable to
certificated aircraft.
FAA Order 8130.2D Airworthiness Certification of Aircraft and Related Products
dated 9/30/99 (with Change 1 incorporated 2/15/00 and Change 2 incorporated
12/18/00) establishes procedures for accomplishing original and recurrent
airworthiness certification of aircraft and related products, including
amateur-built aircraft. The procedures contained in this order apply to both
Aircraft Certification Manufacturing and Flight Standards Airworthiness Aviation
Safety Inspectors, and to private persons/organizations delegated authority to
issue airworthiness certificates and related approvals. Chapter 4, Section 1
provides general guidance material associated with special airworthiness
certification. Chapter 4, Section 7 provides specific information for special
airworthiness certification of experimental amateur-built aircraft.
Forms: AC Form 8050-88 (PDF) Affidavit of Ownership FAA Form 8130-12 (MS Word)
Eligibility Statement: Amateur-Built Aircraft FAA Form 8130-12 (PDF) Eligibility
Statement: Amateur-Built Aircraft FAA Form 8130-6 (PDF) Application for
Airworthiness Certificate or, electronically completeable word version

12/05/01 TEST FLIGHTS IN PHASE 1
A recent email exchange with a model 12 pilot flying off his 40hr test period
prompted me to remind you guys of some of the requirements. With acro airplanes
in the US (Canada different & rest of world too I am sure), you have to
perform all acro figures during phase I (test period) that you want the airplane
to be legal to do in Phase II (all flying after test period). So, do all the
acro figures you can and list them in the log book after each flight. List the
figures once along with entry speeds, etc. If you do a loop, list it but don't
list it again if you loop in a later flight. Only the acro you do in phase I is
legal to do it phase II. If you (or a test pilot) don't do everything, you will
have to go into a new test period to add the acro to you list of approved
maneuvers.
Before you sign the airplane into Phase II, you should list all the figures that
your actual airplane has flown (not what you know others have done in theirs).
For example: take off and landings, xwind TO and landings and wind speeds
demonstrated, stalls, loop in and out, roll slow, barrel, point, vertical, snaps
L&R pos and neg, spins upright and inverted L&R, knife edge, inverted
flight, tumbles (Lumcevak), rolling turns if you do them, hammer heads, stall
turns, cuban 8, lazy 8, tailslides, torque rolls, immelmann(sp?) etc etc. List
everything.
I have heard that entry speeds are now required to be listed too. It is a good
idea anyway as the next guy to fly your plane will know what to do and not do in
the thing.
While we are on the subject of logbooks, it is a good idea to list some of the
following items in the airframe book: fabric system used, # coats etc, paint
used, brand, color code etc. primer type varnish type etc. It sure saves some
headaches later............
And don't forget that if you use an aircraft part that has an AD on it, you need
to comply with the AD even if your airplane is exp homebuilt. That is, ADs on
engines, mags, props, radios, lights, wheels, whatever. If you have an
experimental engine that is based on a lyc (modified lyc), you sill have to deal
with any lyc ADs on the lyc parts that are in it. It only makes sense. If there
is an AD on a type of mag because it is unsafe, the AD should be complied with
no matter what airplane it is bolted to so the airplane is safe. Of course, if
you have an exp engine (auto, m14petc), exp prop (Whirlwind, exp wood ones etc),
you don't have ADs on them. But, you have 40hr test instead of 25hr.KK

11/12/01 INSURANCE, TEST PERIOD
Bill, Insurance costs vary with the hull value you pick for the airplane and
with the agency you use. As an average, lets say $170k for hull value. You are
looking at about $4k per year for insurance. If liability only, you are looking
at about $300-$500. If you add open pilot, acro competition, or airshow coverage
to the hull costs you can add another 10-10% for each of these.
Some insurance companies will not offer hull coverage until 10hrs are flown off
unless the airplane is flown by an EAA flight Advisor who is qualified in that
airplane. The trick with one-off airplanes like some of them in this group, how
do you find a person with experience in that type of airplane? Any pilot can
become a flight advisor if he/she is an EAA member and can fill out a form.
Likewise a tech Councsellor, just fill out a form and fax it to EAA and you are
one. I had always thought there was more to it but when we finished N80JR,
AVEMCO required an EAA flight Advisor do the first 10hrs, so, Dad and Steve Wolf
filled out a form off the internet, faxed it in and in a matter of hrs, were
flight advisors!!!
A model 12 built by an ameteur is required to have a 40hr test period. This is
true for any homebuilt that is in Am Built catagory if either the engine, prop
or both are experimental!!! So, ALL airplanes in the US that are Amateur built
with an M14P or other variation of it, will have 40hr test periods!!! I have
heard that some builders have gotten away with a 25hr period but this was due to
the DAR making a mistake. There is NO room for interpretation of this
requirement. 40 hrs is the law if a non certified engine or prop is used.
Not in the case of Experimental Exhibition catagory, the test period is at the
discretion of the FAA (DAR can't do it) Inspector who can set the test period
from zero to infinite # of hrs depending on what he sees and feels.
KK

10/01/01 PILOT REPORT FROM JOHN ROSS - N80JR
I'm stuck in enhanced class B, and can only fly with a CFI. With more time on my
hands, I took a bunch of pictures of my Pitts 12 yesterday in the sunny weather,
and now I'm posting a report on it, for those of you who might be considering
building or buying one...
If you were at OSH 2001 you may have seen N80JR; it was the purple and black
round-engined bipe by the registration shack in the IAC area. It got a lot of
positive comments from various people, both knowledgeable builders and
unfamiliar tourists alike. Steve Wolf and I flew it there from Florida and we
had a great time with it.
The plane is in the "Exhibition" category as it was built 100% by the
Kimballs, who are well known for their restoration work. They sell complete sets
of component parts for the Model 12, such as finished fuselages, wings, rib
kits, cowlings, gear, etc. They will also sell plans alone for the person who
likes to do all the work himself.
Some history on how I ended up with this plane:
In 1979 I built a Quickie, and that experience convinced me that although I like
building things, I did not ever want to tackle a 4000 hour project, particularly
not one that involved so many different skills, where a shortage of one talent
could poison the whole project.
For 25 years I have wanted a Pitts, but a) they were a bit small and b) they had
flat engines. Then in 1985 I saw Steve Wolf's SAMSON re-creation in Sport
Aviation. *This* was what I wanted, a Pitts with a Great Big Round Engine! I
(incorrectly) assumed that having such a plane constructed would be many times
the cost of a new S2, so I did nothing more than daydream about it.
Fast forward 10 years, and I see Curtis has designed a new Pitts around the
Russian M14P. Looks great, but I'm not going to build it myself.
Then, a year or so later, I see that the Kimballs have negotiated to sell plans
and subassemblies. Further, the design has been refined (by the Kimballs and
Curtis working together) for more roll rate, a better canopy system, and other
improvements. People are building them all over. It is beginning to look more
and more like a round-engined Pitts might be in my future. I call Steve Wolf
(flying the Kimballs' demo bird in airshows) to ask about how it flies. He tells
me it is very close to Samson, and definitely better in roll rate and inverted
flight. He says maybe he could build one for me, but to call Jim Kimball first
and check his schedule.
I do and am quoted an 18 month delivery date for a turnkey 12, at a price a bit
less than a new S2 from Aviat.
This is what I want to hear. I ask Jim how much a smoke system would add to the
cost. "Oh, that's standard." I go test-fly the demo plane (purple and
yellow, now owned by Keith Campbell in Atlanta) and it is the best airplane I
have ever flown. I go ahead with the order.
My plane is finished in July, on time and at the price quoted. It is gorgeous.
My own contribution to its construction is limited to helping lay out the panel
and designing the paint scheme. Steve Wolf spends 2 days doing the 10-hour
fly-off and flight test regime, and the next day we take off for Oshkosh.
Since then, I've put about 40 hours on it. Here are my impressions:
It is a real delight to have an airplane that does exactly what you tell it to
do. In order to wring the last few percent "performance" from the
unlimited-class monoplanes, designers have made these craft behave in ways I
would not tolerate; i.e. let go of the stick and push left rudder in level
flight and the nose drops and the plane rolls RIGHT. Pull the stick back and
then you have to start pushing because if you let go the elevator will go to
full deflection. There is none of this in the Pitts. Controls are light, but you
don't have to unlearn normal flying techniques, just refine your smoothness.
With that whacking big Russian radial hooked to the the 3-blade MTV, thrust is
magnificent. I'm not proud; I decided immediately I was always going to go
around if I didn't like how I had set up my landing. This plane is the king of
the go-arounds. Flare a little high and realize it's dropping in from 4 feet?
Full throttle and it stops 3 1/2 feet off the runway and starts climbing like a
rocket. There may be other planes that do this equally well but I have never
been in one.
Aileron design (now also used on the Super Stinker) is boosted, and adverse yaw
is almost undetectable. The elevator is boosted just enough that forces are
always modest. The rudder, according to some aeronatical engineers, is much too
big. "Yeah, but my planes all come out of spins right away," Curtis
has been quoted as saying. He's not kidding. Using the Beggs emergency recovery
technique, the spin seems to stop the instant that opposite rudder comes in.
Knife-edge flight is wonderful (much better IMO than a monoplane), and the Model
12 will climb over 1000 FPM at full gross in this attitude(!)
From 240 mph, you get a half-mile of vertical and seven vertical rolls, for
those of you who like going straight up.
Cruise 175 mph at 8500 feet and 14.2 gph.
Perhaps the benefit I like best about this plane cannot be quantified, and that
is the peace of mind I get flying behind a zero-time (REALLY zero-time) radial.
The crankshaft on a 540 Lyc is as long as my arm, while the one on The M14P is
as long as...something a lot shorter. Engines with long cranks don't like hard
acro, esp. tumbling maneuvers. I don't think a lifetime of aerobatics (by me) is
going to shorten the TBO of this engine. I would not say the same of a flat
motor.
Other construction benefits are Wolf plywood leading edges instead of aluminum
(stronger with smoother fabric adhesion) and cantilever ribs instead of plywood
as on the new Aviat S2C. (Will there be a wing rib AD on the S2C a few years
hence? Remember what the factory always said about Sparcraft...?)
Last of all, the way it looks! An S2 looks downright homely next to Samson or
the M12.
Things I'd change? MAYBE two: Having landed tailwheel-first on a number of
occasions, I can't help but wonder what would happen if the tailwheel were
6"-8" higher. Drag on rollout would be greater, requiring less
braking. The other is that 99% of my flying is at positive Gs. I'm 44 years old,
and Curtis admits he designed the Model 12 as an "old man's airplane."
This old man thinks he MIGHT prefer the conventional wing used on Samson (forget
the number, same airfoil as a Bonanza IIRC). Better low speed characteristics
and even more climb right side up. Wouldn't have the bragging rights, but...
Don't know if anyone else would choose a flatwing 12, but Steve Wolf wants to
build anotherSamson, and he intends to make it with 4 ailerons but the same
conventional wing as the original. That got me thinking. I'd have to fly both
and see.
If you're considering ANY 2-place conventional biplane, take a long look at this
one. You'll be getting the absolute best biplane technology in existence, and
the finished product will probably bring three times the amount on the used
market that an equally hard and expensive to build Skybolt or Starduster would
fetch.
No, the Kimballs don't pay me. On time, on budget, and flawless workmanship
deserve a testimonial. John Ross

06/29/01 CURTIS' ORIGINAL 3-VIEW, HISTORY
Regarding the original 3-view I have for the Model 12 as Curtis first conceived
it. This 3 view is what his first thoughts of an M14P powered Pitts biplane
were. It has been a while since I looked at it so I pulled it out and found some
interesting stuff there. Interestingly, one copy I have of it was given to Dad
and I in 1996 at SNF when we had the Gee Bee there. We had Curtis sign it then
as a keepsake. This was a year or more before Dad and I ever gave a thought to
building an M14P powered biplane. Interesting facts:
Length: 19ft 3in
Height: 7ft 8in
Span Upper: 23ft
Span Lower: 22ft 3in
Total Area: 152.8sq ft
Wing Loading: 13.08 PSF
Gross Weight: 2000lb
Datum: 50 in. aft of firewall
CG Range: 65.624 to 71.712
The wings and tail look pretty much exactly as they do on the stock plans
version of the model 12. The fuse is short and maybe even shorter than what we
build as the HP short fuse. The engine mount is shorter than can possibly be
built, approximately 10" long. The next itteration of sizing thew airplane
resulted in a 164" long fuse and a 14" mount. The final version was
169" long fuse and 23.75" mount.
Another feature I see here is that the fin is offset like the super stinker
instead of the engine mount having offset thrust in it. The SS has a straight
engine mount and offset fin to fix the torque. When the model 12 was fully drawn
and designed, the fin was changed to straight ahead and the engine mount was
changed to have 2 deg left side thrust, zero down. This works perfectly and is
not ugly as heck like the fin to turtle deck joint on the super stinker. The
WACO we put the M14P on has a straight mount and straight fin. It takes all the
rudder that big WACO has to keep the airplane straight on takeoff just like a
Nanchang yak does. The Model 12 with its 2 deg offset takes less left rudder on
takeoff than an S2B takes right rudder on takeoff. It works perfectly. Curtis
hit it just right. I suggest you M14P powered airplane builders use 2 deg offset
left on your mounts.
I'll try to get a digital pic of this 3 view and post it for you to see. It is
kinda cool to look at.
This 3-view shows a very short nose and represents the mental picutre Dad and I
had for what the model 12 would look like. Then it grew the longer nose for
reasons of both equipment location and CG. That's why Dad and I felt the stock
airplane had a nose that was too long. We expected this nose. That led us to
rework the fuse to get the look we wanted.
The final interesting fact is when this 3-view was drawn by Curtis. It was done
on 1-5-1993. That's 8.5yrs ago! Goes to show you that it takes a long time to
get from idea to airplane if you take all the required steps to get there (first
flew in 1996, a little over 3 yrs after this 3-view). KK

06/21/01 ROUND ENGINES IN SKYBOLTS, PITTS vs. SKYBOLT
Jim, I remember the white homebuilt with the R670 but I thought that it
was a Starduster Two. The engine weighs 465 lbs dry without a
startor or alternator and that is 100 lbs heavier than an IO 540 and you
still have the weight of the oil tank, startor, alternator and that big propto
add. It makes the engine package 200 lbs heavier and that is hard to
make up. You might have noticed that he mounted the engine as far forward
as he could and he still had to add a lot of lead to the tail. That
what makes me think that you fellows that are putting the M-14 in your Skybolts
are going to be disappointed unless you make many modifications to the
airframe. Power is only one element of a good performing ship.
Wing loading and some other things are there too. Believe me I am not
trying to be a wet blanket. It is just my opinion as an almost fifty year
pilot who has flown about everything from a Midget Mustang to a DC-3. When
we started our Skybolt we gave a lot of thought to a radial engine and the M-14
was one that we considered. We talked to a lot of people, including
the fellow with the R670, and in the end decided that radials were either too
heavy, not enough power or both. If I could have found a 185 hp
Warner I might have gone with that. It is a quite light engine.
(about 335lbs but you still need to add all those goodies. I am
officially off my soapbox. Keenflyer
-----------------------
The white one was a Skybolt but it did not have the craftsmanship of the red
one. Somewhere I might have a picture of it. C.G. is definitely a
concern and maximum wing loading is mostly a function of gross weight (partly of
distribution as well). I'm analyzing the airframe for a 2000 pound gross
weight. The wing cellule looks marginal. So far I have a 3%
margin of safety on the aft wire for a 9g ultimate low angle of
attack condition. I've not finished looking at the rest of the wing
structure. You're right about major structural modifications to employ an
M-14. As far as CG goes I've moved the pilots aft quite a ways - same
relative position as that of Kevin's version of the M-12. Here's my
reasoning. There's not much difference between the Skybolt and the Model
12 from an aerodynamic perspective - same airfoils, gap, stagger, and tail
volumes are close and they have very nearly the same wing area (151 sf for
M-12, 159 sf for 'Bolt). The wings of the Skybolt are of comparable
weight, therefore if a Skybolt wing cellule is mounted on a fuselage configured
like a M-12 such that it's aerodynamic center is in the same position as that of
the M-12 wing cellule the CG should work out and performance should be basically
the same. My airplane is neither a Skybolt nor a M-12. My fuselage
is structurally based on the M-12 and the tail is my own design. There are
structural concerns of course but I'm comfortable addressing them. The
'Bolt wing will never carry the 2300 pound gross weight capability of the
M-12. That's okay. I will simply determine a safe acro
gross weight and a safe standard category gross weight. I can't see myself
wanting to tear up the sky at full gross weight. Again, what you say is
true, bolting an M-14p to a stock Skybolt airframe without careful modification
and consideration is borrowing trouble. Compromises abound: less useful
load, higher landing speed (for increased gross weight), poor visibility, higher
operating cost, longer build time (oh man!), untested nature of modifications,
etc.
If I did it again, I would build a M-12 with round surfaces. It's stronger,
it's well thought out, and it's made for my engine. In fact, I would
highly recommend the M-12 to anybody interested in a round engined
biplane. From a sportplane standpoint, mods are best kept
to aesthetics.
Warner...yeah we considered both a 185 and a 165. Two problems with this:
marginal power for a Skybolt and availability of parts. I discussed this
with Hale at Bartlesville about 5 years ago and he begged us not to mount
Warners in the Skybolt. In fact, he had photos of Culp's airplane and he
suggested a similar approach - but only if we could live with it's limitations.
He still thought the fixed pitch 260 hp Skybolt was the best biplane you
could build. Jim Doyle Stress Analyst
---------------------------
Gentlemen, Jim's comments are well said.
I've been bugging you guys for accurate weights, examining different plans sets,
and digging for Russian engine info. I've been asked why I'm going with a
Skybolt, and I haven't said much. I guess it's time to spill what I've
been cooking. Comments are welcome. Please.
Some of you are aware of previous attempts at creating a lighter, direct drive
version of the M14 series engine. The M14P is well known, but there are
several other variants. The common ones seem to be the M14B, which was
used on a transport, and the M14V-26, which was used (in pairs) in a helicopter.
The best know previous attempts at direct drive involve taking the nose case
from an M-3 (a direct drive 3-cyl radial of 110 hp) and bolting it to an M14 or
Huosai core. This was the original basis of the Culp/Bloomquist Sopwith
engine package. Same main engine case bolt pattern, so it's simple to
do. Ron Bloomquist is flying two of them on WW1 replicas. They're
working fine (at limited hours), but he doesn't flog them very hard. Not
much gyro load, not much HP. The problem with the M-3 conversion is that
it has no front bearing behind the prop flange. Prop loads are carried by
the crankshaft, the front crank roller bearing, and the thrust plate ball
bearing. According to the engineers in the Old Country, none of these
parts were ever intended to see this load.
I understand Steve Culp designed (or commissioned) some sort of direct drive
front case and shaft that included a proper bearing for the propeller
loads. I know nothing about that setup. I've asked him about it, but
all I get is "Aw, you don't wanna do that, just beef up a Skybolt and bolt
on a M14P". Ok.
Here's the latest news. George Coy had the engineers in Romania design a
direct drive setup. He will intro the new "M14D" at OSH,
complete with a cutaway engine for his display. Not a giant secret.
I can't be the only one who knows, and George says I can talk about most of
it. The first engines arrive next week. I've more or less spoken for
one.
The base engine is a Romanian overhauled M14V-26. Same overhaul as the
M14P engines from the same source. They will come with western fluid
fittings, the full dress kit, Champions, silicone wires, tool kits, spares and
pretty blue paint. Yeah, blue.
The old right-angle helicopter gearbox gets tossed. The new drive system
includes a proper set of support bearings, and the output shaft matches the
standard 20-spline found on round Continentals and similar. The prop hub
is a copy of one typical for wood props on a 220 Continental. The nice
thing about this hub is that the front crush plate is splined to the hub, so
driving friction is applied to both the front and the rear face of the wood
prop. Big 'ole hub.
George sent the engineers a custom carved Sensenich for the dyno work.
It's a copy of a Stearman prop but left-hand rotation. All the dyno work
has focused on a 220 hp @2000 RPM application, sort of a 220 Continental
replacement package. It's doing great in that configuration. I have
dyno plots, etc, and the numbers are fine.
Now the plot thickens. When George told me about it a few weeks ago, he
was focused on the above application, not sportplanes. My thoughts were
more performance oriented. Take a close look at the M14P manual.
It's 360HP for 5 minutes, at least if you do like the Russians say you
should. After that it's the "Nominal 1" power setting, 2400 RPM
and 290 HP for continuous operation.
Ok, with one exception, there are no internal differences in the M14P and the
M14V cores, at least not that we know about at the moment. The exception
is the cam plate. The "V" reportedly makes about 260 HP at
2400. It's perfectly possible to swap the cam plates, something the
engineers suggested when asked. That would bring it up to the 290 HP
level. It's also possible to install the PF-model blower gears <g>.
Here's the important part: The first engine was weighed at the end of the
assembly line. Weight was reported at 450 lbs with the mount ring,
compressor, and all accessories except generator. We don't think that
included the exhaust, but hope springs eternal. George doesn't have a
actual hub weight yet, but I've derived 19 lbs pulling geometric shapes from
AutoCAD drawings. That includes the prop bolts and the shaft nut. An
80" P-tip hard maple/composite from Prince is (according to Mr. Prince) 15
to 17 lbs. That totals 486.
If we use the M14P book numbers and the weights supplied by my friends here, the
apples-to-apples comparison would be 470 lbs, plus 6.5 (compressor), plus 6.5
(mount ring), plus a little more for the "fine filter".
The V530 prop is 90 lbs with bolts. Total is 573 lbs.
The difference is 87 lbs, all of it very much firewall forward, with a vast
reduction in prop mass moment effects. Other auxiliary systems (air, oil,
etc) woud be the same for both. The drawback is a fixed pitch prop.
No question a constant speed would be a better performer. On the other
hand, fixed pitch is cheap and almost maintenance free. No overhaul
costs. There are no significant tip speed issues. The M14 itself
should last a long time when prop-limited to about 2500 RPM. No planetary
gears, no prop governor, no pressure seals.
Nobody seems to have a really accurate direct drive IO-540 weight.
Published weights for base engines start at 402 and run to 476, but I don't know
for sure what is included. For this discussion I'm gonna use the
AEIO-540-L1B5D. Most guys want the heavy case for acro, and it's the only
one that includes an inverted oiling system. Published weight is 476 lbs, plus
perhaps 15 for a lightweight wood prop, so you have 491 lbs. Yeah, I know,
nobody is gonna put a FP wood prop on an AEIO-540. It's just an
example. I'd be tickled to death to hear from somebody that has actually
hung a 540 on a scale and knows what was included.
So, there you have it. My plan is a lightweight, more or less
"normal" Skybolt that happens to have a round engine. Same
structural concerns as a fixed pitch IO-540 Bolt, so without
"beef-ups", hopefully similar empty weight. With 290 HP and a
light airframe, I won't be very far off the big horsepower guys. Close
enough for this dumbass country boy anyway. My goal is 1300 lbs max.
Everything will get the "Rutan test", so I hope to do better. My
gram scales have taken a prominent position on the workbench.
My airframe is a very nice unfinished early Skybolt project, complete with wing
kits, tanks, fittings, all the wires, wheels, the works. Not expensive,
enough said. Fuselage was well done, not much to change. I wanted to
build my own wings. I'm not a trusting soul.
Disclaimers: George will weigh the package when he gets it in his
hands. Until then, weights are unconfirmed. If the weight
craps out and comes in heavy, all bets are off. It's pointless. I'll
do something similar to Jim's plan, or sell the project and start over. The
engineers have not dynoed the "sportplane" setup described above, only
the 220 HP "Continental replacement" package. They plan to be at
OSH, and we'll talk more then.
I'd like to take the opportunity to thank all concerned with this list.
The archives have been a tremendous asset, and the opportunity to be in contact
with serious builders is priceless. It's been quite a learning
curve. Not finished yet, I'm sure. Sorry to be so long-winded.
Comments? Dan
--------------------------------
...I didn't say it couldn't be done. It's risky, in my opinion, without
some sort of structural assessment. Even mild acro can lead to high g
loads. If he operates at published Skybolt gross weights (1650 acro) he'll
probably be okay assuming that the higher "working" loads from the
heavier engine don't cause fatigue failures in the engine mount lugs or fuselage
longerons. I say "probably" because he almost certainly had to
add weight to the tail to get the airplane to balance properly to get the CG
envelope to work out. A large concentrated weight in the tail would
further increase the load on the fuselage longerons during maneuvers.
Anyway, structures are sometimes forgiving, stress guys are usually
conservative (and opinionated), and ignorance is always bliss. Jim Doyle
Stress Analyst

06/10/01 FAA INSPECTIONS
The FAA inspection of your homebuilt is quite simple. The inspector will
not look at the airplane until it is completely finished, covered, painted,
assembled and test taxied. They will look at the paperwork, markings and
tags as well as the general appearance of the airplane. The really don't
care much about how it is built. An airplane that exhibits a minimum of
fair quality exterior workmanship will not create enough doubt in the mind of
the inspector that the workmanship is poor inside. If you use a DAR to get
your A/C, the requirements will, in all likelihood, be even more lax.
My point here is that you, as the manufacturer, must be satisfied that your work
is of the required quality. The inspectors will basically check off that
fact that YOU think it is good to go. To quote a friend of mine with
respect to making info avail to the feds......."No need to burden them with
that information." KK
----------------------------------
The DAR that did my inspection did just about what Kevin described. He had me
mail him copies of the paperwork so he could check all that before he made the
trip to see the airplane. I had glue and weld samples, but he never requested
them. He spent about 1/2 hr looking over the airplane, had me run-up the engine
while he looked at engine gauges. He did take a good look at my weight and
balance figures. Charged $300, ate lunch, gave me a temporary certificate and
was on his way. Bill

360 HP vs. 400 HP, M14P vs. M14PF
Jerry Guy asked me about the results of the 360hp M14P vs 400hp M14PF head to
head flight tests. At SNF, we had a chance to fly the 2 model 12s against
each other. The results were quite interesting. Seems our 360
powered model 12 was able to get a jump on the other one at each start, level or
climbing. The 400 one was never able to catch up and the pilot of the 400
was to one to call the end of each race. So, unless his airplane is 400lb
heavier than he says it is and it is rigged real bad, I'd say the 400 vs 360
thing is a wash if you use the same size prop and same airplane...............
Now, as I see it, almost every time someone has changed to a 400hp engine on a
Sukhoi or whatever, they also put the larger diameter prop on. We put the
big prop on Jeff's sukhoi and 360hp engine and it made a huge difference in
static thrust and hang time without the added hp. So, I am not sure what
the gains are from the extra $8000 for the PF engine other than to be able to
say you have it. These tests were not formal in any way so the results may
vary if someone else does it.
So, why not more of a speed difference gicen that the model 12 easily hits
260mph in a slight dive at cruise power? I have a theory or 2.
First, lets say the PF makes 400 hp at 41" MP like the book says it
does. What if the rings can't hold back the added cylinder pressure and
most of the added squeeze blows past the rings at combusiton? Or what if
the whole thing is a ploy by the russians and the engine dealers to get more $
from us with little invested..... The 400hp PF engine has been around
since the late 80s early 90s and it was not on any russian national world
competition team airplane thru the mid 90s. If it was such a big
improvement, why didn't they use it?
I know we have customers that want the 400 engine. That's ok. I'll
use one because I got a good deal on it and it will add value to the airplane in
the eyes of some. But, the 360 is a good, solid, known quantity that is
shown reliable for many years. The PF is relatively untested thru time. KK

04/14/01 PITTS vs. SKYBOLT, COMPARISON
I just got done looking at the skybolt vs. model 12 prices. Now, this is
based on SNF 2001 prices on the Model 12 and SNF2000 prices (the price list
avail this year from SAL with a caveat that the prices are not current). I
included the cost of the plans for each too.
If you go thru the SAL list and pick out the items that best add up to a near
complete Skybolt kit, you will get $35,307.50. But this does not include
all the items that are in the Model 12 full kit. This price total of SAL
products has more 'kits' and less prefab items like we have. Like the
Canopy for example. I found several items that we include that they do
not. They are: Gear Cuffs, all fuse alum skins pre cut and bent,
front cockpit headrest bulkhead, fully assy t-deck, fully assy alum
ailerons(they hint that they are forth coming), a full cowl instead of a nose
bowl only, rudder cables, trim cables and rods, and canopy assembly labor.
If you use the current price for our version of the above items in place
of the non published SAL price, the total goes up to $43,434.50. I find
this to be a virtual wash to our $46,388.00 when youfactor in the extreme high
quality of our parts in comparision.
Now, lets say a composite 3 blade prop for the 540 bolt and Model 12 each costs
$11k. That's a wash. The engines to compare have to be both acro
engines to be fair and should be of near the same HP. That means a Barrett
or Lycon AEIO 540 Lyc hopped up to a range of 325hp to 375hp. That'll cost
you $45k to $75k depending on what you get. If you choose a brand new AEIO
540 Lyc of 300hp like in an Extra, that'll cost $55k. The $15.5k for M14P
or or $20k for M14PF is a bargain.
If I total up the complete kit, prop, engine, engine install stuff, covering,
instruments, radios, paint, etc I get $100,500.00 for the skybolt with a $45k
engine.
The same pile for the Model 12 I get $89,000.00 with the M14P $15.5k engine.
Now, I know that most of those building a bolt will not buy a top drawer engine
but rather use a cheaper o/h unit. Heck, probably a cheap prop too.
But, I wanted a true comparison. KK

03/26/01 PLANS, S1S, S1T, S1C, SUPER STINKER
I've decided to obtain a set of those outstanding S1 plans I've heard about to
improve my understanding of Pitts designs. Now, there are different choices: As
far as I know Aviat sells "S-1S" plans, SAL sells "S-1C"
plans, "S-1SS" plans and "symmetrical wings" plans. I'd like
to hear about the differences of the above plans sets and would really
appreciate some tips which one to get. -Tom
--------------------------
I've seen the SAL S-1C plans and they look nice and include some full sized
non-dimensioned drawings. In addition, some very useful isometrics are
included. I have not bought a set...yet. As for the Aviat S-1S plans, they
are factory plans. Everything is there, but some of the non-dimensioned
drawings are not full size. They've been ECN'd/updated over the years and
they are quite thorough. In my opinion, they are definitely worth the
money. If I were going to build a Pitts I would get both. If you
just want a reference I'd get the Aviat plans. - Jim
--------------------------
The S1T is an updated airplane based on the S1S. S1S was factory built and
certified. S1S has been homebuilt as well yet in many cases until the
80's, a homebuilder was not allowed to call his an S1S by the FAA. Most
opted for S1X or S1SX etc. The S1T his a 200hp constant speed prop for
power vs the 180hp fixed pitch on the S1S. To fix the added weight of the
200hp/const spd, the top wing on the T was moved forward. The S1T has
symetrical ailerons like on the last 10-15 S2A and all S2B airplanes.
S1C has flat bottom wings with the M-6 airfoil. The S1C has a shorter fuse
that the S or T models. The C has pin type tail hinges like the skybolt
copied rather than the more desirable strap type hinges used on A,B, C, Super
stinker, Model 12 etc.
Yes, as far as I know, you are correct that the S1SS drawings from SAL are for
the wings only. These drawings show sym airfoils like on the S1S, super
stnker etc as well as a version of the ailerons developed by curtis for the
super stinker model 12 S2C etc. The C had flat bottom airfoils.
$250 is a real bargin! My copy is of great reprint quality compared to the
Super stinker plans I have. Many of the Super Stinker plans I have a
nearly unreadable. KK<
--------------------------
While I agree with Denis that the Pitts Model 12 plans are nice, they require
some understanding of aircraft construction to use them and do not have any info
on general systems. These general systems details are addressed in our
kits. The Super Stinker plans and th efactory S1S plans, both avail from
Aviat Aircraft, have lots of system info. Heck these even show all wiring
and labeling. Very detailed. The Current Skybolt plans are a very weak 14
pages. Factory S1S, Super Stinker, Model 12 are all over 40 sheets.
I do not know what level of detail or number of pages are avail in the
firebolt or S1C plans from SAL. So, if you are interested in having
help with systems, etc. get the S1S or Super stinker plans from Aviat. KK
--------------------------
S-1C Flat bottom wing, one set ailerons, 1 seat 180hp fixed pitch
S-1S Symetrical wing, two sets ailerons, 1 seat 180hp fixed pitch
S-1T Symetrical wing, two sets ailerons, 1 seat, 200hp, constant speed
S-2A Symetrical wing, two sets ailerons, 2 seats, 200hp, constant speed
S-2B Symetrical wing, two sets ailerons, 2 seats, 260hp, constant speed
S-2C Modernized S-2B, some aerodynamic and ground handling improvements
S-2E The kit version of the S-2A, AVIAT sold these.
S-2S I think its like a 1 seat S-2B, i.e. bit lighter

02/26/01 AIRPLANES FLOWN SO FAR
Here is the run down on Model 12 that have flown so far.
1.) Black Prototype by Curtis Pitts N80XP
2.) Ben Morphew N69BM Red one (later lost in crash by new owner)
3.) Ours, the Yellow and Purple one N360KJ now N360KC
4.) Neil Forsyth of South Africa ZU_BXX
5.) Phil Bohner yellow and Purple (the one in Darin's poster)
6.) Phil Bohner Chromalusion with some yellow.
Now, as you can see, Phil has 2 spots on this list. #5, the one in Darin's
poster made several flights the last of which ended in a landing that came in
contact with a 2000lb large round hail bail causing the airplane to tumble over.
It was severely damaged but Phil and pax got out unhurt. The
insurance Co. totaled it and Phil was gonna buy it back and rebuild it.
But, the ins. co. was taking too long with it and Phil wanted to fly NOW!
So, he bought a Model 12 project that was already underway with wings etc.
covered. He bought it in September I think and it is finished already!
He plans to buy the wrecked one back from the insurance co. and rebuild
it. He sure LOVES the Model 12!!!!
Other news is that Phil is planning on having his new 12 at SNF and Keith
Campbell is planning on flying N360KC to SNF too. So, we will have 2
there. I expect 2 or 3 more to be done by Oshkosh this year. We have
one in the shop that will be complete in about 2.5 months. IT will most
likely be # 7 to fly and then I expect, 2 or 3 from Daytona to be done, 2 from
Canada to be done, 1 in Mississippi to be done too. I can't wait to be
able to see a line of them at a flyin! I'll be able to walk amung them
like a proud papa!!! KK

02/24/01 HORSEPOWER
The Model 12 airframe is designed for up to 450hp. Curtis knew someone would want more hp on it so he planned ahead. The airframe, as you can see from the drawings, is far more robust than that of most other designs that are of similar size and type. KK

11/19/00 KIMBALL CHANGES, HISTORY
The changes we made to the Model 12 from the original vary in reason. I'll
address the hows and why of each here so others can have the info too.
First, the orignial 3 view of the Model 12 by Curtis showed a very short nosed
airplane. Curtis gave us a copy of this 3 view in 1995 signing it for us
and planting the seed of the Model 12 in our heads. He and the 'boys' built the
airplane from the firewall aft complete and weighed it and the firewall forward
unit separately. Curtis used these weighed to determine the proper
location of the engine for CG reasons. As it turned our, this was 10"
farther forward than the pre design 3 view showed. So, for everyone who
looks at the stock Model 12 who never saw the original 3 view, it looks exactly
right. Dad and I had the misfortune of knowing the original snub nose look and
then decided to we had to shorten the fuse a bit to try and get closer to the
1995 3view. We soon realized that there was no way to get the nose as
short as it was first drawn and that only about 5" could be taken our
of the mount length without having to use bent or curved engine mount tubes
like Steve Culp did on the green special.
Next I had to determine how far aft to move the wings to get the balance correct
again for the CG. As it turned out, the fuse is about 5" shorter too.
I say about because both are not exactly 5" change. When you
move the wings aft, the FW and all wing related and gear related stations move
with them. The length of the fuse was done to please us. WE wanted
to improve the look of the side view. In addition to the length change, we
eliminated the pot belly look.
The performance of a model 12 with long fuse vs a short one like we
sell is virtually unchanged. I think it would take a supreme being to
actually tell the difference between the 2 in flight. So, fuse length = no
performance difference.
The wings are a different story. This was the next thing to get a redesign
by me. In April 1996 right after SNF that year, Ben Morphew did all the
hard acro and spin tests in the Black airplane (prototype model 12) for Curtis.
He fell in love with it as at the time he owned the prototype one design,
the prototype Super Stinker (model 11, 11-260, S1-11B). He is one of the
world's best airshow pilots according to people like Sean Tucker. Anyway,
Ben would have bought the black airplane if it rolled a bit faster. It
rolled faster than an S2B and bunches faster than an Eagle, S2 A or skybolt but
Ben had been flying the other planes mentioned above as well as Sukhois etc.
SO, Curtis said build your own and Ben agreed.
Ben hates wood work and called us to see if we would build him a set of 12 wings
as we were already building stuff for ours. We said yep and He and I
became great friends before ever actually meeting face to face. Ben had a
list of requirements for the wings. Reduce the span from 23' to 22',
bigger ailerons, 3 hinges per aileron, square tips. I combined his desires
with mine which were a smooth center section, slave rod aft of I strut and
ailerons made of aluminum. We beefed up the wings in key areas too all the
while reducing the weight of the wings and ailerons by over 20lb from the plans
version.
With the new wings designed, we had to redesign the tail for 2 reasons.
One to make them look like the wings (square corners). And two, to
get the tail volume coefficients back to the correct #s. You see, the tail size,
both horizontal and vertical are a function of many dimensions of the wings.
SO, when the wings change that tail must change if you want the new system
to act like the old one. The end result is the control of the HP vs stock
is mathmatically identical.
We went on to clean up or improve many other systems or components for the Model
12 all in an effort to please ourselves. AS it turns out, many others like
what we did and began to buy our parts. Our fuselage jig is designed to build
both long and short fuselages yet we have never built a long one.
A few guys like Darin and 3 more in IL have built their own versions of the
short frame. That's ok with us. Builders can build the entire
airplane from scratch or mix and match kit and scratch parts to suit your
talents or pocket book. The fitting set we sell is the same set we use for
the HP version and includes the tail ribs etc. As Bud or Darin and a few
others can tell you, it is well worth the price of $500 flat laser cut or $755
fully bent ready to weld. Some have purchased our ailerons to use in
scratch built wings making the mods needed to fit them in. So, as you can see,
anything goes in our program. You decide the cost/benefit of each item as
it applies to you then let me know what you need from us. KK

11/19/00 PITTS vs. CULP, COMPARISON, CULP, PERFORMANCE, STALL SPEED, COST
Just got my Kitplanes Kit issue. Here is a point by point comparison of
the listings for the Culp Special and the Model 12 as printed in the Kitplanes
Mag. Top speed of the 12 determined using FAA FARs for certified A/C.
Special not. Should be the same as the Stock Skybolt. Actual Cruise
speed of 12 shown for 15.8gal/hr burn. Actual cruise speed for Special is
150mph. Stall of 12 calculated and tested to be 64 mph. 70 mph stall of
Special seems high. Range of 12 is 525 miles with 30 min reserve on 54gal
standard fuel. Range of 600 miles shown in Special listing required 70gal fuel
no reserve. Green Special has 38 gal total fuel. Blue one
more. Rate of climb of 4500 on Special listing is estimated when engine was set
to 4000rpm. ROC at 2950rpm much less. 12 ROC measures at
3300fpm at gross for several minutes, take off and landing distances are
similar.
Engines same. Fuel Capacity mentioned above. Empty Weight 1470 of Special before
cowl, pants, smoke system. Empty Weight of our 12 is 1472 complete with smoke
system, all parts as shown in pics. Number completed and flown 5 Model 12s
3 Specials if you count the single place Russell plane as one of the 3. Rest of
list as you see it.
Kit price of special higher than 12 kit if you take out the $3500 canopy, and a
few other things to get apple to apple component camparison. Cost to build:
Ours actual number with new engine and new 3 blade MT prop, full
instruments and radios, etc. Can build a 12 for less than $70k with o/h
engine, 2 blade prop, few instruments etc.
Plans for the Model 12 are 44 sheets D size CAD generated plans. Special plans
require purchase of Skybolt plans, PLUS purchase of Special supplemental
drawings for the mods to the skybolt structure. Skybolt plans are only 14
hand drawn sheets C size(half size of Model 12 plans). Supliments are a
few hand drawn sheets I think.
Keep in mind that the Culp Special kits Steve now offers are Model 12 fuse,
tail, controls modified to accept skybolt wings and gear. We build the
frames for him 3 so far. He has his fuse kit price the same as we do for
the 12. Steve an I are good friends and we share/team up on many things
for the various airplanes we build. Like finding special items, making
parts etc. He has just found it more efficient to start with the 12
structure and round it up a bit rather than shoehorn the M14P into the bolt
structure.
The short of it is this..........The mags will print whatever you give them
without verification. It is up to the kit or plans provider or
manufacturer to back up their claims with the builders. Time and time
again, airplanes are listed faster, longer range, lighter than they really are.
We decided years ago NOT to lie or stretch the truth to our customers and
this has gained us a reputation of being straight up and honest in the industry.
We continue this with the Model 12 program as it is with our restoration
biz. Expect this with our 2 new offerings, the McCullocoupe and the Raptor
A.S. both Non-biplanes......(sorry) Kevin

10/18/00 MAGAZINE ARTICLES
Group, take a look at the October 13 issue of The Flyer on the cover and on page
41 for a story on the Model 12 written by Doug Hinton. Also see the new
Custom Planes December 2k issue page 56 for a story on reading blueprints.
Wayne Scraba, a Model 12 builder, wrote this story and uses his Model 12 plans
as the subject. Kevin

09/07/00 RUDDER SIZE, AEROBATIC CAPABILITIES
Bret, the big rudder does make quite a difference on Pitts type airplanes, S1s S2s (S2C has bigger rudder than S2B). Granted, for most the stock rudder is OK. INTERMEDIATE!!! Hmmm. The Model 12 has competed in Advanced so far and scored well. Most of the competitor types who are building them are aiming at advanced. Some for regional unlimited. The airplanes capabilities are such that is is on the "too good to be allowed list" for Advanced World Aerobatics Contest, AWAC. The Model12 has aerobatic capabilities beyond that of the Eagle or skybolt. The Model 12 IS that type of aircraft. But, like with a high performance car, you don't have to use all of it if you don't want. A great number of our builders either have had eagles or do have them. Many have S1s or S2s. All know the Model 12 outperforms their existing/past airplanes and are moving up. Kevin

09/03/00 PITTS vs. SKYBOLT, COMPARISON, CULP
Mike, good to hear from you on the subject of M-14P powered biplanes. This
group has several builders of M-14P powered modified skybolts. Andy, Bill
V. and others. I noted a few items in your email to me and some of the
posts to the group by you and others on this subject. I'd like to address
a few points here if I may.
Andy pointed out that the gross weight of the Skybolt is 2000lb. To date,
the lightest M-14P powered homebuilt bipe I have heard of is 1472lb empty as you
see it in all the photos with smoke system. It is our Yellow and Purple Model
12. Steve Culp's modified Skybolt called the Culp special is 1477lb empty
plus, cowl, wheel pants, ply covered wings added later etc which add up to an
empty weight of over 1500lb with no canopy. I estimate Andy's plane will
weight over 1550lb. So, if you go by the 2000lb gross, you have 500lb
useful based on a1500lb empty. You said you are just under 300lb leaving
200lb for the front seat, fuel and oil. Min fuel is 30 minutes or about
10gal =60lb. Oil is 3.5 gal or 21lb leaving 119lb for baggage and front
seat person. Most of the M-14P powered skybolt builders are raising the
gross weight to allow for two people and gas.
The Model 12 has a gross weight of 2250lb standard as compared to the 2000lb
gross of the 'bolt. So, you start at 1472 empty, 300lb for you, 200lb
front pass, leaves enough room for 46gal of gas. Typically, the
model 12 can be loaded with two 220lb people, 54gal of gas, 40 lb baggage and be
at gross weight. So, you can actually fly the airplane at typical
loadings and be within the design limits of the structure. The model 12 is
stressed to an ultimate load of +9, -7.5 gs at full gross weight of
2250lb. I don't know if anyone has done the numbers for a skybolt at
2250lb to see the g limits there.
I think you have the wrong idea of the size of the model 12. It has larger
cockpits than a skybolt. This ain't no S2A. The amount of floorspace
in a hangar for a model 12 and a skybolt is nearly identical. We have
6'4" 300lb guys building Model 12s because they fit in much better than a
skybolt. Heck this year at oshkosh, I sat a 6'5" 325lb guy in the 12,
closed the canopy with 1.5" to spare over him, he had full range of
controls, and his sides didn't hit the longerons. The 12 is wider than the
skybolt at the rear seat. Curtis Pitts designed the airplane for big guys.
Basically, you can fit into the Model 12 without mods unilke the changes you
mention you will need in the bolt. You should try on a model 12 before you
commit to the project. You will be surprised. Let me know where you
are in the country and I 'll hook you up with a Model 12 builder nearest to
you.
Keep in mind that you will not be able to just bolt the M-14P onto the stock
skybolt frame. The frame will have to be shortened up front, cabanes
reworked, firewall moved aft, beefed up, etc. to fit the M-14P in. The
green culp has the oil tank in the aft fuselage to be able to balance the
airplane.
The Model 12 has constant chord wings. It also has the latest in wing and
aileron technology. The bolt and the 12 share the same airfoils as the
rest of the symmetrical pitts series wings.
There are countless times I have heard......."If I hadn't started the
skybolt already, I'd be building a Model 12!" Some in this group have
said that. Heck Steve Culp himself now buys Model 12 fuselages, tails etc
from us adding stringers to shape them into Culp Specials. He doesn't
build modified skybolt based Culp specials anymore.
Please take a closer look at the Model 12 and you will see that it is 23ft span,
near 20ft long purpose built M-14P powered airplane. Curtis Pitts designed
this airplane exactly for the M-14P. It works Perfectly. It is
25years newer technology than the skybolt and has a higher resale value compared
to a one of a kind, modified skybolt.
We support the Model 12 completely. You can scratch build from plans, buy
some parts or buy all the kits we sell. Its up to you what level you wish
to do or buy.
You want great cruise performance too. Then the Model 12 is definitely for
you!! The model 12 cruises a full 20kts faster than the green Culp
special on the same gas burn. That's 170kts on the GPS on the way home
from Oshkosh on 15 gal/hr. Our bonanza on the same day and 15gal/hr was
showing 190kts on the GPS. That's almost 200mph ground speed in a
aerobatic biplane. Range is 500miles.
I look forward to hearing back from you as you choose your project. The
Model12..........The Best Pitts Yet!! Kevin
------------------------------------------------
Mike, thanks for the reply. I'm no expert, but I think I have gone through some
of the same consideration you are now. When I was considering what to build, I
bought 3 sets of plans....Skybolt, McKenzie Firebolt, and Pitts 12, and have
decided to build the pitts. By the way I'm 6'-1" and 175lbs. Here's
why I shamelessly recommend the pitts:
Airplane | Kimball Pitts 12 | Stock Pitts 12 | Skybolt | McKenzie Firebolt |
Length | 19' 8" | 20' 6" | 19' | 21' 4" |
Wing Area | 150 sq. ft. | 150 sq. ft. | Plans don't say - Same as firebolt? | 150 sq. ft. probably same as skybolt |
Gross Weight | 2300 lbs | 2300 lbs | 1800lbs | 2000 lbs |
Aerobatic Gross Wt | 2300 lbs (+6 to -4.5 G) | 2300 lbs (+6 to -4.5 G) | 1650 lbs | Plans don't say |
Fuel Capacity | 54 gal | 54 gal | 38 gal | 39 gal |
Distance between longerons at rear pilot shoulders | 25.25" | 25.25" | plans dont say- used autocad to draw it out - 21.28" | 21.524" |
Finished Airplane Considerations: The skybolt is the
slightly smaller airplane from what I can tell from all my plans I just laid
out. I have sat in Kevin's Pitts 12 in both seats and it's very roomy,
especially the front seat, you could probably put a bench in there and fly 2
kids up there, but they'd only fight over the stick. The canopy system is very
well thought out and does give you room to spin your head around with about 2-3
inches of headroom left. I think the skybolt canopies are usually a little
tighter. I have only seen skybolts up close, but not sat in one, but they look
noticably smaller (of course, the 4 or so extra inches of width in the pitts is
a lot, especially if you have to bail out in an emergency!) and the front
passenger area seemed kinda tight too, compared to the pitts.
For cross country flying, I'll bet there wouldn't be much difference in
"hands off stability" between them with rigging probably more
important, but I'm sure someone in the hangar with more biplane flight time
could shed more light on that topic. I would assume with you being 300 lbs your
airplane would be at a more rearward CG anyway with some corresponding decrease
of pitch stability. The airplanes are all pretty much the same size, the
difference between the skybolt and the firebolt being a few inches added to the
fuselage of the firebolt. Kevin's Pitts is about 5 inches shorter aft of the
cockpit and 5 inches shorter in the engine mount than the plans version, so the
cockpit is the same for both. However the pitts carries 15 more gallons of fuel
than the skybolt which would be a major consideration for your cross country
flying, Also the pitts is designed right from the start to fly at a higher gross
weight which would be a nice advantage for you.
Building considerations: The skybolt plans are difficult for us first time
builders. They are very spartan at about 14 pages, and leave many details to be
figured out by the builder, in fact the biplane hangar skybolt builders here
devote quite a bit of time to this task. Mac McKenzie's plans for the Firebolt
are truly works of art with many many pages and every little detail drawn, by
hand. He also supplies a full parts list for each sheet. If you still end up
building a bolt, I recommend getting his plans too, just for the
details. The pitts plans are very complete also with good detail,
and are done on a CAD system. The parts list is on each page.
The new owners of the skybolt business will have to work hard if they are to
eventually provide the kind of support that Kevin already does to pitts builders
right now. For example, I have purchased from Kevin a complete set of machine
laser cut fuselage weldments that should save a couple hundred hours cutting
small parts out of sheet metal. It looks like the area of the skybolt that
you would like to widen is in the taper from the main 30" wide front
section back to the tail, at STA 85. I'm not sure how much hassle it would
be, not to mention figuring out the engine swap and all the changes it would
cascade. I'm sure Andy and the other guys building radial skybolts have thought
most of that stuff through already though. You wouldn't need to modify the
pitts at all. As far as falling in love with the sig skybolt, I used to
fly R/C too and remember them too, they ARE neat airplanes. However, I'd bet
your skybolt, if you built it like you mentioned, would look more
like a pitts 12 than a skybolt though. If you decide to build a skybolt
let me know and I'll sell you my set of plans, they aren't much use to me. I
will hang on to the Firebolt plans however, they are too cool! Darin

06/22/00 INSURANCE
Group, it is my understanding that there are only about 6 aviation insurance
underwriters. The various agencies like Avemco, Forest, Falcon, etc,
simply offer your case to the underwriters and mark it up for their own piece of
the $ pie. From our experience, the various underwriters have vastly
different policy requirements and guidlines as well as prices. In the case
of our Model 12 in March 99, we used Forest agency. We got liability, full
hull coverage, airshow coverage(add 10%), competition coverage (add 10%), and
open pilot coverage(means any pilot with 500TT, 250tailwheel, 50Pitts could fly
our Model 12), we could name up to 6 pilots on the policy. Deductable was
$500 Except for the canopy which had a deductible of $2500(lots of S2Bs lose
their canopies). All this was $4200.00 per year.
Since March 99, their have been several accidents with experimental biplanes of
various brand names as well as Factory Pitts accidents. In December 99
when the new owner of our 12 got his coverage still thru Forest, he saved some $
by dropping the open pilot part but kept the rest as he intends to compete and
do airshows. A different underwriter was used by Forest for the Model 12
which saved some $ for Keith but, he CAN'T have an open pilot clause with them
and can only name a MAX of 2 pilots on the policy. Keith didn't ask
how many pilots could be named and the limit of 2 has been a problem for him
(and us in moving the plane for shows and giving rides)
So with this example, you can see that knowing what options you want or think
you may want in the future is important at the time of getting your
insurance. Also, their is a very small network of underwriters for
aviation. They all know what the other offers. The Agencies, Forest Avemco,
AUA are "Dealers" for the underwriters and call all of them shopping a
deal for you. KK

04/27/00 SPORT AVIATION ARTICLE, HISTORY
From what I could get from the July
1999 EAA Sport Aviation article, the airplane as shown in the plans had a
C.G. problem that required the engine mount to be 11" longer. Do you make
two different engine mounts, one for your version and one for the plans
version? Are they 11" different? that sounds like a lot. Darin
------------------------------------
Darin, The SA article is slightly misleading. Curtis
designed the model 12 with a 14" engine mount. The airplane had a
very short Samson like nose in the orig 3 view we first saw in 1995.
Because of a lack of hard CG data on the engine, prop, accessories, etc., Curtis
decided to build the airplane complete from the firewall back. I mean
everything, belts, cushions, pants etc. Then they weighed it. They
assembled the engine, prop, cowl oil tank air system, etc on a temp. engine
mount and weighed that. They determined the CG of the FWF unit.
Curtis then did the math and found out that the engine mount needed to be
23.75" long rather than 14" long. About 10"
difference. The FWF stuff was lighter than he first planned on. So,
the engine mount drawing was updated and very first engine mount built for a
Model 12 was 23.75" long. As it turns out, a 14" mount would not
have been long enough to get all the FWF stuff in place anyway.
So, the plans we sell have an engine mount and fuse length just like the plane
Curtis and the Boys built, 23.75" mount, 169" fuselage.
When we started the wings for our Model 12, the prototype had not yet
flown. Dad and I had a copy of the stub nosed 3 view and when we saw the
actual airplane after the engine was on, we were shocked as to how long the nose
had gotten. We saw it with the engine on but without a cowl and it didn't
seem too bad. But when the cowl was added, it had gotten real long.
We were disappointed. So, we determined how short the engine mount could
be and stilll get all the FWF stuff in it. Next we redesigned the fuse to
allow for the shorter mount. The net result is a plane that is about 10 to
11" shorter than the black prototype. In making these changes, we
adjusted the seating, changed the canopy, made the rudder bigger, partly req'd
for shorter wing span, partly because it needed more rudder. Then Ben
Morphew test flew the black on some for Curtis doing all the acro tests.
He loved it and decided he wanted one too but didn't want to build the
wings. He contacted us and because the wings were yet to be built, he
asked for some changes to them based on flying the stock wings on the black
12. He wanted 1ft less span, bigger ailerons, 3 hinges, slave rods to
behind the I struts. So, with him wanting these things, we decided to add a few
wants of our own to the wings. Smooth cross-section, alum ailerons, beefed up
spars in spots, tighter rib spacing to help the fabric stay put, and we wanted
to keep the same wing area as stock which forced the square-ish tips. The
end result is the wing set we have in kit form now. Now, this meant the
ribs we had built so far from based on the stock wings were not gonna work and
we had to start over.
This gives you the basic genesis of the Model 12 as it is today. The
plans mount is exactly the length of the black 12 prototype. Our mount is
approx, 4.5-5" inches shorter than the stock one. We have a jig that
makes both the stock and our length mounts. If you build the mount per the
plans, it will be the longer stock unit. KK
