Piper Tomahawk and stalls/spins
Sean Shenold
that may have escaped some people's attention.
Before I go on, I'd first like to state that I'm an A&P mechanic,
that I've done some work on the Tomahawk, and I'm not out to 'bash'
the Tomahawk, or to scare anyone. But in my opinion there are
problems with the Tomahawk that pilots need to be aware about.
All this came about following an accident involving a Tomahawk near
Inman, Kansas on March 5, 1994. It appears that, during a BFR
(Biennial Flight Review, for those not familiar to the FAA), the
airplane entered an inadvertent spin that the pilots were unable to
recover from in time. Both pilots were killed.
During the NTSB's investigation (National Transportation Safety
Board), for whatever reason, one of the investigators compared the
actual design blueprints from the certification of the airplane to
the wreckage on the ground in Kansas. To make a long story short,
there were significant differences between the actual airplane, the
one particular airplane that underwent certification flight testing,
and the airplanes that left Piper's Lock Haven plant and were sold to
customers.
I have a copy of the complete NTSB report, and I will post it here
in the next day or two. (It's fairly long, and I don't have a
scanner or any other means of entering it other than by keyboard.)
This accident holds particular significance for me. From the NTSB
report, the registration number of the accident airplane was N2495L.
I used to work on another Tomahawk occaisionally, a few years ago at
a different job than the one I work at now. The registration number
of that airplane is N2496L. As you may or may not know, Piper (and
most other manufactureres) obtain a 'block' of registration numbers,
and assign them sequentially. In other words, the one I used to work
on (owned, at that time at least, by a man named Paul Wade, if memory
serves) was the next airplane off the assembly line after the one
that crashed in Kansas. This airplane (96L) would stall and spin
with no apparent problems. (I knew Mr. Wade and his flight
instructor, Tom Rush, personally, and they did do spin training in
that airplane.)
Sean Shenold
Inman, KS, March 5, 1994, as close to verbatim as I can get it. This
will read best if you expand the screen.)
NATIONAL TRANSPORTATION SAFETY BOARD
FACTUAL REPORT AVIATION
NTSB ID: CHI94FA097 Aircraft RegistrationNumber:N2495L
Occurance Date: 03/05/94 Most Critical Injury: FATAL
Occurance Type: Accident Investigated by: NTSB
Location/Time
Nearest City/ Place State Zip Code Local Time Time Zone
INMAN KS 67546 0830 CST
Accident Location: Off Airport Distance from Landing Facility: UNK/NA
Direction from Airport: UNK/NA
Aircraft Information Summary
Aircraft Manufacturer: Model/Series Type of Aircraft
PIPER PA-38-112 Airplane
Sightseeing Flight: UNK/NA Air Medical Transport Flight: UNK/NA
Narrative
Brief narrative statement of facts, conditions, and circumstances
pertinent to the accident/incident:
HISTORY OF FLIGHT
On March 5, 1994, at 0830 central standard time (cst), a Piper
PA-38-112, N2495L, registered to Marvin Hall dBa Hutchinson Aviation,
of Hutchinson, Kansas, with a commercially certificated flight
instructor administering a biennial flight review (flight review) to
a private pilot, was destroyed during a collision with the ground and
subsequent fire. Visual meteorological conditions prevailed at the
time of the accident. The 14 CFR Part 91 flight was not operating on
a flight plan. Both pilots were fatally injured. The flight
departed Hutchinson, Kansas, at 0800 cst.
Three witnesses said they observed the airplane during its descent to
the ground. Two witnesses observed the airplane in a five or six
turn spin to the left. One witness said he saw the spin stop just
above the ground, with the airplane's ". . . nose pulled up slightly,
but then back down before it hit."
During the interview the witnesses were asked to show, with a model
airplane, what N2495L had been doing during its descent to the
ground. Each witness made a motion with the model airplane that
replicated a left spin that had an approximate 45 degree nose down
attitude.
PERSONNEL INFORMATION
The logbook for the pilot receiving the flight review was destroyed
in the post crash fire. According to Federal Aviation Administration
(FAA), the pilot obtained his private pilot certificate on November
27, 1991. The pilot reported he had 50 hours of flight time when he
obtained his second class medical certificate on March 20, 1992. The
pilot's supervisor said that to his knowledge the pilot was current
and had taken annual leave to obtain a biennial flight review before
his currency expired.
The flight review recipient's wife stated that he had accumulated
about 75 to 100 hours of flying time since obtaining his private
pilot certificate. She said her husband had told her that his flight
check was due before they moved to Des Moines, Iowa, in May 1994.
The wife of the flight instructor administering the flight review
stated the other pilot had not flown the PA-38 since May 21, 1993,
according to company records.
The flight instructor administering the flight review had completed
an FAA airman competency flight check according to 14 CFR Part
135.293, .297, and .299 on December 31, 1993. This pilot's number
three logbook showed he had a total time of 7,944.9 hours, 1,803.5
hours as a flight instructor, as of January 25, 1994. The logbook
began with the entry of August 16, 1985, showing a total flight time
of 4,943.2 hours. The first Piper PA-38 (PA-38) logbook entry was
made on August 18, 1985. The pilot's total flying time in the PA-38,
as found in the number three logbook, was 104.9 hours. Complete
pilot logbook records were not made available for review. The NTSB
Form 6120.1/2 that was sent to the pilot's wife was not returned.
She did say that he had a total time of 745 hours in the Piper PA-38.
The instructor's flight review methodology was revealed during
interviews with two pilots and a written statement from a third
pilot. One pilot said the instructor had him do approach to landing,
and takeoff and departure stalls on headings and in turns. He said
that he demonstrated these stalls to the instructor with landing
flaps retracted and extended. The second pilot said the instructor
asked to see imminent stalls only. His written statement said, ". .
. I proceeded one time to go to a full stall and Marvin quickly
detoured that route."
A pilot, training for a flight instructor rating, said the instructor
had spun the PA-38 on several occaisions during his training. He
said the instructor had demonstrated one turn spins to him and the he
had performed spins under his direction. The pilot said the
instructor had discussed stalls, spin entry, and spin recovery with
him during ground training. He said the instructor had told him to
avoid getting the airplane into a spiral and that he had to enter the
spin forcefully.
AIRCRAFT INFORMATION
The PA-38 was certified under the Delegated Option Authority granted
to manufacturers of aircraft by the FAA. The PA-38 received its
airworthiness certificate from the FAA on December 20, 1977. The
PA-38 was certified in the utility and normal category by the FAA.
This certification allowed it to perform spins when operated in the
utility category.
According to the pilots operating handbook (POH), "Normal recoveries
may take up to 1 1/2 turns when proper technique is used; improper
technique can increase the turns to recover and the resulting
altitude loss." The POH continues, "In all spin recoveries the
control column should be moved forward briskly, continuing to the
full forward stop if necessary. This is vitally important because
the steep spin attitude may inhibit pilots from moving the the
control column forward positively."
The POH says, ". . . one half of the spin (rotation takes) . . .
about one second . . . Improper application of recovery controls can
increase the number of turns to recover and the resulting altitude
loss. Delay of more than about 1-1/2 turns before moving the control
wheel forward may result in the aircraft suddenly entering a very
fast, steep spin mode which could disorient a pilot. Recovery will
be achieved by briskly moving the control wheel fully forward and
holding it there while maintaining full recovery rudder." "If such a
spin mode is encountered, the increased rate of rotation may result
in the recovery taking more turns than usual after the control column
has been moved fully forward. A one-turn spin, properly executed,
will require 1,000 to 1,500 feet to complete and a six-turn spin will
require 2,500 to 3,000 feet to complete."
Three Piper Aircraft Corporation Service Bulletins (Numbers 609, 661,
and 800) were issued on the PA-38's control column. Number 609 dealt
with ensuring that the control column (tube) was securely welded to
the control wheel. This service bulletin was made into a Federal
Aviation Administration Airworthiness Directive (AD). Service
bulletin numbers 661 and 800 dealt with the binding of the control
column when positioned fully aft (full up elevator).
According to N2495L's airframe logbooks, service bulletins 661 and
800 were complied with. Service bulletin 609, and its accompanying
airworthiness directive, did not apply to N2495L.
----------------------------------------------------------------------------
This is the end of Part 1. As it is now 2:20 am cst here in Okla.
City, I will finish the rest tomorrow.
Sean Shenold
Sean Shenold
National Transportation Safety Board
Washington, D.C. 20594
Brief of Accident
Accident Date: 03/05/94
Report adopted on: 07/12/1995
NTSB Accident ID: CHI94FA097
NTSB File No.: 1793
Place of Accident: INMAN, KS
Aircraft Reg. No.: N2495L
Local Time of Accident: 08:30 CST
----------------------------------------------------------------------------
Aircraft Make/Model: PIPER PA-38-112
Aircraft Damage: Destroyed
Engine Make/Model: LYCOMING O-235-L2C
Number of Engines: 1
Operating Certificates: None
Type of Flight Operation: Instructional
FAR Flight Conducted Under: 14 CFR 91
Crew Injuries, Fatal 2
Crew Injuries, Serious 0
Crew Injuries, Minor/None 0
Passenger Injuries, Fatal 0
Passenger Injuries, Serious 0
Passenger Injuries, Minor/None 0
----------------------------------------------------------------------------
Last Departure Point: HUTCHINSON, KS
Destination: Same as Accident
Condition of Light: Daylight
Airport Proximity: Off Airport/airstrip
Weather Information Source: Unk/Nr
Basic Weather: Visual (VMC)
Lowest Ceiling: None
Visibility: 0015.000 SM
Wind Direction: Calm
Wind Speed: Calm
Temperature (F): 38
Precipitation: None
----------------------------------------------------------------------------
Age Pilot-in Command (PIC) 54
PIC Certificates/Ratings Commercial, Flight Instructor, Single-
Engine Land, Multi-Engine Land
PIC Instrument Ratings: Airplane
PIC Time, All Aircraft: 7945
PIC Time, Last 90 days: Unk/Nr
PIC Time, Total Make/Model 105
PIC Time, Total Instrument Unk/Nr
----------------------------------------------------------------------------
Accident Narrative:
THE PURPOSE OF THE FLIGHT WAS TO PROVIDE A BIENNIAL FLIGHT REVIEW FOR
A PRIVATE PILOT WITH ABOUT 100 HOURS TOTAL FLIGHT TIME. WITNESSES
OBSERVED THE AIRPLANE SPIN 5 OR 6 TURNS TO THE LEFT & REPORTED THAT
THE AIRPLANE STOPPED ROTATING JUST BEFORE IT HIT THE GROUND. THE
SPIN IS BELIEVED TO HAVE OCCURRED INADVERTENTLY WHILE THE PRIVATE
PILOT WAS DEMONSTRATING A STALL OR SLOW FLIGHT. ALTHOUGH THE PA-38
HAS FOUR NON-ADJUSTABLE STALL STRIPS, INTENDED TO IMPROVE ITS
LATERAL-DIRECTIONAL CHARACTERISTICS, ITS STALL/SPIN ACCIDENT RATE IS
SIGNIFICANTLY HIGHER THAN COMPARABLE TRAINER-TYPE AIRPLANES.
----------------------------------------------------------------------------
Occurrence #1 LOSS OF CONTROL -- IN FLIGHT
Phase of Operation: MANEUVERING
Findings:
1. -- STALL/SPIN -- INADVERTENT -- FLIGHTCREW
2. -- INSUFFICIENT STANDARDS/REQUIREMENTS -- MANUFACTURER
----------------------------------------------------------------------------
Occurrence #2 IN FLIGHT COLLISION WITH TERRAIN/WATER
Phase of Operation: DESCENT -- UNCONTROLLED
----------------------------------------------------------------------------
Accident Cause:
AN UNINTENTIONAL SPIN WHICH OCCURRED DURING THE MANEUVERING PHASE OF
A BIENNIAL FLIGHT REVIEW. A FACTOR RELATED TO THE ACCIDENT WAS: THE
AIRPLANE'S LATERAL-DIRECTIONAL CHARACTERISTICS AT OR NEAR THE STALL
SPEED.
----------------------------------------------------------------------------
Sean Shenold
WRECKAGE AND IMPACT INFORMATION
N2495L collided with the ground on an approximate magnetic heading
of 040 degrees. The first ground scar was oriented on an approximate
magnetic heading of 130/310 degrees, measuring about 38 feet. A
second ground scar, originating from the midpoint of the first, was
about 120 feet long and on a magnetic heading of 345 degrees. The
second ground scar led to N2495L's wreckage. The airplane's wreckage
heading was 355 degrees magnetic.
The first ground scar varied in depth between two and four inches.
It had white paint transferred onto sections of compressed dirt. A
piece of curved, green, glass was found at the extreme southeast edge
of this ground scar. At the center of this ground scar an
elliptically shaped depression measuring about five feet wide and six
feet long. It was about seven inches deep at the center. Gouge
marks were found in the approximate center of this area. The largest
gouge mark matched one of the airplane's propeller blades.
Examination of the blade found chordwise scratches, some having the
same colored dirt in them as found in the gouge.
The main landing gear legs had separated from the fuselage mounts.
One main landing gear was found on top of the left wing at the
mid-span position. A second main landing gear leg was found about
100 feet northwest of the first ground scar termination point. The
wheel and tire assemblyies were attached to the main landing gear
legs. The tires matched ground indentations that were found south of
the elliptically shaped ground depression. The ground indentations
were equally spaced on either side of the elliptically shaped ground
depression.
The inboard sections of both wings were burnt. The fuselage had
burned between the engine compartment and vertical stabilizer. The
propeller had partially separated from the crankshaft flange. The
propeller was 'S' shaped, one blade curved forward about 90 degrees
from its hub. The second blade was curved aft about 40 degrees from
its mid-span position.
The right wing was twisted about 70 degrees upward at the mid-span
point outward to its wingtip. Leading edge skin on the wing was
wrinkled and had separated from the main wing spar. The inboard
portion of the leading edge skin was burnt. The ground under the
right wing fuel tank area had a strong odor of aviation gasoline.
The left wing leading edge skin was wrinkled.
Flight control continuity between the respective surfaces and
control yokes and rudder pedals was confirmed. The left control
yoke/mounting sleeve combination had separated from its torque tube.
The right control yoke was attached to its torque tube. The control
yoke torque tubes, chain sprockets, chains, and tee bar assembly was
found complete and unseparated.
The elevator and rudder stops were not damaged. Elevator trim
cable and springs were fire damaged. They were attached between the
cockpit trim wheel and trim tab. The top of the left rudder stop was
3/8" from the vertical stabilizer spar mount. The top of the right
rudder stop was 5/16" from the vertical stabilizer spar mount.
The engine was fire damaged; it was rotated confirming internal
component continuity when the magnetos were removed. The right
magneto was fire and impact damaged and could not be turned. The
left magneto was fire damaged but could be rotated. The carburetor
had separated from its mounting flange and was fire damaged. The
muffler had been crushed aft and upward into the engine's sump.
ADDITIONAL INFORMATION
Research into the PA-38's design, certification, and manufacture
revealed the design originally started out with a conventional tail,
i.e., a low mounted horizontal stabilizer/elevator rather than the
"T" tail it was certified with. The prototype was designed, built,
and test flown during late 1969, 1970 and into 1971. For reasons not
defined, the design was placed into storage at the manufacturer for
about four years. The PA-38 prototype was taken out of storage and
reconfigured with a "T" tail. One of the two original design
engineers remained with the company and worked on the resurrected
prototype's development.
Originally, the wing was designed using the NASA GAW-1 airfoil and
11 full ribs from wingtip to wing root on each side. This wing had a
"U" shaped channel main and secondary spar from wing root to wing
tip. The two-piece main spar was joined next to the aileron/flap
junction of the wing. Both original design engineers said the PA-38
prototype had been built with a rigid wing structure. One of the
design engineers said this type of structure is necessary when using
the GAW-1 airfoil.
The certificated PA-38 had its main wing spar made from flat
aluminum stock. The "U" shaped secondary spar was retained.
Lightening holes were cut out along the main spar's outboard half.
The main spar had span length "L" shaped extrusions attached to its
top and bottom.
The reconfigured airplane retained the same airfoil but had its
wing rib numbers reduced to four full sized ribs and four nose ribs
per wing. Wing surface shaping extrusions replaced the ribs that
were eliminated from the prototype. The extrusions were positioned
between the main and secondary spars. There were no vertical braces
between the top and bottom extrusions. The original design engineers
were aked why the design had been changed. Both said that it was
their opinion that the airplane's structure had been simplified for
manufacturing purposes after it left their design shop. The design
engineer said that removing wing ribs and and changing the spar
design would make the wing less rigid, i.e., "soften" the wing.
According to this engineer, the wing's softened structure would not
enhance the wing's stall and spin characteristics. He said the
softened wing structure could change the airfoil shape, making the
wing a new and unknown commodity in stalls and spins. He said he had
inspected a PA-38 wing and found it to be very soft, and able to be
torsionally twisted without substantial effort.
FAA Service Difficulty Reports related to the wing were examined
for the period between 1986 and April, 1995. Fifteen reports showed
loose rivets in the wing, bent aft spar attach fitting, and
undertorqued wing spar attachment plate bolts. Before sending the
airplane to the production design shop, the remaining design engineer
stated the airplane had problems with "A very strong rolloff, I
think, to the left." He said he designed a wing root glove that was
very effective ". . . in terms of cooling off the stall
characteristics." He also revealed that the airflow next to the wing
root, aft fuselage, and tailcone was not adhering as it should. He
said the purpose of the cuff was to improve the airflow along the
aft fuselage and give the airplane better stall characteristics. The
company design engineers removed the cuffs from the airplane after
they had received it from the design shop. The airplane received its
FAA type certificate without the leading edge cuffs.
A NASA aerodynamicist who worked with Piper Aircraft Corporation
during the development of the PA-38's wing said the GAW-1 wing
requires attention to the wing root area. He said this was due to
the airflow separation found at the wing root and along the fuselage
during high angles of attack.
The remaining design engineer said that stall strips were installed
on the wing's outboard section after the wing root glove had been
removed. He said he ". . . searched all over the wing for a position
of the stall strip that would work. And, I was getting, I just
couldn't find the location. And, the guys that were doing the flying
said, okay, . . . where do you want it next? I said, oh, put the . .
. thing out on the tip [in front of the aileron]. I was just being
facetious. They did that and it worked. It got the stall
characteristics to the point where they were certifiable." Without
the stall strips the aileron would have "Very little authority . .
.," according to the designer.
The designer was asked if the type ailerons the Piper PA-38 was
certified with would be effective in stopping the wing's rolloff at
the time the stall occurs. He said, "I doubt it. They're marginal
ailerons." He was asked to explain what he meant by his statement.
He replied, "They have a big gap at the bottom. And the [air] flow
would like to come along the bottom of the wing and follow up on
[the] trailing edge [of the] aileron, but it see this forward facing
step [bottom edge of the aileron's leading edge] and it says, pfff,
sorry, and it becomes turbulent. So, plain flap [and] ailerons are
marginal at slow speeds."
The PA-38 was exclusively built at Piper's Lock Haven,
Pennsylvania, manufacturing facility. A production engineer at the
manufacturing facility stated, "The production Tomahawks [PA-38] I
eventually became airborne in, only as part of my job, were, to a
plane totally unpredictable, one never knew which direction they
would roll-off, or to what degree as a result of a stall. The wings
flexed noticeably . . ." One of the original designers of the
airplane stated, "The aerodynamic performance of a GAW-1 wing is very
sensitive to airfoil shape. If the shape became distorted, the
performance would rapidly deteriorate . . ." He continued, ". . .
the use of a flexible surface representation of the profile sensitive
GAW-1 design opens up a Pandora's box regarding its performance. The
effects of a wide range of steady and unsteady aerodynamic flows
encountered by an aeroelastically soft GAW-1 wing in stalls and spins
would be impossible to resolve in a conventional flight test program."
Autopsies on both pilots were conducted at the Ryan Funeral Home in
Salinas, Kansas. Toxicological testing was conducted by the FAA's
Civil Aeromedical Institute. The results of both tests were negative.
----------------------------------------------------------------------------
This concludes part 2 of the NTSB report on the crash of a Piper
Tomahawk near Inman, KS March 5, 1994. It is verbatim, complete with
a couple of misspellings I ran across.
Sean Shenold
records of interviews conducted by the investigation team, and are
included as attachments to the report itself.)
NATIONAL TRANSPORTATION SAFETY BOARD
IIC RECORD OF INTERVIEW
ACCIDENT NUMBER: CHI94FA097
INTERVIEW DATE: 08/11/94
TIME OF INTERVIEW: 1100 CDT
PERSON INTERVIEWED: Dr. Richard Kroeger
RELATIONSHIP TO ACCIDENT: One of the original design engineers on the
Piper PA-38 project.
SUBJECT: Information regarding the PA-38's design
TEXT:
Dr. Kroeger siad that the design team at Piper was nervous about
the softness of the airplane's wing after it had received its FAA
Type Certificate. He said the GAW-1 airfoil must retain its shape to
get the proper airflow over it. According to Dr. Kroeger, the
airflow separation point oscillates fore and aft when the wing is
stalled.
Dr. Kroeger said the prototype's development was stopped before it
could be spin tested. He said the design team did not believe the
airplane would have good spin characteristics because of the airfoil
being used.
He said that Piper resurrected the airplane shortly after the
company was purchased by another company during 1975 or 1979. He
said the company decided to put a "T" tail on the airframe. Dr.
Kroeger said the airplane was FAA certified shortly thereafter.
INTERVIEWED BY: FRANK S. GATTOLIN (signed)
ADDITIONAL COMMENTS:
----------------------------------------------------------------------------
NATIONAL TRANSPORTATION SAFETY BOARD
IIC RECORD OF INTERVIEW
ACCIDENT NUMBER: CHI94FA097
INTERVIEW DATE: 08/11/94
TIME OF INTERVIEW: 1435 CDT
PERSON INTERVIEWED: Ralph Kimberland
RELATIONSHIP TO ACCIDENT: Former Piper Aircraft Corporation engineer
on the PA-38 project. Made some test flights in the
prototype PA-38.
SUBJECT: Stall and spins characteristics of the PA-38.
TEXT:
Mr. Kimberland stated the original prototype was a very good
spinning airplane as best as he could recall. He said the flight
test team had placed a 20 pound lead weight on the airplane's
firewall for empty weight center of gravity attainment.
Mr. Kimberland stated that the first production line PA-38's were
"beasts" in a spin. He said that small changes in the airframe had
large influences on how their airplane reacted to stalls and spins.
He said stall strips were added to the wing and that they didn't do
much for it-- he said they would work only if they were properly
positioned. He said the airplane had a lot of airflow separation at
the fuselage/wing junction.
INTERVIEWED BY: FRANK S. GATTOLIN (signed)
ADDITIONAL COMMENTS:
----------------------------------------------------------------------------
NATIONAL TRANSPORTATION SAFETY BOARD
IIC RECORD OF INTERVIEW
ACCIDENT NUMBER: CHI94FA097
INTERVIEW DATE: 08/29/94
TIME OF INTERVIEW: 1300 CDT
PERSON INTERVIEWED: Dr. Richard Kroeger
RELATIONSHIP TO ACCIDENT: One of the original design engineers on the
Piper PA-38 project.
SUBJECT: Characteristics of the PA-38's GAW-1 airfoil when in
a stalled condition.
TEXT:
Dr. Kroeger said the airfoil's center of pressure is further aft
than a normal airfoil. He stated that the nose of the airfoil also
produces more lift than a normal airfoil during the stall.
INTERVIEWED BY: FRANK S. GATTOLIN (signed)
ADDITIONAL COMMENTS:
----------------------------------------------------------------------------
NATIONAL TRANSPORTATION SAFETY BOARD
IIC RECORD OF INTERVIEW
ACCIDENT NUMBER: CHI94FA097
INTERVIEW DATE: 12/01/94
TIME OF INTERVIEW: 1400 CST
PERSON INTERVIEWED: Mr. Barnaby Wainfan
RELATIONSHIP TO ACCIDENT: Aerodynamicist familiar with GAW-1 airfoil
as found on N2495L's wing.
SUBJECT: Information about the GAW-1 airfoil.
TEXT:
Mr. Wainfan stated that the airfoil was a trans-sonic airfoil that
had many positive characteristics as a trans-sonic airfoil. He said
the airfoil developer's thought was that if the GAW-1 is a good
trans-sonic airfoil then it should be a good low speed airfoil. He
said the airfoil shape developed a substantial amount of lift due to
its aft cambered shape of the airfoil's underside.
Mr. Wainfan stated that the GAW-1 airfoil has had a history of
spinning problems when used on general aviation airplanes. He said
the blunt leading edge of the airfoil creates substantial lift during
the spin. This is most noticeable on the outboard wing of the
spinning airplane. He added that the under-cambered trailing edge of
the airfoil also creates lift during this phase. These two
conditions, according to Mr. Wainfan, drives the wing further into
spin auto-rotation.
He said that the wings of the spinning airplane create different
amounts of lift and drag. In order to recover from the spin these
forces must be brought into equalization. Obtaining this
equalization on a wing with the GAW-1 airfoil is more difficult than
other conventional and more widely used airfoils according to Mr.
Wainfan. He said this was due to the extremely high lift and drag
differences that occur during the spin.
Mr. Wainfan emphasized a second time that a wing with the GAW-1
airfoil, when spinning, will be driven more deeply into the spin,
i.e., it produces auto-rotational forces that sustain it in a spin
and can keep it in a spin. He said the orginal lift and drag numbers
showed that a wing utilizing the AW-1 airfoil must be very "stiff".
The wing with a GAW-1 airfoil would be very sensitive to oil-canning
according to Mr. Wainfan.
During the conversation Mr. Wainfan discussed the Beech BE-77
Skipper. He said it had a lot in common with the PA-38. He said
that Beech engineers solved most of the problems with the airplane's
wing and fuselage airflow. He said it had good airflow to the rudder
and was easier to recover from a spin than a PA-38.
INTERVIEWED BY: FRANK S. GATTOLIN (signed)
ADDITIONAL COMMENTS:
----------------------------------------------------------------------------
NATIONAL TRANSPORTATION SAFETY BOARD
IIC RECORD OF INTERVIEW
ACCIDENT NUMBER: CHI94FA097
INTERVIEW DATE: 12/02/94
TIME OF INTERVIEW: 1556 CST
PERSON INTERVIEWED: Dr. Richard Kroeger
RELATIONSHIP TO ACCIDENT: Party to the investigation, one of the
original design engineers on the Piper PA-38 project.
SUBJECT: PA-38 airframe development, GAW-1 airfoil
characteristics and affect on airframe.
TEXT:
Dr. Kroeger stated that the original prototype PA-38 had been
designed with a stiff wing because a stiff structure is needed for a
wing using the GAW-1 airfoil. He stated that the prototype was not
spin tested during his employment with Piper Aircraft Corporation.
Dr. Kroeger stated that the GAW-1 airfoil was found to
aerodynamically shorten the distance between the airplane's wing and
empennage because of the amount of lift being generated near the
airfoil's aft end. He said the airfoil effectively moves the wing
back and center of gravity forward.
According to Dr. Kroeger, before manufacture of the FAA approved
PA-38, two engineers employed by Piper Aircraft Corporation found
that the airflow around the wing's root and aft fuselage was not
adhering as it should. They recommended that the wing leading edge
cuffs be added to the wing at the root. He said the purpose of the
cuffs was to improve airflow along the fuselage. Dr. Kroeger stated
that the company decided not to put cuffs on the airplane because of
the manufacturing costs.
INTERVIEWED BY: FRANK S. GATTOLIN (signed)
ADDITIONAL COMMENTS:
----------------------------------------------------------------------------
NATIONAL TRANSPORTATION SAFETY BOARD
IIC RECORD OF INTERVIEW
ACCIDENT NUMBER: CHI94FA097
INTERVIEW DATE: 12/16/94
TIME OF INTERVIEW: 1326 CST
PERSON INTERVIEWED: Richard Margason
RELATIONSHIP TO ACCIDENT: Aeronautical engineer familiar with the
GAW-1 airfoil and Piper PA-38 wing.
SUBJECT: Information on the GAW-1 airfoil and Piper PA-38 wing.
TEXT:
Mr. Margason stated he had worked on the GAW-1 airfoil and the
Piper PA-38 wing and body combination.
Mr. Margason stated the GAW-1 airfoil requires a stiff wing
planform to work correctly. He said the airfoil was tested on a
rigid wing supplied by Piper Aircraft Corporation. He stated that a
flexible wing could create stability problems during the stall phase
of flight.
According to Mr. Margason, the trailing edge of the GAW-1 equipped
wing creates a large amount of lift at the trailing edge throughout
the angle of attack range. He suggested that the IIC compare the
wing's of the Piper PA-38 and Beech BE-77.
INTERVIEWED BY: FRANK S. GATTOLIN (signed)
ADDITIONAL COMMENTS:
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And that's it. Any comments?
jtwel...@gmail.com
> There has been quite a bit of controversy over the Tomahawk lately,
> that may have escaped some people's attention.