By: Timothy O’Connor
Overview….
The gyroplane or Autogyro was
invented by Juan de la Cierva in
1919.
Cierva wanted to build a flying
machine that was safer than fixed
wing aircraft and could not stall or
spin.
Cierva succeeded and the safety
record of his autogyros is
unparalleled in aviation.
The Autogyro…
Development of Helicopters
Return of the gyro…
New Designs, New Problem
Returning to the Dream
Overview….
Ironically, Juan de la Cierva died when
the fixed wing commercial transport in
which he was a passenger stalled and
crashed on takeoff.
Desiring the short take off and landing
abilities of the autogyro, plus the ability
to hover, the helicopter was developed
principally from Cierva’s patents.
The remaining autogyro companies
did not survive the great depression.
Engineers continued to develop the
helicopter and the autogyro was
almost forgotten by industrial
aviation.
The Autogyro…
Development of Helicopters
Return of the gyro…
New Designs, New Problem
Returning to the Dream
Overview….
Igor Bensen, an aerospace engineer
working for General Electric was given
the job of studying German WWII
gyrokites used for target spotting by
submarines.
From this, Bensen designed and
developed a kit-built, single person,
pusher autogyro he called the
‘gyrocopter’.
The gyrocopter plans were sold
through catalogs and magazines.
Essentially creating the homebuilt
aircraft hobby.
The Autogyro…
Development of Helicopters
Return of the gyro…
New Designs, New Problem
Returning to the Dream
Overview….
As the homebuilt market developed and
took off many companies copied Bensen’s
gyrocopter and sold kits of their own.
These companys tried to ‘improve’ the
gyrocopter by adding larger props, new
engines, better looks and new styles.
Unlike Cierva’s autogyros or Bensen’s
gyrocopter these new machines were not
designed by aeronautical engineers.
The new designs failed to take into
account the ramifications larger engines
and props would have on the
aerodynamics of the gyroplane.
Many of these designs were terribly
dangerous and the resulting high fatality
rate changed the autogyro from being
the safest aircraft in the sky to the most
dangerous.
The Autogyro…
Development of Helicopters
Return of the gyro…
New Designs, New Problem
Returning to the Dream
Overview….
As gyroplane fatalities grew a number of
people started to look into the causes.
What they found is the kit
manufacturers that copied Bensen’s
gyrocopter failed to take into account
the importance of placing the center of
gravity (CG) in the thrust-line of the
propeller and the necessity of pitch
stability.
With these lessons learned, the current
generation of gyroplane kits have now at
last returned to Cierva’s dream of a safe
aircraft that cannot stall or spin.
The Autogyro…
Development of Helicopters
Return of the gyro…
New Designs, New Problem
Returning to the Dream
What is a “Push-Over”?
What happens if
you push on the
back of grandma’s
rocking chair near
the top of the head
rest?
What is a “Push-Over”?
What happens if
instead of pushing
on the back of the
headrest of
grandma’s chair
you push on the
back of her butt?
What is a “Push-Over”?
When you push on
grandma’s seat your
thrust is in-line with
her center of gravity
and she is pushed
forward.
When you push
on grandma’s
headrest she
rotates around
her center of
gravity.
What is a High Thrust Line
and Center Line Thrust?
When you push
above grandma’s
center of gravity
(CG) your thrust
line is high (HTL)
When your push is
centered on
grandma’s CG you
have Center Line
Thrust (CLT)
HTL
CLT
What does HTL and CLT have to do with
gyroplanes?
As stated earlier the original
autogyros and the Bensen
gyrocopter were designed by people
with aeronautical engineering
experience.
These machines were designed so
that the thrust line from the engine
passes through the center of gravity
(CG).
Cierva patented this design and
Bensen documented it in his
manuals.
So all engineer-designed gyroplanes
were CLT.
What does HTL and CLT have to do with
gyroplanes?
When hobbyists got into the business of
making gyroplane kits they made some
changes…
Larger engines…
Larger props…
2-side-by-side seats…
Enclosures…
“sports car” styling
But when they made these changes they did
not hire aeronautical engineers to audit the
designs..
The result: A flaw.. Gyroplanes that were
unstable, HTL and thus…unsafe.
PPO events are the leading killer of both
low and high-time gyroplane pilots and
passengers.
Some Post-Bensen Design Changes..
1.
2.
3.
4.
5.
6.
Larger Engine
Larger Prop
Reduction Drive
Lowered Gas Tank
Side by Side Seating
Enclosures
Each change increases the
thrust-line off-set and the speed
and ease in which the gyro can
pitch over.
Result… a HTL gyroplane design.
What is wrong with a HTL design?..
HTL gyroplanes can be very safe and
reliable. However, let’s first talk about
potential safety issues with HTL
designs…
The problem with HTL designs is that
they have the potential to pitch over. A
gyroplane pitch over is called a Power
Push Over (PPO).
If the rotorblades stop producing thrust
(such as in a near-zero G event) then the
power from the engine can pitch the
gyro over (PPO).
This event is unrecoverable and almost
always fatal.
A Center Line Thrust (CLT) gyroplane
can not PPO. Therefore it is immune to
this problem.
Rotor-Thrust
Engine Thrust
What can cause a near-zero G event?
1.
PIO – Pilot induced oscillation
2.
Strong turbulence
3.
Steep Climb and Push-over
4.
Strong down drafts
What can reduce the causes of
near-zero G events?
1.
PIO – Pilot induced oscillation
1. Training
2. Flying a Stable Gyro
2.
Strong turbulence
3.
Strong down drafts
1. Training
2. Weather Awareness
3. Flight Planning
4. Good Decision Making
5. Flying a Stable Gyro
1. Training
2.
Weather Awareness
3.
Flight Planning
4.
Good Decision Making
5.
Flying a Stable Gyro
4. Steep Climb and Push-over
1. Training
2. Flying a Stable Gyro
What can reduce the susceptibility of
gyroplanes to Power Push Overs (PPOs)?
1.
Fly a stable gyroplane
Adding a horizontal stabilizer
will GREATLY reduce the risk of
PIO, the leading cause of PPOs.
Horizontal stabilizers are more
effective when placed on a long
moment arm (like an extended
keel) or in the prop-wash.
2.
Lower the Thrust Line Offset
If the thrust-line of your
gyroplane is more then 2-3
inches higher then the CG you
can reduce the susceptibility of
PPOs by lowering the thrust-line.
Any HTL gyroplane can PPO,
however the larger the offset the
faster the PPO will happen and
the less warning you will have
before the event (if any).
Can Power Push Overs (PPOs) be
eliminated by TRAINING?
1.
No.
(HTL, Unstable)
If the gyroplane has a very high
thrust-line offset and no
horizontal stabilizer, there is no
amount of training or
experience that can make you
PPO-proof. Many well trained,
experienced pilots and CFI’s
have died in PPO accidents in
gyroplanes like these.
No
Very High Thrust-line+Unstable
2.
Almost.
(HTL, Stable)
If your gyroplane is very stable
throughout its flight envelope,
has a large horizontal stabilizer
and the thrust-line of your
gyroplane is only a few inches
(1-4) you are ‘near center-line
thrust’. PPO avoidance
training can reduce your
chance of PPO greatly.
Moderate Thrust-line + Stable
Almost
How to Eliminate PPOs Completely!
1.
Center Line Thrust!
CLT gyroplanes can not PPO.
Many gyroplane designs use CLT
to eliminate PPO events.
2.
Effective Horizontal
Stabilizer.
A large properly designed
Horizontal Stabilizer in the
propeller wash can keep a
gyroplane from PPO-ing.
What is the best placement for Horizontal
Stabilizers?
Good
1.
Size
2.
Moment Arm
(as far back as possible)
1.
Prop Stream
Better
The more effective the Horizontal
Stabilizer the better it reduces
PIO/PPO events.
However to eliminate PPO at all
airspeeds it almost has to be
immersed in the prop stream
Mitigating and fixing design flaws in
legacy gyroplanes..
Flawed
Mitigated
HTL & Unstable
Prone to PIO/PPO
HTL & Unstable
Fixed
HTL & Stable
Resistant to PIO/PPO
Hstab Added
Large Hstab on
Extended Keel
CLT & Stable
Unable to PPO
Resistant to PIO
Dropped keel lowers
Engine and thrust line
Brings stab into wash
CLT & Stable
Unable to PPO
Resistant to PIO
Learn more…
www.pra.org
www.rotaryforum.com
http://gyrowiki.com
www.prachapter34.com
www.gyronation.com
www.TheGyroBee.com
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GREAT video..
http://video.google.com/videoplay?do
cid=3094889465571781052
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(or search for Basics of gyroplane
stability on google video..)
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Thanks!
Chuck Beaty
Greg Gremminger
Doug Riley
Michael Guard
John Stahl
And everyone at…
The Rotary Forum