the words every pilot should commit to memory
. . .Dare
to dream, hope, believe, seek, find, build and fly.
Special Six-Page Report from RAF on The Stabilator to
Article by John Miller, SA Flyer magazine
There are few niche aviation pursuits that attract the contention found
amongst gyrocopter enthusiasts. This is no recent development the die was
cast when Juan de Cierva licensed his unique rotary-wing invention, the
Autogiro, back in the twenties and if we think "lawyer-mania" is a function of
the late nineteenth century, think again. During the thirties, as technology
accelerated following the Great War, patent offices hummed at the giant leaps
in mechanical ingenuity. Cierva's aerial tractor autorotational device was
just one of them. Apart from a short but stunning appearance during the
fifties when Fairey Aviation built the only Rotodyne, and brief unfulfilled
military interest, the Autogiro was to remain on the fringes of commercial
Cierva, amongst others, licensed his creation to a US gentleman by the name
of Harold Pitcairn who was to drive the Autogiro's US development. Their patents
not only enshrined early autorotational principles, but went a long way to
determine current helicopter technology and it was only after Harold's death
that Bell, Kaman, Piaseki and Hiller were obliged to pay royalties following the
world's longest running patent action.
The Fairey Rotodyne was one of the technologies' last commercial adventures
and since the British government ceased funding the project in 1961,
autorotational flight has mostly become the preserve of recreational pilots and
homebuilders. Nowadays, gyrocopters are almost exclusively pusher designs a
configuration championed by the industry's celebrated designer, Igor Bensen. (Bensen
wasn't the first. Lawrence Buhl flew the first pusher design in 1931 based on
Cierva's unflown 1930 C.21 model).
Virtually all current pusher gyrocopters owe their basic design layout to Bensen
and his original glider version. Bensen's early interest was formed whilst
working as an engineer and pilot for General Electric, who had bought an army
surplus Kellett XR-3 in 1945 to study its rotor hub technology. In 1951, Bensen
joined the Kaman Helicopter company but by 1953 had started his own business
marketing and selling, initially a gyro glider and then a powered version sold
in kit form as the B-7 and B-8M, many of which are still around today powerd by
72hp, two-stroke McCulloch engines.
The first autogyros featured a fixed rotorhead, directional control being
achieved by manipulating traditional ailerons, elevators and rudders. By the
early thirties, Cierva was quietly developing his first "direct-control" rotor
system by which control input was passed directly to the rotor plane to alter
attitude. When Harold Pitcairn found this out he was disappointed that Cierva
had not passed on information about his experiments, casting the seeds of
distrust that were to lead to the eventual polarisation of the two companies.
Nevertheless, direct control of the hub was to be universally adopted in all
further gyrocopter designs.
During the sixties, Igor Bensen and protégé Ken Brock were to be the most
successful Gyrocopter proponents and as this form of flying became more popular,
other designs began to appear including the successful Rotary Air Force (RAF)
1000, designed by Canadian Dan Haseloh. Dan's interest was fanned by his uncle
Bernard who was a gyrocopter enthusiast and designer. In 1987 Dan launched his
single seater RAF 1000 followed two years later by the familiar two-seat RAF
The gyrocopter's apparent simplicity is deceptive, as are its basic principles
of flight. Cierva's concept of continually autorotating blades, led the
helicopter industry by some fifteen years. Gyro designers have historically
attempted to usurp the role of the helicopter both by talking up the minimal
runway requirements of their aircraft and by developing the "Jump-takeoff"
concept where the main rotor is pre-rotated to well above its normal rpm and
then suddenly "pitched" to provide a vertical capability. This takeoff method
was developed by Cierva although the concept of collective control had been
discovered by Argentinian, Marquis Raul de Pateras Pescara in 1924. It was to be
used by a number of gyroplane designers including the Groen Brother's who are
currently developing their commercial Hawk gyro. Collectively altering rotor
pitch was used in jet-powered rotor form by Fairey for the Rotodyne and has been
adopted as the primary control arrangement for all current helicopter designs.
One of the gyrocopter's greatest benefits, is its ability to operate safely in
gusty wind conditions that would keep most ultralights on the ground. The reason
for this is the inherent stability of its rotor disc and the disc's traditional
resistance to turbulence. Upward and downward gusts have minimal effect on a
gyro, which makes no use of a horizontal stabiliser. Late thinking has also
determined that the engine's thrust line needs to be in line with the horizontal
centre of gravity to minimize the achilles handling heel of gyrocopters, the
dreaded Power Push Over (PPO). This phenomenon can follow a pilot induced
oscillation (PIO) or an abrupt push of the control stick at the end of
particularly energetic power climb. The best configuration to counter this
tendency is the subject of heated debate amongst gyro pilots. However, one of
the world's most famous authorities, Commander Ken Wallace, believes that,
provided the gyro is well designed, they are quite safely operated without the
need for a horizontal wing in any form.
The gyrocopter's natural stability is derived from its low centre of gravity
with the airframe, engine and occupants weight being suspended from the lift
generating rotors. The engine provides forward thrust and a simple vertical
stabiliser, directional stability. Dan Haseloh, the RAF 2000's designer,
believed a horizontal stabiliser wasn't necessary for his machine. However, the
company, (Dan Haseloh was killed in June 1998 after a mid-air collision whilst
flying for a promotional video), has recently developed a rotor-disc stabiliser
mounted to the mast and hub and adjusted in pitch by the pilot's control input.
Some homebuilders have also included a small stabiliser on the lower rudder
frame. More of this later.
Like most gyrocopter designs, the RAF 2000 uses a single length-wise keel, upon
which is mounted the undercarriage, cockpit, power plant, control systems and
rudder. The gyrocopter is an exceedingly short device, measuring a mere 12 feet
from the nose to the end of the rudder tip. An eight-foot (folding) vertical
section carries the teetering blade rotor, control rods, 2.2 litre 130hp Subaru
boxer engine and its flexible prerotator drive. The undercarriage is fixed to
the keel. It is in essence, an elegantly simple structure and obviously robust,
especially the masthead, which, just like a helicopter, carries the RAF 2000's
entire weight once airborne.
As the gyro is a homebuilt, no two interior layouts are the same apart from the
location of the trim adjusters, throttle and control sticks as well as the
simple bicycle brake grip used to engage the pre-rotator. There are however some
essential instruments, in particular the rotor rpm readout, typically presented
in digital format. This is placed right in front of the left-seated pilot in
command and always sits next to an equivalent engine tachometer. As the RAF 2000
is a two-seater, it is sensitive to weight location in both roll and pitch.
Consequently a pair of prominent trim knobs occupy a central position on the
floor between the occupants.
The egg-shaped cabin appears tiny for two people but is perfectly adequate. The
RAF 2000 is almost unique amongst gyrocopters in having this feature and it goes
a long way to provide an all-weather or rather, an all temperature capability.
The doors are quickly removed for those really warm days.
It is curious to see how some fringe aviation pursuits have aligned themselves
with the flat-four Lancia derived Subaru engine. Amongst other things, it is an
all aluminum unit and it's weight is eminently suitable for aircraft and as
Rotary Air Force has discovered, ideal for their RAF 2000. The engine comes from
Subaru's four-wheel-drive shopping and kid's runabout Legacy model Ð the engine
is called, in the trade, an EJ22 overhead cam. For the RAF 2000, it produces
130hp in normally aspirated form and boasts a 1500 hour TBO. Weight is around
100kgs. Those who may be nervous about adopting obscure automotive engines into
aircraft should be reassured that Steve's Auto Clinic has a great deal of
expertise on this type of application. Through their distributor, Soob Aviation
in Port Elizabeth, overhauls can be done for under R20,000. The engine drives a
2:1 reduction belt to the four-blade composite propeller.
Flying the RAF 2000
There's something quite comical to stepping into a gyrocopter and taxiing out.
On the ground, apart from the rotor blades, there's little to suggest that it
actually flies. Indeed, normal procedure is to taxi out with the rotor static.
To get to this stage had taken a leap in faith. My last and only gyrocopter
experience was some years ago flying a European-manufactured tandem machine, a
VPM. I was alarmed by the handbrake-type pre-rotator handle breaking off in my
hand and the sudden departure of one of the drive belts during our pre-takeoff
checks. When we eventually got airborne, the high vibration through the controls
was enough to end any spark of enthusiasm that may otherwise have won over
another sympathetic member of the flying media (I discovered much later that the
vibration was due to ill-balanced blades).
It happened that Southern Africa's RAF distributor, Dave Armstrong was attending
Oshkosh. As usual, he was accompanied by his family and was spending a great
deal of time at the busy Rotary Air Force exhibition stand. Dave introduced me
to CEO Don LeFleur a legendary figure amongst gyro pilots. Their enthusiasm wore
me down and with a certain amount of misgiving, I volunteered to accompany
demonstration pilot Duane Hunn on an RAF 2000 flight out of Fond du Lac airfield
where they were giving rides.
Duane is RAF's Chief Flying Instructor and has some 5 000 RAF 2000 hours
including 3 000 on his own 1994 machine. This is a lot of airborne time and it
went a long way to settling any disquiet I felt before climbing aboard his
bright yellow gyrocopter. I was about to be converted.
After a careful pre-flight, the Subaru boxer engine fired up easily and was
allowed to warm up before Duane called for departure clearance. With a burst of
power, (the throttle is mounted on a tube that stretches the entire width of the
seat below your knees) we moved off towards the active runway holding point.
Helicopter pilots have, for years, scoffed at the gyro's inability to takeoff
vertically. However, this misses the point somewhat, especially as a Robinson
R22 helicopter is about US$100k more expensive.
In the twenties, getting the rotors to wind up on early autogyros meant taxiing
energetically around the airfield before sufficient rpm had built up to allow a
takeoff. Later, this task was accomplished by winding a rope around the main
shaft and pulling it much like a spinning top. Nowadays, such Heath Robinson
solutions are thankfully a thing of the past and the RAF 2000's blades benefit
from a flexible pre-rotator shaft, engaged by gripping and pulling on a clutch
lever attached to the left stick. Duane gave me this job as I was sitting in the
left seat. With the run-up complete and lined up on the runway, the lever is
held until a magic 140rpm appears on the rotor tachometer. The throttle is then
advanced fully and the RAF leaps forward.
It is important to grasp that when manipulating the stick, the gyro pilot is not
maneuvering the body of the aircraft but the rotor disc. Consequently, special
attention needs to be paid to it during all phases of ground operation as well
as flight. It is vital that the rotors do not contact the ground easy to do if
the stick is not held forward whilst taxiing. At about 100rpm, the rotors begin
to support their own weight and forward pressure on the stick can be relaxed.
The most important skill to be acquired when training is a feel for power,
airframe and rotor disc harmony. The rotor slows down if the disc is presented
to the airflow at too high an angle on takeoff, requiring more power to maintain
rotor rpm. Conversely, too low an angle and the disc will also slow. If this
sounds confusing, then it is. Duane explained that the power needs to be
"feathered in" to achieve a smooth acceleration and best transition to takeoff,
at the same time keeping the nose wheel "light" on the ground.
Done correctly and the RAF becomes airborne very smoothly with little
perceptible change in airframe attitude. Duane further describes the process as
not unlike that of getting a speedboat on the "plane" he says the gyro needs to
"plane out" of the ground run to about 55mph with two on board before it gets on
the step and flies away. We headed east, low level over the flat but picturesque
Wisconsin countryside, taking in the extensive swamp areas that reminded me of
the Okavango Delta. It was a very pleasing experience with a magnificent view in
all directions one of the great attractions of gyrocoptering. Better still, was
the almost complete absence of stick-shake and comfortable ride, even with the
doors removed. I could get used to this!
Duane's RAF is fitted with the latest advance in gyro aerodynamics a "Rotor
Stabilator" that he himself has developed. I was able to fly a standard RAF 2000
without this accessory and the difference enabled me to fly Duane's gyro, free
of any PIO tendencies. RAF claim this device is set to revolutionize gyro
handling. The stabilator is hinged at the mast and is controlled by an
electrical trim pushrod attached to an extension of the torque tube. The
stabilator stabilizes changes in rotor rpm, compensates for turbulent conditions
and helps maintain a constant airspeed. It also dramatically reduces any PIO
tendency. It appears to work very well and once testing is complete, it will be
offered as standard on new machines.
Duane reckons a helicopter pilot will adjust to the gyrocopter quicker than a
fixed wing pilot. However, for each, the handling experience is new. There isn't
a great deal of "feel" through the stick although the RAF 2000 is very happy
being trimmed "hands-off" for extended periods. The biggest challenge is to
remember you are flying the rotor rather than the airframe and it's easy to make
stick inputs in response to tiny changes in the attitude of the airframe. It is
these airframe responses that lead to PIO and they need to be minimized to
achieve a smooth path through the air. Despite my own helicopter time, I
reckoned I needed a good couple of hours to get used to this input. I found I
could happily control Duane's RAF immediately, the Rotor Stabilator, damping out
the small pitch changes found on a standard model. Turning is also easy although
gyro students are taught the effects of this maneuver on rotor speed. It
requires no noticeable rudder input for a coordinated turn. The rotor speed
rises during a turn a result of simple lift and drag vector principles, well
understood by helicopter pilots. Upon returning to the straight and level, a
gyro will start a gentle climb until the rotor rpm stabilizes again.
We eventually returned to Fond du Lac and I returned the controls to Duane. He
talked me through the approach and landing phase, explaining that the gyro needs
to be powered onto the runway. Interestingly, we held our height until over the
threshold, gently reducing the power and flying the rotor disc to a 45-degree
approach angle at some 60-65mph.
With an almost imperceptible back pressure on the stick, the RAF 2000 plopped
ever so gently onto the runway, coming to a stop in a few meters. If I were in a
Robbie, I would then lower collective and heave a sigh of relief that I was
safely back on the ground. The gyro pilot needs to continue monitoring the rotor
rpm and fly the disc as it is still effectively "loaded", making sure that the
stick is moved forward as the rpm dissipates to avoid an embarrassing and
expensive contact with the ground.
|My ride in the RAF was a great aviating experience and I would be encouraged to
do it again. I can understand the gyro's appeal and why passion and opinion run
high within this activity. An RAF 2000 is not an expensive method of becoming
airborne and kits sell for about half the price of current new ultralights.
Africa RAF Distributor, Botswana based Dave Armstrong, left,
Don LaFluer, Rotary Air Force CEO and Garth Armstrong, right.
Seen here at Airventure 2003.
|This article is republished with the permission
of SA Flyer magazine