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Bensen gyrocopter illustration  

GYROPLANES AND HORIZONTAL STABILIZERS
Autogires HORIZONTAL ET STABILISANTS
HORIZONTAL STABILIZER REDUCES NEED FOR PILOT SKILL DURING TRAINING

Identifying Benefits and Risksbit


  • The purpose of a horizontal stabilizer on a "pusher style" gyroplane stabilisateur surn un autogire
  • Where did the inventor of the gyrocopter place the horizontal stabilizer for gyroplanes?
  • What is the one big danger of horizontal stabilizers on gyroplanes?
   
    TAKE NOTE: stabilator and horizontal stabilizer are two different mechanisms. Note this for reference as you read.    
   

A Stabilator uses airflow over it's surface to modify rotor head position and influence rotor blade tilt. A stabilizer uses airflow over it's surface to control the airframe or body of the aircraft. A Stabilator does not influence the body of the aircraft.


   
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Autogyros sans stabilisateurs horizontaux
(Flying autogyros without horizontal stabilizers.) From the air he gave a big wave, a big smile, kicked his legs out, flew backwards and even took a picture of the crowd below.
Wing Comdr. Wallis lives at nearby Reymerston Hall and is best known for inventing Little Nellie, the autogyro which flew in the Bond movie 'You Only Live Twice'. He still holds around 20 world records and despite his age, is considering trying to win some back which he has lost to other pilots. After landing Zeus III, Wing Comdr. Wallis said there had been no question of aborting his plans to fly into the Wallis Days due to winds gusting at around 15 knots - and recalled times when he had been up in seriously bad weather.
"No way!" was his reaction when asked about postponement.
"Weather doesn't bother me. In 1966 there was a storm in Brazil and the authorities would not let any planes in or out. They said no plane would survive it and palm trees were being broken out of the ground.
"But I flew a prototype gyroplane which is the elder sister of Little Nellie."*2
-> Official Wallis Website

Note: gyroplane airframes can be adversely affected by a horizontal stabilizer set downward to counter a nose heavy machine.
 

First some history on the gyroplane design. Looking at old photos of the gyroplane, called the autogiro (autogyro) we can see that they looked exactly like an aeroplane with a rotor blade on top much like a helicopter rotor. Later the main wings were removed from the design as they were unnecessary for flight. (Reference book available: P.W. Brooks, Cierva Autogiros: The Development of Rotary-Wing Flight.)

The purpose of a horizontal stabilizer on a "pusher powered" gyroplane is to make it easier for inexperienced gyroplane pilots to fly the gyroplane in windy conditions. Many experienced gyroplane pilots have flown for years making trim adjustments automatically. New pilots having to think and react, find learning to fly without a horizontal stabilizer very difficult. On a "pusher" gyro the horizontal stabilizer is fixed, meaning it has no pilot input controls. An aeroplane does have control surfaces on the horizontal tail stabilizers. A fixed horizontal stabilizer only works for positive effect during fast forward motion of the gyroplane. It has some effect on landing when positioned directly center on center with a rearward facing propeller. However, normally, gyroplane landings are accomplished in a parachute style setting down of the airframe and flare. Many gyroplane pilots execute aeroplane style landings which are dangerous on unknown grass surfaces. Such landings can, and do result in dangerous nose up or down situations. see:



A study of flying without a horizontal stabilizer is a must for this discussion. Lets look at the "Feral* Gyrocopter" flown by a man in Oz. "Birdy" uses an open frame gyrocopter to "muster" cattle on a large ranch in Australia. His machine uses only a vertical tail and NO fixed horizontal stabilzer. He has been flying many years. A study of his flying technique: see

Note the tail area of the gyrocopter. What's happening here? He's flying the overhead rotorblades using the rudder, stick and throttle

Watch his foot in the turns in

It's interesting to note that the American inventor of the affordable gyroplane, Igor Bensen, did put a small stabilizer on his designs that was below the propeller, not behind. It was also of a specific design and size. (stone deflector? maybe, but still a fixed horizontal stabilizer unaffected by the prop wash) Mr. Bensen is considered to be the inventor of the 'pusher-prop' style of gyroplane design, he trademarked as a 'gyrocopter'.*1 Later designs by other manufacturers of gyroplanes have been experimenting with bigger and bigger fixed horizontal stabilizers placed behind the propeller in positions ranging from the top of the vertical tail fin to the bottom of the vertical tail fin. Some designs put the horizontal stabilizer in place of the vertical tail fin and add two vertical tail fins on either side of the horizontal stabilizer. All of these more recent designs are counter to the Bensen design. The noticeable difference would be that the Bensen design would force air over the top of the horizontal stabilizer where as the other designs use prop wash above and below the stabilizer 'wing'.
Is there a 'best postion' to mount a horizontal stabilizer when positioning it behind the propeller? Yes, and not where you think. Placed between the tip of the propeller blades and the center of the propeller thrustline would give the best airflow over most of the horizontal stabilizer.*3

So, what is the one big danger of large horizontal stabilizers on gyroplanes? That would be in a situation of low forward air speed, close to the ground (landing) and receiving an unexpected gust of wind to the side of the gyroplane. Why would that be a problem? It wouldn't be a problem if the gyroplane airframe is allowed to vane and face the gust of wind. However the automatic response would be to try and correct the direction of the gyroplane, which in turn would cause the airframe to roll over on it's side. This is due to three things happening. First is a large horizontal surface receiving pressure from below. Second is that the prop wash coming off the propeller is not like a cooling fan at home, it's coming off in a cork screw fashion and unless the prop is pushing a lot of air, useless. In sideways gusty conditions it would add to the upward horizontal stabilizer force into a roll over situation. Done quickly enough it would be too fast to counter. Did you ever try to carry a sheet of plywood across the yard to the house on a windy day? It's not difficult to see the effect of a sudden gust of wind below a large fixed horizontal surface.
This happened to a pilot recently in Perth, Australia. On take off a gust of wind to side of the gyro caused it to loose control and flip on it's side. The man was injured and the gyro was a "write-off". December 18, 2011.
The final danger is twisting the rotor blade 'plane'. You know what happens to a spinning vertical bicycle wheel (gyro effect) when you suddenly try to tilt it in a large movement, it flips dramatically 90 degrees horizontal and 45 degrees to the direction of spin (try it).

The smaller the tail area, the bigger wind gusts it can handle, the larger the tail area the less stable it will be in gusty wind conditions at slow forward air speed. - "Food for thought".
In fact, on "pusher" gyrocopters, reducing engine speed reduces horizontal stabilizer control. Or put another way, the less the prop speed the more the horizontal stabilizer is subject to influence from wind.

The number one fact to remember with gyroplanes is that you're really flying the rotor disc above your head. Be knowledgable about it, and it will behave properly for you.

Well, you've certainly shown some variables about fixed horizontal stabilizers on gyrocopters, so what have you to show on "movable Stabilators on gyrocopters"? Ok: -see -> stabilators


   
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--> Piet's first flight
   
   
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Revisions: * - Feral is a name associated with a domestic animal living in the wild on it's own.
*1 - Early Bensen designs were unpowered and towed by a ground vehicle, with a long cable, to fly
*2 - EDP, uk, August 2006
*3 - Don Shoebridge Hypothesis