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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 Operate / Practice Change / Learn Pilotage GREAT video.. http://video.google.com/videoplay?do cid=3094889465571781052 Optimize / Test (or search for Basics of gyroplane stability on google video..) Support / Join Thanks! Chuck Beaty Greg Gremminger Doug Riley Michael Guard John Stahl And everyone at… The Rotary Forum