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#11
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helicopter-glider
"One immediate problem I see is that friction in the rotor axis would
tend to make the fuselage counter-rotate, and that would have to be countered somehow. A secondary rotor out on the boom is what real helicopters use, but that would be cheating in a glider model. Johan Larson, mad-scientist wannabe" Wait. You need to study helicopters. The tail rotor is called an anti-torque device and is there to counteract the torque of the main rotor. If someone shoots the tail rotor off, or the mechanism fails, you simply reduce the throttle to zero (and drop the collective). It is called autorotation. Once you go into autorotation, the main rotor continues to turn, you are a heli-glider - and there is no torque developed by the engine so the tail rotor is not necessary for anti-rotation. Of course there is a minor problem in that the change in pitch of the tail rotor determines which direction the helicopter is facing, but that is a minor detail. If you are not careful hovering during certain wind conditions, you may end up in an uncontrolled spin. At that point, you simply throttle the engine down, try to put it down level, shut the fuel supply off and then try to explain to the insurance company that it was not your fault. As soon as the throttle is shut down, you stop spinning - or so the book says. I have not tried it yet. Colin |
#12
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#14
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helicopter-glider
The Bensen Gyroglider ? Any left flying ? Any one
flown one off-tow ? Ian |
#15
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helicopter-glider
COLIN LAMB wrote: "One immediate problem I see is that friction in the rotor axis would tend to make the fuselage counter-rotate, and that would have to be countered somehow. A secondary rotor out on the boom is what real helicopters use, but that would be cheating in a glider model. Johan Larson, mad-scientist wannabe" Wait. You need to study helicopters. The tail rotor is called an anti-torque device and is there to counteract the torque of the main rotor. If someone shoots the tail rotor off, or the mechanism fails, you simply reduce the throttle to zero (and drop the collective). It is called autorotation. Once you go into autorotation, the main rotor continues to turn, you are a heli-glider - and there is no torque developed by the engine so the tail rotor is not necessary for anti-rotation. Of course there is a minor problem in that the change in pitch of the tail rotor determines which direction the helicopter is facing, but that is a minor detail. If you are not careful hovering during certain wind conditions, you may end up in an uncontrolled spin. At that point, you simply throttle the engine down, try to put it down level, shut the fuel supply off and then try to explain to the insurance company that it was not your fault. As soon as the throttle is shut down, you stop spinning - or so the book says. I have not tried it yet. That doesn't sound quite right. With the engine shut down, and the main rotor spinning freely, there should still be some friction between the rotor shaft and whatever mechanism attaches it to the fuselage. This friction would be slowing down the rotor, and by action-reaction causing the fuselage to rotate in the direction of the rotor. And if there's no tail rotor, there isn't really anything to stop this rotation of the fuselage. I'm a bit surprised this isn't mentioned in the book, but at a guess, the force is low enough compared to engine-torque to be dismissed in a powered aircraft, since it is only relevant in a rarely-encountered emergency situation. But in a glider-variant, it could well be significant. |
#16
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#17
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helicopter-glider
That doesn't sound quite right. With the engine shut down, and the main
rotor spinning freely, there should still be some friction between the rotor shaft and whatever mechanism attaches it to the fuselage. This friction would be slowing down the rotor, and by action-reaction causing the fuselage to rotate in the direction of the rotor. And if there's no tail rotor, there isn't really anything to stop this rotation of the fuselage. I'm a bit surprised this isn't mentioned in the book, but at a guess, the force is low enough compared to engine-torque to be dismissed in a powered aircraft, since it is only relevant in a rarely-encountered emergency situation. But in a glider-variant, it could well be significant. Well, the main rotor bearing in a small helicopter costs over $30,000 and has a limited lifespan. They are good, low friction berings and need to be so to avoid heat buildup. I understand physics, but your basic premise is based upon friction. If there is slight friction, then the mass itself of the fuselage would tend to keep it in place - plus the small angled vertical fin. That provides all of the stability necessary until you start powering the main rotor. In any event, there are helicopter pilots who have had their tail rotor jam or be completely shot off and they are still alive to tell you about it. Maybe you should tell them why they should have spun to their death. And neither the pilot operator's handbook nor the FAA helicopter mentions that the helicopter will go into a death spin if the tail rotor fails. By the way, I calculated that the Schweizer 300C has about a 2.5 to 1 glide ratio according to the factory specifications, but could never reach that. I was always under 2 to , but it may simply be poor gliding technique. Colin |
#18
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helicopter-glider
Ian Cant wrote:
The Bensen Gyroglider ? Any left flying ? Any one flown one off-tow ? Ian When I visited the Udvar-Hazy division of the National Air and Space Museum a couple of months ago I saw a W.W.II vintage, unpowered, folding gyroplane designed to be carried aboard a U-boat and launched tethered to the ship as an reconnaissance vehicle. I have a snap shot, but, alas, it can't be posted here. If interested send me an e-mail and I'll send you a copy. Al |
#19
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helicopter-glider
"When I visited the Udvar-Hazy division of the National Air and Space
Museum a couple of months ago I saw a W.W.II vintage, unpowered, folding gyroplane designed to be carried aboard a U-boat and launched tethered to the ship as an reconnaissance vehicle. I have a snap shot, but, alas, it can't be posted here. If interested send me an e-mail and I'll send you a copy." These gyroplanes were not used very long as there was a flaw. If the pilot saw and reported an enemy nearby, the submarine would release the gyroplane and submerge. If they got in a hurry, they would submerge without releasing. The entire project lasted only a few months if I recall. I wonder if an allied pilot got credit for shooting down a tethered gyroplane. The secret was probably to buzz the submarine and cause it to release the gyroplane, then shoot down the gliding gyroplane - after all it is an aircraft. Colin |
#20
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helicopter-glider
Actually, Bensen developed several Gryogliders. The first was the B6 in
1953. They were designed to be towed by a car to 150 feet or so, and then released. He also developed a version on floats that was towed by a boat. |
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