Double hang test.

[GraemeMonro]

Thanks Sam.

[Mark Horan]

Sam,I like to get discussion on this topic, so here goes.While I agree that a Gyro will pitch, yaw and roll around its CoM, I dont belive that the CoM is the same in static and dynamic situations.In a fixed wing the CoM stays the same. In flight, a fixed wing aircraft is in the same configuration as it is on the ground, ie the wings are in the same place.In a gyro the "wings" move around a bit. when the balance test is done the rotors are in the fore and aft position. when the rotors are turned 90 degrees from that position, you need to pull the nose down to find the balance point (in static situation). I think this is one of the reasons why the mast wriggles around during flight? Add to this different airspeeds creating parasitic drag on the airframe and huge "wing areas" that we have on Gyros, meaning that higher drag loadings equate roughly to more weight at the leading surfaces of the aircraft.In a fixed wing, the aircraft can be trimmed to allow for the drag, but a gyro has a "flexible" coupling to its wing and so the airframe finds its path of least resistance in relation to the wing. With this in mind, I should imagine that the CoM for want of a better term, must change along the arc of movement.I suspect that this is the reason that Pusher Gyros get twitchy at higher speeds, because the CoM changes in relation to the wing. If this is the case, I have no doubt that the thrust line is important to stability, but its relationship to the rotor and angle of attack, rather than the airframe and its CoM may be more important. Here is the can of worms, I look forward to the answers. I have only been flying since 2002 and I am still learning. Mark.

[asra]

I have seen pictures of gyro"s with high fuel tank and seating arrangements and these are described as CLT. My gyro would be described as high thrustline. With very light blades and a full tank of fuel the gyro would tend to nose over if I accelerated with full throttle. With heavy blades and a full tank of fuel the gyro would accelerate without changing attitude. As the fuel load dropped the nose would lift on acceleration. This was without a H.S. If I had the seat tank lifted to where it would be called CLT I doubt I could have held the nose down enough to be able to accelerate at full throttle without climbing. Although it is hard to tell looking at photos, some of these gyros apear to have the thrust line through the CM without taking into account the weight of the rotors, then requiring large horizontal stablizers because the thrust line is too low.Going off the balances I have done since changing the machine I think it would have balanced out at CLT with heavy rotors and a full tank of fuel. There was a good thread on the US forum a couple of weeks ago that explained CLT very well. Using center line thrust which includes the weight of the rotors to stabilize the machine for acceleration and deceleration, then a horizontal stabilizer to sort out drag differential at different airspeeds seem the way to go.The length of the gyro I suspect would also cause them to be twitchy at hight speeds, like a short wheelbase car.

[asra]

G"day Mark,My simple mind thinks that the C of M would stay about the same (allowing for fuel useage, etc), but that the forces acting about the C of M would change i.e. Your "drag". So that as speed increases, drag up top decreases, drag below increases. Which should still equate to a forward turning motion around the C of M if the machine was CLT at static. Which I think is what you are saying? What I don"t understand about the CLT argument is how not knowing the drag figures allows you to determine flight characteristics. For instance, that little single that Sam used to fly. If you put a light weight vertical flat plate of (say) 4 sq. ft. between the wheels, it wouldn"t change the hang test, it wouldn"t change the C of M. But it would make it a bit interesting to fly, especially with a bit of speed up. ;D (Unless I"m missing something).CheersFred

[Mark Horan]

Fred, you is coming onto the same page as me!When I stick my arm out the window of the landcriser at 140 (its a turbo), it requires a fair bit of force to keep my arm on the same place.

[asra]

My understanding of it is the thrust required to push an open frame single seat gyro through the air at best LD causes the machine to swing forward from the vertical about 9 degrees due to the difference in drag between rotor and fuselage. This seems to be a rule of thumb that works as I have always set it up to hang 9 degrees nose down when hang testing and it would fly level between 30 and 60 knt"s.I am thinking that to use thrust to counter a difference in drag the gyro would only be balanced at the airspeed it is setup for and would be out of balance above or below that speed.

[asra]

Just thinking about that bit of plate Fred. I put a nose cone on the gyro that pulled the nose down. Same effect as the flat plate underneath. It would fly level up to 50 knt"s then the nose would start to pull down. At 60 it was very noticeable and at 70 I was looking at the ground which didn"t seem good. I made a couple of airfoils and bolted on the back at a slight angle to pull the back down and give it a try. Flew dead level from 30 to 80. The pressure causing it to nose over and the pressure from the air foil holding the tail down remained balanced at all airspeeds.If I had dropped the thrust line it would have flown nose up untill 50, level at 60, and nose down at 70.

[asra]

Has anyone tested a rosco machine with AK or Patroney rotors. Although I have heard them called high thrust line I am wondering if they are not too far off the mark with heavy rotors.

[asra]

Sam,I like to get discussion on this topic, so here goes.While I agree that a Gyro will pitch, yaw and roll around its CoM, I dont belive that the CoM is the same in static and dynamic situations.In a fixed wing the CoM stays the same. In flight, a fixed wing aircraft is in the same configuration as it is on the ground, ie the wings are in the same place.In a gyro the "wings" move around a bit. when the balance test is done the rotors are in the fore and aft position. when the rotors are turned 90 degrees from that position, you need to pull the nose down to find the balance point (in static situation). I think this is one of the reasons why the mast wriggles around during flight? Add to this different airspeeds creating parasitic drag on the airframe and huge "wing areas" that we have on Gyros, meaning that higher drag loadings equate roughly to more weight at the leading surfaces of the aircraft.In a fixed wing, the aircraft can be trimmed to allow for the drag, but a gyro has a "flexible" coupling to its wing and so the airframe finds its path of least resistance in relation to the wing. With this in mind, I should imagine that the CoM for want of a better term, must change along the arc of movement.I suspect that this is the reason that Pusher Gyros get twitchy at higher speeds, because the CoM changes in relation to the wing. If this is the case, I have no doubt that the thrust line is important to stability, but its relationship to the rotor and angle of attack, rather than the airframe and its CoM may be more important. Here is the can of worms, I look forward to the answers. I have only been flying since 2002 and I am still learning. Mark.Hi MarkYour gyroplanes CofM doesnt move regardless of what type of flying you are doing. Example, a motor bikes CofM dosent change regardless if the bike is standing still or in a turn fully banked over. The onlyway the bikes CofM may alter is if the rider shifts his weight. In a gyro this only occures during the burn off of fuel.As for aerodynamics, and drag producing structures (form drag) Parasitic drag) on the gyro, yes it will effect how it flys. It effect it by producing drag vectors that pull in the opposing direction to thrust. If the total value of such drag vectors is greated below the CofM then they will caused the machine to lower its nose during flight. This

[asra]

What I don"t understand about the CLT argument is how not knowing the drag figures allows you to determine flight characteristics. For instance, that little single that Sam used to fly. If you put a light weight vertical flat plate of (say) 4 sq. ft. between the wheels, it wouldn"t change the hang test, it wouldn"t change the C of M. But it would make it a bit interesting to fly, especially with a bit of speed up. ;D (Unless I"m missing something).CheersFredHi FredHi Fred Setting up a machine to be CLT wont allow you to predict its flight charactoristics. But what it will do is 1) ensure the machine doesnt pitch up or down during throttle application.2) Produce better aerodynamics due to the engine usually being mounted behind the pod centrally reducing drag.3) No negotively loaded HS required (usually) which also reduces drag.Overall a correctly setup Gyroplane will be much more efficient and stable. A correctly set up gyroplane will also fly much more like a fixwing as it will/should react and fly in the same way. Regards Sam.....

[asra]

Fred, you is coming onto the same page as me!When I stick my arm out the window of the landcriser at 140 (its a turbo), it requires a fair bit of force to keep my arm on the same place.

[asra]

Just thinking about that bit of plate Fred. I put a nose cone on the gyro that pulled the nose down. Same effect as the flat plate underneath. It would fly level up to 50 knt"s then the nose would start to pull down. At 60 it was very noticeable and at 70 I was looking at the ground which didn"t seem good. I made a couple of airfoils and bolted on the back at a slight angle to pull the back down and give it a try. Flew dead level from 30 to 80. The pressure causing it to nose over and the pressure from the air foil holding the tail down remained balanced at all airspeeds.If I had dropped the thrust line it would have flown nose up untill 50, level at 60, and nose down at 70.Sounds good PeterYour problem sounds like and aerodynamic issue. An aerodynamic issue should always be solved aerodynamically.This is because both the cause and the fix will alter at the same aerodynamic rate ensuring equillibrium in flight.SamL.........

[asra]

What I don"t understand about the CLT argument is how not knowing the drag figures allows you to determine flight characteristics. For instance, that little single that Sam used to fly. If you put a light weight vertical flat plate of (say) 4 sq. ft. between the wheels, it wouldn"t change the hang test, it wouldn"t change the C of M. But it would make it a bit interesting to fly, especially with a bit of speed up. ;D (Unless I"m missing something).CheersFredHi FredHi Fred Setting up a machine to be CLT wont allow you to predict its flight charactoristics. But what it will do is 1) ensure the machine doesnt pitch up or down during throttle application.2) Produce better aerodynamics due to the engine usually being mounted behind the pod centrally reducing drag.3) No negotively loaded HS required (usually) which also reduces drag.Overall a correctly setup Gyroplane will be much more efficient and stable. A correctly set up gyroplane will also fly much more like a fixwing as it will/should react and fly in the same way. Regards Sam.....

[Brian]

Quote SamWhat most people fail to understand about flying gyroplanes is that you fly the rotors and the pod simple follows. The greater the pods stability, the better it will follow.end of quote.So true Sam, its something I think gets overlooked cause its such a simple thing.