Explanation of "rotor disk" = rotary wing = aerofoil

[quoj]

This was not meant to be funny. If you are going to teach "rotor disc theory", you may as well teach "weight shift theory".Both are wrong for gyro"s. Know what you are on about before you correct others.Yes, I realise this.What I was chuckling about was, if I had difficulty explaining the basic idea, then it would be indeed a challenge to explain anything on top of that.But yes, as I am not a multi-hour gyro pilot, I don"t have an intricate knowledge of all facets of a gyro"s flight.My original point was that it"s often a struggle to convince some people of the most basic part of a gyro"s flight - i.e. although it has a large, spinning rotor, it is un-powered and works quite differently to a helicopter, which most lay-people believe it to be.But as I said, my original understanding of the theory came from two aeronautical engineers and a helicopter pilot which I had no reason to question.If they misled me, well... I guess we all live and learn.

[quoj]

i usually just say , it"s like a 2 bladed windmill

[jumeau]

many years ago when i was a young bloke one of

[asra]

Every now and then the "weight shift" theory raises its ugly head. Also,I would have though any helicopter pilot would have learnt what happens in autorotation quite early in his/her training.Do they think the air still flows down wards during autorotation?Gyro"s like helicopters are controlled primarily through cyclic pitch control. There would be thousands of pages on the net that would cover it in detail.I have found the easiest way to explain it is by moving the stick back and forward and side to side while on the ground with the blades stopped. Watching the blade pitch changes at different blade positions around 360 degrees instantly gives students the proverbial "light bulb" above their head.Although explaining that the reaction is 90 degrees past the change in pitch (gyroscopic precession) is also needed.Spin the blades up to 300 RPM and do the same with the stick and the whole disc moves in the direction of the stick,nothing to do with "weight shift" but an aerodynamic force created by changing the cyclic pitch of the blades.If you were to do the same thing in a vacuum the pitch would change BUT the disk would stay level,no aerodynamic force to change the disk angle.The early Cierva gyro"s used ailerons and elevators to control the gyro and had a fixed rotor IE the same constant rotor/airframe relationship.All aircraft including gyro"s would be capable of being manoeuvred by changing weight and no doubt you could lock the stick on a gyro and control it by moving a large weight from side to side and fore /aft,but it doesn"t mean they are weightshift controlled.

[Disco]

Well put Murray

[asra]

When I said in a vacuum the disk would stay level I should have said"The disk will stay in the same place".If you spun the blades up in a vacuum the position they were in as you introduced the vacuum could not change,no mater what you did with the stick.

[tonydenton]

murry, i"ve never heard the vacume bit before, so if the rotors are spinning and you move the stick the disc will stay in the same place. so where/what does the movement/travel of the control rods go to or do.??????????

[asra]

Same place it has always gone to Tony,into the torque tube to move the head back and forward/side to side.The cyclic pitch will change but without air to react on the blades nothing will happen.In normal operation if the gyro is on the ground and the stick right back with blades doing 300 RPM.Move the stick forward and you change the pitch at the 3 O"Clock (pitch down)9 O"Clock position (pitch up)The pitch changes take effect 90 degrees on so the whole rotor disk tilts forward.Without air going over the blade you have no force up or down.Like trying to manoeuvre the space shuttle in space, ailerons and elevators are useless.Don"t forget the blades are allowed to teeter freely no mater what position the head is tilted.

[Disco]

That Undersling would give you a good shake tho

[tonydenton]

i thought later i knew the movement would go into the head but never ever thought about the rotors without air around them and not changing.. learn something everything day ya gotta love that.

[Tim]

many years ago when i was a young bloke one of

[Tsemler]

Good to have ya posting again Tim, Love the way you explain things.