is a gyro a weight shift or 3 axis

[crashtestdummy]

I reason it is weight shift any comments to contrary

[Gyronaut]

CTD, I think this may have been discussed elsewhere in the forum but is something I have a keen interest in and have studied quite extensively.

In my humble opinion a Gyro is NOT a weight shift aircraft. Since the weight hangs off a central point under the disc a gyro is subject to pendular motion, which should not be confused with weight shift.

I say this for the following reasons. The controls of a gyro change the rotor tip path plane in relation to the relative wind, right? If the tip path plane changes the angle of the disc changes which results in a directional change. The weight follows.

Thats a statement which I can only substantiate by discussing a two-bladed rotor system and how gyroscopic precession affects the movement of the tippath plane. (lets not go into the intricacies of 3 bladed rotors or teetering here)

Moving the cyclic control increases the angle of attack (relative to the wind) of one rotor blade with the result that a greater lifting force is applied at that point in the plane of rotation. This same control movement simultaneously decreases the angle of attack of the other rotor blade the same amount, thus decreasing the lifting force applied at that point in the plane of rotation. This changes the angle of the disc relative to the wind. The rest follows.

Just as a matter of interest, the blade with the increased angle of attack tends to flap up while the blade with the decreased angle of attack tends to flap down. (hooray for teetering or it would simply roll over) Because the rotor disk acts like a gyroscope, the blades reach maximum deflection at a point approximately 90° later in the plane of rotation but this is not evident due to the positioning of the controls and is a whole other subject.

I am keen to hear other opinions and encourage debate since I firmly believe that a pilot that fully understands the dynamics of his disc and applies that knowledge during flight is a far safer pilot than one that doesnt and simply does what he has been taught parrot fashion.

[John Boucher]

I concur JR.....

If it was not as you explained then one would have grounds to argue that a helicopter is also weight shift, NO?

So, left is left and right is right up is up and down is down....

Weight shift is alternative.... it's like trying to turn left quickly on a speeding motorcycle.... you turn left to go right!!!!

[Vertical Tango]

You are both right when you go into the deep theory of the lifts that apply to the blades on a gyro, and when you apply input to your stick.
But the original question is still an interesting one.
Lets forget about the details of why the disc plane changes angle etc... and replace in our mind the whole disc as seen from your seat as you fly by a wing, like the one of a trike. If we had like on the original gyro designs (Ken Brock ???) a stick coming from directly the rotorhead. The controls are very similar to that of a trike. Expanding on that, I always believed that the RAF2000 is a weight-shift and does not have a tail plane. It has however a rudder for obvious reasons because the wing of a trike has direction stability and a trike does not have a rudder, but the disc on top of the RAF has no direction stability and without a rudder would spend its life rotating on itself.
Further to this, the whole debate on why a RAF is more difficult to control than more conventional gyros is that if they had a stick coming from the rotorhead instead conventional controls, the pilot would be less confused. A RAF behaves like a trike, and the pilot must learn to divorce himself from the sensation that the cabin gives him, like a trike pilot must let the undercarriage do its thing.
LJ, I know that you are going to shoot me down for may be not using the correct terminology, but I wanted this discussion to also look at a different angle.

[Gyronaut]

Sorry Vertical Tango, I cant agree.

1. Why on earth would a RAF "spend its life rotating on itself" ?? There is no torque on the rotor so why would it spin? The vertical stabilizer is simply there to let you 'point' in the direction you wish to.

I dont get your logic. Elaborate please?

2. A RAF is no different to any other gyro, except that it has no Horizontal Stabilizer and you therefore have to be a little more alert for PPO and PIO.

[John Boucher]

Okay..... lets see now

What is a helicopter then - 4 AXIS ?

[Vertical Tango]

JR, I did not explain myself correctly but we are on the same wavelength.
What I mean is due to the shape of the fuselage, and the same applies to a Magni, if you remove the rudder, how can you point to a particular direction ? It could naturally prefer weather cock in reverse. (5 rudders on the Sycamore with doors closed). A trike does not need a rudder and find its direction by the natural shape of its wing. That is my explaination. I understand what you are saying and you are correct.
Your point no 2 is exactly what I mean.

[Gyronaut]

Good VT, we're all agreed then, a gyro is not weightshift.

Bad Nav, you make an excellent point which I shall use in future when debating this. Thank you. If a Gyro is considered weightshift then so also a helicopter (at least in autorotation) must be, which it clearly is not.

Lekka topic and I am sure we have all learned something, which is the whole point mos ne?

[crashtestdummy]

jetranger your explanation is good and difficult to argue with so I wont but I have a few questions

Consider the rotors as a disc spinning with all the gyroscopic and coriolis forces keeping it going
now if you put input in to the stick ie force into the stick - one component of the force goes up to the head where is the reactive force aka newton "for every force there is an equal and opposite force" I think it is moving the cg of the gyro body relative to the rotating disc and thus shifting the weight of the body away from the equalibrium point of the rotor thus creating movement in the rotor plane

I also think 3 axis is elevators rudder ailerons giving us three distinct axissess about which to rotate

but I am still studying you explanation

[Condor]

Everything is extremely interesting and technical.

No problem discussing to understand better but what are we going to do with the answer?

[crashtestdummy]

i would like to use it to Say "i told you so" but otherwise I dont think it is much use even in an engine out

[Gyronaut]

Another very good point CTD... The most useful purpose of this discussion is probably to say "I told you so!" or in the alternative "I spoke a lot of crap before I applied my mind"

As I understand it, the leverage of the controls on most Gyro's is roughly between 13:1 and 16:1 (as far as I know), therefore the force tilting the rotor is many times the weight. Thats another reason I contend that it is not weight shift per se. If it was 1:1 Vertical Tango (Ken Brock ???) my argument may not be that relevant.

Bad Nav, Does all this mean a rotorwing is a 360 axis?

The primary value of this forum and this kind of discussion is to learn from each other which I think we already have so VIVA Microlighters!

Len

[John Boucher]

I have actually given the 4-axis thing a bit of thought....

We should refer to a chopper as "SPHERICAL - AXIS" as it's directional input is within any axis emminating from a centre point within that sphere!

Does that make sense? In technical drawing we used determine what a line ( a set of points.. ) would look like in the Z-axis or Phantom-axis thus determing the multi-direction of such said line!

Oh boy, the brains are rusted... what am I actually trying to say now?

[Gyronaut]

Eish! My head can only get around a 360 degree axis in the directional plane for a fixed pitch rotorwing.

Ek volstaan hiermee!

Len

[crashtestdummy]

I thought I told you so

ek volstaan ook

PS my rotor head is nearly here
Painting my tail
and my wife is gatvol of me starting the engine