Reflexion about cyclic stiffness

aerobatic

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I have now about 1 hours of flight on Magni Orion, 2 hours on Auto-gyro Calidus and about 5 in MTO Sport.

I was thinking about all the debate about the stick stiffness of the Magni. Is it only related to a heavy rotor that act as a fly wheel who want to keep it's rotational momentum?

My observation is that since the Auto-gyro Calidus and an MTO Sport shares exactly the same rotor system, the difference of stick stiffness between the Calidus and the MTO Sport cannot result from the rotor assembly. My guess is that the weight of the whole machine make the difference between the Calidus and the MTO Sport :

When you move the cyclic, you move the rotor in a direction, but you also push the rest of the gyro on the other way (action/reaction). If we look at a gyro as a pendulum, the more weight we have under the rotor, the more effort will be needed to push the rest of the apparatus from the rotor axis.

If I'm right, all enclosed tandem or side-by-side gyro should have a stick clearly harder to move in flight than a light single open machine.

Flying solo or with a passenger should also impact the stiffness of the rotor control. Since I'm not yet solo, this is an hypothesis that I cannot verify.

So can someone confirm/infirm that all enclosed or heavy machine are prone to stick stiffness? And if flying alone or tandem make any noticeable difference?

Maher
 

Vance

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I will give it a try.

I will give it a try.

I have now about 1 hours of flight on Magni Orion, 2 hours on Auto-gyro Calidus and about 5 in MTO Sport.

I was thinking about all the debate about the stick stiffness of the Magni. Is it only related to a heavy rotor that act as a fly wheel who want to keep it's rotational momentum?

My observation is that since the Auto-gyro Calidus and an MTO Sport shares exactly the same rotor system, the difference of stick stiffness between the Calidus and the MTO Sport cannot result from the rotor assembly. My guess is that the weight of the whole machine make the difference between the Calidus and the MTO Sport :

When you move the cyclic, you move the rotor in a direction, but you also push the rest of the gyro on the other way (action/reaction). If we look at a gyro as a pendulum, the more weight we have under the rotor, the more effort will be needed to push the rest of the apparatus from the rotor axis.

If I'm right, all enclosed tandem or side-by-side gyro should have a stick clearly harder to move in flight than a light single open machine.

Flying solo or with a passenger should also impact the stiffness of the rotor control. Since I'm not yet solo, this is an hypothesis that I cannot verify.

So can someone confirm/infirm that all enclosed or heavy machine are prone to stick stiffness? And if flying alone or tandem make any noticeable difference?

Maher
Hello Mather,

I am not clear on your questions so I hope I have covered it. These are my opinions and observations without quantifying or actual measurements.

I have flown three different Magnis on very short flights. I found them very pleasant and smooth.

I have flown 2 different Dominators, several SparrowHawks, several modified RAFs 2 stock RAFs, a Parsons 2 place, a Snowbird and my own unique 2 place tandem gyroplane, The Predator.

In my opinion a heavy 2 place gyroplane is slower to respond than a light single place gyroplane.

All of the two place tandems I have flown except the Dominator are heavier than a Magni.

In my opinion, comparing all of the two place tandems I have flown, the Magni was the least responsive and required the highest stick forces to make it respond quickly. I did not do any actual measurements so this is a subjective opinion.

The Dominator, which is the lightest also had the lowest stick forces and felt very responsive.

I feel the reasons for these differences are related to more than just the weight difference.

With all of the gyroplanes I have flown progressively higher stick forces produce progressively faster response times. In other words they respond slowly to light stick forces. If I want her to react quickly greater stick forces are required.

I do not think of (action/reaction) as you describe it because of the way the rotor changes angle. In my opinion I am not forcing the rotor to its new angle, rather I am asking it to fly there with aerodynamic imputes that require less force than what would be required to tilt a spinning disk without the aerodynamic assistance.

I feel that thinking of a gyroplane as a pendulum can lead to many erroneous conclusions because the sky hook (rotor) is not fixed in space. This allows the gyroplane to rotate around the center of gravity rather than swing under a skyhook that is fixed in space.

The Predator does not seem to require noticeable higher stick forces with a passenger compared to solo.

Thank you, Vance
 

PW_Plack

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When you move the cyclic, you move the rotor in a direction, but you also push the rest of the gyro on the other way (action/reaction). If we look at a gyro as a pendulum, the more weight we have under the rotor, the more effort will be needed to push the rest of the apparatus from the rotor axis...
Maher, as Vance touched on, starting from the "pendulum" premise will get you wrong answers. Gyros are not controlled by weight shift. When you move the stick, you're not directly moving the rotor in a direction. (You're not strong enough to create a rapid change in the orientation of 100 pounds of spinning mass about 30 feet in diameter, and neither is the control hardware.) What you are doing is increasing the airfoil's angle of attack on one side of the disc, while reducing it on the opposite side, which causes the disc to tilt itself to a new position using a differential in its own aerodynamic forces.

The stick movement is adjusting the pitch to be different at different stations around the cycle of the spinning disc. (Hence, why it's called "cyclic pitch control," and the stick itself called "the cyclic" for short.)

This is not the most intuitive of concepts, but once you understand how it works, and how gyroscopic precession contributes by offsetting the effect of the movement 90º from the point of application of the aerodynamic force, it's very elegant the way such simple hardware makes it happen.

If the MTOSport and Calidus are of similar mass and use identical rotor systems (including the airfoil and mass distribution), they should have very similar control forces. There must be differences which are not obvious if they're noticeably different. Could the mechanical advantage in the cyclic controls vary from machine to machine?

Stick force and responsive are not the same thing. One is a measure of force exerted on the control to make a change, while the other is the rate of the change after the input is made. In many mechanical controls, they increase and decrease in sync, not in opposite directions. For example, if you use two steering gearboxes or racks of different ratios on otherwise identical automobiles, the one which causes the more rapid change in direction will also require a higher force to turn the wheel.
 

C. Beaty

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All else being equal, stick force depends entirely upon rotor lag vs. control rate.

Following rate of a rotor depends on its ratio of inertial force to aerodynamic force (lock number) and upon its torsional characteristics vs. chordwise balance.

Heavier, slowly turning rotors produce a heavy stick.

Torsionally soft overbalanced (noseheavy) rotors produce a heavy stick.

Torsionally soft underbalanced (tailheavy) rotors produce a light stick.

It’s only human, I suppose, to invent imaginary things to explain that which we don’t understand.
 

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bopflyer

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have ppl helicopter, ratings in fixed and flexi wing microlights. Learning to fly gyro's.
Ok, going to put my two cents worth in here....Is it something to do with the weight, size of the rotor blades?

A two place machine rotors will be longer than a single place. Will that cause them to react faster?
 

C. Beaty

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It is all a question of how much the rotor lags behind a given rate of stick movement. No lag, no stick force.

What makes a rotor lag behind the stick?

First of all, the ratio of lift to rotor inertia. Skinny, heavy rotors will have more lag and greater stick force for a given tip speed. Wide chord, light rotors will follow the stick with less lag and produce a lighter stick.

In the specific case of the Magni, the blades are noseheavy and torsionally soft (they twist easily). Fiberglass has 1/10 the stiffness of aluminum for a given thickness.

Move the stick nose up, say, and the angle of the advancing blade is increased. But since they are noseheavy, aerodynamic lift force, acting to the rear of the CG twists the blade nosedown, effectively reducing the pilot’s input and tilting the rotor disc less than commanded.

The technical term for this is rotor damping. The Hiller Servomatic system is related to noseheavy rotors.

Skywheels rotors are tailheavy and behave oppositely than a Magni rotor. They have a light, responsive feel in the stick.
 

hillberg

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Note: Hiller blades on the H 23 (H-12c) were Bell 47 blades with the ends cutt off. When asked why supply Hillers blades-Larry bell Bell said "no problem I have confidence with the 47" No problems.......
 

aerobatic

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The main difference between the MTO Sport and the Calidus seem to be the extra weight of the enclosed canope of the Calidus. The stick resistance of the Calidus is something between the one of the MTO Sport and the Magni Orion.

If the rotor resistance is only related to the rotor assembly, who can it differ so much between two models sharing exactly the same rotor system?

Maher
 

C. Beaty

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Look at the sketch on post #4.

It’s pretty obvious that if you double the weight while everything else remains the same, you also double the stick force.
 

SGK

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Are you sure that your MTO and Calidus have the same type of rotors? As I know, most Calidus have been equipped with somewhat modified old "MTO" rotor with changed pich and weights. Those two rotors have significantly different behaviour. The same principle is used on new "MTO" rotors. The "old" one was too responsive, inviting to hard manouvers, therefore problem with cracks... Magni is very stable. Are there any negativities in it (No way back once when stalled for example?)? Where is ELA on this scale? All mentioned gyros fit normally within 275 kg empty weight +/- 10%, the weight shouldn't make diffetence in those cases. Anyone with hard facts about torsional elasticity and such figures for ELA, MTO (new one) and Magni?
 

aerobatic

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It’s only human, I suppose, to invent imaginary things to explain that which we don’t understand.
*****************
Look at the sketch on post #4.

It’s pretty obvious that if you double the weight while everything else remains the same, you also double the stick force.
Sorry M Beaty, I'm not sure to follow your posts :

The first quote seem to suggest that my understandings are definitively wrong, the second seem to confirm that I'm right about the influence of the cabin weight on the stick stiffness.

I'm really confused...

Maher
 

aerobatic

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Are you sure that your MTO and Calidus have the same type of rotors? As I know, most Calidus have been equipped with somewhat modified old "MTO" rotor with changed pich and weights. Those two rotors have significantly different behaviour. The same principle is used on new "MTO" rotors. The "old" one was too responsive, inviting to hard manouvers, therefore problem with cracks... Magni is very stable. Are there any negativities in it (No way back once when stalled for example?)? Where is ELA on this scale? All mentioned gyros fit normally within 275 kg empty weight +/- 10%, the weight shouldn't make diffetence in those cases. Anyone with hard facts about torsional elasticity and such figures for ELA, MTO (new one) and Magni?
Yes, you are right : the Calidus that I flown have the rotor head that come with the new MTO Sport. I didn't thought that the extra rigidity could also affect the stick stiffness...

Maher
 
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