Research report on slips in a gyro

[kolibri282]

Chris, I thought that the name of the test pilot was Jörg (there aren't that many around, are they..;-). I didn't contact him for quite some time so I'll get in touch sometime soon anyway and ask him.

Thanks,

Jürgen

PS: Oh, and I am unfortunately not involved in programming that simulation..;-(

 

[BEN S]

Thanks Kai!
I was kinda pokin fun on the heavies....
I have played with the throttle while slipping and havent noticed a whole lot of rollover tendency.

 

[ckurz7000]

...I have played with the throttle while slipping and havent noticed a whole lot of rollover tendency.

In different designs this rolling tendency will be more or less pronounced. A tall tail centered in the slipstream of the prop provides a lot of compensation, whereas a minimal tail surface outside of the slipstream isn't helping much.

Generally, well designed gyros are perfectly safe to slip in a normal manner as would be used in a stiff crosswind landing. However, when you're pushing the envelope a sudden power change can be the proverbial straw on the camel's back if you're not anticipating its effect.

-- Chris.

 

[Gyro_Kai]

Hello,

I forgot about the torque-compensating tall tails, of course then the risk of torque-over is very much reduced.

Kai.

 

[fara]

The big difference between fixed wings and gyros with respect to this topic is that in fixed wings the orientation of the fuselage and the orientation of the lifting surfaces (i.e., wings) are rigidly coupled. This is not the case in gyros. Your fuselage can point one way and the rotor wouldn't know. The universal joint between gyro fuselage/mast and the rotor pretty much ensures that in flight there are no torques transmitted from one to the other.



I can't speak about details of the model because I am not really familiar with it beyond a couple of conversations. But to a reasonable degree of accuracy you can assume ignorance of the rotor about the orientation of the fuselage.

But there is a caveat for everybody who by rote just thinks of a gyro as a pendulum mass suspended below a rotor. As has been demonstrated in this research, airflow around the rotor is influenced by airflow around the cabin with, in some circumstances, notable effect.



The loads which any part of the gyro has to be able to withstand are spelled out in detail in the BCAR Section T (the MTOSport is certified under that regulation). Side load margins are ample so that aerodynamic loads because of a slip are no worry.

-- Chris.

Chris: Thanks. Makes perfect sense.

 

[cburg]

What are your thoughts about the various slips done during this demo?

Gyro Fun at a windy day in Germany - YouTube

Among other reasons I am building into my current gyro contra-rotating props to cancel torque and rudder offset.

 

[fara]

....

Among other reasons I am building into my current gyro contra-rotating props to cancel torque and rudder offset.

I saw a pilot at the same airport that Chris flies at (near Austria) in his MTO that did a lot more than this gentleman. Probably some of the most aggressive gyroplane slips and turns I have seen including the guys in Florida. Obviously these can be done safely based on pilot technique.

An acquaintance of mine in Austria designed a trike with a Rotax 582 Blue Head with his own gearbox with counter-rotating propellers. Trikes don't have a tail so the torque problem is hard on them and the designers do some tricks to reduce the effects of torque. I am not sure what happened to his gearbox but he had quite a few hours on it and it seemed to be successful. I guess its more complex and expensive and that's why not very popular in aviation compared to dealing with torque effects in design and pilot technique.

Chuck: If you are interested in a counter-rotating gearbox. Here is the website of my acquaintance
http://www.sunflightcraft.com/en/coaxp.php

You can see the trikes it has been installed on already. He is a nice guy and a great trike enthusiast.

 

[Vance]

Unpredictable Nature of the Sky

Unpredictable Nature of the Sky

I saw a pilot at the same airport that Chris flies at (near Austria) in his MTO that did a lot more than this gentleman. Probably some of the most aggressive gyroplane slips and turns I have seen including the guys in Florida. Obviously these can be done safely based on pilot technique.

I feel that nothing going wrong with a particular pilot making a particular maneuver in a particular aircraft is not sufficient evidence to assume the maneuver can be done safely simply based on pilot technique.

There have been some experienced pilots doing what they have done many times before involved in difficult to explain fatal accidents.

I have felt uncertain about how close to the edge I was on some occasions and I suspect the fortuitous outcome was a combination of luck, machine design and unintentional technique.

Many pilots of great skill and experience are no longer with us because they imagined that pilot technique would suffice.

I work on every flight to constrain my overconfidence and remember the unpredictable nature of the sky.

I do not understand all the ways there are to have a mishap in a gyroplane.

I have a great deal of experience with motorcycles that are much simpler and better understood that gyroplanes and I still don’t truly understand how they work. That is why the motorcycle factories have test riders.

Thank you, Vance

 

[C. Beaty]

Chris, does the Arrowcopter use any differential incidence between horizontal tailplane halves for propeller torque compensation?

To my knowledge, only the LittleWing and Aviomania gyros do so.

Ron Herron placed the Littlewing main wheels on bathroom scales and adjusted differential tailplane incidence for equal readings while running the engine up with the tail tied to a tree.

 

[fara]

I feel that nothing going wrong with a particular pilot making a particular maneuver in a particular aircraft is not sufficient evidence to assume the maneuver can be done safely simply based on pilot technique.

There have been some experienced pilots doing what they have done many times before involved in difficult to explain fatal accidents.

I have felt uncertain about how close to the edge I was on some occasions and I suspect the fortuitous outcome was a combination of luck, machine design and unintentional technique.

Many pilots of great skill and experience are no longer with us because they imagined that pilot technique would suffice.

I work on every flight to constrain my overconfidence and remember the unpredictable nature of the sky.

I do not understand all the ways there are to have a mishap in a gyroplane.

I have a great deal of experience with motorcycles that are much simpler and better understood that gyroplanes and I still don’t truly understand how they work. That is why the motorcycle factories have test riders.

Thank you, Vance

If everything is the same, the outcome will be the same. Feeling has nothing to do with it.
The outcome is only different because something was not the same. The variable are weather and pilot technique if the machines are the same.

 

[ckurz7000]

Chris, does the Arrowcopter use any differential incidence between horizontal tailplane halves for propeller torque compensation?

To my knowledge, only the LittleWing and Aviomania gyros do so.

Ron Herron placed the Littlewing main wheels on bathroom scales and adjusted differential tailplane incidence for equal readings while running the engine up with the tail tied to a tree.

No, the ArrowCopter does not. It has a centered tail fin but not differential incidence. However, the next version will have it; it's already on the list of items that will be "evolved". When I became associated with the project it was already too late to change.

We are currently experimenting with differential trim tabs on the HS.

-- Chris.

 

[C. Beaty]

Thanks, Chris.

Way to go.

 

[Vance]

I will endeavor to me more specific.

I will endeavor to me more specific.

If everything is the same, the outcome will be the same. Feeling has nothing to do with it.
The outcome is only different because something was not the same. The variable are weather and pilot technique if the machines are the same.

Some of us feel the word “particular” means a specific item or detail.

I will try to state it more clearly for your Abid.

In my opinion if you change the pilot, the aircraft or the environment what worked once may not work again.

It is possible to change the pilot with fatigue, stress or even exuberance because of an audience.

In my experience the air is ever changing.

I have yet to fly two gyroplanes that fly the same even the same model from the same manufacture.

My point was your post “Obviously these can be done safely based on pilot technique” is not obvious to me.

Thank you, Vance

 

[birdy]

What are your thoughts about the various slips done during this demo?
Didnt see any.
A few tail wags n sum subcoordinated banks, but no slips.

 

[ferranrosello]

Chris,

Thank you very much for your comprehensive explanation. I only can say that everything you have explained is totally understandable, make sense and matched perfectly with my experience. I will be waiting for the official report. It seems to me that this is a wonderful and serious test and that has a lot of value for all gyro pilots. You are giving some flying technique recommendations that are very good. I agree totally with them… Additionally you have given to us the correct explanations behind these slip procedures.

Thank you very much for sharing this knowledge, and congratulations.

Ferran

 

[ckurz7000]

Thank you, Ferrán, for your kind words. They mean a lot to me from such an experienced pilot, and they also give me confidence that research and experience are in line with each other.

-- Chris.

 

[NoWingsAttached]

I think all gyroplane pilots graduated from novice level do this routinely while landing w/o giving it a lot of thought. Many of us routinely also perform slips at much higher throttle settings than described (at and above cruise) at altitude, not just for landing. Depends on level of experience. Certainly at this point a pilot is flying the aircraft in the slip, with very firm control, not letting the gyro fly itself as in a normal cruise, and applying small, careful, gradual inputs.

I really got a lot out of the information regarding slipstream downwash acting upon the fuselage, and how the rotation of the rotor affects control. I have been scratching my head a lot lately over the wisdom of designing a CW prop on a pusher gyro, coupled to a CW (viewed from below) turning rotor. Trying to figure out if a CCW prop makes more sense by adding stability. Jury is still out on that one... but the initial determinations indicate that CCW is better.

The American Gyros are turning the prop in the wrong direction.

Just taking torque roll into consideration, it is instantly obvious w/o any fancy homework that more lift is produced on the advancing rotor blade than the retreating side, so why add torque roll in the same direction as that force with a CW prop?

However, in the slip to the right, there is an advantage to the CW prop, to counteract rotor downwash decreasing stability found in the MTO. Adding power in the MTO will increase instability in this case, whereas adding power on an American gyro will actually
increase stability.

Meanwhile, "fly the gyro", so to speak, eh?

 

[SGK]

The last factor is something I didn't know about before and learned during the dicussion with Jörg. Apparently it is a well known effect in helicopters, though apparently nobody thought it would matter in gyros. During test flights it became clear that the rotor disk behaves different in slips to the right vs. to the left. The stability margin is measurably less in slips banked to the right. The mathematical model was not able to reproduce this until the effect of airflow around the cabin interfering with the downwash of the rotor was added. Apparently there is a significant effect on the rotor dynamics which comes from how the airflow around the cabin interacts with the downwash of the rotor. Banks to the right decrease the stability margin and banks to the left increase it. Once the model was changed to incorporate this effect, agreement between theory and exeriment became extremely good.

This is interesting. I've tried but without success to find out more about it since I found recommendations in some literature to perform side slip towards forward moving rotor blade (which is in conflict with the theory above and my own experience).
On MTO and Calidus that I mostly fly, there is clear difference between feeling in slips to the right and left.
My spontaneous reaction was to explain this difference being result of more effective left rudder (more rudder travel from neutral position to the left than to the right) which exposes larger fuselage area to the air stream when banking to the right with full rudder, especially when applying much power. When not doing side slips with full left rudder applied, I can't say that I can feel significant (if any) difference between left and right side slips.
I imagine that there has to be the difference when turbulent air hits the stalled section of rotor disc compared with the section on the side of forward moving rotor blade but I have difficulties to understand in which way it affects "stability".
As I see it, the turbulent air stream behind fuselage always hits the aft portion of rotor disc. The profile and characteristic of this stream changes somewhat when slipping. Could anyone help me to get better picture of this?
We don't recommend side slips as a method for height reduction on approach. But of course, could be good to know how to perform, for example when filming from gyro.

Roman
www.gyroflyg.se

 

[Vance]

I am confused.

I am confused.

I think all gyroplane pilots graduated from novice level do this routinely while landing w/o giving it a lot of thought. Many of us routinely also perform slips at much higher throttle settings than described (at and above cruise) at altitude, not just for landing. Depends on level of experience. Certainly at this point a pilot is flying the aircraft in the slip, with very firm control, not letting the gyro fly itself as in a normal cruise, and applying small, careful, gradual inputs.

I really got a lot out of the information regarding slipstream downwash acting upon the fuselage, and how the rotation of the rotor affects control. I have been scratching my head a lot lately over the wisdom of designing a CW prop on a pusher gyro, coupled to a CW (viewed from below) turning rotor. Trying to figure out if a CCW prop makes more sense by adding stability. Jury is still out on that one... but the initial determinations indicate that CCW is better.

The American Gyros are turning the prop in the wrong direction.

Just taking torque roll into consideration, it is instantly obvious w/o any fancy homework that more lift is produced on the advancing rotor blade than the retreating side, so why add torque roll in the same direction as that force with a CW prop?

However, in the slip to the right, there is an advantage to the CW prop, to counteract rotor downwash decreasing stability found in the MTO. Adding power in the MTO will increase instability in this case, whereas adding power on an American gyro will actually
increase stability.

Meanwhile, "fly the gyro", so to speak, eh?

Hello Greg,

When I read your post I feel like I must have missed something in the thread or at least not received as much from it as you did.

What is “slipstream downwash”?

How does slipstream downwash act on the fuselage?

What is the connection between “torque roll” and dissymmetry of lift?

What is “rotor downwash”?

How does a CW propeller counteract “rotor downwash”?

The propeller on The Predator turns anticlockwise when viewed from the rear as does the rotor when viewed from the top. Based on your hypothesis is this the correct way?

Thank you, Vance

 

[ckurz7000]

This is interesting. I've tried but without success to find out more about it since I found recommendations in some literature to perform side slip towards forward moving rotor blade (which is in conflict with the theory above and my own experience).

I am sorry I don't know more than I wrote in the thread. But I am also eager to learn and will not hold back any information when I get the full written report.

-- Chris.