Gyro Roll tendency

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Induna
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Gyro Roll tendency

Postby Induna » Sun Jul 24, 2016 7:47 pm

Hi all.

I am flying an Magni M18 gyro, and it is such a nice little gyro, very stable and it flies great also! The only issue I have is the roll tendency to the left, which requires constant pressure on the stick to keep it from rolling. This is not an issue while flying around the patch but could be tiresome on longer flights.

Now, as a basic principle of flight, with a anti-clockwise rotor spinning and asymmetric lift during forward flight, the gyro will naturally have the tendency to roll left. This has been compensated for by the manufacturer by either offsetting the rotor to the right a small amount, offsetting the trim attachment to the right or a combination of both.

The M18 does not have an offset rotor assembly and the trim cable is already attached to the far right of the holes provided. I think what adds to the issue is that the Rotax 582 engine turns clockwise, when viewed from the rear, so the torque will add to the roll tendency to the left.

This is only noticeable at high throttle settings and the gyro completely neutralizes when the rpm gets below 4000rpm (too low for sustained flight)

What is your experience with similar issues and what is the solution?

Jacques
ZU-IIJ | Zenith CH650B Taildragger
ZU-RHT | Magni M18 Spartan
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Re: Gyro Roll tendency

Postby greg vos » Sun Jul 24, 2016 8:22 pm

Induna wrote:Hi all.


This is only noticeable at high throttle settings and the gyro completely neutralizes when the rpm gets below 4000rpm (too low for sustained flight)

What is your experience with similar issues and what is the solution?

Jacques

I was just going to suggest coming off the throttle a bit, that will reduce this tendency you experience, its normal for all gyro's when running fast and near there higher speed limitation.

I had it on a long x/counrty flying a New MTO sport to CT a while back (very annoying) we have it on the M16 as well just more noticeable two up at high power settings.

M18 you want to cruising around at +- 60mph or a bit less

Hate to remind you, Gyros are not designed for long distance flying :wink: ...although many forum members will argue vhpy

It can be tuned out by moving the CG aft (engine back giving a more favorable crusise speed) but dont do this type of thing until you have a bit more gyro exp and be mindful it will compromise the legendary magni stability, lets chat about it next time your at FAFK? fiddling with the aerodynamic profiles requires some in depth understanding of whats happening above vhpy
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Learjet
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Re: Gyro Roll tendency

Postby Learjet » Mon Jul 25, 2016 12:19 am

I'm going to start by suggesting that you contact Butch (SA MAgni agent) or anyone else familiar with the M18 to find out if this roll tendency at higher power settings is normal or not? I would suspect it isn't but I don't have any experience on the M18 and it is a much lighter and smaller Magni.

So assuming it's not normal....

Let me try and untangle this:
Induna wrote:Now, as a basic principle of flight, with a anti-clockwise rotor spinning and asymmetric lift during forward flight, the gyro will naturally have the tendency to roll left. This has been compensated for by the manufacturer by either offsetting the rotor to the right a small amount, offsetting the trim attachment to the right or a combination of both.
An anti-clockwise free-spinning rotor will create only a negligible degree of clockwise yaw compensated for by the vertical stab.

Asymmetric lift is compensated by the teetering rotor. This is exactly how Cierva overcame the L disymmetry problem. In reality there is actually no significant disymmetry of lift in flight (as long as the rotors are able to teeter within their "flapping" range).

Offsetting rotor to the right - (not to be confused with an offset gimbal rotor head which stabilizes pitch by balancing the lift vs drag) some gyros use an offset in the actual gimbal itself to compensate for the prop torque (nothing to do with the spinning rotor)

Which leads us to prop torque and P factor.

P factor - this assymetric centre of thrust from the prop is caused by the differential thrust produced by the ascending and descending prop blade relative to the wind flow when the ac AoA is increased. It results primarily in a yaw effect though.

Prop torque (often confused with P factor) is "the equal and opposite reaction" imposed upon the aircraft by the engine torque. This results in roll. And the clue here was the fact that you report diminished roll response at lower power settings.

Prop torque roll can only be compensated by control input. In a FW by aileron and in a gyro by stick input as you report.

And this is where I would have put my money - except for one utterly (**) (**) (**) little snag - and that is you are experiencing left roll (and not right roll as would be expected with an anti-clockwise prop)!!!

So where does this leave us?

The only thing I can speculate is that what you may actually be experiencing is primarily a right yaw and resultant (X-control like) "cabin drag induced "roll".

So what could cause right yaw...

P Factor - counter-rotating prop produces right yaw.
Rotor torque - in the event that there is increased rotor-bearing friction or the rotor brake is not properly disengaging.
Rudder deflection offset - on the Magni the rudder is usually offset by 10' degrees to the right. (too much more could be causing the right yaw)
Trim Spring - the trim spring shackle attachment to the rotor-head fork/yoke has a number of holes allowing for some offset tension when trimming.

My 2 cents worth of guesswork and elimination!
Dave Lehr
Magni Gyro M22 ZU-EPZ
“You're flying Buzz! No Woody we're falling in style!”
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Learjet
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Re: Gyro Roll tendency

Postby Learjet » Mon Jul 25, 2016 12:25 am

Hate to remind you, Gyros are not designed for long distance flying :wink: ...although many forum members will argue vhpy
Listen here Mr Cabbage Patch vhpy vhpy vhpy ol Senior Cierva most certainly envisaged his Autogyro to be utlised in any way a fixed wing would. In 1928 he flew his gyro across the English Channel and in 1930 from England to Spain... :lol: :lol: :lol:
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Induna
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Re: Gyro Roll tendency

Postby Induna » Mon Jul 25, 2016 8:23 am

Hi Dave

Thanks for the useful info! I have also contacted Butch, and the Magni factory, over the weekend and will await their response.

Note that my engine (582) indeed turns clockwose, opposite to the 912, so torque is expected to the opposite direction. It is most noticeable on high rpms. If i throttle down all the way, then the roll tendency dissapears completely. This is regardsless of speed, wheather i fly at 50mph or 80mph. So i suspect it to be due to engine torque.

If thats the case i guess i have to live with it. But lets see what Butch and the Magni factory suggests.

Have a great day!! I am off flying this morning. Beautiful weather... :)

Jacques
ZU-IIJ | Zenith CH650B Taildragger
ZU-RHT | Magni M18 Spartan
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Re: Gyro Roll tendency

Postby Learjet » Mon Jul 25, 2016 9:46 am

Induna wrote:Hi Dave
Note that my engine (582) indeed turns clockwose, opposite to the 912, so torque is expected to the opposite direction. It is most noticeable on high rpms. If i throttle down all the way, then the roll tendency dissapears completely. This is regardsless of speed, wheather i fly at 50mph or 80mph. So i suspect it to be due to engine torque.
Aha! Then I'd agree with your suspicions about the roll being by the engine torque.
In theory though your torque should reduce at higher airspeeds due to the change in relative airflow and reduced angle of attack (on the prop) - but it may still be worth checking that your blade pitch isn't perhaps a little too coarse?
Dave Lehr
Magni Gyro M22 ZU-EPZ
“You're flying Buzz! No Woody we're falling in style!”
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Re: Gyro Roll tendency

Postby greg vos » Wed Jul 27, 2016 5:01 pm

Learjet wrote:
Induna wrote:Hi Dave
Note that my engine (582) indeed turns clockwose, opposite to the 912, so torque is expected to the opposite direction. It is most noticeable on high rpms. If i throttle down all the way, then the roll tendency dissapears completely. This is regardsless of speed, wheather i fly at 50mph or 80mph. So i suspect it to be due to engine torque.
Aha! Then I'd agree with your suspicions about the roll being by the engine torque.
In theory though your torque should reduce at higher airspeeds due to the change in relative airflow and reduced angle of attack (on the prop) - but it may still be worth checking that your blade pitch isn't perhaps a little too coarse?
Dave how does one adjust blade pitch on a Magni? I am familiar with adjusting to attain better tracking if we are chasing down a vibration. Having spent frustrating hours at the field adjusting the castle nut to achive improvement :?:

Below I quote direct from Magni I did not scribe the text in italics I took this from the owners manual.

There are no provisions for adjusting either the blade pitch or the “string”
alignment of the two rotors.    The blade pitch and
“string” are controlled by the very precise fabrication
of the rotor blades that provide for very exacting blade
aerodynamic and weight symmetry between the two
blades.



Im always keen to learn and I can say from trial and error using a Chadwick instrument and around 40 test flights I got my M16 to fly with almost zero stick shake, (after I made it perfect I sold it vhpy )

I did still suffer the issue of induced roll at high thrust / power settings and was more prevalent when I had a heavy pax on board at straight and level flight at say 35MAP in fact it was quite uncomfortable at say 110 MPh with a noticeable skew or offset bum in seat position :?:
If you suggest the prop blade pitch is to course then surely by reducing power you remove energy as the Rpm comes down? what am I missing? the small Rotax with a too high pitch on the prop will bog and will run out of torque? as airspeed increases, real prop thrust decreases – at high airspeeds prop thrust is much less than at lower airspeeds because of the faster incoming air. 

Not wanting to argue, I instruct on these contraptions and the more we share the more we know the safer the hobby will become IMO  

Im interested in this thread vhpy and dont want to gloss over technical aspects of in flight conditions if I do not understand? after all its us who take admirers and turn them into pilots and therefore we need in depth understanding of the dynamics between the two sets of turning blades
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Re: Gyro Roll tendency

Postby greg vos » Wed Jul 27, 2016 5:06 pm

Learjet wrote:
Hate to remind you, Gyros are not designed for long distance flying :wink: ...although many forum members will argue vhpy
Listen here Mr Cabbage Patch vhpy vhpy vhpy ol Senior Cierva most certainly envisaged his Autogyro to be utlised in any way a fixed wing would. In 1928 he flew his gyro across the English Channel and in 1930 from England to Spain... :lol: :lol: :lol:

I think it was Jean T that proudly gave me the cabbage patch badge I wear with pride? I consider a flight from FAFK to Morningstar as a long cross country flight :lol: and I will not venture that far in these cold winter days vhpy

off topic sorry
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Re: Gyro Roll tendency

Postby greg vos » Wed Jul 27, 2016 5:09 pm

Induna wrote:Hi Dave

Thanks for the useful info! I have also contacted Butch, and the Magni factory, over the weekend and will await their response.



Have a great day!! I am off flying this morning. Beautiful weather... :)

Jacques

Please let us know what Butchie said :?: Mr Brown is a very knowledgeable man
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Re: Gyro Roll tendency

Postby Induna » Wed Jul 27, 2016 7:40 pm

Hi All,

today I had the pleasure of flying the M18 for a full 2 hrs! What a pleasure. The stick is so calm, almost zero shake! She flies lekker at 70 - 80mph and a typical "2-stroke" fuel burn of around 17-18lph.

I am getting used to the constant roll tendency, and must say that it does not really bother me that much. I got a reply from Butch that he also asked the opinion of the factory, of which he is waiting a reply.

In the meantime, I am enjoying every moment of flying these gyros! There is a reason why Magni's are so popular... :roll: I am still a low-time gyro pilot and I build valuable experience everytime I fly the little red gem.

Jacques
ZU-IIJ | Zenith CH650B Taildragger
ZU-RHT | Magni M18 Spartan
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Re: Gyro Roll tendency

Postby Learjet » Thu Jul 28, 2016 8:53 am

greg vos wrote:
Learjet wrote:
Induna wrote:Hi Dave
Note that my engine (582) indeed turns clockwose, opposite to the 912, so torque is expected to the opposite direction. It is most noticeable on high rpms. If i throttle down all the way, then the roll tendency dissapears completely. This is regardsless of speed, wheather i fly at 50mph or 80mph. So i suspect it to be due to engine torque.
Aha! Then I'd agree with your suspicions about the roll being by the engine torque.
In theory though your torque should reduce at higher airspeeds due to the change in relative airflow and reduced angle of attack (on the prop) - but it may still be worth checking that your blade pitch isn't perhaps a little too coarse?
Dave how does one adjust blade pitch on a Magni? I am familiar with adjusting to attain better tracking if we are chasing down a vibration. Having spent frustrating hours at the field adjusting the castle nut to achive improvement :?:

Below I quote direct from Magni I did not scribe the text in italics I took this from the owners manual.

There are no provisions for adjusting either the blade pitch or the “string”
alignment of the two rotors.    The blade pitch and
“string” are controlled by the very precise fabrication
of the rotor blades that provide for very exacting blade
aerodynamic and weight symmetry between the two
blades.
Hi Greg,
I was referring to the propeller blade pitch (not the rotor blade pitch) in respect of the engine torque. vhpy
Dave Lehr
Magni Gyro M22 ZU-EPZ
“You're flying Buzz! No Woody we're falling in style!”

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