Problem with CLT?

[rehler]

I have a "Theory of Flight (Aerodynamics)" question:

On a non-CLT gyro with a high torque engine (such as a Magni) there is a resistance to the torque tipping the gyro over. Assume a 500 pound gyro with a 6" offset from thrust line to CG, there will be a 250 foot pounds of torque needed to tip the gyro over on its side (from 0 to 250 as it turns).

However, with a CLT gyro with a high torque engine (like mine) there is no offset and therefore no resistance to tipping the gyro over, other than tilting the rotor to the side. If the engine torque is 100 foot pounds this requires the pilot to tilt the rotor to the side about 2.5 degrees to have the rotor thrust line run 2.5" to the side of the CG to keep the gyro from tilting over.

Am I correct in this theory?

[C. Beaty]

No Ken, torque is a rotational force. A ft-lb is a ft-lb wherever it's applied.

The greater the distance between CG and teeter bolt, the smaller the lean angle to compensate.

Either a tall tail or a full span horizontal centered in the prop slipstream mostly eliminates torqueover.

The sketch below may or may not bring clarity.

[rehler]

Chuck,

Then you agree that a lean angle (rotor tilt) will be needed to offset the torque, if a tall tail or full HS is not used?

Glad to hear I was wrong on the CLT being the problem, as I spent a lot of work to reach this goal. I guess the 912S engine torque is my main problem. I used to think you couldn't have too much power, but I guess too much of anything is not good. I am not looking forward to rebuilding my tail, but it is now on my list.

[mceagle]

Re engine torque - years ago I joined a convoy of Gyros on a cross-country. It soon became obvious to me (from the rear) that the WV gyros had a rotor tilt one way and the Subaru's the other.This went against current thinking at the time that the rotors will always fly right side high due to differential lift.

[C. Beaty]

Ken R., A short gyro; one with a smaller distance between teeter bolt and CG will fly at a greater tilt angle with a given torque than will a tall one. But it's not related to engine location Vs. CG.

I suppose the sketch I posted earlier would have been clearer if I'd said flex cable (core from prerotator cable) instead of drive shafts with CV joints.

xxxxxxxxxxxxxxxxxxx

Without engine torque, Tim; with counter rotating props for instance, the rotor would tilt slightly to the right. That's because of coning angle; the front blade gets slightly more wind than the rear blade.

Some of the older helicopters with slow turning fabric covered blades and attendant high coning angle flew with a very apparent rotor tilt.

[GyroRon]

Flying Scott Lewis' 912S powered single place Dominator, I noticed no torque roll at any power settings. It flew straight and true. Must be the tail.

[Chuck Irby]

Ron, does Scott's 912 Dom have a 60" 3 blade WD, or was it bigger? Also, is it a 912 or 912S?

[GyroRon]

60 inch warp and yes as I wrote above it was a 912S

[Chuck Irby]

Thanx Ron, and please excuse me for dare questioning you about the S?

[GyroRon]

Ssssssssssssssssssssssssssssssssssssssssssssssssss ssssssssssssssssssssssssssssssssssssssssssssssssss sssssssssssssssssssssssssssss!

[Chuck Irby]

Sorry Ron, but that's another one one of your replys that went over my head.

[rehler]

Chuck,

Your drawing was excelent - made the point very clear.

Thanks.

[jos]

Hello,

Any engine rated at 100 hp spinning any prop at 2400 rpm give identical torque.
Multiply torque and rpm (with a constant conversion factor)and you have hp. To reduce torque you must increase the rpm to keep the 100hp.
you can reduce the rpm and the torque but you loose the horses.
If torque dominates your gyro specially noticable during take off, but also in flight(torque does not dissapear but is lower because less hp),the first step to take is to offset the rotorhead half inch to the left or right(depending on the rotation direction of the prop)to counteract the prop torque.
In a reduction drive gyro there is no engine torque on the frame.
The only torque is prop torque.
Prop torque is engine torque multiplied by transmission ratio.
An engine with 15kgm torque and a transmission ratio 2.44 produces at max engine torque 15x2.44=36.6 kgm prop torque.
An ej22 with max torque 19kgm and a ratio2.25 gives 42.75kgm
The same engine with a four blade slow and less noisy prop gives 50.16 kgm torque with a 2.64 redrive ratio.


JOS

[quadrirotor]

Jos and the torque effect!... ;)
http://www.piasecki.com/index.html

do you see the offset?

[rehler]

Jos, you stated: "the first step to take is to offset the rotorhead half inch to the left or right".

I have not heard of this or noticed a side offset on gyros, but it sounds like a good idea. Andre's illustration really shows a large offset. Has this been done by anyone on a "normal" gyro?

[jos]

Hello Ken,

It is done on many gyro's and helps to make the machine take off more straight.The difference is noticeable in cruise.
But with your engine on a single seater you open after blade spin up the throttle more moderate,this avoids the high prop acceleration torque.
When you open the throttle softly the engine power is identical to what your prop needs.
When you open at once the engine power has to overcome your high inertia arplast prop and puts out even in the midrange everything it can give to accelerate the prop.
The faster you want to accelerate your prop the more acceleration torque.
Give it some time and the brutal torque effect 'll be a lot less.
I'll have a look for some pics on the offset on the rotorhead on "normal" gyroplanes.
Have a look at a Magni M16 with rotax and arplast combination.


JOS

[C. Beaty]

Ken R; Cierva experimented with rotorhead offset to counteract propeller torque but settled on differential tailplane incidence as a preferable solution.

Some versions used a Clark Y sort of horizontal stabilizer that was inverted on one side. Others with flat plate stabs used either differential incidence or very large trim tabs bent differentially.

The only way I can think of to eliminate the flywheel effect JS is talking about is with counter rotating props.

I'm sure you remember the days when automobile engines ran North/South. Blip the throttle with the car standing still in neutral and it would lean to the right.

[quadrirotor]

on a RAF type with a left handed prop: the lonesome pilot seats on the left! On a Raf with a right handed prop: the pilot seats on the right place! isn't it Birdy?
Did you (Birdy) change the preset angle of the rudder too, when you switch to the rotax 912?

[joeheli]

So guys... Correct me if I am wrong. The torque of my engine will make my gyro nose to drift to my left (with a mac). and on take off will make the gyro to try to flip over the left hand side too? (same direction that drift the gyro nose).

[birdy]

Sorry Andre,I only just read your question.No,I didn't have to change the rudder coz the props got the same rotation with the 914.

JOS said,
When you open at once the engine power has to overcome your high inertia arplast prop and puts out even in the midrange everything it can give to accelerate the prop.

And he's spoton.
When tak'n off short in the RAF,there was a little roll when the soob accelerated the lighter warp drive prop.
But when I suddenly open the tap on the 914,push'n a Ivo magnum,the RAF want's to do a tunnel roll down the road.

[rehler]

Birdy, you said: "But when I suddenly open the tap on the 914, push'n a Ivo magnum,the RAF want's to do a tunnel roll down the road."

This is what I am experiencing too. I feel better knowing that I'm not alone. Looks like it's just something I need to get used to and be aware of.

Thanks.

[birdy]

Yeh,it's no way near as bad when you fly it off gently,but when you gota git off short you find out real quick wot 115 angry horses feel like.

[gyromike]

So guys... Correct me if I am wrong. The torque of my engine will make my gyro nose to drift to my left (with a mac). and on take off will make the gyro to try to flip over the left hand side too? (same direction that drift the gyro nose).

Jose,

On your Bensen the spiraling slipstream comes off of your prop, striking the left side of the rudder, causing the nose to yaw to the left. You'll have to hold some right rudder to counteract this. You can also rig your rudder cables with the right cable shorter than the left so that when your rudder pedals are in the neutral position, your rudder is cocked over to the right. Mine is like that, and I believe Bensen called for a 10º offset (but I don't have the construction manual handy).

However the torque of the engine (counter-clockwise rotation as viewed from the rear) will tend to roll the frame to the right, requiring left stick to counteract. It's most noticable on take off at full power, less so during cruise. Again, you can adjust the rigging with the right push-pull tube a little longer than the left with the stick in the neutral position. I think I did mine this way, but without measuring I can't be certain.

Or maybe I just got used to it.

[StanFoster]

Mike: On my RAF...I had to rig the rotor head as you described...by tilting it to the left side by 1-2 degrees.

The need for right rudder is easily felt on takeoff. In case someone here doesnt know...the RAF's prop and engine turns CCW from the rear.

Stan

[joeheli]

However the torque of the engine (counter-clockwise rotation as viewed from the rear) will tend to roll the frame to the right, requiring left stick to counteract. It's most noticable on take off at full power, less so during cruise.
.

Mike, my rudder already has the 10 degree offset with the rudder pedal on neutral. I ask if the frame will tend to roll because I know the theory
that "any force has a opposite force (torque)" this will tend to roll the frame to the other side of the prop movement, but I really don't remember if I did it the first time that I did my first hops, I don't recall if I move my cyclic stick to compensate that torque. ( maybe I did it with instinct movement :D ). Thank you Mike for recalling me that ;) !

[gyromike]

Jose,

I've found that on the Mac powered machines you won't feel the torque roll as much as you would a Rotax powered machine. We are spinning smaller diameter props in the 50" range vs. 60 inchers on the Rotaxes.

If you weren't at full power on your crow hops the effect may have been negligible, and easily compensated for.

I flew a 582 powered KB-3, and it felt as though I had full left rudder and right stick on takeoff! Large prop and little rudder makes it more noticable.

[joeheli]

Good point! Maybe that is why I din't recall it. Thank's Mike