I have a H9 Edge that I want to reduce the Torque Roll speed. I'm currently using a Moki 1.8 with a Bambula 18x8. Will 18x6 reduce the TR speed?

no, the oposite

bla bla, I don't agree with you

Even though I don't have all the aerodynamic facts up front, just by common sense I can deduct its the opposite (lowering the pitch generates less counter-torque or slower torque-rolls).

You can easily see this in a helicopter ... first assume you're using a governor to keep the head speed constant and that you're not using any of the new AVCS gyros ...

So, while keeping the head speed constant, try incrementing the main rotor pitch and you'll see the tail rotor (TR) increase its pitch to counter the rotational torque.

A higher pitch will require more engine power which in turn will produce more torque thus resulting in faster torque rolls.

Noname is correct. The prop with the greater pitch requires more horsepower therefore it will have greater torque reaction.
basmntdweller

Sure, higher pitch has higher drag, hence load, hence torque at equal speed, but....

Power increases with rpm until you hit the power peak.... which mecam is probably not operating beyond.... let's assume.

If you lower the speed you lower torque (and power). No need to think about the prop so far...

With less pitch the engine will run faster... hence more power hence more torque.

So there is room for confusion here.... is the assumption that the rpm will be constant?

Jim is right also.

As you can see there is a relationship between prop pitch and rpm's as far as torque is concerned. You need to find the correct combination of both pitch and RPM's to lower the torque. But you will not be able to make it any lower than where those two variables intersect as the two variables change.

Ouch... My head is hurting now!

Ok I'm gonna take a shot at this but, I'm not great at explaining things so try to stick with me. First we need to establish the constant, we'll say the plane weighs 10 pounds so thats how much thrust we need. Now lets talk horsepower, simply put horsepower is torque X RPM. If we spin a 18/8 at 7000 rpm to develop the 10 pounds of thrust we need the prop will absorb a given amount of torque. In order to develop the same thrust with the 18/6 we will need to spin the prop faster. Now here is where it gets confusing, in both case the HORSEPOWER absorbtion of the prop is close to the same {torque X rRPM}, but since the RPM's are higher with the 18/6 the torque is lower. For the prop to absorb the same TORQUE with a lower pitch you would have to increase the diameter, this would add to the "disk" area of the prop and result in higher thrust. I hope this helps
Now I need a nap.

What about useing your aileron to slow the roll.

Aileron is ineffective in a Torque Roll.

Think of putting a Paddle on the engine instead of a prop. If the paddle was with the rotation there would be very little torque because the wind moves cleanly past the paddle. Turn the paddle 90 degrees and think of all the torque caused by the drag. Or think of your planes wing. It doesn't like to fly in directions other than the way the wing is facing (Excluding 3D stuff of course!). A "Wall" (3d) is a perfect example of this idea!

Phil (Mesa, AZ)

yes this indeed a mind bender...
and I'm tending to know be drifting the other way... with the heli guys.

Surely the amount of torque generated by the engine can never be greater than it's natural point of max torque... regardless of which prop is used. If max torque is occuring at say 6.500rpm and propeller that places the rpm in that region will be contributing to max torque.

But we are hovering... at a reduced throttle setting...thus the RPM will be lower, say for example 3.000rpm... way below the point of max engine torque.
By reducing the pitch and leaving the diamiter constant the resulting effect will be a higher rpm say 3.500 thus placing use closer towards the point of max engine torque.

...but the trust will increase thus requiering a lower thottle setting?????aahhhhhhhhgggggg!
yep... I give up.

OK I have a OMP 540 profile. I had a 11.5x4 wood on the plane....then i went to a 11x5....the rpm went up and the plane tr faster. Sounds like you need to lower your rpm to get it to slow down the tr.
hope this helps.

If he slows down his RPM, will his plane drift down? After all he is hovering too. I would think that a large dia X low pitch prop would be the answer. It would require a high RPM, but also will create more HP without causing more torque. I am no expert by any means, but this seems right to me. Example: HP = torque X RPM right? So to get the same HP by decreasing the torque will require more RPM. My 2 cents.

Richard

Don't confuse RPM with torque. Yes there is an RPM where the engine produces Max Torque, but that doesn't mean every time the engine is there it's at max torque. You could remove the propeller completely and reach 6500 RPM with almost no throttle opening, thats not max torque. Max torque only happens at FULL throttle, and since we don't hover at full throttle we need to think in terms of the amount of torque absorbed by the PROP at a given RPM. We could have 100 foot-pounds of torque available, but if the prop only absorbs 10 foot-pounds at 6500 thats what rolls the airframe. Forget about the engine completely, think only of the force {torque} required to spin the prop at the speed required to produce the needed thrust, then for every action there is an equal and opposite reaction.

My comments, all in theory:

Generally, I would say engine's torque and power curves are fixed. The details of the prop are irrelevant as far as torque is concerned. The rpm is all that matters. If you put on a bigger prop load (pitch or diameter), and retune the engine for max performance (i.e. the needle)... the max rpm will be lower, so will the power, and so will the torque.

That assumes that you are operating beneath the engine's peak torque.... which is probably the case. If not... well then you may see a small increase in torque before you see the decrease.

Bounded by those constants... you pick the right prop. Since you're hovering... you do what people have already said. Larger diameter and lower pitch.... if the engine spins slower than you're torque is lower.... question is: Do you still have enough thrust... have to experiment.

If you want to try something a little wacky, you could try slowing down the roll rate of the plane by putting some weight out at the wing tips. At least, in that case, it will take longer to "come up to speed" when rolling. It would degrade performance in other areas I suppose.

How retro fitting about a tail rotor?

Split the elevator and run then reversed (a bit) to control roll?

Tiny retractable parachutes (or something) from the wing tips to add drag?

Dip the tail fin in water while hovering. That'll do it!

The only thing I can say is what I have seen first hand. My 33% edge 540T would torque slow with a 3W 100 and a 3W 26-10. I changed to a 3W 27-10, the torque speed went up about 50% with slightly less power. Explain that one!

Later, Scott

i guess it depends on if your above or below your power band. Sounds like you need to burn fuel.

A torque roll is produced by the amount of torque placed on the engine, right? You need a prop that will produce more thrust, to keep the plane hovering,with out producing much torque, load on the engine. If your 18 X 8 is producing to much torque on the engine, then try a 19 X 6 or, if ground clearance is a problem, try an 18 X 6 or even an 18 X 4. Both will require more RPM, but will put less load, torque, on the engine.

Good Luck,
Richard

Where do I find a 19x6 prop? I ordered an APC 18x6W and will give that a shot.

BTW, thanks for all the info guys. Lots of info!

I'm going to agree with noname

OOOh Boy...Here is my twist
On my Big Block Chevy I think of torque much the same as everyone else has (I think) suggested here...RPM, Drag, etc.

On an airplane I generally think of torque as the adverse yaw effect caused from increasing or decreasing the prop speed. When you add power you step on the right rudder and when you pull power you step on the left rudder. Using this description (effect of torque on flight) would lead me to believe (given the same engine) that the weight of the prop, length of the prop, and to a much lesser extent pitch of the prop would affect the "feeling" of torque.
I think going up in length and down in pitch will still increase the adverse effects of torque. So I guess if I wanted to torque roll I would use a big'o heavy flat prop. If I wanted to decrease the effects of torque I would use a light weight short high pitched prop.

Oh well, just another opinion.

OOOOOPPPPPPSSSSSSSSS! No 19" props. My mistake! They jump from 18" to 20". Anyway you are headed in the right direction by going to the 18 X 6. IMO, what ever that is worth!

Richard

In order to hover a 10 lb airplane you, obviously, need to provide 10 lbs of thrust. Many different RPM/diameter/pitch variations will provide this amount of thrust. However, the amount of drag from the propeller will determine the roll coupling during hover due to the resistance of the prop to movement through the air. The propellers efficiency will be a factor in the drag it produces. Higher pitched props are more efficient at higher air speeds. Lower pitched props are more efficient at low airspeed. More drag is produced with the higher angles of attack associated with high numbers of prop pitch.
During hover, the engine/prop are making static thrust since we really don't have any flying speed. Higher pitched propeller are much nearer stall at low forward speeds.

Given these assumptions I would expect:

Larger diameter prop => More torque coupled to airframe.
Lower pitch prop => Less torque coupled to airframe
Higher prop efficiency => Less torque coupled to airframe


If there are no ailerons within the propwash during the hover, you cannot cancel the roll coupling with those controls.

Hope this helps,
Lloyd

OUTCAST is mostly correct. The torque that causes the airframe to roll in a hover is derived from the torque the engine exerts on the prop shaft needed to sipn the prop fast enough to hover (thrust = weight). In a constant hover (not bouncing up and down) the torque force is constant.

However, there is another force that works to slow the speed of the roll. This force is from the rotating airflow from the prop as it interacts with the wings and stabs. Same force that requires right rudder on take-offs. This force partially counteracts the torque exterted on the airframe by the engine.

So, that means there is not a simple answer to the question. A larger diameter prop may tend to create a more powerful counter-rotating prop-wash that slows down the roll.

Also, don't forget that a prop is a "wing" that creates lift (thrust) due to pressure differential on the front/top of the blade in addition to force created by raw pitch of the blade. So, lower pitch props create greater lift/thrust (at zero airspeed) while requiring less rotational torque to spin.

This is unfortuantely a complicated subject. The easiest thing to do generally is try different combinations through trial and error until the aerodynamic qualities of different props become second nature.

Jason

Adverse yaw has nothing to do with engine torque, it happens even in gliders. Adverse yaw is the tendency for the airframe to YAW in the opposite direction of the roll input. Roll the wings right the fuselage yaws left. The force you are reffering to is called "P" factor and is caused by the combination of asymetric thrust and the fact that the air from a prop doesn't go straight back, it rotates sorta like a tornado on its side.
The only thing that rotates a plane in hover is the amount of torque used by the prop to produce the thrust needed. Change the needed torque and you changed the rotational force.