Couple of us were having a little debate at the field the other day as to whether prop wt./flywheel effect has an effect on an airplanes torque rolling characteristics?


I'm thinking a heavier prop will aid in torque rolling if you goose the throttle? Equal/opposite reaction?


Opinions?


Facts/physics?

Proptop,
I agree with you, the gyro effect of a heacier prop does help stabilize the plane, although the amount is probably not enough to justify the losses. As with everything, it's a trad off, you loose some throttle response with a heavier prop. One thing you didn't mention was number of blades, also a contributing factor. A four blade prop would be more stable in a hover also, but again, you have to give to get. With a 3 or four bladed prop you have to use smaller diameter meaning less prop wash over control surfaces.

I think the gains and losses are negligible with any of the above. The biggest issue is getting the correct diameter and pitch to get maximum performance from the motor (with good pull out and throttle response).

So what we really need is a really long four bladed prop that's extremely light and heavy at the same time, variable pitch so you can flatten the pitch in a hover and keep the RPMs very high to take full advantage of the gyro/flywheel effect, and liquid cooled supersharged engine

Kev

Torque is equal to Force multiplied by distance. In other words, forty pounds of force at 1 foot from the pivot point is equivelant to forty foot pounds. Force, also, is equal to acceleration multiplied by mass. It takes 20 Newtons to accelerate two kilograms at 10 meters per second per second.

Let's assume that the propellor is spinning at a constant 10,000 rpm, and ignore wind resistance because we're talking about propellor mass. Because the propellor is already spinning, and we're ignoring aerodynamic drag on it, there is no force required to keep it spinning (besides the force needed to overcome the aerodynamic drag, which we're ignoring). Force equals mass x acceleration, and if acceleration is 0, mass is inconsequential.

However, if the prop is accelerated to 12,000 rpm, acceleration is no longer zero for the time it's accelerating, and mass is of considerable importance. Force, and therefore torque, and therefore resultant torque on the airframe, are greater for the heavier prop.

So, in laymen's terms, the airplane will not torque roll any faster or slower with a heavier prop. It will, however, experience more torque when revving the engine up, spool up slower, have more gyroscopic effect, blah blah blah.

these four bladed props you mentioned.... when will they be coming onto the market?

as soon as the BME 55 extreme does,,[8D]

The ratio of the mass of the prop vs airframe is very large. A heavier prop won't really change it much.

I like the maths and reasoning of Cody-RCU.

Safe Flying!

Interesting responses...

I'm thinking that a heavier prop will be more resistant to acceleration (flywheel effect ). Of course, that might be negated (to a certain extent ) upon deceleration, right? You hear a lot of guys "jockeying" the throttle while hovering and throttle fluctuation during hovering/torque rolling.
Sure, a lot of it is to maintain altitude, but if you watch and listen closely, the airplane wants to torque roll more as each "goose" of the throttle has to accelerate the prop. (equal/opposite reaction )

The ratio of mass of the prop to airframe is high, for sure, but we still can do torque rolls...Why?

I'm wondering what the MAJOR force involved is then?

Why would we ignore aerodynamic drag on a spinning propeller? There is a lot of drag on a spinning prop...that's one of the major forces on a prop. I know, we're talking theoretical, right? But, that's one of the reasons we can torque roll in the first place, isn't it? It takes torque and horsepower to turn that prop, and the "equal and opposite reaction" is "torque rolling" whether the aircraft it in an upright or level position, right? (or wrong? I don't know for sure, I ain't no physicist... just wonderin' )


Prop wt. has a major influence on throttle response, but I think it also effects the rate of (torque ) roll...JMO

Like I said, the torque is affected by propellor mass when the propellor is accelerating, or spooling up.

The major force is aerodynamic resistance on the propellor.

I ignored aerodynamic forces on the prop because we were considering mass only. You are correct in your assertion that what makes the plane torque roll is the opposite reaction of the propellor torque on the airframe.

I disagree. The major force, as indicated, is the aerodynamic force. 100% of the engine's power goes towards overcoming that force. The resultant torque on the airframe is what causes the plane to torque roll.