3 Blade MT Prop

[N53LW]

I was wondering how many others out there have the 3 blade MT counterbalanced prop? We've noticed that if you carry a little power on landing, then chop the throttle after touchdown the RV-8 makes an immeadiate right turn. We are assuming this is a breaking effect of the prop. Just curious if any others have had this happen?

[Norman CYYJ]

http://www.vansairforce.com/communit...ons/icon10.gif That's what the rudder is for, keeping it going straight.

[osxuser]

The prop definitely has a turning tendency, much more than a comparable Hartzell. I don't know why, but when one was tested on a Lancair locally that flew straight as an arrow with the Hartzell, it needed significant right rudder in cruise to fly straight. If your plane is tuned to this tendancy (it's always had that prop, and flies straight in cruise) I'd imagine you are seeing the opposite effect when you bring the power out. Lack of need to compensate for the turning tendancy of the prop...

If you follow this line of thought, it lends itself to a theory why the MT is so much slower than others... more rotation on the wash=trimming requirements for the airframe+less directly forward thrust.

[N53LW]

As far as speed, it isn't any slower than any other RV, have no trim tab on the rudder, feet on the floor at any speed the ball is centered. I wheel landed & chopped the power off after 150' roll out & the result was an immeadiate 15 degree turn to the right!

[USCANAM]

Originally Posted by N53LW

I was wondering how many others out there have the 3 blade MT counterbalanced prop?

Are you sure that you have a counterbalanced prop? This is usually used only on a fully aerobatic plane.
This is what I have on the One Design, and in over 400 landings, have never had the plane swerve one way or the other when landing
A counterbalanced prop goes into coarse pitch with a loss of oil pressure, and obviously will be in course pitch with the engine shut down. If the engine hasn't been run for a while, it will be rough when first started until the prop gov gets oil to rotate the blades to fine pitch. This is one way of telling what you have.
I have a standard 3 blade MT prop on the RV9A, and have not experienced any problem when landing.
Jack

[rvmills]

Phil,

I don't have an MT, so can't say I can repeat this scenario (I have a 2-bladed Hartzell and don't normally carry power during the rollout)...just had some thoughts (that the smarter-than-me aerodynamicists here can vet ).

When you chop the power, perhaps you're cutting out (or just decreasing) any remaining torque, P-factor and slipstream effects that the prop may be generating, so cumulatively I could see some right-turning tendency coming from that; and if it takes place as you're beginning to feel the effects of decreasing rudder effectiveness as you slow, perhaps the turning tendency becomes even more marked, and it takes more left rudder to correct it.

Not sure about braking effect from the prop, though I'm not sayin' it aint so...just seems like at the low power settings you're talking about, the prop is likely already at the pitch stop, so the blade pitch probably isn't changing when you chop that last little bit of power, you're just decreasing the thrust vector from the prop (and since a bit more is coming from the downward moving blades on the right side, the effect is the right turn...that leads me back to the thoughts in the paragraph above).

One other question would be whether the tail is on the ground when the power is chopped and the turn occurs, and (please don't take this wrong) I'm interested in why you're keeping the power on after touchdown. I was taught to bring the power to idle at or before touchdown, then (on a wheel landing) to let the tail down smoothly, then get the stick in my gut for better controllability and more effective braking. Not bashing your technique, it could be a very valid technique that I'm not familiar with...just thinking that there is a lot going on with changing power settings and changing rudder effectiveness with the tail wheel off the ground (if it is still up).

Just some thoughts, and it'll be interesting to hear what the guys with mucho TW experience say, and whether there's a difference between 2 and 3 blades, or MT vs. Hartzell.

Cheers,
Bob

[SteinAir]

Originally Posted by N53LW

As far as speed, it isn't any slower than any other RV, have no trim tab on the rudder, feet on the floor at any speed the ball is centered. I wheel landed & chopped the power off after 150' roll out & the result was an immeadiate 15 degree turn to the right!

Just curious here (and perhaps didn't understand you post so please forgive me)...are you saying that you still have power on the plane 150' into the landing roll on the ground? I know you said you carry a little power "on landing", but I didn't know if you meant throughout the landing roll too?

Cheers,
Stein

[N53LW]

Yes it is the counterbalanced prop. I still had about 900 rpm on the engine when I chopped the power. I've talked to some of the Aerobatic guys in my area & they said 210 hp, big prop, light airplane, & abrupt power changes w/that rotating prop equal undesirable results. Hence from now on milk the power off on landing, & you don't need to carry near that much power on landing! BTW thanks Stein for the great wiring job you did for us.

[SteinAir]

Hi Philip,

Now I see..."the rest of the story"! I think you're right, no sudden power changes and you'll probably be golden.

cheers,
Stein

[B25Flyer]

I have a 3 blade MT counterweighted prop and I have done nearly everything you can do with it, landed with power, taxied with the tailup, quickly added and chopped power and I have found no abnormal tendancies what so ever. Actually there is less gyroscopic effect with the MT than other props because it is lighter.

I am not a big MT fan, and I don't know what you are experiencing, but I don't think it relates to the MT....

Tailwinds,
Doug Rozendaal
F1 EVO w/MT