Prop effects and knife edge?

[hardlock]

I have a neutral rigged flat-plate 3D bipe that will knife edge perfect to the left hands off but has tons of coupling to the right. So much so I can't even figure out what kind of coupling yet. (very light W/L BTW - <3)

The wings are set with 0 stagger, 0 dihedral, 0 incidence, etc. The thrustline runs exactly between them as does the horizonal and is CGed with no trim incidence needed for upright or inverted flight at a given airspeed. The motor is mounted with no offset either up or or to the right. Lateral balance is neutral in upright and on it's side and the CG is at about 35%.

I would think the only thing left to mess up right side KEs is the prop effect somehow?

I wouldn't think it would be torque as adding right thrust to get rid of it would only have a pitch effect once rolled on it's side?

Maybe P-factor or gyro-presession? Am looking for perfection but maybe it can't happen without counter-rotating props? :confused:

Thanks for any insight into this in my never-ending quest for knowledge. ;)

[da'rock]

Gyroscopic precession only works when you're changing your pitch or yaw axis, so it's not happening if you're sailing along in a maneuver that's basically a stablized motion.

As for p-factor, one would think that your two directions actually have the prop running the same orientation either left or right. You're basically yawed the same amount, just basically yawed to the left in one direction and yawed right in the other direction. And p-factor is an effect that works on the prop fan yawed or pitched to the direction of travel. And your model is the same yaw each direction, right?

I'd guess that your a/c cg contributes to the problem and is working with/against the engine/prop torque. You know how a heavy wing will roll your a/c in a loop? Same concept here, except turn your a/c on it's side and try to envision where the cg is and where the center of lift is for the lift that's carrying the a/c on it's side. If the "laying on it's side" cg isn't in line with the aerodynamic center for the airframe that's "laying on it's side" you're going to have a torque. And you've already got a engine/prop torque.

So going left, you wind up with the cg displacement either aiding the engine/prop torque or countering that torque. And going right, you wind up with the opposite. And going one way they cancel each other, while going the other way, they add to each other.

Just a guess... hmmmm.... just a bunch of guesses......

[Thomas B]

Almost has to be spiral propwash effect that is having very different effects on one side of the model than the other.

A Contraprop would probably split the difference between the two behaviors..;)

[hardlock]

da'rock - Makes complete sense as you describe it. Due to the asymetrical fuse planform I bet I'm getting a toward the LG moment lift wise so the torque is balancing it out to the left. Opposite to the right. Since I can't even seem to get it into a stable KE to the right, the Gyro- efect maybe be coming into play during the transistion as the couple isn't distinct.

Thomas B - Let's see, normally with the prop rotating to the right, the prop wash goes counterclockwise viewed from the back?

It should cancel out over the major part of the fuse I'd think but once it reaches the rudder that sticks up then I'd get both pitch and yaw coupling in KE. Hum... Lots of things to consider, none of which can easily be fixed without compromising one thing for another.

Maybe the contraprop would be the best answer. Anyone know of a dual counter-rotating CDR motor? :)

[ElectroLawndart]

Hi all,

Can you get a prop that spins in the opposite direction and check the results?

Dart

[hardlock]

Sure can - good idea! Have a Maxx products counter-rotating pair of 10x4.5s sitting around. Should wait for my 22.7 25T motor to turn it however as bigger than a 9x5 on the 20t us pushing it.

This might get interesting! :)

[hardlock]

Little update - I didn't try the CR prop yet but did switch to 3S and 8x4 down from the 2S and 9x5 HD prop. What a difference. MUCH less adverse yaw at high alpha and KE to the right. It's manageable now so the prop torque (or something prop related) is causing the effect for sure.