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Lazy Bee: Thrust angle & tailplane angle

Monte.C

Well-known member
#1
Hello all. I'm posting this under the balsa subforum because I'm hoping to find someone familiar with Andy Clancy's Bee series.
I've started a foamboard build of my own design very much inspired by the Bee planes, styled like a WW2 fighter but with as much wing as a Clancy Bee.

MesserBee.jpg


I have one specific question that's breaking my brain. On the Bee plans I find that they're building in a significant downward thrust angle AND a downward tailplane angle to match. Or if you want to look at it this way: The thrust angle and the tailplane are dead level and that giant wing is given a significant upward angle. I guess I can see what he's doing there, especially at very low speeds you'll need to fly the wing at an alpha angle well above level anyway.

One difference is that I have a bottom-mounted wing, so motor thrust would want to pitch it down. I'm not sure if I'll need any down (or up) pitch to the motor. But that tailplane dammit. I can't predict what I'll need to do with that. I suppose the worst that could happen would be that I build it level but then find I usually need some up elevator.

Please, any advice? Thank you!
 

Merv

Well-known member
#2
I’m thinking you need to build it with the thrust & tail angle as suggested. I can’t see making it a low wing would change any angles. The up angle of attack on the wing made the bees a slow flying plane.
 

Monte.C

Well-known member
#3
Thanks for the response Merv, I appreciate the input. I'm with you, mostly. Just the one thing: An increase in throttle does try to torque against the wing. You know that. Like if you build something with a very high motor mount above the wing, it'll torque you into a downward-pitch direction.
But my prop axis isn't too far above my wing chord, so the response isn't much - I was just comparing it to the Bees that have a high-mounted wing. So you think I'll need to build in some "up" into the wing as I mount it to the fuse?

Wait - I just checked the plans for the Speedy Bee. It has a central-mounted wing something like Josh's Sportster. The thrust axis stands just above the wing chord, and the thrust axis and the wing are both dead level. They've just built in a little bit of down angle to the tailplane.

Speedy Bee Complete Plan.jpg

Looks like we found the answer we need. Wouldn't have found it if we didn't start the discussion. Thanks!
 

TooJung2Die

Well-known member
#4
I was taught you trim the tail so the airplane glides smooth without the motor helping by test gliding the airplane. Then you adjust the motor thrust angle to compensate for whatever happens when the motor is pulling. Maybe you can build a reduced size chuck glider from your plans to see what angle works for the tail before you build the full size model?
 

Monte.C

Well-known member
#5
I was taught you trim the tail so the airplane glides smooth without the motor helping by test gliding the airplane. Then you adjust the motor thrust angle to compensate for whatever happens when the motor is pulling. Maybe you can build a reduced size chuck glider from your plans to see what angle works for the tail before you build the full size model?
Wow, breaking down the problem like that completely simplifies it. Makes me wonder why it seemed like such a mystery in the first place. Thanks a lot!
 

leaded50

Well-known member
#6
what @TooJung2Die writes are a smart idea on how to set it up.
I see by many of mine scratchbuilds i set the angle of incidence between 0 and 2.5 degrees on main wing, and 0 on stabilizer. Most RC planes do have 0 degrees on main wing too, with more differences if a jet, or 3D acrobatic.
"Thrustangle"/posistion of motor depends on plane, the bigger/heavier have less problem by torque twisting.
Your plane seems have big wing area, and wouldnt be so much affected of torque , and should float pretty easy in air. I would set incidence angle on both wing and stabilizer on 0 degree.. and checked, and if necessary adjusted thrustangle on motor after a flightcheck. (tried different angles, to find where it fly best.)
 

Monte.C

Well-known member
#7
what @TooJung2Die writes are a smart idea on how to set it up.
I see by many of mine scratchbuilds i set the angle of incidence between 0 and 2.5 degrees on main wing, and 0 on stabilizer. Most RC planes do have 0 degrees on main wing too, with more differences if a jet, or 3D acrobatic.
"Thrustangle"/posistion of motor depends on plane, the bigger/heavier have less problem by torque twisting.
Your plane seems have big wing area, and wouldnt be so much affected of torque , and should float pretty easy in air. I would set incidence angle on both wing and stabilizer on 0 degree.. and checked, and if necessary adjusted thrustangle on motor after a flightcheck. (tried different angles, to find where it fly best.)
Thanks @leaded50, this helps.
I think for thrust angle I won't worry about it - I can set it to zero, then shim it or rebuild the motor mount if I have to. Not a big job. For the tailplane, based on the tips I'm hearing here I'll either set it level or build in a little bit of angle (equivalent to up aileron). But if it's only a small angle needed and I build it level, then maybe a little trim with the ailerons will be all that's needed.
Sounds like either way isn't a crime, and either way I can fix it to fly great. (Without needing to rebuild the tail!) I'm wanting a slow floater here anyway.
 

Monte.C

Well-known member
#9
Looks like I'm pretty much resolved.

Just a clarification for anybody who might read this:
When I said "the motor will torque you into a downward pitch" I don't mean what we call "motor torque". The acceleration of the motor & prop spinning one way will roll your plane the other way. What I mean is torquing about an axis from wingtip to wingtip. So with a thrust axis below the wing it'll pitch you up, with a high-mounted motor like some seaplanes it'll pitch you down.

I hate loose ends! I feel better now... :)
 
#11
I've started a foamboard build of my own design very much inspired by the Bee planes, styled like a WW2 fighter but with as much wing as a Clancy Bee.
I was designing a very similar plane and decided to build a scaled up FT Sportster first. Can't wait to see this one fly when you finish it.
 

Monte.C

Well-known member
#13
I was designing a very similar plane and decided to build a scaled up FT Sportster first. Can't wait to see this one fly when you finish it.
Awesome! My first build was a Mini Sporster. The build process worked but it was a learning experience; My builds are a lot cleaner now. When this one proves itself in flight I'll shoot the plans over to you.