Arrghh... how to balance a biplane?

[jasmine2501]

I can't figure out how to find the CG on my Pitts... if I put my fingers under the top wing, it balances wherever I put them... if I try to balance it upside-down, I can't find the balance point... I can't use the bottom wing because the CG is supposed to be slightly forward of its leading edge.

How can I balance this crazy thing? It's the one in the pic...

I think it's really nose-heavy because I can not make it hover... it wants to pitch forward badly.

[Grasshopper]

Hi Jasmine,

I balanced mine by holding my finger tips at the CG point under the top wing. That was with the plane right side up. I'll bet Murph will know how.

[CHELLIE]

I can't figure out how to find the CG on my Pitts... if I put my fingers under the top wing, it balances wherever I put them... if I try to balance it upside-down, I can't find the balance point... I can't use the bottom wing because the CG is supposed to be slightly forward of its leading edge.

How can I balance this crazy thing? It's the one in the pic...

I think it's really nose-heavy because I can not make it hover... it wants to pitch forward badly.

Hi Jasmine :ws: turn the plane upside down, make a balancing tool from a piece of 2x6 about 10" long, drill 2 holes in it, about 4" apart and insert 2 pencils, with the erasers poining up, balace on the erasers at the CG, hope that helps, Chellie

[Biplane Murphy]

Typical CG on a bipe is directly above the lower wings leading edge....

A good test is to fly normal and straight... Then try flying inverted straigh and level...if it drops the tail in both conditions, then it's tail heavy....

If you fly normal and inverted and the nose drops, then it's nose heavy....

Hope this helps...

[CHELLIE]

All great advice :ws: here is one more idea that works great, make a small hole in the top wing in the middle, where the CG should be at, glue in a string there, hold the plane up with the string, this will also tell you if your plane is balanced from wing tip to wing tip, if the wing stays level, hope that helps, Chellie

Ps just leave a short piece of the string there, so you can check your CG with different batteries

[jasmine2501]

When I do that it seems to be balanced, but it wants to pitch forward so much I'm not sure... with fingers under the top wing, everything is hanging underneath....

The photos show where I put everything, if that helps...

[Biplane Murphy]

Also try using Chellie's eraser trick under the top wing... holding the pencils at a 45 degree angle to clear the bottom wing....

The smaller contact area will help get a more accurate test...

Most bipes tend to be tail heavy do to the short nose, but being a foamie, the battery might need moving rearward to get your CG set right...

[jasmine2501]

Ahh ok... those are all good tips... I'm trying to get it close before I try flying at any altitude. Just hovering a bit with my hand on the tail to see if it has enough power, and it wants to pitch forward a lot. If the weather is decent tomorrow I'll try flying and see what happens. I've got it close, I think :p

I'll take it over to the paved runway, tell the slimers to GTH, and try ROG takeoff I guess. If I totally waste the thing, it's not a big deal.

[CHELLIE]

When I do that it seems to be balanced, but it wants to pitch forward so much I'm not sure... with fingers under the top wing, everything is hanging underneath....

The photos show where I put everything, if that helps...


Hi Jasmine, Its always better to be nose heavy than tail heavy, I would start with a CG 1" behind the leading edge of top wing, glue in a string there, and hold it up on the string, also run a length of velcro on the side of your fusealage from the front to the wing, also add velcro to your lipo, so you can slide the lipo forward or back to get the CG, Hope that helps

[Biplane Murphy]

So.... you are just hover testing it holding the tail.....It will try to Torque roll everytime without your adding aileron input to counteract it ...

You wont really be able to tell untill you fly it....remember... normal and inverted....
tail drop=tail heavy
nose drop=nose heavy

If it tucks to the top/canopy in both conditions...or to the belly/landing gear in both conditions...then that would be a motor thrust line issue....

Good luck with the maiden...

[CHELLIE]

Ahh ok... those are all good tips... I'm trying to get it close before I try flying at any altitude. Just hovering a bit with my hand on the tail to see if it has enough power, and it wants to pitch forward a lot. If the weather is decent tomorrow I'll try flying and see what happens. I've got it close, I think :p

I'll take it over to the paved runway, tell the slimers to GTH, and try ROG takeoff I guess. If I totally waste the thing, it's not a big deal.

Your a great pilot, you wont Waste it ;-) We all wont let you :)

[jasmine2501]

Your a great pilot, you wont Waste it ;-) We all wont let you :)

Thanks for the vote of confidence... it's supposed to be windy tomorrow so I'm going to bed early and see if I can get out there at 7am before it starts blowing like crazy. That's one issue with living in Colorado Front Range area, winter is windy... sometimes hurricane force winds :eek:

[E-Challenged]

Most scale bipes are critical with respect to cg. For first flights, it's safer to be nose- heavy and use small control throws on rudder and elevator and have noticeable down and right thrust. You might want to use a little down elevator trim to counter the biplane tendency to zoom upward and tip stall after lift-off. Have a trusted helper standing by to feed in trims as you keep it flying.

[jasmine2501]

That is good advice. I did get her flying though... I've crashed and repaired it once already :)

But as you can see here, I need a bigger field! And I need to think a little bit when landing...
4deEznMWMMA

[hillbille]

Hey jasmine2501,

Someone somewhere referenced this and I went and "copied" it and posted it to my site - cause I didn't know when or if I could ever find it again. Anyway here it is and although quite in depth it is very good!!

http://www.bakehead.com/rc_cg.htm

Sorry no simple explanations!! LOL!!

Hillbille

[jasmine2501]

Yeah I was going to write something similar myself. I didn't realize this thread was so old... the video I posted is from a different Pitts. Both fly good, but I took the motor off the profile Pitts to use for something else.

[rhuber40]

Jasmine2501

Nice vids, what camera are you using?

[jasmine2501]

Jasmine2501

Nice vids, what camera are you using?

It is the FlyCamOne version one... can't really get it any more, but you can get the new one.
http://www.hobby-lobby.com/video-camera.htm