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Old Feb 05, 2013, 09:22 PM
gravityking is offline
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Help!

Calling all Pitts experts!


Jamara Pitts Special ARF is the topic. I won this baby at the club Christmas raffle, yea cool huh!
I'm to the point to where I need to zero in on the CG. The 4 page instruction sheet that is in 2 languages I don't understand, German and English translated from German, are confusing me. I know this topic is beat to death out there. I've seen CG is root of bottom wing, 1 inch back from bottom wing on top wing (that one confused me too). I guess I need to have my own thread because this plane is mine!

It's 53" span so little under 1/4 scale. Knowing bipes are usually tail heavy I opted for a RCGF 26cc instead of the .90 glow recommended.

Here's the rub. The English translation from German says "CG is 4.5cm from the front of the wing underside."

Me too!

I entered the German text into Google's translator and got "At the lower support surface measure 4.5cm from the front edge of the leading edge."

I get 4.5cm from leading edge of lower wing. Anybody else see it that way? Tell me what you think.

Thanks in advance,
Craig
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Old Feb 05, 2013, 09:46 PM
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in AMERICAN! lol that comes ta about 1 3/4 inch!

I for the life of me can't find or remember where I saw the Cog for my 1/4 scale pitts, but that sounds about right!

make a mark 4.5cm back from leading edge of lower wing(on top of lower wings,) turn plane over and set CoG!

oh and I don't know if I am an expert pitts guy! just cuase I am building one! as it is my first!
Old Feb 05, 2013, 09:58 PM
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Originally Posted by whiskykid View Post
in AMERICAN! lol that comes ta about 1 3/4 inch!

I for the life of me can't find or remember where I saw the Cog for my 1/4 scale pitts, but that sounds about right!

make a mark 4.5cm back from leading edge of lower wing(on top of lower wings,) turn plane over and set CoG!

oh and I don't know if I am an expert pitts guy! just cuase I am building one! as it is my first!
Cool, that's what I get out of it too.

This will be my first biplane as well, aside from the CL one I had as a kid. I have a 1/3 scale Weeks Special Piits kit in the closet with a G62 waiting to build and I really didn't want it to be my first!
Old Feb 05, 2013, 10:09 PM
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I can't translate German English. But I would wrap one of these around both wings and go by where the plumb hangs,and make it a little nose heavy to start with. Just in case

http://home.mindspring.com/~the-plum...%20Machine.htm
Old Feb 05, 2013, 10:23 PM
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Originally Posted by Crowfly View Post
I can't translate German English. But I would wrap one of these around both wings and go by where the plumb hangs,and make it a little nose heavy to start with. Just in case

http://home.mindspring.com/~the-plum...%20Machine.htm
Awesome. I did a maiden on a little electric P-51 today and was relieved that the CG they specified was correct. Lately it seems the mfg has been anywhere from wrong to very wrong on my recent maidens. I was wondering just then how to set it up and use the specs as a guide only. This is it.

Thanks a lot.
Old Feb 05, 2013, 10:45 PM
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They meant 4.5cm back from the bottom of the leading edge of the upper wing. CG on biplanes is measured off the top wing or upper wing, not the bottom or lower wing.
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Old Feb 06, 2013, 12:02 AM
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ok I may have been mistaken! upon further review, it might have been 1 1/2" on my ultimate!

from what I can tell, the CoG on a pitts is right close to the leading edge of the lower wing!

and now that I say that, it reminds my that I was thinking, how am I going to balance it there!

cuase it was so close to the front edge of the lower wing! and yes my ultimate is balanced upside down from the lower wing!
Old Feb 06, 2013, 10:27 AM
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We'll find out for almost sure! I'm building one of those Vanessa plumb bob deals. Have to go through the metal rack at work today and find some stock.
Old Feb 08, 2013, 11:31 AM
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Update Built the CG machine and tried it out on the model below I've been trying to trim out. According to it I am 1.5" nose heavy from spec, which I always felt. So this weekend I'll try, in several adjustments, to move it back the 1.5".

Cross your fingers. I hate handling a tail heavy plane back down!
Old Feb 10, 2013, 12:03 PM
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Originally Posted by gravityking View Post
Update Built the CG machine and tried it out on the model below I've been trying to trim out. According to it I am 1.5" nose heavy from spec, which I always felt. So this weekend I'll try, in several adjustments, to move it back the 1.5".

Cross your fingers. I hate handling a tail heavy plane back down!
Don't worry, you can do it. Nose heavy planes fly like sht. I once had to land a 30cc yak woth 3d throws that had about 1/4lb of weight break loose and wedge itself in the tail. Not a big deal if you're not heavy handed on the elevator.
Old Feb 10, 2013, 12:30 PM
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Don't worry, you can do it. Nose heavy planes fly like sht. I once had to land a 30cc yak woth 3d throws that had about 1/4lb of weight break loose and wedge itself in the tail. Not a big deal if you're not heavy handed on the elevator.
I knew it was nose heavy regardless of the manual I could easily tell. And getting older I don't think my heart can take to many more tail heavy returns. Bringing 'em back down is the longest 2 hours I've ever had. I'll gladly try it a little nose heavy first.
Old Feb 19, 2013, 07:19 PM
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Well so far this CG machine is dead on. Took the Air Tourer out this weekend and kept adding weight until I got to the 1 1/2" mark. Plane flies awesome. I've never seen a plane come alive like this thing did with CG adjustment.

Should get the Pitts out this coming weekend so we'll see.
Old Mar 03, 2013, 08:03 PM
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Finally a nice flying day! Took her out for maiden flights Saturday. Using the CG I got from the "machine" I started out nose heavy. To nose heavy. Took forever to get off the ground and landed hotter than an F-18 on a carrier. Added 2 ozs to the tail, got better. Added 2 more, putting it at the new CG mark and viola. Perfection.

So I will now always check the factory spec with my new found gizmo.

Thanks for all your input.

Craig


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