CG and Kit Bashing
02-12-2005, 05:30 PM
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CG and Kit Bashing
Hey All
Hopefully this question is in the right place, as there is no Kit Bashing Forum... I am presently Bashing an Avistar mated to a set of PT-40 wings. To make them fit properly was no small feat. I had to cut down the rear spar to fit the fuselage saddle, and used a bellcrank actuated aileron system utilizing one servo in the center of the wing. I had to build up the fuselage saddle to mate properly with the wing. In addition to this I had to scratch make the tail section. The tail plane incidence has not been modified. I have figured where the CG is supposed to be by utilizing a home made CG finder, courtesy of a web site referred to as The House of Balsa Dust. (It works pretty sweet) Finally for my question... How much does the main wing incidence angle affect the flying CG of the airplane? I am using the horizontal stabilizer for a level flight reference. In addition to all of the mods, this airplane will be powered by a K&B pumped .61 swinging a 12/5 prop and is of the conventional gear configuration.
Thanks in advance for all of the input.
-Tom
Hopefully this question is in the right place, as there is no Kit Bashing Forum... I am presently Bashing an Avistar mated to a set of PT-40 wings. To make them fit properly was no small feat. I had to cut down the rear spar to fit the fuselage saddle, and used a bellcrank actuated aileron system utilizing one servo in the center of the wing. I had to build up the fuselage saddle to mate properly with the wing. In addition to this I had to scratch make the tail section. The tail plane incidence has not been modified. I have figured where the CG is supposed to be by utilizing a home made CG finder, courtesy of a web site referred to as The House of Balsa Dust. (It works pretty sweet) Finally for my question... How much does the main wing incidence angle affect the flying CG of the airplane? I am using the horizontal stabilizer for a level flight reference. In addition to all of the mods, this airplane will be powered by a K&B pumped .61 swinging a 12/5 prop and is of the conventional gear configuration.
Thanks in advance for all of the input.
-Tom
02-12-2005, 07:28 PM
#2
RE: CG and Kit Bashing
The incedence of the main wing in relation to the datum line AND the horizontal stab has a HUGE INFLUENCE on how a plane flies.
I would suggest the following:
Horizontal stab parallel to the datum line (line running from the center of the nose of the plane [prop shaft] to the center of the end of the fuselage when looking at the plane from the side )
Main wing should range from 0 to ABOUT +1 degree (at most ) for MOST trainers. Unless you have reason to do otherwise stay at 0 on the main and 0 on the horizontal stab.
Too much positive incedence and the plane will leave the ground before it is ready to fly and if it doesn't stall out, climb like crazy.
Too much negative incedence and the plane may never even get off the ground, and if it does it will dive like crazy.
I would suggest the following:
Horizontal stab parallel to the datum line (line running from the center of the nose of the plane [prop shaft] to the center of the end of the fuselage when looking at the plane from the side )
Main wing should range from 0 to ABOUT +1 degree (at most ) for MOST trainers. Unless you have reason to do otherwise stay at 0 on the main and 0 on the horizontal stab.
Too much positive incedence and the plane will leave the ground before it is ready to fly and if it doesn't stall out, climb like crazy.
Too much negative incedence and the plane may never even get off the ground, and if it does it will dive like crazy.
02-14-2005, 04:55 AM
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RE: CG and Kit Bashing
APIA, funny but I did almost the same thing as you. Cessna 40 fuse, horizontal stab from my Super Stick 60, home made rudder, and a flat bottom wing. MDS .78 for power with a 12x6 and sometimes 12x5. Since I did not know much about incedence, I just put it all together and flew it. I guess I was lucky because it flies really well. Knife edges from one end to the other. I love to do touch and go's and as soon as I lift off, I jam the sticks and pull out 2 snaps then continure flying.
Have fun, I think that you'll enjoy your BASH as I did mine.
Have fun, I think that you'll enjoy your BASH as I did mine.
02-14-2005, 09:38 AM
#4
RE: CG and Kit Bashing
What Campy said...
To answer your other question, the incidence has NO relation to CG. The CG location is an integral part of the wing. Wherever you determine the CG will be for a given wing, that will always be the CG for that wing. Whatever you decide to build around that wing (within reason, and discounting Canard and tailess planes) has no affect on where the CG will be.
To answer your other question, the incidence has NO relation to CG. The CG location is an integral part of the wing. Wherever you determine the CG will be for a given wing, that will always be the CG for that wing. Whatever you decide to build around that wing (within reason, and discounting Canard and tailess planes) has no affect on where the CG will be.
02-14-2005, 11:18 AM
#5
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RE: CG and Kit Bashing
In addition to MinnFlyer’s comments the spar is generally located at the CG on most wings. My experience indicates the CG should be located 1/4 to 3/8” forward of the spar for the first flights so the bird will live long enough to shake out the inevitable design problems.
Bill S
Bill S
