I need building advice!

Hi,
Can someone tell me how to figure where the wing should be mounted in
relation to the length of the fuselage on a model airplane. I recently
purchased a duraplane on e-bay. When I received it looked as though the
wing was set back too far toward the tale. However, it did appear to be
balanced with the battery pack at the back of the servo compartment.
Another question is at exactly what point on the wing should you
measure the center of gravity from. On most trainers I've seen it is at
approxamately the thickest part of the wing and is usually stated as
_._
inches behind the leading edge of the wing.
Thanks,
GADMO
Reply to
gdmoore
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This can be a pretty complex design issue. If you're not interested in designing airplanes then the answer is -- wherever the designer put it. If you _are_ interested in designing airplanes then do a web search on "tail volume coefficient" -- I know this was in magazines, I dunno if it's made its way to the web yet. The idea is to find a plane who's pitch stability you like, then copy its TVC and CG placement.
You generally have quite a bit of latitude with the wing location, as long as it balances. If you have the wing at the design location and it balances -- go fly.
On most model aircraft with a conventional layout you want the CG to be 25 to 30% back from the leading edge. With a longer tail moment or larger tail you can go back farther, with a shorter tail moment or smaller tail you must go forward more (a straight-chord flying wing needs the CG to be between 19 and 22%, depending on whether it's high wing or low). Do a web search on "Heintz" and "Stability" and you'll find a paper on finding the CG for full-scale light aircraft written by Chris Heintz. It's for homebuilders, so it's pretty accessible by modelers.
Reply to
Tim Wescott
I think you will find that for a flying wing, its as low as 16% of chord..for conventional arrangements it can go much further..well aft of the trailing edge..in cases where there is a large or remote tailplane. Continue in this way towards two equal wings, or a canard, and its a moot point as to which is the main wing anyway.
The rule of thumb 'between 20% and 35% of chord' only suits more or less conventional-looking planes.
Reply to
The Natural Philosopher
| Hi, | Can someone tell me how to figure where the wing should be mounted in | relation to the length of the fuselage on a model airplane. I recently | purchased a duraplane on e-bay. When I received it looked as though the | wing was set back too far toward the tale. However, it did appear to be | balanced with the battery pack at the back of the servo compartment. | Another question is at exactly what point on the wing should you | measure the center of gravity from. On most trainers I've seen it is at | approxamately the thickest part of the wing and is usually stated as | _._ inches behind the leading edge of the wing. | Thanks, | GADMO |
What I usually do with a new airplane is initially balance it at, or a little in front of, the recommended CG range noted on the plans/instruction sheet. This follows the reasoning that it is better to be a little nose heavy than a little tail heavy. Then I slowly adjust the CG aft in 1/4 inch increments over several flights to the aft point of the recommended CG range.
If you didn't get any instructions when you bought it on ebay you should do a search for it on Yahoo, Google or some other search engine. Most manufacturers list the manual on their site.
Reply to
Jarhead
|
| | Hi, | | Can someone tell me how to figure where the wing should be mounted in | | relation to the length of the fuselage on a model airplane. I recently | | purchased a duraplane on e-bay. When I received it looked as though | the | | wing was set back too far toward the tale. However, it did appear to | be | | balanced with the battery pack at the back of the servo compartment. | | Another question is at exactly what point on the wing should you | | measure the center of gravity from. On most trainers I've seen it is | at | | approxamately the thickest part of the wing and is usually stated as | | _._ inches behind the leading edge of the wing. | | Thanks, | | GADMO | | | | What I usually do with a new airplane is initially balance it at, or a | little in front of, the recommended CG range noted on the | plans/instruction sheet. This follows the reasoning that it is better to | be a little nose heavy than a little tail heavy. Then I slowly adjust | the CG aft in 1/4 inch increments over several flights to the aft point | of the recommended CG range. | | If you didn't get any instructions when you bought it on ebay you should | do a search for it on Yahoo, Google or some other search engine. Most | manufacturers list the manual on their site. | | -- | Jarhead
Here is Duraplanes site:
formatting link
and they do show the manuals are available with each airplane they make.
Reply to
Jarhead
Chris Heintz's paper on stability gives a formula that's valid for anything from conventional to canard to flying wing.
I can believe the 16% rule for flying wings on a model at least. It would increase the speed at which you could keep the nose up, however.
Reply to
Tim Wescott
If you want the info Tim gave you - and more - in a book you can sit in your easy chair and read, check out "Basics of R/C Model Aircraft Design" by Andy Lennon, published by Air Age Media, the same folks who publish Model Airplane News. Once you absorb what's in it, you'll be able to actually design models.
Reply to
Geoff Sanders
Now THAT is a good book.
If you want the info Tim gave you - and more - in a book you can sit in your easy chair and read, check out "Basics of R/C Model Aircraft Design" by Andy Lennon, published by Air Age Media, the same folks who publish Model Airplane News. Once you absorb what's in it, you'll be able to actually design models.
Reply to
Six_O'Clock_High
This is great! I had no idea that I could get as many responses and really appreciate all of you that offered advice. This is a hobby that I think could be challenging from many aspects and I look forward to learning them! Thanks to all of you. G Moore
Six_O'Clock_High wrote:
Reply to
gdmoore

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