How do I find my CG of my scratch built delta wing before I fly it ?
02-05-2017, 10:22 AM
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How do I find my CG of my scratch built delta wing before I fly it ?
I am building a Delta Wing from a piece of 20 x 30 1/4" foam board. Its 30 " long 20" wide and will only have the 2 elevons in the rear. I am using a pusher prop located about 2/3 of the back from the front of the plane. I have no idea how to even get close to the CG without going out in the yard and give it a hand toss and see how it reacts? Is there a better way to get close before I take it on its first real flight?
any info would be greatly appreciated. Do you need a picture of what I'm building ?
thanks much.
Bob
any info would be greatly appreciated. Do you need a picture of what I'm building ?
thanks much.
Bob
Last edited by schomper42; 02-05-2017 at 07:39 PM.
02-05-2017, 10:43 AM
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make a jig with two thin vertical post. wide enough to be at about 25% way out the wing on each side that are a couple of inches wide and vertical to the center line of the fuselage; this way it can tip fore and aft. then move the plane to a place where it wants to balance. make sure the pivot point is at the same place on both wings!!
02-05-2017, 07:43 PM
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well, ok I realize that would give me the CG of the plane . BUT that probably isn't where the CG is "suppose to be" in order to fly good. do you understand what I'm trying to say ? Because this is a scratch built with no plans , I have no idea where the CG should be ?
02-06-2017, 06:04 AM
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I just found this on the internet and this is exactly what I was looking for.
#4
you don't have to find the cg, it's always there and really easy to find...the hard part is figuring out where it needs to be in order to make your plane fly the best it can...glide testing or drop testing is what I do...I hold it up high, all flight ready and drop it, if it noses down slightly, I am on the right track...then I glide test it on the grass...
I always make my battery Velcro longer than it needs to be so I can move the battery forward or back, I constantly adjust my cg's, almost every flight depending on battery size and what I want the plane to do...if I want to fly slow I move it back, if I want to fly fast pattern I move it forward..also if you use different size batteries on the same plane, each size has a place to Velcro onto the plane..I can fly my cheap-n-easy with a 1500 2 or 3 cell or a 450 3 cell, it's a huge difference in weight and flight characteristics...it's really interesting to see how it effects the flight of the plane...do your own experiments, especially with a scratch built...that's the funnest part of this game...its the puzzles and the unknown...but don't say you need to find the cg of a plane, it's not like it is hiding from you or something, it's right there...you need to find out where you want it and where the plane wants it...
squishy, Nov 18, 2010 I always make my battery Velcro longer than it needs to be so I can move the battery forward or back, I constantly adjust my cg's, almost every flight depending on battery size and what I want the plane to do...if I want to fly slow I move it back, if I want to fly fast pattern I move it forward..also if you use different size batteries on the same plane, each size has a place to Velcro onto the plane..I can fly my cheap-n-easy with a 1500 2 or 3 cell or a 450 3 cell, it's a huge difference in weight and flight characteristics...it's really interesting to see how it effects the flight of the plane...do your own experiments, especially with a scratch built...that's the funnest part of this game...its the puzzles and the unknown...but don't say you need to find the cg of a plane, it's not like it is hiding from you or something, it's right there...you need to find out where you want it and where the plane wants it...
#4
02-06-2017, 03:37 PM
#5
My method is to find the center of area of half the wing ( span wise ). Then draw a line parallel to the fuse through that point. This is the mean cord . You can find the balance point on this line as a percentage of the line . For a delta I would start at 25% for a test glide.
02-06-2017, 04:24 PM
#6
After you get it flying and trimed for level flight take it up to a safe high height. Cut the throttle and see how it glides . This is a good way to fine tune the balance point. If it noses down hard then it's to nose heavy . If it goes the other way then tail heavy. Find a nice glide by adjusting the balance point.
