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I've built many a plane and wanted to share how I measure my CoG.
Its all by feel for me. My pattern planes I balance so they fly inverted and upright without any elevator inputs and so KE needs no elevator correction. Freestyle planes are balanced a little less precisely and purely on how I want the plane to feel(further forward for a faster feel, further back for a more precise, smooth feel). Free |
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I understand what the results of a correct CG (balance point) would be when it is correct but if you design a plane (that has never been flown) at what percent of the MAC would you choose as a starting point? |
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Last edited by Ampbomber; Feb 23, 2016 at 03:36 AM.
Reason: Sp
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Rod Bending
Here are some thoughts on bending the carbon rods. Some rods I have bent have exhibited some weak spots due to air bubbles and twists in the CF tow.
Since the 3/64 tubing shrinks to a minimum ID of .0234 the process may not fully “squeeze the 3K tow. To insure that the 3K tow is fully “squeezed” during the shrinking process it would be wise to tack down both ends of the tow after it has been pulled thru the tubing (keeps the tow straight and tight). Also to eliminate any air bubbles in the rod, one end of the tubing should be tacked down and the tubing should be stretched during the shrinking process (keep tension on the tubing) while heat is applied to the end of the tubing that is tacked down and slowly shrink the tubing from one end to another. This will allow the tubing to shrink to a smaller diameter and will allow excess epoxy and air to be driven out the free end. Also, if anybody is going to experiment with this method it may be wise to place an indicator (a piece of folded tape) on the wire that will pull the tow thru the tubing so that as you pull the tow thru the tubing you don’t twist or spin the wire which would put a twist in the tow before shrinking. I'm open to any thoughts on this. Just thinking, George |
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On the surface it appears to be difficult to hook vacuum to the tube. I'm open to any thing you want to experiment with. The roller may be helpful. Just let us know how it works out.
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George,
I, too, have seen the 50% number for F3P, and I, too, respect the 27 -28% number. My original circa 2012, Robert Youens' (BudgetRc) Arrow had a 50% CG, whereas my 72% scaled-down version needed closer to 28 - 30 %. Lastly, do you remember the weight of the veil you use for the gussets? I made a test piece using CST's EZ_LAM mixed 1:1 vs. their normal 2:1, but mine came out pretty flimsy. I'm going to double it up and West Systems and see how that goes. My test piece weighed out at 0.25 gm/sq.in., though. |
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Last edited by 356Jim; Feb 23, 2016 at 11:00 AM.
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Free |
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I use .2 oz veil. Normal EZ_LAM mix is ? 2:1 is that resin 2 parts to 1 hardner? Remember to use more hardner than resin. Did the extra in the cup harden or did it stay "rubbery" ? West System is normally 5 resin to 1 hardener and I mix it 1:1 to get "rubbery" product. Once the rubbery epoxy/veil cures a good test is to stick a pin thru it and move the pin around. The Gusset material should not tear with moderate force. Veil and a normal epoxy mix only creates a brittle material that tears easily. |
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Maiden flight
BTW, the Eagle flew today. Had a few problems at first but by the end of our session it flew great. The two other fellows that flew her remarked that she flew better than GII. They said that the Eagle was “crisper” in all controls. They also remarked that the Eagle seemed to have more reserve power. The contra in the Eagle uses 28 tooth crown gears and an 8 tooth pinion. GII has 32 and 8.
After the first flight I noticed that I had the ailerons on low rate (duh!) which made for sluggish rolls. The second flight broke the aileron servo loose and broke the right inboard aileron hinge. All was well for the next 7 flights after repairs were made. Happy campers here! I have some cell phone video I'll try to post tomorrow. |
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Video clips from Maiden day
Here are some clips from yesterday. They aren't the best but where we fly ,as you can see, it's difficult to shoot video.
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Jim,
I made up a sheet of gusset material with West System 105 epoxy and West System 206 slow hardner mixed 1:1 and it came out at 0.0534 gm/sq in. Yes it is flimsy but it is tough. Did you post the wrong weight for your experiment? |
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I'm flattered that you think I'm some kind of super designer but you have to realize that I am only a mechanic. The Eagle was sketched over the plans of the Guestimate II which is a clone of Alexey's Victory. See Alexey's thread "Composite Design F3P". My only claim to anything is that I like to do things differently and on a budget which is not always the perfect solution. I'll be looking at the Eagle's different build techniques and discuss the good and bad of each . |
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