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Building Tips and technical articles. => ARF'S => Topic started by: Steve Moore on January 09, 2007, 07:29:17 PM
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Is it just me or ???. This is the 2nd ARF I've completed and both have had wing warps that showed up during initial flight characteristics. And this was ugly, ~6" outboard wing down (upright) and 6" wing up (inverted) few level and landed safely.
Futher analysis with a Incidence Meter showed a 2 deg offset inversely @ the wing tips. A good friend of mine gave me the meter and now I Know what it is used for .;D
Anyway, my question is, has anyone else have had this experience with the ARF's and these trim problems? Building kits off the board, its seams, that I don't have near the trim problems. :-\
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We have talked about this at length locally and I believe that most airplanes have a need for a trim tab.....straight wing or not.
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I own 4 different ARF´s from Brodak and each of them has the wing exactly straight, is the first thing I measure when I receive an ARF!!, before unpack the rest of the items.
Regards.
Manuel.
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Steve,
You my try and hit it with a heat gun while twisting out the warp.
We have one ARF Flite Streak with this problem, but I have not taken the time to hit it with the gun yet.
Later.....
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Heat gun first. Bend it the opposite way. Heat on both sides. Keep at it. Leave it alone for an hour or two. Look at it again... Repeat as necessary. I've found it better, sometimes, to leave a few wrinkles in the covering. Heating out the wrinkles can put the warp back. It's also possible to put slits in the trailling edge, bend opposite warp, and run thin CA. When it flashes off, you've got a mini spar soaked into the trailling edge. It helps. Patch covering and go fly. Do it from the bottom. It won't look too bad. Makes the ARF look right. Kind of. Patched together and improvised. Helps it to be stealthy. Beside you've marked your plane. Trim tabs work to even things out and compensate for aerodynamic anomalies that show up as you fly the pattern. Bawsa warps. A wing can come out of a jig dead straight than warp weeks later. I web trailling edges and mainspars, in part, to keep out the WARPS. Probably there are lots of ARFs and kit builts out there that have wings, stabs, fuses out of kilter. Depends on how close you look. At Brodak's a gentleman was selling an ARF that had just won Intermediate. Was it warped. Let me count the ways. Would be nice if experienced builders talked about how to keep out the WARPS and compensate for warps that show up. How do people age their BAWSA, do they. etc. It's possible to ruin a few hours obsessing about warps that suddenly appeared on pride and joy. Usually means time to stick on THE TAB and GO FLY.
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Thanks for the input Dennis,
Sneaked out today for a 4oz run, (way windy) down to 3" offset now, I think, was only heating on one side, the outboard wing looks good but that inboard is not wanting to give way. See pic's
I think I'm on the right track...
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Dennis did a fine job of explaining how to unwarp the wing. Nice work Dennis.
Allen Brickhaus
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Wow. Thanks Allen. Now, how do you store your Bawsa. Have you ever had bawsa look great at a Hobby shop (or a swap meet), only to have it spring some nasty curves when back at the house? And... and... I love working with bawsa but it's tricky stuff isn't it.
Hey Steve. It's part of the initiation. Consider yourself vetted. Soon you will be ready for THE TAB. By all means do some more work on the wing. Perhaps you can get the wing straighter with more heat gun work. The CA slits (you can make a few) may be needed to finish the job
Tabs are usually made from aluminum scrap about an inch and a half by three inches. Slit the outboard flap at the tip and insert tab lengthwise. The long side parallel to the wing. It's possible to bend the tab up or down and compensate for wing up wing down orientation. Bend tab up if outboard wing is up, down if outboard wing is down. You're creating lift to offset the aerodynamic anomaly. At times the tab is used flat with no bend in order to offset hinging in square maneuvers. I've seen this work. Get a beer and listen to the various theories about why... you will hear many different explanations.
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Tabs do not look good. That is why Charlie Reeves and I prefer to heat and twist wings to get the model flying level. I have added tabs to increase surface area on models which have problems trimming since an area is incorrect or designed wrong. Smoothie flaps are one item which need help. I do like the way Randy Smith suggest to use a fixed inboard wing tip flap and an adjustable outboard wing flap. The outer one can be used to trim the wings level after your wing has been twisted to correct the un-level state of level flight. The outer tab is used to finalize the wing. Twisting the flaps only cause problems with flight characteristics.
Allen Brickhaus
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First order tweak the flaps--according to George Aldrich, that feature is one of the major motivations to have flaps. All you are doing is counteracting the warp that is likely to be there in any plastic covered wing. Trying to heat the plastic to warp out is the best thing too do.