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Help!
Gentle Lady Scratch with Wing Mods (Oh and Hello!)
Hi, Hoping someone can help me...
Over a decade ago I built and flew a Gentle Lady, flying with the Chester Model Flying Club (NW U.K), on a very casual basis. The years and house-moves since have seen the aircraft reduced to firewood but as I still have (most) of the other gear, and the plans I've been thinking I'd crack on and build another, hopefully doing a better job of it than first time round. As I have the 'Kit' plan I only have the airfoil profile for the centre wing section, the tapered outers have to be generated. I figured I could mess around with a photocopier and alot of T&E but instead I DL'd Profili 2 and have knocked up a couple of rough ideas using the "Aquila 9.3% smoothed" (the nearest, visually, I could find to the one on the plan) airfoil and the 'Panel Management' tool. So-far, so-good. My first GL suffered terribly with fluttery wings, that bent horrendously on the bungee (Hi-Start?), and were visibly distressed by high windspeed. Although they never broke, I always thought the single-run spars through the centre of the wing were a bit of a poor effort. And so to the crux of my ramble... If I were to build the wing as a D-Box/Tube, with the LE fully sheeted to upper and lower spruce spars (say 1/4 x 3/16), should I postition the spars at the same distance from the LE as the single spar in the original, or should I position them at max thickness (in this instance, according to profili2, at 31.3%)? The original position is around 68mm from the LE, the modded posi would be 72mm. Would this make any difference at all? As far as shear-webb is concerned, what are the relative advantages/disadvantages of having sheeted webs affixed to the fore/aft surface of the spars, against having 'block' web sandwiched between the upper and lower spars? Is there a right/wrong method to complement 'D' constuction? Would I still need, in this instance, to keep the secondary spar that this model has nearer to the TE, and given the mod, would it be ok to leave this as a single run? I understand that the mods may incurr a weight penalty, but getting the GL to stay up was never too much of a problem, and she did like to wander off in the breeze! A minor increase in AUW will probably (hopefully?) be of little detriment? I'm not really (I don't think) a modeller's modeller, and most of the terminology I've used has come from messing around with the Profili app and looking through this site. If it's incorrectly applied, please forgive me. Thanks in advance, Steve. Manchester, England. |
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Hi Steve;
I personally agree with you that the GL wing could use re-engineering to increase the strength. I have one that is over 20 years old and have had multiple spar failures. The conventional D-tube spar design will do the trick. To get some insight on maximizing the strength of a spar you should spend some time reading Dr. Drela's spar design which he uses on his Bubble Dancer. Check out this link: http://www.charlesriverrc.org/articl...edancer-3m.htm I think if you follow Dr. Drela's design for the GL you will have a far better wing design. Good luck in your efforts. Most of all, have fun and take the opportunity to learn. Kurt |
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I have a electrified GL and it makes a good photo plane.
I have a second GL kit here, and I have been looking at a way of making the wing lighter and collapsible into 4 parts. I dont need the strength required for a bungee launch since the wing will only be used for electric. No doubt the GL wing could changed to improve it (D box etc) but just re-engineering the spars might be enough. The Spars in the GL are fairly heavy and I have been looking at Mr Drelas advice on making lightweight and strong spars. The idea here would be to build the wing as standard, but with lighter spars. If the new spars are strong enough it may be possible to eliminate the rear spars too. So far I have stuck the bits of end grain balsa together, in the next day or two I will be adding carbon tow to the caps. |
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Modified GL
Hi,
I did a GL with mods last winter and have been popping it up all summer. I would by a new kit to start with and just change it up. I used the Drela air foils for the alegro lite. You can down load the foils plans etc for the Alegro free from Charlesriverrc.com You can also order laser cut ribs if you like from various cutters. Here are some pics of my GL. The tail group is stock with covering hinges. Keep the tail LIGHT. The GL has a rep for being tail heavy. Place all the RC gear in front of the wing, Hollow out the nose block enought to get the battery part way into it. I extended my nose block 1" and used a little light fiber glass over it. ( Remember this plane usually needs nose weight so a little "beef" in the nose won't hurt) I did a pull pull rudder control to get the pushrod out of the tail. I used a light weight carbon fiber tube for the elevator push rod with as little wire as possible. I kept the tow hook threaded portion an inch or so long to double as the ballast mount with a wing nut. Do a search here for "Gentle Lady mods" you'll get lots of info. I did a full D tube wing and top and bottom spars to the tips. DO KEEP THE TIPS LIGHT AS POSSIBLE . |
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Last edited by ozmo01; Dec 22, 2009 at 01:05 AM.
Reason: pour spelin
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