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Post by st on May 10, 2007 13:11:56 GMT 10
Yep, I've started the build ;D No quarter sawn wood at local depot, but yesterday picked up this bit of hoop pine anyway: 140x19x2050mm Weight of just over 2.4kg At least 500g of wood shavings have come off it already. Almost all with the hand plane too!! Planform and the trailing edge (top side) roughed out ;D Ailerons will be added to, rather than cut out of, plank. hmm, this is fun ;D
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Post by callun on May 10, 2007 13:17:41 GMT 10
Nice. Brave. Interesting I'd thought of making something out of solid timber but don't really feel like wasting my time cos I'll invariably jump in head first and not make enough plans and it'll cost too much or at least more than I'm prepared to spend. Keep us posted on how ya go!
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Post by callun on May 10, 2007 13:22:00 GMT 10
By the way, do you have any hard plans to go by? Or just eyeballing it? What're your plans?
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Post by st on May 10, 2007 13:51:57 GMT 10
Um, did you have to ask Yes, I'm largely making it up as I go ;D $17 for a plank of wood and a few hrs is all it's cost me so far
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Post by callun on May 10, 2007 14:22:40 GMT 10
I was thinking of ways you might be able to reduce weight (at the expense of work ). You could drill small holes and fill em with a bit of putty, or even cut out panels, hollow them and reapply veneers, but that might not be in the spirit of what you're trying to do. What power tools do you have at your disposal? What do you anticipate requiring?
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Post by st on May 10, 2007 16:44:34 GMT 10
I've got a router and circular saw, as well as other hand tools. At the moment I don't see any need for additional tools Have to wait and see though.... The Thorn is meant to be a heavy beast, and this one will be heavy alright...... I'm trying to keep it pretty simple and basic. It aint going to win any competitions, but it should fly ;D I hope Anyone know what the max wing thickness is on the real thorn? edit: if HS85s stick out slightly, and HS125s don't, it must be about 11-12mm thick.
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Post by thevon on May 10, 2007 17:59:00 GMT 10
Sean could probably give you more advice on this - he seems to understand about profiles etc. But he's away till early next week. I have mixed feelings about it ... sounds good and cheap, but also very difficult!
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Post by st on May 10, 2007 21:21:26 GMT 10
Difficult? Nah Only a few more hrs work and the wing should be ready for servo's and ailerons ;D Profile used is proprietary - code is EB01 ;D Not sure about dihedral though - leave it flat, cut and join, or bend it with weights and water (& heat?)? Will have to work something out
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Post by sean on May 10, 2007 23:21:30 GMT 10
Hi Simon,
Cool idea, should be very interesting! The Thorn profile is an RG15 thinned to 7% thickness, which is quite thin. Thicker would give slightly better handling at the expense of weight. I'd recommend trying to at least get close to an existing model-specific aerofoil (eg RG15), as making up your own can really hurt performance (I tried this on powered own-designs when I was a teenager and the models just weren't as fast as they should have been).
I'd just make the wing flat with no dihedral, it'll make the handling nice and neutral with good inverted handling.
Sean.
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Post by st on May 11, 2007 9:07:44 GMT 10
Thanks for the comments Sean. I'll leave the wing with no dihedral and see how it goes. A lot easier to add dihedral later than to remove it I've got to take some thickness out of the wing (the bottom is still flat/untouched so it won't be hard). I'll take 3mm off first, which will give me about 9% thickness. Will then see what the weight is like and go from there. Hopefully that should be enough. I've been wanting to avoid shaping to exact profile (RG15 etc) for ease and speed of manufacture. However, it probably wouldn't add a lot of time/difficulty, so I might make up a profile card/section (or whatever its called) and see how what I've done so far compares. It's proving to be a lot more fun than I thought it would. Probably providing some entertainment for others too
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Post by st on May 16, 2007 19:08:37 GMT 10
The build is progressing along nicely Wing is shaped, ailerons shaped, servo holes cut out. Just got to attach the ailerons. Will try using a silicon hinge I think Profile ended up being about 8% thickness, and kinda similar to an RG15. (I'm glad you suggested that Sean, cause the profile was way to fat at the leading edge). The fuselage is largely assembled. Faced and glued two bits of U channel towards each other (hole in centre). Had to enlarge the hole/channel a bit for batteries and receiver. It's nice and strong, and a bit lighter than if I'd used solid wood. Still got to do the tail end of things. Weight of the wing by itself will be 1.5kgs. Total weight probably about 2.5 kg, or a touch more. I was glad to hear that Andrews Drongo flew well at 2kgs. This thing has a larger wingspan and hence probably similar wing loading. I'm looking forward to trying this thing out ;D
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Post by callun on May 16, 2007 19:31:07 GMT 10
Any new details? Wingspan? Weight? Length? etc
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Post by st on May 17, 2007 9:31:57 GMT 10
Any new details? Wingspan? Weight? Length? etc Wingspan is just over 2m (2.03m or so). Weight - wing only is about 1.5kg, total expected to be about 2.5kg or slightly more. Length about 1.6m or so (tail end yet to be done). a couple more pics:
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Post by thevon on May 17, 2007 9:51:26 GMT 10
Simon, might be worth thinking up some sort of an impact release system btn the fuse and wing ... lots of differential momentum to cope with at that joint. Something that either gives a bit (eg rubber bands) or releases (eg nylon wing bolts that shear; or a spring clip that undoes but I don't know how you could do that. The nose is so olong and stiff that even in a slow speed cartwheel, it will put a huge force on the wing/fuse join. An alternative would be to go for an EPP fuse with a fibreglass rod stiffener, which can flex when hit. Not a carbon rod - would break too readily. But it sounds good. I thought you were building a plank wing like the Drongo, with no nose or tail. But is this going to be a conventional wing, not an elevon wing?? If you're putting a tail on this you'll have to make it very light.
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Post by st on May 17, 2007 10:29:48 GMT 10
Yep Andrew, if a wingtip strikes ground, there will be a huge amount of force on the wing-fuse joint. If it lands on its nose, there would still be a fair bit of force/momentum, but not nearly as bad. As you suggest, the actual thorn has nylon bolts that will shear. At the moment I'm thinking one solid bolt, and another something that will give, so that the wing can rotate around the solid bolt on a big wing tip hit. I think both wing and fuse should have plenty of strength to cope when still held togethor by a bolt. The good thing about this timber stuff is if something splits/breaks it is easy to repair and modify Man, you'd want quite a few large rubber bands.... The nose isn't as long as it looks in those photos (you can't see the whole plane, and it's only 30mm wide, 35mm high). I'm definitely sticking with wood - I don't think EPP would cope given the impact forces, weights and distance (to tail), even if reinforced. I'd prefer the nose to impact rather than a wing tip. A bit of weight will probably be needed in the nose to balance the tail, and to make it faster Yeah, plan has been for a conventional glider, as per the commercial thorn. I found this today: shredair.com/thorn/ - a very nice 100" thorn. How does 11lb (5kg) sound ;D A much better quality finish than mine will have! I've been planning on putting elevator servo at rear also, though still not sure exactly how. It's been lots of fun doing this
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