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Post by jirvin4505 on Sept 4, 2008 18:51:49 GMT 10
I am watching the plank build threads and wonderin' could it be done as a vac bag wing and built in an evening? If I was to build a plank like the reaper, jw moth what planform and airfoils would I use? Anybody already got templates I can use - hate making templates Can somebody point me to some relevant build/design threads. I have seen a similar idea on the Oz rcgroups - plank with vac bag wing down NSW way- can't find the link What I had in mind was a single tapered wing 60" span with a fibreglass molded pod'n'boom (disposable in crash) Am I crazy??? [glow=red,2,300]edit... was going to be a wing but now looks like being a 60"slope trash machine[/glow] ;D cheers Jeff
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Post by sean on Sept 4, 2008 19:06:51 GMT 10
Hi Jeff,
Give us a call, I can give you all the info you need. If you're really keen I'd love to shape a plug for you to make a mold from. I already have the design.
The biggest concern I'd have with a fast composite DS plank is landing - even my little Moth is so fast I think I'm gonna break it every time I have to land it. However the weak point in the Moth is the rather delicate fuse - if you had a fuse made from a really heavy glass layup that would possibly be much stronger in a fast landing on grass.
Sean.
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Post by felix on Sept 4, 2008 19:41:48 GMT 10
jirvin i have a set i eagle wings i am "grudgingly willing" to let you practice on......just coz i'm such a great guy lol. seriously though i am really looking forward to seeing your results.
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Post by jirvin4505 on Sept 4, 2008 21:57:27 GMT 10
Just had the honour of the VON visiting the shed .... might get him turned onto composites sean... will discuss ideas with you. Somebody willing to carve a plug - now that's enough to get me listening. Somebody to do templates? felix... I keep looking at the work that goes into these foamies and I get intimidated. Will have to find my copy of the Phil barnes videos for you to watch and will hold your hand thru the vac bag process. Shiny painted wing after an evenings work! Had a quick rcgroup search - started with looking at anything to do with Peter Wick PW51 great thread with lots of ideas.... www.rcgroups.com/forums/showthread.php?t=387891Found this model "the frettchen" and it already has me inspired www.epp-fun.de/frame.htm?/frettchen.htmwith this rave from surfimp on rcgroups... The Frettchen is an awesome plane. Weighs about the same as a Weasel, flies in same lift, also goes A LOT faster on the top end. A very, very good plane. Not quite the thrash-about that the Weasel is, but sort of a great blend between Weasel and Moth, if that makes any sense. Highly recommended.What do you recon? ...."blend between Weasel and Moth" Plane has to have a single taper wing (easy to cut - less taper is easier) - could have rounded tips (more work) sean .. >slowing them down I see some planks have flaps although I have no experience with them. I was thinking a heavy slide on nose cone would become the crumple zone 0s something similar (nose cones are easy to lay up) . I like the taped on wing idea that you have on the ERWIN. cheers jeff
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Post by thevon on Sept 4, 2008 22:09:24 GMT 10
Jeff, for a DS plank I can't help thinking a four servo setup would be good. I was impressed at how Ken's Reaper worked well. These things only fly fast, and when the wind's good they're heavily ballasted too. If you could have a crow setup it would be a great help.
You'd need to incorporate a ballast tube too.
What about a multipanel wing like the Bat, that doesn't have a fuse, but has a protruding center section? I'd be really keen! Very prang proof and very fast.
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Post by sean on Sept 4, 2008 22:41:41 GMT 10
Hi Jeff,
I'd be happy to make the wing templates as well, would just need a few pointers on how you like them.
I was thinking of a design with Erwin-style tape-on wings as well. It would have to be either that or nylon bolts IMO, I think tape would work better.
There aren't too many fast model plank foils to choose from really. The PW51 would be the pick, apparently there's nothng as fast these days. The only other genuine alternative IMO for a DS plank would be the PW98, though it's so close in shape to the PW51 a small build error would mean you could end up with either (or neither)...
The JW60 aerofoil was specifically designed for EPP - it's thick, has a very chunky LE section for crash resistance and a thin TE area to enable the use of thin balsa elevons. So while the JW aerofoil works well on an EPP wing I don't think it would be as good a choice for bagging, the PW is a more efficient design.
To my knowledge pretty much all of the other plank aerofoils around were either designed to make a strong EPP wing or were designed 10 or more years ago and are outperformed by the PW51 at speed. The other nice thing about the PW51 is it doesn't seem as CG sensitive as some others.
As far as planform goes for efficient DSing you want a highish aspect ratio. A high AR would make for a faster plane but if you made it too high the wing could get too touchy in pitch and overly sensitive to CG changes. If the AR is too low you sacrifice turn performance which is vital in DSing. For a 60" an AR of around 8 or 9 would work well I reckon. You could try different ARs by cutting various cores and varying the span on each one.
Next thing to decide is taper ratio. Too high (small tip chord) and it'll have a tendency to tip-stall, too low (large tip chord) and it'll be less efficient.
Control surface chord should be narrow to reduce the possibility of flutter, but still wide enough for good control.
Once those things have been decided you have yourself a wing! With no tail volume/decalage etc to worry about I think it would be hard to build a bad one. The vital thing to get right is the aerofoil shape and the CG location, if you stuff up either of those two things then the pitch stability could be unpredictable.
Flaps could be used but they won't work nearly as well as they do on a conventional plane, and increase complexity which spoils the inherent simplicity of the plank a tad, IMO.
Looking forward to discussing ideas further!
Sean.
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Post by jirvin4505 on Sept 4, 2008 23:02:37 GMT 10
sean yes pw51 is the go - not out to reinvent the wheel. Thinking to have a model that is usefull for a variety of sites. 60" single taper moth inspired planform seems a place to start. Goal clarification.... Not ready to design the ultimate but want to build a fast slopey to highlight the vac bag process as a simple alternate to the epp models I see being built. A chance for the builders on the forum to develop there composite skills. I see the work in the planks being built and keep thinking it's got to be easier - especially if it's easy enough to be disposable. @andrew - no multi panel wings as this means extra cutting. Plus the nose is vulnerable - would rather have a sacrificial fibreglass pod out the front. >ballast.. easy to build into 2 piece wings (complicates wing build). My initial thoughts are carry it in the fuz - easier to lay up a new fuz if things get messy. jeff
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Post by sean on Sept 4, 2008 23:52:11 GMT 10
Hey Jeff, if versatile is what you're after a smaller span than 60" might be worth considering - a smaller wing gives you the necessary wing loading for fast flight while keeping the weight down, improving survivability in a crash.
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Post by jirvin4505 on Sept 5, 2008 0:20:58 GMT 10
sean Just did another big troll though rcgroups and some of the German forum - certainly some serious stuff out there to do with planks. >versatile is what you're after a smaller span than 60" might be worth considering ..yes I am thinking that way to get a simple thing happening. Still impressed with the ferrett (frettchen) what would be an appropriate Oz name? Starting to look like an osprey type of model - but i wanted this to be open source as a home build. I just finished downloading some of the ferrett DS videos - does it go a light weight!!!! Time to ponder - looking at the frettchen what do think its dimensions are? Still very much in the impressionable stage and open to ideas. Fixed on single taper wing, vac bagged- fibreglass pod/body I should throw it open - what model would be inspirational enough to prove worthy of a composite build and motivate the eppers to learn some bagging skills. As I said I am impressionable at this stage. I tend to follow thru when i have others interested and participating. sean - what model would you want to do? I see some commercial versions of this idea - zipper comes to mind. cheers jeff
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Post by shane on Sept 5, 2008 0:30:30 GMT 10
Hi guys still looking to buy some hi-load foam myself. it would be good on this project too,it would help de-lamination of top and bottom skins in a big crash or hard landings in ?? locations. Looking at ordering next week, need to start my DLG soon.
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Post by sean on Sept 5, 2008 1:16:01 GMT 10
Jeff, my preference would be for an original design... the EPP planks out there have all been designed with EPP in mind, with a bagged wing we have much more freedom to create a more efficient wing.
Also I think any plank needs a long tail to fly well, the ones that have the fin over the wing or immediately behind it all wallow around in yaw, especially if they have a long heavy wing. That's acceptable in smooth air but unfortunately we're not blessed with smooth DS hills... the hardest thing about DSing for us is getting the plane to track through the turbulent conditions, if you can't hold a consistent line it's not much fun and your speeds aren't high. My modified long-tail Reaper was one of the easiest to DS planes I have ever flown, more stable than my Carbon Bird.
For DS planes there is a sweet spot for wing-loading. Too light and they become too hard to fly smoothly and don't retain energy. Too heavy and they can only fly comfortably in strong wind, which we don't see a lot of here either. For DS 800g is an absolute minimum IMO. If the plane doesn't have good energy retention then it's too easy to find yourself stuck on the back of the hill with not enough speed to get back to the frontside.
My favourite DS plank design is the Reaper - PW51, stiff high aspect ratio wing and the earlier version had a longish tail moment. With composite construction you could improve the design further. I like the broad root chord and higher taper ratio of the JW but otherwise it's not an ideal design for composite construction - it was clearly designed with EPP in mind (everything is ultra-chunky). I'm enjoying my new Moth but it's a much fussier plane to setup, CG is critical and it seems to wander in pitch a bit compared to my old reaper. It's definitely a harder plane to DS.
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Post by jirvin4505 on Sept 5, 2008 8:13:50 GMT 10
sean.. goood points Yes i agree this is an oppurtunity to optimise for bagged wing construction - lets take that advantage. Happy to have a reaper inspired design I like the underslung pod that doesn't trap the wing. Would probably need plastic bolts to hold. Shane had already carved a reaper style plug but he went and put it on the model before molding it Will talk on the phone cheers jeff
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Post by ezza on Sept 5, 2008 8:43:37 GMT 10
Hey guys, This is a very interesting topic. I think it is excellent for all to combine their knowledge like this. Jeff, did you read the thread in RCG 'Razor' or 'Razor Mk 2'. These are planks made down in Newcastle. I also remember PJM(rg tag), did a 2m plank with PW98 airfoil. This one also had a split tail airbrake. Might be a little complicated just yet. You really want something robust. Another interesting plank was the experimental J8 by NCFM. It was a plank but had a fixed horizontal stab on the tail that worked as an elevator. It was strange that it went 190+mph on maiden yet the project was never taken further? I believe it was a composite wing with EPP fuse. Do think the horizontal or even a t-tail would cause drag during high speed turns? I like the pod idea for the fuse. Maybe you could have tabs to tape on the wings similar to the Erwin? I don't know enough about bagging, maybe this is too difficult. Probably the easiest way to add ballast as well, to have a generous sized space in the fuse for ballast. Totally agree with Seans' last post. Some great info/ideas in there. The longer tail is a definate positive with a high speed plank. It can make a huge difference, just needs to be stout. I don't know if it was the tail or the shorter wingspan but my 50" inch reaper handled better than my old 60". I''ll have to build my other Reaper to the same specs to know this for sure. Eric
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Post by sean on Sept 5, 2008 11:00:12 GMT 10
An underslung pod would be good. Nylon bolt attachment would be nice and easy to build. It's good to have a design where the wing can slide forward in a nose-in crash.
Tape-on wings would be the best solution I reckon, but I'm guessing that would require more fiddly molding work? The nice thing about tape is it's cheaper and easier to get hold of than nylon bolts (if you keep breaking the bolts that is). With a fast landing speed and somewhat dodgey DS sites it's quite likely you'd go through a lot of nylon bolts.
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Post by thevon on Sept 5, 2008 15:11:43 GMT 10
This is exciting. Molded wings are slicker and bagged foam is obviously very tough. We can make it very strong, not worrying about weight in the case of a DSer. My humble experience (from the Reaper) is that it's the front and back of the fuse that break up, not so much the wing. My wing's still serviceable after many fuse rebuilds. I A bit of brain crunching at this stage may lead to something that goes to a new level ... particularly in terms of planned fail points, for crash survivability. This also reminds me of a thought I had for a Reaper fuz, but haven't done. Sean can attest to the strength and simplicity of tape retention systems eg on the Erwin. Since looking at Jeff's composite work, I see a whole new world of possibilities! What about using a molded fuz too, but with up to 3 tape retainers. Yes I understand that it would be much harder to build the first one, compared to a simple EPP fuse. But once we had the mold we could knock them out repeatedly and hopefully, they'd last well too. So I'll throw these suggestions in, stand back and wait for the reaction! 1) How about mold a strong fuse with a 8mm flange running around the wing cutout area. Wing slides thru fuse, and run some clear tape half over the flange and half over the wing?? I suspect it would be a very strong join, and if you got the amount of tape "just right" it would give in a big hit. See the attached sketch: I've used red to indicate tape. Looks messy but the real deal would be clear tape. 2) Plug-in nose join, only inserts about 3mm and taped around the join. 3) Plug-in tail join, similarly. Waddya reckon??
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