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Post by sean on Jan 6, 2008 18:21:51 GMT 10
Yesterday I started on my first build for '08 - a Wowings Skua. This is the 48" version as opposed to the 60" Skua S15. My intention is to build this one light so it can be used at a wide range of slopes with bad LZs - I'm aiming for 700g. I also wanted to get it done ASAP so have worked pretty fast on it - two full days of work and it's nearly ready covering - that's fast for me anyway . I'll keep this post short, highlighting the mods I've made over the standard Skua. I was going to make some stiff custom spars but to speed up the build I ended up using the standard spars. Once I had them glued in I found the wing to be quite flexy, especially at the centre so I PUed in a 310mm length of golf shaft that I had lying around - it's the tip of the shaft and doesn't taper much. I know - it'll create stress risers at the ends - but this stiffened up the wing a lot and I think it will be OK. You can also see the slot cut for the custom tail boom. I modded the elevons by making them narrower in chord and longer in length. This should make them more effective but also reduces the weight behind the CG, makes them less likely to flutter and reduces servo torque required, and I believe will reduce drag when the elevon is deflected. I made the longer elevons by splicing the standard TE stock together (see zig-zag pattern where the taper changes). Radio gear - battery pack in two to get weight as far forward as possible and tiny Corona rx mounted vertically, takes up very little space. Jaycar Switch jack used for power and charging. Spackle applied. Shows overall config including custom long tail. It's made using the end of a golf shaft - once again leftover from another build. The shaft is glued securely into the EPP, the shaft will never break but would tear out in a horror smash so I'll have to be a little careful flying . Tall narrow fin mounted far back should make it track like it's on rails. The tial assembly is quite light too, I estimate it'll need about 50g extra in the nose to balance - well worth it for a plane that tracks well.
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Post by ezza on Jan 6, 2008 20:10:30 GMT 10
Boy, you build a nice foamie Sean!! Looks super fast. You are getting quicker at building them as well. I really like the mods, and the overall look. Eric
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Post by ding on Jan 6, 2008 21:17:06 GMT 10
cool I reckon the rear mounted fin will be a big help. The skua looses directional stability if it gets to slow with the stock arrangement IMHO
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Post by thevon on Jan 6, 2008 22:28:19 GMT 10
Sean the way you have the ends of the extra golf club spar butting up very close to the main wing spars will help reduce the stress riser effect. If you can make the end of a shorter spar close to a long stiff spar, there's less potential for 2 sections to move independently. I've done the same with the paired vertical ribbons in the middle of the Reaper which have curved back up to the main spar. Not a wrinkle has appeared next to their ends and they add enormous stiffness.
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Post by ruralringo on Jan 7, 2008 23:21:16 GMT 10
Hi Sean, how close are you to the Maiden Flight?
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Post by sean on Jan 8, 2008 9:43:46 GMT 10
Thanks for that Andrew, looks like a good idea.
Pete, I hope to have it flying by the weekend. It's ready to cover but I'm going to add a few coats of goop to the nose which takes time to dry.
I have a new project to start as soon as this is done - the cores for my 2M DS plank arrived yesterday ;D.
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Post by skyzking on Jan 10, 2008 18:53:29 GMT 10
Thanks for that Andrew, looks like a good idea. Pete, I hope to have it flying by the weekend. It's ready to cover but I'm going to add a few coats of goop to the nose which takes time to dry. I have a new project to start as soon as this is done - the cores for my 2M DS plank arrived yesterday ;D. Sean, what brand is this 2M plank, is it the R72?
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Post by sean on Jan 10, 2008 19:06:07 GMT 10
Hi Abdullah - it's an own design EPP plank, I'll post some build pics when I get started on it. How is your R72 coming along?
Sean.
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Post by skyzking on Jan 10, 2008 20:18:53 GMT 10
Hi Sean, good on you mate. Ive always wanted to design my own DS plane but never had the time to. I might design one as my major project for my degree.
As of the R72, expect to see a thread on RCG Dynamic soaring soon. Possibly next week if my full scale flying permits.
Good luck with you project...
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Post by atmosteve on Jan 11, 2008 9:27:05 GMT 10
Thats a really cool looking glider.
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Post by atmosteve on Jan 11, 2008 9:43:45 GMT 10
In fact it could be my next glider also, along with three other candidates. Sean if you could give us your impressions of its general performance it would be great. steve.
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Post by sean on Jan 11, 2008 9:53:09 GMT 10
Will do Steve. I haven't finished it yet though, might be able to do some more tomorrow.
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Post by sean on Jan 13, 2008 20:17:26 GMT 10
Finished the Skua today and maidened it. Very bad lift at Bald Knob, so didn't get to dial it in, I'll leave it until I fly it in better lift before I report on how it flies. I underestimated the amount of lead needed in the nose to balance so had to strap 70g of lead sheet to the nose prior to maiden. This means there's 170g of lead in the nose for balance... AUW is now 815g, heavier than hoped but still not too bad.
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Post by thevon on Jan 13, 2008 21:41:18 GMT 10
All I can say is I had the Minij (floaty composite) going back and forth across the slope in lightish lift, doing tight turns either end, and Sean's Skua was staying up in the same zone and going a bit quicker too. So it mightn't be dialled in but it looked and flew like a million bucks as far as we were all concerned. Very nice.
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Post by sean on Jan 14, 2008 18:39:57 GMT 10
I was in Maroochydore today so popped over to Pt Cartwright to fly the Skua. It was blowing about 15kt SE, straight up the slope. The slope here doesn't look much but lift is always rock solid and dead smooth in 10kt and above, and you can fly quite high as well. To cut a long story short the Skua flew very well today ;D. I played around a bit more with CG and throws and found I had it pretty much spot on to begin with. At one point while flying with the Cg right back, I flipped it over to check out inverted performance, and was surprised when it started climbing rather than descending! Once the CG was a bit more forward that stopped happening... This plane is very aerobatic, rolls incredibly quickly and bangs a very fast turn. Speed and energy retention are good, handling is very forgiving - never drops a wing unless you have the elev rates too high. As mentioned earlier inverted performance is very good. Landing the Skua was a but tricky today - there's only a small patch of grass on the front of the hill - to land I came in low, lost as much speed as I could in a slight climb and dropped in onto the grass, after which it would slide quite a way before stopping. Despite these fast heavy landings there wasn't even a wrinkle at the end of the day ;D. A few people came up and were very interested in it too. One interesting manoeuvre it can do is a true, perfectly controlled spin! A true spin is where one wing is stalled while the other keeps lifting, causing the plane to autorotate straight down, while airspeed remains low. This usually requires a rudder so was a nice surprise with the Skua. With the Skua it's entered by gradually slowing the plane down, feeding in more and more elev to maintain (or very slightly gain) height. When the plane reaches its stall speed you can see it bobbing back and forth in pitch. At this point, keep the ailerons centred and feed in full up - one wing will drop and the plane will begin to quickly autorotate heading straight down with no aileron input required as long as you keep holding full up. To stop the spin simply release elev back pressure, wait for the spinning to stop and pull out of the dive. I tried this with the Bat a couple of times and it didn't recover, kept spinning to the ground . Also many years ago I deliberately put a powered model into a flat spin but unfortunately was a unable to recover - it kept going all the way to the ground turning it into balsa confetti . Skua minuses? Firstly I'm pretty sure it's not as fast and doesn't hold energy as well as my old Bat when it weighed about the same (800g). For me this isn't really a downside, I built his plane to fly in tight places so being a bit slower makes it a bit easier to land without causing damage. Secondly the rolls are a bit strange - lots of pitch and yaw when you roll quickly - but in my experience this tends to be the norm for planks (except for my Reaper, which rolls beautifully yet quite slowly). Reducing aileron rates tends to make these effects less noticable, and it must be said that a Skua built standard without mods might behave differently. Lastly, it does feel a bit squirrelly in the air especially flying through turbulence, but again this seems to be the norm for planks with a short tail and no fuse - you just need to be very smooth with your inputs. Overall I'm very happy, I've come to really enjoy flying on the coast in smooth air, unfortunately around here this tends to be at sites with a small or non-existant LZ, so this plane should serve me well on those days. I'm looking forward to seeing how it DSes, I hope to use it for testing DS sites as well ;D. Sean.
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