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Post by thevon on Dec 17, 2007 16:26:56 GMT 10
Now here it is finished.
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Post by atmosteve on Dec 17, 2007 18:09:14 GMT 10
Looks very nice and clean, I really want to see a modified bat fly next year, hopefully can come down to a meet. It looks like it would be quick.
Andrew the marine goop arrived today, many thanks, i will be going over this thread and many others before i use it though.
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Post by skyzking on Dec 17, 2007 18:14:17 GMT 10
Nice job with the covering Andrew, good on you.
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Post by windsock on Jan 4, 2008 10:00:56 GMT 10
Due to the weather I decided to build my Bat that I have been putting off for sometime. I looked at strengthening the plane only and haven't done the extensive mods that Sean or Andrew have done. Now like any new build I have to wait for the weather.
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Post by skyboyken on Jan 19, 2008 16:44:56 GMT 10
Hi Guys, here's a few shots of my modified Bat build. I'm not a very good builder and this was my first time in 20 years using shrink covering. I made what may have been a fatal error when I got Andrew's instructions wrong and cut off twice as much angle from each side as I should have - resulted in a swept back TE rather than swept forward as is standard. I talked with Andrew and he was able to convince me to keep going - I pretty much had nothing to lose anyway. This shot shows the sweepback - I cut 61mm from each half at the TE (0 at the LE) to get this result. It should have been about half that. Here's a closeup showing the servo holes filled in You can see the routed slots for the rear (main) and forward spars here. I got the spars from Briskites - 3mm carbon rod for the main spar and 3mm glass rod for the front spar. I paired them top and bottom as usual. 2 minutes after the last shot, here's the spar installation completed. I love thick CA!! Here's the wing after 3 coats of thinned Goop to LE's and tips, plus 1 layer of 45 degree bi-di tape top and bottom. In this shot I have just coated the tape with a very very thin Goop layer to help the Oracover stick. And here it is after it's first day flying, including ending my DS virginity ;D . Note that the purple tape is Tesa tape, which worked great with a light ironing from the covering iron. And to finish, here's a shot of the underside: As this Bat has a unique shape I had to use the MAC calculator to figure out where to put the CG. Using 20% MAC as a starting point gave me 161mm back from the LE. In practice this is too far aft. I ended up taping lead to the nose to bring the CG to 155mm aft of the LE at the point and so far that's where it has stayed. Because of the sweepback I had to use far less lead than Andrew. This must be about the lightest Bat out there. I don't have scales but it feels about the same as my combat wing and that's under 600 grams.
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Post by thevon on Jan 20, 2008 7:12:11 GMT 10
Good one Ken. I like your spar method. I'd like to get a router ... would make those spar holes easier. (small router trimmer is the go, apparently).
Always interesting to see what other junk people have on their workbench too ...
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Post by atmosteve on Jan 20, 2008 10:09:20 GMT 10
Thanks for pics Ken, in the back of my mind I like others here no doubt have contemplated slightly backswept wings for a bat, and what it might do for flight characteristics with that aerofoil.
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Post by skyboyken on Jan 20, 2008 20:15:18 GMT 10
Thanks Andrew,
actually I just used a Dremel router attachment. It came in the box with my Dremel, but they are available separately at the male house of pleasure (Bunnings).
I was having a tough time trimming the Bat today in light lift. It seems that it's pretty sensitive in CG but I'll need better conditions to really know.
How do Bats generally go in light air - good, bad or indifferent?
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Post by thevon on Jan 20, 2008 20:25:37 GMT 10
Ken I don't think they suit light air. Like most fast-ish planky things, there's a point below which they just don't seem to work. Trying to keep them up just makes them worse. They need to fly fast. I've flown my Bat (before the rebuild) on mild days at SC, but there was a decent breeze and the lift band there is pretty solid. I wouldn't even try it at Bald Knob on a light day. The conditions we had at that Christmas BBQ day were about as light as mine could fly in.
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Post by sean on Jan 20, 2008 20:56:17 GMT 10
Ken, Andrew's certainly right for a heavy Bat but if your Bat weighs 600g or so I reckon it should go OK in light air. When my Bat was 780g it was pretty good that way, but you couldn't throw it around like a Bee/Duck etc.
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Post by skyboyken on Jan 21, 2008 18:50:47 GMT 10
Thanks Sean and Andrew, NOTE FOR PROSPECTIVE BAT BUILDERS: For now I can't really recommend the swept back Bat. It may yet work out fine and I'll certainly keep this site updated as I get to know the plane. The potential problem is that it appears INCREDIBLY sensitive to CG, to the point where it may not be possible to reliably set it up to fly well. I simply don't know yet, but I will pretty soon . In the meantime I can heartily recommend the slightly swept forward version ala Andrew (thevon). That's what I meant to build in the first place.
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Post by skyboyken on Jan 22, 2008 18:39:33 GMT 10
This is probably my final update on the slightly swept back Bat.
I don't recommend it.
Sean and I flew at the Camel Hump today in 10 - 20 Knot wind which was about 20 degrees off axis to the slope. Sean was using his 48" Skua and I had the Bat. At first I couldn't climb or accelerate at all on the frontside, whereas Sean's plane was going off. So after advice from Sean I started taking lead off the nose. I should note at this point that I had also changed receiver to a Schulze 8 channel and my last flying session had the new Rx protruding from the top of the Bat by about 1.5mm. For today's flying session I had reset it to be flush with the wing and this made a MAJOR difference to the handling, allowing me to remove nose weight.
Anyway each time I took a small amount of lead off the plane went better. I kept at it until it was tip stalling badly whenever it slowed, and then added a bit back. At this point I consider the wing to be trimmed about as well as it's going to get, so here's the result:
It still wouldn't even go close to staying with Sean's plane in either height or speed. Even when we went to the top of Bald Knob and flew frontside in big lift the Bat was only OK provided I didn't let it lose energy. If it did slow down it was very hard to get the speed back and it almost always flicked and spun in. Even with good height it would not recover from the spins. Sean said this is what his Bat was like as well.
I will be keeping the plane as a DS'er to use in moderate to high winds, and I expect it will do OK in this role. It's problem will be getting enough frontside height to drop in and start DS'ing. I won't be flying it frontside generally - it's waaay too touchy and no fun anyway.
So for those of you considering a Bat I suggest you follow Andrew's advice and only take a maximum of 3/4 of the sweep forward out of the wing if you modify it. I do recommend my spar method if you have or can borrow a Dremel router. It was quick and easy, durable through many high speed crashes and reasonably stiff, although not as stiff as Andrew's method it is more durable.
And Go Great!
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Post by thevon on Jan 25, 2008 11:29:58 GMT 10
Guys, just to clarify, don't let Ken's experience put you off getting a Bat. His swept back wing was a mistake and he has persevered with it as an experiment. I hope he gets another one and tries again! The Bat in standard shape is a fantastic high-wind flyer and DS'er. But if you mod it like mine or Sean's, it's unspeakably good in a much broader range of conditions. Probably the best most fun fast aerobatic bombproof DSable thing I've ever flown. It always drew comments and praise.
But when I rebuilt mine I added a lot of reinforcing, lots of Goop and so on, and the extra weight has made it less friendly in marginal conditions. Same thing happened to Sean - adding weight in the rebuild was OK the first couple of times but it seems there's a critical point above which it doesn't go well, and you can't slow it down. Mine is still a fantastic flyer in good lift, or when you can get it DS'ing but I do have to watch that I don't slow it down too much. If I do a loop and it's too slow at the top it will tip stall inverted and roll back to normal!But it's still my first choice flyer for anything above moderate breeze. Then if it goes well I'll put the Reaper up.
Actually I'm keen to get another Bat and build it as before, but using round spars instead of flat ones, as I miss its amazing performance.
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Post by atmosteve on Jan 25, 2008 12:33:26 GMT 10
Thanks for the info Ken and Andrew, it doesnt put me off doing a modified bat in the near future, but an S15 could come first for many practical reasons and local flying conditions, not 100% sure yet on next foamy. Ken there might be a couple of things you could do to your Bat to breath control life back into it, the other guys here will know what i mean, you probly do to. Should be very ressurectable. Sean and Andrew it sounds like your versions of the bat could be a good thing for throwing off Mt Coolum, next time i take the treck up there the bee will be staying at home. In fact if anyone decides to take a 30 minute climb up there it would be great to ride down and join you for a climb and an afternoon of flying.
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Post by thevon on Jan 26, 2008 18:08:42 GMT 10
I have had a bit of an issue with my Bat recently - when I did a loop, unless very very fast it would roll out at the top. A bit scary but it recovered. Sean said it looked like it was tip stalling when inverted and slow. Today at Woody Pt I tried a loop and it did it and without lots of sky to play with, it had a big crash onto the footpath. So I had a good look at its flying behaviour again, banged it left and right and to me it looked like it was yawing inwards (lots of "normal" not adverse yaw). Also it was still pitching up a bit in turns. So I cut back the "up" strokes by 10% and increased the down by 5% and it definitely fixed it. I did a lot of loops after that and no tip stalling. These planky things are very pitch / differential sensitive! And it was much much better behaved after that too, generally, much more like its former self.
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