Kyosho Sukhoi Su31

[Andy W]

extracted from this thread (http://www.rcgroups.com/forums/showthread.php?t=235910)..

--
Flew it this evening.. Takeoffs: 1 Landings: 0
:)

I'm actually not to distressed by this. Download this video of the takeoff (http://awilletts.ezonemag.com/su-31.mpg) to see why (sorry for the camera work).. this is at under half throttle. When I applied blips of throttle to get it out on the runway, it scared the daylights out of me. The model was flying faster than I was comfortable with at 2 clicks above idle! Sheesh - and I thought I should perhaps try the 15x10 instead of the 15x8.

My mistake was thinking it would handle the aft CG - I was probably at 115mm, vs. the 105 recommended. I figured - I can handle the Diablotin with a crazy CG, so this couldn't be THAT hard. Plus I had 50% low rates dialed in.
Well, the CG was a BIG issue. The throws on low rates were WILD! Roll rate of >>360 degrees/second! I tried to slow it down and it dropped like a stone. Get the speed up again, try to bring it around high to fly some circuits, but turning under the sun I stalled, got in a spin or spiral (nose down in any case), would not recover. Tried powering up to pull it out, just accelerated the decent. Killed power and watched as it plunged into the ground just over a rise at something like 50-60 mph..
Walking over, Ric asks if I have something to carry back the pieces in. I was expecting a bag of sticks myself. Well, it went down in long grass - probably 3' high. When I found it, I could not believe it - other than the cowling and the cover for the bottom of the wing, the model was intact! My home made ply motor mount was toast - but that probably saved the motor from any damage. The ESC-Motor wires were nicely wrapped, and one has been yanked off the ESC - need to repair that and see if the ESC is working (Hacker 77! Yikes - $300 controller).. Closer inspection back in the pits showed that the inner ply bulkhead that supports the LG block is gone, and the cowl will require more than a little work, but otherwise, the model is in perfect shape! Unbelievable.

If I fly it again, the CG will be forward, and the throws will be about 25%!

..a

[Andy W]

Before..

[Andy W]

After..

[Andy W]

You know, to see a model weighing 100oz go in that fast, yet have as little damage as it does, really shows just how darned overbuilt these things are!!! :D
..a

[fumblethumbs]

Shucks Andy, I've done worse with the trunk lid! One nice thing about gobs of power: at least you know the extra ounce or two of repair epoxy won't hurt the envelope much. Get her back up soon. -thumbs

[Andy W]

Drat.. the controller is good, resoldered the pulled wire, but the shaft on the GB is bent..
..a

[Goleith]

Sorry to hear abt the crash. That thing looked so fast in the video. The damage looks very minimal, you got lucky :D . I hope you have better success next time. You may have seen my posts on the simprop su-31 I just got and its great. I have been following your thread, thinking I might copy it. I am really thinking of converting this plane as well.. Good luck on flight 2. Ill keep my fingers crossed!

[fumblethumbs]

Bend it back Andy, it's worth a shot and nothing to lose really. -thumbs

[Mark Wood]

I've seen brushless SlowStiks pop off the ground slower than that. :eek:
Good to hear of the minimal damage considering the outcome. Whew!

mw

[Andy W]

It's 6mm.. the only way to bend it back would be to crash it again and hope it comes out straight! :D
..a

[chadtyro]

It's 6mm.. the only way to bend it back would be to crash it again and hope it comes out straight! :D
..a

I think you're onto something here:D. Shouldn't have let the cat out of the bag before you got a patent;)! Too bad about the crash. If you rebuild it, it will fly.

Chad

[Andy W]

It took off as shown in the video with just the slightest touch of 'up', and required no trim whatsoever.. I was pleased with that.
I am eager to try it with the CG back where it should be, but still wonder how much room it will need to slow down!
..a

[Mike Parsons]

I am eager to try it with the CG back where it should be, but still wonder how much room it will need to slow down!
..a

Lots! It doesnt like to bleed off speed very quickly

Sorry about your Terra Firma "curb check" Andy.

-Mike

[GregG]

Darn, I hate it when that happens. It looks like a fairly easy fix, I'm glad to see that. Bummer about the bent shaft though. I'm sure that you'll have it going again soon and better than ever! :D

[fumblethumbs]

6mm is pretty portly, but it's less than 1/4", so a brass hammer and a flat steel surface could do it if you can get the shaft free of the GB first. If it were mine, I would chuck it in the lathe with a collet holder, put the dial indicator on it, and tap the high spots 'til true. On second thought, better just order another:). Okay A., what's the avatar now? Is that the weiner wagon? -thumbs

[Andy W]

Cadbury Creme Egg mobile..
..a

[GregG]

I just checked out the video. She sure didn't lack perfomance did she? Hope to see the next video tearing up the sky soon, Andy! :D

[Andy W]

Grr..
Called Aero Model on Wednesday, they said they'd ship that same day UPS ground, so there was a chance I'd get it flying by SEFF. Get an email today, out of shafts! I say, OK, send everything else - a friendly RCGroupie offered to help straighten the shaft - and I may have it flying next week. Then tonite I find another email "how would you like it shipped"??

ARGH!!!! I could have ordered it from my UK source and had it here by Monday!
..a

[Andy W]

Oh yeah.. came here to ask..
What LiPo combination would fly this? If I can sell some of my Aveox F-series motors and controllers, I may go ahead and try a large pack. I'm using 16 FAUP 1950's now, so 24oz of battery that can handle 70+A in short bursts.. I'm thinking 5s? I would look for a deal @ SEFF, but need to know what to look for in advance..
Keep in mind, I'm going to need some weight up front to get the CG right. I may have to put the Rx pack up in the nose, that might help..
..a

[henke]

5s3p TP 6000mAh :) about 655grams, first charge helt 16volts @ 80A (that should go up a couple of volts)

[Andy W]

Well, I tried to buy some LiPo's @ SEFF.. there were 5s3p packs, but no 3s3p and 2s2p packs - I know for a fact I'll never get it to balance without splitting the packs and putting them in the cowl.

I'll have to shop for a deal.. :)
..a

[Mike Parsons]

Well, I tried to buy some LiPo's @ SEFF.. there were 5s3p packs, but no 3s3p and 2s2p packs - I know for a fact I'll never get it to balance without splitting the packs and putting them in the cowl.

I'll have to shop for a deal.. :)
..a
Andy,
Check with Cue. He had a 3S4P and 2S4P for sale at a good price a few days ago. Also sending a PM.

-Mike

[temacc]

Andy,

I have the Kyosho Breitling CAP 232, and run an old Aveox with the 3.7:1 gearbox (motor: 1412/3y) with a 15x10 prop on 8s Tanic 2600's. I had to split the packs 4 - 4 to fit inside the fuselage where they needed to be.

If your prop is turning that fast, what would reducing the number of series cells by one do for the rpm?

Mine weighs 94 ounces; the 15x10 when it is barely turning is a very effective air brake. Landings are a lot slower than I expected; but then, it is as light as one would be with a OS .46 in it, with fuel. Not a Floater, but pretty near.

Terry

[Andy W]

I may end up switching motors, as I have no idea how long it's going to take to get a replacement shaft from the US hacker distributor. :( I have several Aveox motors, I may try the F16, I've seen this size model fly well on this motor..
..a

[Andy W]

Oh, and I'm talking to Cue..

[Andy W]

Looks like I have my LiPo's..
Now to get the replacement shaft. I thought I could use a spare Kontronik or Aveox motor I have sitting around, but I'll just sit on my hands for a while..
..a

[Mike Parsons]

Good to hear Andy.

[Andy W]

I'm working on this one again - took weeks to get the replacement shaft for the GB, but now I have that, a heatsink, and the nice AeroModel aluminum mount, I'm ready to roll.. A couple of hours last night and the bulk of the airframe is repaired. Only have to remount the LG block, after I drop a new forward bulkhead in to hold the wing in place. That is, all except the cowl repair - I've started another thread on this (http://www.rcgroups.com/forums/showthread.php?t=259034). I've got the LiPo's now (http://www.rcgroups.com/forums/showthread.php?t=246997) and I'm making a hatch under the cowled in area (I know the LiPo's are going to have to go this far forward to get it to balance).. Given the power I had, I don't want to drop in prop size much - perhaps a 14x8 instead of the 15x8 I had - so I think I'll go with 4s TP7800. That will make it about the same weight as I had with 16 1950FAUP's, and similar power levels (I should not need anywhere near full throttle at any time!) I plan to get the CG right this time! I am amazed I managed to fly it at all with how far off I was on the maiden.
..a

[temacc]

Andy,

I added 4 inches to the nose of my MAGIC when I switched to Lipo's...flew it yesterday again, got it trimmed out and flying well.

How about 1440 Watts of power? Turns out that I forgot to check the full throttle power/amp draw - instead of 30 amps @35 volts, it was 40 amps. Good thing I did not use full throttle much, as I could have wasted the $258- lipo's. Another question was resolved when I realized the current draw...the airframe was not 'comfortable' with that much power - and neither was I!

Good luck on your next flight :)

Terry

[Andy W]

Thanks..
If the model won't balance with the LiPo's under the cowled in area of the fuse (there's a ton of room there), I'll see if I can mount them up near the motor itself - but I'm not happy having them hanging out where they could be damaged (I can really protect them in the area I have in mind.. lots of foam padding! :D)
..a

[temacc]

Andy,

I don't recall the current you intend to pull from the Lipo's, but I don't recommend foam...I have an intake hood bringing air right over the Lipo's on my MAGIC, with the 3-4x requisite amount of exit area back of the wing TE. Keep'em kewl, Keep'em long.

I believe the Lipo's are more heat-sensitive than the Nicads and NiMh's, aren't they?

Besides, you won't crash again :D

Terry
Terry

[Andy W]

Thanks for the vote of confidence.
I have no air exit at all behind the wing. I've been thinking of lightening this part up. Mike, did you install any type of air exhaust?
..a

[Andy W]

Mike?

On another note, I bought a B50 13S setup from Cue. This will let me stick with the 15x8 prop without pushing the LiPo's too hard. I think the 9S was a tad warm for the voltage I planned to use.
..a

[Mike Parsons]

Sorry Andy...not sure how I missed that last question..

Yes. I cut a rectangle out of the bottom rear of the plane (closer to the tail than the wing). The sheeting is extremely thick back there, but an exacto made small work of it.

-Mike

[Andy W]

This model is sure overbuilt - to survive the mishap I had..
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[Andy W]

I took the liberty of extracting my crash discussion out of this thread for the benefit of those who want to see the damage in this forum!
..a

[Andy W]

Another thread on how I fixed the cowl is here (http://www.rcgroups.com/forums/showthread.php?t=259034)..
..a

[Robert May]

Why did you pull the CofG so far back? Had you done a calculation that showed the recommended one was in the wrong place or were you trying not to add any lead up the front?

I always re calculate the Cof G for any model I fly and balance the model just in front of that by 3-5mm. After flying the model I might move to cells aft or remove balancing weights, but only if the stall characteristics allow.

I rember Ron test flying a Bi-plane for someone who had got a rearward CofG, 3mm of elevator travel still gave him a roller coaster of a ride.

Regards

Robert

[Andy W]

The CG in the manual differed greatly from the supplement, and discussion here had me believe I'd be OK. I fly 3D aerobatic models with the GC back much further than I had on this, but on reflection, they also have MUCH lower wing loading.

..a