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Design & Build Sport Twin

Sport Aerobat for 2 x 40s

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Nigel R22/09/2019 06:50:50
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3174 forum posts
487 photos

Some progress. Covering now half way done:

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At this point I discover a 5m roll is not going to be enough! sad

Chris Freeman 325/09/2019 09:18:24
282 forum posts
371 photos

Looking good Nigel, the worst is over. I found the wing a real pain to cover.

Jon - Laser Engines25/09/2019 09:43:55
4899 forum posts
188 photos

for some reason i have not kept up with this thread. The model is looking great and should be a blast to fly. DOnt be worried about loosing an engine, just tune each to max rpm that it is happy with an then forget it. Usually engines to rich in flight but of one starts to sag a bit then when you land just open the needle a click and try it again. Dont worry if the tuning is a bit out on the ground as it will be correct in the air. My old twin ace was like that as the 25fp's were nowhere near eachother on the ground but came on song in the air once up to full temperature.

I would also recommend against the cut and glide. Twins are too heavy for this work well and you still have a perfectly healthy engine to carry you along. Just fly flat out and dont slow down using rudder to correct for yaw. Its not as tricky as is often made out.

I lost an engine on my twin at wings n wheels but was able to do a perfectly acceptable landing even with the cross wind...although to be fair, i was quite smug about it!

Mark Elen03/10/2019 22:37:04
401 forum posts
738 photos

Hi Nigel,

I have been watching your build with great interest. Beautiful neat and precise build. I will be interested to see how you get on with the set up/flying as I have plans for a Grumman Cougar that is getting further up my build list.

Keep up the good work

Cheers

Mark

Nigel R04/10/2019 08:36:57
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3174 forum posts
487 photos

Many thanks gents. Yes, looking forward to getting it airbourne now.

No photos of the last nights progress, but, the covering is proceeding nicely - the fuselage is covered and the only thing left to cover is the nose cone. I had about three feet of hobbyking white film left over from my last build and that has made up the shortfall I discovered upon completion of the wing. All told it has taken nearly twenty hours to get the film on! And of course I still have the trim strips and sunburst or similar to finish it off after that.

I'm starting to wonder if it might have been quicker or easier to do a dope and tissue, or poly-c and glass type finish. Film is pretty good at big flat panels, like regular wings, and simple boxy shapes like a Stik, but with lots of corners and curves and so on, it starts becoming much slower and trickier to get a nice finish.

Edited By Nigel R on 04/10/2019 08:43:38

Nigel R05/10/2019 10:45:59
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3174 forum posts
487 photos

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Nigel R05/10/2019 10:46:59
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3174 forum posts
487 photos

Film done! Starting to get controls glued on now before doing the coloured trim.

Denis Watkins05/10/2019 11:02:56
3937 forum posts
64 photos

" When it looks right, it is right "

That is so going to fly Nigel

Spectacular work

cymaz05/10/2019 14:38:40
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8817 forum posts
1195 photos

That’s a pretty shapelove

Paul Marsh05/10/2019 15:15:44
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3742 forum posts
1070 photos

Looks like the Scorpian Twin I had years ago; there were two versions, think still have the red one in the attic - for 2 x .15 to .25 engines. the last one had 2 25's where the 15s were bit marginal...

Nigel R12/10/2019 21:55:14
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3174 forum posts
487 photos

Thank you gents.

Paul it is quite similar and before starting this project I was fifty fifty on doing my own design or getting a twin scorpion.

Right then. A couple of hours on trim has got me thus far:

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Getting there...

Bob Cotsford13/10/2019 11:02:18
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8067 forum posts
444 photos

That's looking the mutt's nuts now Nigel. Can't help thinking what a nice electric model it would make with battery access through the nose devil

Mark Elen13/10/2019 18:03:59
401 forum posts
738 photos

Hi Nigel,

That looks beautiful mate. Well done. Don’t start thinking about the ‘dark side’ as Bob alludes to 😂😂😂

Cheers

Mark

Nigel R13/10/2019 22:39:01
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3174 forum posts
487 photos

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Nigel R13/10/2019 22:43:57
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3174 forum posts
487 photos

Last segment of the sunburst done. Appreciate the comments gentlemen.

No chance of going to the dark side for this one mark!

Although I could be convinced to re engine it one day with a pair of four strokes...

Nigel R04/11/2019 14:09:54
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3174 forum posts
487 photos

Setup day for the engines.

Found that the starboard is about 400rpm weaker than the port. I'm not sure why, perhaps it is a bit more worn.

Otherwise, a bit of adjusting and they both idle at a notch over 3k rpm. Full throttle on the 10x6 is 11k (port) and 10k6 (starboard). Quite happy with that, I don't think the difference at full chat will be noticeable in terms of flying characteristics.

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Jon - Laser Engines04/11/2019 15:52:31
4899 forum posts
188 photos

Dont worry so much about full throttle rpm. Its all about the mid range where i would aim for +/- 200 if at all possible.

The other thing to remember is that it will all change in flight anyway so just get it in the air and see what happens. If one sounds rich, lean it a smidge for the next flight and go from there. My old Pilot twin ace had 25fp's in it and they were a mile out of whack on the ground. Once in the air and a circuit or two in they came on song and ran together very sweetly.

Nigel R04/11/2019 16:51:22
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3174 forum posts
487 photos

Thanks Jon. I didn't tacho the mid range but it sounded quite close, and pickup was even.

I'm waiting on a noise check before getting airbourne now.

Timo Starkloff04/11/2019 17:01:56
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357 forum posts
794 photos

Good luck Nigel for the first flight!

The nacelles are close to the fuselage, motor size seems not to be oversized, fuselage sufficiently long and rudder big enough. Should fly fine on single engine. And with that big wing you should be able to reduce power on the remaining one if the other fails, and still keep flying. Not too much wind helps in that case. Keeping a good speed for good control response is a suggestion I would give, the slower you are the more difficult it is to conquer a failing motor.

Never had a twin were the rpms mattered. In fact, I never measured them. Take a setting were each motor is running fine. It only gets interesting if one quits completely. Differences don’t matter when the model flies at speed and your rudder is therefore efficient in keeping the course.

Timo

Nigel R04/11/2019 17:19:25
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3174 forum posts
487 photos

Many thanks Timo smiley

I forgot to add a few figures - the final weight minus fuel is 6lb 9oz (3kg) and wing area is just over 700sq in. Loading is 22oz/sq ft. Cubic loading, for those that take notice of it, is 9.6 oz / cu ft.

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