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RM Trainer

1980s design electrified

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Nigel R20/02/2018 13:38:37
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1211 forum posts
275 photos

Last night saw (almost) everything installed, and only a few details remain to be sorted out before the test flight:

Mounting the RX (should be velcro'd to the servo tray)

Lipo front/rear restraint (some lumps of soft balsa to glue in)

Epoxying in the wing dowel.

Adding some silicon to the wing saddle.

CG - its come out nose heavy, about half inch in front of the 30% mark. I have some scope to move the servos back in the fuselage by a couple of inches, but I'm not sure I will bother, as (a) I don't think it will need a lot of weight in the tail to correct the CG, and (b) it's far too much effort now everything is in. For the test flight I'll probably use some kind of malleable mass bundle retained with an advanced adhesive temporary attachment mechanism (bag of nuts & bolts gaffer taped around the tail). I can sink the weight into the rear of the fuse properly later on.

AUW including lipo is 1.25kg almost exactly, or 2lb 12oz in old money - plus whatever ballast is required in the tail (1 or 2 oz I guess). Quite happy with that - I was looking for about 3lb. Wing loading comes out at a svelte 13oz/sq ft.

john stones 120/02/2018 14:48:27
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9347 forum posts
1428 photos

Great job Nigel, enjoy the maiden. yes

Nigel R21/02/2018 08:33:51
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1211 forum posts
275 photos

Thanks John smiley

RX in, Lipo secured, wing dowel in, movements checked, TX setup, CG checked, all that's left is to make an offering to the gods of flight and get her aloft. If the weather hot holds I will have a go today.laugh

Nigel R21/02/2018 13:46:45
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1211 forum posts
275 photos

yesyesyes

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Nigel R21/02/2018 14:06:06
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1211 forum posts
275 photos

Maiden done smiley

All smiles! She flies great. One click of trim on all three controls. Super slow as the wing loading would indicate but moves quick enough under power - I'd say the power level is just right for the model. Enough grunt to pull her up for a decent vertical before a stall turn. I spent most of the four flights goofing around with low and slow circuits and approaches and touch and goes just skimming the grass on the strip. The landing speed is comically low, with a bunch of up elevator held in it is just childs play to dial in the sink rate using throttle for spot landings at your feet.
 
With the CG as it is today, I can't get a meaningful stall out of her and no chance of a spin. Way, way more docile than I expected - I will need to move the CG back a bit more to get snaps and spins.
 
The power train cooling is all good, all three of motor, ESC and batt are cool to touch. I had 3 x 9 minute flights coming down at 25-30% each time, that included a few loops/stall turns/cuban eights/etc as well as some low level stooging.
 
Basically, I'm made up with that - she's a keeper.
 
Snag list:
 
The ESC seemed to lose sync with the motor when snapping the throttle open. Not a dealbreaker but does suggest I might need to dig into the timing settings.
 
I noticed last night that despite measuring about a gazillion times, the tailplane is low on one side by a couple of mm. I might fix this (a knife slit or two just about tailplane, squeeze and reglue, a film patch)... or I might not mess around with it.
 
The film covering hasn't quite stuck at the wing root (on the bandage area) - just needs going over again I think.
 
Balance point needs moving back another 1/2".
 
The wheels are ridiculously noisy and vibrate horribly when rolling.
Simon P21/02/2018 14:17:05
72 forum posts
4 photos

Nice to see this one done! It's the first I can recall seeing with nose gear - others were all tail draggers. I would love to see a video sometime if that is reasonably possible smiley

Nigel R21/02/2018 14:44:05
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1211 forum posts
275 photos

Thanks Simon - I'll see if I can get a Go Pro strapped to my head next time I fly (I'm usually by myself).

She'll need some decorating before any more camera exposure though!

Mike Etheridge 121/02/2018 19:34:53
1409 forum posts
388 photos

Well done Nigel your flight description sounds familiar and your flying field looks very attractive with plenty of open space.

I look forward to your next report and perhaps I should dig my RMT out of the loft once the weather warms up ?

Nigel R21/02/2018 22:28:51
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1211 forum posts
275 photos

Thanks Mike smiley

Yes our site is lovely. Edge of the Cotswolds, makes for a lovely backdrop. You can see a few of the sheep we share the field with in one of those pictures. Occasionally you have to buzz the strip to clear them off before landing!

The strip itself is a perfect match for stuff like this that can come in slow at a steep angle but can become remarkably small with a streamlined heavier model!

For certain, I'll post a few more times on the thread when I have the snag list worked out and some decoration done.

Nigel R23/02/2018 22:56:52
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1211 forum posts
275 photos

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Nigel R23/02/2018 23:01:03
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1211 forum posts
275 photos

Classic sort of colour scheme seems appropriate smiley

Cabin and fuselage trim yet to come.

Having the wings fully sheeted sure helps when adding the trim. Gives something reasonably solid to press on when cutting back the ends of the bits with a razor blade.

Percy Verance24/02/2018 08:01:25
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6478 forum posts
110 photos

Nigel, I'm not sure what type of bandage you used or what you applied it with, but a coat of PVA wood glue would ensure the covering film adhered well enough. Indeed, when joining a wing I used normal medical gauze type bandage - sometimes two layers - applied with aliphatic glue. Dries rock hard and covering film sticks superbly to it......

Congratulations on a successful maiden flight by the way..........

Edited By Percy Verance on 24/02/2018 08:03:55

Jonathan M24/02/2018 10:02:00
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470 forum posts
258 photos

That looks SO happy Nigel!

Nigel R24/02/2018 14:22:11
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1211 forum posts
275 photos
Thanks Jonathan!

Percy it's glass tissue stuck with PVA. I've only got my own laziness to blame as I didn't use any filler or sand it. It's fine if the film is properly stuck to the layer underneath which is where I've had the oops.
Nigel R24/02/2018 14:24:06
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1211 forum posts
275 photos
Oh and thanks Percy! It's always nice when they go that smoothly
David Mellor24/02/2018 14:41:07
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670 forum posts
230 photos

Very nice indeed, Nigel. Well done mate.

Dave

Nigel R24/02/2018 23:27:25
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1211 forum posts
275 photos

Thanks David smiley

Got a couple of hours in doing the remaining trim.

Pinstripe and cabin...

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And lazy man's chequerboard...

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Cleared a couple of items from the snag list, wheels are greased and quieter, rx aerial has a tube to sit in, and the ailerons have a bit more movement.

john stones 124/02/2018 23:47:58
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9347 forum posts
1428 photos

Excellent, looks like an ARTF. smiley

Nigel R26/02/2018 12:57:18
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1211 forum posts
275 photos
Thanks!
 
I was hoping to get another flight report posted, with there being a moderate breeze today I wanted to see how it handled that. However, I realised whilst attempting to assemble the model at the field that I had left a crucial piece of kit (wing bolts) at home...
 
Anyway.
 
I think its worth a kind of 'wrapping up' post, as the project is pretty much done now. Thanks to everyone who has followed along and contributed
 
A few stats on the project in case anyone is interested.
 
Costs: £150 all told. The woodwork in the airframe was only about £40 of that - the rest being somewhat equally spread between drivetrain, covering, radio and hardware. I didn't reuse very much of anything on this build - all I had upfront was a handful of servos and a few horns and clevises.
 
Shop time: ~90hrs logged. Wing and fuse took around 30hrs each, tail & a few misc bits totalled 10hrs, and around 20hrs between rigging and covering.
 
Depending on your views, that's either tremendously good value for the hobby money at about £1.50 per hour, or a massive waste of time (in the face of ARTFs)!
 
Airframe stats:
 
In numbers - 41" long, 52" span & 9.5" chord; tail area 22% of wing.
 
I used a NACA 2412 section. It comes in almost any airfoil plotting software, is flat from 40% back, and thus builds easy - but is better behaved than Clark Y or the "round the shoe" airfoil shown on the plan (less ballooning). Incidence was set with LE about 1/8 above TE, and that trimmed out with no elevator needed for cruise at mid throttle.
 
Total weight, just under 3lbs including lipo. Wing loading 13.5oz/sq ft, more crucially, wing cube loading, 7.2oz/cu ft. Power between 300 and 350 W depending on state of charge in lipo.
 
Things to remember for the future... Measure at least three times on really important stuff like wing & tailplane alignment, arrange for servo location to be moved around late in the build to help with balance, and, importantly, don't build it with 3 degrees upthrust when it is supposed to have 3 degrees downthrust (one of my least clever moments!)
Mike Etheridge 126/02/2018 13:48:44
1409 forum posts
388 photos

A really impressive conclusion plus a great colour scheme, well done again!

So what's next , it seems there is plenty of poor weather ahead of us so there is lots of building time if you are not like me dreading working in the garage after clearing the drive way of snow with more flakes falling!

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