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RM Trainer

1980s design electrified

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Nigel R06/12/2017 09:44:25
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1408 forum posts
309 photos

Thanks Piers, no need to apologise!

I used aliphatic for joining the skins, what I didn't do was to sand them properly flat on the board after joining - hence the slight ridge. I also didn't manage to get the edges quite straight before joining - although I thought I had - and when they had dried several sheets had bowed a little. However they do look OK from a few feet away so will be alright when they're under the covering

I think in future I would overbuy the sheeting and try and pick the sheets that have good uniform thickness and match them up carefully. Not getting the edges straight was just daft, I have a long straight sanding bar so no excuse there. Live and learn.

On the whole I'm pleased with how the wing is turning out. It's come out rigid and warp free, and the weight is right on track for a 3lb end result. Happy days.

john stones 106/12/2017 17:20:23
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9680 forum posts
1435 photos

All looking good Nigel, torque rods are a pain, much more choice for servos now. Nice lyer when you've done though. yes

Nigel R07/12/2017 09:06:22
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1408 forum posts
309 photos

Thanks John, I hope it will be smiley

More torque rod fun last night:

tmp_3274-20171206_22593576471856.jpg

Servo connected up and being tested.

Note two things;

1) I've used holes offset on servo disc (they're about 30 deg away from right angles) - this is to counteract the offset on the torque rods.

2) I also re-drilled the torque rod nylon arms, so that the new hole which the clevis clips into is as close to the threaded bit of the rod as possible.

Without either of these, I had reverse differential (and quite a lot of it) - more down than up. Never a good thing. If this had been a low wing model with the servo on top, that would be reversed, more up than down, and that might be ok. However with this being a high wing and servo underneath, getting more down than up, is never a good thing.

Anyway, with the offset disc and modified rod arms, as they are in the photo, I get even movement up and down. Which will do nicely.

That's pretty much it for the wing. The remaining few jobs can wait until I've rigged the plane. And that will need a fuselage...

Edited By Nigel R on 07/12/2017 09:09:22

Simon P07/12/2017 11:19:38
73 forum posts
4 photos

I am very glad to see one of these being built. You might recognise my name on the outerzone credits. I bought the magazines some time ago and still intend to build one for myself. I was originally inspired by this video of an electric one on Andrew Shering's youtube channel. A few months after I found this video the very same model showed up on eBay for just £60 all electronics included. It was understandably collection only and I decided I'd rather build one myself instead of driving. I have been kicking myself for that decision ever since because I still haven't gotten around to it.

Nigel R07/12/2017 13:15:59
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1408 forum posts
309 photos

I have you to blame for all this then Simon! wink

Many thanks for uploading. I came across the plan about six months ago when I saw the Pronto plan uploaded. I was originally going to build a Pronto (it's almost identical in size and construction) but the RM Trainer looks so much better, for what seems like only a little extra effort.

Nigel R13/12/2017 08:53:12
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1408 forum posts
309 photos

A little more progress.

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...a pair of sides cut out.

Ever the crafty sausage, Boddington designed this so that the sides can each be cut from a single piece of 4" x 36" timber. The side is about 35.5" long in total, and the tapered section at the underside rear is large enough to glue on to the top at the front, and make the cabin/saddle area. I'd say this makes it just about the largest fuselage you can build without doing any complicated joins. Neat.

In the photo, the wing saddle is yet to be cut. The plan, with its flat bottom wing section, doesn't really have any shape here, so I guess this counts as a bit of a deviation. I will use the same structure around here (1/8 treblers inside the ply doubler, etc). I'm going to try using an airfoil template printed from DevWing to trace the profile of my wing onto the side. This will then get about 1/16 clearance all round to allow for the wing joining glass cloth, and some space for a little silicone goop or foam tape (one of which will be added when the model is finished and being rigged).

The plan calls for 1/32" doublers and this is what I have used. They are just traced from the sides, cut out and then glued on with the thickest of cyano. A bit of a hairy operation, as they need lining up very carefully, but when the workshop is 1 degree above freezing, the cure time of cyano seems to go up quite a bit, which gave just about enough working time to get glue over the whole doubler, before lining up and pressing down. After that, a quick trim with sanding block and they're done.

Now, I've used 1/32" doublers on many models I have built in the past and will undoubtedly use them again. They will certainly add a lot of stiffness to the nose area. But... they do feel a bit much for a model of this size. Especially an electric. Seeing as I would be happy to use the same 1/32" ply even right up to a 0.60 sized glow model, it does feel like a complete overkill for a model of 3lb or around 0.20 size. I think next time around I will try 1/16" med balsa, with the grain at an 45 degree angle to form a ply with the sheet side, that should be perfectly sufficient in the future, and come in about half the weight of the ply doubler, and as a bonus be quicker and easier to cut to shape.

 

Edited By Nigel R on 13/12/2017 09:05:31

Mike Etheridge 113/12/2017 15:39:22
1426 forum posts
397 photos

A brick out house to be sure and a trainer that will stand a lot of abuse from a beginner. The first and last time my trainer flew with the new wing at Bartons Point.

001.jpg

Nigel R14/12/2017 09:07:05
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1408 forum posts
309 photos

Mike, I hope it won't end up being quite as heavy as a brick outhouse! I would like to see the model end up around 3lb, which will give a nice light loading and good low speed manners.

Last night saw a little shop time, before the cold got to my toes and I retreated indoors.

First, the wing saddle was cut out. The DevWing printout worked quite nicely, I used a pin to mark out the airfoil outline and then marked a 1/16 clearance around it. Fretsaw and dremel to cut out, then checked against the wing root itself, all looks good. There will be some 1/8 treblers on the saddle, now that I have the outline cut.

tmp_8392-20171213_225621892077475.jpg

 

And second, the firewall was cut out to size. Bit of workshop thrift (or being tight, to phrase it differently) in action here, I used up some rather low grade 5/32" ply, laminated to a scrap piece of 1/32" birch (i.e. 3/16" total). You can just see the difference between the pithy stuff and the nice birch in the photo:

tmp_8392-20171213_225726-1814262847.jpg

Edited By Nigel R on 14/12/2017 09:09:02

Mike Etheridge 114/12/2017 15:41:48
1426 forum posts
397 photos

Nigel,

I think the RM Trainer is typical of some of the 1970's designs and not too different to some of the modern ARTF model planes such as the Irvine Tutor I have. At the same time it is nothing like the lightweight Weston Cougar or Ripmax Extreme Lite or equivalents so it will not stunt as well but is far better suited as a trainer as it would penetrate better and be more crash resistant. It would of course qualify for some of the vintage model flying events although I could be wrong as the models / designs have to have been created prior to 1976 ?

Nigel R15/12/2017 06:52:38
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1408 forum posts
309 photos

No, it is definitely not like the fun fly or 3d types, but they are never intended as trainers. If you wanted a slow, floaty trainer type then there are plenty of lightweight artf foamies around. Personally I think something like this, with a bit of penetration and inertia, has more to teach. A few hours on the simulator can also teach the orientation and basic flight skills / reflexes that a foamie can.

I think this design has the potential to turn out rather heavy if you don't pick the wood carefully. Much like any all sheet design I suppose. Also there is lots of ply shown in the fuselage - I'm not sure I will be using that much, I'm almost up to my limit already with doublers & firewall, the only other ply parts will be the second former (carries the wing peg), UC moutns, and the bits to hold wing bolts. Probably some liteply for lipo tray and servos. The rest will be balsa. I'm not sticking a giant slab of 1/16 under the fuselage!

Nigel R18/12/2017 09:03:01
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1408 forum posts
309 photos

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Nigel R18/12/2017 09:19:23
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1408 forum posts
309 photos

A couple more shop hours and the main formers are all cut.

Left to right

  • F1 (firewall)
  • liteply lipo tray
  • 1/8 birch F2 (and a small reinforcement bit where the wing peg locates)
  • liteply servo tray
  • liteply F3

The front half of the servo tray may well end up also serving as the back half of the lipo tray - the plan is that I can slide the lipo forwards or backwards (through that hole in F2) to get the CG correct.

I will probably cut another couple of holes in the lipo bit of the servo tray to add some more lightness, as I have in the main lipo tray. I've not made the servo cutouts in the servo tray yet.

Next I have a couple more bits to do under the heading of "kitting up" - cut the birch ply gear mount parts and the wing saddle treblers.

 

Dodged a bullet in the workshop last night - the recent cold spell, followed by the warmer damp conditions, added to a new leak in the roof, conspired to produce condensation on the various bits of planes I have stored in the shed for the first time ever - including the uncovered wing I have just finished for this build. I honestly thought I would lose the wing, as some of the sheeting was starting to expand and ripple but LUCKILY bringing it indoors has brought the sheeting back down to size and it now looks perfectly healthy again. More by luck than judgment. The covered models are ok, they can tolerate a bit of damp on the outside of the solarfilm but I'm not loving the idea of any electrics having moisture in them.

I'm going to make some wing bags from bubble wrap, not sure what to do with the fuselages yet, maybe I can knock up a cover with gaffer tape and wrap to keep the sensitive bits covered up.

Obviously a nice dry new shed would be the ideal answer but not very realistic sadly.

Edited By Nigel R on 18/12/2017 09:22:03

Nigel R18/12/2017 23:25:27
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1408 forum posts
309 photos

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Nigel R18/12/2017 23:26:22
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1408 forum posts
309 photos

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Nigel R18/12/2017 23:27:11
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1408 forum posts
309 photos

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Nigel R18/12/2017 23:33:47
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1408 forum posts
309 photos

1st pic, main uc mount plate, 4mm ply rebated into the sides so the 1/16 sheeting will sit flush.

2nd pic, measure once measure twice and still get it wrong. Servo cutout ended up made 1/4 too large. Mistake sort of rectified with a strip of lite ply.

3rd shot, reverse of servo tray. Lite ply doublers under servo screw area. And some balsa infill to tidy up.

Edited By Nigel R on 18/12/2017 23:40:56

Nigel R19/12/2017 09:02:27
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1408 forum posts
309 photos

Meant to add, for the 3rd shot, usually I would just use some scrap 1/8" balsa on the back of a servo tray, but in this instance where I'd messed up the servo opening and had to backfill it with liteply, I went with something a touch stronger.

Next jobs are

* making the vertical support parts for the main gear torque rods

* wing saddle (almost forgot that)

* preparing the firewall, so drilling for motor mount and cooling hole. I'm leaving the nose gear mounting until later, I might need a bit of wiggle room to adjust the model's "sit" on the ground.

 

Edited By Nigel R on 19/12/2017 09:06:05

Nigel R27/12/2017 23:21:57
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1408 forum posts
309 photos

tmp_4824-20171227_230217800200648.jpg

Nigel R27/12/2017 23:27:19
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1408 forum posts
309 photos

Front half of fuse in the jig after a bit of fettling on the formers and trays. Almost ready to glue up.

onetenor28/12/2017 06:13:49
1718 forum posts

A nice alternative model is trainer No5 also an Outerzone plan.

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