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RM Aerobat

Another electrified 1980s design

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Nigel R06/08/2018 10:15:42
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1701 forum posts
348 photos

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Nigel R06/08/2018 10:17:08
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1701 forum posts
348 photos
Summer holidays have slowed the pace of construction a bit!
 
Anyway. I got a couple of hours of shop time in and cleared up a number of small jobs in the last week or so:
 
* attached the front & rear caps to the tailplane.
* made the rudder, cut from sheet 1/4" (yet to be tapered) with some anti-warp strips at top & bottom
* made the elevator blank, also cut from sheet 1/4" (and also yet to be tapered). I'm using a spruce joiner at the LE. Rather than try to cut that into two individual elevators, the whole front 1/2" portion was made up separate to the main body of the blank, by scarfing the spruce on to two 1/2"x1/4" strips of balsa. A while ago I bought one of those small disc sanders from LIDL which made the job of the scarf joint a piece of cake. I could then glue on the large part at the back after. The large central cutout to allow for rudder movement has yet to be made (and I left the spruce only part glued around the centre area to make this easy to clean up).
* put a bevel on the aileron LE
* put a couple more coats of PVA on the glass tissue wing bandage, to fill the weave
* lastly, made a proper start on the fuse, by cutting some sides out (very simple pattern to the lower sides, just two diagonal cuts needed). The top of the side is the datum line, which is nice, as it means later on there is a nice obvious external reference line to measure up the wing and tailplane and motor. I have yet to make the wing saddle - the plan here is to cut this out when the ply doublers have been attached, and the tailplane saddle is not made either, but, as I am sticking the tailplane on the top of the fuse, that will just be a flat cutout parallel to the datum.
 
Nigel R10/08/2018 10:42:33
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1701 forum posts
348 photos

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Nigel R10/08/2018 10:43:05
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1701 forum posts
348 photos

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Piers Bowlan10/08/2018 10:52:17
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1428 forum posts
41 photos

Nice work Nigel, what servos are you using?

Nigel R10/08/2018 10:54:06
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1701 forum posts
348 photos

Last night I got the fuselage doublers cut out and attached to the sides. Decided to go with 1/32 ply in the end, rather than liteply or balsa.

The wing saddle area was marked using the same rib templates as I previously printed using DevWing. I used a pin to transfer onto one doubler, then gave about 1/16 clearance all round to allow space for the wing bandage (and some RTV, much later on, when the thing is covered). The second doubler was simply cut to match the first.

I've allowed 1/4" along the bottom to put some longerons on the sides. The plan shows wider longerons but I don't think any more is needed.

I laid out the lipo and servos, to check whether my single lipo/RX/servo tray would work - doesn't look like I can run a one-piece tray all the way from firewall to wing sadle rear. The lipo tray needs to be quite high (I'm going for a hatch underneath) and the servo tray needs to be somewhat lower. So I'll have to split that in front of the servos.

In the end I didn't bother cutting any holes in the doublers. I didn't think I could get much of a useful amount removed.

I reverted to contact adhesive to do the doublers. Using an old credit card to spread it, it can be got on very very thin. In this weather it is almost instantly dry. As I usually do when using contact adhesive, I drilled and pegged the sides and doublers using toothpicks to make sure everything was in line before pressing down and fixing in place.

Nigel R10/08/2018 10:58:27
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1701 forum posts
348 photos

Thank you Piers

Those are some JR 507s. Mainly I am using them because I have quite a few! It was a toss up between these and a pair of Hitec 225MGs, but I have something else in mind after this build that I want to use them for.

By contrast, the wing has received two HS81s.

Nigel R13/08/2018 04:37:37
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1701 forum posts
348 photos

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Nigel R13/08/2018 04:38:22
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1701 forum posts
348 photos

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Nigel R13/08/2018 04:38:51
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1701 forum posts
348 photos

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Nigel R13/08/2018 04:39:27
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1701 forum posts
348 photos

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Nigel R13/08/2018 04:39:57
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1701 forum posts
348 photos

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Nigel R13/08/2018 04:46:08
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1701 forum posts
348 photos

Formers cut to size if not exact shape and no cooling holes yet.

Lipo tray and radio tray being cut. Lots of holes to make!

Finished tray.

Formers and trays up together

Lipo on tray to check holes are ok for a retaining strap.

All those holes save about 30% of the trays weight. A bit fiddly to cut manually but there we are, done now.

I also doubled up the firewall with some 1/16 ply where the motor attaches and the next former back where the wing dowel passes through it.

Nigel R15/08/2018 09:21:30
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1701 forum posts
348 photos

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Nigel R15/08/2018 09:22:01
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1701 forum posts
348 photos

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Nigel R15/08/2018 09:30:30
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1701 forum posts
348 photos

Got the bevel put on the top part of the front two formers. I'm deviating from the plan a little here - it shows a big chunk of 3/8" used to form the sides and top of the curved deck. I'm intending on using some thinner wood here. So the shape of the top bit of the former is less complex for me, as the bevel is just cut across the corner, rather than being an inset step kind of affair:

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Also got the motor mount nuts in place, which showed I will need to relieve the lipo tray where it butts against the firewall. Always best to discover these things before glueing it together!

Incidentally, the bevel was done with one of those benchtop disc sanders that Lidl sell from time to time. It makes these kind of sanding jobs an absolute piece of cake.

Edited By Nigel R on 15/08/2018 09:39:32

Nigel R20/08/2018 12:46:30
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1701 forum posts
348 photos

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Nigel R20/08/2018 12:46:46
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1701 forum posts
348 photos

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Nigel R20/08/2018 12:47:02
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1701 forum posts
348 photos

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Nigel R20/08/2018 12:56:29
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1701 forum posts
348 photos

Time to get the fuselage together - prev three pics:

First lot of glueing, I did the firewall and second main former.

Then the lipo/servo trays in the wing saddle area.

And then some reinforcement around the formers. Usually this is just whatever scrap comes to hand. I aim for around 1/4" sq on the firewall and get progressively lighter further back in the fuselage.

Next up, joining the tail with a wedge shaped block of about 2" x 1/2" x 1/4", tapered to fit, and adding uprights and cross-members in the rear half of the fuselage. The plan shows full 1/8" sheet formers in three places, but making these "formers" from 3/16" square strips should save some weight. The deck will still need a "proper" former to hold the sheet sides in place.

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