Aeromaster

[Martin McIntosh]

I get round the T nut problem by making firewalls from 6mm liteply then facing the front with 1/16" birch.

I did not recognise your formers because the angled one is the firewall, quite different to mine.

[Martin McIntosh]

Tail started and top deck added. This actually went on quite well for a change. I would normally build wings first to get them out of the way but since I wanted to make the fus. simpler I have gone down this route. At least I have most of the ribs cut ready but again I shall be changing the construction a fair bit.

 

Edited By Martin McIntosh on 25/05/2020 18:05:12

[Nigel R]

That is looking good Martin.

[Nigel R]

Small progress this week; a few repairs on the fleet have taken the normal workbench time away from building.

I rough cut my fuselage sides and doublers:

The datum line (the top straight edge of the sides and doublers) is cut as accurately as I can. As is the rear angled cut on the doubler. The other cuts are simply "large enough" to trim down to size. Note small forest of toothpicks holding everything neatly aligned. I also had to join some bits of balsa together to make a wide enough sheet, these things are about 5-1/4" wide around the wing saddle.

Next, I got the doublers stuck in place with contact adhesive. I put it on with a credit card to scrape it out nice and thin. It was measured out using a 10ml syringe which also makes distributing it across the face of the joint easy. Each doubler needed 5ml on each face of the joint. Easily done with the syringe. When scraped out, the adhesive dries in seconds, in the warm weather we are having. Again, lots of toothpicks to keep it all in alignment when pressing the joint closed. I then started cutting the oversize bits down to proper size:

The top of the fuselage side and top of doubler had come out nicely lined up (phew), so the next move was to get both sides together to run the sanding block around and get them as identical as possible:

The remaining job here is to cut the wing saddle out. Then I can start thinking about getting the formers and sides into the jig to glue it all up.

You might note my sides look a bit different to Martin's. I am not doing the stringers on the rear underside - I am making my fuselage a little more like the Bi Fly, with a standard sort of sport type 'box' build, where the underside is sheeted with some cross-grain wood. See here:

Bi Fly plan on outerzone

 

Edited By Nigel R on 01/06/2020 10:18:01

[Martin McIntosh]

I have been building the top wing and since there will be four ailerons I have shortened them to outboard types. I found these a little tricky to make since that part of the wing construction is different to the way I normally do it.

I have not used any of the small fiddley bits of ribs, in fact all of mine are identical. Just got to the stage of butt joining the halves ready to make up and fit the scarfe joints. Very rigid and light so far.

[Nigel R]

Hope your ailerons turn out better than mine did! I made a right fist of that part of the build...

How have you done the 'edge of aileron' area without riblets?

[Martin McIntosh]

I built the basic wing half with spars and shear webs then sheeted the top front and the aileron top. Double ribs spaced 1/16th apart at the aileron root and tip. I then marked the aileron underside with the chamfer ready to face with 1/8th and similarly faced the aileron cut out on the wing. My ribs taper at the TE almost to a point so when the rest of the sheeting was applied I just glued the sheets together here and dispensed with the 1/2" TE piece. Horn and hinge areas were done with bits of 1/4". Too late to show you now but will try to remember to take some pics of the other wing.

[Martin McIntosh]

An update on my bottom wing. I decided to sheet the upper surface only on the tips because 1) any more would just add weight and 2) I got fed up doing it. I have the ply plate installed for the wing bolts and one servo mount. Because there is no dihedral and I have extended the centre sheeting straight across there is no need for bandage.

I have cut away the TE a bit to fit since my method of construction made the chord a little broader.

When this is finished I only need to do it all again!!!

[Nigel R]

Quick work again Martin.

That is going to have a lot of aileron area with four ailerons that size!

I'm curious about the sheeting, doesn't the plan show the main panel D box (and TE) sheeting extending right to the central rib?

[Martin McIntosh]

I built the wing halves first, then added the centre which may explain why my sheeting looks different.

Bottom wing now completed, so just have to do it all again.

[Martin McIntosh]

The way I made up the ailerons using R1 throughout.

basic structure first

removed and upper sheeting added

aileron bevel marked out ready for cutting then facing with 1/8th

a facing part and some 1/4" to do the hinge and horn reinforcement

[Nigel R]

You're certainly pressing on. Complete airframe next week!?

Slower progress here. Limited workshop time has recently gone on sorting out some small issues in the rest of the hangar (slack solarfilm, the odd loose UC clamp, that kind of thing).

Jobs ticked off were, motor on mount:

It has wound up being 5-1/2" from firewall to prop driver.

And I carefully sanded out the wing saddle (dremel and some tidying with paper wrapped around dowel):

it's ever so slightly larger all around, giving a bit of space for glass bandage and a tickle of RTV.

Anyway, enough kitting up, I'm now ready to start getting the fuselage built up in the jig.

[Martin McIntosh]

Got the upper wings joined which has turned out to be a very much more complex job than the lower ones. It will not look too pretty but I have decided that fitting the wing bolts from the top will simplify it a bit. I went a little overboard with the ply but this will be very strong. 1/16th birch on top and 2mm lite underneath with lots of spar bracing. It already feels quite heavy but the rest of the build should compensate for this.

Some infill still needed.

[Nigel R]

Meanwhile, on the slower build...

Finishing off the formers by cutting some holes, was my next job:

Former at wing LE (on the left) has to have the tank poke through that big hole, and has a temporary brace of scrap balsa at the top to keep everything the right shape - this can be knocked out after the top deck formers get added. It also has a piece of 1/32 ply on each face around the area where the wing dowel locates, for which I've drilled a starter hole ready to be opened up later.

The former on the right is liteply which, as seems to be usual with this stuff, was warped like a banana and is not that strong across the grain anyway. After the above pic I added some bracing from scrap balsa to flatten it out and strengthen up the thin cross grain bit. All of which makes me wonder why I didn't just knock the whole former up from scrap balsa, probably would have been easier and a bit more 'efficient' with materials.

The firewall has also warped slightly. I didn't take a picture, it is about 1/8 out on one corner. I will need to be quite careful when gluing it in, to make sure it stays flat. Perhaps the usual triangular bracing can go on the fuselage sides in the right place and then I can clamp the firewall in place.

With that out the way, it was time to dry fit in the jig:

Several things to note;

The firewall is not in place yet.

There are a few sticks of 3/16 under the fuselage holding it flat, but slightly off, the jig base.

The most part of the fuselage will be built flat along the straight edge of the fuselage but the firewall is too tall to allow it to go in without being hung over the edge of the jig. Plan is to get the main wing saddle area in and aligned, the tail pulled in, a few crossbraces put in the tail end, then the firewall will be easy to add to what is at that point a reasonably strong and straight structure.

As for the bits of 3/16, I have made the longerons stick over the top of the fuselage by about 1/8 - this gives and easier joint with the rear deck sheeting.

Can just about see the centre line on both formers, the jig, and the tailpost all lining up here. Fuselage jigs are a great tool.

Onward and upward!

[Martin McIntosh]

Looks nothing like mine. I take it that you are going to add the former tops later, which should achieve a straight structure. I used a jig once on my Mew Gull because there was not a single part at 90 deg. to the fus. bottom, very difficult to align everything.

Why don`t you scrap the warped firewall and try my method of 6mm lite ply faced with 1/16th birch? The 6mm stuff is very flat and warp free as supplied and makes pulling in the T nuts simple. I also added triangular bracing behind it.

At last I have my upper wing ready to fit the tips. I made a booboo with the wiring holes, forgetting that, using R1 pattern only, they would be in the wrong place at the centre. Now fixed.

Not looking forward to sheeting a second set of tips. Cap strips will need adding all round.

[Nigel R]

I'm following (broadly speaking) the Bi Fly structure - which is quite different to the Aeromaster original plan. Yes on mine, I have split the top deck from the formers and it will go on after the basic box section is put together. I find it makes life easy when lining things up at this stage.

The FW does not take much force to hold flat - I'm going to try and use it, if it turns out to be unworkable I'll make another, I have 3mm liteply so two layers would make up the 6mm needed.

[FlyinBrian]

Martin, bit late now but: The swept wing is best built as a single unit as is described in the instructions - if you have a long enough building board that is.

Re the fire wall - 1/4 birch ply works fine and to hold the motor mount to the fire wall Model Fixings sell some inserts that can be fitted from the front of the FW > INSERTS

[Martin McIntosh]

I did not build my wings according to the plan at all, not wanting to cut that mass of odd shaped ribs and bits. After building the halves, with the spars left long, these were scarfe jointed together effectively as one piece at the end of the day. Much stronger and simpler.

I only trust T nuts for the motor mount.

[Martin McIntosh]

Yesterday I got the wing tongue former in place, the ply tongue fitted to the wing and the bolts and T nuts done with the whole lot left overnight for the glue to dry. This means that the nasty top wing fixing has to be attacked next.

This will be done as seen in the pics of progress so far. I have cut two pieces each from 3mm lite ply for the front and back, also one each from 1/32nd birch which has been laminated to one of each and slots cut for the strut ends. Like my cross stitching? One done so far; the other pieces of lite ply will be glued underneath these thus building up the depth to fit the T nuts under.

[Nigel R]

Neat. I presume you'll use four bolts to secure the wing?

[Nigel R]

I've been moving my fuselage along.

I put some uprights in the tail of the fuselage. One right in front of the tailplane, and two more to divide up the area. These are just scrapbox wood, 3/16 square, I think.

And more wood from the scrapbox for a tailplane seat, some thicker, softer stuff:

Next up, some crossmembers right next to the uprights:

I decided to add a former at roughly the middle of the wing saddle area:

it occurred to me immediately after I had tack glued it, that the cabanes would mount near there. Lo and behold, I'd put it right on the area I needed clear for the ply plate I plan to use for the cabanes. So it had to move back a bit.

And then I got the former next to the LE in place, bringing me up to here:

A block will go at the tailpost before removing the fuselage from the jig. Then I will reset the jig with the firewall right up close to the edge of the jig so it is clamped tightly by the jig itself without having to rely on clamps dangling out in free space.

When the firewall has gone on, I plan to move on to getting both wings aligned nicely with the front end of the fuselage - time to dive into some wire work on the cabanes.

Edited By Nigel R on 11/06/2020 08:46:44

[AndyD]

that's a nice jig,i must really get one as it must make life so much easier.

[Nigel R]

Andy, it does - they're one of the most useful shop tools we can make or buy, I think. Makes it dead easy to get a nice upright tailpost and an even taper amongst other things. The one I made was published in RCM years ago, the pdf with all the detail has been posted on outerzone here:

**LINK**

The wood clamps are more rigid than the plastic angles that the SLEC jig contains, I've seen builders using rubber bands or clamps to prevent those from splaying out.

[AndyD]

thx for that,i now know what my next project will be.

[Nigel R]

Re: the wooden squares used for the clamps, it might be worth getting a laser cutter to knock them out, you need 32 squares! I made mine by hand and it was by far the most time consuming bit. Plus, mine, being hand cut, needed a little tuning up to make them properly square.