Aeromaster

[Nigel R]

Those spats look smart. Mine will be a little more agricultural in that area, some big wheels for grass field.

I've been installing servos too, although mine are in the conventional location. First job was fitting the bearers, these are 1/2" wide liteply strips, backed with some hard 1/8". They rest on some scrap balsa rails which both located the rails, and provide more gluing area; these were carefully positioned using the most basic of jigs (1/2" wide piece of scrap balsa) to get them parallel to the top of the fuselage side. To get the rails spaced correctly I pre-mounted the servos to them, before dropping them in place and tacking with cyano. Then servos out, and glue the joints properly.

Next up, time to get the control runs in place. I start at the back and work forward. I have a hi tech drill jig to make the exit hole. A piece of sharpened steel tube is the perfect drill:

And inside that hole, some soft thick sheet to support the snake exit:

There, looking good so far:

Then sort the other end. Servos in to get the location right. The elevator snake just passes through the former. I also added some scrap thick, soft sheet, to provide extra support:

I did the same with the guides for the closed loop rudder (snake inners from cheap snakes), and added some intermediate support pieces every few inches:

And presto:

I realise, since doing this lot, that I may not have left enough space between the elevator servo and the end of the snake - should have around 3", I think I have about 2" - I will need to cut the snake back and add some new support blocks - but as everything is in place this will be an easy job.

Next session proper will be on the throttle linkage.

Edited By Nigel R on 06/07/2020 09:16:58

[Trevor]

Just thought I would let you know that, probably due to following these builds, the Aeromaster now heads my shortlist for next Winter's build project. I'll just be lurking for a while but then brace yourselves for a load of 'why did you do it that way?' questions!

Keep up the good work,

Trevor

[Nigel R]

Lurk away!

Just bear in mind I have gone a little off-piste with mine.

[Martin McIntosh]

Looks fine. Not a problem on this model but when I am using my normal closed loop on rudder I raise the servo a bit so that the wires go above the elevator one. Helps in tight spaces.

My cowl has been a problem to align. Thought I had it right but not so and by the time I had sanded bits off the rear end the motor was sticking out more than intended so I cut a disc of 6mm lite ply and glued this to it; also removed quite a lot of material to save a bit of weight up front. Rather than add filler to the imperfections I have tissue covered it. Lots of sanding but it is now perfect. The spats seem fine without doing this.

I intend to paint these parts with matt white Humbrol enamel as a base but am a bit low on it so may use Halfrauds white primer which I already know from experience does not go too well with the water based Ferrari Red but I think that I can get round this. I really need this wind to drop so that I can spray outside.

I have not yet dared to assemble it all again to check on the cg so shall wait until it is completed.

[Nigel R]

Yes the raised servo is a useful dodge finely engineered solution. But as you say, space not at a premium here.

I'd usually go with two rows of servos on something this big, with the closed loop in the rearward "row" and throttle and elevator in front. But your CG comment made me think that all of them at the back of the wing saddle might be better. There's lots of width in this fuse to provide clearance for the output arms.

I'm expecting/preparing to have to mount the battery behind the wing somewhere. Maybe up in the decking, somehow, if I can fix it on a plate for install/removal, or in a box right behind the TE.

[Martin McIntosh]

Cannot remember what you are going to power yours with but my Laser 80 is pretty beefy which is why I put the servos in the rear. Fingers crossed.

[Nigel R]

OS 81, which comes in about 3oz lighter than the Laser I think. I'm not planning on a radial cowl either, just a regular light balsa block job. The OS is still a fair lump for this size airframe.

Last night's short sessions - I moved the end support block and there is now 2-1/2" from servo disc centre to the snake outer - happier with this:

[Martin McIntosh]

One up for grabs in the "Latest For Sale" ads for £75. Looks OK to me.

[Martin McIntosh]

Nearly there now, just the cockpit to sort out and wait for the fuel proofer to harden off since it was only applied yesterday. The cg as expected is a little forward but only about 12-14mm. The cowl needs a little packing at the rear to get it to align with the spinner but that will wait.

Some picks before I try to wreck it. Quite chuffed with the outcome.

[Martin McIntosh]

Almost forgot. Final dry weight is 124oz, 7 3/4lb, 3.5kg. More than I expected as usual.

[martin collins 1]

Very nice, you`ve done a good job there, no wing struts?

[AndyD]

looks fntastic

[Martin McIntosh]

Those wings are so rock solid that struts should be superfluous I hope. It also means that to assemble I shall only need to fit six bolts. The u/c and cabane struts are similarly rigid so I decided not to add any unnecessary weight. Glad that you like it. Can anyone else who has one of the 62.5" version tell me the AUW of theirs please?

[Nigel R]

That looks brilliant Martin. Some very neat results on the cowl and spats.

[Martin McIntosh]

Thanks. I have added 55g of lead to the tail, swapped those lousy 5mm wing bolts for 6mm since one actually snapped when tightened and set up the throws, rates and expo. Trying to figure out how to glue a windshield to the covering film, otherwise it is ready to fly.

[Bob Cotsford]

That sounds a good weight for a 62" bipe Martin. The GP Super Skybolt kits at 58" regularly came in at 9-11lbs depending on the finish and power plant, I've not weighed my WotsWot (50" but the quoted weight is 7lb.

The orange and white looks good together, you've done a very nice job trimming the paintwork and colour matching.

[Martin McIntosh]

Thanks Bob. I doubt if the model could have been built much lighter. The `orange` is actually Ferrari Red. I had some water based paint mixed up a few years ago to match the HK red.

[Nigel R]

The muse has not been with me much this week, and I've been making some slow progress getting the throttle hooked up.

The throttle arm on the engine is - like many four strokes - close to the firewall. I decided I would do one of the standard dodges and use a rocker arm, to give me some breathing space with the linkage. However, I was constrained a bit on this - I couldn't just bolt a bellcrank to the outside of the engine mount (like the commercial offering) as the offset (from rightthrust) on the engine mount places the mount very close to where I believe the inside of the cowling will be. So the rocker needed to be mounted somewhere else. This is what I initially came up with:

The bracket is a steel right angle used for putting cupboards together, I think. It came from a DIY shop years ago. Bellcrank is a normal right angle bellcrank.

It needed a bit of trimming from that point. After trimming the M3 bolt and cutting off the surplus bellcrank arm:

Getting there. Next up, a link, closed:

and open:

And then time to get the throttle cable itself in place. I like bowden cables, although they need a solder job to attach a threaded adaptor they result in a nice solid link and can be routed around things if needs be:

Spot the deliberate mistake... servo is in back-to-front - oops.

At the engine end:

All seems to operate smoothly enough, and, I can install it from above (access will be a bit restricted with the cowling).

It needs a bit more fettling yet - trim the rocker arm bolt down a little, and put a slighty bend in the link arm.

For next time, a better mousetrap would involve a slightly longer bracket, so that the rocker can be in front of the two engine mount screws/bolts, instead of half way between them. This would give a longer link arm.

I did then look at getting the tank in place, but there is a lot of room and it will only need packing in place with foam, so the only job to do there is to make some holes in the firewall for the fuel tubing.

As far as gear install goes, I think that just about concludes the work I need to do before I can get back to the remaining woodwork and think about fuelproofing the tank bay and closing up the fuselage with the underside sheeting and undercarriage mounting plate.

[Nigel R]

7 3/4lb is fair weight for the model I think. If you've gone for both wings at 52" then you have the far side of 900sq in to carry the weight. Even allowing for a 10% reduction (to fudge the issue a bit because it is a biplane), the cubic loading is still under 10.

I guess like any bipe there's a bit of weight penalty to cabanes and all that sort of stuff.

[Martin McIntosh]

I have found easier ways although the first option has not been used much.

[Bob Cotsford]

Having tried both variants over the year I settled on the big 'ole in the bulkhead (second) method, though with four stroke throttles every installation ends up with it's own issues. I often ended up with a wire pushrod with a big bend to allow it to avoid the tank. The bend never caused any problems as there's no load on a throttle pushrod.

I don't think I've seen anyone else use Bowden cable since about 1985, do you have any problem getting it now Nigel or do you just raid the kids' pushbikes?

I remember it getting gunged up and needing regular cleaning, though that was back in the days of castor based fuels.

[Martin McIntosh]

I now just use 16swg piano wire or maybe a 2mm pushrod, neither of which requires any tubing support and does not gunge up. At least the throttle does not require to be perfectly linked. I cannot remember the last time I bought quick links, the small SLEC ball links are all I use now. Flying an old model the other day the throttle nylon quick link pin broke off nearly spoiling my day.

Edited By Martin McIntosh on 13/07/2020 16:48:59

[Nigel R]

No problems getting it! Most model shops stock it.

It's definitely a bit old school but I'm happy using it. The nylon outer avoids any problems with snagging stuff like tanks or formers. It always needs a solder job if some sort - unless you use those screw fixtures - but that's no big deal.

I will convert the links to ball joint though. The nylon snap links are OK for some applications. But there is a sideways component to the movement here. I just don't have any ball joints handy...

[Martin McIntosh]

The SLEC translucent snap on ones are what I use. They need a bit of doctoring before use though. Hold a brass ball in long nosed pliers and get it hot with a heat gun then snap on the nylon link and wiggle it about briefly. They will then pivot freely with no friction or play. I use these on quite large models for everything.

[Nigel R]

Do you mean these ones?

**LINK**

I have a packet in the post to finish off the throttle links with.

On the bench, I polished on with a few noodley little jobs these past few days;

Finished up the fin by adding 1/4 edge LE and TE strips; sanded down the excess sheeting on fuselage decking ready for sorting the elevator and fin fairing block; sanded down the excess wood in front of the firewall, ready for building a cowl, opened up the main mount holes in my throttle rocker arm bracket a touch to allow complete clearance for the screwdriver to get to the front engine mount screw, and, corrected for a drawing error by adding some scrap 1/8 sheet to both tips of the upper wing (I drew out the wing panel just a tiny bit too short in span). Nothing particularly photogenic in that lot, although it all takes up shop time.

And also made a start on building up the elevator and rudder:

This be my hardwood joiner; I don't like wire joiners as they seem to flex rather easily. My joiner is 1/4" x 1/2" spruce. The disc sander makes getting a nice accurate scarf joint a snap:

I will scarf the hard(ish) balsa stock to the 5" length of spruce joiner before butt joining the end result to some lighter 1/4" sheet pieces to form the whole elevator assembly. The spruce is a lovely hard mount point for control horns. It takes less time than you might think with the sander.

I will do a similar assembly on the rudder; a 3/4" wide "leading edge" of balsa, scarfed to a short hard section made from a sandwich of 1/16" ply - 1/8" balsa - 1/16" ply (the balsa is there to receive a hinge).

Onwards... slowly...