Two Wings and a Round Engine

[David P Williams]

Thanks all for your contributions. It's amazing how many "little jobs" the other half can come up with the get in the way of modelling.

A couple of questions for those of you running the Evolution engine - what is the fuel consumption like? What size tank do you run for what duration? If I use the kit engine mounting method the tank is pretty much built in, so would need to get it right from the start.

Do you run onboard glow? They seem to add a fair bit of weight given the size of battery needed to run 7 plugs.

[David P Williams]

Progress so far -

Tailplane and fin completed, lots of wrestling with warped liteply (surprise, surprise). The liteply parts are die-stamped very cleanly and accurately - I guess this was one of the early kits when the dies were still sharp! The fuselage section is just dry slotted together to check fits.

The normal ply parts are CNC routed, and the various slots for longerons and interlocking formers are a fair by undersize. Fortunately, one of my Christmas presents was a set of Permagrit Spar Slotters, which worked fantastically well and made a pain of a job enlarging the slots into an easy one.

The headscratching and agonising now is around the engine mounting. The kit uses a tubular structure made up of 1/16 ply rolled around a lamination of two 1/8 ply discs at the front and a 1/8 ply ring at the rear, which slides into the first two fuselage formers, allowing you to set the correct fore and aft position of the engine mount depending on your particular engine. Seems strong enough for the suggested Laser 180 at 1.25kg, or 2.75lb, but this engine is 2.85kg or 6.25lb, so maybe I need to engineer something stronger. The manual with the engine prohibits standoffs (the engine is already on three standoffs between the crankcase and the mounting plate).

So - keep the tube setup, remake the front couple of formers of thicker ply without all the fretting out, with a second layer of 1/16 ply laminated inside the tube, or forget the tube setup and remake the front former in 1/4 ply and build a 1/4 ply box on it to carry the engine. The instructions recommend 2 to 3 deg right and downthrust for larger engines, so would need to build that in too.

Keeps me awake at night!

Lastly, an idea of the difference in size between this and my last build (I have built at this size before though). The tailplane is bigger than the wingspan of the TN Provost...

[David P Williams]

After several days of pondering, headscratching and scouring the internet for info and useful pictures I decided to ditch the tube mounting arrangement and spent a happy hour or two with the CAD designing a replacement engine mounting and revised front two formers. A further happy day or two with sheets of ply, bandsaw and scroll saw and a few scrap pieces and design changes and I ended up with something I'm happy with. Also took the opportunity to beef up the undercarriage strut mountings.

Just need to epoxy this lot together, work out a tank mounting platform, fuel proof the inside of it and then crack on with building the fuselage.

I also invested in this from Just Engines for starting and to keep the fires lit at low revs

[Jon H]

Rebuilding the engine mount is a good call. Its not the engine thrust loads that are the problem its gravity that will do all the damage. Imagine a bit of a rough landing and that big old engine will still want to head south even if the wheels/ground is opposed to the idea. The mounts need to take that and your solution looks much better than the ply tube.

[David P Williams]

Thanks Jon - it's getting triangular stock reinforcement inside the box and round the box to firewall joint too. The kit supplies a fibreglass bandage to epoxy round the front of the tube, so that will go round the front of the box too. The box also builds in 2deg right and 2deg down thrust as recommended by Flair for larger/more powerful engines.

Agonising over the tank at the moment - the kit supplied one is 20oz which I'm sure won't be enough. I have a 24oz and a 30oz. Cymaz reckons his Evolution version does 2oz/min at full throttle. Problem is, the tank is inaccessible once built. I considered having some sort of removable front to the engine box, but decided on strength rather than convenience.

[Jon H]

Posted by David P Williams on 05/05/2020 16:20:24:

Problem is, the tank is inaccessible once built.

Not a fan.

Tanks need access for maintenance so i would always give myself an option to get at it. If you box it in a simple plumbing error or a leak means major surgery.

Also clunks fall off, tubing rots out, bung screws loosen over time. You just know that if you box it in you will need access so i would mod it now as its much easier to do while its all in bits

[David P Williams]

Yes I'm not keen either. I might be saved by the spacious American cockpit opening which might give me enough room to manouvre the tank in and out. Otherwise it's all a birds nest of formers and stringers covered with thin ply simulating aluminium panels around the front. Tricky to provide an access panel without compromising the structure. I think I'll have to give up on the idea of full depth cockpits anyway as they are really the only access into the fuselage so I think false floors with servos, glow unit, batteries etc under them will be the way to go. I will replicate the 'baggage' hatch behind the rear cockpit but probably only to hide switches in.

[David P Williams]

Progress - the balsa for fuselage longerons is supplied in 36" or 915mm lengths, but they need to be around 48" or 1200mm long, so lots of scarfe joint splicing required.

The lower half of the fuselage is built upside down on the plan on the main longerons, starting with the engine/undercarriage/cabane/lower wing mounting structure.

followed by the remaining former lower sections and seventeen longerons. Everything fitted perfectly, resulting in this

Next step is to remove from the board, turn over, fit the former top halves and complete the upper longerons.

[Jon H]

i love the framing up stage. Its just a giant 3d puzzle and after a really short time you end up with something that looks like it will be done in hours. It never is, but it always looks that way!

WIth your fuel tank entrapment problem, could you cut a 'letterbox' through the firewall that was big enough to post the tank though, and then bolt the engine on the front to trap it? The bolts for holding the engine on look a good distance apart so you should be able to squeeze a tank between them??

[David P Williams]

Thanks Jon - someone else on my club has a Flair Stearman, and he's been pretty helpful with tank info. He made the front instrument panel removeable along with the cockpit floor and can slide the tank in and out that way, so that's my current plan. Wouldn't work with a Tiger Moth, but this thing's AMERICAN sized.

BTW his hasn't flown. It has a Saito 180 and he reckons it's not enough power to make him want to try to heave it off the ground. He has other engines to choose from so he's fitting either a 360V or an ASP 400 radial converted to petrol.

[Jon H]

Posted by David P Williams on 15/05/2020 17:44:24:

 

BTW his hasn't flown. It has a Saito 180 and he reckons it's not enough power to make him want to try to heave it off the ground. He has other engines to choose from so he's fitting either a 360V or an ASP 400 radial converted to petrol.

tell him to fit the 360v. I have an sc 400 radial and its 6lbs of dead weight. Dont get me wrong, i love the theatre of the thing, but as a power plant the 360v will leave it in the dust. Also, if he has not already spent the cash tell him not to waste money converting it to petrol.

Edited By Jon - Laser Engines on 15/05/2020 19:31:38

[David P Williams]

A lot of headscratching and not much progress. Sorted out a (hopefully) strong enough but lightweight support structure for the fuel tank that should accommodate the largest tank I may need, and smaller ones with padding. I think it will need modifying to site the onboard glow unit without having to lengthen the leads too much.

I didn't like the spindly look of the piano wire tailwheel leg, so I 3D printed some covers. They may not survive any flexing of the leg, but we'll see.

I didn't like the suggestion of an arrangement of soldered on washers and steel plates which would have had to be soldered in situ. With my poor soldering skills I would have either had poor joints or solder running into the tube, or both. So I fired up the lathe and turned up some collets and a combined collet/steering arm.

Not true scale, but looks a bit better than plain wire I think.

I also turned up a domed spinner for the engine.

I've now assembled everything I need to test run the engine, just need to knock up a mount/test stand.

Next I need to sort out servo, battery and receiver location and mounting before I restrict access by adding the top fuselage stringers.

[David P Williams]

Slow progress. No indication of where and how to locate servos in the instructions, just a note that anyone building this will have previous experience so these details are left to the modeller. Well I do have a fair bit of previous experience, but the combination of a cavernous fuselage with no obvious mounting points, a desire to keep the cockpit areas clear for some scale-ish detail, and the feeling that fitting an engine that is twice as heavy as the one recommended in the kit instructions meant a lot of agonising and guesswork.

I thought I would probably need the servos and batteries fairly far rearward (similar builds on other forums have put them in the rear cockpit area) so decided to make the 'baggage' hatch behind the rear cockpit operational. I could have the rudder and elevator servos mounted lowish in that area, possibly batteries above, along with switches hidden away in there too.

So - here's where it's up to -

Servos look a bit lost in there.

Next up are elevators and rudder, hingeing and control run sorting, then a start on the wings and centre section.

Pleasantly impressed with the fit and finish of parts so far.

[David P Williams]

Wow - over 6 months since I last posted on this thread. Various family issues, including my wife having a stroke last September (now 95% recovered), house maintenance, and building my artist wife a new studio in the garden meant that I had very little time in the workshop.

I have managed to finish the tail components and build three of the four wing panels. I just need to finish the fourth and then the centre section, and almost all of the woodwork will be complete.

I should be able to get some uninterrupted workshop time over the next few weeks, so hope to make some significant progress. I'd like to get it ready for painting for when the weather improves and I can set up my outdoor spray booth (cheap Ebay 3m square gazebo).

Some pictures of where I'm at -

Tail slotted together to check fits - nothing glued yet of course. All pretty straightforward.

There was a fair bit more headscratching over the wings. Flair published a set of notes on their website correcting some errors with the early batch of kits (of which this is one), including the fact that the printed plans are undersize by up to 25mm in some places. The notes say to go with the precut parts where you can and where you can't things will be around 1.5% undersize. Well, we don't want that do we? Lots of measuring and scaling from precut parts to the plan indicated that the plans were OK across the width but were indeed a fair way out on the length. I had already recalculated and redrawn the positions of the formers when I built the fuselage, so now I had to do the same for the rib positions and spar lengths etc. All part of the fun.

The leading edges are 1/2 inch balsa dowel with 1/16 balsa wrapped round. With the soft sheet supplied and lots of soaking this worked better than I feared.

The ailerons feature inset hinges made from CNC cut Tufnol or Paxolin, with a 1/64 ply leading edge.

Upper and lower views of mostly complete lower wing panel, still lots of sanding to do.

Finally, the obligatory trial fit of the lower wings.

Yes I was watching the cricket at the same time. I've now got a Sky Q mini box in there so even better

You will also see that the window is open and a fan in front of it as I've finally started to get sensitive to CA fumes.

More progress soon I hope.

[Jon H]

Looks ace. I bet we would all finish our builds in half the time if we stopped putting it together to admire our progress, but its got to be done!

[Gary Manuel]

Oh my goodness. What a thing of beauty that is!

[cymaz]

Two of my favourite things.....radial engines and biplanes. Oh, I need a sit down

[Rich too]

Great build David👍 Sub’d

[David P Williams]

Thanks chaps, great encouragement, really itching to crack on with this now. Finishing the last of SWMBO's "little jobs" this weekend, so in the workshop first thing Monday. I've also found my hoarded stash of Solartex - 10m of Natural and 10m of white. Flair reckon 10m for the wings and 2m for the fuselage if you're careful.

I've used Mick Reeves precut rib tapes on previous models, so I calculated the total length of rib tape needed if I do it all including the fuselage stringers. Gulp. About £120, and quite a bit of weight. Time for a rethink maybe.

[Geoff S]

You could always cheat on rib stitching/tapes by only doing the upper wing surfaces. After that's all that will be seen when the model's on the ground and, in the air when the undersurfaces will be open to view it'll be too far away to be seen. As Peter Miller says - it'll look great at 50 feet.

I must admit, I almost lost the will to live when I was doing stitching and tapes on my Sopwith Pup and chose life I gave up on stitching and just put tape (cut from Solartex) on the top wing. I should be ashamed but I'm not.

Geoff

[Dwain Dibley.]

Same here Geoff on my moth, dabs of PVA covered with strips of Solartex, Ripping the solartex makes a good effect.

D.D.

[David P Williams]

Plenty of time to decide on rib tapes etc. Top surfaces only is definitely an option.

Fourth wing panel is coming along nicely.......

[bert baker]

[bert baker]

[bert baker]