Bowman Spatman

[Alan Gorham_]

Yes I have seen and read lots too, I'm just after some real world advice before I start! Do you have to alter weights and settings for different lengths of core.

[Ron Gray]

Well my (limited) experience is no, the weight stays the same as it is a 'balancing' act between the pressure applied to the cutting wire and the temperature that is being generated from the wire. Different foams may mean an adjustment is necessary and that is why I can add or reduce weights accordingly. I'll get the photos for you later on this evening.

[Alan Gorham_]

Thank you Ron, that is very interesting. look forward to the photos too!

[Ron Gray]

OK, so here are some photos of my setup which copies things used by others that I found on YouTube. I made most of it from bits of scrap I had laying around, the only things I bought in were the main pulleys and the cutting wire (Nichrome 28 gauge).

The bow frame using a tourniquet for tensioning the wire. I started by using some elastic luggage straps but they didn't give it enough tension and the wire bowed when cutting.

When cutting the frame rests on the board so I made (3D printed) a couple of wheels so that it could move smoothly. I plan to surface the board to make it smoother.

On the end of the board are 2 plates on which are mounted the pulleys to route the pull cord down to the pivot weight bar.

I attached some swivel links to teh ends of teh pull cord so that they can be easily detached when I want to do 'free hand' cuts.

The next shot shows it rigged up with the frame fairly well back on the board. I need to make a hold back to retain the frame, a battery serves this purpose at the moment.

This is the pull cord weight which is adjustable. I can also separate the 2 pull cords to position them apart in order to carry out taper cuts.

the pull cord quick release attachments.

The bow frame running wheels.

When cutting an airfoil I put some lead weights on the bow frame arms to ensure that the hot wire follows the profile end plates.

My DC power supply.

I've tried different foams. The first I tried were odd bits of packaging, the white polystyrene type. This cut really well on low power settings and gave a nice clean cut. Off cuts from model 'plane kits (the leftovers from veneered foam wing!) cut really well as you would expect and again required low power settings and also less weight on the pull cord weight bar. Next up was some Kingspan insulation board I ordered from Wickes, oh dear what a mistake it will not cut and made a horrible smell! Lastly the grey foam board that I eventually cut the wing cores from, this was supplied by Bluefoam.co.uk and is a very dense foam which cuts really well but I had to up the voltage to 18v and I needed double the weight on the weight bar. I'm going to get some white polystyrene boards in to compare the finished article but it will have to go some to beat the grey board.

The interesting thing is that I was going to veneer the foam cores but the grey board is so dense and smooth that I'm going to use laminating film directly onto it. I tried it on a scrap bit of board and it can really take a lot more heat than white foam can and on my test piece I got no crock skin look. I'm going to glue on balsa leading edges although I could probably get away without them as the edges of etc foam are quite firm even before laminating them.

Bottom line is, this is an incredibly cheap form of construction which I think will be very strong.

 

Edited By Ron Gray on 25/11/2020 20:08:39

[Ron Gray]

I forgot to take some photos of another bit of the hot wire cutting kit and that is a jig to ensure nice square and plumb cuts. I'll do that tomorrow.

[Piers Bowlan]

Thank you for all the info Ron, very clear and saves me having to trawl the internet for info! Amazing finish you achieved with your hot wire cutter.

How does the weight compare with EPS or the old blue styrofoam? If laminating film is sufficient as a covering it should still end up very light as much of the weight of a foam wing is often the weight of obeche veneer and adhesive. I had trouble getting the laminating film you very kindly sent me to adhere to an EPP wing I was recovering. Perhaps the iron was not hot enough or the wing completely dust free? In the end I used 3M Super77 (aerosol) as an adhesive which was very successful and light too. Not too sure if one could use it on the black Xenergy foam as Super77 contains acetone.

[Ron Gray]

I would say that the weight of the grey stuff is about the same as the old blue styrofoam. so slightly heavier than EPS. The advantages, in particular the strength, IMO outweigh the weight penalty. I've got to go out to the workshop to take a photo of the cutting jig so I'll weigh the Spatman wings when I'm up there.

Applying laminating film does take a bit of getting used to as you do need more heat than normal covering film and of course that can be a problem when applying it to foam. There is, with some foams, a very fine line between sticking and creating crock skin, the HK RadJet I'm currently putting together is a good example of this where I'm having to use a very low (for lam film) heat setting. And again this is where the grey foam is brilliant in that I can use my normal heat setting and this has no effect on the foam.

[Ron Gray]

As promised here is a shot of the jig to make sure I make square cuts (as in previous photos the battery is just being used as a 'stop'

Regarding the weight of the foam, well I've weighed the Spatman wings which haven't yet been joined (epoxy and bandage) but they do have the balsa LE and they come in at 156g for a wing area of 0.2032 m2, so what's that 5.5 oz for a 40" x 8" wing approx 1" thick (Clark- Y section)? 

Edited By Ron Gray on 26/11/2020 09:20:58

[Alan Gorham_]

Really excellent info Ron! Thanks so much for doing that.

Edited By Alan Gorham_ on 26/11/2020 10:09:55

[Ron Gray]

The build has started! After the success of the foam cutting I decided to progress the build so stuck the balsa LE to the foam cores. This time I'm using Gorilla Glue clear which I've not used before, the brown expanding type and the white one being my usual ones.

[Roy Thompson]

That is a top class finish Ron

[Ron Gray]

Had a couple of hours on the build today

LE sanded to profile and wings joined together

Cut out the fuselage sides, ply doublers and tailplane and fin.

Made up the balsa former using my magnetic building board for the first time in ages

Glued the ply doublers to the fuselage sides

[ROBERT BENSON 1]

Good to see all this activity on Spatman - I thought I was the only weirdo who appreciated minimalist models. I still haven't flown my recent build - have a bad attack of sciatica which has floored me.

Good job Ron Gray on the foam wings - once you have a setup like that you can knock out tons of wings.

Jeff2Wings - great job on the colour scheme and quality of graphics - you have a great imagination there.

Regarding wings I am currently exploring the foam core board route. I have build one set Jedelski style and am now evaluating the foam core wrap-around style. I'll post pics when I have made progress. When I think about it I love building wings. Conventional built up wings are very light and I just love how they come together, though it does take a while. Foam and foam core are quick and easy and thus almost disposable.

Executive from Trueline. Very similar to Spatman in terms of wingspan/chord and engine size. Build-wise a little more esthetic than Spatman (I think) hence some sanding to produce radiuses on fuselage. I had posted pics previously. I used to fly this when I lived in the village of Launton just outside Bicester. Spent many hours dislodging it from trees or hunting for it when it went out of site behind the railway embankment. Anybody else build one of these years ago? I'll post the plan on AeroFred and OuterZone.

I also built a Spatman SunDuster. That was when I realized that Spatman was to hairy for me straight off. It ran on a .75cc DC Diesel. Although a lot more delicate in terms of crash resistance I got a huge amount of use out of this model. The wing was repaired dozens of times and only broke beyond repair when I attached it to the Spatman fus and attempted a loop. You know what happened. I hope someone can upload the plan as I have a PAW .06 that would be ideal for it.

On one occasion, during a lunchtime, on a dreary autumn day I decided to have a quick fly over by the railroad tracks. The engine started on first or second flip. I launched and the plane climb slowly and banked to the right. That was the point I realized that I hadn't connected the receiver battery. And so it gently completed a half circle and buried itself in the brambles on the embankment. It started to drizzle a fine rain. I climbed over the fence and waded through the brambles. The model was amazingly undamaged. I legged it back to my take off spot, connected the battery and I was away again. As I gained height I started to lose site as it seemed to be disappearing in low cloud. But that was not the case, it was my glasses steaming up from my frantic bramble excursion - so I took off my glasses and wiped them with my diesel oiled fingers - not a great idea. I'm not sure how but I did get control back and landed safely. (Dad's Army - Stupid boy) Guess we've all had similar incidents.

[Roy Thompson]

My kit of parts is coming together hopefully l can start assembly tomorrow.

Hopefully I won't be to far behind you Ron

[Ron Gray]

Coming together nicely Roy. I've progressed mine bit further today but have spent a bit of time working out the servo locations and fixings together with the tank platform. Trouble is that I'm eating for the engine mount to be delivered as it will be easier to mark and fit it before I glue the bulkhead to the fuse sides and until I do that I can't draw the tail end of the sides together. So I plan to laminate the wings, tailplane and fin then the build may well have to wait for bits to arrive. I've got to check out my 'stock' of old U/C to see if there is something suitable otherwise that may also delay things!

[Piers Bowlan]

My Spatman build so far...

[Piers Bowlan]

I thought I would use some popular light ply for the fuselage sides I had hanging about. I may cut some lightening holes to lighten up the rear end but after a trial run with the 'oily noisemaker' in the front I might do with some weight in the tail! Haven't built anything like this for a looong time as I am a died in the wool gliderist really.

I thought I would mount the engine (OS Max 15FP) sidewinder style to keep some of the goo away from the rest of the model. Only trouble is I had to slim down the fuselage which created all sorts of problems further down the line, not least of which is getting my fingers in it. Note to self;- Keep it simple and stick to the plan in future!

[Piers Bowlan]

I am going for this landing gear arrangement although not this one borrowed from another model. The wire sits in a slot in a piece of ply underneath and the rubber bands provide the shock absorbing - which this model will need!

I am mounting the top of the fuel tank inline with the engine carb. Is this correct?

[Ron Gray]

I did think about sidewinder mode but changed my mind and stuck to the plan, likewise I decided that the engine mount I was going to use would stick up above the firewall so gone back to engine bearers and a play engine mount (I haven’t got any Paxolin!). I’ve tried to keep the tank so that the outlet is in line with the carb but as it’s going to be exhaust gas pressurised I don’t think it will make much difference.

So, for me, this morning has been 2 steps forward, three back as I cut out bits I’d glued in based on the nylon engine mount design. Still, after coffee it’s glueing in the new bearers and cutting the ply mount, the, as I don’t have to wait for the nylon mount I can get on with finishing the fuselage.

[Piers Bowlan]

I did actually change the nose profile slightly Ron to accommodate the engine, yours will be a bit more authentic. I hope to get a bit more done today.

[David Lane 2]

Nice to see the Spatman revival coming along - I have started sanding off the old covering from mine to resurrect it, rather than building anew. I can't remember what I used for a fuel proofer back then, but it's damn tough!

@Piers - it's usual to mount the tank so that its centre line is in line with the carb..

[Piers Bowlan]

Thanks David. The good thing about the rectangular tank former is that I just have to rotate it 180 degrees and the centreline of the tank will line up with the carb. Make the throttle servo position easier too.

[Ron Gray]

More progress despite the slow start today.

Engine bearers installed, front former fitted and fuselage sides joined together

Servo tray and tank / throttle servo platform added

Some black spray applied to engine bay and fuselage sides brought together

Underside ply sheeting was preformed whilst damp then attached. I've added a ply U/C mounting plate to the inside of the ply sheeting.

And I even had time to cover the wing in laminating film.

Edited By Ron Gray on 29/11/2020 22:04:56

[Roy Thompson]

It’s looking nice Ron you’re doing a great job 👍🏻 I especially like the wings.

going to need to pull my finger out.

[Ron Gray]

Control snakes installed and the balsa sheeting added to the fuselage, together with tail skid; I did think about fitting a tailwheel but decided to keep it as per the original (plan that is as mine never had U/C as I only flew from rough fields).

And then some covering. My wife suggested that it would be nice to try and replicate my original one so here goes