Cambrian 55" Spitfire - a build for 2015

[Trevor Rushton]

I have managed to secure conditional planning consent for a 55" Cambrian Spitfire - Condition 1 is that I pay for half of it and condition 2 is that it's my Christmas present - not a bad start!

So, I can now spend the next couple of months planning and deciding exactly what to build. First off - electric or IC.?

I have looked at the impressive build logs on the forum but at the moment I am tending towards using my Saito 52FS. First question is whether there is sufficient space for the Saito to be mounted inverted as opposed to what looks like the offset angle on the Cambrian website?

Secondly, if I converted to electric, would the model be suitable for a sound system or would that be impracticable/too much of a weight penalty? I suspect that I would need a bit more hollow space in the fuselage. Its probably a silly idea

Third, I see that several builders have used E-Flite retracts. Has anyone tried the Turingy ones with Oleos? I'd be interested to know the required leg length. Presumably I'd need the type that go to about 100 deg? How much thickness is there in the wing?

As to covering - I will probably use glass and Poly-C. I suspect that I will go for a variant with Invasion stripes, but I have not really researched anything yet. I will go for some scale detailing - panel lines and rivets - very theraputic although I think that most will be flush.

I'd welcome thoughts and advice on the above.

[Robert Parker]

Hi Trevor,

Well done in gaining planning permission always, difficult to obtain without too many conditions attached.

I built mine a way back in the 1990's. I used the then new OS FS52 four stroke for power, I kept the fixed undercarriage, that said I did buy a set of wing panels from Cambrian and fitted a set of spring air units, the wing is quite thin as per full size, and covered mine in tissue and dope and spray painted.

A word of advice keep the back end light as possible it does turn out a bit heavy with the ply sides.

And don't do as I did on my maiden..... let the speed build up before you pull up or a tip stall will follow, they don't bounce too well as well.

Good luck with the build.

Regards

Robert

[Concorde Speedbird]

Mine has a Saito 62 which is basically the same size as your 56. It is an excellent fit and although you need it fairly open for cooling the engine looks good and from the rear it is not noticeable, and probably from the air too. My build log.

For electric, here is an excellent ongoing build. Good if you want an uninterrupted nose. Sound system would add too much weight for an aeroplane of this size in my opinion, it needs to be around 6lbs to have a reasonable wing loading, 6.5lbs max. Electric with no sound will easily make that, and I think I will with the Saito too, last time I checked I was very happy with the weight. If you want sound then the Saito is the best bet in my opinion.

I am at priming stage. Leg length from pivot is 105mm. There is not much thickness in the wing, thin wheels are needed! Keep light, I am doing invasion stripes (fancy starting a squadron?!) and panel lines.

Have fun with it, it is a nice build!

CS

[Trevor Rushton]

Thanks for the advice Robert; I am thinking of using a built up rudder and elevator as Concord Speedbird has done on his build log. Hopefully that will save a little weight at the tail.

Tissue and dope is a possibility; I have not done that since my old Kielkraft building days; do you think that would be lighter than glass fibre? I am getting good results with Poly C but always open to something new. The only snag with water based resins is the risk of rippling in the surface. This has happened with my Skyways Kestrel build although it's not too bad.

[Trevor Rushton]

CS thanks for your posting; I have been following your log; infact I am sorry to say that you are probably responsible for my hankering!

I last used my Saito in my Wot trainer; it proved to be very reliable in service so I am reassured about the fit; yours looks as though it's gone in well. I think the FS is the more likely route for me, so some experimentation with a bespoke exhaust could be worthwhile.

I'm at the priming and painting stage on my Kestrel at the moment ( this also has foam wings); you just think you have got it right and then you find something else! I hope that I have not added too much weight.

T

[Concorde Speedbird]

I used tissue and Eze dope which I found difficult to use and some creases are there, but that is as much to do with me not being very good at it! It is light though, I am trying to be careful on paint to save weight. Built up rudder and elevators look fantastic!

CS

[Trevor Rushton]

Can you sand the creases out with 1500 grade wet or dry? I have just started using this grade and have found it really good; at least on Poly C or Ezecoat.

Your build looks really good by the way.

T

[Concorde Speedbird]

That is what I have been doing, it improves it significantly. Primer will help. My responsibility for your hankering means mission successful! Thank you very much.

CS

[Trevor Rushton]

A pleasing sized box arrived this week but I am not allowed to open it - outrageous.

Good communications from Cambrian as well; I have not dealt with them before but Steve is very responsive - even out of normal hours.

CS - I have a question on your retracts. From your build I see that you used e-flite ones. Cambrian sell a set that I think (from the model number) come from Perkins distribution; a good price, but I cannot find the dimensional specs to compare with Turingy. If I am right they are a 90 degree set

Do you happen to know what model number your e-flite ones are? I can them compare the dims. Many thanks

[Concorde Speedbird]

Hello Trevor, you should sneak it to the workbench!

EFLG200 are my ones, the 15-25 sized ones. Cambrian first got them in for me, excellent service from them.

CS

[Geoff Gardiner]

Hi Trevor.

Good to hear that you are building this model. I am currently about half way through building one and converting to electric. I will be glassing it and, initially, was going to use Eze-Kote. I am know considering using epoxy as it is tougher and no risk of lifting the veneer on the wing. I have invested in some Z-poxy finishing resin.

I am also using the EFLG200 retracts - same as CS.

I did toy with the idea of a sound system but decided against - will save that for the next build.

Will you be starting the build after your Christmas dinner or wait until boxing day

[Wiltshire Flyer]

I restored a Cambrian fun fighter a while ago, nice strong air frame!

[Trevor Rushton]

Thanks everyone; I will probably order the e-flite retracts. I had another look at the Turingy units but they may be a bit bigger by the look of the dimensions on the specifications. I have fitted some oleos to my Skyways Kestrel and am very pleased with them; presumably the sprung wires can be removed from the e- flite units and I can fit oleos to them?

Geoff, I will be interested to see how you get on with the glassing; I think that you still have to be a bit careful to avoid rippling. I think it's quicker than using the PU products but only if you take care to get the coats very thin and avoid excess resin. I used it on my Chipmunk and found it quite difficult- but that was my first build for many years and as a first attempt the results were not brilliant; it took a lot of wet or dry to get it right, but as you say it's very tough. The rippling occurred on a section of balsa sheeting to the fuselage and was a real pain to get rid off. On my Kestrel, the fuselage was fine, but you can certainly see rippling on the venerred wings.

I am not sure what it would do weight wise, but I once covered a wing with brown paper stuck on with diluted pva and then smoothed out with a covering iron. It took ages, but the result was very satisfactory; a bit like using solarfilm. I think in this case though it's got to be glass or tissue; I wonder if the iron on technique would work with that? Might get rid of the creasing problem that CS found.

Wiltshire Flyer, I am impressed with your Funfighter restoration; it looks very slippery! Is that electric? The colour scheme reminds me of my now departed Calamoto

[Trevor Rushton]

Thanks everyone; I will probably order the e-flite retracts. I had another look at the Turingy units but they may be a bit bigger by the look of the dimensions on the specifications. I have fitted some oleos to my Skyways Kestrel and am very pleased with them; presumably the sprung wires can be removed from the e- flite units and I can fit oleos to them?

Geoff, I will be interested to see how you get on with the glassing; I think that you still have to be a bit careful to avoid rippling. I think it's quicker than using the PU products but only if you take care to get the coats very thin and avoid excess resin. I used it on my Chipmunk and found it quite difficult- but that was my first build for many years and as a first attempt the results were not brilliant; it took a lot of wet or dry to get it right, but as you say it's very tough. The rippling occurred on a section of balsa sheeting to the fuselage and was a real pain to get rid off. On my Kestrel, the fuselage was fine, but you can certainly see rippling on the venerred wings.

I am not sure what it would do weight wise, but I once covered a wing with brown paper stuck on with diluted pva and then smoothed out with a covering iron. It took ages, but the result was very satisfactory; a bit like using solarfilm. I think in this case though it's got to be glass or tissue; I wonder if the iron on technique would work with that? Might get rid of the creasing problem that CS found.

Wiltshire Flyer, I am impressed with your Funfighter restoration; it looks very slippery! Is that electric? The colour scheme reminds me of my now departed Calamoto

[Trevor Rushton]

Possession granted; given the existing build logs on this model I am not intending to publish a build log as such, but to pick up on points of interest.

I have built the wings and fitted the electric retracts supplied by Cambrian. The written instructions suggest reducing the main wheel diameter from 75mm down to 50mm but I was not so keen on that and have settled on 65 mm which seems to be a reasonable compromise. I am going to glass the wings so hopefully that will impart sufficient strength.

Having been following the Chipmunk builds and Danny's instructions on fibreglass techniques I am tempted to try peel ply; my previous attempts with resin were not very successful and I have tended to go the PolyC route of late. However, Following some problems of rippling in the wings of my Mason's Kestrel, I think epoxy is worth another try.

Decided to keep the Saito in my Wot trainer and have taken delivery of a new ASP 4s instead. I quite like the idea of fabricating some kind of bespoke muffler within the cowl, even discharging this via working exhausts like the BT plan; I am not sure if that would be feasible at this scale, but I'd like to experiment with it. I have not researched construction yet, but perhaps a bit of folded and soldered tin plate sheet would be a good starting point? Comments or suggestions very welcome.

[Wiltshire Flyer]

Hi Trevor, I was pleased with it myself! Lol.

No specific power type in mind.

I filled in the cut out from the previous engine and sold it.

[Trevor Rushton]

Working on the fuselage now; all very straightforward save that as shown on the flan the floor of the tank bay is about 25mm too high to permit the centre line of the tank line up with the carb ( I am setting the engine inverted). I have adjusted the position of the deck which means cutting down one former and extending another.

[Trevor Rushton]

After a lot of experimentation I abandoned the idea of trying to exhaust through the actual exhaust stubs. The problem was essentially lack of space and the difficulty of getting a suitable manifold out of the engine. I fabricated a matchbox sized silencer out of tin plate that might have worked but it started to get too heavy. So back to the drawing board and a decision to get the silencer out under the chin of the model rather than the side. To start with I ised some aluminium rod and whilst this was nice and light the 10x.75 mm thread needed was too fine for the metal and the thread stripped when I tried to tighten it up.

Settled on mild steel and tried again ( well 3 times actually) and eventually ended up with something that works. I used brass to make a connection to the engine and silver soldered this to the steel adaptor - see photo. My silver soldering leaves a lot to be desired but I was pleased with my first attempts at blacking by dropping the hot unit into oil.

[Trevor Rushton]

After a lot of experimentation I abandoned the idea of trying to exhaust through the actual exhaust stubs. The problem was essentially lack of space and the difficulty of getting a suitable manifold out of the engine. I fabricated a matchbox sized silencer out of tin plate that might have worked but it started to get too heavy. So back to the drawing board and a decision to get the silencer out under the chin of the model rather than the side. To start with I ised some aluminium rod and whilst this was nice and light the 10x.75 mm thread needed was too fine for the metal and the thread stripped when I tried to tighten it up.

Settled on mild steel and tried again ( well 3 times actually) and eventually ended up with something that works. I used brass to make a connection to the engine and silver soldered this to the steel adaptor - see photo. My silver soldering leaves a lot to be desired but I was pleased with my first attempts at blacking by dropping the hot unit into oil.

[Trevor Rushton]

Oops sorry double post

[Trevor Rushton]

Who is a twit then?

Fitted the engine to get the chin in the right position, fitted the thick balsa sides and bottom and shape d it roughly with a rasp; all went well until I went to take the engine out.......

So I have modified the construction to make the chin part removable. Not sure exactly how it will be fixed yet, but it will make the whole thing much easier to service so it's probably done me a favour.

[Former Member]

[This posting has been removed]

[Trevor Rushton]

Hi Percy

Well sort of but not quite.. the 90 degree knuckle that they supply was not quite long enough. I bought a section of threaded pipe from them but that was not quite right either. I fancied the idea of making something and a bit of lathe work seemed to be a good project. Metalwork was not my thing at school so I wanted to practice and explore the possibilities of my mini-lathe.

Now that I have made it I think that perhaps I have created problems for myself in terms of fitting the modified cowl so I might just end up with it coming out the side after all. However, I will still need to fabricate an extension piece that will join on to the standard "banana' shaped manifold, now that I have found out how to do it it should not take long (famous last words). Now I know what the thread is all manner of possibilities suddenly present themselves!

[Chas Morgan]

How about a few more pictures Trevor

[Trevor Rushton]

Okay Charles, I've not posted many because the model has been covered very well in other bloggs. However, I have made some more progress, made a few more mistakes and learnt some more lessons.

So a few points. First of all here is the fuselage as it stands today. I cut the canopy out (not very well) and found that it no longer fits; I either modify the fuselage to fit or order a second canopy. I took the extravagant route and bought a new canopy. Take more care next time!

I started out to use tissue and dope on the fuselage but was not happy with the result so went back to my tried and tested glass plus water based varnish. This time I applied sanding sealer first to prevent the balsa from swelling. I think that there were about 4 coats of pu in all plus a coat of filler primer, the latter being rubbed back down again virtually to nothing before using the grey primer. Although there are a few small blemishes the net result was good and with a bit of care I think that I can improve the few minor niggles. I am tempted to add some panel lines using the masking tape and spray method. Perhaps a few rivets as well (I suffer from Danny Fenton's problem as well).

I have an irritating niggle with the edge of the wing fairing as the corner sticks up a bit from the wing surface - I may have to take the corner off and build an isopon replacement.

I have fitted the slinky tubes for the rudder and elevator; these exit per the drawing but I am not very happy with the length of control rod inner that is then unsupported. I don't want that to kink under load, so I may modify this. The kit supplied bowden cable looks good but I am nervous of it and may go for wire instead.

The front end has worked out okay following my blunder with the engine. The chin needs to be cut out again (I glassed it all in situ) but that should not present any problems. Its only designed to be removable for engine replacement purposes.

My other niggle area is with the top of the fuselage where I have developed a small groove or depression between the fuselage sides and the top capping. Its very shallow but its proving very difficult to fill. I have tried lightweight filler but trying to get it to stay put in a shallow, convex groove is very difficult. I have just tried some knifing stopper and we will see how that goes.

I decided to go back to glassfibre for the wings and see how I got on with that. PUV is great, but I find that the number of coats of varnish that you need is a bit of a pain. My thought was that 2 coats with the West Systems resin would be quicker - well I am not so sure now. Having watched Danny Fenton's glassing video (Poor Man's Spitty) I decided to give it a try. I was tempted to buy the official plunger dispensers to enable the correct quantities of resin and hardener but was put off by the price. However, help was at hand - the local pound shop had some travel bottles for a pound - they will not last long but they did the job perfectly - 5 squirts of resin to 1 squirt of hardner, all mixed in the bottom of a paper cup (cut the top off a Starbucks cup) to leave a container about 30mm deep - (skinflint!) but a good compromise for the proper stuff. I used a credit card to spread the resin and kept scraping it out until I had a nice matt surface with no glossy bits. That was all good. However, leaving the wing in the garage was the wrong thing to do - too cold! The resin stayed sticky pretty well all day. In the end I brought it indoors (hidden in the spare bedroom!) where it set properly quite quickly thereafter.

Given the time taken for the resin to cure I am not sure that in time terms there is much to choose between resin and varnish. I think varnish is both very easy to use and easy to sand (wet or dry used wet) and if you fill the weave of the cloth you can get a really good finish.