SLEC Chipmunk build blog

[Tim Flyer]

Yes the oil reduction will help I think . That’s interesting re you using epoxy as outer coat . What I found with clear epoxy on my boats is that it can also yellow a bit especially in sunlight.... what we used to do is coat enamel with epoxy then cover that with class Kote to stop sunlight damage . That’s quite a faff having double layers so I’m thinking of just using polyurethane on the cowl and baking it on the radiator. I have bought some “RC colours” enamels. Their white was slow drying but worked well on the cockpit glass. I have also bought their clear spray to cover the stickers . It’s supposed to be very fuel proof . It’s quite dear and in silly small cans . I had problems already getting two of them to work. Their Red was also a poor match for Oracover Red so I ended up using Halfords “ Audi Laser Red”.

[Tim Flyer]

I’m now doing the undercarriage. Rather than use all wire as per the kit , I cut down some spare Oleo legs from my Seagull Hurricane and shortened them and drilled them to accept the undercarriage wire. I am also now thinking about the oleo fairings. I will probably construct them from thin aluminium sheet bent round the oleo legs and pack them with gorilla glue and balsa.

[Chris Freeman 3]

Hi Tim

The Chipmunk is really looking very nice, I like the colours you have used and should look stunning in the air. I hope to get some work done on mine as my son has the FlyBaby for painting.

[Tim Flyer]

Cheers Chris. I’m pleased you like the colour scheme. It’s based on the one at RAF Museum Hendon . I quite liked that scheme too( my paint job is far from perfect though! I’m afraid that’s not my forte!) . I’m just in finishing stages now . I’m building the oleo fairings simply from thin aluminium plate bent round and epoxied to the oleo legs ( the oleos were first epoxied onto the 6mm wire undercarriage to prevent twisting). Last stage will be fuel proofing which I will try the RC colours polyurethane. I will post a picture up when it’s all done.

Edited By Tim Flyer on 27/12/2019 21:14:45

[Tim Flyer]

I have just made the Oleo fairings . Rather than all wood as in the kit version I chose to use thin aluminium “litho plate” which is easily available at Model shops and really quick and easy to use . I first made a card template then snipped out a copy from the aluminium sheet. I then bent the metal fairing round the Oleos to shape . Then I used epoxy filler (epoxy with chopped fibreglass sheet) to stick liteply spacers on the front and rear of each oleo. I then put the metal sheets on and clamped them to set . Once set I filled them with wood and gorilla glue which expands to fill any voids. Here is a pre painting picture. Ps..I’m not sure whether I will make the landing light now or later but it will be easy to add on .!

[David P Williams]

Tim - The fairings look great. I cut mine away at an angle where they meet the wing, as the legs do spring backwards on landing even with the oleos, and the fairings punch into the wing surface (assuming you have kept the rest of the torsion spring setup of the wire undercarriage)

[Tim Flyer]

Hi David Thank You very much for your comments on that. I thought the oleos might spring back a bit/ or possibly even stretch forward on a flat hard landing. On the torsion bar set up I did partly fill the channel with epoxy . That might reduce spring back but obviously could result in a bend in a hard landing. I have just used gorilla glue inside the fairings so I’m hoping that a hard landing might just split the metal litho plate away from the wood I did use some p38 filler under the fairings after initially leaving a gap . I will probably leave any further modifications to the fairings until after maiden flight . Initially I had thought of leaving a gap and putting in flexible acrylic filler, but then thought my fairly lightweight gorilla foam glue inside the fairings might just be ok .

Edited By Tim Flyer on 30/12/2019 22:36:38

[Ron Gray]

Tim, David is correct, they will rotate back, after all that is what the torsion rod is supposed to do, and will damage the wing covering. On my Seagull Radial Rocket I cut the fairings back, as per David’s suggestion, but have also covered the gap with film so that it’s not too obvious. The film deforms when the legs rotate backwards on landings.

[Trevor]

Yes, you'll be surprised at how much movement the torque rods will allow. The oleos are a good idea though, if only to reduce the 'bunny-hoppng' tendency when taxiing. On my Chipmunk (not a SLEC one), I cut a piece of foam to fit between the top of the fairing and the underside of the wing - see the last picture on this page. I've still picked up dents in the underside of the wing over the years though!

Trevor

[Tim Flyer]

Trevor your Chipmunk looks superb. Thank You for your advice. That “BA” colour scheme is a great idea. It certainly seems that the oleos Should spring back . Hopefully they won’t do much damage as the inside of my fairings are soft gorilla glue and balsa. Cutting them at this stage to leave a gap will do a fair bit of damage as they are aluminium sheets . If they work loose on the maiden landing I will remove and modify them . I think what I should have done is to have simply built the fairings as hollow “aluminium shells” leaving the inside unfilled. I could then just glue the fairings  to the wing from the base with acrylic sealant. That would allow maximum free oleo movement.

Edited By Tim Flyer on 31/12/2019 10:41:04

Edited By Tim Flyer on 31/12/2019 10:42:42

Edited By Tim Flyer on 31/12/2019 10:44:16

Edited By Tim Flyer on 31/12/2019 10:45:35

[Tim Flyer]

Here is a picture of it finally finished

[Applewood]

Looks great Tim, well done. Maiden this week??

[David P Williams]

That's fantastic Tim, and quick too. I spent about 2 years on and off to finish mine. I tried to take a couple of pics of my u/c fairings for info. Didn't have space to get the wing down from racking but you may be able to see marks where it's hit the wing surface. They're unsupported litho plate, just attached to the oleos at the front, so they bend easily. The good news is that these models fly so nicely that they make even my landings into greasers.

[Tim Flyer]

Thank You very much for that David that’s very helpful. I must have spent quite a lot of my time on it this year too and and put quite a lot of other jobs aside to make way for it . Im afraid maiden flight has to wait until our strip dries out. It’s a complete bog at the moment. I didn’t even fly last time I visited our club last Sunday. One chap said he had added a kilo of mud to his model ...sounds a lot worse than icing up ! Happy New Year All!!

[Tim Flyer]

Just a few extra details that might help others . My build ended up with quite a forward C of G as I was using a bigger than required engine (Laser 180 rather than a Laser 155 which is a much more natural choice on this model ). My total all up weight is just above 14lb so the 180 will not need much throttle! I added 50g of lead into the tail and centrally placed my RX batteries. I swapped out the metal spinner for an Irvine plastic white one to reduce nose weight ( that reduced 50g of weight on the nose). My C of G is now around 1cm or less in front of the wing spar which I hope should be ok on the maiden flight in a month or so. ( our field is still wet !). I also cut out the oleo fairings as per David’s advice to save wing damage when the U/C flexes backwards. 

Edited By Tim Flyer on 11/01/2020 14:14:17

Edited By Tim Flyer on 11/01/2020 14:16:31

[ASH.]

Great job Tim, she looks superb.

She's quite a heavy bird at 14lbs, (don't know how much my one weighs with Saito 120S plus lead).

You could place your RX battery as far down into the tail as possible and remove the 50gms.

[Tim Flyer]

Thanks very much Ash . The 50g is glued internally in the very end of the fuselage ....so I’m not going to move it ( I use lead shot and gorilla glue) and I’m keeping the batteries in the central board as it’s neatest plus all done now . I had already thought of rearward batteries but didn’t fancy it as mine are fairly light plus I don’t like long leads and prefer a neat installation. I have used twin decent sized LIFE batteries and twin Futaba switches with internal mounts so I wasn’t worried about the weight. 14 lbs is a mere wisp for the Laser 180 😉 It does feel “light” to me I’m looking forward to flying it. 😊

[ASH.]

You don't do anything by half measures do you Tim? You must get through an awful lot of epoxy.. I always fix weights (when I absolutely have to ie in wing for lateral balance) with velcro. But you're right - an ounce here or there is not going to make much difference on a model that size.

What size LiFe's did you use and how are they rigged with the two switches to Rx to make the redundant system?

I hope the varnish and clear spray you used work well, do keep us informed.

If you want to fly your Chipmunk anytime sooner, you can fly at my club patch in East London anytime..

[Tim Flyer]

I use gorilla glue to glue weights in as it expands nicely in voids and clings well to lead etc. It’s great too in engine compartments as being a polyurethane foam it’s also fuel proof. Yep I must admit I do use epoxy a fair bit but the weight added to this plane with it is quite minimal ( about 20g of interior fuel proofing) It has mainly been built with Titebond Aliphatic. Im using two 1600mah LIFEs and twin Futaba electronic heavy duty switches.

[Tim Flyer]

That’s it hanging on the ceiling 😊. Thanks for the offer Ash. Hopefully it won’t take too long before our field is ok. While that happens I hope the polyurethane will become more fuel proof. I painted the oratex on the wings with JP brush on polyurethane “high grade fuel proofer”. Although it looks dark, when it’s brushed thin the browning effect is minimal. I sprayed the cowl with RC colours clear gloss which I think is polyurethane. As I only use 5% nitro I think it’s going to be ok! Of course I use my favourite epoxy for all interior fuel proofing and firewall etc 😉

Edited By Tim Flyer on 11/01/2020 21:36:36

Edited By Tim Flyer on 11/01/2020 22:12:14

[ASH.]

That is a neat interior, just how I like mine... and roomy too. I have wiring tied-up and tucked away properly as well. Yes, I can see you've been at it with the finishing epoxy - on the inside!

[Tim Flyer]

Cheers Ash yes that’s my West Systems Epoxy inside . I must admit as I had an early model boat background I like to build to “last” . I think it’s a big advantage interior coating with epoxy. Otherwise one fuel leak can cause permanent damage , plus the epoxy massively strengthens the wood .

[ASH.]

Totally Agree.. I build my artf's to last and seal all visible wood with clearcoat after strengtening.

By the way - who did you get your clearcoat from at W&W?

Does finishing epoxy really add enough strenght without cloth?

Edited By ASH. on 11/01/2020 22:40:40

[Tim Flyer]

Agreed .. very important on ARTFS . I think it might have been balsa cabin but it was year before last . I always do loads of shopping there for “stock “ as sadly there are no local model shops near me in Hertfordshire. I bought a big tin of it . I wish I had bought more . It’s brilliant for repairs ands sticking film onto, 

Edited By Tim Flyer on 11/01/2020 22:42:13

Edited By Tim Flyer on 11/01/2020 22:42:30

[Rich too]

Nice Tim, good luck with the maiden.