Colin Leighfield's Chipmunk build.

[Nigel Day]

Yes, it's all helpful Colin, thanks.

[McG 6969]

Hello Mr Colin, hello to all,

Sorry to jump in 'uninvited' but I thought this could be of help to some of you regarding finishing techniques for foam. This method is not really intended to add some structural strength though, but still very applicable where no lamination is required.

Freddie B's Secret Sauce...

Not such a big secret, as Freddie B - an American foamie guru - himself talked about it in an RCgroup’s earlier thread. Here are some photos to help 'show and tell' in case some of you'd want to try this.

Basically, it’s a filler & primer coat (all-in-one) that doesn't weigh much but works really well. He does this on his foam builds often when there is no covering, lamination or other coating involved.

While many have been amazed by Fred’s finished airframes, this was the process he used. Let’s have it in sequence.

1). Take some light weight spackle (Polyfilla or cellulose based filler) and put a nice size plug in a little mixing bowl. This time the plug of filler is about the size of a nut.

2). Next add some Polycrylic clear varnish (water based of course), about the same volume as the plug of light weight spackle.

3). Get some Talc Powder. Baby Powder or Foot Powder, but the Baby kind smells best… Watch out because many powders are Corn Starch, which we don't want! Talc is the magic that made balsa filler work in the old days of tissue and dope finishes. It is very fine and does a great job of getting those tiny imperfections filled, but sands away nice. Note the 'pile' of powder about equals the volume of the light weight plug we used too.

4). Add two or three drops of acrylic paint (craft paint, water based), and it can be white paint, but often you can use a colour to see the work in process and the finished results shows up better. Anyway, use a colour that works for your intended top coat. Light for light topcoats, gray for everything else. You can use Yellow in the primer if you are painting Yellow top coats, because Yellow (and Reds) don't always cover well.

5). Now mix it well. It is very thick, but get it creamy and all one colour and texture, working out any chunks. Now add water until it is like very thin whipping cream, thin shaving cream, or even thinner like a very thick paint. Brush this on your pre-sanded foam, making sure to completely wet everything and force mixture into any hollows, dings, scratches, etc.

Let this dry. Then sand it all with some 180 grit, and 220 grit papers, mounted to some sheets of beaded white foam. The foam sanding blocks are flat, but 'give enough' to not cause grooves and scaring. Just make sure to remove sanding dust often and use a reasonable pressure while sanding.

When you have sanded most of this formula away, you will see some original foam, but also many areas of filled and flush mixture and the surface will be very smooth. Little weight gain, yet ready for top coating with paint. You can sand with even finer papers, depending on what top coat paint you will be using. This is good enough using craft paints, but if you intend to spray with Model Master or Tamya paints, you could go to 320 or 400 grit paper. All three kinds of paint work well with this process.

I’m truly convinced by Fred’s method and really worth trying this out on a piece of scrap foam or Depron.

Last photo is a sample on a scratch build FFF (Folding Fan Foam) Russian Mig that Freddie B built with his filler/primer method.

Merry Christmas & successful 'building 2015' to all.

Chris

Brussels / Belgium

ps: I'm a 'silent witness' of all the Chipmunk builds around here & already love that Depron/balsa hybrid approach. Learning a lot and really looking forward to follow your project's progress. Thank you all.

[Colin Leighfield]

Thanks Chris, that looks brilliant. Another good idea worth trying out. The MIG (3)? is beautiful.

I hope the composite approach on the Chipmunk doesn't turn out to be a lemon, but I think it will be fine.

[Colin Leighfield]

I've managed to get a bit more done in the last few days, although progress is slow. All of the recent work has been around ailerons, flaps, undercarriage, hinges and horns. Fellow builders will recognise it all from the photos. I'm sticking with the plan on the hinges, the glass fibre bits are certainly tougher than Dennis's plywood originals. Also I am using socket head bolts for the hinges. Shortly I will cover the flaps and ailerons with silk and dope, which will really stiffen them up.This is a slog, I need to get onto the fuselage and hope to have made a start on it before leaving for Hong Kong next weekend. That will be it then until February, time is running away on this one.

[Danny Fenton]

Looks great Colin, its definitely not a quick build is it
Cheers
Danny

[john stones 1 - Moderator]

Time always runs away Colin, you've made good progress though, the oleos look the business

John

[Colin Leighfield]

Thanks Danny and John. I'm famously good at grossly under-estimating just how long a build is going to take, sadly. I think I've broken the back of the slow bits though and hope that the pace can increase now. However, although being away in Southern climes for the best part of a month is very welcome, it takes a big slice out of building time. I will do as much as I can in the next few days however!

[Colin Leighfield]

I would not call this a "fun-build", it requires a lot of "trial and error" and fitting up, there is a lack of the kind of helpful detail on the plan that you would normally expect from the designer, based on his build experience. Danny has picked up a lot of this in his build thread. I decided to finish the aileron and flap detail on one side of the wing before doing the other. The flap is right straight away, but clearance on the aileron was problematical. In the end I decided to remove part of the shroud to give me a better idea of what was going on. A bit more detail work on the leading edge profile sorted it, so now I need to restore that part of the shroud.

[Danny Fenton]

Nice one Colin, do you think perhaps the shrouds should have gone on last?
Cheers
Danny

[Colin Leighfield]

With hind-sight Danny, yes, but it was such a simple job to make the Depron strip wide enough to do it all in one piece that it was no big deal. The mistake was probably putting the triangular piece in instead of leaving it until later. Having said that, I should probably have been a bit more intelligent in my first attempt at profiling the aileron leading edge. I was guided by the illustration on the plan and it simply isn't sufficiently curved at the top to give clearance, at least on my example. Replacing the shroud won't be difficult now and hopefully, as the other half, both wing and flap/aileron, are a mirror image, it won't be so difficult to get it right. I picked up the point you noted about the hinge positions on the outer flap and inner aileron positions causing a misalignment, but rather than cutting them about, I'll correct it by paying some attention to the trailing edges so that they line up. I'm hoping to make some gesture to beginning the fuselage before going away next week, but I'm very reluctant to put this pesky wing down before I've got it completely sorted.

I'm not overly impressed by this design, although Dennis certainly knew how to build light. It makes me wonder if the knowledge we are accumulating on this build would enable an up-date of the plan, correcting some of the errors, simplifying it and improving the detail? As Dennis is sadly not around now, I wonder if Traplet would be in a position to do that? A re-issue would make a nice subject article for the mag (I appreciate that it's the other one) and renew interest in the subject, which is a good one.

[Nev]

I hope not.

Getting on well Colin, nice work. I’ll be trying the same thing in a day or so.

Nev.

[john stones 1 - Moderator]

Good to read you're enjoying the wing Colin it's character building the fuzz you'll sail through, bit of head scratching on the fairings though.

John

[Colin Leighfield]

Not sure the word "building" is the one I'd apply to what it's done to my character John!

[Nigel Day]

Thanks for the experience Colin. I'm leaving the shrouds 'til last because I think they'll be a bit tricky to get right and, if I'm honest, because I'm pretty kift and will damage them easily.

[Colin Leighfield]

No problem Nigel, but you're doing the right thing. I've got a lot of things going on today so went into the shed at 06.30 to get a couple of hours in. I had a good look at this combined flap/aileron hing/horn set-up and putting a washer in between gives working clearance. However, I don't see how you can get any kind of linkage onto the aileron horn because it's too close to the hinge bracket in the wing, whether using one servo with bell-cranks or separate servos. I've got the bits and servos to do it either way, but favour the separate servos because of the better choices with differential etc. I jammed one of my thin wing servos in just to see if there is sufficient depth and there is. I'm going to do the same as Danny and remove the horn from the aileron hinge plate. I will make another one and fix it into the aileron leading edge further along, as well as determining the servo position, sorting out the mounting arrangements and creating a hatch under the wing for access to it. However, having worked out how to do it, I'm sick of the wing right now so have made a start on the fuselage. I will be in a better frame of mind to go back to the wing later if I do this, I think. I'm sticking with the beechwood engine bearers because I like them, but need to widen the spacing slightly to suit the OS FV62.

Edited By Colin Leighfield on 03/01/2015 09:02:13

[cymaz]

Morning, though not building a Chipmunk I am following all the various builds.

I just wonder if all chip builders were aware of this stuff. I've used it on several planes with success. It simply glues on with CA glue. It does come in two sizes though I don't remember if Tower Hobbies stock both.

Pity it's only in the US though but Tower Hobbies have given excellent service to me over the years and I have no hesitation in ordering it from them......pass it on.....

[Colin Leighfield]

Thanks for that Cymaz, I've saved the reference to look at later. I've got work commitments this week before leaving on our travels and I'm sneaking this in at the office. In desperation I got into the shed at 06-00 this morning and spent 45 minutes doing this. I've decided to use 3mm. Depron planking behind the cockpit and 3mm. balsa forward of that. This looks ok to me, I'm sure that with the Ezekote and glass on top it will be more than adequate. It's a shame not to see the attractive look of sanded balsa before planking, but what's the point, it will all be covered up anyway and this is a Chipmunk, not a beautifully varnished Ansaldo SVA4.

[Terry Walters]

Just catching up again with the blog Colin - got to get back in harness this week!

Have a good trip (when are you leaving?) - will give me a chance to catch up with you and maybe get ahead!!

Saw an excellent model of the Ansaldo at the World Championship last year - beautiful!! Too good to put in the air.

Terry

[Colin Leighfield]

Thanks Terry, off to Heathrow Friday pm to fly to HK on Saturday am. You will be well ahead of me by the time that I get back on 06 February.

Thirty years ago I was friends with Graham Smith in the Tamworth MAC and he was a regular in the UK national R/c scale team, flying several times in the World Championships with an o/d Ansaldo. His workmanship was magnificent and the varnished plywood finish on the fuselage had artwork of a cathedral standard, I think based on the Lion of St. Mark. The one that you mention was probably based on the same original.

[Danny Fenton]

This is the one I think Terry is referring to

Cheers

Danny

[Danny Fenton]

Very impressive!!

[Colin Leighfield]

Good one Danny, that is exactly the scheme that Graham used on his example. He had an amazing ability to design large very light airframes using small section balsa, real examples of applied engineering design. I think his plan for a Miles Messenger is still available, it must have been 8ft. wingspan and flew with a Veco 61! (it was his preferred engine. I had the HB61 and they were the same engine).

I wonder how old the video is? Graham was older than me and must be getting on by now. The last time I saw him he was planning with another club member, Cliff Hughes, who like me had a PPL, to do a home-build aircraft but I can't remember now what it was. Graham was a very decent and talented man, then Head of Graphic design at Birmingham University.

[Colin Leighfield]

This is where it is today. I've only managed to get a couple of hours in the shed in the last few days, fortunately this bit is fairly quick and easy. At this stage the half shell is rigid and very light. The object for me is to put the strength in where it is needed. As I intend to use glass and Ezekote/PolyC on the sheet areas and Esaki silk and dope on the open bits, I've been thinking about the points that Danny made about the amount needed on wood and risks of warping. In this case warping won't be an issue on the solid bits, that might be more of a problem with the dope and silk on the wing! However, I've decided to put two coats of sanding dealer on the wood bits before glassing. It's very quick and easy, light and with a quick sanding provides a super smooth base for the next stage. Also and most importantly, it will stop the Ezekote soaking into the wood and minimise the amount that is required. We are off to Heathrow later to stay overnight in preparation for the flight to HK in the morning, so that's it I'm afraid until early February. Sadly I'll fall further behind, but hope to move a bit more quickly when I get re-started. If I see any Chipmunks in Oz or NZ, I'll stick the pictures on here.

[Danny Fenton]

Looks great Colin, did you measure the circumference at F8 and the circumference at F13 then divide them by the number of strips to get the thick and thin ends of the wedge shapes? Been meaning to try that....

Have a safe trip and enjoy yourselves, see you when you get back

Cheers

Danny

[Colin Leighfield]

Thanks Danny. I confess I didn"t go that far. For the tail end I did the same as Martyn and started off with a few strips 12mm wide at one end and 3 at the other. As I moved round it was clear that 3mm wasn't enough so I increased it to 5mm. The last 3 strips were then measured exactly and fitted. Because the contact adhesive sets slowly, you can squash the strips/planks up against each other as you fit them, so it comes out nice and tight. For the part just behind the cockpit, I cut a number of parallel strips and adjusted the last few to get an exact fit. I'm doing the same with the balsa planking on the forward part.

Anyway. off on our adventure. if we don't get lynched in Hong Kong, eaten buy a great white in Oz, cannibalised by a Maori in NZ and the planes don't crash, we'll be home on 06 February! In the meantime, son James is protecting the house (I hope)!