OK guys (and girls) here we go!

First a bit of background. I rarely build kits, I have a pile of RC ones that sit there, and over the top of them I'll happily scratch build whatever I want. Up to now all my control line models have been scratch built from someone elses plans, or worse, my own. I noticed recently that my local hobby shop has SIG kits in stock. The running joke at the LHC is that they never have anything I want, but after seeing a few Kobras and smith miniplanes (another kit I'll probably never build), I got all hot under the collar, and started enquiring about what else they could get.

As it turns out they were happy to get me a chippy, one of my life-long loves. Seeing as they could get it in, I jumped in, maybe a touch prematurely

I'm planning to build this ala Dave Fitzgeralds modifications, and maybe a few others to shave some weight out of it. As it stands the wing will lose it's asymmetry and I've stretched the span out an extra inch each side.  The wing will move forward a little and the tail will be stretched as far as I can on the supplied  fuselage sides. I don't plan to use the heavy wood for the tailplane, and instead will go for a 1/8" ribbed core and 1/16" sheeting over that. Should look the same but weigh less. I still haven't decided as to whether I'll do the same for the flaps. I may do if I have a rush of blood to the head. I've got a 4" bellcrank that will find it's way inside, of course it will be fitted with a weight box and adjustable leadouts. If I can get my head around it, it'll probably also have an adjustable elevator horn. After much discussion on the engine a trip to said hobby shop will probably procure me a nice new 46LA to power it.

I read everything I could find on the chip and found that with some modifications it could be a pretty good stunt model. I gingerly opened the box and was greeted by a pile of printed sheet balsa, some sticks, a nice canopy, and some heavy ABS parts.

I then do what I usually do, which is put the plan up on the workshop wall, have a cup of coffee, and stare at it, until I know exactly how it goes together. I don't lay plans down unless they're under my glass worktop, and in this instance there's really no point as the rib spacing and spar positions aren't the same.

I read the instructions and sniffed at the method of construction of the wing for a starter.

The plans call for laying down the trailing edge sheet and building the wing off that. I'm not to keen on this method for tapered wings. while you may end up with a flat side, I always worry I'll build two sides with the same washout, making a nice propeller shaped wing!

I thought about building using rods, but eventually caved in, and built a sacrificial jig using rock hard 3/8" stock I had lying around. Centrelines are marked on the blocks, and the fronts are set up to accept the diamond leading edge, and the TE is notched for the 1/4" SQ TE.

Using a long straightedge I set up the TE in the right position, and using the root and tip ribs, set the LE to be in the right spot. After that, I fed in the lower mainspar, and fitted the rest of the ribs. Each one was slightly too long or just a little short, so some 'micro fitting' was called for. eventually I had the ribs all in with a few CA tacks, and checked it for straightness.

As each rib was pulled out, I made a quick tracing, just in case I need to do some repairs, and the root and tip ribs will be used for cutting the fuselage and tip blocks later.

A few asides, meet Catty, he's a fixture in most of my recent build threads (on other forums) and he's usually hovering around  or looking at an area of importance. Keep an eye out for him! Another thing to note is my trusty new scales from hobbyking. A paltry 9.90 to ensure you know what weighs what.


Some pics of yesterday's work.

Here's some details of the jigging blocks, Nothing special.

Dave Fitzgerald mentions fitting 1/16" ply doublers to the landing gear ribs, and moving the gear blocks to touch the spar. Who am I to argue?

If you want to go over the top on the control system, replace the nylon bushing with brass or aluminum and integrate that into a hanging pivot.  That's what I did on my first stunter, which was a whole lot of work for a plane that was going to get crashed in less than a year.

On pictures: Most digital cameras will let you set the resolution.  If you can't, then there are slews of picture resizing utilities out there.  I use Gimp, which is basically an open-source version of Photoshop.  Using it just to resize pictures is kind of like using a milling machine to whack holes in plywood, but it does do the job.

Here's a pic of the control horn from my Waiex.  I made a vertical rod with a shoulder to match the ID of the bellcrank, then made a spacer to match the rod.  The whole thing bolts up to a pair of parallel plywood plates.  It was durable enough to last longer than the airplane (which didn't last for a year).

Note that this picture was taken at 2816x2112 resolution, then cropped and resized using Gimp.

We're still a little behind, so we may as well get up to speed.

Now that the ribs are down, and everything has been trued, it's time to fit the top spar and aft sub-spar.

I'd hate to say it but in one of my scratch builds the spar line is a little better than what I've been given, and while the checkouts for the spars may look ok, they don't neccesarily align. a little tweak here and there with a rat-tail file does the job.

After that, I drop the spar in and push it flush with a big T-bar. If it's not sitting flush, some tweaking of the checkouts is required, so that the spar will seat nicely and end up flush with the ribs to ensure the sheeting isn't warped, or worse, the spar is sanded away to a nub to ensure flat sheeting.

With that said however, the aft sub-spar I chose to let it hang out a touch, so that a simple lick with a long permagrit bar would give me a nice mating surface to glue the trailing edge sheeting to.

We're now at the point where I can start to get the hinge lines knocked out, and possibly devise a nice bellcrank mount. Using a 4" bellcrank has meant that I will need to do some surgery to the ribs though.

Knowing me they may well end up as a pile of dust. Once I start with a sanding drum on my dremel even my engine mounts will probably get lightened. Considering that I've now run around with CA and locked the structure down, I may have to steal my right-angle drive from my good buddy to sneak in between ribs.

Until I manage to procure a motor to engineer my crutch, the fuselage is on hold. As far as I'm concerned, any extra width from the engine crankcase to the fuselage sides is wasted space. So apart from starting sheeting (the supplied SIG sheeting is like 1/16" mahogany, so that'll be put in the scrap bin) on the wing, the tail feathers should get a look-see soon.

are you saying the NEW Sig Chimpmunk kit has printwood?

David_Ruff, yeah, mine's printwood!

It's actually a muddly mix of printwood, unmarked sheeting, laser cut stuff, and die cut stuff. Some good die cut, some die crunched.

Weird!

Charles, thanks for the help with the masks, but I have a guy here in Perth that does stuff like that for me. If I didn't though, I'd be shooting you a PM quick smart!

Joe, I wish my flaps were printed, mine are lazer cut! they're look nice but they're too small, and assymetrical!

I haven't stepped foot into the workshop since my last posts, as I've been nursing a sick partner, so I've been cooking chicken broth (and a huge mess) while she convalesces on the couch.

Hopefully today she'll be back on track and I can get back to making a bigger, balsa coloured mess.

Charles, thanks for that, what format do you use?

In all fairness, I'll more than likely do it as the box art. I have a strange hangup with 'classic' models, it was the box art that usually sold us, and I feel that my builds are tributes to that. My other love is vintage sailplanes, so my last two, a Graupner Cirrus and a Airtonics Sagitta look like the box art (only prettier).

And yes, if I ever get around to grinding out a Curare, you can bet your bottom dollar that it'll be done in Hanno Prettner's scheme.

Anyway back to the build, or lack thereof.

I decided that I'd let my friend keep the right-angle drive, as I've borrowed gear of him that he's pretty much given me, and it's probably worn out already   So after work, I went to Bunnings, (our home depot in australia), and guess what, no right angle drives. A 20 minute drive home saw me swing past their competitors, and guess what, NO DRIVES!

Geez, I'm going to have try a few more stores or go cap-in-hand to my buddy and steal it back.

Well, it's been slow going for the past few days, progress is being hampered by two things: the absolute inability to find a right angle drive for the dremel so I can eek out those ribs, and worse, I've become paralysed by detail and second guessing myself.

My partner calls it "overbraining". It's a bit of a weird one this time. Building a kit lead me into a false sense that someone had thought about enough that I could build it, and to certain extent that's true, it'd probably fly ok box stock, but I made a rod for my own back (and a ache for my own head) when i started to divert from that plans. Its really easy for me to end up paiting myself into a corner mentally and doing the worst possible thing, not enjoying building.

Bellcrank positioning and mounting is still twisting my head off, but I think I've got that licked to some extent. I hope...

Horn geometry is another. AS is horn material, I'm really struggling to find decent guage steel that's not galvanised. I was tempted to use brass, but I think I'd prefer steel.

SO to get over my mental and building paralysis, I've taken a leaf out of Bob Hunt's Purple project thread, and done a little bit each night.

I added a couple of 1/32" ply doublers to the spar join on centre, and added extra meat to the TE to accomodate flap hinges. I also laid out some laminated flap leading edges out of 1/32" sheet, to sort out my hinge pockets. After doing this once before, I'm totally sold on it, as I HATE gouging balsa to fit hinges in. It feels barbaric!

Today I'll be getting a few things sorted, and using my time at work to draw up some internal structure for the tailplane. Having a look at the plans I suddenly realised just how small the tail area is, it must be close to 15%. I've realised I'm going to have increase it a fair way to get area. I know I'm looking at an increase of about 4" all up, and maybe even a little increase in chord too.

I hope it doesn't end up looking too much like a giant flipper!

In other news, engine is on it's way!

Hehe, Tim the only russian saying I know is "the first pancake is always lumpy"

Heopfully tonight I can frame up flaps and tailplane, and on saturday my good buddy is bringing the right angle drive down to me in exchange for a timing light so he can finally fix his car.

Once I get that sorted, I'll be futzing around with horns for a while.

PROGRESS!

While waiting for my pal to turn up with the right angle drive, I set out the plans for the tail plane (flaps too but they're a little hard to shoot). I don't build much with pins these days, as it's hard to push them through glass. I use the spray adhesive method outlined in the Hot stuff Building Tips videos, Brett Buck mentioned it a while ago and it's certainly changed the way I build.

Link for the interested :





I'll laminate the leading trailing edges to make the hinge slots, then slice it in half to ensure the hinges line up exactly.

Another little move forward was getting the horns soldered. Everything I'd read on the SIG horns made me trust them about as far as I can kick them. If you've ever tried to kick a horn you'll know it ain't far. So I set out to build my own, for the first time. I'd worked out the geometry (for better or worse), and made the parts. I'd bought a Bernzomatic torch and a silver soldering kit. I cleaned everything, fluxed it, and then was completely bemused as the flux went black before I could even melt some solder on it! Further investigations detemined that the flux wasn't right for steel, it activated at too low a temperature, and so was all burnt by the time the steel was ready to accept the solder. One of my good friends loaned me their flux, and I tried again.

The results aren't going to win any beauty prizes, but they're solid enough for use, and they're hidden anyway. Not bad for a first try I think. Next time they'll get better I'm sure.

Well it's been a while between drinks, and it's probably time for an update.


It's not good though.


While I was working on making a set of foam cored wings for a profile, I had the cores on the workbench opposite the chippy wing in the jig, ready to start sheeting.

My way of doing sheeting is stolen directly from Bob Hunt's tutorial, so nice flat bench, cores down, big flat chunk of slate on top and then more weights on top of that to give enough compression.

Well the wing had cured and it was time to get rid of the weights, when I misjudged the CG of all the stuff on top of the cores, when the slate toppled straight onto the chip wing, and all the weights slid right through it.

It's a mess. I've left it to have a good think, but I don't think it's worth persuing at this stage.

So, decision time, foam wing, or built up wing? This mild kit bash appears to have degenerated into a virtual scratch build 

I have repaired severely crash damaged wings ... tough part is getting them straight again.   You can get a replacement wing kit from Sig cheap.

I have rebuilt some planes that were beyond economical repair and made a plane out of the wreckage of 2.   When it comes down to it they are almost scratch built as there are more fabricated replacement parts than original.

Your wing jig is the correct way to align the leading & trailing edges.  Systems that use rods through holes only align a row of holes, not the wing.  

The LE jigs with the diamond cuts can be used for future projects.  You will just need new TE fixtures unless your next build has idential TE stock.

Well it's a long weekend here in australia and in between sporadic bouts of flying I'm getting so spend some quality time mashing balsa.

I finished sheeting the tailplane, and some of you helped me determine whether I was on the right track in terms of the stab's strength, I'm reasonably happy with the result, and I think once a bit of silkspan goes down, it'll be tuff enuff.

The complete stab assembly including brutally overbuilt horn weights in at 60.8 grams, that's 10 grams lighter than the stock blank for the stab!  I'm doing the same construction for the rudder, and the sheeting is drying now, so tomorrow I should be able to dress that and that's the tail assemblies ready to finish.

All up the stock fin weighs 17g, and mine weighs 11g now, so after dressing I should think I'd be at about 10.


About a week or two ago I came to the conclusion that a foam wing would be the way i'd want to go, for a couple of reasons. Built up wings are a known, and I try to learn on every model I can, whereas creating light wing mounted gear foam wings isn't something I've done. Also I prefer finishng foam wings than open bay. So I cut some templates.

I managed to clear the workbench and cut some cores. While they're not the greatest in the world, and they could have been a bit better, they're certainly the best I've ever done to date.

If I get some time tomorrow I'll hack up the cores, and get my spar and rib cut to start mounting the wing blocks, thanks to Bob Hunt's beautifully detailed pics.

Notch the mounts for the plates.   

Some shots of today's work.

Thanks man, but I'll be the first to admit, I wouldn't have ever got this far if it weren't for some of the good souls on Stunthangar.

So, here we are at another post.

I've knocked up the basics of a fuselage. In order to get the engine centreline to match the cowl AND use aluminium mount plates, I've had to sink the plates into the maple bearers, no mean feat given my lack of proper tools for dealing with hard woods. Still I managed to get the mounts close enough and whatever misalignment crept in, I linished the pads till they were flat. Photos can be found above. Once I'd glued the formers to the crutch I set about assembling the fuselage. The formers in the tail are 1/16" at about 1 1/2" spacing, dropping down toward the tail to provide (I hope) some support to the tail, and the pushrod.

Windy's videos (ala Paul Taylor) show this better than I ever could.  After that I filled in between the formers with 1/8 x 1/4" diagonals to give the fuse some torsional ridgidity. We'll see in time whether or not my efforts have been in vain or not.

After that I moulded up a set of front and back  3/32" (as opposed to the stressed 1/8" stock parts) turtle decks and massaged them to be about 1/64" oversize. It's starting to look like a chip now.

Well it's been a long time coming, and I kind of lost interest in doing this build thread, but I thought that some of you might like to see the finished product.

It's been finished for a few months, but I haven't had a chance to get some pics of it, till now.

Things conspired to make the model heavier than I'd like, they always do, and I had fits finishing it, (simple colour scheme but it endup taking years off my life) but all in all it came out ok.

Not front row standard, but better than most.

It looks damn good to me. I did the Chipmunk in 1971 and used that scheme. I came close to tossing it in the trash three times and I used K&B super poxy paint. In the end the only problem was a constantly over heating Fox .40 stunt, the big one. Found out years later the engine was not fully broken in. 

Lots of good time and a little earned "hardware" with this ol' Super Chip first with an OS 35, followed by a Bob Wilder tweeked OS 40 and later changed to a modified ST35 with a 40 sleve, piston and liner. Put many years on that old Chip...with sooo many folks who also  got to fly that ol bird before I lost it on the back corner of a horz. 8 a couple of years ago at the Gig Harbor Narrows airport.

Shultzie, I saw some pics of that chip that you posted a while ago, a real stunner!

Chris, thanks for the kind words.

A bit of an addendum to the old chipper, After building it and flying on the 46LA, I regret my decision to go glow.

Most of my other aircraft are electric, and having to cart a fuel bottle AND a pile of batteries down to the field is getting really old, really fast.

In the next week or so, the LA will be coming out, (and the motor mounts  ) and a nice 4S electric setup with a KR timer will be shoehorned into the front.