Scratch built CAP-like for .46

[Trevor 25]

I've always had the urge to try to build a plane from scratch and this year I decided to have a go. I also fancied a CAP-like plane so I combined the two desires. I downloaded some pictures and dimensions of other models and the real thing from the Internet and drew some plans on old wallpaper. I have a spare .46 Irvine so I tried to keep the dimensions consistent with this (span 57" fus 48" inc. cowl and rudder). I kept the weight as low as I could by using lightweight balsa where possible and as few ply formers as I could get away with. I could have cut holes everywhere but the covered fuselage only weighs 1lb3oz with 2 servos and linkages installed (no engine, battery, Rx) so I don't think I needed to.

 

The wing is all balsa with ply joiner. i made the ribs by sandwiching sheets of balsa between two ply shapes matching end ribs and planing/sanding to shape. Didn't take very long really. Wing section I got using some free software Javafoil. Section is E169 15% (does that mean anything to anyone?). I included some washout in an attempt to improve slow speed manouverability (so I have read anyway). The uncovered wing weighs about 1lb. I will be happy if the completed plane weighs less than 6lb.

 

Everything I used in the construction I already had. Most materials, like the covering, bought cheaply at shows (£4/roll solartex, that's why it is the wrong shade of yellow) or left over from previous models. Ply formers made from drawer bases from old sideboard I dismantled.

 

Construction techniques are generally based on the Flair kits I have built.

 

Some pictures:

 

Before covering

 

Lots of air inside

 

Lots of space for installation. Ply base for undercarriage. Simple balsa/rod linkages. Elevator linkage end Y-shaped. Engine mounting box bolts on as I want to try different engines (if it flys okay, that is). I have a nice ASP61FS in my Harvard, which probably only has one life left having crashed so many times and survived.

 

Covered and partly painted. Not perfect but it wont show at 400' altitude (some hopes!). Wing in background, not yet covered.

 

Will post more pics as I do some more. I want to try making my own canopy and cowl from fibreglass. Not aiming for perfection just want to try it.

 

Hope to attempt to fly it later this year. Interesting experiment for me. Any volunteers for the test flight?

[Trevor 25]

Have made some progress with the canopy.

Had to glue two pieces of blue foam together with white wood glue to get the right thickness. Then drew outline of canopy on ends using fuselage as a guide.

 

 

Carved it roughly to shape with an old bread knife. Tried a saw but it made too much dust, knife is better

 

 

Finally sanded it to shape with 80 grit sandpaper. If you do this yourself use a dust mask, it produces lots of clingy dust

 

 

It took surprisingly little time to get to this stage, about an hour after the glue had dried. Next stage is to fill in the little dings, make this into a mold and create a fiberglass canopy. Will post some more later.

[Darren 0]

Trevor,

 

Looking good, wish I had the time to have a go at scratch build. If the dimensions are similar to other kits/plans then I'm sure it'll fly.

 

My experience with these types (CAP/Extra/Sukhoi) is that you can always do with a bigger engine. I've had a couple of kits that were supposed to be for 25's and I flew them with 46's !!

 

So the idea of a bolt on engine box is inspired, look forward to seeing/hearing how it turns out

[Nutz 0]

Thats the talent & skill I wished I had building a plane from scratch. The plane is looking really good. Good luck with the project, I am sure your CAP will fly great.

[Trevor 25]

Over decorated as usual!!

 

 

The next stage creating the fiberglass canopy. I have noticed the epoxy resin doesn't stick to polythene sheet so I tried covering the blue foam mold with some, after painting it with emulsion and sanding smooth to protect it. I used a heat gun to shrink some thin polythene (actually some scrap solarfilm backing sheet). Need to go very careful with the heat gun to avoid damaging the blue foam. It shrank nicely and made a good membrane over the canopy. Held loose ends underneath with masking tape. I then put 2 layers of 25g woven glass (leftover from another model) and a final coat of resin, over the polythene sheet. Here is the result.

 

 

When I separated the fiberglass from the mold it stuck in a couple of places and caused slight damage. Also the canopy wasn't as transparent as I had hoped so I decided to paint it and here is the result after sticking it to the fuselage. Not brilliant but very light and it does the job. Might spray it black to get a better finish.

 

 

and here is the assembled fuselage with Irvine 46. Will have a Flair in cowl silencer too. Everything as far forward as possible to balance.

 

 

Finished weight is 5lb 13oz. A bit heavier than I would have liked but within my original limits. Must be all that decoration!!

 

Next thing is the fiberglass cowl but I will make sure it flies before I embark on that little project!!

Edited July 25, 2006 by Guest

[Trevor 25]

Took it to the field yesterday and Simon kindly test flew it for me. The throws were way too high and it took some trimming but it seemed to fly quite well, though I am sure that was due more to the pilot. Didn't get any pictures but I will next time.

 

Main problem was the attitude of the plane in the air. It flew tail down and needed quite a bit of up elevator trim. Balance is okay I think. This seemed to me to be more due to wing/tailplane incidence. I built 2 degrees of washout in the wing but the wing root incidence is 0 degrees to the tailplane so the wingtips have negative incidence. I read on the Internet that if there is washout the wing root incidence should be positive to give an overall neutral effect. Does this make sense to anyone?

 

I am going to raise the front of the wing by trimming the wing seat though I might try padding the rear of the wing downwards first to test my theory. Anyone got any other suggestions?

Edited July 25, 2006 by Guest

[Trevor 25]

Can someone tell me how much throw they put on their CAP232 elevators, rudder and ailerons? Also what scale their CAP is so I can scale the throws? Inboard throws on elevators please due to the tapered shape. Thanks.

 

Trevor

[Darren 0]

I'll have a look at the manual that came with my 68" glens cap tonight, that should give you a reasonable start point.

[Peter 0]

Hi Trevor,

Model looks great and glad to see it flew well. Re your query on the incidence and wasout etc a good starting point is Gordon Whiteheads book on Every day scale models I am sure it is still in print but he really answers most questions anybody would ask when embarking on designing scale models.

I believe they are serializing the book in the monthly mag Flying Scale Models.

I will look up your question and try to get an answer. As the Website only hits 35 or so of our members why not write an article for the newsletter I will be happy tro includeit. This really is the type of interesting story we want . Why not share it?

regards,

Peter

[Trevor 25]

Hi Peter,

I will definitely write an article for the newsletter. How many pages should it be? Photographs alright? Microsoft Word okay? I will try and get a flying picture included when the flying attitude thing is sorted.

 

I had a look for Gordon Whiteheads book. It is going for £100 on Amazon. I can't find a website for RM Books I will have to keep looking, it looks like my kind of book.

 

Trevor

[Peter 0]

Trevor,

Thanks for the offer of doing an article for the newsletter. Photos will be very welcome. If you want to you can spread over a couple of months I am sure it will make good reading.

Ref the Gordon Whitehead book I will photocopy the relavant pages and make sure you get them within the next few days

Regards,

Peter

[Trevor 25]

Peter,

Many thanks for the copy about wing incidence. I will study it but on the first quick read it seems to confirm what I thought, that a positive incidence is required to neutralize washout. I will let you know how I get on.

 

Thanks again

[Trevor 25]

I made some changes to the CAP and flew it today for the first time in a few weeks. I have swapped the Irvine .46 for an Irvine .53, moved the CofG forward to 25% wing chord instead of 30% and changed the wing incidence by padding the rear down by 1 degree to compensate for the 2 degrees washout. It flew very well, much improved over previous flights. The extra power meant it took off much quicker and climbed better, the change in wing incidence made it fly straight instead of tail down and the forward CofG seemed to give it better penetration and glide. Looping was also much improved, it didnt fall out of loops like before. I think this is due to a combination of above changes.

 

Overall I was happy with it. Only problem, the .53 with the Flair in-cowl silencer was quite noisy, I'll have to get it tested and maybe get a better sliencer.

 

Gives me more incentive to make a cowl for it

[Trevor 25]

I started the cowl for the CAP. I decided a glassfibre one is too much work for now so I made a balsa one and will glassfibre over it. I could use it for a plug to create a mold sometime in the future if I want to.

 

I created a boxy looking cowl to start with. Doesnt look much at this stage but you have to imagine what is inside it (like Michaelangelo when he started the statue of David )

 

Then added a front piece and planed and sanded it down to the required shape.

 

It isnt exactly to scale, it is more a cross between a CAP cowl and a Giles one but I think it looks "wicked"

 

It's a lot heavier than a glassfibre one would be but I can remove the lead balance weight to compensate. Next thing is to glassfibre over it and paint it

Edited December 28, 2006 by Guest

[Nutz 0]

Very nice finish on the cowl. It is like a magic trick, we start with a few pieces of balsa and wahlla.................It is a piece of art that workmanship.

[Trevor 25]

Finished cowl weighs 4.5oz but I can remove a 3oz balance weight so not much weight added overall. Looks okay. Not perfect but better than no cowl.

 

[Trevor 25]

Must put the paintbrush down before I add too much weight to the model

[Trevor 25]

Thought I would have a go at making spats. Started just making one and will make the other if sucessful. This took about 1.5 hours, not too bad.

[Trevor 25]

At last it is finished including home made spats. I call it my CRAP232 Zetec. CRAP232 because it only bears a passing resemblance to a CAP and Zetec because it now has mesh grilles on each side of the cowl to stop the rather large cowl acting as an air scoop.

[Trevor 25]

Gave the cowl a bit of a "Nip and Tuck", doesn't look so goggle-eyed now.

 

Also added a purple pipe so I can experiment with tuned pipes. Just for fun. Had to add some spacers between engine and manifold to clear the fuselage so I expect that has messed up the tuning. I'll sort that out later after I see how it runs.

 

Now I call it a Piped CRAP232 Zetec or PCRAP-Z for short.

 

(Hey, now I know how the chinese think up the names for their micro electric planes)

 

 

 

Edited February 20, 2007 by Guest

[Nutz 0]

Looking good Trevor, I quite liked the google eyed cowl, also the acronym you have for it does not do it justice as it looks quite nice in the air..............I just thought of something........... It fly’s, so it is a flying CAP LOL.....sorry, bad joke.......... I know, I know.

[Trevor 25]

Put a bigger engine in, a Super Tigre 90 2 stroke. Really goes well, vertical performance.