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Aug 13, 2019, 01:26 AM
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If you could source the sponge foam rubber that the RC car guys use for their tires you could make your own wheels too! You cut it to size and after mounting it is trued by running the wheel at speed and using a sanding drum or stick to shape and true the wheel round. For a plane's wheel you would need to use collets to lock the wheel to the arbor for shaping or build a dog that would engage the spokes of the wheel to spin it with the arbor.

Having mounted and trued a few RC foam tires it is a messy job and isn't commonly done anymore as everyone buys pre mounted and trued wheels . Only the rubber tires are still sold where you build your own wheels mounting them to rims that are compatible with your RC car.

You should be able to find a lightweight foam wheel in 36mm size, you might need to make hubcaps for it to look like a scale Thunderbird's tail wheel.

Nice work shaving the couple grams off the gear. Saves you 6 or more grams of nose weight.

David
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Aug 14, 2019, 04:14 PM
Father by day, hacker by night
JornWildt's Avatar
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I have considered making my own wheels, but never found a source of useful foam, so for know I'll buy prefabs.

Found a nice light wheel, mounted it on a piece of carbon rod and some piano wire. Then dug out some more foam from the fuse - and, voila, a nice retractable tail wheel.

I have ordered some of that modern wonder fishing line made of Dynema and intend to do a pull-pull setup for both the steering and the rudder. I am even considering a pull-pull setup for the retract mechanism as two lines of 0.17 mm fishing line is a bit lighter than a suitable push-pull carbon rod.
Aug 14, 2019, 04:21 PM
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Later on I worked on the rudder and elevator arms, which is some really fiddly stuff as the elevator servo arm moves into the rudder - and similarly the rudder pull-pull servo arm has to be embedded in the rudder too.
Aug 14, 2019, 04:30 PM
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And here is a nice photo of the real thing (from David Aungst at https://www.arcair.com/awa01/401-500...Aungst/00.shtm)
Aug 17, 2019, 11:13 AM
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Just got the fuselage halves joined and estimated that I used 30 g glue for that! Then I remembered that I started with a full Gorilla glue and still have an extra full at hand. The full one weights 320, the used one weights 110 g ... what? 210 grams of glue in that aircraft! I'll be damned - Panzer balsa might just be my smallest issue!

For comparison there is about 180 grams of foam in the aircraft ...

Well, now I know I can sand off most of balsa sheeting since there will be an layer of iron right beneath it

Next time I build in foam, it will be foam sheeted and glassed only.
Aug 17, 2019, 11:22 AM
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On the other hand - the math doesn't sum up ... if I sum up the estimated amount of glue from the wings, fuselage and fuselage join , I end somewhere around 100 - 120 grams of glue. So there is about 100 g I cannot account for
Aug 17, 2019, 11:29 AM
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Oh, wait a second - the glue probably evaporate quite a bit of water - silly me. Sorry.
Aug 17, 2019, 01:11 PM
Registered User
You can premix the Gorilla Glue with water in a cup to activate the foaming and then spread the foamed glue on your joints to control the expansion as well as use less of the GG on your joints.
Naturally, if you need the expansion to fill a few gaps to fit you apply or don't scrape away as thin a layer of the glue.
Aug 17, 2019, 01:55 PM
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Thanks. Expansion is actually the thing I love about PU-glue, especially for foam like this where it fills all the voids. Didnít realize how heavy it is though ...
Aug 18, 2019, 10:30 AM
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A milestone


Finally it seems like I have all the components I need to start assembling the aircraft!

- The fuselage has been sealed up and awaits the wing sadle cut-out as well as cut-outs for the tail assembly and cockpit.

- The tail unit is done

- The wing is done

- Cowl and motor will be added later.

- Cockpit can also wait until the whole aircraft is assembled.

Now I just need to figure out the right sequence of assembling the stuff ... the flaps for instance need to be assembled and mounted before the wing halves are joined - otherwise I won't be able to insert the torque rod that drives it. That implies the flaps need to be covered soon ... and so on.

The plan right now is to start covering all the small pieces (flaps, ailerons and tail unit) and then assemble the wing. When the wing is ready I'll be able to do the wing sadle cut out.

I have decided to cover the aircraft in tissue and water based PU varnish (WBPU). Everything seems really strong in itself, so the added strength of fiberglass is not needed - I only need something to make a nice smooth paintable surface - and the balsa itself should make the surface reasonable ding and hangar rash resistant. Tissue may seem a bit odd for this kind of balsa-covered model, but I really need to save some weight!
Aug 20, 2019, 01:10 AM
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If you take a look at the fuselage where it meets the cowl (https://www.arcair.com/awa01/401-500...-Aungst/15.jpg) you can see that it curves a bit inward to open up for airflow (I assume) through the cowl and the cowl flaps. I wanted to include the curve and figured I would just sheet it with the rest of the fuselage ...

But I didn't realize, at design time, how tight the curve was, so I have left the front open so far. Last night I decided to finish it though. I dug out pieces of expanded Gorilla glue to make room for it, took a saw and cut a hundred small notches on the edge, smeared Gorilla glue on the inside and then pulled the balsa inward with half a kilometer of masking tape Turned out pretty good although the process felt a bit odd.

There were also time to build two hatches for the aileron servos.
Aug 20, 2019, 08:42 AM
Registered User
That fuse detail looks good Jorn.

Michael
Aug 22, 2019, 02:46 PM
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Covering ...


I'be been doing some experiments to find a covering technique that suits me and my project.

First I looked at 25 g glass + epoxy vs WBPU. That yielded the two examples in the first photo - two 1.5 mm pieces of balsa, spackled, sanded and covered with glass and epoxy or WBPU. Then WBPU + talcum was applied as a filler to both examples. The result was that there is very little difference in weight - both examples gained approx. 4 g equivalent to 100 g/m2.

This model has a total surface area of approx. 1.5 m2 (wings, fuselage and tail unit) yielding 150 grams of covering! Yuck!

But since there is lots of strength in the balsa sheeting already it really does not need the strong glass cloth. Tissue should be fine - but I've never tried that.

So I found some non-modellers "domestic" wrapping tissue and tried to apply it over spackled balsa with WBPU - with tons of wrinkles as a result. It didn't matter if the balsa was WBPU'ed first or the tissue was applied wet or whatever ... it always bubbles up and the WBPU is not sticky enough to keep it attached to the surface. See photos.

It may very well be that Esaki Japanese tissue won't wrinkle and bubble in the same way - but I haven't ordered any of that stuff yet.

But all of the tissue instructions I have found online always uses dope - and maybe that's just the trick? I guess dope, being non water-based, won't wrinkle the tissue and be more sticky and thus able to keep the tissue on the surface?

I don't have dope - but I do have an older can of oil/solvent-based PU varnish (don't know what it is called in English). So I tried that - and so far it looks much better! No wrinkles at all - but it stinks a bit more than the WBPU and requires thinner/solvent to clean the brushes. Now I just have to, eagerly, wait until tomorrow to see how it turns out when cured

As a last thought I tried to brush some of the thinner on a corner of the test piece - and that seemed like a good idea as it soaked both wood and tissue much better.

I haven't weighted the tissue pieces as there were too many failed attempts to make it worthwhile. Will do that if the combo works.
Aug 22, 2019, 05:27 PM
Gorilla glue rocks
Spit100's Avatar
Looks like you are really making a lot of progress. Nice details as usual. Will be interested in the tissue outcome. It is a nice light way to finish balsa for sure. Have not seen it before....

Jon
Aug 22, 2019, 05:28 PM
EB-66C Team Member
J Morgan's Avatar
Actually the oil based varnish will be better for you for another reason. Using WBPU on raw balsa tends to swell and warp it. I have covered many with tissue and WBPU but always gave the airframe a coat of oil base varnish first to seal the wood. Make sure you give it plenty of time to gas off and cure, then sand lightly and it's ready for tissue and WBPU.

J


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