Prather QM Little Toni build thread - Page 6 - RC Groups
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Apr 18, 2012, 01:30 PM
Registered User
Live hinges sound great, but I've already beveled my ailerons for standard hinges so will keep riding the horse I chose An interesting option though so will be interested to see how it works out for you if you give it a try. And if I were to do another similar airplane, I might well consider going full carbon with live hinge directly on the foam core. Otherwise, sure looks like I'm not going to beat the traditional techniques, but I wanted to get some of these materials to see for myself.

Thanks for all the great feedback!

Originally Posted by 3D-Novice
Rick hi\i would tend to agree with fizzwater2
in all the pylon applications ive seen , they all had 1 thing in common
lightweight glass for the finished coat (0.5oz)
also using 2 oz cloth for the middle section spread out in 2 or 3 layers

the only thing i am waiting to see / learn from you is if you are now going the skin hinge route , ( as i said before , wish i was living in US ) so that i could pick up some live hinge material easily

looking forward to progress
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Apr 22, 2012, 02:08 AM
Registered User

Glass the wing

I reinforced the bottom of the wing using three layers of 3 ounce cloth and the dimensions suggested by Fizzwater. On the top, I thought about going the same way but decided to narrow it down a bit -- the first layer follows the outline of the wing saddle in the fuselage (about 3 inches, but tapering slightly), a 2 inch and finally a 1 inch wide layer. This way it'll be invisible when the wing is mounted As Terry only calls for a single 1-inch wide strip of 4-6 ounce cloth I should be at least as strong if not stronger, and fine for just about any outside maneuver that the plane can do. After doing the bottom side, I wrapped only the 2" top layer over to landing gear box on the bottom side.

The 3-ounce cloth is only about three and a half thousands thick, but it took some time with my sanding blocks and 280 grit paper to get the bottom joint glass tapered down to where I can barely feel or see any of the joints. I'm thinning out each glass layer quite a bit at the edge of each layer, ideally in a long thin taper, but each layer is full thickness at the point it meets the next layer. It's easy to avoid going through the glass where you don't want to -- that's the most important -- but it wasn't very easy to taper out the glass to the point where it will be invisible later.

After that, I had just one or two tiny bubbles near the leading edge from the center reinforcement to touch up with 5 minute epoxy and micro-balloons, and then on to finish sanding the entire wing with new 600 grit paper, giving it a good dusting and then glassing the entire bottom half. I wanted to maximize my resin working time so after thorough mixing I poured it into a foam container that I picked out of the recycle bin, to keep the epoxy layer fairly thin and avoid quick heating and curing.

This is the first time I've glassed a wing with this light cloth... the 3/4 ounce stuff is actually pretty well behaved as long as you handle it with care. The biggest issue I found is that I couldn't use large brush stokes to lay out the resin or else I would end up moving an entire section of fabric. And if I brushed too much left to right, for instance, the entire panel would slowly but surely move to the right. I did one surface at a time, and started by tacking down a few spots along the high point of the wing, then just had to work slowly in small areas to fully saturate the cloth everywhere. Even with a 1 inch soft natural bristle brush this took a while. I then used a plastic scraper to slowly and carefully scrape off excess resin (almost all that I had put down ended up coming right back off). Finally, I rolled out toilet paper over the wing and used a small roller to gently but firmly roll over the entire wing. This picked up only a little bit extra, but left the wing with a uniform, dry sheen appearance. I also overlapped the left and right panels by a total of about 2 inches in the middle, and also wrapped the cloth around the tip blocks and to the edge of the upper surface (and held the ends in place with tape to keep the cloth nicely wrapped around the tips). I'll do something similar when I glass the top.

Terry calls for glassing the ailerons separately, but I wanted to do them together on the wing to get a uniform trailing edge. I'm going to apply the same trick I used to use on my helicopter blades back in the day. I've left the thickness of the very trailing edge about 1/64th. But I can use the glass to taper that back to an even finer edge. Apply the cloth so there is a uniform short overhang, about a quarter of an inch, and wet out the cloth all the way back. The cloth overhang has to be short enough to let the cloth simply keep going along a tangent following the taper at the very trailing edge, and the overhang should be as even as possible over the entire trailing edge for this to work properly. After doing the bottom, I'll trim and shape this up and repeat on the top. This will end up extending the trailing edge another 1/64 or 1/32nd or so, and theoretically you could take it back to a razor. I'll not go that far, as this glass would break too easily, but I can still narrow that trailing edge down quite nicely.

Weight of wing before glassing the bottom with 3/4 ounce cloth: 254 grams
Weight after glassing bottom side: 270g
Gain = 16 grams. So doing the entire wing in 3/4 ounce cloth will only add about an ounce!!
Apr 22, 2012, 02:08 PM
Registered User
Lookin' good!

When you do the three layers, you put the larger layer on first, then the medium, then the narrow one. I used to do it the other way, but then a friend pointed out to me that when you sand it, you may cut the fibers of the wider layer where they pass over the edges of the narrower layers - which pretty much negates the effectiveness of the wider layer. By putting the narrow layer on last, you don't cut through the fibers of the wider layer as you sand it.

Can't wait to see the finished product, the Prather Toni is a neat little airplane, and it looks like you're doing great work!
Apr 23, 2012, 04:42 PM
Registered User
Thanks, Fizzwater!! I really love the Prather Toni too -- it's such a cool semi-scale racer. It evokes not only the nostalgia for the great air-racing days of the full-scale Toni, but also of the classic pylon era back in the 70's as well. And it's great to be able to bring back to life something that's been sitting around in a box for thirty years!! I'm even tempted to pull a mold off that fuselage before I do any cutting on it so I can make another one.

Speaking of the box, I was poking around in the Toni's packaging materials the other evening. It included a single page of crumpled-up newspaper. I took a look at it... it's dated from 1980... and from Anchorage!! Do you suppose Prather was contracting the kits out to other companies or individuals?

PS another potential motor, mentioned in the Midget Mustang thread, is the HET 3W25 Typhoon motor. 1750 kV, said to put out about 870W on 4s with a 7x6 and good for 120-130 MPH on that airplane. And only weighs 110 g!! The specs seem quite suitable for the Toni but on the other hand that Mustang is half the weight and a foot less span...
Apr 26, 2012, 01:00 AM
Registered User

Carbon trailing edge

After glassing the bottom of the wing, I had left about a quarter inch of overhang at the trailing edge (of impregnated cloth). After curing, I trimmed this back to 3/32", which I felt would be the theoretical point at which the top and bottom sufaces would intersect at a point, or maybe even a little bit longer.

If I'd used heavier glass, I've have just gone directly back over the other side in a similar manner and ended up with a reasonably strong trailing edge. But in this case, that 3/4 oz cloth just didn't give me the confidence I wanted that the thin TE would be strong enough to withstand the occasional bump during transportation etc.

I decided to try an experiment to strengthen the glass, as I had nothing to lose (at worst I could just trim back to the balsa trailing edge). I first laid down a ribbon of tow, after wetting it separately with epoxy. The tow is the same stuff I used as a spar inside the sheeting. I laid the tow directly from the top side of the wing, on the 3/32 glass overhang, right up to the balsa trailing edge but not over it. I propped up the wing such that the trailing edge was perfectly flat on the workbench and did this all on top of parchment paper.

After I let that cure and trimmed back to 3/32" again, I was quite impressed with how strong that alone made the trailing edge. Even that thin layer made the trailing edge quite stiff, even more so than with heavier glass, but still extremely thin.

I noticed that there was still a triangular space or void that would be formed between the top and bottom layers of glass as they extended back from the trailing edge. That would normally just be filled with resin when I did the top layer of glass, which would help strengthen it. Why not attempt to fill that with more carbon? For this application, I only used about a 3/16" wide section of tow which I just peeled off from the 1/2" wide tow that I have. After again soaking with epoxy, it naturally rolled itself up into a long thin cylinder about 1/16" in diameter. I carefully laid this in directly behind, and touching, the balsa trailing edge, and then ran my finger from root to tip to compress and mold that strip to bridge the gap from the top of the balsa trailing edge to the rear edge of the glass overhang, and do so in a shape that followed the airfoil curve of the top of the wing. I already had the wing propped up so the trailing edge was flat, on parchment again, so covered the wet carbon with a strip of parchment, then a flat piece of wood aligned tangent to the trailing edge airfoil, and finally weighted that down until cured.

After trimming back to 3/32" again and a little touch up sanding, it came out true and sharp. It's also stronger/ding resistant than the glass would ever be, or even balsa for that matter. I can hardly wait to glass the top of the wing now and get the wing finished off!
Last edited by rjtw; Apr 26, 2012 at 01:47 AM.
Apr 26, 2012, 10:47 AM
Kinetic Sculptor

Now, THAT's clever!

I usually try to put a strip of 2-oz. cloth between the top and bottom skin when sheeting the wing, but this looks much more stout than that. Well done! How much for an individual license for this technology?
Apr 26, 2012, 01:57 PM
Registered User
Duane! I just discovered your Loki build log yesterday by accident. Now THAT is how you build an EF-1 racer. And about 10x faster than I'm doing it.

For anybody that hasn't seen Duane's log, if you like my build log at all I guarantee you will love Duane's:

PS Duane, if you use my carbon technique I'll "license" it to you for a beer
Apr 26, 2012, 02:03 PM
Registered User
By the way, has anybody used a Tru-Turn electric spinner? How's it hold up under high RPM?

And now they have a spinner with cooling slots cut out...

Do you think, given adequate cutouts on a front-mount and otherwise good airflow, that I could rely on "spinner intake" alone for adequate cooling? It would be great to not have to cut into those glass cheek cowls!!
Apr 30, 2012, 05:30 PM
Registered User
Finally got the top surfaces of the wing glassed late last week.

Note to self... next time don't wait so long between doing bottom and top surfaces (edit: a week)... got a slight bow from shrinkage on the bottom side. Should have known better but this is what happens when you take a 30 year break from model building. I was stunned to discover this, even given the very high spanwise rigidity of this wing including carbon tow reinforcement. The good news is that the top is already "shrinking to fit" and has all but erased the bow so I think I've dodged at least the worst of that bullet... I'll give it another day or two with fingers crossed that I'll end up with that trailing edge straight as an arrow again and move on to a final resin coat and cutting loose those ailerons.

I was also very pleased with how well the TE came out with the glass coat on both sides now. I was a little concerned that I'd end up with a slight reflex to the airfoil, as I extended it out quite a bit, but as far as I can tell it's a seamless extension of the airfoil back to a point. (Remember, the trailing edge started out as 1" aileron stock, but the trailing edge of the sheeted core was so thin to begin with that I had to remove at least a third of the thickness of the leading edge portion of that aileron stock... so the ailerons have a very thin taper). Even if I later discover a small ripple or reflex, I can take care of it between the final resin coat and/or sanding back the TE extension as necessary. Maybe I'll gain an mph or two this way :-) But now I have 1 3/32" ailerons instead of 1"!!
Last edited by rjtw; Apr 30, 2012 at 07:53 PM.
Apr 30, 2012, 06:25 PM
Kinetic Sculptor
Excellent, sounds great!

The resin must be polyester if it's shrinking that hard. I've only used it once, 30 years ago on another QM15 -- Jim Gager's Estrellita kit. Beautiful plane, but I almost buried it on the first flight because the wing was warped so badly.
Apr 30, 2012, 06:41 PM
Registered User
No, that's the strange part, it's epoxy resin -- from Z-poxy. Maybe should have gone with the more expensive stuff I was discussing a few posts back rather than something I found at the hobby shop... BUT hopefully no harm no foul in the end, and no twist warp induced at least, that was the first thing I checked after I discovered the issue!!
Apr 30, 2012, 07:14 PM
Kinetic Sculptor
Well, color me surprised. I use Z-Poxy. But I always do both sides within 48 hours, so I guess I should keep on doing it that way.
Apr 30, 2012, 08:50 PM
Registered User
RJTW - I have one of these planes, in slight disrepair. I bought it last year from a guy that crudely converted it to electric. He must of had a love affair with the hot glue gun. I started to clean it up and rebuild, but didn't get to far with it. I am probably going nowhere with the thing, I would offer it up for almost nothing for parts if you were interested. The wing and fuse seem to be in somewhat decent condition, except the guy hot glued two $3 servos into the wing that will need to be carefully removed. I am in Golden, CO.
May 03, 2012, 02:58 PM
Registered User
Thanks for posting Rifraf, I have my hands plenty full with this one but good luck with yours. Would be great to fix that up nicely and return it to life.

Update -- top side seems to have shrunk equal to the bottom in the end!! I was really sweating that one. Now that I can keep this wing I've gone ahead and given it a fill coat of resin, thinned about 20% with acetone, and sanded most of it back off. I have a couple of touchup areas waiting to dry now, then a final sanding and I'll cut loose the ailerons. I've also picked up some Duplo high-build primer (Thanks Duane, I think I got that from your build log) so will be able to shoot primer soon!
May 05, 2012, 11:12 PM
Suspended Account
Never thought the little Toni was a high performance plane
But I guess it is as its unbreakable in th e air

I got the nitro version with 91 surpass and it's fast

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