Prather QM Little Toni build thread - Page 2 - RC Groups
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Mar 11, 2012, 03:52 PM
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I always loved the little extractor pipe too coming out of that cowl... it just screams speed.

LOL - that's not all they screamed! The 15's and .40's with the mini pipes were loud.. they sure sounded like race planes!
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Mar 11, 2012, 08:52 PM
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Oh no!! I had two instances where I loaned out plans or rib templates and never had them come back, but an entire airplane -- ouch. I will say this though, that as a young modeler I had far, far many more instances of great kindness. I do my best to repay it to the next generation as I can. Strange thing is, out at my local flying site there are few kids, it's all a bunch of the older generation. Something about instant gratification I think

Originally Posted by ViperZ
Oh man... Back in the late 70's I had a Curare with a Webra Speed 60 rear Exhaust with a tuned pipe that exited the canopy. I bought ROM Air retracts for it and gave all the parts to a fellow club member to construct... He left town during construction with no where abouts. It was a total loss

One of those life lessons... It would have been slightly more gratifying to fly it into the ground
Mar 11, 2012, 09:35 PM
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Next steps

I'm taking a small breather now to think about how I want to handle the next series of decisions needed before I epoxy the wing halves together.

Take the landing gear. The gear is hefty dural aluminum, single piece, with two holes to L and R of center. The two forward wing hold down bolts (nylon) go through these holes. The plans call for first joining the wings, then cutting away a rectangular patch of the bottom skin just behind the LE and sinking in a 1/8" plywood plate low enough such that the forward edge of the gear is at the outer level of the sheeting. Later, two dowels are centered over the holes on the top side of the wing, going down to the plate. The dowels transfer the bolt clamping force to the wing saddle, prevent the wing getting crushed, and also help hold the gear in place. Finally, after glassing the wing, the dural gear gets epoxing into place and covered with a fillet of epoxy and micro-baloons. As such, the gear gets pseudo-permanently embedded in the wing. Or at least until the first rough landing!

However, I'm not entirely sold on this idea. If the gear were to get torn out, it would take a huge chunk of the wing with it. Not only that, shearing off those two forward bolds would almost guarantee that the wing will separate as well, likely causing further damage to the rear bolt area (which only is supposed to go though the relatively thin aileron stock at the very back). Even discounting that possibility, this raises some construction and finish issues. First, cutting out the center section is going to be hard to do with any precision once the wings are joined -- getting the gear truly aligned with the centerline of the airfoil, as Terry requires, is pretty hit and miss at that point. And digging through the cured epoxy in the center joint is never good. Second, once you epoxy in the plywood plate, you're then supposed to go in from the top to drill out holes and then epoxy in 1/2" dowel sections. But the top side of the plate is going to be covered in gobs of epoxy, mirroring the shape of the foam underneath (very rough) so there's no way those dowels are going to make flat and direct contact with the plate (though I guess you could put the dowels all the way through the plate). And third, I'm not sure I want to be sanding and then painting around the legs of the landing gear sticking out of the bottom of the wing -- the chances I'm going to be able to achieve a uniformly smooth and mirror finish around there is about nil. I need big smooth straight areas to use that big sanding block!!

Viper, I kind of like that photo you posted of the Little Toni in the hobby shop. You can clearly see from underneath that they simply bolted on the gear using the wing bolts only, apparently directly on the surface of the sheeting. (It's hard to tell but it doesn't appear to be sunk in the wing at all, and it definitely isn't covered by a big fillet). I think what I may do is carve or route out the rectangular area similar to that called for by the plans, but do it before joining the wings so I can guarantee everything is parallel to the wing centerline -- or alternately set up a special jig with my Dremel to route it out afterwards and just not use much if any glue in that particular spot when joining. Then, I'll make the gear removable, but actually do up the fillet only on the dural gear itself. The wing bolts will hold the gear to the wing and the wing to the body. I may even go to metal bolts rather than nylon -- hard to tell what would result in less damage in a hard landing/crash but I might feel more comfortable that way. The end result should be indistinguishable from that called for by the plans, but will be easier to construct and finish. I've also thought about substituting carbon gear for the aluminum, so I'll do a little looking around and see if there's a close substitute out there anywhere.

Another issue is servos... I want to go with two servos in the wing, one for each aileron (that way I can get both precise adjustment of each aileron and also do spoilerons or flaperons). I'd like to get the servo bays cut out before I epoxy the wings together (again because I do not want to be cutting through a cured epoxy joint!) but I haven't quite decided on servos yet. Ideally the servo will be shallow enough to be able to mount aft of the high point of the wing, sink the mounting tabs flush with the sheeting, but not touch the bottom sheeting.

I'm considering Futaba S9650's all the way around but need to confirm they will fit. Great torque (about 50 oz-in)and speed, relatively small package, coreless motor/digital, but perhaps a tiny bit on the heavy side (15/16 oz). There are some other analog servos out there in the 40 oz torque range that are a bit lighter too... like JR MN48 -- even 40 oz I'm sure will be plenty... but if I can save an ounce or even the better part of two ounces on four servos if I can get adequate torque/safety from servos in the .5-.6 ounce range each. Any servo recommendations?
Mar 11, 2012, 10:28 PM
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Install the ply in the wing and use the nylon bolts, don't bother with mounting the gear to the wing. In the rear use one 10/24 nylon bolt in the center. Don't use metal bolts, the nylon will shear off without too much damage. For servos 9650's for ele and one on the ale., two servos on this plane for ale. is going to be too heavy and too big to mount in that thin wing. Flaps or spoilers are not needed. Keep it light, they will slow down.
Mar 12, 2012, 01:10 AM
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Thanks for the advice Promod... KISS may be the order of the day here in that regard! :-)
And I can save an ounce while I'm at it too with only that single aileron servo. Appreciate the feedback, this is obviously my first little racer!!
Mar 12, 2012, 01:41 AM
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Note on TE shaping

I forgot, I never posted about what I felt ended up being the hardest part of sanding the wing -- the trailing edge!

Many if not most trailing edge designs that I've built in the past have, in cross-section, essentially straight lines from somewhere just in front of the aileron to the very trailing edge of the aileron. The ailerons themselves then have perfectly flat (noncurved) upper and lower surfaces that blend in with the section of the wing immediately forward of the ailerons.

Not the Toni! That tip section never gets much thicker than the aileron leading edge itself. After gluing on the aileron stock at the back and using my sanding block to sand in a continuation of the smooth contour of the wing proper from front to back, taking that countour straight onto the aileron, I was left with an abrupt transition from wing to aileron. Picture the top and bottom skins almost parallel as they meet the aileron stock, then the sudden transition to the wedge shape of the aileron. Not good.

To add to the problem, the root section actually blends in almost perfectly with the aileron taper. Again we have a compound curvature.

I was leery about simply "rounding" what amounted to a hump, that sudden transition near where the aileron met the wing proper. But if I left it as a sudden transition, I'm sure it would cause drag, turbulence or instability, in addition to just plain looking bad. Gloss paint would make it show up like a sore thumb. Another way to try to make that transition would be to leave the wing proper largely untouched, but blend in most of the curvature into the aileron area itself. The ailerons in cross section would then not be a straight "V", but more of something like a "U" albeit coming to a sharp point at the bottom. I generally don't think that curving the top and bottom surfaces of the aileron itself is a good idea, though. As the ailerons stop well short of the tip anyway, though, I ended up reasoning that it's likely OK and frankly there is little choice in how to proceed.

I ended up really doing a bit of both... I just took my time over the course of several evenings, used my big sanding block, and kept making light passes over the transition area until I could no longer feel or see any sudden or sharp changes in camber. I also used my calipers to measure TE thicknesses on both wings at several locations to make sure I was on track. It ends up that I thinned out the sheeting towards the TE of the foam cores, almost imperceptibly, and also spread that curvature out over most of the aileron. And that curvature disappears more and more as you move away from the tip until it's gone somewhere perhaps a third of the way out from the root.

I guess the proof will be in the pudding once I get that gloss paint on, to see if it's truly invisible, and in how it flies, but I'm pleased with how it came out. You can see it in the tip pictures I posted a little bit back.

Sure makes me jealous of all you carbon-wing guys who have these perfectly mirror-finished wings coming out of machined molds with airfoils precise down to a few mils... with ailerons pre-hinged to boot...
Mar 12, 2012, 01:34 PM
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when I built F1 and .15QM planes, I did it a little different.

Cut out the bottom sheeting of the wing to allow the gear to set in where you want it. I lined the edges of the cutout with 1/16" balsa, might consider a piece of 1/16" ply on the back edge(vertical).

Dig the foam out clear to the top sheeting, but don't cut out the top sheeting.

Cut the 1/8" ply for the l/g to set on so it fits in the hole you've cut and lined.

Mix up a batch of epoxy and filler, we used to use something called Viscofil, I think. It's harder than microballoons. Pour the glue into the cavity with the wing upside down and level. Pour in enough to allow the 1/8" ply to "float" on the glue, but not any more than that. Let it all set up, and you now have a hard point between the gear and the fuse that you can drill through.

If the bolt holes in your l/g are far enough apart, you could put in another flat head 10/24 bolt in the center of the ply plate, countersunk flush, so if you do knock the gear off, the wing is still bolted to the fuse. The ply 1/16" vertical piece at the rear helps save the wing from much damage if you do land hot and knock the gear out.

Easier to do than it is to write about..
Mar 12, 2012, 02:37 PM
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Thanks Fizzwater, that explanation makes perfect sense and it's very straightforward. Removing all the foam and filling with epoxy makes a broad stable hardpoint to transfer force right into the fuselage, not the wing. The floating idea is great!

What do you end up doing with the landing gear -- is it held in place only by the two wing bolts then? Do you put any type of fillet over the base of the gear to cover from the front of the gear (where I guess it would have little or no thickness) to the little bit of vertical plate at the back? Maybe I could make the fillet attached only to the LG itself, the whole thing would still be removable but would blend right in once bolted in place.
Mar 12, 2012, 03:03 PM
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dkane's Avatar
I did the same thing a little different...

I don't remove all the foam. I remove just enough for the 1/8" plate to sit flat and have the gear flush with the outside of the bottom skin. I then glue this plate to the foam with 5 minute. Next I mark the front wing bolt location through the gear by drilling a small pilot hole all the way through the top skin. Next I take a dremel sanding drum and cut round cylindrical hole throught the top skin and foam up to my 1/8" landing gear plate. (make one for each wing bolt) What you end up with is two holes up to the plate. Now I fill these two holes with wooden dowels and epoxy. After the epoxy sets up I grind the top of the dowels to match the airfoil. Next mount the wing as normal and I glass the center section as normal.

I also think the 1/16" vertical spar at the rear of the plate is critical to not tearing the whole thing out in a hard landing. Nylon bolts are also very important!

Just a different way to do it. Fizz's way works as well.

Mar 12, 2012, 05:44 PM
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You can make a filler block out of balsa if you'd like, but I usually didn't go to the trouble. I've seen blocks that were glued to the gear, or blocks that taped in place over the mounting bolts.

I liked the third bolt between the two gear mounting bolts into the front, I recall that it might have saved a plane once, but that's been about a hundred years ago. Knock the gear off with a high speed bounce, and the wing was still bolted in place..
Mar 12, 2012, 05:57 PM
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PylonDave's Avatar
Fizz , I did that on my little Toni EF1 as well. The third bolt as well.
Mar 12, 2012, 06:19 PM
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Awesome -- thanks guys -- great ideas! I'm itching to get back to work on it now. Ordered 3 9650s today and an aluminum spinner. And based on some other threads in this forum, I'm seriously considering the Hyperion zs3025/6 as an alternative to the eflite Power 25. The plane won't be NMPRA legal to begin with (and I don't intend to race at this point) so no need to stick with the approved motors. But the Hyperion is said to be fine on both 4s or 5s, which gives me room to go 5s if for some reason I become a speed maniac. I'll front mount it if I can; that seems like the simplest way to go.
Mar 12, 2012, 08:07 PM
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Engine thrustline

Looking ahead a bit here but instructions call for mounting the engine by lining up the spinner backplate with the molded front of the fuselage. Looks like it's 0-0. I plan to follow it unless some of you have seen a need otherwise.

Did anyone feel there was any need for any different right or down thrust? How about the current generation of electric pylon racers, any right or down?
Mar 12, 2012, 08:55 PM
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Kevin Matney's Avatar
Just build it 0,0,0.
And you will be very happy,I have some other Q/15 kit I make electric power
Mar 12, 2012, 09:00 PM
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Kevin Matney's Avatar
I cut a hole were the pipe went to put in the battery pack and cover it with the check cowl

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