Prather QM Little Toni build thread - Page 8 - RC Groups
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Nov 02, 2012, 12:48 PM
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Nov 02, 2012, 07:00 PM
Kinetic Sculptor
Originally Posted by rjtw
[A]fter explaining all this to the nice folks at Neu Motors, they have graciously agreed to build me up a new motor with a 5mm shaft ... [T]hey obviously really care to see their customers succeed. THANKS NEU MOTORS!!
Wow, that really is outstanding service. And, who knows? You may have planted the seed for a new and improved product offering for this type of model. It's a win-win!
Nov 03, 2012, 03:36 AM
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Pushrods & Servo rails

Yes... win/win indeed. I'm looking forward to firing that motor up. I'll be at something like 1500 watts, which is going to be 2.5x to 3x the power that the old Conquest ever made. It's going to be a whole new ballgame!

Moving on to getting that stabilizer installed... The stab traps the elevator joiner, you have to make at least the elevator pushrod prior to installing the stab.

I thought about using the original dowels, but had some carbon fiber tubes lying around that were both stronger and significantly lighter (and should also better match the coefficient of expansion of the fiberglass fuselage better than wood, meaning less elevator trim changes with weather changes). I cut a 1 1/2" piece of fully threaded 2-56 rod, threaded 1" into a further 1.5" piece of small carbon tube just big enough to hold the rod (about .115" OD), and slipped that into a larger carbon tube of .115" ID/.155" OD that forms the main pushrod with epoxy on all parts. Should be plenty strong. On the rudder pushrod, pretty much the same except I used a longer rod and used my Dremel cutoff to make some gouges near the end of the (unthreaded) wire to give the epoxy something to grab into.

I decided to position the two servos in the fuselage as far back as I can conveniently place them (basically the rear part of the servo will be vertically above the back of the wing saddle cutout) to give plenty of room for the battery. According to my quick CG test with motor, spinner and tail installed, but nothing else, the airplane basically balances at the required CG already -- which is great -- so the battery will have plenty of room right at the CG location (2" back from the leading edge). I then marked the center/thrustline down the side of the fuse, which happily provides a good reference position for the intended final position of the elevator and rudder pushrods, and from there calculated the position of the servo rails -- while leaving enough room for the aileron servo and torque rods, which stick up at max about 1" above the wing. You can just see the reference marks in the photo. The elevator and rudder servo arms will end up at the thrustline, but the tail ends of the pushrods are about 1/2" below the thrustline, so I also calculated in a very slight angle for the servo rails to line up with the pushrods.

Finally, I made a small 1/16" plywood plate and epoxied it in the fuse just underneath the stabilizer cutout. This will provide a little extra stability and also a whole lot more surface area to which to attach the stabilizer later. I have the stab loosely fit now, with the elevator pushrod connected, so this weekend I'll get it positioned the way I like and then glue it in.
Nov 04, 2012, 02:06 AM
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Stabilizer position

Everybody has their own favorite way of making sure wings, fin and stab are all square. Usually I measure corner-to-corner and eyeball it from there, at least on the stab. For the Toni, I wanted to get the stab lined up just right so did a little extra setup. At the end of the day, though, I eyeball everything very carefully. The eye can catch some tiny differences that are sometimes hard to measure.

First, incidence... I made sure the stab slot was cut at 0 degrees incidence to the wing. The 0 degree line on this airplane runs from the prop shaft to 5/16" below the leading edge of the stab. I marked the line and ensured the stab cutout was parallel. And, frankly, Terry makes things pretty brainless by molding in a small dot right at the leading edge of the stab on each side, and another right at the trailiing edge, which form another 0 degree incidence line. That was the easy part.

Next, I put the stab in loosely in its slot along with the elevator joiner connected to its pushrod. I bolted in the wing. I had to wait to set the stab until after I finished doing the wing saddle a week or two back, as that cements the relationship of wing to fuselage. Also, I had already established during the wing mount phase that the leading edge of the wing is exactly square to the centerline of the fuselage -- e.g. measuring from wingtip to tail end of fuselage is exactly the same both sides.

I put the airplane on a glass table -- something big enough to hold the whole airplane and perfectly flat. I blocked up the low wing until both wingtips, measured at the trailing edge (which is a sharp point and thus easy to measure accurately) were exactly the same height above the table.

I use some combination of an 18" metal ruler, 1 meter metal ruler, and 12" square for all the various measurements. When measuring distance back from the table edge or distance off the table, I make sure I'm always at 90 degrees in all dimensions.

I also squared the leading edge of the wing relative to one side of the table, by measuring from the leading edge to the table edge both wingtips. I then taped the tail skid down to the table to help prevent any movement.

Finally, I squared up the stab with three measurements: First, centering the stab in the fuselage by measuring from fuselage side to stab tip along its trailing edige and making left and right the same; second, by measuring wingtip trailing edge to stab trailing edge both sides; and third, by measuring the distance of each stab tip off the glass table. As any adjustment in any direction affects all measurements, I repeated each measurement if I made an adjustment. I used some blue painter's tape in a couple of spots on the stab to keep it in place once I got close, and then could just press a bit in one direction or the other for fine adjustments. Oh, I also double-checked squareness by measuring the distance from the edge of the table to the trailing edge of the stab both sides, just to make sure the stab was also exactly square to the centerline of the fuse when viewed from above.

After all that, I double-checked by eyeballing from about five feet directly behind the airplane. I've always found this to be the most accurate measurement of them all!

I was lucky this time, as I did not need to make any further adjustment on the stab relative to the wing (the stab tip height was exactly the same each side) -- otherwise I would put a little block under the low tip to prop it into the right position.

Now the tricky part: The stab is in, there's tape everywhere, but no glue! I knew I couldn't just coat this thing in glue and slide it in, so went with this dry-fit method. Instead, I used a toothpick to place a thin line of epoxy inside the fuselage along the top of the stab, where I have access from the vertical stabilizer cutout. This is just enough to keep it in place. As a next step, I'll come in later, mask off the stab and fuse and leave only a 1/16" or so line along the mounting line top and bottom, and squeeze in plenty of epoxy -- especially to fully cover that plywood plate just underneath the stab.

A side note on epoxies... I almost never use anything faster than 45 minute epoxy because I've found that the faster the epoxy, the sooner it turns into gummy rubber and starts disintegrating. I will rarely if ever touch the 5 minute stuff as in my experience it starts changing color and going soft within just a few months, at least in warmer climates. I also tend to mix at least 1/8 ounce or so at a minimum, even for small jobs, just to help increase my accuracy in getting the epoxy and catalyst measured out in the correct ratio... if you have even a little too much of one or the other, you're again going to face decreased lifetime of the finished product. I've occasionally weighed out each component (by keeping the mixing cup on a gram scale) for the most important jobs.

Next up... I have some final fitting and sizing of the vertical stabilizer to do... as right now with the rudder attached to the vertical stab, the bottom edge of the rudder doesn't reach all the way down to the bottom of the fuselage. I'll have to shorten the vertical stab (by trimming its base, where it fits against the horizontal stabilizer) just a little bit. I still have to trim the wheel pants too. Then it's on to more primer!!
Nov 12, 2012, 11:57 PM
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(edit... will repost later)
Last edited by rjtw; Nov 13, 2012 at 01:44 AM.
Feb 01, 2013, 12:34 AM
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Time to catch up on this thread.

First, some early experiments I did on the "exhaust" (functional hot air outlets). I used my first attempt at molding the left cowl as a mule...
Feb 01, 2013, 12:45 AM
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I didn't like how that turned out, so went with fabricating some carbon fiber tubes of various sizes instead. I finally found a look I liked with this. Tubes are cut about two inches long or so and extend inside the cheek cowls. I shaped them to match the inside of the cowls by using my first cheek cowl mold as a guide, then tacked them in place to shape the cutouts in the cowls, and finally them removed until after painting is complete. I'll finish the inside of the tubes with clear so the carbon weave will really pop and have a nice contrast with the exterior finish. They're about 5/8" diameter each side.

It is fun to make these little tubes... they're so strong it's silly...
Last edited by rjtw; Feb 01, 2013 at 01:07 AM.
Feb 01, 2013, 12:27 PM
Kinetic Sculptor
Wow, that is CRAZY GOOD WORK! What's the powerplant again? I have a Prather Toni and a Jim Gager Estrellita, too. They've both been sitting untouched, but that may have to change.

BTW, those pinholes in the finish are best handled early in the process. What you can do is rub ordinary vinyl spackling paste over the raw glass fuselage using a piece of an old cotton sheet or T-shirt, then sand the whole thing with #100 drywall screen. Too late on this one but you can try it on the next one.

I have no other building tips to share with you, since you've already mastered everything I ever learned in 30 years plus a whole lot more. Thanks for the awesome demo!
Feb 01, 2013, 12:40 PM
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DHG - don't forget, we know where we can lay our hands on a Folkerts and a Polekitty... and a Stinger or two, maybe.

But there's no way I'd ever post build thread pictures. Not after watching the artist building this one! Wow...
Feb 02, 2013, 01:07 AM
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Kevin Matney's Avatar
I still make Q/15 kit for sale too.
Feb 05, 2013, 01:33 AM
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Thanks for the kind words! And spackling paste -- that's a great suggestion. Will definitely do that next time around. Thanks, DHG!

Here's the new Neu, by the way... it just came in today. It's an 1115/1Y upgraded from the stock 3.2mm to a 5mm shaft by the great folks in San Diego. Can hardly wait to get it hooked up. The calculator says it will be good for about 34K RPM on a 6x5 or 6x6, pulling about 100A from a 4S.
Feb 05, 2013, 03:59 PM
Registered User
Hey DHG, if you have an F1 size Prather kit you'd like to sell, let me know. Its larger size would be a great platform for shooting north of 200 while retaining the classic racer look... and also a great platform for one huge Neu...
Last edited by rjtw; Feb 05, 2013 at 06:17 PM.

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