Prather QM Little Toni build thread - Page 4 - RC Groups
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Mar 21, 2012, 01:10 PM
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Hi Izzy,
Great to hear you're starting the Toni!

Not sure what you mean by microglass though -- is that lightweight fiberglass cloth? I wouldn't use anything like glass on the inside as I think it would be too heavy. I guess the guidance I would give would be, to the extent you go above and beyond the instructions, to keep low weight as the biggest priority. Can't go wrong with carbon tow though, as that's going to provide a big boost in strength with virtually no weight penalty whether you glass the entire wing later or go with film.

Just curious, what glue to you intend to use to bond the skins to the cores, and are you going to glass the entire wing later?
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Mar 22, 2012, 12:11 AM
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Hi Rick
i was looking at my Q40 plane from Big Bruce Racing, and he uses microglass ( yes very light glass) both on the inside and outside of the skins , ( the wing is composite) so no foam, but the foam has really no weight
my plan is also to use skin hinges ( never did this before) so that will be a challenge

i am planing on using epoxy resin to gue the skins

i really like your build thread it helps me a lot, so i am hoping to make a build thread of mine too but will post in pylon forum, as i plan to use a rossi f3d motor and pipe or q40 nelson motor for power plant

just hope i can build as nice as you
Mar 22, 2012, 12:45 AM
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Well good luck on that Izzy, that Rossi will be cool and I'll definitely look forward to your build thread. I think skin hinges are great too but just no experience there so will be interested in how you do that. Are you going to vacuum bag it? In any case please post a link here when you start it!!
Last edited by rjtw; Mar 22, 2012 at 01:16 AM.
Mar 22, 2012, 01:16 AM
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Landing gear (cont'd)

I epoxied in the landing gear plate and plywood reinforcements tonight (but sorry... no pictures!!)

I wanted some additional strength around that plate and was thinking about whether to fiberglass over the plate and on to the fore and aft plywood pieces to really make a single strong unitary structure, but the dural gear is a nice snug fit as it is and the additional thickness of the fiberglass would have just been too much. The gear would not have fit in any more without some serious filing. The plywood plate provided in the kit is really just exactly the fore-aft width of the base of the landing gear and no more.

So instead of putting fiberglass on the outside, I thought I'd put it on the inside. I got out some 6-ounce cloth and cut it up into small fibers -- perhaps 3/8" long or so on average -- then mixed that up with a batch of 45-minute epoxy. This kills two birds with one stone, as this is both stronger and lighter than plain epoxy would have been. I put in enough fibers so that it really comes out of the mixing dish almost like one big mat. After separately epoxing in the four ply sides of the little box area, I scooped in and leveled out this big fiberglass mat. I had previously marked where I wanted the plate to end up, so I knew about how much to fill the bottom of the box and just slightly overfilled. The plate almost touches the top sheeting in front, so it's pretty thin up there but gets thicker as it goes back. I then put the landing gear plate on top, carefully pressing down and in. I figure I got in just about the right amount of epoxy to ensure solid contact all the way round because the excess seeped up around the left and right edges of the plate (and eve a bit leaked though the sheeting joint on the top of the wing). I used a piece of sheet balsa scrap to carefully wipe all the excess out of the corners and let it start to cure. Just as it was starting to set, though, I put the dural gear in place once more to verify that the gear was level and square and left the gear on until final cure.

Later on for fun I stuck everything on the scale... wings, gear, fuselage, all remaining parts and hardware, servos and a 2650 4s battery. The only major component missing is the motor and ESC. Weight was 2 pounds 1 ounce. The Hyperion motor weights 7 ounces. (The old Cox Conquest 15 weighed a little over six ounces, almost the same, but the LiPo weighs more than the 4 oz fuel tank would!) Subtract some balsa dust for shaping the tail, add in glass and finish weight... and am going to have a hard time meeting the old QM 2.5 pound minimum weight... though that was not including 4 oz of fuel. I could always save some weight by going to a smaller battery if needed. If I do allow myself to shoot for the old minimum weight plus a full fuel tank, or 2 3/4 pounds, that means I can give myself about 4 ounces for the glass and finish which should be more than enough. Must definitely continue to work on keeping weight down during the build!!
Last edited by rjtw; Mar 22, 2012 at 01:28 AM.
Mar 22, 2012, 01:41 PM
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Motor choice?

What's a good motor choice? I'm starting to wonder whether the Hyperion ZS3025-6 may be too much motor. The Conquest .15 back in the day was rated somewhere between .6 and .8 horsepower according to the best information I can find on the Web, or about 450-600W, though it's unclear what version is referred to and it's possible the QM-tuned engines produced more.

Here are some interesting links on the Conquest: (including original power test 1977) (still being produced?) (interesting discussion from a few years ago)

The Eflite Power 25 is advertised as suitable for models "requiring up to 850W". The Hyperion is rated with a "max power" of 1500W. The speed freak in me wants to go with the Hyperion but it may be almost triple the power of the power the airplane was designed for. I'm glad I put that carbon tow in the wings -- I'll have to do the same on the stab and maybe the nose too!

Comments on a good motor choice?
Last edited by rjtw; Mar 22, 2012 at 02:11 PM.
Mar 22, 2012, 05:31 PM
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motor choice

Rick hi
i am not sure what props the .15 ran at the time, but from on of the links you posted , a 7x5 cut down a bit seems the prop

i have been using the turnigy 3648 1450kv motor with 8x8 prop on 4s and 4000mah motor for aprox 4 1/2 minutes flight. motor is fairly cheap aprox $25 or so

depending on what prop you need , this might be a good choice
i used this motor with 2 other set ups
1 - 5s 4000 mah 7.4x7.5 q40 props

i am also using this same motor on a funjet with 6s and 6.5x6.5 prop for extreme speed but time is limited to 2-3 minute flights as i am using 6s 2650mah 45c batteries

hope this helps

sure want to see this project complete
Mar 22, 2012, 07:02 PM
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Thanks Izzy -- will look into that motor.

By the way, I was thinking about using composites with skin hinges etc. and ran across this:

This company sells a bunch of different composites products but also has an extremely helpful set of tutorials including how to bag composite wings. Very interesting. Makes me want to do a full carbon wing
Mar 23, 2012, 11:33 AM
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build thread F1 prather

Rick hi
as promised , started thread in pylon forum , but progress on my side will be slow
prather F1 with Rossi 40 F3d motor
Mar 23, 2012, 03:00 PM
Need 4 Speed!
pdawg's Avatar
Great build thread Rjtw! We need more threads like this!
Latest blog entry: original Y/A F-18 Kit
Mar 25, 2012, 01:54 AM
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Only got a little done this weekend. I think I'm at that stage where progress seems to slow to a crawl as you deal with various detail work. I made the initial fit of the wing to the fuselage after trimming the center trailing edge. The wing chord was just a little too big to cut flat across the center trailing edge, so I ended up with about a 1/8" notch there.

The next step Terry calls for is to drill through the wing mount areas, install corresponding blocks in the fuselage, and sink 1/2" dowels from the top down to the landing geat plate. I don't have a 1/2" drill, and even if I did don't think that would be the best way to approach it. I'll check out my hardware store to see if I can find a 1/2" hole saw, though I doubt they have anything that small. If all else fails I'll get some 1/2" brass tubing, grind it sharp, and grind some teeth on it to cut out those big holes. I'd like to have the dowels go down flush against the landing gear plate, not through it, and it's going to be a little tricky to get through all the fiberglass I backfilled in there now! I thought about whether to try to place the dowels at the same time I put in the landing gear plate, but getting them fitted in just the right place (and also preventing epoxy from leaking out around the dowels!) would have been tricky.

So I'm punting on that for now and moved on to the tail surfaces. Terry uses what I think will be a great construction technique -- he calls for placing a 1/4" strip of 1/64th plywood at the outside edges of all surfaces. The balsa comes pre-slotted for the plywood. This should make shaping the tail surfaces down to almost a knife edge a piece of cake, and keeps the edges strong as well. For tonight, I cut and fitted all the strips in place and will use thin CA to glue them all in next time.
Mar 25, 2012, 10:16 AM
Registered User
Originally Posted by rjtw
What's a good motor choice? I'm starting to wonder whether the Hyperion ZS3025-6 may be too much motor. The Conquest .15 back in the day was rated somewhere between .6 and .8 horsepower according to the best information I can find on the Web, or about 450-600W, though it's unclear what version is referred to and it's possible the QM-tuned engines produced more.

Here are some interesting links on the Conquest: (including original power test 1977) (still being produced?) (interesting discussion from a few years ago)

The Eflite Power 25 is advertised as suitable for models "requiring up to 850W". The Hyperion is rated with a "max power" of 1500W. The speed freak in me wants to go with the Hyperion but it may be almost triple the power of the power the airplane was designed for. I'm glad I put that carbon tow in the wings -- I'll have to do the same on the stab and maybe the nose too!

Comments on a good motor choice?
When powering a QM-15, it is wise to consider the RTF weight. These models were 2.5lbs when raced and were designed to fly at this weight. Many of the power-systems are way overrated for what this model needs as they will make the model too heavy.

What kind of performance are you looking for and what do you want to spend? I have set up a few QM conversions with 36mm in-runners set to run 6-7" props and they performed quite nicely. What kind of flight time are you looking for?

Some of the EDF or Heli out-runners would be good choices as well. They might even offer a bit lighter installation. Something like a 450-500 sized Heli motor would be perfect.

I would stick to 3 or 4S. With the right motor combo, you can get a really quick model that flies well as it will weigh what it needs to.

Archie Adamisin
Muncie, IN
Mar 25, 2012, 12:10 PM
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Motor choice

I agree with Archie. I would look around at different set-ups. I have 3 qm15 kits I am going to convert to electric. The motor I was looking at is the Cobra c2814/10. According to the prop chart it will turn a 6x5.5e at 20711 rpm at 107.9 mph pitch speed on 4s. It also weighs only 3.84 oz. Keep up with the beautiful work on the Toni.

Mar 25, 2012, 01:38 PM
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Thanks for the great advice Archie & Bruce! I'm really excited that there are some other choices out there, especially that may be significantly lighter but still deliver the performance. And with a lighter motor than the Hyperion I was considering, I should be able to make that 2.5 pound weight RTF!

To help narrow it down a bit, I want to be able to fly at similar speeds as the old QM racers did. I think they ran a 7x5 prop at about 28K rpm which works out to about 135 mph pitch speed. I don't have any firm requirements on cost or flight time. I do have a few 2500 or so 4s packs lying around which I'd like to use if they're suitable. Do you think the heli motors you mentioned would be in the ballpark? I'll check on how much power they put out too.

Last edited by rjtw; Mar 25, 2012 at 01:44 PM.
Mar 31, 2012, 01:24 AM
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Hinging the ailerons

I've always hated hinging. It seems like no matter what, I can never get the hinge slots lined up just right, or the gap closed on the aileron quite as I like it, or the hinges are a little off center or a little too high or low, or the hinged surface sticks up somewhere. Oh, and don't forget the hassle with the glue. If it's an actual hinge, I'm guaranteed to get epoxy or CA into the hinge joint every time. And some people like to put slow CA on the hinge and then push it in... forget it, I'm going to get the hinge halfway in and then it will freeze up, necessitating some surgery.

CA hinges are better, but they're not quite perfect. It's usually not the hinges themselves, which thankfully cannot be frozen despite getting CA in the actual hinge area, but I still have the same issues with getting the hinge slots lined up (a constant) plus, because we usually glue the surfaces on after they are painted or covered, the drying CA then proceeds to make a foggy mess around the hinge joint. Oh, and let's not forget the old trick of putting on a little too much CA on a close-fitting surface (close fits are good, right??) and having the CA run into the contact between the surfaces. Yet another problem with frozen surfaces, and a hassle to clean up!

I'm waiting on some CF cloth to reinforce the center section of the wing, so I took the plunge and started the aileron hinges. I already had some CA hinge "cloth" on standby, from which I'll cut my own hinges. (I thought about maybe using the 30-year old original hinges... they appear as new... but I'd rather take my chances with CA hinges at this point.) I spent so much time on shaping the wing and ailerons that I vowed to take whatever time it took to get this done right the first time. Only one shot to get this right, there's no way to replace those ailerons if I screw up!!

I used the Du-Bro hinge tool -- one part lines up a cutting slot on the center of the part to be hinged, then you push in a special cutting blade to make the slot. What could go wrong?

I thought all was going great. The hinge slot tool worked as advertised and made nice pretty centered co-linear slots just as I had imagined. I did both wings, then one aileron, then went to test fit the aileron. And...

The CA hinge material practically fell out of each slot. And when I mounted one aileron, I could easily push the entire aileron up and down (not rotate, imagine keeping the aileron flat, but the whole thing moves up and down). What happened? The Dubro slotting blade was about 2x thicker than the CA hinge material!!

I could have gone back to the nylon hinges, or I could have doubled up the CA hinge (two layers fit almost perfectly) but no, I didn't want to settle for some stupid hinge compromise. So out came my Prather micro-balloons -- I knew I'd have a chance to use them sooner or later! -- mixed up with a batch of 30-minute epoxy. I found a plastic food container lid of about the same thickness as the CA hinge, cut out a bunch of hinge-size rectangles, and proceeded to glue them in place with the epoxy/micro-balloon mixture. After it cured, I yanked out each plastic rectangle, which didn't stick to the epoxy well, and this left behind a very nice hinge slot. A little work with my sanding block and it's finally back to where it should have been to begin with.

For the remaining aileron, I threw away the Dubro tool, got out an ancient 1/2" wide Exacto knife, and just eyeballed it on the front of the aileron. Came out better than any of the others

Did I tell you how much I hate hinging??
Mar 31, 2012, 01:57 AM
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Stabilizer shaping

I also got the horizontal stabilizer most of the way there tonight. As Terry instructs, I first glued in 1/64" strips all the way around the outside perimeter, then tack glued the elevator halves to the stabilizer.

I really do like the shape of the stabilizer on this airplane... nice sweep to the leading edge, a squared off corner where the leading edge meets the outside edge, then a small graceful curve around to the trailing edge, and just a hint of a curve where the elevators are cut in for rudder clearance. A great stabilizer design alone won't make a plane look great, but a plane can't look great without a great stabilizer design. I really love the lines of this airplane. But I digress...

I thought I'd try to document the steps I took in shaping. However, the pictures I took along the way don't really tell the story very well. I think it's almost like painting a picture... everybody has their own technique and there aren't really any rules. It's also, I think, a fairly nonlinear process in that there's a lot of checking, backtracking, doing the other side, flipping over, doing the other edge and so forth. I learned a lot from those whose planes I really admired. All I can recommend is, the most important thing is to have the right tools and a big workbench with lots of light, and take your time. And by the right tools, I mean at a minimum several long sanding blocks each with different paper. I get into nothing but trouble if I don't have my 18 inch block, and you can't get any uniformity with anything much less than a foot.

Terry also recommends an interesting shape to the stabilizer profile. Rather than just rounding the leading edge, Terry calls for sanding in an airfoil shape with the thickest part at the hingeline. It's an interesting airfoil to say the least! I love how the 1/64" ply strips at the leading and trailing edges not only provide an ideal center reference point, but also keep that area relatively strong even as you narrow the leading edge down to a long point.

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