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QB-150 Sheet Wing Racer Build

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QB-150 Sheet Wing Racer Build

Old 07-25-2010, 11:07 AM
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ProBroJoe
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Default QB-150 Sheet Wing Racer Build

It seems that I can't go more than a couple months without getting the itch to build something.

This design started out as the deisre to throw something together that would be sporty, but quick and easy to build. Originally it was going to be aileron/elevator only and have a built-up symetrical wing, but after a friend told me that it'd be just another "DNU type plane" (not that there's anything wrong with that), I decided to kick it up a notch and build it as a true Sheet Wing Racer.

The goal is still aileron/elevator only, about 150 sq. in., a ready-to-fly weight between 10-12 ounces, and to be powered by a Cox T.D. 049 fed by a 1 ounce latex bladder.

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Old 07-25-2010, 11:09 AM
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Default RE: QB-150 Sheet Wing Racer Build

Here we have the start of the basic wing layout.

My LHS didn't have 5 or 6" wide 1/4" thick balsa sheet, so I edge-glued two 3" wide pieces to a 1/8" x 1/4" full length spruce spar and cut the forward 1 1/8" off, resulting in a wing of 5" x 30". If you look closely, you can see my "no touch zone" layout lines that forms the high point of the airfoil. I've set this zone 1 3/4" back from the leading edge and it's 1 1/8" wide. If this looks wrong to any of you SWR experts, please speak up now!

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Old 07-25-2010, 11:10 AM
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Default RE: QB-150 Sheet Wing Racer Build

The basic "kit is cut out. No plans were used - model dimensions were carefully marked out directly onto the wood. The fuselage sides and sheeting are 3/32" medium balsa, bulkheads 1/8" balsa with a 1/8" birch ply firewall. Tail surfaces are 1/8" medium-hard balsa.

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Old 07-25-2010, 11:12 AM
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Default RE: QB-150 Sheet Wing Racer Build

Things started happening real quick at this point as I was on a roll, so I didn't bother to stop to take pictures. It's a simple box fuselage with 3/16" square stock in the corners, so it builds real fast using basic balsa construction techniques.

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Old 07-25-2010, 11:15 AM
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Default RE: QB-150 Sheet Wing Racer Build

Time to weigh the progress for a reality check.... Being that the wing is unshaped at this point and weighs over two ounces, I was quite happy to see that I'm sitting just a hair over 8oz with all equipment on board. A preliminary CG check also proved that I was in the ball park with this layout. For the record, this has been entirely TLAR up to this point. I was getting nervous about this little fact and ran the numbers - darn if things weren't spot on according to several online references.

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Old 07-25-2010, 11:16 AM
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Default RE: QB-150 Sheet Wing Racer Build

A bit about the onboard equipment - that's a Radical RC 400 mAh NiMh battery in there and I plan on running these Futaba S3114 servos - they're a little smaller than a HS-55, but put out a bit more torque. Don't know how well they'll fare, but there's only one way to find out...

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Old 07-25-2010, 11:38 AM
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Default RE: QB-150 Sheet Wing Racer Build

Nice Joe - I have one I built a couple of years ago for the NC races that is a SWR that looks about like yours only mine has a Black Widow due to the rules. It flew great, but was under powered - I like Norvel 061's
Looking forward to seeing how it looks when your finished. I have not been flying for over a year now - I guess a racer gets my blood going again.
Dale
Old 07-25-2010, 09:37 PM
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Default RE: QB-150 Sheet Wing Racer Build

That's real good progress! You'll have a speeding TD bullet pretty soon.
Don't forget to smooth everything in the bladder compartment. Any sharp edges will give the latex one more excuse to rupture.

Also, do as much of a mock up assembly as you can before closing up the fuselage, with this basic layout I've had a devil of a time getting enough weight forward....without resorting to lead.

I have had to place the battery right behind the firewall, which put the fuel closer to the CG.
It might have been a result of me building heavy, though.
Old 07-26-2010, 09:19 PM
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Default RE: QB-150 Sheet Wing Racer Build

Thanks for the kind words guys!

Worked a bit more on it this afternoon after work. No stellar progress like shaping a wing or nuttin', just busy work like rear sheeting, hinging the elevator (gawd I hate hinging 1/8" sheet!) and making some filler blocks for the vertical fin. Elevator pushrod is in - just need to come up with a clever way to mount the elevator servo flat without gluing it in (I'm open to ideas). Oh, started knocking off the corners too and I'm liking the way it's coming together.

RE: the bladder compartment - I'm thinking it's probably not a bad idea to either baffle it somewhat to keep the bladder from flopping around, or to fit in an appropriately sized cardboard tube - completely sealing the area from the rest of the plane. (I'm hoping that the longish nose is going to allow me to keep the battery under the leading edge of the wing.)

Time to dive into this wing, as it's pretty much holding me back at this point. So speaking of the wing CP, do ya think the "no touch" zone on the wing looks about right? I'm not used to seeing a high point that far back... or am I just thinkin' too much again?



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Old 07-26-2010, 09:53 PM
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Default RE: QB-150 Sheet Wing Racer Build

Joe, the high point of a speed plane airfoil should be back there like you got it. Try to form a smooth transitioning arc with no flat areas. Working the wood with strong light off to the side will reveal dips and flat spots. You'll see how easy it is once you dive into it. Once the 40 grit rough shaping is over, your 80 grit gets worked progressively closer from each end of the foil till you reach the no sand zone, then go ahead and wipe out those lines.
I'd just do a good job of fuel proofing the fuel cell before you put the lid on. You can smear the underside of the lid with epoxy before installing it. Epoxy can raise the grain of the wood and make it *****ly, so I'd do the floor and sides, then sand out any burrs before putting on the lid.
When the bladder is full, it doesn't take much irritation to pop it, so even just a swatch of napkin or TP can help if the bladders seem to be popping for no good reason.
You DO bring TP when flying these things, don't you?
Old 07-28-2010, 06:04 PM
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Default RE: QB-150 Sheet Wing Racer Build

Well, gee, that was easy. Frankly I didn't even expect to have time to work on the thing this afternoon and the next thing I know the wing's almost done! (Hence no "during" pictures again...)

In order to ensure I was planing nice and straight, I drew a series of span-wise lines, spaced about 1/2 to 3/4 of an inch apart - they helped, but I doubt they were even necessarry as the nice, uniform, full span curls coming from the razor plane were very reassuring. It didn't take much time at all to get the rough shaping done - 10 minutes tops. Time to switch to the heavy grit sandpaper.... that's when I realized all I had was 120 grit, so what you see here is the result of final shaping with 120 and a couple passes with 220. Not bad for a first time sheet wing if I must say so myself!

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Old 07-28-2010, 06:08 PM
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Default RE: QB-150 Sheet Wing Racer Build

While I was on a roll, I went ahead and cut in the ailerons. They're 3/4" x 9 1/2".... but now I'm at a loss, how in the devil am I going to install torque rods when these little boogers are only about 1/8" thick at their max height????? Time to raid my wire stash and see what I can come up with...

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Old 07-28-2010, 06:41 PM
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Default RE: QB-150 Sheet Wing Racer Build

Very nice Joe, but I'm not surprised. You're the kind of guy who dives in and gets it done.
At this point, I cut out the ailerons, install chunks of dowel for the wing screws, cut out for the servo, build the servo mount with the bottom of the servo flush with the topside of the airfoil.
The underside of the wing gets a strip of FG cloth applied with medium CA, then the trenches for the torque rods can be dug out. I make a digging tool out of a short hunk of brass tubing that has been scraped to a sharp edge. Chuck the tubing into a drill motor and use your Xacto to create a sharp, inner edge on the tubing. Silver solder a handle made out of wire to your brass tube digging tool. To install the torque rods, you've heard about using grease as a barrier so that you can glue them in with thickened epoxy....but you can also wrap the torque rods with "reversed" tape to create an instant, slop free bearing, then glue them in. I use aluminum foil tape, but other types of tape should work, too?
The torque rods are 2-56 threaded push rods, sharpen the tails that insert into the ailerons, so they don't break through the surface of the ailerons. I pin ***** the ailerons where the torque rods are imbedded and harden the wood in that area with CA. You can also apply 2 oz glass cloth there if you are paranoid....[]
Old 07-29-2010, 11:28 PM
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Default RE: QB-150 Sheet Wing Racer Build

Joe, Paranoid?
Skitz, Scitz, Sceetzufre,,,,,,,,,,,,,,,,,,,,,,,,, er , crazy as hell maybe.
Old 07-30-2010, 11:22 AM
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Default RE: QB-150 Sheet Wing Racer Build

Thanks for the vote of confidence CP! I was really surprised just how easily it came together... I mean, I was up nights worrying about this thing. Well, OK, OK, maybe it wasn't that bad...

I found a few pictures from your other threads, and they tell the tale perfectly - I've reposted 'em here for easy reference.

No real progress lately, so I'll let people admire your work!

Oh yea, Jeffie, don't you read the forum rules? "Please resist the urge to curse, flame, degrade, insult or embarrass someone in your post. " It may be true, but jeeze, ya don't have to rub it in!

[img]{akamaiimageforum}/upfiles/79212/Yv65799.jpg[/img]

[img]{akamaiimageforum}/upfiles/79212/Nl28439.jpg[/img]

[img]{akamaiimageforum}/upfiles/79212/Mk27146.jpg[/img]



Old 07-30-2010, 04:11 PM
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Default RE: QB-150 Sheet Wing Racer Build

Joe, notice the wing tip in the photo.....these wings tend to curl easier if you don't cap the ends. I've skipped [forgotten] that detail and it's not a big problem, it just looks kind of funky.

The other detail is that forward dowel.....I don't trust them any further than I can throw them any more. They're fine for lower performing stuff, but are prone to fail so I've lost confidence in them. A pair of screws that passes through inlaid dowels in the wing, then bite into ply plates in the fuselage will give peace of mind. I think a pair of screws uses less material VS the forward dowel method. Otherwise, the block that receives the dowel should be glued and screwed to the wing.
Old 07-30-2010, 08:56 PM
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Default RE: QB-150 Sheet Wing Racer Build

Joe, notice the wing tip in the photo.....these wings tend to curl easier if you don't cap the ends.
Dude, I'm, already on it! Mine are capped with 1/4" x 1/2 hard balsa.... I woulda went with spruce, but I have a feeling I'll be trimming this wing back after the first couple of flights and that would have been a bit too much effort shaping them only to hack 'em off of there!

Now, about your method of wing hold-downs.... would you hate me if I chintzed out and used 1/16" ply plates on the top of the wing? That center, trailing edge seems mighty frail - so the ply can only help. I'd use 1/32", but I don't have any here at the moment, and for the first one (SWR) I'm not going to get too anal about anything. Heck, I already have visions of a 1/2A, SWR version of the Magnum R!

I glassed the bottom center section by tacking the cloth down with Super 77, then hitting it with medium CA. Thanks for that little tip on handling FG cloth! The torque rods are bent, ailerons hinged, and everything is nearly ready for final assembly / covering. I think I'm going to give the lubed and epoxied torque rods a try... The CG is still looking good too, sitting right around 30% and that's without forward sheeting in place...

Oh, I found a couple of nice chunks of pink foam in the trash at work today... looks like this thing might even end up with a fiberglass cowl - that'd be another PBJ first!
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Old 07-30-2010, 09:42 PM
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Default RE: QB-150 Sheet Wing Racer Build

I see your vitamin B&C supplement there, are you trying to make me jealous?[sm=tongue_smile.gif]

If you harden the balsa wood with CA and go with plywood washers to support the hold down screws, I'll sign you off on that.....

I built a TD049 powered SWR that did have the wing seperate, come to think of it. It's amazing how you can analyze failures after the fact and see how 1/4 oz more wood could have prevented this or that. OTOH, it is even more of a shame to build a mediocre under-performing plane that has 1/4 oz too much wood in about 10 locations.

You practically have to have the attitude that it is impossible to build a TD powered plane too light, even though it is possible if you try hard enough.

A 1/2A Magnum WOULD be very cool [8D]! So would Angel's Rifle, but he might not appreciate it without permission. OTOH, the Rifle is quite similar to a Magnum.
Old 07-30-2010, 10:49 PM
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Default RE: QB-150 Sheet Wing Racer Build

Oh my! How'd that get into the picture?

So, speaking of weight, would ya believe I'm sitting pretty at 7 5/8 oz right now? The only thing missing is the Rx (Berg 4L) and the covering... I'm gonna have to say sub 10oz is very doable! Of course, there'd be a better chance of hitting that goal if I didn't have that 400 mAh NiMh in there, but I do like the insurance of the extra capacity!



Old 07-30-2010, 11:05 PM
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Default RE: QB-150 Sheet Wing Racer Build

Yep, I'll bet these small batteries have helped me to crash more 1/2A planes than any other cause......even more so than using Berg Rxs.....

I'm done with 150s and 220s...350s are my standard now.

These little batteries need more vigilance than what I am willing to provide at times.

Load test them little [email protected]*#$ every time!

I had a Pyramid Thunderhead IPA tonight. Thunderhead is a very powerful name for a pretty mild IPA, I was expecting something that would strip the enamel off my teeth. It was still pretty good, but no match for SN Torpedos!!
Old 07-30-2010, 11:40 PM
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Default RE: QB-150 Sheet Wing Racer Build

And he keeps the SN's on hand while building on a Marble slab. That's "CLASS".

How about a pic of your new preferred wing hold down method Mr. Pigg
Old 07-31-2010, 10:42 AM
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Default RE: QB-150 Sheet Wing Racer Build

This is similar to the way Q500 pylon racers do it. I use wood screws that bite into CA hardened plywood.

Course thread sheetrock screws work pretty good. Some guys use nylon machine screws into threaded maple blocks or into blind nuts.
I double the sides and build little foundations for the plywood plates to glue to.
To support the screw in the sheet wing, I drill with a 1/2" forstner bit and glue in a hunk of 1/2" dowel, then countersink the dowels if I want the screw heads to be flush with the surface.
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Old 07-31-2010, 11:32 PM
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Default RE: QB-150 Sheet Wing Racer Build

Icant degrade or flame Joe, heck Idont have anything to say any more.
Old 08-01-2010, 04:09 PM
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Default RE: QB-150 Sheet Wing Racer Build

Gee CP, you really don't like those Bergs do ya? Knock on wood, but I've had great luck with 'em and haven't had a reason to doubt them... now that being said, I've probably just jinxed myself!

I can appreciate your frustration with beer hype and advertising cleverness, but I had just sort of the opposite happen the other day. I picked up a Bear Republic Racer 5 IPA on a whim, totally expecting it to be a joke, but it was actually pretty darn good! (Even according to the experts.)

Anywho, in between yard work, house work, and work work, I've gotten the little beasty ready to cover. Probably got a little carried away with the ply plates, but I don't think this wing is coming off of there! FWIW, my local home improvement mega-store (Lowes) has a pretty good selection of nylon screws ranging from 6-32 to 1/4-20. I ended up using an 8-32 in the rear and a 10-24 in front. These get screwed into corresponding, doubled 1/8 ply plates glued into the fuse. When tapping the wood directly, I like to use laminations of the thinner ply because there are more laminations for the same thickness and I feel it will hold a thread better. Of course, after tapping the ply, I harden the threads with CA.


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Old 08-01-2010, 04:25 PM
  #25  
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Default RE: QB-150 Sheet Wing Racer Build

Looks outstanding Joe! Just like the drawing. It'll make a nice home for some screamin' 1/2A engineware.

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