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Old Sep 27, 2008, 10:29 AM
in persuit of low wing loading
Gordon Johnson's Avatar
Boston, Mass
Joined May 2001
6,430 Posts
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Skeletonized Mega Sport

I like my BSD Mega Sport kit so much it's become my favorite front yard flyer. At 70g it has unlimited vertical with the 10g LCD BL motor. And, I have flown it indoors where it is also great. All in all it's an excellent flyer and I've logged lots of hours on it since the beginning of the summer. If you are looking for an easy to build, sporty BL micro plane, l can personally recommend the Mega Sport.

Inspired by Bill Lowe's Ghost Bipe, I decided to do some CAD work, fire up the laser, and see if I could make an even lighter version of the Mega Sport for indoors only. Here it is, just assembled ready for equipment installation. The airframe with landing gear weighs about 18g.
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Old Sep 27, 2008, 10:38 AM
in persuit of low wing loading
Gordon Johnson's Avatar
Boston, Mass
Joined May 2001
6,430 Posts
Ok, now the details. Wing span is the same 20-inches as the original. I extended the control surfaces aft a bit to enlarge them somewhat.

Wings and elevator are made from 3mm Depron, with laser cut slots to accept 1/32 balsa strips glued in as stiffeners. The fuselage was too flexible when made from 3mm Depron, so I went up to 6mm. Covering is Reyolds plastic wrap. The airframe weighs about two-thirds what the airframe in the BSD kit weighs.

The procedure involves more than one step. The first step is to cut out the openings and the slots for the balsa stiffeners. The balsa stiffeners are glued in. Then, Reynolds Wrap is taped and stretched out tight, the Depron piece is sprayed with 3M77, and then placed sticky side down on the wrap. The last step for that piece is to laser out the perimeter of the piece, cutting the Depron and the plastic wrap in one step.

Borrowing Bill's idea of a "air brake" leading edge, the LE of the wings is Depron that extends above and below the LE a bit. It stiffens the wing. The middle of the wing and the trailing edge have the balsa stiffeners embeded. Airfoil is via Depron ribs, just like the Mega Sport kits.

The fusealge is a bit trickier as it has to be sprayed on both sides with 3M77, then applied to a stretched out piece of Reynolds wrap, trimmed with a knife, then flipped and applied to another already taped down piece of wrap. Then, it's cut out around the perimeter on the laser, cutting through the plastic wrap on both sides. 1/64 ply stiffeners are glued on, which have slots to accept the motor mount, and slots for the landing gear/wing struts to pass through.
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Old Sep 27, 2008, 10:43 AM
in persuit of low wing loading
Gordon Johnson's Avatar
Boston, Mass
Joined May 2001
6,430 Posts
Equipment for the model all came from BSDmicroRC. It uses one of the DSM2 compatible Parkzone bricks that BSD now carries. And, it will use one of the new brushed ESC to brushless controller converters that BSD will soon be introducing. BL controller is the new 0.6g controller from China. Power is the Mighty Midget Gold 13mm Std-wind 1-cell motor with a 5x3 prop and a single Full River 130mAh cell. The equipment will weigh about one-third that of my regular Mega Sport.

Projected weight at this point is about 35g, about half the 70g of my regular Mega Sport. Thrust-to-weight for this skeletonized version won't be as high as the regular Mega Sport, but for indoor flying it should be plenty at about 1.3x weight. Wing loading should be about 1.6 oz/sq.ft, pretty low, and about half the loading of the regular Mega Sport.

This plane does not have ailerons. I stuck with 3-channel control like the Mega Sport and went with the lightest equipment available. It's intended to cruise around indoors very slow with high alpha angles of attack, and possibly the occasional loop. A 4-channel version would have to wait for a 4-channel DSM2 compatible Parkzone Brick. Besides, I'm not sure my flying skills are up to such a 4-channel plane.

Next up is soldering up the equipment and installing it. Hopefully I'll get that done sometime before our Boston Micronauts October indoor session.

Gordon
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Old Sep 27, 2008, 11:11 AM
Bringer of lasers
dill's Avatar
United States, MA, Greenfield
Joined Dec 2006
831 Posts
SWEET! that is so cool! Good luck! Cheers, Dill
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Old Sep 27, 2008, 11:47 AM
RC WANABEE
Bremerton, WA
Joined Nov 2006
320 Posts
Gordon, great looking plane btw. Hey when will BSD be offering that esc converter? I'd love to have one to use with their edf 30 motor and the pz brick.
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Old Sep 27, 2008, 12:04 PM
in persuit of low wing loading
Gordon Johnson's Avatar
Boston, Mass
Joined May 2001
6,430 Posts
Email or call Bob at BSD. He may have a couple now and if so can sell you one. Or, you can get on the waiting list. That's how I got mine. I think initially they are being made in limited quantities.

Gordon
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Old Sep 27, 2008, 12:42 PM
4000 posts?!
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United States, TX, Fort Worth
Joined Jan 2005
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Super clean as always, Gordon. That lazer must be a handy toy to have, I cant imagine trying to cut all that out by hand.

Sure wish they'd hurry with that 4 channel system...

Nick
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Old Sep 27, 2008, 01:53 PM
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Mike Taylor's Avatar
Camarillo, California
Joined Apr 2002
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The 'air brake' LE is an interesting idea. One of the STOL Cessna 150s that used to be at Santa Paula had a forearm-sized cuff around the LE to aid high-alpha take-offs and landings in the Andes. Granted, he had a big motor conversion, but his take-offs were ridiculously steep. You might consider a round tube over the LE instead of a flat plate; you might lose the braking but get more predictable airflow.
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Old Sep 27, 2008, 03:21 PM
Registered User
West of California Speedway, East of LaLa, North of Disneyland
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Quote:
Originally Posted by Gordon Johnson
Ok, now the details......Then, Reynolds Wrap is taped and stretched out tight, the Depron piece is sprayed with 3M77
Good grief!! Doesn't 3M77 attack foam with the "new" formulation (thanks to the California (and other) state VOC nazis)? Or, do you have a trick up your sleeve?
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Old Sep 27, 2008, 05:29 PM
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Economy, Pa.
Joined Mar 2002
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Gordon, that is vantastico, how slow do you think you'll get it to fly?

Kits?
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Old Sep 27, 2008, 07:30 PM
in persuit of low wing loading
Gordon Johnson's Avatar
Boston, Mass
Joined May 2001
6,430 Posts
Jim,
3M77 doesn't attack foam if used in moderate quantities. This is "dusted" on, which is plenty for adhering covering.

Mike,
Glad you like it. No plans for kits. I don't have the time. And, it's pretty time intensive because of the several steps per part. However, kits for the all Depron Mega Sport are available now from BSD and it's a very very nice kit and goes together well.

Nick,
Yes, lasers are good for cutting out bits. But, the rub is the CAD time to get to that point, and a bit (sometimes a lot) of trial and error. I made the fuselage four times, this being the fourth as I kept refining it. I made two trial wing panels before I was happy and made the pair of panels on this plane. So, it's a tradeoff timewise.

Gordon
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Old Sep 28, 2008, 09:05 AM
in persuit of low wing loading
Gordon Johnson's Avatar
Boston, Mass
Joined May 2001
6,430 Posts
Mike Taylor,
If I had it to do again I'd lose the "air brake" LE. But, I had the wings built so went with it. We'll see how it does.

Gordon
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Old Sep 30, 2008, 07:32 PM
in persuit of low wing loading
Gordon Johnson's Avatar
Boston, Mass
Joined May 2001
6,430 Posts
The motor mount worked out better than I had hoped. I took one of the BSD bulkhead plastic motor mounts for the MM motors and cut off all four tabs for the screws. Then, I cut a 1/32 ply mount with a hole that the BSD mount just fit into backwards. This is a press fit on the MM motor. So, a bit of glue on the BSD mount where it mates with the 1/32 ply, and then a bit more on the back side, and the MM motor is mounted in the 1/32 ply plate very securely, and light. The 1/32 ply mount has slots that the 1/64 ply fuse doublers fit into, and it all slips together nicely. A bit of glue where the bulkhead 1/32 ply piece mates with the 1/64 doublers and it's all mounted with minimal weight.

Now, on to soldering up the rest of the equipment and then mounting the Parkzone brick in the plane and hooking up push rods.

Gordon
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Last edited by Gordon Johnson; Sep 30, 2008 at 08:23 PM.
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Old Sep 30, 2008, 08:13 PM
is it flying time?
Jerry Combs's Avatar
Wyandotte Oklahoma
Joined Oct 2004
2,777 Posts
Quote:
Originally Posted by Gordon Johnson
Mike Taylor,
If I had it to do again I'd lose the "air brake" LE. But, I had the wings built so went with it. We'll see how it does.

Gordon
Gordon,

The "air brake" LE helps soften the stall so you may yet be glad that you did it that way. I have been playing with this style of LE for a while on my F3P models, it has an advantage beside aerodynamic ones........it stiffens the wing with less weight gain than if carbon were used.

Mike,

I have tried the cuff type of LE and while it did work well it was much harder to construct accurately and tended to be heavier. The "air brake" is a decent compromise.

Jerry
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Old Sep 30, 2008, 08:30 PM
in persuit of low wing loading
Gordon Johnson's Avatar
Boston, Mass
Joined May 2001
6,430 Posts
Jerry,
Thanks for the input. I hope the "air brake" works as you say it might. In this case it's probably lighter than CF rod. But, it's more than triple the weight gain from one of the 1/32 balsa stiffener's I've used elsewhere ('course the balsa stiffeners aren't as strong as CF rod). I think the balsa stiffeners were about 0.10g each (glued in place) compared to the "air brake" stiffener at about 0.36g each. So, in the end, I left the "air brakes" in place. Six of one, half a dozen ...

Gordon
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Last edited by Gordon Johnson; Oct 01, 2008 at 11:32 AM.
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