OpenSwift - 1m 3D Printed (mostly) flying wing - Page 2 - RC Groups
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Nov 21, 2014, 12:32 AM
KE your cub.
Curare's Avatar
Not my math thankfully, I just went to the first conversion website that popped up.

have a look at this!

having done the calc by hand, yes I agree, 10.6 oz/sq ft.

Carry on!
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Nov 21, 2014, 06:35 PM
Just Keeping UP
Curare, there is nothing wrong with that conversion web page. That web page converts Kgm^2 to ozf^2. That is the wrong entity. The problem is the conversion needed is Kg/m^2 to oz/f^2. A Kgm^2 is NOT the same as Kg/m^2.

Nov 22, 2014, 04:34 PM
Registered User
I made 2 maiden attempts today and learned a few hard lessons.

1. The plane is pretty rugged and takes hard landings well. Nothing is broken.
2. Hand launching isn't going to happen. That is disappointing. I will have to make a new plane design that can be hand launched after this one. I will build an elastic launcher in order to make a flight.
3. CG placement is key and sensitive.
Nov 29, 2014, 05:41 PM
Registered User
Added some winglets. Changed the look quite a bit.

I now have a few 10m lengths of 6mm silicone rubber bungee cord. Getting close to having another go.
Mar 24, 2015, 08:54 AM
Registered User
jocke1963's Avatar
Maidened yet??
Apr 02, 2015, 12:33 AM
Registered User

I had a few attempts. Launching with bungee cords. Turns out I made a mistake in where the CG should be. Unstable in pitch . Took damage.

No problem, I can print another! I'm almost done printing out the parts for a second prototype. I'm reusing the carbon fibre spars.
Apr 02, 2015, 06:59 PM
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jocke1963's Avatar
Sorry to hear that. Better luck next time. It's a beautiful construction!
Apr 03, 2015, 09:55 AM
supreme being of leisure
ZAGNUT's Avatar
Originally Posted by circuitgrove
nfhill's conversion is correct.

I'm also using the following source for calling the wing loading of 10oz/sqft as glider-like:

that's really only relative for a single size of model, something like a .40 sized power or maybe 2m glider. double the size of a specific model and the wing loading also gets doubled, half the size and the wing loading is also halved....weight and volume are cubed while area is squared.

charts like that were relative 40 years ago when all models were pretty much the same size but today it's useless.
Apr 06, 2015, 02:22 PM
B for Bruce
BMatthews's Avatar
I wouldn't say totally useless. But it is highly limited in scope.

As Zagnut says size counts! The value given for a "glider" would be equivalent to the loading for a warbird on a 30 to 36 inch span model. By the same token the "warbird" wing loading from the chart would be "glider like" if one found such a loading on the big models over 100" wing span that show up so often these days.

Circuitgrove, as you've found even a model which is easy to hand launch has to have a light enough wing loading that it is at or DARN close to the flying speed when you release it. Otherwise you're pushing it ahead while it's still well below the stall speed and clearly bad things are going to happen unless it's got HUGE amounts of power and low speed bite from the prop..... such as flat foam flippy 3D flyers.

An alternative to a launch rail and bungees would be a wheeled take off dolly. But then both have their needs and limitations regardless of which you use.

Best of luck with the repairs and subsequent testing.
Apr 12, 2015, 09:01 PM
Registered User
bcredneck's Avatar
i think if you had a little more power and discus launched it you would not need the bungee launcher
Apr 14, 2015, 09:05 PM
Registered User
I'm building a 2nd prototype now after the first prototype slammed in the ground during a maiden attempt due to pitch instability. I miscalculated where the CG should've been. Sad.

The plane was tail heavy. I'm reducing the motor power. This reduces the weight and helps shifts the CG forward.

Check out a parts list breakout I made:

I'm slowly working on documentation.

Zagnut: I think a wing loading of 3kg/m^2 is pretty light for models right?

bcredneck: I think you are right. My problem was pitch instability. After I fix that I bet I'll be able to hand launch.
Last edited by circuitgrove; Apr 14, 2015 at 09:38 PM.
Apr 15, 2015, 03:16 PM
supreme being of leisure
ZAGNUT's Avatar
10oz per foot for a model that small is decent but not what i would call light and definitely not "glider like".

i'm also a bit confused as you previously stated:
It currently weighs 835g without the battery
which would mean over 2lbs. WITH the battery and that to me sounds on the heavy side for a plane that size.
i'm also not seeing the 3+ square feet that would be needed at that weight to end up with the 10oz loading. maybe it's the photos but i just don't see a low enough aspect ratio to make up that much area in 1m of span.
Apr 15, 2015, 04:39 PM
B for Bruce
BMatthews's Avatar
That's the thing. Wingloading vs the style of flight performance varies with size. For 30 to 40 inch span a hand launchable wing loading will be in the range of your 10 to 12 oz/sq ft. It won't be a good glider at that wing loading but it'll hand launch just fine and glide down without creating a crater at the "landing site".

But this assumes you can hold it well enough to get a good straight ahead energetic launch. I didn't see any hand grips or fold in doors or any other method for achieving a good stable hold on your wing. It may be that you simply built yourself into a corner in this regard. It may also be a case of the unstable launch led to a wild diversion and trying to fly from the launch while stalled and this is what caused it to crash. I've seen odder things.

EDIT- I tried to open your DWG drawing to measure the wing area but the file you provide in the link in your first post won't open for me when I try to open it in TurboCAD. Can you confirm just what the wing loading really is?
Last edited by BMatthews; Apr 15, 2015 at 04:49 PM.
Apr 15, 2015, 05:48 PM
supreme being of leisure
ZAGNUT's Avatar
Originally Posted by BMatthews
For 30 to 40 inch span a hand launchable wing loading will be in the range of your 10 to 12 oz/sq ft. It won't be a good glider at that wing loading but it'll hand launch just fine and glide down without creating a crater at the "landing site".
i agree with that and fly a lot of models that fit that range....but they usually weigh somewhere between 14-20oz...2lbs+ is a whole different story.
Apr 15, 2015, 07:23 PM
Registered User
Hey folks,

Awesome discussion.

First, you can always grab the latest CAD file versions from my GitHub repository. Here's a link to the .dwg only:

For those that want the STLs for 3D printing, check out the whole GitHub repository:
I'm going to release a V1.0 release soon, waiting for that first flight and some documentation.

I checked the wing area (fuselage is a wing): 0.254 m^2. If we assume it weighs 1kg, that's 3.9 kg/m^2 wing loading, or 12.8 oz/sq.ft.

What kind of wing loading do RC gliders tend to have?


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