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Old Jun 30, 2009, 11:02 AM
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scrubs's Avatar
Rio Rancho NM
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Discussion
wing loading on small stuff

I've got a number of kits and plans for OT stuff at 30". Kits of the Sniffer, Viking and Buzzard Bombshell. I also scaled plans for the Coronet and Wedgy. Originally I thought I'd do them for CO2 or electric FF. But I'm having problems chasing FF since a knee operation. So I may do a few as RC assit FF. Not so bad really, just use the Tx to shut down the motor and bring it back to me after it comes down.

What would be a good weight / wing loading to shoot for on these? They're around 150 sq inches give or take.

I'm also sorry to see most of the simple GWS brushed setups getting harder to find. The long can LPS A would have been ideal. The IPS seems a little heavy altho I will be needing nose weight on something like a Wedgy.
bill
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Old Jun 30, 2009, 01:25 PM
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Africa
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Scrubs I've built a few 36'' span models around 210 sq inches & always ended up with about 6.8 - 7.5oz. per sq ft. I think with electric you could get it lower but it all depends on how much wind you have at your flying field. I find that below that it doesnt penetrate even in a moderate breeze ends up floating backwards ...then again I was flying ic so didnt have the luxury of applying a little power to bring them home.
I never built the KK slicker mite (32''?)simply because I crunched the numbers again & again and could get a satifactory loading.
cheers
Simon
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Old Jun 30, 2009, 01:46 PM
Deletedfor proving Nauga wrong
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One reason the GWS IPS systems are dissapearing is because some really neat TINY brushless motors are showing up.

GWS "A" IPS motor + gearbox = appx 29 grams.
Add appx 7 grams for the ESC+ wire...

2Dog RC had (might still have) a 15 gram brushless outrunner that turns the same prop appx 30% higher RPM.
Appx 9 grams for the brushless ESC + wire...

36 grams for brushed...
24 grams brushless...
Significant weight saving and significantly increased power. Put the weight saving into a bigger battery if you want...
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Old Jun 30, 2009, 02:38 PM
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Arvada, Co
Joined Feb 2006
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Hi Bill,

I e-converted a Goldberg 1/2A Blazer and High-Thrust Viking and they are lots of fun. The Viking flies the best and is completely unique on a usual Sunday outing at the club, I agree about the brushless. They are the way to go for weight and power. The Viking is about 15oz so a little heavy, but will climb out of sight in 40 seconds or so. Wind is a big factor though.

Franny
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Old Jun 30, 2009, 02:41 PM
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Thanks guys.

Simon,
I agree on the wind my tiny 24" stuff just gets blown off the field if I try it fly it as RC assist FF.

FHH,
Yeah the future is brushless & I've got one of those little 10 gm gems too. But I was hoping to use some brushed esc's I have. Cheap is as cheap does.

bill
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Old Jun 30, 2009, 03:01 PM
North East England
Joined Feb 2004
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I've built a few 30" span models, both sports and WW1 scale, and although I never weigh them (got no scales), if they're balsa/ply construction and built in the free flight manner they fly just fine.

One in the pic is a 30" version of the 'Little Ship'; 1500kv outrunner, 2s 540 LiPo, 5 gm servos. Very light - you can see the construction through the Litespan covering.

30" is a nice size; big enough to see but handy for storage and transport.

Steve
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Old Jun 30, 2009, 05:25 PM
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A rough guide which works quite well, for scaling a known model up or down is to multiply the wing loading by the scale factor. In this manner, the flight behaviour (could be called the "character") of the original size model is maintained, albeit at a lower speed.

Going into more detail:
- Size is proportional to scale factor
- Wing area is proportional the square of the scale factor = (Scale Factor)
- Weight is proportional the cube of the scale facto= (Scale Factor)
- Power required is is proportional to the 3.5 power of the scale factor(Scale Factor)^3.5
- Flight speed is proportional the square root of the scale factor.

These are guidelines which were spelled out long ago by Bob Boucher (Mr. AstroFlight) and others

As an example, a half-size model would obviously see its dimensions halved.
The wing area would be divided by 4
The weight would be divide by 8
The wing loading would be halved;
Flight speed would be 0.7 of the original;
Power required (or IC engine capacity) would be divided by 11 (= 2 to the power 3.5).

Say the original flew with a .60 engine, then the half-size model would fly in a similar manner with a .049 or .060 engine.

Another example : The original model uses a .15 engine. Say I want to build a smaller replica for an .020 engine. What scale factor? Answer : root 3.5 of (.020/.15) = 0.56 or 56%
A replica for an .049 would be scaled 73%, etc...

The same reasoning equally applies to electric powered models.
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Old Jun 30, 2009, 05:36 PM
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The 'Wack, BC, Canada
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I believe that the smaller 150 sq inch replicas flew well at between 4 to 5 oz for free flight. With the need to ride even the lightest lift somewhat taken away and a more sport flying style role I would not be bothered by having the weight of them go to around 6.5 to 7 oz. But obviously the lighter the better if you wish to retain that free flight look to their flying.

There are some amazing little 9 to 13 gram brushless motors out there these days. Those with the ultra light Berg Rx and a couple of 3.6 gram servos and a small ESC and there's no reason why an RC version can't come in well under 7 oz since the 5'ish oz free flight versions were keeping that light with a TeeDee .020 and a heavy Tatone fuel timer on board.
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Old Jun 30, 2009, 08:10 PM
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Rio Rancho NM
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That's what I was hoping to hear Bruce. The 24" RC sport models I've built came in a hair over 3 oz. A 24" SE5A was about 4 1/2 oz. So I should be able to do 5 oz on a 30" replica, especially with good balsa and esaki covering.
bill
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Old Jun 30, 2009, 10:36 PM
Deletedfor proving Nauga wrong
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A use for the old brushed ESCs... Put em on a switched channel and put lights on the plane.
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Old Jun 30, 2009, 10:54 PM
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Mt Evelyn, Melbourne, OZ
Joined Dec 2008
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I've been having lots of fun with this little DH02.
20" span, Schlosser 0.25 and weighs about 8 oz.
Under power it can handle a moderate breeze, loops rolls all good fun.
Gets about 3 1/2 minutes on 2cc of fuel (and that's long enough on this little beasty).
It glides very well if I leave it alone on it's favourite glide slope.
If I pull up to slow it down it falls out of the sky.
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Old Jul 01, 2009, 01:20 AM
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The 'Wack, BC, Canada
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Warren, your DH02 had easily twice the wing chord of the OT replica models we're talking about. Plus with these much of the fun is to glide for thermals following motor shutdown. Different requirements......
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Old Jul 01, 2009, 01:23 AM
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Africa
Joined Jan 2005
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Quote:
Originally Posted by JMP_blackfoot
A rough guide which works quite well, for scaling a known model up or down is to multiply the wing loading by the scale factor. In this manner, the flight behaviour (could be called the "character") of the original size model is maintained, albeit at a lower speed.

Going into more detail:
- Size is proportional to scale factor
- Wing area is proportional the square of the scale factor = (Scale Factor)
- Weight is proportional the cube of the scale facto= (Scale Factor)
- Power required is is proportional to the 3.5 power of the scale factor(Scale Factor)^3.5
- Flight speed is proportional the square root of the scale factor.

These are guidelines which were spelled out long ago by Bob Boucher (Mr. AstroFlight) and others

As an example, a half-size model would obviously see its dimensions halved.
The wing area would be divided by 4
The weight would be divide by 8
The wing loading would be halved;
Flight speed would be 0.7 of the original;
Power required (or IC engine capacity) would be divided by 11 (= 2 to the power 3.5).

Say the original flew with a .60 engine, then the half-size model would fly in a similar manner with a .049 or .060 engine.

Another example : The original model uses a .15 engine. Say I want to build a smaller replica for an .020 engine. What scale factor? Answer : root 3.5 of (.020/.15) = 0.56 or 56%
A replica for an .049 would be scaled 73%, etc...

The same reasoning equally applies to electric powered models.
Very interesting JMP. Does it work the same in reverse? ie as in scaling up?
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Old Jul 01, 2009, 01:53 AM
Deletedfor proving Nauga wrong
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Quote:
Originally Posted by Snorks
Very interesting JMP. Does it work the same in reverse? ie as in scaling up?
Yes... the scaling factors work well in both directions.
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Old Jul 01, 2009, 02:05 AM
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Quote:
Originally Posted by BMatthews
I believe that the smaller 150 sq inch replicas flew well at between 4 to 5 oz for free flight. With the need to ride even the lightest lift somewhat taken away and a more sport flying style role I would not be bothered by having the weight of them go to around 6.5 to 7 oz. But obviously the lighter the better if you wish to retain that free flight look to their flying.

There are some amazing little 9 to 13 gram brushless motors out there these days. Those with the ultra light Berg Rx and a couple of 3.6 gram servos and a small ESC and there's no reason why an RC version can't come in well under 7 oz since the 5'ish oz free flight versions were keeping that light with a TeeDee .020 and a heavy Tatone fuel timer on board.
Depending on the model...

The RC system might add amazingly little weight now. Consider the Parkzone Vapor. You can take its radio and motor system and make an AMA "Cub" into an RC model.

The new ultra-micro Sukhoi's RX and a micro brushless power system would allow 5 channel operation of a Guillows 18 inch span P-40. Possibly 6 channels! Just a matter of designing the tiny retracts.
1.5 gram servos are wonderful things.

AR6300 RX at 2 grams and there are 2.5 gram servos available to use with it for under $10 each.

I wished this kind of stuff was available when I was a kid....

The Electric power system + RC system COMBINED could weigh very close to the original rubber power syetem...

Aim for the rubber power FF's design weight.
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