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May 14, 2007, 03:57 AM
Parkesflyer
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Discussion

Why is this 6 oz plane so good in high wind


Ive always thought that there is no substitute for weight when the wind gets up. After years of slope soaring I have always thought that in a blow bigger heavier models handle the conditions better, and are easier to fly.

I recently got quite a surprise. I have built a 29 1/2" span Extra 300 from 3mm Depron, and its simply the best high wind electric model Ive ever flown and I am wondering why.

It weighs a measly 6.9ozs ready to go complete with.

High End Technologies Micro 3/3D - 70Watts max @ 7.4v
8x4 prop
Castle Creations phoenix10
15C 640mah 7.4v 2S1P LiPo
3 off 3.7gm servos
GWS 4 ch Rx (because it was the lightest I had)
light weight wheels and 2mm wire undercarriage


Wing area 214 sq ins
1.48 sq ft
Wing loading 4.7 ozs/ft2
Power 171 W/lb


The 10% symetrical wing is made by folding 3mm depron over a balsa spar

I have it setup for 3D style surface trhrows, using the Futaba dual throw button, but I have now taken to flying all the time with the larger surface movements.

It penetrates like crazy with lots of control. Inverted needs no elevator trim change. It hovers using less than ˝ throttle. Aerobatic capable using very little throttle, with unlimited vertical when the throttle is fully open.

When the wind is up this is the one I power up, with so little weight, and with the low wing loading this seems all wrong - has anyone any thoughts ?

Richard
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May 14, 2007, 05:38 AM
gpw
gpw
“There’s no place like Foam”
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Clean means alot in the wind ... less DRAG , more wind penetration ...Nice plane !!!
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May 14, 2007, 08:35 AM
Bernoulli+Newton=Lift
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I'm guessing it also has to do with the relatively small wing area and enormous power to weight ratio (171 watts per pound!!! ).
May 14, 2007, 10:49 AM
Parkesflyer
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Light weight aerobat


My interest was really picqued because I have made a 67% bigger 1250mm (49 1/4" ) span Edge 300. The fuslage is 6mm Depron, the wing symetrical rolled 3mm depron with carbon tube and depron spars.

It weighs 5 times more 30 oz
Has much greater wing area 517 sq ins 3.6sq ft
Double the wing loading 8.3 oz/sqft
It is fitted with a more powerful Emax motor from 4000mah 20C 11.1v LiPo 26A max giving 275W
148W/lb

The bigger one was MUCH MUCH harder to fly in the same wind conditions. It required much more throttle to overcome the wind and turbulance

Gusts had a dramatically larger effect, much of the time I was recovering from the effects of gusts and turbulence. Its mass made it a little better with aerobatics, but it just wasnt so much fun

I guess a dead stick might have taught me a lesson or two, the lighter one would I suspect have just disappeared.

Richard
May 15, 2007, 09:12 AM
Registered User
Flying straight into the wind I can see how your larger model seems to have a significantly fatter fuselage which will definitely make a difference in penetration. I also noticed that your rudder seems significantly smaller in comparison to your smaller model. Either way, wind penetration is hugely important. I can fly delta wings that are low profiles in very high winds and as long as I keep the throws down the fact that they have very low wing loading doesn't seem to affect it too much. Almost the opposite is true on my scale-ish cub which has more power than my deltas.

Salter
May 15, 2007, 09:22 AM
Larger planes simply force their way through the wind. But most smaller planes don't have that punch needed to fight the wind properly, but your plane is shaped so aerodynamically that instead of forcing it's way through the wind, it simply slides through or cuts through the wind. It's pretty much the same thing as using a saw verses a razor blade when cutting paper. The saw can cut paper, but only by force. The razor however is so sharp and slim, it can cut the same paper but with much less force.
May 15, 2007, 09:59 AM
Parkesflyer
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Thread OP

small vs large


Putting on my control engineering hat of course I realise that the small Edge has little mass, and the control surfaces need to generate very low forces to make flying corrections.

Its friontal area is of course significantly smaller, although the fin and rudder remain true to scale on both so the larger one is proportionate.

Linear dimesnions were increased 1250mm span to 750mm span, a factor of 1.67. The areas are of course 1.67 squared = 2.78 so the frontal area is almost trebled.

In high winds the small one needs very small amounts of throttle to penetrate, it also has a 10% thick wing.

I guess all these factors add up, to make the smaller one a lot more fun to fly in extreme conditions.

Richard
May 25, 2007, 02:36 AM
Parkesflyer
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Went out again last weekend and it was gusty and turbulent. The 30A esc on the 1250 span version gave up after a few minutes flying, it was down wind of me but had good altitude - a little down trim brought it home without any real drama - good penetration

I didnt have a spare 30A with me so flew the 750 span 6 oz version but loaded it up with an 850mah 2Cell rather than the usual 600. Just out of interest I put it at the same position as the larger model when the ESC failed. I throttled right back to bring it home dead stick like the larger one, no way it was simply blown down wind further and required the addition of power to penetrate.

So I conclude that the smaller, light, easily manoevered, reasonably earodynamic smaller one relies on the high power/weight ratio to overcome the wind's effects.

Richard
May 25, 2007, 07:34 PM
Electric Hippy
Rigid wing.
May 26, 2007, 01:03 AM
Slopeosapien
jonesymj's Avatar
I think you're correct with your conclusions.... 170w/lb will penetrate wind well..... and trees, and dirt, and soccer fields....
May 26, 2007, 05:53 AM
Parkesflyer
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Thread OP
Not so much the 170W/lb, more importantly I think its the 170W fighting the drag forces, which must increase by the square of the ruling dimensions. Wing thickness, Trailing edge thickness, Projected area et etc

Richard
Jun 12, 2007, 04:14 PM
Parkesflyer
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light weight planes in wind


Now heres a thought took a new light weight design out for its maiden flight tonight. Similar spec to the small Extra

1/10 Scale Mudry CAP 21
Span 808mm - 31.8"
175.2 sq ins AUW 9.7 ozs Wing loading 8 oz/sqft
High End Technologies Micro 3/3D motor
75W from 2Cell 121W/lb Thrust 640 gm

It was a really difficult plane to fly in the breeze. As the wind died down it became easier.

The wing root chord is smaller, the tip chord is shorter, and the wing loading is higher - so it should go faster and handle wind better

Its bult ok no dropping of wings but a beast to keep flying well.

Richard


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