... about wing loading

[gigelus2k3]

Hi,

I'm in process of building my first own scratchbuilt warbird. It's a 33" wing span model, with 5.15" average chord and I expect the AUW to be in the range of 15-17oz.

The powerplant will be an outrunner putting out about 150W.

A back-of-the-envelope computation shows that the wing loading would be very high, between 12.5 and 14.5 oz/sqft.

The question I have is, is it too heavy for a park-flyer (i.e. will it fly like a brick)?

Thanks,

Serban

[vintage1]

It will be FAST.

I had a similar sized and weight model;: Finally about 200watts of brushed (permax 450T on 3s LIPO) and it sure flew like a warbird.

Used to accelerate out of the hand like a rocket, almost unlimited vertical and a top speed around 60mph or more.

A bit to much for e really. Biggest problem s getting it down. It used to do about two circuits of the field just slowng down, and then I was always hovering between tip stalling it on a tight turn, and overshooting the strip. Use to break a prop every three or fourth flights too.

[BarrelRoll]

With wing loadings like that the stall speed is going to be around 18-20 mph.

[gigelus2k3]

Hmm,

Not very encouraging.

I checked the GWS F4U specs; it shows a wing area of 1.61 sqft. Mine has around 16oz, which gives about 10oz/sqft, and is reasonably easy to belly land (i.e. I never crashed it during planned landing).

Does this mean that the extra 2 to 4 oz/sqft wing loading are significant and that I should try to shave off some of my model's weight before I complete it?

Thanks.

[BarrelRoll]

Hmm,

Not very encouraging.

I checked the GWS F4U specs; it shows a wing area of 1.61 sqft. Mine has around 16oz, which gives about 10oz/sqft, and is reasonably easy to belly land (i.e. I never crashed it during planned landing).

Does this mean that the extra 2 to 4 oz/sqft wing loading are significant and that I should try to shave off some of my model's weight before I complete it?

Thanks.

I don't think 2 to 4 oz/sqft are significant. The stall speed increases approximately as a square root of the wing loading.
The thing is I assumed CLmax = 1, which is a pessimistic estimate.
For CLmax = 1.5 (optimistic) we get the stall speed about 14-15 mph for 12.5 oz/sqft.

[slipstick]

I'd say a 20-40% higher wing loading coupled with a considerably smaller wing area could be very significant.

It should fly but it's likely to be "interesting" ;).

Steve

[vintage1]

The model I described needed power to get it above stall. when it only had 50W it was a pig to launch. With 200 you sorta let go..

I'd estimate stall about 16mph. Which is right on the limit as far as hand launching goes.

Hard and dangerous to fly at much less than 25mph...tip stalls..etc.

[gigelus2k3]

Guys,

I definitely will let you know how it went (in about a month from now, given my building speed).

Cheers,

Serban

[BMatthews]

At these smaller sizes yes 2 to 4 oz/sq foot makes a huge difference. Smaller models need smaller wing loadings to fly well.

As Vintage says, you're right on the max of what I would consider to be fun to fly. Even with all that power I'd be sure you give it a healthy shove into a moderate breeze for the first flight. It'll accelerate fast with that power but the first second until it gets up to speed will be critical. Once you find out how well it flies you'll be able to modify the launch but be sure to keep it safe. No sloppy "just let go" for this one. There's much too little wing area for it to fly from a standstill like a flat foamie 3D model does.

[Texas Buzzard]

With just 170 sq. in wing area and weighing in the 14-15 oz. range you are going to have to fly it fast just to stay in the air.

You have been given some good advice so far.

If that plane was in my hands the first thing I would do is to stretch the chord from 5.25" to at least 7". That would give you a health 231 sq. inches.

None of my 6 scratchbuilt Depron electric ships have a chord less than 7" And at that, they still don't float in upon landing - they plop. Keep working, flying and having PHUN.

[vintage1]

The plane I was describing didn't flop. It came in like a cruise missile.

I only have about 140 yards before the trees..and you couldn't see it at 150 yards below the tree line..or judge it that well.

Landing was a question of a 30 mph wide turn at low level with the power off..hoping it slowed down enough to land..mostly it didn't and I would fly it in at 25mph or so and smash the prop.

[ChrisP]

It'll fly about like this :
http://www.rcgroups.com/forums/showthread.php?t=174572

In other words it WILL fly, but FAST.

My PRAT weighs 17.8 ozs and has a net wing area of 168 sq ins. I haven't got round to flying it yet - need to buy some brown trousers and bicycle clips first.

[Sail 'n Soar]

Hi,

I'm in process of building my first own scratchbuilt warbird. It's a 33" wing span model, with 5.15" average chord and I expect the AUW to be in the range of 15-17oz.

The powerplant will be an outrunner putting out about 150W.

A back-of-the-envelope computation shows that the wing loading would be very high, between 12.5 and 14.5 oz/sqft.

The question I have is, is it too heavy for a park-flyer (i.e. will it fly like a brick)?

Thanks,

Serban


Actually, if this isn't your first model the wing loading at that weight isn't that bad IF you have the space to fly - OK as a park flyer if your park is quite large. Assuming you are nor going through a gear box and have a reasonable pitch prop you'll either have a wicked max speed or rate of climb, but it should still slow down to a reasonable landing speed with a reasonably cambered wing airfoil.