Wing Area & Wing Load

[svaughn]

Hi,

I the thread 'Guillow series 500' the question about which model fly better was discussed and several of the replies talked about 'building light'.

In his book Don Ross suggested that in order for a rubber powered aircraft to have good flight performance, it needed to have a wing load of 1/2 gram per square inch of wing area. So if you have a plane with 40 square inches of wing area, it should be less that 20 grams to fly well.

I've never been able to build my planes that light, but I did buy a small electric scale to keep track of weight and it definitely helps me.

Measuring the wing area of planes with tapered, rounded or elliptical wings isn't simple.

Has anyone seen a chart of how much wing area each Guillow model is? I'm mainly interested in the 500, the 900 and the 100 series.

[mark]

Hello,

Take a look at this web page, should help you out in calculating the model kit wing area.

http://webpages.charter.net/rcfu/HelpsHints/WACalc.html

Mark

[supercruiser]

That looks like a handy website Mark linked to. For the Spitfire wing,
I divided the wing drawing into sections and figured those sections using an ellipse formula. An internet search of geometry formulas , should get you what you need. By the way, I calculated the kit 504 Spitfire wing area at 46 sq. in. I am curious to see what you get. My model's wing loading came to .695 gm/sq. in. Thats with the kit wood and tissue. I really can't tell you how well it flew because it only made 3 powered flights before the wing was damaged. I just haven't gotten around to repairing it.

[svaughn]

Thanks Mark,

The formulas in the link you sent make sense, but it looks like they don't deal with the wing tip. It probably isn't much space, so maybe that is okay.

I tried a different approch. I scanned the wing plan for the 501 FOCKE-WULF. Then I imported it into google schetchup. I set the camera to top and parallel projection and I could see the wing drawing like it was laying on a table top. Then I used the line and curve tools to draw the outline of the wing. I used the tape measure tool to set the length of the front edge of the wing. The length from were the wing tip starts to curve in to where front edge breaks forward is 6 and 5/16" as I measure it on the plan. When I made a complete circuit around the edge scketcup created a surface inside the outline. When I select that surface and look at the entity informaiton and it shows the surface area to be .141672 sq ft or 20.4 square inches. The two wings would have and area of 40.8 square inches.

I didn't count the underside of the fuselage in the calculation.

I'm wondering if anyone else gets a similar number.

I'll try this on some of my other plans too.

Steve

[supercruiser]

Your wing area calculation sounds accurate to me. I would include the area of the fuselage where the wing intersects.

[thymekiller]

If you hate math as much as I do, Theres another way to figure wing area. Trace the wing out line onto newspaper. Weigh it the newspaper outline. Cut a piece of newspaper to 1 square inch and weigh it. Divide the weight of the one square inch into the weight of the newspaper outline.

thymekiller

[kittyfritters]

The reason that the Hellcat and Avenger have the reputation as the best fliers in the 500 series is that they have the most wing area. The also have good tail area, and despite being models of radial engined aircreft, relatively long nose moments. Also, even with tapered wings, the tips are not sharply tapered making them easy to trim.

Building a 500 series light with the wood supplied in the kit, usually means anything under 30 grams with the rubber. This is usually achieved by running the sheet stock through a thickness sander and/or cutting lightening holes in the formers and ribs and reducing the width of the wing and tail surface outlines. Using all of the above, and covering with Japanese tissue, I built a 23 gram Hellcat with a kit that came with 15 pound/cubic foot wood.

Building lighter requires substituting the wood. I built a Bf-109 that weighed 19 grams, all up, but I used lighter wood, 1/16 inch strip stock outlines for the keels and 1/32 inch sheet formers aft of the center of gravity. This one is definitely not tail heavy.

Tailheavyness is a major problem with most of the 500 series kits. The Spitfire and Hurricane are the worst offenders. For these two you have to use every trick you can to keep the tail light. One good one is to move the motor peg forward by one former. The motor is shortened, but moving bulk of the motor forward moves the C.G. forward and more than makes up for the shorter motor in ease of trimming.

While the Hurricane is the most tail heavy of the bunch, the Spitfire and Stuka are the most difficult to trim because of their sharply tapered wing tips. It's difficult to keep them from falling off into a spin during the transition from powered flight to glide and if either of them stalls under power they probably will bore in without recovering. The Stuka dispite it's high drag is probably the easier of the two to trim if you make the ailerons and flaps adjustable (Sandwich tie wire hinges.) Trimming either of them will remind you that balance is not just fore and aft, but side to side.

Don't be discouraged! You will become a very skilled builder if you persist in trying to make 500 series kits fly. Even the Stuka and the Rufe, built by an experienced builder, can be made to fly for 30 seconds. It's very satisfying and you will amaze other modelers at the flying field.

[svaughn]

I love thymekiller's method of calculating wing area. Can't get much more practical.

I used sketchup to calculate the wing area from two ww2 I have:
505 ME-109 - 38sq in; 905 P-51 49sq in.

The 500 series are all 16.5 in wing spans so planes like the ME-109 with narrow wings are going to have less wing area.

The 900 series wingspan varies some, but mostly they a bit larger that the 500 series.

Kittyfritter's comment makes sense to me. I don't have either the Hellcat or the Avenger plans, but I think the chord on their wings are larger that most of the 500 series.

I also did a couple of 100 series.

ww-9 is the folker D8 (a parasol monoplane). it has 50sq in. It is an 18" wing span. This folker may be my next project.

ww-5 is the SE-5A (a biplane). It has a wopping 108sq in. I understand that the upper wing of biplanes interferes and reduces the lift from the lower wing so it is apples to oranges comparing monoplane to biplane wing area. Aligning everything on a biplane is a major problem too.

I haven't included the area under the fuselage (between the wings) because I don't think that the fuselage produces life in most cases. But supercruiser maybe right to include it. I don't know what the convention is.

[supercruiser]

I haven't included the area under the fuselage (between the wings) because I don't think that the fuselage produces life in most cases. But supercruiser maybe right to include it. I don't know what the convention is.

Lift distribution still occurs over the fuselage (low wing airplanes) and is shown in the graphs and formulas that I have. When you calculate wing area for planes such as the Fokker D8 and 0-1 Birddg (high wing airplane) you are in essence calculating the fuselage/wing section contribution to lift.
Did I make any sense with that?

[supercruiser]

Thanks for the wing area calculations. Your data shows the 905 P-51 at
49 sq. in. That would indicate my P-51 model (photo of it on VA) is .470 gm/sq. in. That is with the kit wood and tissue, no rubber motor. I used a homemade 4 blade prop which aggravated the trimming process, so far I have only a couple of very low powered flights.

[ranarc]

supercrusier, I traced the wing outline in Visio. The results I got from Visio's area calculation are 50 sqin (wingtip to center former F1), 46 sqin (wingtip to F2, edge of the fusekage).

Regards, Rana

[ranarc]

Same process, using Visio - on a Hawker Hurricane scan - the results are 44 sq in (including area under the fuselage) and 40 sq in.

Regards, Rana

[svaughn]

Hi Supercruiser,

Looking for lift on the area under the fuselage on a low wing airplane is counter intuitive to me since most of the lift is generated by the shap eof the upper suface of an airfoil and the fuselage of a focke wulf doesn't resememble and airfoil to me. But I can recalcualte to include it.

What would you recommend for mid wing planes like the Hellcat or Wildcat? (the chuncky Wildcat is just my favorite ww2 plane)

I can understand including the entire wing structure in the calcualtion on the high wing models though. The folker D8 is a parasol configuration so I would expect lift on the entire wing. The birdog has the fuselage hanging under the wing to interfere with lift, but the upper suface of the fuselage is the same shape as the rest of the wing.

Steve

[svaughn]

Hi Rana Roy Chaudhury,

The first plane you calculated (the one with 50/46 sqin), that was a 905 (P-51)?

I have visio 2007 too (I love it). How to you get the area in visio?

[thymekiller]

On the tail heavy craft [ nearly all to some degree ] , I have used thin styrofoam for the tail feathers. I cut it out from cheap dinner plates. Cuts ALOT of weight where you need it most. Lightweight 1/32 sheet can work also. At least sand the built up structure as thin as you dare.

I'm confused a bit about something. When figureing wing area, We figure the entire lengh and with? We do not figure both top and bottom of the wing?

thymekiller