Please Help! (wing loading)

[Ed-C]

How do you calculate wing loading? what would be a good all up weight for a 28" -32" warbird?

[CloudyIFR]

Wing loading = Weight of Model in ounces divided by wing area times 144

30 ounce model weight
300 square inches wing area

14.4 ounces per square foot wing loading.

[ADB2]

Hi,
May I suggest switching from imperial to metric units?
For RC models the usual unit for wing loading is in grams per decimeter square (g/dm2). For WWWI warbirds, it's better to never exceed 40g/dm2. For WWWII warbirds which fly faster, the max. limit is 60g/dm2. Staying well below these limits will vastly improve the flying characteristics of your models, making them a lot less prone to wingtip stalls for example.
Wing area is wingspan times average wing chord.

[vintage1]

Ive flown from 6oz to around 20oz on 32" models.

if you can keep it to about 12oz, it wont take a football pitch to land in!

[Ed-C]

Thank you kindly, guys!

[Ed-C]

Ok, so i'm trying to convert a 28" rubber powered, free flight Hawker Typhoon to glow power, 5ch, and this is my first project of this nature. As far as I can tell the area is about 140"sq. (or 900 cm2 for those of us living in the 21st century ;) ) On the scale at the post office she weighs about 14oz. (400g)
but she still needs covering and fuel. Should be okay, right?

[BMatthews]

Sorry but if it's already 14 oz then I would suggest you hang it from the cieling and move on or try again. I even cringed a bit at Vintage's reference to 12 oz for a smaller model. But where a 32 inch span model with around 1600 to 180 sq inches would be fine with a 12 to 14 oz weight a 28 inch model with only 140 sq inches is going to be really pushing things. And when you add on another 2 oz it's going to get ugly. It may fly and you may even manage to land it in one piece but it won't be a fun model to fly.

Small models are just not as tolerant to overwieght wing loadings. As the size drops the tolerance range tighten up quickly. There's never a lower limit but the upper limit where fun is enhanced tightens up quickly as the span and area is lowered.

If I was making a small warbird in the 28 to 30 inch size range I'd be looking at just 3 channels (motor, elevator and ailerons) and forget the rudder and flaps or landing gear you're planning on. And I'd be looking at keeping the weight down to no more than 10 oz. 8 oz would be better and would ensure a snappy fighter like climb. A hand launch would eliminate the need for the landing gear be it retracting or fixed and with light weight you don't need flaps. Besides such a small model would require a paved strip to take off and land on wheels anyhow. Grass on such small models is very unforgiving to landings and takeoffs unless the wheels are grossly over scale size.

[Rodney]

Use WVL (wing volume loading) for your flyability index, it is much better than using wing loading as it works for all size models. If your WVL is less than 10, it should fly okay, if less than 7 it will be a floater.

[JetPlaneFlyer]

WVL (wing volume loading) is defined as (weight in ounces) divided by (area in square feet raised to the 1.5 power).

Below anything over 10 is a problem.. You are at 14.6 and it will get worse when covered. As suggested earlier; hang it from the ceiling and build something else because that one is a brick.

[Brandano]

If the original was a rubber powered model chances are the fuselage was over-engineered to take into account the stress from the rubber motor, while the wings are probably too weak to handle maneuvering.

[Ed-C]

Hmm, discouraging.. Time to put her on a diet I suppose... Lots of stuff that can go, but losing 4-6 oz might be a stretch. Thanks for the science, guys.

[vintage1]

I am not so sure. For a warbird, if its strong enough, weight isn't too much of an issue if you have the power..

I had - well I stil have most of it - a 30" span sort of sporty thing originally designed for a speed 400. It was pathetic, It ended up with a Permax turbo 450 and 3s LIPO pulling about 200W. And weighed in at 20oz.

That proved the key. I couldn't launch above stall speed, (about 20mph) but the power was enough to get it to flying speed very quickly..about a 1:1 thrust to weight ratio.

It topped 60mpgh, would pull three vertical rolls and was..exciting. My main problem was landing it..it need a long level approach which doesn't exist here.

However it wasn't a converted rubber model with a flimsy wing. It was all sheet.

I would not have liked to try it with an undercart tho.

[DT56]

This online calculator will provide wing loading and wing cube loading.

http://www.ef-uk.net/data/wcl.htm

[Ed-C]

DT56- Thanks, thats exactly the kind of thing I was hoping for!

Vintage- I'm hoping you're right.

Power is certainly not going to be a problem, The original (dumb) idea behind this model was that I figured due to the uh, unusual shape of the typhoon front end, I could fit a currently unused .20 nitro engine inside without cutting any ugly holes (except the needle valve :mad: Glow plug fits into scale radiator shutter.).
Makes TONS of power and it swings a scale diameter 3 blade prop. Problem is with its 4 oz tank full it weighs over 10 oz. Im going to try to loose a few oz of servo cases, wire length, pushrod guage and such, and I'll try to post some pics to so if anyone has any suggestions that may help ...Just have to make the computer and camera get along.

[DT56]

If the original was a rubber powered model chances are the fuselage was over-engineered to take into account the stress from the rubber motor, while the wings are probably too weak to handle maneuvering.


Exactly!!!

Most of the glow engine conversions of aircraft of that type and size were using the Cox .020 and .049 engines. Even then, they were free flight or control line. Without substantial modification of the structure, I'm afraid your .20 size engine will virtually insure a short lived airframe.

You might look around the following site for conversion info.

http://balsamodels.com/phpBB/viewforum.php?f=2

Better yet, here's a link to a build thread on a converted Hawker Typhoon.

http://www.rcgroups.com/forums/showthread.php?t=885228#post10036470

Some more conversion threads.

http://www.rcgroups.com/forums/showthread.php?t=827861

[Ed-C]

The fuselage AND wing have both been reinforced substantially. A ply firewall and heavier basswood stringers were used. The formers were laminated to another balsa sheet, grains crossed. I actually ran in the engine installed in the airframe to make sure it didn't shake itself apart. All that extra wood is the other half of my weight problem.

[JetPlaneFlyer]

Ed-C,
Is sounds like your all up weight will rival or exceed Vintages 20oz model (fuelled up it would be 18oz as it is without covering and trim).. Given that yours is smaller in span (and presumably smaller in wing area) and being scale will probably have less easy going handling than Vintages sport model then I think you are wasting your time on this one.
I did a quick calculation of stall speed and it works out about 25mph.. That means (allowing for margin of error and wind gusts) your landing speed will need to be at least 30mph. For a 28" span model that's known as crashing, not landing :rolleyes: If you have a long paved runway to land and take off from then 'maybe' it would be just about possible to fly such a model but it would be no fun and it would not last long.. Without the big runway forget it.

I'd put it down to experience and go build another with a target weight under 9oz all up.

[vintage1]

It will fly, but landings will be a nightmare. And takeoffs almost impossible except off tarmac.

You have built a radio controlled control-liner!!

The remarks about coming inat30mph are exactly what I had on my model. I'd have to keep it in a gliding circuit or three to bleed speed off..never knew when it was near a stall or not, and it would cone in hotter'n'hell and usually I'd overshoot and ether dump it into the field or risk it hitting the trees.

I'd say you would be OK up to around 18-19oz. More than that you have a real handful on our hands..the three blader will last a flight only. It will wipe out on every landing, or the undercart will.

[Ed-C]

Ok, so im looking at a catapult launch, drogue chute landing :p Yikes! was that 30 MILES an hour!? Well, when she's covered, im obviously going to try to fly her once, even if she maidens and de-comissions in the same flight (or cant fly at all :( ). It was not an expensive kit, and ive been building it between other projects, so even if she turns to dust I wont lose any sleep over it. Unfortunately the retracts are now built right nto the wing spar, and the best I could do now would be to remove the wheels and legs. Also I"m worried a typhoon/tempest with a balsa cowl might fare particularly poorly in a 30mph belly landing. I do have a good strip of blacktop for her to take of from, if she gets up to speed quick enough. Also by the time its covered, here in Canada we'll likely have the mixed blessing of being able to land on snow.

[dk944s2]

I have a related question involving scale change and wing area, for a Cub I'm building. Original model has 259 sq. in. of wing area, and I reduced the plans to .75, or 3/4 scale. How do I determine the new wing area? I did some ratios and came up with a figure of 56 percent (or 145 sq. in.). Is this correct? And is there an easy formula to figure it out?

Thanks!

P.S. Span is right about 30".

Ed-C...the silver lining is that it will be exceptionally stable in wind!

[JetPlaneFlyer]

The change in wing area will be the square of the linear scale factor. So for 0.75 scale that would be 0.75^2 which as you have already calculated is 0.56 or 56% of the original wing area.
If you want the model to fly at the same 'scale speed' (i.e. 0.75 of the original speed) then the model weight would need to reduce by the cube of the scale factor: 75^3 = 0.42 (or 42%)

Same thing applies if you scale up.

Steve

[dk944s2]

Thanks, Steve. Then wing loading should be about 7.5 oz./sq. ft. That's with an AUW of 7.5 oz., roughly 55% of the original model's weight. So I guess I can count on it being a little speedier!

[JetPlaneFlyer]

Thanks, Steve. Then wing loading should be about 7.5 oz./sq. ft. That's with an AUW of 7.5 oz., roughly 55% of the original model's weight. So I guess I can count on it being a little speedier!

The wing loading you have should be almost identical to the original size model, (both wing area and weght having reduced by 55-56%) so the flying speed should be similar to the original. But it will appear faster because the model is smaller.

[dk944s2]

Got it. Thanks for the information.

--Doug