Hi,

I am currently building a really small plane (29" wingpan, with a wing area of 106sq in), and I was wondering about wing loading. My calculations foresee me having around 14 oz./ft2. For a plane of such a size, do you think it is very high?

The way I understand it, wing loading is a constant relative to the size of the plane;meaning, if your plane has this wing loading, it would have similar flight characteristics to other planes of larger or smaller wingspans that also have the same weight relative to wing area (wing loading). Anything under 18-20 oz./sq.ft will be a floater.

However, since it is a small plane with low weight, wind will be a bigger factor while flying.

According to scaling rules, the wingloading of a scale model should be reduced by the scale factor's ratio.
For instance, a 1/6 scale model of a full-size Piper J-3 Cub should have 13.3 oz/sq.ft wingloading instead of 80 oz/sq.ft as the full-size.
Another reference is the cubic wingloading.
For instance, the wing loading of a full-size Cessna 152 is about 167-oz/sq.ft. - a model with such a wingloading would hardly be able to fly.
However, the full size Cessna has a cubic wingloading of about 13 oz/cu.ft, which puts it at the high end of a scale model category regardless of size.
As a comparison, your model has a cubic loading of 16 oz/cu.ft, which is rather high if compared with a typical sail / park flier cubic loading of 4 - 7 oz/cu.ft.

Want it to fly easily?
land easily nice moderate flying speed --outdoors?
get wingloading down UNDER 5 ounces per sq ft.
We build a shi- pot ful of small electrics - mostly 275 squares -to - 400 squares
The smaller ones work best at 3-4 ozs per sq ft.
Not guessing here - having done lots of em for indoor /outdoor
Tho these are aerobtic - th kids 8-10years old -can steer em around as the speed and maneuverability is nice and easy .
No amount of airfoil futzing will change this - just go for any airfoil strong enough to be reasonably free from floppiness.
a flat plate is as good as it gets .
seriously.

Tony Frackowiak is flying a mule for NASA..
10 foot span, 15 inch chord.
Takeoff weight seventy six pounds!
Uses about 400 feet to get up.
DA-100 power.
Wing loading.......... 92 oz/sq.ft.+

The stall speed would be about 40mph (assuming no flaps or slats).
Not so easy for the average model flier to land it at the average flying sites…

Those tanks that Tony is flying -are like other research vehicles my friend Dave Stuart flies .
I bet Tony doesn't see these clunkers as fun flyers.

The take off roll is from horizon to horizon.
they are simply military mules
The original question was regarding a model which has a wing planform of roughly 3.5" by 29".
3-4 ozs wing loading is a decent range-for a sport model of that configuration.
Boys - how many of you have built one that size?
They are fun but amazingly enough -you can easily detect the flying difference in weight changes of less than one ounce!

While not perfect, a definition of "Wing Volume Loading" proposed by a Mr. Reynolds who wrote for Model Builder, seems to work better than anything else I have tried. His formula is WingVolLoading = (weight of model in ounces) divided by (wing area in square feet raised to the 1.5 power). If your calculation comes out in the 7 to 10 area, you have a good chance of a flyable airplane. If the value is greater than 10, you are approaching a lead sled type vehicle. If less than 7 the plane becomes a real floater. Most trainers fall in the 6 to 8 range.

the little 29" span model would have .736 sq ft area (106/144). now times by 1.5=1.104
so --I plugged in 3 ounces -a good working weight for this size - I get 3/1.1.
so I get a number far lower than the 7 you mention
Any of you actually fly a 100 sq in model for sport use rc?
I remember the articles by Reynolds-I also was writing for Model Builder .
Maybe my math is incorrect --

Dick, yes, I do fly 100 sqin models for sport use. I don't fly flat plate foamies, however.

The gentleman did not say what type of model this was to be... he only asked if the wingloading was unreasonably high.

I can say from extensive personal experience that the wingloading of 14oz/ft2 is completely and totally reasonable and the model should fly quite nicely, provided it has reasonable power. It will probably not be a great 3D aerobat, but it will be fine for pattern style aerobatics and general sport flying.

I currently fly a 75 sqin pylon racer with a wingloading of 23 oz/sqft, a 96 sqin pylon racer at 18 oz/sqft and several 100-130 sqin sport/scale models (warbirds) at ~14 oz/sqft. All of these models are quite safe and fly very well, provided you have realistic expectations and decent piloting skills.

-David

Interesting!! [sm=thumbup.gif][sm=thumbup.gif] Do you have any sites where there is more information?

Cheers!

Jim

I once flew 1/2 A pylon and some were 13 ozs and 200 squares - NOT floaters
So what is reasonable is in the eye of the beholder .
doing lots of small foamies for fun, casual flying - the 14 oz loading is not desireable
flyable sure .but not back yard stuff.
.

Except for a TD.020 pylon model I built many years ago, all of my small pylon models are built for the 7-cell Speed 400 rules. This gives you a rather high minimum possible weight. Experience has shown that using larger wings to reduce wingloading (above a point) just results in a slow airplane due to all the excess drag. For S400, the "happy medium" is around 100 sqin area... with the model built as lightly as practical. Flying weight is then 11-14 ounces and wingloading is 16-20 oz/sqft. The 75 sqin "Stinger" is the fastest in a straight line, but suffers a little in the turns.

"Floaters" don't make good pylon racers, since they tend to get tossed around and won't hold a line. 3D planes need to be as light as possible, with an absolute minimum wing loading and maximum power loading for the extreme manoevers. Sport/aerobatic planes work best somewhere in the middle, but I'm sure it's also a matter of taste. I like my warbirds to be light, but within reason. I like my models to have sufficient inertia to fly smoothly and handle a little wind. The two park fliers I have see very limited use because I don't like getting up at 5AM to beat the wind.

Again, the guy never said what type of model it was... he just gave the size and predicted wingloading.

Which is why I qualified my early comments - his question was not specific concerning type/use/etc...
I really enjoy the little highly maneuverable foam aerobats and if you really get into them - the performance is nothing short of amazing.
On my two workbenches tho, set my 33% EDGE and a 40% Extra being worked on for others .
We get plenty of exposure to the various sizes-----
But honestly - the most pure fun are the little foamies -if you really like wild aerobatics -these are where it happens!

Dick Hansen, do not multiply by 1.5, raise it to the 1.5 power, quite a different result.

Gentlemen,

I bit the bullet and totally changed what I had in mind. The plane that I'm gonna scratch build will now be a bi-plane, since I've been getting opinions at the field that 14oz/sq ft would be "too high for a sport model of that size". Well, another wing would lower the wing loading down to 8 oz/sq ft. It will have an airfoil, as I don't believe that flat plates are the most capable wings for a sport model.


The plane I am building a sport plane.

Flat plates are the best foil for these -really.
Most who doubt it -simply don't have any experience with them.

dick,

You might wanna consider slope soaring with them, tell me how it goes eh?

csisfun,
You're probably making a good decision to go with a biplane if you are not experienced with "heavy" models. Lighter planes takeoff and land more slowly, and are generally easier to fly. Lowering the wingloading by adding a second wing is a good way to go. I'm including a couple pictures of small airplanes I designed and built to give you a little encouragement. The biplane has a 23" wingspan and weighs about 13 ounces. The low-wing sport plane has a 32 inch wingspan and weighs about 12 ounces. Both fly very nicely.

David,

Those are beautiful planes. I'd love to see them fly. Is that monokote you used?

One problem with Bipes that I'm having is their wing arrangement (difference in incidence between both wings, positioning on the fuselage, struts, flying wires etc.) . I've seen some plans, and all of them are different in their own ways. Currently I am planning to place the top wing further towards the nose than the bottom wing.

Thank you!

I used the light-weight, low-temperature covering film. There is even lighter stuff available today, but I wanted the covering to be pretty durable. The specific film I used was "Top Flight Econokote."

I avoided all of those decisions about wing placement on the biplane by keeping it simple. The two wings are at the same position along the length of the fuselage, and they have the same incidence angle (everything is basically 0-0). It may not be the "best" setup, but it works. Because the model was so small and the top wing mounts to the fuselage, it also did not need any struts or flying wires. The airfoil is an E-205, but it's not all that accurate because the covering sags between the ribs and spars.

Good luck!

Nice! Econokote looks great, quite opaque! Not sold here , unfortunately. I doubled back to the heavy Monokote, it works, so oh well...

Great, thanks for the tips, I might adopt your setup

Hmm...

Does anyone have any idea how I can put ailerons on the Bi plane wings? Do I have to put ailerons on both wings or just the bottom wing will do?

Ailerons on just the bottom wing will do fine. Some aerobatic bipes have upper and lower ailerons, but it's not needed and it's extra weight you can live without on a small model.

dick,

what motor/cell combination are you using to get such a light model?

thanks