Wingloading 101 help
 

Hi,

I am trying to understand the wingloading concept vs. strapping on the biggest most powerful engine you can on a model.

I have a Zenoah G20EI 20CC that weighs in around 42oz that I had put on a 90 size Yak. I feel it was underpowered and I had to add tail weight to balance the plane, which in my opinion increased the wing loading and messed up the flight characteristics of the plane; however, 20CC gas engines are recommended for that model also. I now have an Extra that is basically the same plane, but the glow engines produce much more Horse power and torque and their lighter weight means I do not have to add weight. The Yak glided like a lead sled on a dead stick btw.

Here are the specs of the extra:

Specs
Wing Span:63 in (160cm)
Overall Length:59.4 in (150.8cm)
Wing Area:728 sq in (47 sq dm)
Flying Weight:8.4-9.9 lb

Engine Size:.91-1.25 2 or 4 stroke
Radio:6-channel with 6 servos
Needed to Complete
Needed to Complete - Gas

Engine (ZENE20EI)
Propeller (APC15060)
Servos, 6, (JSP20070 or JRPS821)
Battery (JRPB5000)
Switch (JRPA004)
Extensions, 4, (JRPA098)
Receiver (JRPR720 or JRP790)

Needed to Complete - Glow

Engine (EVOE1100) - 2-stroke
Propeller (APC14060) - 2-stroke
Engine (SAIE125A) - 4-stroke
Propeller (APC16060) - 4-stroke
Servors, 6, (JSP20070 or JRPS821)
Battery (JRPB5000)
Switch (JRPA004)
Extenstions, 4, (JRPA098)
Receiver (JRPR720 or JRPR790)

So, I am trying to understand/calculate whether I am turning the airplane into a brick by putting the heavier small gas engine on it the extra batteries for the gas engine and tail weight to balance, even though it is recommended as an option for the plane.

Is this basic wing loading?

Thanks,

Chuck

RE: Wingloading 101 help
 

Chuck, wing loading is calculated using this formula:

Weight in ounces divided by wing area in sq. ft. [Since most manufactures provide the wing area in sq. inches, divide it by 144. Multiply the weight in lbs. by 16 to get the ounces.]

Different types of planes can handle different ranges of wing loadings. Glow powered sport aerobatic models typically have wing loadings between 20 and 25ozs/sq. ft. Larger models, like 1/4 and 1/3 scale, can still fly well with higher wing loadings.

But, as a rule of thumb, you should always try to make your plane as light as possible while still having enough power.

There was an article in a recent Model Aviation about the Domino theory, or effect. Basically, the more engine you add, the more weight you add, which means the more power you need, etc., etc. It becomes a vicious cycle.

Your plane will have a wing loading of 28.5ozs/sq. ft. at 9lbs. In my opinion, that is already on the heavy side for a model with 728 sq. inches of area.

If you can get your total weight down to 8lbs you'll have a wing loading of 25.3ozs. That will make for a much better flying model. At any rate, I would definitely keep the wing loading under 30ozs. per sq. ft, i.e., no more that 9.5lbs total weight.

David

RE: Wingloading 101 help
 

Thanks David, what type of scale should I use to weigh my components? I was going to weigh the model first with all the bits and try to keep it down to 8 lbs.

RE: Wingloading 101 help
 

for what it's worth you already have the model so baically you will not be able to change the "built in " weight - therein lies the rub.
It is a pretty sturdy model (the Seagull YAK?)
I have done a number of the Seagull model in fact the smaller YAK I am doing as a electric using A123 cells and a 60 size electric motor
The only weight to be shed on these is the landing ger - I swap to wire with Depron sheeting to simulate the gear legs - NO wheel pants - No spinner etc..
On a model this size wing loading under 20 oz to the ft is highly desireable
The most power to weight is two stroke glow on a tuned exhaust - period.
OR a high performance electric setup -which is good for only about 6-7 minutes flight time but bette power overall.
It's really tough to find alight scale model in these sizes most are built quite solidily
In the future try to find the lighter airframes - or strip the covering and put it on a diet. The difference in performance can not be believed
It is physically impossible to make a model this size, too light - to flimsy yes- but not too light.

RE: Wingloading 101 help
 

It is the Seagull Extra 260 90 size, I use to have the Seagull Yak 54 90 size, but is deceased. I wanted to weigh it to get an idea of what I am starting with, you can also take out the pilot which could shave some weight and swap out the landing gear.

Any ideas on a scale to use to weigh the parts?

RE: Wingloading 101 help
 

I bought a digital postal scale off that action site. There are lots of them on there being sold dirt cheap. You can also get a $20 digital fish scale and suspend the model.

David

RE: Wingloading 101 help
 

At the high end of the weight, your wing volume loading is >14, at the low end it is still >12. This will tend to be a lead sled, if everything is correctly set like CG etc. it should be flyable but will require excessive speed for takeoff and landings and will not fly well. A wing volume loading in excess of 12 is not a model I'd be comfortable with.

RE: Wingloading 101 help
 

What Action site?

Also, I flew the Seagull Yak with a Zenoah G20EI(almost the same plane), which made the plane heavy and it did fly, just did not glide well with all the extra weight. I also flew the plane with an O.S. 120 AX and it flew fine, so I do not understand the previous comment
Sounds like you are saying that the plane will not fly with any of the recommended engines . I am planning on an O.S. 120 AX or Saito 125 at this point.

RE: Wingloading 101 help
 

I did not say it will not fly, I said it will fly but be very unforginving in all aspects. It will be easy to stall unitentionally like on that downwind turn on landing and will use a large amount of runway for both takeoff and landing.

RE: Wingloading 101 help
 

Thanks for the Wing Cubed Loading numbers, Rodney. I had to look up the formula since it's been a long time since I used it.

For others, the quick and dirty formula is:

Wing area in sq. inches times the square root of the wing area divided by 1728. Take this number and divide your weight in ounces by it. Hopefully, you will get a number between 6 and 10.

David

RE: Wingloading 101 help
 

Yes Rodney thanks for the input, I do appreciate all the input, I am trying to understand the aerodynamics of models more and I do appreciate feedback. I know I have a lot to learn about aerodynamics and that is why I posted the question in this forum, figuring you experts could educate me.

:D

RE: Wingloading 101 help
 

David,

Are you saying this: weight / ( (Wing_area * square_root(wing_area) / 1728 )

If so, what would it mean a 12.6 result for an aerobatic airplane?

Pedro

RE: Wingloading 101 help
 

Pedro, my degrees are in the Humanities, I can't read math equations, not even simple ones.:D

I will write it how I see it:

Wing area in inches times the square root of the wing area in inches divided by 1728.

500 X 22.36 / 1728 = 6.47

Now, divide your weight in ounces by 6.47:

72ozs / 6.47 = 11.13

So, 11.13 is the Wing Cubed Loading.

From what I understand, trainers usually have a WCL of 6 or less and heavy, scale Warbirds are in the 14+ range. A sport aerobatic model should probably be somewhere in-between those extremes.

David

RE: Wingloading 101 help
 

I took the opportunity to calculate the wing loading in oz. per sq. ft. for an Aero-Works 50cc Extra 260 that I sometimes fly. It weighs in at 16.5 lbs. and has a wing area of 1270 sq. ins. That works out to 29.93 oz. per sq. ft. This plane is a joy to fly and seems very light and nimble when flying. My CG Sukhoi works out to very similar numbers and yet it seems to fly very heavy. (Lead sled) The numbers are 963 sq. ins. of wing and 11.5 lbs. I'm getting confused trying to make sense of this as there doesn't seem to be anything valuable in the numbers to me. These two planes are as different as night and day in the way they feel. On the Sukhoi, I've moved the CG as much as 1.7 inches and while it changes the way it flies it still flies "heavy" especially with it more forward. Are there other factors at work here? The Sukhoi is OK when you are moving faster but as it slows it turns into a chunk of lead whereas the Aero-Works is pretty graceful until it stops flying and just starts falling. (It's quite easy to do elevators on this bird because it's so docile) The wing cubed loading is not that much different what gives?

RE: Wingloading 101 help
 

Thanks David.

The formula is the same then. My model, a Giles 202, does not feel heavy. As a matter of fact, it feels right. Landings are not difficult and kind of slow for the type of airplane. I am just trying to figure out what 26.1 wingloading and WCL 12.4 mean in practical terms.

Pedro

RE: Wingloading 101 help
 

Jezmo, It's been my experience - and it may be different for others - that the smaller a model the less it can handle high wing loadings.

But, I think your differences might have more to do with things like wing incidences and the lift that the two wings are generating.

RE: Wingloading 101 help
 

Both wing loading formulas are simply subjective. Things based on subjective values are based on someones opinion or interpretation. Yeah, they both are based on math, and equations aren't subjective. But the evaluation of the resulting number is totally subjective. So.............

And the way an airplane flies isn't based solely on one of it's characteristics. So..........

So, when the Sukhoi slows differently in flight than the Extra, and the Sukhoi's tapered wing stalls easier than the Extra's planform, and the prop/engine on the Sukhoi gives a different braking effect, and the Sukhoi winds up tip stalling easier, it's easy to see that there are more things involved in interpreting wing loading than just wing loading.

Both of the wing loading formulas really give the same thing. They give a list of numbers that someone has decided mean something else. And that something else tries to predict a result that is affect by many more things than just the weight of the airplane and how the wing can carry that weight.

RE: Wingloading 101 help
 

I agree 100% with da Rock. That is what I was trying to suggest in my last post. There are so many factors involved in how a particular plane flies, and weight alone is not the determining factor.

David

RE: Wingloading 101 help
 

da Rock and David,

Thanks for your explanations. It makes sense in my mind now.

Pedro

RE: Wingloading 101 help
 

formulas-
Here is a basic truth which applies to all sizes of models (and full scale):
The smaller the craft - the more difficult it becomes to make it light enough.
The larger the craft - the more difficult it becomes to provide enough power.
I little THINKING will let you apply this to any model.
If this is too obtuse - please ignore it.

RE: Wingloading 101 help
 

The wing volume loading (WVL) INHO is much more indicative of how well a model will fly than wing loading is. It will work for all size planes from the little foamys to the giant scale. Jesmos's [planes have a WVL of 9to 10 for the big one and 11 for the smaller one. As he says, a WVL of 11 or more approaches the performance of a lead sled. If less than 9 it becomes a nice flyer, if less than 6 you may have to shoot it down as it will be a floater.

RE: Wingloading 101 help
 

Thanks for the answers everyone. I kinda figured it was complicated with lots of factors involved. One thing I did manage to accomplish today, I got it (the Sukhoi) to do elevators really nice by adding just a tiny bit of spoileron. It comes down now without the slightest hint of wing rock. Also, for some odd reason it seems to glide better with the ailerons up just a tad like that. Like for some weird reason that seems to have reduced drag. I know it sounds strange but it sure seems that way at least when I throttle back to land. I'm thinking about whipping out the incidence meter tonight and see if I can get a more clear picture. Thanks again for the answers.

RE: Wingloading 101 help
 

Here's an example for a giant scale airplane - my 40% J-3 Cub, powered by a DA-100 which flies a lot like a trainer - and then some.

Wing span - 14 ft. - 168 inches.

Wing chord - 26.25"

Wing area = 168 x 26 25 = 4410 sq. in. / 144 = 30.625 sq ft,

Weight of airplane = 42 lbs. = 42 x 16 = 672 ounces.

Therefore = wing loading = 672 / 30.625 = 21.94 oz./sq.ft.

And calculating wing volume:

Sq. Root of wing area is 66.4

Wing area x 66.4 / 1728 = 4410 x 66.4 / 1728 = 169.5

Wing volume = 672 / 169.5 = 3.96 call it 4.0 and you have a very light flying airplane with lots of power.

Attached is photo of J-3 climbing out.

RE: Wingloading 101 help
 

Don't all Cubs fly like a trainer though?

RE: Wingloading 101 help
 

most all do - but if you want one THAT size n weight to hover and pull out vertically you need power far in excess of the little DA100
The DA100 at our altitude is all played out at under 30 lbs of total airframe weight Once again - no formulas required - the sliding scale remains go bigger - weight is not a problem -but power is.
go smaller , power is not a problem - weight is the tricky part.
For those who have built competitive indoor FAI aerobatic stuff and 40% aerobatic stuff - there is no mystery to this "rule of thumb".

It is obvious.