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WING LOADING APPROXIMATIONS

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WING LOADING APPROXIMATIONS

Old 09-21-2005, 08:03 PM
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iaclmac
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Default WING LOADING APPROXIMATIONS

Hi all .. Ok I know how to calculate the wing loading and display the results in OZ/SQ.FT. What I don't know is what are the realistic ranges of wing loading for a plane. In other words what would be the best "ball park" range for the following categories of planes: (1) Trainers: (2) Sport/Stunt: (3) Scale.
Thanks in advance!!
Old 09-21-2005, 09:02 PM
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WS
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Default RE: WING LOADING APPROXIMATIONS

Trainers are usually < 20
Sport is usually 20-30

Scale depends on the airplane and the scale. But ultimately, the size of your field will determine how much real estate you have to land on (you can fly heavier planes on a bigger field). For scale, there is a very specific weight that will give you scale speed (call it the low end limit) and another specific weight that will give you a scale turning/looping circle (the high end limit). Anywhere in that range will give you an airplane that appears to fly "scale like". No matter the weight, it's the power loading that is most important to keep "scale".

The airfoil plays a large part in it too. A thick, high lift airfoil can produce nearly double what a thin, symmetrical wing can, equivalent to cutting your wing loading in half. likewise, if you have flaps, you can increase lift by 50%, or take a 45 wing loading down to about the same as a 30 wing loading with no flaps. I currently fly a B-24, which has a high aspect ratio, high lift wing with fowler flaps. It has a wing loading of 62, but it lands no faster than a sport model with a 30 wing loading.
Old 09-21-2005, 11:05 PM
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Default RE: WING LOADING APPROXIMATIONS

The best range of values also depends on the size of the model. A large model will carry a heavier wing and yet have the same performance as a smaller model with 1/2 the wing loading. The effect is even noticable easily between 20 to 25 size range models and your typical 40 powered model.

But remember that you can't go wrong making it lighter. It'll fly better, land slower and easier, take off sooner and makes a better cup of coffee.
Old 09-22-2005, 06:27 AM
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Default RE: WING LOADING APPROXIMATIONS

Wing loading for models is commonly measured in Ounces per Square Foot.

Calculate wing area and divide by 144.

Weight of model in ounces divided by area in square feet is wing loading.

20 or so for trainers, 25 - 30 small sport planes, giant planes, 40+ isn't too bad, but with all of them, less is better.

"Heavier airplanes only make deeper holes in the ground"
Old 09-22-2005, 06:47 AM
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rmh
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Default RE: WING LOADING APPROXIMATIONS

Make it lighter - always - you simply can't make it too light.
Not flimsy
lighter.
On scale types
try even harder as they are the worst types to do at a low weight
Not to confuse the issue but thicker wings don't lift better - they are more tolerant of angle of attack and can be stronger.
Flaps don't add lift (unless they increase area) they CHANGE the lift /drag relationship which reduces the need for the entire airframe to pitch up to increase lift.
absolutely flat plates can produce excellent lift -but are flimsy.
On models ,wing loading and power loading is everything - shape of the airfoil really means little except in very high speed situations.
Old 09-22-2005, 10:38 AM
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Default RE: WING LOADING APPROXIMATIONS

Regarding the comment - "On models ,wing loading and power loading is everything - shape of the airfoil really means little except in very high speed situations. " I agree for the most part. I will make an analogy with my favorite of all subjects: food! Wing loading and power loading are to powered aircraft what the flour, eggs, and sugar are to a cake; the airfoil is to powered aircraft what icing is to that same cake. Without proper selection of wing loading and power loading, you have little hope of meeting your design goals. The airfoil adds that last let's say 10% of some performance measure (I just made that up, clearly it depends on the details of the design and the parameter in question).

An interesting contrast exists however with sailplanes. Sailplanes are typically task oriented designs, and power loading has no meaning for obvious reasons. In the case of sailplanes, the wing loading defines the basic performance of the ship. However, the airfoil selection for sailplanes becomes much more important than for the powered counterparts. This is true for several reasons: the first is Reynolds number, which generally speaking are very small on typical sailplanes, and the second is the optimization of the ratio of lift to drag at some design flight condition, as sailplanes are truly about efficiency.

A great place to start in your pursuit of understanding appropriate wing loading for your application is to compare the wing loading of an existing design which you know to be of roughly the same size and performance as the model you are working with. For instance, if you are looking at trainers, there are at least 20 great designs out there for which data is readily available. Gather information on weight and wing area, and do the calculation.

Cheers.
Old 09-22-2005, 11:44 AM
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Default RE: WING LOADING APPROXIMATIONS

yes -I keep forgetting about non-powered models these typically stay at very low pitch attitudes and getting best l/d is crucial to performance.
On aerobatic powered models- power n weight loadings are the targets
even on full scale competition aircraft
these guys drool over the power /weight loadings we have with models
the best of these are the ones with highest power to weight - no exceptions.
Try as I might -I can't make an aerobatic powered model which is too light.
in the tiny world of electric foamies -we are now down into 3-4 ozs per sq ft on high power aerobats and the performance is simply unreal. stop start -reverse directions- etc., instant.
The world we knew ,as a kid - was watching B17's and B24's flying off to war -
these designs were primitive -in power and the flight envelopes were simply put- a disaster for many--but they were as good as we could do at the time

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