iron eagel

Regarding a design that I am working on someone made mention of the following, because of the low aspect ratio of my wing the apparent wing loading will be higher, and is something I should think about.
I do not understand this term could someone explain it to me.

Ed_Moorman

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I am not sure since my engineering field isn't aero, but I would think the reverse. I would say, given equal areas, the longer chord of the low aspect ratio wing would generate more lift.

The claim to fame of the high aspect ratio wing is its lower induced drag, giving it a better lift to drag ratio.

On an RC plane, escept for a sail plane, we can use gross power to overcome the greater drag of the low aspect ratio wing and get tighter turns, a faster roll rate and a stronger structure.

What brought this up, anyway? Was someone knocking your low aspect ratio wing plane?

iron eagel

Hi Ed,
No I asked because I have no idea what he meant by this. It is a plane that is built using a reversed delta as the main wing and fuselage. It is an oddball design that I am working on, it is in the build and design forum, in a thread called oddball design.
I had switched over to spoilers for roll control thinking due to the low wing loading of my plane I would be better off using that method as opposed to anything that added lift given the low wing loading of the plane 4/5 oz/ft. I have no idea what "apparent wing loading meant" as I replied to him. I am not an aerodynamic engineer and don't know what he meant so hence the question. The person who said it is someone whom has a lot of knowledge, so now he has me worried that I missed something else. Last night I found I may still have a problem with tail volume due to the short tail moment arm.

P.S he may be a neighbor of yours...

Shoe

Wing loading is a useful parameter because it gives at least a coarse indication of how you might expect an airplane to handle. If you perturb a low wing loading airplane (or expose it to a gust), you would expect to see a bigger change to the flight path than you would for a high wing loading airplane. A good example of an airplane with high wing loading is the F-111. I would expect the "ride" in an F-111 on a bumpy day to be much smoother than in a Cessna 152 on the same day because of the F-111's higher wing loading.

A low aspect ratio airplane will appear to have higher wing loading than an airplane with the same actual wing loading, but higher aspect ratio. This is because a low aspect ratio wing will have a shallower "lift curve slope" than a high aspect ratio wing (a given change in angle of attack will generate less change in lift for a lower aspect ratio wing). The F-111 can illustrate this as well. I would expect an F-111 with its wings swept aft (low aspect ratio) to offer a smoother ride on a bumpy day than the same airplane with the wings swept swept forward (same wing loading, but higher aspect ratio). I think this example provides a somewhat intuitive explanation for apparent wing loading.

iron eagel

Lets see if I understand this...
I am still not sure that I have a good grasp on this.

It is all about the lift, at a given area a low aspect wing produces less lift at the same AOA and speed than does a high aspect ratio. So the airplane while it has the same area will "fly" heavier.
I understand that low aspect wing is far less efficient than a high aspect ratio wing, what I don't understand I guess is just how much less efficient it is.

rmh

The ratios of chord to span are meaningful for man carrying craft but in our much slower models - the low aspect models are really much easier to use.
the "apparant"wing loading ?
in practice - the models with aspect ratios of 6-1 or lower are easier to fly at low airspeeds.

iron eagel

Thanks for taking the time to reply guys, I think I understand this now.

scratchonly

I fully agree with Dick; built a RV3 this winter with an aspect ratio of 4.5-1 and it flies like a dream; wing loading 28 oz, 840 squares.

buzzard bait

No aerodynamicist here, but this is how I learned it: In general, higher aspect ratios are more efficient, i.e., better L/D (ratio of lift to drag). That's because the wing tip vortex prevents the end of the wing from generating lift. A high aspect ratio minimizes the proportion of the wing that isn't generating lift. It's why gliders have such long skinny wings. I suspect this is what someone meant who said that low aspect ratios have higher effective wing loadings. More of the wing is not carrying the load.

But for models thats not the whole story, because our little wings are operating at such low Reynolds numbers that they are not as efficient as large wings. What matters is how big the wing is in cross section. So there is a contradiction for models: low aspect ratio loses more from wing tip vortices but works at higher Reynolds numbers, while high aspect is the opposite.

That contradiction has generated experiments from time to time with low aspect ratio models, and without much conclusion, as far as I can tell. Which makes sense because the two effects work against each other. In the final analysis, it all depends...

Jim

iron eagel

Thanks for taking the time to reply to this question.

It is indeed that very contradiction that led to the design/experiment, which has generated this question.
I am not an aeronautical engineer, either but love to experiment...

BMatthews

That beast of your's is going to have soooooooo much wing that the loading, real or imagined, is not going to be a problem. But for the record when the aspect ratio gets down to one or less like in your case the model will often experience large wing tip vortices and a lot of air that flows from below and around onto the top of the wing. I guess they are reffering to the loss of that reverse flow area. But it's not so much the loss of area but the huge increase in drag that will be a possible problem. But to generate that strong a vortex the model needs to also be quite heavy and need to fly at a higher angle of attack so these vortices are generated. Again it sounds like your model will be quite light for it's size so that may not be a problem.

iron eagel

I am going to use tip plates to try to limit, at least to some degree the wing tip vortices, or the reversed airflow. I know I have not showed them on the sketches yet but they are a planned part of the design. Now regarding the drag that is indeed a real issue! I am figuring that the induced drag with this beast will be very high. The end result will be that the top speed will be limited by the amount of induced drag. I am going to try to keep the weight as low as possible the goal for the foam test unit is two lbs if I can do that then the thrust to weight ratio will be close to 1-1 given the df unit I will be using. Given that the wing area is 1080 square inches with the goal of 32 os total weight that gives me a wing loading of 4.3 oz/ft2.

The balsa unit has a design goal of 10 lbs max on 30 square ft of wing, which will pump the loading up to roughly 5.5 oz/ft2.

BMatthews

But induced drag is the drag made from making lift. The larger the wing and lighter the wing loading the less work it has to do and the lower the induced drag. But in your case you are replacing induced drag with profile drag. That being merely the drag from the large bulk of the model. So it won't be a fast flyer but it's not due to the induced drag you'll be making.

Watch out for the tip plates. With your oddball tip forward style the tip plates will act as forward fins. That's fine but if you make them overly large (like everything else on your design ) then you need to make the rear fin/rudder areas larger to ensure that you've got the right yaw stability.