Aspect ratio for a flying wings?

[Slow Riser]

Just wondering how to calculate aspect ratio for a swept wing?

Constant chord is a no brainer but I'm perplexed at how to calculate for a flying wing.

I know you include elevons to calculate area but do you also use this as part of the aspect ratio calculation?

Do you add the root and tip chord, divide by 2 and divide over the length of the wing?


Thanks!

[berniep1]

Hi Slow Riser!

Elevons (just like ailerons) should be part of the airfoil --- I'm saying "should" because quite a few designs I've seen seem to have elevons that appear to have been added on as an afterthought --- and need to be added in the calculation...
And you are right: you add root and tip chord and divide by two. Then take your wingspan and divide it by the number you've gotten....

What kind of wing are you planning?

:) Bernie

[Slow Riser]

I'll post a picture once I get the 2nd generation of my wing completed.

I am intrigued by the smaller GWS 50XC with 3x2 prop. I have been flight testing a number of wings optimized around this smaller engine. I want speed and also duration which is why I am designing for a higher AR in mind.

AUW 6.0 oz, 29" wing span, 6" root and 3" tips. Highly modified Clark Y.

I flight tested the 1st generation and results were fantastic; I met all the objectives I've set for myself Excellent glide ratio; hand toss without prop was about 100 meters. Speed was fast, no way I can hand catch unless I'm going into a good headwind. Inverted flight is fantastic, I can actually climb up to attitude inverted.

This is one ship that will be able to cruise and stay up a long time.

One of the things I have learned, there is no such thing as an all-in-one design. There are always trade-offs.

2 problems I have yet to overcome.

1. Wing too thin: at 5/8" max thickness at root, fiber tape and packing tape is not enough to keep the wing stiff. Next generation has a 3/32" spar which should do the trick. Servos are embedded in wing (HS-55) but esc and rx (GWS 4P) on "keel".
2. Too much sweep: loops are pretty large. Less sweep should correct this and also provide better glide performance.

I feel this is about as good performance as you can get with eps foam and tape. To take this to the next level, I'll have to go into the more exotic techniques like bagging but that defeats the purpose of cheap inexpensive fun. The cost of these planes I figure is about $5.00 CDN, or about $3.00 with the CF spar.

I'll post results of the 2nd generation flight test in the Foamies section.

[Slow Riser]

Here is a photo, construction and finished, and some details of the wing that so many of you have helped me design.

http://www.rcgroups.com/forums/showthread.php?s=&threadid=57786

[berniep1]

Nice wings!....be carefull though about reducing the sweep angle to much -- you are going to have to use more twist if you don't want to loose stability (estimation would be about 1 degree if you reduce the sweep from 20 to 15 degrees; assuming an average flight speed of 20 mph)

Keep us posted!

Bernie

[Slow Riser]

My 2nd gen wing flies fast and its really not squirly at all provided you keep the speed up. If I try to fly slow, I'll get a tip stall but I attribute this to the thinness of the airfoil.

I may increase the thickness a bit to get some better lower end characteristics.

Now, what is "twist"...is this similar to washout?

[berniep1]

Yep..it is. Critical for any flying wing....can be calculated, but is a bit of work (and you need to know the parameters of the airfoil -- difficult in your case since yours is of the "homebrew" variety)
I would definitely recommend some on your wings...approx. 2 - 3 degrees should do it. Tip stalls should then be greately reduced...

Cheers,

Bernie

[Tom Hunt]

Originally posted by Slow Riser
Just wondering how to calculate aspect ratio for a swept wing?


Ar= B**2/s

Aspect ratio = span squared divided by wing area. (make sure you "units" are correct! span in "inches" and wing area in square inches!)

It does not matter what the wing shape is. No need to measure root and tip chord.

Tom Hunt

[berniep1]

Tom,

That's true...but to get the wing area you have to take the chord lenght of the root airfoil and add the tip, then divide by 2 (and then multiply with wingspan)

:D :)

Bernie

[Tom Hunt]

Originally posted by berniep1
Tom,

That's true...but to get the wing area you have to take the chord lenght of the root airfoil and add the tip, then divide by 2 (and then multiply with wingspan)

:D :)

Bernie

Opps... yes.... I had assumed that it was kit.... don't all kit manufacturers list wing area?:D

Tom