Comment by Corey Upton on December 17, 2012 at 2:12pm

Do you have more pictures and info on your layup process?  Looks really good.

Moderator Comment by Gary Mortimer on December 17, 2012 at 2:19pm

Beautiful finish, that in itself should help with efficiency.

Comment by Pbreed on December 17, 2012 at 4:19pm

Rectangular wing is not the most efficient. Theoretical best is an eliptical planform.  best practial easy to build is probably a multi segment trapazoid approximating an eliptical platform. For best no wind range you want maximum L/D,  go find a competition sailplane wing of about the right size, these have been optimized for a good trade off between best L/D and min sink (most duration) usually by changing the flaps on the wing from one mode to another.  If price was no object then order one of the larger electric sailplanes from someplace like:    http://www.kennedycomposites.com/ These are the result of multiple generations of design for efficiency.

Comment by Harry on December 17, 2012 at 5:04pm

I'd say it looks like a good choice over the draggy Clark.  The Selig doesnt look to have too much camber or thickness and werent they developed specifically for low reynolds.  Just my opinion of why it'll probably be good.

Comment by Andrew Rabbitt on December 18, 2012 at 12:50am

Nice work Joe! Good luck for the flight testing. Looking forward to seeing the results.

Comment by frederic reblewski on December 18, 2012 at 12:53am

the choice of the airfoil should not be on the top of the list of what to do to have an efficient design. it is true that everything else being equal a "better" airfoil can improve efficiency, but there are a lot of thing to do before optimizing the airfoil that will have a bigger impact on efficiency. that being said I agree with Gary that a smooth finish is always a good start. I also agree with Pbreed that starting from a proven composite sailplane design is also a short cut as the serious ones have been through multiple cycles of optimization as long as you find one that suits your mission profile. what are the constraints? the weight of the payload? the maximum capacity of the battery? the wingspan? the AUW? the motor? the time to reach maximum range?

Comment by Phill Scott on December 18, 2012 at 2:27am

Joe, could you post a link up to the original discussion so I can read the background to your post - don't want to re-cover old ground!

Comment by frederic reblewski on December 18, 2012 at 3:11am

Phil, I found the original post here. Joe, your max auw is 4.5 kg. what part is the payload? atwhat altitude do you plan to cruise? you state that your fuselage is low drag do you mean that the cross section is minimum? do you have a constraint on the take off length?

considering your data WS 2m, C 300mm, AUW 4.5KG, cruise speed 20m/s your Cl should be around 0.3 which seems pretty low if you want to be at max L/D @cruise. your aspect ratio is 6.6 which is also pretty low with a negative impact on induced drag ( half of the total drag at max L/D ).

Comment by Gustav Kuhn on December 18, 2012 at 3:13am

Hi Joe,

I also wanted long distance/duration, but decided that a sledgehammer, sometimes, is the better tool.........

http://diydrones.com/profiles/blogs/drastik-50cc-build-log  :-)

Ok, not quite, also in the shed, and project list, is an old "Wanderer 99" polyhidral wing, that I rebuilt completely straight, sheeted the bottom with 1.5 mm balsa, "D- boxed" the leading edge, and cap stripped the ribs.

Yes, this will be electric !

Comment by frederic reblewski on December 18, 2012 at 3:20am

Gustav, you are absolutely right for distance duration gas engine is so far impossible to beat. as long as gas energy density will be about 100x better than the best available batteries ( 42MJ/Kg vs 0.5MJ/Kg) you will go far further with a gas engine even if it was pulling an "ugly stick"!

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