Airfoil Suggestions

[gi8u2racing]

I am working on a long endurance UAV, and would rather not keep using the same old NACA 2412 I seem to be attached to, haha. I was wondering if you guys could give me some recommendations for airfoils to use. Here are the relevant numbers on the plane:

Reynolds range: 600k-800k
Endurance: 6 hours
Weight Loaded: 90 kg / 197 lb
Wingspan: 5m / 16.4 ft
AR: 10.0

I am just trying to get a better L/D than just a NACA 2412, that's all, haha.

[aeroanalysis]

gi8u2racing,

The NACA2412 is not a great airfoil. For comparison, here are polars for the NACA 2412 and an SG6040 airfoil. The SG6040 isn't optimized for your application, but nonetheless it yields a ~30% reduction in profile drag at the design CL. Also, you can see in the geometry plot that the SG6040 is significantly thicker, which will give you a lower weight structure, more room for fuel in the wing, etc.

As an aside, can I ask you why your aspect ratio is so low? For an endurance airplane, unless you have a constraint on the wingspan, you will get huge gains in performance by going to a higher aspect ratio.

-Daniel

[gi8u2racing]

The AR of 10 is more of a manufacturing limit to be honest. I would like to see 15 personally, but this our first project together, and we want to keep the structures portion pretty simple.

I am not sure how this will be constructed all that much right now even with only an AR of 10.

I have figured out how to plot 1 airfoil using XFoil, using this method:
http://web.mit.edu/drela/Public/web/xfoil/sessions.txt

What are you doing differently and how do you plot 2 or more drag polars at the same time?

Thanks!

[Curtiss Chiang]

I think that SD7032 is a good choice for small UAV.
The max. lift coefficient and L/D are both well enough for low stall speed and long endurence.
The thickness ratio is about 10%. If a thicker airfoil is preferred, SD7062 (14%) is a suitable one.

[aeroanalysis]

I think that SD7032 is a good choice for small UAV.
The max. lift coefficient and L/D are both well enough for low stall speed and long endurence.
The thickness ratio is about 10%. If a thicker airfoil is preferred, SD7062 (14%) is a suitable one.

Curtiss is right, the SD7062 has even better performance than the SG6040 at the higher CL's. This is due to the SG6040 being designed as a stall protected wind turbine airfoil.

That being said, you are going to find that for your low aspect ratio design, the performance is completely dominated by induced drag at the higher lift coefficients. You will see this if you create a 3-D airplane polar.

[aeroanalysis]

The AR of 10 is more of a manufacturing limit to be honest. I would like to see 15 personally, but this our first project together, and we want to keep the structures portion pretty simple.

I am not sure how this will be constructed all that much right now even with only an AR of 10.

I have figured out how to plot 1 airfoil using XFoil, using this method:
http://web.mit.edu/drela/Public/web/xfoil/sessions.txt

What are you doing differently and how do you plot 2 or more drag polars at the same time?

Thanks!


You are right to be thinking about the structure, and manufacturing at this stage. How much airplane building experience does your group have?

To plot multiple polars in XFoil all you need to do is enter the pplo command and XFoil will plot all of the polars it has in it's buffer. You can see a list of the polars by typing psum or pdel. Remember that typing ? brings up a list of available commands for that operating level. To add existing polars to the buffer, use pget. To obtain a hardcopy of the plots, type hard. This will create a post script file. You can't do anything with the .ps file because XFoil keeps it open, so make a copy of the file and rename it before you try to view it. To view it, convert it to a PDF using Acrobat.