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Prantdl/Bowers Application to Homebuilts

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StarJar

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Edit: Sorry everyone. After posting below about my experiment, I was checking the results, and found that the normally loaded wing WOULD fly as fast as the Prantdl loaded wing. My mistake had to do with not properly accounting for the fuselage width on one of the models. Again I appologize, and want to make sure you know that the following is totally incorrect and innacurate.

Hi everyone.
I wanted to tell the latest on my humble little experiment regarding using a 70% span positive to negative loading on a flying wing.
I had a recent problem with xflr5 in that it was not finding the new airfoils.
So until I could figure that out, I thought I would just try xplane. Now mind you I thought xplane might not reflect the advantages of the Prantdl-Bowers concept, because it does not use some of the more advanced analysis methods. On the other hand it is always being upgraded to give more realistic performance.
Having said all that, xplane showed a 21% reduction in drag for my entire Me 163 Komet ultralight after converting to the Prantdl-Bowers method.
As if that was not amazing enough it also lowered the stall speed 1 or 2 mph. It also made all control inputs rock solid, even through the brief stall.
There's more too this, about some things I learned how to make the concept work on my particular planform, that I could share with anyone interested.
I would like to see what others get who would like to experiment with the idea.
Questions or ideas?
 
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Swampyankee

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Dec 25, 2015
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Earth USA East Coast
Is this a design study or a report of test results? If the latter, most heartfelt congratulations on completing a build. If the former, do beware of both drag and CLmax predictions from airfoil codes: they are sensitive to details of the boudary layer model and separation criteria.
 

StarJar

Well-Known Member
Joined
Sep 6, 2011
Messages
1,723
Location
El Centro, California, USA
Is this a design study or a report of test results? If the latter, most heartfelt congratulations on completing a build. If the former, do beware of both drag and CLmax predictions from airfoil codes: they are sensitive to details of the boudary layer model and separation criteria.
Edit: Retesting showed I was in error. Upon retesting the non Prantdl wing flew just as fast. Sorry
It is comparing two different riggings one against the other on xplane. So they both go through the same xplane calculations. If xplane errors in some direction, the chances are IMO, that it would error in the same direction on both riggings.
Here's a 4 min video. The model has a ]25 HP engine and test weight of 450 lbs. It's wingspan is 25 ft.
 
Last edited:

StarJar

Well-Known Member
Joined
Sep 6, 2011
Messages
1,723
Location
El Centro, California, USA
Is this a design study or a report of test results? If the latter, most heartfelt congratulations on completing a build. If the former, do beware of both drag and CLmax predictions from airfoil codes: they are sensitive to details of the boudary layer model and separation criteria.
Yeah Swampyankee that is totally true. I might play with it again on xflr5 if I can get mine working again. Vortex Lattice Method is much more realistic for something like this.
 
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