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PRANDTL-D Foam Board Wing by FoamyDM

What plane should I add the Prandtl-D Wing to?

  • Mini-Arrow

    Votes: 20 38.5%
  • FT-Explorer

    Votes: 15 28.8%
  • FoamyDM-HS Carrier

    Votes: 6 11.5%
  • FT-Simple Cub

    Votes: 6 11.5%
  • FT-Tiny Trainer

    Votes: 12 23.1%
  • FT-Bloody Baron (somehow)

    Votes: 7 13.5%
  • Airliner

    Votes: 14 26.9%

  • Total voters
    52

FoamyDM

Building Fool-Flying Noob
So, there is reflex? That's what an upturned trailing edge is.
It sounds like what you mean is that the ailerons are not reflexed.
Right @Tench745, the Airfoil Shape has a slight "reflex" in the shape. However, Like Most Wings I have seen, or built (like the Arrow, or Comet, et al.) the ailerons in those builds are reflexed, see the Clark Y, and CYH (modified Clark-Y) to compare the trailing edge
1638331950089.png
 
Kudos for building a model of the PRANDTL-D. In your initial video you posited, "how hard could it be?" After the glide tests you appear to have moved on to a new design, so I think you've discovered just what you're up against; here it is for those of you reading this who, like me, are wondering how to get this done.

The PRANDTL-D flying wing shape is extremely complex, making manufacturing difficult at best. Furthermore, NASA only gives us the root and wingtip airfoil, which are quite different. Without knowing the intermediate airfoil shapes, duplicating their work is essentially impossible.

• The wing has a range of of “twist”, or angle of attack, ranging from 8.3 degrees at the root to 8.9 degrees approximately one-quarter of the way down the wingspan to -1.7 degrees at the wingtip. The rate of change of twist is non-linear.
• The root airfoil has a significant amount of reflex while the wingtip has none.
• The root airfoil is around four times thicker on top (above the y = 0 line) than on the bottom, and its bottom is virtually flat. The wingtip airfoil is almost symmetrical and is half as thick as the root airfoil on top and thus twice as thick as the root airfoil on the bottom.
• At smaller scales, the thickness of the wingtip airfoil becomes extremely small, being 1/10th the chord for the PRANDTL-D wingtip. Assuming a 1 meter (3.3’) wingspan, the wingtip airfoil chord is 27 mm (1.06”) and the airfoil has a maximum thickness of less than 3 mm.
• The PRANDTL-D has a stated 2.5 degree dihedral. Front elevation drawings in the paper indicate that the lower surface of the wing has a 4.7 degree dihedral while the upper surface is at 2.8 degrees. Note that the "upper surface" and "lower surface" does not correspond to the mean chord line due to the changes in angle of attack of the airfoil sections from root to wingtip.

Attempting to make this from foam board with a wingspan of 2 m is laudable, but also impossible, due to the wingtip airfoil thickness of 6 mm: 3/16 inch foamboard is almost 10 mm thick if entirely flat, not to mention how to get foam board to have a complex twist across its wingspan.

I believe I will hotwire cut sections of foam corresponding to various sections shown in the paper, where the rate of change of twist is more or less linear, hoping to build the wing out of four or five of such sections, from root to wingtip. Nonetheless, given the dihedral and sweep, the geometry is complicated to be sure, and we still have the problem of not knowing intermediate airfoil shapes means that it will be a rough approximation at best.
 

FoamyDM

Building Fool-Flying Noob
@hcj48009 you summed up some of the challenges of this build quite well. Post#1 was attempting a faithful replica (which I did... ok). #2 was the complete re-think and re-application of the concepts to make a FB plane that exhibits the proverse yaw characteristics. Which was a DECIDED success. They may or may not be more efficient than an equivalent wing, #3 was an attempt to shrink and adapt the idea further, for which the jury is still out.

In an effort to mount the battery easier, I decided to make a battery/fpv pod. this can be added to the modified Prandtl-D wing or the FT style modified Prandtl-D Wing
IMG_20220210_001914688.jpg IMG_20220210_001911189.jpg IMG_20220210_001920651.jpg IMG_20220210_002517934.jpg
 
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Really wanted to give yours a go, but am currently workin 3 builds of the 3D printed Eclipson PRANDTL, and have tons of backlogged builds of planes and multirotors.

Maybe I should ship you one of the Eclipson PRANDTLs for comparison purposes.... I recently acquired a surplus of LW-PLA and could print off an extra.

PM me if interested...
 
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FoamyDM

Building Fool-Flying Noob
Really wanted to give yours a go, but am currently workin 3 builds of the 3D printed Eclipson PRANDTL, and have tons of backlogged builds of planes and multirotors.

Maybe I should ship you one of the Eclipson PRANDTLs for comparison purposes.... I recently acquired a surplus of LW-PLA and could print off an extra.

PM me if interested...
not to be pushy, but if you have 2+ scrap sheets of DTFB and iron, and about 2 hrs you can have yours up and running.

When you get the print settings honed for LW-pla please share it.
should I (or someone else) ever go down the path, we all have a good starting point. and one thread to review.
 
not to be pushy, but if you have 2+ scrap sheets of DTFB and iron, and about 2 hrs you can have yours up and running.

When you get the print settings honed for LW-pla please share it.
should I (or someone else) ever go down the path, we all have a good starting point. and one thread to review.
I have had extremely good luck with LW-PLA just printing with the "stock" .gcode files provided by Eclipson even on my slightly modded Monoprice MP10 (mostly Extruder related mods). I bumped the temp up 10C, but other than that, no changes. Stock files were 135C, and it wasn't foaming enough. Super thin/flimsy. 145C works perfect on my printer. I played a bit with re-slicing some parts for the Model-S that had the seams in bad places. Just used their recommendations off their build sheet found here https://www.eclipson-airplanes.com/_files/ugd/f2f22d_5208f3353dab45aa811ecfeabd3b5586.pdf
The Eclipson files assume a 200x200 print bed, and mine is 300x300, so it prints off center, but I'm OK with that. Think there is a plugin I could use with OctoPrint that would allow me to shift the print over. I should look in to that and give it a try.
 

L Edge

Elite member
That was an interesting assessment hjc48009.

When FoamyDM introduced us to what he was doing, it drew my attention. As you can see, he did his version and it came out rather well. By exploring the concept, he has all kinds of acquired knowledge.
Where your trying to improve it, he has decided to investigate if it has different usages. That's the fun of working with foam. Who knows, maybe he will come up with something that doesn't exist.

In fact, if it wasn't for FoamyDM, he has sidetracked me to researching, layout an approach of a subset of Prandtl-D type wing. Is it going to work? don't know, but it is going to fun rather than tweaking a fixed design. Need to scale it and figure how to build it so it duplicates the concept.
 

FoamyDM

Building Fool-Flying Noob
That was an interesting assessment hjc48009.

When FoamyDM introduced us to what he was doing, it drew my attention. As you can see, he did his version and it came out rather well. By exploring the concept, he has all kinds of acquired knowledge.
Where your trying to improve it, he has decided to investigate if it has different usages. That's the fun of working with foam. Who knows, maybe he will come up with something that doesn't exist.

In fact, if it wasn't for FoamyDM, he has sidetracked me to researching, layout an approach of a subset of Prandtl-D type wing. Is it going to work? don't know, but it is going to fun rather than tweaking a fixed design. Need to scale it and figure how to build it so it duplicates the concept.
Super cool all around!
 
Quick pic of an Eclipson part printed with Colorfab LW-PLA @ 235C vs 245C.
Cooler part (bottom) is very holy/translucent/flimsy, and the hotter part (top) is solid
IMG_20220211_170328595.jpg



EDIT: Also appears that Eclipson sliced the parts for a 250x250 bed. I can use the "M206" command to set the offset to center those parts on my 300x300 bed. "M206 x-25 y-25" "M500". Basically move X/Y over by half the difference. :) Just need to remember to reset the offset to 0/0 when done printing the Eclipson .gcode files. "M206 x0 y0" "M500"
 
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Been having issues with my enclosed printer. Had been printing some stuff for my buddy most recently with some junk old filament and after it was done with that, the filament busted up in bad places requiring the hotend to come out. Got it back together, and of course had to re-level the bed.... Printed a few leveling tests and some random parts to dial it back in and looks OK.
The Center body of the Eclipson PRANDTL V2 tends to warp unless printed in an enclosed printer. So, Hopefully this comes out OK and will be moving on to the LW-PLA parts. Those don't have the same issues caused by asymmetry like the center so I should be able to print most of those on my newer, bigger, better printer. Really need an enclosure for that printer. The center wing section and the main canopy are done in regular PLA for the Eclipson PRANDTL. Just the Wings/ailerons are LW-PLA.
1647632891167.png
 

FoamyDM

Building Fool-Flying Noob
Wow, that is so cool - and 6 years old! I saw that NASA donated the models to museums. Are they done with it?
Yes. Albion Bowers wrote two white papers on the findings, and has since retired. The Prandlt-D and M projects appear closed, and they are working on other projects. doesn't mean we can't find uses for the findings in our hobby, right? :geek:
 

Mr NCT

Elite member
Yes. Albion Bowers wrote two white papers on the findings, and has since retired. The Prandlt-D and M projects appear closed, and they are working on other projects. doesn't mean we can't find uses for the findings in our hobby, right? :geek:
Might be tough with foam board but 3D is probably doable (by someone with a skill set well beyond mine). Looks like they did theirs with carbon fiber.