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PRANDTL-D Foam Board Wing by FoamyDM

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

  • Mini-Arrow

    Votes: 16 44.4%
  • FT-Explorer

    Votes: 10 27.8%
  • FoamyDM-HS Carrier

    Votes: 4 11.1%
  • FT-Simple Cub

    Votes: 3 8.3%
  • FT-Tiny Trainer

    Votes: 8 22.2%
  • FT-Bloody Baron (somehow)

    Votes: 5 13.9%
  • Airliner

    Votes: 11 30.6%

  • Total voters
    36

FoamyDM

Building Fool-Flying Noob
#1
This is Reserved for my Attempt to build a PRANDTL WIng as featured on an FTCC when they spoke with NASA engineer. The one that flies with *proverse* Yaw


I looking into it here: http://www.amaflightschool.org/PRANDTL and https://www.nasa.gov/centers/armstrong/news/FactSheets/FS-106-AFRC.html
and of course the link of the nasa site showing the summer inters building a fiberglass one.
and looked through the White paper from NASA.

From the White Paper:
There is enough information there for anyone to build this sucker. and the AMA site as the IGS files (whatever they are)
but I took the paper coordinates and ploted it in EXCEL xy graph. and got this:
MainWingSection.PNG

I'll continue working on the wingtip section...
4/29/19 Edit:
OuterWingSection.PNG

as you can see it is symmetrical.

Then they have a table describing the Wing's twist over the wing length broken into 20 sections. 0 is the base 20 is the wingtip
WingTwistTable.PNG Wing Tip.PNG <-Wing Tip Config from AMA site

With a 12.3 ft Wing Span, The base is chord 15.75" and 3.94" tip chord, with a 2.5° dihedral, with a 24° sweep (<- edit 4/29/19)
I think I will make mine 9ft. that will make each half 4.5 ft and should fit in my Toyota Yaris Trunk.

WingLoadVisual.PNG

Project Goals:
Phase 1 - Build a working version per the paper with the same wingform, and twist as prescribed using DTFB.
Phase 2 - See if this can be replicated using basic FT build technique and styling so EVERY wing lover can use it.
Phase 3 - apply it to other planes... and remove the Vertical Stabilizer
 
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FoamyDM

Building Fool-Flying Noob
#2
Phase 1 - DTFB Build

As with all things. it must have a plan. For the most part, the plan came from Nasa's White paper.
PLANS
Alpha Plan. ~72" wing span. :unsure: transport will be difficult, Maybe. Shaded parts are an ironed taper.

Note - the CG Marks too far back by 0.89" (7/8", 22.5mm)

THE BUILD
5/6/19

I began cutting out my print of the design... the thin strips are spars. The build methods are to iron the edges top and bottom. and on the top, remove all the paper, except a tapered strip along the guide line where the spar goes, (from 1" to 1/2")

While getting this started I am also pursuing a more traditional build method similar to Balsa. As a different way to ensure proper twist.
While I do that I will try the Balsa model approach too. working that out now...
That will likely end up as a couple sheets of letter sized paper, cut two. with a leading edge profile, and trailing edge profile...
still working out spar material - right now, yard stick seems right.

5/7/19
I started gluing it up this this morning, and ran out of time looking for my glue sticks. (it was supposed to take 2 minutes. :mad:) I finished the inner half, I used an aluminum ruler to help cool the glue faster.



5/8/19
I found my glue stick nest... And got to working.

Note the curve and the bump in the leading edge.


Then I got to work on the other half:



The I put them together, and viola!








How I got the Curve:
The Key is the 1/2" wood block. and hot glue being hot, slippery at first and sticky.

For the twist to occur, the front edge height as it tapers goes from 1" at the base, to 1/2" at the first segment then the second segment stays near that 1/2" for the inner 1/3 of the outer Segment. the end is Flat. The build Process is get the inner segment glued up, line up the rear edge the front edge supported as described. weight it down, pressing the rear edge closed which is flat against the table.and wait for it to fully cool. (heat sinks, like the ruler help). then do the other section. which is 50% two sheets direct pressed, creating a shear surface rigidity. but as it is rubbery glue there is flex. (I suppose gorilla glue might be stiffer.


This is where I need to quit...
I started measure in balance spots and weight.
View attachment 130748
Tradition is I go fly it in the front yard... In the dark...
It will wait. It is one piece of DTFB with almost no waste. So... ~100g estimate?

Here my video test of the rigidity. Stiffer might be desired. But we shall see.

Back to the beginning.... I wait. And done't be a fool.😜

5/9/19
I had very little daylight minutes to test this yesterday. Balanced at the plan CG marks with 21g (4 quarters) at the pencil mark ~1" from the nosetip is much to tail heavy. It looped nearly immediately.
so I added more weight. about 11 grams (2 Quarters) and another go.. push- curve up-stall. I'm close. add more 5g, and push it up. to the nose tip.
Now it flies! something isn't symmetrical. it consistently turns left. (Of three balanced launches).
my launch was more of a dart toss at the rear apex (where I would put a motor mount.)

Based on those three tosses I learned little. BUT, of those I learned it Yaws left as well - PROVERSE YAW B!TCHES!

More tests coming. And video.

Later that night - next morning
I did my glide test now, I put 40 g of coinage in the very nose of the plane and had it glide very well at this point it's probably just a variation of a couple grams to make it optimal I noticed that when it would Bank it would also proverse yaw even if it's just a little this point which is spectacular!

Take a look for yourself:

On a decent dart toss. It traveled clear across the lot. ~100'/5' drop = 20:1.

5/10/19 - Daylight Tosses
I think I could use *just* a little more weight: 2.5->5g
Last night it hit the garage and bent. you can see crease at the very end.
 
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FoamyDM

Building Fool-Flying Noob
#3
Phase 2 - Prandtl - D using FT build style
IMG_20210605_184139314.jpg
Since I have experienced the failure. for the success and failed motorized attempt (see above) I have been thinking 'bout when I would be getting back to this project.

over the last two years many others have managed creating various forms of this craft as a glider or a 3d printed plane and been successful.
Through the Aviation RC Noob Podcast, Joe and I have chanced to have a great interview with Red Jensen (Episode 25, Episode 26) who was a chief pilot over much of the Prandlt-D project headed by Albion Bowers. As we prepared for the interview, and doing research about the Neil Armstrong Research Center I saw Different versions so I took a moment to create a simple modification of the plane to change the planform, but not the other key elements.
2-sheet -no waste
The new plane is un-wasted sheets of DTFB. cut longways from 8" to 12" from one side. Then cut off a 1/2 strip from both sides. to build a spar. This allows the construction of the wing half.
The important piece to this puzzle. is how to Place the spar, and how to shape the trailing edges of the wing halves. It is important that the inner section functions like a modified Clark Y, and the outer like a Symmetrical wing, with a twist from +8° AoA on the inner section, and it twist to a -2° AoA at the tips.
IMG_20210605_184129615.jpg
Spar line
The spar line on the bottom of the wing should be from ##" to ##" at the wingtip
IMG_20210529_145619344.jpg

On the top it must be moved back a 1/4" on the wing root and remain at ##" at the wingtip.
Trailing Edge
Outer edges
The trailing edge treatment is also important. the outer half must bevel the edge in 1" from the trailing edge insides, top and bottom.
Inner Edge
The top must have the trailing edge beveled 1" in along the inside trailing edge, like the outer half.
The bottom of the must have a 1" bevel on the outer side of the trailing edge (not the inside), opposite the outer wing half.
IMG_20210529_145628930.jpg
Glue-up
The last key bit is the trailing edge of the root half top sits on the bottom ~1/2 to 1/4" from the TE. and fairly constant for the inner half of the wing. this then transitions to matching trailing edges for the outermost wing quarter to the tip.
The key to this and getting the twist, is to put the wing flat, place a ruler under the trailing and lift the Wingtip 1 3/8" at the tip TE, while keeping the front tight against the build surface with weights. (such as bean bags, rice, or shot), It is VERY important to let the glued cool completely before releasing the weights. (10 mins. min.)
IMG_20210529_164116975.jpg
Symmetry
Do the same but mirrored to the other side.
It is important the section is symmetrical airfoil at the tips and 10° angle from the table on BOTH WING HALVES.
IMG_20210529_145340881.jpg IMG_20210529_145432596.jpg IMG_20210529_164116975.jpg IMG_20210529_145555755.jpg IMG_20210529_145703125.jpg
Once completed the wings can be joined, and glued together. If you are concerned about strength, imbed a 10" BBQ skewer in an 1/8" wide track glued in directly over the spar. ensure glue setting before moving on (10 min.) and put a piece of tape from wingtip to wingtip.
Control surface should only be on the outer 1/8 to 1/4 of the wing. as this is where the twist coupled with surface deflection of a roll will yield the forward lift, and thereby the proverse yaw, which allows for no rudder.

Electronics Location
Once the body is build and the Control surfaces are place. I used a 9g servo placed in front of the spar at the inner edge of the Control Surfaces.
The Motor Must be mounted at the back edge of the wing so to have a 10° with the Top of the Wing.
IMG_20210531_161357489.jpg
Weight
Base Weight: 230g
IMG_20210531_003510080.jpg
Dry weight: 360g
AUW: 645g
SPECS:
winspan - 60"
WingChord - 12"
Motor: 2306 1700kv Emax ECO
Esc: 35A 2-6S opto (with Separate BEC)
Prop: 6"x3"
Battery: 2200 mAh,
Ballast: 1300 mAh
2-9g Servo with 20" leads
IMG_20210605_184155724.jpg IMG_20210605_184145324.jpg IMG_20210605_184133430.jpg IMG_20210605_184139314.jpg

PLANS
1623101733789.png

Beta Version Plans Link

Glide Test

Maiden Flight and Proof of Concept

A Graceful 2nd flight Video:
 

Attachments

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FoamyDM

Building Fool-Flying Noob
#8
This is the outer wing section as per the white paper.
OuterWingSection.PNG

I thought I had covered it above, (and will add it). There is a 24° sweep of the wing. with the controls in the outer 14% of the wing at the rear 25% of the chord. (see diagram above).
 
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FoamyDM

Building Fool-Flying Noob
#11
While I do that I will try the Balsa model approach too. working that out now...
That will likely end up as a couple sheets of letter sized paper, cut two. with a leading edge profile, and trailing edge profile...
still working out spar material - right now, yard stick seems right.

WingSectionsWithTwist.PNG
 

FoamyDM

Building Fool-Flying Noob
#14
Me too. I was planning on building a 1 in step to rest the front edge, the tapers down to a 1/2 inch for that inner section, and then twisting the end flat to the table that should create pretty close to the same twist. I know it's supposed to be parabolic but my thought is if I can get pretty close and make it consistent on each side with the last 2" are that -1 1/2 degrees I should have that proverse yaw that Al Bowers speaks about.
I suspect it will be slow. Possibly using packing tape or pins to keep it held in place once set.

At least that's for the fold-over type.
With the individual sections I was going to use a vertical spar and glue the front and back sections to it or keep them in or I'm going to do it and then with a front piece on a back piece of foam I was going to then cover it with cellophane essentially shrink wrap the rest.

As I've never done it terribly successfully it should be interesting results. The balsa guys have mastered it, I figured we should try it's in foam too.
 

wov

New member
#15
I am very interested in the Prandtl flying wing design, but I am not convinced that foam board is the right answer to build one. Just take a look at the leading edge of the 3D model provided by NASA:
LE.jpg

It might be quite challenging to make this happen from foamboard and as far as I understand the white paper provided, this is rather important. Anyway, I love flying wings and if it works out, I will definately build one as well.
 

FoamyDM

Building Fool-Flying Noob
#16
I am not convinced that foam board is the right answer to build one. It might be quite challenging to make this happen from foamboard and as far as I understand the white paper provided, this is rather important. Anyway, I love flying wings and if it works out, I will definately build one as well.
@wov you are likely correct. Foam board is rigid, but it may not be enough for such a slender section, but it is the slenderness that allows it to shift once glued...
where is that model from ? link please?

I started gluing it up this this morning, and ran out of time looking for my glues sticks. (it was supposed to take 2 minutes. :mad:) I finished the inner half, I used an aluminum ruler to help cool the glue faster.
IMG_20190507_074046761.jpg IMG_20190507_082122464.jpg IMG_20190507_082146708.jpg
IMG_20190507_082159158.jpg
 

GMalatrasi

Active member
#17
I was playing around with their model a few weeks back... Thinking of doing a 3D printed build for it later.
Models are available from one of their online papers, I looked but don't have the link saved.
 

FoamyDM

Building Fool-Flying Noob
#20
I know this sounds dumb to my brain, but has anyone 3d printed a dissolving mold scaffold for a FG or CF plane build. Like a sacrificial Foam Build?