prandtl-d wing with bell shaped lift distribution in VSPAERO

[marco]

Hello,

I have modeled the prandtl-d wing (design A.Bowers and others) from this document NASA/TP—2016–219072 in openVSP.
The calculation in VSPAERO VLM method seems (I am a noob at this) to go well and I can display a nice graph of the load distribution Cl*c.

I would now like to compare this spanload to the design 'bell shaped' spanload,
is there an option to show the elliptical, and set the exponent for the bell shape,
to plot together with the calculated spanload?

thank you
M

[Rob McDonald]

The plot of span load in OpenVSP does not have the ability to plot
other load distributions. While I can see this being useful, if we
support too much, we will need to have an arbitrary plotting program
embedded in OpenVSP.

You will need to take our load distribution out and plot it in another
program that lets you plot other curves. You can export by clicking
the 'Export CSV' button on that GUI, or there are other ways if you
want to use the API.

Rob

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[marco]

Thank you for the quick response.
The csv export and some spreadsheet magic will work for me.

Marco

[Felix Finger]

Hi Marco,
would you consider uploading the Prandtl-D to the VSP Hangar?  I'd be cool to toy around with it in VSPAero.
Or maybe you could upload your file to this thread?

Thank you,
Felix

[marco]

here u go

[marco]

be advised:

the tip is not correctly rounded, as I have not figured out how to model the design elevon_config in OpenVSP.
attached is the file as it should be.

[Felix Finger]

Thanks Marco, that's awesome!

Am Donnerstag, 26. Oktober 2017 08:57:33 UTC+2 schrieb marco:

here u go

[Rajat Singh]

Hi Macro, can you please tell which software you used for simulations. We used xflr5, but calculations did not converge.

On Thursday, 26 October 2017 12:27:33 UTC+5:30, marco wrote:

here u go

[marco]

Hello Rajat,

Sorry to not be more helpfull (i'm only a hobbyist in this airplane stuff).

If the VSPaero calculations did not do it for you and if xflr5 does not work for you

then you might have a look at http://flz-vortex.de/

Just yesterday I discovered http://aero.go.usu.edu/machup/

marco

[Rajat Singh]

Thanks alot!!

[anirudh pv]

Hey marco,

have you adjusted the geometry of airfoils at each span location, or are they the same airfoil just varying in chord due to the taper

[marco]

the geometry varies per airfoil

the root foil and tip foil are different, and the foils inbetween are lineairly interpolated for their span position.

[anirudh pv]

Hey Marco 

Thanks for the info, 

1.Would you know the reason to why there is a symmetrical airfoil at the tip (which has a negative twist) as it would produce a downforce (negative lift ) at the tips.

2.I ran some simulations on XFLR5 for the airfoils to determine the lift at various angles of attack and low Reynolds numbers.Using this analysis I was able to determine new angles of twist throughout the span to generate the “bell shaped lift distribution”. Using just the center airfoil at all points along the span 

The curves were much smooth.

Original - from your files 

Using my twist with the same airfoil throughout the span 

On Mon, Aug 17, 2020 at 2:32 AM marco <marco....@gmail.com> wrote:

the geometry varies per airfoil

the root foil and tip foil are different, and the foils inbetween are lineairly interpolated for their span position. 

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[Harshal Joshi]

Negative lift at the tip means that there is upwash at the wingtips. Which means that the vortics are not formed at the tip like a regular airplane wing. In the prandtl the vortices were purposely made to be located inside the span and not at the tips. This causes the tip to experience an upwash. This upwash causes the wing to have an induced thrust at the tip. This induced thrust helps to achieve proverse yaw. That means when you roll rightwards you will also yaw rightwards. This eliminates the need for a vertical tail. 

This is exactly why birds don't have vertical tails. 

a) Ordinary wing with elliptical span load

b) Prandtl wing with proverse yaw

I hope that helps! :)

Regards,

Harshal Joshi

B. Tech Aerospace Engineering 

IIT Bombay

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[marco]

I used this paper to make the model:

https://ntrs.nasa.gov/citations/20160003578

Al Bowers, the author of that paper frequents this facebook page, for questions I's suggest posting them there:

https://www.facebook.com/groups/413028845405427/?ref=bookmarks

[marco]

The Prandtl'd is an adaptation on the footlaunched Horten Xc. Supposedly Horten "did not like the thought of using a cambered section at the tips where the elevons are located".

[anirudh pv]

Thanks Marco!

On Mon, Aug 17, 2020 at 1:47 PM marco <marco....@gmail.com> wrote:

The Prandtl'd is an adaptation on the footlaunched Horten Xc. Supposedly Horten "did not like the thought of using a cambered section at the tips where the elevons are located".

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[marco]

if you are going to use the model to build an actual (scale) plane, then you should probably still have to play with the sections dihedrals (and also with the chordlengths) to get a straight TE. Also I believe I didn't know the correct total wing dihedral, so that needs to be corrected too. Here is a link with more information from a team that made an RC version http://nestofdragons.net/weird-airplanes/flying-wings/special-horten-flying-wings/dragonwing/wing-design-by-albion-bowers/

[anirudh pv]

thanks marco, the site is amazing!

On Mon, Aug 17, 2020 at 8:16 PM marco <marco....@gmail.com> wrote:

if you are going to use the model to build an actual (scale) plane, then you should probably still have to play with the sections dihedrals (and also with the chordlengths) to get a straight TE. Also I believe I didn't know the correct total wing dihedral, so that needs to be corrected too. Here is a link with more information from a team that made an RC version http://nestofdragons.net/weird-airplanes/flying-wings/special-horten-flying-wings/dragonwing/wing-design-by-albion-bowers/

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[chie...@hotmail.com]

Hello Marco, thank you for creating and sharing your OpenVSP model of the Prandtl-D. 

I am a Horten enthusiast, and plan to do some CFD work on the Prandtl-D, including transition prediction, so I am looking for the best geometry.  I am interested to see to what extent viscosity influences the results. 

I studied your OpenVSP model and have a couple of comments/questions.

(1) I think the profiles in your model are perpendicular to the global horizon, and I suspect they should be perpendicular to the true plane of the wing, which is at a dihedral of 2.5 degrees. Although you have selected the option “Correct Foil Thickness For Dihedral Rotation” I suspect that the camber surface will be less cambered than intended. 

(2) I think you applied the twist distribution about the trailing edge (TE), which may be correct.  I have not seen documentation from Albion Bowers and his team to the contrary, but there is a chance that they twisted about the elevon hinge line (to keep the hinge perfectly straight), although the elevon is fairly small so that binding may not be an issue. 

I suspect the model documented in NASA/TP – 2016-219072 is the Prandtl-D2 which had the center chord corrected compared to D1, and which shared the same elevon shape, hinged at 75%c and at the top.  I think both D1 and D2 had a dihedral of 2.5 degrees.  By contrast, the larger Prandtl-D 3c had elevons in the shape of a trapezoid, with the elevon chord becoming larger toward the tip.  Also, the dihedral of the 3c was 5 degrees, I believe. 

Your model’s true span is 147.6” (12.30ft), while the projected span (tip-to-tip span) is 147.6cos(2.5) = 147.45952” (12.2883ft), and that excludes the rounds at the tip.  The center chord is 15.75” (1.3125ft), and the tip chord is 3.94” (0.32833ft).  NASA/TP – 2016-219072 reports the span as 12.30ft, and it reports the same root and tip chords that you have. 

OpenVSP reports the reference area as 1453.122sqin (10.09113sqft), and the average chord as 9.845” (0.820417ft), with or without rounded tip.  NASA/TP – 2016-219072 reports the wing area as 10.125sqft, which is slightly larger. 

Did you post your model on OpenVSP Hangar?  I have not been able to get to the hangar for a few weeks.

If you don’t mind me asking, why are/were you interested in the Prandtl-D?

Many thanks, Christoph

[Tim Swait]

This looks very good, thank you for sharing. FYI VSP Hangar is probably down permanently but is likely to be replaced by a Git repo (https://groups.google.com/g/openvsp/c/tqodIHQ0Pz0). Please do push this to the Git repo when it's up.