Hi all,

In a discussion with local DS fans, an interesting point was raised regarding airfoil choice for DS models.

It can't be very efficient to torture F3B airfoils into the 2,000,000 re# range, since they're not exactly designed for that. That said, has anyone tried to optimize airfoil choice for these big speeds?

I would think that full-size sailplane airfoils might be a good place to start, but I wouldn't think that there were many available to us humble modelers.

Any help would be gratefully accepted. I'm in decision mode regarding my next project, and its either a DS model, an XC ship, or a new DLG. Help me decide please

Hehe, if you have a place nearby to DS, I would say make a DS-ER ! :-D

To answer your question in a simple way.... Yes.

To be slightly more specific, I think the foamy "JW" has an airfoil made by Joe wurts that is specific for DS.....

My thinking would be that any Fast, high lift airfoil is pretty well suited.... Apparently the Rg-14 works pretty well!! 232mph!

Yes there are a number of DS specific, or DS modified airfoils out there.
Acacia II DS has modified HN airfoil
Miraj F3F DS has modified MG06 airfoil
I'll bet the Extreme and Mofo have DS specific airfoils.
The EPP JW most definitely has a DS specific airfoil.
I'm sure there are more.

ian

At speeds over 200MPH and circuit times of over about 1.5 or 2 seconds the maximum lift coefficient of the wing only has to be about 0.4 or less. Any airfoil, even a flat plate, can achieve such a low lift coeficient. What's needed is a laminar flow airfoil with very low drag and the low drag bucket covering lift coefficients between 0.2 and 0.4. Such airfoils are readily available. The trick is to reproduce them accurately enough with very smooth, ripple free surfaces.
NACA66-212has a drag coefficient of 0.004 at Rn=3million.
NACA65-212 has a drag coefficient of 0.0045 at Rn=3 million.
Naca 65-210 has a drag coefficient of 0.004 at Rn=3 million.
I challange you to find lower drag airfoils than these for high speed DSing.

If, at speeds of over 200 MPH, the wing were to pull lift coefficients of over 0.4 the plane would turn so tightly and the circuit time would be so short that the plane could not be guided with precision.

BTW, the NACA laminar flow airfoils were deloped about 60 years ago when only the birds were DSing.

The Extreme uses an 8.5% JWDS19. It's an airfoil that Joe Wurts originally designed for the Icon, that was then modified for DS use.

RG, HN or MG airfoils. I suspect more important will be the stiffness of the spar, small control surfaces on ailerons and a clean /stable tail section.
The Opus with 232mph has an old RG14.
Try some airfoils from the F5E guys and beef- up the construction.
Cheers
Thomas

Ollie,

I couldn't help but feel that there must be a better DS specific foil then the (60 yr old) laminar flow NACA foils - and indeed it is difficult to find foils that work in your required Rn and Cl range. So I gave it a shot to design one myself - keeping in mind the design goals for ds such as stoutness, etc. Below is the xfoil (through profili) graph of the foil vs good ol' NACA 66-212 at Rn= 2M ( I felt this might be a better comparison point for a largish 130" glider at 250mph.)


DS 2.5M shows a significant improvement over NACA 66-212 throughout the Cl range while maintaining the 12% thickness for a stout wing.

Cheers,
Sash

... and the airfoil

Hi Sash,

Thanks for the coordinates, they look promising. If I use them, I'll let you know how things turn out.

Cheers,
Adam

Background on DS19 section that Joe designed for the Extreme.

About 4 years ago I asked Joe for a F3F section that turned very well, and would be a good section for DS.
My only requirements were about 8.5% thickness at about 2%
camber.
Immediatly we noticed how well it flew at different wing loadings and airspeeds.

The first exciting report came from Laguna Niguel, the 200 ft slope that has some decent energy above 20 MPH wind speed.
The report was on a 100 yard course it was going faster during the 10 lap than the 3rd.
I reported to Joe the performance and he actually wanted to give me another section that was a little faster in a straight line, I decided to stay with what we had as it was plenty fast in a straight line.

The polars compared to the MH32 are better everwhere except
at max CL where they are were about the same, where the MH32 is excellent anyway. With 1 degree positive camber the DS19 was even better.

Since the 229 mPH run I talked to Joe again and he said the section should be fine up to 280 MPH plus, basically that the section would hold up well past any airframe out there.

We will know more this summer when the new CNC 100" Exxtreme's are out there. The new molded spar will be designed buy an Engineer that designed a full size sailplane.

I am sure a thicker section would pull harder but ther many other issues, such as circle size, straight line speed, parisitic drag, pitch and yaw stability and of course wing planform, and over all airframe design and strength.

BTW Joe did not asked for anything when he gave me the airfoil.

Regards,
Brian McLean