Beulzabob

My Feedback: (1)

Does anyone have the specs on the airfoil used for Goldberg's Gentle Lady? Could someone send me a scan of the main rib?

Thanks in advance,

Robert[8D]

kingbee

Robert,
I don't have any "specs" as such but I do have copies of the ribs full size if you want them.

Let me know.

Cheers,
Dave

bjaffee

I've always assumed it was the ubiquitous Clark Y?

Smythe

[link=http://marlongofast.tripod.com/zipped_aeronotes/clarky.htm]Clark Y aerofoil[/link]

I don't think it's the Clark Y... the Lady foil is much flatter on the bottom and, I think, is proportionally thinner.

Smythe

[link]http://www3.sympatico.ca/louiscimon/gladya.htm[/link]

That site clames it's a "Cirrus type" aerofoil.

evlwevl-RCU

See if this helps out

I scanned in rib # 9 which should be the same as rib#1

I can email you the high resolution image if you need it

Beulzabob

My Feedback: (1)

That's great!

I just copied the picture in bitmap format. Sure looks like a flatbottom foil to me. Just the way Thornburg discribed it in his book. I'm flying a 78" with an S3021 and on low wind days I'd like something a bit less speedy. I think that airfoil would be just the trick.

Thanks evlwevl and everyone else,

Robert

[sm=thumbup.gif]

Beulzabob

My Feedback: (1)

Just one more question....

Does anyone know the thickness or thickness percentage of that airfoil?

Thanks again,

Robert [&:]

michpittsman

My Feedback: (11)

If it's a slower, floater airfoil, get a hold of the old Windrifter foil; they were unbeatable in calm winds. Gentle Lady does not have a real floater airfoil. Jim B LSF796

MTT

My Feedback: (8)

What do you mean by that ? The Clark Y is an airfoil with straight underside .
doesn't get any flatter than that .

Michael

Jack Hyde

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The s3021 has a maximum sectional lift coefficient of 1.2 at Reynolds number of 100000 (Profili). The Clark Y max cl =1.3 at the same Re. If you don't change model weight or wing area you will be able to fly less than 5% slower with a Clark Y wing than with the S3021. If minimum speed is now 20 mph, the new wing will let you fly at 19 mph. That doesn't seem worth the effort.

Tall Paul

.
A common misconception.... The Clark-Y is quite similar to the NACA 2412...
Here's some plots of airfoils in the class...
The GL airfoil is superb for low-speed flying. It will outperform more sexy types like the 3021 in sink rate. The other foils have a wider speed range, and perform better on electrics.

Beulzabob

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What type of airfoil is on a Windrifter? Also, what components of an airfoil affect lowest airspeed?

Robert

kingbee

The Windrifter used a flat bottom section, 11.5% thick, with turbulators between the leading edge and the high point.

The Windrifter and it's relatives were awesome light air machines, the epitome of the gasbag floater. BTW, the Paragon airfoil is almost identical to the Windrifter.

I'll look for a drawing to scan in and attach.

Cheers,
Dave

kingbee

Here's a fatty for ya! This is from a set of Drifter 2 plans, but the Drifter, Windrifter, Viking Mk. 1, and I believe also the Sailaire all used this airfoil.

Cheers,
Dave

Beulzabob

My Feedback: (1)

Thanks Kingbee,

I haven't seen a glider with the turbulators before(wonder if exlax would help). How are they attached? Do you have any pics of gliders with them?



Thanks again,

Robert

Tall Paul

The turbulators are the spars between the leading edge and the main spar. These help prevent the covering from sagging between the ribs, and turbulate the air as a side benefit.

BMatthews

The turbulators in this case are the sub spars that you see in that windrifter pic. They aren't shown in the side view of the airfoil but in pratice they are something like 1/16 x 1/8 cut into the ribs so as to be narrow edge up. Tip, it's been shown that adding an additional supportive "turbulator" spar behind the main spar helps support the covering in that critical area just behind the high point and may aid the slow speed flying near the stall.

The Gentle Lady airfoil is a custom Carl Goldberg airfoil. I can't prove it but I think it saw the light of day on some of the company's free flight power models of the 60's like the Viking. There was some reference to this fact in the original RCM article of the Gentle Lady IIRC. Certainly the plans of the Viking I saw showed a remarkably similar airfoil. This is also one reason why the pure glider Lady flies so much better than the Electras I've seen. This airfoil doesn't seem to like to be heavily loaded like in the Electra. Yes the Electra's fly but the ones I've seen just do not float like the GL's. I can accept faster thanks to the extra loading but the glide slope just does not seem to match the GL. And the stall on the Electra is horrible to see.

Terror Dactyl

If you are just wanting to build a wing use the copied rib pattern, but if you want to try new things you might want to try this. You can get an ARF replacement wing of the Hanher9 Aspire, as it is a 7037 airfoil it could be a nice change.

You could either strip the covering and modify the wing center section in thw saddle area and then cover it the way you want or just make shim plate and use it as it is.

Take care Jim

Jack Hyde

My Feedback: (1)

I don't know what airfoil is on the Winddrifter.

Airfoils are best described by %camber and %thickness. More camber and thickness tend to produce higher lift coefficients so can fly slower. Flat bottom wings are just particular combinations that result in the lower surface being more or less flat. They are moderately cambered. There is nothing special about the flat bottom.

Airfoils with more than 10-12% thickness are on the thick side, less than 8% is getting in the thin zone. Camber of 0% is a symmetrical foil. Clark Y has 3.4% camber. Thin symmetrical airfoils produce lift coefficients of less than 1.0 at the angle of attack just below stall. Some really thick highly cambered foils get nearly cl max = 2.
Most sailplanes use airfoils that produce cl max of 1.0 (eg RG15) to 1.5 (ClarkY, SD 7037). Planes like the GL that float great are very light, therefore don't need much speed to generate enough lift to fly. A 40 oz GL won't float.

Beulzabob

My Feedback: (1)

Okay, so you only have turbulators on non-D tube wings. I can see that that design would help to keep weight low on the gentle lady as a side benefit. Sounds interesting.

Take care,

Robert