airfoil on Gentle Lady

[kevin6Q]

At the risk of committing blasphamy, I was thinking of building some composite (foam/FG/CF/Kevlar) wings for my GL. Reason: I like the way the ship flies and want a winter project w/o constructing a complete new ship and figure the comparison might be fun. Reading through the plans I cannot find the airfoil that was used. I assume it is a C.G. original. I can make templates off the plans and from copies I have of the foil but was hoping to take the lazy way out and use Compufoil. If the foil is a C.G. original any idea of a close approximation? Thanks, Kevin

[tommyt]

I think it was a thinned Clark Y but don't know what it was thinned to.

[sierra-gold]

Why not try something a little more exotic and have a "sleeper." The Dr. Drela wing for the Allegro 2M would be interesting. Maybe even a whole new state of the art floater. :)

Info available here:

http://www.charlesriverrc.org/articles/allegro2m/markdrela_allegro2m.htm

Sierra Gold

[Sparky Paul]

I believe Carl used a Size 12 Thom McAn for the upper surface, and a ruler for the lower.
Scan the airfoil on the plans into the computer and make up a template for your cutter...

[kevin6Q]

Thanks for the help. I guess I'll scan the foil and make up templates. The idea of putting on a differant wing is also interesting. I think I'll bag up a new wing for my old Windfree too. The original hit a grade stake on landing and trashed the wing. I'll let you know what I do and how it goes. Thanks again, Kevin

[TLyttle]

One of the reasons for using spruce dowel for the leading edge, backed up with le sheeting, is so that the grade stake suffers some damage too!

Probably a good assessment of the airfoil by Paul. Interestingly, the high point looks quite far back, which would explain its unusually good flight characteristics IMHO. I also think that a Drela, Selig, or Eppler airfoil (I'm a big 193 fan; old, eh?) would certainly make a difference alright, but the drag of the rest of the airframe might not help any differences in performance. If you put a 454 in a Chevette, ya really have to do something with the frame...

[kevin6Q]

The grade stake did have a mark on it. The biggest reason for bagging the wing is time. It's faster and I live in a small house with two little kids (no ungarded project is safe) and an understanding wife. There are no spare rooms that can be taken over for the time needed to scratch build a new wing. I can grab the kitchen table for a few hours which is the time needed to build a composite wing. I like the look of the GL and just want to get it back into the air and not so much as "hot rod" the glider. The original wing has ben repaired a number of times and now I'm fixing the fixes.

[steelhead]

I think we found the airfopil to be one of a series of "french curve airfoils" and the proverbial "shoesole airfoils" I did a search once for the airfoil to put into my CNC machine but no one seemed to have spent the time or effort. Anyone have the time?

Dean

[TLyttle]

A buddy of mine had the same space problem, and solved it this way: he assessed the clothes in his closet, reorganised them so that they were only taking up the top half, and put in a folding bench in the lower half. I saw some pretty large models appear out of that closet, including one Standard sailplane (100"span)! Opened the door, plugged in a lamp, pulled up a chair, and close the door after building session is over. You may have to put a slide bolt high enough to be out of reach of the kids on the door...

[steelhead]

How hard would it be to place the GL airfoil into a dat file?
I've never done it. Im guessing it wouldnt have to be too perfect, but might be kinda fun to make a bagged wing "SLEEPER" GL

Dean

[Peytr]

I've got a *.cor file of a GL wing profile. Scanned it from a BMP into the Profili database and did some manual and automated smoothing. This would enable you to make templates for cutting wing cores. Never used it myself for anything else than doing X-foil analyses.

The profile definately isn't a thinned Clark Y. The camber is heavier compared with a thinned Clark Y. These are much more versatile foils than the GL foil which is very 'one speed', which actualy is a slow speed, optimised for min. sink and slow flight.

If anyone's interested in the cor file I could send it by email.

[TLyttle]

Wow, I'll have to tell my GL about that, given the opportunity it speeds along quite well... Mind you, I D-tubed and capstripped the wing, BIG difference in performance.

[erikdahlchriste]

Hi,

The GL airfoil is something like the Aquilla:
http://www.gliders.dk/aquilla.htm

It is definitely NOT a thinned Clark Y:
http://www.gliders.dk/clark_y.htm

If somebody want to build a new wing for their 2-meter-something, use a REAL thinned Clark Y. Thinned to 9.0% should do the trick.
You'll get longer legs and about the same sinking speed with a slightly higher flying speed.
http://www.gliders.dk/simplex_2m.htm

cheers
Erik Dahl Christensen
Denmark
www.gliders.dk

[Peytr]

Clark Y, thinned to 9%, tips to 7% is exactly what I did on my polyhedral electric. It thermals beyond belief and has very good l/D. Picking up speed and regaining height (energy retention) is excellent. It's hard to find a better foil for recreational thermal flying than a thinned Clark Y. If you find one it's likely to be very similar to the Clark Y. You should f.i. compare MH32 and SD 7037 with thinned Clark Ys of the same thickness. Please keep in mind to modify the camber pro rata. Funny thing, because the Clark Y was developed in the thirties.
Goldberg otoh designed the Gentle lady to be as gentle as can be: Not to pick up too much speed when accidently diving. He had the beginner in mind and did the right thing. That's why he used a slowish, high lift foil.

Still, the Goldberg and Aquila-like foils are nice if you want a floating plane. You'll be sorry when you hit massive sink however, because you won't be able to pick up enough speed to get out of it, without loosing a lot of altitude. In still air these foils are hard to beat for their low sink. In the real world anything else seems better.

@Erik:
Excellent writing BTW and very, very true.

[erikdahlchriste]

Hi Peytr,

Thank you.

Just one little correction - Clark Y was made in 1924 by Verginia E. Clark

cheers

Erik Dahl Christensen
Denmark
www.gliders.dk

[Peytr]

@Erik

Thanks for the correction.

@Kevin

If you insist on using a high camber flat bottomed foil, the Neelmeyer foil is a very close match to the Aquilla and GL foil. It's in the Profili database f.i.

[steelhead]

Peytr-

Did you get my email address for the .cor files?
Email address is sent in PM
Please send them to me

Dean

[Ronbo]

@Erik
If you insist on using a high camber flat bottomed foil, the Neelmeyer foil is a very close match to the Aquilla and GL foil. It's in the Profili database f.i.

which one is that? #, description, etc?

[Peytr]

Found all PMs, will send you all the *.cor file

@Ronbo:

No # or further description available. I found the Neelmeijer foil in some old book from the 70s and (much to my surprise) also found it in the Profili database. Did an overlay of the GL scanned cor file and the Neelmeijer and they're realy almost similar. The Neelmeijer has a tiny bit more of phillips entry, but barely so.

[IMG]

[TLyttle]

Wow, how close is that???

[steelhead]

well, I think that one is almost too close. As in- when was the neelmeir drawn up and tested, becasue I think they are the same, but maybe a photocopier got a little distortion in there :)

That is almost within scratch building tolerances of wood ribs :)

I bet there is no noticeable difference at the wingloadings and speeds of a 2 meter glider.

Awesome- thanks for that. Peytr- could I bother you for the file ont he neelmeir as well ? MY version of profili doenst have it.

Dean

[Peytr]

Hi Dean,

Wil send the Neelmeyer.cor file to you.

This close one might think Carl looked at it when he drew up the GL. Thickness, camber and location of max. camber are practically the same. The entry of the GL is a bit lower, which should give the foil even more lift and higher resistance at low Cl, which Carl Goldberg intended.
But otoh many so called 'shoe sole', absolutely flat bottomed foils where used from the 50s up until the 80s, because people tended to optimise for min. sink.
The 'dent' in the upper front of the GL foil could very well be copier distortion. The hand of the person who drew the GL plans might also have induced the difference. I don't know if Carl said anything about the origin of the foil in the original RCM GL article.

There will not be any discernable difference in performance between the GL and Neelmeyer anyhow.


That is almost within scratch building tolerances of wood ribs

At least when taking my abilities into account :rolleyes:

[steelhead]

I poisted this on a new thread, please respond there, thanks

Howdy all-

Several people have been inquiring about a foam replacement wing for their Gentle Lady sailplane and I've never really made too many of them, but...

Theres been a lot of talk in my email account again lately about this subject.

One question I have and a favor to ask-

What does a RTF Gentle lady wing weigh? Does anyone have one and a scale nearby? Just need the weight of the wing from a couple of people. I just realized this weekend that I cant find my GL balsa wing anywhere. I have a fuselage though

Thanks for the help. I will try and find in my notebook what the foam wings I've built in the past ended up weighing.

Thanks again,
Dean