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Old Dec 27, 2002, 02:32 PM
R. Tyson
Guest
n/a Posts
[RCSE] Leading edge radius

I am making a built up wing for a 100" RES.
The airfoil is Selig 7037.
I have planed the leading edge to match the front profile of the
D box section.
The leading edge is now a fairly sharp radius it is also slightly
too deep so I could sand it back to a blunter more rounded profile.

Having no real knowledge of airfoils I am tempted to think that
the sharper leading edge (more streamlined) looks as though it
would be better. I also suspect I would be wrong !

Do I sand it back to the proper radius so the leading edge is then
the same as the original drawing ? What would be detrimental about
using the sharper leading edge ?

Regards,
Reg (poised with sanding block ready)







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Old Dec 27, 2002, 02:32 PM
Jim Larkin
Guest
n/a Posts
Re: [RCSE] Leading edge radius

Sand it back--If not--you dont have a 7037 !!! Jim
----- Original Message -----
From: "R. Tyson" <r.tyson@lineone.net>
To: <soaring@airage.com>
Sent: Friday, December 27, 2002 1:23 PM
Subject: [RCSE] Leading edge radius


> I am making a built up wing for a 100" RES.
> The airfoil is Selig 7037.
> I have planed the leading edge to match the front profile of the
> D box section.
> The leading edge is now a fairly sharp radius it is also slightly
> too deep so I could sand it back to a blunter more rounded profile.
>
> Having no real knowledge of airfoils I am tempted to think that
> the sharper leading edge (more streamlined) looks as though it
> would be better. I also suspect I would be wrong !
>
> Do I sand it back to the proper radius so the leading edge is then
> the same as the original drawing ? What would be detrimental about
> using the sharper leading edge ?
>
> Regards,
> Reg (poised with sanding block ready)
>
>
>
>
>
>
>
> RCSE-List facilities provided by Model Airplane News. Send "subscribe"

and "unsubscribe" requests to soaring-request@airage.com. Please note that
subscribe and unsubscribe messages must be sent in text only format with
MIME turned off.
>



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Old Dec 27, 2002, 02:52 PM
Bill Swingle
Guest
n/a Posts
RE: [RCSE] Leading edge radius

Good question.

Short answer: Make it exactly like the foil shape. (available on line or
from other modelers, I have it if you need it)

Discussion: Airfoils are very complicated. Even with lots of experience it
can be difficult to make valid assumptions. The "feel" of an airplane is
subject to the pilots style and personal preference. Personally, I generally
(opinionated assumption coming) don't like a sharp LE. Whether I put it's
the design of the foil or I just put it there myself. But, there are foils
designed with a sharp LE for very good reason.

The 7037 is a foil which I don't think will be very picky either way. BUT, I
don't *really* know. Thus, unless you're designing your own foil, it's
always best to stick to the published shape.

Bill Swingle
Janesville, CA
bill_swingle@onemain.com

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Old Dec 27, 2002, 02:52 PM
Jeb Bushell
Guest
n/a Posts
Re: [RCSE] Leading edge radius

--- "R. Tyson" <r.tyson@lineone.net> wrote:

> Do I sand it(the LE) back to the proper radius so

the
> leading edge is then the same as the original

drawing ?

Yes. If you want to fly a 7037 which is probably the
most popular sailplane airfoil around at the moment.

>What would be detrimental about using the sharper

leading edge?

This is really one for the experts (i.e. someone else)
but if you don't hear from them...

A) if the foremost part of your LE is not in the same
relative position as the official 7037 then you will
have changed the camber. This will affect a bunch of
characteristics.

B) Sharpening the LE tends to make the stall occur at
a lower angle of attack which means that you may not
be able to get the maximum possible lift out of the
wing which will mean that thermalling is difficult.
This point should clinch it for a thermal soarer.

It is unlikely that you would render the plane
unflyable by leaving the LE sharp, but it might become
a slope-soarer

HTH,

Jeb





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Old Dec 27, 2002, 04:42 PM
Raschow@aol.com
Guest
n/a Posts
Re: [RCSE] Leading edge radius

In a message dated 12/27/02 2:23:51 PM Eastern Standard Time,
r.tyson@lineone.net writes:

> What would be detrimental about
> using the sharper leading edge ?
>


Typically, an earlier (at lower angle of attack) and sharper stall. Not
desirable, particularly if it occurs outboard (nearer tip) first. Best to
restore design LE radius (and use a little washout).
Good Lift!

Old Dec 27, 2002, 06:42 PM
Harley Michaelis
Guest
n/a Posts
Re: [RCSE] Leading edge radius

Reg. . . I see that others have addressed the pros and cons.

Before you go any further, drop that sanding block and make a suitable tool
for working LE's. No, don't bother with a T bar .

Get a cheap carpenter's level made from an aluminum extrusion. I've had a 3
footer for over 20 years. Having recently found a 2 foot level for 2 bucks
in a bargain box, now I have a handy 2 footer. Before buying, eyeball it to
be sure the edges are flat and straight.

Get some cloth backed, roll type sanding tape with #80 and #120 grits. If it
comes with a sticky backing just attach it to the two flat sides. Trim any
excess. Otherwise 3M77 applied to both the level and the tape will work, but
mask where you don't want the stuff. Goo Gone will remove the overspray,
though.

Lay the wing on a flat surface with the tool adjacent to it. Work the tool
to shape the LE. Easy does it. Tilt the tool and the wing (or invert it) as
needed to get all around the LE.

Frequently check with the LE templates to see how you are doing. If you
totally mess up, use a bandsaw, etc. to remove all but about 1/16" of the
wood, true it up with the tool, attach another strip and start over.

----- Original Message -----
From: "R. Tyson" <r.tyson@lineone.net>
To: <soaring@airage.com>
Sent: Friday, December 27, 2002 11:23 AM
Subject: [RCSE] Leading edge radius


> I am making a built up wing for a 100" RES.
> The airfoil is Selig 7037.
> I have planed the leading edge to match the front profile of the
> D box section.
> The leading edge is now a fairly sharp radius it is also slightly
> too deep so I could sand it back to a blunter more rounded profile.
>
> Having no real knowledge of airfoils I am tempted to think that
> the sharper leading edge (more streamlined) looks as though it
> would be better. I also suspect I would be wrong !
>
> Do I sand it back to the proper radius so the leading edge is then
> the same as the original drawing ? What would be detrimental about
> using the sharper leading edge ?
>
> Regards,
> Reg (poised with sanding block ready)
>
>
>
>
>
>
>
> RCSE-List facilities provided by Model Airplane News. Send "subscribe"

and "unsubscribe" requests to soaring-request@airage.com. Please note that
subscribe and unsubscribe messages must be sent in text only format with
MIME turned off.
>


RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to soaring-request@airage.com. Please note that subscribe and unsubscribe messages must be sent in text only format with MIME turned off.
Old Dec 28, 2002, 03:22 PM
R. Tyson
Guest
n/a Posts
Re: [RCSE] Leading edge radius

On Fri, Dec 27, 2002 at 03:34:35PM -0800, Harley Michaelis wrote:
> Reg. . . I see that others have addressed the pros and cons.
>


Thank you for the timely advice. I had not started sanding so I will
use your method. I have a good 3ft level, double sided sticky tape and
enough sanding materials, so I can get going.

Your idea is a good one and thank you for the further information on how
to recover from the situation if I get it wrong.

I am new to RC (left it a bit late in life to discover it) I built my
first glider a 100 inch RES from a kit at the beginning of last year.
Learnt to fly by chucking a zagi off my local slopes, then moved up to
the RES. My first plane flies very well and I thought I would buy the
wood and build another copy with just a few small modifications.
Whilst initialy shaping the leading edge I realised I could have it
thinner... fortunately I have just enough knowledge to know that I
don't know.... thought I had better get advice !

Thanks again for the replies, once I thought about them it all
made sense.

A very happy New Year to everyone,
Reg
> Before you go any further, drop that sanding block and make a suitable tool
> for working LE's. No, don't bother with a T bar .
>
> Get a cheap carpenter's level made from an aluminum extrusion. I've had a 3
> footer for over 20 years. Having recently found a 2 foot level for 2 bucks
> in a bargain box, now I have a handy 2 footer. Before buying, eyeball it to
> be sure the edges are flat and straight.
>
> Get some cloth backed, roll type sanding tape with #80 and #120 grits. If it
> comes with a sticky backing just attach it to the two flat sides. Trim any
> excess. Otherwise 3M77 applied to both the level and the tape will work, but
> mask where you don't want the stuff. Goo Gone will remove the overspray,
> though.
>
> Lay the wing on a flat surface with the tool adjacent to it. Work the tool
> to shape the LE. Easy does it. Tilt the tool and the wing (or invert it) as
> needed to get all around the LE.
>
> Frequently check with the LE templates to see how you are doing. If you
> totally mess up, use a bandsaw, etc. to remove all but about 1/16" of the
> wood, true it up with the tool, attach another strip and start over.
>



RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to soaring-request@airage.com. Please note that subscribe and unsubscribe messages must be sent in text only format with MIME turned off.
 


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