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Author Topic: HQ35/12 Airfoil  (Read 42142 times)

joe

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HQ35/12 Airfoil
« on: December 11, 2006, 11:19:22 AM »
Recently read an article in a mag about HQ35/12.The writer had used this profile on many sailplane to great effect.
It is aparently designed specifically for use with scale sailplanes.
It has a good level of efficiency and excellent low speed behaviour.
Where the root of many vintage gliders is quite thick.The thickness of the airfoil(thats the 12 part of 35/12) can be incressed at that point to say 16%and than tapered back to 12% at the tip.
All sound pretty good and apparently no need for washout!
Maybe worth looking into for a next project?
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Fred

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HQ35/12 Airfoil
« Reply #1 on: December 11, 2006, 12:38:56 PM »
Hi there,

On the Retroplane forum, there is a scale airfoil project going on.
We are lucky to have some professional Aerodynamist working with us !
The latest profile is the MS 535


Most of the vintage sailplanes are using the Go535. Mathieu (MS) have updated this profile for us with a bigger TE (easier to cut) and made some calculations for 3 thickness :


The file can be found  here : http://www.retroplane.net/forum/download.php?id=177

A second profile has been developped : The MS Retro. Flat profile, a bit like the ClarkY, but once again, developped for our scaled use. Easy to build also with a big TE too :


And the file, with 3 thicknesses can be downloaded here : http://www.retroplane.net/forum/download.php?id=26

If interrested, I can give you the use on the glider for each thickness.

Fred
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Happy Days

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Where does the lift come from?
« Reply #2 on: March 23, 2008, 16:40:22 PM »
Okay chaps,

If the lift from an aerofoil is suposed to come from the camber on the underside, how does a flat bottomed wing creat lift?
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IceWind

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HQ35/12 Airfoil
« Reply #3 on: March 23, 2008, 19:38:28 PM »
There is more in it than the camber. :)
If not how a flat wing shockflyer would fly.
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..Nando

Alan_Perse

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HQ35/12 Airfoil
« Reply #4 on: March 23, 2008, 19:48:06 PM »
Hi Happy Days. Welcome to the forum.

A wing can still have camber with out having a curve on the botton of the wing. I'll try to explane with the diagram at the bottom. The straight line distance (the blue line) from the leading edge of the wing to the traling edge is called the chord line. The line that is equally distant from the top surface and the bottom surface (the red line) is called the camber line. The maxium distance between the chord and camber line is the camber of the wing.
Also, hopefully this won't mess things up  :D , a wing does not have to have camber to creat lift. It's the angle that the wing meets the air at (called the angle of attack) which creats lift.
Hope this helps.

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Alan_Perse

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HQ35/12 Airfoil
« Reply #5 on: March 23, 2008, 19:51:01 PM »
Fernando got there before me  :D . Doh!!  :D . Yes there is more to lift generation than camber.
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IceWind

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HQ35/12 Airfoil
« Reply #6 on: March 23, 2008, 19:53:56 PM »
Ahh!
I changed back mine because your explains way better! :)
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Happy Days

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HQ35/12 Airfoil
« Reply #7 on: March 23, 2008, 20:27:04 PM »
Yes,..........I'm fine with the concept of lift being derived from having pressure exerted on the underside of a wing. As I remember from my school days (circa 1897) about 25% of a wing's lift comes from air 'hitting' the underside of the wing.
However. I'm sure we were taught that 75% of the lift comes from air having to travel over the greater distance over the top camber of the wing and thereby ahving to travel faster than the air traveling under the wing This causes a reduction of pressure on that top camber due to what I think was called the "Venturie" effect. (The same effect that causes petrol to rise from the float chamber in a carburettor. But let's not get bogged down with internal combustion engines. Horrid smelly things.)
This then leaves the wing with relatively higher pressure on the botton, and relatively lower pressure on the top, hence LIFT.

Am I right so far???
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Fred

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HQ35/12 Airfoil
« Reply #8 on: March 23, 2008, 20:27:20 PM »
The lift is generated by the top surface (difference of speed between the top and the bottom of the traveling air), usually, on the first 1/3 of the root (then, the air layer simply don't stick to the surface).

So, basically, you don't need camber to generate lift (Clark Y and so on..) but... :D

...Adding camber to a wing will generate more lift ! Same story, the air travel further, generating more lift, increasing also the critical angle of attack before stalling (a cabered profile generate lift, even at 0 degrees of angle of attack)
 All perfect in the good world ? Well, not really, as adding camber, generate more drag too... Question of compromise !  :D
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Fred

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HQ35/12 Airfoil
« Reply #9 on: March 23, 2008, 20:30:23 PM »
Quote from: "Happy Days"
Yes,..........I'm fine with the concept of lift being derived from having pressure exerted on the underside of a wing. As I remember from my school days (circa 1897) about 25% of a wing's lift comes from air 'hitting' the underside of the wing.
However. I'm sure we were taught that 75% of the lift comes from air having to travel over the greater distance over the top camber of the wing and thereby ahving to travel faster than the air traveling under the wing This causes a reduction of pressure on that top camber due to what I think was called the "Venturie" effect. (The same effect that causes petrol to rise from the float chamber in a carburettor. But let's not get bogged down with internal combustion engines. Horrid smelly things.)
This then leaves the wing with relatively higher pressure on the botton, and relatively lower pressure on the top, hence LIFT.

Am I right so far???


Yep, you are right !
The lift is created by the difference of pressure between the top and the bottom.
Generaly, most of the lift is generated by the first 1/3 of the profile, on the upper surface.
This is the air speed difference between the top and bottom that create the lift.
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Happy Days

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HQ35/12 Airfoil
« Reply #10 on: March 23, 2008, 20:37:06 PM »
Okay,.............Thanks Fred, and you other guys, for replying. I must go away and think about this. It's all very interesting stuff. Hmmmmmmmmmmmmm.................!
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Fred

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HQ35/12 Airfoil
« Reply #11 on: March 23, 2008, 20:39:14 PM »
You're welcome !  :D

btw, forgot to say, Fernando, in a shockflyer, this is the incidence of the wing that create the lift (well, sort of lift, I will more call that a air deflection  :P ), not the "profile".  :D
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Happy Days

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HQ35/12 Airfoil
« Reply #12 on: March 23, 2008, 20:44:27 PM »
So Fred, you're saying that the shockflyer merely deflects air in one direction and the wing "reacts" in the opposite direction? like a rudder perhaps?
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Fred

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« Reply #13 on: March 23, 2008, 20:51:30 PM »
Exactly !  :D

The wind speed at the top and bottom are the same (flat), no lift generated, only drag.
Change the incidence, and you will go up or down.  :D  As you say, abit like a rudder / elevator or your hand through the window of your car in good speed !  :D
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Happy Days

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HQ35/12 Airfoil
« Reply #14 on: March 23, 2008, 21:35:20 PM »
I'm thinking of a symmetrical wing. the camber on the top is equall to the camber on the bottom. Assuming zero angle of incidence and zero angle of attack where does the lift come from?
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