ASG 29 or Ventus
Problem for sailplane manufacturers could be one of survival over the next couple of years, don't think much money will be going on R & D.
When I was flying (18 years ago) Sailplane design was very much in the head of the designer, since then computers have played their part & wind tunnel testing has become more available. Winglets which had been experimented with in the past unsuccessfully (only real development tool was flight testing) are now much more optimised & common. Performance has been pushed forward largely by a new aerofoil section & laminar flow over the wing is extensive, I don't see where a performance jump can come from although it would be foolish to suggest the limit had been reached although I think its probably very close. Historically a number of people have claimed that by boundary layer control they could achieve extreme performance, why then has nobody tried & anyway today's wings have such extensive laminar flow that there is probably not much to be gained if you could do it. Lower wing surface turbulators have for over 20years been fitted just infront of control surfaces so boundary control on the lower wing is not needed, not sure what percentage of the top surface is laminar but I bet it leaves very little that could benefit from suction.
Interesting projects over the years that tried by less conventional means to advance performance are, FS29 with its telescopic wing, Sigma with its variable wing area, SB11 with variable wing area (WGC winner as well) The South African BJ series the last of which had a variable aerofoil section although I'm not sure it flew.
When I was flying (18 years ago) Sailplane design was very much in the head of the designer, since then computers have played their part & wind tunnel testing has become more available. Winglets which had been experimented with in the past unsuccessfully (only real development tool was flight testing) are now much more optimised & common. Performance has been pushed forward largely by a new aerofoil section & laminar flow over the wing is extensive, I don't see where a performance jump can come from although it would be foolish to suggest the limit had been reached although I think its probably very close. Historically a number of people have claimed that by boundary layer control they could achieve extreme performance, why then has nobody tried & anyway today's wings have such extensive laminar flow that there is probably not much to be gained if you could do it. Lower wing surface turbulators have for over 20years been fitted just infront of control surfaces so boundary control on the lower wing is not needed, not sure what percentage of the top surface is laminar but I bet it leaves very little that could benefit from suction.
Interesting projects over the years that tried by less conventional means to advance performance are, FS29 with its telescopic wing, Sigma with its variable wing area, SB11 with variable wing area (WGC winner as well) The South African BJ series the last of which had a variable aerofoil section although I'm not sure it flew.
I don't know if you now Prof. Loek Boermans. He is one of the leading designers of new airfoils for gliders. He has designed the wing for the Antares, Dg-800 and has helpt with the wingdesigns for SH and Schleicher. With the most modern wingdesigns they get about 40% laminar flow on the top surface. So there is still 60% left to put laminar flow on. The problem is that laminar flow is easier to separate than turbulent flow (less kenetic energy in a laminar boundary layer than a turbulent one). So keeping a laminar flow further and further over the wing would seriously affect the stall angle of atack (you will notice that the modern preformance sailplanes stall easier and more sudden than the old wooden gliders with mostly turbulent boundarylayers). It would be an other big leap in preformance if you can keep a laminar boundary layer from separating over a big part of the upper surface of the wing.
PH-1504, KOE
A little, but the problem is that laminar flow tends to separate real easy. It causes real handeling problems having to much laminar flow.
A stall depends on 2 things: The adverse pressure gradient (pressure rising from the thickest part of the wing to the trailing edge) and the kenetic energy (energy due to air moving) in the boundary layer. To overcome the adverse pressure gradient (air does not like to flow from low to high pressure) the kenetic energy gets used until it runs out and the flow separates. The more the adverse pressuregradient (for instance if you raise the angle of attack) the earlier the boundary layer runs out of kenetic energy and the flow separates. Or if you fly slower and the air has less kenetic energy to overcome a given adverse pressure gradient it also separates early. If you get to much flow separating, you stall.
This means that if you have less kenetic energy in the boundary layer to begin with (with a laminar flow wing) you tend to stall earlier (as with the modern gliders). So you can't just make the airflow laminar all the way to the end of the wing. You would probably stall even if you try to get off the ground. What would realy get preformance further up would be some way of putting energy back into the boundary layer so that it can overcome big adverse pressure gradients.
A stall depends on 2 things: The adverse pressure gradient (pressure rising from the thickest part of the wing to the trailing edge) and the kenetic energy (energy due to air moving) in the boundary layer. To overcome the adverse pressure gradient (air does not like to flow from low to high pressure) the kenetic energy gets used until it runs out and the flow separates. The more the adverse pressuregradient (for instance if you raise the angle of attack) the earlier the boundary layer runs out of kenetic energy and the flow separates. Or if you fly slower and the air has less kenetic energy to overcome a given adverse pressure gradient it also separates early. If you get to much flow separating, you stall.
This means that if you have less kenetic energy in the boundary layer to begin with (with a laminar flow wing) you tend to stall earlier (as with the modern gliders). So you can't just make the airflow laminar all the way to the end of the wing. You would probably stall even if you try to get off the ground. What would realy get preformance further up would be some way of putting energy back into the boundary layer so that it can overcome big adverse pressure gradients.
PH-1504, KOE
Problem with boundary layer control & gliders is that it can be argued that the glider would then become a powered aircraft. Also having sucked a large volume of air from the wing you need to get rid of it, the obvious way would be to discharge it somewhere around the base of the fin/rudder which would also give a bit of thrust, I suppose you could use some to 'blow' the flaps/ailerons but again you would get into the thrust arguement . That's all before you start worrying about how to provide the power necessary to 'pump' air from the wing & what happens when it rains or when you are at high altitude 
The topic has been discussed since before I started gliding & that was long before you were born I bet it will still be discussed long after I'm gone as well
The topic has been discussed since before I started gliding & that was long before you were born
I bet it will still be discussed long after I'm gone as well 
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mumbles
- Posts: 3
- Joined: Wed Apr 05, 2006 10:57 pm
- Location: Lynchburg, Virginia, United States
- Contact:
There is a lot of research going into how to extend the laminar flow back without additional sources of power. Deturbulators are strips of tape that are put along the wing to help maintain laminar flow farther back on the wing.
http://71.18.117.131/aero.asp
The website here claims a 25% increase in glide ratio. On some flight tests, glide ratios of 100:1 have been observed on a Standard Cirrus. Still has a ways to go for everyday use on gliders, but some interesting research.
http://71.18.117.131/aero.asp
The website here claims a 25% increase in glide ratio. On some flight tests, glide ratios of 100:1 have been observed on a Standard Cirrus. Still has a ways to go for everyday use on gliders, but some interesting research.
Joshua Clark
M41
N9223S
"Mumbles"
M41
N9223S
"Mumbles"
There's some very interesting stuff there although I wonder why after 2 years of the Cirrus flying with it there does not seem to be manufacturer interest. I would have expected a few experiments to be underway in Germany as things can move quite quickly in the gliding world & its not something you could test without it being noticed.
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TimKuijpers
- Posts: 3214
- Joined: Sun Apr 24, 2005 12:33 am
- Location: The Netherlands
It's too much rubbish I've heard.
The measurements are not reliable,
and when you ask serious questions he cannot answer.
Why didnt we see a cirrus like that on the WGC clubclass?
or maybe even standard class..
I wouldnt mind to give it a try though, but if he really is sure about it, he should have promoted this much and much sooner.
The measurements are not reliable,
and when you ask serious questions he cannot answer.
Why didnt we see a cirrus like that on the WGC clubclass?
or maybe even standard class..
I wouldnt mind to give it a try though, but if he really is sure about it, he should have promoted this much and much sooner.
Think positive, flaps negative.
I agree with Tim.. a few months ago, I gave mr. Sinha an e-mail and asked him about the status of the project.. he said the project was finished and he now sells his deturbulator strips.. he also said a price and it wasn't cheap.. 
That must be the reason why not every competition glider is equiped with the strips..
I have learned something about marketing strategics, and this is the strangest product-selling I have ever seen.. I think there is a monkey in a sleeve..
That must be the reason why not every competition glider is equiped with the strips..I have learned something about marketing strategics, and this is the strangest product-selling I have ever seen.. I think there is a monkey in a sleeve..
