WIX Archives
Somewhere there´s a line ......
Posted by Christer on Sun Nov 17, 2002 06:56:16 PM
In reply top Not offended in the least! I've been busy at work... posted by bdk on Fri Nov 15, 2002 07:56:51 PM
...... and when you cross it someone might get annoyed. It?s not easy to make a joke on the web since people can?t see your face and said line could be crossed much sooner, don?t You think?
: I've never heard this (doesn't mean it is false, of course
: ). Comparing a helicopter under power to a gyroplane you h
: ave a different flow direction through the rotor disk, but
: a sailplane should have exactly the same requirements as
: a powered plane I would think.
The designer explained that the air flow is laminar further back on the lower surface than on the upper due to the camber. Something like 60 % on the upper and as far back as 90 % on the lower surface.
At low speeds, e.g. when thermalling, it?s important that the airflow stays laminar as long as possible on the upper surface for good climbing performance.
At high speeds these profiles don?t work without beeing blown or having a mechanical trigger fitted (a zig-zag tape 3 mm wide and 0.5 mm thick). If the airflow is allowed to reach separation on it?s own, then kind of a vortex is generated which rotates backwards in under itself. It tries to even out the underpressure at the transition point and the oncoming airflow "sees" this as a bump on the profile and the drag increases dramatically. If the transition is triggered, by blowing or mechanically, before this happens the airflow gets turbulent but is still attached and it can even regain laminar properties.
: A sailplane normally flies at the best glide angle, which
: would probably be a higher angle of attack than a powered
: aircraft (assuming sufficient wing area). Maybe that is wh
: y a laminar flow section is not used, it would be outside
: the drg bucket at that angle of attack.
I was trying to be funny, it is a laminar flow profile which exceeds Your quoted criteria (30-70%).
The guy with whom I share the glider also flies a thingie called seven-six-seven. He says that it too flies at best L/D (glide ratio) when cruising. At cruising altitude the true airspeed for the best L/D is that high. Flying at the best L/D gives the best fuel economy.
: Hmmmm... Maybe this boundary layer control (maybe a vortex
: generator) is for pressure recovery at the rear of the ai
: rfoil? This is a component of the flow pressure gradient t
: hat pushes the airfoil forward. Vortex generators re-energ
: ize the flow and if designed properly can cause the flow t
: o re-attach itself to the airfoil.
When am I going to learn to read the whole post before replying, at least I think that?s what I said above, in poorer english though.
: I understand that the best racing Merlins use Allison conn
: ecting rods as they are more robust. Different connecting
: rod length and water/alchohol injection will really upset
: the engine performance equation. Some racers also used to
: add manganese to thier fuel as a combustion enhancer.
I almost expected this answer when I typed the question ...... modifications en masse ......
: I'm all for it! Do you have a rich uncle that could be a s
: ponsor???? :-)
Nope, none that I?m aware of but I?m on the lookout for a rich widow ...... ;-)