WIX Archives

Not offended in the least! I've been busy at work...

Posted by bdk on Fri Nov 15, 2002 07:56:51 PM

In reply top Well, disturbed ones too ...... posted by Christer on Wed Nov 13, 2002 07:04:51 AM


: For a sailplane, laminar flow on the lower surface of the
: wing is important for good gliding performance and laminar
: flow on the upper surface is important for good climbing
: performance.

I've never heard this (doesn't mean it is false, of course). Comparing a helicopter under power to a gyroplane you have a different flow direction through the rotor disk, but a sailplane should have exactly the same requirements as a powered plane I would think.

: According to the above definition, the glider I?m flying (
: ASW 27) wouldn?t have a laminar flow profile though.

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 why a laminar flow section is not used, it would be outside the drg bucket at that angle of attack.

: Since
: the transition point on the lower surface moves along the
: chord depending on the speed the designer decided to trig
: ger the transition at a certain position to make it as fav
: ourable as possible. This is done by injecting air into th
: e airflow through small holes drilled in the wing (approx.
: 2,000 of them, 0.8 mm dia.). The holes are not positioned
: in the wing but as far back as in the flaps and the ailer
: ons at close to 90%!

Hmmmm... Maybe this boundary layer control (maybe a vortex generator) is for pressure recovery at the rear of the airfoil? This is a component of the flow pressure gradient that pushes the airfoil forward. Vortex generators re-energize the flow and if designed properly can cause the flow to re-attach itself to the airfoil.

: That?s exactly how I remember it. Good performance at low
: CLs and somewhat worse at high CLs.

Much lower drag in the drag bucket, but much higher drag outside compared to a conventional airfoil.

: Okey, I understand but I didn?t mean reducing power. I saw
: it on TV years ago and maybe slower aircraft use a techni
: que that resembles my memory of it? When they started bank
: ing they pitched up at the same time getting the nose in t
: he new direction rather quickly. I understood it at the ti
: me I saw it as trying to fly the shortest distance around
: the pylons and there must be some optimum between drag inc
: rease through control input and distance flown.

Maybe so in the slower classes, but it may also be an involuntary (or voluntary) reaction to avoid overcontrolling and sinking into the ground at high bank angles. It can also get quite turbulent flying in the wake of other aircraft pulling high G's (lots of lift = strong tip vortices). This year, the final gold race at Reno was held in very high winds (50 + MPH!).

: I wonder what the average speeds are, calculated over the
: actually flown distance! Fit a GNSS-logger and find out!

I wonder if anyone has done that yet? I am not aware that any of the teams are using data loggers, but maybe they are now.

: Do they modify the superchargers or are they standard?

Even the T-6 racers polish their supercharger housings to be competetive these days. I believe they also shim the back of the impeller to reduce the clearance with the housing.

: If they are standard the best performance should be at app
: roximately 5,000ft above rated altitude. IIRC rated altitu
: de for the V-1650-7 in low gear is 7,000ft which would bri
: ng us to maximum performance at 12,000ft.

I understand that the best racing Merlins use Allison connecting 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.

: Yes indeed and Carbon/Aramid/Polyethylen springs to my min
: d.
: Maybe a new WIX-project for our american contingent!?

I'm all for it! Do you have a rich uncle that could be a sponsor???? :-)

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