WIX Archives

Well, disturbed ones too ......

Posted by Christer on Wed Nov 13, 2002 07:04:51 AM

In reply top Great minds think alike... posted by bdk on Tue Nov 12, 2002 08:26:27 PM

Interesting discussion but I think that all others are bored stiff, so, let?s continue! ;-)

: Following the link, we find, "The usual definition of a la
: minar flow airfoil is that the favorable pressure gradient
: ends somewhere between 30 and 75% of chord."

Yes, that?s what I seem to remember.

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.
According to the above definition, the glider I?m flying (ASW 27) wouldn?t have a laminar flow profile though. Since the transition point on the lower surface moves along the chord depending on the speed the designer decided to trigger the transition at a certain position to make it as favourable as possible. This is done by injecting air into the 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 ailerons at close to 90%!

: Yes, it was you... My apologies.

No need for that, I just didn?t want someone else to take the heat for my bad memory.

: See an example of the drag bucket on the last illustration
: here: http://www.dreesecode.com/other/aflprimer.pdf The
: NACA 0012 is a symmetrical non-laminar section as I recall
: and has no drag bucket. The 65-215 is a non-symmetrical l
: aminar section (again, my recollection). You can see that
: it features a trough at the bottom where drag is less than
: the shape of the remainder of the curve would seem to ind
: icate as being expected. As long as you stay within a lift
: coefficient of 0.0 and 0.5, you will have less drag than
: would otherwise be expected.

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

: What angle of attack is a P-51 at in cruise? Dago at 500 M
: PH? Maybe we can calculate this to prove our theories?

I?ll have to think about that one. My mind isn?t as great as I?ve mislead You to believe ;-) but maybe I?ll find that book ......

: Christer, I think you need a vacation! Go to Reno next yea
: r!!

Well, I?d really enjoy it, I?ve tried to go to Legends for some ten years now but not succeded ...... and Duxford is closer to Sweden than Reno ...... something or someone always intervenes.

: Far from being like a sports car race where you slow down
: for the turns, Reno is flown at a continuous power setting
: around the course. Of course you may fly at a somewhat lo
: wer power at the beginning of the race to save the engine,
: then increase power to sprint the last two laps or so if
: the race is tight. At the manifold pressures being run, yo
: u wouldn't want to be jockeying around up and down with th
: e throttle at every turn.
:
: There are different techniques used, and some may differ d
: epending on the airplane as well. In addition, the course
: at Reno is not at a constant elevation. At nearly 500 MPH,
: Dago would spend a great deal of time in banked flight (2
: 0-40%?). At 500 MPH you could probably zoom climb to 8 or
: 10 thousand feet, so a hundred feet or so of elevation cha
: nge would not slow the aircraft significantly. I think the
: advantage would be to fly the course as smoothly as possi
: ble and minimize the control surface inputs which can caus
: e significant drag.

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

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

: Superior in what way? Reduced span improves roll rate, and
: the high atmospheric pressure at low altitude makes reduc
: ed wing area acceptable.

The short version of the test results:

Level speed; at 10,000ft clipped +5mph; at 15-20,000ft no difference; at 25,000ft standard very slightly faster.

Sustained Climb; differences not measurable.

Zoom Climb; from 10,000ft to 15,000ft no difference; from 20,000ft to 25,000ft standard 15 seconds faster.

Rate of roll, Acceleration and Dive; clipped superior

Turning circle, the minimum turning circle was increased by 55ft at 1,025ft for the clipped.

Manouevrability in combat, up to 25,000ft clipped is superior, above 25,000ft no difference.

: Reno runs fastest at the highest
: temperature and lowest atmospheric pressure (highest densi
: ty altitude- similar to what you might find at 10-12 thous
: and feet) where drag is lower than at sea level. This far
: overcomes the improved cooling and engine breathing at coo
: ler temperatures and low altitudes.

Do they modify the superchargers or are they standard?
If they are standard the best performance should be at approximately 5,000ft above rated altitude. IIRC rated altitude for the V-1650-7 in low gear is 7,000ft which would bring us to maximum performance at 12,000ft.

: Sounds like the right choice to me...but how about buildin
: g another Tsunami? A little more tailored to racing than a
: warbird. I mean the idea is to go the fastest, right?

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

Christer

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