WIX Archives

Great minds think alike...

Posted by bdk on Tue Nov 12, 2002 08:26:27 PM

In reply top Re: A little more technical this time (back to school!) posted by Christer on Tue Nov 12, 2002 08:55:29 AM

: This is an interesting "lecture" and as a matter of fact Y
: ou agree with me on quite a few points!?

Great minds think alike... ;-)

: : Note the lip on the top of the scoop that prev
: : ents the radiator from ingesting air disturbed by the ai
: rc
: : raft belly skin.
:
: Isn?t this laminar flow theory as well?!

In a way, basically the scoop only picks up the laminar air and discards the "dirty" air.

: Which is the actual definition of laminar flow profiles?
: Is there a specific transition point from laminar to turbu
: lent in percentage of the chord?
: Is there a specific point for maximum profile thickness th
: at should be far back enough?

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

: It was me who mentioned the "laminar pocket", maybe it?s c
: alled the laminar bucket or as You say the "drag bucket".
: I?ve seen "CL (lift coefficient) to drag" diagrams showing
: the Mustang profile to have considerably lower drag under
: angle of attack conditions corresponding to 1G but higher
: drag at higher and lower angles of attack, when compared
: to a "non-laminar-flow" profile.
: It also has a lower maximum CL at a lower maximum angle of
: attack.

Yes, it was you... My apologies.

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 laminar 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 indicate 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.

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

: Don?t they have to slow down quite a lot to take the turns
: ?
: Even at 6Gs they would see half the state of Nevada at 500
: MPH. Don?t they use some kind of climb-turn-decend techni
: que to convert speed to height to get an optimized turn an
: d then use the height to accelerate out of the turn?
: I don?t know how much time is spent turning and straight a
: head respectively during a lap but I think that they spend
: relatively short time at low speed turning and much longe
: r at high speed straight ahead.
: If they go 550 MPH flat out then they can go pretty slow a
: t the corners and still acchieve an average of 500 MPH.
: I don?t know however, I?m just speculating!?

Christer, I think you need a vacation! Go to Reno next year!!

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 lower 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, you wouldn't want to be jockeying around up and down with the throttle at every turn.

There are different techniques used, and some may differ depending 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 (20-40%?). At 500 MPH you could probably zoom climb to 8 or 10 thousand feet, so a hundred feet or so of elevation change would not slow the aircraft significantly. I think the advantage would be to fly the course as smoothly as possible and minimize the control surface inputs which can cause significant drag.

: Tests carried out by Supermarine, comparing two identical
: Mk.Vs (apart from the wingtips) showed that the clipped wi
: ng was superior at low altitudes, they were quite equal a
: t medium altitudes and the normal span wing was superior a
: t high altitudes.

Superior in what way? Reduced span improves roll rate, and the high atmospheric pressure at low altitude makes reduced wing area acceptable. Reno runs fastest at the highest temperature and lowest atmospheric pressure (highest density altitude- similar to what you might find at 10-12 thousand feet) where drag is lower than at sea level. This far overcomes the improved cooling and engine breathing at cooler temperatures and low altitudes.

: : My conclusion is that you need to install a P-51 scoop o
: n
: : a Spitfire, enclose the wheels/retract the tailwheel, in
: st
: : all a small canopy, buy a racing engine, and hope you ca
: n
: : land in a 50 kt crosswind at Reno with that narrow gear.
: T
: : hen you are ready!
:
: If it?s a new build airframe I would opt for a Spiteful wi
: th the inwards retracting main gear and low back fuselage.

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

: : I would really like to see a competitively raced Spitfir
: e
: : at Reno some year (along with the 3-engined P-38 and the
: P
: : -82 with the Griffons). Maybe it will happen some day. T
: he
: : variety would be nice. :-)
:
: I agree!
: Are those two on the web? If so, do You have the links?

Nope, just some rumors that I've heard in the past few years. I think that the P-82 rumor was from this past year on one of the other forums.

Laminar flow theory

Follow Ups: