WIX Archives

Re: A little more technical this time (back to school!)

Posted by Christer on Tue Nov 12, 2002 08:55:29 AM

In reply top A little more technical this time (back to school!) posted by bdk on Mon Nov 11, 2002 09:06:28 PM

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

: NACA did a number of studies during the war years

I haven?t checked but I think those reports can be found here: http://naca.larc.nasa.gov/

: Note the lip on the top of the scoop that prev
: ents the radiator from ingesting air disturbed by the airc
: raft belly skin.

Isn?t this laminar flow theory as well?!

: Spit/109 system poor to begi
: n with (by modern standards)

Supermarine did a lot of research to improve the design and Meredith managed to get the installation as a zero drag component and under some conditions even added some thrust but not of the same magnitude as the Mustang radiator design.

: P-51 had fully enclosed gear and a retractable tailwheel.
: The others did not (maybe Spit 24 did?).

From the Mk.VII-VIII-XIV-XVIII-XIX the tail wheel was retracted and fully enclosed.
Not until the twenty-series did the main wheels get fully enclosed when retracted.

: Rare Bear, the S
: uper Corsair (R.I.P.), and Dreadnought do not have laminar
: flow wings (by definition), but they actually see signifi
: cant amounts of laminar flow when properly finished

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

: Cees mentioned something about the "drag bucket". Most air
: foils have significantly reduced drag as they approach zer
: o angle of attack. I don't know if this is responsible for
: a stock Spitfire's ability to out-turn and out climb a Mu
: stang or not. Wing loading and the maximum coefficient of
: lift on the airfoil section also play a part in that equat
: ion.

It was me who mentioned the "laminar pocket", maybe it?s called 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.

: What I wonder though is if Dago Red EVE
: R gets out of the drag bucket when turning a 497 MPH lap a
: t Reno. Lift always comes at the price of drag, but the dr
: ag bucket is related to angle of attack (the orientation o
: f the relative wind to the airfoil section) only. At nearl
: y 500 MPH around the pylons it doesn't take much of an ang
: le of attack to pull 6 G's compared to the angle of attack
: to achieve 6 G's at 300 MPH in combat. If the drag bucket
: theory is true though, just imagine how fast Dago is goin
: g in the straights! Maybe 540? 550?

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 technique to convert speed to height to get an optimized turn and then use the height to accelerate out of the turn?
I don?t know how much time is spent turning and straight ahead respectively during a lap but I think that they spend relatively short time at low speed turning and much longer at high speed straight ahead.
If they go 550 MPH flat out then they can go pretty slow at the corners and still acchieve an average of 500 MPH.
I don?t know however, I?m just speculating!?

: Clip t
: he elliptical wings and you end up with somewhat of an abb
: reviated elliptical lift distribution so the advantage is
: even less.

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

: My conclusion is that you need to install a P-51 scoop on
: a Spitfire, enclose the wheels/retract the tailwheel, inst
: all a small canopy, buy a racing engine, and hope you can
: 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 with the inwards retracting main gear and low back fuselage.

: I would really like to see a competitively raced Spitfire
: at Reno some year (along with the 3-engined P-38 and the P
: -82 with the Griffons). Maybe it will happen some day. The
: variety would be nice. :-)

I agree!
Are those two on the web? If so, do You have the links?

Christer,
in anticipation of more beauties

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