WIX Archives

Well, I considered to recline in my chair ......

Posted by Christer on Mon Nov 11, 2002 09:28:55 AM

In reply top Christer, teccie question posted by Cees Broere on Mon Nov 11, 2002 06:41:49 AM

...... and wait for Steve Hinton to pick this one up, he knows the answers, I?ll only speculate!

Anyway, a few thoughts:

The weight of a two stage Merlin is approximately 750 kg and of a two stage Griffon approximately 900 kg. That?s a 20 % difference but if you calculate for the Mk.XIV with the two different engines fitted it would be only 5 %. I?m discussing the empty weight of a standard Mk.XIV.

Aerodynamically it would be equal to fitting the bits and pieces from a Mk.VIII, forward of the firewall, to the Mk.XIV. Frontal area would be slightly reduced and the wet area too.

I?d think that, if the power output was the same, it would increase the speed from 445 mph to maybe 450 mph.

(Maybe a better proposition would be to fit one of the high powered Merlins to a low-back, clipped-wing Mk.VIII? Then you?d relieve yourself from a lot of reverse engineering!)

You mustn?t forget that the comparision limps a bit since in this example the standard Griffon 65 used 130 grade fuel and +18 psi boost whereas the late production Merlins used 145 grade fuel and +25 psi boost or +28 psi boost with water/methanol injection.

(I?m not sure about the figures quoted for the Merlin but it certainly wasn?t 130 grade and +18 psi. A Griffon running at those higher boosts would yield something like 2,500 HP.)

If you compare the standard Mk.XIV with the standard P-51D, they had approximately the same maximum speed at approximately the same altitude, the Mk.XIV using 2,000 HP from a Griffon 65 and the P-51D using 1,600 HP from a V-1650-7. That?s an indication of the aerodynamical differences and why you don?t start with a Spitfire.

Many of the most successful P-51's that are modified for racing are more like "Mustang Lookalikes" than a stock P-51. I?ve heard that Learjet wings are very popular ...... among other things.
It?s possible that the basic design of the Mustang is better suited for modification, such as replacing the wing altogether.

If Steve cares to comment on this, maybe he?ll explain why they fitted a Griffon to a Mustang and not a Merlin to a Griffon-Spit, which would make it a Merlin-Spit!

Christer,
in anticipation of being corrected

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