Acceleration-aircraft versus car

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Sir,

As an Elizabethan pilot whose hobby is cars, I think I may be able to help Mr Carver, who expressed an interest in the comparative acceleration of aircraft and car.

Mr Carver was correct in admiring the acceleration of the Elizabethan, although the figures were obviously approximate, but in fact the acceleration does not match up very favourably to a Grand Prix car.

This its due to a number of facts such as propeller slip, lower bhp per cwt figure, and others brought about by the fact that an aircraft is, of course, out of its element on the ground. To obtain exact figures I carried out some tests and the results were as follows :—

First Case : With throttle opened as quickly as possible without causing “blowback” or “surge”

(a) Airborne at 115 kts. ie 132 mph.

(b) Power from each engine at 100 kts was 2,350 bhp.

(c) Headwind component 10 kts, ie 11.5 mph.

(d) Auw of aircraft 52,972.92 lb.

The acceleration from 0-132 mph was 35 sec. but the most rapid part of this was in the last 5 sec when the aircraft was virtually airborne, and the air speed indicator jumped 15 kts or 17.25 mph. This is due to the enormous amount of power lost through “propeller slip” and drag of heavy ancillaries on the engine. When one considers that at maximum power on take-off the Elizabethan only produced approximately 10 bhp per cwt as compared to over 20 bhp per cwt of a Grand Prix car the aircraft’s acceleration is very good.

To demonstrate, the amount of difference in weight and propeller slip, etc, make to the aircraft’s performance, a take-off was timed at the low weight of 49,623.5 lb, an increase of nearly 1 bhp per cwt. At the same time the throttles were opened until there was no boost or depression in the manifold, the brakes were then released and the throttles opened fully. The acceleration time from 0-132 mph was 30 sec. As this is the take-off procedure used when take-off distance available is limited, it will be seen that this figure cannot be improved on, to a great extent.

I think that this is about as far as any comparison can be undertaken, the objects being so different. One might as well try to compare the acceleration of a fish with a rabbit. I hope this has interested Mr Carver in its basic form, personally I find accelerating from 0-50 mph in 104 sec in my Wessex converted VW much more exhilarating,–and from only 3 bhp per 1 cwt. 

I am, Yours, etc,

TSC. (This correspondence has been very interesting but is now closed. -Ed.]