Beverley Shenstone: On Biplanes

This section is a short collection of anecdotes about the Canadian aerodynamicist Beverly Shenstone, who, seems to remain somewhat more anonymous than he ought to in the usual popular chronicles of aviation – in his role as one of the most important aerodynamicists ever to have worked for Supermarine. These short pieces about some events he wrote about are intended to increase awareness about the man, and also act as interesting historical snippets in their own right.

Beverly Shenstone

Biplanes: How did they survive so long ?

Shenstone wrote a very interesting piece in the 1966 Centenary Edition of the Journal of the Royal Aeronautical Society, on why Biplanes managed to stick around for so long. Shenstone – wrote:

“When I reached England in 1931 looking for a job, I was asked what I would do if told to design a fighter. I said I would have to consider whether it should be a monoplane or a biplane. The answer was rather final…’no you wouldn’t; it would be a biplane’, I finally found a job under R. J. Mitchell at Supermarine”

RAeS Centenary Journal 1966

Mitchell was the designer of the Spitfire, and all the racing planes that won the Schneider Trophy for Britain, using the 2000bhp+ Rolls-Royce Type-R racing engines. Shenstone – not R.J. Mitchell – was eventually responsible for much of the Aerodynamics of the Spitfire, including the eliptical wings, designed to produce the lowest possible induced drag.1

Shenstone shed light on WHY it had taken so long for aircraft designers to move to monoplane layout, which explained why it needed brave visionaries who stuck to their own ideas to do it. “Early development work on the monoplane was held back by misleading aerodynamic data, in my own experience the NACA test #TN-456 full-scale windtunnel test of a low-wing monoplane. This showed a surprisingly high minimum drag coefficient, and was barely any better than a biplane with a retractable undercarriage mainly because the wind tunnels available were all highly turbulent and the wing sections tested in them showed much higher drags than they would have had in real flight”(NB actual picture of this test below in the oval tunnel)

“It was much later that the true drag of the smooth monoplane wing was realised – but in 1928 Martin Schrenk measured the in-flight minimum profile drags (accurately, showing very low drag)…why was this ignored ? Hardly anybody knew about it as it was not available in English, and many of those who HAD, could not believe it”

(see last 2 pictures of Shrenks in flight test, a cine-camera was used to log the pitot tube variations).

REFERENCES & NOTES:

  1. “Induced drag” is a bit of a strange term, as of course ALL aerodynamic drag is “induced” by the shape and movement of an object through the air. What it is intended to describe however, is one part of this drag which collected together is called (obviously) “total drag”. The induced drag is the part of drag which is specifically created by the mechanism of the wings creating lift, which is in turn highly dependant on angle of attack. The result of this is that induced drag can become the largest component of total drag at very low speeds with a (necessarily) high angle of attack, i.e. coming in to land. It can be extremely dangerous if it is high (perhaps over 70% of total drag), many crashes happen coming in to land with plans with very high induced drag, as the pilot may -counterintuitively- have to actually increase the engine throttle to stay aloft the slower he goes, as induced drag rises. In normal flight induced drag is low, perhaps 10% of total drag.

Shrenks papers, originally from Luftfahrtforschung. May 18, 1928. / Jahrbuch 1929.der Deutsche Versuchsanstalt fur Luftfahrt, and the 1933 paper on landing gears.

Papers Referenced by Shenstone:

These papers are all available on the NACA NTRS archive site, but to prevent bad links occurring when they reorganize themselves the papers are presented here for download directly.