This text was only possible after finding the June 1990 edition
of the magazine "Aeroplane Monthly". Thanks Paul Deweer for helping
to find this text.
Why a tandemwinged Lysander?
The Westland Lysander sure is a classic WW2 airplane. Less known
is its P12 variant. Why this variant? It all starts with the Battle
of France (September 1939 to May 1940). 88 of the 174 Lysanders
were shot out of the sky. It proved that the Lysander with its
maximum of two Browning guns in the rear cockpit was a easy prey
for the German Messerschmitts. What was needed? More guns in the
rear! But ... placing heavy guns in the tail will lead to a CG
(center of gravity) going beyond the rear limit. Dangerous
flight-behavior!
Westland meets Delanne
The Westland chief designer, Arthur Davenport, knew the Flying
Flea of Henri Mignet. He also heard about another Frenchman,
Maurice Henri Delanne, who was making a prototype of a tandemwinged
fighter. The thinking became easy:
"Need heavy guns in rear leads to CG going too far
backwards.Possible solutions:
- less heavy guns
- more backwards aft limit for CG
A larger wing in the tail would create more lift in the rear and
a resulting more backwards CG range."
The Delanne was close to what you needed. So... two persons were
sent to Paris in early 1940 to meet Delanne. The technical director
"Teddy" Petter and testpilot Harald Penrose Flew to Paris. Penrose
even flew the Delanne 20T and was happy with its
flight-behavior.
Prototype K6127
After a number of windtunnel tests with models the work on the
prototype began. Lysander prototype K6127 lost its original rear
cockpit and got a mock-up of a Frazer Nash turret.
Maiden flight: July 27, 1941.
Testflights
Testpilot Penrose reports that all was like the original
Lysander expect that the rudders only became effective at higher
speeds (see disadvantages of Delanne). Weird thing was that the
airplane proved to be ... more stable. That testflight ended with a
loop. Now, if that is not a proof of confidence by its pilot. He
sure liked it.
Later tests proved the wide CG range which is common in the
Delanne configuration.
During later handling trials they did the tests in three
conditions.
- CG at forward limit (45% of aerodynamic mean chord (AMC))
- CG at normal limit (52,3% of AMC)
- CG at aft limit (58,2% of AMC)
Conclusions:
- Rudders were ineffective below 64 km/h (40 mph).
- Little swing to left if loading at aft limit.
- Initial climb was like the original Lysander, only needing a
little rudder.
- Aircraft proved easy to fly
- Rudder control became heavy at 450 km/h (280 mph). Below that
speed it was rather light.
- The automatic slots in the front wing caused problems when they
changed position (close to open).
- Dives were "smooth and remarkably steady".
The end of the Lysander P12
Before full tests were done, the official support was lost. The
P12 was official of duty on June 13, 1944.
They first had thought that the Delanne concept could be used in
other projects. Heavy bombers in special. A heavy (in weight and
power) rear turret on those would be good. Petter proposed a
four-engine bomber with a four gun turret to specification B.8/41.
Westland thought about a Halifax modification with a turret in the
rear.
The test-pilot Penrose proposed a rather light airplane, the
Penrose Gremlin. Stress and performance calculations were already
done. But the proposal never got build because the intended light
engine (Wren) never got materialized. All the others engines at
that time with the same performance were too heavy for this
proposal. The engine was placed on the rear of the airplane and a
heavier engine would have placed the engine needlessly
backwards.
No more data is found yet about later English Duo-Mono
projects.