I told the question to Google IA and here is the answer ! That's only we can find quickly on this subject !!!
I think that a lot of investigative work is needed to find numerical data and other test reports from the Lysander P9105 !
The concept of the Blackburn-Stieger wing was not retained after the 1941 flight tests for several major reasons, combining fundamental technical limitations and the urgency of the military context:
1. The problem of aeroelastic divergence
This is the historical structural flaw of the inverted arrow. When airspeed increases, aerodynamic forces tend to twist the wing upwards, increasing its angle of attack, generating even more lift and increasing torsion until failure.
At the time, the Mono-Spar structure of Helmut Stieger, although ingenious, was not rigid enough to counter this phenomenon at high speed without adding a considerable weight. It was not until the 1980s and the appearance of oriented carbon fiber composite materials (as on the prototype Grumman X-29) to solve this problem. [1, 2]
2. The mechanical complexity and lack of reliability
Replacing the ailerons with wing tip spoilers (to free up the full span for the flaps) proved to be complex. The linkages and spoiler behavior lacked progressivity, making flying unpredictable or too rough in certain flight configurations. In addition, the maintenance of a fully mechanized wing (flaps + slots + spoilers) represented an unacceptable logistical challenge for the time.
3. The performance of the original Westland Lysander was already sufficient
The production Westland Lysander already had exceptional short takeoff and landing (STOL) capabilities thanks to its own automatic leading edge slats and movable flaps. The marginal gain in performance brought by the Blackburn-Stieger wing did not justify the risk and complexity of a complete overhaul of the aircraft. [3]
4. The context of the Second World War
In 1941, the Royal Air Force and the British aircraft industry were engaged in an intensive production war. The absolute urgency was to mass-manufacture fighters (Spitfire, Hurricane) and bombers proven. The Air Ministry could not allocate industrial resources or time to develop such a radical and immature concept, leading to the suspension of research funding for this project.
[1]
https://www.researchgate.net
[2]
https://www.reddit.com
[3]
https://backcountrypilot.org
