Seeing that a contra-rotating propeller was patented by F. W. Lanchester in 1909, why wasn't it experimented more with, maybe not for WWI but for WWII?
Was there anyone who fiddled with this more than others, US, GB etc., etc?
What difference would it have made, in for instance the Spitfire or the Bf 109, would it have improved their performance enough to make it worth while?
Maybe something for the Halifax/Lancaster or B-17/B-24?
I don't believe there would be much improvement in performance, though there is an improvement in propeller efficiency for a given diameter.
However contra rotating propellers can produce enormous improvements in handling and safety to the extent that an aircraft with poor handling can develop excellent handling.
One problem is the effect of gyroscopic precession caused by the propeller. Hence when the aircraft is taking off and lifts its tail the pitch change causes a swing right or left depending on direction of rotation. This problem can be serious and if not handled by a well trained pilot has killed many pilots.
The second problem is that the circulation caused by the prop wash can cause one wing to stall before the other which can cause the aircraft to flip, ground loop etc. This effected both the Me 109 and Vought Corsair and was partially cured, at least in the landing/take off configuration in latter models the same way by fitting of an extended tail yoke so that the vulnerable wing was above its stall angle when sitting on the tail in the three point attitude.
The third problem is that the direction of flight is altered due to prop wash which forces the pilot to continuously adjust the trim of the rudder depending on power. Apparently some ww2 pilots used this to make their aircraft 'crab' sideways to throw of the deflection aiming of the enemy.]
A fourth problem was directionality of turning, eg something to the effect that a Zero can out turn a Wildcat turning left but not right (something like that)
During the first would war rotary (as opposed) radial engines would rotate the whole engine to achieve sufficient cooling. The effects of gyroscopic precession were very severe with very strange handling in the Sopwith Camel. Some Siemens Schukert fighters had a gear box to ensure the prop rotated at half speed in the opposit direction thereby cancelling the gyroscopic precession effect.
To me its a dam fine idea and would have cut training time, pilot work load and improved handling significantly.