Supermarine S 4.

[TASSE]

Hi Schneiderman
Thank you for the R.A.E. report. It appears that the under wing radiators created the most disturbance and this in turn would have effected the ailerons when in use. Of course the ailerons were an integral part of the wing on the wind tunnel model and therefore were never tested in use. At one point the model was tested with the tailplane removed, i do not understand why.

Our model in the Bristol wind tunnel was also tested without moving the ailerons or the elevator and as stated before, the problem was caused by the tailplane being in line with the wing, but now i see that that it might have also been enhanced by the radiator air flow. It should be noted that our model was to 1/6 scale whereas the R.A.E. model was to 1/8 scale. It is strange that the pilot said that he always felt that he was being followed when he flew it. I often wonder if the elevator fluttered.

I have always found aerodynamics fascinating. Years ago i tried to get into London University to study it but my maths were not good enough although i have gained a lot of knowledge through building and flying r/c models. A knowledge that cant be obtained with plastic models, but i have nothing against that (he quickly added !)

Roy.

[schneiderman]

Roy,

Scale effect for the narrow-finned Lamblin radiators was a problem for the RAE on a relatively small scale model, but yes, the real thing would most definitely disrupt airflow on the S4 to some extent. In the long research programme to develop the S5 Mitchell ran multiple wind tunnel tests on individual components and partial assemblies to try and understand the impact of interference effects which may well suggest he was aware of the issue . He concluded that a high percentage of the total drag on the S4, 30% I believe but will check, was due to the radiators. Lowering the wing from mid to bottom fuselage on the S5 was done to improve bracing wire angles and to bring the spar attachment below the engine mounting but clearly there would have been benefits in getting the tailplane out of the slipstream.

I wonder whether there ever was any real evidence for flutter? It was mentioned as a possibility at the time but mainly it comes from Henri Biard's autobiography. Unfortunately most of what he wrote concerning the contest in 1923 is wrong so I have to have my doubts about 1925 too.

[schneiderman]

OK, I can't find the drag figure quickly but these are the impact on speed the Mitchell attributed to the various changes from S4 to S5

Wire-braced wings and chassis +5 mph
Smaller floats +4 mph
Smaller fuselage +11 mph
Flush radiators +24 mph
Additional HP and gearing +30 mph
Separate wing fairings (lowering wing) -3 mph

Cheers

Ralph