Ball Turret Drag

[mike_cyul]

Would anyone happen to know by how much the ball turret slowed a B-17 or B-24? Extending such a large object into the air stream must have had a considerable effect (or did it?), but whereas things like cowling flap drag are mentioned in the manuals, so far I haven't been able to find mention about the ball turret.

Anyone know?

Thanks!

 

[swampyankee]

The least drag coefficient for a rough sphere is about 0.2; the ball turret had a diameter of about 4 feet (somebody fit inside), so it added about 2.5 square feet of equivalent flat plate area. The turret, its retraction mechanism, and its traversing mechanism probably added about a 1500 pounds to the aircraft directly (this excludes the structural changes needed to accommodate a big hole in the fuselage). The equivalent flat plate area of a "clean" B-17 that had a ball turret was probably about 40 square feet; the ball turret would increase that by about 6%.

WW2 bombers were running into the "flying airbrake" territory of aerodynamic efficiency, but the low accuracy of dumb bombs dropped from high altitude made mass formations necessary, so features like speed and maneuverability (see: Mosquito) were useless in a bomber, although I think a case can be made for reducing B-17 and B-24 armament, thereby reducing crew numbers and equipped empty weight, to increase bomb load and thereby reduce the number of sorties to cause the same effect on targets (removing 1,000 lb of machine guns and flight crew can increase the bomb load by 25% on longer range missions; the cumulative effect can reduce bomber crew casualties, although not reduce casualty rate)

 

[mike_cyul]

Thanks for that. I'd noticed in a few formation photographs that some aircraft had the ball turret extended, while others didn't (I assume this was outside the immediate combat area), and had wondered if this wasn't being used to increase fuel conservation or to more easily keep up with the formation (assuming the ball turret gunner wasn't just temporarily occupied elsewhere in the aircraft). If 6% of flat plate equates to some 12kt difference in speed at an assumed speed of 200kt, I could see that being a significant difference.

 

[jimh]

I've flown Witchcraft many times with the ball turret extended. I honestly never noticed a difference in speed or performance. The B-24 has such poor flying characteristics the only thing that really affects speed in normal operations is dropping the gear. The wing design is angle of attack critical and there is a ballet dance of keeping it on the step for max speed. A heavy hand on the elevator can cause a 20mph difference in cruising speed. The ball turret, being round and sealed doesn't really cause all that much drag.