The prone postion for tail gunners versus turrets.

"Keith Willshaw" wrote in message ...
"The Enlightenment" wrote in message
om...
American and British aircraft were known for their use of power driven
tail turrets. In the case of British aircraft the aircraft was
designed around the turret. (It must have been effective: British
bombers showed no loss in performance compared to more sexy looking
yank aircraft which seemed to have less nimble but more streamlined
looking tail turrets, the Wellingtons performace was remarkable for
its small engines)


While the Air ministry specn called for turrets I rather doubt the aircraft
was designed around them , especially since the Halifax used BoultonPaul
turrets while those on the Strirling and Lancaster came from Frazer Nash.

Yet they were physically very similar. The whole shape of British
aircraft seem to have been designed around them. Whereas the B17 was a
conventional aircarft with a conventintional tail that had its tail
cone replaced with spherical gun turret. There is no way a B17 could
have accomodated a British style turret. Even a B24 Liberator would
have difficulty.



I wouldnt exactly describe the Wellington as having small engines
either. The mk 1C had two 1000 hp Bristol Pegasus XVIII's and
the Mk X had a pair of 1675 hp Britsol Hercules engines

A lot less than a B26 which had much more powerfull engines in the
2200hp range.

Some marks also had merlins and perfomed. All had good performance in
the 280mpp to 300mph range, powefull armament (the front and rear
turrets had such a good range of traverse and elevation a dorsal
turret was unnecessay I expect)




Tail armament was however rare for Russian, Japanese, Italian and
German bombers. When it did appear if usually consisted of a gunner
in the tail or (nose) in a prone position opperating a gun manualy. I
can't see a problem with this except that the allowable movement would
probably be limited to +/- 25 degrees.


The Germans experimented with gun turrets but rejected the idea
because of the extra drag, late model He-111's did have a
single remotely operated gun in the tail cone and the Ju-88
had a rotating disc with gun mount at the rear of the cockpit

I've never understood this 'remote controlled gun' in the tail cone.
Was it remotely trigered or could it be trained as well? The latter
Do 217 had a similar arrangement I believe.

The Arado 234B jet bomber could carry a pair of 20mm cannon that were
fixed but aimed by periscope.



The Germans were capable of making power driven turrets and tested
british style rear turrets for the He177. The loss in speed and the
cost in skills short germany must have disuaded them and the fact that
their small 2 engined tactical bombers would not have accepted maned
tale turrets gracefully. It appears that their objective were 400mph
bombers like the Ju 288 with remote control barbetts in the dorsal,
ventral and tail position. (Bomber B due in 1942 failed for reasons
to do with engine delays for unknown reasons). Some german bomber did
have remote controlled tail armament.

Back to the prone position. Intitially this postition seemed poor to
me but then I read the sumarised results of extensive German WW2
research which indicates that it was comfortable for 1 to 1.5 hours
and that the G tollerance in this position was much higher than the G
tollerane of a sitting pilot.

The reseach is sumarised he
http://www.luft46.com/prototyp/berlin9.html

The cost in CD (Coefficnt of Drag) I estimate as follows: 1 meter (40
inch) diameter flat hole of 0.77 m2 area in the tail of an aircraft to
me seems to add a coefficint of drag of about 0.2.

( A bullet has a CD of about 0.30 and a near perfect streamline
0.1-0.05 so I assume the conversion of a strealine tail to a flat cut
off would result in a
Cd = 0.78 x (0.3 - 0.05) = 0.2 on the basis of the kamm effect.

The power this would absorb at 440 mph or 200 meters/second would be
calculated from this.

drag = 1/2 x Cd x Area x air density x speed^2

extra power = drag x speed x 1/prop efficiency.

Doing those caculations for an air density of 0.5 at about 25,000 feet
and a prop efficiency of 0.75 I come up with a maned rear gun
absorbing about 2000N force or 200 kg drag at 200m/sec which would
require 533kW or 700hp.

At 100m/sec spped or 220mph the drag is only 500N (50Kg) and the power
only 66kw or about 100hp.

For 150m/sec or 330mph the firgures a
1150N drag (115kg)
225kw power (300hp)

******************

It seems to me that a 400mph aircaft with tail armament was possible.
I daresay a mosquito would not have suffered too much in speed if the
tail had of been completely redesigned to accomodate a prone tail
gunner. Little other armament would be necessary.

In other words an aircraft so fast it would be very difficult to
intercept and upon which only a tail chase attack would be possible.

It also looks like that speed did not suffer much at speeds below
330mph.

I of course have not include the effect of weight of such an
installation.

The mosquito was much too small to provide a 3rd crew position
at the rear, you would need a remote operated turret with periscope
sighting as on the A-26 Invader. Given that mosquito loss rates
were as low as they were and the utility of such guns was doubtful
it seems likely such a solution would not have been adopted.

Low drag guns can also be installed on the sides of the fueselage, Me
410 style or in the rear of the engine nacells.

The problem with perisopes seems to have been the difficulty in
detecting the aircraft. I don't know if episcopes / periscopes
improved.

However I still suspect that a simple rear gunner lieing in the prone
position could be built not to reduce speed too much.