Why Did the He 177 Fail?

GregP · Jun 23, 2015

The power of 5 law comes in when you take into account that the target is maneuvering. I have a good book on artillery accuracy, but am not sure off the top of my head of the 5th power proportionality. It was certainly more than a square law due to the plane)s) changing course, but exactly how much more, on average, is a good question.

It is probably a square law for straight line flight and bombers on a bomb run would do that until bomb release. They were also constrianed by the closeness of adjacent bombers in formation. A B-17 or Lancaster isn't exactly a Red Bull racer. Nobody else would fly straight in flak if they had any sense. Most people who survived had either luck, sense, or both.

Juha · Jun 23, 2015

Koopernic said:
The distribution of bombs for a typical CEP (circular area probable) is approximately as follows.
A/ within one radius of the CEP 50%
B/ outside of one radius but within two 43%
C/ outside two radii 7%

Within one radius of the CEP the distribution of bombs in terms of area is approximately even though there is a some clustering towards the centre.

The distribution is Rayleigh (two dimensional Gaussian) ie the normal curve. Form a statistical mathematical point of view it would have been nicer for the CEP to be defined as the radius which contains 63% of hits. I've seen that the Germans at least defined the accuracy of their FLAK radars in this way.

Accuracy degrades as per a cube law though I've heard it claimed that the probability of a hit in naval artillery is according to a power of 5 law. I am not convinced, I can see how a square law applies to ballistic fall of an side ways deviation of a projectile which accelerates and thus integrates according to a square law.

Hence a 10% increase in bombing altitude would increase CEP by 33% or 50% depending on which law you believe is the truth and apply.

The Lancasters that attacked the Tirpitz bombed from between 12500ft and 16000ft. The former is likely what achieved the hits.

It is thought that bombs No 1 and 4 were hits, the first was probably Tait's, dropped from 13,000 ft, the second hit was by Lee's from 14,400 ft, Kell's from 12,800 ft or Anning's from 16,000 ft

Koopernic said:
If we assume 617 squadron achieved 170yards/150meter CEP at 17000ft they would achieve significantly better at 16000ft and dramatically better at 12000ft.

But take the example of 32 bombs with a CEP of 170yard/150meters, 617's assumed CEP at 17000ft, and noting that each 50% reduction in radius would have 25% of the bombs.
A 16 bombs would be within 150m
B 4 bombs within 75m
C 1 bomb within 37.5m. Suggesting a high probability of a hit, greater than 50%, since the radius with an area equal to Tirpitz was around 45m.

These radii could be reduced about 6.5% for 16000ft as compared to 17000ft.

Using the cube law bombing at 12500ft as opposed to 17000ft should double accuracy but using a conservative linear approximation reduce CEP 12500ft/17000ft x 170yards = 125yards/112meters.

Lets run our calculation again, for 32 bombs dropped from 12500ft with a CEP of 112 meters.
A/ 16 bombs would fall within 112 meters
B/ 4 bombs would fall within 56 meters
C/ 1 bomb would fall within 27 meters, the Tirpitz can be assumed to have an area with a radius of 45 meters on the basis of its area.

If we consider the slight clustering effect and that the improvement between 17000ft and 12500ft was probably due to a cube law then the odds look quite good.

One must remember that according to the HQ 5 Group '...only the first 50% of the aircraft to attack will have had a clear run and a reasonable clear AP and that smoke must have made subcequent aiming very difficult.' 9 Sqn Mean Point of Impact was some 300 yards offset from the target. And only one bomb within 200 yds of the M.P.I., 7 of the remaining 9 within 700 yds. 617 got 7 within 200 yds and rest within 700 yds. One case of a photographic malfunction.

Koopernic said:
It's worth noting that the raid was a repeat of another 32 bomber raid conducted in October 1944 in the same fjord so in effect about 60 bombs were dropped.

29 Oct 44 raid failed because of the clouds shrouded Tirpitz a few minutes before the planes arrived at the dropping point. It's pretty difficult to hit an unseen target with a one shot weapon like a Lanc with a Tallboy.

kool kitty89 · Jun 23, 2015

Koopernic said:
The first major improvement in bombsights seems to have been the introduction of gyroscopically stabilised optics. Quite oddly it seems the RAF tried a computing bombsight without a gyroscopically levelled platform in the SABS I and so did the Luftwaffe with the Lotfe 7B, it would seem pointless to carry out accurate calculations from such an unstable datum. Once stabilised, using a pendulum that was averaged out by gyroscopes there was a stable datum.

The difference between the Mk.14 bombsight and the SABS IIB was that the Mk.14 simply told the bomb aimer/pilot where the bombs were going to land, even in a slight dive and while manoeuvring, the sight also helped the bomb aimer set a course to run over the target. The wind drift or estimated target motion had to be estimated and manually entered so it was no good against a moving ship if bomb fall time was a factor or stiff winds. Meteorological aircraft and master bombers probably provided this information.

So the Mk.14 was a more conventional non-computing optical sight with gyroscopic stabilizer? That does seem indeed to be the most sensible step to take between simpler sights and computing sights. Developing more complex computing sights without stabilizers doesn't seem to make much sense at all. (more complex than basic stabilized sights, more difficult to get in service in a timely manner, and ineffective given the lack of stabilization)

As far as attacking a ship is concerned it would make little difference if it was stationary or moving to a wind correct bombsight. So long as it moved in a straight line as merchant ships did.

Not the case for those photos of bombing over Midway. Those warships were quite obviously taking evasive maneuvers given the sharp turns clearly visible in their wake.

stona · Jun 23, 2015

The Mk XIV was a computing sight, but wind speed and direction had to be input manually, leading to inevitable errors. It was stabilised. The 'computer' was not integral to the sight but in a separate cabinet, usually fixed to the left of the bomb aimer (as in the Halifax and Lancaster). Sperry manufactured the Mk XIV in the US as the T1 sight, producing 23,450 examples for use by British and Commonwealth air forces between November 1942 and June 1945. The Mk XIV required only a 10 second straight and level bomb run.

The SABS (Mk IIa) was a descendant of the older unstabilised tachometric (tachymetric in US English) Automatic Bomb Sight (ABS) and was described as 'tachometric, precision, bomb sight'. It was stabilised. Like the Norden it therefore required a long, straight and level bomb run with no freedom of manoeuvre to take evasive action. For the SABS this was a minimum of about forty seconds, which would have seemed an eternity for the crew when flying through flak.

Cheers

Steve

pbehn · Jun 23, 2015

Oh please! how can attacking a stationary battleship be the same as attacking a moving one? If the ship is able to sail in a straight line then you have a small chance of predicting where it will be, if a battleship is steering in any way at all you need a massive fleet of bombers to cover all the possibilities. If a heavy bomber was spotted attacking a ship in open water the ship only has to turn 90 degrees to make an impossible target to hit.

Attacking a stationary target is different, the Tirpitz was completely crippled by a near miss in the first tall boy attack it had a damaged propellor on the second and was sunk on the third. Each tall boy attack resulted in it being impaired as a threat but to the British only its sinking was satisfactory, a massive amount of resources were deployed against its threat only the Tirpitz being sunk would allow their re deployment.

Elmas · Jun 24, 2015

But, AFAIK, no bomb sight could predict and compute temperature gradient from flight level to ground and much less air density: and just this could induce an error of several tens, if not hundreds, meters.

Shortround6 · Jun 24, 2015

People, both during and after the war (decades after) sure spent a lot of time and money on guided ordnance (and the cost per unit/bomb dropped that entails) if mid/late war bomb sights were so accurate.

Why Did the He 177 Fail?

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GregP

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Juha

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