Best medium bomber of WWII?

[Koopernic]

HAD the Mosquito used nitrous oxide (Rolls Royce did experiment with it) the Mosquito could have flown even higher and faster
So a plane with 50-70 examples built is a contender for best medium bomber or WW II?

This is fantasy, just adding black crosses to a plane that didn't fly in black cross publications doesn't change the laws of physics. A three ton bomb load isn't much in strategic terms, taking three tons of bombs to 48,000 ft is a dream with 1944 piston engine tech. You cannot hit anything dropping a dumb bomb from 48,000 ft over Europe and no guided bomb could either.

The Ju 388 with BMW 801TJ-1 engines had a service ceiling of 44000ft and in fact managed 46000ft. The Ju 488, which added an additional pair of engines and wing roots plugged in to the Ju 388 wing had lower wing loading, higher aspect ratio etc.

You should study the BMW 801TJ. Unlike most turbo charged engines it retained its two speed supercharger and added a large turbo charger with a very significant intercooler on top. Hence its critical altitude was very high, competitive with the R3350 at very high altitude.

 

[pbehn]

The Ju 388 with BMW 801TJ-1 engines had a service ceiling of 44000ft and in fact managed 46000ft. The Ju 488, which added an additional pair of engines and wing roots plugged in to the Ju 388 wing had lower wing loading, higher aspect ratio etc.

You should study the BMW 801TJ. Unlike most turbo charged engines it retained its two speed supercharger and added a large turbo charger with a very significant intercooler on top. Hence its critical altitude was very high, competitive with the R3350 at very high altitude.

How does a plane that didn't go into service have a service ceiling? Did BMW get their incredibly complex engine working for hours continuously at 48,000ft? The Americans had a lot of troubles with the B-29 and a lot more resources to fettle them. The Ju488 had a similar wing span to a Lancaster about 40 ft less than a B-29, it was no more a WW2 bomber than the B-36.

 

[Koopernic]

Hey Koopernic,

Because I am an AR type, and as a matter of passing interest:

The below assumes a falling time of 35.35 sec from 20,000 ft release height, with an average acceleration due to gravity vs aerodynamic drag of 32 ft/sec^2.

If the dropping aircraft has a sideways vector of 25 mph at time of bomb release, then the point of impact due to this sideways motion would be 1296 ft off to the side of the aim point.

If the aircraft has 0 sideways vector at time of drop, then the bomb's point of impact would be about 648 ft (assuming the bomb has a 25 mph sideways velocity at impact).

If we add the minimum practical optical line of sight error (plus or minus 1/2 degree) for the (pick any bombing system you feel was the best) bombing system (ie aircraft-bomb sight combination) that saw service in WWII, you have to add +/-174 ft to the point of impact. WWII blind bombing systems were significantly less accurate in terms of minimum achievable aiming error. The reason I say minimum practical achievable is that there really was no practical method of aircraft-bomb sight calibration that could reliably achieve more than plus-or-minus 1/2 degree LOS error. (As far as I know. If anyone has better information please let me know.)

Slight correction I should have said 91 meters (300ft). This assumes the wind drift of the bomber has been nulled out and that the bomb is accelerated by wind:

Bombsight - Wikipedia
The M65 (US GP 500lb bomb) will be dropped from a Boeing B-17 flying at 322 km/h (200 mph) at an altitude of 6096 m (20,000 feet) in a 42 km/h (25 mph) wind. Given these conditions, the M65 would travel approximately 1981 m (6,500 feet) forward before impact,[8] for a trail of about 305 m (1000 feet) from the vacuum range,[9] and impact with a velocity of 351 m/s (1150 fps) at an angle of about 77 degrees from horizontal.[10] A 42 km/h (25 mph) wind would be expected to move the bomb about 91 m (300 feet) during that time.[11] The time to fall is about 37 seconds.[12]

It seems to work out if you assume a certain bomb Cd.A and run it through the drag equation.

 

[Shortround6]

Service ceiling is simple the altitude at which a plane can still climb at 100fpm (or the metric equivalent)
It can vary enormously depending on the weight of the aircraft. A detail that seems to be lacking in some descriptions of the German bombers.
Some other German bombers had service ceilings that varied by thousands of feet depending on load status, could egress thousands of feet higher than the ingress. This is true of just about all bombers to a greater or lesser extent.

Early B-17s had service ceilings of around 37,000ft but later ones lost several thousand feet ceiling. Later ones were "rated" at 54-55,000lbs while they were taking off on long range missions at over 70,000lbs ceiling was??????

Please note that at such altitudes if the plane does ANY maneuver (bank and turn) that the excess power (the power available to climb at 100fpm) cannot compensate for the plane WILL descend. Please note also that this ceiling is achieved while running the engine at max climb or max continuous rating. Much longer range can be achieved at even somewhat lower altitudes with much less fuel burn.

 

[Shortround6]

Slight correction I should have said 91 meters (300ft). This assumes the wind drift of the bomber has been nulled out and that the bomb is accelerated by wind:

Bombsight - Wikipedia
The M65 (US GP 500lb bomb) will be dropped from a Boeing B-17 flying at 322 km/h (200 mph) at an altitude of 6096 m (20,000 feet) in a 42 km/h (25 mph) wind. Given these conditions, the M65 would travel approximately 1981 m (6,500 feet) forward before impact,[8] for a trail of about 305 m (1000 feet) from the vacuum range,[9] and impact with a velocity of 351 m/s (1150 fps) at an angle of about 77 degrees from horizontal.[10] A 42 km/h (25 mph) wind would be expected to move the bomb about 91 m (300 feet) during that time.[11] The time to fall is about 37 seconds.[12]

It seems to work out if you assume a certain bomb Cd.A and run it through the drag equation.

High altitude bombing assumes/depends on the air between the bomber and the ground moving at a constant speed at all altitudes and in a constant direction at all altitudes.
It doesn't matter how good the navigation aids are or how fancy the bomb sight is if the wind direction/s and speeds at several intervening altitudes are unknown to the bomb aimers.

 

[ThomasP]

Hey Koopernic,

Thanks for the link.

So I overestimated the longitudinal drag factor by about 2.5% and underestimated the lateral drag factor by about 50%. Correcting to the values implied by the Wiki link, the sideways velocity would be about 12 mph at impact.

My point is that the accuracy to be expected when bombing from high altitude is very much higher than in your original post. There was no level bomb sight/aircraft system operational (or planned as far as I am aware) in WWII that could (sort of reliably in training) achieve a 300 ft CEP from higher than about 10,000 ft. Obviously the CEP would be much greater from 40,000 ft.

 

[Koopernic]

High altitude bombing assumes/depends on the air between the bomber and the ground moving at a constant speed at all altitudes and in a constant direction at all altitudes.
It doesn't matter how good the navigation aids are or how fancy the bomb sight is if the wind direction/s and speeds at several intervening altitudes are unknown to the bomb aimers.

The wind drift at mid altitude can be estimated by dropping bombs with smoke trails (as the USAAF did) or meteorological reconnaissance aircraft flying at intermediate level or having a 'master bomber' correct the aim of subsequent bomb impacts. Ultimately there were a number of guided weapons projects as well.

Wurzburg radars received the "Windlaus" circuit to replace the wurzlaus coherent pulse doppler to overcome 'windows' jamming. The Windlaus circuit could offset high altitude wind that was causing a doppler shift. Given that many targets would be in radar range even this could be used to measure wind speed for some targets. German anti Windows circuits came our of weather radar research and research to find target aircraft in ground clutter because after the German development of "duppel" (jamming with aluminium strips) research was banned as a security measure.

Either way some measure of compensation of winds at intermediate altitudes could be found. Id say even dive bombing. A 25 degree dive might add 80m/s downward velocity that would cut bomb fall time by 1/3rd.

So long as an accurate position is known an aircraft can pick up a target marker and calculate prevailing winds from that.

It can be done.

 

[33k in the air]

My point is that the accuracy to be expected when bombing from high altitude is very much higher than in your original post. There was no level bomb sight/aircraft system operational (or planned as far as I am aware) in WWII that could (sort of reliably in training) achieve a 300 ft CEP from higher than about 10,000 ft. Obviously the CEP would be much greater from 40,000 ft.

Especially considering the complications of operational reality. The Norden bombsight worked great in training over the clear skies of Arizona. But when faced with the often-cloudy skies over Europe, faced enemy fighters or flak, with decoys and smoke screens, accuracy in actual combat was far lower.

Weather by far was the biggest factor in visual bombing. Which is why the USAAF had to develop non-visual bombing equipment (i.e. H2X) and tactics in order to be able to bomb with any degree of useful frequency.

But regardless of all that, by 1945 Germany was in no position to bomb much of anything given the military and economic realities at that point, so what the aircraft could have done seems unsubstantiated speculation.

 

[Koopernic]

Hey Koopernic,

Thanks for the link.

So I overestimated the longitudinal drag factor by about 2.5% and underestimated the lateral drag factor by about 50%. Correcting to the values implied by the Wiki link, the sideways velocity would be about 12 mph at impact.

My point is that the accuracy to be expected when bombing from high altitude is very much higher than in your original post. There was no level bomb sight/aircraft system operational (or planned as far as I am aware) in WWII that could (sort of reliably in training) achieve a 300 ft CEP from higher than about 10,000 ft. Obviously the CEP would be much greater from 40,000 ft.

I think that is the case for average crews or is the result of the formation 'spreading' the bombs. I'll quote two exceptions
1 Convoy Faith in 1943 using Lotfe 7 computing bombsights.. The three Condors made their attack from an altitude of about 15,000 feet against moving ships . They had 3 hits on moving merchant ships out of about 6 bomb runs had about a 50% hit rate with typically two sometime 4 bombs dropped per run. The misses were often straddles or they were the ones directed against sloops and frigates which were fast enough to manoeuvre out of the way.
2 Operation Tungsten. I think 42 Lancaster dropped bombs on Tirpitz, a Stationary elliptical target about 285m long and 28m wide from staggered altitudes of between 12000 to 16000ft with several hits or near misses. (also some fantastic misses as well)

As soon as you start talking CEP remember if 16 aircraft drop 48 x 1000kg bombs. Then 24 might be outside the CEP circle and 24 in it but 2 to 3 might smack be on target.

If this is a 1000kg bomb it has a big destructive circle. If the B17 or B-24 had of been dropping 4000lb and 8000lb cookies and block busters the destructive blast radius might have exceeded the CEP of the Norden. As it was a formation of bombers spread the load and dropped a tail of 6 bombs.

 

[Koopernic]

Especially considering the complications of operational reality. The Norden bombsight worked great in training over the clear skies of Arizona. But when faced with the often-cloudy skies over Europe, faced enemy fighters or flak, with decoys and smoke screens, accuracy in actual combat was far lower.

Weather by far was the biggest factor in visual bombing. Which is why the USAAF had to develop non-visual bombing equipment (i.e. H2X) and tactics in order to be able to bomb with any degree of useful frequency.

But regardless of all that, by 1945 Germany was in no position to bomb much of anything given the military and economic realities at that point, so what the aircraft could have done seems unsubstantiated speculation.

Just like to say I'm not a proponent of pickle barrel accuracy from the stratosphere. However when a visual sighting was possible computing bomb sights could be very accurate so long as the crew was well trained to apply the bombing procedure under the extreme stress of being under and fire (which 633 squadron could). I note that Little Boy (Edit Fatman) was ordered to be dropped by visual bombing. The crew swapped to radar bombing (they were supposed to abort) and then swapped back to the Norden because they got a clear view. I got dragged into this because I defended the Ju 388 being in this 'vote' because it was still in essence a Ju 88. I mentioned the Ju 488 as a derivative with excellent operational and service ceiling.

 

[XBe02Drvr]

I note that Little Boy was ordered to be dropped by visual bombing. The crew swapped to radar bombing (they were supposed to abort) and then swapped back to the Norden because they got a clear view.

I just reread that episode yesterday. Check it out. I think you just described Fat Man at Nagasaki, delivered by Col. Sweeney and Bock's Car.

 

[33k in the air]

As soon as you start talking CEP remember if 16 aircraft drop 48 x 1000kg bombs. Then 24 might be outside the CEP circle and 24 in it but 2 to 3 might smack be on target.

Two or three bombs on a factory isn't going to do much. Hence why strategic bombing involved hundreds of bombers and thousands of bombs aimed at one target. And even then the capacity for recovery by an industrialized nation-state were enormous.

 

[pbehn]

Two or three bombs on a factory isn't going to do much. Hence why strategic bombing involved hundreds of bombers and thousands of bombs aimed at one target. And even then the capacity for recovery by an industrialized nation-state were enormous.

Also, there were frequently other means or methods. For example with ball bearings the Americans didn't know if they had completely flattened Schweinfurt whether Germany could source ball bearings from Sweden or Switzerland.

 

[wuzak]

Also, there were frequently other means or methods. For example with ball bearings the Americans didn't know if they had completely flattened Schweinfurt whether Germany could source ball bearings from Sweden or Switzerland.

Or that, in many cases, the ball bearings could be replaced by plain bearings.

The problem for the 8th AF at that time was that the losses on that mission prevented a timely follow up mission.

The RAF was supposed to bomb Schweinfurt later in the evening, but they went to Peenemünde instead.

 

[XBe02Drvr]

The RAF was supposed to bomb Schweinfurt later in the evening, but they went to Peenemünde instead.

Higher priority, ATC.

 

[pbehn]

Higher priority, ATC.

Ball bearings, Peenemunde, V1 and V2 silos, submarine pens, shipbuilding, Tirpitz and other surface raiders, Aircraft production, oil production and processing, rail road and canal transportation, electricity production and grid, tank production, tank formations. The list of "top priority targets" was almost endless.

 

[XBe02Drvr]

Ball bearings, Peenemunde, V1 and V2 silos, submarine pens, shipbuilding, Tirpitz and other surface raiders, Aircraft production, oil production and processing, rail road and canal transportation, electricity production and grid, tank production, tank formations. The list of "top priority targets" was almost endless.

Well, with the advantage of hindsight, the petroleum offensive had more potential benefit than the ball bearing one, and any opportunity to impact the V-weapons programs shouldn't be overlooked.

 

[pbehn]

Well, with the advantage of hindsight, the petroleum offensive had more potential benefit than the ball bearing one, and any opportunity to impact the V-weapons programs shouldn't be overlooked.

From the very start the RAF and later USAAF targeted oil as much as they were able, it is a massive task, but there is no doubt at all targets concerning the battle of the Atlantic took priority.

 

[33k in the air]

Well, with the advantage of hindsight, the petroleum offensive had more potential benefit than the ball bearing one, and any opportunity to impact the V-weapons programs shouldn't be overlooked.

A sustained campaign against German electricity production could have had just as much of an impact.

Arguably, the attack on the transportation network was essentially attacking all other system targets simultaneously. It doesn't matter how much oil you can refine if you can't move it from the refineries to where it's needed. It doesn't matter how much coal you can dig out of the ground if you can't get it to the electrical generating plants and steel mills and rail yards.

Of course, you first have to win air superiority in order to get your bombers to where you want them within acceptable loss rates . . .

 

[Koopernic]

Two or three bombs on a factory isn't going to do much. Hence why strategic bombing involved hundreds of bombers and thousands of bombs aimed at one target. And even then the capacity for recovery by an industrialized nation-state were enormous.

I merely used the case of 16 bombers dropping 48 x 1000kg bombs as an example of the statistics of bomb drops. Within the CEP the distribution of bombs, if it follows a gaussian 'bell curve' distribution (Rayleigh in 2 dimensions) is surprisingly even with a slight clustering around the centre. If you have a CEP of 300m/1000ft that means if 48 bombs are dropped, 24 are within a 300m/1000ft circle which roughly equals one 1000kg bomb per hectare. The bomb centres would be separated by 100m/300ft and no point would be less than 50m/160ft from a 1000kg blast.

If the Luftwaffe had of tried sustained strategic raids against UK targets with the BMW 801TJ engine version of the Ju 488 (I'll call it the Ju 488 V401 to differentiate it from the faster but lower flying Jumo 222 engine versions) I suspect it would have been a Kampfgruppe (4 x Staffels, i.e. 4 x 12 aircraft i.e. total of 48) and so we would see 144 x 1000kg bombs. With this density we are starting to get into some serious damage. I don't think the jet stream was a problem over the UK as Japan. In the 30% of days visibility was adequate such results might be achieved half the time.

With a service ceiling of 48,500ft I would imagine they would be able to attack at about 10% less (usually a good estimate of operational ceiling) i.e. 44,000ft. No RAF or USAAF fighter had a service ceiling above this. The RAF's Spitfire XIV had a service ceiling of 43500ft and might be modified with the extended wing tips of the Mk VII, guns apart form the Hispano's stripped and G restrictions applied (for the wing tips) but it would be a difficult intercept. The Ju 488, unlike the Ju 86 was armed.

The Luftwaffe did use Ju 86R reconnaissance aircraft (which could still carry a 250kg bomb) on harassment raids over the UK in 1942 and no doubt was aware of the problems of bombing accuracy from those heights.

There was an extreme high altitude program aimed at flight over 15000m/50,000ft throughout the war and it lead to aircraft such as the BV.155 (service ceiling 55,610ft), the Ju 86, Ju 388, Ju 488 and He 274 and a turbo charger development program focused on extreme altitudes. It sometimes gets called the Hubertus program and the engine test cells which could produced temperatures as low as -60, low pressures and high wind speeds that were developed for piston engines turned out to be useful for axial jet engine development. After they were captured they were shipped to the UK and USA and I think may still be in use. The British put them to immediate use in Germany in fact before dismantling them.

Part of that high altitude program was a realisation that guided weapons would be needed. Fritz-X had versions that were designed to home on radar or Loran (Raddischien, guidance tested on a BV.244 glide bomb) ) and infrared (intended for blast furnaces and power stations in the UK)