Ju-88 vs He-111 & Ju-188 vs Do-217

Greyman said:

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50 km/h speed loss for just the racks? That seems excessive. British tests on an A-5 (originally an A-6) indicated a loss of 5 mph (8 km/h).

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50 km/h was loss due to the bombs.
The bomb-less A-5 cruised at 425 km/h; max speed (475 km/h) was not just without racks, but also with greater engine power.
Racks indeed were not such a great source of drag, IIRC German figures were in ballpark with British.

Sounds to me like both the Ju-88 and Ju-188 were racehorses optimized for speed, but in service, aworkhorse carrying a heavier load like the He-111 or the Do-217 was preferable?

Ju 88 ended up as a workhorse, too.
Junkers, when designing the Ju 88, made a mistake by designing it to be a low-wing aircraft. That meant the restricted bomb bay, that in turn required bigger bombs to be hung outside, directly killing the Schnellbomber idea. At the end of the day, neither Ju 88 nor Ju 188 were racehorses.

Greyman said:

Yeah, as Vincenzo says it was 4 x 500 lb in the fuselage and 2 x 500 lb external (6 x 500 lb total).

The top speeds of an internally-loaded Hampden and externally-loaded Ju88 are similar, but the critical altitudes of the Pegasus are a few thousand feet lower giving a speed advantage approximately from 0-6,000 ft and from 10,000 ft to 16,000 ft. At other altitudes the speeds are close enough that it's a wash.

With 2 x external bombs the Hampden falls behind the 4 x 250 kg Ju88 at all altitudes.

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Oh, You and Vincenzo are right and Mason had made a mistake. I was checking info on Hampden TB I and noticed that Green & Swanborough give the four 500 lb internally and two externally load to Hampden I. And after reading Vincenzo's message remembered that I got ADS' of Hampden I and TB I from somewhere, possibly from here, 7 years ago.

The problem with measuring performance with full or partial loads is moot in a combat environment with heavy bombers, particularly if the aircraft are flying as part of a stream, as the Luftwaffe was doing during the BoB - performance was always based on the slowest aircraft in the stream, regardless of type. Obviously a higher cruise speed is helpful in a stream, but it has to be averaged out in comparison to the slowest aircraft in the group. Higher acceleration to high speed after the delivery of warload is of equal importance and makes a difference in terms of survival in a fighter rich environment. There are a number of combat reports where Ju 88s escaped from pursuing Hurricanes when free of bomb load and the Hurricane pilots called off the pursuit because they could not keep up.

During the battle Ju 88s and Do 17s were often used on low level attacks against airfields, with devastating results. In this scenario, the faster the aircraft, the more advantageous during and after the attack - it also made interception very difficult.

[QUOTE="tomo pauk, post: 1588028, member: 17608"low-wing aircraft. That meant the restricted bomb bay, [/QUOTE]
Low-wing = restricted bomb bay? Is it due to the wings protruding well into the fuselage for stability?

Acheron said:

tomo pauk said:

low-wing aircraft. That meant the restricted bomb bay,

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Low-wing = restricted bomb bay? Is it due to the wings protruding well into the fuselage for stability?

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Wing spars that connected and reinforced the mainwings.
If the bomber was designed with a higher wing, the spars passed over the upper portion of the fuselage, like a B-24, allowing for a larger bomb bay.
If the wings were at mid or lower configuration, the spar(s) intruded into the area of the fuselage, causing an obstruction that limited the useful area.
This was an issue that limited several bomber types (heavy, medium, etc.) both Allied and Axis.

Acheron said:

[QUOTE="tomo pauk, post: 1588028, member: 17608"low-wing aircraft. That meant the restricted bomb bay,

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Low-wing = restricted bomb bay? Is it due to the wings protruding well into the fuselage for stability?[/QUOTE]

Mid wing or high wing is preferable because you can place the bomb load inside the fuselage closer to the centre of lift and CG. The He 111 was low wing, so its internal stowage was confined to particular sizes of bombs that fit inside the cassettes in the fuselage and they had to be mounted vertically to save space. Externally it could carry a hefty load, but with that comes drag penalty. The Ju 88 had a mid wing design, but its bomb bay was the depth of the fuselage because the bombs fit between the spars. This did restrict the size of bombs it could carry internally because of the length of the bay. The Dornier bombers were high or shoulder wing, so the bombs sat in the bay beneath the wing.

He 111 bomb bay, note the cells. It did have two bays like this.

Bomb doors

Ju 88 equipment bay - this is a Ju 88 nightfighter, but this would have been the bomb bay in the bomber variants.

bomb bay doors

Sorry for messing up my quotation marks.

Regarding wing placement, now I wonder why any bomber would be anything but shoulder-wing. What was the advantage of a mid- or low-wing for a bomber?

Speed is always a tricky question, it depends on so many things. In the BoB some of the bombers - I think the Do17 but not sure - would climb to maximum altitude while still over France. They would then conduct basically the entire mission in a shallow dive, crossing the Kent coast on the way home going like a bat out of hell, right on the deck. Difficult to intercept partly because of speed, and partly because height is changing all the time.

As for high/low wings, it's all about compromises. Want high wings for a big bomb bay? Great, have them .... it just means your engine nacelles are so high up that the fitters get vertigo trying to service them, and your undercarriage legs are a mile long. Oh you want to put the undercarriage in the fuselage to avoid that .... ok, but where are the bombs going to go? In the engine nacelles? Well ok again, but why do you want them so far off the ground .... oh I see, it's for the bigger bomb bay ... that now has undercarriage in it ....

Who'd be an aircraft designer, eh?

macguba said:

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As for high/low wings, it's all about compromises. Want high wings for a big bomb bay? Great, have them .... it just means your engine nacelles are so high up that the fitters get vertigo trying to service them, and your undercarriage legs are a mile long. Oh you want to put the undercarriage in the fuselage to avoid that .... ok, but where are the bombs going to go? In the engine nacelles? Well ok again, but why do you want them so far off the ground .... oh I see, it's for the bigger bomb bay ... that now has undercarriage in it ....

Who'd be an aircraft designer, eh?

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Let's recall that there was a lot of bombers with proper bomb bay and sturdy undercarriages, be it from Germany, UK, SU, USA, Japan. So apparently it was not something beyond the reach of contemporary engineers, technicians or whomever.

macguba said:

As for high/low wings, it's all about compromises. Want high wings for a big bomb bay? Great, have them .... it just means your engine nacelles are so high up that the fitters get vertigo trying to service them, and your undercarriage legs are a mile long. Oh you want to put the undercarriage in the fuselage to avoid that .... ok, but where are the bombs going to go? In the engine nacelles? Well ok again, but why do you want them so far off the ground .... oh I see, it's for the bigger bomb bay ... that now has undercarriage in it ....

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The higher-up placed engine being more inconvenient to service seems like a rather minor issue. The longer undercarriage also does not sound much like a deal-breaker.

If you look closely at "high wing" types like the B-24 or He177, you'll see that their maingear wasn't all that long.
The B-24 had low enough clearance that the ball-turret had to be retracted when on the ground.
The He177 appears to have long gear only because it was a conventional configuration (tail-dragger).

For a long undercarriage, take a look at the Sterling.

Acheron said:

I have some questions about German WWII bombers:

1st, comparing the Ju-88 and the He-111. At least during the Battle of Britain, it seems to me, that the Ju-88 was the faster aircraft, while the He-111 could carry heavier loads. So a racehorse versus a workhorse. Is this perception correct and if so, was it true in general or only for the BoB? And would that be the reason the He-111 was produced in such large numbers when the leadership was (as always, correct me if I am wrong) more enamored with the Ju-88?

BTW, I am not asking about the Do-17 because I got the idea that it was a dated design, inferior to the other two in almost every way. Again, let me know if this it not quite correct.

2nd, comparing the Ju-188 and the Do-217. These were the most modern bombers of the Luftwaffe produced in quantity, apart from the He-177 which was a rather different beast. When it comes to the Ju-188 and the Do-217, I know very little. I heard that the Do-217 had an impressive bomb load, even being called a heavy bomber except for range. Wikipedia suggests that it had greater bomb load and higher speeds than the Ju-188. Can anyone tell me more about either aircraft and especially how they compared to each other?

As always, thank you

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The Do 17Z-2 gets underrated. It was 'forced' to use the Bramo 323 radial of about 986hp which due to the drag of the radial limited speed to 255-260 mph despite earlier variants using Daimler Benz DB600 series in lines. What might have been is shown by the Do 215E1 which was an export version of the Do 17 with improved DB601Aa engines of 1075hp that gave a speed of 290mph. About 68 of this variant were upgraded with the DB601N0 engine which allowed a speed of 316mph.

I darer say it could have been developed with the BMW/Bramo 323-R2 of 1200 hp, the DB601E of 1350hp or the DB605B of 1450hp.

The Do 215 was thus the fastest of the German BoB bombers because it could carry 1 ton (2200 libs) of bombs internally whereas the Ju 88 generally used it two internal bomb bays for fuel. (It could carry 880lbs of bombs there, maximum bomb size was 70kg.

The Ju 88A1 was a good aircraft but the dive bombing requirement had reduced its speed and range significantly leaving the Luftwaffe seriously short or long range aircraft. The Ju 88A4 (an A1 with larger wings, more armour and more powerfull engines) had to solider on till 1944 because of the shortage of higher performance engine and high octane fuel.

Attempts to improve the Ju 88 lead to the following
Ju 88S0 with BMW 801 radials, a streamlined canopy and nose glass, no dive brake but still retained the ventral bondola gunners station. Speed 336mph.
Ju 88S1 With BMW radias, bondola removed and speed of 379mph. GM1 was used to increase speed further. Mainly used as a path finder.
Ju 88S2 With BMW 801TJ radlials with turbo charging, did not require GM1. Very few must have been produced since this engine was only entering service in 1944.
Ju 88S3 with the Jumo 213 engine.

Most of the BMW 801 radials allocated to the Ju 188E however some went to the Ju 88R and Ju 88G1 fighters (mainly night fighters)
A few went to the Ju 188E (which shared the new wings and tail of the Ju 88G fighters)
There was also the Ju 188A which had the Jumo 213 engine.

By 1944 the Ju 388, still rooted in the Ju 88/Ju 188 was just coming into service with the BMW 801TJ. A variant with Jumo 222 (scheduled for production in late 1944/45) was expected to operate at 440 mph.

The Do 217 didn't see use in the BoB. More use of it might have occurred had the Ju 88/188/388 just not been set up for mass production so well. It managed 346mph on the 1750hp DB603A and likely would have managed 390mph or so with more powerful versions of this engine.

Koopernic said:

The Do 17Z-2 gets underrated. It was 'forced' to use the Bramo 323 radial of about 986hp which due to the drag of the radial limited speed to 255-260 mph despite earlier variants using Daimler Benz DB600 series in lines.

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There was no such thing as earlier variants of Do 17 using DB 600 series engines (bar 2 prototypes).

[/QUOTE]...
The Do 215 was thus the fastest of the German BoB bombers because it could carry 1 ton (2200 libs) of bombs internally whereas the Ju 88 generally used it two internal bomb bays for fuel. (It could carry 880lbs of bombs there, maximum bomb size was 70kg.[/QUOTE]

Ju 88A was able to carry 1400 kg of bombs internally - 18x50kg + 10x50kg.

The Ju 88A1 was a good aircraft but the dive bombing requirement had reduced its speed and range significantly leaving the Luftwaffe seriously short or long range aircraft. The Ju 88A4 (an A1 with larger wings, more armour and more powerfull engines) had to solider on till 1944 because of the shortage of higher performance engine and high octane fuel.

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Ju 88's flaw was that it have had restrictive bomb bay, mostly due to it being a low-wing aircraft. Luftwaffe needed actual bomber carrying actually useful bombs - 500 kg and on - so the Ju 88 has gotten the wing racks. Add the tall, wide and non-streamlined cockpit, guns here and there, aircraft's big size and indeed not sterling engines and it was no wonder that Schnellbomber idea went in the trash can for the Ju 88.

So, more opinions on the Do-17? Underrated hidden champion or outdated design used well beyond obsolescence?

The whole Schnellbomber concept seemed to me to be dead with radar. A bomber needs bombs, a fighter needs guns. Bombs are heavier than guns. Ergo, it seems impossible to me (bar a significant technological edge) to make a bombers that would be faster than a fighter (again, of roughly the same tech level). Now, without radar, bombers might surprise the enemy and be out again before an intercept can be mustered but with radar, that was no longer a possibility. Or is my logic flawed?

While I am a fan for the Do 17 & 215, I would consider the design outdated by the BOB. Its engine HP (in the Do 17z, m, & p versions) was less than 1000 hp per side. Just not enough to carry the needed Fuel, Bombs, and defensive armament needed when opposed by a directed fighter force.

It could not carry larger bombs, due to the small size of the bomb bays. I always thought it was an interesting comparison with the Bristol Blenheim, or PZL 37b. The PZL is slightly faster and can carry a larger bomb load, but all other spec's seem similar.

I think the Do 17 was a very good design for 1937-38, but like almost all Bombers designed in that time frame quickly showed its limitations when faced with the conditions of 1939-42.

Something that always amazes me is the light defensive armament that was considered to be adequate between WWI & WWII. When you look at late WWI aircraft they were getting more and more defensive guns & armor protection. Yet the disigns of the early to late 1930's do not seem to benefit from the prior conflicts experiance in those categories. Just my opinion and observations.

Acheron said:

So, more opinions on the Do-17? Underrated hidden champion or outdated design used well beyond obsolescence?

The whole Schnellbomber concept seemed to me to be dead with radar. A bomber needs bombs, a fighter needs guns. Bombs are heavier than guns. Ergo, it seems impossible to me (bar a significant technological edge) to make a bombers that would be faster than a fighter (again, of roughly the same tech level). Now, without radar, bombers might surprise the enemy and be out again before an intercept can be mustered but with radar, that was no longer a possibility. Or is my logic flawed?

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As-is, the Do-17 was the least capable German 'proper' bomber.

Bombs might be heavier than guns, but manned gun turrets with ammo add considerable weight and, many times, drag. You need more men to train for you bomber force, and you put more men in risk of loosing their life. Bombers with several turrets will be more expensive to make.
Weight does not kill speed as much as the drag does (see MC.202 vs. Re.2001, or P-40 vs. Hurricane) - the increased drag coming from gun turrtes, the 'open-air' MG positions, and increase in A/C size due to need for bigger wing and fuselage to carry all of that in the air. Note that you still can escort the gun-less bombers, even easier than the 'classic' slow-ish bombers since the escorts don't need to ess too much. A fast bomber spends less time in range of AA guns, and it is a harder target to tackle than a slow bomber.
A gun-less bomber does not need to be faster than enemy fighter, a speed parity is also very good thing if it can be achieved.

cammerjeff said:

I think the Do 17 was a very good design for 1937-38, but like almost all Bombers designed in that time frame quickly showed its limitations when faced with the conditions of 1939-42.

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Wow, that is a really short shelf-life there.

tomo pauk I thought the idea of the Schnellbomber was for it to be too fast to be catched by fighters? It is that concept that I do not understand, even if two-engine designs were faster than smaller single-engine aircraft, wouldn't the opposition simply build fast two-engine fighters which would be able to catch up with bombers?

Again, I have this idea in my head, that a fighter inherently needs to carry less weight than a bomber, so all else equal, the fighter will be faster.