Ju-88 vs Do 217

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P

Piper106

Airman 1st Class
196
31
Nov 20, 2008
I am trying to decide which would have been better for level bombing (using standard 250 to 1000 Kg bombs) at a altitude of 3000 to 6000m (10000 to 20000 feet) up to 600 kilometers (350 miles) away from its base. JU 88A or Ju88S vs. Do 217E / K / M. Let's not discuss which is better as carrier for guided weapons, or longer ranges away from base. I am interested in which has a higher maximum continuous cruising speed (payload still on board), can carry a larger load out to 600 km, better able to defend itself, reliability, easier to build, and any other useful considerations.
 
Shortround6 said:
Do 217
The Ju 88 can't carry 250 kg or larger bombs inside, so range and speed drop in the toilet real quick.
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Its not even that much. There were two bomb bays, one before the main spar, one after. The maximum bomb size was 70kg/155lbs (a rather uncommon bomb size for the Luftwaffe ). The aft bomb bay was usually used for fuel and often the forward one often as well. Nevertheless the bomb bays seem to have been usefull for the Ju 88S variants for their pathfinder role: parachute flares, target marking and dropping Schwann See(floating) and Schwann Luft (parachute) radio markers.

Keeping the bomb bay small kept the aircraft slim, light and fast. When carrying external bombs it didn't really slow the Ju 88A4 aircraft below the speed of a twin engined aircraft enlarged to carry its bombs all internally. Plus the Ju 88 could carry two torpedoes even though the Do 217 could carry one internally. This made the aircraft fast when its bombs were released and made it a useful night fighter. Speed free of bombs without dive brakes could be 316mph with Jumo 211J.

In reference to the OP. It's probably unfair to compare the Ju 88 to the Do 217. The appropriate comparison is Ju 188 to Do 217 as they had the same engine class. As speed rose external bomb drag did become a disadvantage and a ventral Panier was developed for the Ju 388.

My feeling is the Ju 217K/M (with BMW 801/DB603A) was a slightly better aircraft than the Ju 188 E/A (with BMW 801/Jumo 213A) due to its 24mph higher speed of 346mph and large bomb bay but it was considered underpowered (should have rectified itself as engine power grew). I'm surprised they never developed a remote controlled tail gun to streamline and improve the aircrafts defences as they did for the Ju 388.

The Ju 88 was under mass production and that's what the Luftwaffe had to use mostly and that's why they cancelled Do 217 production in 1944 not Ju 88. Ju 88A4 was forced to soldier on well into 1944 beyond what it should have.
 
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Keeping the bomb bay small didn't make the aircraft slim, and certainly made it slower since it meant that bomb racks need to be added (= more drag), so the meaningful bombs can be carried (= even more drag). Two times of more drag not just means that speed takes a substantial reduction, range also suffers. Note that Junkers went with the high wing and a proper bomb bay for the Jumo 288, still the fuselage was slimmer than of the Ju 88.
Dropping the bombs prematurely to make bomber faster is a mission kill.
With Jumo 211J, the historical Ju 88 without the bombs was doing 425 km/h on max continuous (1020 PS; the 30 min power was 1180 PS at altitude; no Notleistung for the Jumo 211J). It would likely require a rocket in the tail to do another 80 km/h.

The Ju 88 was under mass production and that's what the Luftwaffe had to use mostly and that's why they cancelled Do 217 production in 1944 not Ju 88. Ju 88A4 was forced to soldier on well into 1944 beyond what it should have.
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As noted by Vincenzo, German bomber production was slashed in 1944, including bomber versions of the Ju 88.
 
In general -- as in always -- carrying a weapons load inside the fuselage will result in lower drag than carrying the same weapons load outside, although an aircraft designed for no internal weapons carriage will probably be faster than one designed for internal carriage without weapons, dependent on how much drag remains when the external weapons are dropped.

The Ju88 would lose much more speed and rate climb with an external load than would the Do217 with its internal load unless the Ju88 is carrying a marked smaller war load.
 
The Do 217 was supposed to carry eight 250kg bombs internally, or four 500 kg bombs or two 1000kg bombs and two 250kg bombs, It could carry more bombs outside. But It's max cruise with the 2500kg load was supposed to be around 248-258mph at best altitude, best range is at a slower speed.
If the Ju 88 wants to carry 250kg bombs they have to go outside, and it won't carry eight. The A-4 could carry up to four bombs outside of up to 500kg each, modifications may have allowed larger bombs but only two?
The JU 88S could carry two bombs out side, they could be up to 1000kg each.
Somebody may have the performance with such a load but most published figures for the 88S are in clean condition.
 
Obviously the ventral panier on the J-88A-15 and Ju88S-2 reduces speed when empty compared to a similar version without the panier because of the increased frontal area. But while the bombs are still on board, which gives better speed; carrying the bomb load inside the panier or externally on a aircraft without a panier. I think I know the answer, but would like someone to confirm.
 
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The late Do 217M with its 1750PS DB 603 inline engine would likely be a lot faster than the early Do 217E with 1600PS BM801 radials, the Ju 88 bombers did not really got much of an engine upgrade, most had the 1420PS Jumo 211J inline.
 
The Do 217 always gets my vote. It was always outshone in the publicity stakes but was fast, well armed, carried a good payload. It's no contest
 


tomo pauk said:
Keeping the bomb bay small didn't make the aircraft slim
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Lol, this statement defies the laws of physics except in Dr Who's tardis. You are saying that breaking the stressed metal skin of an aircraft, interrupting its ribs, interrupting it's stringers or spars and putting in heavy beams to carry the load around where the skin would have been and adding internal bulkheads doesn't add weight? You are saying that the space occupied by the bomb bay doesn't displace internal fuel or force an enlargement of the whole structure?

tomo pauk said:
and certainly made it slower since it meant that bomb racks need to be added
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The weight costs of external bomb racks is definitely much less than the weight cost of compensating for the disruption a bomb bay causes and the weight caused by the enlargement of the fuselage needed to accommodate it. The increased weight causes more induced drag and requires a greater wing area to compensate which requires greater power.

On the issue of drag with bombs you can argue the point but you'd still be wrong with certain caveats. On the issue of the extra weight of a bomb bay you can't. 2 or 4 removable bomb racks adds less drag than the enlarged fuselage. Obviously external bombs does slow the aircraft down but its much less than you claim.


tomo pauk said:
With Jumo 211J, the historical Ju 88 without the bombs was doing 425 km/h on max continuous
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I don't know where you got this data from, what model it pertains to and what bomb load out its from nor do I care. It is wrong, made up. You quoted nothing specific. It's possibly a Ju 88A5 with bombs with enlarged wings but with early 1200hp Jumo 213B engines.

Speed of the Junkers Ju 88A4 with Jumo 211J2 engines, dive brakes fitted and 4 external bomb racks but otherwise clean was 470km/h (292mph). Here are two links to confirm that,
Junkers Ju 88 Schnellbomber

With external bombs the speed dropped to 272-278 mph. 4 x 250kg bombs was less draggy than 2 x 500 and 4 x 500kg (4400lbs) was about the same as 2 x 1000kg (4400lbs). It would have been a bit more with dive brakes removed. beimzugmeister.de had scans for the load out, performance and planning tables for the Ju 88 but his website is down.


With the external bomb racks and dive brakes removed, which still allowed a small internal bomb load of nearly 1000kg) the speed was around 311mph.
This link confirms that as about right. The Ju 88C6 fighter was a Ju 88A4 with Jumo 213J engines with bomb racks and dive brakes removed but 3 canon and 3 machine guns added in the nose and its speed was 494kmh (307mph)
Junkers Ju-88 - Technical pages - German U-boats of WWII - Kriegsmarine - uboat.net

Until the event of internal bomb carriage for the sake of stealth almost all post war fighter bombers carried their weapons externally because it gave better performance. There were very rare exceptions: F-106 delta dart, YF-12A, F-111, F-105 Thundercheif. These aircraft had small bomb bays for a small number of AAM. In the case of the F-111 it was hardly used and in the case of the supersonic fighters it carried a very small loadout of AAM, the F-105 was to carry a single nuclear bomb in it but it was useless for anything else so fuel was carried there (like the Ju 88). F-15 carried missiles externally.


tomo pauk said:
As noted by Vincenzo, German bomber production was slashed in 1944, including bomber versions of the Ju 88
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What is your point? Ju 88A4 was forced to soldier on longer than expected since the BMW 801 was prioritised to Fw 190 and Ju 88R & Ju 88G1 night fighters and Ju 88S pathfinders. Nor was the high octane C3 fuel around to fuel a large bomber fleet. "Bombers" such as the Ju 388K, Do 335, Ar 234B and Ar 234C remained on the production program. The Ju 88G1/G7 night fighters could have bomb racks fitted and Even fighters such as the Fw 190 and Me 262 could use the up and coming toss bombing sights and could used radar blind bombing. Any other aircraft had inadequate performance anyway.
 
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(my bold)
It might have be a good idea not to put the words in my mouth.
Proper ww2 2-engined bombers were having fuel in wings and above bomb bay - see Do-217, Mosquito, B-25, B-26, A-20, A-26, Ju-288 (minus the engines' sorry saga), and still an useful bomb bay. Basically people were designing a bomber around a bomb bay and fuel tanks. Neither of the listed types have had spars interrupted.


There is the problem - the Ju 88 design flaw was that it was not designed around a proper bomb bay from day one.

Drag increments due to having bombs happily hanged out in the slipstream was a source of much greater drag than it will be the weight increase. You can see the heavy & bigger P-51 being faster on same power than Spitfire, Bf 109 or Fw 190 - weight has a negligible infulence on speed, but increase of drag kills the speed. Or, the drop-tank outfitted P-51Bs barely being able to keep up with Mosquitoes.


When buying bombers, the respective air ministries expected, for a reason unknown to me, that their bombers actually bomb the enemy. Having bomb dropped just anywhere so the bomber can be faster than the enemy fighters that just appeared kinda defeats the purpose of a fast bomber (even if it will not be fast enough, even vs. P-36 or Hurricane).
Note that Ju 288 or A-20 fuselage was slimmer than the fuselage of Ju 88, and that fuselages of A-26 or Mosquito were in the ballpark. The widest & tallest item on the Ju 88 was cockpit, not fuselage.


Yes, I'm notorious when it is about making out the data to suit my agenda.
This is posted by someone else: link


I shudder when web sites discussing German equipment don't have a single source in German language.
No Jumo 213 on bomber Ju 88s - you mean Jumo 211?

beimzugmeister.de had scans for the load out, performance and planning tables for the Ju 88 but his website is down.
Click to expand...

There is a lot at the cockpitinstrumente site.


I'm not sure that Jumo 213J was ever fitted on any aircraft,, Perhaps you mean Jumo 211J?
Again, not a single German-language source is listed in that article, even a secondary source.


Discussion of post-war aircraft look to me as slightly, just slightly off topic.


I have a hidden agenda against the Ju 88, but don't tell anyone.
Neither of the listed aircraft has no bearing on Ju-88 vs. Do-217 discussion.
 

It's TARDIS, but that's not important except to Whovians, a group of which I am not a member.

While any aircraft engineer will tell you weight is evil, they will also tell you that internal carriage of weapons has lower drag than carrying them outside. Between interference drag of external weapons and drag due to their racks, putting the bombs on the inside results in lower net drag than putting them on the outside. The people designing bombers realized this, as did the people designing fighters. The fighters put things like bombs on the outside because that wasn't their main role, and the size and weight increase from internal weapons carriage was too damaging to their performance in their primary role.


A strut-braced biplane has less weight than a cantilever monoplane, but it also has much higher drag; the same is true of fixed vs retractable gear. What's important is total drag, which is (for a subsonic aircraft, a category of which all WW2 aircraft were members) total drag is zero-lift drag plus induced drag. External carriage of weapons can increase the zero-lift drag of an aircraft by quite a lot, sometimes as much as 100%. If you wish to leap into the modern era, one of the aerodynamic problems of the F-18E/F is that the aircraft had problems with clean separation of some weapons/tanks from wing stations, requiring the pylons to be skewed relative to the local airflow, significantly reducing performance.

Positing two aircraft designed for the same range, laden speed, cruising altitude, and bomb load, the one with internal bomb carriage will be smaller and lighter when compared to one with external weapons load. One problem with this comparison is that nobody specified aircraft like that: along with the internal weapons load, air force types of the WW2 era wanted defensive armament (figure about 1000 to 2000 lb for each turret, including gunner and ammunition, plus a significant increase in zero-lift drag), dedicated navigators, radio operators (each with a work space), yada, yada, yada. Yes, I know that some modern attack aircraft don't have internal weapons carriage. Part of the reason for this is that modern aircraft are packed with various systems (electronics, hydraulics, fuel, engines, ....) and part is that air-air refuelling relieves many of the concerns about maintenance of low drag on the outbound leg of a strike. Another part may be that after the weapons are expended, the aircraft with no capability for internal carriage is much cleaner and can escape more quickly.
 
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People may also want to check out the Blackburn Buccaneer as an example of internal vs. external stowage. Granted it was designed at a time before the British adopted the US style low drag bombs.
Something that really screws up a comparison of jets vs WW II aircraft is that the jet external bombs (US MK 80 series) had a much lower drag, so the penalty for a few under wing weapons wasn't as great in proportion.
 
Another thing that has been confused. As bomber, it seems the Do217E / K / M and the Ju 88A / S were a close match in speed. As a night fighter, the Do217 J / N versions seem to have been real dogs compared to the Ju 88 C / R / G. What was about the Dornier that made it such a bad choice to turn into a night fighter or what special sauce did the Junkers have that made them so good??
 

Ju 88A and Ju 88S were not close match in speed themselves
About the question: the bigger the bomber, the more under-performing it will be as a (night) fighter when modified into one (talk making a N.F. out of Vickers Wellington). See how Mosquito was a much, much better fighter than Ju-88.
This is IMO still true even if we talk night fighters, where there was an actual disadvantage if the aircraft is too small.
 
Shortround6 said:
If the Ju 88 wants to carry 250kg bombs they have to go outside, and it won't carry eight. The A-4 could carry up to four bombs outside of up to 500kg each, modifications may have allowed larger bombs but only two?
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That is not quite correct. The Ju88 A-4 had a total of 6 wing stations capable of carrying 250 kg bombs, although probably only the four inner ones were commonly used. the permissible loads were up to 1800 kg on the inner pylons, up tp 500 kg on the middle ones, and 250 kg on the outer ones. Let's not forget the 1400 kg of bombs that could be carried internally, albeit in 50 kg-bombs - by weight alone that surpasses the maximum load of, for instance, the Ki-21 or Ki-49. It's true that by the time the A-4 went into combat, 50kg bombs were of little use (parafrags to attack airfields?) and the internal bays were mainly used for fuel. I don't know about the dimensions of the bays and how the bombs were carried, but I'm surprised someone didn't come up with alternative uses - dispensers for incendiaries or SD2-kind submunitions, for instance. I'll attach an official Ladeplan (load sheet) for the A-4 that shows the different possible loadouts. As the Ju-88 was intended to be used as a dive bomber, external carriage of bombs was necessary anyway.

By the way, they found out in the eighties that carrying two Mk8x bombs in Tandem externally caused more drag than two conventionally shaped bombs of the same weight.
 
If I could read German this might be easier to answer. But (to the op's original question) wasn't the design intention different? I understand they were both schnellbombers but wasn't the Do217 more of a dedicated level-flight bomber and the Ju88 more of multirole aircraft? Intended to fill roles as dive bomber, long range fighter and torpedo bomber?
 

Such things usually get down to fundamentals wing loading, power to weight ratios and maybe aspect ratios we can check. The larger internal fuel capacity and much larger, actually usable, bomb bay of the Dornier came at a cost in weight. Higher wing loading reduces drag but worsens climb and takeoff. As engines in the 2000hp or more class become available these issues would have faded away. However the 2000,2050,2100 and 2250hp engines belatedly available and fuel available had to be reserved for fighters and in any case providing 2000hp WEP Noteleistung in a fighter flying at 400mph is easier to accomplish than the same power duing takeoff due to cooling flow over the engine and its oil cooler. A Dornier Do 217M with Jumo 213E1 might have been a real beast.
 
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