Optimize the Ju88 for speed

[wiking85]

Starting with the basic design of the Ju88 in 1935, how would you optimize it for speed with a minimum of 900kg internal payload and 1000 mile minimum range?
Junkers Ju 88 - Wikipedia, the free encyclopedia
Ju-88, Ju-188, Ju-288, Ju-388, Ju-488, .... Ju-888
http://moderndrawings.jexiste.be/WW...anes/Axis/1-Germany/4-Bombers/Ju-88S-1/p1.jpg

 

[Shortround6]

Starting with the basic design of the Ju88 in 1935, how would you optimize it for speed with a minimum of 900kg internal payload and 1000 mile minimum range?
Junkers Ju 88 - Wikipedia, the free encyclopedia
Ju-88, Ju-188, Ju-288, Ju-388, Ju-488, .... Ju-888
http://moderndrawings.jexiste.be/WW...anes/Axis/1-Germany/4-Bombers/Ju-88S-1/p1.jpg

Uh, starting in 1935 you have crap for engines. You aren't going to get 1000-1200hp engines until 1939/40, you aren't going to get 1200-1400hp until 1941, You aren't going to get 1500-1600hp until 1942.

If you are trying to build a German metal Mosquito then you have to figure out a lower drag airframe than the JU-88 used. A few "tweaks" are not going to do the job. You need a lower drag design and a better surface finish.

It did pretty good speed wise but what are you giving up for operational capability (things like vision).

 

[tomo pauk]

1935 is not too late to change wing position from low to high. That way the bomb bay can be of decent size, unrestricted, so even the big bombs can be carried internally. Improves both top and cruising speed, along with range/radius when bombed up, vs. bombs being carried externally. I'd go with wing of ~50 sq m, and try to avoid increase in the size as the development progresses. The switch from annular radiators towards leading edge ones should be attempted, at least once it is recognized that British and/or Soviets are introducing that.

 

[wiking85]

Are there any buffs for the airfoils that would improve things?

 

[tomo pauk]

Was there any problem with wing profile of the Ju 88? Airfoil, thickness?

 

[wiking85]

Was there any problem with wing profile of the Ju 88? Airfoil, thickness?

Perhaps laminar flow wing from the beginning?

 

[tomo pauk]

I know this is a what if, but going for a laminar flow wing for an aircraft conceived in 1935 is really pushing it
Junkers can shop at NACA if they want. Supermarine did so, so did NAA, Grumman, Focke Wulf, Lavotchkin etc. A not too thick wing of NACA 230 series will provide both benign flight characteristics and useful turn of speed.

 

[GregP]

As a brief exploration, I offer this.

Take a Ju 88 A-4 as out starting place. Let's say you want the new Ju 88 to be able to go 420 mph at best altitude to sort of match the P-38J/L.

1. Max speed was 317 mph at 17,389 feet on two engines of 1,400 HP each. I chose Wiki for these numbers, but any
numbers will do to show the end result.
2. To make the same aircraft go 420 mph would take 6,512 HP is there was no change in frontal area.
3. If we decrease the frontal area by 20%, the required power would fall to 5,209 HP.

3. So, if the engines can go from 1,400 HP each to 2,500 HP each AND if we decrease the frontal area by 20%, we can make it. Getting the engiens in 1939 would be impossible. When they WERE avialable, it's is doubtful whether or not a decrease in frontala rea of 20% would render the new aircraft a useful bomber with good internal payload, but you never really know until you try it.

From this it should be clear that the only way to make the Ju 88 perform like a P-38 would be a major redesign that would probably render it not suitable as a bomber with impressive internal capacity.

 

[wiking85]

As a brief exploration, I offer this.

Take a Ju 88 A-4 as out starting place. Let's say you want the new Ju 88 to be able to go 420 mph at best altitude to sort of match the P-38J/L.

1. Max speed was 317 mph at 17,389 feet on two engines of 1,400 HP each. I chose Wiki for these numbers, but any
numbers will do to show the end result.
2. To make the same aircraft go 420 mph would take 6,512 HP is there was no change in frontal area.
3. If we decrease the frontal area by 20%, the required power would fall to 5,209 HP.

3. So, if the engines can go from 1,400 HP each to 2,500 HP each AND if we decrease the frontal area by 20%, we can make it. Getting the engiens in 1939 would be impossible. When they WERE avialable, it's is doubtful whether or not a decrease in frontala rea of 20% would render the new aircraft a useful bomber with good internal payload, but you never really know until you try it.

From this it should be clear that the only way to make the Ju 88 perform like a P-38 would be a major redesign that would probably render it not suitable as a bomber with impressive internal capacity.

How about using the Ju88S or Ju188S as a start? Plus the S-3 had the Jumo 213 engine:
Junkers Ju 88S

S-3

The S-3 was the last model of Ju 88 bomber to see production. The BMW radials of the S-1 and S-2 were replaced by Jumo 213A 12 cylinder liquid cooled inline engines, with turbo-superchargers and GM-1 boost. These engines could provide 2,300hp with wartime emergency boost, and also gained 340 pounds of thrust from their carefully designed exhausts. The S-3 had a top speed of 382mph at 27,900 feet, but although a small number did enter service in late 1944, they arrived at a time when virtually every German bomber was grounded due to lack of fuel.

 

[tomo pauk]

Hmm - a Jumo 213A with turbocharger, and plenty of exhaust thrust, with GM-1 added for a good measure?? The writer of Wiki article smokes something bad
At any rate - tailoring a 420 mph bomber + Jumo 213 in 1935? Give it jet engines, I say

 

[davebender]

High speed is nice only if it doesn't degrade primary mission of placing bombs on target with great accuracy. Otherwise it makes the aircraft less capable. So you cannot degrade weapon load, delivery accuracy or crew protection against ground fire.

Perhaps this high speed optimization should be considered only for Ju-88 recon variant. But even then you cannot do anything which detracts from ability to take aerial photographs.

 

[Denniss]

Don't stress the airframe for steep angle dive bombing, this may enable designers to add a proper internal bomb bay for 250 or 500 kg bombs and a fuselage fuel tank, maybe even larger capacity wing tanks. Some stressing should be done for shallow dive glide bombing to enable higher speed runs into target and away. Should also save some weight
Use a streamlined nose, bombardier may require large curved glass surfaces for visibility; multiple small glass panels may be cheaper but are aerodynamically inefficient. bombardier should have a trainable gun or pilot may have one or two fixed forward MGs on the fuselage sides or bottom.
Cockpit front with a larger single-piece glass with option to install armored glass.

 

[Shortround6]

Forward bay held eighteen 50kg bombs. A He 111 could fit four 50kg bombs in the space of one 250kg bomb. It may not work backwards and I have no idea what was going on (can't find picture/s of JU-88 bomb bay) but they were able to stick rather sizable one piece tank/s.

Agree with Denniss on lousy aerodynamics of JU-88 nose cap and canopy. Something between the Ju-88 and He 111 nose???

Once again we are designing with hindsight. In 1935-37 they had no idea what engines were going to be available in 1942-44 and they proboably would have laughed at the idea of using a 1936-37 airframe as a first line piece of equipment in 1944.

 

[GregP]

The Dornier Do.335 was pretty fast, used only 1,750 HP or so on each end, and carried a 2,200 pound bomb load. If they had just gotten it to front line units in some numbers maybe a year and half earlier, the Germans would have HAD their 470 mph bomber in time to do something with it.

Dornier solved the issues without resorting to huge HP, but it came a bit too late.

Some radical surgery on the Ju 88 might have gottten similar reaults, but it would be a thinner wing, much better streamlining, and some very good attention to shape and details. The Germans never had a problem with attention to details and still don't. It probably could have been done, but the end result would also probably not be a Ju 88 as we know it. Rather, a different design with roots traced to the Ju 88 as an ancestor.

I don't really see the Ju 88 basic design as getting more than 15 - 20% better than it was with the engines and shape as it was.

 

[davebender]

That's a useful payload for army support. Drop on an enemy artillery battery and it has an effect somewhat similar to cluster munitions.

 

[Koopernic]

1935 is not too late to change wing position from low to high. That way the bomb bay can be of decent size, unrestricted, so even the big bombs can be carried internally.

Now you have the main spar and wing box routed through the area the rear observer/gunner's chest would normally be. Now we either have to drop one or two crew members or move the crew cabin forward and the knock on effect of this is likely a need for greater tail area or tail length that will cost us a little in speed due to extra weight drag. It should work however in the sense of offering higher penetration speeds (due to internal bombs) at the cost of slightly lower egress speeds. With the bombs now carried internally and without the internal fuel capacity offered by the bomb bays one would need to use drop tanks for longer ranged missions, that should be OK so long as they can be jettisoned early enough in the mission for it to prevent enemy interception.

The Ju 88's bomb bay was sub divided: I believe 18 x 50kg/110lb bombs in the forward bay and 10 x 50kg/110lb bombs in the rear bay. Usually at least one bay was used to carry fuel.

I'm sure a stick of 28 50kg/110lb bombs could still make a mess. I believe such small bombs were superior in stopping production of a factory but that the damage was easier to repair than the total destruction a big 1000kg or 4000lb 'cookie' might make.

There is an argument that by having a bomb bay one thickens the fuselage and increases its weight and that these costs are so high one is better of with external carriage. Just look at modern fighter bombers.

In its developed form the Ju 88 became the Ju 388. with Jumo 213E or Jumo 222A2/B2 it was expected to do over 400mph, with the Jumo 222E/F, which has a two stage supercharger, its speed was estimated at around 440mph.

The Ju 388K still needed a ventral bomb pack, so the Germans never did fix this problem. The intention of course was to have the Ju 288 in production in 1942, it had a superb and large bomb bay but it was not to be, due to the Jumo 222 engine issues. Jumo 222A1/B1 had been fixed and the Jumo 222A2/B2 was actually scheduled for production in September 1944. It was suspended at that time to Feb 1945 due to the need to quickly disperse and increase the all important Jumo 213 production.

The Ju 88 is too big to be as fast as the Mosquito until late 1944 or early 1945 when bigger engines as powerful as the RR Grifon become available to German builders.

 

[Koopernic]

As a brief exploration, I offer this.

Take a Ju 88 A-4 as out starting place. Let's say you want the new Ju 88 to be able to go 420 mph at best altitude to sort of match the P-38J/L.

1. Max speed was 317 mph at 17,389 feet on two engines of 1,400 HP each. I chose Wiki for these numbers, but any
numbers will do to show the end result.
2. To make the same aircraft go 420 mph would take 6,512 HP is there was no change in frontal area.
3. If we decrease the frontal area by 20%, the required power would fall to 5,209 HP.

3. So, if the engines can go from 1,400 HP each to 2,500 HP each AND if we decrease the frontal area by 20%, we can make it. Getting the engiens in 1939 would be impossible. When they WERE avialable, it's is doubtful whether or not a decrease in frontala rea of 20% would render the new aircraft a useful bomber with good internal payload, but you never really know until you try it.

From this it should be clear that the only way to make the Ju 88 perform like a P-38 would be a major redesign that would probably render it not suitable as a bomber with impressive internal capacity.

That's a pretty accurate calculation. The Ju 388 streamlined the cabin area and removed the ventral bondola gun station. Perhaps that's equal to 20% reduction. Armament was confined to a single remotely controlled tail gun aimed by upper/lower periscope.

The power for the Jumo 222A2/B2 version was estimated at 2500hp/engine on B4 fuel. There was a Jumo 222A3/B3 with a slightly better altitude performance as well.

The Jumo 213E engine offered less power but it had a two stage supercharger.

The one thing I would mention is that you didn't go to the complexity of taking into account air pressure but this is a good estimate. At 20000ft air density and therefore drag is 50% less however due to a supercharger the Jumo 211 has probably only lost 30% in power, so a net gain. The Jumo 213E with a two stage supercharger has noticed virtually no power loss.

Ju 88 speed can be improved if the superchargers are improved, but only at high altitude.

 

[GregP]

Thanks. I was thinking of making the wing slimmer, eliminating the flat sheet windows and nose in lieu of streamlined units, and making it as light as possible while increasing power. That would get you part way there, but then you'd need to make a slimmer overall fuselage.

We could work at it and maybe arrive at a solution ... maybe not. Doing it in wartime Germany should have been a top priority, but somehow it wasn't. The Do.335 didn't really fly until the end was a foregone conclusion. Germany never really HAD a stragetic bomber, and that was a big mistake.

If you are going to base your attack on quality instead of quantity, you'd better have the quality in-service when it is needed, and it wasn't. It was in work, and that's not the same thing. Also, it's tough to prevent the enemy from inventing the things you are working on all by himself, and there's no guarantee they won't invent something you haven't thought of.

 

[tomo pauk]

Now you have the main spar and wing box routed through the area the rear observer/gunner's chest would normally be. Now we either have to drop one or two crew members or move the crew cabin forward and the knock on effect of this is likely a need for greater tail area or tail length that will cost us a little in speed due to extra weight drag. It should work however in the sense of offering higher penetration speeds (due to internal bombs) at the cost of slightly lower egress speeds. With the bombs now carried internally and without the internal fuel capacity offered by the bomb bays one would need to use drop tanks for longer ranged missions, that should be OK so long as they can be jettisoned early enough in the mission for it to prevent enemy interception.

The new location of spar attachment points would not interfere with crew placement, since those points would still be at Fuselage Rib 9 and 12. The spar attachment points are numbered 11 here:

With high wing location, the unrestricted bomb bay would be spanning between ribs 9 and 15.

There is an argument that by having a bomb bay one thickens the fuselage and increases its weight and that these costs are so high one is better of with external carriage. Just look at modern fighter bombers.

Modern fighter bombers are fighters that can carry bombs, not really comparable with ww2 bombers. In ww2 a decent bomber with a bomb bay was a better performer than an aircraft that carried bombs outward. Even once the bombs are gone, the racks/shackles cost drag.

In its developed form the Ju 88 became the Ju 388. with Jumo 213E or Jumo 222A2/B2 it was expected to do over 400mph, with the Jumo 222E/F, which has a two stage supercharger, its speed was estimated at around 440mph.

The Ju 88 is too big to be as fast as the Mosquito until late 1944 or early 1945 when bigger engines as powerful as the RR Grifon become available to German builders.

Burdening the aircraft with additions, like Bola weapon station, external payload with racks, ever bigger wing and sometimes fuselage certainly cuts the performance; not just speed but also range/radius. Hence my proposal to keep the wing at 50 sq m, internal bomb bay etc. Such a clean and not too big an aircraft would be a better performer than historical Ju-88.
When it's about the engines, the BMW 801 would make a lot sense here, at least for a part of Ju-88 production.

 

[kool kitty89]

Uh, starting in 1935 you have crap for engines. You aren't going to get 1000-1200hp engines until 1939/40, you aren't going to get 1200-1400hp until 1941, You aren't going to get 1500-1600hp until 1942.

The BMW-801 was in the 1500-1600 power range in 1941, plus the Jumo 211s the bulk of Ju-88s employed had worse altitude performance than the contempoary DB-601s (and 605s).

It did pretty good speed wise but what are you giving up for operational capability (things like vision).

How about a Misquito class aircraft for 1935-1942 standards at least? Similar emphasis on limiting unnecessary size, weight, and bulk. No compromises for including defensive armament and limited to just two crew members.

Managing to retain initial and sticking with the initial concept without compromises for RLM doctrine, you might have something much more competitive that will last well as newer and more powerful engines arrive while minimizing growths in size/weight wherever possible. (inevitable given perception of combat requirements of the late 30s with 1940 onward -crew armor and self sealing tanks being big ones, but you've also got a big leap in power and altitude performance from 1935 to 1940, let alone beyond)

Dehavilland managed to work around most of the British Air Ministry's clashing requirements that would have compromised the Mosquito's success, the Ju-88 didn't have that luck. (that and the Mossie had the advantage of some of the best engines already being slated for bomber production, at least initially -2-stage merlin models might not have gotten volume priority later on, but having the Merlin XX from the start was significant)

1935 is not too late to change wing position from low to high. That way the bomb bay can be of decent size, unrestricted, so even the big bombs can be carried internally. Improves both top and cruising speed, along with range/radius when bombed up, vs. bombs being carried externally. I'd go with wing of ~50 sq m, and try to avoid increase in the size as the development progresses. The switch from annular radiators towards leading edge ones should be attempted, at least once it is recognized that British and/or Soviets are introducing that.

Couldn't the existing wing configuration still have allowed for the ability to carry some larger bombs (even if not using the space as efficiently), or at least allow for that if it was planned for from the start? (that and adopting a bulged bomb bay for special heavy bomb runs like the Mossie did would make more sense than using external racks)

And embedded radiators might work, but also take up wing space and increase vulnerability. (the compact annular configuration limited vulnerable engine area considerably on top of being relatively efficient weight/bulk/drag wise) Granted, the lack of pressurized cooling systems on the early Jumo engines means larger radiators for similar cooling capacity. (optimized annular radiators on contemporary DB-601s should be less)

There's a reason most late-war adaptations of DB-603s and Jumo-213s used similar arrangements.

I know this is a what if, but going for a laminar flow wing for an aircraft conceived in 1935 is really pushing it
Junkers can shop at NACA if they want. Supermarine did so, so did NAA, Grumman, Focke Wulf, Lavotchkin etc. A not too thick wing of NACA 230 series will provide both benign flight characteristics and useful turn of speed.

They could have gone with a symmetrical NACA (or other airfoil), less lift but less drag per area too, and less parasitic drag. (maybe a slightly higher critical mach number, but that's also dependent on thickness ratio)

The B-17 actually used a 00xx series airfoil I believe, though rather thick at the root. Low drag per area is good if you want space for fuel or other components inside the wing, beyond that there's trade-offs for lift/drag efficiency at varying speeds and sheer size/weight of the wing. (I'm not that versed in the finer points here, but I think lower parasitic drag is where the bigger advantages come in)

Heinkel was using its own series of low-drag (often symmetrical) airfoils on its high speed aircraft as well, and both the Me-262 and F-86 opted for 00xx series NACA profiles. (or modifications thereof) Republic's fighters used their own in-house low-drag (low lift) airfoils as well. The later CF-100 appears to have used an unmodified NACA 0010 airfoil.

In any case, relatively low drag, high speed suited airfoils did already exist, even if their full advantages weren't yet understood. (I assume Messerschmitt either DID understand a great deal of that, or just got very lucky with the designs employed in 1939 for the Me 262 for the drag and critical mach characteristics of that airfoil)

As a brief exploration, I offer this.

Take a Ju 88 A-4 as out starting place. Let's say you want the new Ju 88 to be able to go 420 mph at best altitude to sort of match the P-38J/L.

3. So, if the engines can go from 1,400 HP each to 2,500 HP each AND if we decrease the frontal area by 20%, we can make it. Getting the engiens in 1939 would be impossible. When they WERE avialable, it's is doubtful whether or not a decrease in frontala rea of 20% would render the new aircraft a useful bomber with good internal payload, but you never really know until you try it.

From this it should be clear that the only way to make the Ju 88 perform like a P-38 would be a major redesign that would probably render it not suitable as a bomber with impressive internal capacity.

What if you take reduced weight into account on top of reduced drag area and make the comparison more akin to the 1939 YP-38 at medium altitude? (or Fw-187 with DB-600s)
Or more practically, just compare it to the speed of contemporary enemy fighters at its given combat altitude?

The Mosquito didn't match the performance of the contemporary P-38 models, or even contemporary Spitfire models in level speed (or contemporary 109s, let alone 190s) or P-39s at favorable altitudes. (closer to P-40 performance with similar engines) But it was fast ENOUGH to be hard to catch, let alone hit and take down.

Some radical surgery on the Ju 88 might have gottten similar reaults, but it would be a thinner wing, much better streamlining, and some very good attention to shape and details. The Germans never had a problem with attention to details and still don't. It probably could have been done, but the end result would also probably not be a Ju 88 as we know it. Rather, a different design with roots traced to the Ju 88 as an ancestor.

I don't really see the Ju 88 basic design as getting more than 15 - 20% better than it was with the engines and shape as it was.

Had the follow-on designs to the Ju-88 focused more on just that sort of performance envelope with emphasis on minimal size/weight as well as drag (unlike the 188 and 288), then they might have had something considerably better to move forward with.

As it was, a 15-20 percent gain would have been enough to get it close to or into the Mosquito's performance range.

Don't stress the airframe for steep angle dive bombing, this may enable designers to add a proper internal bomb bay for 250 or 500 kg bombs and a fuselage fuel tank, maybe even larger capacity wing tanks. Some stressing should be done for shallow dive glide bombing to enable higher speed runs into target and away. Should also save some weight

Increasing weight in all those other areas could require structrual enhancement as well, though. Providing more provision for modification later on with that in might might have been more useful. (or high maximum fuel capacity AND more flexible/larger internal bombload, but not actually able to safely carry max bombs+max fuel at once)

Ineavitable gains to weight and loss to fuel capacity due to armor and self sealing tanks are assumed, too.

Use a streamlined nose, bombardier may require large curved glass surfaces for visibility; multiple small glass panels may be cheaper but are aerodynamically inefficient. bombardier should have a trainable gun or pilot may have one or two fixed forward MGs on the fuselage sides or bottom.
Cockpit front with a larger single-piece glass with option to install armored glass.

Making those optional depending on mission profile would be good too. (as the Mosquito managed) But defending against frontal attacks and ability for ground strafing are significant, and those positions don't require added crew or excessive drag. (plus frontal attacks are more problematic psycologically, so having protection there -be it armor, guns, or both- would be useful, and speed or not, you can't outrun a head-on attack)