combat altitude in the ETO

[renrich]

HoHun, I can't remember the exact definition of service ceiling but it is something like the altitude at which the AC can no longer climb at 500 fpm(or maybe less) If the service ceiling is 29000 feet, one does not want to get in a fight at that altitude because your performance is so poor. Also if an AC which has good maneuverability at lower altitudes gets really high his wings don't deliver the lift necessary to turn well. That is the reason that AC meant to perform at high altitudes such as the Spitfire HF MkVI or the TA 152 (or the U2) had long span wings to provide more lift at high altitudes. Of course, those long span wings don't perform so well at low altitudes.

 

[kool kitty89]

The long span wings will improve turn performance at low altitude as well (in addition to the increased area, the high AR results in more efficient wing with higher CL and lift:drag ratio, assuming the airfoil doesn't change). Stall speed is also much lower. The penalty is roll rate, which the 152H made up for partially with boosted ailerons. (while the 190, and short wing 152C would still roll better, most allied a/c still wouldn't have an advantage)

 

[HoHun]

Hi Renrich,

>HoHun, I can't remember the exact definition of service ceiling but it is something like the altitude at which the AC can no longer climb at 500 fpm(or maybe less)

It's 0.5 m/s in international units, or the almost equivalent 100 fpm in Imperial units.

>If the service ceiling is 29000 feet, one does not want to get in a fight at that altitude because your performance is so poor.

Quite right - the Germans used the term "Arbeitshöhe" ('work altitude') to describe the altitude at which the aircraft could still achieve 2 m/s climb. That would usually mean that the margin of specific excess power still was at a tactially useful level.

>Also if an AC which has good maneuverability at lower altitudes gets really high his wings don't deliver the lift necessary to turn well.

Of course, power has a large impact as well - if you have a big wing but little excess power, you can still make instantaneous turns but pay for it with a high sink rate. With a smaller wing and good excess power, you might not be able to match the other guy's instantaneous turn, but you'll be able to get above him while turning - which is an obvious advantage

Regards,

Henning (HoHun)

 

[renrich]

Good info, thanks HoHun! Even in aviation, there is no free lunch. Thanks also to KK, I bet the U2 had a horrible roll rate. Of course, if you can't roll pretty fast, you can't start turning very fast. I wonder what the roll rate of the P47N was compared to P47D. By the way, speaking of high altitude performance, in the period after WW2, the SecDef under Truman(I think his name was Denfield) had been convinced by the Air Force that no new carriers need be built because the B36 with it's high altitude performance could not be intercepted and dropping nukes was all the deterrent we needed in the air. The USN countered by saying that their F4U5 could get up there and intercept the B36. I don't know if there was a demonstration or not but the Korea thing came along and there suddenly seemed to be a need for more carriers.

 

[SoD Stitch]

I would bet that the vast majority of ACM took place below 25000 feet. It might have started higher than that but it would most likely end up lower.

You are quite right about that; even assuming ACM started out at 20K+, it quickly degenerated below that, sometimes right down to GL, as the competing pilots constantly tried to get an advantageous position by trading altitude for speed. I would guess the "average" height for ACM was right around 10K in the ETO.

 

[parsifal]

There are two factors that might be an influence in this debate

1) The effective ceiling of the US Heavy Bombers. I am relying on a book, "German Anti-Aircraft defences 1914-45", E.B. Westermnann, Univesity press Of Kansas, 2001, Westerman says that the effective average ceiling of the B-24 was about 25000 ft, whilst those of the B-17 varied from about 24000 to 27000 ft. Given that the job of the P-51 escorts was to escort those bombers, and the primary mission of the German fighters was to go after the Bombers, it seems logical to me that the predominant number of combats is going to occur at the bomber altitudes, and not the fighter altitudes (I have read that normal procedure for the US fighter escort was to be stacked above and behind the Bomber force, at altitudes ranging from 1000-5000 ft above the Bombers. The reasons are obvious, if Germans started attacking, the Mustangs are in an ideal position do go into a diving passing attack against the fighters, and thereby provide the best defence for the bombers.

2) The effective operating ceiling of the german flak defences. As a generalization, German 88 mm batteries, which accounted for about 80% of the german Heavy flak defences, had an effective ceiling of about 26000 ft, consequently the bombers always tried to minimise the effects of the flak by trying to fly above it. It should also be noted, that by 1944 German flak was beginning to show signs of excessive wear and tear. Barrel wear was in particular a big problem for the German flak defences. by 1944, the real effective ceiling, according to Westermann, for an 88 had, on average fallen to well below 25000 ft, and and flak barrels lost to accidents were going through the roof. There were on average 380 88mm flak guns per month lost to accidents in 1944, whereas the number in 1942 was less than a quarter of that. As an aside, the average number of Heavy AA shells expended to shoot down each bombe was about 16000, wheras in 1942, it was, again, about a quarter of that number

 

[HoHun]

Hi Renrich,

>By the way, speaking of high altitude performance, in the period after WW2, the SecDef under Truman(I think his name was Denfield) had been convinced by the Air Force that no new carriers need be built because the B36 with it's high altitude performance could not be intercepted and dropping nukes was all the deterrent we needed in the air.

Remarkable coincedence - I just today read about that Air Force vs. Navy battle for the first time in the 1950s' book by Camille Rougeron I purchased recently!

He points out that due to the difficulties the B-29 encountered in Korea, the USAF decided to specify a heavy jet bomber that combined speed of the B-47 then in service with the mass of the B-36 in order to get payload and range. Ambitious, but successful - the specification resulted in the B-52!

Regards,

Henning (HoHun)

 

[kool kitty89]

Good info, thanks HoHun! Even in aviation, there is no free lunch. Thanks also to KK, I bet the U2 had a horrible roll rate. Of course, if you can't roll pretty fast, you can't start turning very fast. I wonder what the roll rate of the P47N was compared to P47D. By the way, speaking of high altitude performance, in the period after WW2, the SecDef under Truman(I think his name was Denfield) had been convinced by the Air Force that no new carriers need be built because the B36 with it's high altitude performance could not be intercepted and dropping nukes was all the deterrent we needed in the air. The USN countered by saying that their F4U5 could get up there and intercept the B36. I don't know if there was a demonstration or not but the Korea thing came along and there suddenly seemed to be a need for more carriers.

True on the roll rate, but in the majorety of high AR wings on fighters they were twins like the P-38 wjich had the outboard engines with spread out mass which would considderably limit roll-rate, even with boosted ailerons the P-38 had a mediocre roll below 250 mph, but an advantage above 350 mph as roll continued to increase, while non-boosted controlls would degrade with increasing stick forces of manualcontrolls. (usually ~250-300 mph, but closer to 200 mph for the early Spit and the Zero)

Wing shape also has a big effect, squared off tips usually bing best, rounded tips in the middle, and sharp eliptical tips the worst. The P-47N despite the increase in span had considerably improved roll rate over the normal wing. The P-47D's max roll being being ~85-90 degrees/s, the N's over 100 degrees/sec. This was due both to the clipped tips and the larger ailerons employed. Plus the increase in span was only ~2ft.

And in the case of the Ta 152, seing as the Fw 190 was one of the best rollers, it would obviously not compare (except at high speeds due to boost), but I think it would still be competitive. (just speculation) But seeing as the P-38 with boost was decent even with the spread out mass, the 152 should be in much better shape. And once in a turn it should be very good.

 

[FLYBOYJ]

And the early P-38's had serious cocpit heating problems as well, and some engine problems at high altitude. Most with the ineffective intercooler, but also sometimes due to overcooling of the engines crusing at engine temps below safe limits without warning due to over-effective radiators (and sometimes problems with the rasiator flaps) poor coolant/oil circulation at those temps resulting in false temp readings. When rapidly throttling up for combat in such cool operating levels the engines would fail.

And in the Pacific?????????

 

[kool kitty89]

The problems were not very important (due to warmer climate and lower alt operations) and they did very well. Similar in the cases in the MTO and NA, abeit not to the same extreme as in the pacific.

But were were talking ETO, and I was comparing the problems of the P-38 to the conditions the bomber crew had to suffer as well in response to a comment about the high alt bomber conditions.

 

[renrich]

Michael, good post with some very good info. In a high velocity gun like the 88, barrel wear must have been a serious problem. Surely can occur in rifles too, if you know what I mean.

 

[parsifal]

Yep, but we'd better not go there right now

 

[phoenix7187]

Soren that was a piece of info I was missing thanks.

A question I was going to bring up was. I have all these charts that show power and to a extent performance at different altitudes. I also have pilot accounts of combat. you can see how as aircraft gain altitude performance changes. pilots of the radial A series complained that above about 20K in round numbers there performance was well under that of the allied protection fighters. Also as they gained altitude performance fell off very quickly. 190A pilots saying climb from 20 up was slow and very poor. It seems the jumo A powered D's performance started to fall off at about 22K, but the rate at which it did was far less than that of the radial BWM powered A's. Pilots of the jumo A mechines saying that they coulds keep paces with allied fighter at about 24/25K. I'm using performance charts and pilot accounts to get this info. You guys talked about operating at or near the aircraft service as well. Have anyone seen test done that evaluate the dogfight ability of the aircraft at various altitudes. Things like rate of turn, turn radious, power/altitude bleed off, roll rate and such. Speed at various altitudes and climb rate give some info but doesn't tell the whole story.

Second question. The US did test of this kind to a extent, but alot of it is one sided. Most of the aircraft they tested had problems. The one D powered G-10 they tested gave excellent results, but becasue they were not useing the MW50 system it could have been far better. The US though the MW50 system was like there WEP, This is fales from what I have read. It was not a emergency power that over taxed the engine. The Those engines were designed to use that as a power booter system. All the way back to the 109E the luftwaffe had the mind set of small light weight power plants that provided "power on demand". From that I'm reading late jumo's and DB could operate not a few mniutes but almost as long as the supply held out. Some info stated 10 min and then a cool down period. Do any of you have info on this as well. I'm not sure if this was just some engines or what. The jumo A seems to have a limit, while the jumoF/EB and the DB605DCM I'm not seeing this restriction.
thanks fo the input guys.

 

[kool kitty89]

Most of the 190A's also had quite a bit less power and more weight than the 190D-9, the A-8 about the same up to 18,000 ft, though I think the A-9 would compare more favorably, altidude performance was better with the 801E/S than the 801D of the A-8 and had more power. (a bit more than the D-9's Jumo 213A as well)

The A-8 and D-9 having similar power ratings (moth ~1,750 hp and ~2,000 hp with boost albeit the 213 held it a good 3,000 ft higher) The 801S of the A-9 having 2,000 hp and something like 2,200 hp with boost.

 

[Soren]

Regarding the MW-50 system;

Yes, the Bf-109 FW-190 could run this system at full boost for 10min and then they needed a cool down period.

But one must also note that using the system too often put a lot of wear on the engine and used up a lot of fuel, and since the LW was low on both this boost system was only to be used in absolute emergencies. Like some LW pilots say; they never used the system for longer than 2 - 3 min at a time, as doing so meant the engine had to undergo maintenance allot sooner.

 

[kool kitty89]

There was also an alternative system, particularly used with the 801, that sprayed fuel into the charge to lower the temperature instead of water/methanol mix. (though this resulted in even higher fuel consumption)

 

[drgondog]

This is an interesting question re: combat altitude in the ETO as you have to consider both the specific air campaigns and the tactical/strategic doctrine.

With the RAF, particularly the Spit, the doctrine was either night raids in which no escort was really performed early and only increasing later with Mossies - or performing the early escort to 8th AF over France and Holland or escorting mediums. So, the Spit which was superb high and low engaged very little except in Sweeps and the occasional escort of early 8th AF/9th AF raids into Occupied countries. Most of these were 'middle altitudes and more like MTO.

In the 'middle game' of 8th AF ops, the escorts were at high altitudes, but except for LuftFlotte 3 of JG26 and JG2, the doctrine was to pull back out of range and 'pile on'. In this time frame the Me 110 and Me 109 and Fw 190 would attack after the Penetration Escorts of P-47s and Spifires ran out of Range... so, the performance of the 190 and 109 at altitude was not a great factor as they were still a lot faster than B-17s.

The P-38s had excellent performance at altitude everywhere except the ETO but still were a substantial annoyance to the 109 and 190 at B-17/B-24 altitudes but were easy to spot and either stalk or avoid.

The 51 had the performance, the range and the profile to be somewhat innocuous compared to the 38 and the 51B/Merlin in High Blower was superb at B-17/B-24 altitudes and also great at middle altitudes in low blower.

So, the point of ETO combat altitudes.

In Target Escort the combat typically started at Bomber escort levels which ranged from 1/2 to 1 mile above the bombers - in intercept mode then went wherever in the chase.

In Sweeps the 51s might be at 20K, spot German aircraft taking off and hit them on the deck.. or catch them forming out in front of the bombers about
50 miles.. so these engagements were more middle and low altitude.

The importatnt thing to remember is that the OOB could be described over Central and Eastern Germany as between the few P-51 and P-38 groups versus LuftFlotte Reich and it was a chess game to try to a.) cover the bomb divisions, and b.) attack where the escort were thin or non-existant.

The bombers were bait. the objective from january 1944 forward was draw the luftwaffe up and kill them in the air or on the ground prior to Normandy campaign.

The P-47 was a great fighter and did a lot of damage to the Luftwaffe on the coast all the way to west Germany, but the LW learned to avoid them. The P-51 stripped the LW of places to form up in peace, stripped them of their aggressiveness and pursued them everywhere from December 1943 in small numbers to December 1943 when in any one day there were more fighters capable of going to Berlin than capable of defending it.

 

[kool kitty89]

The biggest advantage of the P-51 was that it costed less than the P-47 (and ~1/2 that of the P-38 ) was also cheaper to operate and used alot less fuel, while still having good performance. (in most respects the P-51 was a better "dogfighter" as well against the Jug or P-38 prior to boosted ailerons)

For actual range capabilities of the three:

http://www.wwiiaircraftperformance.org/p-47/p-47-tactical-chart.jpg
http://www.wwiiaircraftperformance.org/mustang/p-51-tactical-chart.jpg
http://www.wwiiaircraftperformance.org/p-38/p-38-tactical-chart.jpg

 

[parsifal]

All this is excellent stuff, and helps a lot in understanding how the battles panned out. Something I dont understand though, whereas the germans could co-ordinate thair CAP to attack at certain points and in certain strengths, due to the GCI control, how did the bomber groups, and escorting fighters cordinate and concentrate their efforts. Was it all determined by a predetermined plan, or was there some sort of aerial Command Control going on????

 

[drgondog]

All this is excellent stuff, and helps a lot in understanding how the battles panned out. Something I dont understand though, whereas the germans could co-ordinate thair CAP to attack at certain points and in certain strengths, due to the GCI control, how did the bomber groups, and escorting fighters cordinate and concentrate their efforts. Was it all determined by a predetermined plan, or was there some sort of aerial Command Control going on????

Two answers for 8th AF side. First, the routes, timing, R/V points, Fighter Group assignments, etc were all part of a detailed plan for every mission. Execution is a different discussion.

The fighters were tied to the bombers but from January 1944 forward, the Fighter Group Commander had discretionary authority to delegate to Squadron commanders to dispatch flights, sections and even the entire squadron to meet an attack while the rest of the group stayed with the bombers.. and as a german force was noted to be too large for a squadron to withstand, more and more fighters were sent to meet the attacks.

Bomb Wings were late, fighter groups missed R/V points, Bombers strayed off course because of weather or late form up.. mistakes were made and bombers were left unescorted. Sometimes too few fighters were available to cover too many independent targets or insufficient to ward off a large determined attack from German fighters with overwhelming local superiority.

Second, 8th AF doctrine and tactics evolved with Type 16 and Beachyhead control originating from UK. These ground control types assimilated radar signatures and other intelligence to direct certain fighter groups operating under Freelance or Sweeps to points where German fighters were believed to be concentrating. In these situations the fighter group has no assignment to escort and are out in a 'free hunt' to use LW terminology and looking for trouble.

Many times the re-direction resulted in a wild goose chase. Sometimes it hit the jackpot.

I forgot to mention that several attempts were made to give a Fighter Group CO (say 4th FG Blakeslee in May, 1944) airborne Command and Control over several other Fighter Groups but these were not entirely satisfactory and it was deemed less a solution than resorting to local group control as noted above