High altitude intercept: Spitfire and P47

[BiffF15]

Isnt 49,000 ft. above the point you need cockpit pressurization or a pressure suit?

The USAF requires you to wear a pressure suit above 50k, with exceptions. Armstrongs line is 63k, at which point your blood boils (not good). Most US fighters have a 50k "ceiling", however it's due to the lack of suit and not aircraft capability.

Cheers,
Biff

 

[wuzak]

The USAF requires you to wear a pressure suit above 50k, with exceptions. Armstrongs line is 63k, at which point your blood boils (not good). Most US fighters have a 50k "ceiling", however it's due to the lack of suit and not aircraft capability.

Cheers,
Biff

But aren't they pressurised aircraft?

 

[syscom3]

For some reason, 45K sticks out for me. Something to do with your lungs not working correctly even with O2 under pressure ( force delivery).

 

[fastmongrel]

For some reason, 45K sticks out for me. Something to do with your lungs not working correctly even with O2 under pressure ( force delivery).

The RAF late war and early post war worked on a sort of semi pressurised suit for high altitude. It was a waistcoat pressurised by either a compressor or the oxygen supply to give the pilots lungs something to work against. Originally it was designed for high altitude flight in unpressurised or partially pressurised cockpits but as cockpits got better it became part of the escape apparatus designed to get a pilot down to 20,000 feet so he could breathe unassisted. The early models had to be controlled manually which cant have been easy for the pilot as it would be one more control to look at when they were already juggling with the flight controls.

My father was an RAF mechanic and he worked on the early prototype models and he said pilots hated using them but the alternative would have been a full pressure suit and getting in and out a fighter cockpit wearing one of them would have been impossible.

This is a Mk3 Pressure Jerkin which would have been used in the 50s by V bomber aircrew.

 

[BiffF15]

But aren't they pressurised aircraft?

Wuzak,
Yes they are pressurized. I didn't answer your question very well. The USAF also limits pilots to 25k unpressurized, and it appears from what I found on the internet that about 40k is as high as you want to go without a suit or pressurization.
Cheers,
Biff

 

[wuzak]

Wuzak,
Yes they are pressurized. I didn't answer your question very well. The USAF also limits pilots to 25k unpressurized, and it appears from what I found on the internet that about 40k is as high as you want to go without a suit or pressurization.
Cheers,
Biff

That is interesting, since B-17s, for one, regularly operated at altitudes >25,000ft, totally unpressurised, and I presume that the escort fighters would fly at higher than that for extended periods too.

Also must have been a form of defence for high altitude PR aircraft, which were pressurised (like Spit XI, XIX) and whose persuers were usually not.

 

[stona]

That is interesting, since B-17s, for one, regularly operated at altitudes >25,000ft, totally unpressurised,

Luftwaffe combat reports claiming to have shot down bombers or engaged bombers at 9,000m are few and far between. 6,000-8000 are far more typical. I would say, without having done an analysis, that the lower end of this (6,000-7,000m) is the most often quoted height for US formations when intercepted.
8000m works out at about 26,000ft and I wonder if the difficulty in tolerating altitudes higher than this might be a contributing factor.
Cheers
Steve

Edit I just picked a dozen combat reports at random. Only three cite bombers at above 7,000m. One gives 7,000-7,200m. One gives his own altitude as 7,200m and estimates the 'Fortresses' to be 1000m higher. A third gives the bomber formation's height as 8,500m.
The other nine reports all quote heights of 6,000-7,000m for the bombers, roughly 20,000-23,000ft, which makes sense.
A dozen might not seem a representative sample, but the result confirms what I remember from reading many more.

 

[GregP]

There are three types of Oxygen Breathing Systems used today: Continuous flow - used up to about 25,000 feet (7,620 m); Demand- used up to about 35,000 feet (10,670 m), and Pressure demand – used up to about 45,000 feet (13,720 m).

Not sure what they used in WWII, but continuous flow would have been dangerous at altitudes higher than 25,000 feet. A demand system furnished Oxygen to a user only when he or she inhales. A small lever allows the pilot to select "normal Oxygen" or "100% Oxygen." The selection depends on flight altitude. Most demand regulators give 100% Oxygen by the time 30,000 feet is reached. The mask is tight and a straight demand system can be used to bout 35,000 feet.

Higher than that requires a pressure demand system. It operates exactly the same as a demand system except the Oxygen is delivered under pressure. No effort is required to breathe in, but you must force and exhale and talking is difficult. The mask MUST be leak proof.

So ... the question I'd ask is what type regulator and Oxygen system were used in WWII? I don't know that.

I believe a presure cabin is more or less required above 45,000 feet (13,720 m)and anything higher than that in an unpressurized airecraft is very risky to the pilot involved. Some people can do it; others cannot. One person might survive 49,000 feet (14,935 m) while another riding alonside, doing nothing in the way of work, might die.

 

[BiffF15]

That is interesting, since B-17s, for one, regularly operated at altitudes >25,000ft, totally unpressurised, and I presume that the escort fighters would fly at higher than that for extended periods too.

Also must have been a form of defence for high altitude PR aircraft, which were pressurised (like Spit XI, XIX) and whose persuers were usually not.

Wuzak,

I'm not helping here much! The current USAF regulation is 25k limit if unpressurised. I'm sure back then they didn't have enough data points on when it becomes bad for your health to set a limit. I think I read somewhere that guys were getting into the high 30's or low 40's in P-38's / Spit's / P-51's.

Cheers,
Biff

 

[GregP]

That's right. The Spitfires, P-38's, and P-61's were flying about 25 - 35,000 feet (7,600 - 10.600 m or so).

At least the Germans had a pressure cabin on the Ju-86P.

High-altitude version of the Bf 109 had more or less comparable ceilings, and their performance characterisics when at altitude were not significantly different from our planes. Near the ceiling everythign was done gently with not much bank angle or else you'd fall a ways before recovering. The pilots were obviously not doing very well there either. So, yes, they COULD fight at 35,000 feet but it was not a "dogfight" by any means. Unless they were in a very shallow scissors, it was more or less one pass since the enemy would be a LONG way off by the time you could make a 180° turn while remaining at altitude.

For the Germans it was easier because they could attack from the side and make shallow turns back into the bomber stream ... unless they were being chased by an fighter opponent or opponents. In that case, it was another case of one pass and evade. Things were MUCH more agile at 20,000 feet and below ... but you were also in range of flak there. That seems funny to me since the Martin B-26 operated there and was the safest medium bomber in US service, and one of the safest for the Allies period. Mosquitoes were safe, too, and flew pretty much at whatever altitude they wanted to fly. Speed sure helped, but so did a low radar cross section. I think it was more speed and camoflague since even the fast planes in the PTO, like the Ki-46 and Ki-84, were fairly immune to Allied interception unless bounced from ambush.

All in all, I think that while some high-altitude intercepts were attempted and some were made, they were few and far between relative to missions flown at or below 35,000 feet (10,600 m or so). Even if at 25,000 - 25,000 feet, the fights were mild maneuvering compared with fighting at or below 20,000 feet. They simply didn't have the excess power for much maneuvering when at high altitude and the pilots weren't very sharp there, either, compared with their lower-altitude selves.

There were also instances, above 35,000 feet, of frozen guns when they were lubricated with other than high-altitude grease and oil. It was and IS a hostile environment for unpressurized airplanes and pilots, even if they were in a for-the-time cutting edge aircraft. It is worth remembering that the pistons flew considerably higher than the jets did in WWII.

The Germans had the Ju-86P, the Ju-388, and a couple of one-off units. The Allies had modified Spifires, P-38's and P-51. But flights above 45,000 feets were rathere rare except for the occasional Ju-86P. While the Vickers Wellesley was a "high-altitude" unit in the 1930's, it's normal ceiling was only about 25,000 feet. By 1943, almost everything modern flying in Europe could do that, but above 35,000 feet was rare territory.

 

[stona]

I don't think operations at these elevated altitudes were at all normal. A quick check of 56th FG combat reports for bomber escort missions again confirms that they were operating for the most part at close to the altitude of the bombers. Many combat reports have a starting altitude in the 21,000-23,000ft range.
Cheers
Steve

 

[wuzak]

Luftwaffe combat reports claiming to have shot down bombers or engaged bombers at 9,000m are few and far between. 6,000-8000 are far more typical. I would say, without having done an analysis, that the lower end of this (6,000-7,000m) is the most often quoted height for US formations when intercepted.
8000m works out at about 26,000ft and I wonder if the difficulty in tolerating altitudes higher than this might be a contributing factor.
Cheers
Steve

Edit I just picked a dozen combat reports at random. Only three cite bombers at above 7,000m. One gives 7,000-7,200m. One gives his own altitude as 7,200m and estimates the 'Fortresses' to be 1000m higher. A third gives the bomber formation's height as 8,500m.
The other nine reports all quote heights of 6,000-7,000m for the bombers, roughly 20,000-23,000ft, which makes sense.
A dozen might not seem a representative sample, but the result confirms what I remember from reading many more.

I just quickly glanced at a few combat reports from the 303rd Bomb Group USAAF.

Mission 213: 28/7/44, Target: Leuna Synthetic Oil Plant at Merseburg, Germany, Bombing Altitudes: 26,200, 25,200 24,200 ft
Mission 231: 24/8/44, Target: Leuna Synthetic Oil Plant at Merseburg, Germany, Bombing Altitudes: 25,100, 24,950 24,500 ft
Mission 242: 13/9/44, Target: BMW Motor Plant at Eisenach, Germany, Bombing Altitude: 29,100 ft
Mission 263: 26/10/44, Target: Marshalling Yard at Munster, Germany, Bombing Altitudes: 29,850, 28,400, 27,700 27,400 ft
Mission 286: 12/12/44, Target: Leuna Synthetic Oil Refinery at Merseburg, Germany, Bombing Altitudes: 25,200, 24950 25,500 ft

 

[wuzak]

Wuzak,

I'm not helping here much! The current USAF regulation is 25k limit if unpressurised. I'm sure back then they didn't have enough data points on when it becomes bad for your health to set a limit. I think I read somewhere that guys were getting into the high 30's or low 40's in P-38's / Spit's / P-51's.

Cheers,
Biff

Biff, not at all. It seems I am the one confusing the issue.

The point is that they were testing the limits of what could and couldn't be done, since there was little or no data to work with. And they were working at the edge of what is now considered acceptable, and often above.

 

[GregP]

Hi Biff,

You were and are a fighter piilot. If anyone in here is confusing the issue, it isn't you.

Probably me.

 

[Koopernic]

We all know about the Spitfire being used for high altitude interception of JU86P(I think) at 49,000 feet. The P47 was also very good at high altitude, one of, if not the best high altitude fighter of WW2.

Could a P47 have made the 49,000 foot interception? I know it would have to be lightened, so lets ditch 6 of the 8 machine guns and all of the armor plate to make it a special, high altitude PR interceptor.

Was the P47 capable of doing the job?

I would tend to check the accuracy of these kinds of claims. There are lots of reports that once subject to post war analysis don't pan out. The stories of modified Spifire V or VI intercepting Ju 86R for instance turn out to be false (as do the claims of Sunderlands shooting down 8 x Ju 88, but that's another story). There are claims of a Ju 388L being intercepted at 46000ft over England and then being shot down I can't find any validating reference to the Luftwaffe undertaking these missions let alone the names of pilots on either side.

As far as I can tell the highest "name plated" service ceiling of any operational interceptor was the Focke-Wulf Ta 152H. The aircraft was pressurised, had double walled canopy to stop the stratospheric cold from causing condensation on the inside of the cabin (which could completely blind a pilot). The technology used was the Jumo 213E1 engine which used a two stage three speed supercharger combined with cryogenic nitrous oxide (GM-1) which drove the service ceiling up from about 44500ft to 48500ft. The aircraft was very heavily armed and armoured and I suppose they might have achieved more if they stripped down the aircraft somewhat.

The argument against turbo-superchargers is that they add a lot of bulk, weight and drag, they reduce jet thrust somewhat and for all the extra power generated a larger and heavier propeller is also required. For this and other reasons cryogenic nitrous offered a good solution. The RAF also used it as well as experimenting with pure oxygen.

Without pressurisation there is the possibility of the "bends": nitrogen coming out of solution in the blood and forming bubbles as the aircraft climbed similar to a diver coming up after a long deep dive. A partial solution to that was to breath near pure oxygen during the climb and even before takeoff to let the nitrogen dissolve out of the lungs into the lower partial pressure created by the pure oxygen.

I really don't know how Me 163B rocket pilots did it.

Interesting to me is the 'special diets' some ww2 pilots and crew received to stop the pain caused by gases in the gut expanding. I have never found a menu or a recipe. I imagine all that is required is the avoidance of any wheat based products such as bread, pasta, likely oats as well and beans. Rice does not cause much if any gas, vegetables such as spinach and fennel do not either. Meat, fat and eggs are also OK.

As far as the P-47 goes:

At At 0ft (seal leve), the standard barometric pressure is 101 kPa (760 mmHg).
At At 44000ft (service ceiling), the standard barometric pressure is 17 kPa (131 mmHg).
At 49000ft, the standard barometric pressure is 14 kPa (103 mmHg)

So we've only got 103/131 78% as much air density at 44000ft as at 49000ft and therefore lift.

That would suggest you need to lighten the aircraft by 22%. (100%-78%). Might be possible with guns, armour and of course P-47 tests were probably carried out with near full fuel tank.

I used the following calculator and assume temperature is stable at these altitudes so that pressure and density are proportional.
Altitude.org | Altitude air pressure calculator

critical altitude of the latter turbo R-2800 was about 28000ft (earlier 25000ft) and so there would also be a decline from there, which I assume is approximately linear
At 28000ft, the standard barometric pressure is 35 kPa (264 mmHg) so I'm figuring that at 44000ft power was reduced to 131mmhg/264mmhg 49% (half power)
whereas at 49000ft the power might be 103/264 = 39% (ie there has been a 20% loss from 44000ft to 49000ft). There would also be a reduction in parasitic drag.

If there was a low fuel load, armour removed and most armament reduced, the airframe in good condition it might be possible. Worst case one would have to reduce the weight to 0.78 x 0.8 = 63%, but as I mention, parasitic drag is reduced.

As far as German aircraft high altitude champions that reached prototype stage but didn't get to a first flight: there was to be the Ju 488 with 51000ft with 4 x BMW801TJ (more with the 801TQ) and the Blohm and Voss BV.155 Service ceiling was to be 16,950 m (55,610 ft).

The massive size of the BV.155 intercoolers gives an indication of the technical challenges in compression the air to this degree. The aircraft is an almost unrecognisable Me 109 developed from the Bf 109T (with extended wings for the aircraft carriers) with turbo charging and intercooling added to a new laminar flow wing.

As far as I know the USAAF usually attacked at below 25000ft, where both the Fw 190 and Me 109 still had reasonable performance, but occasionally went higher for heavily defended targets. At 30000ft the principle German FLAK gun, the FLAK 37 was ineffective whereas as the Me 109/Fw 190 were at a big disadvantage unless using cryogenic nitrous oxide with which only a few hundred fighters were equiped. The German 10.5cm and 12.8cm FLAK 38 and FLAK 40 as well as the 8.8cm FLAK 43 were still effective but there was much less of them. Perhaps 15% as many.

 

[Juha]

I would tend to check the accuracy of these kinds of claims. There are lots of reports that once subject to post war analysis don't pan out. The stories of modified Spifire V or VI intercepting Ju 86R for instance turn out to be false ...

Who hit on 6-9-42 the Ju86R1 5101 of 3(F)/123, which crashlanded with 60% damage at Bir el Abd following Feindbeschuss ( Luft QM's report dated 6-10-42 )?

Juha

 

[stona]

I just quickly glanced at a few combat reports from the 303rd Bomb Group USAAF.

Mission 213: 28/7/44, Target: Leuna Synthetic Oil Plant at Merseburg, Germany, Bombing Altitudes: 26,200, 25,200 24,200 ft
Mission 231: 24/8/44, Target: Leuna Synthetic Oil Plant at Merseburg, Germany, Bombing Altitudes: 25,100, 24,950 24,500 ft
Mission 242: 13/9/44, Target: BMW Motor Plant at Eisenach, Germany, Bombing Altitude: 29,100 ft
Mission 263: 26/10/44, Target: Marshalling Yard at Munster, Germany, Bombing Altitudes: 29,850, 28,400, 27,700 27,400 ft
Mission 286: 12/12/44, Target: Leuna Synthetic Oil Refinery at Merseburg, Germany, Bombing Altitudes: 25,200, 24950 25,500 ft

Nine out of fourteen around the 25,000ft mark doesn't disagree too badly with the Luftwaffe combat reports, just a couple of thousand feet higher.

The Luftwaffe didn't intercept that very high Mission 263, so obviously there is nothing from that side.

I've just read all six of Otto Stammberger's US bomber claims, all except one prior to May 1943 when he was severely wounded, and the highest is 7,000m. Formations may have been pushed higher later in the war, but again, reading late war reports I struggle to find anything over 8,000m.
By the period you are citing 8,000m does appear more frequently. Coincidentally this is also the height at to which intercepting Luftwaffe fighters were often ordered by their controllers.

Cheers

Steve

 

[Glider]

I admit to not knowing how they compared at altitude but there is little doubt that the Spit would get there first and that alone would be a significant advantage assuming that the target was already up there. Had very high altitude combat become more common the RAF were already prepared with aircraft such as the Welkin ready in the wings. They didn't enter service but a number were built but the need wasn't their.

 

[stona]

Had very high altitude combat become more common the RAF were already prepared with aircraft such as the Welkin ready in the wings.

But it didn't which is one of the two principle reasons (the advent of the Mosquito being the other) that the Welkin never went into service and only 67 were delivered complete, with a further 33 engineless. Very high flying Luftwaffe aircraft intruding into UK air space never really became a problem for the RAF.

A mock combat was held between a Mosquito IX and a Welkin up to 35,000ft. The results were inconclusive as the Mosquito's performance was severely curtailed at this altitude and the Welkin couldn't follow it as it dived to lower altitude due to its compressibility problems. The Welkin experienced compressibility effects, manifested in pitching motion a fore and aft oscillation of the control column and loss of elevator authority, at a Mach number of only 0.65. The Welkin was also noted as having very poor aileron control for combat manoeuvres. A trial at 38,000-40,000ft concluded that a Welkin would be able to attack a bomber despite its limitations.

On the positive side a production Welkin climbed to 40,000ft in 19 minutes. DG558 made 351mph at 40,000ft whilst being tested at Boscombe Down.

Cheers

Steve

 

[fastmongrel]

Was the Welkins poor flight control a consequence of the wing being designed for high altitude or simply a flawed design. A quick look on the web and it seemed to have a very thick wing in proportion to width front to back.