Bf-109 vs P-40

[Dan Fahey]

One of the things that is not well discussed. US and British used 100 octane as the prime fuel because of availability. However the Brits used their 100/130 octane on US aircraft like the P51 and P40. Describing them as different beasts. Which is where you hear of the 70 inchesmanifold pressure used on the Mustangs. I wonder what fuel was used most in Africa and CBI. Burma Oil controlled by the Brits refined fuel. If so created different blends. Africa the fuel was shipped in from the US and Britain or Egypt. General Montgomery and Alexander always had a 4 to1 ratio of troops vs the Axis. Most of them were to protect the Suez Canal. They also took over Syria and Iran oil from the Italians. Had Hitler by passed Moscow and headed for Iran there would have been a different conversation.

The P40 with an extra 100/200 hp would have give the Me109 fits. Especially at combat weight!

 

[Schweik]

One of the things that is not well discussed. US and British used 100 octane as the prime fuel because of availability. However the Brits used their 100/130 octane on US aircraft like the P51 and P40. Describing them as different beasts. Which is where you hear of the 70 inchesmanifold pressure used on the Mustangs.

And P-40s too.

I wonder what fuel was used most in Africa and CBI. Burma Oil controlled by the Brits refined fuel. If so created different blends. Africa the fuel was shipped in from the US and Britain or Egypt. General Montgomery and Alexander always had a 4 to1 ratio of troops vs the Axis. Most of them were to protect the Suez Canal. They also took over Syria and Iran oil from the Italians. Had Hitler by passed Moscow and headed for Iran there would have been a different conversation.

The P40 with an extra 100/200 hp would have give the Me109 fits. Especially at combat weight!

Well they rated the P-40K for 60" Hg manifold pressure for 1580 hp 'officially' for both V-1710-39 and V-1710-73, apparently due to pressure from combat units, so I think that actually did happen. From what I gather so far it only really worked at very low altitude. Unofficially per the memo I linked above you'll notice that Allison acknowledges that they (Australians and and unnamed US Fighter Group in the Middle East) were running P-40s at 70" or 66" of mercury too for what they estimated was ~1700 hp (again only down low).

The P-51 memo you are probably referring to noted that the English were running P-51A / Mustang I and II at 70" mercury for up to 20 minutes without problems, and that is on the V-1710-39 I believe, whereas the -73 was much stronger.

The memo also specifically mentions that it was safer to do this using "amendment 5" fuel (item 4 on the memo). So I assume that is higher octane

Overboosting was also of course done with Merlins, both on Spitfires and Mustangs and P-40s too. And Hurricanes no doubt.

S

 

[Dan Fahey]

And P-40s too.



Well they rated the P-40K for 60" Hg manifold pressure for 1580 hp 'officially' for both V-1710-39 and V-1710-73, apparently due to pressure from combat units, so I think that actually did happen. From what I gather so far it only really worked at very low altitude. Unofficially per the memo I linked above you'll notice that Allison acknowledges that they (Australians and and unnamed US Fighter Group in the Middle East) were running P-40s at 70" or 66" of mercury too for what they estimated was ~1700 hp (again only down low).

The P-51 memo you are probably referring to noted that the English were running P-51A / Mustang I and II at 70" mercury for up to 20 minutes without problems, and that is on the V-1710-39 I believe, whereas the -73 was much stronger.

The memo also specifically mentions that it was safer to do this using "amendment 5" fuel (item 4 on the memo). So I assume that is higher octane

Overboosting was also of course done with Merlins, both on Spitfires and Mustangs and P-40s too. And Hurricanes no doubt.

S

The added boost does impact higher altitudes! Figure a few more thousand feet of useful performance. Interesting that performance tables were not developed using Combat operations Boost levels. The P40 should have hit the 380mph mark. The impact was in climb and sustained turn performance.

The early Allison supercharger was redesigned. Allowing for higher boost performance as it wore out the gears on earlier models.

Again was DAF using British 130 octane or US 100 octane?

 

[Schweik]

The added boost does impact higher altitudes! Figure a few more thousand feet of useful performance. Interesting that performance tables were not developed using Combat operations Boost levels. The P40 should have hit the 380mph mark. The impact was in climb and sustained turn performance.

The early Allison supercharger was redesigned. Allowing for higher boost performance as it wore out the gears on earlier models.

Again was DAF using British 130 octane or US 100 octane?

This test gives an example of climbing at higher boost. They took a P-40N-1CU and climbed at 57" mercury (nominal WEP rating)

Climb rates were

Sea Level
1000 ft / 57" / 3100
2000 ft / 57" / 3140
3000 ft / 57" / 3180
5000 ft / 57" / 3220
6800 ft* / 57" / 3370
7500 ft / 55.5" / 3270
10000 ft / 50.5" / 2930
12500 ft / 46.25 / 2610
15000 ft / 42.25 / 2300

*6800 ft was the 'critical full throttle height' ,meaning after that the boost started gradually declining.

Note that in the test - the plane got to 15,000 feet in 5 minutes flat. Rate of climb actually increased until the plane got to 6800 ft. but then declined sharply. Without boost the initial climb rate (in another test also posted to wwiiaircraftperformance.org) for the same plane was 2,300 fpm and it took 6 and a half minutes to get to 15,000 ft.

I wasn't aware the supercharger was redesigned, unless you mean the change in gear ratio. I know they strengthened the crankshaft considerably on the V-1710-73

 

[Dan Fahey]

This test gives an example of climbing at higher boost. They took a P-40N-1CU and climbed at 57" mercury (nominal WEP rating)

Climb rates were

Sea Level
1000 ft / 57" / 3100
2000 ft / 57" / 3140
3000 ft / 57" / 3180
5000 ft / 57" / 3220
6800 ft* / 57" / 3370
7500 ft / 55.5" / 3270
10000 ft / 50.5" / 2930
12500 ft / 46.25 / 2610
15000 ft / 42.25 / 2300

*6800 ft was the 'critical full throttle height' ,meaning after that the boost started gradually declining.

Note that in the test - the plane got to 15,000 feet in 5 minutes flat. Rate of climb actually increased until the plane got to 6800 ft. but then declined sharply. Without boost the initial climb rate (in another test also posted to wwiiaircraftperformance.org) for the same plane was 2,300 fpm and it took 6 and a half minutes to get to 15,000 ft.

I wasn't aware the supercharger was redesigned, unless you mean the change in gear ratio. I know they strengthened the crankshaft considerably on the V-1710-73

 

[Dan Fahey]

More of a redesign upgrade using larger bearings to prevent gears galling at high pressure! Field reports from CBI where the Early Tomahawks we're losing power after a few hundred hours. Again coming from snipit comments from field reports. Russians experienced the same issues. Later model Allison SC were able to overboost without failing.

 

[Schweik]

More of a redesign upgrade using larger bearings to prevent gears galling at high pressure! Field reports from CBI where the Early Tomahawks we're losing power after a few hundred hours. Again coming from snipit comments from field reports. Russians experienced the same issues. Later model Allison SC were able to overboost without failing.

The Russians had all kinds of maintenance problems with P-40s but in part that was due to their not realizing the importance of keeping dust out of the oil etc., not having spare parts and being forced to drill holes in all kinds of systems to drain out all the fluids every night during Winter.

S

 

[Dan Fahey]

The Russians had all kinds of maintenance problems with P-40s but in part that was due to their not realizing the importance of keeping dust out of the oil etc., not having spare parts and being forced to drill holes in all kinds of systems to drain out all the fluids every night during Winter.

S

Not to mention there were no oil or air filters. Plus their oil quality was poor. They quickly caught up. But maintenance in minus 20 degree weather did not help.

The P40 N made good power and equal to the late model zeros. What was the power and performance when the Brits by-passed the boost limiters and went to 70 inches?

 

[Schweik]

Found an interesting example of overboosting in combat. First my sources and then some background:

The anecdote comes from the diary of an American P-40 pilot with the 57 FG, George Mobbs, who survived the war with 4 victory claims. This was in "P-40 Warhawk Aces of the MTO" by Carl Molesworth (Osprey 2002) on pages 15 and 16.

I cross referenced it with Christopher Shores (et al) Mediterranean Air War Vol II, pages 365-368

In the leadup to El Alamein, Allied squadrons started engaing in more aggressive tactics against the Luftwaffe by bombing and strafing their fighter bases. On Oct 9, 1942 there was a massive raid at a LW base at what they called El Daba. DAF aircraft / forces included:

92 Sqn RAF (Spitfire Vc)
301 Sqn RAF (Spitfire Vc)
250 Sqn RAF (Kittyhawk III)
450 Sqn RAAF (Kittyhawk III)
5 Sqn SAAF (Tomahawk IIb)
2 Sqn SAAF (Kittyhawk I)
4 Sqn SAAF (Kittyhawk I)
33 Sqn RAF (Hurricane IIc)
213 Sqn RAF (Hurricane IIc)
238 Sqn RAF (Hurricane IIc)
335 Sqn RAF (Hurricane IIc)
1 SAAF (Hurricane IIc)
64 Sqn / 57 FG USAAF (P-40F)
65 Sqn / 57 FG USAAF (P-40F)

About 120 fighters in total, 80 of which were loaded with bombs.

+ and at least 62 Baltimore Bombers from 223 RAF and other unnamed bomber units, and at least 6 USAAF B-25s possibly more.

These were up against 4 /5 /6 /7 /8 and II Stab .JG 27, 7/ JG 53 from the LW (about 30 planes all Bf 109F-4 Trop), and 73,74,75,84,91,96 and 97 RA Squadrons, (about 70 MC 202 fighters).

Germans and Italians claimed 50 Allied fighters shot down in the days action, Allied claimed 10 shot down plus 50 destroyed on the ground.

Actual losses were 15 DAF (8 Hurricanes, 1 Spit, and 6 P-40s, all Commonwealth) vs. 5 Axis (4 Bf 109 F-4 Trops and 1 MC 202). 10 more German planes were destroyed on the ground and 20 seriously damaged. It's worth mentioning that two of the Bf 109s lost were indicated by the Luftwaffe as being shot down by P-40s in their records (per Shores).

DAF claims broke down as: 4 by the Spits and 6 by P-40s (3 by 250 Sqn Kitty III, 1 by 3 RAAF Kittyhawk I, 1 by SAAF Tomahawk, and 1 by a USAAF P-40F from the 57th FG). No claims were made by Hurricane pilots. The 57th FG claim was the first USAAF claim in the Med while flying as an independent American Squadron, 57 FG pilots also making a probable and a damaged claim. The anecdote corresponds to the damaged claim by a pilot called George Mobbs.

The incident occurred on Oct 9 1942 at 10:20 AM as 6 P-40Fs from 64th Sqn / 57th FG were escorting 18 Boston Bombers in a raid on "El Daba", an Axis base used by both Luftwaffe and Regia Aeronautica Fighters.

Spitfires flying high cover were diverted to help Hurricane squadrons in big trouble at another airfield so the P-40s were on on their own, though 250 Sqn RAF (flying Kittyhawk III) and 3 RAAF (flying Kittyhawk I) were operating in the same area at the same time.

Incident to follow in the next post.

 

[Schweik]

Found an interesting example of overboosting in combat.

The incident occurred on Oct 9 1942 at 10:20 AM as 6 P-40Fs from 64th Sqn / 57th FG were escorting 18 Boston Bombers in a raid on "El Daba", an Axis base used by both Luftwaffe and Regia Aeronautica Fighters.

Spitfires flying high cover were diverted to help Hurricane squadrons in big trouble at another airfield so the P-40s were on on their own, though 250 Sqn RAF (flying Kittyhawk III) and 3 RAAF (flying Kittyhawk I) were operating in the same area at the same time.

Incident to follow in the next post.

This is all directly from P-40 Aces of the Med, page 16:

Another 64th FS [57th FG] pilot taking part in the 9 October mission was 1Lt George D Mobbs, who had a much rougher time of it. He recorded this description in his diary:

'We got mixed up and got to the landing ground ahead of the bombers, but went in to strafe anyway. That is, most of us did. I was on the outside, and just as we started to go down, for or five '109s started to attack me. I turned into them and got a short burst at one, but it was a 90 -degree deflection shot. Three of them kept attacking me, and I kept evading them, and occasionally getting a shot. Meanwhile, the rest of our aeroplanes had gon in to strafe and then flown out to sea, but I couldn't join them because the three German fighters kept on attacking me.

I was running the engine at 55 to 65 inches of mercury and 3,000 rpm, so I could pretty well stay with them. They would keep alternating the attacks between them. After a few minutes I got on one of their tails and was overtaking him. I didn't open fire until i was about 100 yards from im. I gave him a squirt and nothing happened. I moved over a little and changed my sighting, and on about the third burst his aeroplane burst into flames and fell off to one side. i was going to watch him go down so i would have a chance of getting credit for one destroyed, but one of the other jokers attacked so i was busy evading him. However, I spotted the first one moments later a few hundred feet below me, still spiraling down, but I never got another look at him after that.

I was still in a hole. The other two kept attacking, one after the other. Later, I got a few shots at one from directly behind and slightly above as we were diving. I could see the aeroplane jerk each time I pulled the trigger but saw no debris or fire from it., and I was driven away by the other one. attacking. I must have hit the Jerry, because I never saw him again.

Now I just had one to worry about, but on his next attack I finished my ammunition. He kept following and attacking, but with just him to worry about, I was making pretty good time back toward our lines. On another attack we met head-on, and I didn't think he fired his guns. I didn't see them, anyway, and i was already out of ammunition.

We were down pretty low by then - 1000 ft - and the German ack-ack had opened up at me. But I was going so fast that they were shooting behind me. I had everything forward. I was running awfully hard, and the ack ack was getting pretty close to the Jerry behind me. It was kind of amusing, becuase it looked as if I was going to make it back if my engine didn't quit. We were so low that I could see the ack-ack gun emplacements below.'

In fact the engine in 1Lt Mobbs' P-40F did hold together and the Bf 109 gave up the chase. The American returned safely to base, where he was awarded one Bf 109 probably destroyed for the mission. Four days later, Mobbs recorded his first of four confirmed victories during a scrap with 20 Bf 109s over El Alamein.

Mobbs probable claim was later downgraded to a 'damaged'.

I looked up that second combat mentioned above on the 13th. On that day Kittyhawk I from 4 SAAF claimed 2 Ju 87, and P-40Fs from 57th FG claimed 2 Bf 109s, one by Lt George Mobbs. Actual German losses (per Shores MAW II P. 372) were two Bf 109F-4 and one Ju 87.

DAF losses were 4 (USAAF lost one P-40F in the action, plus a Spitfire was FTR -apparently a recon plane that blundered into the fight- and 2 Hurricanes collided). 4 SAAF Kittyhawks were also damaged but made it back to base. Germans claimed 8 (5 P-40s, 2 spitfires and a P-39). Once again significant overclaiming by the Germans. If you are generous and give them the two Hurricanes that is still 2-1, otherwise it's 4-1.

Analysis to follow in the next post.

 

[Schweik]

From the previous anecdote, I conclude the following:

1. Based on the German records, Lt. Mobbs 'damaged' claim may have been a victory after all. Possibly making him an Ace since he had 4 confirmed later in his tour. Its hard to say for sure but Germans lost three fighters in that area at the same time - the victories may have been from RAF Kittyhawks. The other LW loss was later and in a different area.
   
2. This is a clear example of overboosting to 55" - 65" Hg. You can certainly understand why.
3. It sounds like he was alternating from 55" to 65", both settings would be considered WEP, and the fight appears to have lasted much more than 5 minutes though it doesn't indicate precisely how long it actually was.
4. He was able to hold his own fighting three Bf 109s from the elite JG 27 unit, possibly shoot at least one of them down and then outrun another.
5. From all this I conclude that using overboost, P-40F could outrun Bf 109F-4 (Trop) at low altitude
6. I also conclude P-40F was at least an even match with the Bf 109F-4 (Trop) at low altitude, maybe a little better.
7. German overclaiming is notable in both incidents and by a wider margin than Allied claims. 4-1 LW vs 2-1 for DAF on Oct 9, and 2-1 LW vs 4/3 DAF on Oct 13.

It is also possible that he was actually fighting MC 202s or that he made it all up. But considering that his victory 4 days later over another bf 109F-4 it seems to be legitimate and backed up by German records I doubt it.

Comments welcome of course.

S

 

[Shortround6]

Uh, If he was flying a P-40F then he had a Merlin engine.

 

[Schweik]

Uh, If he was flying a P-40F then he had a Merlin engine.

So?

 

[Shortround6]

So a lot of this thread lately (and a few others) has been about how good the Allison powered P-40s were when over boosted.
The P-40F had a lot more power higher up and didn't lack much (if any) unless very, very low compared to the P-40E/K.

There are arguments that the Merlins should have been stolen from the P-40Fs (at the factory ) and used in early Mustangs because the Allison was so good at low altitudes.
Also please note that 12lbs boost (54.3in?) was the normal take-off rating for the Merlin V-1650-1 used in the P-40F and that 61in was the WEP power setting listed in the pilot's manual. 48.2in was the military rating and 44.2in was the max continuous.
It doesn't sound like this pilot was exceeding the recommended limits (or what would become the official limits?) by very much.

 

[Schweik]

I have similar DAF accounts with Allison engined P-40s as well (mainly Kittyhawk III or P-40K), though they don't all mention the throttle settings. They do mention running down or out-running Bf 109s.

I know we were discussing Allison engine overboosting in another thread, but the point here is per the Op and Thread Title - could P-40s contend with the Bf109.

While I think it's quite clear P-40 pilots suffered from the poor to limited altitude performance of the type, and inexperienced pilots or those using flawed tactics (flying in Vic formations, lufberry circles and so on) died quite a bit being bounced by Bf 109s and MC 202s. The altitude performance issue, especially with the Allison variants but with the Merlin ones as well to a lesser extent, was the major flaw or vice of the P-40. One never addressed.

Once they learned to fight disciplined - they could take advantage of two known virtues of the P-40 -dive and maneuverability, and one which they developed or learned in combat - overboosting. I am now convinced that on high boost, down low, the P-40 was a beast. I believe this is why it was still viable through 1943 even into 1944, despite not appearing to be on paper. The dive as disengagement coincides with excellent low altitude performance (using boost) to make for a dangerous opponent.

Still not very comfortable for pilots since they always faced the prospect of being bounced from above, and therefore often had to concede the first round to the enemy.

And frustrating for commanders because they could not escort heavy bombers or do a very good job of intercepting high flying targets.

This to me explains why the P-40 seems to be at once so hated especially by senior officers and administrators, and so loved by some of the pilots who flew them (in spite of the big flaw). They would get you home. The 'ruggedness' was of course a factor, but a limited one. No amount of ruggedness won't save you from a shower of 20mm cannon shells, or even one well aimed machine gun bullet. The dive, maneuverability (high speed roll rate especially even though it turned well too) and the beast like low altitude performance is what saved lives.

S

 

[Schweik]

So a lot of this thread lately (and a few others) has been about how good the Allison powered P-40s were when over boosted.
The P-40F had a lot more power higher up and didn't lack much (if any) unless very, very low compared to the P-40E/K.

According to my records, the V-1650 / Merin 28 on the P-40F/L got up to ~1450 hp at max boost, whereas (by mid 1942) the P-40E was rated at 1470 hp at the 'official' WEP setting of 56" and the P-40K was rated at 1550 hp at it's official WEP setting of 60" Hg. Both engines were reportedly sometimes operated at overboost as high as 66" or even 70-72" Hg for over 1,700 hp.

so please note that 12lbs boost (54.3in?) was the normal take-off rating for the Merlin V-1650-1 used in the P-40F and that 61in was the WEP power setting listed in the pilot's manual. 48.2in was the military rating and 44.2in was the max continuous.
It doesn't sound like this pilot was exceeding the recommended limits (or what would become the official limits?) by very much.

65" is overboost for that engine, by a considerable margin. And it's obvious he was using it a lot longer than 5 minutes. It means he was probably operating at ~1,500 hp or more.

I believe the 61" rating had actually developed from combat experience, increased from a previous lower rating. Much like the "official" WEP rating had gone from 45" to 57" for the Allisons and in the field 60" (secretly acknowledged by Allison) and routinely 65" - 72" by actual combat units, for up to 20 minutes according to that report on the Mustang I.

In this case it appears Lt Mobbs was running his P-40F on 65" boost for more than 20 minutes. Enough Hp for long enough to outrun a Bf109F-4.

S

 

[Shortround6]

There is little argument from me that the P-40 could pull above it's weight in certain circumstances. Sometimes well above.
For the Generals however those circumstances were too limiting. The same "investment" in ground crew(and supplies) airfield space ( dispersal points) and fuel/ammo supplies) could be used by more "all round" aircraft.

Even in your example the P-40Fs were initially given top cover by Spitfires until the Spits were called away to cover the Hurricanes.
what the starting set up ( no plan survives first contact with the enemy) would have been with P-40Es instead P-40Fs I don't know.

 

[Schweik]

There is little argument from me that the P-40 could pull above it's weight in certain circumstances. Sometimes well above.

Maybe not from you, but read through the earlier pages of this thread - a lot of people can't get their head around it. Many people will never admit that a P-40 could hold it's own with a Bf 109 or an A6M. I myself wasn't sure a couple of years ago.

For the Generals however those circumstances were too limiting. The same "investment" in ground crew(and supplies) airfield space ( dispersal points) and fuel/ammo supplies) could be used by more "all round" aircraft.

I agree with you - if I was a General I'd want a more capable plane. But the reason that the P-40 endured so long and saw action in so many places all around the world is that so many intended replacements failed (or had extended teething troubles), so few types in production could hold up to the attrition, and P-40 pilots managed to keep shooting down enemy aircraft in spite of their major flaw.

We tend to forget how late the P-51B (and later) types were to the show, so to speak. And while you and I know how much trouble they had with the P-38, or the operational limitations of the Spitfire, that doesn't always make the translation to the general public.

Even in your example the P-40Fs were initially given top cover by Spitfires until the Spits were called away to cover the Hurricanes.
what the starting set up ( no plan survives first contact with the enemy) would have been with P-40Es instead P-40Fs I don't know.

Yes but contrary to legend, USAAF P-40s did not typically have Spitfire or P-38 escorts for high cover. P-38s were used to escort the 4 engine heavies at 25k', and still had trouble. Spits had limited range and were mostly used to defend the airbases and on shorter-ranged raids.

P-40Fs often escorted P-40K or P-40E on fighter bomber sweeps. Both the RAF 'Wings' and the USAAF Fighter Groups did this, though especially the latter. USAAF P-40Fs were also used a lot to escort medium bombers, mainly A-20s and increasingly, B-25s.

At least this was the pattern from Autumn of 1942 through spring of 43. Shores Vol III book ends in May. After that there seems to have been a lot of air to air action at Panterelina, Sicily, and Italy, particularly at Anzio where they were contending with Fw 190s quite a bit.

 

[Shortround6]

I would also note that anecdotes are not really good indicators of service averages.
when you build engines by the 10s of thousands some perform much better than average and some perform worse.

Anecdotes for Merlins include.

" I had to return from Nurnberg in a Wellington II on one engine and used maximum boost and rpm on a Merlin X for 5 hours with no sign of distress"

The Captain of Lord Mountbatten's Avro York,
" We struck the most appalling weather with extraordinary icing conditions. To maintain height I had to use 2850rpm and +12lb for 3 hours."

One Lancaster pilot is supposed to have lost an engine on climb out and continued on to bomb Stuttgart on 3 engines running at climb power for the whole trip.

Perhaps not examples of overboosting but certainly operating engines well beyond recommended book limits.

 

[wuzak]

Merlin 24, which is generally similar to the V-1650-1, had the following ratings at +18psi boost (66.4inHg MAP):

Takeoff: 1,610hp @ 3,000rpm
MS: 1,640hp @ 3,000rpm @ 2,000ft
FS: 1,500 @ 3,000rpm @ 9,500ft

With 100/150 fuel the boost could be taken up to +25psi (80.8inHg MAP) and the ratings would be:
Takeoff: 1,730hp @ 3,000rpm
MS: 1,730hp @ 3,000rpm @ sea level
FS: 1,780hp @ 3,000rpm @ 4,000ft

The engines could probably take the over boost on lower grade fuels, but detonation would be a big risk.