Corsair and Hellcat in Europe

Shortround6 said:

We have at least 2 variables that contribute to the difference in cruise speed vs the power used.
1. may be the efficiency of the respective propellers at cruise speed/altitude.
2. maybe a difference in exhaust thrust. However this may not be great. The P-47 gets darn little (I think?)
But the amount the F6F gets at cruise speeds may not be a lot either. At 36in and 2300rpm the engine is moving about 57% the amount of air it is at 54in and 2700rpm and since exhaust thrust is mass times velocity the fact that you are running lean means less fuel per pound of air.

F6F exhaust is better than than an early F4U but not as a good as a V-12
View attachment 503723
That middle pipe in the upper 3 may do pretty good but the top pipe doesn't look so good. The longer the pipe and the more/sharper bends the lower the exhaust gas velocity.
An engine running 54in of boost in the cylinders will have higher pressure/velocity gas leaving the exhaust ports than one running 36 in of boost.
Trying to compare a 1200hp V-12 running at 48in boost to a large radial loafing at 1200hp with 32-36in of boost may not be accurate.

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Awesome stuff as usual SR6. I'm going to need a little time to digest what you said so I understand it completely...

DarrenW said:

Far enough. What about throttle response, is "turbo lag" prevelant with aircraft engines as it is in cars? From what I've learned a supercharger has power on demand, does this ever give the supercharger an edge over a turbo in aircraft operations?

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Probably not. You have a few things going on with the aircraft engine that you do not have with cars/motorcycles.
Many racers use lightened flywheels to improve throttle response in land vehicles. In aircraft you had an over 300lb prop (in most cases) going to well over 400lbs on the high powered engines you were trying to wind up. Quick throttle response probably wasn't going to happen.
No WW II aircraft used a turbo only, you had the engine supercharger and if you were cruising it wasn't maxed out. Some planes cruised with the throttle wide open but with the prop at coarse pitch and low rpm. To accelerate the propeller governor was changed to a higher rpm and the propeller pitch mechanism reduced to the pitch to allow the engine to speed up. The engine supercharger could probably keep up with the increased demand for air for a while the turbo, reacting to increased exhaust flow, sped up.

There may be some lag but not to the extent of an engine with only a turbo and how long does it take to increase the RPM on that big propeller?

Getting back to the Thunderbolt's wing pylons and the extra drag they caused, in America's Hundred Thousand (Dean) a pilot is quoted as saying that his P-47D-16 was exactly 50 mph slower due to those "monstrosities" (wing pylons) used on it. Most likely a bit of an exaggeration but it does hit home the fact that they were without a doubt noticeably large and cumbersome.

Shortround6 said:

Probably not. You have a few things going on with the aircraft engine that you do not have with cars/motorcycles.
Many racers use lightened flywheels to improve throttle response in land vehicles. In aircraft you had an over 300lb prop (in most cases) going to well over 400lbs on the high powered engines you were trying to wind up. Quick throttle response probably wasn't going to happen.
No WW II aircraft used a turbo only, you had the engine supercharger and if you were cruising it wasn't maxed out. Some planes cruised with the throttle wide open but with the prop at coarse pitch and low rpm. To accelerate the propeller governor was changed to a higher rpm and the propeller pitch mechanism reduced to the pitch to allow the engine to speed up. The engine supercharger could probably keep up with the increased demand for air for a while the turbo, reacting to increased exhaust flow, sped up.

There may be some lag but not to the extent of an engine with only a turbo and how long does it take to increase the RPM on that big propeller?

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Exactly, turbos on cars have to deal with constant changes of rpm and power requirements, while aircraft engines tend to be fairly constant speed.

Even an aero engine not connected to a turbo will take some time to accelerate from cruise rpm to military rpm and boost.

As for the turbo, opening the throttle and dumping more fuel in is going to increase the exhaust energy and thus accelerate the turbo. Also, depending on the altitude, the exhaust may already have enough energy to accelerate the turbo, but is dumped overboard by the wastegate for turbo speed control.

"The performance of the Moresby radar was poor as judged by the operators. The sets were "experimental" models and were still on the south side of the Owen Stanley mountains which limited their range. They still could not adequately warn of incoming raids.

Milne Bay is on the eastern tip of NG and was not obstructed by mountains. It also provided a panoramic view of the Japanese held areas.

The P-39s obviously could intercept Japanese bombers at over 22000' as they did on numerous occasions".

Milne Bay was of no assistance in the air defence of Moresby. It was 300miles away, and more than 600 from Rabaul. There was a mountain range in the way of Moresby that created just as bad a radar shadow as the mountains behind Moresby. I don't know what your data sources are telling but as a person that has been there and seen the place first hand, there is virtually no radar signatures detectable to the north and NW. And no radar set available in 1942 with air search capability and a range of 600 miles. We have had this conversation before, and still you keep pedalling out the same garbage over and over. I will tell you again ive been there, I know the conditions, and milne does not have much to offer the air defence problems facing Moresby.


They were standard US SCR sets, experimental to the RAAF because we had never used them before, but more or less standard issue in the US. Performance was initially poor and improvements were slow to take effect, however even when given ample warning of impending attacks P-39s proved nearly useless as defending CAP.

Even when P-39s were given ample early warning, they generally were a failure in intercepting IJN bomber raids over Moresby. they did inflict losses and eventually these losses mattered because the IJN was very susceptible to losses. but claiming they were effective is a joke, surely.

As an example of P-39 performance even when given plenty of warning, look at the raids of 18 May 1942

During the morning of May 18, 1942 at Rabaul 18 x G3M2 Nell bombers from the Imperial Japanese Navy (IJN) Genzan Kokutai led by Lt. Rokuo Nikaido took off from took off from Vunakanau at 5:55am armed with 60kg bombs on a mission to bomb 12 mile airfield. Also participating were 16 x G4M1 Bettys from 4th Kokutai led by Lt. Commander Hatsuhiko Watanabe. This group was tasked with the suppression of 7 Mile Airfield. Escort was provided by 9 x A6M2 Zeros from the Tainan Kokutai from Lakunai but two Zeros aborted the mission due to mechanical problems, leaving only seven on the mission.

Due to their different cruising speeds, the two different bomber formations proceeded separately to Moresby. Later, 11 x A6M2 Zeros from the Tainan Kokutai took off from Lae FPO2c Masayoshi Yonekawa aborted for mechanical reasons with the other ten rendezvousing with the Nells over Ioma at 9:15am and were spotted by Australian spotters who provided an early warning to Moresby via radio. The coastwatcher intel gave accurate and timely information on course speed, raid size and heading. The defending p-39s had plenty of time to scramble. Raid was coming in at 22000 feet.

Meanwhile at Port Moresby, P-39 and P-400 Airacobras from the 36th and 35th Fighter Squadron plus attached aircraft from the 39th Fighter Squadron and 40th Fighter Squadron took off to intercept an incoming formation of G4M1 Betty bombers. The precise number of Airacobras involved in the scramble is unclear, but it was at least 32 involved in the scramble operations. There had never been this many fighters committed to the defences at Moresby.

At 8:40am, the Betty formation sighted eighteen enemy aircraft approaching and successfully bombed at 8:43am, hit the northwest end of the runway and dispersal area damaging water supplies, telephone lines, tents, a mess hall and two trucks from the Australian Army 17th anti-tank regiment, C Troop. P-39s, despite the long warning were still trying to gain altitude at the time the order for 'bombs away" was given. At 9:00am the Nell formation bombed 12 mile airfield, again with no immediate opposition from the defending p-39s, that were again still trying to make altitude This raid by the Nells hit the runway, damaged huts and destroying two parked Airacobras and damaging another Airacobra. This last aircraft was written off.

Eventually about 15-20 minutes after their bomb run, the Betty formation was intercepted by the Airacobras with great difficulty managed to shoot down G4M1 piloted by Oyama (he was KIA). Shot down in return Missing was P-39F 41-7 - 7191 with the loss of the pilot. Damaged was a second G4M1 piloted by Inoue which later crashed after diverting to Lae. Inoue and most of the crew survived. Six other Bettys suffered minor damage but returned safely. Afterwards, escorting Zeros from the 2nd Shotai A6M2 Zeros engaged the Airacobras and prevented them from making further attacks. Three were claimed.

As indicated above the Japanese formation returned to base. Returning, Inoue's G4M1 diverted to Lae, where it crash landed but as far as I know the pilot and most (if not all) of the crew survived. The others returned safely to Rabaul. All the Nells and Zeros returned safely. The Zeros claimed three Airacobras shot down. The Betty bombers also claimed four Airacobras shot down. On the American side,P—39F 41-7191 was lost outright, with three others damaged, of which two never flew again. Effectively three squadrons of p-39s had been scrambled, could not gain altitude in time despite being. given ample early warning, had managed to bring down two enemy bombers for the loss of one crew. No IJN fighters were lost (despite 8FG claims to the contrary) , whilst losing one aircraft outright with pilot and writing off two other aircraft as well as losing 3 on the ground. All up , the lost of 6 aircobras, and damage to an additional two to shoot down two bombers, and slightly damaging 6 others.

A typical day at the office really……..

Yep, typical day at the office for the 8th FG at PM (Port Moresby).

I'll try to pedal more garbage to you, please hold your nose. May I get your source for the May 18 mission, would like to read it myself.

I think we are in agreement that the PM radar was of little use to the two squadrons of P-39s defending the town. Between PM and the Japanese bases at Lae stood the 12000' Owen Stanley mountains. Not much radar getting through those. And coastwatchers were of very sporadic help since they were constantly being hunted by the Japanese. When the radar did alert the 8th FG it was often only clouds or a flight of birds. But the 8th had to go ahead and intercept those clouds/birds because they had no way of knowing.

The AAF was struggling in those early days of WWII at PM. Outnumbered, short of parts, inexperienced crews against an established IJN opponent with experienced pilots. I'm sure you have heard of the two attempts to ferry P-39s from Australia to PM that April. Over half the planes were lost to weather on FERRY missions. The Japanese must have been laughing their butts off, the AAF can't even move planes from one base to another without losing them. That was the state of AAF readiness/competence in April '42. They just weren't very good.

Specifically to the mission of May18, 34 bombers and 17 fighters was a huge mission for the Japanese at the time. Plus they had split into at least two groups further complicating the interception. PM had been under constant attack since the P-39s arrived there in April. From April 30 the Japanese flew missions against PM constantly with multiple missions on many of those days. It is unlikely that either 8th squadron was at full strength. It is also unlikely that the 8th scrambled whole squadrons since they only had two squadrons at PM. Normally they had two flights (4 planes/flight) ready to scramble with more available at longer notice. A normal squadron at PM was 16 planes That's just all they had, at that time.

You say that ample warning was given of the raid at 9:15am but then say that the Bettys attacked PM at 8:43 and the Nells at 9am. If correct, the attacks occurred before the warning was given.

And the P-39 could certainly intercept enemy bombers at 22000' with adequate warning. That they did on a regular basis is proof. The attached P-39K original source graph clearly shows the P-39 would do 360mph at 22500' and get there in about 11minutes. And that's climbing at 2600rpm when 3000 was available. The little black circles represent contemporary Zero performance.

Hmmm, first P-39K was "delivered" in Buffalo NY in July 1942. a little late to do much of anything in New Guinea in May of 1942.

And then we are back to tests done and/or corrected to "standard" day conditions (59 degrees F) which was never the conditions in New Guinea.

If you look at the take-off, climb and landing chart for the "K" it calls for 14.5 minutes to 25,000ft at 7800lbs at 0 degrees C/32 degrees F and call for a 10% increase in time for every 20 degrees F above that, so a rough 30% increase in time to 25,000ft on a 92 degree F day.
The hot temperatures also play hell with ceilings and climb rates at high altitudes.

You may also have trouble with keeping the coolant and oil temperatures within limits if doing full throttle climbs. Not to mention that, one again, you are flying in formation, even if a small one and the formation speed/climb is limited to worst performing aircraft in the group.

Shortround6 said:

Hmmm, first P-39K was "delivered" in Buffalo NY in July 1942. a little late to do much of anything in New Guinea in May of 1942.

And then we are back to tests done and/or corrected to "standard" day conditions (59 degrees F) which was never the conditions in New Guinea.

If you look at the take-off, climb and landing chart for the "K" it calls for 14.5 minutes to 25,000ft at 7800lbs at 0 degrees C/32 degrees F and call for a 10% increase in time for every 20 degrees F above that, so a rough 30% increase in time to 25,000ft on a 92 degree F day.
The hot temperatures also play hell with ceilings and climb rates at high altitudes.

You may also have trouble with keeping the coolant and oil temperatures within limits if doing full throttle climbs. Not to mention that, one again, you are flying in formation, even if a small one and the formation speed/climb is limited to worst performing aircraft in the group.

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I don't have an official P-39D or F performance graph so I use the K graph which was the next model but the test figures for the D are virtually the same. Both have 8.8 gears and weigh about the same.

I agree with you on the brutal tropical conditions, played hell with everybody.

But the air gets colder with altitude, wouldn't the conditions be pretty much standard at about 16000' when the air temp is 32 degrees approx?

P-39 Expert said:

But the air gets colder with altitude, wouldn't the conditions be pretty much standard at about 16000' when the air temp is 32 degrees approx?

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Nope.

Most people (countries/test groups) could agree on standard conditions at sea level.
Hot day standards were all over the place. They may be better now with international air travel demanding better standardization.

One chart in an old book (1943) shows a "standard day" going from 59 D/F to about -65 D/F at 35,000ft in a straight line and holding steady at -65 D/F as altitude went above 45,000ft.

A "typical" hot day line is also provided. It holds 100 D/F till about 6,000ft then falls to around -25 D/F at 35,000ft and then flattens out to hold that -25 D/F to over 45,000ft

At 15,000ft the temp for a standard day is between +5 and +10 D/F while on the hot day line it is +60 D/F.

The caption under the chart says that the "Hot day" curve is typical of the several "Hot day" standards in use.

some of this depends on actual location and weather conditions. A 100 degree day in Buffalo NY or in England in the summer may very well have lower upper air temperatures than a 100 degree day in Egypt or Northern Australia-New Guinea were it may be 100 degrees for days (actually weeks ) at a time and the upper air currents are coming from areas that are equally as hot.

Gentlemen

I am enclosing the P-39 Tactical Planning chart from 1943. It includes data for the P-39D. From a planning stand point, there was no difference between a P-39D, F, or K. I also found a graph of the P-39D-2 performance. This was/is located in the library of the Wisconsin Historical Society.
FYI
Eagledad

eagledad said:

Gentlemen

I am enclosing the P-39 Tactical Planning chart from 1943. It includes data for the P-39D. From a planning stand point, there was no difference between a P-39D, F, or K. I also found a graph of the P-39D-2 performance. This was/is located in the library of the Wisconsin Historical Society.
FYI
Eagledad

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There goes three hours that I'll never get back. Thanks.

eagledad said:

Gentlemen

I am enclosing the P-39 Tactical Planning chart from 1943. It includes data for the P-39D. From a planning stand point, there was no difference between a P-39D, F, or K. I also found a graph of the P-39D-2 performance. This was/is located in the library of the Wisconsin Historical Society.
FYI
Eagledad

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Why wasn't the pilot of the Airacobra given the option to operate at 25,000 feet at any power setting less than max continuous? Looks like he wasn't given the option to carry a drop tank or bomb at that height either. What am I missing here?

but if D-2&K had a engine with more TO power they would not climb a bit faster almost at low altitude?

My mistake. Got the interception and sighting times back the front. Airstrike was detected over Ioma (see map below) about 110 miles from target. There was an immediate scramble (AFAIK), which means the strike was intercepted somewhere over the owne Stanleys Despite all this early warning the p-39s were still not up to the correct altitude at the time of interception.

Why wasn't the pilot of the Airacobra given the option to operate at 25,000 feet at any power setting less than max continuous? Looks like he wasn't given the option to carry a drop tank or bomb at that height either. What am I missing here?

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What you are missing is the plain fact that the P-39 had difficulty operating in formation at that altitude with those kinds of loads.
chart in pilots manual (rather incomplete, only 1st and last columns) shows the 75 gallon drop tank costing about 30mph at 9,000ft at most economical settings
and over 50mph at 15,000ft at max continuous power (2600rpm and F.T.)

British figured you needed a climb rate of 500fpm to fly in a small formation as an indicator of reserve power. P-39D as per the chart so kindly provided shows that is just out reach when using max continuous power (Normal) at 25,000ft without an under fuselage load.

Vincenzo said:

but if D-2&K had a engine with more TO power they would not climb a bit faster almost at low altitude?

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Not necessarily. I was reading on the weekend about the CA12 and CA13 boomerangs. The CA13 according to the account I was reading had about 100 extra HP comparared to the earlier rendition, but this was cancelled out by the additional weight penalties.

parsifal said:

My mistake. Got the interception and sighting times back the front. Airstrike was detected over Ioma (see map below) about 110 miles from target. There was an immediate scramble (AFAIK), which means the strike was intercepted somewhere over the owne Stanleys Despite all this early warning the p-39s were still not up to the correct altitude at the time of interception.


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Whether they were able to intercept the bombers on that particular mission is meaningless. The chart shows that a P-39 will climb to 22000' easily on normal power 2600rpm with combat 3000rpm available. How did all those Japanese planes get shot down May-December '42?

Shortround6 said:

Nope.

Most people (countries/test groups) could agree on standard conditions at sea level.
Hot day standards were all over the place. They may be better now with international air travel demanding better standardization.

One chart in an old book (1943) shows a "standard day" going from 59 D/F to about -65 D/F at 35,000ft in a straight line and holding steady at -65 D/F as altitude went above 45,000ft.

A "typical" hot day line is also provided. It holds 100 D/F till about 6,000ft then falls to around -25 D/F at 35,000ft and then flattens out to hold that -25 D/F to over 45,000ft

At 15,000ft the temp for a standard day is between +5 and +10 D/F while on the hot day line it is +60 D/F.

The caption under the chart says that the "Hot day" curve is typical of the several "Hot day" standards in use.

some of this depends on actual location and weather conditions. A 100 degree day in Buffalo NY or in England in the summer may very well have lower upper air temperatures than a 100 degree day in Egypt or Northern Australia-New Guinea were it may be 100 degrees for days (actually weeks ) at a time and the upper air currents are coming from areas that are equally as hot.

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SR6,

Aviation today uses a standard lapse rate of 2' Celsius per thousand feet, or air cools by 2'C per 1k climbed up to about 36k.

Cheers,
Biff

DarrenW said:

Why wasn't the pilot of the Airacobra given the option to operate at 25,000 feet at any power setting less than max continuous? Looks like he wasn't given the option to carry a drop tank or bomb at that height either. What am I missing here?

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You're not missing anything. These early P-39s cruised at 25000' burning 54gph at normal/max continuous 2600rpm, although this chart shows it burning 71gph (120gal divided by 1.7hr). Remember this chart says "ALL PERFORMANCE ESTIMATED". Not a performance test, just guidelines.

It's only burning 54gph, want it to burn less at lower power?

Also remember the N model will be out in December with much better performance.

P-39 Expert said:

It's only burning 54gph, want it to burn less at lower power?

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Yes, to extend it's rather meager range.

The P-39N had even shorter legs with it's reduced fuel load.