XP-39 II - The Groundhog Day Thread

[buffnut453]

IIRC, the SBD went from ONE .30 to a twin .30 mount during it's time of service, too. Apparently, the .30s were sufficient for the task at hand.

No they weren't. They were useless. P-39 Expert said so....so it must be true.

 

[glennasher]

No they weren't. They were useless. P-39 Expert said so....so it must be true.

Well, I'm not any kind of ex-spurt, so I'll defer to your vast knowledge, and his, I guess, maybe........................................

 

[jmcalli2]

Hello jmcalli2,

The most effective Japanese Naval Fighter Unit that was fighting from Lae was the Tainain Air Group.
The unit was formed in October 1941, so it was hardly a veteran unit.
Although they had some experienced pilots from the war in China, that war was hardly comparable to a modern war.

Here are a couple questions for you regarding inexperience with the V-1710:
How much more experience would the AVG have had with their P-40s in China?
Did it make a difference that all the USAAC personnel in New Guinea were at least US Army instead of a mix of USN, Marines, US Army and civilians? Would these other people have had better experience working on V-1710 engines?
Would their supply chain have been any better than a base in New Guinea that was within shipping distance of Australia?
How well did P-40s do in New Guinea?
Did the Australians have the same problems with Allison equipped aircraft?
They could not possibly have had any more knowledge than the service that gave them the aircraft or could they?

- Ivan.

There were also a few missions with P-40s in the New Guinea combat book. I didn't get the impression they did any better or worse than the P-39s, but then again they were not the feature of the book either.

Hello jmcalli2,

I figure that if it was experience working with the Allison engine, the air service from the country manufacturing the engine would have the most experience especially since they had operated it in the P-40 for over a year.
In any case one would expect Army mechanics to have more experience with a piece of Army equipment than the assortment of mechanics that were rounded up from various places for the AVG.
I believe AVG logistics and support was wherever they could get it and usually they did not. If they did, it was coming through the port of Rangoon, Burma or from India. Technically they were not a part of any major air service. They were just a bunch of mercenaries fighting for China.

Saburo Sakai's books make pretty good reading if you are curious as to the issues faced by the other side and that was from the unit with the greatest success. Other naval units were doing rather poorly in general. The Japanese pilots were not going to places like Australia every so often. They only way they were leaving was if they were injured too badly to fight or if they died.

- Ivan.

Good points.

I looked up a little on the AVG. It seems their Maine fighter opposition was the Nick, and later the Oscar. They started out with P-40Bs and eventually got some P-40Es. The Chinese they flew with also had a mixture, including P-43s & P-66s. Their original hit & run while keeping your speed high was formulated against the Nicks.

I also found something interesting; I was looking for P-40 encounter reports 9never found any) on WWII Aircraft performance when I found these at the bottom of the P-40 page:
http://www.wwiiaircraftperformance.org/P-40/Performance_Data_Pursuit_Airplanes.pdf
http://www.wwiiaircraftperformance.org/P-40/PHQ-M-19-1307-A.pdf
And finally this on high power use of the Allison:
http://www.wwiiaircraftperformance.org/P-40/V-1710_Service_Use_of_High_Power_Outputs.pdf

The last I thought at first was talking about the P-38, but then it gave the model numbers as -81, -83, and -85. These were P-40, P-39, and P-51 models.
I'd love to see performance figures on them with 1700+hp!

Anyway I found them interesting.

 

[GregP]

Hey Ivan,

I went back to a post of mine on the last page and posted a pic of the Planes of Fame Zero about to taxi out for the first post-restoration test flight in 2016. Just FYI. It's a beautiful airplane!

 

[wuzak]

The last I thought at first was talking about the P-38, but then it gave the model numbers as -81, -83, and -85. These were P-40, P-39, and P-51 models.
I'd love to see performance figures on them with 1700+hp!

1700hp at sea level only.

 

[wuzak]

Not discounting or ignoring their comments. I just believe that 836lbs of weight will affect climb rate and nobody on here will acknowledge that. A slightly different propeller or a slightly altered CG or slightly varying HP are just small discrepancies that would be present in any test of the exact same airplane. Especially when there is no proof whatsoever that the CG was not proper in either airplane, or that the HP varied at all. In regards to the propeller, what was the exact difference in the two propellers? Any at all? They were of the same diameter.

There is a straightforward binary association between two airplanes of the same type and model, when the only difference is a substantial amount of weight. And again, please explain to me the difference between the two propellers.

We don't know what the difference between the propellers were, but a design changed could change the performance on climb or all out level speed. The change to paddle blade props improved the climb performance of the P-47, for example.

Joe Baugher notes that the propeller was different on the P-39D and that there were other differences:

A different 10 foot 5-inch Curtiss Electric propeller was fitted and the fuselage length was increased to 30 feet 2 inches. In addition, a very small dorsal fin was added just ahead of the rudder.

Bell P-39D Airacobra

Not sure how much the fuselage length was changed.

First of all, YOU can't quantify the differences between the test aircraft in propeller or engine performance nor can you determine what the airframe differences were. All you can really state with reasonable certainty is that they were built to the same basic design.
These two tests were not on the same aeroplane!
The lighter aeroplane did climb faster but there were probably other factors that made a difference in performance as well.

The engines were also not the same, even though they were the same model.

Engines were allowed to vary by a small percentage from the rated power, so the power from on engine on the production line to the next could vary by 5 or 6%. Maybe even more.

And there may be evidence in this in the tests of the P-39C and P-39D.
http://www.wwiiaircraftperformance.org/P-39/P-39C_40-2988.pdf
http://www.wwiiaircraftperformance.org/P-39/P-39D_41-6722_PHQ-M-19-1325-A.pdf

As noted by others, the engine powers were derived from different documents. This may indicate minor detail changes to the engine, or that it was re-certified.

The critical altitude for the P-39C in its test was at 13,050ft, at which its speed was 379mph at 3,000rpm and 1,150hp (obtained from chart in TO No. 025AD-1).

The critical altitude for the P-39D as 13,800ft, at which it made 368mph at 3,000rpm and 1,150hp (obtained from chart in Specification No. 123E).

Critical altitude for Normal rated power (1,000hp @ 2,600rpm) for the P-39C was 12,600ft at 362mph, for the P-39D it was 13,100ft @ 347.5mph.

Critical altitude in climb for the P-39D was 12,400ft. The report for the P-39C doesn't identify the critical altitude for climb in military power, but it appears to be 10,000ft (last altitude listed with max power).

Cruising speed at 2,280rp and 750hp was 327mph @ 11,600ft for the P-39C and 311mph @ 13,000ft for the P-39D.

Clearly the aircraft were not identical other than the weight.

 

[wuzak]

Also, would the guns in the wings cause more drag, reducing climb and speed?

 

[DerAdlerIstGelandet]

Well, I'm not any kind of ex-spurt, so I'll defer to your vast knowledge, and his, I guess, maybe........................................

Actually we all started out as a spurt, so that would make us ex-spurts.

 

[pbehn]

A soldier in WW1 could cross no mans land faster without his rifle ammunition and helmet. A C-47 can carry more paratroops if they leave all their equipment weapons and clothes back in their base. Taking military equipment off military machines is just an argument for Reno racers being superior in performance to planes they were developed from. Taking guns off a fighting machine is a very hard "sell".

 

[Ivan1GFP]

Hi Ivan1GFP,

When I plug in 1105 rpm, 13.5 feet diameter, 473 mph, at 15k feet, I get M.98977! Standard conditions. Definitely above M.88.

I'd say that is in the area of degrading propeller efficiency, but it IS going 473 mph. And it's probably quite LOUD, too, at that speed and rpm.

The Russians still fly the Bear bomber, and it supposedly has supersonic flow over 1/3 or more of the prop at maximum speed of 575 mph or so. It could be that all the research into supersonic propellers isn't all that accurate since the Bear is the fastest propeller-driven aircraft of all times. But ... and here's the rub, it works for the rest of us in our flight regimes.

Hello GregP,

Another thing worth examining is the Advance Ratio and most likely propeller pitch that would represent for these two aircraft at maximum speed and the likely propeller efficiency that would suggest.
The other thing to remember is the actual shaft horsepower that these Turboprops are putting to the propeller. It isn't something even the best Turbo-Compound engine could ever do though I suspect some of the Unlimited class racers you hang around with can come close to what the P-3 Orion is doing.
The last thing to consider is that the exhaust thrust from these engines is relatively high and it becomes a very large portion of the thrust at high speeds.
No, they really aren't playing by quite the same rules.

- Ivan.

 

[Ivan1GFP]

There were also a few missions with P-40s in the New Guinea combat book. I didn't get the impression they did any better or worse than the P-39s, but then again they were not the feature of the book either.

Good points.

I looked up a little on the AVG. It seems their Maine fighter opposition was the Nick, and later the Oscar. They started out with P-40Bs and eventually got some P-40Es. The Chinese they flew with also had a mixture, including P-43s & P-66s. Their original hit & run while keeping your speed high was formulated against the Nicks.

Hello jmcalli2,

Those were not Nick which is a twin engine fighter. They were Ki 27 Nate which is a little tiny fighter with fixed landing gear.
The other thing worth mentioning is that from the Curtiss aircraft Construction Numbers, the batch of "P-40s" which were technically just "Hawk 81s" fell into the range for the P-40C and not P-40B.
Curtiss basically used the contract to get rid of old parts that would not satisfy current military contracts because the contract fr the Chinese did not specify a lot of features that the military contracts did. So much for Mil-Spec.
That is why older fuel selectors without provision for drop tanks and fuselage fuel tanks with external sealing material were found on these planes. The folks in China saw these pieces and thought they were flying earlier models, but they were not.

And finally this on high power use of the Allison:
http://www.wwiiaircraftperformance.org/P-40/V-1710_Service_Use_of_High_Power_Outputs.pdf

The last I thought at first was talking about the P-38, but then it gave the model numbers as -81, -83, and -85. These were P-40, P-39, and P-51 models.
I'd love to see performance figures on them with 1700+hp!

That document you found is the Allison Memo that I have mentioned a few times. I didn't find it on that site though.
The engines models they cover are not actually the ones you are thinking though.
They were the F3R (V-1710-39 and V-1710-35) and F4R (V-1710-73 and V-1710-63). Basically the 1150 HP and 1325 HP engines for the P-40 and P-39.
This is probably why the P-39D-1 pilot flying against the Aleutian A6M2 probably figured he could run a LOT more boost than the manual allowed.

- Ivan.

 

[GregP]

If you look at the Zero pic I posted, you can see the ejector exhaust stacks. They add significant thrust at high power settings.

Some of the Reno guys are making 3800 or so hp, and the R-4360 guys can probably make maybe 500 more ... at least for awhile. None of the race engines would last to Berlin and back at high powers, but its possible they could be operated at ... say ... 2300 hp for some time. I don't know myself and would have to ask the racers. I don't know how much heat (in BTUs) a stock radiator in a P-51, for instance, can dissipate. I don't know any who can put out torque like an Allison T-56 turboprop, though.

But, their answers might be a guess, because they build for the engines to last maybe 60 - 70 laps of 6.5 miles each at high power, with some lower-power breathing in between the high power laps (a Reno race campaign). That definitely won't get you to Berlin from the U.K. much less back again.

Pretty much everyone in here knows that, of course. For you new guys, we have moderators who crew or have crewed on Reno races planes and work as A&Ps.

 

[GrauGeist]

...Russians considered the .30s useless on P-39s. US must have considered them useless since no P-38, P-40, P-47, P-51, F4F, F6F, F4U, B-17, B-24, B-25, B-26, A-26, SB2C, TBF had them. The AAF P-39 pilots may have been required to keep them, again I don't know. Wagner did say that they weren't as effective or dependable as .50s. Had the P-39 pilots known how much better their planes would climb without them then they may have removed them. We're only talking about the period between May and November 1942.

The list of types that had .50 MGs is a bit off. Keep in mind that most types in production before 1940/41 had .30 MGs.
The SBD was one of the first American aircraft that was designed to have two .50 MGs instead of the traditional .30/.50 cowl combination - however, it retained the .30 MG defensive armament.

The P-40B had .30 MGs.
The F4F-1/2 had .30 MGs.
The B-17 was originally armed with .30 MGs and even the B-17E still had one .30 MG left (skylight position).
The early B-25 models were armed with .30 MGs and the .30 MG remained in the nose position for several variants.
The B-26 was designed to have flexible .30 MGs in the nose and tail.
The P-38 prototype had two .30 MGs, two .50 MGs and a 23mm cannon...

P-47, F6F, TBF, A-26, F4U and so on, were after the USAAC moved toward the .50 MG as a standard.

For what it's worth, early war Soviet types (I-16, I-153, MiG-1/3, IL-2, Pe-2, AR-2, Su-2, etc.) were armed with 7.62mm MGs. - 7.62mm is...you guessed it: .30 caliber.

 

[Stig1207]

I had difficulties to understand what Claringbould means. Some of my thoughts.
But on page 76 he writes that of the 44 Aircobras lost in combat in 1942 in New Guinea only 15 were shot down by Zeros. Who shot down the rest, ground fire got some but the first JAAF fighters unit, the 1st Chutai of the 11th Sentai, became active in New Guinea on 26 December 1942 and it did not claim Airacobras during the last few days of 1942. Japanese air gunners seems to have got a few but what about the rest. Did the combat losses include those destroyed on ground by bombing and strafing? But Claringbould notices earlier that the results of Japanese strafing attacks against Port Moresby airfields were minimal. Some Airacobras were destroyed by bombing, that is true but still the figures seem not to add up. And it seems that the 15 Zero losses does not include losses on ground because already the first Airacobra strafing attack on Lae on 30 April 1942 destroyed three Zeros according to Claringbould and according to Tagaya burned one and wrecked another Zero. Lae and other Japanese airfields in the area were also bombed rather regularly.
I could have read the book one more time and count the P-39/P-400 losses, but did not bother. Instead I went through the P-39/P-400 losses in New Guinea in 1942 on the Pacific Wrecks site. When it in few cases does not give a clear reason, I checked what Claringbould says. All Airacobra losses are not mentioned on the site. Results were:
P-39s/P-400s reason of loss:
Zeros 20
Possibly Zeros 5
Forced landing because of Zero, plane not recovered, so lost 1
Ground fire 3
Friendly fire 1 possible
Engine 4
Probably engine 1
Weather 4

Claringboult says that operational losses were 14 Airacobras and 13 Zero-sens

There are definitely more combat losses than 44 P-39's and 15 Zeros in Claringbould's book; but it does seem to me that the 44 vs 15 comparison he makes is losses that occurred on missions where they met each other in combat; I am not sure if losses here means failed to return or whether it includes DBR, except that the 15 Zeros all FTR along with the pilots. About half the P-39 pilots survived and returned and could relate what had happened; but for those that remained MIA, the cause of loss was not always observed by their squadron mates. In the majority of cases some cause is given as a likely cause of loss but in some cases no assumption of the cause of the loss is given.
I would think that on the Japanese side, for those Zero's that FTR the cause was probably not always observed either but it may be that the Japanese recorded the loss as being to P-39's because that was what they were in combat with.

 

[GregP]

Not to beat a dead horse, but attached is a spreadsheet I just made to calculate propeller tip Mach Number at Standard Conditions.

We know all conditions are NOT standard, but this is only for forum conjecture, so I didn't add compensation for non-standard conditions. Instructions are included on the first tab. If you want to account for non-standard conditions, then enter the density altitude as your altitude.

The spreadsheet is protected, but without a password, so you can unprotect it if you want to do so.

 

[pbehn]

But, their answers might be a guess, because they build for the engines to last maybe 60 - 70 laps of 6.5 miles each at high power, with some lower-power breathing in between the high power laps (a Reno race campaign). That definitely won't get you to Berlin from the U.K. much less back again.

.

During the war it was bombers who most frequently had engines running for long periods at high power ratings. An unladen Lancaster could limp home on two engines, of course you don't hear so much about those who didn't.

 

[P-39 Expert]

We don't know what the difference between the propellers were, but a design changed could change the performance on climb or all out level speed. The change to paddle blade props improved the climb performance of the P-47, for example.

Joe Baugher notes that the propeller was different on the P-39D and that there were other differences:



Bell P-39D Airacobra

Not sure how much the fuselage length was changed.




The engines were also not the same, even though they were the same model.

Engines were allowed to vary by a small percentage from the rated power, so the power from on engine on the production line to the next could vary by 5 or 6%. Maybe even more.

And there may be evidence in this in the tests of the P-39C and P-39D.
http://www.wwiiaircraftperformance.org/P-39/P-39C_40-2988.pdf
http://www.wwiiaircraftperformance.org/P-39/P-39D_41-6722_PHQ-M-19-1325-A.pdf

As noted by others, the engine powers were derived from different documents. This may indicate minor detail changes to the engine, or that it was re-certified.

The critical altitude for the P-39C in its test was at 13,050ft, at which its speed was 379mph at 3,000rpm and 1,150hp (obtained from chart in TO No. 025AD-1).

The critical altitude for the P-39D as 13,800ft, at which it made 368mph at 3,000rpm and 1,150hp (obtained from chart in Specification No. 123E).

Critical altitude for Normal rated power (1,000hp @ 2,600rpm) for the P-39C was 12,600ft at 362mph, for the P-39D it was 13,100ft @ 347.5mph.

Critical altitude in climb for the P-39D was 12,400ft. The report for the P-39C doesn't identify the critical altitude for climb in military power, but it appears to be 10,000ft (last altitude listed with max power).

Cruising speed at 2,280rp and 750hp was 327mph @ 11,600ft for the P-39C and 311mph @ 13,000ft for the P-39D.

Clearly the aircraft were not identical other than the weight.

Clearly the additional 836lbs had nothing to do with the P-39D being 11mph slower or climbing 1000fpm slower.

How about this, what if the P-39D weight was reduced to that of the P-39C? Would it not have the same performance as the P-39C?

 

[windhund116]

There were also a few missions with P-40s in the New Guinea combat book. I didn't get the impression they did any better or worse than the P-39s, but then again they were not the feature of the book either.

Interesting. Couple books and articles I've read said the units (like 8th FG) with P400 fared not-so-well against the IJNAF fighters, early in those New Guinea air battles. Later, these early units were replaced with P40s.

 

[Ivan1GFP]

Hi Ivan,

I am sitting here with the 1944 Fighter Conference Report in front of me, and I see the evaluation of the handling qualities, but the actual performance charts only are shown for the Allied airplanes that we were flying.

However, the Planes of Fame Zero is an AM5 Model 52. The specs say max speed at 19,685 feet was 348 mph. Climb to 19,685 feet was 7 minutes and 1 second, so the initial climb rate was likely around 3,600 fpm, tapering off as you climb. Cruise speed was 230 mph. The A6M5 added exhaust ejector exhaust, and the speed bumped up by some 11 - 13 mph over the A6M3, so that puts that A6M3 at about 335 - 337 mph at the same height.

Happy Haloween.

Oh, and, I do not believe they ran a complete performance test on the A6M5 Model 52 Zero used at the 1944 Fighter Conference. After the conference, it wound up as a squadron commander's hack on the west coast, and eventually went inoperative. After some years, Ed Maloney bought it, and it sat inoperative for some 25+ years until about 1977. It was restored with the assistance of Mitsubishi and Nakajima (Fuji Heavy Industries, today), flew again in 1978 and still flies. The Planes of Fame / Fighter Rebuilders did a 100% disassembly overhaul down to bare aluminum a few years back. EVERYTHING was redone except the engine and propeller since they were running great and still are.

Here is the Zero about to make the first post-restoration test flight in 2016:

View attachment 600325

All the paint colors are 100% authentic, even the interior and oxygen bottles, etc. The guys did a superb job! I helped a very little in initial disassembly and prep for control surface fabric only, which doesn't amount to much at all. But, I DID get to help a little . The regular crew knows that A6M5 VERY well indeed. Corey O'Brian did most of the restoration with help from the other Fighter Rebuilders people. If I win a big lottery, he can restore whatever fighter I get for myself then!

Hello GregP,

I did a little more checking yesterday. Here is a little more history that might interest you:
I am sure you already know most of it but I restate it for others here who may not know.

The A6M5 that is currently flying with Planes of Fame was originally captured on Saipan in 1944.
Its original markings which it carries today were "61-120". 61 was the unit identification: 261 Kokutai.
There were quite a few A6M captured there along with a lot of spares.
About a dozen A6M (A6M5 mostly and a couple A6M2) and a bunch of engines were packed aboard a CVE and shipped back to the US.
61-120 was one of the aircraft that was in the best condition. It was assigned the number TAIC 5 which replaced the 61-120 marking and WAS flown in performance testing.
The differences with this aircraft were that it was equipped with a Sakae 31 engine which is normally the version equipped with Water Methanol injection however this aircraft was not so equipped.
The test report can be found here:
TED PTR 1111

The interesting results are that the maximum speed achieved seems quite low: 335 MPH @ 18,000 feet which is well under the critical altitude.
There are no discrepancies or faults noted in the aircraft however on page 2 in note 2, there is a statement that tests are of a "qualitative" rather than a "quantitative" nature.

- Ivan.

 

[GregP]

They didn't need quantitative test because all the active PTO combat pilots knew what they could do.

When we did the full airframe overhaul, about a 30-cal bullet in the canopy frame was found, just inside about a 30-cal hole. The bullet was removed and the hole was repaired.

I doubt the flight test got to "best power" and :max speed" as they didn't seem all that sure what that might be at the time. They put about 190 hours on the airframe during the 1944 Fighter Conference. In that time, Zero 61-120 was the only fighter aircraft being flown that didn't break down even once ... it was dead reliable.