With the P-38K, was the P-51 and F4U even necessary?

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I was responding to your post where you said the following.

"Fighter design was mostly for a critical altitude of 15,000 feet and they were primarily to support ground troops, with a few exceptions. The AAC bought and paid for a program they designed, and they were flat wrong about the war they were about to fight. All the basic technology was there to produce higher flying and faster fighters at the beginning of America's involvement, but working out the bugs after the basic design takes time. I think overall, America did better than it had a right to expect."

Nothing there about "high altitude long ranged fighters" is there?

Just the basic "were primarily to support ground troops, with a few exceptions" which is wrong and "All the basic technology was there to produce higher flying and faster fighters at the beginning of America's involvement" which is part right but doesn't say anything about long range does it?

If you want a multi-stage supercharger and not just a multi-speed supercharger the ONLY things you get rid of is the exhaust turbine and the exhaust plumbing. You need the second supercharger impeller and casing, a way to drive it and you need an inter cooler of some sort.

The P-39 and P-40 were not designed to support ground troops, they were adapted to do it.

As for "The late model Allisons with 2 stage superchargers might have been nice. Would have been nicer if Allison had been contracted to develop them earlier"

Lots of counties would have loved time machines and the ability to use 1943/44 engines in 1940/41. Allison proposed the two stage engine back in 1938 (gee, right about the time P W was starting work on their 2 stage engine), Allison didn't have the engineering staff to work on it fast enough. There may be some doubt as to whether a 1940-41 Allison would have stood up to the strain of producing the power the late model two stage engine delivered. Allison changed the size of the impeller in the aux stage, changed the drive mechanism, tried to get an intercooler and were let down by a sub contractor and a few other details that caused to project to slip, not by months but by years.
What the USAAC wanted is one thing, what they could actually get is another.
 
dobbie said:
I cant recall exactly where I saw it, Tomo pauk, but early on there was some sort of restriction against drop tanks on fighter aircraft which I found baffling to say the least.
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What would be the time frame of the 'early on'? I'm afraid that supposed restrictions are product of the hanger talk.


USAF bombers were also to fly higher, oce equipped with turbos, and, that failing, to fight their way in out. The 'self-defending' bombers thinking.

I think its sad that the P51, which because it was designed for the RAF and didn't have to go through the normal channels, had to be fitted with a British engine in order to become the fine escort fighter it became.
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It was not sad, just the contrary


+1 on that.


Just to comment on the P-47 part - saying that it didn't have the range is way out of mark, the late D models were capable to fly 600 miles escort (= combat radius), the combat radius of the N was 1000 miles. We can compare other fighters of the world and quickly arrive to the conclusion that P-47 had legs. Plus, when people talk about P-47 being a big brute because of turbocharging, they tend to forget the honking big R-2800 the turbo was to cater about, and 2000-2800 HP at 25-30000 ft that no other aircraft could hope to match.
The P-38's main problem was that it was not available in quantity (so USAF needed to prioritize), a much greater problem than this or that technical issue.
 
Still has that miserable mach limit. In fact that maximum speed would be very close to its mach limit, coffin corner indeed.

A (very) rough calculation shows that its mach limit was about 460mph (TAS) at 30,000ft, with this being the 'lawn dart' mach limit of 0.68.

Even a very slight dive and you go out of control.

The P-51's was (tactical limit) 0.8 or about 540mph at 30,000ft and you you could push it a bit further too (albeit with things getting a bit uncomfortable).

That's one of the reasons why they went for the Mustang and swapped over from the -38 and -47, their mach limits were too low for the tactical environment.

And 48,000ft in a -38, only for the (brave) test pilots that one.
 
Gotta hand it to Kelly Johnson on the P38. Back when it was designed, there really wasn't a way to meet the AAC requirement on a single engine and his design team did an excellent job in working within the constraints of the RFP. For a twin engine fighter, the Lightning probably came closer to an effective fighter plane than any of the rest in that time period. True, the mach numbers were lower than the 47 or the 51, but this was at a time in aviation where a lot wasn't completely understood let alone managed. The later models overcame a lot but with the advance of technology, the Lightning needed more modifications to stay competitive with the newer aircraft.
 

The number one, (and two through 21) reason was escort range combined with performance. The need for the P-51B was so great that its test phase was nowhere near a thorough cycle before the production line was spiiting them out to the docks on the east coast. Ergo, a series of field kits to replace main gear uplock kits, strengthening the eppenage, changing horizontal stabilizer incidence, replacing fabric elevators with metal ones and adding reverse rudder boost...

Also buried in the flight test data at Wright Pat and Eglin test reports was the simple fact that at 440mph, 29,000 feet @3000rpm the 1650-3 engine was driving the tip speeds on the P-51B prop into the tip shock wave region
 
"wasn't so much 'out of control' as it was 'unable to produce enough aft stick force to overcome the pitching moment until the density of the air and subsequent airspeed reduced below Mcr. The Dive btake/flap under the wing at 30% chord, a.) delayed the time from pitch down in a dive and subsequent airspeed build up to Mcr and it affected the associated change to CMac."

They were called dive recovery flaps for a reason. Because they effected a smooth, relatively low G pullout from an out of control dive due to compressibility. Their main purpose was to recover from an out of control situation.

Without those pilots would pull back (or worse adjust trim) too much, so that when they got into the thicker air they could (and often did) overstress the airframe.
Worse you could pick up enough speed to either cause structural damage or even still be over the critical mach limit at lower altitudes, with no recovery possible (lawn dart).
The procedure was that when you were in that position was to pop the flaps, ideally before you picked up too much speed and wait. The plane would then come out of its dive, particularly as you hit lower altitudes, by itself relatively smoothly.

Yes they could be used just as you hit, or even before compressibility to delay the nose tucking down. But they only gave you another 15mph (about mach 0.7), from the pilot notes: "With these flaps extended, the nose heaviness is definitely reduced but the diving speed should never be allowed to exceed the placard by more than 15 or 20 mph".

The extra drag helped keep the speed down in a dive, so you could do steeper dives without building up so much speed: From the pilot notes again: "With the dive recovery flaps extended before entering the dive, angles of dive up to 45 degrees may be safely accomplished. Without dive recovery flaps extended the maximum angle for extending dives is 15 degrees. Diving characteristics are better with power off than power on."

Pilot notes: http://www.spruemaster.com/blog/wp-...eed P-38 Lightning Pilot Flight Operation.pdf

They were not a panacea, you could, if you were determined or stupid, still dive too fast and do a lawn dart or take the wings off. In Eric Brown's test he popped them at 0.75M and the nose came up, slowly at first then positively. But if you lost it and got into 0.8M. or worse more, there might not be enough altitude for them to take affect (by the extra drag slowing the plane) and allow a smooth pull out (from their nose up effect).
 
I cant see any scenario in which the P-38K does a better job than the F4U or P-51 in their respective roles, especially considering production economic factors and maintenance economic logistical factors.
 
I agree.

"Without dive recovery flaps extended the maximum angle for extending dives is 15 degrees."

That's not a fighter its a bomber...
 
The P-38K is the unicorn of World War II fighter aircraft. No one has ever seen one yet everyone has heard of it. Like the unicorn it has taken on magical qualities; it's faster than a P-47M, can climb higher than a T-152H, climbs faster than a Spitfire XIV, flies farther than a P-51B and according to Warren Bodie "it was superior-outstandingly superior-to the best fighter models in contention." Blanket statements like that should always raise a red flag.

It all sounds too good to be true; and in fact it is too good to be true. Some laws of physics are being violated here. The truth is somewhat less spectacular. The Lockheed test results are posted on Mike William's site (of course, where else). The document in the following link compares the performance of the P-38J to the P-38K. Note that these are not USAAF test results, but are a reprise of Lockheed's tests:

http://www.wwiiaircraftperformance.org/p-38/P-38J_performance_11march44.pdf

As you would expect from similar tests on the P-47 the paddle blade propeller does not have much impact on level speed, but does have a significant impact on rate of climb and it does extend the performance envelop above critical altitude, with a consequent increase in service ceiling. A perusal shows that claims of speeds of 450 mph are pure fantasy as are ceilings above 48,000 ft.

Considering that combat above 30.000 ft was rare the improved altitude performance probably isn't worth the production penalty, but the rate of climb would seem worthwhile. However the idea that the P-38K outclassed the P51B does not hold up, it's still slower at all altitudes.

Incidentally this document also makes the case against water injection for the P-38, in that the substantial increase in weight that can only be compensated for by a reduction in fuel load and hence range.

The comparison test of paddle blade vs. needle blade for the P-47 is also on William's website:

http://www.wwiiaircraftperformance.org/p-47/P-47D_43-75035_Eng-47-1714-A.pdf

davpalr posted

Some caveats are needed here, I think. First is that most of the reviewers are Navy and almost all military pilots are highly bias for one
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Actually most of the pilots were contractors (manufacturers) test pilots. The P-38L was flown by 1 army, 9 navy, 5 British and 13 contractor's pilots. The Brits and the contractors were ALL test pilots.
 
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The truth was probably between this, and W.Bodie's praise-without-boundaries story. Nobody stated that P-38K would've been faster than P-47M (~470 mph); it should be able to climb higher than P-38J/L (if the engine is making 3200 rpm, and ADI works as advertised). Bodie clearly overstates the speed on WEP, as seen from the report you've kindly provided the link, as he does for the RoC. Without leading edge tanks, the radius/range would've suffered.
However, P-38 was the best,or one of the best climbers USAF had.


Thanks for the link. Both P-38s were flown without leading edge tanks, and we are left in dark why the P-38K was not faster under ~30000 ft on WEP - it did have 2x1725 HP, vs 2x1600, in the same time featuring a better prop.


While P-47D made a good use of paddle blade prop, along with ADI system (allowing greater boost), it's engine remained with same RPM all the way, hence the performance above ~30000 ft remained about the same. The performance was improved under full throttle height, since there the supercharger system was able to provide greater manifold pressure.
The Allison F-29 engines were allowed to make 3200 rpm, vs. 3000 rpm for the engines found in the serial P-38s - more RPM means full throttle height is at higher altitude. Higher altitude (thinner air) combined with more power means higher speed.
But, the P-38 making 430-440 mph between 30-35000 ft (almost Mach .65 there) would encounter another hurdle, and that would be the compressibility - P-38's dive limit was at Mach .65.


Agreed, once the Merlin Mustang arrived, P-38 was unable to offer anything more, while costing much more both to purchase and operate.

Incidentally this document also makes the case against water injection for the P-38, in that the substantial increase in weight that can only be compensated for by a reduction in fuel load and hence range.
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The weight of 30 gals of ADI liquid (water-methanol) in the P-47 was 124 lbs. Lockheed assumed that ADI system would've weighted 600 lbs, 400 lbs being the ADI liquid - seems they intended to replace the LE fuel tank with ADI tank - 400 lbs is almost 100 gals of water-methanol?

The comparison test of paddle blade vs. needle blade for the P-47 is also on William's website:

http://www.wwiiaircraftperformance.org/p-47/P-47D_43-75035_Eng-47-1714-A.pdf
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Thanks.
 
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Actually, it managed it much better.

I'm sure there was quite a bit of inefficiency in the US allocation of resources to weapons production, but business leaders were quite used to large centrally planned organizations (what do you think large corporations are?) and were also willing to accept that "most productive" is not the same as "least wasteful" or "most efficient." The US was also more efficient in utilizing its ample labor resources (and if they were short, it would have been easy to recruit -- not enslave -- workers from Mexico, Central and South America, and the Caribbean), had ample material resources, probably had better understanding of industrial engineering and mass production technology, and started with a much larger economy. Redundant weapons systems may have been inefficient (they also had somewhat different capabilities, e.g., the Hellcat was, in many ways, a better aircraft than the Corsair, and the B-24 was, in some ways, better than the B-17).
 
IIRC there is one other factor to consider Merlin Vs Allison, other than a couple of hundred extra pounds. Namely specific fuel consumption is better in the Allison. If strictly true in the configuration then the combat radius of the P-38K should be less than the J and perhaps the same as the H. In the ETO this would not be a good thing.
 
That would sound better if P-38 engines didn't have such a poor reliability record over Europe. I would rather have one reliable Merlin or DB601 engine then two unreliable Allison engines.
 
Didn't read the entire thread, so forgive me if this has been said already: In no way would the P-38K replace either one. Later modells of the '51 and '4u flew in Korea while the P-38s were being scrapped in Arizona. P-38 was a great fighter, but it had its place.
 
Are these the same Allisons that had a rather good record in south east asia once they fixed the turbo controls?

The tech reps in the CBI theater had figured out a "fix" for the turbo controls and a tech rep with 300 locally built kits was sent to the SWPA to modify their engines. Once modified a number of engines went to 300 hours without any major problems. the originating squadron went over 5 months without a single non-combat related engine failure. Sure sounds like an unreliable engine to me..........

The basic engine was very good, the turbo controls had some problems and flying them against the recommendations of both Allison and Lockheed and then calling the engine unreliable is hardly unbiased. fly the Merlin or DB 601 for hundreds of hours in violation of the manufacturers operating instructions and see how reliable they are.
 
Once the fix was in the Allison was fine.
I like the P38, it was a goo looking bird that had range and firepower to burn. Always nice to have that spare engine when you are flying a lon, long way on your missions!
I would still have the P51 and F4U to compliment the P38.
The F4U for carrier use if nothing else!
 
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