The P-38J and L in the European theater.

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I'm not really seeing that, according to the page posted in post #240, the Mustang out rolls the P-38 significantly, 78 degrees per second v 39. (See the second to last sentence in paragraph 2)
For the Lightning using boosted ailerons, they only give an estimated value, no actual test numbers are given.

Climb is almost a wash but goes to the P-51 by a small margin, 40 fpm.

Turning is reasonably close as well, 838 v 883 @ 400 MPH for a slight advantage to the P-38.

Diving speed, no contest - Mustang.
 
P-39 Expert said:
So, if that P-38 was below critical altitude, it could not be overboosted because of the turbo regulation? Just asking.
Click to expand...

No, it should not be able to. Or, at least, not very much.

SR explained the different gear ratios used by the V-1710s in the P-38.

It went from 6.44 to 7.48 and finally 8.10:1. As the V-1710 developed and could take more boost, the supercharger gear ratios were increased to give the extra boost.

The altitude versions used 8.8 or 9.6 gears.

There is a couple of ways that the P-38 could have been overboosted.

One was to over-speed the engine, and the other was if the turbo put in more boost than nominally required (through faulty regulator).
 
jmcalli2 said:
This may give some idea; http://www.wwiiaircraftperformance.org/mustang/Performance_Data_on_Fighter_Aircraft.pdf
Seems the P-38 could our roll, out turn, and our climb the P-51 and P-47.
Click to expand...

You need to look deeper into the report - the roll rates were at 40lb stick force for P-51B/P-47D but 80 pounds for P-38J (With Boosted ailerons);

The tests were at 10,000 feet instead of say 25,000 feet where both the P-47 and P-51 have increasing Power Available over Power Required due to high drag of P-38 (in comparison) and the turns are CALCULATED for 4G with no comment regarding whether the altitude is maintained in the 4G turn (it can't) using max CL (unrealistic for sustained turn in high AoA Drag condition with extensive cooling drag.
 

Bill,

Curiosity forces the ask, but why would they test the P38 at 80lbs and the rest at 40lbs?

Cheers,
Biff
 
BiffF15 said:
Bill,

Curiosity forces the ask, but why would they test the P38 at 80lbs and the rest at 40lbs?
Click to expand...

My guess is that they figured 40 pounds was a reasonable upper limit for manoeuvring for the stick fighters while 80 pounds could be generated with about the same effort using the Lightning's wheel.
 
Control forces were studied in NACA Report No 755 Requirements For Satisfactory Flying Qualities of Airplanes. See attached file.

The target for maximum aileron control force at below 80% of maximum speed was:
a. Wheel-type controls: +/- 80 pounds applied at the rim of the wheel.
b. Stick-type controls: +/- 30 pounds applied at the grip of the stick.
This was determined by the limitations of pilots in applying forces to the lateral controls.

This explains why the P-38 had a wheel.
 

Attachments

  • Satisfactory Flying Qualities.pdf
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RP,

So if I understand correctly the wheel force at 80 was of similar exertion to a stick at 30lbs. That must mean a pilot put roughly 40 of down with one arm and 40 up with the other to initiate the roll?... And that was similar to a one arm stick throw of 30?

cheers,
Biff
 
It would have been a disaster. Think Bf 110 except a little bit faster, but still meat on the table for luftwaffe pilots in single seat fighters. There's no place for romance and sentimentality in warfare. That's like saying how would the Mosquito have done as a fighter escort. In a word, terribly!
 
A few minor differences between the P-38 and the Mosquito. For one the P-38 was stressed to do fighter type maneuvers. It might not have done them as well as some single engine planes but there was less chance of breaking the P-38 in a high G turn or pull out.
The P-38 did have few things going for it.
It had the best power to weight ratio of any American Fighter (and the best acceleration) when figured at military power and it had a very good rate of climb. Slightly better climb than a P-51 in the low/mid 20,000ft range. and better than a P-47.

It couldn't do some of things the single engine planes could do but it could do a few things better than they could do.

There is a lot of room between "not as good as a P-51" and a "disaster."
 


SR6,

This thread branch leads me to the question of upgrades for the P38. It did receive improvements, but not on the magnitude of the P47 & P51. The Mustang went from the Allison to the Merlin, 3 blade to 4, and eventually the H. Was it "allowed" upgrades due to two production lines? Same for the P47, much bigger more engineered upgrades at multiple production locations. Yet the "brass" decided not to go with the P38K variant which would have been fairly large step for the Lightning.

The P40Q is another. Most likely the production loss was not deemed enough to warrant the production line interruption.

I ask rhetorically as the answers are lost to time.

Cheers,
Biff
 
My own opinion for the P-40Q is that it came too late. First test flying in the Fall of 1943 when Mustangs are being shipped to England by the hundreds (even if not fly flying operationally.) The Spring of 1944 (April) test figures are with the -121 engine compared to the Fall '43 test being done with the -101 engine. Spring of 1944 having one or two prototypes is way too late compared to P-51Ds showing up in Europe in June of 1944 in quantity. Earliest P-51Ds showed up in March.
The other problem is that the US was planning on adding substantially to the armament, going from four .50s to either six .50s or four 20mm cannon. Plane was already 20mph slower than the P-51.

Major change to the P-38 that seems not to have been done is changing the propellers/reduction gear. Late models seem to have gotten broader blades than the early P-38s but not to the extent that P-47s got or the change to four blade props the Mustangs got. Perhaps not as big a deal was made of it? P-38 J props were about 72-73lbs heavier than a YP-38 prop (each) while power had gone from 1100hp to 1600hp.
Props are rather hard to figure out. Larger/heavier may cut into payload or change the CG?
 
from a thread on the P-38 and props.

P-38 Lightning-why no 4-blade paddle prop?

We have another thread going about long range fighters.
A large prop with many blades or broad cord blades may be the best for climb or high altitude work.
However while cruising (even high speed cruise) it may be transmitting 50-70% of the "peak" power of the engine and the larger surface area prop will have more drag and lower efficiency in cruise.
DO you want that last few percent in climb/rate or top speed at 25,000ft and give up a few dozen miles in operational radius? or go for the range/radius and give up a bit on peak performance.

Think of propellers a bit like tires on a car. What works best on pavement (low altitude air) doesn't work so good on sand/mud (high altitude air) and vise versa.
 
That was my first thought but I also think you are using different groups of muscles
 
Hi Bill,

I saw you noted the 40 lbs for the P-51 with a stick and 80 lbs for the P-38 with a wheel.

I would say that the 40 lbs is the stick side force with one arm, which is probably the way most people fly. You might be able to get a bit more with two hands, but you are pulling or pushing with with much weaker muscles than the biceps and triceps. The wheel allows you to use BOTH hands and stronger muscles to affect a roll. P-38 pilots toady state that the P-38 can be muscled around much quicker than contemporary flight reports indicate, and that they can apply much more force with two hands lifting and pushing down than they can with one arm pushing or pulling sideways.

I'd not make too big a thing of the difference in force since the P-38 pilots were almost surely using two arms versus one for the P-51 ... MOST of the time.

Not a big argument from me, just saying I can do more with two arms going up or down than with one sideways. Why shouldn't they?
 
Regarding the P-40Q, I firmly believe that was a lost opportunity. That engine (actually just the auxiliary stage supercharger, the actual engine was the same as any contemporary two stage Allison with 8.1 internal supercharger gears) was in series production as the -93 from March 1943 for the P-63. The P-40Q engine had a few refinements not in the -93 like putting the carb on the engine stage supercharger instead of the auxiliary stage (why this wasn't done sooner is a mystery to me). This engine (either the E or F variant) could have been installed in the contemporary P-39, P-40 and P-51 giving those planes the high altitude performance of a two stage engine. The two stage Allison was in development since 1940 so the airframe manufacturers would have had a head start on modifications necessary to retrofit the new auxiliary stage.
By the way, the first P-63s began trickling out of the factory in October, six months after it's engine (-93) was in series production. Six wasted months in mid '43, right when two stage fighters were sorely needed.
 

I will be among the 1st to support installation of the 2-stage V-1710 on P-51, and wherever it can give it's service. With that said, the P-40Q is/was not an answer to what 8th AF needs, or any other American AF - a proper LR escort fighter - hence no oportunity was lost with not manufacturing it.

By the way, the first P-63s began trickling out of the factory in October, six months after it's engine (-93) was in series production. Six wasted months in mid '43, right when two stage fighters were sorely needed.
Click to expand...

As before - how many 2-stage V-1710s were produced in 1943?
At any rate, P-63 does not solve the problem the USAAF had at ETO, same as the P-40Q. From operational view of the USAAF commanders, P-63 or P-40Q is equal to a Spitfire VIII, while being later for a year or more.
 
Per posts 256 and 257, I thought the issue was that the Allison two stage engines (as historically packaged) did not fit into the 'original' Mustang fuselage. I was under the impression it required a redesign (ala the P-51J) to install the two stage Allison, where as the Merlin 60 series (and the Packard V-1650-3, -7, -9, etc.) fit into the Mustang I / P-51A with minimal changes.
 
way back to the first post; 2. The early Allison had an issue with the intake manifold that took some months to sorts out; the solution was simple and easy, but they had to FIND it ... and did.
What was the issue with the intake manifold and what did they do to correct it?
thank you
 

The Allison coupled two stage/2 speed engine was not considered by NAA for the XP-51B. From a design standpoint, the airframe forward of the firewall could have been modified. That said, NAA was thoroughly pissed off at Allison and only stuffed the Allison in the XP-51J because AAF asked them to do so - probably because they wanted different options to paying RR/Packard for Merlin license. AAF did declare victory with XP-82, permitting only 20 to have the Merlin.

As to 'minimal' changes to stuff 1650-3 into the P-51-1 airframe?
Drop wing 3", re-build lower cowl for carb intake and integrate with new wing position, major re-design of cooling system and lower cowl with design iterations to cure the rumbling problem at high speed. IIRC more than 30,000 hours between Feb 1942 and 'ready for flight' in October 1942.
 
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