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

[Shortround6]

I would note that a P-38J with 300rpg for the .50 cal guns and 300 gallons of fuel ( 16,597lbs) was rated at climbing to 23,450ft in 6.49 minutes and was climbing at 2665fpm at 25,000ft. using WER power

A P-51D at 9760lbs took 6.4 (6.6?) minutes to climb to 20,000ft and was climbing at 2375fpm at 25,000ft.
The P-38 was over a minute quicker to 25,000ft using WER power on 100/130 fuel, 100/150 might change things a bit.

The P-38 might well have done better with 4 bladed props but since it could out climb both the P-51D and the P-47D with paddle blades and water injection the actual need for four bladed propellers doesn't seem to anywhere near as marked as for the P-47.

 

[drgondog]

The combat weight of the P-38J is 17,360 with 420 gallons of fuel. The Test report (IIRC) you are referencing SR, did not have fuel in LE tanks.

That said the P-38J/L out climbed the 51B/D below 20K at respective full combat weights, after that the P-51 ROC was higher. Moral of the comparison is that the P-38 was superior from SL to 10K, then steadily lost advantage until the P-51 overtook it near FTH based on the rated RPM of the Turbos'.

When 75" could be pulled with 150 octane to the 70" of the P-38J, the Mustang matched comparable combat weight P-38J/L to 20 and 25 and 30 K.

 

[Shortround6]

It may have been a bit light on ammo too. Performance for the K showed no difference in speed until over 30,000ft although a large difference in climb was at all altitudes.

However the K used a 12ft 6in three bladed prop.

I have no idea how a 12ft 6in 3 blade compares to a 11ft 3in four blade (or any 4 blade of approximately the same dimension.)

The P-38K prop had 18% more disk area than a normal P-38 and obviously much more blade area. How a smaller 4 blade would have done is the question. Better than the stock props but not as good as the big 3 blade?

 

[FLYBOYJ]

If Kelly Johnson said it flew better with three blades rather than four I'm inclined to trust his judgement.

The decision in this matter would not be Kelly Johnson's anyway. After the design was bought by the government any major design changes had to be approved by the government.

 

[tomo pauk]

If Kelly Johnson said it flew better with three blades rather than four I'm inclined to trust his judgement.

I'll politely ask for source to back up that staement.

Chuck Yeager told me in person he thought the P-38 was better.

Better than what, and based on what?

 

[GregP]

Chuck likes the P-38, for sure. Said so himself at many airshows. Down low, he liked the P-39, too.

 

[FLYBOYJ]

Than the P-51D

My source for the Kelly Johnson fact is The Skunk Works by Ben Rich.

OK - I'm throwing up the BULLSHIT flag. In the book "Skunk Works" by Ben Rich, he (or his collaborator) mentions that the P-38 "was the most maneuverable propeller driven fighter of the war" (Page 111 and nothing is mentioned about Kelly Johnson except that he designed the P-38) which was proven to be not true; this was just the opinion of Mr. Rich (I briefly worked with him, knew his step-daughter) and although the man was brilliant and I will always have tons of respect for this man, he was obviously wrong on this one.

With that said, if you wish to be a useful contributing member of this site, please do some research. Three syllable responses don't go over well here.

 

[wuzak]

Can I ask, was the P-38 ever flown with 4 bladed props, even if only experimentally?

 

[FLYBOYJ]

Can I ask, was the P-38 ever flown with 4 bladed props, even if only experimentally?

AFAIK no

 

[Peter Gunn]

Just curious and maybe I missed it in the thread somewhere, (gotta splittin' headache this morning), but is there any data to compare the P-38 with the 12ft 6in three bladed prop and the stock thin three blade? It sure looks like the props in SR6's photo would take a heck of a bite out of the air.

 

[Shortround6]

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

take two aspirin and enjoy the nice weather until about 10;30 am, then find the air conditioning.

 

[Peter Gunn]

Thanks SR, funny you should mention 10:30, have a meeting I really don't want to go to then, well, at least the A/C part is covered. I already took the aspirin.

Looking over the chart you posted, I can see why, based off just that and my laymans logic, they felt the standard props were fine. Unless you're low down or over 30K there doesn't seem to be much difference.

 

[tomo pauk]

Than the P-51D

My source for the Kelly Johnson fact is The Skunk Works by Ben Rich.

Unfortunately, you didn't posted a single picture showing a real P-38 with 4-baded props in the 1st place. Further, no specific quote on Lockheed testing the alleged P-38 with 4-bladed prop.
Re. Yaeger saying he liked P-38 more than P-51 - fact has it that eg. P-51s were thashing Luftwaffe big time during the Big Week, vs. a similar number of similarly long ranged P-38 that barely claimed an aircraft in same time and area. (me loving the P-38 for around 40 years) Not that P-38 didn't have had it's qualities.

 

[soulezoo]

Is this where one is supposed to throw in a "fork-tailed devil" comment? Just kidding...

Well, I wasn't around for any of these purported conversations so I am in no position to refute them, but as members on this forum know I live close to Gen Yeager and have had a couple of brief conversations. (Although, out of respect for him, I don't pry any-- just let him say what he wants to. I figured he's been grilled enough times by enough people over the years on his opinions that I didn't want to add to that)

Anyway, other than having a lot of respect for the Dora, he's indicated that the Mustang was his favorite to fly. (I write it that way because I have not heard him directly say to me that xxxx aircraft was "best")

 

[drgondog]

Just curious and maybe I missed it in the thread somewhere, (gotta splittin' headache this morning), but is there any data to compare the P-38 with the 12ft 6in three bladed prop and the stock thin three blade? It sure looks like the props in SR6's photo would take a heck of a bite out of the air.

Yes - the P-38K (Allison 75/77 with different reduction gear ratio than 2:1) had 12-6 Curtis props. In the only published Flight test I have seen it offered nearly 500 fpm advantage at low altitude climb rate compared to P-38J. Top speed at 24 or 25 K was 414mph IIRC at 3000 Rpm and 60" Hg

 

[Peter Gunn]

The combat weight of the P-38J is 17,360 with 420 gallons of fuel. The Test report (IIRC) you are referencing SR, did not have fuel in LE tanks.

That said the P-38J/L out climbed the 51B/D below 20K at respective full combat weights, after that the P-51 ROC was higher. Moral of the comparison is that the P-38 was superior from SL to 10K, then steadily lost advantage until the P-51 overtook it near FTH based on the rated RPM of the Turbos'.

When 75" could be pulled with 150 octane to the 70" of the P-38J, the Mustang matched comparable combat weight P-38J/L to 20 and 25 and 30 K.

Just need clarification (my bad, sorry) on your last sentence, with the Mustang pulling 75" and 150 octane and the 38J pulling 70", were they equal in ROC through all altitudes then? I have no doubt the Mustang was faster considering how slippery it is.

 

[wuzak]

Just need clarification (my bad, sorry) on your last sentence, with the Mustang pulling 75" and 150 octane and the 38J pulling 70", were they equal in ROC through all altitudes then? I have no doubt the Mustang was faster considering how slippery it is.

The P-51 would only be able to hold the 75" MAP to a certain altitude before it fell off (critical or full throttle altitude). The P-38 should be able to maintain the 70" to a higher altitude.

So it may be that at the higher altitudes the P-38 gains the upper hand in ROC.

 

[drgondog]

Wuzak - Interestingly, the P-38 had the advantage during the turbo supercharged full power delivery which tapered off around between 20 and 22,000 feet to fall to the equivalent Allison non-supercharged power rating as it climbed further. Depending on the engine and boost the Mustang ROC crossed over and exceeded the P-38 thrust in the area of FTH for both engines.