P-38 bandwagon - #2

[Guppy]

I thought I'd take the opportunity to start a new thread for this one...  

Firstly, thanks to gripen for posting the link to the NACA lift-coefficient tests. That confirms the pilot accounts I've seen about the P-51 having the edge above 20-25,000 ft.

About factors affecting the P-51B's maximum speed; if I recall rightly, one of the P-51 tests (not the Navy one) stated that the presence or absence of wing racks made a 15 mph difference in top speed.

Regarding turning comparisons, I've never seen a flight envelope I would consider reliable either. Doghouse E-M plots didn't even enter the picture until about the 1970s.

The two turning comparison reports I've seen (P-38F vs Fw 190A-3 and P-51B vs P-38J) are low on specific test detail (general conclusions only) and make no mention of combat flaps at all.

The published figures do indeed support the P-38's combat flaps being most efficient around 140 mph IAS (150 mph CAS, correcting for instrument error). However, I don't think that a turn advantage of any substance would simply disappear instantly once the airspeed indicator ticked above 150--it would fade away with increasing speed as the drag rise of the flaps inhibited the P-38's ability to pull G and still maintain a fixed speed in the turn. I'd think that, if not superior, it would at least still be competitive at 200 mph (at lower altitudes where the Clmax decrease was not appreciable).

Don't misunderstand, please--I'm not interested in P-38 boosterism. I'm simply trying to pull together the best picture I can of the aircraft. I have to say this thread's been very helpful in that respect.  

(By the way--I'll be on holiday for the next couple of weeks, so my Internet access may be intermittent. Happy holidays, all!)

[ 12-16-2001: Message edited by: Guppy ]

[bolillo_loco]

Hohun and grippen, Hi you guys seem to be well versed in many of the planes used in ww2 and I enjoy reading your posts. I would be interested in hearing any facts or opions on this question I have.

Both the P-38J and L used the B-33 turbos and both had the same turbo limiting speed. what baffels me is why the J model has a critical altitude of 26,400 and the L model has a critical altitude of 28,700ft. One would think that the turbo limiting speed would tie both to the same critical altitude, yet it does not seem so.

I know the L used a different turbo regulator than the J, and the allisons were different series, but why the different critical altitudes and different hp figures in military power? 1425 for the J vs 1475 for the L. even if it is just an opinion would be appreciated. thanks guys  

[Seeker]

Can we shift emphasis a bit to the planes as is in AH?

Of all Bigweek's FG's, the 38, while scoring well it's self, seemed to be the least survivable ride.

Why was this?

[wells]

bolillo,

The MIL power is the same for the J and L, 1425 hp using 54" and 3000 rpm up to 26600' (no ram) or 29000' (with ram).  War emergency power is 1600 hp using 60" and 3000 rpm up to 25800' (no ram) or 28700' (with ram).  Where do you see 1475 hp?  

Ah yes, I think I see...

In Vee's for Victory, the G model engine had many modifications made to allow 1725 hp at 3400 rpm and 68.5" with enlarged supercharger of 10 1/4" and either 7.48 or 9.60 gears (The P-38, using a turbo, would be able to get same power with reduced pressure or rpm).  Some of these improvements also made it into late production E/F model engines (post 97 model?).  That would mean the 111/113s in the P-38L would have had the stronger components.  That book gives it 1500  hp at 3000 rpm (probably around 57" Hg).

[ 12-17-2001: Message edited by: wells ]

[gripen]

Well, I quess this will be another huge thread again but who cares...

About speeds of the P-51B should be noted that the USAF test I have quoted claimed 15mph speed loss with the racks (435mph at 30k, with racks and combat load about 9000lbs) and actually I have claimed just "over 430mph at 30k" earlier. Generally I tend to doubt a bit all those NAVY tests and information because there appears to be some errors (as HoHun noted). An interesting sidenote is that the A&AEE got speed increase with reduced rpm. About racks it should also noted that there were racks in the other USAF planes too if configured for long range missions...

About flight envelopes it shoulb noted that there is some documented envelopes which are based on the real world tests and also behave like Clmax seems to confirm. There is envelopes for the Spitfire I and the Bf 109E in the RAE Bf 109E report. Another well documented is for the P-47 in the Aero Digest 9/45, this article also contains computations including Clmax data. There is a NACA report on F2A in the Niklas's document page which also have envelopes. Some manual also contain flight envelopes like the manual of the P-38 and F4U-5. The flight envelope in the P-38 manual is not very accurate but it behaves just like Clmax data lets us to believe ie. concave curve, it also seems to be plotted for a very lightly loaded plane (compared to data in the AHT). In the case of the P-51 Clmax data indicates that envelope curve should be convex up to around mach 0.6. Anyway, I pretty sure that there exists envelopes for the all major american fighters, all we have to do is find them.

About combat flaps it should be noted that the are some tests which claim that they were used. Also we can't use CAS values without knowing angle of attack, so better to stay in IAS values (and it's same for all other planes too).

About critical altitudes and ratings of the P-38J and L are as Wells noted (same for both ie. 25800ft without RAM and 28700ft with RAM). Some ratings claimed by manufacturer are different because MAP values are different ie. case of the military power IIRC 56.5" or something. The F-30R/L had the 12 way counter balanced cranckshaft like later models (3200rpm rating with grade 150 fuel).

gripen

[Citabria]

I'm loving the p38 in AH since last patch.

I get to have the fun of loosing:

radiator
oil
aileron
rudder
vert stab
elevator (somtimes both!)

and all these parts seem to get hit without the vert stab ussually falling off the airplane  

very fun to shoot them now and get shot in them  
they dont splode so easily but will still splode when hit w solid burst

[bolillo_loco]

wells, you are correct on the 1425 on the L, I do not know where I saw the 1475 figure, I just went to zenos and looked at the specific engine flight chart, maybe it was americas hundred thousand that stated that figure. I do not have my copy of the pilots manual any more, that was lost also, but wells if you have the manual can you look in to see the critical altitude. I thought for sure that the J had a lower critical altitude of 26,400 ft. Hi citabria!!

[HoHun]

Hi Seeker,

>Of all Bigweek's FG's, the 38, while scoring well it's self, seemed to be the least survivable ride.

>Why was this?

Here's a quote from a recent interview with P-38 ace Gerald Brown on Dogfighter.com:

"DF: What was a better fighter plane? The P-38 or the P-51?

GB: I liked both! But the P-51 was a better aircraft against the Germans. Early on the German, like a street bully, could pick a fight and then break it off against the P-38. He couldn’t do that with a P-51."

Obviously, the fighter that can decide when to fight and when to run has better chances of survival.

Less obviously, online pilots tend to select their fighter to match their ideas of fun. A manoeuvrable low speed-fighter will be flown predominantly by action oriented pilots, a fast, non-manoeuvrable one by pilots who prefer safe landings over quick kills.

It's the man, not the machine ;-) With pilot personalities the same but aircraft types reversed, I'd bet that the same group of action-oriented players would have suffered the heavier losses just the same.

Regards,

Henning (HoHun)

[wells]

The critical heights I posted are from the manual.

[Badboy]

Originally posted by Guppy:
Firstly, thanks to gripen for posting the link to the NACA lift-coefficient tests. That confirms the pilot accounts I've seen about the P-51 having the edge above 20-25,000 ft.

Can someone post the report number please?


 

The two turning comparison reports I've seen (P-38F vs Fw 190A-3 and P-51B vs P-38J) are low on specific test detail (general conclusions only) and make no mention of combat flaps at all.

Can you post the reference/source for those reports please?


 

The published figures do indeed support the P-38's combat flaps being most efficient around 140 mph IAS (150 mph CAS, correcting for instrument error). However, I don't think that a turn advantage of any substance would simply disappear instantly once the airspeed indicator ticked above 150--it would fade away with increasing speed as the drag rise of the flaps inhibited the P-38's ability to pull G and still maintain a fixed speed in the turn. I'd think that, if not superior, it would at least still be competitive at 200 mph (at lower altitudes where the Clmax decrease was not appreciable).

If we assume a maximum performance turn where the aircraft is flying on the edge of the envelope, and that the corner speed for the P-38 is over 200 mph, then an increase in speed would result in more available lift, more G, and subsequent increase in turn rate. However, one other effect of increasing the speed while the flaps are fully extended, is a nose down pitching moment, which would grow worse as the speed increased. That might well eventually have a serious impact on turning ability, up to the point where the speed was high enough to possibly damage the flaps. These issues appear to have been avoided in Aces High because the flaps appear to retract prior to adverse effects. Lasty, my own analysis of the use of flaps in combat reveals that you simply can’t just consider changes in Clmax because the change in the aerodynamic efficiency (L/D) is more meaningful for comparison… Hope that helps.


Badboy

[gripen]

Here is it. It's also discused under this thread, but note that thread is very large, 176 messages + images.

gripen

[laz]

Festie.. I see the radiator goes as much if not more than p51's now.. almost every p38 i see has oil/coolant leak. Also happens to me a lot =)

[Tac]

Hey Badboy, you know if the 38 L's had auto-retracting flaps? I know they had locks to prevent them from extending past 250mph, but I havent found any reference to them self-retracting  

[bolillo_loco]

wells, looks like I was wrong again, thank you for setting me straight.

[wells]

bolillo_loco,

The P-38H has different critical heights (with same engines as J, the 89/91), they are:

MIL (54" @ 3000 rpm):  1425 hp @ 22000' (24900 with ram)
WEP (60" @ 3000 rpm):  1600 hp @ 7000' (10000' with ram)

Some H models had the B-33 turbo and it still wasn't as good as the J and L with the same turbo, although it was an improvement over the B-13.  So there was a combination of factors involved in the lower critical height for the H model, not just the turbo.

[ 12-18-2001: Message edited by: wells ]