Are you a P-51 freak?

drgondog said:

The Allison equipped Mustangs, and particularly the P-51A/Mk II with V-1710-81 was faster than B/D under 12,000 feet - except for the specially modified V-1 Mustang III's.

It was extremely well equipped to serve as armed recon and did so through the end of the war.

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Don't forget the good performance of the A-36, another Allison powered version that doesn't get alot of credit

While I like the P-51, I'm a die hard fan of the AT-6. These were the first planes I saw as a child at Stallings Airforce Base at 4 years of age and I can't get the rows of yellow Texans out of my memory.

at6 said:

While I like the P-51, I'm a die hard fan of the AT-6. These were the first planes I saw as a child at Stallings Airforce Base at 4 years of age and I can't get the rows of yellow Texans out of my memory.

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Both of these planes were produced by North American...pretty cool!

Greetings, pardon my newbie-ness (OK, that's not a word but...) but I just registered and this is my first post. With that said, I am a total Mustang lover, not to the exclusion of all others though. I find most WWII fighters interesting and all have pros and cons, but to me the Mustang is "it". With that being said I have a question for GregP (and any others in the know) regarding modern day P-51s and warbirds in general.

I have an acquaintance here that insists that no P-51s use superchargers anymore, they are all normally aspirated and "never" go above 15,000 ft. Thoughts?

Thanks.

Also, as far as the Mustang, I agree that it did everything "well" and somethings exceptional, but to me, it's the whole package which is why I'd rate it a cut above others, that and those totally Smexy lines, I have yet to find an angle to look at a Mustang that it doesn't scream "mechanical poetry" to me.

Thanks for reading my rambling bleeber blabber.

Interesting question, and something I've wondered about for various 'warbirds'.

GrauGeist said:

Don't forget the good performance of the A-36, another Allison powered version that doesn't get alot of credit

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Dave the -89 did have 10% more power but it peaked at ~5500 feet and for whatever reason - maybe the drag of the cheek 50 cal it wasn't quite as fast as the P-51A and/or P-51B.

Peter Gunn said:

Greetings, pardon my newbie-ness (OK, that's not a word but...) but I just registered and this is my first post. With that said, I am a total Mustang lover, not to the exclusion of all others though. I find most WWII fighters interesting and all have pros and cons, but to me the Mustang is "it". With that being said I have a question for GregP (and any others in the know) regarding modern day P-51s and warbirds in general.

I have an acquaintance here that insists that no P-51s use superchargers anymore, they are all normally aspirated and "never" go above 15,000 ft. Thoughts?

Thanks.
...

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All warbirds today, piston-engined, use superchargers.
Supercharger not just adds the air and, hence, the power at all altitudes, they perform 'mixing' of air and fuel to get the mixture right (not the case with direct-injected engines, like most ww2 German types). The engine-attached superchargers were not called 'integral superchargers' for no reason, it would be quite a trouble to delete suc a supercharger from the Merlin.
Most of P-38s flying today even use the turbo + integral superchargers.
No supercharger means no manifold pressure over the standard 0 psig/29.92 in Hg (or so). Such low manifold pressure means low power, especially for small capacity engines, like Merlin or V-1710 - 600 HP at 3000 rpm at sea level; 300 HP at 15000 ft?
Don't think anyone will fancy flying the P-51 on 300-600 HP.

Thanks Tomo.
I realise that, on the Merlin, for example, the supercharger is part of the rear of the engine casing, and therefore will 'kick in' as required. My interest was mainly concerned with the altitudes flown by 'display' aircraft, obviously way below WW2 operational altitudes. I don't think I've seen an operational oxygen system on any of the Spitfires, Hurricanes or P-51s in the UK !

I know nothing about Aero engines but car and motorcycle engines with turbos and superchargers are constructed completely different to those without. They have lower compression ratios because the incoming mixture is pressurised. Running a standard engine with a blower will make it explode pretty quickly, just disconnecting a supercharger will give you an engine that probably wont start. I doubt it would be certified for flight. The supercharger wasnt a bolt on goodie it was an integral part of the engine.

pbehn said:

I know nothing about Aero engines but car and motorcycle engines with turbos and superchargers are constructed completely different to those without. They have lower compression ratios because the incoming mixture is pressurised. Running a standard engine with a blower will make it explode pretty quickly, just disconnecting a supercharger will give you an engine that probably wont start. I doubt it would be certified for flight. The supercharger wasnt a bolt on goodie it was an integral part of the engine.

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Not only that, but I'm sure the supercharges on AC engines provide additional power at all altitudes, not just above certain altitudes....

drgondog said:

Dave the -89 did have 10% more power but it peaked at ~5500 feet and for whatever reason - maybe the drag of the cheek 50 cal it wasn't quite as fast as the P-51A and/or P-51B.

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I agree about the cheek guns and suspect drag created by the airflow over the dive brakes (when retracted) may have contributed to a certain degree.

While it wasn't a dog fighter in the true sense, that being outside of it's mission profile, it certainly did rise to the occasion - I believe one of the A-36 pilots made ace in that type, too (don't recall his name at the moment)

FWIW - the USAF used A-36 to escort the medium bombers in the MTO, granted at low altitudes.
Due to the low-altitude geared supercharger, the A-36 won't be that fast above 5000 ft, let alone climb well above that alt.

Mike Russo - 27th FG is the only pure A-36 Ace

Lt. Russo, that's the one!

Thanks

drgondog said:

Mike Russo - 27th FG is the only pure A-36 Ace

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And, I believe, the first "Mustang" ace.

grampi said:

Not only that, but I'm sure the supercharges on AC engines provide additional power at all altitudes, not just above certain altitudes....

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A supercharger or turbo is always working, how much boost it provides above normal pressure is another matter, since I am not a pilot but would only ever be a passenger I want to know the engine is working properly on take off and landing if that is OK.

There are some guys on the forum who work on these warbirds, I would be surprised if any P51 is flown without the Supercharger, even if physically possible there would be all sorts of regulations to get past.

Hi Peter Gunn,

First, there are some "experts" around like Drgondog, JoB, Graugeist, Wuzak, Njaco, DerAdler ... (the Crew Chief" in English), Viking Berserker, Milosh, Tomo Pauk and quite a few others. If any of you guys disagree with what I say below, chime in here. I apologize in advance if I left anyone out, it wasn't intentional. The list was getting long enough ...

All Allison V-1710s flying in WWII fighters are supercharged including the A-36 and P-51. It is correct to say the Allisons in most flyable P-38s (all 6 or 7 of them) mostly don't use turbochargers, but they all still have superchargers or they wouldn't run. All wartime Allisons were single-stage supercharged, even the ones on P-39s and P-40s that did not have turbochargers fitted. That is, they have one centrifugal compressor feeding the mixture to the cylinders. The P-38 also had a turbosupercharger, as they were called at the time (turbocharger today), for each engine. Of the worldwide population of P-38s flying, I believe there is one still running operational turbochargers. I also know of ONE P-47 still running a turbocharger, but it has an R-2800 radial and not a liquid-cooled V-12. Well, ONE of them had a liquid-cooled engine, but I digress ...

When the P-51 Mustang switched from the Allison and got the Merlin engine, it started right off with with the Packard-built V-1650-3 (a U.S.-built Merlin) which has a 2-stage integral centrifugal supercharger. The engine cannot operate without the supercharger compressors. Well, it COULD, but not without some serious modifications that certainly weren't done in the war and have never BEEN done as far as I know. So ALL flying P-51 models from the B onward (P-51B/C/D/H/K) are all running 2-stage superchargers. Some have an intercooler fitted between the stages that looks like a big rectangular box on top of the back of the engine. It cools the compressed air since compressing air heats it up. Normally it wouldn't be a big deal, but if you are going to compress it twice, then you pretty well HAVE to cool it before it reaches the cylinders or detonation may set in early. Once it gets so hot, it will ignite spontaneously.

Short answer, the Allisons and Merlins (Rolls-Royce, Packard, and a few others) ALL run superchargers, and anywhere from one to maybe 2 of the remaining P-38s still run turbochargers. The rest (a population of 5 or 6) still have the turbochargers in them, but they are disabled (don't spin). Our P-38J at the Planes of Fame has disabled turbochargers, but the exhaust still exits through the turbos out the top, making it one QUIET warbird until it rolls with the topside toward the audience. When it does, it is just as loud as any other warbird. Mostly it is quiet since we only do aerobatics when the airspace is ours, the aerobatic box is open, and the P-38 is the scheduled warbird to do the aerobatics.

Here is one such time:

View: https://www.youtube.com/watch?v=jWrSQQlRYgw

Incidentally, the P-51s make a whistling sound when they dive past the crowd, That is the superchargers spinning up as they pick up speed on the downside of a vertical maneuver.

Interestingly, the plucky little FM-2 Wildcat makes almost exactly the same sound as it flies by.

LOVE the supercharger whine! Got boost?

GregP said:

Incidentally, the P-51s make a whistling sound when they dive past the crowd, That is the superchargers spinning up as they pick up speed on the downside of a vertical maneuver.

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Hi Greg,

My knowledge of the mechanical operations of aero engines is, at best, that of a layman so I have a honest question(s) for you about the quoted sentence above if I may.

It's my understanding that the Merlin's superchargers are engine driven and so spin faster or slower depending on the engine rpm (hence the "superchargers spinning up as they pick up speed") or is it something else that causes them to speed up when the P-51 is in a dive? Which leads to another question, why isn't that whine/whistle audible during the take-off run when (I assume) the engine is running at high rpm?

I must admit I thought to ask these questions because I has heard elsewhere that the whistle is caused by the airflow passing over assorted apertures (like blowing gently on the top of a glass bottle) which, at the time, made sense to me because I wondered why the Spitfire IX/XVI has a less noticeable whistle despite having the same engine.

Regards,

HB

Well, to be honest, I stated the case wrong above.

Any mechanical supercharger spins at a set faster speed than the crankshaft in a piston engine. The speed is set by the crankshaft-to-supercharger-impeller gear set ... unless the supercharger has hydraulic drive. In the P-38J (V-1710-89 / 91) it was 8.10 : 1, so at 3,000 engine rpm the supercharger was spinning at 24,300 rpm. The prop was 2:1 so it was spinning at 1,500 rpm. It is ALSO true to say both the P-51 and the P-38 both had/have constant-speed propellers, and at no time in the above demo did they get slow enough to fall out of the constant-speed range.

So, the real explanation is that the superchargers are spinning at pretty much the same speed throughout most of the show, but we are hearing the Doppler shift of the supercharger whine, just like when a car or a train passes by. We HEAR them as "spinning up," but they really aren't changing much. I only say "much" because constant-speed propellers aren't EXACTLY constant speed ... they DO vary a small bit, but not much.

Ya' got me there, HBPencil, and I should not have stated it wrongly in the earlier post. Slap me. If I really asked more than one person in here to do that, they would .... even grade school kids know about Doppler shift these days.

Thanks for all the replies, wow, great stuff!

Tomo - appreciate the quick response, I do know what a turbo/supercharger does (not being a jerk, just informational) but thanks for the explanation. I'm pretty well versed on the history of the P-51, just don't know much about what happens with them now a days. Again thank you for your very informative (and fast) post.

GregP - Thanks for the welcome and all the head-spinning info (and the awesome video). As I said, I'm pretty much up on my Mustang history but post war, eh, not so much. The person I was "debating" with on the way warbirds work is a self-professed (or self congratulatory pompous) type of chap that just "knows". Unfortunately I tend to let pesky things like facts get in the way, that's why unless it's a source document I tend to cast a somewhat jaundiced eye when discussion starts.

I'm quite jealous, I'd love to be around those old birds as you are, so I'll just have to enjoy vicariously through you...

I'm looking forward to joining in on the discussions here, just as long as we all agree my love for the Mustang may cloud my judgement now and again. But I did major in history with emphasis on WWII at the University of Michigan and was raised on an airfield so I am not a total punter when it comes down to it.

Again, trying not to come off as anything other than a lover of WWII aircraft, also going forward, ALWAYS take any comment from me that sounds pompous or officious with a big grain of salt. I tend to crack the wise quite often and no offense will be meant.

Now, must travel west to soundly slap Greg for forgetting about Doppler shift.