P38 a super plane?

[Captain Virgil Hilts]

Originally posted by Angus
Hmm
" The Merlin was also not designed to be turbocharged, meaning that it would have given up considerable power above 20K. "

Spitfires were cruising at 43K in 1942.
Not designed for a turbocharger? By 1942 the RR had 2 with an intercooler between, so power was quite good at high alt.
Merlin 66 or 70 could peak out at close to 1700 hp.
It looks as if there is quite enough space in the Nacelles.
And if there had been a drag penalty, well, it's a different setup anyway with the air intake.
Wonder instead how a Griffon powered P38 would have performed, hehe 2200 horses grrrrrrr...

Angus, the Merlin had a two speed two stage crankdriven centrifugal supercharger, it was not turbocharged. The Merlin had to be specifically tuned for a certain altitude. If tuned for low altitude, it gave up power at high altitude. If tuned for high altitude, it gave up power at low altitude. Further, the crankdriven supercharger absorbed huge amounts of power when shifted into high gear. The P-51 was down to around 700HP at 30K. There is a distinct difference between a crankdriven centrifugal supercharger and a turbocharger, which is exhaust driven. And the Merlin was NOT turbocharged. At least no Merlin I've ever seen in 30 years, as a factory installation in an aircraft.

The Griffon was huge, and would not have fit the P-38 any better than the Merlin.

If you want power, try taking the Allison used in the P-82 Twin Mustang (not turbocharged) and installing it in a P-38 with the turbocharger. This could have been done in 43-44, it was a bolt in swap.

[MiloMorai]

Angus,

TURBOcharging: using exhaust gasses to spin a turbine that turned the compresser wheel

SUPERcharging: using a mechanical/fluid coupling to turn the compresser wheel


There was an attempt to put 60/70 series Melins in the P-38 but massive lobbying in Washington and elsewhere by GM, the parent company of Allison, had the idea dropped.

It should be noted that the Unlimited hydroplanes used both  Allison and Roll-Royce TURBOcharges engines. The R-R engines even using some parts from the Allison engine. Technical specs for the engines can be found here, http://www.unlimitedexcitement.com/

I see Virgil has made a post, but I leave mine as is.

Virgil, the Griffon was not as massive you think it is. It was slightly longer than the Merlin but fit into the cowling area of any Merlin powered Spit with only a slight enlargement of the bulges already there for the Merlin.

[Angus]

2 stage turbochargers could be optimized at will in regards of altitude, and don't tell me that the Merlin61 did not develop power at high alt....
Now for the size, the only time I've seen the Allisons was in P40 and P63. Can't really say that they look smaller. Do you have any dimensions and weigh numbers for those?

Now the Griffon is a wee bigger than a Merlin, but the power is just massive. Can't remember where the final ones peaked out in operational use, - 3000 hp contra rot?

[Angus]

Ah, thanks Milo, so I am corrected.
In my language we always call it a Turbine, regardless the method how to drive it.
I run a turbo engine every day BTW. 4 liter perkins diesel.

[gwshaw]

Originally posted by Angus
2 stage turbochargers could be optimized at will in regards of altitude, and don't tell me that the Merlin61 did not develop power at high alt....
Now for the size, the only time I've seen the Allisons was in P40 and P63. Can't really say that they look smaller. Do you have any dimensions and weigh numbers for those?

Stages have nothing to do with optimizing at different altitudes, multiple gear ratios do. You can only provide so much compression per stage, multiple stages allows higher overall blower compression ratio, about 6.5:1 for a V-1650-7 compared to about 3.5:1 for a V-1650-1.

Having multiple gears only allows you to optimize at multiple altitudes, ie 2 speeds allows a V-1650-7 to peak at about 8500 ft and again at about 21,400 ft. A turbosupercharger doesn't have peaks and valleys like a mechanical supercharger, flat power curve from SL to 25,000 ft for a P-38J.

In addition a mechanical supercharger is sucking up power from the crank, around 400 hp for a Merlin 61/63 in high gear. The Merlin 61 could manage a bit over 1300 hp at about 23,000 ft, the V-1710-F17R/L - B33 in the P-38J could manage 1600 hp to 25,000 ft, the V-1710-F30R/L in the P-38L could do 1725 hp to 25,000 ft or 1600 hp to 28,700 ft.

Greg Shaw

[Angus]

And ceiling?
Was the P38 then simply so heavy?

[Crumpp]

Here is the Pot calling the Kettle black....

Oh, and by the way, I find it VERY interesting that you want to use Lockheed RECOMMENDATIONS as the gospel on flap usage, but you want to ignore what Lockheed and Allison said about the 8th AF, and their ratings for the P-38L. But then, I'd expect nothing less from you. You seem to love to pick and choose that which you think supports your arguement, and vehemently deny the rest, even coming from the EXACT same source. You can't even differentiate between a recommendation and an absolute limit.

Verge,

It's about standards.  Which standard is AH going to use?  If they pick the very best data for some aircraft and do not use it for others then the results (modeling) will be skewed.  You cannot scream to have Lockheed data used and then pounce on someone for posting Vought, supermarine, Messerschmitt, or any other manufacturer.

Nor can you artificially inflate performance off of "stories".

Talk to Pyro.  That is one reason individual plane models are great in AH but the combat results are skewed.  They simply do not have good data on some of the planes.

As long as the standard are maintained it makes little difference which data set is used.

Crumpp

[F4UDOA]

Here is a peice of the Wright Patt test between the P-51B and P-38J-5.

The turning circle of the p-51B is smaller than that of the p-38J-5, at all altitudes. It has a far faster rate of aileron roll through all speeds. The p-51B accelerates rapidly away from the p-38J in a dive, after reaching speeds of 325 I.A.S. With both planes in formation at cruising speed in level flight, when full power is applied, the p-38J will pull several hundred feet out in front before the p-51B can reach maximum acceleration and overtake the p-38J. With slight advantage in altitude, the p-51B can jump the p-38J successfully and engage in combat, due to its superior diving and top speed. The p-51B can evade being jumped by the p-38J, if it is seen in time, by dropping the nose and diving away. If the p-38J has built up its speed in a dive and is not seen in time, the p-51B can turn sharply into the p-38J and evade its fire. The p-38J cannot follow the p-51B at high diving speed at altitude, due to its lower limits of allowable diving speeds. At high speed, it is impossible for the p-38J to keep its sights on the p-51B due to the p-51B's rapid rate of aileron roll, allowing it to reverse its direction of turn faster than the p-38J can follow.

[gwshaw]

Originally posted by F4UDOA
Here is a peice of the Wright Patt test between the P-51B and P-38J-5.

Very interesting, but note that it is a pre-aileron boost J-5.

As for dive speed, without knowing what altitude it was the 325 mph IAS doesn't help much. We need to know what Mach number it corresponds to. The P-38J initially accelerates away, then then Pony runs it down, about what I would expect if above 20k or so and the P-38 is hitting the drag rise about 40-60 mph before the Pony does.

(Misread that part: doesn't say P-38 initially gained edge, comments are still true however, the Pony doesn't gain an advantage until after 325 mph IAS)

Level accel, again the P-38J pulls away initially, then the Pony catches and passes it. Again, about what I would expect, the Pony has lower drag as speed increases, the P-38 lower induced drag at low speeds.

Note, we need to know what cruising speed was, the P-38 cruised 30-40 mph slower than the Pony. The P-38 is going to have better results starting at its cruising speed than it will at the Ponys. It won't make as much difference for the Pony if it starts slower.

Don't get me wrong, those are precisely the type of documents I like seeing, but what they don't tell you is just as important as what they do.

Greg Shaw

[Crumpp]

With both planes in formation at cruising speed in level flight, when full power is applied, the p-38J will pull several hundred feet out in front before the p-51B can reach maximum acceleration and overtake the p-38J

Very interesting and just as I thought.  I have yet to see an instance where the science does not back up what the pilots say.  Here we have the basis of the pilot claims of the P38's great accelleration and the engineer data which contradicts the pilots. Both are correct.

 

Murdr says:
Ok well only having select snipits of the TAIC narrative report that you have posted, and the partial intelligence summarys that I have, I would say here is an example.

F4UDOA has posted this report on numerous occasions.  I do not have the webspace to host the entire report but would be glad to email it to you.  All the pertinant information as to aircraft type, engine settings, etc... has been posted.

Crumpp

[Captain Virgil Hilts]

Originally posted by Angus
And ceiling?
Was the P38 then simply so heavy?

The P-38 routinely reached altitudes of 44K. In the MTO, it was retained in at least small numbers by groups that replaced them, because the P-38 was the best plane for climbing up to intercept the various German recon planes.

[Captain Virgil Hilts]

Originally posted by Crumpp
Here is the Pot calling the Kettle black....
Verge,

It's about standards.  Which standard is AH going to use?  If they pick the very best data for some aircraft and do not use it for others then the results (modeling) will be skewed.  You cannot scream to have Lockheed data used and then pounce on someone for posting Vought, supermarine, Messerschmitt, or any other manufacturer.

Nor can you artificially inflate performance off of "stories".

Talk to Pyro.  That is one reason individual plane models are great in AH but the combat results are skewed.  They simply do not have good data on some of the planes.

As long as the standard are maintained it makes little difference which data set is used.

Crumpp

I didn't jump on anyone for using data for planes from the company that manufactured the planes. I did question the use of one manufacturers data for planes they did not manufacture.

There is no artificial inflation of performance from "stories". It is well documented that BOTH Lockheed AND Allison certifed the engines in the P-38L at 1725HP. It is also well documented that the USAAC arbitrarily decided to remove the WEP rating from the L model for "reliability" reasons, when in fact the report from Levier proves beyond a doubt that the reliability issues were due to 8th AF procedures and nothing else. Finally, it is also true that both Lockheed and Allison sent engineers and pilots into the "field" and they informed both mechanics and pilots of the 1725HP WEP rating and how to get it.

Of course, you can choose to follow Lockheed's  "recommendations" on flap usage, and ignore their certified ratings of the P-38L engines. Nothing about that would surprise me.

What really is funny is that despite the fact that there is no WEP rating for the P-38L except that provided by Lockheed and Allison, the AHII P-38L HAS WEP. But the WEP speed is actually the speed that the P-38L was certified to as Military Power.

[HoHun]

Hi F4UDOA,

>Thus, same aircraft that has the better climb at any given speed also out-accelerates the other aircraft at that given speed by the same factor as long as the conditon of the aircraft remains the same in both states.

Roger that! I knew we'd reach agree complete agreement :-)

With regard to radiation drag, I recently found an interesting bit from a pre-war Messerschmitt speech: He praised the Junkers radiators for requiring a constant power to overcome drag regardless of the airspeed and thus contribruting significantly to solving the problems of high-speed flight.

Though Junkers worked with liquid cooling, I think to a certain degree air-cooled engines benefitted from that, too. I'm not sure why the cowl flaps were such a bad speed brake anyway - maybe it's because they projected into the free airstream and caused a lot of turbulence there.

Regards,

Henning (HoHun)

[HoHun]

Hi Hilts,

>So much has been made of the lackluster performance of the P-38 with the 8th AF, I thought it might be nice to have an inside look at what went wrong.

Quite interesting, but it really touches only one aspect of performance: Range.

("Sort of engine trouble" doesn't seem to be very serious - or maybe the pilots just had a lot of confidence due to engine redundancy :-)

With regard to the turbocharger RPM: The British test of the P-38F mentioned the turbos spun up from idle to full take-off boost in about 10 s. That spin-up time was considered a serious issue tells us a lot about how fast-paced the fights must have been ...

Regards,

Henning (HoHun)

[HoHun]

Hi Hilts,

>THE USAAC downrated the P-38L by disallowing WEP (see the report from Levier above for their reasons) engines

Hm, you're not referring to the same report in which Levier solves the range issues, I guess? That one seems to be about boosts in the cruise range entirely.

>The Merlin was also not designed to be turbocharged, meaning that it would have given up considerable power above 20K.

Well, the Merlin 61 was a pretty good high-altitude engine anyway. I've not looked at the weights, but I'd be surprised if the Merlin outweighed the Allison if you feature in the latter's turbo-supercharger. However the Merlin's weight distribution would have been all wrong since it was all in front of the firewall, while the turbo-superchargers brought back the centre of gravity nicely. In my opinion, it would have required a major redesign of the P-38 to fit the Merlin.

Regards,

Henning (HoHun)