SHOULD the P39 have been able to handle the Zero? Was it training or performance?

[pbehn]

View attachment 486693
Think i made a mistake coming back !
Shame really

Its just one post from one poster, have a Parmo and relax.

 

[wuzak]

The single stage V-1710's power curve follows the same shape as the V-1650-1, but without the second gear.

The reason for this is that the throttle causes a pressure loss and a reduction in efficiency of the supercharger. So the power rises as altitude increases, the throttle progressively opening to maintain the required boost level, until the critical altitude/full throttle height where the engine makes its peak rated power. The power then, pretty much, falls off a cliff.

The difference for the V-1650-1 is that when the power begins to fall off, another gear can be engaged. Note that the change point is determined by when the high gear has the same power as the low gear. Once in high gear the throttle has to be closed again, to prevent overboosting, and is, again, progressively opened until critical altitude/full throttle height. Hence the sawtooth shape.

The advantage in the 2nd speed can be seen in the Merlin XX (of which the V-1650-1 was a derivative) and Merlin 45. They were essentially the same, except for the supercharger drive. The XX had the 2 speed drive, low speed (Medium Supercharged gear or MS, in British jargon) had a lower ratio than the 45's single gear and high speed (Fully Supercharged, or FS, gear) had a higher ratio than the 45. Thus the XX had more power at low altitudes and high altitudes, with the 45 basically having the advantage around its full throttle height (~18,000ft).

Just going back to the single speed s 2 speed supercharger discussion for a moment, this is what I would expect the power curve of the V-1710 to look like, though the peak power will be at lower altitudes, for some versions, than shown for the Merlin 45 and 46.

Only for a small altitude band around the single speed engine's peak will it have any marked advantage over the 2 speed engine, and then only if that corresponds to the gap between FTH in low gear and FTH in high gear. If the 2 speed engine had a low speed gear ratio the same as the single speed engine, the performance would be identical as the single speed engine until the supercharger was changed into high gear, after which the 2 speed engine would be vastly superior.

 

[Shortround6]

Actually you may have the reverse. The Merlin 46 & 47 having about the best performance at altitude of any single stage supercharger. to get 9lbs of MAP (48 in?) it was compressing the ambient air at 22,000ft 3.8 times. Which is about as good as it got for a single stage compressor in service in WW II, even for jets.

A second gear was often used to increase the power available at lower altitudes and for take-off. Less power to drive the supercharger, less heating of the intake charge, throttle plates open wider.

For example a Wright R-2600 was limited to about 1450hp in high gear, anywhere from 8000ft to 12,000ft (or higher?) using a 10.0 gear set to drive the supercharger.
Using a 7.0 gear set in low gear they had 1700hp from 0 to 3000ft and did it at about 2 1/2 less inches of MAP.
I would note that the two speed drive to the supercharger on the R-2600 increase the weight by about 25-35lbs over a single speed engine.

 

[wuzak]

Actually you may have the reverse. The Merlin 46 & 47 having about the best performance at altitude of any single stage supercharger. to get 9lbs of MAP (48 in?) it was compressing the ambient air at 22,000ft 3.8 times. Which is about as good as it got for a single stage compressor in service in WW II, even for jets.

I wasn't suggesting that the V-1710 was as good as those, just that the shape of the curve will be similar.

The peak altitude (for similar boost) will be at a lower altitude, but I would expect the power to climb to the FTH, as the throttle would cause power loss until it is fully open.

A second gear was often used to increase the power available at lower altitudes and for take-off. Less power to drive the supercharger, less heating of the intake charge, throttle plates open wider.

I realise this.

I was just point out that if the first gear on the 2 speed engine is the same as the gear ratio on the single stage engine, the performance would be the same between the two. A few thousand feet above the FTH of the first gear the high gear will be engaged, giving the 2 speed an advantage over the single stage.

It is also true that the high gear could be the same as the single stage engine's supercharger ratio. That would mean the same altitude performance, but enhanced low altitude performance.

In the case of the Merlin XX compared to the 45, the low gear ratio was lower than the 45's single, and the high gear ratio was higher.

IIRC, the 46 had a larger impeller, which gave improved altitude performance, at the cost of low altitude performance.

 

[Shortround6]

You are correct and have been around long enough to have been through a number of these supercharger discussions and you may well have known most of this already.
We always seem to get new members who think you can just up the gear ratio and get even higher altitude performance and don't realize that each compressor had a limit at which it couldn't deliver more air regardless of how fast the impeller was spun.

On the Allison the "curve" was actually pretty much flat from take-off to rated altitude, then sloped down.
There was a slight rise from sea level to rated altitude but nowhere near what the Merlin often shows.
This may be because the Allison supercharger was smaller and required less power to drive (it also delivered less volume and pressure) and the slight difference in engine displacement and compression may also enter into it.

The Merlin 46 could make about the same power in WEP as the Allison but do it 5000ft higher up.

 

[pbehn]

Nobody is saying the P-39 didn't do good work, However this attempt to rewrite history is getting a bit tiresome.
P-40s also did a lot of bombing attacks with single 500lb bombs, later P-40s could and did carry three 500lb, there are photos of them with six 250lb bombs,
View attachment 486662
There was at least one instance in Italy of P-40s carrying a pair of 1000lbs, not one plane but one or more squadrons attacking one target. Granted it was only about 30-40 miles from the airfield.
While the 37mm was nice you don't need a 37mm to kill a truck. You also have to hit the truck in order to kill it. You need about 4 seconds to fire ten 37mm shells and a 300mph airplane covers over 500yds in 4 seconds, making aiming and hitting a single target with such a gun a bit of problem, spectacular when it does hit but actual number of hits?
Most trucks don't take well to even rifle caliber bullets let alone .50 cal bullets, punctured fuel tanks, punctured radiators, holes in the cooling jacket of the engine block, holes in the transmission and final drive casings, punctured tires. Multiple machine guns batteries certainly missed a lot but had a higher chance of getting some hits.

You are also taking one test of a lightly loaded P-39 and trying to extrapolate from it. Many other tests were done at full load clean.
like one for a P-51B using 67in of MAP,
"High speed and climb performances have been completed on this airplane at a take-off weight of 9205 lbs. This loading corresponds to the average P-51B combat weight with full oil, 180 gallons of fuel and specified armament and ammunition."
P-51B Performance Test
Climb to 25,500ft in 8.28 minutes.

Interesting S/R, I don't know when the final decision was made on D-Day but after the Dieppe raid I think the idea of taking a channel port was abandoned. The straight line distance between Portsmouth and Caen is 125 miles.

 

[pbehn]

You are correct and have been around long enough to have been through a number of these supercharger discussions and you may well have known most of this already.
We always seem to get new members who think you can just up the gear ratio and get even higher altitude performance and don't realize that each compressor had a limit at which it couldn't deliver more air regardless of how fast the impeller was spun.

On the Allison the "curve" was actually pretty much flat from take-off to rated altitude, then sloped down.
There was a slight rise from sea level to rated altitude but nowhere near what the Merlin often shows.
This may be because the Allison supercharger was smaller and required less power to drive (it also delivered less volume and pressure) and the slight difference in engine displacement and compression may also enter into it.

The Merlin 46 could make about the same power in WEP as the Allison but do it 5000ft higher up.

Isnt the part now in bold what Stanley Hooker brought to the RR Merlin, noticing the compressor was stalled he boosted maximum performance, or am I barking up the wrong tree?

 

[Hansie Bloeckmann]

View attachment 486693
Think i made a mistake coming back !
Shame really

F.U.C.K.-- goes back to the days of King Henry V111- Fornication Under Consent (of the) King-overused in today's parlance, IMO..

 

[Hansie Bloeckmann]

Its just one post from one poster, have a Parmo and relax.[/QUOT

 

[Shortround6]

Sort of, He did notice fairly quickly that actual results did not match the formulas/assumptions used in design. Then he went looking for why.
First big change was "simply" a change in the curve in the inlet between the carburetor and the impeller.
A 90 degree bend right before the inlet is not a good idea but a more gentle radius (and a bigger cross section?) can make a large difference. Not only in airflow through the bend but in getting an even airflow hitting the impeller instead of more air hitting one side than the other.
SInce the inlet bend had been cast in one piece with the front supercharger cover getting different castings to try wasn't all that simple.
Picture of model

On the Merlin XX series engines (and 45s) it was like this

 

[pbehn]

Parmo-- same as our "Bromo-Selter" in The Colonies??

No, it is a local dish, and you are seriously pushing my buttons. Now start your thread, I suggest the following title. "Is the Kings Speech" the best source of information on the build up to WW2 because its the only thing I know". or "Are Hollywood dramas better than books as a source of information". Now get back on topic.

 

[Hansie Bloeckmann]

I don't think that you were involved in the ww2.
At any rate, you as a member of the board are very much allowed to start a thread.

Correct-I was born some years later- My main source of information came from the Allied side of things, with two uncles who flew in Combat, one in the PTO, and one in the ETO--I had no family that served in the ground forces. Thanks for the clarification, and just how does one start a thread here? Hansie

 

[Hansie Bloeckmann]

No, it is a local dish, and you are seriously pushing my buttons. Now start your thread, I suggest the following title. "Is the Kings Speech" the best source of information on the build up to WW2 because its the only thing I know". or "Are Hollywood dramas better than books as a source of information". Now get back on topic.

Thank you, and please forgive my "faux pas" regarding the Parmo- as that word has the number of letters as Bromo, I took a "WAG"- looks like I missed the mark. The only English dishes I have heard of, besides beef Wellington, are steak and kidney pie, and bangers and mash.

 

[tomo pauk]

Thanks for the clarification, and just how does one start a thread here? Hansie

Hit the 'Post new thread' button, you can see it when checking out the topics listed in a (sub-)forum. The button is roughly at top right.

 

[pbehn]

Thank you, and please forgive my "faux pas" regarding the Parmo- as that word has the number of letters as Bromo, I took a "WAG"- looks like I missed the mark. The only English dishes I have heard of, besides beef Wellington, are steak and kidney pie, and bangers and mash- all from movies. I haven't yet seen "The King's Speech" as of yet, shall remedy that deficit post haste.

Strange because it was not commonly known that Elizabeth called her husband Bertie until the film was shown I didn't know, you are educated by Hollywood. That whole post acts as a summary of the movie, the director would be proud.

 

[Peter Gunn]

I was looking over the P-51B performance data referenced in SR6's post earlier: P-51B Mustang
( Not that I'd obsess over a Mustang performance chart or anything... )

But about two thirds the way down in chart "C Cruise Data", there's this little gem:
RPM Hg. Mix Setting Mix Temp BHP True Speed MPH
2400 42.5 AR 45.5 937 349.0
2250 37.0 AL 38.5 763 624.0
1950 35.0 AL 26.5 650 302.0
Suck on THAT Me 262!

Utilizing P-39N logic, I have found the fastest piston engine fighter of WWII. Because there's NO WAY that's a typographical error...

I might be forced to continually cite this reference in future debates, which I categorically declare myself the winner of based on the data stated above. /sarc.

*edit* stupid editor messed up my formatting, sorry about that, it was supposed to be in a nice little table.

 

[Shortround6]

I think some of us need a Pimm's or two after that interchange

 

[wuzak]

Was just reading part of America's Hundred Thousand in the pilots' comments about the P-39.

It says:

A pilot report that in North Africa P-39s doing low level strafing missions were considered quite resistant to ground fire. However another said "In North Africa the German 109s shot them down almost at will."

The Russians liked the P-39 even though German fighters on the Eastern Front were reported to have picked them off with ease.

German pilots reported on the Russian front they knocked P-39s down almost at will, and in North Africa they reported they were always looking down at P-39s, which gave them no trouble.

 

[Peter Gunn]

Was just reading part of America's Hundred Thousand in the pilots' comments about the P-39.

It says:

A pilot report that in North Africa P-39s doing low level strafing missions were considered quite resistant to ground fire. However another said "In North Africa the German 109s shot them down almost at will."

The Russians liked the P-39 even though German fighters on the Eastern Front were reported to have picked them off with ease.

German pilots reported on the Russian front they knocked P-39s down almost at will, and in North Africa they reported they were always looking down at P-39s, which gave them no trouble.

But... but... HOW can that be SO? We have data that PROVES the P-39 was superior, especially in climb, to the the Fw-190!!!

 

[Shortround6]

But... but... HOW can that be SO? We have data that PROVES the P-39 was superior, especially in climb, to the the Fw-190!!!

Germans were using Bf-109s???