Advanced French Fighters vs 1942/1943 contemporaries (8 Viewers)

[Elan Vital]

@ThomasP Interesting, I plotted the figures for the V-1710s compared to the late 12Ys, this is the result:

The V-1710s soundly outperform the 12Y-51 with small H-S supercharger (the 12Y-51 with S-P supercharger should do better), especially past the critical altitude.

However, the 12Y-45 and -49 engines with S-P supercharger actually outperform the 12Y-51 with H-S supercharger at altitude and get much closer performance to the V-1710s at high and very low altitudes relative to their limited baseline output. In fact, the 12Y-49 which has a S-C tuned for higher altitude gets very close performance to the Allisons past 5500m. An hypothetical 12Y-51 with 12Y-49-style S-P supercharger might accordingly have somewhat greater output at high altitudes than the Allisons.

This would suggest that the swirl throttle S-P supercharger is somewhat beneficial compared to the Allison supercharger, especially when tuned for higher critical altitudes. The French may want to push and assist the Americans to integrate swirl throttles into the Allison supercharger, in which case the V-1710 would achieve a very useful superiority margin compared to the 12Y series.

But in turn, this means that Allison-powered French fighters like the VG 32 and 50 should perform better than most other French fighters, except 12Y-51-powered VG 36es if the latter possess S-P superchargers at higher altitudes. There is the caveat that the Allison installation is alleged to be longer on the VGs, which might reduce drag if exploited like the 12Z "long noses". Weight is increased, but the reduced drag might cancel that out, leaving a large increase in power.

 

[Steamed_Banana]

I don't think that there is anything to be explained there. The charts posted by him are in agreement with the data posted at Peril's site and other creditable websites, as well as in the book 'Vee's for victory'. A few HP down or up at a few feet up or down is nothing to loose sleep about.

Well, here's the thing. In this chart, it's clear that power starts falling off sharply for the V-1710-33 at a higher altitude than it does for the V-1710-39.

This is also shown, to varying degrees, in multiple other charts and period sources I've seen.

I initially ignored this more or less along the lines of "a few HP down or up a few feet".

But combat reports and commentary by pilots also support this. So I've come to around to believing the historical sources, which seem to also be reflected in the engineering specs, although I still don't understand precisely why the -33 would have a higher critical altitude. It seems to.

A fighter that has a limited altitude performance is a worse fighter than another fighter that has no such problems, or these problems are less acute. Accolade of being "a more effective fighter for the longer time than the Hurricane" is a damning with a faint praise.

This is one of those declarations based on technical specs which modern enthusiasts like us are wont to indulge in. I've noticed that the operational history tends to tell what you might call a competing story.

In theory, a MiG 3 or a Hawker Hurricane had much better altitude performance than a P-40. The P-39 and P-51A were much faster. And yet P-40s had a much better combat record. Not just in one place - In the Middle East, in North Africa and Sicily and Italy, in the South Pacific, in China and Burma and India. For many years. Even in the Aleutians. Russia is the exception of course for the P-39, but for reasons we are still trying to figure out. Some people would rather dismiss the history, for me, it's always worth considering. It's the reality check for what we think we understand about the technical specifications.

And to be clear, the Hurricane did have better altitude performance. The P-39 was faster. But other things seemed to ultimately matter more on the battlefield. Range for one. Roll rate. Dive speed and acceleration. Tropical fittings. Maybe other things we don't yet fully understand. Ultimately, if you had a choice to defend your island or your desert army or your jungle air base with 50 Hurricanes or 50 P-39s or 50 P-40s, the choice was pretty obvious.

It's the same for the F4F, or the Ki-43, or the A6M, or the D3A. Or the Ki-48. Or the Hawk 75. Or the A-20. Any number of aircraft which did better in reality than expected based on their stats and how many guns they had or how many bombs they carried. And many that were the opposite. The Typhoon looks so good on paper, but in reality, it fell short, in spite of it's mighty engine and performance. The Ki-49 looked like a big upgrade over the Ki-48, but it was a disaster. Same for the SM 84 compared to the SM 79. It was faster, more heavily armed, had more armor, better fuel tank protection. But it did terribly in combat, so badly they went back to the S.79.

Operational histories have their limitations as well. There are reasons on the battlefield - leadership, training, illness, logistics, field conditions, weather, mistakes or genius of the enemy - which can obscure the technical factors. But the paradox is that part of the technical merits of any war machine include it's adaptability to the real world, the real opponents they face, the real conditions they had to operate in. Sometimes these are not the traits we are looking at closely enough.

And while there is a lot of such noise, over time and multiple Theaters, it evens out.

P-40 was a fighter in the late 1940 (with weak firepower and no protection), and then in 1941-43. Comparison should've been made vs. the types entering the service in the same time. Also, for something to be really of note, comparison should include the best competition available, too.

Well, I agree of course. I think P-40 came up (I think?) because the French had them on order. If the war would have gone on, they would have been using some of the Tomahawks that ended up going to the British in North Africa and the Middle East. And then maybe Kittyhawks. Along with Hurricanes and Spitfires and everything else that worked that they could get their hands on.

Once with full firepower and protection, P-40 was indeed too heavy & draggy for the feeble horsepower available.
The US types of note were all with far better engines; even with similar engines, the P-39 and P-51 were faster than the P-40.

And yet, compare the P-39 combat outcomes in the South Pacific, or the (indeed, much faster) P-51 in Burma. or the Spitfire Mk V in the South Pacific and Burma. Even the P-38 and F4U in the South Pacific through 1943. It's now pretty clear that their record was equivalent or slightly worse than the P-40 and F4F against A6M and Ki-43-II etc. The only real advantage of the P-38 and F4U for the first year was 1) range, which did matter, and 2) ability to escort or intercept bombers at 20,000+ ft, which mattered as well but not as much because most bomber sorties at that altitude couldn't really cause much harm. And the lower altitude rated fighters could still intercept enemy bombers at high altitude (they couldn't really escort US heavy bombers though).

The real combat history, when you look at the data from both sides, tells us a different story than we were told and came to believe in the previous era.

As above - timing is crucial.
French and British will need something amazing for the more temperate climate, if not cold climate, with vast majority of air combat happening above NW Europe.

That's true, but they also clearly need aircraft for the battlefield if we are talking about a war continuing on the borders of France and Germany.

 

[Steamed_Banana]

This would suggest that the swirl throttle S-P supercharger is somewhat beneficial compared to the Allison supercharger, especially when tuned for higher critical altitudes. The French may want to push and assist the Americans to integrate swirl throttles into the Allison supercharger, in which case the V-1710 would achieve a very useful superiority margin compared to the 12Y series.

Now that is an interesting idea!

But in turn, this means that Allison-powered French fighters like the VG 32 and 50 should perform better than most other French fighters, except 12Y-51-powered VG 36es if the latter possess S-P superchargers at higher altitudes. There is the caveat that the Allison installation is alleged to be longer on the VGs, which might reduce drag if exploited like the 12Z "long noses". Weight is increased, but the reduced drag might cancel that out, leaving a large increase in power.

I know they were looking at adapting both Merlin and Allison engines for French fighters, but I always wondered about the weight. Why would drag be reduced?

 

[Elan Vital]

I know they were looking at adapting both Merlin and Allison engines for French fighters, but I always wondered about the weight. Why would drag be reduced?

From what has been said on the 12Z fighters with the longer reductor and accordingly longer nose, the longer and finer nose contributed to reduced drag.

Specifically, Cuny and Danel included that as one of the aerodynamic improvements envisioned for the D520 series, reducing the 100 Cx by 0.10.

 

[tomo pauk]

Wrt. the different flavor of the P-40 and V-1710, as well as their suitability and abilities, not just for this thread: I don't think that I have anything more to add, without becoming repetitive and tedious for the other forumites.

 

[ThomasP]

Hey Steamed_Banana,

re

And I note here once again that the military rating for the V-1710-33 is at a higher altitude (13,200') than the -39 (12,000'), in both cases at 3,000 rpm, and in both cases engine power falls of quickly after that altitude in full throttle. To me that says there is an engine issue here as well as airframe weight.

Possibly this will help explain what tomo pauk & Shortround6 have been saying up-thread.

These are the same charts I posted up-thread, but with the the altitude and manifold pressure ratings for 3 different outputs for each engine - 1150, 1090, 1040 BHP - in order to show what the performance differences are between the V-1710-33 and -39. Assuming the supercharger uses the same impeller, and no changes are made other than the impeller speed ratio (ie 8.77 to 8.80) the higher impeller speed will provide a higher rated altitude. These values are from various charts, but I checked out the math as well and it comes out to within +/-1% BHP , 0.2"Hg MAP, and 200 ft altitude, relative to the actual charts.

NOTE that each of the BHP outputs for the -39 occur at higher altitude than for the -33.

V-1710-33

V-1710-39

Basically, what these marked-up charts show is that the V-1710-39 could use 1090 BHP at 13,400 ft - or 200 ft higher than the -33, while the maximum output for the -39 was 1150 BHP at 12,000 ft. The unmarked-up charts apply specifically to the engines as they were rated per the dates on the charts, but the -33 was later rated for 1150 BHP at 11,800 ft. I do not know exactly what the specific parameters were that resulted in the different ratings, but Allison tried various modifications during the careers of the engines, including such things as adding/removing backfire screens of varying design, different valves and valve timing, at least one attempt at a different intake manifold design, at least one early-war increase in coolant volume flow, etc. (There was another increased coolant flow change made in late-1944 in an attempt to allow reliable cooling at over 1425 BHP, but that obviously does not apply here.)

In addition, the "AN-9531" (found next to "FUEL" in the title block) is the designation for the testing procedure used to find the 'lean mixture octane performance number' of the contemporary 100 octane fuel grade used in the engine power rating process. In the case of the 1939 dated chart for the -33 it is definitely pre-100/120 grade fuel, while the -39 may have been rated on 100/120 (if my information is correct the USAAF did not settle on 100/120 until late-1940 at the earliest). Higher grade fuels would allow higher manifold pressures and/or higher impeller speeds, either/both of which would allow higher altitudes and/or higher power ratings.

Make sense?

 

[Shortround6]

I will add or correct that
Higher grade fuels would allow higher manifold pressures and/or higher impeller speeds,
is a bit confusing.
Higher grade fuel will allow at the gear ratio/impeller speed used, higher power at lower altitudes. Which is where the WEP high powers come in.
Using a different gear ratio, like the 9.60 gears in the -81, -99, -115 engines changes the slope of the max power line.
The 9.60 gears also need more power to drive the impeller at any given air flow. At 9000lbs per hour the 9.60 gears need around 30-35hp more. The 9.60 gears will flow more air at any given engine rpm ant that is were the 1125hp at 15,500 rating comes from with the higher gears. It needs a whole new chart.

either/both of which would allow higher altitudes and/or higher power ratings.
Higher grade fuel with the same gear ratio allows for more pressure/power below the critical altitude (throttle is fully open to get that particular power level) by allowing the throttle to be fully opened at the lower altitude without wrecking the engine but does nothing at higher altitudes.
Changing the gear ratio (or adding 2nd stage) with the better fuel will allow higher pressures and increase power at both low and high altitudes but at the cost of higher intake temperatures and supercharger drive costs.

The 7.48 gears in the -87 engine in the A-36 used about 50hp less for the same 9000lb air flow and that was one way to help get the 1325hp for take-off rating.
It also gave the 1500hp at 5400ft at 52in compared to the 1490hp at 4300f at 56in WEP rating of the -39. Problem was that it no longer made 1150hp at 11,700ft.

I hope I have not confused things further.

 

[Steamed_Banana]

Wrt. the different flavor of the P-40 and V-1710, as well as their suitability and abilities, not just for this thread: I don't think that I have anything more to add, without becoming repetitive and tedious for the other forumites.

Sorry to belabour it, I don't mean to take the fun out of the discussion. I'm just a stickler for correcting what I perceive (correctly or otherwise) some of these embedded tropes.