How good a plane was the P-40, really?

[PAT303]

I agree, I think those are 52 gallon drop tanks from P-40, or even bigger ones.

They are 62G P51 tanks by the looks of them, the Seafire photo you posted are P40 tanks.

 

[Wild_Bill_Kelso]

So did most other aircraft. Some had more problems than others. The Hurricane was marginal in speed compared to other allied fighters and that was before they hung the Vokes filter on it.
The Hurricane climbed better than P-40s, but thay may not show up as often. Some Japanese aircraft had trouble with cooling due to small openings in the cowl.
Hotter, thinner air is hotter, thinner air. It doesn't care who make the plane, It matters what the wing loading is and perhaps the boost being used by the engine. But the changes are are going to be percentages.

And we get to individual aircraft. P-40F & Ls never got Vokes filters. They also went through engines at a much higher rate than the P-40E/K/M/N did.
Part of the difference between the over cowl intake and carb intake being in radiator/oil cooler opening in the Merlin P-40s.
This is why the British gave the Americans 600 used Merlins as a source for rebuilds.
Maybe the P-40Fs should have gotten a better filter even at the cost of performance?
A slower plane that is flying is of more use than an plane waiting for a replacement engine (or crashed).

The largest performance differences are between the Merlin powered versions and all the others. The -81 engine difference made up some of the difference in altitude but only about 1/2

The P-40s, of all types, did use tropical filters. They were just smaller and lacked the huge carapace of the Vokes, and they could be cut out after takeoff so that you didn't lose power.

On the Allisons the intake being on top, instead of under the nose clearly helped. I don't know the details of the filter used with the F/L but they clearly worked.

The 600 extra engines, which is something we have discussed before, are just because Packard didn't make enough of the V-1650-1 and they didn't ship the usual number of replacement engines. The British, who ran the Desert Air Force, knew how important the merlin P-40s were, so they made sure there were enough spares to keep them operational. Trouble with the P-38s that were brought in meant they had to use them longer than they originally had intended.

The Vokes had a cutoff too but you were still carrying around this huge thing, with extra oil and other stuff, and even with the filter bypassed it apparently still constrained the airflow somewhat.

 

[Wild_Bill_Kelso]

This is the 52 gallon tank used frequently (though not exclusively) on P-40s, mounted on P-40s

here's one with 3 of them

 

[Wildcat]

PAT303 is correct. That Seafire photo shows a P-40 89-gallon drop tank acquired from the RAAF for use with the BPF.
See photos for comparison and read this Armoured Aircraft Carriers - noted about 3/4 of the way down the page.

 

[Wild_Bill_Kelso]

I'm more familiar with the 52 gallon used by the US tanks, my point is the first photo looks like those.

 

[Wild_Bill_Kelso]

Please forgive me as I lost track of who posted the link for this one, but this is pretty enlightening vis a vis Tropical filters:

Looks like the Tropical filter on the Spit V cost 16 mph, and the Vokes filter on the Hurricanes cost 20-25 mph.

The Allison engined P-40s were set up to use the filter only on takeoff. Same for the Bf 109F, which lost 15 mph due to the filter. This is all very good data.

 

[Wild_Bill_Kelso]

Looks like Vokes filter (I think?) is costing 20-25 mph

 

[Wild_Bill_Kelso]

This is with the improved filter, I gather

 

[Wild_Bill_Kelso]

So this is the original Darwin test. Looks like it was done with a Spit VC with a Merlin 45 and a Vokes air filter.

View Digital Image

recordsearch.naa.gov.au

View Digital Image

recordsearch.naa.gov.au

The test was all part of a long bureaucratic discussion and debate (you can page back and forth) on whether to make a new and lighter / less draggy filter for the Spitfire, since the Vokes filter cost it 20-25 mph in speed, which was particularly notable at lower altitude.

Some were arguing that Spit VC is a high altitude fighter meant to fight at up to 38,000 ft, others were pointing out that being 20-25 mph slower at 20,000 ft and less was a major problem, I would guess because so many of the combats in the Pacific Theater took place that low or considerably lower.

In the end it looks like they just decided to keep the Vokes.

 

[Greyman]

A&AEE has the Hurricane II losing 7 mph and 2,800 ft in full-throttle height when tropicalized.

These were two different aircraft, so not a perfect comparison. Also, the tropicalized aircraft was a IIa vs. the normal IIb tested, so the tropical conversion is probably a 9-8 mph loss.

I'm not sure what to make of the Australian 20-25 mph figure.

 

[PAT303]

I'm not sure what to make of the Australian 20-25 mph figure.

Running 9psi boost instead of 16?. I don't believe for a moment that the Volkes filter is as bad as it is made out to be, if you look at other aircraft like Beaufighter it only lost around 3-4mph when tropicalised, likewise UK MkV Trops only lost around 7-8mph, for the RAAF MkV's to lose 20-25mph there has to be more too it than just the filter.

 

[ThomasP]

I am not sure how this plays, but there were at least 3 different air filter set-ups used on the Spitfire/Seafire. The original Vokes, the Aboukir, and the 'Universal'.

The Vokes had no bypass for normal RAM, only the ability to intake from within the engine compartment through the filter with no RAM, or directly through the filter with significantly reduced or no RAM.

The Aboukir could intake from the engine compartment through the air filter with no RAM, or could bypass the filter and use normal(?) RAM.

The 'Universal' was used on all Spitfire after the Mk V (except maybe a few of the early Mk IX) and on the Seafires from the later Mk II(?) on. The 'Universal' had the ability to feed through the filter via the normal intake with reduced or no RAM, or bypass the filter and use normal(?) RAM.

The loss of speed for the Vokes came from both the lack of RAM and the large housing/installation drag.

The loss of speed for the Aboukir and for the 'Universal' came primarily from the small housing/installation drag.

I think.

 

[PAT303]

The MkV lost 20mph carrying a 90G drop tank, the Volkes didn't have that much drag

 

[WARSPITER]

The other effect of the Vokes was a decrease in RAM air for the supercharger. Performance testing showed an 8% drop
in efficiency.

 

[Wild_Bill_Kelso]

Running 9psi boost instead of 16?. I don't believe for a moment that the Volkes filter is as bad as it is made out to be, if you look at other aircraft like Beaufighter it only lost around 3-4mph when tropicalised, likewise UK MkV Trops only lost around 7-8mph, for the RAAF MkV's to lose 20-25mph there has to be more too it than just the filter.

They mention that in the correspondence in the very detailed report that I posted a link to

 

[Wild_Bill_Kelso]

I am not sure how this plays, but there were at least 3 different air filter set-ups used on the Spitfire/Seafire. The original Vokes, the Aboukir, and the 'Universal'.

The Vokes had no bypass for normal RAM, only the ability to intake from within the engine compartment through the filter with no RAM, or directly through the filter with significantly reduced or no RAM.

The Aboukir could intake from the engine compartment through the air filter with no RAM, or could bypass the filter and use normal(?) RAM.

The 'Universal' was used on all Spitfire after the Mk V (except maybe a few of the early Mk IX) and on the Seafires from the later Mk II(?) on. The 'Universal' had the ability to feed through the filter via the normal intake with reduced or no RAM, or bypass the filter and use normal(?) RAM.

The loss of speed for the Vokes came from both the lack of RAM and the large housing/installation drag.

The loss of speed for the Aboukir and for the 'Universal' came primarily from the small housing/installation drag.

I think.

Thanks, that explains a lot. Did they ever use the Universal Filer for the Hurricane?

 

[Wild_Bill_Kelso]

A couple of other key points from the report - they noted that they were getting an average of 50 hours of life out of the Spitfire engines, which is why they felt the urgent need to keep using the filters, whether Vokes or some other type. I guess this was specifically around Darwin which is a very dusty area. They also noted the major disadvantage of having the air intake on the bottom and that the (Allison) Kittyhawks had less problems simply because the intake was on top of the filter. They used a filter for them anyway but apparently figured out a 'cut-out' version pretty early on. They mentioned that the Bf 109F had a tropical filter which also had a cut-out. Sounds like this is eventually what they did for the Spit XIII and IX and later versions.

My question is where is the air intake for the DB 601? I know on Bf 109s the supercharger intake is on the side, but in engine diagrams and photos it looks like the air comes in from the bottom / back, was that just piped over to the side? Did they turn the supercharger?

 

[ThomasP]

re the early Bf109 air intake and filter

I believe that all of the air intakes for the [DB powered] Bf109 series were on the left side.
[edit: per Graugeist post#424, the Jumo powered 109s had the intake on the right side.]

I think this is the early Fieseler design of air filter on a Bf109E, but I am not 100% sure of the designation for either

plus a link to images of a few other early types, some of which appear to be field modifications.
"BF 109E-4 Air filter ( Fieseler type)"

There were other types of air filter arrangements not included in the above. Here is one type that seemed fairly common in NA.

 

[tomo pauk]

My question is where is the air intake for the DB 601? I know on Bf 109s the supercharger intake is on the side, but in engine diagrams and photos it looks like the air comes in from the bottom / back, was that just piped over to the side? Did they turn the supercharger?

View attachment 768010

Supercharger is 'within' the red ellipse.
(also - note the impeller blades)

 

[Shortround6]

Supercharger is 'within' the red ellipse.
(also - note the impeller blades)

Tomo has pointed out the actual supercharger intake. The 109 turned the air 90 degrees to enter the supercharger.

The Standard Merlin intakes turned the air about 90 degrees twice (180 degrees total) to enter the supercharger.
The Allison turned the air about 90 degrees twice. I don't know what the very long intake duct did to air. There are a several things that could be going on, depending on the exact changes in the dimensions of the duct.

A lot of the problems with British "filter" was that they hid a large oil tank inside the filter fairing and pushed the actual air filter (or intake) down into the airstream making the frontal area bigger.