Japanese Zero vs Spitfire vs FW 190

[stona]

The Australians were worried about engine wear caused by removing the Vokes filter. It does seem to have been effective. They were balancing this against a performance penalty, which was generally less on their service aircraft than feared, particularly at altitudes above 20000 ft where the Spitfire worked best.
Cheers
Steve

 

[pinsog]

So how serious do you gentlemen think the actual, real world performance hit on a Volkes filter equipped Spitfire was? 10mph? 15mph?

The test on post 204 says the P40E was faster from 0-16,000 and, even more surprising to me, could out accelerate the Spitfire. Wouldn't both of those indicate a pretty substantial decrease in the Spitfires performance?

Or was the P40E closer to the Spitfire below 16,000 than most people like to believe?

 

[Greyman]

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[Greyman]

So how serious do you gentlemen think the actual, real world performance hit on a Volkes filter equipped Spitfire was? 10mph? 15mph?

Data from a Spitfire Vc 'improvements' document. Figures are in reasonable agreement with Spitfire Vb testing of normal and tropical examples at the A&AEE (wwiiaircraftperformance.org)

Tropical Vc (6,883 lb) +9 and +16 boost
Normal Vc (6,737 lb ) +9 and +16 boost

The P40E / Kittyhawk I is generally shown to be about as fast (or slightly faster) as the normal Vc Spitfire at +9 in this graph up to about 15,000 feet.

 

[pinsog]

Good info. Thank you. Too bad they just couldn't keep the weight gain under control on the P40. Wouldn't a P40E be 1,000 to 1,500 pounds heavier than a Spitfire V?

 

[Greyman]

Good info. Thank you. Too bad they just couldn't keep the weight gain under control on the P40. Wouldn't a P40E be 1,000 to 1,500 pounds heavier than a Spitfire V?

8,475 lb is a good average number from what I've seen from various sources.

 

[pinsog]

And the SpitfireV coming in around 6,700. Amazing a P40E is even in the ballpark. Makes me wonder how it would have done if they could have kept the weight around 6,700.

 

[swampyankee]

You have two basic aspects of the filter to consider.
1, is it actually stopping the dirt from getting into the engine.
2. How much performance loss is there, which can also be broken down into two parts.
A. pressure loss before carburetor .
B. Aerodynamic drag caused by larger intake/fairing.

I have no idea how well the Vokes filter worked at keeping dirt out of the engine.

as far as pressure loss goes, hard to figure but a tropical trials aircraft in England managed to keep 9lbs boost while climbing (2850rpm) to 14,000ft at 196mph TAS and to 17,400ft in level flight at 354mph while an early MK V held 9lbs to 15,000ft while climbing and to 20,100ft without snowguard at 371mph and to 18,800ft with snowguard fitted at 365mph.
Different serial number aircraft with different engines. The engine/s should have been able to provide more boost at less than the full throttle heights. The snow guard only seem to make a difference in speed at over FTH.

In one of the posts above, (Japanese Zero vs Spitfire vs FW 190 | Page 11 | WW2Aircraft.net Forums it states that the Vokes filter cost something like 25 mph in top speed, or about 7%. This would be about a 2.5% power loss, or about 40 or 50 horsepower. This strikes me as a lot, although one would need a comparison with a different filtration system to be sure. What sort of filtration was used in, say, the P-40? Air filtration systems aren't trivial; one of the problems with the M1 tank was that the original air filtration system was not very good at keeping sand out of the engine; that part of the system was Chrysler's (later, that part of Chrysler was taken over by GD Land Systems), and it wasn't until GD took over that the air filter was sorted out.

 

[pinsog]

Someone smarter than me will reply soon, but I thought I read somewhere the P40E Allison air intake was up high out of the worst dust? Wasn't the Spitfire air intake down lower where dust was worst?

 

[Shortround6]

Good info. Thank you. Too bad they just couldn't keep the weight gain under control on the P40. Wouldn't a P40E be 1,000 to 1,500 pounds heavier than a Spitfire V?

What do you what to take out of the P-40?

It wasn't a matter of keeping the weight gain under control. It was a matter of meeting different requirements in the initial specifications: Spitfire I vs P-36.

Once you try to turn the P-36 into a P-40 you are faced with the inevitable weight gain unless you do something drastic. Like limit the P-40 to pair of .50 cal guns and 2-4 .30 cal guns or leave out the self sealing fuel tanks or accept a lower strength/load factor.

 

[wuzak]

Someone smarter than me will reply soon, but I thought I read somewhere the P40E Allison air intake was up high out of the worst dust? Wasn't the Spitfire air intake down lower where dust was worst?

Exactly that.

The P-40 (except the Merlin powered versions) had a top intake behind the spinner.

All Spitfires had intakes below the fuselage.

The Allison in the P-40 came with a downdraft carby, the Merlin (and Griffon) in the Spitfire had an updraft carby.

 

[Shortround6]

And the SpitfireV coming in around 6,700. Amazing a P40E is even in the ballpark. Makes me wonder how it would have done if they could have kept the weight around 6,700.

P-36C had a max gross weight for "safe flight" of 5840lbs, this meant no restrictions. The plane could be loaded to a heavier weight buthen had to flown under restrictions according to AIr Corps Circular 60-9

Now please note that at 5840lbs the tank behind the pilots seat was empty, there is only 105 US gallons of fuel on board. The oil tank is only part filled, 40 quarts, an additional 14 quarts are needed if the fuel tank is filled. Armament is one .50 cal gun with 200 rounds and three .30s with 500 rounds each. total weight of guns ammo 292lbs.
Now add 200lbs worth of cooling for the Allsion engine (the Allsion was lighter than the R-1830 which cancels out around another 90lbs.
Add armor, add self sealing tanks etc.

And BTW the P-40 no letter picked up a heavier wing (165lbs) heavier tail, heavier landing gear and so on. Early P-36s suffering from skin buckling over the landing gear and wing roots.

A P-40 No letter grossed 6800lbs and that is with just two .50s and two .30s, no protection and only 19 gallons in the rear tank.
P-40C went about 7600lbs without belly tank.

 

[pinsog]

Wing buckling obviously needs addressed, but did they over build the tail, landing gear etc? I know 6 50's and ammo were very heavy. If equipped with 2 30's and 2 20mm, could the P40 have been kept near the Spitfire on weight, or was it just impossible to do even with hindsight?

It is mind boggling to think that a Spitfire XIV weighed the same as a P40E.

 

[stona]

Someone smarter than me will reply soon, but I thought I read somewhere the P40E Allison air intake was up high out of the worst dust? Wasn't the Spitfire air intake down lower where dust was worst?

This is true, and the Australians commented on it.

Cheers

Steve

 

[stona]

In one of the posts above, (Japanese Zero vs Spitfire vs FW 190 | Page 11 | WW2Aircraft.net Forums it states that the Vokes filter cost something like 25 mph in top speed, or about 7%. This would be about a 2.5% power loss, or about 40 or 50 horsepower. This strikes me as a lot, although one would need a comparison with a different filtration system to be sure.

The British, specifically the RAE, told the Australians that the full tropicalisation of the Spitfire V would reduce the speed at 370 mph by 2%, that is by 8 mph. This did not agree with the Australians own rather unscientific tests which indicated a loss of speed in excess of 20 mph.
The Australians noted that at 330 mph the reduction in speed of their Beaufighters equipped with Vokes filters was just 3 mph.
Something did not add up, and the Australians embarked on a series of tests to establish whether fitting a copy of the temperate air intake could improve performance and whether the tropical filter was really necessary (they would tow aircraft to the end of runways to reduce the ingestion of dust for example).
As I have shown, the locally produced copy of the temperate intake/cowl didn't work well at all. In my experience the Australians are not people to be easily discouraged, but producing a suitable air intake locally proved much more difficult than had been assumed. The results were the reverse of those anticipated:

The Australians now came up with a plan B, even though the real performance loss with the Vokes filter was not really known.

When the Australians finally got a modified cowling to replace the Vokes filter to work the results were not what they had hoped for.

Now the Aussies really got their knickers in a twist and another debate started. The figure of 16 mph for the penalty incurred by the Vokes filter now appears from somewhere. Some obviously felt that fitting a temperate air intake to the original Supermarine design might give a better improvement than the locally produced copy.

Eventually the British replied.

The Australians had no real way of measuring the performance difference which is why all sorts of odd reports came back from operational units, hardly best qualified to make them. There was no RAE or A&AEE to which they could refer. A report like this is pretty meaningless:

It's really no more than pilots' impressions, helped by a stop watch

In the end the Australians did fit a temperate cowling to most if not all of their operational Spitfires. Whether the performance gain was 10 mph, 16 mph or more than 20 mph nobody can say for sure, because nobody ever measured it accurately and scientifically in Australia.
The 16 mph loss of maximum speed is, I think, the official British figure for the Merlin 45, as is the 12 mph loss for the 20,000ft max. weak cruising speed.

Cheers

Steve

 

[Shortround6]

I would note the the vokes filter may not have been the only difference.

From Spitfire Mk. VB (Tropical) AB.320
Spitfire Mk V Performance Testing

"This aircraft was fully tropicalised; this included an air cleaner installation whose fairing produced an external bulge beneath the nose, and tropical radiator and oil cooler installations. In addition various items of desert equipment were carried. Details of this equipment and of the weights and loadings will be issued in a separate report."

Bolding by me. IF tropical Spitfires were fitted with larger radiators and oil coolers than "standard" Spitfires then there is going to be additional drag even if such units fit in the original ducts/housings. There will be either more airflow or a larger pressure drop through the matrix or both.

Perhaps the 9lb restriction was due to inadequate cooling at higher boost levels?

 

[stona]

Bolding by me. IF tropical Spitfires were fitted with larger radiators and oil coolers than "standard" Spitfires then there is going to be additional drag even if such units fit in the original ducts/housings. There will be either more airflow or a larger pressure drop through the matrix or both.

They certainly had a slightly larger radiator, which is why the British included the third drawing, deeming it relevant.

I can't look it up now, but from memory the difference was really very small. There may have been changes to the internal ducting as well as the slight bulge in the fairing (hence the drawing), and the radiator flap actuator was certainly altered to allow the flap to open further.

Edgar Brookes wrote:

"The matrix, itself, had more honeycombs, and was physically larger, but a note, on the drawing, says that it was to be fully interchangeable with the standard Morris Radiators item, which sounds as though it was accommodated in the already-available space. In their listings, Vickers also give the frontal area, on all of the Vs, including the tropical version, as identical."

But this does not preclude a bulged fairing which would still attach in the same way to the aircraft underside. The fact that the British sent a drawing of the radiator fairing to the Australians certainly implies that there were some differences.

As for the oil cooler, I believe the unit was essentially the same, the tropical version having a 'flared' exit, meaning a larger outlet duct.

Cheers

Steve

 

[Shortround6]

Frontal area does not measure airflow or drag inside a duct.
The shape of a duct can also vary a bit without changing the frontal area.
Look at the lumps and bumps on top of Spitfire wings. Unless the top of the "bump" is higher than the thickest (highest) point of the wing it doesn't add to the frontal area although they can certainly add to the drag.

Perhaps the radiator only changed things a few mph or perhaps it didn't, just trying to figure out why there may have been a difference between the "tropical" aircraft and the normal ones aside from the Vokes filter if changing the Vokes equipped aircraft back to a standard inlet didn't restore full speed/performance.

 

[stona]

Frontal area does not measure airflow or drag inside a duct.
.

Indeed, and the radiator matrix was certainly larger, meaning that the ducting for the airflow through the radiator core may well have been different.

The Australians came up with a list of things to improve the performance of their Spitfires very similar to one I have seen in the UK, featuring everything from a streamlined mirror to filling and polishing that infamous double row of rivets along the wing leading edge.

Generally just improving the finish and fit of service aircraft could gain them anything up to 15 mph, which puts the loss due to the tropicalisation into some perspective.

The Australians even tried to polish their Spitfires, but one plaintive report from Townsville notes that they had only been polished to "a slight degree" as it had proved "impossible to obtain any wax or polishing compounds in this area."

Having seen the definitely non factory standard cars tear arsing up and down Townsville's sea front first hand I very much doubt that the same is true today

Cheers

Steve

 

[stona]

It seems that most of the Vcs operated by the Australians DID retain the Vokes filter.

In an article by Anthony Cooper, author of 'Darwin Spitfires' he writes:

"It is noteworthy that the standard VCT aircraft demonstrated a maximum speed of 316 knots at 22 500 feet in several separate tests - achieved once again at 3000 rpm and plus 9 pounds of boost. This was a much better performance than might have been expected, given the Vokes Filter's bad press, for it was only a little less than the 321 knots achieved by temperate-intake aircraft in the UK powered by the same Merlin 46.


In short, it appears that the adverse reputation of the Vokes Filter was greatly exaggerated! Under the pressure of further perceived performance shortfalls while chasing speedy Mitsubishi Ki.46 reconnaissance machines during the 1943 Darwin raids, the matter was revisited and comparative tests re-run, but these confirmed that the performance difference was less than 5 knots. A few of the re-engineered temperate air intake cowlings saw service with aircraft of 79 Squadron in New Guinea , but the bulk of the Mark VC fleet soldiered on to the end with its unsightly air filters doing the prosaic but necessary job for which they were designed."

His source for the 5 knot difference (316 and 321) is a signal from RAAF London to the Air Board of 26/12/42 (NAA A1196: 1/501/478. I'm not familiar with NAA filing).

The Australians jumped on the Vokes bandwagon, already up and running in the MTO. The performance deficit was not as large as suspected and it certainly wasn't entirely due to the filter.

This may be of interest.

http://www.darwinspitfires.com/index.php?page=performance-of-spitfire-vc-tropicalised-version-2

And, in the context of this thread:

http://www.darwinspitfires.com/index.php?page=spitfire-vc-versus-the-zero

Cheers

Steve