Early Spitfire V combat boost?

[HoHun]

Hi everyone,

I'm looking for something definite on the boost level (and rpm) specified for the early Spitfire V.

I'm convinced that it was +12 lbs/sqin @ 3000 rpm, but I can't prove it wasn't (as suggested by someone else) +9 lbs/sqin at either 3000 or 2850 rpm.

The copy of the Pilot's Notes I've seen are of no help as they are referring to the "late" situation with +16/+18 lbs/sqin cleared.

I've also found Alfred Price quoting an Air Ministry memorandum from August 1942 pointing out that the conversion of Spitfire V aircraft for +16 lbs/sqin was in progress then, but no mention of the previous boost limit is made.

Do you know of any documentation proving (or disproving) my point about the +12 lbs/sqin @ 3000 rpm?

Thanks in advance! :-)

Regards,

Henning (HoHun)

[GScholz]

MiloMoron will be here in a flash to tell you it ran on +25 lbs and 9000 rpm and had a grater range than the P-51.

[Nashwan]

I'm convinced that it was +12 lbs/sqin @ 3000 rpm, but I can't prove it wasn't (as suggested by someone else) +9 lbs/sqin at either 3000 or 2850 rpm.

I've seen somewhere, though I can't put my finger on exactly where at the moment, that initial ratings were 3000 rpm 9lbs wep, 2850 rpm 9 lbs 30 minutes, 3000 rpm 12 lbs takeoff.

I'm pretty sure those were the figures to begin with.

I've also found Alfred Price quoting an Air Ministry memorandum from August 1942 pointing out that the conversion of Spitfire V aircraft for +16 lbs/sqin was in progress then, but no mention of the previous boost limit is made.

The limits before 16 lbs was approved were definately 3000 rpm 12 lbs, as noted in the trials against Faber's 190. I don't know when the change from 9 lbs to 12 lbs was approved, though.

[MiloMorai]

Originally posted by GScholz
MiloMoron will be here in a flash to tell you it ran on +25 lbs and 9000 rpm and had a grater range than the P-51.

LOL, what a first post in what would have been an intersting thread. Congratulations for being your usual ultra melon self, Col Klink's lap dog.
 
btw, a grater is something you use to grate cheese with.
..........


Henning, Nashwan or Mike Williams would be the best source.

[GScholz]

Ah, thank you for pointing that out. I strive to improve my spelling.

[HoHun]

Hi Nashwan,

>I've seen somewhere, though I can't put my finger on exactly where at the moment, that initial ratings were 3000 rpm 9lbs wep, 2850 rpm 9 lbs 30 minutes, 3000 rpm 12 lbs takeoff.

I figured that as with the Spitfire II, take-off figures would be cleared as WEP.

>The limits before 16 lbs was approved were definately 3000 rpm 12 lbs, as noted in the trials against Faber's 190.

That's interesting! Do you know where I could find these? Though Price' Spitfire book features the Spitfire Vb vs. Fw 190A-3 tactical trial, no boost pressure is given there.

I've found:

http://www.fourthfightergroup.com/eagles/aa878.html

This report describes that prior to +16 lbs/sqin, the combat rating was indeed +12 lbs/sqin.

However, it doesn't confirm that it was used from service introduction of the Spitfire V on.

Regards,

Henning (HoHun)

[Nashwan]

I figured that as with the Spitfire II, take-off figures would be cleared as WEP.

It does seem strange they went from 12 lbs on the Merlin III and XII to 9 lbs on the Merlin 45. The info I've seen might have been from before service introduction. It might simply have omitted the 12 lbs rating, as the issue of wep didn't seem clearly defined by the RAF at the time.

If you do find a definite date when it was cleared, I'd be very interested.

>The limits before 16 lbs was approved were definately 3000 rpm 12 lbs, as noted in the trials against Faber's 190.

That's interesting! Do you know where I could find these? Though Price' Spitfire book features the Spitfire Vb vs. Fw 190A-3 tactical trial, no boost pressure is given there.

Ring's site has details of the tactical trials of Faber's 190:

http://prodocs.netfirms.com/

Section D page 8 of the "Various Fw 190 test reports" has the ratings used for the test.

[gwshaw]

HoHun,

Look at this one on 4th Fighter Group:

http://www.fourthfightergroup.com/eagles/x4922.html

I has 3000 rpm +9 psi as the highest rating

This one as well:

http://www.fourthfightergroup.com/eagles/w3134.html

Greg Shaw

[Charge]

"It does seem strange they went from 12 lbs on the Merlin III and XII to 9 lbs on the Merlin 45."

Did the displacement change from III & XII to 45?

If it increased so I'd imagine it run on lower boost.

-C+

[VO101_Isegrim]

The Merlin III/XII is simply not the same engine series as the 45s. It`s quite believable that they had different max. allowed boosts cleared for them at the same time.

As the two early Spit V trials show, in the first year or so, the 45s appear to be limited to +9/3000rpm for level flight, and +9/2850rpm for climbs.

[Nashwan]

The displacement didn't change between the XII and 45, indeed I don't think it changed between the Merlin I and Merlin 145.

The Merlin 45 was essentially a Merlin XII with a different supercharger.

The problem with Isegrim's assertion is that he's basing it on tests of the Spit V, which were only carried out at 9 lbs, then at 16 lbs.

However, the Merlin XII in the Spit II was rated at 9 lbs, and tested at such, even though 12 lbs boost was definately authorised.

Early in the war, the Spitfire didn't really have a WEP setting, the max boost was 6.25 lbs for cruise or combat. With the introduction of 100 octane fuel, they allowed 12 lbs boost, but only in "emergencies". They did some tests of what improvements could be expected, but 12 lbs wasn't considered a "normal" rating.

WEP was not really standardised until later on.

The other thing that contradicts what Isegrim says is that there isn't a test for 12 lbs on the Spit V at all, yet it was definately authorised at some time.

In the test of 16 lbs WEP, they say that the prior limit was 12 lbs, and in the comparison tests against Faber's 190, they ran the Spit V at 12 lbs.

We know for a fact that 12 lbs was authorised at some time, yet no tests seem to exist for it, which points to it being authorised from the start. After all, when 16 lbs was authorised, they tested it.

the 45s appear to be limited to +9/3000rpm for level flight, and +9/2850rpm for climbs.

9 lbs 3000 rpm was a 5 minute rating, 9lbs 2850 rpm was a climb rating, not a max allowed for climbing, ie it was allowed for 30 mins or 1 hour, and compares to the German designation "climb and combat power"

[VO101_Isegrim]

The problem with Isegrim's assertion is that he's basing it on tests of the Spit V, which were only carried out at 9 lbs, then at 16 lbs.

You claim no +12lbs tests exist for the MkV? On what basis? Oh, it isn`t on the 4th FG website, I see, now THAT proves it.

Originally posted by Nashwan
However, the Merlin XII in the Spit II was rated at 9 lbs, and tested at such, even though 12 lbs boost was definately authorised.

Well let`s apply the same "definiete" logic to the DB 601N and E, since we know the 601N was rated at 1.35ata, we can definietely say the 601E, a different engine, was cleared for 1.35ata, too. After all, 1.4ata was already authorized on the 601A.

The typical silly strech-as-far-as-you-can story from Nashwan.

The other thing that contradicts what Isegrim says is that there isn't a test for 12 lbs on the Spit V at all, yet it was definately authorised at some time.

Contradicts? With what? With that :

"what Isegrim says is that there isn't a test for 12 lbs on the Spit V at all"

Well since Isegrim says that not, it`s only a classic strawman argument typical from Nashwan (not surprising), then we can only conclude Nashwan contradicts with himself (well that isn`t surprising either)

No +12lbs test at all? Maybe not on the 4th FG website, but that hardly proves anything. 4th FG hasn`t got the paper that shows no Spits had any armor fitted at the start of the Battle of France, yet we know such documents exist, and that`s the truth. 4th FG also shows figures for MkXIVs at +25lbs, a rating we all know was never cleared for them in service, because there are documents that show that, even though 4th FG website doesn`t show that either, for some odd reason.

We know for a fact that 12 lbs was authorised at some time, yet no tests seem to exist for it, which points to it being authorised from the start. After all, when 16 lbs was authorised, they tested it.

That`s a classic one.

No proof is proof enough for Nashwan when it comes to Spitfires.

9 lbs 3000 rpm was a 5 minute rating, 9lbs 2850 rpm was a climb rating, not a max allowed for climbing, ie it was allowed for 30 mins or 1 hour, and compares to the German designation "climb and combat power" [/B]

Source?

Apperatnly +9lbs and 3000 RPM could not be used below 22k ft in a climb at all.

http://www.fourthfightergroup.com/eagles/ab320.html

See the switch of RPM : "R.P.M. changed from 2850 to 3000 at 22,000 ft. "

The document states these are maximum climb figures, so I guess they were done at max. available settings.

[HoHun]

Hi Greg,

>I has 3000 rpm +9 psi as the highest rating

Thanks!

Unfortunately, I have to suspect that the tested power levels were not necessarily identical to the permitted operational power levels, with differences possible in both ways.

(For example, we know that the Spitfire I/II were cleared to +12 lbs/sqin combat boost, but the tests only show the original +9 lbs/sqin rating.)

I think the manuals would be a good guide if we had the contemporary issues. Of course, most manuals were carefully amended to keep them up to date, so today we mostly see latest developments fixed in print.

Regards,

Henning (HoHun)

[HoHun]

Hi Nashwan,

>We know for a fact that 12 lbs was authorised at some time, yet no tests seem to exist for it, which points to it being authorised from the start.

That's illogical, captain! ;-)

I'd agree that +12 lbs/sqin very likely was cleared from the beginning, but in my opinion, the absence of +12 lbs/sqin tests would point towards the opposite. (Due to the Spitfire II analogy, I don't consider that important.)

>9 lbs 3000 rpm was a 5 minute rating, 9lbs 2850 rpm was a climb rating, not a max allowed for climbing, ie it was allowed for 30 mins or 1 hour, and compares to the German designation "climb and combat power"

Hm, though I think you're right, that's another can of worms. We have

+9 lbs/2850 rpm (30 min)
+9 lbs/3000 rpm (in my opinion 30 min wartime concession, in your opinion 5 min)
+12 lbs/2850 rpm (could be deducted from comments on 3000 rpm only to be used at altitude)
+12 lbs/3000 rpm (5 min)

To make matters worse, some Spitfire tests refer to the highest setting as "flat-out level power", implying that it could (or should) not be used in a climb.

I'd tend to think that both 3000 rpm settings were the wartime Climb & Combat/Emergency power settings respectively and applicable in climbs as well as in level flight, but I have to admit that there's not enough data for absolute certainty :-(

Regards,

Henning (HoHun)

[Nashwan]

That's illogical, captain! ;-)

It might well be wrong, but my logic is that when they increased the rating from 12 lbs to 16 lbs, they tested it.

I haven't seen any tests of the Spit V at 12 lbs. Nor the Spit II.

They already knew how the Merlin III performed at 12 lbs, they simply based the Merlin XII figures on that, and, I think, did the same with the Merlin 45 as well.

If they had restricted 12 lbs on the Spit V to begin with, I think they'd have done tests to check it was okay when they finally allowed 12 lbs. Spitfire the History makes no mention of them.

If they allowed 12 lbs from the begining, there'd be no more need to test it than on the Spit II.

Hm, though I think you're right, that's another can of worms. We have

+9 lbs/2850 rpm (30 min)
+9 lbs/3000 rpm (in my opinion 30 min wartime concession, in your opinion 5 min)
+12 lbs/2850 rpm (could be deducted from comments on 3000 rpm only to be used at altitude)
+12 lbs/3000 rpm (5 min)

I think 3000 rpm was always rated for 5 mins, apart from on the Spit V in high alt climbs (and the same is true of the 109K4 climb chart, iirc, with a revs increase at 8,000m)

So, I doubt 12 lbs 2850 rpm was ever a valid rating on the Spit V.

You claim no +12lbs tests exist for the MkV? On what basis? Oh, it isn`t on the 4th FG website, I see, now THAT proves it

There's no mention in Spitfire the History either, that I can see.

Plenty of description of tests with modified ailerons, drop tanks, different exhausts, different temperatures, elevator bob weights, etc.

Of course, that doesn't mean such tests weren't done.

Well let`s apply the same "definiete" logic to the DB 601N and E, since we know the 601N was rated at 1.35ata, we can definietely say the 601E, a different engine, was cleared for 1.35ata, too. After all, 1.4ata was already authorized on the 601A.

The typical silly strech-as-far-as-you-can story from Nashwan.

We know the Merlin XII was authorised for 12 lbs boost because the manual says so.

Go to http://www.fourthfightergroup.com/eagles/spit2.html

and scroll down to the bottom. It clearly says combat limit 12 lbs.

Perhaps it's not such a silly stretch after all?

Contradicts? With what?

You claimed that because there was no test at 12 lbs, it was not authorised.

We know it was, yet there are no tests.

Abscence of a 12 lbs rating  on a particular test cannot be proof it was not allowed, even at that time. They may simply have tested at normal rated power, not wep. ie not used the "emergency" rating.

4th FG also shows figures for MkXIVs at +25lbs, a rating we all know was never cleared for them in service, because there are documents that show that,

Are there? I've never seen them. I've seen documents saying it is not yet cleared, but will be in the future. If you've found anything new in the meantime, I'd be glad to see it.

No proof is proof enough for Nashwan when it comes to Spitfires.

I didn't say it was proof, I said it points to.

We know 12lbs was allowed, and tested, in the Spit I. We know it was allowed in the Spit II, yet the performance test of the Spit II, carried out on the 27th September 1940, when 12 lbs boost was in widespread use, didn't include a trial at 12 lbs boost.

If they banned the use of 12 lbs in the Spit V, then I'd have thought they'd have wanted to test it before finally allowing it.

It's nothing like proof, as I said it points to it.

We do know, for certain, that the abscence of the use of 12 lbs on the Spit II test doesn't mean the Spit II couldn't use 12 lbs, though.

Source?

The Spit V manual.

See the switch of RPM :  "R.P.M. changed from 2850 to 3000 at 22,000 ft. "

See the Bf 109 k4 climb chart at 1.8 ata. There is a line showing a revs switch at 8,000m, and the "time to climb" line, which is at climb and combat power, reflects that change above 8,000m.

I believe we had a big argument about that before you finally accepted it

I'm not an engineer, so I don't know why rev increases were permitted during high altitude climbs, but it does seem to have had a valid reason on some 109s and Spits.

The document states these are maximum climb figures, so I guess they were done at max. available settings.

Note the test of AA878, where climbs were done at combat rating (16 lbs, 3000 rpm) and "Normal" rating, 9 lbs 2850 rpm.

http://www.fourthfightergroup.com/eagles/aa878.html

The Spit V manual I have says

Maximum climbing limit 2850 rpm +9 lbs