Author Topic: Spitfire I Speed  (Read 1662 times)

Offline Nashwan

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Spitfire I Speed
« on: July 17, 2004, 08:42:06 PM »
I just did a quick check of the Spit I at sea level, as AH II now models it with the correct 12 lbs boost used during the BoB.

However, the max speed I could get was 291 mph at sea level. I don't have the latest patch, and can't update at the moment, so I don't know wether this has been corrected yet, but it's not something I've seen mentioned.

The Spitfire II, which was almost identical to the Spit I, except having an engine tuned for higher altitude, did 290 mph at sea level at 9 lbs boost.

The Spit I, because of the engine, should have done slightly better than the Spit II at low altitudes at the same boost. At 12 lbs, it should perform much better.

When switching over from 6.25 lbs on 87 octane fuel, to 12 lbs on 100 octane fuel, the Spitfire gained around 28 mph at sea level.  See the docs on MW's Spit  site http://www.fourthfightergroup.com/eagles/spit1.html

In AH II, the Spit I going from military 2850 rpm, 6.25 lbs to wep 3000 rpm 12 lbs gains only 12 mph.

The Spitfire I should do between 305 and 310 mph at sea level, as such it's about 15 mph too slow.

Offline VO101_Isegrim

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Spitfire I Speed
« Reply #1 on: July 18, 2004, 08:02:03 AM »
Your figures don`t take into account the weight and bulk of additional equipment that was put onto the Spit`s during which +12 lbs was authorized in a limited scale.

These included adding of rear armor, front armor glass (-6 mph), adding of IFF aerials (-2mph) etc.

Also the Spit II`s engine was noticably more powerful than that of the Spit I`s.

Spitfire VB. W3134 did 291 mph at SL at +9 lbs, which means it had apprx. the same or even more power than the Spit I at +12 lbs. So I think AH2`s speed values are very generous, considering they model the latest and rarest variant of Spit I and not that one that did most of the fighting in `39-40.

Offline Nashwan

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« Reply #2 on: July 18, 2004, 08:53:41 AM »
Quote
Your figures don`t take into account the weight and bulk of additional equipment that was put onto the Spit`s during which +12 lbs was authorized in a limited scale.

These included adding of rear armor, front armor glass (-6 mph), adding of IFF aerials (-2mph) etc.


Yes, that is taken into account.

Note the Spit II test: http://www.fourthfightergroup.com/eagles/spit2.html

Quote
This aeroplane was fitted with a bullet-proof windscreen, armour plating over the petrol tank and externally, apart from the radiator, was similar to the Rotol Spitfire I, N.3171, previously tested at this establishment.


What it doesn't take into account is the speed increase from removing the mirror, which AH doesn't model.

Quote
Also the Spit II`s engine was noticably more powerful than that of the Spit I`s.


The Merlin XII was less powerful than the Merlin III below critical altitude, but had a higher critical altitude, when run at the same boost.

The Spitfire II tested at 9 lbs boost did 290 mph at sea level. The Spit I at 9 lbs would have been slightly faster, the Spit I at 12 lbs would have been considerably faster.

Quote
Spitfire VB. W3134 did 291 mph at SL at +9 lbs, which means it had apprx. the same or even more power than the Spit I at +12 lbs.


What sort of circular logic is that?

Because you don't know the performance figure of the Spit I, it had to have less power than the Spit II?

Neil Sterling posted the power figures from AIR 16/328 some time ago.

Merlin III

6.25lbs boost
875hp at SL
1025hp at 16250ft.

12lbs boost
1190hp at SL
1305hp at 9000ft


Merlin XII

9lbs boost
990hp at SL
1150hp at 14500ft

12lbs boost
1170hp at SL
1300hp at 10750ft

As you can see, at the same boost levels the Merlin III, as fitted to the Spit I, had slightly more power than the Merlin XII fitted to the Spit II.

The Spit II did 290 mph at sea level with 990 hp. The AH Spit I does 291 mph with 1190 hp.
 
Quote
So I think AH2`s speed values are very generous, considering they model the latest and rarest variant of Spit I and not that one that did most of the fighting in `39-40.


The Spitfire did very little fighting in 1939. In 1940, the vast majority of it's fighting was done with 100 octane fuel.

According to Wood and Dempster, Fghter Command used 22,000 tons of 100 octane 10th July to 10th October.

That's something over 6300 Spit or Hurri sorties per week, the average number of combat sorties was something under 4000 per week.

The fact remains, the Spit I should go from approx 280 mph at sea level at 6.25 lbs to 305 - 310 mph at sea level on 12 lbs. It only manages 291 mph.
« Last Edit: July 18, 2004, 08:56:01 AM by Nashwan »

Offline Wotan

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« Reply #3 on: July 18, 2004, 09:42:08 AM »
Just for comparisons sake the 109E-4 in AH:

109E-4 100% fuel 2 x 20mm / MGFF 60 RPG, fuel mod set to lowest value.

SL

Military Power – SL 37.6 MP @ 2400 RPM = 285 MPH

Emergency Power – SL 40.5 MP @ 2400 RPM = 292 MPH

5k

Military Power – 5000 FT 37.6 MP @ 2400 RPM = 304 MPH

Emergency Power – 5000FT 40.5 MP @ 2400 RPM = 311 MPH

10K

Military Power – 10000 FT 37.6 MP @ 2400 RPM = 323 MPH

Emergency Power – 10000 FT 40.5 MP @ 2400 RPM = 330 MPH

15K

Military Power – 15000 FT 37.6 MP @ 2400 RPM = 341 MPH

Emergency Power – 15000 FT 40.5 MP @ 2400 RPM = 344 MPH

MP falls off drastically at 20k. WEP adds no MP boost but the E-4 gains about 3 mph.

20K

Military Power – 20000 FT 32 MP @ 2400 RPM = 329 MPH

Emergency Power – 20000 FT 32 MP @ 2400 RPM = 332 MPH

22.5K

Military Power – 22500 FT 28.5 MP @ 2400 RPM = 320 MPH

Emergency Power – 22500 FT 28.5 MP @ 2400 RPM = 323 MPH

Here's the most "prolific" DB601A numbers I have found:

DB601A-1

SL@1100PS@2400rpm@1.40ata (1' minute)
SL@990PS@2400rpm@1.30ata (5' minutes)
SL@910PS@2300rpm@1.23ata (30' minutes)
SL@810PS@2200rpm@1.15ata

4.5km@1020PS@2400rpm@1.30ata (5' minutes)
5.0km@960PS@2400rpm@1.23ata (30' minutes)
5.7km@890PS@2400rpm@1.15ata

4.9km@860PS@2200rpm@1.15ata
5.5km@800PS@2200rpm@1.10ata

10km@500PS@2400rpm@0.70ata

FYI DB601N numbers

DB601N
SL@1175PS@2600rpm@1.35ata (5 minutes)

SL@1020PS@2400rpm@1.25ata (30 minutes)

SL@910PS@2300rpm@1.15ata

5.5km@1190PS@2600rpm@1.35ata (5 minutes)

5.4km@1060PS@2400rpm@1.25ata (30 minutes)

6.1km@970PS@2300rpm@1.15ata

(times according to the original 109T-2 manual)


As you see the AH2 109E-4 runs at 1.40ata (40.5mp; 1 min limit) for 5 min.

As such Max continous is at 1.3ata (37.6mp) in AH2 which should be the 5 min limit.

Offline VO101_Isegrim

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« Reply #4 on: July 18, 2004, 11:16:31 AM »
Quote


Originally posted by Nashwan
Yes, that is taken into account.

Note the Spit II test: http://www.fourthfightergroup.com/eagles/spit2.html

What it doesn't take into account is the speed increase from removing the mirror, which AH doesn't model.


Nope, despite you want to make it look like. The desription does not mentions the mounting of IFF aerials, so by all likelyhood they were not present. It doesn`t mention what type of windscreen is fitted, by all likelyhood it`s an internal windscreen.

As for the removed rear view mirror, I haven`t seen too many Spits without it. That mirror was basically the only way to see backwards from the Spit, without it, it was possibly the blindest fighter to rear ever.


Anyway, by what weird logic you want to use base the Spitfire I`s speed on the Spitfire II`s? Different planes, different engines, haven`t you notice...?



Quote

The Merlin XII was less powerful than the Merlin III below critical altitude, but had a higher critical altitude, when run at the same boost.


That the report you are basing your claim on says the exact opposite than you. To quote :

4.0 Level Speeds.

.......The top speed of this aeroplane is the same as that of N.3171 but is reached at 17,600 feet, 1400 feet lower than the Mk.I Spitfire. Consequent upon this and the increase in power of the Merlin XII over the Merlin III below full throttle height the aeroplane is about 6 - 7 miles per hour faster at heights less than 17,000 feet and about 4 - 8 m.p.h. slower at heights above 20,000 feet. It should be noted that though the boost pressure on the Merlin XII is +9 lb. per sq.inch as against +6 1/4 lb. per sq.inch on the Merlin III there is little difference in the engine power at heights of 16,000 feet and above.


It says :

- the XII is more powerful below FTH than the III (exact opposite what you claim)
- the Mk II Spit is 6-7mph faster below FTH (exact opposite what you claim)


Frankly we have seen quite too many examples of you overexxegaration the Spit`s performance in every possible way. So, as long as you don`t provide credible evidence of what you say (you may start with engine charts for the Merlin III and XII), I won`t, and I doubt anybody will accept your claims here. They are far too much unsupported.



Quote

The Spitfire II tested at 9 lbs boost did 290 mph at sea level. The Spit I at 9 lbs would have been slightly faster, the Spit I at 12 lbs would have been considerably faster.


Yes that`s the mantra and the claim. And where`s the Spit I flight test at +12 lbs...?

No-where.



Quote

The Spitfire did very little fighting in 1939. In 1940, the vast majority of it's fighting was done with 100 octane fuel.


Wishful thinking as always.
To start with, +12 lbs wasn`t approved until late March 1940. Modifications need to use it took place at a slow pace, with only every 4th fighter having the ability to use 100 octane fuel... "vast majority" you say. :rolleyes:

Then also there`s Dowding`s restriction laid down upon the use of +12lbs as it wore down engines quickly, August :

http://www.fourthfightergroup.com/eagles/dowding1.jpg
http://www.fourthfightergroup.com/eagles/dowding2.jpg

Probably it has to do something that they couldn`t secure a solid import of 100 octane at that time anyway...

Appearantly, the RAF could not convert all of it`s fighter to 100 octane until NOVEMBER 1940, by the time the BoB already ended (by British standards).

So as opposed to your claim that the Spits did their 'vast majority' of combat on +12lbs, the truth is that it wasn`t until the last two months of the year they were all capable to use it, even if there was enough fuel for that.  In other words, the use of +12 lbs didn`t came into real widespread use until 1941.


Quote

According to Wood and Dempster, Fghter Command used 22,000 tons of 100 octane 10th July to 10th October.



22 000 tons for 3 entire months of heavy fighting? That`s a ridiculus amount, Nashwan, only 7000t per month.

Quote

That's something over 6300 Spit or Hurri sorties per week, the average number of combat sorties was something under 4000 per week.


LOL, stretching it far out as possible, isn`t it? Yo overblown it, m8.

If your numbers were correct, the RAF would have flown 6000+ sorties per week. You admitted that in fact they never flown more than 4000 sorties.

So even your own manipulative numbers show that you are 50% overstreched the possible sorties that could be flown, even if all sorties were flown on 100 grade fuel, which was far from reality.

Here`s a relevant qoute Pips found at the Australian War Memorial Archives :


"The first bulk shipment of 100 octane fuel had arrived in Britain in June 1939 from the Esso refinery in Aruba. This and subsequent tanker shipments from Aruba, Curacao and the USA were stockpiled while the RAF continued to operate on 87 octane petrol. Having secured what were considered reasonably sufficient quantities of 100 octane, Fighter Command began converting its engines to this standard in March 1940, allowing boost (manifold) pressures to be raised without the risk of detonation in the cylinders. This initial increase in maximum boost from 6 lb to 9 lb delivered a useful power growth of around 130hp at the rated altitude.

By the time of the invasion of the Low Countries by Germany in May 1940 the RAF had converted approximately 25 % of it's total fighter force to 100 octane fuel use. The subsequent escalation in air activity and demands placed upon Fighter Command over the next two months put great strain on both the 100 octane fuel stockpiles and aircraft modified to use the fuel. Against the backdrop of total war the RAF found that it's reserves of 100 octane fuel was well below the level considered necessary for widespread use, for any sustained length of time.

Two actions were immediately undertaken by the British War Cabinet in May to resolve the looming crisis. Firstly 87 octane fuel was deemed the primary fuel source to be used until further supplies could be discovered and delivered in sufficient quantities to allow the Merlin conversions to again take place. Those existing fighters already so converted (approximately 125) would continue to use what supplies of 100 octane were available, but all other fighters that had not been modified to continue with the use of 87 octane (of which there was more than adequate supply). The second action was for the British Government to contract the Shell Oil Refining Company to assist the British-controlled Iraqi Petroleum Company at Kirkuk to produce 100 octane fuel. This arrangement proved quite successful as production was quickly converted to 100 octane fuel.

The first Middle East shipment of 100 octane fuel arrived in Portsmouth on 12th August, with a further two deliveries in September and four in October. Although too late to allow widespread conversion for the use of the fuel the deliveries did ensure that from this point on Britain would not be lacking in 100 octane fuel levels. With the newfound supply RAF Fighter Command again embarked upon a Merlin II and III conversion to 100 octane use from late September, finally achieving 100% conversion of it's fighter force by the end of November in 1940.



Speaks for itself. And appearantly this is from an report, from an expert, and not some notoriously biased Spit-fan`s claims on the events.



Quote

The fact remains, the Spit I should go from approx 280 mph at sea level at 6.25 lbs to 305 - 310 mph at sea level on 12 lbs. It only manages 291 mph.


It`s not a fact, my dear, far from it. In fact, it borders manipulation -  just merely another step in the campaign of a spitdweeb who would like to be modelled vastly better than it really was.

310 mph at SL is a wet dream, nothing more. Good luck convincing anybody about your 'facts' without backing them up with real facts.

Offline Neil Stirling

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Merlin II and III +12lb boost.
« Reply #5 on: July 18, 2004, 11:26:50 AM »
The Defiant Mk1 K-8620 went from 303 mph at 16,600ft and 247mph at 1000ft when using +6lbs boost to 303mph at 16,600ft , 312mph ( +33mph) at 10,000ft and 280mph (+33mph) at 1000ft when using +12lbs boost. AVIA 18/689.

Hurricane 1 L1717 went from 294mph at 10,000ft and 273mph at 5000 ft when using +6lbs to 323mph (+29mph) at 10,000ft and 304 (+31mph) mph at 5000ft when using +12lbs boost. AVIA 8/434.

Spitfire at War 3 by Dr A Price states that a Spitfire 1 using +12lbs, would have an increase in speed of 25mph at sl and 34mph at 10,000ft.

The fuel situation.

http://hometown.aol.co.uk/JStirlingBomber/100+grade+fuel.jpg

>In article , Lawrence Dillard
> writes
>>Done. Now, with respect, I suggest that you read "I Kept No Diary" by RAF
>>Air Commodore FR (Rod) Banks, 1978.
 
I have actually read this book, and Banks is wrong when he states that
- "...100 octane became available to Fighter Command ready for the
Battle of Britain through Roosevelt's "cash and carry" compromise."
 
In fact Britain had been importing 100-octane from three seperate
sources, Shell, Standard Oil and Trinidad Leaseholds, and only
Standard Oil importation was affected by the embargoes involved in
pre-war Neutrality Acts as the others were not US companies and did
not export 100-octane spitit from US terrirtory.  100-octane supply
began in 1937 to selected airfields for trials and was then withdrawn
to build up a large (400,000 ton) reserve stock.  I'm read the
official records and even the damn Air Ministry purchase contracts,
something I suspect nobody else commenting on this issue has.
 
When it comes to the BoB, the British imported as much as Fighter
Command used in July - October 1940 from BP in Abadan alone.  Banks
worked for the British Eythyl Corp, a subsidiary of ICI and Eythyl
Export importing tetra-eythyl lead for the Air Ministry, and was
clearly not a party to 100-octane supply policy as a whole.  He
confuses Standard Oil's 100-octane supply to the Air Ministry with the
totality of supply, and is unaware of pre-1939 importation despite the
fact that 100-octane had been delivered in barrels by rail to selected
RAF bases as early as May 1937.
 
>The question is more of where the fuel came from. I haven't got an
>accurate breakdown but I understand 100 octane fuel from several
>sources:
>
>1) British refineries
>2) Dutch Shell refineries (in the US) handed over to British control
>3) US refineries
>4) Refineries in the Caribbean (not sure about this?)
>
>Obviously a lot of it came across the Atlantic (possibly in US tankers),
>but that doesn't necessarily make it supplied by the US.
 
Here is an extract from a presentation I made on the subject at the
Transatlantic Studies Conference, Dundee in July 2002.
 
"It has often been asserted that the supply of high-octane aviation
fuel was an operationally-significant factor attributable to American
supply in the Battle of Britain [22].  This rests on two largely
unsubstantiated foundations - firstly, the operational impact of
100-octane fuel to fighter operations, and secondly the paramount
importance of American supply of this fuel.
 
100-octane fuel allowed aircraft engines to exceed their normal
supercharging limits at lower altitudes.  This provided higher power
output with a consequent improvement in performance, without the
premature detonation that would result from doing this with lower
octane value fuel.  However, the constraints involved in this facility
are never fully articulated.  In fact, exceeding normal supercharger
boost was only permitted for a maximum of five minutes, and the engine
power settings involved in most operational sorties were identical to
those obtained on lower-octane fuel.  The level of benefit gained from
increasing supercharger pressures decreased with height, declining to
no additional benefit at or above the full-throttle height of the
engine [23].  Nevertheless, the use of this fuel did confer a real, if
often overstated, operational advantage in terms of speed and rate of
climb at lower altitudes.
 
A larger problem comes with the assertion that high-octane fuel was
exclusively attributable to American supply.  100-octane fuel was
developed in the mid-30's in the U.S., firstly by Shell and then
Standard Oil, in response to a USAAC requirement [24].  However
British purchasing of this fuel began in March 1937, from three
sources, while the Hartley committee was formed to steer the
development of production expansion for the RAF.  100-octane fuel was
also produced within Britain [25].
 
100-octane fuel was made by blending additives (iso-octanes) with
lower-octane feedstock and tetra-ethyl lead.  Iso-octanes were
originally manufactured by a process of hydrogenation, pioneered by
Shell and copied by Standard Oil in the United States.  Almost all of
the British supply of 100-octane fuel in the period up to 1940 was
dependent upon this process, but the massive expansion of high-octane
fuel production which followed was contingent upon the development of
iso-octane production by another process (alkylation).  This was
discovered by British Petroleum in Britain in 1937.  BP production of
100-octane fuel using this process began at Abadan in Iraq in 1940,
and in that year sufficient 100-octane fuel was delivered from this
source alone to replace that issued to Fighter Command during the
critical period of the Battle of Britain [26].
 
The procurement of 100-octane fuel for RAF use involved the use of
several sources of supply, and was not contingent upon supply from the
United States in isolation, as Table 2 indicates.  
 
Table2.  100 Octane fuel production:  current production estimates
exclusive of American domestic production, November 1940.  From PRO
AIR 19/254 - 23A
 
Plant Production (tons per annum)
Heysham, UK 150,000
Billingham, UK 15,000
Stanlow, UK 55,000
Abadan 50,000
Trinidad 80,000
Palembang, Dutch East Indies 50,000
Pladejoe, Dutch East Indies 50,000
Aruba, Dutch West Indies 50,000
 
After early 1941, to economise on tanker shipping tonnage and take
advantage of lend-lease supply, a deliberate policy decision was made
to favour "short-haul" supply across the Atlantic instead of the
longer routes associated with sources of supply in the Dutch East
Indies and Persia.  Nevertheless, this indicates a more complex
historical picture regarding the supply of 100-octane fuel than is
admitted in most accounts.  The availability of 100-octane fuel for
the RAF in the Battle of Britain was contingent upon a variety of
sources of supply, and the procurement process involved originated in
pre-war rearmament policy, not in the emergency measures of 1940[27]."
 
Footnotes:
 
22 "..a contribution of profound significance to the operational
success [of British fighters]", Richard P. Hallion, "The American
Perspective", in Paul Addison and Jeremy A. Crang (eds), The Burning
Blue.  A New History of the Battle of Britain (Pimlico, London 2000),
p. 84.  Hallion's appreciation is derived from Richard Hough and
Denis Richards, The Battle of Britain (Hodder & Stoughton, London
1989) Appendix XII, p.387.  Deighton emphasises similarly the
performance benefits, Blood Tears and Folly, p.352.
 
23 Approximately 18,000 feet for the Merlin III engined used in
the Spitfire I and Hurricane I in use in the Battle of Britain.
 
24 For the evolution of 100-octane fuel for the USAAC, Lowell
Thomas & Edward Jablonski, Bomber Commander.  The Life of James H.
Doolittle (Sidgwick & Jackson, London 1977), p.136-142 and Kendall
Beaton, Enterprise in Oil.  A History of Shell in the United States,
(New York, 1957), p.535 and p.561-569.  For the evolution of BP
production, J. H. Bamberg, The History of the British Petroleum
Company, Vol.2.  The Anglo-Iranian Years, 1928-1954 (Cambridge
University Press, 1994), p.199-218, and for Shell, George P. Kerr,
Time's Forelock.  A Record of Shell's Contribution to Aviation in the
Second World War (Shell, London 1948), p.36-59.  An overview is in D.
J. Payton-Smith, Oil - A Study of War-time Policy and Administration
(HMSO, 1971), p.55 and p.260-279.
 
25 Air Ministry importation of 100 octane was established in 1937
at 17,000 tons per year from Trinidad Leaseholds, 32,000 tons from
Shell and 25,000 tons from Standard Oil (New Jersey).  Payton-Smith,
Oil, p.55.  These quantities were doubled after Munich.  Domestic
production was in progress at Billingham and Stanlow, with a further
plant planned at Heysham.
 
26 By 11th July 1940 the RAF had 343,000 tons of 100 octane in
store, and the rate of importation was such that stocks rose to
424,000 tons by 10th October, 1940 after 22,000 tons had been issued
during the Battle.  Derek Wood and Derek Dempster, The Narrow Margin.
The Battle of Britain and the Rise of Air Power 1930-1940 (Hutchinson,
London 1967.  First published  1961), p.101-102.  Importation from BP
at Abadan alone was sufficient to meet this consumption.  Bamberg, The
History of the British Petroleum Company, p.244
 
27 100 octane was delivered to selected airfields and used in
trials from 1937, with priority going to those where Spitfires and
Hurricanes were to be based.  PRO AIR 2/3424.  A date was set by the
Air Ministry in April 1939 for introduction into RAF service in
September 1940 after a sufficient stockpile had been accumulated.  In
the event this was accelerated due to events in 1940.  PRO AIR 2/3531
- 3A.

Neil.
« Last Edit: July 18, 2004, 11:34:40 AM by Neil Stirling »

Offline VO101_Isegrim

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« Reply #6 on: July 18, 2004, 11:42:11 AM »
Neil, do you happen to have a simple document simply showing the amount of 87 and 100 octane fuel consumed by RAF fighters by month in 1940?

That would very much solve all interpretation problems.

Personally, I believe that from the roughly 25% usage of 100 octane as in May 1940, it probably increased to an avarage of 50% during the BoB, and the complete switchover happened in the very end of 1940.

At least, there`s absolutely no written and credible indication that 100 octane was anywhere near as widespread as Nashwan suggest (he had similiar suggestions about 150 grade fuel, which had been also proven incorrect).

In regards the 310 mph@SL claim, I find it deeply puzzling that then why did the RAF need to introduce the Mk V. at all, when it would be 20 mph slower than the allegadly 310mph Spit I at SL, in it`s initial +9lbs form..?

Offline HoHun

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Re: Spitfire I Speed
« Reply #7 on: July 18, 2004, 02:26:20 PM »
Hi Nashwan,

>The Spitfire I should do between 305 and 310 mph at sea level, as such it's about 15 mph too slow.

Here's my calculation, based on the data on MW's site.

http://www.x-plane.org/users/hohun/spit_vs_me109_speed.gif

I get 303 mph @ sea level, confirmung your estimate.

Regards,

Henning (HoHun)

Offline Neil Stirling

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« Reply #8 on: July 18, 2004, 03:51:14 PM »
No document at present Adam, however the I feel the need  visit to the NA shortly.

"In regards the 310 mph@SL claim, I find it deeply puzzling that then why did the RAF need to introduce the Mk V. at all, when it would be 20 mph slower than the allegadly 310mph Spit I at SL, in it`s initial +9lbs form..?"

The Merlin 45 fitted to the Spitfire MkV could maintain +9lbs to about 20,000ft, the Merlin III could only manage +6lbs to about 16,000ft. Height was the key at this stage of the war, I wonder how many Battle of Britain combats were fought below 15,000ft and in particular below 10,000ft ?

Neil.
« Last Edit: July 18, 2004, 03:56:07 PM by Neil Stirling »

Offline hawker238

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« Reply #9 on: July 18, 2004, 08:40:00 PM »
This is just me, but I'd let it go.

Offline Wotan

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« Reply #10 on: July 19, 2004, 04:44:15 AM »
Hohun,

I have some question about the 109E curves on your chart. The AH E-4 doesnt match your curve at all.  I will start another thread so this one doesnt get hijacked.

Offline mw

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« Reply #11 on: July 19, 2004, 11:38:58 AM »
Hi Nashwan:

“AH II now models it with the correct 12 lbs boost”.  Are you just referring to the boost gauge?

Check the FTH.  That will tell the story.  If its around 18,000 ft, which I expect it is, the FM would not reflect +12 boost.  

AAEE Trials of Spitfire I R.6774 with Merlin III running at +6.25 lbs./sq.in., DH CS airscrew, external bullet proof windscreen and armour plating over the tank gave 288 mph at SL.

Sea level horsepower for the early Merlins III, XII and 45 at +12 lbs/sq.in. is very close:

Merlin III
SL 1190

Merlin XII
SL 1170 (1175 at +12.5 for takeoff)

Merlin 45
SL 1185

See Merlin Engine Chart

This chart shows a Spit V with Merlin 45 at +12 lbs/sq.in. boost achieving 311 mph at SL. The Spit I with Merlin III running at +12 had a tad more HP at SL and a bit less drag, therefore your estimate of 305 to 310 is good.  

I concur with your assessment that 291 at SL doesn’t reflect +12 lbs boost.
« Last Edit: July 19, 2004, 11:58:33 AM by mw »

Offline Nashwan

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Spitfire I Speed
« Reply #12 on: July 19, 2004, 12:41:50 PM »
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Nope, despite you want to make it look like. The desription does not mentions the mounting of IFF aerials, so by all

likelyhood they were not present. It doesn`t mention what type of windscreen is fitted, by all likelyhood it`s an internal

windscreen.


It says an armoured windscreen.

What does it matter if they were internal or external if it was fitted with one?

Or are you claiming normal armoured windcreens were external, but you are assuming this particular one was internal?

If so, on what grounds?

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As for the removed rear view mirror, I haven`t seen too many Spits without it.


Neither have I. The AH Spitfire doesn't have it though, so shouldn't have the drag from it either. A mirror is going to

cause more drag than an IFF aerial, even if the IFF aerial wasn't fitted.

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Anyway, by what weird logic you want to use base the Spitfire I`s speed on the Spitfire II`s? Different planes,

different engines, haven`t you notice...?


Based on the fact they are almost identical with almost identical engines. The only difference is the Merlin XII was rated

for higher altitude and 9 lbs boost instead opf 6.25 lbs. Both used 12 lbs as a wep setting.

According to Spitfire The History:

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The differences between the early Mk I and the new Spitfire were minor and apart from the Merlin XII engine running

on 100 octane fuel they consisted of a Coffman cartridge starter instead of the original electric starter of the Merlin II,

and a small fairing on the port side of the engine housing the new starter. In the air they were identical and the

designation was just a means to identify the aircraft as  CBAF  (Castle Bromich Aircraft Factory) built when ordering

spares


Perhaps we should ignore the figures for the Spit II because it had a different starter?

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That the report you are basing your claim on says the exact opposite than you. To quote :

4.0 Level Speeds.

.......The top speed of this aeroplane is the same as that of N.3171 but is reached at 17,600 feet, 1400 feet lower than

the Mk.I Spitfire. Consequent upon this and the increase in power of the Merlin XII over the Merlin III below full throttle

height the aeroplane is about 6 - 7 miles per hour faster at heights less than 17,000 feet and about 4 - 8 m.p.h. slower at

heights above 20,000 feet. It should be noted that though the boost pressure on the Merlin XII is +9 lb. per sq.inch as

against +6 1/4 lb. per sq.inch on the Merlin III there is little difference in the engine power at heights of 16,000 feet

and above.


Little difference is not no difference. I said myself there was only a minor difference at the same boost, and of course at

high altitude the boost will be the same.

It's you who claimed at the same boost pressure the Merlin XII put out much more power.

The reduction in speed above critical alt would be because the Spit II on that test was heavier, and had the bellet proof

windscreen which the Spit I they were comparing it to didn't have.

Look at the rated altitudes from AIR 16/328 I posted above.

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It says :

- the XII is more powerful below FTH than the III (exact opposite what you claim)


Isegrim, I said it was less powerfull at the same boost pressure

If you look at the test, they are running the Merlin XII at 9lbs, the Merlin III at 6.25 lbs. At those pressures, the

Merlin XII is more powerfull.

Loo at the figures from AIR 16/328 again:

Merlin III

6.25lbs boost
875hp at SL

Merlin XII

9lbs boost
990hp at SL

Of course the XII at 9lbs is more powerful than the III at 6.256 lbs, bust as I said at the same pressure the III is more powerful:

Merlin III
12lbs boost
1190hp at SL

Merlin XII
12lbs boost
1170hp at SL

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- the Mk II Spit is 6-7mph faster below FTH (exact opposite what you claim)

Again, I said the MK II is slower at the same boost

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Frankly we have seen quite too many examples of you overexxegaration the Spit`s performance in every possible way.

So, as long as you don`t provide credible evidence of what you say (you may start with engine charts for the Merlin III and

XII), I won`t, and I doubt anybody will accept your claims here. They are far too much unsupported.


Well, if you won't believe AIR 16/328, try this. From The Merlin 100 Series, by RR Heritage publications:



The Merlin II is essentially the same as the III except the III has a prop shaft capable of taking a CS prop.

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Yes that`s the mantra and the claim. And where`s the Spit I flight test at +12 lbs...?


Here's the Spit I at 6.25 lbs:

http://www.fourthfightergroup.com/eagles/spit1.html

N.3171 was tested with a Rotol prop, speed at sea level should be just over 280 mph.

R6774 was tested with a DH prop, the type the RAF used on the Spit I, and that  was somewhat faster, although within the normal tolerances between aircraft. Note both were fitted with external armoured screens, armoured tanks etc,.

All the docs on the same page say 12 lbs boost increases speed at sea level by 25/28 mph.

There's plenty of information there that shows around 305 mph at sea level. Do you have any information that contradicts that, or just your prejudices?

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with only every 4th fighter having the ability to use 100 octane fuel... "vast majority" you say.


Source?

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Then also there`s Dowding`s restriction laid down upon the use of +12lbs as it wore down engines quickly, August :

http://www.fourthfightergroup.com/eagles/dowding1.jpg
http://www.fourthfightergroup.com/eagles/dowding2.jpg


Those restrictions are simply saying it's to be used in emerency only. You know, like war EMERGENCY power, WEP

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Probably it has to do something that they couldn`t secure a solid import of 100 octane at that time anyway...


Source?

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Appearantly, the RAF could not convert all of it`s fighter to 100 octane until NOVEMBER 1940, by the time the BoB already ended (by British standards).


Source?

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So as opposed to your claim that the Spits did their 'vast majority' of combat on +12lbs, the truth is that it wasn`t until the last two months of the year they were all capable to use it, even if there was enough fuel for that. In other words, the use of +12 lbs didn`t came into real widespread use until 1941.


Source?

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22 000 tons for 3 entire months of heavy fighting? That`s a ridiculus amount, Nashwan, only 7000t per month.


It's 13 weeks.

22,000 tons / 13 weeks = 1692 tons per week

1692 tons = 3,790,000 lbs.

A Spitfire held 85 gallons of fuel, at 7.2 lbs per gallon. No drop tanks were used, so that's the maximum a spit sortie can use.

That equals 6,192 sorties per week. The RAF had something less than 700 operational serviceable fighters at any one time, so that equals about 9 sorties per fighter per week, or something over 1 per day, assuming the tanks were totally emptied each time.

In fact, the operational sorties were substantially lower than this, Hooton, Eagle in Flames gives figures of an average of 4,000 FC sorties per week.

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If your numbers were correct, the RAF would have flown 6000+ sorties per week. You admitted that in fact they never flown more than 4000 sorties.


No, the 4000 number is operational sorties. To this must be added fuel used test running aircraft on the ground, ferry flights, training sorties (although only by operational squadrons, the figures don't include training command), wastage, pilots fillling their cars to go down the pub, etc.

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Here`s a relevant qoute Pips found at the Australian War Memorial Archives


Why not wait and see what Neil finds in the British archives? The British archives should have more accurate info on the supply of fuel in Britain, after all.

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310 mph at SL is a wet dream, nothing more. Good luck convincing anybody about your 'facts' without backing them up with real facts.


Apparently not to anyone else. HoHun has done his own calculations, which show my original statement of 305 - 310 is almost spot on.  As shown above, R6774 did better than 280 at sea level at 6.25 lbs boost. The docs on MWs site show 100 octane increased speed by at least 25 mph.

The Spit II did 290 mp with 990 hp, the Spit I with an extra 200 hp is going to go quite a bit faster.

There is nothing to support your assertion 305 - 310 is wrong, other than you own assumptions.

Wotan, thanks for the info on the 109. It looks like the boost is wrong on that, but I don't know enough to tell wether the speed is out as well.

HoHun, thanks for the calculations. I've got the figures you calculated for climb from AGW as well, and I'm testing climb in AH II now.

Offline Nashwan

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Spitfire I Speed
« Reply #13 on: July 19, 2004, 01:03:17 PM »
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“AH II now models it with the correct 12 lbs boost”. Are you just referring to the boost gauge?

Check the FTH. That will tell the story. If its around 18,000 ft, which I expect it is, the FM would not reflect +12 boost.


The boost gauge and the E6B. Both show 12 lbs, but you are right, 12 lbs is maintained at climbing speed up to 15,000ft.

However, the fuel consumption looks like 12 lbs as well.

Climbing at 6.25 lbs 2850 rpm the AH Spit I uses 79 imp gal/hr, which looks about right. However, under WEP it uses up to 115 gal/hr. The real Spit II used 98 gal/hr at 9 lbs.

So it's not just the boost gauge and the E6B, the plane is using as much fuel as it would at wep, just not getting the power.

I've done a quick climb test as well, and can't get better than about 3,000 ft min at low level at 12 lbs.



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In regards the 310 mph@SL claim, I find it deeply puzzling that then why did the RAF need to introduce the Mk V. at all, when it would be 20 mph slower than the allegadly 310mph Spit I at SL, in it`s initial +9lbs form..?


Because the Spit V was designed for higher altitudes. It would have had better low level performance if fitted with a two speed engine, ie the Merlin XX, but they were used for Hurricanes. Instead, they essentially used just the FS gear for high alt performance at the expense of low alt.

Offline gripen

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Spitfire I Speed
« Reply #14 on: July 19, 2004, 01:56:29 PM »
The main difference between the Merlin III and the Merlin XII was different SC gear ratio. The Merlin III had SC gear ratio 8,588 (or 8,58 on another source) and the Merlin XII had SC gear ratio 9,089 so the diference is quite small as ratings show. The Merlin 45 had same SC gear ratio as the merlin XII but the intake system as well as carburator was improved (same as in the Merlin XX).

Regarding supply of the 100 octane fuel, at least the Blenheims IVs which arrived here from Britain during Winter War were partially prepared for 100 octane fuel and there are pictures of these planes which  are tanked (here in Finland) from the barrels marked as 100 octane. The 100 octane fuel had been commercially available couple years in 1940.

gripen