Spitfire Vb WEP time limit does not match ingame specs

[453=Thornley]

According to both the ingame tech specs and the copy of the pilot notes I have, the Merlin 45/46 had a 5 minute limit on WEP (16 PSI at 3000rpm). 

However, If you go to full WEP on either engine, the warning message that you have exceeded the WEP time limit will appear at 3 minutes exactly.

I tested to see if this message was wrong but suffered engine damage on the four tests I did at 3:18, 3:37, 4:16 and 4 minutes 50 seconds, so the three minute limit is enforced.

 

Could we please increase the WEP limit to its historical 5 minute limit.

 

Bloodsplatter

 

p.s. I searched for this topic and couldn't find it. If this is a repeat, please delete.

[-=PHX=-SuperEtendard]

Yep, also the +12 at 3000 RPM is only 4 minutes before the "Emergency time limit exceeded" message appears.

Edited October 4, 2018 by -=PHX=-SuperEtendard

[Talon_]

The engine we have is currently using the settings from the Spitfire IIB

 

 

Except still wrong as even that engine had 1hr at climbing, not 30min.

[Kurfurst]

On 10/4/2018 at 8:25 AM, Bloodsplatter said:

According to both the ingame tech specs and the copy of the pilot notes I have, the Merlin 45/46 had a 5 minute limit on WEP (16 PSI at 3000rpm). 

However, If you go to full WEP on either engine, the warning message that you have exceeded the WEP time limit will appear at 3 minutes exactly.

I tested to see if this message was wrong but suffered engine damage on the four tests I did at 3:18, 3:37, 4:16 and 4 minutes 50 seconds, so the three minute limit is enforced.

 

Could we please increase the WEP limit to its historical 5 minute limit.

 

Bloodsplatter

 

p.s. I searched for this topic and couldn't find it. If this is a repeat, please delete.

 

That would be incorrect as Mark Vs had a 3 minute WEP limit when +16 lbs was finally cleared for them. It is well documented.

 

Perhaps this was changed to 5 minutes at a later stage, but cooling would be likely to remain insufficent, given the original +9 lbs rating the cooling system was originally meant to handle.

[unreasonable]

AP 156E Spitfire MkV Pilot's Notes, May 1941 reprinted Jan 1943

 

Combat 5 minutes limit 3,000 rpm,  +16 (+18 on M type engines) max coolant temp 135 C.

 

So yes it should be 5 minutes: and the cooling system is obviously pressurized as well. 

[ZachariasX]

2 hours ago, VO101Kurfurst said:

 

That would be incorrect as Mark Vs had a 3 minute WEP limit when +16 lbs was finally cleared for them. It is well documented.

 

Perhaps this was changed to 5 minutes at a later stage, but cooling would be likely to remain insufficent, given the original +9 lbs rating the cooling system was originally meant to handle.

Cooling was „insufficient“ in ground operation and slow flight or especially slow and steep climbs. You fly at decent air speed, it worked and it worked well. It is not that the RAF had a main frontline fighter for two years that eas constantly cooking and people were deaf and blind not changing anything. Douglas Bader never came back, saying something like „Oh, darn. Overheated the engine. Again.“.

Edited October 22, 2018 by ZachariasX

[Kurfurst]

Oh yes, design a coolant system with the capacity to handle the temperature output at +9 lbs, it will just as easily handle the heat output from several hundred additional horsepower at +16 lbs.

 

Because that is EXACTLY how it works.Oh wait, it doesn’t.

 

Summary

 

The operational limitations of the Merlin 45 have been increased, the use of 3000 R.P.M. and +16 lb/sq.in. boost being now permitted for periods not exceeding 3 minutes during combat. Tests have been made to determine the performance of the aeroplane at this new rating, and also whether the oil and radiator cooling are adequate. The performance fiqures obtained at the normal engine rating are included for purposes of comparison.   The results show that below 8,800 ft. the rate of climb is increased by about 1,050 ft/min. by the use of combat rating. The maximum rate of climb is 3,710 ft.min.    In level flight below 13,000 ft. the maximum level true airspeed is higher by about 35 m.p.h. using combat rating than at the same height using normal rating. The maximum level speed is 369 m.p.h. at 13,000 ft. Above this height the increase in speed is less and falls to zero at 19,900 ft., the full throttle height at normal rating, where the speed in either rating is 360 m.p.h.   DISCUSSION OF RESULTS    A.A.878 is fitted with a temperate type cooling system. The engine oil inlet and coolant outlet temperatures were measured on two climbs to 24,000 ft. This takes considerably longer than the 3 minutes for which the combat power may be used, a concession for test purposes. The observed temperatures are therefore likely to be higher than would normally be obtained in a 3 minute period at the same outside temperature. Even so, the oil inlet temperature is within requirements (100 deg C) for temperate summer conditions and does not exceed the emergency maximum temperature of 105 deg.C when corrected to tropical summer conditions.   The radiator suitability ratio for temperate summer conditions is below unity for less than 4 minutes on the climb and reaches a minimum of 0.985. For tropical summer conditions, the minimum radiator suitability is 0.865.           Oil inlet temperatures and coolant outlet temperatures were measured in level flight at the end of a 3 minute combat period at 12,000 ft. (approx. full throttle height). The results show that under these conditions the oil inlet temperature is within requirements for both temperate and tropical summer conditions, whilst the radiator temperature is within requirements for temperate but not for tropical summer conditions.           Further cooling tests at combat rating on a Spitfire V with tropical modifications are being made.   The engine oil inlet and coolant temperatures were measured on two climbs to 24,000 ft. This takes considerably longer than the 3 minutes for which the combat power may be used. The observed temperatures are therefore likely to be higher than would normally be obtained on a 3 minute period at the same outside air temperature. Even so, the oil inlet temperature is within requirements for temperate summer conditions and does not exceed the emergency maximum temperature of 105 deg.C when corrected to tropical summer condition.           The radiator suitability ratio for summer conditions is below unity for less than 4 minutes of the climb and reaches a minimum of 0.985. For tropical summer conditions, the minimum radiator suitability is 0.865. These figures would be improved if Tn could assume emergency maximum figure of 135 deg.C for combat periods.           In level flight at the end of a 3 minute period at combat rating with the radiator shutter in minimum drag position the oil temperature is within requirements when corrected to temperate or tropical summer conditions, whilst the radiator suitability is within requirements for temperate but not for tropical summer conditions.

6 hours ago, unreasonable said:

AP 156E Spitfire MkV Pilot's Notes, May 1941 reprinted Jan 1943

 

Combat 5 minutes limit 3,000 rpm,  +16 (+18 on M type engines) max coolant temp 135 C.

 

So yes it should be 5 minutes: and the cooling system is obviously pressurized as well. 

 

Looks like another post war reprint since in may 1941 were not cleared for +16 at all.

[JtD]

"May 1941, reprinted Jan 1943" is nothing but an updated manual.

 

The version I have is dated February 1944, and combat rating is 16lbs for 5 minutes. As with every other Spitfire V manual including the 16lb emergency boost.

 

Originally, the Merlin 45 for the Spitfire V was designed to operate at 12lb maximum, not 9lb. These figures can be found in concepts for the aircraft dating back to February 1941, well before the first one was actually built. As they were built, the first series were converted Mark I's with different, smaller oil coolers than later used for serial production. Overheating oil was a common problem with the first batch, owing to the insufficient oil cooler.

 

When 16lb were adapted into service, the maximum permitted oil and coolant temperatures were higher than in the test you quote. Maximum oil temperature being 105°, maximum coolant temperatures 135°, thereby eliminating all troubles for moderate summer conditions and leaving marginal troubles for tropical summer conditions - mostly for the climb. The engine evolved and could deal with higher temperatures and boosts than originally designed for.

 

That said, temperature limits and engine ratings are two completely different pairs of shoes, and a pilot would always keep an eye on engine temperatures.

Edited October 22, 2018 by JtD

[Talon_]

Even disregarding the multiple manuals we have on the subject, the Spitfire still doesn't match the published in-game specs.

[MiloMorai]

AA878

Vc

2248

EA

M45

FF 31-10-41 first prod Vc CRD VA 31-10-41 required for one month for gun testing AAEE 1-4-42 climb level speed trials at combat rating with (1) Vc with univ wing (2x20mm and 4x.303 guns) (2) Vc (4x20mm) (3) Vb Gun heat trials FAAC 15-10-42 ros CRD VA 24-10-42 wing insufficiently stressed for firing of four can simultaneously 411S 4-6-43 341S 17-10-43 453S 27-10-43 overshot landing Sumburgh tip onto nose CB LMS 1TEU 17-8-44 SOC 25-10-45

[NZTyphoon]

On 10/22/2018 at 5:16 PM, VO101Kurfurst said:

Perhaps this was changed to 5 minutes at a later stage, but cooling would be likely to remain insufficent, given the original +9 lbs rating the cooling system was originally meant to handle.

 

This is, of course, based on a ridiculous assumption that no further development of the cooling system was undertaken after the first Spitfire Is were built in 1938: the fact is that the Spitfire's cooling system underwent constant testing and redesign as engine powers increased: note, also that the purpose of the tests undertaken on AA878 were...

 

Quote

...to determine the performance of the aeroplane at this new rating, and also whether the oil and radiator cooling are adequate. The performance fiqures obtained at the normal engine rating are included for purposes of comparison.

 

While Kurfurst is assuming that no improvements were made to the cooling system, that clearly isn't the case because, by April 1943, the Merlin 50 was cleared for +18lbs boost for 5 minutes  when tested in an early VB airframe (W3322) in April 1943.

 

Quote

2.2     Engine numbers and limitations. A special Merlin 50 engine No. 115153/A.375557 was fitted for these tests. The relevant limitations at the time of the test were:-

 

	RPM	Boost lb/sq.in.
Maximum permitted for combat (All-out level or climb)(5 min. limit)	3000	+18

 

The differences between the Merlin 45 series and Merlin 50?

 

Quote

The only difference between a Merlin 45 and 50 is the fitting of a "negative g" carburettor and a fuel de-aerator on the latter engine, and these are unlikely to have a marked effect on performance.

 

So, yes, sticking a 3 minute limitation on +16 lbs boost for the Merlin 45 is wrong.

 

[453=Thornley]

Our Spitfire Vb doesn't represent the 1941 RAF version but the version supplied to the Soviets in 1943. That's the reason we're missing all the RAF mods and 50 series engines; the Soviets never had them. 

 

We have the 1943 Spitfire pilots notes. It's very exact.  5 minutes for 16psi/3000rpm and 1hr for 9psi/2850rpm. There's absolutely no confusion here. 

[NZTyphoon]

2 hours ago, Bloodsplatter said:

Our Spitfire Vb doesn't represent the 1941 RAF version but the version supplied to the Soviets in 1943. That's the reason we're missing all the RAF mods and 50 series engines; the Soviets never had them. 

 

We have the 1943 Spitfire pilots notes. It's very exact.  5 minutes for 16psi/3000rpm and 1hr for 9psi/2850rpm. There's absolutely no confusion here. 

The only confusion is that some people mistake a series of tests, undertaken specifically to find out if the cooling systems were up to allowing the +16 lbs boost setting, for the definitive operational settings. Clearly, the tests using AA878 showed that the cooling system was marginal for sustained, 3 minute use of +16 lbs, whereas, by April '43, another Spitfire Vb was tetsed and rated for +18 lbs boost for five minutes. To claim that Rolls-Royce and Supermarine hadn't modified the cooling system to cater for 5 minutes @ +16 lbs by 1943 is clutching at straws.