Does anyone know what ** TO BE USED IN PRE-COMBAT ZONES ONLY means?

[ThomasP]

Hey guys,

Saw this at the bottom of the V-1710-73 SEFC and do not know what it really means. Does anyone know what the note "** TO BE USED IN PRE-COMBAT ZONES ONLY" means?

Also I though that REMARK #2 at the bottom is interesting, particularly in the phrasing.

 

[MiTasol]

48" (23.5psi) boost is somewhat more than the Merlin could take on Dec 18 1942 (or was that part of the April 24, 1944 revision - if so could a 1944 version of a 1942 Merlin take that boost)

 

[ThomasP]

Hey MiTasol,

I had kind of the same question originally. It did not make sense to me so I did some checking. The "SPEC AN-H-8 December 18, 1942" notation is apparently the specification for the SEFC data sheet format, and the data is not necessarily for the engine described on the sheet as of December 18, 1942.

I ran into this before when I noticed that there were many claims of (US) engines (particularly the V-1710) having outputs that I could not balance with the development timeline and inservice records. For US aircraft SEFCs you need to know the date of the manual/revision to know what the engine output was at the time of the manual/revision publication. Because of this misunderstanding there have been a lot of claims of higher US engine ratings/outputs for the December 18, 1942 time period that were actually not valid.

 

[cvairwerks]

I suspect the "Pre-combat zone" reference is for functional flight test after engine replacement at an operating location. When pushed to War Emergency, a witness wire was broken and the ground crews had additional maintenance that had to be performed, up to and including engine and prop changes based on the particular circumstances.

 

[MiTasol]

Hey MiTasol,

I had kind of the same question originally. It did not make sense to me so I did some checking. The "SPEC AN-H-8 December 18, 1942" notation is apparently the specification for the SEFC data sheet format, and the data is not necessarily for the engine described on the sheet as of December 18, 1942.

I ran into this before when I noticed that there were many claims of (US) engines (particularly the V-1710) having outputs that I could not balance with the development timeline and inservice records. For US aircraft SEFCs you need to know the date of the manual/revision to know what the engine output was at the time of the manual/revision publication. Because of this misunderstanding there have been a lot of claims of higher US engine ratings/outputs for the December 18, 1942 time period that were actually not valid.

Thanks Thomas
That makes sense
I have never paid attention to notes like that before so I was caught out by it. Many thanks for the clarification.

 

[AMCKen]

Is it relating to the 'desired fuel pressure'? Perhaps it is the desired pressure until one is actually in combat.

 

[MiTasol]

Fuel pressures before the engine are limited to 5psi or less. Imagine a 23.5psi fuel leak in the cockpit of a Spitfire or Hurricane or forward of the firewall on any aircraft. One spark or exhaust flame and the aircraft goes woof.

Higher pressures are used downstream of a fuel injection pump but the Allison and Merlin used carburetors. The Allisons carb was a pressure carb, as were later Merlin ones, but these still use low pressure fuel right to the nozzle.

 

[waroff]

From Ammison engine manual

excerpt P40N flight operations

P40N check list

the P40K & K-1 checklist: 50" Hg but the line "Precombat or combat zones only" is missed

HTH

 

[ClayO]

From Ammison engine manual

View attachment 631370View attachment 631371

excerpt P40N flight operations
View attachment 631372


P40N check list
View attachment 631373

the P40K & K-1 checklist: 50" Hg but the line "Precombat or combat zones only" is missed
View attachment 631375


HTH

That's very informative - and you caught it, that the ** refers to the WEP. So, it sounds like the spec is saying that the 5 minute limitation only applies to pre-combat, and that in actual combat,the limit is different (see Note on page 133). Is that what you get out of that?

 

[ThomasP]

I think the manual excerpts are saying that you may only use War Emergency Rating for 5 minutes at a time, regardless of whether you are in pre-combat or combat zones. But different operating conditions will determine the total amount of time at WER allowable between bering "pulled for tear down inspection and reconditioning".

But I still do not understand what they meant when they said - or why they said ". . . PRE-COMBAT ZONES ONLY" on the chart I posted. Did they make a typo and not include the words ". . . OR COMBAT . . ." as in the following chart?

 

[waroff]

if I understood correctly, each cycle does not exceed 5 minutes, but it only takes one to overhaul the engine.


before use war emergency ratings the engine must run 10/15 minutes at 80 percent or less of military power. may be it's also the delay between two cycles of WEP?

in pre combat zones used WEP to reach altitude or combat area quickly the duration of WEP do not exceed 5 minutes, but in combat zone, the duration depends of the conditions.

If you have a Hun ready to shoot you, you check your six, not your watch, and if you go over that 5 minutes, the most important is your life, not your engine's life.

 

[K5083]

"48" (23.5psi) boost is somewhat more than the Merlin could take on Dec 18 1942"

48 inches Hg is not particularly high for a Merlin 20 series. It equates to +9 boost. +12 was in regular RAF use from the first Hurricane Mk II.

 

[Deleted member 68059]

48" (23.5psi) boost is somewhat more than the Merlin could take on Dec 18 1942 (or was that part of the April 24, 1944 revision - if so could a 1944 version of a 1942 Merlin take that boost)

These are absolute pressures for the Allison, not gauge, as used by the Merlin.

The Allison here has a maximum manifold pressure of 60" Hg = 29.5 PSI ABS -14.7PSI = +14.8 PSI Boost (Gauge)

The Merlin exceeded that in 1942 with the Merlin 61 which initially had a service limit of +15 PSI (Gauge), by 1944 that was +25 PSI (Gauge)
with the Merlin 66 = 25+14.7 = 39.7 PSI ABS = 80.8" Hg Absolute Manifold pressure.