With every post of yours the more I realise that you know nothing about the subject. He plainly says that you would fatally damage the engine by going up to that rating. Furthermore the ABC job is to stop that from happening but you can disable it in order to achieve some increased power for a short period (WEP) or manage your own boost pressures.

Did I understand that correctly Wedge?

I think you are the one that do my dear.

If you think that the FC was modifying the Merlin's engines like a car tuner will do, tht is a real problem.

As I have alrdy said it's not my personal thinking that prevail in my word. You are wrong on the all line. If I had a personal idea on the subject I won't bother other with my own thinking.

I think you 100octer and 17lber shld read this with much attention and stop lobbying every forum that deal with the Spitfire and smokes any discussions with insult and name calling etc.. etc..;

As I alrdy said, this theory does not makes any sense either on historical or mechanical grounds.

If there was a switch for emergency boost right on summer 1940 it certainly wasn't for a 17lb boost that even in 1944 still posed some problem.

Oh yeah let me guess, if you unfold your SpitPufPuff.com doc you certainly are already with injected nitroglycerin and so on at this same date.

The fact is that guys like you are bitching so much on every forum with YOUR idea of the spit (not the real one) that no sim devs can makes a FM with serenity.

What is senseless is that if such is done, it would be a really good plane to fly and fight.

By the way stop bad mouthing on me Osprey that's getting pretty boring. You don't know me. Thx

you clearly missed the point.

the plane could go to 17+ boost, but would go BOOOM if they tried to go that way. Im sure eventually they got aroudn that problem and managed better engines who could go more than +6.5.

Even myself who thinks of a pittie as a uselless kite, can get the fair point wedge is making.

Believe me or not but military services do test planes to remove any Go&Boom features.

If there was such a lever, it wld be instantly sealed, locked and patched with every possible red tapes ;)

Bench test is not Flight test that is no Op Tests that are not them self Op limits. And I did it short.:cool:

Sorry Tomcat you really didn't understand the concept of a supercharged engine. Below full throttle height every supercharged engine produces more boost than it can handle. Guess where the name full throttle height comes from ... exactly it's the height where the throttle can be moved fully forward without overboosting the engine.

There is no magic device needed to get +17 boost from the engine, it's simply the supercharger that is capable of producing this pressure at sea level. Of course this is a overboost condition for the engine and will kill your engine in no time. That's the problem with supercharged engines, the pilot has to keep the boost below the limits and has to adjust the throttle with every altitude change (as boost changes with altitude).

Thats why there is the automatic boost control that limits the engine boost below full throttle heigth automatically. However there might be a failure in the automatic boost control or a emergency situation ... so there was a boost control cut-out that disabled it and allowed the pilot to control the boost himself. Then however he could seriously overboost the engine. So they modified the engine that even with disabled boost control the boost pressure couldn't be raised above +12 boost.

So the "modification" didn't allow the engine to produce higher boost, in fact it limited the boost from around +17 to +12.

PS: Please use whole words to write your sentences it's hard to make sense of these abbreviations.

http://www.airpages.ru/eng/uk/spitf1.shtml http://www.airpages.ru/eng/lw/bf109e1.shtml

One Question Banks : when do you actually get max boost with a supercharged engine ?

And by the way if you were not charging us every three month on the same subject and with the same arguments I would hve been pleased to check out any abbreviations out of my phrases.

As I hve alrdy said, in the RR test manual the latter merlin is rated at 9lb of boost at 15kft not 12 or ...17

By the way I think I am qualified to deal with that subject - just went to check my diplomas just in case ;)

I suspect this is a hypothetical question: Highest boost possible boost is at lowest possible altitude at highest possible engine rpm with throttle valve fully open.

Highest allowed boost is available at with highest allowed engine rpm at all altitudes below full throttle height.

But really it's not about getting a high boost at low altitudes but make the engine survive the high boost. No one is telling that +17 boost didn't kill the engine.

So what is your point? There is a difference between "maximum-possible-boost-produced-by-the-supercharger-at-sea-level-that-the-engine-can't-handle-at-all" (around +17), "maximum-allowed-boost-in-case-of-emergency-for-no-longer-than-5-minutes" (+12 for 100octane fuel, +6 1/4 for 87octane fuel), "maximum-allowed-boost-for-no-longer-than-30 minutes" and "maximum-boost-for-infinite-time-...-well-not-infinite-as-your-engine-will-die-even-with-that-boost-after-200hrs-running-without-inspection"

There is no difficulty in getting a high boost at low altitudes from a supercharged engine. The difficulty are:
- Find the highest boost that does only acceptable "damage" to the engine and find ways to reduce the "damage" even further to permit (=allow) the use of higher boosts
- Find ways to maintain the high boost at high altitudes

But he's not giving you an argument. He's giving you a documented fact from Rolls Royce and the RAF. If you don't believe this to be true then I would suggest you provide the evidence, though I suspect you've been asked in the past and haven't managed to. My questioning was around understanding this evidence because I have seen this data in the past and never understood what it actually meant. I want to operate the engine properly and I am grateful to Wedge and Banks for the explanation, now I understand what the cutout actually does.

PS. A personal diploma isn't evidence btw, it just says you went to a college and passed some tests. Congratulations.

This is a very good answer Tomcat, well known facts btw. Just read any articles or books about the history if the Merlin II & III engines and you'll see it really is as simple as that. The actual boost was around +16PSI, that was considered as unsafe for normal service and engine life, therefore, a 3mm hole has been drilled to get the excessive pressure out of the system limiting it to +12PSI. That was what it says - Boost Control Cut-Out so it simply overrided the rated limit by moving certain bits to block certain openings via bowden cable. The actual gauge only showed +8PSI and slightly above (was +4PSI max. only on first production Spitfires and +8PSI max on later Spits) and pressure went from +6.25 to +12PSI straigt away, eg no boost of say +10PSI was possible. You can find exact technical info about how exactly this was achieved, you can find another pieces of information about the RAF pilots flying over France well before BoB period ''pulling the plug'' all the time. You can also find info about a +25PSI rated Speed Spitfire (same Merlin III) if you really care.

No matter what your opinion is, these are simple and well researched facts, not much space to argue I am afraid.

I am a blue pilot and not a Spitfire jockey, mind you. ;)