Spit Mk1 Boost?

[SEE]

Originally Posted by =XIII=Wedge

So given that we currently have an earlier Spitfire using only 87 octane fuel:-


With the ABC enabled (normal situation)

• The maximum boost obtainable will be +6.25 lbs.
• Once set the selected boost (datum) will be maintained regardless of changes in altitude up to the rated altitude.
• Above rated altitude the pressure will drop off, but the datum point will remain the same.
• Pilot workload is reduced and there is no risk of overboosting the engine.

With the ABC disabled (done by operating the cutout)

• The maximum boost obtainable would be +17 lbs @ sea level.
• Any rise above + 6.25 would have disasterous impact on the engine due to pre-ignition of the fuel.
• Provided that the pilot retarded the throttle they would have manual control of the boost, but would have to be careful not to overboost the engine.
• The indicated boost pressure would change as the altitude changed.

Thanks guys, just one qestion. At alt 17K and above, the manifold pressure in Clods Spit Mk1 drops significantly (less than 2 Ibs per Sq.in.) - full throttle - straight and level - The boost cut out has no effect as pointed out earlier in the thread. So, based on the above - this appears to be incorrect for that altitude?

[Crumpp]

The maximum boost obtainable would be +17 lbs @ sea level.

The maximum boost is only +12lbs at sea level in emergency override in the Spitfire Mk I.

That is all the Merlin II and III were capable of handling and that was a definite over boosting of the engine.

[Skoshi Tiger]

Although not Merlin engines, I assume these engines were running above their maximum allowed boost!

http://www.youtube.com/watch?v=aUkXriHjQeI

http://www.youtube.com/watch?v=vq5cj...ture=fvwp&NR=1

Well at least it put a smile on my dial!

Cheers!

[Al Schlageter]

Originally Posted by Crumpp

The maximum boost is only +12lbs at sea level in emergency override in the Spitfire Mk I.

That is all the Merlin II and III were capable of handling and that was a definite over boosting of the engine.

The maximum boost obtainable would be +17 lbs @ sea level.

There is a difference in 'would' and 'were'.

Merlin III
1,310 hp at 9,000 ft, +12 lb/sq.in, with 100 octane fuel (5-minute limit).
1,440 hp at 3,000 rpm, +16 lb/sq.in boost, 5,500 ft in Sea Hurricane

Harvey-Bailey, A. The Merlin in Perspective - the combat years. Derby, England: Rolls-Royce Heritage Trust, 1983. ISBN 1-872922-06-6

[Crumpp]

The discussion is the Battle of Britain. Sea Hurricanes are a much later development and the boost increase came after some significant upgrades to the engine.

A 1940 Merlin II and III were only capable of +12 lbs and that boost was achieved by engaging the boost cut out.

[Al Schlageter]

The first of the Sea Hurricanes to see service with the Fleet Air Arm arrived in February 1941.

Yes be sure that is much later than the BoB.

[Robo.]

Originally Posted by Crumpp

The maximum boost is only +12lbs at sea level in emergency override in the Spitfire Mk I.

That is all the Merlin II and III were capable of handling and that was a definite over boosting of the engine.

Yes, Sir, you're kind of correct - +12PSI is the rated boost for a Merlin III with the plug pulled. +17PSI was never a rated boost for this engine, but the engine was actually capable of it.

In fact, the BCC-O was still limiting the 'natural' boost DOWN TO +12PSI by drilling a 3mil hole in there. It is also known fact that some pilots during Battle of France liked to put a matchstick into that hole getting +16PSI effectively on Waybridge prop Hurricanes, beating the hell out of the poor thing. No, I don't want that modelled, I just mentioned it because I find it interesting.

Noone ever said the Spitfires were flying at +17PSI, even the +12PSI was restricted. The reason he mentioned it was TomcatVIP's post regarding overboosting I believe.

[Seadog]

Originally Posted by Crumpp

The maximum boost is only +12lbs at sea level in emergency override in the Spitfire Mk I.

That is all the Merlin II and III were capable of handling and that was a definite over boosting of the engine.

The Merlin III was capable of handling 16lb boost:



and the Sea Hurricane IC used 16lb boost in combat, but not in 1940.

[Crumpp]

Sea Hurricane IC used 16lb boost in combat, but not in 1940.

Only after significant modification to handle such pressure, modifications that did not exist in 1940. Your document clearly separates it from the earlier Merlin II and III engines.

The +17PSI is not mentioned in any Spitfire book, this is simply a figure the Merlin III achieved (not safely mind you!)

It has no bearing or relevance. BMW tested the BMW801D2, including flight test of the aircraft, to 2.2 ata but the engine never saw a service rating above 1.65ata.

It is not intellectually honest to make the claim the engine was then capable of 2.2 ata. It was not capable of reliable operation at that boost level and that is reason it did not enter service. Same goes for the Merlin II and III.

If you want to know what an airplane can do, check the latest edition of the Operating Instructions. That is what was approved and in use.

No speculation required!!

[Robo.]

Originally Posted by Crumpp

Only after significant modification to handle such pressure, modifications that did not exist in 1940. Your document clearly separates it from the earlier Merlin II and III engines.



It has no bearing or relevance. BMW tested the BMW801D2, including flight test of the aircraft, to 2.2 ata but the engine never saw a service rating above 1.65ata.

It is not intellectually honest to make the claim the engine was then capable of 2.2 ata. It was not capable of reliable operation at that boost level and that is reason it did not enter service. Same goes for the Merlin II and III.

If you want to know what an airplane can do, check the latest edition of the Operating Instructions. That is what was approved and in use.

No speculation required!!

The +16PSI on Sea Hurris are irrelevant indeed.

Sir, as stated before, the Spitfire Mk.I was flying at +12PSI Boost. The figure of +16PSI was only mentioned in a reply to TomcatViP regarding the overboosting of early Merlin engines. No one ever said that such a rating should be modelled for Spitfires Mk.I or Hurricanes Mk.I ingame!

We're saying the same thing btw, no need to argue.