Effect of boost control cutout prior to +12 psi boost modifications

[lane]

Originally Posted by Corsair9

For some odd-ball reason all flight sim developers appear to ignore the +12 boost advantage that 100 octane fuel and the CS propeller gave both the Spitfire and Hurricane. I'm not sure why this is, but it is. It appears this is the same for this sim (I don't have a copy of it.)

It’s been public knowledge since the publication of the March 28, 1940 issue of Flight Magazine, in the case of 100 octane and the May 23, 1940 issue of Flight, in the case of the constant speed propeller.

"The 100-octane fuel (which enables the Merlin to receive no less than 12 lb. boost in emergency) must have been an asset."

"A new airscrew specially designed for the fast single-engined fighters of the Royal Air Force, but which can, of course, be applied for civil purposes, is now in production at the factory of Rotol Airscrews, Ltd., and is also in service with the squadrons."

So flight sim developers haven’t much excuse for getting it wrong every time

Thanks for sharing the 100 octane info, very interesting!

Originally Posted by Viper2000

I wrote the OP because the engine instruments indicate that we've got 87 octane fuel, and I figure that if we're going to have the wrong fuel modelled, we might as well have it modelled correctly.

<Chuckle></Chuckle>I still maintain we should have the right fuel modeled and model that correctly

[Seadog]

Some real world results:



There was no physical time limit on the use of 12lb boost, just a requirement to log the use and a suggestion that it be limited to 5 mins but some pilots used it for 30 mins. It did effect engine life but not severely, and later versions of the Merlin III on the Sea Hurricane were modded to allow 16lb boost and 1440hp, which was effective up to about 5500ft.

[Seadog]

These are test results from 1939, showing that a Merlin III could be run for many hours at 12lb boost:



In the above test a Hurricane was run at 4.25 and 12lb boost for 20min and 5min repeatedly and only terminated at 49.5 hours when a glycol leak developed, by which time the engine had been run for over 8 hours at 12lb boost.

[TomcatViP]

Yeah I wonder why RR still state for the merlin XX perfs in 1941 the following (quote)

Max T.O 3000rpm + 12lb/sq.in boost (M.S only)
Max climb 2650rpm + 9lb
Max all out level 3000rpm + 9lb
Max cruising 2650rpm +7b

But certainly RR R&D dep didn't new all abt field's Merlin.

Baahhh those stupid engineers ...

[Seadog]

The Merlin XX played only a small part in the BofB, but it was approved for 12lb boost during emergencies in Nov 1940:


and, since 12lb boost was available during TO right from its introduction, any pilot, at his discretion could use 12lb boost at any time or any altitude where it was possible, and there was no physical lockouts in the cockpit engine management system to prevent a pilot from doing this.

[TomcatViP]

Lol

- The XX was a post BoB product hence as a fighter eng it shld hve beneficed of the former improvements
- If 12lb MS is indicated it EXCLUDE any use of this level of boost above s/c alt

Sry but your statement does not match any engineering rules and is contradicted by the submitted text.

Let me explain : Supercharging put strain on your eng (300HP at recovering s/c alt)
If at low alt a boost level is restricted it certainly can't be achieved at alt !!

To give an exemple, my car has a turbocharger at 1.4 bar of boost (nearly 1.4 atm)

I once had a friendly race against a motorbike in a mountainous road from 1K up to 3K meters. My boost is electronically regulated. My turbo s/c is capable of much higher boost value to be reliable in a series car. The higher we went the better was my engine against the motorbike naturally aspirated engine (same boost same HP for me- Lowering boost for him) up to the point that my 1.4t cars "matched" his much lighter vehicle. BUT the temp went to high as did the strain and (hopefully) the electronic module give it away before I blew the eng.

That's what you risk with super/turbo charging. The lower the outside pressure is, the more the strain on the engine (mechanical or thermal respectively) will be.

If a limit is settled at low alt, it means that it can't be superseeded at high alt otherwise the limit would be put at s/c alt (but as it was difficult to have accurate pressure measurement at alt in a moving ac at the time they might have choose to rely on a low alt limit).

Baaah forget it I know that I am certainly loosing time writing this

[Seadog]

Originally Posted by TomcatViP

Lol

- The XX was a post BoB product hence as a fighter eng it shld hve beneficed of the former improvements
- If 12lb MS is indicated it EXCLUDE any use of this level of boost above s/c alt

Sry but your statement does not match any engineering rules and is contradicted by the submitted text.

The Hurricane/Merlin XX was introduced to combat in August 1940, but not given the designation Hurricane II until Sept 1940.

The text specifically allows 12lb boost in M gear for short periods of time during combat and during TO. It states the the boost override will provide 12lb boost up to 8500 ft after which it will gradually decline (to 9lbs at about 13000 ft):

3. The increased boost pressure will be effective up to approximately 8500 ft, above which the boost pressure will fall with increase of height.

However, as I've stated there is no physical interlock preventing a pilot from using the boost override in S gear, and using the Boost Override in S gear will provide additional power up to about 19000ft. Yes, this is an overload on the engine and cooling system but every pilot flying a Hurricane II always had the option to engage the boost override at any altitude and in either M or S gear.

[lane]

Originally Posted by Seadog

The Merlin XX played only a small part in the BofB, but it was approved for 12lb boost during emergencies in Nov 1940:


and, since 12lb boost was available during TO right from its introduction, any pilot, at his discretion could use 12lb boost at any time or any altitude where it was possible, and there was no physical lockouts in the cockpit engine management system to prevent a pilot from doing this.

Hmmm, it comes to mind that the publication date of 20 March 1940 for A.P. 1590B/J.2-W, Merlin II and III – Use of + 12 lb./sq.in. Boost Pressure followed actual unit conversion to 100 octane/+12 in the field in some cases; see for example 602 Squadron Operations Record Book, 151 Squadron Operations Record Book, 111 Squadron Operations Record Book & 74 Squadron Operations Record Book - Fwiw.

[ICDP]

Originally Posted by lane

Hmmm, it comes to mind that the publication date of 20 March 1940 for A.P. 1590B/J.2-W, Merlin II and III – Use of + 12 lb./sq.in. Boost Pressure followed actual unit conversion to 100 octane/+12 in the field in some cases; see for example 602 Squadron Operations Record Book, 151 Squadron Operations Record Book, 111 Squadron Operations Record Book & 74 Squadron Operations Record Book - Fwiw.

Remember your linking to info on the Merlin II and III, the document Seadog is linking to is for a Merlin XX. The Merlin XX was not used by fighters during the Battle of Britain so its boost rating is irrelevant since we don't have any flyable plane in CoD with a Merlin XX.