Spit Mk1 Boost?

[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.

[Al Schlageter]

Originally Posted by Crumpp

Only after significant modification to handle such pressure, modifications that did not exist in 1940.

So it only took RR maybe 1-2 months to make the significant modification and test the engine at +16lb boost and obtain certification for that boost level. Not bad at all.

[Crumpp]

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

There is no argument at all. I was trying to help you guys find answers to your questions about these machines.

RR maybe 1-2 months

I don't know as I would have to see the actual timeline. I highly doubt it though.

Changes to aircraft do not generally happen overnight. First the change has to be thoroughly tested because the safety margins are by their very nature very tight in aviation.

Once approved, it can't happen overnight either. The changes have to be disseminated to the folks who will implement them. They need the knowledge to enact the change.

Just as important, the people making those changes need the resources to enact it. That means the manufacturer has to retool or reset the production lines, train employees, and get the new parts made. Making enough for the aircraft in service is just the tip of the iceberg too. You have to have enough replacement parts sitting on the shelves to keep the airplanes in service flying. The standard rule of thumb is one part on the airplane, three replacements on the shelf.

So if you have 25 airplanes, you need 100 parts in total.

Of course once the part is made, it still has to reach the flight line too.

In short, it has to be approved, disseminated, manufactured, and distributed before anyone picks up a screw driver to loosen up the first screw to make the change. On average, that process took ~6months in WWII for most designs. The more technical the change, the longer and vice versa.

Just because a memo says it was approved does not mean it was in operational use from that day forward.

[41Sqn_Banks]

Maybe the +16 lbs were allowed for Sea Hurricane IA that operated from CAM ships (catapult armed merchantman) without the possibility to land - engine life is not a problem in this case.

[Al Schlageter]

Since Sea Hurricanes were in service in Feb 1941, then the +16lb boost Merlins were available in 1940 since it took, according to you, ~6 months.

[Viper2000]

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.

The Sea Hurricane was a special case; it was used on CAM ships and could not be recovered. The pilot would either parachute out or ditch when he ran out of fuel, as CAM ships had no way of accepting the aeroplane back for landing.

As such, both engine and airframe life were expected to be no more than one sortie, and it was therefore perfectly reasonable to give them a Viking funeral.

[Crumpp]

As such, both engine and airframe life were expected to be no more than one sortie

You know I read that part about one sortie life span. Thanks for pointing that out. Makes perfect sense to put your obsolete motors and so extremely over-boost them in a disposable airplane. Even then I would like to see what the engine was approved for at the boost. I would think it was just to get off the CAT.

Even a disposable fighter is worthless if it cannot fly to a target and fight.

[Viper2000]

Originally Posted by Crumpp

You know I read that part about one sortie life span. Thanks for pointing that out. Makes perfect sense to put your obsolete motors and so extremely over-boost them in a disposable airplane. Even then I would like to see what the engine was approved for at the boost. I would think it was just to get off the CAT.

Even a disposable fighter is worthless if it cannot fly to a target and fight.

I don't think they needed the power for takeoff because the "catapult" in this context was a whacking great rocket.

Given the stability & control difficulties associated with using really high powers at low speeds in these aeroplanes, and the obvious risk of engine failure at low speed & altitude off the bow of a ship which probably can't stop or avoid the aeroplane if it ends up in the drink, I would have thought it more likely that the launch was conducted at normal takeoff power.

I think that the extra combat power was primarily intended to be used for a rapid climb to cloudbase in order to intercept/scare off the bomber that was threatening their convoy; in the absence of RADAR, the CAM's fighter was only launched when the enemy was within visual range, and so warning time was strictly limited.

The climb would be unlikely to go higher than cloudbase because the bomber would just cloud-hop home (and probably couldn't hit a ship from any higher anyway, so either way it would be a mission kill); the fighter would be unlikely to give chase because of the obvious navigational challenge of finding their convoy again afterwards in an aeroplane not really equipped for naval navigation (at this time, most Fleet Air Arm aircraft, even the fighters, had a navigator).

For this reason, I suspect that they'd be unlikely to use the extra power for more than a couple of minutes in the sortie; I'm guessing that an early Hurricane with +16 would probably exceed 3000 fpm climb rate, and the cloud base would usually be less than 6000 feet...

[Crumpp]

I don't think they needed the power for takeoff

That low I would think you needed all the power to maintain flight even with a catapult. You only have a few feet until your in the drink.

It would be worth it to accelerate the aircraft quickly to flying speeds and then returning the engine to less catastrophic power levels.

I think that the extra combat power was primarily intended to be used for a rapid climb

You think? I know climbing is the most demanding portion of flight on an engine and it is the time period an engine is most vulnerable to detonation. Such an extreme level of over-boost is begging for detonation in a climb out.

By nature, aircraft engines are high output to weight and very vulnerable to detonation failures. Even with a disposable aircraft, the few minutes climbing in detonation scenario would make the accomplishment of the aircraft's intercept mission unlikely. A normal Hurricane will catch a Condor so I don't see the risk for the reward in it.

Here is a typical aircraft engine failure due to detonation scenario. Here one cylinder begins detonating and the motor makes it another 9 minutes before giving up the ghost.

http://www.to-avionics.com/insight/case.html


Even with modern steam catapults, it is typical to launch at full power with afterburner.

http://www.youtube.com/watch?v=lbbSYb7kDLY

Anyway, it is all speculation until someone comes up with a Sea Hurricane POH!!