Spit IIa is now so much more inferior to the 109

[Kwiatek]

Originally Posted by Crumpp

It also shows maximum boost at emergency power at 12,500ft as +10.55lbs at 3000 rpm for the Merlin III when you use boost override or pull the tit on 87 Octane.

Absolutely NOTHING to do with the use of 100 Octane fuel.

Yep it is also interesting

[Crumpp]

Yep it is also interesting

I thought something like this might be discovered when I saw the 1937 instructions for boost cut out in the RAF Training Manual......

[41Sqn_Banks]

Actually this is not the emergency power rating, these are the results from the power test to determine to performance of the engine.
As +12 boost has a FTH of 10,000 feet this is the power achieved with throttle valve fully open.

[Crumpp]

As +12 boost has a FTH of 10,000 feet this is the power achieved with throttle valve fully open.

Two possibilities.....

If our FTH is at 10,000 feet and our boost is 12lbs then by 12,500 it will be reduced and 10.55lbs is certainly in the ballpark.

OR

12,500 ft was the FTH at 10.55lbs on 87 Octane.

It warrants more investigation.

Actually this is not the emergency power rating

That is exactly what it says and the 1937 RAF Training Manual talks about boost cut out and emergency ratings on RAF aircraft under the general definitions. It revises the old definitions of "Normal rpm" and Maximum Permissible rpm".

[41Sqn_Banks]

Originally Posted by Crumpp

That is exactly what it says and the 1937 RAF Training Manual talks about boost cut out and emergency ratings on RAF aircraft under the general definitions. It revises the old definitions of "Normal rpm" and Maximum Permissible rpm".

Do you mean this one: Air Publication A.P.129 Royal Air Force Flying Training Manual Part I - Landplanes?

I will look it up, thanks for the info.

[FS~Phat]

Here's an interesting doco on the subject from discovery channel.
Probably a little biased but its still interesting just the same.
Sounds to me like it had more to do with pilot experience since the maximum performance windows of each aircraft were so very close.

http://www.youtube.com/watch?v=ugBpA...eature=related

[Crumpp]

Probably a little biased

Yes there are some details that make one raise an eyebrow. "Smaller and weaker wings", the canopy is jettisoned on the 109, the lack of stall warning on the 109.....

I would not say it was bias so much as just not knowing. The discovery channel says, "weaker wings". The RAF veteran is asked to go off what he sees and he does just that.

The lack of stall warning is also the Discovery Channel narrator. LE slats by their very nature give excellent stall warning and are an anti-spin device. It is a very silly thing to say.

The handling reports, especially the RAF detailed report on the Bf-109E is exactly what one would expect from an LE slat equipped aircraft.
From ~83mph to 75mph, the aircraft must be controlled with both aileron and rudder to keep it on a commanded flight path. It wants to go wings level. In a level flight stall, the left wing would drop just 10 degrees at the break.

There was never any tendency to spin under any flight condition.

The RAE's pilots opinion was the Bf-109 was too Longitudinally stable. Of course, the RAE did not have any defined stability and control characteristics at the time.

It is interesting to note their complaint about dive recovery!!

when diving at 400 m.p.h. a pilot, pulling with all his strength, cannot put on enough g to black himself out if trimmed in the dive.

The RLM did have defined stability and control characteristics and the Bf-109 had to meet those requirements.

http://kurfurst.org/Tactical_trials/...ls/Morgan.html

[NZtyphoon]

Originally Posted by 41Sqn_Banks

It's interesting to note that publications from 1938 and 1939 give maximum take-off engine speed of 2850 rpm for both Merlin II and III. Publications from 1940 give 2850 for Merlin II and 3000 rpm for Merlin III. The increase is not associated with the use of 100 octane fuel.

This most likely has a great deal more to do with the adoption of two speed and CS propellers; in 1938 the majority of the Hurricanes and Spitfires were still using the fixed (coarse) pitch two bladed wooden props, so the maximum allowable rpm was fixed at 2,850.

The Merlin III had the universal prop shaft allowing de Havilland or Rotol propellers to be fitted, and the availability of two-pitch and especially CS props would have allowed for higher rev limits with less strain on the engine than a fixed-pitch unit. It also makes sense that in wartime some restrictions are lifted to allow for maximum power. One of the reasons 100 Octane fuel was originally adopted was to allow greater take-off power.

[41Sqn_Banks]

The Hurricane I Pilot's Notes mention that during take-off 2850 RPM will not be achieved with fixed-pitch propeller.
IIRC the Merlin II was only able to take the DH propeller (2-pitch and later converted to CSP) and the Merlin III could take both. Some early Merlin II were not able to take a CSP at all as they didn't have a connection to drive the CSP unit. I can't remember where I've read this ...

[Crumpp]

CS props would have allowed for higher rev limits with less strain on the engine than a fixed-pitch unit.

No they won't allow for higher rpm. It is also not less strain on the engine. CSP's are much harder to aerodynamically balance while a fixed pitch is very easy and will run with less vibration. RPM is a function of the engine speed and reduction gearing. You can change those items to increase rpm to adjust for different propellers. If you mount a fixed pitch propeller that is grossly underpitched for the application, you will also see an rpm increase and very soon have a big bill to pay.

You control the manifold pressure and rpm in a CSP unit. Fixed pitch, you can only control the rpm and manifold pressure is irrelevant.

That is why the RAF amended their definitions in 1937!

With a two position fixed pitch, the Spitfire pilot is controlling rpm and not manifold pressure. The airplane is equipped with a manifold pressure gauge but it serves as a diagonistic tool only. He flys the airplane by rpm setting.

If you read the Spitfire Mk I Operating Notes, the maximum rpm is the same for all propellers.

It seems very likely that RAF pilots were authorized to "pull the tit" on their aircraft using 87 Octane fuel with a lower manifold pressure boost gain. It appears to be independant of 100 Octane fuel use.