Spit/109 sea level speed comparisons in 1.08 beta patch

[Crumpp]

That is obviously wrong

Do the math....

[JtD]

The 12lb boost calculation done by the RAE is an absolutely reasonable extrapolation.

[Kurfürst]

Originally Posted by JtD

The 12lb boost calculation done by the RAE is an absolutely reasonable extrapolation.

I have my doubts about it having been made by RAE. It's an obvious farce.

[Crumpp]

The 12lb boost calculation done by the RAE is an absolutely reasonable extrapolation.

Well, then walk us through the explaination of how the engine data aligns with the graph. I would love to hear it.

Performance graph showing FTH of 11,000 ft:

http://www.spitfireperformance.com/s...-rae-12lbs.jpg

Engine data with RAM effect at max level speed showing FTH of 8,500 feet:

http://www.spitfireperformance.com/merlin3curve.jpg

[41Sqn_Banks]

Originally Posted by Crumpp

Well, then walk us through the explaination of how the engine data aligns with the graph. I would love to hear it.

Performance graph showing FTH of 11,000 ft:

http://www.spitfireperformance.com/s...-rae-12lbs.jpg

Engine data with RAM effect at max level speed showing FTH of 8,500 feet:

http://www.spitfireperformance.com/merlin3curve.jpg

Let's have a look at +6.25 boost ...

FTH at 17,000 ft (http://www.spitfireperformance.com/merlin3curve.jpg)
Max level speed at 19,000 ft (http://www.spitfireperformance.com/s...-rae-12lbs.jpg)

Looks like max level speed is achieved 2,000 feet above the FTH. Pretty much in line with the difference for +12 boost.

Edit: I want to make clear that this 2,000 ft difference between FTH and max speed must not be present in reality, it's more a systematical difference between the two charts that must be considered when they are compared.

[Crumpp]

That chart was not used because it does not align. The engine chart you linked already includes RAM effect at Vmax.


That means the FTH should match. Not be close or have the same margin of error, but match if that is the correct engine data.

I used the power figures as listed in the flight reports NOT a seperate engine curve that does not match the performance data.

[Crumpp]

[41Sqn_Banks]

I know that, I can read. You asked how the engine data align with the speed graph. They align with an consistent altitude difference of about of 2,000 ft.

The altitude difference between the FTH in the charts can be explained by a different level flight speed. E.g.
Hurricane I has a FTH of 17,750 ft at 316 mph.
Spitfire I has a FTH of 18,600 ft at 364 mph.

As we see the 50 mph speed difference results in a drop of 1000 ft for the FTH.

There is nothing contradicting in the charts ...

[Crumpp]

I know that, I can read.

Then what is the issue with the data not aligning?

The altitude difference between the FTH in the charts can be explained by a different level flight speed. E.g.

It will align. If you looked at other aircraft and not just confined yourself to one specific type, you would see this the case.

A speed difference is not going to account for a 2000 ft increase in FTH.

How do you explain the fact this chart comes from an investigation of performance with an experimental high altitude engine.

The chart exactly matches the one found in:

Messerschmitt Me. 109

Handling and Manoeuvrability Tests

BY

M. B. MORGAN, M.A. and D. E. MORRIS, B.SC.

COMMUNICATED BY THE PRINCIPAL DIRECTOR OF SCIENTIFIC RESEARC (AIR)

MINISTRY OF SUPPLY

__________________________________

Reports and Memoranda No. 2361

September 1940*

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

[Crumpp]

Originally Posted by 41Sqn_Banks

I know that, I can read. You asked how the engine data align with the speed graph. They align with an consistent altitude difference of about of 2,000 ft.

The altitude difference between the FTH in the charts can be explained by a different level flight speed. E.g.
Hurricane I has a FTH of 17,750 ft at 316 mph.
Spitfire I has a FTH of 18,600 ft at 364 mph.

As we see the 50 mph speed difference results in a drop of 1000 ft for the FTH.

There is nothing contradicting in the charts ...

The data matches the same fan plot in another report on a Spitfire equipped with a Merlin XX engine.

AFAIK, the Spitfire Mk I was equipped with the Merlin III engine.