Spit/109 sea level speed comparisons in 1.08 beta patch

[Crumpp]

But your graph Crumpp bears little resemblance to the RAE chart.

Do some math....

The RAE chart is at 12,000 feet and was taken off one data point. It did puzzle me as our radius and other data aligns. It puzzled me until I stated getting into the details of the chart.

According to that chart, the Spitfire Mk 1 is capable of reaching 340mph (+) at 12,000 feet on 1050 bhp.

The RAE graph found in AVIA 6/2394 is a performance estimate from September 1940.


A flight report from March 1940 gives the power at 12,000 feet:

Normal B.H.P 950/990 at Rated Altitude 12,250 ft

And lists the Vmax for the type as 326 mph TAS.

http://www.spitfireperformance.com/n3171.html

The AVIA 6/2394 does not fit the only +12lbs estimate we have for level speeds.

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

This estimate shows 359mph TAS at 12,000 feet.

That is over a 5% error from the speed found in AVIA 6/2394. It would be unusual for such a large estimate error in an established design.

I don't know what Spitfire data they used but I suspect it was for an improved high altitude version as we saw before in a similar report previously posted on these forums in which you were involved in the discussion.

All that can be said is we don't know the details and the ones we do know, do not fit any existing service model at the time.

When we plug in the data from the Spitfire Mk I serving in the RAF during the BoB, we get a different result.

Another anomaly is the CLmax. In order to get a CLmax of 1.87 on the Spitfire, you have to drop the stall speed far below what the Spitfire POH list's to a scant 62 knots.

At the 76mph Vs (69mph IAS Vs + 7mph PEC) found in the POH, we get a CLmax of 1.69 which is far below the 1.87 Gates uses in the report.

I am pretty sure Gates was not using a standard Spitfire Mk I for his base data in the estimate. It does not align with one.


Calculate Sea level CL max:

CL = Lift/(dynamic pressure * Reference Area)
Dynamic Pressure = density ratio * Velocity^2 / 295

Dynamic pressure = (1 * 66^2)/295 = 14.76610169psf

CL = 6050lbs / (14.76610169psf * 242sqft) = 1.693067034

Lift = CLqS

Lift = 1.87 * 14.76610169psf * 242sqft = 6682 lbs of Lift generated.

[IvanK]

"I don't know what Spitfire data they used but I suspect it was for an improved high altitude version as we saw before in a similar report previously posted on these forums in which you were involved in the discussion.

All that can be said is we don't know the details and the ones we do know, do not fit any existing service model at the time."

"Normal B.H.P 950/990 at Rated Altitude 12,250 ft '

Garbage ! you are confusing rated power at 2600RPM with maximum power at 3000RPM. Here are 2 inspection test certificates for 2 different Spitfire MKI's one with a Merlin II the other with Merkin III. As you can see Max power is 1030hp at 16,250ft. at 6.25lbs boost 3000RPM.

The RAE chart references 1050hp at 6.25lbs Boost 3000RPM at 12,000ft.





You are again trying to change history. You cover up your case by a smokescreen of Mathematical verbiage. RAE calculated that the Spitfire MKI had better sustained turn performance than the BF109E3. Pretty much every other report technical and general from either side of the conflict say the same. You on the other hand construct a graph that clearly shows the opposite.

Find another single independent reference that proves the BF109E3/4 had better sustained turn performance than a Spitfire MKI.

Whilst you are at it show us what this Mythical improved high altitude version that I supposedly referred to in another report and how this is supposedly used in the RAE turn chart

[NZtyphoon]

Originally Posted by Crumpp

Do some math....

The RAE chart is at 12,000 feet and was taken off one data point. It did puzzle me as our radius and other data aligns. It puzzled me until I stated getting into the details of the chart.

According to that chart, the Spitfire Mk 1 is capable of reaching 340mph (+) at 12,000 feet on 1050 bhp.

The RAE graph found in AVIA 6/2394 is a performance estimate from September 1940.


A flight report from March 1940 gives the power at 12,000 feet:



And lists the Vmax for the type as 326 mph TAS.

http://www.spitfireperformance.com/n3171.html

The AVIA 6/2394 does not fit the only +12lbs estimate we have for level speeds.

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

This estimate shows 359mph TAS at 12,000 feet.

And what do we see on the 109 data? Estimate on chart = 1,200 Bhp at 2,400 rpm 15,000 feet, TAS 340 mph + at 12,000 which Crumpp, conveniently has ignored, whereas the true output was about 960 ps 2,300 rpm at about 3,500 metres

http://www.wwiiaircraftperformance.o...oct40-pg22.jpg

So Gates was also using an unusually powerful 109 for the chart as well. I suspect it was probably an experimental high-altitude 109E.

Question is what data did Crumpp use to compile his chart? There's no engine rating shown, no take of weights, nor anything else to indicate on what basis Crumpp's "calculations" were made. For any proper analysis Crumpp's chart is totally useless.

[Crumpp]

There's no engine rating shown

The data is listed in the thread.

Here it is too, right off the spreadsheet:

Spitfire Mk I

Aircraft Data
weight 6050lbs
Power 990bhp
Level speed 247KEAS
Propeller efficiency 0.8
Wing area 242 sqft
wing efficiency 0.85
Dynamic pressure 206.8101695psf
Aspect Ratio 5.6
Mass 187.8881988 ft/s^2


Bf-109E-3

Aircraft Data
weight 5580lbs
Power 990bhp
Level speed 269KEAS
Propeller efficiency 0.85
Wing area 174.9 sqft
wing efficiency 0.85
Dynamic pressure 245.2915254
Aspect Ratio 5.77
Mass 173.2919255 ft/s^2

[Crumpp]

And what do we see on the 109 data?

Again, it just calls into question the validity of the RAE estimate. I just figured it was a given the RAE would not have the best data on the German aircraft.

They did a lot of estimating off very few data points. The CLmax for both aircraft closely matches the full flaps CLmax and not clean configuration.

[IvanK]

Originally Posted by Crumpp

Again, it just calls into question the validity of the RAE estimate. I just figured it was a given the RAE would not have the best data on the German aircraft.

They did a lot of estimating off very few data points. The CLmax for both aircraft closely matches the full flaps CLmax and not clean configuration.

Well clearly you haven't read AVIA 6/2934 They had reasonable data on the aircraft in question. AVIA 6/2934 is based on actual flight test of a BF109E3 in RAF hands.

Here is AVIA 6/2934 summary of turn performance based on Flight tests and calculation :



So the RAE determined the opposite to you based on flight test and calculation.

[Kurfürst]

Originally Posted by IvanK

So the RAE determined the opposite to you based on flight test and calculation.

To me it seems RAE determined something entirely different than Crumpp's calculation... (turns at and only at minimum turn radius vs. Crumpps calculations over the speed range)

[IvanK]

The RAE chart on its own shows sustained G over the complete speed range at 12,000ft altitude.
Its the a similar but more detailed chart to Crumpps.

[NZtyphoon]

Originally Posted by Crumpp

The data is listed in the thread.

Here it is too, right off the spreadsheet:
Bf-109E-3

Aircraft Data
weight 5580lbs
Power 990bhp
Level speed 269KEAS
Propeller efficiency 0.85
Wing area 174.9 sqft
wing efficiency 0.85
Dynamic pressure 245.2915254
Aspect Ratio 5.77
Mass 173.2919255 ft/s^2

Interesting how the Bf 109E-3 loading chart http://www.wwiiaircraftperformance.o...ladeplanes.jpg shows the weights as 2,608 kg (5,749 lbs) fully loaded for combat while, without ammunition for training flights, the weight is 2,532kg (5,582 lbs)...

[NZtyphoon]

Originally Posted by Crumpp

The data is listed in the thread.

Here it is too, right off the spreadsheet:

Spitfire Mk I

Aircraft Data
weight 6050lbs
Power 990bhp
Level speed 247KEAS
Propeller efficiency 0.8
Wing area 242 sqft
wing efficiency 0.85
Dynamic pressure 206.8101695psf
Aspect Ratio 5.6
Mass 187.8881988 ft/s^2

Where did you assume the propeller efficiency was 0.8?
De H 55409 B 0.930

Rotol RA 611 0.924
Rotol RA 621 0.920
Rotol RA 600 0.911
Rotol RA 640 0.940

Take your pick, which propeller did you claim had an efficiency of 0.8?


http://www.spitfireperformance.com/spit2prop-b.jpg