Spit/109 sea level speed comparisons in 1.08 beta patch

[Osprey]

All that extra power from 12 fewer litres. According to some of the logic here I conclude, mathematically, that the DB601 was rubbish.

[Kurfürst]

Originally Posted by Osprey

All that extra power from 12 fewer litres. According to some of the logic here I conclude, mathematically, that the DB601 was rubbish.

Well good for you, now would you kindly push that thing you call a flight stick forward. :p

[Crumpp]

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)...

I got the weights from several flight test but did not have a ladeplan. The weight I used leaves out the pilot.

I fixed it and it narrows the gap but does not eliminate it.

The RAE chart shows a Spitfire sustained turn advantage across the entire speed range

The RAE chart uses CLmax neither airplane can attain in clean configuration by any calculation or measurement, including the RAE's. Read the report you claim I have not!

In fact, the CLmax comes very close to matching full flaps for both aircraft.

[Glider]

Originally Posted by Osprey

All that extra power from 12 fewer litres. According to some of the logic here I conclude, mathematically, that the DB601 was rubbish.

I don't know about rubbish, that is a bit strong, but its worth remembering that it was soon changed for the DB 605 and the Germans wouldn't have done that without a reason. I can only assume that it lacked development potential

[Glider]

Originally Posted by Crumpp

I got the weights from several flight test but did not have a ladeplan. The weight I used leaves out the pilot..

Why on earth would you leave out the pilot?

Seriously are you going to redo the numbers with the extra Merlin power, 30% will make a huge difference.

[bongodriver]

Originally Posted by Glider

Why on earth would you leave out the pilot?

Seriously are you going to redo the numbers with the extra Merlin power, 30% will make a huge difference.

Crumpp has to be carefull...if he starts using realistic figures the results won't come out as he intends.

[IvanK]

I guess RAE were clueless ... and you have superior knowledge Crumpp... trouble is your graph reflects the opposite of pretty much every known record,chart,computation or actual flight test or pilots account of the facts !



One more from the RAE clearly showing better turn performance of the Spitfire in all regimes.

[Crumpp]

Ivank says:
Its the a similar but more detailed chart

It is not a more detailed chart. It is the same thing.

Only difference is the CLmax estimates. The RAE used a trailing rake to measure speed.

Those are very accurate when properly operated but are complex to operate. They measured the CLmax in flight. I see a problem with operating such a system at the edge of the envelope trying to stall a high performance fighter.

As for the weight of the Bf-109, my original estimate just used the one the RAE used for the test. Using the ladeplan does not change the relative performance significantly.

The all-up weight was 5,580 lb. with the C.G. 24.8 in. aft of the leading edge at the root (h = 0.302). This loading agrees well with the value of 5,600 lb. quoted for the all-up weight by the Germans.

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

My calculated CLmax agrees with the RAE measurements for the Bf-109.

Speeds Dynamic pressure CL
82 22.79322034 1.433906325




My Spitfire CLmax agrees with the NACA findings and the calculations were made using standard data on the type with the weights and stall speed listed in the Operating Notes.

Kurfust says:
RAE's calculation also using estimated/guessworked stall speeds, Clmax and rather questionable power values for both the Spit and 109 (the latter probably understood with the effect of engine thrust). That's the problem with these charts in general - there's such a margin of error with the base values, that the results are all over the place. (estimated) Propeller effiency can vary results by 5-10% alone, drag values are unknown, the wing's oswald effiency factor is unknown (directly shifts the results, since its a multiplier in the equation), Cl max is unknown.

That was my first thought. Gates was using high angle of attack theory to determine turn performance. High angle of attack theory is good for estimation but has to be based on measured data otherwise it is a complete crapshoot and guesswork.

The stumbling block to the assumption that Gates used high angle of attack theory is the fact he clearly list's the 1G stall CLmax for both aircraft.

That listed CLmax is clearly labeled on the chart as "assumed values of CLmax":

Spitfire 1G CLmax = 1.87

Bf-109E-3 1G CLmax = 1.95

The only way either aircraft can achieve such a CLmax at 1G is in landing configuration with full flaps and gear down.

The CLmax Gates used matches both aircraft in landing configuration.

It is definate proof Gates used the landing configuration CLmax for his estimate.

[Glider]

Originally Posted by bongodriver

Crumpp has to be carefull...if he starts using realistic figures the results won't come out as he intends.

Give the guy a chance, he said he would

[Crumpp]

IvanK says:
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I guess RAE were clueless ... and you have superior knowledge Crumpp... trouble is your graph reflects the opposite of pretty much every known record,chart,computation or actual flight test or pilots account of the facts !

Explain the "assumed values for CLmax at 1G" listed on the chart, Ivan??

I am listening....

Here is the mathmatical proof it is not correct for a clean configuration fighter:

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.