Spit/109 sea level speed comparisons in 1.08 beta patch

[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.

[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.

[pstyle]

Hi crumpp, I've no issue with the math. Frankly I'm not scooled up in the formulae to critique it anyways. My interest is more as a historian, rather than engineer.

Can you advise why the Merlin power assumption is around 990bhp? And, when you use, say the Merlin 3, the auto prop and/or the 100 octanes, how do the graphs look?

Sorry if this creates loads of work....

[Crumpp]

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

With landing gear and flaps down......

[ATAG_Dutch]

Originally Posted by Crumpp

With landing gear and flaps down......

Crummp, when quoting other people in the thread, please could you leave in the name of the person you're quoting as above? Quoting people without reference to who it is makes following the conversation very difficult.

Many thanks.

[bongodriver]

Originally Posted by Crumpp

With landing gear and flaps down......

At 300MPH?

[Crumpp]

Psyle says:
Sorry if this creates loads of work....

No problem at all. In fact I am going to clean up the sheet and post it so others can use it. It just runs the math for the conditions given.

I wish I was more computer savvy to make it more user friendly. Perhaps some in the community can improve upon it.

The 990 hp comes directly from the RAE.

SUMMARY OF TRIALS

AEROPLANE Spitfire I No. N.3171
SPEC. NO. 16/36
CONTRACTOR Vickers-Armstrong (Supermarine)Ltd.


TYPE Landplane DUTY Single Seater Fighter.

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

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

Once I get good engine data on 100 Octane, I will do the estimate.

On these charts the data does not line up. The FTH do not even come close to assume RAM effect.

Level speed - FTH MS Gear = 11,000 ft

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

Engine power estimate at Vmax (RAM effect) shows a FTH MS Gear = 8,000 ft

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

Not saying the data is bad, just that this engine does not match this airplane. We need to find the same engine in the same airplane to get good data points.

[Crumpp]

bongodriver says:
At 300MPH?

Exactly....

Once again, explain the assumed values of CLmax on the RAE chart. I am listening.

[Crumpp]

ATAG DUTCH says:
Crummp, when quoting other people in the thread, please could you leave in the name of the person you're quoting as above? Quoting people without reference to who it is makes following the conversation very difficult.

Sure thing.

[pstyle]

Originally Posted by Crumpp

No problem at all. In fact I am going to clean up the sheet and post it so others can use it. It just runs the math for the conditions given.

I wish I was more computer savvy to make it more user friendly. Perhaps some in the community can improve upon it.

Thanks. I think this would be a good idea.
At least then we are all able to work to the same assumptions and review each others work. It's be good to see how the manipulation of one or more of the variables influences tge overall outputs.