109 Flaps

[Porta]

Crumpp,

That data from Rechlin is "TAS" without compressibility correction. You can compare it with the Focke-Wulf sheet so often posted here that shows Fw 190 A-5 speeds at different ratings, each rating with a pair of curves: one with IAS corrected only for density and the other with density and compressibility.

[Knegel]

Hi Justin,

according to the datasheet the plane didnt reach mach 0,89.  606mph at -32°C are less than mach0,88.

Edit: What was the weight of this plane??

Greetings, Knegel

[niklas]

Originally posted by Nashwan

Where is this figure coming from?

The Spitfire manual notes
* S.L. and 20,000ft. - 450 (385)
* 20,000 & 25,000ft. - 430 (370)
* 25,000 & 30,000ft. - 390 (335)
* 30,000 & 35,000ft. - 340 (292)

430 at 20,000 ft is about 590 TAS. That's about mach 0.84 (and the manual says limit is 0.85)

Ok, i just had a closer look. Actually it´s quite easy.
430mph = 692km/h. Going up FW-190 chart to 6km -> ~880km/h, 546mph Mach 0.77.



Recalculated by Hand:
R...........287,0500
Kappa...1,4050
Tgrad...-0,0065
G..........9,8100

Rho0....1,2250
T0 [K]...288,1500


Höhe [m]....6000,0000
CAS km/h...692,0000

At Altitude:
Temp.........249,1500
Rho...........0,6595
A [m/s].....316,9913......(speed of sound)
   
   
   
CorrRho   0,7337

Step0 Calc:
CAS m/s   192,2222
TAS_C0   261,9738............(applied corrrho, density correction of IAS->TAS)

M_C0     0,826438284......(using step0 TAS)
KorrM   1,0873................(fw190 formula)

Step1 Calc:
TAS_C1[m/s].......240,9302............(applied KorrM)
TAS_C1 [km/h]....867,3486
M_C1   ..................0,7601

I used two steps because Machnumber must be determined by a kind of iteration actually. I mean as long as you don´t know your exact TAS where you need Mach number, you can´t calculate the exact Machnumber. So you need an iteration.

In any case claiming M0.85 for 430mph IAS is pretty off.

niklas

[gripen]

Niklas,
If you have Excel spreadsheet, it has a handy solver tool which is great to solve problems needing some amount of iterations like speed corrections. Or did you allready use it?

gripen

[Crumpp]

That data from Rechlin is "TAS" without compressibility correction. You can compare it with the Focke-Wulf sheet so often posted here that shows Fw 190 A-5 speeds at different ratings, each rating with a pair of curves: one with IAS corrected only for density and the other with density and compressibility.

Your absolutely correct!  Arrgh, I hate the subtleties of German sometimes.  These corrections just twist your mind.  It was not until I got a report were Focke Wulf made a correction error on the FW-190A8 series that the light bulb blinked on.  You will see the correct corrected speeds annotated VwKC.  If not then you have to run the curves through the conversion curve.

Considering the weights the curve gives good agreement and easily falls in the 3% guarantees.  


 

What I like best is just when they spell it out:
 
 

All the best,

Crumpp

[justin_g]

Those last two are for speed increases acheived with "special emergency" power over the previous (start-emergency?) power rating. There are no airspeed corrections listed.

Erreichte Ladedrücke bei 2700 U/min und eingeschalteter erhöhter Notleistung:
"Reached load pressures during 2700 U/min and switched on increased emergency achievement:"

angezeigte geschwindigkeiten / geschwindigkeitssteigerung
"indicated speeds / speed increase"

Eg: ES+GL with 1,63ata reached Va(ias) = 575km/h @ 100m, an improvement of 40km/h. This a/c appears to be the + marks and _._ line in the graph.

[gripen]

Below is an example how the calculated speed charts (like A-5 chart mentioned above) were created in the FW. The speed marked as x) is TAS calculated from the data (like polar , engine chart etc.) and the speed marked as xx) is calculated TAS without compressibility correction. Might look like a bit backwards system but apparently they needed TAS without compressibility correction for example for specsheets or such things.

gripen

[Crumpp]

Might look like a bit backwards system but apparently they needed TAS without compressibility correction

It is called a correction, Gripen.  It is used to account for things like positional error.
 
 

for specsheets or such things.

Yes in order to compare the Ground Speeds of the FW-190's variants with a different pitot tube.

When they moved the tube outside the influence of the propeller it required new corrections to show the correct True Airspeed.

All the best,

Crumpp

[Crumpp]

Eg: ES+GL with 1,63ata reached Va(ias) = 575km/h @ 100m, an improvement of 40km/h. This a/c appears to be the + marks and _._ line in the graph.

I think that is about right.

It reached 580kph(ias) at 0 meters.

At Start u Notleistung or 1.42ata @ 2700U/min we can estimate the speed at 580kph (ias) - 40kph = 540kph

We can borrow the correction curve for EB-104, another FW-190A5 series (FW-190G3).  Assuming the USAAF was not incompetent and the correction is in the ballpark, of course.

540kph + 19kph correction = 559kph which is within 1% of the Rechlin and Focke Wulf listings.

Pretty good agreement I would say.  

All the best,

Crumpp
 

Forgot to add the correction curve:

 

[gripen]

Originally posted by Crumpp
It is called a correction, Gripen.  It is used to account for things like positional error.

The chart I posted above has nothing to do with positional error, all values are calculated.

gripen

[Crumpp]

The chart I posted above has nothing to do with positional error, all values are calculated.

Where do you think corrections come from?  The correction fairy?

All the best,

Crumpp

[gripen]

Originally posted by Crumpp
Where do you think corrections come from?  The correction fairy?

In that chart compressibility correction comes simply from calculated TAS which gives mach number at given conditions. After mach number is known, the total compressibility error can be calculated and the assumed compressibility correction (for sea level) of the metering system is accounted resulting the compressibility correction for the TAS corrected only for density.

Note that compressibility and density errors are the same for any calculated or real world tested speed and condition combination. But the position error of the metering system depends just on that particular installation; the EB-104 had one kind of position error curve and another plane had a different (as you probably allready know).

gripen

[Charge]

Concerning metering device errors I'd like to point out that eg. In FW the pitot system was mounted in a tip of a long pole which extended well forward of the main wing thus being, IMO, relatively error free (not counting the possible deficiencies in pitot systems metering speed in general). Whereas in Spitfire the pitot device is quite close under the wing and suspect to generate some errors due to changing pressures around the wing. I'd imagine that the Brits used a different kind of metering device in test flights?

-C+

[gripen]

Originally posted by Charge
Concerning metering device errors I'd like to point out that eg. In FW the pitot system was mounted in a tip of a long pole which extended well forward of the main wing thus being, IMO, relatively error free (not counting the possible deficiencies in pitot systems metering speed in general). Whereas in Spitfire the pitot device is quite close under the wing and suspect to generate some errors due to changing pressures around the wing. I'd imagine that the Brits used a different kind of metering device in test flights?

As noted several times in this thread; the RAE used several different metering devices and instrumentation for those high speed test dives (as an example rakes to measure pressure distribution). IIRC Morgan&Shackladys book contains some illustration on these devices. They tried to continously improve the methods and also corrected results afterwards once the better corrections became available.

There might be some amount error in the measurements, specially in the earliest but overall the results should be quite reliable.

gripen

[Crumpp]

There might be some amount error in the measurements, specially in the earliest but overall the results should be quite reliable.

As for the dives, sure within the limits of the technology of the day.

As noted several times in this thread;

I don't think Charge is refering to the dives however, Gripen.  He is pointing out that Focke Wulf's system worked for Focke Wulf designs.