109 it fly wrong

[gripen]

Originally posted by HoHun


The relation to the Me 109 analysis is that the P-40 and the Me 109 spreadsheets are the same. I simply entered new parameters and a new engine graph because I figured the laws of physics are just the same for both aircraft types :-)

 

Here HoHun  forgets to told that the parameters were wrong in the case of the MT-215.

gripen

[HoHun]

Hi Blogs,

>When I saw the origonal plots I wondered about the standard errors of these estimates.

The problem is that the Finnish test only measured speed over altitude, not power over altitude, and the engine was not performing in accordance with the DB605A power graph.

However, from observation of the full throttle heights and the drop of the power it's possible to arrive at an approximated power curve (using a 3rd order polynom) that can be used for further calculations in order to estimate the standard deviation.

Here is the calculated drag (relative to the average) for the full set of data from the Finnish table:

140 m: 95,3%
1130 m: 96,8%
2130 m: 96,5%
3120 m: 95,5%
4120 m: 96,6%
5120 m: 98,7%
6120 m: 97,2%
6420 m: 96,6%
7110 m: 109,7%
8110 m: 103%
9110 m: 95,4%
10100 m: 118,8%

Standard deviation: 7,2%

This gives the following data:

631 km/h @ 6420 m +/-11 km/h
581 km/h @ 10000 m +/-11 km/h

However, one look at the drag values should be enough to recognize that the data gathered above full throttle height is considerably less reliable than that gathered below full throttle height.

Standard deviation drops from 7.2% to 1.1% by simply disregarding all (four) values above full throttle height.

Here's the data resulting from that decision:

0140 m: 98,6%
1130 m: 100,1%
2130 m: 99,9%
3120 m: 98,8%
4120 m: 99,9%
5120 m: 102,2%
6120 m: 100,6%
6420 m: 99,9%

Not considered:
----
7110 m: 113,5%
8110 m: 106,5%
9110 m: 98,7%
10100 m: 122,9%
----

Standard deviation: 1,1%

635,6 km/h @ 6420 m +1,9/-1,3 km/h
586,0 km/h @ 10000 m +1,6/-1,6 km/h

Due to the incomplete nature of the Finnish test, this should be only taken as an illustration of the inherent inaccuracy of performance measurements.

>I think its under appreciated how noisy these numbers can be when only 1 or 2 tests are run under any set of parameters.

Well, the values below full throttle height are quite consistent in my opinion.

Above full throttle height, they're extremely poor, but considering that up there, the limited excess power up combined with the increasing difficulties of getting accurate measurements at high altitude, that shouldn't come as a surprise :-)

Regards,

Henning (HoHun)

[gripen]

Originally posted by HoHun

The problem is that the Finnish test only measured speed over altitude, not power over altitude, and the engine was not performing in accordance with the DB605A power graph.

The problem with HoHun's (so called) analysis is that he continously refuses to use  real tested value for the 10100m CINA ie 552km/h (for obivious reason)   seen here:



Hohun's entire analysis above FTH is based on one errorneous value in the  FAF graph. Basicly he picks up the value which supports his agenda and ignores the rest.

gripen

[gripen]

Actually output of the MT-215 can be estimated by using RPM and MAP values from the test data and comparing it to the RPM and MAP values of the DB Spitfire:



Up to the FTH output difference between 2600 RPM and 2540 RPM is pretty much directly relative to the RPM diffrence because MAP is same. Above FTH lower RPM also affects MAP making relative difference bigger.As an examples

MT-215
6420m CINA 2540rpm 1,3ata => about 1221ps
10100m CINA 2540rpm 0,74ata => 690ps (measured by comparing to the DB Spitfire climb data).

DB Spitfire
6420m CINA 2600rpm 1,3ata => about 1255ps
10100m CINA 2600rpm 0,81ata =>about 800hp (measured by comparing to the DB Spitfire climb data).

So at FTH output diffrence between 2540 and 2600rpm is just about 30-40ps ie around 3%. But at 10100m the output difference is about 15%.

gripen

[gripen]

Here is the DB Spitfire climb data to use for output estimates:



And here is the DB 605 output chart. Note that the chart is with about climb speed RAM, this can be easily verified by looking FTH for 1,3ata 2600rpm; it's 5800m in the climb chart and in the output chart.

 

The output of the DB Spitfire at high speed  and at 10000m can be estimated by looking  MAP value in the DB Spitfire chart which is about 0,84ata. Then by looking the MAP value in the climb chart it can be seen that at climb speed  MAP has value 0,84ata at about 9500m. After that output can be measured  easily by looking output chart at 9500m and  the value there is about 800ps.

gripen