Author Topic: 109 it fly wrong (Read 15959 times)

HoHun · « **Reply #345 on:** June 03, 2004, 01:16:59 PM »

Hi Gripen,

>May I remind you that measured speed of the MT-215 at 10100m CINA was 552km/h which I corrected to about 580km/h at 10000m CINA 2600rpm with altitude correction, rpm correction, output correction and tailwheel. This value is in a very good agreement with other really tested data sets.

Well, I don't think the value I calculated (based on your data) of 585 km/h @ 2540 rpm is far off either, considering the difficulties of your previous correction.

Anyway, my point is twofold: The shape of the corrected curve as shown in

http://www.x-plane.org/users/hohun/me109g-2.jpg

is unrealistic. A realistic curve would be convex, with the speed decay accelerating at altitude. This qualitative argument leaves it open whether the aircraft is too fast or too slow, so I imagine you might agree on this one.

The second part of the argument is that my calculations agree with your calculations at 6.4 km and at 10.3 km, while I get a faster speed at the altitiudes in between. That leads me to conclude that your 7 - 9 km speeds are on the low side, though of course you could argue with equal justification that your 10.3 km speed is in fact on the high side.

>Generally creating a chart does not prove anything if you don't want explain how did you reach such numbers.

If you're interested, I'd not only provide the explanation but actually send you my complete spreadsheet :-) It's not user-friendly at all, but I think you have the know-how to find it interesting anyway.

In fact, I'd be thankful for your comments! Either you agree with my calculations, in which case I'd have my point confirmed, or you'd find an error in my calculations, in which case I could improve the accuracy of my spreadsheet. A win-win situation! :-)

>Shortly we are back in the beginning; you just want to believe unrealisticly high performance numbers without real world tested proof.

Gripen, don't pretend you can read my mind. Either you're right, and then you'd not gain anything by telling me because I'd behaving the way you perceive on purpose, or you're wrong, and then you'd do me injustice. Looks like a lose-lose strategy to me :-(

Regards,

Henning (HoHun)

gripen · « **Reply #346 on:** June 03, 2004, 02:21:56 PM »

HoHun,
The measured speed of the MT-215 at 10100m CINA was 552km/h not 574km/h, later number is an error in the chart (I think this has been pointed out at least 3-4 times). Got it? So why your chart contains a wrong value and why your theory is based on the curve created with wrong value?

This has nothing to do with my corrections or my errors, you are simply using the wrong value to support your agenda.

gripen

HoHun · « **Reply #347 on:** June 03, 2004, 03:15:03 PM »

Hi Gripen,

>The measured speed of the MT-215 at 10100m CINA was 552km/h not 574km/h, later number is an error in the chart (I think this has been pointed out at least 3-4 times). Got it?

Actually, no :-)

What you wrote before was:

"May I remind you that measured speed of the MT-215 at 10100m CINA was 552km/h which I corrected to about 580km/h at 10000m CINA 2600rpm with altitude correction, rpm correction, output correction and tailwheel."

I understood that you thought 580 km/h was the realistic value for an aircraft with an engine up to the specifications. If I misunderstood you, just point it out and I'll fix it.

>So why your chart contains a wrong value and why your theory is based on the curve created with wrong value?

Note that I suggested: "You could argue with equal justification that your 10.3 km speed is in fact on the high side", which seems to be what you're actually doing :-)

You're charging open doors.

>This has nothing to do with my corrections or my errors, you are simply using the wrong value to support your agenda.

Gripen, please do the paranoia check. Not everyone who disagrees with you is out to get you. It would be very unfortunate if you'd be trapped in the same "agenda/bias" thinking that has struck so many people here, because I really used to appreciate your contributions to this forum.

I guess I won't post in this thread for a while to allow all participants (including myself!) to get a bit of self-critical distance to what was written here. If you'd like to check out my spreadsheet in the meantime, just drop me an email - I still think your comments would be helpful.

Regards,

Henning (HoHun)

gripen · « **Reply #348 on:** June 03, 2004, 03:56:22 PM »

HoHun,
Nonsense, this has nothing to do with my corrections, your chart contains simply a wrong value. If you want to use a corrected value for the curve, you must correct all other data values too.

Regarding your agenda, I don't know what else should I think based on your attitude?

gripen

Badboy · « **Reply #349 on:** June 03, 2004, 07:30:18 PM »

Quote

Originally posted by Seeker
Thx for trying; but I still don't get it! :-)

Seeker, it's too late now, but tomorrow evening I'll type up a proper explanation for you and I'm sure you will get it. Standby...

Badboy

Seeker · « **Reply #350 on:** June 04, 2004, 04:45:47 AM »

Thanks Badz! :-)

Badboy · « **Reply #351 on:** June 04, 2004, 03:44:03 PM »

Quote

Originally posted by Seeker
Thanks Badz! :-)

I've started a new thread for it...

http://www.hitechcreations.com/forums/showthread.php?threadid=118997

Badboy

gripen · « **Reply #352 on:** June 05, 2004, 02:12:24 PM »

Here is the original FAF speed chart of the MT-215. Note speed at 10000m (10100m CINA): 552km/h

gripen · « **Reply #353 on:** June 06, 2004, 07:59:46 AM »

Here is the MT-215 measured speed points marked with blue and the above mentioned error marked with red. Note again speeds above 7000m CINA:

7110m 614km/h
8110m 614km/h
9110m 610km/h
10100m 552km/h

gripen

gripen · « **Reply #354 on:** June 06, 2004, 09:29:07 AM »

Here is the real FAF MT-215 data compared to HoHun's version of the FAF Bf 109G-2 data (2540rpm). Up to the FTH HoHun is quite faithfull to real data set but above that altitude his version of the FAF data starts to live it's own life. And HoHun's theory is based on data set above FTH. Shortly this is called data manipulation.

Note that it's not just speed at 10100m CINA which is falsified but also speeds at 9110m and 8110m. Funny thing is that real values at 9110m and 8110m are quite close to HoHun's calculated version. The real data is actually more concave than his calculated version.

Again it should be noted that all this has absolute nothing to do with my corrections, errors or what so ever. This is strictly HoHun vs FAF data.

End of the story, well, actually not quite. Seems that HoHun has actually done some RAM calculations because he noted that the first FTH of the supercharger (better term could be the first rated altitude) with high speed RAM does not agree with calculated RAM effect. Behind this is a very common misunderstanding with DB 605; the operation of the second oil pump of the supercharger is not governed by MAP but altitude. Therefore the engine is allways a bit throttled up to the second FTH. Below is a picture from the DB Spitfire report which clarifies the issue.

gripen

edit: Corrected an error in the chart

HoHun · « **Reply #355 on:** June 06, 2004, 01:16:20 PM »

Dear Gripen,

Would you please be so kind to tell our readers which speed values you read off the grey "5.4.43" chart for the following altitudes?

7600 m
8700 m
10300 m

Thanks in advance.

Regards,

Henning (HoHun)

gripen · « **Reply #356 on:** June 06, 2004, 02:33:38 PM »

Ah, noted an error, corrected.

Dear HoHun,
You mean values in line fitted with error value for 10100m CINA? Not relevant for an obivious reason; measured speed at 10100m CINA was 552km/h not 572km/h.

gripen

HoHun · « **Reply #357 on:** June 06, 2004, 03:33:51 PM »

Dear Gripen,

>Ah, noted an error, corrected.

Would you now please compare the data points you read off the "4.5.43" chart you posted with the data points in the orange graph in the top speed comparison you posted, and tell us what you found?

Thanks again,

Henning (HoHun)

gripen · « **Reply #358 on:** June 06, 2004, 03:45:56 PM »

HoHun,
I see that none of the real values fit to your version of the FAF data. Clear concavity can be seen above 8000m in the real test data but not in your version. Actually your version does not even match with FAF line with wrong value for 10100m CINA.

Could you now tell us why do you use manipulated data?

Could you now tell us why did you tried to mix 2600rpm corrected data to same graph with 2540rpm data?

gripen

HoHun · « **Reply #359 on:** June 06, 2004, 03:53:54 PM »

Hi Gripen,

>I see that none of the real values fit to your version of the FAF data.

That's why I specifically asked you for the data points you read from the 5.4.43 chart at:

7600 m
8700 m
10300 m

These are the data points I used for the orange graph.

So what do you think are the correct speeds for the altitudes I gave, read from the diagram you posted?

Regards,

Henning (HoHun)