Author Topic: D9 compresses to early. Test and source given... (Read 911 times)

Naudet · « **Reply #30 on:** March 28, 2002, 07:16:23 AM »

Here the results on the numbers from the document gripen mentioned:

i tried to hit the following speeds:

435mph IAS @ 16,393 ft

497mph IAS @ 9,836 ft

528mph IAS @ 6557 ft

the test was flown with a FW190D9, full fuel, full ammo, fuel burnrate set to 0

the procedure was the following, climb to 25k, than dive to the 1st altittude and level there out, looking when the plane stops shaking.
Again while in the test, i noticed i would not be capable of going far over the given speeds, but that was not necessary at all

results:

415-420 mph IAS at 16k, plane stops shaking
475 mph IAS @ 9,5k, plane stops shaking
500-505 mph IAS at 6k, plane stops shaking

all results show that the speed in AH is off bye about 15-30 mph.

A digital speedometer would help alot, but due to the fact that at 9,5k and 6k the needle stop at a marking it was quite easy to estiminate speed, more problem at 16k but needle always stayed under the 425mph marker.

And as HoHun mentioned, german safety speeds/data are quite conservative, planes, U-Boots and other types of vehicles could usually exceed those limits without taking harm.

P.S. i did a brief test on FW190A8 dive speed a few weeks ago, and that plane roughly matches above numbers. So it is really just an D9 related issue here. Why should we have one FW190 dive slower, when i fact it was the best diver of all 190s.

FLS · « **Reply #31 on:** March 28, 2002, 09:32:18 AM »

The placarded never exceed speeds are not the onset of buffeting speeds.

Nothing in this thread proves that the D9 is too slow or compresses too easily.

--)-FLS----
Musketeers

Raubvogel · « **Reply #32 on:** March 28, 2002, 10:24:03 AM »

Very simple question here: In AH why does the D9 compress before the A8 and have worse control authority at high speed? That is my question. They use the same wing.

HoHun · « **Reply #33 on:** March 28, 2002, 01:45:50 PM »

Hi FLS,

>What you posted so far gives the airspeed indicator reading without correction. You haven't proven anything by posting uncorrected IAS figures.

To be more accurate, the numbers Naudet posted are of unresolved status.

Since there are indications Kurt Tank conducted a controlled test in a specially instrumented aircraft (note the mention of a G meter that wasn't usually fitted to production aircraft), I'm confident that the test results were carefully corrected for all relevant factors.

In fact, the account looks to me like the author took the description of the test procedure and tried to turn it into something more gripping. The procedure he discribes is actually very similar to that used by Messerschmitt (according to Radinger/Otto/Schick's "Me 109" books). Even the altitude at which the top speed was achieved is close for both types: The Me 109 achieved 906 km/h TAS at 5800 m, so a 955 km/h TAS at 6000 m for the Fw 190D-9 seems not unlikely.

Regards,

Henning (HoHun)

HoHun · « **Reply #34 on:** March 28, 2002, 01:51:16 PM »

Hi FLS,

>You have to correct Naudet's posted IAS speeds to CAS before adding the compression correction.

If someone could provide the D-9-specific correction factors, I'd run the numbers again. I'd guess the error is in the region of 2%, and since the placarded numbers are usually conservative, I don't think the numbers I posted are too unrealistic as they are now.

Regards,

Henning (HoHun)

HoHun · « **Reply #35 on:** March 28, 2002, 01:56:54 PM »

Hi Gripen,

>It is not real tactical limit but just a speed where the wing entered the compressebility region, tactical limit should be somewhat higher.

Thanks for the details! Mach 0.64 seemed very low indeed.

>In the case of the Tempest similar number was mach 0,73 but the tactical limit was mach 0,8.

The P-51 manual mentions 0.75 for that purpose, and this seems to have been the placarded number as well. Like the Tempest, it could actually go still faster. I'd say it would be reasonable to assume the same applied to the Fw 190D-9 as well.

Regards,

Henning (HoHun)

FLS · « **Reply #36 on:** March 28, 2002, 02:27:12 PM »

HoHun

Don't IAS position errors have to be determined empirically?

I wasn't doubting your figures, I was just pointing out that the chart used CAS not IAS.

I'm not saying it's impossible for Kurt Tank to have calculated the actual TAS, I just don't see that in the material Naudet posted. I also don't see anything to indicate that Tank thought the IAS figures were accurate at that speed. Don't you think it's significant that there was no buffeting?

I haven't taken the position that the AH D9 model is correct. I'm just saying that I don't believe the information Naudet provided has shown that it's incorrect.

--)-FLS----
Musketeers

SageFIN · « **Reply #37 on:** March 28, 2002, 04:28:05 PM »

The absolute figures are not too worrisome, the (apparent) fact that the D9 compresses before A8 is.

Naudet · « **Reply #38 on:** March 28, 2002, 05:27:46 PM »

Also it is impressive that critical mach for D9 is 0.76 for the tiffie 0.64.

As tactical limit seems to be usually higher, the D9 should be capable of higher mach as the tiffie, or atleast the same.

But in AH you have a totaly different picture.

D9 compresses, shakes and losses elevator authority.

But yet, i never managed to compress a tiffie, nor did i manage that its elevator got somewhat heavier.

And as Raubvogel and SageFIN mentioned, there is still the point, why the D9 compresses earlier than the A8. The D9 was known for its better dive, but in AH the situation is inverted.

Why is this so?

MANDOBLE · « **Reply #39 on:** March 28, 2002, 05:32:19 PM »

Quote

Originally posted by Naudet
Why is this so?

Only Pyro and perhaps HiTech knows ...