Author Topic: Spit 16 (Read 12970 times)

dtango · « **Reply #120 on:** February 28, 2007, 08:12:42 PM »

Accusation? Wow, I'm not accusing anyone of anything as if something was wrong.

I am saying that the 109K4 we have in AH seems to be pretty darn close to the 1.98 ata performance.

Let's just take the Mtt documents that Kurfurst has posted. Here's the 1.98 ata C3 + MW50 K4 max speeds:

http://kurfurst.allaboutwarfare.com/Performance_tests/109K_PBLeistungen/files/5026-18_DCSonder_MW_geschw.jpg

Top speed at critical alt we have ~727 kph/ 452 at 21k. The AH K4 top speed is ~452 mph.

At SL max speed is ~610kph/379mph. The AH K4 is slower at ~370mph.

Let's take a look at the Mtt documents again for the 1.98 C3 without MW50:
http://kurfurst.allaboutwarfare.com/Performance_tests/109K_PBLeistungen/files/5026-26_DCStart_noMW_geschw.jpg

For the 1.8 ata and 1.98 ata without MW50 the top speed is ~720kph/447mph (vs. the AH K4 at 452mph).

1.8 ata and 1.98 ata SL max speed is ~590kph/366mph. This is slower than the AH K4 at SL.

So the AH K4 is better than the 1.8 ata and 1.98 ata C3 no MW50 K4. It matches the 1.98 ata C3 MW50 K4 at crit alt and but is slower than at SL.

Tango, XO
412th FS Braunco Mustangs

weazely · « **Reply #121 on:** February 28, 2007, 08:42:08 PM »

LOL loony it turns with a zeke if 1 of 2 things happen

1.the zeke isnt turning
2.the zeke pilot isnt ther

dtango · « **Reply #122 on:** February 28, 2007, 09:05:19 PM »

Knegel:

The compressibility of air creates a lot of different issues. One of the effects is a rise in drag with increasing mach number known as compressibility drag. It's different than what you are thinking about - e.g. the effects of compression on aircraft control (e.g. buffeting, stiff controls, tuck-under, etc.).

At lower subsonic speeds we treat air as incompressible. As airspeeds increase you have to account for the drag due to compressibility because of the changes in the pressure distribution. Here's a graph of the impact of compressibility drag on the XP-51.

For reference to the compressibility control problems, for the P-51 control and stability issues started to be experienced around mach .75. You can see from the chart above that compressibility drag increases the drag of the aircraft well below this airspeed.

All aircraft experience this and to accurately assess performance of aircraft you need to factor this in. The Mtt report on the K4 listed above says that compressibility is not accounted for.

Tango, XO
412th FS Braunco Mustangs

dtango · « **Reply #123 on:** February 28, 2007, 09:19:09 PM »

One other thing I've noticed people referring to here that I thought I would clarify... weight of the aircraft has little impact on the max level speed of an aircraft.

Tango, XO
412th FS Braunco Mustangs

Benny Moore · « **Reply #124 on:** February 28, 2007, 10:11:37 PM »

I admit I'm grinning right now; Kurfy's own documents are being used for something he would not approve of. Bwahahaha!

But really ... this does seem to indicate that we have a 1.98 ata Me-109K and therefore it would be logical to include the P-38L at 66" or higher, since (as Mike Williams so kindly proved in the other thread) it saw a lot more service than the 1.98 Me-109K.

Squire · « **Reply #125 on:** February 28, 2007, 11:14:42 PM »

Poor choice of words, I meant nothing by it.

"Your point was..."

Ok,

...lets see then, we have 447 vs 452 at alt. A difference of 5 mph.

This is easily within the expected error of 1 percentile in any case.

...and its 7 mph slower at S.L.

Your going to have to do better than a measily 5 mph error. I remain skeptical.

dtango · « **Reply #126 on:** February 28, 2007, 11:21:02 PM »

The same could be said the other way.

at alt 1.98 ata c3 mw50: 452mph vs ah 452 mph (by your calc < 1% ) 0 mph diff.
at SL 1.98 ata c3 mw50 :379 mph vs. 370mph (by your calc < 1%) 9 mph diff.

Tango, XO
412th FS Braunco Mustangs

Squire · « **Reply #127 on:** February 28, 2007, 11:42:02 PM »

Actually, the thing that jumps out at me is the lack of performance boost the 1.98 ata rating seems to give over the 1.8 if the tests are correct.

Atmospheric conditions, lack or inclusion of wheel well doors, ect, could throw off a flight test by a few mph either way, and I think it is almost impossible to nail down that precisely.

In any case, I dunno if +/- 5 mph (447 vs 452) is worth getting too excited about. I could see it if the K-4 was way over the top in terms of specs, but it doesnt look like it is.

They could model it do 447 tops, and nobody would ever know it unless you told them.

Bronk · « **Reply #128 on:** February 28, 2007, 11:49:08 PM »

I'd be more interested with acceleration and climb differences.

Top speed might be areo limited requiring much more boost to see bigger gains.

Bronk

Krusty · « **Reply #129 on:** February 28, 2007, 11:50:03 PM »

But according to even Kurfy's numbers, the top speed wouldn't change. Think of it like the spit1, back before it got 100 octane. Same top speed, just more performance below that point.

I e-mailed Pyro to ask him which version they used when modeling the K-4, no response yet. When I get one I'll post the answer here.

I still don't buy that we have 1.98ata, but I reserve the right to change my opinion if better info comes to light.

dtango · « **Reply #130 on:** February 28, 2007, 11:52:23 PM »

I don't have any complaints about the K4 being overmodelled in AH at all am certainly not on some crusade to "fix it!!!"

. I just thought I would point out to folks the AH K4 is pretty darn close to the 1.98ata c3+mw50 version.

Tango, XO
412th FS Braunco Mustangs

Bronk · « **Reply #131 on:** February 28, 2007, 11:59:58 PM »

Quote

Originally posted by dtango
I don't have any complaints about the K4 being overmodelled in AH at all am certainly not on some crusade to "fix it!!!" . I just thought I would point out to folks the AH K4 is pretty darn close to the 1.98ata c3+mw50 version.

Tango, XO
412th FS Braunco Mustangs

Same here and I agree with you on the boost comparisons.

K4 is great fun to hop in once in a while.

Bronk

Benny Moore · « **Reply #132 on:** March 01, 2007, 12:03:25 AM »

Quote

Originally posted by Bronk
I'd be more interested with acceleration and climb differences.

Those are my thoughts exactly. More power means more maneuverability, not just speed. More power means doing literally everything better, including turn and burn flat turns on the deck.

That's a fair enough way of looking at it, Krusty. Like you, I am unsure which version we have, so I await the answer from Hitech.

Bronk · « **Reply #133 on:** March 01, 2007, 12:16:33 AM »

Quote

Originally posted by Benny Moore
Those are my thoughts exactly. More power means more maneuverability, not just speed. More power means doing literally everything better, including turn and burn flat turns on the deck.

IMHO
To a point I'd say Benny.
To much power with insufficient surface to harness it would make it push . (To steal a nascar term.)

I think it is possible to overpower an airframe.
Torque does strange things to turning ability. Which usually increase a bit along with HP gains.

109 F4 as a torque example, slow in a right hand turn.

Bronk

dtango · « **Reply #134 on:** March 01, 2007, 12:24:41 AM »

Quote

Originally posted by Bronk
I'd be more interested with acceleration and climb differences.

Top speed might be areo limited requiring much more boost to see bigger gains.

Bronk

1.98ata c3+mw50 best ROC: 4920 ft/min (3400 kg?)
1.8ata b4+mw50 best ROC: 4440 ft/min (3400 kg)
1.98ata c3 best ROC: 4320 ft/min (3400 kg?)

AH K4 best ROC: ~4800 ft/min (3374 kg - assuming AH chart is normally loaded K4).

Assuming the weights are accurate the AH K4 best climb is nearest the 1.98ata c3+mw50 K4.

A correction to the speeds above, I didn't look at the speed diffs for the 1.8ata b4+mw50 version:
SL: ~595kph
alt: ~727kph

Level speeds the AH K4 seems nearest the 1.8ata b4+mw50 in the charts.

Tango, XO
412th FS Braunco Mustangs