Why still no dive acceleration difference?

[BlackBerry]

This condition is key. Of course, above Vmax we are outside of the aircrafts design envelope and our efficiency curve no longer approximates a slope of zero. Instead it takes on a negative slope.

Just though as it is a good assumption to have a slope of zero in the envelope, it is also a good assumption that all CSP designs will have a similar negative slope outside that envelope.

The most important factor of a propeller is its size/diameter. if you fly your P47 with a 3.3m diameter prop instead of a standard 4m, you'll definitely lose more efficiency, perhaps 10%, at 0.7Mach(above Vmax).

efficiency is Y axis, advance ratio is X axis, although 3.3m prop share same slope curve as 4m prop outside the envelope, the 3-meters prop working point is on the right side of 4-meter due to higher advance ratio, which means less efficiency.

I also think that individual and specific characteristic's are way more trouble than it is worth for dubious accuracy without the actual data. It would also open up a huge can of worms for your developers and people having to decide what data is applicable.

Look at all the arguments over such very well documented performance parameters as climb rates or Vmax. Now you want to add in propeller design?

The whining would never stop, not that it does now.

My suggestion would be to concentrate on accurately modeling the limits and behaviors found in the Operating Instructions.

Yes, this efficiency curve is a Pandora box. If il2 FM gets improved in propeller efficiency curve, the drag coefficient of many aircraft should be different from ealier, otherwise, how could aircrafts get accurate Vmax as historical data? For many years, blue side fans and red side fans argued a lot about engine output, boost level such as 1.8ata, 21lbs ,25lbs boost etc..... Now what ? Taking away 500HP from my engine when high speed dive? To degrade my bf109G6as into a bf109G6? OMG, just kill me.

I think it would be more realistic and easier to model the consequences of exceeding the dynamic pressure and mach limits of the aircraft than trying to find a generic braking point. You don't think, "my efficiency curve will drop off and drag rise due to compressibility will keep me safe" when you point an aircrafts nose down in a steep dive. You think, "don't exceed Vne...don't exceed Vne" as your butt cheeks suck up the seat.

For example, our FW190 tries to dive away from a P47. At ~466mphTAS, the FW encounters compressibility, and loses elevator control. The FW now happily sails to the dirt barrier or the pilot very very carefully uses the elevator trim to recover without overloading the airframe.

At 466 mph TAS, the P47 is in full control. He either:

1. Watches the FW hit the dirt barrier from the comfort of altitude.

2. Catches the FW on its straight path to the dirt barrier and shoots it down. His top speed is ~40 mph faster...

2. Follows the FW on its rather helpless recovery and shoots it down

When dive to 800km/h, the real world air compressibility costs more 200HP power than il2's none compressibility FM. It's not news and is already known by many people. Forthermore, as you said, in il2 4.11m, fw190 still has good elevator control above 466mph=750km/h.

However, my interest is not above 750km/h, just between Vmax(680km/h) and 750km/h. Could P47 get more efficiency than fw190 when steeply dives to 750km/h and then maintains 740km/h for 30 seconds in a shallow 10 degree dive?

Diving away is a very bad option for the FW190 if the limits are accurately modeled.

It is a good tactic for fw190 to dive away from spitfire. As <<Tempest in War>>said, many fw190 tried dive away when pursued by Tempestmkv, of course those fw190 usually got shot down. In history, those fw190 pilots succeeded in outdiving spitfire before they met tempest. That's why they tried dive away from tempest, they thought spitfire and tempest are similar in dive, but they were wrong.

Again, dive limit is NOT dive acceleration, IF my fw190 could dive faster than your P47 WITHIN 750km/h=466mph, I'll try dive away from P47 because that's a good idea. I'll keep dive speed within 466mph, so that your P47 has no chance to show higher dive limit. I'm sure I can get far away from your P47.

But the truth is that within 466mph, P47 still dives faster.