I think initial acceleration is roughly proportional to max RoC.

As Far As I Can Tell Right Now:

As long as you can hold TAS steady, Ps = change in height / change in time.

And there's correction for when you can't that with 10/sec data rate from devicelink should be possible to get closely.

See equation 7.2 on page 14 of this PDF:
http://www.aviation.org.uk/docs/flig...-FTM108/c7.pdf

When change in TAS = 0, the correction factor goes away. A tiny change in TAS at low airspeed will make a small correction necessary.

Ps =dh/dt + VT / g * dVT / dt

where
d is "change in"
h is height
t is time
VT is TAS
g is gravity

dVT being change in TAS, if it is 0 then everything past dh/dt is 0

I have found close to steady IAS climbs to be easier to fly in IL2 than trying to keep level at full power from 200 kph to full speed.

Remember that Ps changes with both speed and alt. Whatever tests are run need to cover as much of the range as you want to chart. You don't have to get speed at every last kph or alt at every meter but the closer you get the smoother/more accurate your connect-the-data-dots curves will be.

That's as good as my NOT-AN-AE-SELF can do right now, the simple things.

Exactly. The climb vs TAS diagram for a certain altitude also represents the Ps diagram for that altitude. To get the exact value of acceleration an aero plane can have in level flight at a certain altitude and airspeed multiply Ps value for said altitude and airspeed by gravitational acceleration and divide it by airspeed. Comparison of the ability of two aircraft to accelerate in level flight takes only a look at the ROC vs airspeed diagram in IL- 2 compare with the two aircraft selected: that which can out climb can also out accelerate. To express that in percents for a certain airspeed just calculate the percentage of advantage in ROC one aero plane holds over the other. Off course, we only have these diagrams available for sea level, but MaxGunz already explained this.

I thought we only have them for 1000m.

But for many speeds at whatever alt we can compare FW accel to other planes *at the same speed*.

For the math challenged who can use the Windoze calculator, if you take the speed of the faster plane and divide by the speed of the slower plane then subtract 1 and multiply the result by 100 you will get the percent that the faster plane is faster.

640 / 620 = 1.032258064516129032258064516129

subtract 1 to get .032258064516129032258064516129

times 100 is 3.2258064516129032258064516129

640 is 3.2% faster than 620.

Comparing acceleration is the same way only it's acceleration, not speed.

Now repeat after me: The Sky Is Falling! The Sky Is Falling! It's A Conspiracy! The Sky Is Falling!

According to that formula, La-5FN acceleration is 55.555...% better than La-5F. I think 15-20, maybe even 30% would be acceptable for a meager 150hp more powerful engine + a tiny little less drag (but 60-100kg higher weight). If you check NII VVS tests, you can see maximum 20-25% improvement in other performance charts, (speed, climb, turn time) nowhere near the 55%. Obviously prototype performance. If you still think this isnt suspicious...

I really don't see where your 55% come from, from il2compare I get climb at sea level La-5F: 17.5 (21.5 with boost) and La-5FN 21.2 (25.3), which both is around 20% better acceleration for La-5FN

I'm starting to wonder whether I'm reading the charts correctly as the ROC advantage the La- 5FN holds over the La- 5F appears to be 4 m/s at it's greatest. At 280 km/h the rate of climb of La- 5FN is 22 m/s, while the La- 5F has the rate of climb of 18 m/s. That hardly constitutes a 50% advantage. 27 m/s of ROC for the La- 5FN would constitute that. This conclusion was reached by looking at the Airspeed vs ROC diagram in IL- 2 Compare, which doesn't include ROC with WEP used. Altitude vs ROC does (darker lines), and the best climbing speeds at sea level appear to be 25,3 m/s for the La- 5FN and 21,5 m/s for the La- 5F, which is, once again, between 15% and 20%.

Beat me to it :)

Ps is for both altitude and speed.

There is no one ratio at any height that expresses La5 vs La5FN.
Even worse is trying to nail one number as the complete plane vs plane comparison.

I have IL2Compare 4.07m. I never bothered to upgrade since because why?

La5 at 0m alt ROC at TAS 280 kph is about 18 m/s and La5FN about 22.
La5 at 0m alt ROC at TAS 400 kph is about 12 m/s and La5FN about 16.
La5 at 0m alt ROC at TAS 500 kph is about 2 m/s and La5FN about 7.

La5FN to La5 Ps ratios?

At 280 kph, 122%. At 400 kph, 133%. At 500 kph, 350%.

FWIW, playing on performance margins is and has been part of aerial combat since fighter pilots noticed such margins in WWI.

And once you get over the charts (some never do) you might realize that what Pilot A can do in Plane X vs what Pilot B can do in Plane Y is -part- of the real difference with start conditions able to overturn that which is why aerial combat tactics always begins with initial positioning and speed.

IL2 has high realism. History tells of whining fighter pilots, at least in the USAAF where they wouldn't get shot for it.

Highlighted for importance.