Acceleration comparisons

[gaunt1]

Originally Posted by FC99

Ps=(VT-VD)/W [m/s]
VT(La5FN) > VT(La5F)  -  more powerful engine -> more thrust
DT(La5FN) < DT(La5F)  -  cleaner airframe -> less drag
W(La5FN) < W(La5F)    -  La5FN is lighter 


Ps=dEh/dt
Eh=h+V^2/2g [m]   - Energy height

From that you can calculate acceleration.

All of the above combine = big difference in performance
When you know specific excess power, you can calculate climb and acceleration performance. Or you can go backward and measure acceleration(Like horseback is doing) and calculate Ps and rate of climb from it.

Dont know... Still fishy for me. La-5FN is only 150hp more powerful, but according to NII VVS tests, it is actually heavier (60-100kg) than La-5F. I strongly suspect that ingame FM is based on the performance of the prototype SN 39210102. If you look at horseback's chart, the performance of the FN is suspiciously better than the F. It should be of course better than the F, but not that much, maybe only 15-20%.

[horseback]

Originally Posted by gaunt1

Dont know... Still fishy for me. La-5FN is only 150hp more powerful, but according to NII VVS tests, it is actually heavier (60-100kg) than La-5F. I strongly suspect that ingame FM is based on the performance of the prototype SN 39210102. If you look at horseback's chart, the performance of the FN is suspiciously better than the F. It should be of course better than the F, but not that much, maybe only 15-20%.

The tables in Soviet Combat Aircraft Volume 1 by Yefim Gordon and Dmitri Khazanov show a top speed of 573 kph at sea level for the -5FN and 551 kph for the -5F, and I got a (rounded off) 560 kph indicated at 100m for the -5FN and a (rounded off) 530 kph for the -5F. True airspeed would be somewhere north of 578 kph and 548 kph respectively, so both aircraft models appear to be close to the RL records. Further reading seems to indicate that the -5F was flown most often with the canopy open in practice, due to accumulated exhaust fumes and (possibly) poor visibility, so there may be some compensation for that in the FM.

However, this is an acceleration comparison, and the extra horsepower of the M-82FN translated into better acceleration even more than better top speed, which with the similar airframes meant about the same major limiter to top speed; the -5FN reaches its intervals sooner (and really, it is only a second and a fraction difference at the initial stages, but the differences are cumulative--they add up over time).

Let's look at another indicator of the added power of the M-82FN taken from the same book I referred to earlier; the takeoff runs of the production La-5F were measured at 350m--compare that to the production La-5FN's 290m. That's a good deal more than a 10-12% difference right there, and I think it means that the FMs for these two aircraft are fairly accurate in this respect within the limits of the game engine.

cheers

horseback

[MaxGunz]

578/560 = 1.032, 3.2% more.

At 100m the difference should be less than 1% in standard conditions.

[gaunt1]

Originally Posted by horseback

The tables in Soviet Combat Aircraft Volume 1 by Yefim Gordon and Dmitri Khazanov show a top speed of 573 kph at sea level for the -5FN and 551 kph for the -5F, and I got a (rounded off) 560 kph indicated at 100m for the -5FN and a (rounded off) 530 kph for the -5F. True airspeed would be somewhere north of 578 kph and 548 kph respectively, so both aircraft models appear to be close to the RL records. Further reading seems to indicate that the -5F was flown most often with the canopy open in practice, due to accumulated exhaust fumes and (possibly) poor visibility, so there may be some compensation for that in the FM.

However, this is an acceleration comparison, and the extra horsepower of the M-82FN translated into better acceleration even more than better top speed, which with the similar airframes meant about the same major limiter to top speed; the -5FN reaches its intervals sooner (and really, it is only a second and a fraction difference at the initial stages, but the differences are cumulative--they add up over time).

Let's look at another indicator of the added power of the M-82FN taken from the same book I referred to earlier; the takeoff runs of the production La-5F were measured at 350m--compare that to the production La-5FN's 290m. That's a good deal more than a 10-12% difference right there, and I think it means that the FMs for these two aircraft are fairly accurate in this respect within the limits of the game engine.

cheers

horseback

That book is a good source, the data matches the NII VVS test results.
Regarding the exhaust fumes, I think the FN still had the same problem.
Im not a too good pilot, so I used IL2 compare for La-5F and FN speed data, and it shows close to prototype performance for the FN. Turn performance is also corresponds to prototype La-5FN. This is why I think that acceleration is also based on that.
I dont know how accurate IL2 compare is, but one thing is sure, all Lavochkins benefit from using Forsazh at all altitudes, while in reality it could be used only up to ~2700-3000m.

[horseback]

Originally Posted by MaxGunz

578/560 = 1.032, 3.2% more.

At 100m the difference should be less than 1% in standard conditions.

I'm using the on-screen display in Wonder woman view from the tracks as my reference, which is what I expect the average player would do; doing the calculations is more work than I want, and I expect it will confuse a majority of the people who are following this thread.

cheers

horseback

[MaxGunz]

Something there isn't right, IAS or TAS.

[IceFire]

Originally Posted by gaunt1

That book is a good source, the data matches the NII VVS test results.
Regarding the exhaust fumes, I think the FN still had the same problem.
Im not a too good pilot, so I used IL2 compare for La-5F and FN speed data, and it shows close to prototype performance for the FN. Turn performance is also corresponds to prototype La-5FN. This is why I think that acceleration is also based on that.
I dont know how accurate IL2 compare is, but one thing is sure, all Lavochkins benefit from using Forsazh at all altitudes, while in reality it could be used only up to ~2700-3000m.

That is the biggest problem with some of the engine boosts. It works well for the types that affected power at all altitudes but not at the ones that had limited altitude applications (except the very specialized GM-1).

The one thing I don't understand about Forsazh is why it has a limit in altitude. Was it something to do with fuel/air mixtures? The way that the supercharger on the engine interacted with higher pressures at altitude? I have no idea.

Also curious... La-5FN prototype... I know it was hand built but how different was it from a stock performance version from middle to late 1944? I was figuring that unless weight was substantially different (i.e. due to inclusion of standard equipment like guns, ammo, radio, etc.) it should be fairly similar to the later models that the game represents. The 1943 tag next to the La-5FN should probably be changed to 1944.

[horseback]

Also curious... La-5FN prototype... I know it was hand built but how different was it from a stock performance version from middle to late 1944? I was figuring that unless weight was substantially different (i.e. due to inclusion of standard equipment like guns, ammo, radio, etc.) it should be fairly similar to the later models that the game represents. The 1943 tag next to the La-5FN should probably be changed to 1944.

Generally, prototypes are handbuilt byskilled & experienced workers in close collaboration with the design engineers. Chances are that the early production La-5s, in many cases built from LaGG-3 airframes and parts lacked the fit and finish that makes an aircraft that last 10-30 mph faster.

When we talk about production models, you have to consider what conditions the work force operated under, how long they had been on the job, and how well the plant is run. In the US and Britain, early war production was performed in many cases by workers relatively inexperienced in the higher quality demands of aviation construction, but they were largely well supervised and worked in (generally) safe and secure facilities, so they improved rapidly and by mid-war, the vastly increased production quality was as good as or better than the pre-war 'artisan' standard.

Mid-war, probably most of the Soviet aircraft production was coming out of factories that had literally been picked up and moved a thousand kilometers or more just a few months earlier; the workers were often plucked off of the local farms and towns and had nothing like industrial experience and education to draw from, so they had to learn from 'scratch' and the surviving workers from the original facilities had to supervise them closely. The facilities where they worked were not as 'complete' as the ones that originally built that bureau's aircraft, and were considerably less comfortable and safe than their Western counterparts. It took them a bit longer to get their standards up to pre-war levels, and given where most of them started and the conditions they worked under, it was an exceptional achievement that they did so by the end of 1943/early 1944.

Japanese and German production quality appears to have gone the other way; the attrition of skilled workers to military demands, material shortages and enemy attacks coupled with the growing dependence upon captive labor made their production quality increasingly worse, particularly for the Japanese (that fighting to the last man ethos cost them a great many skilled technicians who should have been evacuated when things looked bad).

cheers

horseback

[JtD]

Forsazh on the Ash-82 could only be used in first charger gear. The second gear could not handle the high boost. In game, there's no performance benefit due to the increased boost in second gear to mirror this, even though you can switch it on at all altitudes.

[MaxGunz]

Is that like switching on WEP before you cross 100% throttle?