Performance Comparison: Yakovlev Fighter Family

[HoHun]

Hi everyone,

Here is a preliminary performance comparison between the various fighters of the Yakovlev family.

(This thread is a spin-off from Clay's thread here: http://www.ww2aircraft.net/forum/avi...ane-17485.html (P-40 vs. Yak-1 vs. Hurricane) )

I have restricted myself to the most typical ones with M-105P, M-105PF and M-105PF engines. One reason for that is lack of data - anything on other engines used in the Yaks and even on these three engines would be welcome! The M-105PF2 power graph I used is semi-synthetic, based on the assumption that the PF2 was the same as a PF, but cleared for higher boost pressures. The M-105P and PF power graphs are from a scan that appears to be a German wartime summary.

For the basic speeds, I have mainly relied on data reproduced from Yefim Gordon's and Dmitri Khazanov's Soviet Combat Aircraft of the Second World War Volume One: Single-Engined Fighters. (Thanks, Juha! :-)

To minimize possible errors from the semi-synthetic M-105PF2 power graph, I have based the Yak-3 speeds on the sea level speeds, while the other graphs are calibrated for absolute top speeds.

With the faster variants, there appears to be a mismatch between calculated critical altitude and recorded critical altitude. I'm not sure about the reason, some of it might be an artifact of the possibly slightly inaccurate German power graph.

The results are not definite yet, but generally I'm quite happy with them. Better source data might still allow improvements.

A power graph for the V-107A would be welcome as it would allow the inclusion of the Yak-9U! :-)

Regards,

Henning (HoHun)

[HoHun]

Climb rate ...

[HoHun]

Turn rate ...

[Clay_Allison]

I love the Yaks, myself. Really clean, really simple lines.

[Geshvader]

From book "Yak fighters in WW2 time period", author - A.T.Stepanets (chief engineer of "KB Yakovlev")

[tomo pauk]

Nice graphs, gentlemen

My Yak bird is the -3, but it was pretty late in game unfortunately.

[Timppa]

This is how the Yak-3 and Yak-9U are modelled in IL2 (AFAIK they did not have emergency boost, so I don't know how to interpret "100%" and "MAX"):


And "official" speed curves:

[claidemore]

A few websites:
Russian Aviation Museum
WW2 Warbirds: the Yakovlev Yak-1 - Frans Bonn
Yak-1
Yak Piston Fighters

and the best online perf comparison I've seen on Yaks.
Yak piston fighters

[HoHun]

Hi Geshvader,

>From book "Yak fighters in WW2 time period", author - A.T.Stepanets (chief engineer of "KB Yakovlev")

Thanks a lot! This shows different power graphs than the ones I used before, showing that the sequence M-105PA -> PF -> PF2 basically were identical engines with increased boost pressure in the newer types.

I have re-done the entire analysis, selecting slightly different aircraft than the first time around since I'm not more confident that the critical altitude and power figures are accurate (so some of the data points in Gordon/Khazanov didn't appear realistic, thus my switch to others).

Still, the Stepanets power graphs seem to give slightly too low power values at low altitude for my analysis to work, making it difficult to match sea level speed and especially turn rate data, while they are certainly too high at high altitude. The latter is an effect well-known for WW2 power graphs calculated according to the then-standard method, so I'm ignoring it for now.

For the graphs, see below :-)

Some remaining questions:

- How did the M-105P differ from the M-105PA?
- Which types had combined exhausts, and which had single exhausts?
- What were the propeller diameter and the reduction gear ratio used with the VK-107A?
- Which engine did the production Yak-3U actually use? Some sites say it was the VK-107A, others say it was the M-105PF.

Regards,

Henning (HoHun)

[claidemore]

Originally Posted by HoHun

Hi Geshvader,

>From book "Yak fighters in WW2 time period", author - A.T.Stepanets (chief engineer of "KB Yakovlev")


Some remaining questions:

- How did the M-105P differ from the M-105PA?
- Which types had combined exhausts, and which had single exhausts?
- What were the propeller diameter and the reduction gear ratio used with the VK-107A?
- Which engine did the production Yak-3U actually use? Some sites say it was the VK-107A, others say it was the M-105PF.

Regards,

Henning (HoHun)

Difference between 105P and PA:

In 1941 new engine of M-105P family M-105PA was installed on Yak-1. It had new carburetor, improved boost and rate controls, new shaft bearing design.

and:

Beginning in the summer of 1941, Yak-1s were also fitted with the improved Klimov M-105PA engine, which was more reliable than the M-105P, if still not entirely satisfactory, and could operate in inverted flight and negative-gee maneuvers.

AFAIK the Yak-3s which saw combat had the 105PF2 and the Yak-3U had the ASh82FN radial. Basically, the VK107 ones were 1946 models. I've read that there were 100 Yak 3's with the VK107 which were produced and used during hostilities, but there's no seperate model designation for them that I know of.

[HoHun]

Hi Claidemore,

>Difference between 105P and PA:

Ah, thanks! Doesn't sound like there was a difference in the supercharger gear ratio then.

>AFAIK the Yak-3s which saw combat had the 105PF2 and the Yak-3U had the ASh82FN radial.

Oops, I meant to ask for the engine of the Yak-9U, not the -3U!

Below the German information sheet on the M-105 and VK-107 I used for the first analysis ...

Regards,

Henning (HoHun)

[HoHun]

Below the German information sheet on the M-105 and VK-107 I used for the first analysis, second page ...

[HoHun]

Hi again,

>Still, the Stepanets power graphs seem to give slightly too low power values at low altitude for my analysis to work, making it difficult to match sea level speed and especially turn rate data, while they are certainly too high at high altitude. The latter is an effect well-known for WW2 power graphs calculated according to the then-standard method, so I'm ignoring it for now.

Here is a graph showing the effect of modifying the Stepanets power graphs above high gear full throttle height to a power value proportional to ambient air pressure. This is only a rule of thumb, but it seems to give good results.

In fact, the German power graph I posted above seems to be calculated following exactly the same rule.

(Note that Gordon/Khazanov give a ceiling of 9.1 km for the Yak-9D, which the modified graph misses relatively narrowly, while the original Stepanets graph yields a rather exaggerated high-altitude performance. This is a useful sanity check for the "ambient pressure" rule.)

Regards,

Henning (HoHun)

[HoHun]

Hi again,

I just found an interesting subtype in Gordon/Khasanov's list: The 1944 Yak-9PD with a high-altitude engine, 1 m wingspan extension (adding 0.5 m^2 of wing area), and a flying weight of just 2500 kg. This is less than the Yak-3, so I guess it was a stripped-down "racer" like the high-altitude Spitfire V modifications!

Due to its low weight, manoeuvrability and climb rate are quite impressive ...

(The calculations based on power graphs modified according to the "atmospheric pressure" rule of thumb as described above.)

Regards,

Henning (HoHun)

[HoHun]

Hi Claidemore,

>A few websites

Thanks, interesting stuff up there!

Even Stepanets' book can be found online following your links:

Stepanets. Yak Fighters in WWII

In Russian, of course :-/

Regards,

Henning (HoHun)