Yak-9 Klimov M-105PF engine

[the_emperor]

Hello there,

 

I was wondering why the Yak-9 does seem to have more power when the RPMs are reduced:

Maximum power in Nominal mode (2550 RPM) at sea level: 1240 HP
Maximum power in Nominal mode (2700 RPM) at sea level: 1210 HP

 

 

The Yak-9 series seems to be the only M-105PF driven plane that is favoured by this and can convert that power into considerable more speed. All other M-105PF planes dont mention that or cant harness that extra power into speed.

 

Cheers and thanks for the enlightenment

 

 

[CountZero]

27 minutes ago, the_emperor said:

Hello there,

 

I was wondering why the Yak-9 does seem to have more power when the RPMs are reduced:

Maximum power in Nominal mode (2550 RPM) at sea level: 1240 HP
Maximum power in Nominal mode (2700 RPM) at sea level: 1210 HP

 

 

The Yak-9 series seems to be the only M-105PF driven plane that is favoured by this and can convert that power into considerable more speed. All other M-105PF planes dont mention that or cant harness that extra power into speed.

 

Cheers and thanks for the enlightenment

 

 

 

works on all yaks the same, 2550rpm up to 1km gives you more speed

[the_emperor]

Is there any documentation that the engine does produces more HP at lower RPM at low altutide?

I have not found any thus far,

I know its just a minor detail, but it does intrigue me, as I am growing more fondly of the sowjet fighter planes and like to get as much technical information about them as I can.

The Yak-9 does get some 6-8kph more with the reduced RPMs.

all other M-105PF planes ~0-3kph more (Lagg 3 and the other Yak variants).

Cheers

[palker4]

I guess it is connected to supercharger boost. At sea level the supercharger boost at 2700 cannot be used, so it just takes power to drive it at higher rpm and you get nothing in return

[JtD]

The manual of the M-105 as well as a booklet on "How to fly a Yak" both show that the M-105 develops more power at 2550rpm below full throttle height than at 2700rpm. This has mostly, but not only, to do with the wasted power the supercharger consumes.

 

The M-105 by the way is not the only engine where this happens. Additionally, when it comes to top speed, most (fighter) aircraft gain prop efficiency by lowering rpm at high speed and can gain speed by that - even if that doesn't increase engine power.

In real life, running full power at less than maximum rpm would not be recommended, though, due to engine knocking and other foul things that happen with the engine when abused.

But lower than maximum rpm recommendations for cruise are there for several reasons, also because it works more efficiently.

[CountZero]

in game 109k4 manualy going 2500-2600rpm gives you similar boost in speed on deck
109g2 manualy raising rpm to 2800 rpm gives you boost you dont have, and it works up high also, you can safly use it for few min.
P47 going 2550 rpm gives you better speed, p-51 and Spit 9 also and so on... yaks are not alone in this in game, theres probably others i dont remenber with their own tricks.

[the_emperor]

Thank you all very much  ?

[6./ZG26_Klaus_Mann]

P-47 also goes a lot faster with lower Revs. Never ever run it above 2550rpm unless I go into Turbo overrev.

[CountZero]

50 minutes ago, 6./ZG26_Klaus_Mann said:

P-47 also goes a lot faster with lower Revs. Never ever run it above 2550rpm unless I go into Turbo overrev.

From tests i see that 2550rpm is better for top sped up to 23000ft (7km), abow that it slows you down, also in climb more rpm is better at any alt.

[6./ZG26_Klaus_Mann]

On 8/26/2021 at 5:40 PM, CountZero said:

From tests i see that 2550rpm is better for top sped up to 23000ft (7km), abow that it slows you down, also in climb more rpm is better at any alt.

Yup, that's when you run into Turbo Overrev.

[CUJO_1970]

That’s not how the engine operates in real life.

[the_emperor]

here is chart from a Yak manual detailing how to get the most speed of your Yak fighter:

 

[Bilbo_Baggins]

Why doesn't this also apply to the Lagg-3 with the same M-105PF motor?

[the_emperor]

I dont know. The biggest difference is notacible in the Yak-9.

[the_emperor]

Some additional informations from the Lagg3/Yak manual regarding the engine limitions (though I dont now how they are implemented in the game and they are a bit contradicting):

1) Do not allow water and oil temperatures above 110 °C

2) Water: max. 10 min for 110°C

3) Oil: max: 115 for 5min; max 110°C for 10min

4)The recommended water and oil temperature is 90-100 °C

 

The manuals do not specify whether the limits are meant at a stretch (with cooling/recharge periods in beetween) or cumulative per mission.

 

Edited December 7, 2021 by the_emperor