Engine cooling drag on Lavochkins

[Tilt]

I dont know if the lavochkins have ever changed with respect to the effects of non induced drag and "thicker air modelling" as oft mentioned re P51's.

Actually I think this post has little to do with it except that thicker air for one drag effect will also be thicker air for another.

This is with respect to engine cooling feathering.

I note that from the La5FN pilots notes we see that WEP is more than just setting the engine speed from 2400 rpm to 2500rpm (at what ever ideal prop pitch)

WEP or fastest speed setting is also about feathering the inlet and outlet engine cooling vanes to reduce the drag of the engine cooling cavities.

In those notes it states that such feathering makes a difference of some 15km/hr alone on the (I assume) SL top speed.

So given a top speed of some 560-570km/hr how significant is the non feathered drag to pull that down to 545/565km/hr.

What effect may it have on acceleration? across the speed range?

Whilst the engine cowling of the La7 was significantly more streamlined externally. The internal cooling air path and its control vanes was very similar to the La5FN. It was more efficient for cooling but was it also more efficient for drag?


To go further we note that La5FN WEP during climb is severly limited and indeed other sources ( czech regiment during 44) show the generic use of WEP limited to some 2 minutes.

Its not clear if the cooling is feathered during climb but one suspects not or if it was as mentioned in the Rechlin tests such WEP (and feathering) is quickly extinguished during climb.

This sort of fits in with the "quite" slow airspeed used during Lavochkins optimum climb.

Tests on the La7 show that WEP was used thoughout the first altitude stage of climb for optimum climbing.

No lavochkin could use 2500rpm after the 1stage above 13.5K/14.5K ft(during 2nd boost speed) as this would quickly wreck the engine.however the vanes could have been feathered to achieve the top speeds set at higher altitudes.

[Krusty]

You consider over 4,000 fpm climb rate up til 7,000feet "a bit slow"??


Just from what I've seen, HTC takes into account different settings for climb and for level speed. On some planes you'll see the boost drops as you climb but when you level out it will pick up, etc...

I'm almost sure they've got this effect modeled already, they just take the minutae out of the hands of the pilot.

Other sims try to make things overly complicated for complexity's sake, and it ruins the game. I'd rather have HTC model the end result and not have to deal with it personally.

[Fulmar]

Originally posted by Krusty
Other sims try to make things overly complicated for complexity's sake, and it ruins the game.

Oh man my fuel mixture!

/il2

[Tilt]

Originally posted by Krusty
You consider over 4,000 fpm climb rate up til 7,000feet "a bit slow"??


.

Not the rate of climb................ that is very good.

However it is achieved at a comparatively low IAS when  compared to the best climbing speed of other ac of comparable top speeds.

and yes AH boost does vary with alt and possibly with airspeed.

However has AH modelled Lavochkins non WEP (engine cooling) drag accordingly? I would not ask for more complicated pilots stuff but it does seem to me that the Lavochkins peak performance should be very much WEP dependant with quite a drop in acceleration etc when WEP is not fully engaged.

my fundamental question is.........

is a drag effect that takes 15km/hr of the top speed significant enough to also reduce acceleration at lower speeds?

[Krusty]

The top speed doesn't determine the climb speed, the shape and efficiency of the wing itself do. Unrelated, I would think.

[Viking]

Originally posted by Tilt
is a drag effect that takes 15km/hr of the top speed significant enough to also reduce acceleration at lower speeds?

No, I don't think so. At lower speeds parasitic drag is a minor factor.

[Tilt]

Thanks Viking..........

[Tilt]

My appologies re reading the La5FN pilots notes it advises that closing the engine cowl air vanes increases (or decreases if left open) the top speed by some 40 - 50 Km/hr.

Further it increases the optimum turn time by 1.5 to 2 secs.

I am sorry for not checking my figures more thoroughly earlier.............


However it does point to significant differences in top speeds between the two vane settings regardless of the rpm settings

Further it says that rpm based boost should not be used longer than 5 minutes.