What makes La-7 ~30-MPH faster than La-5FN at ALL Altitudes...

[Krusty]

f4udoa, but do you have anything on the la7? I'm wondering why such a big jump from la5 to la7.

[Badboy]

Originally posted by Krusty
Do we have any non-Soviet sources that tested this aircraft? Perhaps NACA or captured LW, or even British/US tests?

The German tests on the La-5FN were flown by Hans-Werner Lerche, who has subsequently published the La-5FN report in the appendices of his book:

Luftwaffe Test Pilot: Flying Captured Allied Aircraft of World War 2.
ISBN 0 531 037118.

In that book he has chapters on aircraft that he tested including a B-17, Ju290, B-26, B-24, Spitfire, P-39, P-47, P-51, La-5, Yak-3 and lastly a Do 335. However, the La-5 is the only one that has the test report included in the appendices.

Badboy

[Krusty]

Okay, but then what about the LA-7? If we can get some independent data on the -5, we then need some independent data on the -7.

[Knegel]

Hi,

is it possible that the La7 Vmax was made with max power, while the La5FN Vmax is made with "combat climb"??

The main and probably most important different between La5FN and La7 was the improved cooling system. The La5FN only had a real energency power, usable at highspeed while it wasnt allowed while climbing. In the La7 it was allowed to run the engine for around 10min on max power, also while combat.
Thats similar like the DB601E vs DB605A, both had a similar max power in 1942/43, but the DB605 could use it for much longer time.
Also the SpitVc in WEP was similar good like the early SpitIXc, but WEP is what it is and dont count much while combat.

The La5FN was great even without WEP.

Why the La7 perform so good in AH i also cant understand. On my side its in the same class like the US "magical flaps" and the FW190A8/P38 "super E-bleed".

Greetings,

Knegel

[Tilt]

All my la 7 data is VVS or Tsagi sourced........the only non Russian La5FN data I have is Lerches.

Having said that ......it is la5FN data that is the rarest and I have no copies of originally sourced La5FN tests as I do La7.

If other non Russian data exists then I am sure you will find it to be Czech as they continued to use both types long after the VVS dropped them. Certainly the most authoritative descriptive (English language) texts on the types are Czech

I have not heard of any pilots that preferred the La5FN over the La7.

Pokryshkin was responsible for converting 16GIAP (9GIAD) from the P39 to the La7.He received them on the 21st Oct 44. each had a distinct red nose and had painted on the side (in Russian) To Aleksandre Pokryshkin from the workers of Novosibirsk However a fatal accident to capt Klubov after a stunt showing of the La7 (it flipped on landing) caused 16 GIAP loose confidence...... some of their pilots flew it to the wars end whilst others remained with the P39.

The early (first batch) La7 was very uncomfortable to fly as the cockpit over heated and some times filled with exhaust gasses.

Other than an upgraded prop the only difference between the two was one of reduced pure drag and a relatively minor weight saving.

There is speculation that the engine cooling on the La7 was more efficient. Certainly Czech pilots flying the La5 FN noted that the upper cylinder could overheat if engine temperature was not monitored. (this sort of indicates that the upper cylinder was more vulnerable than the rest)

I have two speed v alt curves for the La5FN (probably from the same source) that do not indicate WEP (2500 rpm) at all where as the La7 could use it as shown in AH's curves.

Both these curves also show the 2nd stage of boost occurring at approx 4900 m alt on the La5FN but at approx 4300m on the La7. (AH's La7 is inaccurate in this sense as 2nd stage boost is not until after 16000 ft...manifold is back to 40" at 17K)

Both these curves show the speed diferential widening between 4200m and 4900m to approx 52km/hr IAS and then narrowing again to about  48km/hr at 6000m.

The engine was bench rated to run at 2400 continuously, 2500 for 10 mins continuously and 2600rpm for 30 secs (from the La7 pilots notes) however I have no account of any airborne test at 2600 rpm.

Where data is missing is stuff like E bleed and roll rate etc. (Lerches roll rate  for the La5FN is the only roll data I have seen for both types.......he sort of mentions it in passing during one of his reports.)

There are opined comparisons by Czech pilots between the La5FN and the SpitVb there is no data but they find it very comparable once its off the ground

[Meatwad]

I heard the fuselage is rubbed in cheeta blood before flight

[Knegel]

Hi Tilt,

thanks for the reply.

Do you know the power output fitting to the rpm??

2400rpm=??
2500rpm=??
2600rpm=??

For now i only saw two different rpm/power settings for this engine, the continuous and the 10min setting.

Greetings,

Knegel

[Tilt]

I have no original data that refers directly to Hp.

In the set of figures posted on another thread here all tests refer to a "take off power loading" for La7's (1.75 > 1.76kg/hp) which when back calculated reveals the oft quoted figure of  1850hp. (@2500 rpm)

We read many accounts that   state

2400rpm  > 1650 hp
2500rpm  > 1850 hp
and one account
2600 rpm > 2000 hp

However for practical purposes I would forget this reference to 2600 rpm. It may apply to a bench tested Ash82FN but no tests were carried out at this rpm on the la7 to my knowledge.

All tests refer to the manifiold pressure at the rpm used.

2400rpm > 1000mm +/- 10 (39.37")
2500rpm > 1200mm +0/-20 (47.24")
2600rpm > ???


Many tests refer to Altitude boundaries

(1) is where WEP is no longer of any use ie manifold pressure at 2500 rpm @1st stage of Boost is equal to manifold pressure at 2400rpm 1st stage of boost. Above this alt the 1st stage boost manifold pressure drops off at when at 2400rpm to.

(2) is the altitude where the 2nd stage of boost is introduced. (or contrary the highest altitude that 1st stage is used at)

(3)is the highest altitude where the manifold pressure is at max when 2nd stage of boost is engaged.

so we see these "boundaries" when the ac is at max speed for its alt.

(1) is at 2400m, (2) is at 3250m, (3)is at 6250m

For max climbing trials the boundries change........infact they become lower.

(1) is at 1600m, (2) is at 2560m, (3) is at 5100m


This does not seem to be repeated with AH "boundaries"

At Max speed

(1)is at 2675m, (2a) is at 4880m, (2b)is at 5185m, (3) is at 6100m

During max climb

(1)is at 2250m, (2a) is at 4575m, (2b) is at 4880m, (3) is at 5800m.


re 2a & 2b. In AH the lowest 1st stage boost is at 2a and the lowest alt at max manifold pressure (2nd stage) is 2b. I dont know why there is such a lengthy transition.

So whilst AH's max speeds, turn rates and climb times (note I do not say climb rates) seem to agree with historic data on the La7 its manifold guage readouts do not............

I do not know how much the manifold readouts in AH actually interface with the power/drag model. They do seem to interface with the WEP boundries..........so at least this could be considered overmodelled in AH.

[Spikes]

If I am not mistaken...The La-5 is a better turner...and the La-7 is faster (for BnZ, which I most hate). I fly the LA5 more because I dogfight more in it

[Tilt]

Here is a max speed and climb rate test on an la7 showing the boundaries at speeds and during climb with the various altitudes, climb rates and times with and without WEP



One question I always had was given the translationre these boundaries why is the max speed at 2500 rpm faster at 3000m when there is no manifold adavantage?

[Tilt]

Here is the rest of the data I have on ac No.45213276

[Knegel]

Hi again,

thank you very much for this datas, i never saw the original sheet!

1. is rated altitude for WEP.

2. is the point where manifold pressure at 2500 rpm @1st stage of Boost is equal to manifold pressure at 2400rpm 1st stage of boost. Thats why they switch to the 2400rpm.

3. is rated altitude with 2400rpm.

What they miss in this sheet is the point where the 2nd stage of boost is introduced.

You can imagine this point if you draw a speedsheet.

Somewhat like this:


The AH values are all over around 200m higher than what this data sheet show, but its not realy far off!!

But anyway, its not this static performence that seems to be strange in the La7, its rather the extrme smal E-bleed. In relation to the 1100kg more heavy 190A8 or 190D, the La7 should bleed energy like mad, but strangewise its the other way around.

Greetings,

Knegel

[gripen]

Originally posted by Knegel

2. is the point where manifold pressure at 2500 rpm @1st stage of Boost is equal to manifold pressure at 2400rpm 1st stage of boost. Thats why they switch to the 2400rpm.

That makes no sense; if rpm is reduced from 2500 to 2400, it should be done simultaneoysly with gear change (at about 4800m in your chart) and that is what your chart show. AFAIK that's also the way it was done in the La-5/7 ie 2500rpm was allowed just for 1st gear.

gripen

[Tilt]

Originally posted by Knegel
Hi again,

thank you very much for this datas, i never saw the original sheet!

1. is rated altitude for WEP.

2. is the point where manifold pressure at 2500 rpm @1st stage of Boost is equal to manifold pressure at 2400rpm 1st stage of boost. Thats why they switch to the 2400rpm.

3. is rated altitude with 2400rpm.


Knegel

Is that your translation Knegel? I thought the literal translation was

1st stage altitude boundary for WEP
1st stage altitude boundary for Mil power
2nd stage altitude boundary for Mil power

I have some curves generated from the test figures.............I am not sure of their date however I'll post them tonight......your WEP band seems to go higher in alt then my memory tells me.

When you look at the climb rates you can see when the power:drag ratio changes at these boundaries by the changes in climb rate. I always kinda took this as indicating that as the point where (when in climb) the level of boost currently engaged could no longer achieve max manifold pressure.

[Simaril]

Originally posted by Mustaine
the purple power bands

I actually got this joke. Does this mean I'm  hopelessly trapped in net geekdom?