Captured German La-5 flight test

[Kweassa]

Tilt, I have some questions:

The statement re WEP again (for me) confuses the use of WEP in the La 5FN (V). I have other documents that infer that its WEP was not of the duration that could be used on the La7 (Albeit for earlier La5FN models.) And only safely used for 2 mins.

 Does this mean that the La-5FNs had a WEP duration of 2 minutes, as a whole? What are the WEP conditions in that case? Is the quoted '2500rpm @ 1180C.S.' the WEP configuration?

However this quotes the manifold pressure at 2500rpm at 1180......I thought it was higher than this at 2500rpm (1200 ). Indeed at 2600 rpm the pilots notes claim that manifold should be 1260 but his could only be used at take of for no more than 30 secs!

 Then the 2600rpm was the WEP, and the 2500rpm merely a higher power setting? The definition of the WEP status concerning the La-5 is confusing>

Fumes in the cockpit bedeviled all lavochkins

 I've also seen this mentioned, but where exactly does it surface in records? From individual anecdotes?

 All in all, what documents are your claims on the performance based on? I'm just curious If the material may not be disclosed, and cannot be answered on the forum, then I understand.

[Tilt]

Originally posted by Kweassa
Tilt, I have some questions:



 Does this mean that the La-5FNs had a WEP duration of 2 minutes, as a whole? What are the WEP conditions in that case? Is the quoted '2500rpm @ 1180C.S.' the WEP configuration?



 Then the 2600rpm was the WEP, and the 2500rpm merely a higher power setting? The definition of the WEP status concerning the La-5 is confusing>

WEP on the La5FN

Firstly actual performance trial data on the La 5FN is rare......... more so than the La7.


Early on when I started getting basic published curves for the range of Lavochkins in various Eastern productions I found that the WEP curve for the La 5FN was missing.

These publications were not hard data and potentially subject to some romantic aspirations.

One was an Article by Alexyenko and Kondratiev that had been translated. I do not know the credentials of either.

Another were a couple of Czech articles.

In an out of print book called "In the cockpit" there is an article written consulting two Czech pilots who flew La5FN's.

They comment from a pilots perspective that engine temperature had to be watched.

Which gave the impression that even max cont. power 1650hp @ 2400 rpm could not be used continuously under all conditions.


They refer to 2500 rpm "take off power" that could only be used for 2 minutes.......

This then starts to agree with the Russian articles.

We then look at the development criteria for the La7 and we see  the cowling was subject to considerable work. Not only for external steam lining but also with respect to internal air flow.

Forward air vanes were the same as the La5FN but thespinner was smaller and the front cowl lip radius changed to give a bigger radial intake gap also exhaust rooting and the rear air vanes were redesigned. Also the cowl top intake was removed and intake air was rooted to the engine from behind and not over the cylinders.

What we see is a system far more able to distribute cooling air around all the Ash82 FN's cylinders.

I speculate (and always have) that the La5 FN could not make full use of its engines WEP capability due to its engine cooling limitations.

Rechlin also makes comment that WEP could not be used during climb...........its not clear if this refers to it not being useful (which I dont believe) or infact that it could not be used (like it was not allowed). Airflow through the engine cooling system would have been poor during climb in comparison to higher speed straight flight use.

However I have never had hard data to confirm it beyond the above. My comments above refer to the fact that Rechlin seems to support the view.

The 2500 rpm developing 1180 man is WEP.

Rechlin again refers to the power being 1850 hp at take off which the engine stats in the la7 pilots notes refers to as being derived from 2500rpm and 1200mm.

Ex factory the manifold is 1200 at 2500 rpm 20 mm could even be down to gauge accuracy or indeed supercharger wear or even incorrectly set throttle........its not a biggie.

The ex factory Ash82 FNV spec shows it can generate 2000 hp when revs increase to 2600 and then specifies that this can only be done for 30 secs! It refers to it as take off power.

IMO this is  next to useless  which is why I doubt it was ever used.

The ex factory Ash82 FNV spec shows it can generate 1850 hp when revs increase to 2500 and then specifies that this can only be done for 10 minutes! It refers to it as war emergency or combat power.

To sumarise ........my belief is that the use of WEP (2500 rpm) was not actually limited by an arbitary time period. It was infact limited by the engine temperature that the higher revs generated. I advocate that the air cooling system on the La5Fn was not as efficient as the La7 and so WEP duration was reduced.

Basically the way the la5FN engine was mounted and cooled it got hot quicker than the la7.

Every book written on the la5, la5f, la5fn, la7 refers to the two problems of high cockpit temperature and engine fumes and the various solutions tried to solve them.  It would be a reason that La pilots usually "cruised" with the hood pulled back.

[niklas]

Tilt wrote Ex factory the manifold is 1200 at 2500 rpm 20 mm could even be down to gauge accuracy or indeed supercharger wear or even incorrectly set throttle........its not a biggie.

100% correct. Combat power is 1000mm afaik, so there´s 50PS difference at best. BTW, 1180mm is the proof that it was a 1850PS engine with direct fuel injection. Russians still don´t want to believe that it was a late war engine. The difference to their specs (580km/h at sealevel with wep) is astonishing high...But where should germans know about 1180mm boost from?

There are some  mistakes in the english translation of the report. The climbrate with combat power is listed at 16-17m/s instead of 16.17 in the german print. The part about the supercharger should be better translated in the following way:
"The usage of emergency power for the high altitude gear of the supercharger is forbidden"
This is confirmed by russian tests where you don´t see any wep ratings when the engine runs in the high alt gear. AH also simulates this, the engine quickly loses power. AH wep power over 3km is actually normal power in real life, but it´s ok to do it this way. Imo the compressed air was too hot in the high alt gear with wep. It probably would have produced "knock outs" (correct expression??)
The higher fuel consumption in the high alitutde gear of the supercharger also indicates that a rather rich mixture was used in this condition to produce an inner cooling effect.

niklas

[joeblogs]

It think you are exactly right on this.  RAM air can be affected by the plane's angle of attack.  A poor intake design might exaggerate the problem in a climb.

-blogs

Originally posted by Tilt
WEP on the La5FN

...Rechlin also makes comment that WEP could not be used during climb...........its not clear if this refers to it not being useful (which I dont believe) or infact that it could not be used (like it was not allowed). Airflow through the engine cooling system would have been poor during climb in comparison to higher speed straight flight use.

...To sumarise ........my belief is that the use of WEP (2500 rpm) was not actually limited by an arbitary time period. It was infact limited by the engine temperature that the higher revs generated. I advocate that the air cooling system on the La5Fn was not as efficient as the La7 and so WEP duration was reduced.

Basically the way the la5FN engine was mounted and cooled it got hot quicker than the la7.

Every book written on the la5, la5f, la5fn, la7 refers to the two problems of high cockpit temperature and engine fumes and the various solutions tried to solve them.  It would be a reason that La pilots usually "cruised" with the hood pulled back.

[LLv34_Camouflage]

Here's a comparison with AH and FB 1.11 (according to Youss's IL2 Compare).



Camo

[LLv34_Camouflage]

It seems like the La5FN in the report has in fact been a damaged La5F, which didn't reach full performance. It definately was not a La5FNV, since only one experimental engine with the FNV index was produced.

I'll try to get more info.

Camo

[Tilt]

Originally posted by LLv34_Camouflage
It seems like the La5FN in the report has in fact been a damaged La5F, which didn't reach full performance. It definately was not a La5FNV, since only one experimental engine with the FNV index was produced.

I'll try to get more info.

Camo

There are records (Photographs) of an La5 f captured in 43........ it was tested without spinner cap which was destroyed.

But to confuse a late model direct injected engine with a boosted induction carburettor system would be very lax.

Since my posts above I found two publications (that may use the same source) that the La 5FN (V) tested at rechlin was captured in September and tested in October. Albeit that the above report is apparantly dated March 45. (I dont know where Rechlin is but would be surprised if Germany had time to concern its self with testing a 2nd line enemy aircraft in March 45)

The FNV was the only version of the Ash 82- FN (V) series produced from about April/May 44 onwards.

All but a  few of the early La7's had it. La5FN production only continued into October due to a massive stock of wings at two plants and as soon as the older FN engines were used up FNV engines were installed into La 5FN (V)'s. I do not know how many but it would have differred for each plant.

We should not get too over excited about the FNV however. It was able to give out slightly more power at higher altitudes from which I read that the 2nd stage of boost  gave  greater potential power than the previous FN version.

We know some stuff about the Unit tested from the data above.

The machine had been in service for some time. (Design life of an La5FN was 6 months..... expected life was 4 to 5 months..... many were used longer than this.)

There was a 50kg weight imbalance that still intrigues me.

The manifold pressures at 1180 would not have produced full WEP. (this could be an error)

The limited use of WEP seems to be based upon and instruction (not permitted) rather than a technical deduction. ( I have my own theories as to why)

I read a mix of data based upon actual trials and some derived from either captured data or intelligence from captured pilots.

I wonder what octane fuel was used. The proper octane for the Ash 82 FNV was 95. Available at the time of test was B4 (87 Octane) or C3 (96 Octane) and possibly another fuel rated 92 Octane [C2?]

[joeblogs]

Could just be the fit and finish of the plane.  Russian production models (planes and engines) were notorious for a 10-20 percent slip in performance relative to test reports.

-blogs

Originally posted by LLv34_Camouflage
It seems like the La5FN in the report has in fact been a damaged La5F, which didn't reach full performance. It definately was not a La5FNV, since only one experimental engine with the FNV index was produced.

I'll try to get more info.

Camo

[Tilt]

Originally posted by joeblogs
Could just be the fit and finish of the plane.  Russian production models (planes and engines) were notorious for a 10-20 percent slip in performance relative to test reports.

-blogs

That too........ although I would have said upto 10% slip in the main. One plant was notoriusly worse then the other...........often adding significant weight just from over use of glue!

[Tilt]

I am intrigued by the references and terminology used ...........

Upon extension of the slats the aileron control is said to "reduce to the point of overbalance"............. at 200 to 210 Km/hour (the period over which slats extended/retracted)

Lowering speed to 180 it refers to the "damping being reduced".....


I read this that roll rate control (as opposed to actual roll rate) was damped (almost lost) during the slat extension  but returned at lower speeds up until point of stall.

This seems to indicate that there was a considerable roll mushyness between 200 and 210 Km/hour greater than that experienced both above and below that speed range.

Does this seem to fit with what would be expected?

[MiloMorai]

Originally posted by Tilt
I dont know where Rechlin is but would be surprised if Germany had time to concern its self with testing a 2nd line enemy aircraft in March 45

"A central test centre was established at Rechlin on Lake Müritz in Mecklenburg-Vorpommern, in 1933."

Lake Müritz is ~100km NNW of Berlin.

There is a museum there.

http://www.luftfahrttechnisches-museum-rechlin.de/
http://www.luftfahrttechnisches-museum-rechlin.de/html/body_englsich.html

[Bogun]

Gentlemen, you seems to be having problem distinguishing between two different versions of the same engine.
The only engine which was marked as M-82FNV (Firsirovanniy Neposredstvennogo Vpryska – Busted, Direct (Fuel) Injection) was installed on test batch of LA-5FN sent to front sometime in April-May of 1943. Those engines were clearly marked as this - M-82FNV. Shortly after official designation for this engine was finalized and next production batch of La-5FN had engines marked as M-82FN.
Not long  after that the name of the engine was changed again to ASh-82FN in recognition of the contribution of its designer A. Shevtsov.

All following Lavotchkin fighters have modified ASh-82FN engines marked exactly as ASh-82FN. There was no such thing as La-5FN(V).

Engine ASh-82FN(V) – (V for Vysotny – High Altitude) was the modification of ASh-82FN was never installed on La-5FN, nor was it ever installed on any other Lavotchkin prop fighters. ASh-82FN(V) engine was installed on Tu-2 bomber and some of the post-war transport planes.

It looks like that La-5FN tested in Rechlin was one of the first batch of La-5FN produced on April of 1943, which crash-landed in East Prussia sometime in the Fall of 1944 and somehow restored to a flying condition. It was the only La-5FN captured by Germans and it was way past its resource limit.

[niklas]

lol, bogun, always the same weak argument. Actually the FNW term was commonly used in western sources for the direct fuel injected engine. Intelligence maybe heard about the project in russia, thus when they captured the la-5FN they simply called the engine FNW.
In any case, the boost 1180mm clearly indicates that 1850PS rating was used (maybe slightly less, 1850 is 1200mm). Climbrate of 16-17m/s also indicates FNW engine, and furthermore, an engine that develops full rated power.

It was a captured aircraft, of course, and noone expect it to perform like a factory fresh one. The difference to the russian claims is extraordinary high, however, and considering the russian claims in comparison to performance claims of similar german and japanese designs, russian performance claims for serial machines become very doubtable. VERY doubtable ...

niklas

[Bogun]

lol nikas, always same week argument…  
Using the term FNW on the West does not explain correct Russian engine designation M-82FNV in the original German report. The fact that pilot was not able to reach engine rated manifold pressure of 1200 mm C.S. clearly indicate that Germans were not able to bring this engine back up to spec. No wonder considering how many hour this engine had by that time. This in addition to locally manufactured engine cowling and god knows what else Germans needed to manufacture and fit on the plane after crash would explain plane being not capable of reaching its rated speed. Well, Lerhe did the best he could with what he had at hands, but in no way it represent real performance of normal La-5FN.
If you remember – Lerhe was not the only one who was flying La at that time…

[HoHun]

Hi Tilt,

>There are records (Photographs) of an La5 f captured in 43........ it was tested without spinner cap which was destroyed.

>But to confuse a late model direct injected engine with a boosted induction carburettor system would be very lax.

Quoting Lerche:

"After the abovementioned Lancaster flights ended in August 1944, I received the message in mid-September 1944 that the first Lavochkin La 5, the well-known Russian fighter, had been acquired airworthy in Groß-Schimanen in Eastern Prussia."

Lerche also quotes the exact dates of the ferry flight to Rechlin, obviously from his surviving log book:

Take-off 15.09.1944 16:03 h
Stop at Märkisch-Friedland 17:12 h to 18:38 h
Landing at Rechlin 19:33 h

>The limited use of WEP seems to be based upon and instruction (not permitted) rather than a technical deduction. ( I have my own theories as to why)

Quoting Lerche:

"The accusation, though, that the performance of captured aircraft was understated on request by the top brass was absurd."

He mentions this right after his paragraphs on the La-5, so my theory was that the La-5 he tested was indeed performing below standard - else the frontline pilots wouldn't have doubted his findings.

>Stall data..........I wonder what weight this AC was at?

3347 kg with 80 kg for the pilot, which seems low.

>I wonder what octane fuel was used. The proper octane for the Ash 82 FNV was 95. Available at the time of test was B4 (87 Octane) or C3 (96 Octane) and possibly another fuel rated 92 Octane [C2?]

Lerche once mentions (with regard to a western type) that they kept stocks of captured aviation fuels.

Anyway, if they didn't wreck the engine with emergency power, they certainly had "enough" octane :-)

Regards,

Henning (HoHun)