La7

[Dowding]

niklas - the '206' version was basically the La-5FN with a bunch of aerodynamic changes recommended by a Russian aeronautical institute. These changes were then transferred onto the La-7 design, which incorporated new materials not used in either the La-5FN or the '206'.

There are differences - notice the supercharger intake under the cowling of the '206' (which is actually on top of the La-5FN cowling) is gone. It was replaced by a system of intake through the wing roots - you can just about make it out on your schematic diagram.

[niklas]

Dowding, my question was not whether the 206 is a La-7.
My question is whether the speed claim of 630km/h what you can read in several sources, often mentioned for a La-7, is actually from the 206 model. Or did a later "real" La-7 reach 630km/h too?

niklas

[HoHun]

Hi Tilt,

you mentioned a 2000 HP setting for the La-7 engine that was used (at least) in bench tests. Other data points from your website are a 596 km/h sea level speed for the 1944 La-7 and a 616 km/h top speed for the 1945 La-7.

Assuming that the later La-7 actually had the 2000 HP power setting available in flight and made 616 km/h with it, by my crude estimate it would achieve a 598 km/h sea level top speed with power reduced to 1850 HP.

This matches the 1944 La-7 quite well!

Accordingly, I'd suggest that the 1944 La-7 was limited to the 1850 HP setting, while the 1945 La-7 was cleared for the 2000 HP power setting we know from the benchmark.

The problem is that the 1945 model was faster at all altitudes - could it be that the 1944 model still employed the ASh-82FN, while the 1945 model had the ASh-82FNV with improved altitude performance?

I'm not sure I got it right yet, but I feel we're getting closer :-)

Regards,

Henning (HoHun)

[juzz]

Russian performance data is supposedly an average of many a/c's performance - so the rise over time would simply be due to increased production quality, if this is true.

[HoHun]

Hi Juzz,

>Russian performance data is supposedly an average of many a/c's performance - so the rise over time would simply be due to increased production quality, if this is true.

In earlier years of Soviet aircraft construction, this might have been conceivable.

However, considering that the superbly streamlined and meticulously finished Focke-Wulf Fw 190-8 made less than the 1944's La-7 596 km/h sea level top speed - on more power! - , I'm afraid your suggestion that such a high level of performance could be achieved by shoddy workmanship has to be regarded as slightly unrealistic.

Regards,

Henning (HoHun)

[HoHun]

Hi Juzz,

>Russian performance data is supposedly an average of many a/c's performance

Let me clarify that the tests on Tilt's page

 http://www.btinternet.com/~fulltilt/Perform.html

refer to the performance of individual examples of the La-7 that are quoted with their serial number:

"During the period August 1944 La7 serial No.452101-39 underwent production test trials at the NII-VVS."

(The 1944 La-7 achieved 596 km/h at sea level.)

"During the period April 1945 La7 serial No.452132-76 underwent production test trials at the NII-VVS."

(The 1945 La-7 achieved 616 km/h at sea level.)

These values fit very well with the assumption that the 1944 La-7 had 1850 HP available in this situation, while the 1945 model could draw 2000 HP power from an improved engine.

For comparison, the Fw 190D-9 equipped with Ladedrucksteigerungsrüstsatz achieved 1900 HP at sea level while the MW50 injection later increased power output to 2140 HP.

Here's the comparison:

1944 La-7: 1850 HP - 596 km/h
1944 Fw 190D-9: 1900 HP - 612 km/h
1945 La-7: 2000 HP - 616 km/h
1945 Fw 190D-9: 2140 HP - 640 km/h

Regards,

Henning (HoHun)

[Tilt]

Originally posted by HoHun:
Hi Tilt,

you mentioned a 2000 HP setting for the La-7 engine that was used (at least) in bench tests. )

I was in error re the  2600 rpm time duration for the bench figures it was shown as 30 secs. (not 60)

My figure do show a gradual increase in performance over 44/45 for ex production AC.

Please also note that one set of figures is for a twin Shvak armed AC with faulty slats and the others are generally armed with 3 B20 with 130 rounds per gun.

I believe that production consistancy was quite poor. Early AC were "finished" (or not!) in the field by aircraft fiters(particularly with respect to best air mixture settings etc allowed from the cockpit adjustment etc) eg.It is known that the weight of glue/resin varied considerably (it was used as a very high strength filler when parts did not exactly fit!)

I believe all my La7 data is for the V engine.

Figures for the "206" and "etalon march 44" are often used in less thorough texts as being the capabilities of the La7.

I have always "felt" (having touched and walked  around both) that (level trimmed)the La7 fuselage and engine cowl is far more drag efficient than the 190 a or even the d series.

In fact I was able to repeatedly walk between a SpitIX and the La7 at Kbely and came away thinking that what the La7 lost in housing its radial engine was more than made up for by its comparably tiny wings (which were no thicker than the Spits E wing). Plus a varnished La7 had such smooth lines compared to all the rivitted paneled AC. (Something that seeing it in the flesh again impressed)

The other thing that impressed is how small it is. Its shorter and narrower than a bf109. Only its fuselage is taller and of course its nose is broader.

Standing between the wing and tail section you are conscious of a) how close they are together and b) how massive the control surfaces were incomparison to other aircraft (I-16 apart).

Not hard data I know, but if you ever get a chance to go to Prague and see one of the only two in existance..... I do reccomend it.

Tilt

[Tilt]

Originally posted by HoHun:


These values fit very well with the assumption that the 1944 La-7 had 1850 HP available in this situation, while the 1945 model could draw 2000 HP power from an improved engine.

)

I dont think its an increase in engine power HoHun. The figures are given at their RPM and boost settings.

I have the test weights at home for the aircraft and will check for any other small contributing factors.

You must remember that the VVS  were not as scientific in design and specification as their German contempories. Tsagi had done a brilliant job in re engineering the aerdynamics of the La 5 into the shape of the la7. That beyond this development was a series of "suck it and see" intelligent "hunches".

As you know many of tsagi's requests re engine and prop control were never implimented.

Further the La7 was the first Lavochkin to have even semi automatic throttle/ prop pitch control despite it being a so called constant speed prop.

It would not surprise me at all if there was not a whole host of settings and variables still not properly fed back to the factories by August 44 that would be required to achieve various small modifications (or establish standardised settings) to improve such things.

Tilt

[Tilt]

Originally posted by Tilt:
I have the test weights at home for the aircraft and will check for any other small contributing factors.[/QB]

Have checked infact the faster AC was slightly heavier.

Some interesting  stuff tho. Also tested August 44 was AC (203) and another  (150) was found substandard in several ways. (Both from a July batch)

203 repeated the outline figures shown on my page for -39 (but with better climb rates) 150 initially returned a max speed of 554 km/hour at ground and correspondingly less than ideal  speed at higher altitudes. ( 624 @3000m & 640 @ 6000)(all without WEP)

Quote  (translated)

"The same plane after governer RS-2 tuning, standard propellor mounting, improvement of fuselage and cowl sealing, improvement of external finishing"

We can only guess what the phrase "standard propellor mounting" means (translation?). the trials were then re taken at/in LII NKAP (a rear base field?)

Identically loaded the max WEP'less ground speed is given as 582 km/hour with corresponding 1st and 2nd boundry speeds as  647@3000 & 674@6000.

This is a significant improvement and equal to those figures taken in 45 against later production aircraft.

It also shows that planes were rarely tuned prior to despatch to the VVS.

Please note that the ground speed is always translated as deck speed. We cannot always assume this is as low as sea level.

I do not have WEP based figures for these tests on aircraft 150. (full designation 45210150)

Tilt

[HoHun]

Hi Tilt,

>Please note that the ground speed is always translated as deck speed. We cannot always assume this is as low as sea level.

The way the RAE did it was to establish the performance parameters under non-standard conditions and then standardize the measurements, and I think this must have been normal procedure everywhere. (Even at sea level, you'd have to correct the results for temperature, air pressure etc.)

>It also shows that planes were rarely tuned prior to despatch to the VVS.

For comparison, German and British procedure seems to have been that the aircraft were tested by a company test pilot in flight, tuned, and then turned over to the air force for an acceptance flight.

However, there still were occasional trouble aircraft that were either fixed by the squadrons or returned to the manufacturer for further testing.

>I believe that production consistancy was quite poor. Early AC were "finished" (or not!) in the field by aircraft fiters(particularly with respect to best air mixture settings etc allowed from the cockpit adjustment etc)

For comparison, modifications of this type were for example carried out by the USAAF Base Air Depot Area in the UK, or by the Luftwaffe's specialized "Frontschleusen", not at the actual fighting units.

>This is a significant improvement and equal to those figures taken in 45 against later production aircraft.

Good point!

>Have checked infact the faster AC was slightly heavier.

Yes, weight doesn't affect top speed much. I don't think that manual propeller control or the slats malfunctioning at low speeds had an impact on top speed either.

>I dont think its an increase in engine power HoHun. The figures are given at their RPM and boost settings.

It would be highly interesting to have a look at these!

I noticed that the 1944 La-7 was using a higher boost for top-speed flight than for climbing - could it be this was due to improper cooling at climb speed?

>The other thing that impressed is how small it is. Its shorter and narrower than a bf109. Only its fuselage is taller and of course its nose is broader.

In high-speed flight, fuselage frontal area and cooling drag are dominant, and they're significantly smaller for a liquid-cooled inline-engined aircraft.

>I have always "felt" (having touched and walked around both) that (level trimmed)the La7 fuselage and engine cowl is far more drag efficient than the 190 a or even the d series.

Much of the cooling drag is the result of internal airflow ducting, and the internal design of the BMW801 installation was outstanding, though hidden from the observer's eyes.

That the La-7 obviously had a smaller total drag shows that it was just as outstanding a design!

>I was in error re the 2600 rpm time duration for the bench figures it was shown as 30 secs. (not 60)

Looking around a bit, I've found that Eric Brown in "Testing for Combat" mentioned the La-7 to be powered by a 2000 HP engine, too. (He flew a 2-cannon version.)

Regards,

Henning (HoHun)