Lavochkin
Results 1 to 19 of 19

Thread: Lavochkin

  1. #1

    Lavochkin

    Recently I have also been looking over a Lavochkin La-5FN that I built back in 2003.
    This was one of my earliest projects and surprisingly can still be found here.
    http://www.sim-outhouse.com/sohforum...d=la5fn011.zip

    I uploaded this to a library that seems to no longer exist and NMG apparently restored a copy from there.

    I had been looking at this model because it seemed to be the natural adversary to the FW 190A that recently got some attention.
    This project seems to be a fairly clean build but could use a bit of reworking with the slightly improved techniques that I use today.
    The texture layout is very efficient and compact but is not really ideal for someone intending to repaint or for adding canopy framing for a virtual cockpit, so the first thing I will be doing is seeing how I can move around the textures to make any paint changes easier.

    There are many more techniques that can be applied to bring this project up to current standards.
    This may also be the excuse for creating some Russian language Gauges if I can find colour photographs of some of the critical instruments. Of course any changes for this project should be pretty easily applied to the La-7 as well.

    Attached is a screenshot from a test flight after a couple minor changes such as an Alpha Transparent Canopy that was done last night. There needs to be a bit more to be done though they are not so obvious from this angle.


    - Ivan.
    Attached Thumbnails Attached Thumbnails La-5FN.jpg  

  2. #2
    This model was built so long ago that I have no idea which drawings were used as a reference.

    A general check of overall dimensions showed that Wing Span was almost exactly what it should be.
    The difference (about 0.0035 Feet on each side) may be attributed to a rounding error or a units conversion in the reference that I used. The current references all state measurements in Metric which are probably how the actual aircraft was built.

    The Overall Length though was a bit over two inches too short. In looking over some scaled drawings, it appears that the missing two inches is the result of leaving off the Marker Light and Fixture that is attached to the Rudder Trim Tab.
    The new light added a touch under two inches to the OAL.

    A fraction of an inch was left for what I believe is a slight improvement to the shape of the Spinner.
    This also corrected a 0.01 Feet misalignment between the Prop Blur and the Propeller Tips.
    The misalignment probably came about because the template for the Propeller Blades is made flat and when it is rotated to add a pitch angle, the Root and Tip which I use to locate each Blade may not be the points about which AF99 chose to rotate the Blade.
    This was something I should have checked at the time and also should have checked that the pitched Blade was still flat.

    One of the surprising things was that the Propeller Diameter turned out to be correct at 3.100 Meters even though it was wrong in the AIR file.

    The two screenshots show a tail that is 0.12 Feet longer with the new light fixture and a spinner that is 0.05 Feet longer which I believe matches photographs better.

    -------
    Attached Thumbnails Attached Thumbnails LightBulb.jpg   LongerSpinner.jpg  

  3. #3
    The references that will be used for this rebuild are much more extensive than were available to me back in 2003.
    Several months ago, I came across a fairly large online cache of Russian language Aircraft and Weapons manuals some of which are very useful here.

    The most noteworthy sources of information are the following:
    (Note that some of the information, especially performance details are somewhat contradictory so one has to choose what to believe.)

    Evaluation of Captured La-5FN by Hans Werner Lerche at Rechlin.
    La-5FN Pilot's Manual
    La-5FN Construction Manual
    La-7 Technical Guide

    The La-5 and La-7 and other Lavochkin fighters built during the Great Patriotic War were never intended for durability.
    Their structures were built with substantial amounts of wood and plywood and were not very durable when left out in the weather as is typical for combat aircraft.
    The structures also tend to be relatively heavy and not terribly strong or resistant to battle damage.
    Aircraft weights tended to vary a bit as major structural members such as wing spars were made of varying materials.
    First they were made of laminated wood, then of solid pine, and finally of light metal as the war concluded.

    - Ivan.

  4. #4

    Overall Dimensions & Weights

    The general consensus for dimensions for the La-5FN is
    Wing Span: 9.800 Meters
    Length: 8.672 Meters

    The source I originally used when building this model used measurements in feet and inches which made for a slight rounding issue in wing span and as stated earlier, gave an overall length that was about two inches shorter. There is the possibility that the measurements were taken from a museum aircraft and no actual originals survived intact and also the possibility that a rebuild may have combined pieces from the La-7.

    One very simple drawing that I have attached (from the Construction Manual) would have been very useful when building the model.
    Note that although the shapes are not accurate, the reference line for the aircraft is given as is the relative distance to the thrust line and horizontal stabilizer. I believe my model is canted slightly nose up relative to this drawing but I am not about to correct it because it would involve basically a whole new build for no obvious visual improvement.

    -------

    As stated earlier, the weights of the La-5FN varied a bit so one has to decide what source of information to accept.
    A breakdown of loads is given in the Rechlin evaluation by Lerche:

    Weight empty equipped 2773 kg
    Fuel (460 l) 354 kg
    Lubricant (51 l) 46 kg
    Ammunition (2x 200 rounds) 94 kg
    Pilot 80 kg
    Take-off weight 3347 kg

    Weighing:

    Left wheel 1437 kg
    Right wheel 1484 kg
    Tail wheel 426 kg
    Take-off weight 3347 kg


    This was a captured and repaired aircraft of unknown production series and the performance that was recorded was much lower than other sources give. Thus it is a matter of picking what data is useful from this report.
    The weights and general performance from some Internet sources seem to be much more in line with expectations.

    One source states:
    Empty Weight: 2828 Kg
    Loaded Weight: 3290 Kg
    Maximum Take-Off: 3390 Kg

    The difference between Loaded Weight and Empty Weight is clearly too low with what we know the loads to be.
    I believe the numbers are actually labeled incorrectly and if the Maximum Take-Off Weight is taken to be the "Loaded Weight", the numbers add up to within 1 Kg of the recalculated weights of the loads.
    It may seem to some that my math is not so good, but more on this later as I provide more data from the manuals.
    Please note that the Germans were not likely to have had a complete set of aircraft manuals when servicing their La-5.

    - Ivan.

  5. #5

    La 5FN General Configuration

    I seem to have forgotten to attach the General Configuration image from the Construction Manual in the prior post.
    Attached Thumbnails Attached Thumbnails La5FN_GeneralConfiguration.jpg  

  6. #6

    Fuel Tanks

    The first attached image shows the location of the three fuel tanks on the La-5 and La-7 between the wing spars in the wing center section. Note that the center tank is missing in this image.

    The second attached image shows just the fuel cells without supporting structure.

    The third attachment gives a description of the fuel system as three tanks with a total volume of 466 Liters.
    It also gives the volume of the outer tanks as 148 Liters. Note that this is from the La-7 Technical Manual.

    The fourth attachment shows the center fuel tank and a description of the volume as 170 Liters. Note that this is from the La-7 Technical Manual.

    From these manuals, we have the total volume of fuel carried by the La-5FN and the La-7.
    The Rechlin Evaluation was close in its estimate, but I trust the data from the manuals more.

    - Ivan.
    Attached Thumbnails Attached Thumbnails FuelDetail1.jpg   FuelDetail2.jpg   FuelTankOuter.jpg   FuelTankCenter.jpg  

  7. #7

    La-5FN Fuel System - Corrected Data

    It turns out that the Fuel Tank Capacities of the La-5 series differed just a bit from those of the La-7 although the schematics look identical.
    Attached below is the description from the Construction Manual for the La-5FN.

    The Center Tank is 168 Liters Capacity (Not 170 Liters as on the La-7)
    The Outer Tanks are 148 Liters Capacity (Same as on La-7)

    For a Total of 464 Liters instead of 466 Liters.

    - Ivan.
    Attached Thumbnails Attached Thumbnails La-5 FuelSystemDescription.jpg  

  8. #8
    Hi Ivan

    Have you found any photographs of Russian language guages?
    These are screenshots of the cockpit panel of a LA5 from il21946, a sim created a Russian aviation enthusiast Oleg Maddox. I'm guessing that these are pretty authentic renderings of the originals with Russian language cockpit text.I hope they will be of use to you.

    http://www.mediafire.com/file/6gnq16or96q5chw/file

  9. #9
    Hello Rince33,

    Thanks for the screenshots. It seems like the gauges in screenshots from IL2 differ a bit from those in the illustrations in the Pilot's Manual especially the Magneto Switch. I do have some images of the panel, but none that are in colour though it seems that there really aren't any gauges that were anything other than black and white. (If IL2 is to be believed.)

    I was planning on using the appearance from the Pilot's Manual and the colours that I had used for other gauges unless I found out something different. Changing colours on a gauge face is pretty simple. It is all the markings on the face that are tedious.

    I was only planning to do a few of the gauges as Russian versions: Boost, Tachometer, Magneto and Starter, and I forget what else.
    The Tachometer was probably going to be the toughest new gauge because it uses two pointers for a Thousand and Hundred RPM indicator and I don't already have one of those. The rest are just a matter of painting a new gauge face and pointers and doing some minor programming edits.

    - Ivan.
    Attached Thumbnails Attached Thumbnails IL2_Magneto.jpg   La5_Magneto_Starter.jpg  

  10. #10

    Engine Gauges

    Hello Rince33

    Attached is a page from the Pilot's Manual showing the "Normal" readings for the engine monitoring gauges.

    Top Left is the Tachometer indicating 2400 Revs per Minute

    Top Right is the Manifold Pressure or Boost Gauge showing 1000 mm Hg.
    Note that there is a Red border starting just below the 1200 mm mark.
    This is because Maximum boost even under Emergency conditions is only 1180 mm.

    Lower Left is the "Three Way" Gauge indicating from top to bottom:
    Oil Pressure
    Oil Temperature
    Fuel Pressure
    Note that it doesn't look anything like the gauge on the IL2 panel which looks like a US style gauge with different markings.

    Lower Right is a Cylinder Head Temperature gauge showing maximum allowable CHT.

    - Ivan.
    Attached Thumbnails Attached Thumbnails La5_Engine_Gauges.jpg  

  11. #11

    Oil Capacity

    Attached is a description of the Oil Tank of the La-5FN from the Construction Manual.
    It lists the capacity of the tank as 60 Liters.

    The corresponding section of the La-5 Construction Manual for aircraft equipped with the M-82 (Not FN) engine also lists the volume of its oil tank as 60 Liters.
    Interestingly, the La-7 has an Oil Tank of only 58 Liters capacity as described in its Technical Manual.

    - Ivan.
    Attached Thumbnails Attached Thumbnails La5FN_OilTankDescription.jpg  

  12. #12

    Zero Fuel Weight

    With the data that has been presented thus far, we can now calculate the Zero Fuel Weight of the La-5FN with a fair degree of accuracy,

    As noted earlier:
    One source states:
    Empty Weight: 2828 Kg
    Loaded Weight: 3290 Kg
    Maximum Take-Off: 3390 Kg
    For these calculations, we will stay with Kg to make the confirmation easier.

    2828 Kg Basic Weight.
    80 Kg Pilot
    54.1 Kg Lubricant for 60 Liters Capacity. (Rechlin flew with 51 Liters weighing 46 Kg.)
    333.6 Kg Fuel for 464 Liters (2 x 148 Liter, 1 x 168 Liter from the construction manual)
    94 Kg for 400 rounds 20 mm ammunition
    ----------
    3389.7 Kg which is the same as the 3390 Kg as listed but for rounding issues.

    The weight of fuel is assumed to be 6 pounds per US Gallon which differs a bit from the numbers listed in the Rechlin Report.
    The weight of 20 mm ShVAK ammunition is from my data tables which show 8.289 ounces per round which gives 207.225 pounds or 93.9957 Kg which is in pretty good agreement with the Rechlin Report.

    The La-7 manual describes the Oil Tank as having a 58 Liter capacity with a fill mark on a measuring ruler on the cap for 40 Liters.
    I interpret this to mean that 40 Liters is the minimum oil level for inspection before flight which matches up pretty well with the Rechlin Report which describes filling their aircraft to 51 Liters before flight.

    From this, I will make the assumption that a reasonable "average" amount of oil in the tank during the flight would be around 45 Liters out of a total capacity of 60 Liters. Note that the La-5FN was a fairly short ranged bird with an endurance of about 45 minutes according to Rechlin.

    Calculation of Zero Fuel Weight:
    2828 Kg - Basic Weight
    80 Kg - Pilot
    40.6 Kg - 45 Liters Oil
    --------------
    2948.6 Kg == 6500.55 Pounds or 6501 Pounds.

    - Ivan.

  13. #13

    Shvetsov M-82FN / ASh-82FN Engine

    Attached are two extracts from the section of the La-5FN Construction Manual describing the Engine.
    From the first image, one can get

    Basic Description:
    Double Row
    14 Cylinder

    Dimensions for Displacement:
    Diameter of Cylinder - 155.5 mm
    Stroke - 155 mm
    Compression - 7.0
    Reduction - 11:16

    and other interesting but somewhat irrelevant information for the simulator such as
    Overspeed limitations
    Supercharger Drive Ratios for Low and High Blower
    Engine External Dimensions

    Take-Off Boost (WEP)
    2500 RPM
    1200 mm (--20 mm)

    Normal Power (Military)
    2400 RPM
    1000 mm (+- 10 mm)

    Note that the "minus-minus 20 mm" in the Take-Off setting is not a typo.
    Other sources such as the flight manual list this boost setting as 1180 mm (+-20 mm)
    The La-7 manual lists this as 1180 +-20 mm....

    -------
    Attached Thumbnails Attached Thumbnails M-82FN_specifications.jpg  

  14. #14

    Engine Critical Altitudes

    Attached is an image showing Boost limitations and Engine Critical Altitudes as listed in the La-5FN Construction Manual.

    Low Blower
    2400 RPM
    1000 mm Boost
    1650 Meters critical altitude

    High Blower
    2400 RPM
    1000 mm Boost
    4650 Meters critical altitude

    What is not listed here is the following:
    Low Blower - 1650 HP
    High Blower - 1450 HP
    Take-Off - 1850 HP

    Blower Shift Altitude from the Flight Manual is 4000 Meters.
    Take-Off Boost may only be used in Low Blower.

    Note that this is an aircraft limitation that CANNOT be reflected in the CFS AIR file.
    From about 2000 Meters to 4000 Meters, the engine performance will be relatively poor.
    This unfortunately will be the altitude range in which our single speed supercharger will hit peak performance.
    WEP will be pretty much useless just above 1650 Meters but in CFS, if we allow WEP, it will be effective to at least twice that altitude.

    Such are the limitations with CFS flight models.

    - Ivan.
    Attached Thumbnails Attached Thumbnails M-82FN_Boost.jpg  

  15. #15

    Propeller Specifications

    Attached is an extract from the La-5FN Construction Manual which lists Propeller Information useful for Flight Modelling.

    Important information is the following:
    Diameter: 3.1 Meters
    Pitch Range: 29 Degrees 30 Minutes (for Confirmation)
    Low Pitch: 22 Degrees
    High Pitch: 51 Degrees 30 Minutes
    Propeller Weight: 141 Kg - Useful for determining Propeller MOI relative to other propellers.

    - Ivan.
    Attached Thumbnails Attached Thumbnails Propeller_Specifications.jpg  

  16. #16

    Flight Model

    The Engine for this AIR file was built several weeks ago.

    In initial tests, I found that the seemed to be some difficulty in getting engine output to match at
    1000 mm / 2400 RPM and at 1180 mm / 2500 RPM.
    The power levels between the two settings was considerably greater than listed for the engine.
    That suggests that there is some kind of flow restriction which limits maximum power but there is no obvious method of representing such in the AIR file.
    The other issue was that 2500 RPM was very restricted in use.
    To discourage running the engine at 2500 RPM even though it is possible, this engine is tuned so that it makes slightly better power at 2400 RPM than at 2500 RPM.
    I would have wanted to decrease efficiency at 1180 mm as compared to 1000 mm but there is no obvious way to do that.
    Instead, Normal Power is limited to 1150 mm and Emergency Power is limited to 1180 mm.
    This combination of features seems to work sufficiently well.

    -------

    Over the last week or so, Ivan's Propeller Shop has been working on and off on a new Propeller for the La-5FN / La-7.
    Initial prototypes were based on the Propeller for the Ki 61-Id which, strangely enough, seemed to be an extremely good fit.
    With very minor modifications, straight line performance was quite good, it was found that the Version 2 template I was using was insufficient for fine tuning and the prototype was scrapped.
    The Version 3 template took a bit of tuning but seemed to work reasonably well though still with some non-linearity problems.

    As of today, the new Lavochkin Propeller seems to have passed all tests.

    At 500 feet altitude, it seems to be reasonably good at selecting the optimum pitch.

    The La-5FN achieves:
    At 500 feet - 340 MPH on 1598 HP.
    At 12,500 feet - 406 MPH on 1767 HP
    At 15,000 feet - 402 MPH on 1631 HP

    Initial Climb is 3600 feet/minute at 500 feet altitude at 160 MPH.
    Without Autopilot, a realistic climb rate would be more like 3400-3500 feet/minute.

    Screenshot shows La-5FN in climb test. Note that the Pilot's Manual states that the best climb is achieved at 260 Kph which is 161 MPH.

    - Ivan.
    Attached Thumbnails Attached Thumbnails BestClimb3600.jpg  

  17. #17

    Reducing Climb Rate

    After thinking about it a bit longer, I decided that it made sense to reduce the climb rate a bit.
    One cycle of edits to the Propeller Tables brought the climb rate down to around 3400 feet/minute at low altitude.
    Note that this testing was done with full fuel. With a partial fuel load and at a slightly higher altitude where engine power is increasing, climb rate should be considerably higher.

    The La-5FN was not a particularly fast climbing fighter.

    How does one reconcile this statement with the fighter's reputation in combat and with performance comparisons that state this was one of the fastest climbing Allied fighters and superior to all of its opposition on the Eastern Front except for the early versions of the Me 109G?

    One has to take into account the source for the performance numbers.
    The 3400 FPM in my testing was achieved at 500 feet with the typical CFS engine power curve which is a bit low at Sea Level and peaks at medium altitudes. It is probably closer to the original 3600 FPM by 6000 feet or so. It was also tested with Military Power which ranges from around 1600 HP at 500 feet to 1700 HP at medium altitudes.

    The "Fast Climb" reputation of the La-5FN of almost 4000 FPM is based on its engine achieving 1850 HP on Take-Off / Emergency power which has only a 5 minute duration and is not effective much past 1650 Meters (5400 feet) altitude.
    The performance numbers for German aircraft in these comparisons come mostly from the Soviets and are well below what is normally quoted for the same types by other sources.
    Just as an example, the initial climb rate for the FW 190A-5 is stated to be barely over 3000 FPM which is almost 500 FPM below what the much heavier A-8 version could achieve.
    This lack of performance is not surprising for a captured and probably repaired aircraft possibly running on inferior fuel.

    As stated earlier, the La-5FN tested at Rechlin also did not show the level of performance normally expected of the type.

    - Ivan.
    Last edited by Ivan; September 16th, 2020 at 12:16.

  18. #18

    WEP Climb Rate

    Once the basic parameters for climb rate under Military Power were established, it was quite easy to see what would happen when using War Emergency / Take-Off Power.
    Forward speed for best climb was a bit higher at about 175 MPH to 180 MPH.
    That climb rate turned out to be somewhere between 4000 FPM and 4100 FPM though the altitude at which I could get consistent readings needed to be a bit higher because it was changing so fast. As expected, the 5 minute WEP was of such short duration I could not run more than about 3-4 tests before running out of WEP Time.
    In other words, this very high climb rate is a nice statistic but not of long enough duration to really use to gain altitude more than once in a sustained fight. The performance under Military Power is a more appropriate tactical comparison.

    One of the issues due to CFS is that WEP has SOME though decreasing effect up to 12,500 feet which is the actual critical altitude with the CFS single speed supercharger that seems to give performance similar to the two speed supercharger installed in the Shvetsov ASh-82FN.
    The ASh-82FN has no Emergency Power much past about 5,400 feet or 1650 Meters because beyond that altitude, Low Blower cannot supply enough boost to give any extra power.
    This also explains why actual CFS maximum speed is achieved around 12,500 feet rather than the proper 16,000 to 17,000 feet.

    - Ivan.
    Attached Thumbnails Attached Thumbnails 4000FPM_WEP_Climb.jpg  

  19. #19

    Service Ceiling

    Service Ceiling was tested yesterday.

    Altitude is that at which the aircraft can maintain 100 FPM climb rate at an indicated air speed equal to that for best climb.
    Testing is attempted with as close to 50% fuel as was practical.

    The La-5FN carries 122 Gallons of useable fuel.
    Testing was started with 65% fuel at 29,500 feet.
    The aeroplane tended to be quite sensitive to the amount of remaining fuel.

    Once I figured out the amount of fuel likely to be expended in the test, it became quite easy to get fairly consistent results.
    The actual altitudes varied slightly but tended to average a bit over 31,500 feet.
    The details from the last test:

    31,760-Something feet
    18.4 inches Hg
    799 HP
    267 MPH TAS (160 MPH IAS)
    63.3 Gallons of remaining fuel.

    Climb rate was still about 130 FPM, but speed could not be maintained.

    It will be recorded as 31,750 feet though the actual average is 50-100 feet higher.

    Data from the actual aircraft varies a bit with engine power being more in the 850 HP range, but the listings for Service Ceiling do not tend to be consistent. 31,750 feet is entirely within reason for this aircraft. I believe that higher numbers are a bit optimistic.

    - Ivan.

Members who have read this thread: 74

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •