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

[F4UDOA]

Questions,

Does anyone know how a 14 cylinder engine put out so much HP at relatively low RPM, low MAP and without the use of ADI?

I know some amazing things have been done with radials producing rediculous amounts of HP but that with with ADI and high MAP with some of the latest techniques in forging and casting metals.

Has anyone done a HP per pound comparison with comprable engines such as the PW, Centarus, Napier, BMW and Wright Cyclone engines?

[Tilt]

Do these help?


.


altitude choices seem significant..........translat ions may give us more insight

1st stage boost gives Comp ratio 7.14:1 and 2nd stage gives comp ratio of 10:1?

[Tilt]

This engine still exists does it not?  

isnt an Ash 82 variant used to power the latest Flug Werk FW190's.

[F4UDOA]

Tilt,

Are you saying that compression ratio is the key factor?

The rest I cannot read. I want to compare it to other modern radials.

[1K3]

Originally posted by Tilt
This engine still exists does it not?  

isnt an Ash 82 variant used to power the latest Flug Werk FW190's.

There are TONS of AsH 82 engines made in China.  The only flightworthy Fw 190A-8 uses AsH 82 engine.

[1K3]

Originally posted by Tilt
This engine still exists does it not?  

isnt an Ash 82 variant used to power the latest Flug Werk FW190's.

Check out the 190-ASH 82 hybrid
http://www.youtube.com/watch?v=eGhP1s2BF_4

[Knegel]

Hi,

somewhere i did read that the engine in the FW190A8 is not the Ash82, its a engine rather based on the Ash83, i saw this information while googling for the Ash82, but i dont know where.


Gripen,

i refer to this table:


But i also dont see in any other table where 2500rpm got used up to where the 2nd gear get introduced.

The 2500rpm setting seems to be a low level boost only.

Greetings,

Knegel

[Tilt]

Originally posted by F4UDOA
Tilt,

Are you saying that compression ratio is the key factor?

 

I dont know enough to make such a specific comment............

However it seems to me (from 1st principles) that power is a function of fuel burnt per second times  engine efficiency.

the bore and stroke are both approx 155mm the total swept capacity is 41 litres and the rpm is 2400/2500 at a boost pressure of 1000/1200mm

My understanding was that compression ratio assisted the efficiency side of the arguement (higher the design compression ratio the more energy converted to thrust at the crank)

So given optimum fuel air mixture using 95 octane fuel and "average" engine efficiencies may be those with better expertise than I can hazard an opinion at what HP could be expected.

Side Note..... where would the HP be measured? My bike is quoted as 140HP at the crank but some bikes quote the hp at the rear wheel......

[gripen]

Originally posted by Tilt
Could you guys qualify which curves your looking at.................

I have been talking about the output chart in the left which was posted (and apparently made) by Knegel:



The power chart shows constant rpm up to about 4800m. Basicly the engine output at given altitude using 1st gear and 2500rpm is allways higher than using 1st gear and 2400rpm (there is an exception but that's an another story).

Knegel seem to be talking about the speed chart in the right which shows same speed for 2400rpm and 2500rpm with 1st gear at 3250m but that can't be explained by engine output. Possible explanations are that propeller efficiency start to decrease considerably at 2500rpm when the altitude increase or the values might contain some measurement error. Note that there is quite large variation between tested planes.

Originally posted by Tilt
1st stage boost gives Comp ratio 7.14:1 and 2nd stage gives comp ratio of 10:1?

These seem to be supercharger gearing ratios ie at 1st gear supercharger spins 7,14 times faster than crankshaft and at 2nd gear 10,1 times faster than crankshaft.

gripen

[gripen]

Originally posted by Tilt

what occurs at 1600m on page 5?

The Russian speed data for the La-7 is indeed strange. I don't know if the chart below is page 5 but it shows 1600m FTH for 1st gear.



While the another chart shows 2200m:



Also the power chart shows unlogical shape. Confusing overall.

gripen

[Tilt]

Curves on Page 3 seem to point to the altitude boundaries used in the speed trials ........  2200, 3250, 6250?!

Curves on Page 1 seem to point to the altitude boundaries used in the climb tests........... 1600, 2650,5100 even if the speeds are entirely different

Curve  on Page 5 seems to be a power v altitude curve which gives even lower boundaries.......... 600, 1500, 4800 (approx)

Page 5 leads me to ask questions like does an engine develop the same thrust in climb as it does at max level speed? does is develop the same thrust on a bench at various air pressures tested at Tsagi?

Could the ability to cool (or not cool) the engine under various circumstances and the ability to benefit from speed derived air flow at the carburation inlets influence the various boundaries that WEP (2500rpm) may be employed and the subsequent peaks and troughs of various curves?

I think we need translations for the title lines on these curves.

Then I think we have to take into account that I (we) do not have links between these curves and actual tests such as the ones shown in the tables above

Thanks for the explanation re the boost gearing.............

[Nilsen]

Neither the LAme 5or LAme 7 goes faster than my bullets so it doesnt matter.
 

[Tilt]

Knegel has provided me with a translation of some Russian texts that I had (as a series of GIFs) but did not appreciate their value....................

Its basically the pilots instructions for the La5FN...............

it explains a lot in my opinion...............

Some headers...........

All revs refered to are not Engine Revs but prop revs!!!!

So at 2400rpm (prop) the engine revs at 3500 rpm. 11:16

WEP/take off power (2500rpm) was limited to 5mins on the La5FN and was only allowed below 2000m and was to be reduced to limit MP to 1180mm.

In climb the 2nd stage could be introduced (was allowed) at 3500m provided revs were limited to hold MP at or below 1000mm.

Elsewise 2nd stage was permitted in level flight at and above 4000m.

As well as the permitted MP's at 1st and 2nd stage boost the rpm was backed of or increased (with a change in prop pitch) to assist control of the maximum head temperature.

eg.The normal maximum cylinder head temp for all circumstances was 215C or 240C for no longer than 10 mins........... however in level flight it was permitted to run for 15 mins at 260C provided measures were taken to reduce it after wards.

Max speed was attained with engine cooling switched off (louvres closed) making as much as 50km/hr difference.

One comment though gives us a clue to the enigma of the Lavochkins..................

It is mentioned during the instructions advising pilots how to approach (glide is used .......but the engine is on) landing.

It says Study one peculiarity of the La5: speed lost in executing any part of flight is regained slowly

This does not sound like the proficient accelerator the AH La5FN is or the precurser to the astounding accelerator the AH La7....................

FM modelers in sims are able to discern alot of the model purely from best climb characturistics and top speeds............these have been known for the La5Fn and La7 for some time.

However if both machines can use stages of boost in climb that they cannot be allowed to use in level flight (or any other flight than climb) until above another altitude.............. could the total drag/thrust model become distorted to provide an optimistic view of acceleration potential across the whole gambit of conditions.

Is flying by your engine temperature guage to the extent so indicated by the la5FN manual a common aspect of engine management?  

Seems to me that when a Lavochkin wanted top speed one of the things the pilot did was close off his engine cooling..........after which he was on borrowed time until it was run at 240 for more than 10 mins or 260 in level flight for more than 15.

Therefore the AH Lavochkin WEP button may not just be an increase in rpm and subsequent power it is an increase in rpm coupled with a reduction in (engine cooling) drag.

Below 2000m AH could model both, but  above 2000m AH should only model the reduced drag when the WEP button is pressed. In both cases engine temperature (as well as time {5 mins for the 5 and 10 mins for the 7}) should  be a limiting factor

[Tilt]

The figure of 50Km/hr of drag (possibly due to whether the engine cooling louvres are open or closed ) also shows up in the La7 curves with respect to the difference between pages 1 & 3 above.

[F4UDOA]

1st stage boost gives Comp ratio 7.14:1 and 2nd stage gives comp ratio of 10:1?

Tilt,

I think that is the Blower ratio not compression.

The PWR2800-8/10 has three stages 7.8:1, 6.46:1 and 7.93:1 while the compression ratio is 6.65:1 regardless of blower stage.

Also the dry weight of the PW2800B is 2480LBS. That gives a ratio of (weight/HP) .806HP/per pound at a mil power rating of 2,000HP. WEP on the R2800B-8W was up to 2300HP.

The Ash-82Fn seems to show the same ratio as .0876HP/ per pound although the quoted data below seems to be slightly higher.

Specifications (ASh-82)
General characteristics
Type: 14-cylinder air-cooled two-row radial engine
Bore: 155 mm (6.1 in)
Stroke: 155 mm (6.1 in)
Displacement: 41.2 L (2,514 in³)
Dry weight: 868 kg (1,914 lb)
Components
Cooling system: Air-cooled
Performance
Power output:

1,268 kW (1,700 hp) at 2,600 rpm takeoff power
1,140 kW (1,530 hp) at 2,400 rpm at 1,550 m (5,085 ft)
992 kW (1,330 hp) at 2,400 rpm at 4,550 m (14,900 ft)
Specific power: 30.8 kW/L (0.68 hp/in³)
Compression ratio: 7.05:1
Specific fuel consumption:

0.381 kg/(hp·h) (0.627 lb/(hp·h)) at nominal ground power
0.435 kg/(kW·h) (0.715 lb/(hp·h)) at takeoff power
Power-to-weight ratio: 1.46 kW/kg (0.89 hp/lb)