Author Topic: What makes La-7 ~30-MPH faster than La-5FN at ALL Altitudes... (Read 4702 times)

Charge · « **Reply #30 on:** February 05, 2007, 11:01:21 AM »

You probably are. What the heck does it mean? Some StarTrek inside joke or what?

-C+

Knegel · « **Reply #31 on:** February 05, 2007, 11:09:45 AM »

Quote

Originally posted by gripen
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

Yes, you be right, this looks strange if we compare it with the BMW801 curves, but if you look to the speed´s with different rpm, you will see that from point "2." the engine have same power with different rpm, so according to this datas the rpm can get reduced without to lose anything.

This behaviour we can find, if we look to the BMW801D-2 with "Ladedruckerhöhung", while a increased rpm of the BMW801 always result in a higher power.

I dont know what give the Asch82FN such a strange behaviour, would be interesting to find out.

Hi Tilt,

my translation is like yours, but what do they mean with "boundary"??

I would say they refer to rated altitudes of the 3 different settings.

But the speed curve clearly show where the 2nd gear get introduced

1. rated altitude 2500rpm 1st gear.
2. rated altitude 2400rpm 1st gear.
3. rated altitude 2400rpm 2nd gear.

Why there isnt a 2500rpm 2md gear??

They must have used a special main fold presure with the 2500rpm, maybe in cooperation with a special injection, this would explain why it stop to bring a advantage at higher altitude, but not why it cant get used in the 2nd gear.

I have a other Ash82FN sheet, but iam not sure if its allowed to offer it here, probably you have it, its a russian engine sheet, where the DB605DCM/ASCM, Griffon65, V1650-7 and Asch82FN get displayed.

In that sheet all three altitudes of the 82FN are much below even of the climb datas.

1. 500m rated alt wep
2. 1500m rated alt 1st gear 2400rpm
3. 4850m rated alt 2nd gear 2400rpm

Despite the different altitudes, the curve looks exact like my example above.

"......your WEP band seems to go higher in alt then my memory tells me."

I took the datas from the sheet you did offer above.

666km/h @ 2200m(point "1."), above and below 2200m the speed decrease.

Greetings,

Knegel

Tilt · « **Reply #32 on:** February 05, 2007, 01:06:38 PM »

My appologies Knegel..............and I think probably HTC.

I had assumed that the 2nd stage of boost could be switched in as soon as the 1st stage was below max manifold pressure........presumably this would have been too much for the engine.................

Further the derived curves for the La7 in question above do seem to agree with yours

and it shows the point at which 2nd stage of boost is switched on on one of the curves.............

if you have As82FN data then show it here and be damned........frankly I have a distinct hatred for folk who try to "own" such data.

I have some cardboard boxes of stuff somewhere will dig it up for any other data

Tilt · « **Reply #33 on:** February 05, 2007, 01:30:14 PM »

I dont know what this is.......................

Tilt · « **Reply #34 on:** February 05, 2007, 01:36:54 PM »

Knegel I do have the the charts you refer to ..........I will post them below.............

I cannot authenticate the source I just refer to it as "Snow Fox"

Tilt · « **Reply #35 on:** February 05, 2007, 01:40:24 PM »

.

and this does show 10mins of WEP on an la5FN

Tilt · « **Reply #36 on:** February 05, 2007, 01:42:46 PM »

.

Tilt · « **Reply #37 on:** February 05, 2007, 01:45:39 PM »

.

gripen · « **Reply #38 on:** February 05, 2007, 04:20:45 PM »

Quote

Originally posted by Knegel
Yes, you be right, this looks strange if we compare it with the BMW801 curves, but if you look to the speed´s with different rpm, you will see that from point "2." the engine have same power with different rpm, so according to this datas the rpm can get reduced without to lose anything.

No, the chart shows constant rpm (2500) for 1st gear from sea level to about 4800. The point "2." is just FTH for another MAP setting. If there had been a change in rpm at 1st gear, there would have been a "teeth" around 3000m because at higher rpm also result higher map and reducing the rpm would have resulted lower MAP (above 1st gear FTH).

Basicly the M-82 power chart is logical and normal for a fixed SC gear ratio engines.

Quote

Originally posted by Tilt
I dont know what this is.......................

I don't have my Russian stuff here right now so don't take my word as gospel.

Anyway, the first one (22) seem to lift to drag ratio chart (Cl/Cd).

The 21 seem to be wing loading chart.

The 20 seem to be power loading chart.

The 27 seem to wing loading per speed chart.

The 26 seem to be turn time chart.

BTW thanks for posting these

gripen

Knegel · « **Reply #39 on:** February 06, 2007, 01:18:00 AM »

Quote

Originally posted by gripen
No, the chart shows constant rpm (2500) for 1st gear from sea level to about 4800. The point "2." is just FTH for another MAP setting. If there had been a change in rpm at 1st gear, there would have been a "teeth" around 3000m because at higher rpm also result higher map and reducing the rpm would have resulted lower MAP (above 1st gear FTH).

Basicly the M-82 power chart is logical and normal for a fixed SC gear ratio engines.

gripen

Hi gripen,

actually the speed chart dont show any 2500rpm entry above 3250m, but it clearly show that the speed with 2500rpm and 2400rpm is the same at 3250m!! Therefor it looks like 3250m is the point where 2500rpm get dissabled, not 4800m.
4800m is the point where the 2nd supercharger stage get enabled.

Gear change and rpm dont seems to be correlated in the 82FN.

Hi Tilt,

thanks for posting this, i only have two of this sheets, iam never sure if its allowed to offer such datas, i for sure dont wanna hold it back(always willing to shre).

I have a 1944 La5 manual in english. In this they talk about a "boost" at 2500rpm, usable for max 5 min.(in your chart its the La5F, not FN)

Normal take off is 2300rpm, 2450rpm or 2500rpm (looks like without boost).

While climbing they suggest to switch from 1st supercharger gear to 2nd at 3500m, what is a bit above the last 82FN curve and a bit below the La7 climb chart.

If you dont have this manual, send me a PM with your E-mail.

Anyway, the extreme different between La5FN and La7 dont seems to come only from a bit better aerodynamic and a bit less weight.
The rated altitudes of the La7 82FN seems to be a bit higher than that that of the La5 82FN. But maybe they never tsted the La5FN with WEP, cause the short time of usage. Maybe they did use a different propeller in the La7??

Greetings,

Knegel

gripen · « **Reply #40 on:** February 06, 2007, 04:13:49 AM »

Quote

Originally posted by Knegel

actually the speed chart dont show any 2500rpm entry above 3250m, but it clearly show that the speed with 2500rpm and 2400rpm is the same at 3250m!! Therefor it looks like 3250m is the point where 2500rpm get dissabled, not 4800m.

You seem to confuse rpm and MAP relations; at 2500rpm (engine rpm) the supercharger can produce higher MAP than at 2400rpm at all altitudes with same supercharger gear. The chart shows simply constant rpm up to gear change altitude (about 4800m); the point "1" is just FTH for higher MAP than point "2".

gripen

Tilt · « **Reply #41 on:** February 06, 2007, 01:29:51 PM »

Quote

Originally posted by Knegel
Maybe they did use a different propeller in the La7??

Knegel

La5FN used the 3.1m Vish-105V

La7 the later 3.1m Vish-105V-4

The -4 is described in one publication as being "anti-flap"

Interms of the engine the key modifications were to the air flow around the engine..........much time wa spent to arrive at a cooling air flow that offerred the least drag to the total airframe.....presumably a combination of the external cowling shape,its Fit (ie sealing) and the minal resistance to thru flow of cooling air at what ever setting the forward louvres allowed.

.............and the exhaust stacks were switched from the combined sets ** of the La5FN to individual exhausts per cylinder on the La7.

If the -4 was antiflap and if this did create greater efficiency at higer revs then I assume it would also induce higher net thrust and less net load on the engine................... for me this is all specualtion.

The la7 had more efficient cooling (less air cooled more engine) hence under load I would speculate that the La7 could be rev'ed faster for longer or indeed higher (altitude).

**
La5Fn had an exhaust for the following sets of or individual cylinders

Set1) 1st, 2nd
Set2) 3rd
Set3) 4th
Set4) 5th
Set5) 6th, 7th, 8th
Set6) 9th, 10th
Set7) 11th
Set8) 12th
Set9) 13th
Set10)14th

Knegel · « **Reply #42 on:** February 06, 2007, 02:05:56 PM »

Quote

Originally posted by gripen
You seem to confuse rpm and MAP relations; at 2500rpm (engine rpm) the supercharger can produce higher MAP than at 2400rpm at all altitudes with same supercharger gear. The chart shows simply constant rpm up to gear change altitude (about 4800m); the point "1" is just FTH for higher MAP than point "2".

gripen

Hi gripen,

i dont know where you see a constant rpm up to gear change altitude?

Can you please point me to it??

Maybe iam wrong, but i see the speed chart show two curves, 2500rpm from sea level up to 3250m and 2400rpm from sea level to 8000m.
While the 2nd super charger gear get introcused at around 4850m.

At 3250m 2400rpm and 2500rpm show the same result regarding the speed.

Actually i dont know a other engine with such a behaviour.

Hi Tilt,

"................... for me this is all specualtion." Unfortunately much of what we do is more or less speculation, as long as we know this, it cant hurt.

Every detail is important to get at least a idea why the planes behave like we see it in the tests.

The -4 propeller probably got used by a good reason, to think its a better propeller dont sounds like a dangerus speculation.

Greetings,

Knegel

Greetings,

Knegel

gripen · « **Reply #43 on:** February 06, 2007, 03:56:22 PM »

Quote

Originally posted by Knegel

Maybe iam wrong, but i see the speed chart show two curves, 2500rpm from sea level up to 3250m and 2400rpm from sea level to 8000m.
While the 2nd super charger gear get introcused at around 4850m.

You have mixed the curves. The 1st SC gear curve shows two MAP ratings for 2500rpm, higher rating which has FTH around 2200m and lower rating which has FTH around 3250m.

Quote

Originally posted by Knegel

At 3250m 2400rpm and 2500rpm show the same result regarding the speed.

The chart shows just one place where the engine has the same output for 2400rpm and 2500rpm. That is around 4800m where 1st gear at 2500rpm has about same output as 2nd gear at 2400rpm.

gripen

Tilt · « **Reply #44 on:** February 06, 2007, 05:48:07 PM »

Could you guys qualify which curves your looking at.................

pages 3 & 5 show differing alt boundries for different things..............

Re the Ash 82 FN

what occurs at 1600m on page 5?