Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: 1K3 on February 01, 2007, 11:20:33 PM
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What makes La-7 ~30-MPH faster than La-5FN at ALL altitudes when both planes have the SAME engine AND power output...:noid
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Cleaned up detailing, streamlining and wax.
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It's the go-faster stripes.
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type-r badge.
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the "FN" adds a lot of drag & "7" is more aerodynamic then "5" to begin with...
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the purple power bands
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Maybe the 71 lbs weight difference? :D
Some data I stubled upon on Ubi forums suggest 385-394mph for LA-5FN and 408 for LA-7 at 20 000 ft.
So the aerodynamic refinements and update in materials did improve the performance but how much it actually did improve..?
-C+
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Im at work so Im recaling this from memory.The La7 has a revised wing shape which I think was also made thinner.The air intake was moved from the top of the nose to the wing roots.The oil cooler was moved from under the nose to under the body towards the rear.I beleive they brought the weight down a bit.It may have been through the use of less wood and more metal in certain parts.Again this is from memory but more or less gives ya an idea of what they did to the modify the la5 to the la7.It was basicly weight reduction and aerodynamic refinements.
"A bandit at your six is better than no bandit at all"
Pipz
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Originally posted by Mustaine
the purple power bands
:rofl
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I'm still trying to figure out how the La-7 accelerates and climbs so fast considering that it's fitted with a low activity propeller of relatively small diameter.....
I also find it interesting that some Soviet aces preferred the La-5FN to the La-7.
My regards,
Widewing
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Do we have any non-Soviet sources that tested this aircraft? Perhaps NACA or captured LW, or even British/US tests?
I've always thought that the same engine in almost the same plane shouldn't have such a huge performance leap. I always suspected propoganda got into the test data, but this is mere speculation on my part.
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Originally posted by Widewing
I also find it interesting that some Soviet aces preferred the La-5FN to the La-7.
Yeah, but I. Kozhedub would beg to differ.
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Originally posted by Widewing
I'm still trying to figure out how the La-7 accelerates and climbs so fast considering that it's fitted with a low activity propeller of relatively small diameter.....
I also find it interesting that some Soviet aces preferred the La-5FN to the La-7.
My regards,
Widewing
Only thing I could find in what I have is that on the LA-7 they used a Mach Resistant Blade airfoil.Im "assuming" by the way they wrote it that the la5 didnt have the same blade.But they dont get into the hard data stuff that you like.
As far as why they prefered the LA-5FN over the 7.I wonder if it had to do with fit and finish.At least at first.From what ive read la-7s had production problems at first.It got very hot in the cockpit because of bad sealing,but then again so did the LA5.They say that performance wasnt much better for the 7 at 1st because of sloppy construction.After testing the initial production planes they went around and fixed all the production problems and the planes performance improved.I wonder if they preffered the la5 only because they were dissapointed in the LA7.What I mean is that by that time all the la5 faults prolly would have been worked out.Now with the 7 ya have a whole bunch of new faults that had to be worked out.Just a thought.
Pipz
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Krusty,
I used to have the German test of the La-5 on my website, I think I may have taken it down.
I will repost it or email it to you.
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Originally posted by Widewing
I also find it interesting that some Soviet aces preferred the La-5FN to the La-7.
It's not exactly the same case, but maybe La-5FN pilots also distrusted the new type:
http://en.wikipedia.org/wiki/Aleksandr_Ivanovich_Pokryshkin
Finally in 1944 he found an aircraft that he was willing to convert to, Lavochkin La-7. Unfortunately one of his close friends, Soviet 50-kill (31 personal and 19 group) ace Alexander Klubov was killed in a landing mishap while converting to the La-7. The crash was blamed on the malfunction of the plane's hydraulic system. Pokryshkin subsequently cancelled his regiment's conversion, and there are multiple reports that they instead began flying Bell P-63 Kingcobras.
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f4udoa, but do you have anything on the la7? I'm wondering why such a big jump from la5 to la7.
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Originally posted by Krusty
Do we have any non-Soviet sources that tested this aircraft? Perhaps NACA or captured LW, or even British/US tests?
The German tests on the La-5FN were flown by Hans-Werner Lerche, who has subsequently published the La-5FN report in the appendices of his book:
Luftwaffe Test Pilot: Flying Captured Allied Aircraft of World War 2.
ISBN 0 531 037118.
In that book he has chapters on aircraft that he tested including a B-17, Ju290, B-26, B-24, Spitfire, P-39, P-47, P-51, La-5, Yak-3 and lastly a Do 335. However, the La-5 is the only one that has the test report included in the appendices.
Badboy
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Okay, but then what about the LA-7? If we can get some independent data on the -5, we then need some independent data on the -7.
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Hi,
is it possible that the La7 Vmax was made with max power, while the La5FN Vmax is made with "combat climb"??
The main and probably most important different between La5FN and La7 was the improved cooling system. The La5FN only had a real energency power, usable at highspeed while it wasnt allowed while climbing. In the La7 it was allowed to run the engine for around 10min on max power, also while combat.
Thats similar like the DB601E vs DB605A, both had a similar max power in 1942/43, but the DB605 could use it for much longer time.
Also the SpitVc in WEP was similar good like the early SpitIXc, but WEP is what it is and dont count much while combat.
The La5FN was great even without WEP.
Why the La7 perform so good in AH i also cant understand. On my side its in the same class like the US "magical flaps" and the FW190A8/P38 "super E-bleed".
Greetings,
Knegel
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All my la 7 data is VVS or Tsagi sourced........the only non Russian La5FN data I have is Lerches.
Having said that ......it is la5FN data that is the rarest and I have no copies of originally sourced La5FN tests as I do La7.
If other non Russian data exists then I am sure you will find it to be Czech as they continued to use both types long after the VVS dropped them. Certainly the most authoritative descriptive (English language) texts on the types are Czech
I have not heard of any pilots that preferred the La5FN over the La7.
Pokryshkin was responsible for converting 16GIAP (9GIAD) from the P39 to the La7.He received them on the 21st Oct 44. each had a distinct red nose and had painted on the side (in Russian) To Aleksandre Pokryshkin from the workers of Novosibirsk However a fatal accident to capt Klubov after a stunt showing of the La7 (it flipped on landing) caused 16 GIAP loose confidence...... some of their pilots flew it to the wars end whilst others remained with the P39.
The early (first batch) La7 was very uncomfortable to fly as the cockpit over heated and some times filled with exhaust gasses.
Other than an upgraded prop the only difference between the two was one of reduced pure drag and a relatively minor weight saving.
There is speculation that the engine cooling on the La7 was more efficient. Certainly Czech pilots flying the La5 FN noted that the upper cylinder could overheat if engine temperature was not monitored. (this sort of indicates that the upper cylinder was more vulnerable than the rest)
I have two speed v alt curves for the La5FN (probably from the same source) that do not indicate WEP (2500 rpm) at all where as the La7 could use it as shown in AH's curves.
Both these curves also show the 2nd stage of boost occurring at approx 4900 m alt on the La5FN but at approx 4300m on the La7. (AH's La7 is inaccurate in this sense as 2nd stage boost is not until after 16000 ft...manifold is back to 40" at 17K)
Both these curves show the speed diferential widening between 4200m and 4900m to approx 52km/hr IAS and then narrowing again to about 48km/hr at 6000m.
The engine was bench rated to run at 2400 continuously, 2500 for 10 mins continuously and 2600rpm for 30 secs (from the La7 pilots notes) however I have no account of any airborne test at 2600 rpm.
Where data is missing is stuff like E bleed and roll rate etc. (Lerches roll rate for the La5FN is the only roll data I have seen for both types.......he sort of mentions it in passing during one of his reports.)
There are opined comparisons by Czech pilots between the La5FN and the SpitVb there is no data but they find it very comparable once its off the ground :rolleyes:
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I heard the fuselage is rubbed in cheeta blood before flight
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Hi Tilt,
thanks for the reply.
Do you know the power output fitting to the rpm??
2400rpm=??
2500rpm=??
2600rpm=??
For now i only saw two different rpm/power settings for this engine, the continuous and the 10min setting.
Greetings,
Knegel
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I have no original data that refers directly to Hp.
In the set of figures posted on another thread here all tests refer to a "take off power loading" for La7's (1.75 > 1.76kg/hp) which when back calculated reveals the oft quoted figure of 1850hp. (@2500 rpm)
We read many accounts that state
2400rpm > 1650 hp
2500rpm > 1850 hp
and one account
2600 rpm > 2000 hp
However for practical purposes I would forget this reference to 2600 rpm. It may apply to a bench tested Ash82FN but no tests were carried out at this rpm on the la7 to my knowledge.
All tests refer to the manifiold pressure at the rpm used.
2400rpm > 1000mm +/- 10 (39.37")
2500rpm > 1200mm +0/-20 (47.24")
2600rpm > ???
Many tests refer to Altitude boundaries
(1) is where WEP is no longer of any use ie manifold pressure at 2500 rpm @1st stage of Boost is equal to manifold pressure at 2400rpm 1st stage of boost. Above this alt the 1st stage boost manifold pressure drops off at when at 2400rpm to.
(2) is the altitude where the 2nd stage of boost is introduced. (or contrary the highest altitude that 1st stage is used at)
(3)is the highest altitude where the manifold pressure is at max when 2nd stage of boost is engaged.
so we see these "boundaries" when the ac is at max speed for its alt.
(1) is at 2400m, (2) is at 3250m, (3)is at 6250m
For max climbing trials the boundries change........infact they become lower.
(1) is at 1600m, (2) is at 2560m, (3) is at 5100m
This does not seem to be repeated with AH "boundaries"
At Max speed
(1)is at 2675m, (2a) is at 4880m, (2b)is at 5185m, (3) is at 6100m
During max climb
(1)is at 2250m, (2a) is at 4575m, (2b) is at 4880m, (3) is at 5800m.
re 2a & 2b. In AH the lowest 1st stage boost is at 2a and the lowest alt at max manifold pressure (2nd stage) is 2b. I dont know why there is such a lengthy transition.
So whilst AH's max speeds, turn rates and climb times (note I do not say climb rates) seem to agree with historic data on the La7 its manifold guage readouts do not............
I do not know how much the manifold readouts in AH actually interface with the power/drag model. They do seem to interface with the WEP boundries..........so at least this could be considered overmodelled in AH.
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If I am not mistaken...The La-5 is a better turner...and the La-7 is faster (for BnZ, which I most hate). I fly the LA5 more because I dogfight more in it
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Here is a max speed and climb rate test on an la7 showing the boundaries at speeds and during climb with the various altitudes, climb rates and times with and without WEP
(http://www.tilt.clara.net/data/PAGE04.GIF)
One question I always had was given the translationre these boundaries why is the max speed at 2500 rpm faster at 3000m when there is no manifold adavantage?
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Here is the rest of the data I have on ac No.45213276
(http://www.tilt.clara.net/data/PAGE10.GIF)
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Hi again,
thank you very much for this datas, i never saw the original sheet!
1. is rated altitude for WEP.
2. is the point where manifold pressure at 2500 rpm @1st stage of Boost is equal to manifold pressure at 2400rpm 1st stage of boost. Thats why they switch to the 2400rpm.
3. is rated altitude with 2400rpm.
What they miss in this sheet is the point where the 2nd stage of boost is introduced.
You can imagine this point if you draw a speedsheet.
Somewhat like this:
(http://www.raf-roy.com/share/knegel/Screenes/La7_gear_alt.PNG)
The AH values are all over around 200m higher than what this data sheet show, but its not realy far off!!
But anyway, its not this static performence that seems to be strange in the La7, its rather the extrme smal E-bleed. In relation to the 1100kg more heavy 190A8 or 190D, the La7 should bleed energy like mad, but strangewise its the other way around.
Greetings,
Knegel
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Originally posted by Knegel
2. is the point where manifold pressure at 2500 rpm @1st stage of Boost is equal to manifold pressure at 2400rpm 1st stage of boost. Thats why they switch to the 2400rpm.
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
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Originally posted by Knegel
Hi again,
thank you very much for this datas, i never saw the original sheet!
1. is rated altitude for WEP.
2. is the point where manifold pressure at 2500 rpm @1st stage of Boost is equal to manifold pressure at 2400rpm 1st stage of boost. Thats why they switch to the 2400rpm.
3. is rated altitude with 2400rpm.
Knegel
Is that your translation Knegel? I thought the literal translation was
1st stage altitude boundary for WEP
1st stage altitude boundary for Mil power
2nd stage altitude boundary for Mil power
I have some curves generated from the test figures.............I am not sure of their date however I'll post them tonight......your WEP band seems to go higher in alt then my memory tells me.
When you look at the climb rates you can see when the power:drag ratio changes at these boundaries by the changes in climb rate. I always kinda took this as indicating that as the point where (when in climb) the level of boost currently engaged could no longer achieve max manifold pressure.
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Originally posted by Mustaine
the purple power bands
I actually got this joke. Does this mean I'm hopelessly trapped in net geekdom?
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You probably are. What the heck does it mean? Some StarTrek inside joke or what? :D
-C+
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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
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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
(http://www.tilt.clara.net/data/Page08.gif)
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
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I dont know what this is.......................
(http://www.tilt.clara.net/data/ae9.jpg)
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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"
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(http://www.tilt.clara.net/data/ae1.jpg)
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(http://www.tilt.clara.net/data/ae2.jpg)
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(http://www.tilt.clara.net/data/ae3.jpg)
and this does show 10mins of WEP on an la5FN
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(http://www.tilt.clara.net/data/ae4.jpg)
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(http://www.tilt.clara.net/data/ae5.jpg)
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(http://www.tilt.clara.net/data/ae6.jpg)
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(http://www.tilt.clara.net/data/ae7.jpg)
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(http://www.tilt.clara.net/data/ae8.jpg)
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(http://www.tilt.clara.net/data/ae10.jpg)
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(http://www.tilt.clara.net/data/ae11.jpg)
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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.
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
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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
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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
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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
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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
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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.
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
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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?
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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?
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Do these help?
(http://www.tilt.clara.net/data/page122.gif)
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(http://www.tilt.clara.net/data/page123.gif)
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?
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This engine still exists does it not?
isnt an Ash 82 variant used to power the latest Flug Werk FW190's.
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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.
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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.
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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
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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:
(http://www.tilt.clara.net/data/PAGE04.GIF)
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
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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......
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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:
(http://www.raf-roy.com/share/knegel/Screenes/La7_gear_alt.PNG)
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
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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.
(http://www.tilt.clara.net/data/ae1.jpg)
While the another chart shows 2200m:
(http://www.tilt.clara.net/data/ae4.jpg)
Also the power chart shows unlogical shape. Confusing overall.
gripen
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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.............
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Neither the LAme 5or LAme 7 goes faster than my bullets so it doesnt matter.
:)
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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
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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.
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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)
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I think (going back to the original question) the data presented here has changed (and some cases enforced) views I previously held re the performance criteria of and between the Lavochkins La5FN and La7.
All the performance figures we have were obtained and permitted within a regime of engine management dominated by a set of rules relating to engine temperature and engine stress management which impinged significantly on how and when these figures could be obtained.
Evidence that the La5FN did not have the RL WEP duration of the La7 (Possibly 5mins to the La7's 10 mins ) is shown in the La5FN pilots notes. This is re enforced by findings at Rechlin and the memoirs of Czech La5FN pilots fighting out of tri duby in 44.
Evidence from pilots notes that the La5FN was required to close its engine cooling louvres (forward and aft) in order to enjoy its maximum speed figures else incurr a penalty of approx 50km/hr off its top speed figures.
Coupled with rigourous guide lines regarding engine temperature management and how long the engine could be held at 240 or 260 deg c as opposed to the normal 215 deg c.
I think it would be safe to assume that the requirement to close off engine cooling to achieve max speed was also a requirement on the La7 and hence it would also incurr an increase in pure drag with its cooling louvres open . As Tsagi spent a considerable time improving this very area of the La7 drag model it may not be as much as the 50km/hr figure quoted for the La5FN.
We know that engine cooling was less efficient on the La5FN than the La7.
How would this be modelled in AH?
AH has only one generic WEP button and no engine management modelling beyond simple endurance ramifications of some settings.
So how could AH represent the limitations discovered above to more accurately model them within the constraints of its existing "mechanics"?
1) Would be to link part of the existing drag model to the temperature guage. eg when the temperature guage hits max the louvres are opened and remain open with the additional drag until the guage returns to the bottom of the red zone. Effectively this is additional pure drag that is added when the temp hits max which remains until it hits the orange zone.
2) this is independant of the WEP button although (as now) temperature increase is accelerated under WEP and of course WEP is not avaialble when the temperature is at max.
3)presently 2500rpm can be achieved at any alt in AH's La's. Whilst it would be nice to limit the revs to 2400 above 2000m for the La5FN and approx 3000 for the La7 this is purely eye candy if the thrust model is applied correctly in any event.
4)even when WEP is not applied the La5FN should heat up quicker (and cool down slower) than the La7.
The above does not model the real life stuff accurately interms of total engine temperature management. But it does mimic the real life consequences of running a Lavochkin hot for too long (you have to fly around with increased drag till it cools down). This way players can achieve the best that Lavochkins have to offer whilst also risking the worst if running for too long at WEP and Mil power.
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Originally posted by Tilt
I think ............................. .
An alternative would be to just close the louvres when WEP is selected........such that unless WEP is chosen the extra drag is always in play.............
above 2000/3000m there is no extra thrust and choosing WEP simply closes the louvres to reduce drag.