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Author Topic: La-5 Cowling Shape  (Read 12098 times)
John Thompson
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« on: June 13, 2010, 03:41:33 AM »

Here's an interesting thread from Scalemodels.ru, with links to a really well-done Russian site which contains many documents and photos related to GPW weapons, vehicles, and personalities:
http://scalemodels.ru/modules/forum/viewtopic_t_23193.html

This is an excellent site, and well worth investigating carefully. The way some of the booklets are presented in a page-turning format is something I've never seen before - look for the one which shows Russian aircraft propellors, for example.

One of the links from the Scalemodels.ru thread produced this image:



After some reading of Milos Vestsik's "Lavochkin La-7" and Yefim Gordon's "Lavochkin's Piston-Engined Fighters", I concluded that the aircraft in this photo is the La-5 "206" (the designation "206" was merely the last three digits of the aircraft's 8-digit serial number). This was a production La-5FN which underwent extensive tests and modifications in the TsAGI windtunnel during 1943, to try to refine the performance of the La-5 design. These modifications were eventually incorporated into the design of the La-7.

What is interesting (to me, at least!) is the shape of the La-5FN cowling in this plan-view photograph - it is clearly a bulged cylinder like the La-5 and La-5F, and not a straight-sided cylinder like the La-7. And certainly not onion-shaped, as sometimes shown in older drawings!

John
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Massimo Tessitori
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« Reply #1 on: June 13, 2010, 10:41:57 AM »

Hi John,
From the photo, it looks as if the horizontal plans were all covered by fabric, not only the elevator.
Massimo
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Greg C.
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« Reply #2 on: July 29, 2010, 01:01:06 AM »

Great picture, John.
The one observation I'd make is, it's still difficult to really tell the plan-form of the cowl without a direct-overhead view.  I suspect if the camera were moved so that we could see from overhead, it might be more of that "onion" shape of the La-5 and 5F.
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John Thompson
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« Reply #3 on: July 30, 2010, 12:37:39 AM »

Thanks, Greg! Personally, I think the onion-shape idea is incorrect for any of the La-5 series, but that's just my opinion - go here for Massimo's article on the subject, where he does leave the door open to either possibility for the La-5 and La-5F:
http://mig3.sovietwarplanes.com/la5/cowling/cowling.html

John
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John Thompson
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« Reply #4 on: August 01, 2010, 03:17:05 AM »

For those many visitors who just can't get enough of the topic of La-5 cowlings, check this out. Here's what usually appears in drawings and reference photos as the standard La-5FN cowling:



Note the hinge line along the side of the cowling - the two joined panels open outwards and up, being also hinged at the top of the upper panel.


Now here's another La-5FN photo - the La-5FN intake is clearly visible at the top, as is the diamond-shaped "FN" logo on the side of the cowling; it also shows the flat exhaust outlet covers of the La-5FN:



In this second image, the same cowling panel locking devices as used on the La-5 and La-5F are visible. In this case, what was a hinge line in the first photo is now a joint where the upper and lower panels meet. Here, the upper panel opens upwards on a hinge at the top of the cowling, and the lower panel drops down on a hinge at the bottom.

So, apparently there were two types of La-5FN cowlings, early (the second image) and late (the first image). I hope others find this interesting!

John
« Last Edit: August 01, 2010, 03:26:21 PM by John Thompson » Logged
Greg C.
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« Reply #5 on: August 03, 2010, 06:15:30 AM »

Now there's a shock, differently designed and fitted components on the same type of soviet military machine!

Smiley

I've noticed the same, subtle discrepancies while pouring over photos in my references.  Sometimes the cowl looks very rounded, sometimes almost cylindrical.  Maddness, I tell you!
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Massimo Tessitori
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« Reply #6 on: August 03, 2010, 11:24:39 AM »

Hi John and Greg,
I think that the plates were made with simple curavatute (parts of a cylinder) but assumed the bulged look while closing the panel. Probably there is something protruding on the internal horizontal structure aside the engine, and the plates were forced between this internal part and two external steel coils when the panel is closed. This could be a way to prevent vibrations of the panel due to airflow.
Massimo
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mholly
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« Reply #7 on: August 18, 2010, 01:04:49 PM »

Hi all,
amazing how is this topic regularly revived but am afraid it's in the category of "beating the dead horse".
I offer rather simple and perhaps primitive explanation why the idea of "bulged", "onion shape" or, in other words, 3-dimensional shape of cowling panels on ANY La-5 version should be discarded:
1. no reason for it from engineering point of view, engine itself was of constant diameter and complex shape of these panels would present an unwelcome manufacturing nightmare
2. had the cowling panels been 3D how do you explain that in ANY picture the hinge line is STRAIGHT? Technically impossible, or isn't it?
Btw 2 different systems of panels installation/opening (as described by John Thompson earlier) are (should be) well known.
Too much of analyzing outdated drawings and pix taken from variety of angles? I don't know but on the most recent La-5 Zvezda 1/48 kits the cowlings are cylindrical. So are on 1/72 AML kits.
Mario
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John Thompson
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« Reply #8 on: August 18, 2010, 06:13:38 PM »

Btw 2 different systems of panels installation/opening (as described by John Thompson earlier) are (should be) well known.
Too much of analyzing outdated drawings and pix taken from variety of angles? I don't know but on the most recent La-5 Zvezda 1/48 kits the cowlings are cylindrical. So are on 1/72 AML kits.
Mario


Good points; I was specifically referring to the La-5FN, though, not the La5 and La-5F, where the early version (with the clamps) is well known. I never saw it on a La-5FN before, but I probably didn't look carefully enough.

Re the 1/72 AML kits, this also is true, except for the La-5UTI, which has the "onion-shaped" cowling like the VES/Cooperativa "LaG-5", and as shown on the old (outdated, as you have pointed out) Voronin drawings.

John
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learstang
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« Reply #9 on: August 18, 2010, 06:14:24 PM »

Hi all,
amazing how is this topic regularly revived but am afraid it's in the category of "beating the dead horse".
I offer rather simple and perhaps primitive explanation why the idea of "bulged", "onion shape" or, in other words, 3-dimensional shape of cowling panels on ANY La-5 version should be discarded:
1. no reason for it from engineering point of view, engine itself was of constant diameter and complex shape of these panels would present an unwelcome manufacturing nightmare
2. had the cowling panels been 3D how do you explain that in ANY picture the hinge line is STRAIGHT? Technically impossible, or isn't it?
Btw 2 different systems of panels installation/opening (as described by John Thompson earlier) are (should be) well known.
Too much of analyzing outdated drawings and pix taken from variety of angles? I don't know but on the most recent La-5 Zvezda 1/48 kits the cowlings are cylindrical. So are on 1/72 AML kits.
Mario

Mario, you make a couple of good points.  Given the desperate need in the GPW to have easy-to-produce aircraft, it wouldn't make any sense to make anything more complex than it needed to be.  Also, drawings are not to be trusted.  I've learned this, sometimes to my regret, with drawings on the Shturmovik.

Regards,

Jason
« Last Edit: August 18, 2010, 07:19:32 PM by learstang » Logged

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Massimo Tessitori
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« Reply #10 on: August 18, 2010, 07:18:21 PM »

Quote
I offer rather simple and perhaps primitive explanation why the idea of "bulged", "onion shape" or, in other words, 3-dimensional shape of cowling panels on ANY La-5 version should be discarded:
1. no reason for it from engineering point of view, engine itself was of constant diameter and complex shape of these panels would present an unwelcome manufacturing nightmare
2. had the cowling panels been 3D how do you explain that in ANY picture the hinge line is STRAIGHT? Technically impossible, or isn't it?

Hi Mario, Smiley
it's not so obvious. On other similar planes, whose radial engines have the same type of symmetry, the cowling is onion shaped, as on the Kawasaki Ki-100.
From an aerodynamic point of view, this could be advantageous to reduce vortex formation. They are not difficult to build: many other panels of La-5 and other planes have double curvature, ex. the front ring.

Quote
Too much of analyzing outdated drawings and pix taken from variety of angles? I don't know but on the most recent La-5 Zvezda 1/48 kits the cowlings are cylindrical. So are on 1/72 AML kits.
Again, there is no reason to think that models are necessarily more accurate than drawings, and by sure not more accurate than photos.

I've already explained my point: the panels of La-5, all versions, are pieces of cylinder, but they curves when they are forced in closed position. This idea is based on photos. Unless one has quoted factory drawings or remains of the real piece, photos are the best documents that he has in his hands. Smiley

Massimo
« Last Edit: August 18, 2010, 10:36:39 PM by Massimo Tessitori » Logged
mholly
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« Reply #11 on: August 19, 2010, 07:24:09 AM »



Good points; I was specifically referring to the La-5FN, though, not the La5 and La-5F, where the early version (with the clamps) is well known. I never saw it on a La-5FN before, but I probably didn't look carefully enough.

Re the 1/72 AML kits, this also is true, except for the La-5UTI, which has the "onion-shaped" cowling like the VES/Cooperativa "LaG-5", and as shown on the old (outdated, as you have pointed out) Voronin drawings.

John
[/quote]
Supplemental info here
http://www.postimage.org/image.php?v=Pq1W1gyi
Your 2nd pic may show very early production La-5FN (as indicated but "old" green-black camo?) where La-5 cowling panels hinge system was still retained. Just a theory.
Cheers,
Mario
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mholly
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« Reply #12 on: August 19, 2010, 07:50:21 AM »

Massimo,
I just wanted to contribute, after a long time! Grin Grin
Seriously, comparison to Ki-100 is not a good one. It's cowling is made of several individual panels fastened with Dzus'.
I don't think that aerodynamic cleanliness in that area of the airframe would ever overweight increased man-hours for complex parts manufacturing.
Sorry but I just cann't imagine, technically-physically, how can the straight part curve upon closing?
As I said initially there are pix and there are pix, I recommend to go through this thread to see some interesting ones
http://scalemodels.ru/modules/forum/viewtopic.php?t=2645&postdays=0&postorder=asc&&start=0
Cheers,
Mario
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Graham Boak
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« Reply #13 on: August 19, 2010, 11:12:27 AM »

Sorry but I just can't imagine, technically-physically, how can the straight part curve upon closing?

I'm with you completely here - this is a fairly important piece of the airframe, not a simple fairing, which might be flexible (e.g Spitfire wing root fairings).  The rings are clamps, not corsets.  However, any fairing that did bulge out would also open up a large gap, which is clearly not visible.

If it bulges, then it is specifically designed and manufactured to bulge.  As earlier aircraft are straight, then the only reason for doing this would be to reduce the cross-sectional area before and aft of the bulge - again, there is no sign of this.
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Massimo Tessitori
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« Reply #14 on: August 20, 2010, 07:40:17 AM »

Hi Marian, Smiley
your contributions are welcome, of course.

Quote
Sorry but I just cann't imagine, technically-physically, how can the straight part curve upon closing?

You are considering thin metal parts, as sheets and rods, as rigid pieces, and could be not exact. They could bend.
An example: imagine to bend sharply a piece of paper at 90? on a line. When the piece is shaped so, the line must be straight, as the rod of the hinge at mid of the sides of La-5FN cowling when it's open.
But if the sheet is made plain again, as when the cowling is closed, it can be curved, and the old bending line is not necessarily straight.

Now, imagine the open cowling of the La-5FN. When open, the rod of the hinge is obliged to be straight.
When the panel is closed but uncostrained, it becomes more flexible because its rod can bend freely.
But when the panels are closed and constrained, they become more rigid because their front and rear edges are pressed from outside to inside by coils, and a mid point is pressed from inside to outside by the internal strut visible aside the engine.

Massimo

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