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Author Topic: La-7 sand filters  (Read 7165 times)
warhawk
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« on: June 09, 2008, 06:47:55 PM »

Did all Three-gun La-7s have sand filters beneath wings?
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John Thompson
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« Reply #1 on: June 10, 2008, 01:47:01 AM »

That's a really interesting question! The MBI La-7 book (page 81) says:
"The intake ducting to the engines of the first series' aircraft were devoid of any air cleaning device, causing frequent seizures. Aircraft of subsequent series were fitted with filters in the wing undersides.The valves fitted to the front air intakes were cable controlled to close them once the engine ran on the ground, including the take-off and landing. Their closing opened at the same time the intake duct taking the air through the removable mesh screen filter on the wing underside." (This reminds me of the Foreign Object Damage systems on modern Russian aircraft such as the MiG-29!)

However! On page 16 of the same book, it tells us that the first La-7 fighters were delivered in June 1944. Military testing was performed by the 63 GFAR between September 15 and October 15. These tests revealed repeated engine seizures, a problem "that was to bedevil the La-7 until the end of the War. This defect was in fact caused by the relocation of the engine air intakes to the wing roots [compared to the La-5 series]. It was found to be caused by dust particles entering the air intakes on take-off, a situation compounded by the airscrew blades, especially on dusty summertime airfields. These dust particles were the cause of the engine jamming. This defect had not shown up on the frozen snowbound airfields used during the course of the wintertime national testing. Lavochkin's engineers tried to meet this challenge by fitting extra dust filters in the wing roots, as indicated by the additional openings on the underside of the wing in front of the wheel bays. National testing of this solution was applied to the machine s/n 38102663 from the May 1945 production batch as late as July of 1945 and was not found to be satisfactory. Anyway, the modifications recommended as a result of the tests by the 63rd GFAR were only made to aircraft delivered after the War. So engine jamming was, as noted, to be a frequent fault with La-7 aircraft, unlike its sibling the La-5FN."

Based on this last quotation from page 16, I'm inclined to believe that *no* wartime La-7 aircraft had these filters, regardless of armament. More detailed study of production records is required. The MBI book is somewhat unclear on exact details. The B-20 cannon was considered a failure, not achieving the specified service reliability of 5000 rounds fired before rebuilding or replacement was needed (most of the units failed at just over 3000 rounds during tests), but regardless, it was put into production in October 1944. According to the MBI book, a total of only 368 B-20-armed aircraft was manufactured at Factory 381.

As is so often the case, more study of photographs is needed! I suspect I've only added to the confusion; if so, I apologize! Maybe someone can provide information from another reference which will clarify this detail.

John
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warhawk
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« Reply #2 on: June 10, 2008, 09:44:09 PM »

One more question about the three-gun model:
I plan to do Golubov's "white 33", but looking at the article at

http://vvs.hobbyvista.com/Markings/La7-3gun/index.php

I see that "white 33" is in fact not 33 at all! This article raises more questions than I had in the first place.
I found the mentioned photo:



And also I found another photo for which Osprey's "Aircraft of the Aces 056 - LaGG & Lavochkin Aces of World War 2" states that it is Golubov's plane:



Are these two photos of the same plane?
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John Thompson
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« Reply #3 on: June 10, 2008, 10:23:50 PM »

This thread from the hobbyvista forum could be helpful:
http://vvs.hobbyvista.com/Forum/showthread.php?tid=552

John
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warhawk
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« Reply #4 on: June 11, 2008, 10:46:21 AM »

I started that thread, trying to determine the facts. I was hoping I could find some definitive answers on this forum...
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Massimo Tessitori
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« Reply #5 on: June 11, 2008, 07:29:25 PM »

Quote
I started that thread, trying to determine the facts. I was hoping I could find some definitive answers on this forum...

Funny loop indeed!
Massimo
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John Thompson
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« Reply #6 on: June 11, 2008, 11:53:45 PM »

I started that thread, trying to determine the facts. I was hoping I could find some definitive answers on this forum...

Oops - sorry! I guess I should have recognized the avatar!

John
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warhawk
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« Reply #7 on: October 05, 2012, 10:39:41 AM »

Not to start a new topic, thought better to post in this one....
Found a neat little photo of A.V. Aleyukhin's machine, but no date (presumably during GPW?) which clearly shows a sand filter....
Three-gun version, am I right?


http://www.bellabs.ru/Fotab/I-69-9/I-69-9_04.html
« Last Edit: October 07, 2012, 02:05:41 PM by warhawk » Logged
John Thompson
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« Reply #8 on: October 05, 2012, 06:04:59 PM »

It appears to be two guns in this photo:



John
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Massimo Tessitori
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« Reply #9 on: October 06, 2012, 02:15:49 PM »

Quote
Found a neat little photo of A.V. Aleyukhin's machine, but no date (presumably during GPW?) which clearly shows a sand filter....

The thing visible inside the wingroots intakes, you mean? I don't know well the type, but it could be a shutter. Many planes have two alternative inlets for air: one for the plane inflight (the wingroot intake), one for the ground (maybe inside the gear bay) with some filter.
Regards
Massimo
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learstang
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« Reply #10 on: October 06, 2012, 05:59:06 PM »

It's interesting that they would have had this problem with the La-7 since the VVS had had the same problem with the Il-2 in 1941 and 1942 and fixed it with the external carburettor intake filter.  But I suppose it's a different aeroplane with a different engine so it needed a different fix.

Regards,

Jason
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warhawk
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« Reply #11 on: October 06, 2012, 06:32:40 PM »

The thing visible inside the wingroots intakes, you mean?

No, I meant the rectangular mesh between wingroot intakes and wheel well opening. I am still trying to pin whether or not all 3-gun models had them added...
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Massimo Tessitori
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« Reply #12 on: October 06, 2012, 09:34:45 PM »

Hi,
the air filter, on both wings, is described in the MBI monograph. They write that it is a postwar modification.

Regards
Massimo
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warhawk
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« Reply #13 on: October 07, 2012, 02:03:43 PM »

Thank you. I will probably leave them off when I get round to finish my La-7...
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John Thompson
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« Reply #14 on: November 06, 2012, 07:53:29 PM »

Found this image on Scalemodels.ru, while looking for something else:



John
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