1/48 ModelSvit Yak-1B white 6 from GC 3 Normandie-Niemen - some questions

[Basilisk]

Thanks Massimo. I am actually not after the slot shape as such, but how the gun is showing in the slot. How far is it extruding and how does it look. I believe there is some kind of tube and not the actual gun itself.

Cheers, Peter

[Massimo Tessitori]

Hi Peter,
on MiG-3s, there is a small piece of pipe with an oblique cut.
I think you could extend your researches to other types of Yak.
On the photo, I see a black oval hole, inclined of about 30? with the horizon; I suppose that the gun and the tune have still to be installed.
Now I see that the same photo can be found at pag 17 of  of Yakovlev's piston-engined fighters, Gordon and Khazanov, red star vol.5.
On a photo of the engine of a Yak-9T, I see that the barrel of the UBS enters in a tubular manifold about 1/2 meter long. that protrudes (on its upper side) into the slot for  about 1/8, or more, of the lenght of the whole slot; I suppose that it should end oblique, but the photo from above-rear doesn't show the angle of cut, I suppose around 20?.
Regards
Massimo

[KL]

On a photo of the engine of a Yak-9T, I see that the barrel of the UBS enters in a tubular manifold about 1/2 meter long. that protrudes (on its upper side) into the slot for  about 1/8, or more, of the lenght of the whole slot; I suppose that it should end oblique, but the photo from above-rear doesn't show the angle of cut, I suppose around 20?.

Hi Peter & Massimo,

There was a pipe in font of the machine gun. Its purpose was to collect and evacuate machine gun gasses.  On early Yak-1s armed with ShKAS mgs, gasses were vented from the middle of the pipe, so there was a distinctive oval opening above the exhaust pipes.  End of the pipe was cut at close to 90 deg (approx 80 deg) and it did protrude from the cowling.



on Yak-1b, armed with UBS, end of the pipe was feared and "sealed".  This was part of "aerodynamics improvement program".  In the Russian book "Yak-1 nash luchshiy isterbitel' 1941 goda" by S. Kuznetsov on page 79 there is a photo of the modified opening.  In the "Perviy Yak" book by the same author, there is a Yak-1b section; gas collector pipe is clearly drawn - it end is cut at approx 45 deg... Oval vent above the exhausts was also eliminated on Yak-1b as part of the same program...

Most likely, on series Yak-1b, UBS opening was the same as on Yak-3:





How I understand this, on Yak-1b gas collector pipe did NOT protrude from the cowling...

HTH,
KL
 

[Massimo Tessitori]

Hi Konstantin,
the gas tube was solidal to the machine gun. The plane of Bourget could have its UBS removed, so the tube is not visible. If so, it will be difficult to find this detail on museum planes if they were deprived of the armament.
On photos of the building line, I can't see the tube but the plane could be not yet armed.
I see the tube clearly on a photo of Yak-1M Moskit.
Perhaps there is a manual of the plane availabe somewhere.
Regards
Massimo

[Basilisk]

Thank you Massimo and KL. Yes I found lots of pictures how it looks on early (razorback) Yak-1s, but nothing on Yak-1b until this evening.

This picture of the preserved Yak-1b does show the pipe - and it does extrude a little an has an angle on the ending as Massimo said.

So the actual gun is not showing - I guess you will see the barrel if you look straight into the tube.

By the way, what does UBS mean?

Cheers, Peter

[KL]

Hi Peter,
thnks for the photo, but honestly I can't see the gas tube protruding.  

...
On a photo of the engine of a Yak-9T, I see that the barrel of the UBS enters in a tubular manifold about 1/2 meter long. that protrudes (on its upper side) into the slot for  about 1/8, or more, of the lenght of the whole slot; I suppose that it should end oblique, but the photo from above-rear doesn't show the angle of cut, I suppose around 20?.

Massimo said that the tube protrudes into the slot for  about 1/8, or more, of the length of the whole slot -  approx 10 cm or more.  Massimo also guessed that the tube was cut at an acute angle, 20 deg; where do you see that??


Since we don't have a clear photo of Yak-1b UBS slots, the most important piece of information is its description in words! Check this link  http://www.airwar.ru/enc/fww2/yak1b.html
there is a list of modifications included in Yak-1b.  Modification no 7. deals with UBS gas tube end:

7. Установлен обтекатель входного отверстия кожухов пулеметов и заделаны патрубки для отвода пороховых газов.

Translation is tricky, hope you will understand:  
Installed fairing for the intake openings of the machine gun shrouds and covered small tubes for gunpowder gasses removal

Basically all this means that protruding gas collector tubes created drag so the shape of the engine cowling (machine gun "slot") was modified and made more streamlined...

check this movie to see how they looked on early Yak-3s:  https://www.youtube.com/watch?v=IMeubztfEno



at 7:27 you will see what is behind workers elbow...  

Regards,
KL

PS: UBS stands for Универсальный Березина синхронный = Universal Berezin Synchronized.  Berezin is machine gun designer's name.  

[KL]

thnks for the photo, but honestly I can't see the gas tube protruding. 

I have checked the link you provided and there is the photo that shows "mg slot" and "gas collector tube" in all their glory:



Yes, on photos above the tube is protruding... still because this plane is a museum exhibit with guns removed, it is possible that tube isn't installed properly.  IMHO, at least it should be rotated to look like the tube drawn in Yak-1b section in Kuznetsov's book.

Regards,
KL

[Basilisk]

How could I not see the picture showing the tube so clearly! But I think you are correct in saying that the tube shouldn't protrude into the slot as it doesn't make any sens from a design (and aerodynamic) point of view.

I think the tube in the museum aircraft is indeed not properly installed. Also the angle of the tube opening does match the slope of the slot if not protruding which would match the video image you provided the link for - and great to see how these aircraft had been built.

Maybe the drawing you mentioned (and I have also seen it in a Polish publication) is based on this museum aircraft.

So I will have the opening flush, but sloped at around 45 degree which isn't the case with the ModelSvit kit.

Thank you KL for taking the time to investigate this and providing all this valuable information.

Cheers, Peter

[Massimo Tessitori]

Hi,
of course it is possible that the tube wasn't reinstalled properly, but it looks visible on other photos of other Yaks so you can't be sure.
The rotation of the oblique cut is rational, because the most shortened part is closer to the cowling surface seen in trasversal section,  the point that is closer to the air flow. So, I suggest to investigate more before deciding that the museum exhibit is not representative.
Regards
Massimo

[Massimo Tessitori]

Hi,
I had a look at this:

check this movie to see how they looked on early Yak-3s:  https://www.youtube.com/watch?v=IMeubztfEno

At 20:30, we see both Yak-1s and Yak-3s on the same line.  But it looks a production line, not a maintenance depot. What strange!

Regards
Massimo

[Basilisk]

Yes of course there is the possibility that the tube protruded, but unfortunately I can't find a picture of a Yak-1b showing it.

But why would the tube protrude? What was the need for that? Looks like I just have to make an educated guess.

Cheers, Peter

[KL]

check this movie to see how they looked on early Yak-3s:  https://www.youtube.com/watch?v=IMeubztfEno

At 20:30, we see both Yak-1s and Yak-3s on the same line.  But it looks a production line, not a maintenance depot. What strange!

Why is it strange?  The movie describes conveyor production line at Sararatov Factory 292, Yak-1 and Yak-3 main producer.  Conveyor production started in Saratov in March 1944, much later than in other main NKAP factories.  Yak-3 production started in spring 1944 and last Yak-1b left conveyor in July 1944 - so the movie was filmed in spring 1944 when both new Yak-3s and old Yak-1s were made at the same time.

Note that the Yak-3s in the movie are armed with one UBS machine gun only.  Initial 197 Yak-3s (series 1 to 12) were armed with one UBS (same as Yak-1b) - this confirms that the movie was filmed at the beginning of Yak-3 production.     

Regards,
KL

[Massimo Tessitori]

Hi,

Yes of course there is the possibility that the tube protruded, but unfortunately I can't find a picture of a Yak-1b showing it.

But why would the tube protrude? What was the need for that? Looks like I just have to make an educated guess.

I had a look to the monografie loctnicze n.46 and to skrzydla 2/91, them both have drawings with the tune protruding.  On the other hand, I have the impression that it is not always visible on photos. Probably the tube could be installed in different ways, and protrude and be rotated or not.
Probably there was a factory standard, that could have been changed during maintenance due to an approximative reinstallation.

It would be good to know if the protrusion of the tube had some function.

Why is it strange?  The movie describes conveyor production line at Sararatov Factory 292, Yak-1 and Yak-3 main producer.  Conveyor production started in Saratov in March 1944, much later than in other main NKAP factories.  Yak-3 production started in spring 1944 and last Yak-1b left conveyor in July 1944 - so the movie was filmed in spring 1944 when both new Yak-3s and old Yak-1s were made at the same time.

Interesting.

Regards
Massimo

[KL]

It would be good to know if the protrusion of the tube had some function.

My guess is that its purpose was to prevent gunpowder gasses entering engine compartment and cockpit...

I have read again about Yak-1 development and its sub-types and realized that the photo of that fairing and modification I had mentioned refer to a test airframe No 0868.  Some of the modifications were implemented on series planes, others not... This prototype was armed with ShKAS machine guns anyways...

Yak-1b preserved in Saratov museum is representative for early Yak-1b, similar to those Yak-1s flown by Normandie Squadron. So protruding tube cut at angle is almost certainly what was on Yak-1s flown by the French pilots.

HTH,
KL
 

[xan]

Durand's Yak was probably one of the original 10 planes received in Ivanovo training center.  Those planes were made in December 1942 and they were most likely camouflaged in same black-green pattern as old Yak-1s

Yes it is.  the 06-118  piloted by Durand arrived in Ivanovo the 3rd of march 1943. 16 planes (new planes) arrived in Ivanovo between the 27 of january and 25th of March.
sorry to return to an hold discussion...

Xan