Klimov VK-107 - help needed

[GregP]

The Soviet Air Force was straining their gas with chamois cloth through the end of the war (when they strained it at all) and it was not the highest performance number gas flying about. Late-war Allied boost numbers probably could not be run on typical Soviet fuels due to fuel if nothing else. Perhaps they could, if such fuels were avialable. That comes from former Soviet block air force pilost who survived and became buyers of high-tech equipment in the 1990's. We entertained a few of them in our house on several occasions and had some VERY interesting conversations. One of my Russian friends brought his entire family for a visit once, and the son had never driven a car.

We took him out to Bob Bondurant school of driving and put him through a race driver training course. Now THERE was a happy young man.

His dad had formerly been a MiG pilot and I took him out to Deer Valley airport in Phoenix, AZ and introduced him to friends who had MiG-15s and 17s. They had a 4-hour long conversation about flying and maintenance. He said they were running really low-octane gas in WWII mostly due to the inability to get better gas to the front lines in useful quantities coupled with irregular availability in general. When they GOT good gas, they usually used it in Spitfires and P-39's because the engines were run on it normally in their homelands.

Now, I have no way to check that story, but that's what they said.

Perhaps some of our former Soviet members out there know better or can confirm?

 

[tomo pauk]

There might be some truth in that - the 'TsAGI book' mentions that Mikulin engines were designed with ever lower CR, so the odd batch of the fuel that is not quite at 95 oct will not mean a wrecked engine (and dead crew) once the higher boost is used.

 

[Caspian Sea Monster]

I hate to necro a thread (especially on only my seventh post yet) but it's only been a couple months and I think you guys might be interested in this:

The caption says, roughly, "Kinematic schematic of aircraft engine M-108. From technical operation and maintenance manual, 1946." I tripped over it in a Google image search (for "Климов ВК-107"), from a comment on a blog post about tank engines or something. I don't know, my Russian isn't very good and I haven't the patience to go a-translating it right now - my mind is quite firmly affixed on airplane engines.

The file name is "VK-108_kinem_shema.jpg". So if that's indeed accurate, I think you've hit the nail on the head with your valve hypothesis, Mr. Pearce. Follow the rotation of the parts to the valve cam lobes and you can see the air-only valve (on the third cylinder from the rear in the starboard bank, as referenced to your illustration in post #28 ) opens a bit before the fuel-air valve.

Now I've got a question. I'm trying to figure out how the cooling air jackets for the inner exhaust manifolds work.

The perspective is a bit tricky, but this engine does not appear to have openings at the front end of the cooling jackets for air to enter into. Furthermore, taking a look at some original aircraft on display, the one clear photo of a 14-exhaust-pipe (VK-107 powered) Yak-9 I can find has no air intake above the front end of the engine, but does have a dorsal intake scoop above the rear end.

12-exhaust-pipe Yak-3s and 8-exhaust-pipe Yak-9s (M-105 powered, so I presume) typically do not have this scoop:

Exhibit A
Exhibit B
Exhibit C

My hypothesis is that air enters this dorsal intake, flows downwards, reverses 180° and flows forward toward the propeller, passing over the exhaust manifolds on the way, and is dumped overboard out the sides of the cowling, around the forward-most exhaust pipes.

(Modern Allison-powered replicas also have this dorsal air scoop, but based on the intake geometry of the Allison engine as used on the P-40 and P-51A, this is most probably the supercharger intake.)

This engine on the other hand, unlike the first, appears to have ram-air intakes for the cooling jackets at the front (as well as the mystery centerline pipe) which I have circled in orange. The only original aircraft that seems to match this arrangement, with dorsal air intake at the very front and overboard-vent at the rear, is this particular Yak-9U, which very obviously has an M-105 engine installed (given the exhaust stacks.) Maybe it was originally built around the VK-107 but was swapped to an M-105 while in service, and retained the original cowling? What do you guys think? Have I overthought this or missed some glaring detail? I don't know, I'm traditionally a P-51 gal and kinda new to WWII Soviet aircraft.

 

[WJPearce]

Hello CSM,

Thank you for the new image. Your necro of this thread was nowhere near as bad as my 2+ year necro. But I think necro is fine when one is adding new information on a historical topic.

After studying many images in Yakovlev Fighters of World War Two by Gordon and Komissarov x 2 (published in 2015), I think the key to this question is focusing on the armament of the VK-107-powered Yak-9 and Yak-3 aircraft.

It seems when the aircraft has one or two 12.7mm guns or one 20 mm cannon above the engine, it has the front inlet (behind the spinner) and the rear outlet (between the gun bulges).
http://www.museumofflight.org/files/TMOF_Yakolev_Yak-9U_Frank_04_P2C.jpg

When the aircraft has two 20 mm cannons above the engine, then there is just the rear inlet (between the gun bulges).
https://upload.wikimedia.org/wikipedia/commons/5/51/PL_MWP_Yak-9P.JPG

This seems fairly consistent on the VK-107-powered Yak-9U, Yak-9UT, Yak-9P, and Yak-3. Two cannons in the cowling means just the rear inlet between the cannon bulges. I'd guess that there was not room for the front inlet behind the spinner with the larger cannon barrels and their fairings.

What makes it difficult is that some aircraft, like the Yak-9U, used both the VK-105 and the VK-107 engines. Then, it appears some of the VK-107s-powered aircraft had one 12.7 gun in the upper cowling, others had two, others had one cannon, others had two. The first image I linked above is a VK-105-powered Yak-3U with two machine guns in the upper cowling but with what appears to be upper cowling for a VK-107. So, who knows for certain?

As far as how the cooling jackets worked, I think the one with both an inlet and an outlet visible is pretty straight forward. The one with the rear outlet is more of a mystery. There is a picture in the book I referenced above of Yak-9 production. It appears the cooling duct surrounds the "extra" exhaust stack and that is the outlet.

 

[Caspian Sea Monster]

Interesting point! I hadn't really considered variations in armament affecting the intake placement.

In any case, I found something possibly even cooler: Yak-9U with VK-107A Engine - Technical Datasheet (12MB PDF)

The illustrations actually aren't any less confusing that what I've already found, as the very first photograph has the rear-end inlet, while the orthographic diagram on page 6 shows the front-end inlet and rear-end outlet cowling with the M-105 exhaust again, and the illustration on page 67 of the engine with the cowling removed shows no front-end intake scoop on the engine itself. I'm chalking up the M-105 exhaust in the orthographic diagram as sloppiness on the part who whomever composed the manual. Anyway, actually reading it will likely be much more informative, and I've put this on my List of Things Needing To Be Translated, but it'll have to be after I finish the Mikulin AM-42 technical manual translation, which will likely take at least a few months. Anyone else - particularly anyone who actually competently reads Russian - wanting to take a stab at it first is welcome to do so.

 

[WJPearce]

Thanks for the Yak-9U VK-107A file. The diagram on page 67 matches the photo I mentioned of Yak-9P production. I inadvertently left off the "P" in my post above; that was important because the Yak-9Ps had two 20 mm cannons in the upper cowl, which was my whole point about the rear inlet. On the page 67 diagram, item 12 "выходное окно кожуха обдува" translates (with the help of Google) to something like "outlet window shroud airflow." I take that to mean it is the inner exhaust manifold cooling shroud air outlet. Below is a crop of the Yak-9P VK-107 production image I mentioned. I think you can see the shroud/jacket outlet around the first exhaust stack.

 

[Caspian Sea Monster]

Excellent! My original hypothesis about the airflow path was correct then. Thanks for your help!