Lavochkin Hydraulics

[Tilt]

From what I can discern Lavochkins (and maybe some other ac) used sump oil and an engine based pump for its hydraulic system.

Given this once oil had been lost due to leakage then the flaps could not be operated.

They could be "locked" in what ever position  they were in.

Similarly if engine revs were lost the hydraulic pump was lost with them.

Gear was also lowered hydraulically but it had an aircylinder back up of limited capacity. (on the La7 this same air cylinder started the engine and primed the guns if they jammed).

I dont know how much of a game feature it would be but it would be at least authentic to deny use of Lavochkin flaps after a period of oil leakage.

[Bodhi]

That is interesting that they would use engine oil to accomplish something that would be better used in a seperate system.  IE... line damage could cause engine failure...  not to mention the viscosity issues of forcing it through the flap ports and sequencing valves...

My bet is that it is an engine driven pump driving a seperate fluid source.

[Widewing]

Originally posted by Bodhi
That is interesting that they would use engine oil to accomplish something that would be better used in a seperate system.  IE... line damage could cause engine failure...  not to mention the viscosity issues of forcing it through the flap ports and sequencing valves...

My bet is that it is an engine driven pump driving a seperate fluid source.

Inasmuch as the Lavochkins have an accumulator in the aft fuselage (behind that access panel on the left side), I'm leaning towards a separate system operated by an engine driven pump. Using engine oil would be a bad idea. The normal contamination in engine oil (like aromatics from fuel and particulates such as carbon) would utterly destroy the seals in the hydraulic system, especially strut seals.

My regards,

Widewing

[Tilt]

There were actually two oil pumps .....one priming pump that took oil from the oil tank under the gun bay via a filter to the engine and then to an  engine driven oil pump which pressurised the system circulating oil via a 2nd filter thru the oil cooler and back to the tank.

The 2nd pump also powered the ac hydraulics.......... hydraulic pressure that was monitored in the cockpit was a function of this pump although pressure at the engine was monitored separately along with oil temperature.

Flap and gear valves do not seem to be thru flow type in the centre position...hence the same oil was used to raise and lower flaps /gear but it was not circulated thru the engine it just recieved its pressure directly from it whilst not a separate system contamination was not an issue.

All flaps were operated by a single cylinder mounted in the starboard wing and connected by rod links .

If the engine lost its oil this system therefore lost its pressure.

The air bottle seems to have been pre pressurised (150 bar)and not an accumulator as suggested above.(it has reduction valves at its discharge ( to35 bar) and is refered to as a compressed air supply) Whilst this would indicate it has limited capacity it would mean its pressure in the bottle would be higher than could be achieved using an oil/air accumulator system.

The air system was used for starting(La7) , cannon charging and emergency gear lowering (just lowering)

Be aware that many "translations" refer to an akumulator when they really refer to the battery.

[stantond]

Engine oil for hydraulic systems would have several problems.  Not that the Russians did not try this... but they would not use it for long.  Aside from the contaminants and acids eating away the seals, particulates would trash the system quickly.  Also, engine oil viscosity is much too high for an effective hydraulic system.  Given the cold temperatures in Russia an equivalent SAE 30 wt. oil would not flow properly.  Hydraulic fluid is essentially automatic transmission fluid.

This last item leads me to state that the Russians did not used engine oil for their hydraulic system.  They used the pump off the engine, but not engine oil.  Aircraft hydraulic systems (even Russian ones) won't operate with that type of 'oil'.



Regards,

Malta

[Tilt]

Its nice to assume what is good and bad practice and what may or may not have been done.

All I can report (acording to the texts I have) is what was done......... there is no where a reference to any separate pump or oil reservoir for flap and gear hydraulics.


btw Lavochkins were designed to have a service life of 3 to 5 months.

[stantond]

Another thing to consider is that using engine oil instead of hydraulic fluid would not save any weight.  The Russians were using Allied parts to build their planes.  No allied aircraft hydraulic systems used engine oil.  Engine oil is great for engines, but not for hydraulics.   The accumulator you mentioned was for emergency purposes when the engine stopped so the aircraft would still respond to controls.

It's a fanciful idea, just not practical.  Of course, the design may have really been that crappy.  I am giving Russian engineers Allied experience and credit.  Afterall, that's who they learned to design fighter aircraft from and they are good engineers.

Now that you mention it, I have never seen a Lavochkin at an airshow.  Yaks are usually there though.


Regards,

Malta

[MiloMorai]

Originally posted by stantond

I am giving Russian engineers Allied experience and credit.  Afterall, that's who they learned to design fighter aircraft from and they are good engineers.

Cold War propaganda at its best.

Wunder were Alexander Kartveli,  the designers of the P-47, learned his trade?

[stantond]

Yes,

The soviet engineers/designers were not dummies as proven by Dr. Kartveli.  However, he did not learn anything about aeronautics in Russia.


http://www.internet-encyclopedia.org/wiki.php?title=Alexander_Kartveli

http://www.aviationboom.com/pioneers/alex_kartveli.shtml

If you believe the stories of the Luftwaffe, most of their kills were against the Russian airforce. This was not a testament to the ignorance of the Russians, but of their lack of preparation and equipment.  This changed in the later part of WW2.

Regards,

Malta

[MiloMorai]

Alexander Nikolaivich Prokofiev de Seversky graduated in 1914 with an aeronautical engineering degree from the Imperial Russian Naval Academy.

[stantond]

I don't believe Seversky ever let education get in the way of his learning.  At the time (1914) Russia had a world class aeronautics program.  I am sure the education Seversky received was the best for that time.  

Russia let its aeronautical program decline.  By 1941 they did not have a 'world class' aeronautical program or produce fighters comparable to the best European planes.  However, they had a strong motivation and learned quickly.

My point being is that allied technology was available.  While 'official Soviet documents' don't show Russia using or needing any Allied goods or technology, good designers (which Russia had) would use everything available to them and learn from others.  As such, I would be surprised if the Lavochkin aircraft used engine oil to operate the aircraft controls.  However, while it is not a good idea, it is feasible.


Regards,

Malta

[joeblogs]

A large number of US planes (then and now) use engine oil to drive constant speed propeller units. The engine oil drives pistons which deliver pressure against a set of counterweights.

There is typically a second pump used to get the pressure high enough for use in the unit.

Engine oil pressure is used in other systems too. That does not mean that the oil comes into direct contact with the innards of those systems.

-Blogs

Originally posted by stantond
Engine oil for hydraulic systems would have several problems.  Not that the Russians did not try this... but they would not use it for long.  Aside from the contaminants and acids eating away the seals, particulates would trash the system quickly.  Also, engine oil viscosity is much too high for an effective hydraulic system.  Given the cold temperatures in Russia an equivalent SAE 30 wt. oil would not flow properly.  Hydraulic fluid is essentially automatic transmission fluid.

This last item leads me to state that the Russians did not used engine oil for their hydraulic system.  They used the pump off the engine, but not engine oil.  Aircraft hydraulic systems (even Russian ones) won't operate with that type of 'oil'.



Regards,

Malta

[Tails]

The reason propeller control units use engine oil is because

A> Dont need to install a powered hydraulic system on a plane that otherwise doesnt need one.

B> The pressure required to drive the the prop hub is rather insignificant

C> Pressureized engine oil is available right there! All constant speed and variable speed hubs I've seen draw the engine oil right through the center of the prop shaft, either from the engine itself, or from the reduction gear box.

[Tilt]

I am  now even more convinced that lavochkins did indeed use engine oil pressure to drive the gear and flap hydraulics.......

Look at the picture below............ its the left hand side of the la7 cockpit.



You will see two manually operated hydraulic valves........

The upper one is for flaps and the one with the lever poking out of the dash and the valvery behand the dash is the main gear valve.

Running across the floor next to where the fuselage meets the floor are the main oil pipes running from the engine sump pump to the oil cooler below and rear of the cockpit then back to the engine.

You will clearly see two tees off one of these pipes and you will equally see that one goes directly to the centre (pressure) port of the gear valve. The other pipe from the 2nd tee dissappears behind the dash to (IMO) emerge higer up under the fuselage brace to feed the flap valve.

Raise and lower valve ports  for the gear feed smaller hydraulic pipes which drop and split at tees beside the main oil pipes (to feed each gear independently from this point.)

Raise and lower valve ports for flaps route directly from the valve to the single flap actuating cylinder mounted in the starboard wing.


Hence IMO if engine oil pressure is lost (Engine broke) or the oil cooler radiator is holed (pressure lost) Lavochkins cannot raise or lower their flaps and have to use the once only compressed air shot at lowering gear

[Krusty]

Hell they can't even make broken flaps retract. I doubt they can make flaps stop if oil dies.