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[REPORTED] Spitfire - strange engine failure


Reflected

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My only experience with this issues was with a simple mission, in which I flew from Batumi to Tblisi in the winter (very cold IIRC - -10°c), and flew at about 10-15k feet.

 

Yes, the oil temperature was constantly low and pressure high nearly the entire flight, but nothing happened to my engine. I think I was flying at 2.65k RPM and 6psi nearly the entire time, according to instruments.

When you hit the wrong button on take-off

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System Specs.

Spoiler
System board: MSI X670E ACE Memory: 64GB DDR5-6000 G.Skill Ripjaw System disk: Crucial P5 M.2 2TB
CPU: AMD Ryzen 7 7800X3D PSU: Corsair HX1200 PSU Monitor: ASUS MG279Q, 27"
CPU cooling: Noctua NH-D15S Graphics card: MSI RTX 3090Ti SuprimX VR: Oculus Rift CV1
 
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Some dumb questions, but I'm learning.

 

How do you 'dilute regularly' ? Not sure what this mean.

 

Also in this thread https://forums.eagle.ru/showthread.php?t=179160

 

As Sokol1_br notes, the fuel boost pump can be switched ON briefly instead of using the wobble pump during the start-up sequence, but must be switched OFF again before start-up. Once the engine is running and adequate fuel pressure is confirmed, the boost pump should be switched ON again, and left on for the remainder of the flight. Again, the FM is weak in this regard."

 

Is that what you are referring to Art-J when you say "so I stopped bothering with it at all and just flew with booster pump on instead"

 

For clarification that (fuel boost pump) is the switch under the elevator trimmer ? I searched the manual and had no hits for 'fuel boost pump'

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Some dumb questions, but I'm learning.

 

How do you 'dilute regularly' ? Not sure what this mean.

 

 

Not sure myself TBH... will investigate.

 

 

Also in this thread https://forums.eagle.ru/showthread.php?t=179160

 

As Sokol1_br notes, the fuel boost pump can be switched ON briefly instead of using the wobble pump during the start-up sequence, but must be switched OFF again before start-up. Once the engine is running and adequate fuel pressure is confirmed, the boost pump should be switched ON again, and left on for the remainder of the flight. Again, the FM is weak in this regard."

 

Is that what you are referring to Art-J when you say "so I stopped bothering with it at all and just flew with booster pump on instead"

 

For clarification that (fuel boost pump) is the switch under the elevator trimmer ? I searched the manual and had no hits for 'fuel boost pump'

 

Yes, that's the switch Recon. During pre-start this or the wobble pump is to charge the fuel lines and clear any air bubbles so that you have uninterrupted fuel flow for the start sequence.

 

However, if you leave the fuel pump running it will continue to try to pump fuel into a closed system, over pressurising the fuel lines and potentially flooding the supercharger with a large risk of causing a fire in the supercharger when the engine fires, hence why you turn it off.

 

Now, generally the gravitational weight of the fuel and the suction from the engine is sufficient to keep the fuel flowing - until you reach ~15,000ft at which point the lack of ambient air pressure can negate the fuel mass and engine suction. Hence why the pump is needed to continue uninterrupted fuel flow.

 

It doesn't hurt to have the pump operating below this alt, so to save a potentially sticky moment in combat, it is advised to switch the pump on after you have the engine running for takeoff, landing and any other flight regime when you are using the main tank. If your using the drop tank however, you should switch it off.

 

But there's more! As air pressure further decreases ~20,000ft the fuel will start to boil and aerate, and interrupt the feed. It's at this point that the fuel tank pressurisation cock (lower right of dashboard) becomes necessary.

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Reflected,

 

 

As I understand it, you switch on the pressurization cock when you have a low fuel pressure light at high altitude. One of its functions is to prevent the fuel from boiling off when the air pressure in the tank gets low.

 

 

Come to think of it, that might cause your engine to quit the way you've been seeing it.


Edited by Yoda967

Very Respectfully,

Kurt "Yoda" Kalbfleisch

London

"In my private manual I firmly believed the only time there was too much fuel aboard any aircraft was if it was fire." --Ernest K. Gann

 

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Reflected,

 

 

As I understand it, you switch on the pressurization cock when you have a low fuel pressure light at high altitude. One of its functions is to prevent the fuel from boiling off when the air pressure in the tank gets low.

 

Thanks for the explanation, but I've never seen that light on while flying. They didn't come on before these engine failures either, which I'm sure were done to overcooling.

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Based on my understanding of the P-51, oil dilution is used during winter operation in cold weatrher. The engine oil being more viscous when colder, it can cause engine issues during engine start and also during rapid increases of power (as in takeoff). Viscous oil means inefficient lubrication of engine parts, which can explain a very rough engine start or a failure to lightoff the engine.

 

Oil dilution simply means the oil is diluted with fuel. When the engine lights off, the fuel is burned and warms up the oil much more quickly. I assume the oil dilution system is quite similar on the Spitfire as well.

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The issue with cold oil is that it is too viscus (thick). It causes the oil pump to work at very high pressures to press oil through the lubrication system and into bearings.

 

Either the pump will fail through stress, and/or bearings will not receive enough lubrication, causing local overheating and extreme stress on moving parts and excessive wear on the bearings, which can very quickly lead to their loss of tinsel strength and breakage.

 

To lessen this situation, the oil can be diluted by adding fuel to it, thus lowering its viscosity. I've never read if there is some mechanism to mix the oil-fuel mixture, nor that the engine should be turned over without ignition to mix the oil, but once the engine has started, it will certainly be mixed very quickly through motor vibration, and unless the engine has been standing for a long time, the diluted mixture should reach bearings long before they dry out through usage and a lack of lubrication. This is why you should never rev (increase motor RPM's above idle) a cold engine. Damage to bearing will occur long before the extra heat created through additional burning of fuel can affect the temperature of the oil and increase lubrication.

 

Over time the fuel will evaporate from the oil-fuel mixture into the crank case. All motors have blow-by of combusted gases from the cylinders, bc no piston rings seal to 100%. Because of this, to prevent the build-up of pressure in the crankcase, the crankcase is vented through a system which allows for excess pressure to escape, which is where the evaporated fuel leaves the engine.

When you hit the wrong button on take-off

hwl7xqL.gif

System Specs.

Spoiler
System board: MSI X670E ACE Memory: 64GB DDR5-6000 G.Skill Ripjaw System disk: Crucial P5 M.2 2TB
CPU: AMD Ryzen 7 7800X3D PSU: Corsair HX1200 PSU Monitor: ASUS MG279Q, 27"
CPU cooling: Noctua NH-D15S Graphics card: MSI RTX 3090Ti SuprimX VR: Oculus Rift CV1
 
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The booster pump is supposed to be OFF at startup and while taxiing. From takeoff until after landing, it's supposed to be on at all times.

When you hit the wrong button on take-off

hwl7xqL.gif

System Specs.

Spoiler
System board: MSI X670E ACE Memory: 64GB DDR5-6000 G.Skill Ripjaw System disk: Crucial P5 M.2 2TB
CPU: AMD Ryzen 7 7800X3D PSU: Corsair HX1200 PSU Monitor: ASUS MG279Q, 27"
CPU cooling: Noctua NH-D15S Graphics card: MSI RTX 3090Ti SuprimX VR: Oculus Rift CV1
 
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Guys, while I appreciate the sharing of any kind of knowledge, I feel that this thread is being derailed constantly towards fuel pumps. Even if someone is using the pumps correctly, the Merlin overcools and dies at low power settings and high altitudes. (around 0 boost and below 2500 RPM)

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Something's off and the problem is pretty easy to reproduce, actually, just did it twice in a row. One doesn't have to go high, as it's just an oil temperature vs pressure problem, so can be replicated at "tactical" altitudes:

a) create an air start mission in winter conditions, a bit freezing, but nothing radical - default winter Caucasus preset with sea level temp adjusted down to minus 10, altitude of about 2000 m;

b) set the fuel economy engine settings (+2 PSI, 2300 RPM), watch how the coolant and, most importantly oil temp drop (though they're still above minimum recommended figures), while oil pressure redlines the gauge;

c) after 2 minutes listen to pre-failure rumble coming in, after exactly 5 minutes watch the engine fail.

 

Both tracks attached, as it's uncertain which one will play correctly on other PC. Recorded in latest game version.

 

On a sidenote, after other flights at somewhat higher altitudes, It's worth noting, that even max continuous cruise settings (+7 PSI, 2650 RPM) are not enough to keep oil pressure below max rated figure of 120.

 

Needles to say, if that's how the real thing worked, there would've been no British planes fighting in operation Bodenplatte, as they all would've seized within 10 minutes after takeoff :D.

 

NineLine, would you mind poking Yo-Yo about this issue?

winter1.trk

winter2.trk


Edited by Art-J

i7 9700K @ stock speed, single GTX1070, 32 gigs of RAM, TH Warthog, MFG Crosswind, Win10.

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  • 2 weeks later...

Spitfire overcools a bit

 

It is hard to understand why this happens when the Merlin was equipped with a thermostat.

 

You can do near anything at 20C.

You are hard pressed to keep it warm at -1C or less

 

http://www.planehunters.be/wp-content/uploads/2013/06/RR-Merlin-parts-Z6569.pdf

 

 

Thermostat picture is at the bottom. Mind you it is a X

Win 10 pro 64 bit. Intel i7 4790 4 Ghz running at 4.6. Asus z97 pro wifi main board, 32 gig 2400 ddr3 gold ram, 50 inch 4K UHD and HDR TV for monitor. H80 cpu cooler. 8 other cooling fans in full tower server case. Soundblaster ZX sound card. EVGA 1080 TI FTW3. TM Hotas Wartog. TM T.16000M MFG Crosswinds Pedals. Trackir 5.

"Everyone should fly a Spitfire at least once" John S. Blyth

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