Oil Pressure Dynamics...

[JeremyWM]

I can't begin to thank A2A enough for your work. I have the Stratocruiser, B-17, and now the Spitfire. Hours upon hours of pure simulation enjoyment.

So I have a question about the oil system in the Spit. The oil viscosity doesn't seem to change all that much from flight to flight or during start-up. I would expect that on a cold day with a cold engine, that when I finally get the Merlin growling, the oil pressure would be quite high, maybe even high enough to blow a pump until the oil warms up. Also in flight when I move the throttles forward, I don't see a corresponding rise in pressure.

It's not a huge deal to me, as I love everything about the plane. Just something that I wonder about that might be improved in an update. The service pack for the Stratocruiser added some amazing things, especially in regards to oil. Perhaps that can be done for the Spit. Am I wrong in my thoughts about how the oil should work?

As I write this, my Spitfire is sitting at Heathrow airport with a OAT of 2! I've spent about 20 minutes trying to get her started! It's funny how much fun it is trying to coax her to life. Thanks again.


P.S. Pertinent question- what is the best way to start a cold and finicky Merlin?

[r4y30n]

Not only do your observations make sense, I believe it's written in one or other of the Accu-Sim manuals that oil pressure can be dangerously high until the engine warms up. Unless, of course, the Spit was upgraded to modern multi-weight synthetic!

Anyhow, I hear there'll be some engine related tweaks in an upcoming update, maybe there'll be some tweaks to the oil system, too...

[severniae]

Hi Jeremy,

Not being very clued in to the inner workings of the Merlin, I can't answer anything about the oil system.

Starting in cold temps, however, I have had a little practise at!. One thing that is very important - primer! I don't have the manual to hand, but a figure of around 5 pumps for 15degrees temps. So if you're doing a cold start at around freezing, I would usualy use between 10 - 15 pumps on the primer. It may help to crack the throttle open a little more than you would usually do so also. The A2A spit is certainly easier to start up in cold temperatures especially when compared to their other aircraft. Such as the B17! It once took me a full half hour to get all the engines going in -10 temperatures before!!

If you're still having issues cold starting, I'm sure Killratio or Dudley will pop in here with some of their tips and tricks. They really are the A2A Spitfire geniuses!

Regards,

Sev.

[JeremyWM]

Ya, I think the manual for the Stratocruiser mentions the high oil pressure issues due to cold thick oil. Something new that I just observed: the oil pressure does increase with throttle, however it never seems to go above about 30 or 35 at anytime.

As to the cold engine; I managed to finally get her running with some copious use of primer. I don't think I was priming enough before. It might have been flooded at some point too, because she definitely belched smoke for a good while until getting in the air and throttling up.

Man I love this Spitfire.

[Killratio]

Jeremy,

Glad you like her!!

Yes, the oil pressure dynamics are being looked at. For much of the beta they were fine but depending on how you use your Merlin now (although I am not getting as low as some people and can still easily hit 120 on runups) , they can now show low tendancies, something crept in.... Hopefully when the update is available for testing this will get ironed out a bit.

regards

Darryl

[Tigerclaw]

I noticed this belching smoke when I started the Spitfire in temperatures way below what she should've been capable of. Minus 27 I think it was. She smoked for ages, mind you, the altitude didn't help there either 11,000 or so. I had to shut the engine down THREE times to let the rad cool off before I got the oil temps where I needed them to match the rad temps. And still she was belching smoke. I thought I cooked my engine for sure. But no, everything was all right once I was down.

[Scott - A2A]

Yes, accu-sim has modelled oil viscocity for some time. Just start a cold engine and you will see.

Also, the low oil pressure at idle is supposed to me low. It has been raised just a bit for the update however.

Scott.

[Alfredson007]

I think i am finally getting a hang of it: More than 5 hours and the engine is Like New.

Ive been flying in +5 OAT, and i found that NORMAL oil gives me the best oil pressure. Over time the engine will gradually lose its oil pressure i think, so should i at some point change to more thicker Summer oils even with +5 degree centigrade OAT?

So should i consider oil grades as "thin, normal, thick" instead of winter and summer? And choose proper oil grade, not depending on the season outside, but what kind of pressure readings i'll get at take off / cruise. Not too high on take off, not too low on cruise.

And the startup oil pressure bugs me. If i use minimum possible rpm, i have very weak oil pressure, if i use faster tick-over, pressure is better, but still far away from 45psi. I try to set the 1200 by the ear, but i am not sure where that is. I'd like to know the optimum desired oil pressure at startup? Should i give it revs so the pressure will rise, or keep the engine as low rpms as possible at first?

Thanks! Love your product.

[Scott - A2A]

Don’t worry about pressures that low at idle. Remember, the oil is there to keep parts separated and lubricated, but at idle, internal pressures and stresses are very low. 15psi is adequate oil pressure for the Merlin engine at low idle. If you see pressures getting close to 10psi or lower, then you should raise idle a bit, but pressures this low would indicate something wrong is going on, most commonly worn main bearings in the crankshaft. When bearings get worn, clearances increase, and oil slips through easier (less resistance) and pressures get lower.

In general, use regular oil for all but extreme hot or cold conditions. I use winter oil (thin) if the oat (outside air temp) is below 20 deg F and summer oil (thick) if oat is over 90 deg F. What you have to be most careful of is a cold start, as you have a very slim margin to idle that engine until the oil thins out and the pressures come down.

Scott.

[Alfredson007]

In general, use regular oil for all but extreme hot or cold conditions. I use winter oil (thin) if the oat (outside air temp) is below 20 deg F and summer oil (thick) if oat is over 90 deg F. What you have to be most careful of is a cold start, as you have a very slim margin to idle that engine until the oil thins out and the pressures come down.

Scott.

Thank you very much Scott.

If i may, i'd like to ask one last question.

I've asked this under another topic but no-one answered. If i get 30 degrees celsius oil temp, will that be enough for 5-6 PSI take off on MkII? Or should i shut her down and wait for coolant to cool down and start again? Which procedure has more negative effect on the engine?

EDIT: Oh yeah, and what would be considered as "very good" total engine life in hours on mkII? (before engine needs to be overhauled)

[seaniam81]

I believe the min oil temp is 15C for a take off. So 30C should be more then enough.

[Alfredson007]

I believe the min oil temp is 15C for a take off. So 30C should be more then enough.

Yes. 15 is the minimum. But that was a wartime minimum. Modern checklists requires at least 40 celsius.

Flying the spitfire by the book and numbers is pretty easy, but the ground operation is not. As my engine worked out superfine, up until 7 hours, then in a fast pace the oil pressure started to go down, along with cylinder compression, and now it is in a "core ok" situation and i know it wont be long and my main bearings are gone. Again. With super careful flying on mkII

I am 99% sure it is the ground operation that destroys my engine. Would it be better to take off @ 20C Oil, 90C Rad, or 30C oil 100C RAD, or to shut and cool it down and then take off at 40/100? Or shut it down AGAIN and take off at 40/90?

I could always re-load the plane thus having proper temps before an engine start, but that would be cheating =)