An in depth look at engine management in the Mustang

[Diesel_Thunder]

Made this video that covers engine management in the Mustang. It's mostly geared to those considering or are new to the P-51, though has good information for all:
 

 

[RazorbackNL]

Nice one, Diesel. Very informative.

[sthompson]

Very nice video Thanks for making this. I have a couple of related questions:

1. Why do you wait until just before takeoff to turn on the generator? 
2. What's the point of opening the radiators during warm up? Wouldn't the engine warm up faster with them on auto?
3. What are the recommended settings for climb out or descent or diving? (In the Blue Nosed Bastards of Bodney campaign I find that when the AI starts to climb from sea level to 20k I can't keep up.)
4. You got into combat settings a bit in the discussion of Military and War Emergency Power, but I'm not sure I understand fully engine management during combat. Do you keep RPMs at 2700?

[grafspee]

@mitchelrobertson You can easy use 52"/2700rpm without any concerns in P-47 fo combat power.

[kablamoman]

There is no problem whatsoever with running it up to 61"/3000 RPM for combat. With the old cooling model you could run the danger of overheating if you got too slow (I seem to remember it having trouble overheating in extended, aggressive climbs), but with the revamped cooling it's not something you really need worry about, especially considering you'd want to keep speeds 250 mph+ in a fight anyway.

 

Red line it.

[sthompson]

2 hours ago, kablamoman said:

There is no problem whatsoever with running it up to 61"/3000 RPM for combat. With the old cooling model you could run the danger of overheating if you got too slow (I seem to remember it having trouble overheating in extended, aggressive climbs), but with the revamped cooling it's not something you really need worry about, especially considering you'd want to keep speeds 250 mph+ in a fight anyway.

 

Red line it.

This raises another question I've had. My understanding is that the prop lever adjusts the RPM setting of the prop governor, and the governor then adjusts the prop pitch to maintain the RPMs. I assume this means it lowers the pitch when the prop RPMs are below the set level, and increases it in the opposite case essentially equivalent to shifting gears in a car to keep RPMs roughly constant as speed changes. This raises a question my mind about how to manage prop RPM and throttle for maximum acceleration in level flight or while climbing. I've found it hard to maintain speeds above 150 MPH in a climb, let alone accelerate to a higher IAS.

[kablamoman]

36 minutes ago, sthompson said:

This raises another question I've had. My understanding is that the prop lever adjusts the RPM setting of the prop governor, and the governor then adjusts the prop pitch to maintain the RPMs. I assume this means it lowers the pitch when the prop RPMs are below the set level, and increases it in the opposite case essentially equivalent to shifting gears in a car to keep RPMs roughly constant as speed changes.

That's correct. 

Quote

This raises a question my mind about how to manage prop RPM and throttle for maximum acceleration in level flight or while climbing. I've found it hard to maintain speeds above 150 MPH in a climb, let alone accelerate to a higher IAS.

61"/3000 RPM will give you max performance in a climb. To go back to your analogy of shifting gears in a car, the lower the gear, or finer the pitch, the better you will accelerate. This has diminishing returns when it comes to the propeller, though, so the governor will automatically adjust to take a bigger bite of the air as the aircraft speeds up. You can think of it as continuously automatically shifting for you.

Your best rate-of-climb speed is around 175 mph from sea level up to 10,000 decreasing to 170 at 15,000, and 165 at 20,000 to 25,000. It'll climb really well even at max continuous power (46"/2700 RPM) and 200 mph. These are sustained climbs in a piston prop, so you won't be zooming up like in a jet. If you're having trouble maintaining above 150 mph, double check your flaps and gear are up, set your power as desired, and control your speed with your pitch attitude (ie. if you're too slow, lower your nose). It'll settle into a steady climb of 2,000+ feet per minute at the lower levels and will end up being very shallow indeed once you're up above 30,000' -- you won't even be able to maintain above 1,000 FPM at the higher altitudes of the aircraft's flight envelope, and the best rate won't be much different (maybe a bit slower than 165 mph at 25,000 feet).

[Diesel_Thunder]

5 hours ago, sthompson said:

Very nice video Thanks for making this. I have a couple of related questions:

1. Why do you wait until just before takeoff to turn on the generator? 
2. What's the point of opening the radiators during warm up? Wouldn't the engine warm up faster with them on auto?
3. What are the recommended settings for climb out or descent or diving? (In the Blue Nosed Bastards of Bodney campaign I find that when the AI starts to climb from sea level to 20k I can't keep up.)
4. You got into combat settings a bit in the discussion of Military and War Emergency Power, but I'm not sure I understand fully engine management during combat. Do you keep RPMs at 2700?

Glad you enjoyed it!

To answer specifically, the generator doesn’t produce much, if any, power at low RPM. So that’s part of the cockpit flow for me either during the runup to make sure it works, or when lining up on the runway.

Opening the radiators ensures that they aren’t forgotten later, like during takeoff. Plus if you open them before starting the engine, you can hear the door drive motors and know that the doors move and that they are wide open. Closing them does not help as much for warmup. One exception I have is in winter missions, I’ll close the oil door to help keep the oil warm, but open it up again when taking the runway. Way to easy to forget that they are shut leads to a very fast overheat shortly after takeoff. Really wish the Mustang featured the door position indicators like the Jug has.

They still need to work on the AI for the warbirds, very hard to keep with them in most situations. For climbing, @kablamoman has a great technique posted above. I run my climbs at max continuous as well. Descents I run the engine as needed, usually leave the prop at whatever I was running for cruise, throttle as needed. If I need to slow down, I’ll speed the engine up to 2,700 RPM. Sounds counterintuitive, but that extra RPM adds drag and slows you down.

Situation dependent on combat power. If I’m about to be engaged, I increase power to max continuous. If I need more, I can run both handles forward for 3,000 and 61 inches, and can run that for 15 minutes (watch your temperatures). And from there I’ll engage war emergency if needed. 

[sthompson]

2 hours ago, kablamoman said:

That's correct. 

61"/3000 RPM will give you max performance in a climb. To go back to your analogy of shifting gears in a car, the lower the gear, or finer the pitch, the better you will accelerate. This has diminishing returns when it comes to the propeller, though, so the governor will automatically adjust to take a bigger bite of the air as the aircraft speeds up. You can think of it as continuously automatically shifting for you.

Your best rate-of-climb speed is around 175 mph from sea level up to 10,000 decreasing to 170 at 15,000, and 165 at 20,000 to 25,000. It'll climb really well even at max continuous power (46"/2700 RPM) and 200 mph. These are sustained climbs in a piston prop, so you won't be zooming up like in a jet. If you're having trouble maintaining above 150 mph, double check your flaps and gear are up, set your power as desired, and control your speed with your pitch attitude (ie. if you're too slow, lower your nose). It'll settle into a steady climb of 2,000+ feet per minute at the lower levels and will end up being very shallow indeed once you're up above 30,000' -- you won't even be able to maintain above 1,000 FPM at the higher altitudes of the aircraft's flight envelope, and the best rate won't be much different (maybe a bit slower than 165 mph at 25,000 feet).

This is very helpful. Thanks. I suspect my problem was in trying to keep up with the AI who just seem to zoom upward. I probably had too much pitch. Gear and flaps were definitely both up.

[kablamoman]

10 minutes ago, sthompson said:

This is very helpful. Thanks. I suspect my problem was in trying to keep up with the AI who just seem to zoom upward. I probably had too much pitch. Gear and flaps were definitely both up.

Yeah, the AI is notoriously bad for this and it really ruins a lot of missions. They do some weird stuff when it comes to not bleeding energy and warping around to conform to assigned formations and stuff.

I would encourage and recommend to anybody into flying WW2 to take it online (don't be scared or intimidated) and find a fun server to play on instead. There are a few training servers without the map or asset pack requirements that can help ease you into things in a safe environment and get you interacting with "real" aircraft that actually adhere to the same physics as you do. Most popular servers are running on the Open Beta release, so be sure to update to that if you are interested.

[grafspee]

11 hours ago, mitchelrobertson said:

Can I assume you meant P51?  If so thats great news Ive always leaned conservative and this will help.  

Sorry i meant P-47, i get confused by other topic and didn't notice that i landed in P-51 section heh.

Back to topic in case of P-51 you can use 61" at 3000rpm like  was said above but if you want utilize high speed combat patrol and climb you can use 50" at 2700rpm it is completely safe for engine and you still have hours in time limitation because 46" at 2700 is unlimited and 50" is only 4" more so you have still couple hours ahead.

RPM control can't be really compared to gears in cars, Main reason why most or even all ww2 planes were equipped with variable speed props was fuel economy and engine wear, you have engine limitation chart which tells you how much MP can be used for certain RPM, if you fly at 30" you will save great amount of fuel and engine wear by cranking rpm down to 2200. But when you need high MP you need to set proper rpm because too low rpm renders higher working pressure in cylinder and this may lead to detonations which is very unhealthy for engine that is whole story. In DCS you can experiment by running 61" at 2500rpm but IRL pilot would never ever do that and further consequences in DCS are just developer vision of how things work and not RL experience because no of war time tests contain such tests and now pilots of vintage airplanes like P-51 or Spitfire don't use mil power anymore, so talking about mil power at lower rpm is even more unrealistic.

Edited July 22, 2023 by grafspee

[Art-J]

11 hours ago, Diesel_Thunder said:

Opening the radiators ensures that they aren’t forgotten later, like during takeoff. Plus if you open them before starting the engine, you can hear the door drive motors and know that the doors move and that they are wide open. Closing them does not help as much for warmup. One exception I have is in winter missions, I’ll close the oil door to help keep the oil warm, but open it up again when taking the runway. Way to easy to forget that they are shut leads to a very fast overheat shortly after takeoff. Really wish the Mustang featured the door position indicators like the Jug has.

I'd rather disagree here. The whole point of introduction of radiator doors automation in Mustang (one of the first ever US planes to have this modern feature) was exactly to forget about them. And now in DCS, after recent revision of cooling system modelling, the same applies to our sim as well.

When we spawn with them in auto, we already do hear they work when they start closing. I doubt they can fail without combat damage anyway (never in 9 years of flying that bird in DCS have I encountered such failure, but then, apparently "random failures" option in DCS has been somewhat buggy for a long time and doesn't affect all modules - maybe P-51 is one of them?). 

Thermostatic auto control used to be somewhat too slow and ineffective indeed before aforementioned revision, but now it's pretty much impossible to overheat DCS Mustang unless one really, really, REALLY wants to do it on purpose, or does something silly like leaving the doors in manual-closed position and forgetting about them - one more reason not to fumble with them in the first place in my opinion.

I get that real life operators of these very expensive warbirds tend to play it super-safe and often keep the doors manually open on the ground. Thus I can understand some players do it in DCS for immersion reasons, but that's that - there is no single practical benefit of doing it in the sim otherwise. Auto-mode is there for a reason.

That's also why I consider all-manual P-47 vastly inferior in this regard and I find it puzzling that Republic started implementing cooler door automation only in the last model of the Jug.

Edited July 22, 2023 by Art-J

[M1Combat]

I open mine too...  and then set them to auto when I'm raising flaps and gears.  I haven't flown the 51 much recently but it used to be that on a hot day on a server/mission that doesn't arm/fuel you...  you could overheat and blow before or soon after takeoff simply because the doors are "SO" slow.  At this point it's habit for me...  and one I don't mind keeping up with.

[grafspee]

1 hour ago, M1Combat said:

I open mine too...  and then set them to auto when I'm raising flaps and gears.  I haven't flown the 51 much recently but it used to be that on a hot day on a server/mission that doesn't arm/fuel you...  you could overheat and blow before or soon after takeoff simply because the doors are "SO" slow.  At this point it's habit for me...  and one I don't mind keeping up with.

Since cooling update you just flip to AUTO control and you just forget that those even exist.

[Nealius]

In AUTO I'm still getting very hot coolant and oil temps at 200mph, 42" 2700rpm (max cont. IIRC?) with OAT 8C, which seems a bit odd to me.

[grafspee]

9 hours ago, Nealius said:

In AUTO I'm still getting very hot coolant and oil temps at 200mph, 42" 2700rpm (max cont. IIRC?) with OAT 8C, which seems a bit odd to me.

Can you specify what "very hot coolant and oil temps" mean, 46" 2700rpm is max continuous.

Automatic cooling shutters system has hysteresis, opening and closing temps for shutters are spread.

I can't remember exactly but opening coolant shutter temp is something like 110C and closing is something like 100C same with oil cooler shutter 87C opening and 80 closing temp, can't remember  exact numbers it could be that coolant opening is at 113C.

When your coolant/oil temp is 112C/86C automatic system will not open coolers shutter doors, but if you increase power and those temps ticks up by 1C automatic system will start opening shutters and it will stop opening them when temps will drop below opening temps, at this point you have slight opened cooler shutters and if you reduce power and coolant and oil temp will drop by 5C automatic system will not adjust cooler shutters, it will react only when coolant/oil temp drop below closing temps.

That way when you are flying at 46" and 2700rpm temps can be as low as closing temps and as high as opening temps at same speed same OAT same power setting.

Edited January 2, 2024 by grafspee

[Nealius]

11 hours ago, grafspee said:

Can you specify what "very hot coolant and oil temps" mean, 46" 2700rpm is max continuous.

I'll fly it again but I was either at 42 or 46 in a slight climb, around 180~200mph. Coolant was beyond the green zone but not quite at the red line, like maybe 130 or 140? Oil temp was I think pegged right at the max of 90, maybe a couple degrees hotter. I had to open the coolers manually to get temps back into the green.

[Theodore42]

24 minutes ago, Nealius said:

I'll fly it again but I was either at 42 or 46 in a slight climb, around 180~200mph. Coolant was beyond the green zone but not quite at the red line, like maybe 130 or 140? Oil temp was I think pegged right at the max of 90, maybe a couple degrees hotter. I had to open the coolers manually to get temps back into the green.

Keeping it green is for repositioning or other non-combat missions to maximize engine life.

But the Mustang is a weapon of war and weapons break when you use them. IRL this means that the P-51 engine had a lot more maintenance than her GA contemporaries. In DCS it means nothing

The hottest the engine gets is during the climb, so your description of the oil temp being pegged to the red line during climb out sounds about right. As long as the needles don't stray INTO the red then you're ok. If left in AUTO this almost never happens, unless you're running max power at very low speeds. Far more likely you will blow your engine overheating the aftercooler rather than overheating the oil or coolant. (there is no temperature gauge for the aftercooler btw)

Once you get the hang of being ok with the temps always being a little too close to the red, but never in it; the next issue you will have is that now you suddenly need to be closing your radiator doors because they are making too much drag.

If you get into "normal" dogfights, like you see in the movies, you're going to notice the radiator doors are always open, even when you dive into a low yoyo and get going really fast. All that drag!

When your mentality gets to this point, leave it in AUTO and instead fly faster and less aggressively. The Mustang is for "boom and zoom" tactics, you boom the target, then you zoom away, up, and sustain that speed as long as possible, because no matter how good your opponent is at climbing the Mustang will have less drag at high speeds. So you always have an advantage when going fast. And if you leave radiator flaps in AUTO while sustaining high speeds, they will always be mostly closed, compounding your advantage.

But like graffspee said above, the Mustang's AUTO doesn't transition between those two styles well. If you insist on getting into a knife fight in the Mustang then you can expect the radiator doors to be gaping most of the time. I can't honestly say there aren't opportunities to manually min/max drag in those situations... but in my experience, 99% of players would be better served keeping trimmed up and flying the ball rather than thinking about micromanaging radiator flaps.

[grafspee]

5 hours ago, Nealius said:

I'll fly it again but I was either at 42 or 46 in a slight climb, around 180~200mph. Coolant was beyond the green zone but not quite at the red line, like maybe 130 or 140? Oil temp was I think pegged right at the max of 90, maybe a couple degrees hotter. I had to open the coolers manually to get temps back into the green.

Redline for coolant is 121C and for oil 90C. I fly P-51 quite often and in auto mode temps are always below redline, and this is only what matters, automatic shutters aren't set up to maintain temps in green zone as P-51 maintenance manual states. Oil cooler doors won't open until 87C of oil temp is reached. Same with coolant, shutter door won't move until temp goes way above green zone. In case of the coolant temp gauge it may be 2 times thickness of the needle. In climb you will always be above green zone and this is totally fine.

Edited January 3, 2024 by grafspee

[Nealius]

Okay yeah I misread the coolant guage. If redline is 121 then I was at 115 or so. If "below redline" is the only thing that matters, and shutters aren't meant to keep needles in the green zone, then what's the purpose of the green zone? Layman logic is "inside green = good, outside green = not good," but if outside green is still good then that makes the green markings useless as an engine diagnostic tool (if following that logic).

Edited January 3, 2024 by Nealius

[grafspee]

Our P-51 is late war model, where oil and other stuff was improved. Setting higher temps improves performance of the plane, you need much wider opening to keep 100C then to keep 113C coolant temp. In later P-51 manuals you can find that 95C oil temp was allowed while using WEP.

But engine optimal temps won't change.

You still get green temps while cruising at medicore power range. But for climb or combat power temps will get higher.

Green arc on gauges represents optimal temp range but operating temp range is much larger iirc for coolant it is 60C to 121C and for oil 15C to 90C ofc with respect to oil pressure limits.

 

[Art-J]

Given the post-war manual for -D cleared it for even up to 105 on oil, I'm curious how far we can push "ours" with revised cooling model. Anyone closed the oil shutter and tried what happens above 90?  

[Nealius]

I'm pretty sure I've run her at like 93~95 for a few minutes but nothing higher than that.

[grafspee]

I've hit 97c at high alt max power dogfight.

[71st_AH Rob]

Wartime USAAF SOPs indicate that grade 1100 oil is recommended for operating when ground temps are between -7°c and 27°c and the 'safe' max oil temp wold be 85°c.  Grade 1200 oil is recommended for ground temps above 4°c and max 'safe' operating temp is 95°c.  So oil technology makes a difference and it was improving during the war and after.  In all cases it notes that oil pressure is more important.