Mustang at 20.000 and carb temp -50

Hi there,

I'm new here

I thought these times are good to come back to flight simming after about 15 years of absence.

Back then I spent quite some time with the various incarnations of Falcon 4.0 and the PMDG 737 in FS-X.

So I got myself a i9-9900k, 64GB RAM, a Radeon Rx 5700 Xt (8GB) and a coulple Samsung EVO 970 SSDs. Added a TrackIR5 and a TM Warthog. Rudder is still my good old TM RCS plugded into the base of my old Cougar until I get something modern with toebrakes.

Got DCS World 2.5.5 and bought a couple of the discounted modules and currently "learning to fly" again, mostly in the P-51D Mustang module over Normandy.

I can fly and land the Mustang quite ok, but boy do I have trouble learning the engine management.

Right now I can‘t get my head around the following:

After take off I slowly climb with 2700rpm and 170 kts. I trim the rudder all the time to keep drag low. With altitude the manifold pressure decreases until the high blower kicks in. Pressure goes back up to 60.

But shortly after, once I reach around 20.000 ft some wild fluctuation in pressure and rpm happen. I don‘t know what that is. It „feels“ as if the high blower cuts out and then back in again.

I noticed the carb temp is at -50 °C. That can‘t be good, right?

All other temps look fine and are mostly in the greens. Oil temp is a bit low with +40°C.

But when I turn from RAM air to filtered, the engine sputters.

I tried hot air too, although I understand from the manual, that should be automatic, but it didn‘t change anything either.

Rpm and pressure keep fluctuating wildly until I sink below a certain altitude again - then the engine runs normal again.

That process can be repeated. Climb and it begins again.

I know I‘m overlooking something.

Probably something simple.

Any pointer into the right direction would be much appreciated :)

Cheers,

Emacs

Looks like you're doing everything right.

-50 carb temp is ok at high altitudes as long as there isn't any moisture freezing up in your venturi tube, which I've only suspected of happening in DCS at VERY cold temps and while flying in clouds. That's the only time you should use hot air in DCS, and even then I'm not sure about how its modeled.

As far as filtered air, I don't think there are circumstances modeled in DCS that requires anything but RAM air.

Sounds like your problem is legitimately weird.

Are you sure it's happening every time?

At the exact same altitude?

Could you be bumping a switch, like LOW BLOWER, perhapse?

Could you have bumped your throttle or RPMs?

Since you're describing something that seems to be at a ceiling there has to be something about that altitude. Try changing the mission to a different ambient pressure and different temperatures. See how that affects things.

I feel like I've done everything stupid there is to do in a Mustang at every altitude, so let me know what you figure out. But players will get up to 40k ft doing what you're describing, so there shouldn't be a problem.

Post a mission file where it happens (as an attachment to the post) please, so we can try it out ourselves.

- "After take off I slowly climb with 2700rpm and 170 kts."

- "With altitude the manifold pressure decreases until the high blower kicks in. Pressure goes back up to 60"

You should not be climbing with max or high manifold and 2700 rpm. After takeoff reduce the manifold to 46" and 2700 rpm. As altitude increases the manifold will slowly decrease, this is normal. Use the throttle to increase and maintain 46" until desired cruising altitude.

In order to obtain hot air, the Hot Air control handle must be set to HOT and the Cold Air control handle set to UNRAMMED FILTERED AIR. If the Cold Air control handle is set to RAM AIR, the hot air control will be ineffective.

Use carburetor heat as required to keep the carburetor air temperature within limits to improve engine operation during takeoff.

Use carburetor heat as required to improve fuel vaporization and combat carburetor icing, but do not use carburetor heat above 12,000 feet as resultant excessively lean mixtures will cause engine roughness due to the effect of heat on the altitude compensator of the carburetor.

During an approach, use carburetor heat when outside air temperatures are below -12°C (10°F).

To prevent carburetor icing, set the carburetor Ram Air control lever to UNRAMMED FILTERED AIR and the Hot Air control lever to HOT AIR. Use the two controls together. If application of carburetor hot air does not remove roughness, clean out the engine by running it at full Takeoff Power for one minute. If carburetor ice is the cause of roughness, use hot air as needed to prevent further ice formation.

Climbing at 2700 rpm with MP way above 46" will hurt your engine.If you want climb with 60" set 3000 rpm. Use engine limitation chart, right side of cockpit for basic engine management.

When you climb up to 40k ft carb temp drops to very low temp below -50C.

I would check Mixture handle position , often ppl switch it to emergency position not RUN position and this may cause troubles at high alt.

Mp and rpm fluctuation is probably due to engine cutting out.

For 170 kts climb oil temp looks extremely low Coolers doors set to AUTO ?

I agree, 2700 @ 46" is full continuous power and plenty for climb.

One other thing I just thought of, is your fuel boost pump on? It should be on for all phases of flight. The low ambient pressure at high altitude contributes to fuel vaporizing (bubbles) in the fuel lines unless there's sufficient pressure provided by the boost pump.

Post a mission file where it happens (as an attachment to the post) please, so we can try it out ourselves.

Yeah... I was looking at that recording of my flight...

Very, very embarassing.

But hilarious too, so I'll try to add it here anyway.

When looking at that track, please keep in mind, that I have logged 4 and a half hours in the Mustang and maybe total of 6 hours in DCS overall.

Those four hours were spent flying patterns practising touch and gos.

It is obvious, that the pilot of this track has no idea what he's doing. Please be gentle in your comments.

The track is based on a small mission I created for me. I'm flying out of Tagmere with a wingman. There are some B-17s flying a big circle (to train escorting them), there are some other P-51s attacking a small german boat and some trucks (to join them and train ground attack). And there is a lone Me-109 waiting on the french coast.

In this flight my idea was to see if I can find the Me-109 and see what happens.

During the flight over the channel I'm mostly busy with modifying my Warthog buttons. When you see me drift, I'm probably fiddling with some switches and not paying attention.

A number of remarkable things happen here, including the engine problem at 20.000 ft which happens between 06:59 and 07:01 am (that's 20 minutes into the track file) :doh:

1.) I remember that I wondered where in the world is my wingman... looking at the track file I see now, that I killed him first.

Still on the ground at Tangemere. Ground collision. The guy taxied into my tail, cought fire, and died. 6:45am, 5:44 minutes into the mission.

:music_whistling: I recall that I noticed a small bumb during taxiing. Thought I maybe taxied onto the grass a bit...

This shouldn't be my last kill of the day. But more on that later.

From the track review it looks like he took off my rudder. I'm not sure if that is just an optical detail, because I clearly remember that I did plenty of rudder trim all the time to fly straight. And that rudder trim felt perfectly normal.

2.) Next is my climb to about 20.000 feet. I struggle a bit around 6:56am but then the high blower kicks in and I continue to climb until I reach 20.000 ft at 6:59am (19:40 minutes into the track). At this point you can see the manifold pressure and the rpm fluctuating wildly until I decend a bit at 07:01am. This is the two minutes of the track I'm trying to understand. :pilotfly:

3.) I continue to fiddle with the knobs on my throttle and cross the channel. At 7:25am (45 minutes into the track) I have spotted the Me-109 some 3000ft below me, circled behind him and fire a salvo at 1000ft range at his six.

Multiple hits. Iron ass. The 109 isn't impressed at all.

We dance for maybe five minutes. Then my engine dies.

I'm a few miles off from the french coast, so I try to sneak back to land to bail out. But I know I'm too low and too slow. And the 109 is still all over me.

At 7:32am (52:38 minutes into the track), I've decided to bail out as I hear the 109 approaching. I'm searching in the DCS manual for the correct key to bail, when my P-51 explodes. Ok I thought, the 109 was attacking, probably hit a fuel tank or something.

Looking at the track record, I realize, that was actually my 2nd kill of the day :D

As my wingman did, Jerry collided with me too. Both planes exploded at that moment.

If I continue to be this good, I'll be an ace by afternoon !! :megalol:

The mission was fun, but looking at the recording was just hilarious. I'm glad I'm back into flight sim !!

So, now let's see how I can attach a 4MB zipped acmi file here.

Cheers,

Emacs

Tacview-20200328-152417-DCS-P-51D_Training01.zip

Climbing at 2700 rpm with MP way above 46" will hurt your engine.If you want climb with 60" set 3000 rpm. Use engine limitation chart, right side of cockpit for basic engine management.

When you climb up to 40k ft carb temp drops to very low temp below -50C.

I would check Mixture handle position , often ppl switch it to emergency position not RUN position and this may cause troubles at high alt.

Mp and rpm fluctuation is probably due to engine cutting out.

For 170 kts climb oil temp looks extremely low Coolers doors set to AUTO ?

Thank you for that information. I wasn't aware that I need to monitor rpm so closely.

Mixture was in RUN all the time. Coolers door were left in AUTO if I recall correctly. But I was mapping thise switches to my Warthog during the flight. Possibly I did something wrong.

Is a constant 46"/2700 enough to reach 14-18.000ft? I remember I had to struggle to reach the altitude where the high blower kicks in. After that there was enough power, but the last one or two thousand feet to get there the 51 was barely climbing anymore.

But looking at the recorded track, I may have had airplane damage from an earlier collision.

I'll give it another go in another flight this afternoon, more closely paying attention to the rpm.

Cheers,

Emacs

 

You should not be climbing with max or high manifold and 2700 rpm. After takeoff reduce the manifold to 46" and 2700 rpm. As altitude increases the manifold will slowly decrease, this is normal. Use the throttle to increase and maintain 46" until desired cruising altitude.

 

Thanks a lot. I will do another testflight later today and will do exactly that.

Cheers,

Emacs

One other thing I just thought of, is your fuel boost pump on?

Yep, I keep fuel pump running all the time.

Cheers,

Emacs

I reflew the mission.

This time no trouble at all 46" and 2700rpm all the way up to 32.000 ft.

My wingman and me crossed the channel, found the 109 and I killed it.

Then we flew back and I fu*#d up the landing :(

Glad all those patterns and touch&gos tought me something...

Anyhow, looking back at the procedures, I think maybe grafspee was right after all:

> I would check Mixture handle position , often ppl switch it to emergency position not RUN position and this may cause troubles at high alt.

It is difficult to spot if you are in RUN or emergency. Could very well be that I was in emergency on that previous flight.

Cheers,

Emacs

Is a constant 46"/2700 enough to reach 14-18.000ft? I remember I had to struggle to reach the altitude where the high blower kicks in. After that there was enough power, but the last one or two thousand feet to get there the 51 was barely climbing anymore.

 

It's more than enough to climb all the way to the service ceiling of ~42,000 feet. Though you will not be making full power up that high because the critical altitude of the supercharger is 27,000 feet. That's the altitude where there isn't enough air anymore for the supercharger to compress, and you can watch that on your MP gauge. MP will start falling as you climb above 27,000. Though when you are that high up, even with the reduced engine power, your taking advantage of the much thinner air and nice drag reduction that gives you.

Climb rate starts falling as you go higher, worse when you have drop tanks, HVARs or bombs loaded on the wings. Maintain your airspeed, and you'll get there.

EMER RICH definitely catches people off guard, until you take the performance hit at altitude and the reduction in useful range because your burning more gas.

Takeoffs and landings get me too. On takeoff my two big things are nosing over once the tail comes up, or veering off the runway and crashing. Landing, sometime I'll nail the landing, other times (a lot) I bounce. Small bounce I can manage. Big bounce leads me to stalling just above the runway and either bending a gear and ground looping, or a full crash. Wish I had a better HOTAS, I'm still using my old X-45. One day I'll have a Warthog stick and pedals.

Is a constant 46"/2700 enough to reach 14-18.000ft? I remember I had to struggle to reach the altitude where the high blower kicks in. After that there was enough power, but the last one or two thousand feet to get there the 51 was barely climbing anymore.

 

Absolutely no problem.

^ Yep, although the plane is indeed noticeably less eager to climb just below critical alt for 1st blower speed, it should still do it fine. Sounds like you either:

a) was running emergency rich mixture all the time indeed, or;

b) forgot that MAP regulator is unable to maintain partially open throttle setting by itself and requires adjusting (pushing) the throttle all the time to maintain 46" all the way to 2nd blower speed switch.

When you climb at 46" 2700 rpm, you start from partially open throttle, boost regulator has limited range how much it can open throttle in carb. At around 8k - 9k ft Mp start to drop so you have to use throttle lever to open throttle more from this point you will have to add throttle as needed to maintain 46". At some point you will hit crit atl for Low blower for given rpm 2700, from this point you will start loosing MP. But this is not yet time for High blower, Since engine has a lot less power at same rpm same MP on High blower then on Low blower, Automatic supercharger switch will change Low to High at optimal alt.

But remember you are climbing with Throttle wide open so when High blower kick in you will not hit 46" of MP you will hit 61". And this is dangerous for engine, there are two ways to avoid this engine stress event.

1st just about when supercharger will change you can estimate alt where it will happen(after you did couple climbs in p-51 you are pretty much dead accurate where it will be), you retard throttle, so when High blower kick in MP will not jump above 50".

2nd is just simply bumping up rpm to 3000 rpm, you can do it much earlier, not risking any damage to engine since 1-2 min at max power, wont represent any harm for engine.

Lots off ppl thinks that when High blower kicks in engine power increase, this is wrong, 46" 2700 rpm at low blower is maybe power equivalent 50"-52" 2700rpm at High blower. So whne switching from LOW to HIGH MP must drop 6"-8" before switch to not loose power. It will be more for 3000rpm

This is from 75" power charts

62" at 3000rpm Low Blower = 75" 3000rpm High Blower

So above crit alt for Low Blower Pilot will notice great deterioration of climb rate, then after High Blower switch climb rate will remain steady until High Blower crit alt then climb rate will start droping again. I know that there are other factors impacting climb rate, but i'm talking about engine here now

It's more than enough to climb all the way to the service ceiling of ~42,000 feet.

I think for 42k ft climb you would need to bump rpm to 3000 at some point, 2700 may not be enough.

I think for 42k ft climb you would need to bump rpm to 3000 at some point, 2700 may not be enough.

I just tried. Did a takeoff from ramp with full gun ammo, drop tanks, and full fuel (simulating a long range escort).

Maintained 170 IAS as long as I could, 2,700 RPM @ 46". Burned from the fuselage tank after takeoff. Made it to 33,000 feet and took about 30 minutes to get there. The plane was super touchy on the controls (using an old X-45 isn't helping me). Wasn't able to get much higher without risking a stall.

Punched off the tanks, which helped and I got to 35,000. Still running 2,700 rpm at this point. By now I was struggling, I am fighting against my joystick :joystick: as much as the plane while trying to trim it out. Stalled around 35k and got into a spin, recovering at around 27,000. Ended up quitting in frustration.

Really like this airplane, but I am new to it and using a 15 year old stick that I really need to upgrade. Someone else more skilled than me would be able to answer this better if you can make it to 42,000 at 2,700 RPM.

I just tried. Did a takeoff from ramp with full gun ammo, drop tanks, and full fuel (simulating a long range escort).

 

Maintained 170 IAS as long as I could, 2,700 RPM @ 46". Burned from the fuselage tank after takeoff. Made it to 33,000 feet and took about 30 minutes to get there. The plane was super touchy on the controls (using an old X-45 isn't helping me). Wasn't able to get much higher without risking a stall.

 

Punched off the tanks, which helped and I got to 35,000. Still running 2,700 rpm at this point. By now I was struggling, I am fighting against my joystick :joystick: as much as the plane while trying to trim it out. Stalled around 35k and got into a spin, recovering at around 27,000. Ended up quitting in frustration.

 

Really like this airplane, but I am new to it and using a 15 year old stick that I really need to upgrade. Someone else more skilled than me would be able to answer this better if you can make it to 42,000 at 2,700 RPM.

You can't.(Its exact the same like expecting that car would reach top speed with acceleration pedal pushed half way in) at 2700 rpm there will be no power to do it. 46" 2700 rpm = 1000hp 61" 3000rpm 1600hp

p-51 max altitude is something like 43k and you need full power for it.

Full power is achieved when both throttle and prop lever are at max.

Don't take drop tanks, 68% fuel is more then enough. Full wings tanks are way more then you need in DCS.

Then when you pass 35ft level out and gain some air speed so ram air will provide a little more boost. Then start climbing again but go for very shallow climb.

I must say above 40k it is a struggle. At high alt the AOA is quite high this mean that P-factor start to make flying straight tricky.

BTW escort fighters were sitting at around 30k-35k .

As you can see even at 3000 rpm engine can barely pump 27" of mercury at 42k ft