Help with proper RPM management

I'm still trying to figure out how to properly operate the RPM handle in conjunction with the throttle, I generally keep them relatively in the same position but is there a better way? Should I have the RPM handle in a certain position for most operations? And where would the best place to keep it be for certain situations like dogfights? Would it be bad to just keep it full forward and only work the throttle? :helpsmilie:

You'd keep it full forward (3000 RPM) to get maximum power for takeoff and dogfights. Maximum continuous is 2700 RPM and 46" Hg manifold pressure, and cruise setting is 2400 RPM at 36".

Thank! I'll probably write this down to help remember it haha

Thank! I'll probably write this down to help remember it haha

;)

Here's a big, fat rule-of-thumb:

- Increasing Power: RPM first, and then MP.

- Decreasing Power: MP first, and then RPM.

Because of the way the prop-governor works, doing this the other way around can put heavy stress on the engine, and even in the short time of the game, destroy the engine.

In the game you always start with a factory fresh unit, with no Wear-n-Tear™. In reality, it will all add up to eventually bite you in the butt :doh:

Because of the way the prop-governor works, doing this the other way around can put heavy stress on the engine, and even in the short time of the game, destroy the engine.

The how is correct but the why is not. It has nothing to do with the prop governor but instead this procedure is used to prevent knocking. Less RPM means the engine can handle less boost because spark retardation is tied to the power lever setting. If you leave boost where it is and just decrease RPM, this may leave you in an operating condition where spark timing is much too early. This in term will lead to peak pressure occuring at or around the time when the piston is at top dead center, and this puts enormous strain on the piston rod bearings.

Low boost is not a problem on the other hand (well this is not entirely true because underboost influences the piston ring seating and can lead to increased wear as well, but it's not as bad as knocking). Therefore one needs to ensure to never have the engine running at a boost setting higher than what is recommended for the set RPM.

You'd keep it full forward (3000 RPM) to get maximum power for takeoff and dogfights. Maximum continuous is 2700 RPM and 46" Hg manifold pressure, and cruise setting is 2400 RPM at 36".

No no no don't use full rpm for dogfights unless you want to burn your engine out in the middle of it. 2800 rpm and 50" is more than enough. I rarely go over 50" and if I do, its only briefly. I've yet to ever use war emergency power. It's just not needed. The rest of the engine settings are on the placard inside the cockpit. I've never burned up an engine and never required more power than stated to fight and win.

Here's a big, fat rule-of-thumb:

 

- Increasing Power: RPM first, and then MP.

- Decreasing Power: MP first, and then RPM.

 

Because of the way the prop-governor works, doing this the other way around can put heavy stress on the engine, and even in the short time of the game, destroy the engine.

 

In the game you always start with a factory fresh unit, with no Wear-n-Tear™. In reality, it will all add up to eventually bite you in the butt :doh:

That's true in a real aircraft but it doesn't matter in here. I've gone full power and dropped the RPM's to a low setting, something that would hurt a real engine and it's had no effect in DCS. I wish it was modeled, but it isn't and if it is, it's not noticeable.

The how is correct but the why is not. It has nothing to do with the prop governor but instead this procedure is used to prevent knocking. Less RPM means the engine can handle less boost because spark retardation is tied to the power lever setting. If you leave boost where it is and just decrease RPM, this may leave you in an operating condition where spark timing is much too early. This in term will lead to peak pressure occuring at or around the time when the piston is at top dead center, and this puts enormous strain on the piston rod bearings.

 

Low boost is not a problem on the other hand (well this is not entirely true because underboost influences the piston ring seating and can lead to increased wear as well, but it's not as bad as knocking). Therefore one needs to ensure to never have the engine running at a boost setting higher than what is recommended for the set RPM.

Nevermind, I thought you said it was cause knocking because of the spark plugs and I was thinking "WTF?". lol I had originally said something else. I will however, say that if you pull the prop back too far while maintaining high manifold pressure it can stress the engine and parts that control the pitch of the prop blade. I've seen this damage on an engine that was at TBO and the oil was leaking out of the prop hub because of mismanagement of throttle and rpms. That is the real concern for someone flying. Again, this isn't a concern in DCS unfortunately.

That is the real concern for someone flying.

Never heard of that. Seems a bit weird since standard procedure for checking the prop governor is to run up the engine and cycle the prop lever between low and high RPM. Also i see no reason for the pitch adjustment system taking damage, as setting the pitch to full coarse shouldn't require significantly more torque than setting the prop to any other pitch.

Knocking is a real concern for P-51 pilots and it is modelled in DCS. You not having killed an engine doesn't prove anything. Try flying 45"@2000RPM *for a while* and see how that goes.

Never heard of that. Seems a bit weird since standard procedure for checking the prop governor is to run up the engine and cycle the prop lever between low and high RPM. Also i see no reason for the pitch adjustment system taking damage, as setting the pitch to full coarse shouldn't require significantly more torque than setting the prop to any other pitch.

Yes, when you perform governor check you lower rpm a lot (but also shouldn't go too low), but still you aren't going with really that high manifold pressure.

S!

I think overboost damages specially engine itself as governor keeps low revs at all cost while you increase manifold pressure and that means also cylinders pressure.

The cause for the high peak pressure is primarily ignition timing. The timing for certain boost pressures is set to work with the RPMs that are stated for said boost pressures. Use lower RPM and ignition timing will be off.

The torque output will be lower than at high RPM so there is no potential damage to the engine through sheer torque. It's the piston rod and crankshaft bearings that get hammered.

Knocking is a real concern for P-51 pilots and it is modelled in DCS. You not having killed an engine doesn't prove anything. Try flying 45"@2000RPM *for a while* and see how that goes.

Well, 45 @ 2000 doesn't seem to be doing much harm (if any) through prolonged periods of time. 50 @ 2000 kills the engine under two minutes though :D

Never heard of that. Seems a bit weird since standard procedure for checking the prop governor is to run up the engine and cycle the prop lever between low and high RPM. Also i see no reason for the pitch adjustment system taking damage, as setting the pitch to full coarse shouldn't require significantly more torque than setting the prop to any other pitch.

 

Knocking is a real concern for P-51 pilots and it is modelled in DCS. You not having killed an engine doesn't prove anything. Try flying 45"@2000RPM *for a while* and see how that goes.

Why would I do something like that? It isn't within parameters or any real specific setting for a specific phase of flight so it's unrealistic that I'd ever do that. I'm not sure why you'd think someone that knew how to fly would ever use that setting.

Except for extreme conditions, shouldn't we keep the manifold pressure and rpm into the green curve?

Unless you consider climbing to altitude to be an extreme condition, I'd say no. If your engine is properly warmed up (oil at least 40°, water very close to 100°), you should be able to fly off an airfield at 3000 RPM with around 60" MP and maintain that for about 5 minutes without any issues at all.

After that you should reduce to 'Maximum Continuous', which is 46" MP and 2700 RPM, for the remainder of your climb, or for as long as you wish basically, but your fuel consumption will be fairly high.

If you are going for extensive air-time, once you have reached your planned altitude, remain in MaxCont for a minute or two to gain some speed, and then reduce to at the most 36 MP and 2400 RPM, or within the green of both; you should maintain most of the speed you gained at MaxCont after leveling off, and your consumption will be way down.

Don't forget to keep your wing and drop tanks at even fill-levels by switching between left and right every 5 minutes or so.

Btw I wonder, in the quickstart guide, for takeoff and landing they talk about the manifold pressure, but they don't talk about the propeller (rpm) level we should have. How I should setup the P lever for that?

I have read the text below the lever, and they say that for taxiing the lever should be all the way back, but what about takeoff and landing?

Thanks

All the way back - would be min RPM. Very unlikely! I'm not sure If You've read / interpreted the markings correctly. Anyway, it's 3000 RPM for take-offs and 2700 for landings.

Btw I wonder, in the quickstart guide, for takeoff and landing they talk about the manifold pressure, but they don't talk about the propeller (rpm) level we should have. How I should setup the P lever for that?

I have read the text below the lever, and they say that for taxiing the lever should be all the way back, but what about takeoff and landing?

 

Thanks

Ummm... what? While on the ground with the engine running, you should always have 3000 RPM to reduce stress on the engine. Basically, it keeps the prop-pitch very shallow.

So, before start-up, you set 3000 RPM and maintain that until after takeoff, and once you have landed and are taxiing, increase RPM to 3000 and retract the flaps.

EDIT: I just read the Quick Start guide. It actually says nothing about setting the RPM before starting the engine :cry:

It also says nothing about RPM and MP on landing, but the Flight Manual says 2700 RPM. This should give you enough power of you have to abort your landing in an emergency.

I should read the whole handbook of the P51D (guess this flies the same as the TF51D) but for now I have just read the quickguide.

And ok I have understood, the text below the RPM lever says that we should for taxiing keep stick full back, guess this is to have the tail wheel free, it is surely not about the propeller lever but the stick we use for pitch and roll :)

And thanks for the tips

Ok for landing, 2700, this is written in the cockpit if I remember well as a checklist ^^

For taxiing you don't need to keep the control stick back. The only time you really need to hold it back are at takeoff, before reaching about 100 MPH, to assure the tail wheel is on the ground and steering, and if you want to run-up the engine to 35" MP with the breaks on to test the magnetos, you need to pull the control stick all the way back, so that the engine doesn't pull the nose over and the propeller into the ground.

You should however be aware that the tail-wheel is 'lockable'. The tail-wheel has two possibilities:

- freely castering

- locked and steerable

If you push the control stick forward of center, the tail wheel will unlock and become free-castering, until locked again. With the tail wheel freely castering, the only way to steer is with the wheel breaks.

If the tail wheel is locked, using the rudder pedals, you can steer it up to 6° to the left and right of center, allowing adequate steering for most taxiing situations.

To re-lock the freely castering tail wheel, while the A/C is rolling straight ahead, pull the control stick back, after which you may return it to center.

Thanks for the tips.

In what kind of situation we would need to have the wheel free?

And how do I check if the wheel is free or locked?

Thanks for the tips.

In what kind of situation we would need to have the wheel free?

When You need to make a very tight turn, otherwise +/- 6 degrees of steerable movement range in "locked" mode gives You a turning circle of a truck ;). Usually not a problem on these big, wide, modern airbases we've got, but will become a big deal when smaller, tighter bases of a Normandy map become available.

And how do I check if the wheel is free or locked?

If Your plane starts groundlooping out of control, no matter what You do with rudder, that means the tailwheel is still swiveling freely :D. You'll catch and straighten it with differential brakes though.

And we can't use the differential brakes when the wheel is locked?

Indeed, we have airfields designed for big jets, not small planes ^^

Can't wait for normandy map (just wonder from where the german planes will takeoff if the map covers only normandy ^^)

To come back about RPM management (as this thread should not be about tailwheel... my fault ^^) I have unlocked my X55 twice throttle, and I use the right one for manifold pressure, and the left one for propeller, works fine.

Also, guess when you say 3000 rpm at takeoff, this is with manifold pressure to 30 or so... as when I'm idle or taxiing, even with the propeller full, I have not a lot of rpm... only when I increase manifold pressure the rpm increases.

I noticed as well that, as rpm is dependent on manifold pressure, that when we are landing and should maintain 2700 rpm, when we land we are lowering the manifold pressure, therefore we should also adjust rpm to keep 2700...