one throttle on stick- MP or RPM?

[mj3437]

My MS Sidewinder Precision Pro only has one s throttle slider. Which do you assign to it- manifold pressure or RPM? I'm just getting started and don't really know what I will need in the way of controls on my stick when I get into combat but I guess I could use a modifier and the slider for one or the other? If anyone uses a stick with just 8 buttons I would like to hear which actions you assign to them.

MJ

[9.JG27 DavidRed]

in this case, i would definitely go and use it for the throttle...

the p51 has a constant speed propeller anyway...just asign two buttons for the rpm to increase and decrease them, and you should be good to go...

[mj3437]

Thanks DavidRed, That is how it is shown in the training. I didn't know how frequently you adjust the RPM while maneuvering.

MJ

[Yob]

I use it to improve my planes performance, but with only one, go MP any day.

 

Cheers

[Merlin-27]

I agree. MP is the priority control. Prop RPM will be more subtle changes. For now, I have the RPM on an analog wheel potentiometer on the throttle handle and it works great.

[Flamin_Squirrel]

Prop (RPM) control is like a gear leaver in a car; throttle is your primary control. You'll get max performance at in low gears (high RPM) but it's not a good idea to run all day long like that.

[Echo38]

In combat, generally speaking, RPM should always be at max. You only would drop it for specific reasons, such as having to throttle back for an extended period to cool your engine (in which case you'd also want to lower the RPM to match the lower throttle, for energy efficiency), or in a very steep dive (in which case you'd slightly pull back the throttle and then slightly pull back the propeller lever, to prevent over-rev'ing). Other than that, you should just about always have max RPM in combat.

[Flamin_Squirrel]

(in which case you'd slightly pull back the throttle and then slightly pull back the propeller lever, to prevent over-rev'ing).

 

Throttling back will help; pulling back on the prop lever won't do anything. It's a constant speed prop so if RPM is excessive it's because its hit the coarse stop.

[Echo38]

I don't understand what you mean; pulling back the propeller lever reduces RPM, and over-rev'ing is excessive RPM, so how wouldn't it have an effect? I don't have any off-hand, but I could swear I've seen a number of period sources recommending slightly pulling back the prop lever in steep dives to prevent over-rev.

Edited November 3, 2013 by Echo38

[mj3437]

Thanks for all the tips and info. I might have to remap RPM so I can adjust it without letting go of the stick. (Or I could get a HOTAS!)

MJ

[Skoshi Tiger]

I don't understand what you mean; pulling back the propeller lever reduces RPM, and over-rev'ing is excessive RPM, so how wouldn't it have an effect? I don't have any off-hand, but I could swear I've seen a number of period sources recommending slightly pulling back the prop lever in steep dives to prevent over-rev.

 

Over reving isn't the only thing that is going to damage your engine. If you leave the throttle in place and reduce the RPM your manifold pressure will increase and potentially damage the motor.

 

In general you should use the following procedure with a constant speed prop.

 

To increase power

1. Increase propeller speed by pushing the prop control forward.

2. Increase manifold pressure by pushing the throttle control forward.

 

To decrease power

1. Reduce manifold pressure by pulling the throttle control backward.

2. Decrease propeller speed by pulling the prop control backward.

 

There should be someone out there with a CSP endorsement who could explain the ins and outs in more depth.

 

Cheers!

Edited November 3, 2013 by Skoshi Tiger

[SlipBall]

I use the prop lever as well in conjunction with the throttle...I always try to keep her RPM/MP in the green zone's, as simple, green is where you want to be. The minutes out of there cause un-needed harm to the engine, unless you are fighting for your life...go green :P

Edited November 3, 2013 by GT 5.0

[Merlin-27]

I use the prop lever as well in conjunction with the throttle...I always try to keep her RPM/MP in the green zone's, as simple, green is where you want to be. The minutes out of there cause un-needed harm to the engine, unless you are fighting for your life...go green :P

 

Green is fine for transit or sightseeing but I think the OP wanted advice on Combat Settings. If you can stay in the Green in combat and survive...call me impressed.

[sydost]

I don't understand what you mean; pulling back the propeller lever reduces RPM, and over-rev'ing is excessive RPM, so how wouldn't it have an effect? I don't have any off-hand, but I could swear I've seen a number of period sources recommending slightly pulling back the prop lever in steep dives to prevent over-rev.

 

I'll try to explain. Just a moment ago I wrote a lengthy reply but that disappeared to cyber space before I sent it. Too bad, it was a good one.

 

As you probably well know the prop lever controls engine RPM by adjusting the propeller blade angle instead of telling the engine to run at certain speed. For example if the engine RPM is higher than set (set with the prop lever) the propeller governor (which actually is the one you are adjusting with the prop lever) increases the propeller blade angle to increase air resistance which slows the engine RPM back to the set value. Of course when the engine RPM is too low the governor decreases the blade angle to reduce the strain on the engine letting it rotate more freely and hence increase RPM back to the set value. These are the basics.

 

Now when the propeller hits the highest blade angle stop (also called coarse stop), which for example happens in a high speed dive with power on, the governor cannot keep the RPM at the set value as it is unable to increase the propeller blade angle anymore (as the blade angle is at maximum already). Prop lever doesn't have any effect in such a situation which is why you need to decrease power by throttling back to keep the engine from over revving.

 

So in short the same stuff. The prop lever cannot control the RPM if it doesn't have the means to do that.

 

I think the recommendations to set lower RPM for dives is simply to give the pilot more time to notice and react to the governor loosing its capability to keep the engine below redline.

 

Hope this made sense and sorry for the lengthy reply :) .

[Echo38]

Hope this made sense and sorry for the lengthy reply.

 

Thank you, it does make sense.

 

If you leave the throttle in place and reduce the RPM your manifold pressure will increase and potentially damage the motor.

 

Right--hence the order I put the two actions in. Guess the second one's I mentioned isn't necessary, though. Although it's not gonna hurt the engine if you do it as I described, it does make it easier to not have to work the propeller lever in the dive.

[Flamin_Squirrel]

To increase power

1. Increase propeller speed by pushing the prop control forward.

2. Increase manifold pressure by pushing the throttle control forward.

 

To decrease power

1. Reduce manifold pressure by pulling the throttle control backward.

2. Decrease propeller speed by pulling the prop control backward.

 

There should be someone out there with a CSP endorsement who could explain the ins and outs in more depth.

 

Cheers!

 

All correct.

 

The reasons are quite technical and are due to ignition timing. At the point of ignition, a flame front burns through the air/fuel mixture, leading to an increase in pressure in the cylinder, which is what drives the piston. Because it takes time for the flame to burn/pressure to increase, ignition must take place prior to when peak cylinder pressure is desired. Timing will be such that peak cylinder pressure occurs at a point that gives good power at max rpm/manifold pressure.

 

Now imagine what would happen if while at max manifold pressure, you pull the prop lever right back. At max manifold pressure you've still got the greatest possible charge of fuel being burnt in the cylinder (and highest cylinder pressure as a result), ignition is still occurring at the same crank angle, but because of the low rpm, the crank hasn't rotated very far. In worst case, this may lead to peak pressure occurring with the piston near the top of its stroke, with all of that hot gas being unable to expand and drive the piston round, but instead generating excessive temperatures, applying huge stress on the crank and connecting rod. Very bad!

 

Although of course peak pressure will still occur near top of the piston's stroke at low manifold pressure/rpm, there is much smaller charge of fuel at the low manifold pressure so is not a problem.

 

Modern electronic fuel injected engines may help avoid some of these issues.

 

You maybe interested to know that the extent of my training when converting to a constant speed prop was to learn the simple order of doing things that you listed. The detail I described above was learnt through my own desire to understand why!

[aracas11]

All correct.

 

The reasons are quite technical and are due to ignition timing. At the point of ignition, a flame front burns through the air/fuel mixture, leading to an increase in pressure in the cylinder, which is what drives the piston. Because it takes time for the flame to burn/pressure to increase, ignition must take place prior to when peak cylinder pressure is desired. Timing will be such that peak cylinder pressure occurs at a point that gives good power at max rpm/manifold pressure.

 

Now imagine what would happen if while at max manifold pressure, you pull the prop lever right back. At max manifold pressure you've still got the greatest possible charge of fuel being burnt in the cylinder (and highest cylinder pressure as a result), ignition is still occurring at the same crank angle, but because of the low rpm, the crank hasn't rotated very far. In worst case, this may lead to peak pressure occurring with the piston near the top of its stroke, with all of that hot gas being unable to expand and drive the piston round, but instead generating excessive temperatures, applying huge stress on the crank and connecting rod. Very bad!

 

Although of course peak pressure will still occur near top of the piston's stroke at low manifold pressure/rpm, there is much smaller charge of fuel at the low manifold pressure so is not a problem.

 

Modern electronic fuel injected engines may help avoid some of these issues.

 

You maybe interested to know that the extent of my training when converting to a constant speed prop was to learn the simple order of doing things that you listed. The detail I described above was learnt through my own desire to understand why!

Surely ignition advance is governed by engine RPM (mechanical advance and retard as on most spark ignition engines) and not MP setting ?

[Flamin_Squirrel]

Surely ignition advance is governed by engine RPM (mechanical advance and retard as on most spark ignition engines) and not MP setting ?

 

Aero engines using magnetos have fixed timing.