Any ill effects binding throttle and RPM to same axis?

[Remontti]

While ago I combined the RPM and throttle controls to same axis so that RPM and throttle are always at same precentage. So far I've not noticed any problems with it when flying in expert mode with Yak, IL-2 and Stuka. Can someone with better understanding of CEM come up with reasons or situations where this could cause troubles?

 

Watching the throttle lever, RPM wheel, tachometer and manifold pressure instruments, it seems that this is how the engine is controlled in simple mode when you adjust throttle.

[Nibbio]

It would be a little like binding the gears in your car to the gas pedal, but in reverse order, so that when you floor the gas pedal you are in first gear, and when you let it go it's fourth or fifth gear... Doesn't sound too good to me, but what do I know, I ain't no pilot

Edited November 20, 2014 by Nibbio

[M4rgaux]

In normal mode they are tied together, you have to uncouple them. Now, it doesn't change much with the current choice of plane, maybe in the Ju87, however, it tend to make taxing harder in my experience.

[J2_Trupobaw]

Taxying, first stage of takeoff and possibly landings will be more difficult. If the plane cant fly continously on max ATA/RPM, you will not be able to get engine to optimal "safe" performance, unless optimal ATA and optimal RPM falls on the same % of axis. 

[Remontti]

So far I've not found problems with taxing, take off or landing. In Yak I use 70-80% for cruising and 95% for combat. These seem to keep the engine in safe limits.

 

Maybe I will change them back to seperate axis. I got a feeling that I'm teaching myself bad habits...

[-TBC-AeroAce]

It's not really the best idea, think of the throttle as shaft hourse power and the rpm as a means of converting the hourse power to thrust, for each power setting there is propeller rpm that will be most efficient therefore having the best thrust to drag. I'm pretty sure that this is not a 1:1 relationship rpm and throttle. I've been wanting to properly test this but have not yet

 

I fly always with full power for top shaft HP and keep the rpm between 2300-max depending on what I'm doing, then I make the trade off between lowering the rpm and closing the radiator to compensate for the drop in airspeed based on engine temps

 

If I want to slow down I reduce throttle keep the rpm high

 

If diving at max speed no power, I will reduce throttle and rpm to maintain speed increasing rpm if starring to accerate

 

That probly all wrong but seems to work and make Spence to me

Edited November 20, 2014 by AeroAce

[[TGW]Echo]

From what I've researched and found from my own flights, you're fine to combine them on a single axis for most portions of your flight - including combat. The exceptions would be takeoff and landing, for safety and full power availability in an emergency, and cruise conditions where you're attempting to optimize your fuel economy. In the latter case, it's best to select full MAP and settle on the lowest RPM that will provide the desired airspeed. The same holds true when climbing and you're ready to pull back on the throttle. It's better to leave the engine at full MAP and bring down the RPM instead.

 

For CSPs:

 

 

A constant speed propeller allows the engine to develop maximum rated power and rpm during the ground roll and to develop full power throughout its normal rpm range. With a constant speed propeller the pilot controls inlet manifold air pressure [MAP] with the throttle lever and the engine rpm with the rpm control lever or knob/switches. The pilot has several combinations of rpm/MAP to achieve a particular power setting. For example, in one particular aircraft, the recommended combinations for 65% power at sea level are 2100 rpm + 26 inches Hg MAP or 2200 + 25 inches or 2300 + 24 inches or 2400 + 23 inches. So you can use low rpm and high MAP or high rpm and low MAP to achieve exactly the same power output. The low rpm / high MAP combination probably gives more efficient cylinder charging and better combustion plus less friction. The high MAP also acts as a cushion in the cylinders, reducing engine stress. MAP is usually measured in inches of mercury [Hg] rather than hectopascals. Standard sea level barometric pressure is 29.92 inches Hg or 1013.2 hPa.

 

http://www.pilotfriend.com/training/flight_training/fxd_wing/props.htm

 

 

 

How do we set cruise RPM, and what are we trying to accomplish? Remember when talking about wings and airspeeds for “max range” or “m ax glide” or “minimum sink.” What we are trying to do with the wing is change the efficiency by varying the angle of attack. We can go real fast, and run the parasite drag up, or we can slow down to minimize it. At some point, we will be making the “Max L/D” or the most lift we can get relative to the drag, or even slower to find the absolute maximum lift the wing will produce.

 

By changing cruise RPM, we are doing the same thing. A high RPM may produce the maximum power, but at a cost in drag (and fuel). Just like any airfoil, the prop has its optimum angles, too, but data on these are not readily available to the pilot, and they are often overridden by the need for the most efficient airspeeds of the airplane. But generally speaking, for any given power, the lowest possible RPM will reduce friction within the engine, and this may be the most important parameter. Some props are probably more efficient at a specific RPM.

 

http://www.advancedpilot.com/downloads/prep.pdf

[unreasonable]

Interesting question, I have often wondered why I bothered with the two controls in the Lagg and Yak, especially as the engines have been modeled to be so resistant to abuse, unlike the German engines, and fine tuning rpm/ata is not so important so long as the temperatures are kept within specification. (No idea if this is correct, BTW, I have to assume the devs know what they are doing).

 

In the game context, the only situation I find where the throttle is right back and the rpm forwards is at the very beginning of your take off run and when you need to use the prop as an air-brake, either in landing or in dive-bombing. Both of these can actually be done perfectly well with a coarse prop as well, but fine prop really makes it easier.

[chuckinator]

You can combine the RPM and throttle this has worked fine for me, you could also bind the rpm(or throttle) to another control(axis) and still change RPM as needed with whatever setting you set it at being directly related to eachother. It takes some getting used to but it works. Krupinski (an il2 ace if I ever saw one) does the same thing in his videos so if the best of us do it I don't see a problem with noobies doing it. 

 

[AEthelraedUnraed]

Quote

6 years later...

Don't think I've seen necrothreads this old yet...

[Jaegermeister]

Yeah, clearly posted before the Spitfire Mk V was released. 

[Jade_Monkey]

Since we resucitated this thread, I have one question for the more knowledgeable. As I think it through i think I know the answer but want to confirm:

 

What's the difference of running an engine at the same RPM but different manifold pressure? Is it that the pitch of the blades is changed to maintain the rpm? Does the pitch at high MP typically adapt to provide more speed?

 

For example the P-51, at 3000rpm, but at MP of 45 vs 60.

[[CPT]Crunch]

Most advanced mechanical computers or governors are only giving you a vote, they won't under all conditions permit the input you just selected to occur until the correct conditions are met anyway.  Self protections are usually built in.  You want to figure out what method gives you the fasted acceleration you can possibly get.  Generally keep your manifold pressure maxed out in combat setting, that's raw engine power at the ready.

[BlitzPig_EL]

A constant speed propeller will try to hold it's rpm at the set value regardless of manifold pressure, of course it may be possible to exceed the prop governor's range of adjustment, but normally you would probably melt a piston due to detonation before that could happen.   In the sim there is no mechanical penalty for improper engine management though, so go crazy and jack that MP as high as you want to.

Edited August 5, 2021 by BlitzPig_EL

[AEthelraedUnraed]

Well, since this thread is now alive and kicking, another question. Apparently, in the P-47, the throttle and RPM are linked only in one direction because the engine would blow if you'd decrease both simultaneously.

 

Why is it necessary to reduce MP before reducing RPM? What happens if you don't? When, in real life, would you know it's safe to start reducing RPM?

[=FEW=Revolves]

3 hours ago, Jade_Monkey said:

What's the difference of running an engine at the same RPM but different manifold pressure? Is it that the pitch of the blades is changed to maintain the rpm? Does the pitch at high MP typically adapt to provide more speed?

 

Yep the pitch of the blades is adjusted to maintain the RPM. There are a few artifacts you can notice in game due to how this works:

 

1. The pitch isn't adjusted instantly. Sudden manifold increases will first cause a sudden increase in RPM, then the regulator kicks in and reduces the RPM. If you do it too suddenly you can brick your engine with an overrev like that. Conversly, sudden manifold decreases cause a rapid decrease of RPM before the regulator kicks in.

 

2. Sudden acceleration, i.e. from a dive, also causes the RPM to spike a little. If you combine a dive with a sudden throttle increase you've got even worse odds of blowing up your engine. This is particularly noticeable with the P-40, diving increases the manifold and the speed at the same time.

 

3. In really low speed regimes (e.g. taxing) the pitch governor can't adjust the pitch far enough to provide the desired RPM.

 

19 minutes ago, AEthelraedUnraed said:

Why is it necessary to reduce MP before reducing RPM? What happens if you don't? When, in real life, would you know it's safe to start reducing RPM?

 

You can reduce RPM and not MP in the game and nothing bad will happen. In real life, that would be an absolute no go, since that's *the* engine regime which causes an engine detonation (https://en.wikipedia.org/wiki/Engine_knocking). Sudden dead engine if you will. In simple terms, too much air/fuel will be pumped in to the engine, and the engine won't be able to get rid of it quick enough, resulting in improper ignition of the fuel at the wrong spots, which is often fatal for the engine.

Edited August 5, 2021 by =FEW=Revolves

[AEthelraedUnraed]

16 hours ago, =FEW=Revolves said:

You can reduce RPM and not MP in the game and nothing bad will happen. In real life, that would be an absolute no go, since that's *the* engine regime which causes an engine detonation (https://en.wikipedia.org/wiki/Engine_knocking). Sudden dead engine if you will. In simple terms, too much air/fuel will be pumped in to the engine, and the engine won't be able to get rid of it quick enough, resulting in improper ignition of the fuel at the wrong spots, which is often fatal for the engine.

Thanks! So, if I understand correctly, you can start decreasing your RPM as soon as the MP has stabilized? And do you need to do that gently, or can you just slam back the RPM lever?

[BlitzPig_EL]

In general you should never "slam" the throttle or prop rpm controls, no matter which way you are moving them, and they should always be moved in the correct order. I.E.  Always raise rpm before increasing throttle, and always lower throttle before lowering RPM.  Of course that would be for a real aircraft.  As I said in my first post, in the sim there is no penalty for mishandling your engine, so slam those controls like you are driving a Skyline on a Playstation.

 

*EDIT*

 

It would be humorous to see the results for the first few days if real world type damage for poor engine handling were implemented in the sim.  Lots of "online aces" would find their tactics would end their sorties in short order, and the wailing and gnashing of teeth on the forum would be comedy gold. 

Edited August 6, 2021 by BlitzPig_EL

[=FEW=Revolves]

35 minutes ago, BlitzPig_EL said:

 As I said in my first post, in the sim there is no penalty for mishandling your engine, so slam those controls like you are driving a Skyline on a Playstation.

 

While the game is rather generous, I've definitely blown my engine up a few times by slamming my throttle from 0 to full on a stalling yak 9 and yak 7.  But yeah it's super generous and it rarely happens.

 

Somehow in game running low RPM but high MP tends to be good for the engine, since you get a significantly lengthened combat timer.

[Dragon1-1]

That's not really "low RPM", though. Low RPM is what you get when you put the lever most of the way down. A slight reduction in RPM will reduce the available power, but also extend the engine life. In general, though, the RPM lever should be in front of the throttle.

 

I think I've killed the engine on the T-bolt by mishandling the RPM lever, on a radial engine in particular this risks breaking the main bearing because a windmilling prop causes the forces to be the opposite of what the bearing was designed for. That's also why it has the interlock to prevent exactly that from happening. This should probably affect other radials as well, but it doesn't seem to. 

[Voyager]

@BlitzPig_EL I think you're conflating turbine behavior with piston behavior. Turbines are sensitive to power shifts because the blades need to be moving a certain speed to effectively pull energy from the gas pressure/flow. If they're going to slow, they'll stall, and potentially end up flat edge on to the pressure gradient. If you've got enough force going, it can even just snap them right off, rapidly converting them from an engine to a cuiznart.

 

And because they've got inertia, and the fuel flow really doesn't, you need to give the spinning disk some time to catch up whenever you add more power. 

 

For a piston engine, when you're adding power, you are just adding pressure to the cylinder. Either the cylinder can handle it, or it can't. Unlike turbines, that's not something that would have any real dependence on the previous power state.

 

Even rapid prop pitch changes should not cause issues, since you are generally commanding a governor, not directly changing the pitch. They can't keep up with normal engine power setting changes, so it's unlikely they're going to respond overly quickly to setting changes. 

 

Where you run into trouble is transitioning from an economy cruise setting to a war emergency setting. Cruise is generally lower RPM, lower MP and lean fuel mixture.

 

Lean mixtures are burning hotter per unit gas, because they're closer to the best thermal production ratio (also why they're better for efficiency) so, need to go rich to keep from creating hotspots or detonation. 

 

Low RPM is going to increase the pressure in the cylinder, because the prop's pushing back on the engine to keep that RPM. You may not see it initially, because the boost will override the governor for a bit, until it can dial in enough bite to get back to its target RPM. 

 

We aren't always talking about small RPM differences either. Late war R-2800's had guidelines for cruising at as low as 1900 RPM, on an engine that would go up to 2800 RPM at war emergency. 

 

You'll mostly hear about this on the P-38, because the plane was an ergonomic nightmare, with the engine controls scattered all over the cockpit. It was very easy to do things in the wrong order, or forget a control entirely.

 

Pretty much every other single seat fighter had all of the engine controls on the same place, such that if you needed power now, you could grab all of them and slam them forward at the same time, and you'd be pretty much fine. 

 

Again, turbines behave very differently, which led to a lot of accidents when they came in. I feel like it's swung the other way, with people treating props as though they were jets, and leading to an entirely different set of issues. 

[NanashiAnjin]

4 hours ago, =FEW=Revolves said:

 

While the game is rather generous, I've definitely blown my engine up a few times by slamming my throttle from 0 to full on a stalling yak 9 and yak 7.  But yeah it's super generous and it rarely happens.

 

Somehow in game running low RPM but high MP tends to be good for the engine, since you get a significantly lengthened combat timer.

Its actually what the p38 pilots did late pacific to conserve fuel, and extend their operational range low rpm high mp. 

[RossMarBow]

Well the IL-2 and Stuka can be pretty much optimally flown linked 
I aim for 85 85% on the stuka but usually get 85-90
And IL-2 probably fine on 90-90 too but might be better on 100-90? Or something cause it overheats on full power.

Other planes not so much

Edited August 18, 2021 by brahguevara

[AEthelraedUnraed]

35 minutes ago, brahguevara said:

And IL-2 probably fine on 90-90 too but might be better on 100-90? Or something cause it overheats on full power.

You can fly the IL2 on max RPM (and 80% or 90% or so MP) without time limit or overheating. I see no reason to reduce RPM by linking it to the throttle.

[Mollotin]

On 8/6/2021 at 2:28 PM, BlitzPig_EL said:

 

 

*EDIT*

 

It would be humorous to see the results for the first few days if real world type damage for poor engine handling were implemented in the sim.  Lots of "online aces" would find their tactics would end their sorties in short order, and the wailing and gnashing of teeth on the forum would be comedy gold. 

*laughs in german single lever engine control*