Question on Constant Speed Propellers

[azpilot]

I have a question about adjusting propeller RPM with a constant speed propeller. I'm flying a 182S. I've checked the POH and I can't find info on this question.

Let's say I'm flying along at 8000' at cruise. I'm trying to run fairly efficient, so I'm down at 20 in-HG manifold pressure and 2000 RPM. The engine has been leaned appropriately. For whatever reason, I want to climb.

What order am I supposed to adjust things? I believe the correct order is:

1) leave the mixture where it is.
2) increase propeller RPM to 2400 (POH says to climb at 2400 RPM
3) increase power as appropriate for climb

Am I missing something? When I was getting checked out in this plane, I was coming in to enter the pattern, and the I had reduced power to ~17". The prop was down at ~2200 RPM. I was running through the before landing checklist trying to stay ahead of the airplane. I advanced the propeller to full forward while at 17" manifold pressure. My CFI cautioned me against doing this and advised me not to advance the propeller until I was abeam the numbers and had reduced power to 13". I've asked my CFI this same question and I'm waiting to hear back from him as well.

 

[Clip4]

The correct order to increase power is enrich the mixture, increase the RPM and increase the throttle. If you leave the mixture leaned, you risk burning exhaust valves. RED BLUE BLACK.

You will find the prop Governor is no longer effective below -14 MP and you can push the prop control forward with no RPM increase. Above that value the engine speed increases.

 

[midwestpa24]

2,000 rpm at cruise seems low to me. What does the POH state?

Normally at that cruise altitude, the throttle is already wide open and taking all the MP you can get for the altitude.

In your landing scenario, you can push the prop ahead, but just do it slowly to allow the governor to do its thing and prevent spiking the rpm above redline. Normally I teach in the pattern to let the RPM start to drop on its own due to low speed/power, meaning the prop is on the pitch stops, then put the prop control ahead.

 

[azpilot]

2,000 rpm at cruise seems low to me. What does the POH state?

The POH lists prop speeds between 2,000 RPM and 2,400 RPM for cruise flight.

In your landing scenario, you can push the prop ahead, but just do it slowly to allow the governor to do its thing and prevent spiking the rpm above redline.

That makes sense. When I did this with my CFI, I did just abruptly push it in. I should be more gradual with the changes in general, and probably make changes using the Vernier dial rather than just pushing it in.

 

[azpilot]

The correct order to increase power is enrich the mixture, increase the RPM and increase the throttle. If you leave the mixture leaned, you risk burning exhaust valves. RED BLUE BLACK.

You will find the prop Governor is no longer effective below -14 MP and you can push the prop control forward with no RPM increase. Above that value the engine speed increases.

OK, so I was thinking that I could leave the mixture alone because in my hypothetical scenario, I'd be climbing, so the mixture would not need to be enrichened because I'd be climbing to thinner air. But I guess what I missed is that I'm going to be advancing the throttle, so I need more fuel in the mixture, because I'm also about to add more air. If I don't enrichen the mixture, then when I advance the throttle, the mixture will be too lean.

 

[David Megginson]

The correct order to increase power is enrich the mixture, increase the RPM and increase the throttle. If you leave the mixture leaned, you risk burning exhaust valves. RED BLUE BLACK.

The mnemonic I learned was "prop up; throttle down." (Lead with the prop when increasing power, and lead with the throttle when decreasing power.)

 

[David Megginson]

If I don't enrichen the mixture, then when I advance the throttle, the mixture will be too lean.

That depends on where you were to start. You want to stay either on the lean side of peak EGT or on the rich side of 100° ROP. It's not "too lean" or "too rich" per se, but a question of keeping a safe margin from 50° ROP EGT (peak CHT) on either the lean or the rich side. And below 65% power, it doesn't matter anyway.

 

[Clip4]

The mnemonic I learned was "prop up; throttle down." (Lead with the prop when increasing power, and lead with the throttle when decreasing power.)

No red knob increasing power will earn you an exhaust valve as a paper weight.

 

[Radar Contact]

When I was getting checked out in this plane, I was coming in to enter the pattern, and the I had reduced power to ~17". The prop was down at ~2200 RPM. I was running through the before landing checklist trying to stay ahead of the airplane. I advanced the propeller to full forward while at 17" manifold pressure. My CFI cautioned me against doing this and advised me not to advance the propeller until I was abeam the numbers and had reduced power to 13". I've asked my CFI this same question and I'm waiting to hear back from him as well.

I’m sure I’ll get roasted out of here but…

You could just leave the mixture and props set for cruise (mixture slightly enriched depending on what cruise altitude was) and just adjust the throttle for landing. In the event of a go-around (rare if you’re a proficient pilot) you’d smoothly move all forward with a flat hand…it’s going to be there anyway.

This would alleviate dumping extra(not needed) cold fuel in your hot cylinders and the noise for the surrounding community.

 

[455 Bravo Uniform]

Not sure if it helps or is valid for your situation, but when I pull levers for a change in major flight regime, I pull from left to right, and when I push levers I go right to left. My panel is Throttle-Prop-Mixture from left to right.

 

[Clip4]

That depends on where you were to start. You want to stay either on the lean side of peak EGT or on the rich side of 100° ROP. It's not "too lean" or "too rich" per se, but a question of keeping a safe margin from 50° ROP EGT (peak CHT) on either the lean or the rich side. And below 65% power, it doesn't matter anyway.

The 182S checklist gives mixture setting for 2 conditions

Normal Climb - 23”/2400 Mixture -- 15 GPH or FULL RICH (whichever is less)

Maximum Climb - Full Throttle/2400
LEAN in accordance with Maximum Power Fuel Flow placard value.

Both are going to require a mixture change from leaned cruise flight. For maximum climb at 4000 MSL the minimum flow is 17.5 GPH per the chart in a 182S.

There are similar full power minimum fuel flow charts (operational limitation) in a lot of aircraft. It is a violation of 91.9(a) to not follow it and you’ll earn the burnt valve paper weight

 

[Dan Thomas]

No red knob increasing power will earn you an exhaust valve as a paper weight.

He's at 10K already. Even at full throttle he's not likely to get more than 65% power, and Lycoming says you can do anything you like with the mixture in a normally-aspirated engine under that setting.

 

[Clip4]

He's at 10K already. Even at full throttle he's not likely to get more than 65% power, and Lycoming says you can do anything you like with the mixture in a normally-aspirated engine under that setting.

Cessna disagrees with you. The fuel flow from the cruise performance chart at 10,000 ft in a 182s is 11.2 gph and the minimum fuel flow for a maximum performance climb at 10,000 ft is 14.5 GPH.

 

[Tarheelpilot]

I’m sure I’ll get roasted out of here but…

You could just leave the mixture and props set for cruise (mixture slightly enriched depending on what cruise altitude was) and just adjust the throttle for landing. In the event of a go-around (rare if you’re a proficient pilot) you’d smoothly move all forward with a flat hand…it’s going to be there anyway.

This would alleviate dumping extra(not needed) cold fuel in your hot cylinders and the noise for the surrounding community.

No doubt you will.

I do the same as you. We can be roasted together.

 

[WDD]

Keep it simple. Want to climb? Full rich, prop to top of green, throttle to top of green. Get to your new altitude, throttle to 23 (or 20 if your sipping gas), and prop to 2300 (or 2000 if you're sipping gas).

After climbing, readjust mix.

 

[steingar]

What @WDD said. You won't overboost if you adjust the prop first.

 

[Dan Thomas]

Cessna disagrees with you. The fuel flow from the cruise performance chart at 10,000 ft in a 182s is 11.2 gph and the minimum fuel flow for a maximum performance climb at 10,000 ft is 14.5 GPH.

The 182S chart for 10,000 feet:



At that altitude you cannot get more than 66% power unless the OAT is below normal for that altitude.

Lycoming used to say that any mix setting below 75% was OK.

 

[Brad W]

Not sure if it helps or is valid for your situation, but when I pull levers for a change in major flight regime, I pull from left to right, and when I push levers I go right to left. My panel is Throttle-Prop-Mixture from left to right.

That's the way I was taught.
But I like radarcontact's common sense approach to simplify. Probably some nuanced advantages to having the mixture already rich and the prop already in....maybe some delay in there someplace, etc.... but simple is good...and I'm going to try to be pushing the throttle in slow & smoothly anyway...AND I was taught since my discovery flight to spread my hand out to push the mixture and carb heat while holding the throttle in....or holding the mixture prop and throttle on a complex....holding it all to the firewall for takeoff, go around, etc.... so that motion is natural and is happening anyway.

 

[David Megginson]

Lycoming used to say that any mix setting below 75% was OK.

Current thinking from the GAMI folks and pals after running lots of engines on test stands is that the mixture setting doesn't matter under 65% for a normally-aspirated engine, because the red zone shrinks away to virtually nothing. At least, that's what I remember from Busch's articles and books.

 

[Wagondriver]

Keep it simple. Want to climb? Full rich, prop to top of green, throttle to top of green. Get to your new altitude, throttle to 23 (or 20 if your sipping gas), and prop to 2300 (or 2000 if you're sipping gas).

After climbing, readjust mix.

Full rich at 10,000'? That thing is going to be choking on all that fuel! And, MP will be nowhere near 23!

 

[dmspilot]

I have a question about adjusting propeller RPM with a constant speed propeller. I'm flying a 182S. I've checked the POH and I can't find info on this question.

Let's say I'm flying along at 8000' at cruise. I'm trying to run fairly efficient, so I'm down at 20 in-HG manifold pressure and 2000 RPM. The engine has been leaned appropriately. For whatever reason, I want to climb.

What order am I supposed to adjust things? I believe the correct order is:

1) leave the mixture where it is.
2) increase propeller RPM to 2400 (POH says to climb at 2400 RPM
3) increase power as appropriate for climb

Am I missing something? When I was getting checked out in this plane, I was coming in to enter the pattern, and the I had reduced power to ~17". The prop was down at ~2200 RPM. I was running through the before landing checklist trying to stay ahead of the airplane. I advanced the propeller to full forward while at 17" manifold pressure. My CFI cautioned me against doing this and advised me not to advance the propeller until I was abeam the numbers and had reduced power to 13". I've asked my CFI this same question and I'm waiting to hear back from him as well.

Two entirely different scenarios so I'm not sure why you're trying to make them analogous. Shoving the prop full forward in preparation for landing is not the same as advancing it to a specific RPM in preparation for climb. The former will result in a noisy, unpleasant surge dependent upon airspeed and manifold pressure and may also result in an overspeed.

 

[asicer]

What order am I supposed to adjust things?

Spread your fingers and mash all the knobs all at once.

 

[Clip4]

The 182S chart for 10,000 feet:

View attachment 102463

At that altitude you cannot get more than 66% power unless the OAT is below normal for that altitude.

Lycoming used to say that any mix setting below 75% was OK.

It makes no difference. The Minimum Fuel Flow Placard makes the published values an operation limitation and 91.9(a) states no person may operate a civil aircraft without complying with the operating limitations specified in the approved Airplane or Rotorcraft Flight Manual, markings, and placards,


Then there is the simple argument of following the checklist that contains the operation recommendations of the manufacturer.

You also might want to read up on the fuel injection systems and altitude compensating fuel pumps used on several modern injected aircraft models.

 

[21541803]

So in your RV-10, "a civil aircraft", you as builder can write the operating limitations as such to run the engine 100 degrees LOP if you so wish? Or not?

 

[Sinistar]

Full rich at 10,000'? That thing is going to be choking on all that fuel! And, MP will be nowhere near 23!

That's what I am wondering too? OP - is your 182S turbo'd?

 

[azpilot]

That's what I am wondering too? OP - is your 182S turbo'd?

No.

But I should point out that this is really just a hypothetical example. I pulled those altitudes out of my backside. I may as well have said 2k to 4k, or 4k to 6k. The question was more centered around the order of pushing and pulling the knobs. But one thing I've learned from from spending time around pilots is that we'll all revel in the beating of a dead horse, and then spend time arguing over how of its bones we broke along the way. lol

 

[azpilot]

Two entirely different scenarios so I'm not sure why you're trying to make them analogous. Shoving the prop full forward in preparation for landing is not the same as advancing it to a specific RPM in preparation for climb. The former will result in a noisy, unpleasant surge dependent upon airspeed and manifold pressure and may also result in an overspeed.

The way the scenarios relate is that they both involve a condition where the engine is at less than full power, the propeller is at less than full speed, but it we want to advance the speed of the propeller. Other than that, I recognize that the scenarios are different.

I wanted to hear discussion about the particulars and details of why they are different, and what makes them different This thread, along with all of the details and opinions shared has been very helpful in getting me incite into the operations of CS props, which is what I wanted.

 

[kyleb]

So in your RV-10, "a civil aircraft", you as builder can write the operating limitations as such to run the engine 100 degrees LOP if you so wish? Or not?

You could write it to fuel the airplane with toilet water. Not that you'd be very successful, but that's why it is experimental aviation.

 

[Stewartb]

In general increasing RPM in flight without adding throttle results in a decrease in speed, so doing it is usually quickly followed by adding throttle. Not a big deal. At low power settings, like approach to landing, pushing the prop full flat is like applying a speed brake. Useful.

 

[Larry in TN]

Probably some nuanced advantages to having the mixture already rich and the prop already in.

It's just the simplify the go-around procedure. Having the mixture and prop pre-set for a go-around reduces the chance of error if one is required. Leaving them back creates a few threats in the event of an unexpected go-around.

Pushing them back up will divert some attention away from handling the airplane and establishing a climb attitude. This is less of an issue in Kevin's C310, with it's lever-type controls, than it would be in something like a Bonanza or C-182 where it would be more difficult to push all three controls forward at the same time.

A pilot who forgets to push them forward from cruise RPM and mixture settings could have a delay in achieving full power at a time when it is needed quickly. In extreme cases, the leaned mixture could prevent an immediate significant increase in power.

If you want to delay the prop and mixture increase, you need to manage those threats.

Many CFIs teach setting full-increase and full-rich on downwind. This reduces the complexity later in the approach for pilots who are new to constant-speed props. Delaying this until power is reduced below the range of the prop governor eliminates the noise from pushing it forward. As a pilot becomes more comfortable in the airplane that can be delayed further until on Final and eventually, as Kevin does, incorporate it into your go-around procedure. I think that probably works best in airplanes that have relatively more power so you can at least can enough power to climb without the increased RPM and mixture if it's needed immediately. For pilots who only fly, or fly these airplanes, occasionally, I think it's probably best to stick with going full-increase/rich with the first major power reduction on the descent from pattern altitude.

 

[dmspilot]

The way the scenarios relate is that they both involve a condition where the engine is at less than full power, the propeller is at less than full speed, but it we want to advance the speed of the propeller. Other than that, I recognize that the scenarios are different.

I wanted to hear discussion about the particulars and details of why they are different, and what makes them different This thread, along with all of the details and opinions shared has been very helpful in getting me incite into the operations of CS props, which is what I wanted.

I might have missed a nuance in your earlier post, when you said your CFI "advised me not to advance the propeller". Perhaps you interpreted the CFIs advice as not wanting you to advance it at all, but really the concern was about advancing it to fully forward at that time.

I guess if you want to advance from 2000 or 2200 to 2400RPM early (downwind or earlier), and then go full forward later (<=13"MP), that would not be a bad idea. It adds an extra step, but at least if you forget to go full forward, being at 2400 would be a lot better than 2000RPM when initiating a go-around.

 

[Dan Thomas]

You also might want to read up on the fuel injection systems and altitude compensating fuel pumps used on several modern injected aircraft models.

I am a licensed aircraft mechanic. I worked on various fuel-injection systems. Not once did I encounter an altitude compensating pump, though I know they're out there. They're just rather rare.

That chart shows that 66% power is ALL YOU CAN GET at 10K, whether you're climbing or not, and to get that you have to be at redline RPM.

What is YOUR aircraft maintenance experience and certifications?

 

[Dan Thomas]

Full rich at 10,000'? That thing is going to be choking on all that fuel! And, MP will be nowhere near 23!

Yup. I had a student call me from a remote airport. He had returned to land after the engine started running rough on climbout. He said he could see black smoke behind the airplane and got worried. I asked him what altitude that was at, and where the mixture was set; he said full rich, 7000 feet.

There was no aircraft defect. There was an understanding defect. The POH will tell you to lean in the climb if roughness occurs.

 

[Clip4]

Mr Thomas, which of your certifications authorizes you to disregard an operation limitation placard on an aircraft and which ones may you chose to disregard and which ones do you have to comply with?

Cessna placed a Maximum Climb Minimum Fuel Flow limitation placard on the aircraft. It becomes regulatory, use it.

 

[PaulS]

I am a licensed aircraft mechanic. I worked on various fuel-injection systems. Not once did I encounter an altitude compensating pump, though I know they're out there. They're just rather rare.

That chart shows that 66% power is ALL YOU CAN GET at 10K, whether you're climbing or not, and to get that you have to be at redline RPM.

What is YOUR aircraft maintenance experience and certifications?

The conti in the older SR-20 had them, pretty easy during climbs.

 

[asicer]

Mr Thomas, which of your certifications authorizes you to disregard an operation limitation placard on an aircraft and which ones may you chose to disregard and which ones do you have to comply with?

Cessna placed a Maximum Climb Minimum Fuel Flow limitation placard on the aircraft. It becomes regulatory, use it.

This placard? I don't see the word "minimum" mentioned.

 

[Wagondriver]

Personally, when I need to climb from a cruise setting, I leave the prop alone at 2300rpm, and move the throttle to go from 17 or 18 inches to 20 inches or whatever I can get. IF I need more performance than that I will take the prop up to 2500. I leave the mixture alone, BUT I watch the engine monitor to see if I need to add a little fuel, I almost never see the egt's or cht's change any significant amount. Even when there is an increase in egt, it only takes a half turn or so on the mixture.

The POH on my 1953 is somewhat limited, but then there isn't much of the original airplane left anyway.

 

[Dan Thomas]

If the OP is cruising at 10K and 2000 RPM, and at the published 10.5 GPH, and increases the RPM to 2400 to climb, what will the fuel flow do? It will rise considerably, of course. It sure won't stay near 10.5.

 

[iamtheari]

If I am above 5000 MSL and not actively trying to slow down, I'm at full throttle. I probably move knobs and levers more than I really have to, and I'm trying to learn more about that. But the throttle is the one I touch the least in the air.

 

[PaulS]

Summertime in a Cirrus NA 22, if you follow the placard during climb, your engine will start glowing red... and that's at cruise climb. I don't start considering pulling the mixture until 5,000 feet. Although I guess we Cirrus pilots aren't really qualified to touch those levers anyway.