Complex/High Performance aircraft questions

[Eibwen]

Hi all, new here. Pretty impressive how much knowledge there is available on these boards. Looking forward to tapping into it. Thanks in advance. I am a low time pilot looking to get my high performance checkout soon. Lots of XPlane playing has set me up with likely bad habits but a collection of knowledge that has left me with gaps that I now need to fill in. I recently took a flight with an friend who let me ride along in the back seat of their 182M just for fun. I tried to pay attention and it raised a couple questions for me. Hoping to be enlightened a little bit here.

First, in the climb I noticed manifold pressure gradually drops from the maximum continuous 23 inches set at the start of the climb. I'd never thought about this before but that would mean needing to continually increase throttle in the climb to maintain max continuous power (up to the altitude where the POH directs lower than 23 inches as the max continuous for cruise). Is it correct that you'll add throttle to maintain 23 inches during the climb to cruising altitude, or should you set it at 23 inches at the start of the climb and then leave it? I've never heard of the need to increase throttle during the climb. Usually it's seems like youre told to set it and then just lean the mixture in the climb. No adjustment to throttle.

Second, the CHTs were running at 300 or a little under. My buddy said this was normal. There are a million different search results about proper CHTs and all of them are referencing temps running significantly higher than this for an O-470. Is there any risk associated with LOW CHTs? I get the risk of high CHT temps, but nothing every talks about a low CHT. What could be the cause? Is this actually low? What's normal?

In the end, I know a lot of questions will be answered by a CFI when I jump into training for the high performance endorsement. Just want to start my familiarization as early as possible.

Any general tips on engine management in high performance planes would also be appreciated. At some point I'd like to get my commercial license and starting my knowledge growth early seems like a good idea. Thanks all.

 

[psween]

First, manifold pressure in a naturally aspirated engine will always fall with altitude, nothing to do with HP/complex. Just that most non-complex planes don't have a MP gauge so you don't see it. Not sure why you'd be starting at only 23 inches though, unless you're at a pretty high elevation field. Full throttle near sea level should get you within an inch or two of barometric pressure (lose a bit in air filter and throttle body). Generally in a climb you're going to be at full throttle and taking whatever MP you can get.

As for CHT, most HP planes have cowl flaps to help manage temps, and if you're running at lower power settings you can get them down that low. 300 and above shouldn't be damaging, but defer to the manual for specifics. Every manufacturer has recommended limits for Temps, and it can make a big difference how and where the measurement is taken.

If you want a really good explanation of piston engine operation, see if you can find the John Deacon 'Pelican's Perch' articles on AvWeb. Tons of good info in there.

 

[asicer]

Here's an exercise for you: Before starting the engine, what reading do you see on the manifold pressure gauge? Is it the same every day?

 

[WalterH]

Hi all, new here. Pretty impressive how much knowledge there is available on these boards. Looking forward to tapping into it. Thanks in advance. I am a low time pilot looking to get my high performance checkout soon. Lots of XPlane playing has set me up with likely bad habits but a collection of knowledge that has left me with gaps that I now need to fill in. I recently took a flight with an friend who let me ride along in the back seat of their 182M just for fun. I tried to pay attention and it raised a couple questions for me. Hoping to be enlightened a little bit here.

First, in the climb I noticed manifold pressure gradually drops from the maximum continuous 23 inches set at the start of the climb. I'd never thought about this before but that would mean needing to continually increase throttle in the climb to maintain max continuous power (up to the altitude where the POH directs lower than 23 inches as the max continuous for cruise). Is it correct that you'll add throttle to maintain 23 inches during the climb to cruising altitude, or should you set it at 23 inches at the start of the climb and then leave it? I've never heard of the need to increase throttle during the climb. Usually it's seems like youre told to set it and then just lean the mixture in the climb. No adjustment to throttle.

Second, the CHTs were running at 300 or a little under. My buddy said this was normal. There are a million different search results about proper CHTs and all of them are referencing temps running significantly higher than this for an O-470. Is there any risk associated with LOW CHTs? I get the risk of high CHT temps, but nothing every talks about a low CHT. What could be the cause? Is this actually low? What's normal?

In the end, I know a lot of questions will be answered by a CFI when I jump into training for the high performance endorsement. Just want to start my familiarization as early as possible.

Any general tips on engine management in high performance planes would also be appreciated. At some point I'd like to get my commercial license and starting my knowledge growth early seems like a good idea. Thanks all.

If you wanted/POH calls for 23 inches for your climb power in a naturally aspirated complex aircraft, then yes that is how you would achieve it as MP drops with altitude.

Not sure why you'd be starting at only 23 inches though, unless you're at a pretty high elevation field. Full throttle near sea level should get you within an inch or two of barometric pressure (lose a bit in air filter and throttle body). Generally in a climb you're going to be at full throttle and taking whatever MP you can get.

The 182RG I did training in called for 23 inches and 2400 RPM in climb. Taking off from around 1000 feet we’d have something like 27 inches on takeoff, then after passing 1000 FT AGL would pull the black and blue knobs back for 23/24. As available Mp dropped in climb, black knob back in to hold 23 as long as possible.

 

[mandm]

I took my HP endorsement in a Cirrus, but I also wanted to fly a Cirrus. Did I learn anything about HP? Not really, except to be aware about engine temps, keep them in the green, read the POH for the best info and then a checkout in the actual aircraft so that you learn its quirks.

I would personally wait until your commercial multi training unless you need the endorsement to fly PIC beforehand.

 

[dmspilot]

First, in the climb I noticed manifold pressure gradually drops from the maximum continuous 23 inches set at the start of the climb. I'd never thought about this before but that would mean needing to continually increase throttle in the climb to maintain max continuous power (up to the altitude where the POH directs lower than 23 inches as the max continuous for cruise). Is it correct that you'll add throttle to maintain 23 inches during the climb to cruising altitude

There's no "max continuous" rating on a 182M, you can takeoff at full throttle and leave it there. The book "advises" a climb power setting 23 in. Hg. of manifold pressure for engine longevity.

or should you set it at 23 inches at the start of the climb and then leave it?

No, you would not do that. You would adjust the throttle to maintain 23". Otherwise it will drop, decreasing power, and the airplane will stop climbing—I'd guess around 5,000 feet.

 

[Eibwen]

There's no "max continuous" rating on a 182M, you can takeoff at full throttle and leave it there. The book "advises" a climb power setting 23 in. Hg. of manifold pressure for engine longevity.

Interesting. You're correct of course, but it's confusing when a POH says something like "reduce power to 23" and 2450 rpm as soon as practical to reduce engine wear". "As soon as practical" definitely sounds like bad things will happen if you don't...but the POH doesn't give any clear indication that you can't just keep the thing fire-walled throughout a climb.

I guess I'm just surprised at the lack of specifics in the POH here.

Above about 5,000 feet the cruise charts show a reduced maximum MP. So I would assume that would translate into a reduced maximum continuous power in a climb. But your point seems to indicate that wouldn't be the case either... hmmm. Like I said, just the lack of very clear guidelines is interesting.

 

[Eibwen]

As for CHT, most HP planes have cowl flaps to help manage temps, and if you're running at lower power settings you can get them down that low. 300 and above shouldn't be damaging, but defer to the manual for specifics. Every manufacturer has recommended limits for Temps, and it can make a big difference how and where the measurement is taken.

So, everywhere I see with discussions about CHT, the temps referred to are in the 400 range. Is there anything inherently bad about CHTs running around 300? I'd assume maybe incomplete fuel burn and fouled plugs maybe? But no engine damage? Is it most likely that it's just that the single cylinder the CHT probe is mounted on is running much cooler than the others? Is that typical?

 

[dmspilot]

Interesting. You're correct of course, but it's confusing when a POH says something like "reduce power to 23" and 2450 rpm as soon as practical to reduce engine wear". "As soon as practical" definitely sounds like bad things will happen if you don't...but the POH doesn't give any clear indication that you can't just keep the thing fire-walled throughout a climb.

There is no need to clearly indicate the absence of a limitation. Any limitations would be clearly indicated in the limitations section. They would also be stated in the Type Certificate Data Sheet (TCDS).

Above about 5,000 feet the cruise charts show a reduced maximum MP. So I would assume that would translate into a reduced maximum continuous power in a climb. But your point seems to indicate that wouldn't be the case either... hmmm. Like I said, just the lack of very clear guidelines is interesting.

That's not an operating limitation on the pilot. That's a physics limitation. You can't create the same MP at altitude (without a turbocharger) due to the reduced air pressure.

 

[Eibwen]

There is no need to clearly indicate the absence of a limitation. Any limitations would be clearly indicated in the limitations section. They would also be stated in the Type Certificate Data Sheet (TCDS).


That's not an operating limitation on the pilot. That's a physics limitation. You can't create the same MP at altitude (without a turbocharger) due to the reduced air pressure.

re: limitations - Understood. The engine limitations section says only that the "normal operating range" is 15-23 in Hg. But apparently it's still ok to operate outside of "normal operating range" for ... an indeterminate amount of time. It causes increased engine wear but it won't ... err ... explode? Anyway, this is just curiosity speaking. I'm sure that will make more sense down the road as I get more familiar with more advanced aircraft.

Leaning is not described in the POH in reference to EGT. It's just the classic "ROP" setting instructions. So aircraft like this that have been upgraded with an EGT are operated by some knowledge gleaned elsewhere.

re: reduced MP with altitude. Yeah I understand this concept. I just hadn't been in an airplane where you climb at anything less than full throttle before (Cessna 172 and Piper Cherokee). So it's a new thing to add throttle (fuel) during a climb to maintain a certain power output. I've never noticed an instruction or description to that effect and just wanted to clearly understand.

This all comes down to liking very specific criteria for engine operation. Aviation magazines are full of warnings about how critical very careful engine management is - I want to be sure I follow best practices. I'm a curious and admittedly "particular" person. I don't get along with ambiguity - sometimes to my detriment.

Thanks for the discussion and info all.

 

[robin ardoin]

182-S, Full throttle to 500’ AGL, Pull MAP to 23”, prop 2400rpm, mixture 15gph (or more if needed to keep max CHT 380F or under). I am at full throttle around 7500’, MAP 21”. I try to keep CHT under 380F but one cylinder is a problem child so I burn a little more fuel to keep it happy. Other cylinders are 320-350 when it is at 380.

 

[brcase]

So, everywhere I see with discussions about CHT, the temps referred to are in the 400 range. Is there anything inherently bad about CHTs running around 300? I'd assume maybe incomplete fuel burn and fouled plugs maybe? But no engine damage? Is it most likely that it's just that the single cylinder the CHT probe is mounted on is running much cooler than the others? Is that typical?

Nothing wrong with Low CHT's, but might indicate running richer than necessary, but just means the engine is getting more cooling than it needs. With a Single probe CHT it should be on the Warmest cylinder if everything is working as it should, but you never really know if everything is working as it should or if that is really the warmest cylinder. So probably best to run it per the manual during the climb.

With CHT's on all the cylinders, a Low CHT on all the cylinders probably means you could at a leaner mixture below 65% power, up to Peak EGT for best power, leaner for Lean of Peak operations which you probably aren't going to do with most Carbureted engines. Reference Pelican Perch Articles and others that talk about the Red Box for more information.
What you might watch for is Lower than Normal CHT's on one cylinder, but that would also normally be associated with an abnormal EGT on the same cylinder.

What you should learn during your High performance training, especially if it has a multiprobe engine monitor is that the bigger engines with a controllable pitch propeller is you have a lot more options available for power settings, fuel flow and temperature management. A lot of this is personal preference and learning what configurations to avoid, A couple rule of thumbs are avoid low RPM settings with High manifold pressure unless recommend by the operating manual and when possible avoid operating at CHT's higher than 380F.


Brian
CFIIIG/ASEL

 

[mandm]

Older aircraft POH are very thin/small, you could refer to a newer year POH and chat about those differences, maybe something was learned and added over the years.

 

[BillTIZ]

First, manifold pressure in a naturally aspirated engine will always fall with altitude, nothing to do with HP/complex. Just that most non-complex planes don't have a MP gauge so you don't see it. Not sure why you'd be starting at only 23 inches though, unless you're at a pretty high elevation field. Full throttle near sea level should get you within an inch or two of barometric pressure (lose a bit in air filter and throttle body). Generally in a climb you're going to be at full throttle and taking whatever MP you can get.

As for CHT, most HP planes have cowl flaps to help manage temps, and if you're running at lower power settings you can get them down that low. 300 and above shouldn't be damaging, but defer to the manual for specifics. Every manufacturer has recommended limits for Temps, and it can make a big difference how and where the measurement is taken.

If you want a really good explanation of piston engine operation, see if you can find the John Deacon 'Pelican's Perch' articles on AvWeb. Tons of good info in there.

The C182 Manual calls for full power on takeoff, then reduce to 23MP for continuous climb and 2300RPM. Most reduce the power at about 500ft AGL. Yes, keep increasing throttle to maintain the 23MP until you hit full throttle again. A lot of aircraft have max power limits. The L-19 with the O-470 engine calls for max power with a 5min limit which can yield almost 2800RPM, well into the yellow arc on the RPM gauge, then reduce power to the "top of the green" or about 2400RPM.

C172XP are rated to 195HP for takeoff, 5 min max power limit, then reduce power to 180HP equivalent.