Departing a hot and high airport

[DaV8or]

It is true that 250 deg ROP is not best power, but IMO, engine management is a balancing act between flight requirements and engine health. Below is the FAA detonation chart that all our engines were certified to. From this, I believe that 100% power at peak is not the nicest to your engine. It should be noted that detonation and pre ignition are not the same thing. Pre ignition can destroy your engine in less than a minute, where as detonation takes a good deal of time to destroy your engine. You can fly for a short period of time safely with detonation occurring. Unfortunately, we can only guess when that is because there is no gauge to tell us and you can not feel, or hear it when it happens. All we do know is that if it is occurring, some level of damage is happening.

 

So my preference is to stay at least 250 deg ROP on take off and use target EGT in the climb. This does not give me the highest power for this operation, but I use the POH performance tables to plan the take off and they were not calculated using peak EGT. If the POH says I can't make it, I don't go. Maybe with true peak power I could make it, but I'm not willing to go for it just for the sake of my engine.

 

I do have a question for any engine gurus though, for the sake of my prop, the neighbors, my paint job on the tail, my hearing, and my engine, I don't do my run up at full power. So if I use my engine monitor to find say 250 deg ROP at 1800 RPM, does that mean I'll still have 250 deg ROP during a full throttle take off?

 

[chrisk]

It is true that 250 deg ROP is not best power, but IMO, engine management is a balancing act between flight requirements and engine health. Below is the FAA detonation chart that all our engines were certified to. From this, I believe that 100% power at peak is not the nicest to your engine. It should be noted that detonation and pre ignition are not the same thing. Pre ignition can destroy your engine in less than a minute, where as detonation takes a good deal of time to destroy your engine. You can fly for a short period of time safely with detonation occurring. Unfortunately, we can only guess when that is because there is no gauge to tell us and you can not feel, or hear it when it happens. All we do know is that if it is occurring, some level of damage is happening.

 

So my preference is to stay at least 250 deg ROP on take off and use target EGT in the climb. This does not give me the highest power for this operation, but I use the POH performance tables to plan the take off and they were not calculated using peak EGT. If the POH says I can't make it, I don't go. Maybe with true peak power I could make it, but I'm not willing to go for it just for the sake of my engine.

 

I do have a question for any engine gurus though, for the sake of my prop, the neighbors, my paint job on the tail, my hearing, and my engine, I don't do my run up at full power. So if I use my engine monitor to find say 250 deg ROP at 1800 RPM, does that mean I'll still have 250 deg ROP during a full throttle take off?

 

 

A normally  aspirated aircraft engine loses approximately 3.5% horse power per 1000 feet increase in density altitude.  --So, if the density altitude is 8000, you are automatically in the "Safe Operating Area".  Why wouldn't you operate at peak for high density take offs , or very close to it? 

[midlifeflyer]

It's a popular misconception that flaps improve climb. In reality, flaps degrade climb rate and climb angle at any altitude. They do however help you get airborne sooner on the takeoff roll, so setting takeoff flaps may help you clear a close-in obstacle..

 

Excellent point.

 

Related: One of the things one can do when density altitudes are really high, to do a modified soft field takeoff. The idea was to break free of the ground (and its friction) as soon as possible and then accelerate to climb speed in ground effect. It's rarely needed but I regularly taught it during mountain checkouts when we took off from Leadville CO (9934 msl - figure out the density altitude for that one when the temperature is a balmy 70°F).

[PTK]

A normally  aspirated aircraft engine loses approximately 3.5% horse power per 1000 feet increase in density altitude.  --So, if the density altitude is 8000, you are automatically in the "Safe Operating Area".  Why wouldn't you operate at peak for high density take offs , or very close to it? 

CHT considerations perhaps? 

[Lood]

Using target EGT, I'm at around 130 - 150 ROP - regardless of the altitude I take off from. I'm pretty sure that this setting has a rather negligible  effect or limit on engine power and it keeps the CHT's very happy during all kinds of climb rates, even at very high day temperatures.

[DaV8or]

A normally  aspirated aircraft engine loses approximately 3.5% horse power per 1000 feet increase in density altitude.  --So, if the density altitude is 8000, you are automatically in the "Safe Operating Area".  Why wouldn't you operate at peak for high density take offs , or very close to it? 

 

I use the POH that came with the plane. It says at 8000ft, balls to the wall, the engine still makes 80% hp. At peak that still puts me at risk of detonation if you believe the FAA chart. Admittedly, I could likely go to 125 deg ROP and be just fine. I rarely depart at such a high DA, but I should keep a copy of this chart in the plane it now occurs to me. It could be helpful. The last time I did part depart that high, I think I did go close to peak and as I started to climb, I watched the temps, both EGT and CHT skyrocket, so I quickly started dialing in the mixture and got it under control.

[DaV8or]

Using target EGT, I'm at around 130 - 150 ROP - regardless of the altitude I take off from.

 

Just curious how you know that. Do you play with the mixture on the ground first to find the peak before takeoff? If so, where do you set the mixture before ground roll?

[chrisk]

I use the POH that came with the plane. It says at 8000ft, balls to the wall, the engine still makes 80% hp. At peak that still puts me at risk of detonation if you believe the FAA chart. Admittedly, I could likely go to 125 deg ROP and be just fine. I rarely depart at such a high DA, but I should keep a copy of this chart in the plane it now occurs to me. It could be helpful. The last time I did part depart that high, I think I did go close to peak and as I started to climb, I watched the temps, both EGT and CHT skyrocket, so I quickly started dialing in the mixture and got it under control.

 

AOPA has some good recommendations.   They suggest leaning for best power, around 50 to 100 ROP, for both landing and take off.  If I had a normally aspirated plane, I would probably ask a local flight instructor if I was in doubt.

 

Edit:  Your POH can be useful here.  Here is an example.  http://www.zitair.aviators.net/Pilots%20Operating%20Handbook%20G-BJHB.pdf   Page 5-32 gives engine  performance at altitude (8000 ft).  Page 4-11 gives instruction on how to lean for best power at 75% power or less.  In short I would use, 100 ROP above a DA of 8000

[Lood]

Just curious how you know that. Do you play with the mixture on the ground first to find the peak before takeoff? If so, where do you set the mixture before ground roll?

 

I wasn't correct with my statement of being 130 - 150 deg ROP at target EGT, Dave. Your 200 deg is much closer to reality.

Target EGT on my engine is 1230 on cylinder #1 and I peak is normally reached somewhere around 1420 deg. This means I'm at 190 deg ROP when I set target EGT, regardless of the altitude.

Over time, I've learned what the take off fuel flow should be at most altitudes that I generally use, but besides that, the JPI makes setting it precisely rather simple.

[Hondo]

For high DA takeoffs, it is fairly easy and quick to set the mixture for takeoff using fuel flow.

My POH lists the following fuel flows and max power at altitude for best power(100 ROP) and 2700.

Altitude     %Power  Fuel flow

6000             81        13.3

8000             75        12.6

10000           70        11.9 

It also says to use FULL RICH mixture above 75% power, which would apply at 6000 (81%).

If so, it has never been clear to me why it is apparently OK to cruise at that best power setting and fuel flow.

 

If the goal is to set the mixture to produce maximum power for takeoff, what is the risk of setting the mixture to produce maximum RPM?

For high DA, a flight school in New Mexico does a run up at 2200 RPM, leans to max RPM and leaves it there for takeoff.

[Hank]

Our planes achieve Max RPM with the prop lever full forward and enough throttle to push oil through the governor. This should be at less than normal run-up settings. Fixed pitch props are, of course, different.

[DaV8or]

It also says to use FULL RICH mixture above 75% power, which would apply at 6000 (81%).

If so, it has never been clear to me why it is apparently OK to cruise at that best power setting and fuel flow.

 

If the goal is to set the mixture to produce maximum power for takeoff, what is the risk of setting the mixture to produce maximum RPM?

For high DA, a flight school in New Mexico does a run up at 2200 RPM, leans to max RPM and leaves it there for takeoff.

 

Please refer to the detonation map I posted above and also have a look at the GAMI "red box". Then think about that best power mixture while producing 100% power, or even 80% power. It's about preserving the engine long term. Detonation, high cylinder pressure and high cylinder head temps all work towards engine failure. Taking off with anything over 65% power and dialing in the "best power" mixture will be very, very, very hard on your engine. I have always read that best power is somewhere around 10-20 degrees ROP.

[Hank]

My Manual says best power is 100 ROP, best economy is 25 ROP. Your injected engine may be different.

[Hondo]

Hank  

 

For high DA, to copy that NM flight school procedure in the J, I would push the prop full forward with a fairly rich mixture, throttle up to 2200 RPM and

then lean for max RPM.  With DA over 8000, max power is 75% or less. My manual also says best power is 100 ROP and best economy is 25 ROP. 

 

DaV8or

 

The threat of detonation above 75% power at 100 ROP is why I wondered about Mooney showing a best power setting for cruise at 6000 and 81% power.

Best power as defined by Mooney is 100 ROP.  See Lycoming's THE "NEW" OLD LEANING TECHNIQUE, SSP700.

[Super Dave]

I have always read that best power is somewhere around 10-20 degrees ROP.

The APS guys say best power occurs at 75ROP, Lycoming mixture charts show it to be a little richer, Continental charts show it to be a little leaner. My mooney would be on the APS data.