Initial climb with a constant speed prop

... But flame propagation, the actual time delay until the fire begins burning well, varies with mixture. have ever spent.

I have never heard this explained this way before. Thank you!

Was this from work experience knowledge or from that class you mentioned? I’d love to refer my students to something on the web they can research.


Sent from my iPhone using Tapatalk
 
@William Pete Hodges - so pulling the black and blue knobs to lower CHTs, let’s say during a climb, worsens longevity due to peak cylinder pressure? How does the engine know the spam can is in a climb vs cruise, other than maybe less cooling air during climb, assuming no cowl flaps? The info you provided seems contradictory. I haven’t taken that course, so just asking.
 
Thanks to all the guys spreading the knowledge from the GAMI guys. I just didn't have the time to type it all up and explain it.

Some people will still say oversquare is bad because that's the way they learned and no amount of hard data, test stands or explaining will change it. Just gotta let those guys go (usually to the gas pump because they insist on ROP ops too...) :D
 
ive talked to the people at lycoming and they say that in a NA lycoming there is no way to exceed max cyl pressures at pretty much any settings. bottom line is operate your motor the way the designers intended it to be operated. lycoming and continental have volumes of data available on there web sites on engine operation. yes, your POH might be a POS, but the engine makers have lots of data to look at.
 
After takeoff I retract flaps and reduce RPM to reduce noise while still over the runway or once obstacles are cleared. I remain at full throttle until I reach cruise altitude.
 
As mentioned the over square rule of thumb is just a guideline if you don’t know any better or it is not practical to look up that actual engine data. When sometimes flying as many as 8 different airplane types in the same day it doesn’t really make sense to look all the allowable power settings for a 45 minute flight in each plane, and then it will be different in the next plane you fly. So just using a conservative 25/25, 24/24 setting is handy. If you fly the same plane regularly or for a long distance then you should probably learn the acceptable power settings and which power settings you and the airplane like.

CFI’s teach this rule for just this reason. They assume you have done your homework and know what are acceptable power settings. But if you haven’t, then the over square rule works. If they are checking you out in a new plane they can either teach you the conservative over square rule or have you dig deeper into the airplane or even engine manuals (did you know you can get Lycoming and Continental Engine Manuals, even if your POH doesn’t have much data). But if you a have pilots certificate, you should already know how to read a POH.

BTW +1. For pulling the prop back early if you don’t need max performance, for noise reductions. Is a bit annoying when I hear the guys taking off form a 5000ft foot runway from over 5 miles away. I will often set my prop before the take off roll and just take off in my climb configuration if I don’t need a max performance take off. Also requires less engine adjustments after takeoff.

Brian
 
Wait wait... let me get this straight.... you fly over-square at 32/25 and then 30/25 all the way to cruise?? And your engine hasn't exploded into a million pieces????

But we were all told when MP > RPM the result is massive rifts in the space-time continuum and the release of satan's henchmen to claim the Earth as their own... How has this not happened????

I thought I was the only one who thought this was odd.
 
I thought I was the only one who thought this was odd.

just to point out:

my TIO-540 innards aren’t made of different metals than the IO-540 of the non-Turbo cousin.

point being: if me taking off at 36”/2575 doesn’t cause my engine to grenade, probably you running your non-turbo a little high on power and lower on RPM should not cause you immediate concern.

this is not meant to be advice nor am I promoting you to disregard any manufacturer instructions.
 
I have never heard this explained this way before. Thank you!

Was this from work experience knowledge or from that class you mentioned? I’d love to refer my students to something on the web they can research.

Sent from my iPhone using Tapatalk

This came from the advanced engine class (GAMI calls it the Advanced Pilot Class, or Engine Management Made Easy) it is now available as an online interactive class with loads of animated motion drawings. When I took it it was 5? Parts, and the first part was free. I paid up when I realized how in depth the class was. I enjoyed every minute of it.
 
Connies with the Turbo Compound engines took off at something like 60”/2900 RPM and they were running more than 3,000 hours between overhauls.

RTFM. Just because a CFI is too lazy to learn or teach systems to the level needed is not a valid reason to climb slower.
 
@William Pete Hodges - so pulling the black and blue knobs to lower CHTs, let’s say during a climb, worsens longevity due to peak cylinder pressure? How does the engine know the spam can is in a climb vs cruise, other than maybe less cooling air during climb, assuming no cowl flaps? The info you provided seems contradictory. I haven’t taken that course, so just asking.

Okay. At maximum power the WOT setting provides extra rich mixture which delays flame propagation and reduces stress, compared to backing off the throttle some which takes away the extra richness. As you climb the MP reduces with altitude so when you get to cruise altitude you can leave the throttle wide open and control power with RPM and Mixture. I cruise my Mooney WOT and 8 GPH and 140 kTAS. I usually cruise 8500-13500 depending on circumstances.

If you elected to level off at low altitude and stay WOT at max RPM and full rich the sustained high power would cause the cylinder heads to heat up, and get too hot. If you lean some the heads will heat up faster. If you lean to minimum propagation time they will heat up really fast. During all this ROP leaning the power produced will be about the same but the engine stress will go up dramatically. As you lean further to Peak ET and beyond you enter the LOP region as ET falls.

Not all engines will run well LOP, but assuming the engine continues to run smoothly, here's what happens next.
As you continue to lean engine stress is dropping because Flame Propagation is being delayed, but power is also going down as well further reducing engine stress. From Peak ET to about 100F LOP the power produced is about 14.9 or 15 HP per GPH. That means 10 GPH is about 150 HP.

Look at the chart. On my IO-360 9GPH at 50F LOP is 134 HP or 67% load. At 50F LOP this is safe for continuous operation, but at peak ET the cylinders will get too hot, as shown by running inside the Red Fin. The power is the same and the GPH is the same, but at Peak ET there is less air going through the engine, making the mixture less lean with shorter flame propagation time. At WOT increasing RPM will run more air through the engine and at the same 9GPH will make the mixture leaner, producing the same HP with less stress while keeping the cylinders cool. This illustrates how increasing RPM reduces stress on the engine.

Now at the full power setting it won't be possible to run continuously and prevent engine damage no matter how rich you go. Less stress buys you more time before backing off the power to keep the cylinders cool. If you are climbing with a naturally aspirated engine then power is reduced automatically as you climb. But IF you are not climbing and you can run lean enough the power will reduce to a point where the engine can run continuously. That is IF the engine can continue to run smoothly in LOP mode as lean as you need to run to reduce the power. In this regard the mixture control by itself has the capability to produce any power setting from zero to full power.

Clear as mud, right?
 

Attachments

  • RED FIN COLOR DISCUSSION.jpg
    RED FIN COLOR DISCUSSION.jpg
    253.4 KB · Views: 13
I know I have presented a lot of information, and I apologize for being so long winded. I hope I helped but I'm not sure if all the questions have been answered. It took me about 10 days to do the course online. Before I signed up I spent 2 weeks off and on researching LOP operations and I found some really good information, including the Red Fin and a really great video on LOP by Martin Pauley. It took me another two weeks or so to figure out how to add the Fuel Burn curves to the Red Fin chart, and it took me a week to figure out how to get excel to graph it and print it.

The course doesn't mention the Red Fin, instead they discuss the Red Box. The Red Box is easy to relate to and understand but the size of the Red Box varies with load which to me was an undefined variable. The Red Fin is much more descriptive but none of the material had the fuel burn rates printed on the chart they way I have done. I started analyzing the Red Fin and it seemed implied that as you leaned or richened the aim point would move vertically. But if the power is changing as well as the mixture the aim point cannot move vertically, it moves in a curve. That's why I modified the chart.

I bought my Mooney for several reasons but efficiency of travel is high on my list. That means during cruise trying to get the most MPG at relatively fast airspeed without damaging my equipment. Years ago it was put to me that if you can't explain it mathematically then you don't fully understand it yet. I needed to fully understand ROP LOP and engine management before I was willing to fly differently than I was before. Right now I still limit my lean operations to 8 GPH. I installed a new engine monitor system this year and when I get used to it I might use higher fuel burns. We'll see.
 
If you elected to level off at low altitude and stay WOT at max RPM and full rich the sustained high power would cause the cylinder heads to heat up, and get too hot. If you lean some the heads will heat up faster. If you lean to minimum propagation time they will heat up really fast. During all this ROP leaning the power produced will be about the same but the engine stress will go up dramatically. As you lean further to Peak ET and beyond you enter the LOP region as ET falls.

That's going to completely depend on how good the cooling is. It's near impossible for me to get over 350 degrees even at WOT at 1000DA. My engine monitor says the opposite of what you are saying here.
 
That's going to completely depend on how good the cooling is. It's near impossible for me to get over 350 degrees even at WOT at 1000DA. My engine monitor says the opposite of what you are saying here.
Every airplane is different and yours may be an exception. I'm only saying most aircraft engines as installed cannot sustain full power continuously. Most of them are going to heat up, especially if you lean towards minimum propagation time. Its the concept that I'm trying to convey. If your cooling system is really that efficient I wish I had it on my bird too.
 
Anyone have a good source for Which engines/fuel systems enrich the mixture when ran WOT?
I have heard this before and have observed it one some engines by watching the EGT. But other engines don’t seem to have this feature or it isn’t working properly.

My observation is that usually engines with fixed pitch props tend to demonstrate the mixture enrichment at WOT while most engines with a Constant speed prop do not. Is this why we normally don’t reduce throttle on fixed pitch props until we level off for cruise vs. constant speed props where we often reduce throttle shortly after take off.

Brian
 
The OP asked about prop rpm...I run 2650 rpm on takeoff, then 2300 rpm for rest of flight...E-225 Continental on F35 Bonanza.
 
I learned to fly a constant speed prop airplane about 18 months ago and at that time my instructor basically said you take off with the prop full forward and full power similar to a fixed prop. Then he explained when you about 1000’ up or to where you could glide back to the airport if you had to, go ahead and adjust it to 25/25 for the remainder of the climb and then 24/24 for cruise. I have an IO-360 in my plane.

Recently I was discussing this with others and we have mixed opinions. Some will climb all the way with prop forward and full throttle and others will do 25/25.

Opinions?
JD, we are a few days and 2 pages into this conversation. Did you get the answers you were looking for?
 
Back
Top