C172 At what DA would you not enrichen before cruise climb?

alfadog

alfadog

Final Approach
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alfadog
I do not have the $$ to finish my IR but I try to do a bit of hood work every few weeks to keep my hand in. This is not really strictly IR but if I am racing along at 2350 rpm and 2000' (3000' DA) leaned in the mighty 172M and am asked to cruise climb to 3000', I would go full rich and full power and about 100 mph. That should give me 500 fpm, I guess.

So at what DA do you think I would not want full rich? Or always full rich at anything under, say, 8000' DA? And if are not going to go full rich, how much do you enrichen and how do you determine that?
 
Do you have an EGT gauge? If so, next time you take off with full-rich mixture at or near sea level in standard conditions, take note of the EGT indication when it stabilizes in a normal climb, probably 500-1000' or so AGL. (If you have EGT probes for all cylinders, be sure to note which cylinder you're looking at; each cylinder will have a different reading. On mine, it happens to be 1290 deg on the #3 cylinder.)

If you lean in climb - at any altitude - to that same temp for that cylinder, then it can't be any worse than a normal sea level take-off, right?
 
Sounds good except no EGT in these club airplanes.
 
I have no idea.....my home drome is at 3400 MSL If I am at 2000 MSL fuel mixture will be butt last on my list of problems...... :yesnod: But in the 310 and the 172 I don't lean until 4.5 - 5k unless density altitude is a factor on the ground.
 
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The POH says 3000. The engine knows no altitude but DA.

On a painfully hot day, you can exceed 3000 DA at sea level.
 
Doesn't the Lycoming manual use 5000' as the starting point for leaning?
 
Running a different engine in the T-41B, (C-172) an IO-360 at 210HP with CS Prop. So it is tough to compare.

There is a chart beside the fuel flow gauge that states fuel flow for DA, full power. Airport is at 2200MSL, and summer temps have DA well above 5000. Full throttle, lean fuel flow for DA, normally about 14gph, 2800 RPM. 500ft AGL, reduce to 2500 RPM, at TPA reduce fuel flow to 11gph, top of green, monitor EGT to not get too hot in climb.

Cruise normally above 9000MSL which gives DA 2000 to 3000ft higher or more. Full throttle, about 18-19MP, 2300-2400RPM, and fuel flow to about 9 GPH. EGT about 1380F.

Another aircraft, O-540, no EGT. I lean for peak RPM at full throttle climb, resetting (leaning) about every 1000ft in climb. Towing gliders, during climb, the mixture naturally gets richer with altitude gained, extra fuel keeps engine cooler, but too much reduces power.

Based on this, and with no EGT in your C-172, once you are at cruise and leaned for peak RPM, and feel the need for a full throttle climb, I would not go full rich, but might increase it slightly.
 
Pilawt said:
Do you have an EGT gauge? If so, next time you take off with full-rich mixture at or near sea level in standard conditions, take note of the EGT indication when it stabilizes in a normal climb, probably 500-1000' or so AGL. (If you have EGT probes for all cylinders, be sure to note which cylinder you're looking at; each cylinder will have a different reading. On mine, it happens to be 1290 deg on the #3 cylinder.)

If you lean in climb - at any altitude - to that same temp for that cylinder, then it can't be any worse than a normal sea level take-off, right?
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At the same time, cooling decreases as you climb due to the reduced air density, so you should not do this without CHT instrumentation. Absent all-cylinder CHT/EGT data, I do not lean for climb below the altitude recommended in the POH/AFM, which for a 172 is, I believe, 5000 DA.
 
JOhnH said:
I'm confused. Would anyone be doing a "cruise climb" at sea level?
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I suppose you would if you're taking off from Death Valley Municipal or Dead Sea International. But a couple of hundred MSL is close enough to 0 MSL to make no difference in this context, and below sea level DA's are common enough in the winter in coastal regions.
 
Why not just jam the throttle and if the engine coughs or quits, quickly push the mixture to the wall. Your passengers will love it. ;)

My Lycoming manual starts talking about leaning at 5000ft. In practice, I'll lean whenever I'm in cruise config at any altitude 2500ft+, and go full mixture when cruise climbing. Can you climb from 8000ft to 10000ft full rich? sure. Is it the most efficient use of fuel? probably not.
 
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murphey said:
Doesn't the Lycoming manual use 5000' as the starting point for leaning?
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It does, but other aircraft/engine combinations may suggest leaning as low as 3000-3500 DA. And keep in mind we're talking normally aspirated -- turbocharging or even turbonormalization changes things a lot and may significantly reduce the amount of leaning you can do.
 
Leaned my 172 anytime over 2500 ft in cruise.being from the east coast never worried about the density altitude for climb,full power.
 
Ron Levy said:
It does, but other aircraft/engine combinations may suggest leaning as low as 3000-3500 DA.
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In the "Normal Climb" sections of the POH:

C-172L: "The mixture should be full rich below 3000 feet and may be leaned above 3000 feet for smoother operation."

C-172N & P: Adds to the above sentence, "[...] or to obtain maximum RPM."

C-172R & S: "The mixture should be full rich during climb at altitudes up to 3000 feet pressure altitude. Above 3000 feet pressure altitude, the mixture can be leaned as needed for increased power or to provide smoother engine operation."
 
JHW said:
is takeoff a euphemism for cruise climb ?
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If you are using full power what is the difference? 10 mph and a couple hundred fpm. I mentioned full power.
 
alfadog said:
If you are using full power what is the difference? 10 mph and a couple hundred fpm. I mentioned full power.
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The difference is probably the oil temperature you're going to get. I was in AZ this summer when it as touching 120F and I had to stop climbing almost immediately after takeoff and drag the sorry butt of a 172 around hillcocks just to keep the forward speed while going well ROP by EGT. Took me more than an hour to climb out of the desert air. Vy? Haha.
 
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