P

pauldan181

Well Known Member
After flying around the upper midwest for 60 hours since first flight I decided to make the trip to New Mexico last Sun. Upon arrival at my destination I did my normal pattern routine including pushing up the prop and mixture. After extending downwind a bit to allow a Cessna full of jumpers to take off, I needed some throttle on short final and the engine stumbled and popped for a few seconds before responding. DA was over 8K feet. This carburated O-360 hasn't missed a beat since it came out of the box.

Question is, should I just leave the mixture where it was in cruise all the way to touchdown? I was at 10.5K feet leaned 50 deg. ROP. Also how are you high DA C/S prop guys handling the mixture on take-off?

Paul Danclovic RV-8A

Still learning how to operate this machine
 
Hello Sir,

Lean at take off and climb at high altitudes for an EGT reading of:

Sea Level EGT Reading + 25 Deg. F / 1000' (Or 1350, which ever is less)

If the full throttle sea level EGT readings are unknown, the approximate values can be derived using the following formula:

Sea Level EGT at Full Throttle = Peak EGT reading at 70% power -300 Degrees F.

During descent maintain the same leaning method used during cruise (other than the power recovery method). The manifold pressure will need to be reduced during descent to maintain proper power levels for a lean mixture.

When entering a pattern for landing, richen the mixture (as much as possible) for a possible full throttle go arround.

Do you have a multi-point analyzer that will allow you quickly (visually) identify how far from peak EGT you are? A system like that makes this process a lot easier.

Good luck!

Matt Sharp
 
Last edited:
Caution! Full Rich NOT GOOD on All Plane at High DA

Mathew Sharp said:
(snip
When entering a pattern for landing, richen the mixture (as much as possible) for a possible full throttle go arround.
(snip)
Click to expand...

Full rich on some planes at high density altitude will yield black smoke, coughing, sputtering, and low power, so be careful!

The 172 I learned on was like this. Full rich was for under 2500 ASL and below only.


Hans
 
This is a well timed question. We're headed into Taos or Santa Fe (Depending on DA) at the end of July and I've been wrestling with the same question.

Not having the full power at Sea Level is one thing, but at least your prop and wing is operating efficently. However it's a completely different thing when your prop and wings are struggling to find enough air molecules to do their job. Low, slow, and restricted power is recipe for disaster at high DA's.

We're bring a Piper Arrow (Non-Turbo) and the POH says mixture full rich at landing - lean on Take-Off. I have a hard time believing this isn't an oversight in the POH in this case. I've pretty much convinced myself to keep it lean on the approach. If I have to go around 20ft AGL and rapidly approaching stall speed, I want the power to be there.
 
Last edited:
I also think this a timely discussion. I have recently been reading about using the carb heat at high DA. Can anyone expand on this idea of applying carb heat to increase performance when flying around high DA airports?
 
nucleus said:
Full rich on some planes at high density altitude will yield black smoke, coughing, sputtering, and low power, so be careful!

The 172 I learned on was like this. Full rich was for under 2500 ASL and below only.


Hans
Click to expand...


"When entering a pattern for landing, richen the mixture (as much as possible) for a possible full throttle go arround."

This statement was intended to be very aircraft specific. It was not meant to read: "full rich". Even on our field at 3500' we can't be full rich. The equations mentioned are science supported and if you do them you will identify the mixture point you should target. ;)
 
a different perspective

I learned to fly in Boulder, CO and recently moved to Fairbanks, AK.
I found a 172 to to rent and yesterday was the first time I've ever flown with the mixture knob firewalled...

All of the rentals I flew in Boulder had some sort of leaning procedure built into the runup as part of the before takeoff checklist.

Basically the first thing you did during the runup was to back out the mixture knob and watch the RPMs go up until they peak and start going back down, then you turn the knob back in to get back to peak and normally give it another 1/2 or full twist in.

I think most of the owners and FBOs add that last richening part to keep inexperienced people from flying too lean at high power.

To answer somebody's question about carb heat: the carb heat air is warmer and therefore less dense so it enriches the mixture because the amount of fuel stays the same but there is 'less' air (same volume but fewer molecules) . So the ratio changes (more rich) because you are mixing the same amount of fuel with less air.

Another thing to keep in mind is leaning for taxi. Normally on carbed airplanes you would start the engine at full rich and then pull out 3/4 inch or so once it is running and on injected planes you would jut not go all the way to full rich once the engine starts.

Most people just guess at the taxi mixture setting. I don't think you'll hurt anything by being slightly too lean or too rich at such low power settings but if you are way too rich then you might foul your plugs.

I never went from sea level and landed up high so I can't help with the best way to set the mixture for landing, although if you need to go around you don't want to be full rich.
 
I live in Albuquerque, NM. In 172's and T-41's (A 172 with 210hp), I usually pull the mixture knob out about 3/4" for takeoff and landing. This amount was found by using the RPM method mentioned in another post above. If you're coming into a high density altitude airport, definately pull a bit of mixture. It's better to be rich than lean, but everything will work better if you're not full rich.

Guy
 
lcnmrv8r said:
Full rich will usually be too much up there. I usually just richen up a 1/4 inch or so on decent. What will you be cruising at? I find that often this time of year I end up cruising LOP at 8.5k or 9.5k. With DA at the destination not being much different. So it doesn't usually take much to richen it up.
Have fun and Get there early.
Click to expand...

Hi Seth,

Even if it's forecasted for VFR, we'll probably be coming in IFR around 10,000 MSL (~2500 AGL). I have absolutely '0' mountain flying experience and want to do everything I can to stay out of trouble in case the Wx takes an unexpected turn. It's a whole lot easier to be IFR going into the Mountains, than it is to search through paper work and file in the middle of a descending ceiling and rising terrain. This is one of those situations where I don't mind being called a pansy. That's synonymous with the word 'smart' for a mountain rookie like me. :D

It shouldn't take that much of push on the mixture knob to richen it for a 2500' decent to land.

I'm glad I wasn't off base for not taking the POH at it's word. Sometimes common sense needs to replace the words (or at least recognize the omissions in the manual).
 
Leaning Heresy?

I lean as soon as I start the engine at any altitude. I keep it lean through the taxi until TO. I may need to enrich it some for run-up. It helps prevent lead deposits on the exhaust valve stems. This practice seems to be quite standard with a lot of folks.
I was at a CPA (Cessna Pilots Association) seminar on the 172 and John Frank was there. He runs LOP (also getting to be common) at altitude and then does not go back to "rich" for the descent unless the engine starts to run rough. Then he enriches it only enough to make it run smoothly. His take is that if it will run lean in the RPM range of the taxi why go rich at the RPM's seen in the taxi RPM range (i.e. on the descent).
I have followed his plan since hearing of it without any difficulty. I use less fuel; the engine runs smoothly all the way to the runway and through the taxi to the hanger. The key is to REMEMBER it is lean if you need to do a go around and push it to rich (full rich in the low lands of Houston and maybe to a predetermined position if you fly into the high country of this thread). This takes practice as, initially, it is not automatic.
I submit this without recommendation but as food for thought as fuel prices eat our lunch.
 
Base line leaning

Matt Sharp has it right on. You need to be aware of these numbers, try them, and do some EP's (Emergency Procedures) to insure they are viable for your set up.

The 1350 number works for me. You can use this to lean in a climb and descent. At the cost of fuel, disciplined leaning can save you money. During the back side of your 40 hour fly off work on the mixture position at 1000' intervals. Then when you get in the high DA situations you'll be pretty close. This will also be important when starting at high altitudes.

In the interest in safety in high DA's, keep it on the ground longer on takeoff and carry a few more knots on landing. During climb use 120 knots and a use what it gives you. Don't rush it.
 
RVbySDI said:
I also think this a timely discussion. I have recently been reading about using the carb heat at high DA. Can anyone expand on this idea of applying carb heat to increase performance when flying around high DA airports?
Click to expand...

I do know of planes that have "crashed" because the carb heat was left on during a go-around at high density altitude airports.

In regards to carb heat, I go the Piper/Lycoming way of thinking. Only use carb heat if you think you need it, and not as normal proceedure for landings. Afterall, the Lyc has a heated oil sump that the carb attaches to. The Continental powered Cessnas didn't. And that's the basic reason for Cessna using carb heat in it's POH for landings.

And BTW, since we operate out of a 4600' msl airport, it's lean right after engine start, lean again before takeoff, and adjust with altitude. Richen up some for landing, but never full rich.

L.Adamson
 
I think you misunderstood me. I'm talking IFR in VMC. If it's known IMC, there's absolutely no chance that I'd go in there in this airplane.

I'd rather be on a known flight plan, on a known route, at a known location, talking to a controller, and hopefully following a (guinea pig) plane who's 30 miles ahead of me on the same airway. Then if the weather does turn south I will either know about it (because of the guinea pig) or simply transition to my instruments and fly the flight plan as required. Sure there might be updrafts and downdrafts, but at that point your #1 priority is to avoid a CFIT accident. Flying the IFR flight plan is a much better strategy than trying to feel your way through a range of mountains.

It just makes too much sense when you're looking for a way to minimize some of the associated risks for a rookie on a mountain flight. I'll be doing everything I can to add a safety margin to it and only one of those is using an IFR flight plan.
 
LAENING FOR TAXI

morlino said:
I learned to fly in Boulder, CO and recently moved to Fairbanks, AK.

Another thing to keep in mind is leaning for taxi. Normally on carbed airplanes you would start the engine at full rich and then pull out 3/4 inch or so once it is running and on injected planes you would jut not go all the way to full rich once the engine starts.

Most people just guess at the taxi mixture setting. I don't think you'll hurt anything by being slightly too lean or too rich at such low power settings but if you are way too rich then you might foul your plugs.
Click to expand...

I LEAN AT 1000 rpm. I then taxi at 500 to 700 rpm. This way you will never forget to adjust the mixture before take off.... You will catch it during your mag check.:cool: And if not, at least during the first 100 ft of your take off.:(
 
I fly a PA28-140/160 from a field at 6550' elevation. Running up before takeoff at 1800 rpm, I lean to best rpm and then past until it stumbles, richen mixture until it returns to that best rpm again and about 1/4 inch richer and I take off.

If the destination is at a significantly lower elevation, I richen it slightly once in the pattern. One time I did not do this and the engine stopped just seconds after touchdown...! :eek:
 
You don't lean at 1800 rpm? do you! You mean you lean at FULL RPM for best rpm. And then add about 1/4 inch rich. Right?
 
gasman said:
You don't lean at 1800 rpm? do you! You mean you lean at FULL RPM for best rpm. And then add about 1/4 inch rich. Right?
Click to expand...

Up here in mountain country, we certainly do lean at 1800 (or there abouts) rpm during the runup before takeoff. At that point, a Piper's mixture knob on a throttle quadrant might be close to half down for takeoff.

L.Adamson

My own checklist: Airport elevation 4610' msl.

6. Mixture …………………..…………………RICH (BELOW 3000’)
7. Throttle ……………………….……………...…………..1800 RPM
8. Mixture ……………….….…ADJUST FOR DENSITY ALTITUDE

edit again: Lycoming recommends 1800-2000 rpm for the runup. 2000 rpm is max.
 
Last edited:
You must log in or register to reply here.