LOP = Low on Pfuel

[PilotDAR]

I flew a planned 160 miles out to remote coast, a hour of touring out in that area, and 280 miles back to the nearest fuel stop. I planned fuel carefully, and allowed for forecast winds. But they came up more and earlier than forecast. 2.5 hours out on my flight inbound for fuel, I could see that my reserves would be well used making up for the increased headwind. My back up plan would be to land on a lake back of my runway destination, and ask my flying partner to fly some fuel back out to me, which he had agreed to do if needed. But, getting to the runway and fuel was certainly the preferred outcome.

So I optimized the power setting, and played around with Lean of Peak. I have never been a proponent of LOP. I always lean 50 ROP, and the engine seems to like it. I think that 50 ROP is simply cheap insurance against engine maintenance. But, I'm not hard over one way or the other, to each their own. However, this flight, I would want every drop at the end, so I may as well start saving it from the beginning. I had the power setting such that the plane was flying at the best endurance speed, and if I wanted to climb, I enrichened the mixture a little. The resulting increase in power would offer a 100-200 FPM climb, then back to LOP when I had climbed as required. I did not touch the throttle or prop.

I carefully emptied three of my four tanks, slipping slightly for the left main, to get as much as I could - 15 minutes after "empty" was indicated. With GPS distance and time, vs the rate of consumption of fuel, I kept setting "halfway points", which if not achieved, would dictate a water landing, and Sat phone call to my friend, who was awaiting if needed.

Within 5 minutes of the airport, and with one more "last ditch" lake to pass yet, I knew I would make it. The remaining tank still had a "bouncing" fuel indication as I turned final, and I could have slipped for a bit of that fuel if I needed to, I was purposefully high. A perfect touchdown, and roll out, ahhh.... As I turn off the runway, with the tail down, the engine stumbled. I had enough to park, in three point attitude, but nothing more, the tank pickup was exposed with the tail down.

Upon fueling, I had had 15 liters useable yet to go, but still much too close for comfort, and out of the question not good had a water landing not been a option. But LOP operation got me through, I was just glad I started it three hours early, that made the difference!

[Chuck Finley]

So you kept digging in your :30 reserve and kept going because you "knew" you were going to make it? Even after passing your last ditch lake so much that after landing your engine stumbled? That seems like unnecessary risk to me ( i am not a brave pilot ) especially if you had plans for a buddy to come drop you some fuel. What if you had to go around for some reason?

Some good ppl have died trying to accomplish what you tried ( and succeeded this time )

For sake of discussion, what was your comfort level/ how were you feeling say the last :30 of flight? Feeling of relief when you landed?

[ZBBYLW]

It's illegal to take off with less than required fuel + reserves. Once you're in the air, airmanship dictates how you use your fuel (going into reserves, changing alternates (or deciding to burn into your alternate fuel and dropping it)). You made your decision which admittedly does sound "rather brave" from my stand point but to each their own.

Perhaps you were flight planning with too sharp of a pencil and when the winds changed by a percentage point or two you were on the wrong line of your fuel burn figures. Consider it a learning experience and if you want to in the future change your personal policy and be a bit more conservative or add a 10% contingency factor then you may find that you don't run into situations like this as much.

The reality is as pilots we deal with risk on a day and day out basis. Evaluate it, and come up with a plan to eliminate (or mitigate) it. Our goal is not to bend metal. Some are more comfortable flying in strong winds, lower ceilings or with smaller fuel contingencies than others. At the end you just have to make sure numero uno is safe (and any pax if you happen to have them).

[I_Drive_Planes]

I have never been a proponent of LOP. I always lean 50 ROP, and the engine seems to like it. I think that 50 ROP is simply cheap insurance against engine maintenance.

According to Mike Busch, 50 ROP is just about the most stressful place to run your engine as it results in the highest CHTs and internal cylinder pressures. LOP operation is easier on the fuel bill and easier on the engine (as long as it will run smoothly). Give this a listen when you have an hour and a half to kill: http://www.eaavideo.org/video.aspx?v=2274677932001

[slam525i]

I had the power setting such that the plane was flying at the best endurance speed

Disclaimer: I'm a low time pilot and I know nothing.

Question: If you're fighting a headwind, doesn't it make sense to fly a little faster than best endurance? As I understand, there's maximum endurance (minimal power setting), and maximum range (minimal gallons / speed), but both would be slower than the ideal speed when fighting a headwind. (Reasoning is that the longer you spend in the air, the longer you're exposed to the headwind, so there's an optimum speed where you're burning a little gas to go faster, but it's offset by the fact you spend less time exposed to the headwind.

Second question: Maximum endurance is the bottom of the power curve (just slow enough you don't start going up the back-side of the curve) and you can "feel for it" as you fly. Maximum range is minimum total drag = best glide speed. (Am I correct so far?) If I am right about the question above, is there a quick rule-of-thumb way to calculate what speed that is? (i.e. the best range speed compensated for headwind.)

[photofly]

Best range and best endurance can be quite far apart in terms of power and airspeed. I hope he set power for best range.

And yes, into a headwind best range airspeed (and power) is higher than in still air. An oft-quoted rule of thumb is add half the headwind. I don't think that has any theoretical foundation, but at least it's easy to remember.

I'm not sure if PilotDAR is presenting this story as a "mea culpa, don't do what I did, kids" or as an example of good pilot decision making.

[Big Pistons Forever]

I think Pilot DAR's post is less about fuel endurance and much more about what happens when you make the effort to truly learn how the airplanes engine and systems work. This combined with accurate flying and maintaining high situational awareness means you can get the absolute most out of the aircraft. Sadly most pilots could not be bothered and thus waste time and money on every flight by not operating the aircraft near its peak performance.

With respect to fuel endurance, personally the older I get the wider the yellow stripe down my back gets. For light aircraft, as a starting point, I want an hour in the tanks when I touch down. However it is important to not only to think of your fuel reserve only as time, radius of action is sometimes just as important and this is heavily influenced by the speed of the aircraft.

For example last day month I did 2 flights. One was in a Aeronca 7AC Champ and then right after that I flew a Cessna 210. One hour of fuel will get you about sixty five nautical miles in the Champ but the same one hour will get you one hundred and sixty five miles nautical miles in the 210. Obviously you have more options as to where to go in the 210.

Things are getting tight for gas on your flight, what to do.

My 02 cents

1) Have a plan "B" ready to go. That is an enroute airport you can easily make

2) Decide, based on the conditions, what the minimum fuel on board at destination has to be and then do not let your margins erode no matter how temping. If you figure you can't make your already decided fuel reserve, go to your plan "B"

3) Use your GPS ! Pay attention to the ground speed and ETE. If you are losing GS then do something, most likely change altitude.

4) Push fuel or push weather, but never push both at the same time.

Finally a couple of tips

1) If you are flying an airplane with no both selection for the fuel, and it has a carburated non turbocharged engine than select one tank near the end of the flight and run it until the engine stops. With low fuel levels it is much better to have all your fuel in one tank. Restarting is no big deal, simply retard the throttle to idle, mixture rich, boost pump on (if fitted) and select the other tank. The engine will immediately restart as is will be windmilling at significant RPM and you simply have to smoothly advance the throttle to the cruise setting. Note: This procedure is more problematical on fuel injected engines as fuel starvation could result in a vapour lock and prevent the engine from restarting. For these engines erratic indications on the fuel flow gauge will give you have a few seconds of warning before it quits, but you have to be paying attention. Never run a turbocharged engine dry in flight.

2) To know how much you have left you have to know how much you started with and how much you are using. For owners it is worth the effort to make a fully calibrated dipstick and I highly encourage owners make a point of estimating how much fuel the aircraft will take every time you fill it up. With a bit of practice you will get surprising good at knowing how much fuel you will have burned. For operators of anything bigger than a really simple 2/4 place fixed gear SEP, I highly recommend you invest in a fuel totalizer.

[photofly]

Maximum range is minimum total drag = best glide speed.

This however, is not true. It would be, if the engine and prop together were equally efficient at all airspeeds and rpm values at turning fuel into useful power. Since the engine and prop are considerably below peak efficiency at the low airspeed at which the airframe is most efficient, you will get better level-flight range at a noticeably faster airspeed than that at which the best gliding range is achieved.

[PilotDAR]

Mea Culpa. I had made the best I could of the fuel available for a very "away" trip. Out to the coast and back, which would take me 300 miles from fuel at the most distant, plus some touring at the coast. A few variables ganged together to eat away my reserves far into my reserve zone. My plan B was having a partner who would fly fuel back out to me if needed, but I would avoid this imposition if possible.

I planned very carefully from the outset of the flight, knowing it would be close, and I told him that too, so he knew to pay attention, particularly if I did not land as expected at the next fuel stop. We had sat phones available, but they do not work in flight. Our speed difference assured that we would not have radio communication in the last hour of the flight, as he would be too far ahead, then on the ground. Interestingly, my last 30 minutes of flight was the least worrisome, as I had the most precise awareness of the fuel I had left, having run 3 of my 4 tanks totally dry. A 15 minute half ball slip kept it running beyond "empty", which from my planning standpoint was 15 minutes more flying than I planned, and that made the difference. My last water landing opportunity was within 2 mile base to the runway, so I was not too worried about an unsafe landing. I did land carrying measurable and useable fuel (not indicating empty), it just quit, when I let the tail down, and unported the tank pick up, so it was very low. Go around contingency? Certainly, though sometimes, if flight is not safe, my go around would be lateral, rather than vertical. I don't need power to steer.

I did consider flying faster for a shorter time in the bigger head winds. The Teal is rather slow and draggy, so the difference in time would not warrant the increased fuel consumption. In a sleek plane though, I agree this would be worth planning.

My flight worked, and was a lessons learned. There were many reasons it might have worked less well (many more reasons than normal). I am a very experienced pilot, and still got myself into the uneasy corner. I could hush it up, and slink away, or I could use a recent, real life example to remind other pilots that you can still get yourself into a corner, so gather your wits and skills, and make the best out of a difficult situation. Sure, landing at an earlier fuel stop would have been wonderful, were there to have been one, but I set out dipped at 16 gallons a side, (so more than 3/4 showing on both tanks) for a flight which the GPS said was 288 miles to the only airport. My choices were few, so I made the most of it. Would I plan that again? Nope! But I will continue to make the most of my planning, and the capability of the plan to make the most safe possible flight.

I'll take a hit for less than ideal airmanship on this one, if readers will take a lesson form what I have presented....

[slam525i]

@PilotDAR

I really appreciate you sharing the story. I definitely took a lesson away from it.

[Mark Rose]

I've been lurking a lot here lately, hoping to learn what I can before I jump in the left seat, and I truly appreciate stories like this that expand my awareness. Thank you for sharing!

[Pop n Fresh]

Ok I have to ask a question. Maybe I'm ignorant because I don't fly enough.

Why did you not get your flying partner to bring fuel to a location an hour or so from home to give yourself a larger reserve?

[flyinhigh]

So did I, which is don't push fuel or the flight.

Engines don't just quit/stumble for no reason, yours did due to lack of fuel. If you think landing with 15 liters of fuel is ok, you are wrong and upon landing your aircraft told you that you are wrong when the engine STUMBLED.

Take your story as a learning lesson that you pushed it way to much and don't do it again. You had a back up plan and failed to execute it because you did not want to inconvenience your friend, yet he is prepared for it as you discussed it.

IMHO, your decision making in this instance was exactly what has killed many a pilots. Piss Poor.

[AirFrame]

PilotDAR, what instruments do you have for determining LOP? EGT on one, or four, cylinders? And is your engine carbureted or injected?

[slam525i]

I fly behind a Lycoming O-360 (or at least I did until I abandoned it away from home last weekend, but that's another story) but I think this question applies to basically any reciprocating engine:

How lean is too lean?

Yes, it gets rough, but the temperatures go down past LOP. Other than discomfort and additional wear from the vibration, will the engine do anything catastrophic or cause permanent damage if the mixture is kept that low? Does that change if the engine is injected? turboed? Big bore? 4 vs 6 jugs? Geared?

I'm asking out of curiosity and because I don't want to try it. I usually just lean to 400-425*F CHT. I can never get more than 2 cylinders past peak before it starts to get rough.

[Pop n Fresh]

Think of what kind of forces a wrist pin and the other end of a connecting rod has to survive without the extra shock of rough running. Just saying, things are probably pretty gnarly if the engine is "vibrating".

[pelmet]

Range and endurance really can be stretched out if you lean properly with reduced power. A few here may remember the guy who flew a Duchess non-stop from Winnipeg to Ottawa. I talked to him about it and he did admit that he passed up an airport with the guages bouncing on empty and landed with perhaps the same amount of total fuel in a twin.

I guess the tailwinds were good in that case.

[photofly]

Other than discomfort and additional wear from the vibration, will the engine do anything catastrophic or cause permanent damage if the mixture is kept that low?

Not according to Mike Busch. You can run it as lean as you like, he says.

[CpnCrunch]

Other than discomfort and additional wear from the vibration, will the engine do anything catastrophic or cause permanent damage if the mixture is kept that low?

Not according to Mike Busch. You can run it as lean as you like, he says.

Not quite.

LOP operation is fine for any engine that can run smoothly in that configuration. However, LOP operation requires fairly even mixture distribution among the cylinders. That's sometimes difficult to achieve in a carbureted engine

http://www.avweb.com/news/savvyaviator/ ... 162-1.html

Also:

By the way, the roughness associated with excessively lean or rich mixtures is the result of cylinder misfiring. Due to induction distribution irregularities, one cylinder will nearly always lead the others in becoming too lean or too rich, and will misfire, producing a momentary unevenness in engine rhythm, which we call roughness. Such roughness constitutes no immediate harm to the engine so long as it is not continued for any length of time

http://flighttraining.aopa.org/students ... xture.html

I'm not sure you really want one of your cylinders to be misfiring for a long time. Apart from potential damage, I can't imagine that is the most fuel efficient way to operate.

[photofly]

I take your point. And no, it's demonstrably very inefficient. Airspeed starts to drop off quickly as one cylinder loses a lot of power. But that's ok - if you're looking for peak efficiency you won't find it if the engine becomes significantly rough, so there's no incentive to operate there for any period of time. It's not the excessive leanness that generates the roughness problem, it's uneven mixtures.

However - if you can run evenly very lean, then it is possible to be too lean for best efficiency.

PS - the advice not to run lean/rough for an extended period of time comes from AOPA, not from Mike Busch. I remember he wrote something (different) on the subject, I'll see if I can find it.

[eh3fifty]

However, if you can run evenly very lean, then it is possible to be too lean for best efficiency.

Agreed. This is why people who run LOP usually get high tech engine monitors and precision fuel injectors.

High EGT isn't what hurts your engine, high CHT does. Avoid the EGTs that produce high CHTs - namely 50 degrees C ROP.

[PilotDAR]

if you're looking for peak efficiency you won't find it if the engine becomes significantly rough, so there's no incentive to operate there for any period of time. It's not the excessive leanness that generates the roughness problem, it's uneven mixtures.

Yes, this is my thinking. My O-360 is carburetted, and has a four cylinder EGT scanner. I cannot get the four cylinders as close as I would like in mixture, so any leaning, or LOP is a compromise. Though I'm not an LOP fan, I'm not a big detractor either. But, in this case, I preferred LOP to running out of fuel.

Yes, it was an example of a poor situation to put myself in, hence the presentation here for an "I learned from this" example. I would surely rather have not been in that situation, but I had passed the point of having a choice about it. I recognized a not good situation developing from more than three hours back, and used that time to optimize everything I could. It is certain that doing that made the difference, and I landed at my intended fuel stop, carrying useable fuel - just much less than I would have liked.

[photofly]

Have you tried a fraction of carb heat? Busch et al say it helps fuel vaporization and getting an even mixture.

[iflyforpie]

This is why I'm glad I fly a 150 knot airplane with 8 hours of endurance never more than an hour away from SEVERAL diversionary airports with the BC Ministry of Forests picking up the fuel tab. 100F rich, no problematic probes to chase or analyzers to make me nervous if one value is different from another, no burned exhaust valves or blown jugs because I did not make my sacrificial offering to the Bob Hoover of Aviation: Mike Busch.

[photofly]

He doesn't ask more than a couple of chickens and the occasional goat every full moon; it's not too onerous.