Fuel management

[Ulysse]

58 minutes ago, PT20J said:

many autopilots have fuel imbalance limitations

How would the autopilot know? 

[PT20J]

2 minutes ago, Ulysse said:

How would the autopilot know? 

The unbalance causes the airplane to be out of trim laterally. This causes the roll servo to have to apply a constant force to raise the heavy wing to fly level. The autopilot computer monitors this. 

[Ragsf15e]

11 hours ago, Ulysse said:

yes, I have Garmin EIS on all 6 cylinders 

**Ahh sorry, didn’t see you had a turbo.  It’s still not hard to do LOO but one of the turbo folks will have to help you out.  Fuel injected NA is pretty simple.  

Well it might not be too hard to learn the LOP thing then.  Climb to about 7500’ or higher the first few times you try so you’re below ~65% power.  Maybe about 20”mp and 2500rpm.  You won’t hurt the engine with any mixture setting below 65%, so this allows you to play with it.  You can then just lean slowly while watching the egts.  They will all go up and “peak”, then go back down, but not exactly at the same time.  When the LAST one hits peak, lean a smidge more until you’re about 10 degrees below peak on the lean side on that last one.  Done.  Should be ~9gph.

To make it easier, the garmin eis will have a lean find mode.  Use the pilot’s guide to see what buttons to push, but it will monitor your egts coming up and peaking.  When the last one peaks it will flash or highlight it.  Easy.

Edited July 1, 2021 by Ragsf15e

[carusoam]

For lessons on LOP with the M20K…

There are a few threads around here…

My favorite author on the topic is one @jlunseth….  See if you can find those threads…

The TC’d Continental is a great engine for LOP…

Best regards,

-a-

[jlunseth]

1. Let’s remember that the OPs aircraft is an Encore, a turbocharged K, not a normally aspirated aircraft. It can make 100% power in to the low 20s. So you can’t manage the power to 65% simply by flying up to an altitude where ambient pressure is limited and therefore MP is limited. Induction pressure must be managed with the throttle.

2. The example about autopilot limitations is from a Garmin manual. I have a KFC200. It has no problem at all flying with one tank full and one tank empty. I routinely do what is suggested here, use one tank for takeoff and climb, then switch to the second tank and use that for cruise. That way, you have a very good measure from the fuel flow meter, how much fuel is in each tank. Switching back and forth frequently while trying to use nearly all the tank capacity is a very good way to not know how much fuel is in which tank.

3.  If you are really going to fly until you have used 60 gallons, there are several things to be aware of. In my 231, full usable fuel appears to be when the fuel reaches the upper ring in the fuel neck. The Ks have a flapper or antisiphon valve. Whoever fills the tank must use the fuel nozzle to hold that flapper open. If that is not done, there will be fuel resting on the flapper in the filler neck and it will look like the tank is full, but it can be less than full by as much as ten gallons missing because the flapper was not held down.

4. It is very important to properly fill the tanks. It is not enough, if you are going to run the tanks that low (to 60 out of 75 gallons), to just pump in fuel even if you hold the flapper down. You need to gently rock the aircraft as you fill, which moves air across the wing and let’s it escape so you can actually fill the tanks. That technique allows about 3-4 more gallons per side to be onboarded. Conversely, if you don’t do it, that is 3-4 gallons out of your theoretical usable fuel load that is not on the aircraft when you takeoff. The usable in one tank in my aircraft is 37.5, but I have run a tank dry at 33 gallons, if you don’t fill the tanks properly and to the upper rings, that is about what you have. 

5. I would test all this out before flying to 60 gallons. In other words, I would fill the tanks and run one dry to know, with a particular fill technique, how much fuel is in one tank. It can be quite a bit less than 37.5 . What is in the Pilot Operating Handbook does not matter much, it is what is actually in the tank that matters.

6. Do not run a tank dry on a K at a high altitude. You risk being unable to restart if the turbocharger spins down, or you may have to descend several thousand to restart, and if this occurs over mountains you may not have the room to do that. I would not run one dry above 10k. Certainly, if you switch tanks fast enough, it might work. But if you fail to switch instantaneously you have a problem.

[jlunseth]

One more thought. Probably out of an excess of caution, the fuel gauges I have flown with all start red lighting you when there is 10 gallons left, and that can be ten gallons in one tank with a full load in the other. I don’t know the warning system in the Encore. I can tell you that my current setup will give me a “Low Fuel” annunciation with as much as 47 gallons on board, ten gallons in one tank and 37 in the other. Just be prepared for the pucker factor. As I have said before, test your fuel flow meter and adjust it if necessary so it is very accurate. If you are going to use most of your fuel capacity, it is the most reliable way to know within a tenth of a gallon how much you have used. The gauges are hopeless at that level of accuracy.

[steingar]

If I had to cut things that close on a routine basis I think I'd get myself a different airplane...

[Ragsf15e]

1 hour ago, jlunseth said:

1. Let’s remember that the OPs aircraft is an Encore, a turbocharged K, not a normally aspirated aircraft. It can make 100% power in to the low 20s. So you can’t manage the power to 65% simply by flying up to an altitude where ambient pressure is limited and therefore MP is limited. Induction pressure must be managed with the throttle.

2. The example about autopilot limitations is from a Garmin manual. I have a KFC200. It has no problem at all flying with one tank full and one tank empty. I routinely do what is suggested here, use one tank for takeoff and climb, then switch to the second tank and use that for cruise. That way, you have a very good measure from the fuel flow meter, how much fuel is in each tank. Switching back and forth frequently while trying to use nearly all the tank capacity is a very good way to not know how much fuel is in which tank.

3.  If you are really going to fly until you have used 60 gallons, there are several things to be aware of. In my 231, full usable fuel appears to be when the fuel reaches the upper ring in the fuel neck. The Ks have a flapper or antisiphon valve. Whoever fills the tank must use the fuel nozzle to hold that flapper open. If that is not done, there will be fuel resting on the flapper in the filler neck and it will look like the tank is full, but it can be less than full by as much as ten gallons missing because the flapper was not held down.

4. It is very important to properly fill the tanks. It is not enough, if you are going to run the tanks that low (to 60 out of 75 gallons), to just pump in fuel even if you hold the flapper down. You need to gently rock the aircraft as you fill, which moves air across the wing and let’s it escape so you can actually fill the tanks. That technique allows about 3-4 more gallons per side to be onboarded. Conversely, if you don’t do it, that is 3-4 gallons out of your theoretical usable fuel load that is not on the aircraft when you takeoff. The usable in one tank in my aircraft is 37.5, but I have run a tank dry at 33 gallons, if you don’t fill the tanks properly and to the upper rings, that is about what you have. 

5. I would test all this out before flying to 60 gallons. In other words, I would fill the tanks and run one dry to know, with a particular fill technique, how much fuel is in one tank. It can be quite a bit less than 37.5 . What is in the Pilot Operating Handbook does not matter much, it is what is actually in the tank that matters.

6. Do not run a tank dry on a K at a high altitude. You risk being unable to restart if the turbocharger spins down, or you may have to descend several thousand to restart, and if this occurs over mountains you may not have the room to do that. I would not run one dry above 10k. Certainly, if you switch tanks fast enough, it might work. But if you fail to switch instantaneously you have a problem.

Yeah I missed that in the thread/profile.  My bad.

[Will.iam]

3 hours ago, jlunseth said:

One more thought. Probably out of an excess of caution, the fuel gauges I have flown with all start red lighting you when there is 10 gallons left, and that can be ten gallons in one tank with a full load in the other. I don’t know the warning system in the Encore. I can tell you that my current setup will give me a “Low Fuel” annunciation with as much as 47 gallons on board, ten gallons in one tank and 37 in the other. Just be prepared for the pucker factor. As I have said before, test your fuel flow meter and adjust it if necessary so it is very accurate. If you are going to use most of your fuel capacity, it is the most reliable way to know within a tenth of a gallon how much you have used. The gauges are hopeless at that level of accuracy.

Yea +1 on the factory gauges not being accurate. Flew 1.8 hours on right tank and the fuel guage went from showing 30 gallons to 15 but when i landed the wing guage showed 0 but would move when bumping wing. When i opened up the fuel cap and looked in the wing guage was accurate and the fuel guage on the panel still showed 15 gallons. 

[Ulysse]

Thank you @jlunseth for all the advice. I think, given my low experience, that I will make a fuel stop until such time as I know my plane better and get more accustomed to this specific route

[Ulysse]

On 7/1/2021 at 7:47 AM, carusoam said:

My favorite author on the topic is

thank you for calling jlunseth !

[jlunseth]

4 hours ago, Ulysse said:

Thank you @jlunseth for all the advice. I think, given my low experience, that I will make a fuel stop until such time as I know my plane better and get more accustomed to this specific route

I think that is a very wise decision. Your tanks may hold more than mine, I don't know, the different models have different capacities. But with my 75.6 gallon capacity and if I am at an altitude where I can run LOP, I have more than six hours of fuel. I nevertheless, very rarely plan on flying more than 4 1/2, and never more than 5. The reason is that the tank gauges are not that good, the red lights start coming on and even if they are inaccurate the pucker factor goes up, and then unless you have used perfect filling technique, you don't have as much fuel in the tanks as you thought you have. That is not a good thing to find out if you are over the Alps, or in our case the Rockies. Besides, my bladder gets very unhappy. 

Good flying, stay safe.

[CoffeeCan]

1 hour ago, jlunseth said:

I think that is a very wise decision. Your tanks may hold more than mine, I don't know, the different models have different capacities. But with my 75.6 gallon capacity and if I am at an altitude where I can run LOP, I have more than six hours of fuel. I nevertheless, very rarely plan on flying more than 4 1/2, and never more than 5. The reason is that the tank gauges are not that good, the red lights start coming on and even if they are inaccurate the pucker factor goes up, and then unless you have used perfect filling technique, you don't have as much fuel in the tanks as you thought you have. That is not a good thing to find out if you are over the Alps, or in our case the Rockies. Besides, my bladder gets very unhappy. 

Good flying, stay safe.

I agree with all the above. Folks can call me a wuss if they like, but I've found over the years that my sphincter tone goes waaaaay up any time I get a low fuel annunciation, whether in my Toyota Tundra or in my 231. I have also found that my aeronautical decision making process is suspect when I have high sphincter tone, and it's even worse when I also add high detrusor muscle tension (full bladder). Chalk me up as yet another Mooney pilot who on long XC's does a full fuel top-up (with wing rocking) prior to takeoff, then runs the first tank down 10 gals, then runs the remainder of the leg on the other tank. I have never run either tank dry, and don't intend to. 

I rarely take either tank below the 9 gallon hashmark on my panel gauges. If I have burned 57.6 gallons of fuel (indicated), it's time to land and stretch my legs and unstretch my bladder. 

I decided some time ago that on any XC flight projected to last longer than 4.5 hours it makes sense to plan a fuel stop somewhere around the midpoint. The Foreflight map menu has an excellent setting for telling me best fuel prices on my route, and that feature works very well on the ground with good Wifi. It doesn't work so well in the flight levels, so I consult this in advance whenever possible.  My wife and I have discovered some wonderful little airports and towns where there's cheap fuel, a great diner, and friendly people by following this method. And my physiological stress gauges (sphincter and detrusor) remain happy. 

[Warren]

LOP can help extend your range.  If you are not already doing this, you should add it to your repertoire.  10-10.5 gph at altitude gets you 180+ KTAS.

Running a tank dry ensures you use all the fuel in that tank.  You do need to do this to confirm your actual usable fuel on each side.  At altitude a restart can be an issue - my 231 will restart at 18000 (never tried higher), the manual says you may have to descend to 14000 to successfully restart.  Also, best to switch to ROP if you are running a tank dry - you will get some stumbling and have some notice as you run out of fuel.  I have done this multiple times over 20000 and not had an issue.  When LOP and you run out of fuel, the engine goes from running to windmilling almost instantly - much more exciting than when ROP!

[carusoam]

Great turbo / restart experience shared, Warren!

Best regards,

-a-

[rbp]

On 6/24/2021 at 4:42 PM, David Lloyd said:

Part of the certification process requires a non-turbocharged engine to restart by only introduction of fuel in some period of time, I seem to remember 10 seconds.  Turbocharged, it was something like 30 seconds

can you cite the source for this?

[A64Pilot]

I know that one issue with certifying Diesels is that as they are a compression ignition engine, they can have a relatively low max restart altitude due to literally not having enough air density to compress to get to ignition temperatures

A turbo spark ignition engine may have a slightly lower compression ratio, but why would they be harder to re-start at altitude? Low compression non turbo motors don’t. Once restarted I can see as how they may go through an over rich condition until boost returned, but don’t understand why they would take longer to relight than a non turbo?

Just asking not making any assertions

 

Earlier I was not abdicating running a tank dry as a normal procedure, but only if for whatever reason you had to stretch fuel as far as possible, with one dry you know all the fuel there is, is what’s in the other tank.

Just remember the only time you can have too much fuel is if your on fire. That’s a joke 

Edited July 7, 2021 by A64Pilot

[Ulysse]

So, what is the proper procedure for restarting the turbo engine at, say 15000, in case it stops from starvation? Both throttle and mixture off before switching to the other thank or just throttle or mixture? (Not that I want to do that, but it is good to know)

[ArtVandelay]

LOP can help extend your range.  If you are not already doing this, you should add it to your repertoire.  10-10.5 gph at altitude gets you 180+ KTAS.
Running a tank dry ensures you use all the fuel in that tank.  You do need to do this to confirm your actual usable fuel on each side.  At altitude a restart can be an issue - my 231 will restart at 18000 (never tried higher), the manual says you may have to descend to 14000 to successfully restart.  Also, best to switch to ROP if you are running a tank dry - you will get some stumbling and have some notice as you run out of fuel.  I have done this multiple times over 20000 and not had an issue.  When LOP and you run out of fuel, the engine goes from running to windmilling almost instantly - much more exciting than when ROP!

If you watch the fuel pressure, do you see it drop before the engine starts to quit?

[jlunseth]

 

21 hours ago, A64Pilot said:

A turbo spark ignition engine may have a slightly lower compression ratio, but why would they be harder to re-start at altitude? Low compression non turbo motors don’t. Once restarted I can see as how they may go through an over rich condition until boost returned, but don’t understand why they would take longer to relight than a non turbo?

There are a combination of things going on. Remember that the turbocharger is what produces MP above ambient, and it is not mechanically connected to anything in the engine, so it is not driven by the prop. The prop can be windmilling and the engine turning, but unless there is exhaust the turbo winds down. Another complicating factor is that the mags are pressurized and pressurization will fail without your pressurization source (the turbo) in operation. If pressurization fails the spark can arc across the mag cap to a cylinder the spark was not intended for. The resulting phenomenon, called “high altitude miss,” is very hard on the engine. Or the spark may simply be insufficient to cause combustion. See e.g. https://www.aviationpros.com/home/article/10388584/magnetos-under-pressure

At 20k the standard ambient pressure is less than 14”. From experience I can tell you that the engine cools rapidly when you are at best glide and the engine is not firing. So now you are trying to start a cold to very cold, low compression engine, without enough spark. The POH for the 231 warns that you may need to descend below 12,000 for restart to happen. Even then, there are warnings throughout the POH against operating the engine at greater than 16” or 20”, depending on how low the oil temp has fallen. The POH warns that if the OT falls below 100, an attempt to run the engine at power may result in a sudden engine stoppage. What is going on, is that the oil is too cold to properly lubricate the turbo bearings, and the OT must be warmed before making power. Add in that you are crossing the Alps, or the Rockies, and you can’t descend to 12k and don’t have time anyway to warm the engine if it gets cold. It is not a wise move.

These recommendations in the POH are conservative. And sure, if you jump on the fuel switch the instant the engine stumbles it should fire right away. I have done it. But I have done it over the mid-section of the US where I have all day to restart or find an airport if things don’t go perfectly. I would not do it, say, on a jump from Great Falls to Kalispell. Having done it, and having more than 6 hours of fuel on board, I no longer feel the need to  give it a try. Much safer, is to test your fuel flow meter so you know its readings are accurate, fill the tanks correctly, know to a few tenths what is in each tank, and then not run one dry.

Turbo ops are different from NA ops in many ways. For one thing, the NA is unlikely to fly at an altitude where unpressurized mags will not function properly. Turbo ops are very safe, in some ways safer than NA because you have an improved ability to get above weather. But you cannot just blythely apply NA ops to turbo ops or vice versa.

PS I want to say that I admire curiosity and people who are willing to ask questions and seek information. I wish, when I first started flying my 231, that there had been more pilots savvy about turbo ops out there. I am not a CFI nor an engineer, just a pilot with some hours. I learned about “high altitude miss” the hard way, by having the “joy” of experiencing it firsthand, and I also learned the hard way not to “climb to target EGT,” which means leaning in a climb, an NA technique. Turbo ops are not complicated, when I fly, I have reduced my power settings to just some simple techniques. But to do that, one must understand the “why.” If anyone has more to teach about turbo ops I would love to hear it. 

[Warren]

4 hours ago, ArtVandelay said:

If you watch the fuel pressure, do you see it drop before the engine starts to quit?

In the 231 there is no fuel pressure gage.  Fuel flow is the only indication and for me that is a flow meter in the JPI.  I do not see changes in flow until the engine starts stumbling/surging.  Although I have run a tank dry multiple times, I am hyper vigilant when low.  I know my low fuel light comes on about 15 min before I run the tank dry.  At the first signs of stumble I switch tanks as I am frequently doing this in the lower Flight Levels and do not want to deal with a restart issue.

[ArtVandelay]

In the 231 there is no fuel pressure gage.

I don’t understand why. Is that a TCM thing?
I would add one if I own one.

[Warren]

I think this is common with the TCM engines.  It would be nice to have fuel pressure for additional information but I’ve never missed a fuel pressure gage (maybe because I have never had one).  What I care about for engine operation and fuel planning is fuel flow.  Fuel pressure is easy to measure and provides a good correlation to fuel flow but I like the actual fuel flow that I can calibrate and get higher precision.

[jlunseth]

I have the JPI 930 in my 231 and it has a fuel pressure readout. I almost never look at it. Fuel flow is more important. The factory gauge configuration did not have a fuel pressure gauge. From experience, fuel pressure drop, or its more like variation, does occur when you run a tank dry but there is not much warning. The engine is already talking to you.

[A64Pilot]

All of the older combo manifold pressure / fuel flow gauges were actually fuel PSI gauges, just calibrated in fuel flow, but on most of you looked PSI was also indicated.

So fuel flow is PSI, but where the pressure is measured may be different, those combo gauges for instance measure after the servo, where many fuel PSI gauges measure between the pump and servo.