Fuel reserves

[rage83]

Actually it is a reportable incident if you land with less than your fixed reserve

 

 

[rgmwa]

One of the first things I did when I started flying my Experimental was check the fuel flows and level flight IAS at each standard power setting (full power, climb, nominal 2, cruise 1 leaned, cruise 2 leaned, and endurance) and tabulate those figures on my checklist card.

What height/s did you fly at for the IAS tests? I'm having an interesting time trying to determine meaningful fuel flow numbers. With a single tank, it's easy enough to fill up, fly somewhere for an hour or two, record fuel used and elapsed time. However, the calculated average fuel flow can vary markedly depending on time for taxiing, climb to altitude, cruise, throttle settings, etc. With two or more tanks, it would be easy to isolate fuel flows for the various flight phases and so get accurate numbers, but I'm curious to know how others with a single tank have determined their fuel flow rate for flight planning.

 

rgmwa

 

 

[facthunter]

You use the tables in the POH for the particular aircraft, OR if you have established reliable figures of ACTUAL achieved rates you can use them. You would want to have done this accurately, but it is fair enough and practical. A good POH will have perhaps three rates of cruise power as options . AUW has to have an effect obviously.

 

Flight Time and fuel logs will establish a pattern of usage. Beware of changes to engine tuning.. All has to be redone if different enough. and with a float type carburettor a sunk float will use lots of fuel and there can always be a fuel leak so monitor contents if possible .Nev

 

 

[Nobody]

What height/s did you fly at for the IAS tests? I'm having an interesting time trying to determine meaningful fuel flow numbers. With a single tank, it's easy enough to fill up, fly somewhere for an hour or two, record fuel used and elapsed time. However, the calculated average fuel flow can vary markedly depending on time for taxiing, climb to altitude, cruise, throttle settings, etc. With two or more tanks, it would be easy to isolate fuel flows for the various flight phases and so get accurate numbers, but I'm curious to know how others with a single tank have determined their fuel flow rate for flight planning.rgmwa

Don't you have an electronic fuel flow meter? If that is accurately calibrated then you can use that.

 

 

[facthunter]

If it has a total fuel used function it is useful.. Flowmeters are good for setting power, quickly. Nev

 

 

[DGL Fox]

I am hoping to start my navs soon so this is a very useful topic for me so forgive me if I ask stupid questions... but isn't the rule to fly the plane first? I just had a thought of how you are supposed to be doing all this figuring, and I am assumimng with a calculator and pen and log book on your lap , while looking out, checking your course watching your instruments etc etc...and of course actually flying the aircraft.. how are you doing all this...multi tasking?? or is there a simple method that I don't know about yet... I will doing this all manually while learning no Ipad?

 

David

 

 

[facthunter]

A lot of the secret is in the preparation. Much harder in an open cockpit . Nev

 

 

[dutchroll]

What height/s did you fly at for the IAS tests? I'm having an interesting time trying to determine meaningful fuel flow numbers. With a single tank, it's easy enough to fill up, fly somewhere for an hour or two, record fuel used and elapsed time. However, the calculated average fuel flow can vary markedly depending on time for taxiing, climb to altitude, cruise, throttle settings, etc. With two or more tanks, it would be easy to isolate fuel flows for the various flight phases and so get accurate numbers, but I'm curious to know how others with a single tank have determined their fuel flow rate for flight planning.rgmwa

Mine was easy as I have an engine monitor with fuel flow. Also a horsepower reading (not essential but it's one of the nice things about a good engine monitor). For a given horsepower or % power the fuel flow is approximately the same at any altitude, so I did my fuel figures at about 4000 ft. All I have to do is factor in TAS/groundspeed on the day to figure out the range.

My full power fuel flow at takeoff is 150 litres/hour. At Cruise 2 I can get about 45 litres/hr and at endurance I can get it down to 28 litres/hr with the power pulled right back.

 

I climb at 3000+ ft/min so the difference in climb fuel burn between say 2000ft and 10,000ft isn't much! It might be a factor for other types though.

 

 

[K-man]

I am hoping to start my navs soon so this is a very useful topic for me so forgive me if I ask stupid questions... but isn't the rule to fly the plane first? I just had a thought of how you are supposed to be doing all this figuring, and I am assumimng with a calculator and pen and log book on your lap , while looking out, checking your course watching your instruments etc etc...and of course actually flying the aircraft.. how are you doing all this...multi tasking?? or is there a simple method that I don't know about yet... I will doing this all manually while learning no Ipad?David

99% of it will be done pre-flight. If you have calculated your fuel and your reserves and you know the weather and have taken that into account in your calculations, it will normally only be a matter of checking your gauges when you do your routine instrument check. If you have more than one tank you need to keep tabs on how much you have used from each tank. We use a 30 minute timer for that. Thirty minutes left, 2x thirty minutes right, then back to left. FWIW, I have never had to calculate fuel mid flight.

 

 

[rgmwa]

Don't you have an electronic fuel flow meter? If that is accurately calibrated then you can use that.

I do, but the problem is how to get it accurately calibrated in the first place.

 

rgmwa

 

 

[dutchroll]

Are you talking about calibrating the K-factor in the instrument? Just a matter of doing several flights and keeping an accurate total of refuel amounts versus what the instrument says you burned. Then adding them up and doing a simple mathematical calculation will give you a new K-factor, which the instrument instructions should tell you how to change.

 

The preset K-factors in the modern/reputable fuel flow instruments are pretty reasonable. Mine started within about 4-5 litres (on the pessimistic/conservative side). One re-cal swung it slightly the other way, then the latest re-cal has it close enough to spot on (within a couple of litres).

 

 

[rgmwa]

Hi Dutch, yes. I'm in the process of playing with the k-factor. The factory pre-set put the rate at about 28 l/h, but 18-20 is closer to where it should be with a Rotax. I've got it in the ballpark, but need to do a few more longer flights to fine tune it.

 

Your 150 l/hr figure is definitely impressive!

 

rgmwa

 

 

[dutchroll]

Yeah it gets up and goes. Can't sustain it for long though! Still, reducing to cruise power and leaned nicely I can get 3 hrs total out of the main tank and another 75 mins out of the aux. That's well past "need to stop for a stretch and rest break" in a plane without autopilot where you're ratcheted in (literally) by an aerobatic harness!

 

 

[Geoff13]

I am hoping to start my navs soon so this is a very useful topic for me so forgive me if I ask stupid questions... but isn't the rule to fly the plane first? I just had a thought of how you are supposed to be doing all this figuring, and I am assumimng with a calculator and pen and log book on your lap , while looking out, checking your course watching your instruments etc etc...and of course actually flying the aircraft.. how are you doing all this...multi tasking?? or is there a simple method that I don't know about yet... I will doing this all manually while learning no Ipad?David

David

 

You will be taught all of this before you set out on your Navs. Probably best to not overcook it because there are more than one way to skin a cat but your school will have their way. So listen in on the briefings and practice. When I was planning my Navs I ran my Wind, Bearings, Times, Fuel Weights every day from when I got given the route until I had finished the flight. One of my Navs I fully planned every day for 4 weeks due to weather cancellations etc. When you start doing that you get the hang of it fairly quickly, especially if every 2nd or 3rd one you can email to someone you trust, (an instructor preferably) to keep an eye on your number crunching. After all there is not a lot of point practicing the wrong thing.

 

As for getting accurate figures for my own plane it has been an interesting exercise. I am actually still not sure of my full endurance.

 

I have recorded every bit of fuel to go into her since first flight.

 

She has now done 44.7 hours and used 700 litres.

 

So I have an average of 15.67 litres/hour. Would I use that figure for planning purposes, not yet I wouldn't I want a far bigger sample than that.

 

I still plan using the POH figure of 20 l/h even though having crunched my numbers even my worst figure is still 2 l/h below that.

 

Maybe when I have a couple of hundred hours in different conditions I may consider using the actual figures for planning but still unlikely.

 

With an 80 litre tank and 75 litres useable (the book actually says 80 is usable and I have run the fuel pump with the tail on the ground and nose in the air and pumped the tank dry but I will keep my little non usable figure anyway).

 

That gives me 3 hours plus fixed reserve plus those extra 6 to 12 litres that I haven't burned yet.

 

I can live with that. If I want to go further I can carry 15 kgs of luggage or (2 by 10 litre cans). To date I have not yet landed her with less than 35 litres.

 

The added bonus with the Hanuman is that I just need to turn my head and I can see exactly how much is in the tank.

 

 

[facthunter]

Seems as though you are approaching it in a logical way. Unusable fuel is hard to determine often. If your gascolator or single tank has a pyramidal or conical base you should get the lot, but thin, low dihedral wings could be anywhere if you don't run a common reservoir with about 20 mins + capacity and don't fly completely balanced. Nev

 

 

[DGL Fox]

Geoff,

 

Yes I am looking forward to starting my navs...should be very interesting...thanks...

 

David

 

 

[Geoff13]

Seems as though you are approaching it in a logical way. Unusable fuel is hard to determine often. If your gascolator or single tank has a pyramidal or conical base you should get the lot, but thin, low dihedral wings could be anywhere if you don't run a common reservoir with about 20 mins + capacity and don't fly completely balanced. Nev

Yes my tank is a single behind the seat tank shaped like an upside down U with one arm of the U either side of the elevator control rod and rudder lines. There is a joiner from the two lowest points and a small drain/joiner assembly that the fuel pickup comes from in the middle of that. It will drain the tank dry or the aux pump will pump it dry no matter the pitch angle, but I can't simulate flying out of balance on the ground and I certainly have no intention of going up with only 5 litres to fly out of balance and see if she keeps running.

 

 

[facthunter]

You don't have to with that set up. It's only fuel tanks that are long and thin in the wings and the gauges aren't accurate for the same reason. Nev

 

 

[Geoff13]

Cool TY