PA28 Fuel management
 

The longest leg that I have ever flown a PA28 was 1hr 30min in each direction. For this, I used 45min of fuel from each tank.

Recently I've been thinking about manageing fuel in this aircraft on longer trips. Considering that it is not possible to consume fuel from both tanks at the same time, knowing exactly how much fuel (or time) remains in each tank becomes more critical.

I would be interested to know how pilots go about planning fuel consumption on longish routes. I like to consider worst case scenario with regard to fuel consumption and so normally plan to have 1hr 30min fuel available in each tank with a 30 min reserve each side?

The POH actually contains very sensible advice plus a practical method on this. Did you read that?

The other methods I've heard were (all based on full tanks):

Fly half an hour one tank, then switch tanks every hour.

Fly on left tank if the big hand on your watch is on the left side of the dial, right tank right side.

Me personally, I just incorporate things in my FREDA check and fly on the fullest tank all the time. But I'm not making trips to the limit of the endurance in a PA28. Oh, and if I have a weight inbalance in the aircraft (flying solo or with a real heavy bloke in the RHS) I try to compensate for that with fuel management, for what it's worth. Not sure if it actually makes a difference though.

No, I must confess I don't remember reading that :(

Look in the Normal Procedures; Cruise section. It's a bit too long to copy it here verbatim.

I'll have to look it up next time I'm at the airfield. The copy that I am looking at must be abbreviated. It only says:

The outfit I did PPL with had a PA28 checklist (which I use to this day) that instructs to start engine on the fullest tank, then change tanks for the power check, take-off and the first 30 minutes of flight. Thereafter, change tanks every 30 minutes (noting the time at which you do it, or doing a FREDA check every 30 minutes). Obviously, that procedure can be amended as necessary if collecting an aircraft with less than full tanks and/or a fuel imbalance :*

That's an easy way to prevent fuel starvation while having a full tank on the other side (yes, it has happened before)!

Oh, and when changing tanks, always set fuel pump "ON", then change tanks, then switch pump "OFF" and check whether the fuel pressure holds. If it doesn't, then revert to the other tank - and amend your endurance accordingly.

Cheers :cool:

There's you answer them:}

Sicknote

This is my trick for long flights;

First leg, 2 hours, refuel and calculate fuel burn
Second leg 3 hrs, same power setting and leaning technique, refuel and calculate fuel burn.
Should should now have a good average.
Let's say that it's 7.6 gallons/hr, round up to 8 and you can now safely fly long legs and have an hour reserve.
Keep in mind that you absolutely positively have to use the same technique's as in power settings and leaning to make this work.
I have (safely) flown 5 hr legs in a Pa 28-161 with 48 gallon tanks using this trick.
Same altitude, same everything, same day even.....:ok:


Keep in mind that fuel gauges will look pretty scary (empty) when you do this.

To manage fuel properly, one must first find a reliable way of setting the engine to a known operating point for cruise. This means leaning the mixture correctly. For a non-engine-instrumented plane like most PA28s, you would lean until the RPM just drops, and then go a tiny bit rich again. Then check the carb heat still works. Obviously this would be done at a given engine RPM (and MP if VP prop).

Next, determine actual cruise fuel flow. Do two flights, identical profile except for a 30min or 1hr difference in the cruise section length. Start each with exactly full tanks, and compare the refill required. This will give you the fuel usage per hour at that power setting. Never rely on book figures for fuel flow!

If possible, repeat the exercise for two different power settings; one at max cruise power (probably 75% power) and another at about 60% power. The 2nd should yield a much improved range.

Never rely on what anybody previously claims there is in the tank. ALWAYS fill up yourself to the top, or do a physical check to tabs, etc. If the fuel is too low to be physically checked, do not fly - EVER. Even if an instructor tells you there is plenty in there. I have twice walked up to a plane declared by an instructor as having X amount of juice, and it was virtually empty (either because somebody did not log a flight, or maybe fuel theft during the night).

Best thing is a fuel flowmeter (Shadin Microflo etc), especially linked to the GPS. Then you get a constantly recomputed FOB (fuel on board) at the planned destination. Obviously you have to accurately enter the starting FOB into one of these.

There's a very simple trick to this: switch tanks according to the minute hand on your watch. In other words, if the minute hand is in the left hemisphere fly on left tank, if on right, right tank. Doesn't give you the amount of fuel used or remaining, but avoids running one tank dry while having plenty in the other.

On a slightly different tack, if you fill up a PA28 and have two people up front, you will very likely be out of the forward CofG limit, which is why it can need quite a heave in the flare sometimes. Bung 50 kg or so in the back luggage compartment and it gets much easier :ok:.
Fuel balance - look at the gauges every now and then and when one gets visibly lower than the other, change tanks. If you're a fat bastard like me you might want to keep the right tank a bit fuller to balance the belly out.
The only real problem you will have is if you never look at the gauges and let one tank run dry :eek:, otherwise you'll just wonder why the aircraft keeps wanting to roll.

I've flown plenty of aircraft where doing that would result in a very significant fuel imbalance. Guages on light aircraft are totally crap, and noone should ever rely on them for anything.

Changing tanks based on time is a much better system.

dp

IO540 - that's a very professional and involved way of doing it! Do 2 flights, identical profile etc... all very good when you are an FI, or own your own a/c - much less practical when you rent a club aircraft once/twice a month! I'm not too sure most people would want to repeat flights just to assess the fuel burn. I know I wouldn't.

As for leaning the mixture, it's always highly recommended (certainly on longish trips), but there isn't much point doing it up to 3,000 ft or so; you won't get a significantly lower burn.

I totally agree though about checking the tanks, and if possible, flying with full tanks if airfield performance/mass & balance allow. As I've said before, there is hardly any performance penalty for doing so, and on a PA28 with an engine in reasonable nick, you'll have about 4.5 hours endurance. Incidentally, a new PA28-161 is meant to burn slightly less than 9 US Gallons/hr, but an older engine will use up to 20% more. I do my fuel planning using a 10 USG/hr figure (including power check, take-off and climb), and when checking tanks against fuel gauges afterwards, there is slightly more left than my calculations show. The number of different PA28-160/161 airframes I have flown over the years had a fuel burn varying between 8.5 and 10 USG/hr.

But I agree that a fuel flowmeter is ideal; I have "snagged" PA28s a couple of times due to one fuel gauge becoming u/s in flight and showing empty. If the a/c has no tendency to roll and the engine still feeds OK from that tank, it's obviously a gauge problem and not a fuel leak; having no fuel indication on one side is another good reason for proper fuel management (and to calculate fuel remaining at each waypoint).

Cheers :ok:

When I was a student I was taught a very simple means of fuel management on Pipers. Know your endurance before you start and change tanks with fuel pump on at each FREDA check. It is excessive but you will at least burn each tank evenly.

While that 'might' be true in a PA-28 (which after all is what this thread is about), it certainly isn't true in other aircraft. At 70% power and 1000 ft, I burn 21 gph full rich and 14.5 gph leaned. That percentage difference on a 3 hour flight in a PA-28 is the difference between arriving with 1:30 of reserves and being a glider!

I use the clock face method in ours, its simple and works.

12-6 Right Tank
6-12 Left Tank

J.

I did a long over-water trip with a friend in his PA28 last Summer, to the Faeroes (great destination!)

He has a clockwork hour-timer rigged up in front of the passenger seat and briefs the pax that it's their duty to keep an eye on it and holler when it does an hour. Then he changes tanks. Works well when you're using the limits of endurance of the a/c. Incidentally, at the power setting he normally uses, we wouldn't have had an alternate if we'd been unable to land at Vagar. At my suggestion, we used about 150 RPM less and would have made it back to Scatsca with reserves...

TheOddOne

I agree fuel gauges are crap and cannot be trusted - except for very few like the 28V TB20GT ones which are super accurate.

This may sound a useless comment but you pays your money and you takes your choice.

If you want to fly on the cheap, you should not expect the same mission capability.

Put it another way, if you cannot afford to do a couple of flights, total time say 3hrs, and you cannot afford to do them even with 3 people cost sharing the flights and going somewhere for four burgers, then your only option is to fill right up every time and treat the fuel endurance as 3 hours when in reality it might be 5 hours.

The advantage of knowing the fuel endurance is say 5hrs is that you can now do longer flights, and plan your alternates intelligently. Whereas PPL graduates have usually got no idea what the real endurance is - not least because they have never been taught to lean the engine - so they stick to 1hr-2hr trips. This is OK but it cuts out a huge chunk of utility/fun value out of GA, which in turn results in so many people chucking it in very early.

The difference between 3hrs and 5hrs is that you can do a long trip into France; somewhere beyond Le Touquet :)

Similarly
 

I was taught this, but every OTHER freda check you change. Works for me, come back balanced almost every time.

It still makes me shudder when I check and aircraft and see a full tank on one side, but fuel almost dry on the other. Some student has done the QXC and not been changing tanks.

Agree, fuel gauges useless, should be taped INOP from the factory. Funny thing is that where I live, they're on the MEL list ! The most useless instrument on the aircraft !

My method is: Change tank everh 30 mins. That way you won't get too heavy on either side.

Piper vs. Cessna fuel strategy can be discusssed ad nauseum, both potentially dangerous in it's own way. My first PPL lesson , I asked "Shouldn't I change tanks ?" "Yup, good idea" said instructor. I turned it to "off". 30 seconds went in silence. Then: Never seen any one react so quicky.