PA28 Archer - Pre - Flight Fuel Tank Quantiy Check

[d192049d]

All,

Have recently checked out on the PA28 Archer 11 and having being brought up on a Cessna diet of never believe the guages and always dip the tanks, I was a little uncomfortable with the fact that you have to rely on your eye sight to assess the quantity of fuel in the tanks. IE no sticks.....

When I raised this I was told well you cannot dip the tanks because of the Dihedral and that in fact the guages on pipers are accurate and should be believed.

Am I alone in feeling that this is not the best idea? In fact is what I am told true? Most drivers out there will know that it is very difficult to judge how far the fuel is below the tabs so should I make sure that every flight I carry fuel up to these?

Grateful for your collective wisdom.

M

[Genghis the Engineer]

I've flown many variants on this aeroplane, and it's always been done on one (or both) of two bases:-

(1) Dip it

(2) Minimum known value based upon either tabs or top (no other assumptions made).


It's perfectly possible and sensible to use a dipstick, because of the dihedral it needs to be calibrated, but that's not difficult. Most club operators have a calibrated dipstick for each aeroplane, if they haven't I'd argue it's inexcuseable.

Finally, anybody telling you that the electronic gauges on Pipers are believable and accurate is talking utter b****x.

G

[Say again s l o w l y]

Just because it's a Piper, doesn't mean the guages are accurate.

With experience, you can learn to "eyeball" the tank levels using the sidewall, but dipping with a highly sophisticated, calibrated measuring device (a bit of wood with marks on it....) is far more accurate.:rolleyes:

The dihedral does make it a bit more complex than a 'flat' wing, the only problem we've had is getting hold of a properly calibrated stick.

The a/c fuel logs should also be an aid for working out how much you have onboard, but as long as you have no weight and balance or performance issues, then fill it up before flight.

As has been said before, the only time you have too much fuel is when you're on fire!

[Tall_guy_in_a_152]

I always dip the tanks in our PA28 if the level is below tabs.

Tran$air sell a plastic tube designed for the purpose, but you have to calibrate it yourself. A piece of wooden dowel could also be used.

If the wing dihedral causes the dipper to come up dry, then you are well into reserves and need fuel.

The PA28 gauges are certainly more stable (i.e. damped) than the C152 / C172 but I would not trust the overall accuracy any more.

[Genghis the Engineer]

Just in case it's not obvious to anybody, how to calibrate a dipstick...

(1) empty one tank. The easiest way to do this with a PA28 is almost certainly to run it *nearly* empty in the air then use a siphon tube to take the remainder into a suitable clean recepticle. (If you've any microlight pilots about the place, they can probably lend you some 20 litre jerry cans).

(2) Take the aeroplane to the pump (or bowser to the aeroplane), ideally when it's quiet and the refueller is in a patient mood.

(3) Add a fixed amount to the tank (I'd suggest for a tank this size, 10 litres). Put your prototype dipstick in, mark on it the position of the fuel.

(4) Keep repeating (3) until the tank is full.

Take the dipstick away, make the marks permanent, or copy them over to something more substantial. (A bit of sawn off broomstick works well, an item with a long and glorious history of aeronautical applications). For those with money spare, you can even use the little perspex thingy from Transair.

(You can do something similar with the electronic fuel gauge and a "stick-on" calibration placard, but I'd only do it with a system that uses a float sensor. Anything using a capacitance type sensor is likely to vary too much with fuel type, time of year, moisture content, phase of the moon, etc.)

G

[TheOddOne]

Re PA28 fuel gauges - almost useless.

Re dipping the tanks...

Well, you could try the method above, but beware of the following:

Try going through the above exercise, then with fuel well below the tabs, move the aircraft to another location and try again. I bet the results will be different. Getting the 2 wings level is a nightmare. Firstly, hardly any surface is level enough and you can bet your bottom dollar that one surface will have a different slope from the other. You can't guarantee you'l be making the measurements on the same slope every time. Secondly, you'll not get the oleos to settle in the same place.

Try this. Get a tape measure. Carefully measure the height of each wingtip from the ground. Get hold of one wingtip and vigorously heft it up & down a couple of times (like you do during your pre-flight check). Re-measure. I bet you get a different result. I also reckon your dip will give a different result, too.

To my mind, the only sure method is to measure usage over a period of time, then apply this to the time flown since the last tank-fill, then apply a comfort factor (at least 10%).

Our Warrior 1 does about 6 hours from full tanks at about 2250 RPM, suitably leaned, about 4 hours from the tabs. Personally, I never go below 2 hours reserve, just in case, that's 4 hours flying from full, plenty I'd have thought between loo breaks!

My favourite application of a sawn-off broomstick is in the story about Chuck Yeager. About to go off to break the sound barrier for the first time, he finds he can't lock the door 'cos he's cracked a rib falling off a horse. So his trusty engineer saws off a bit of broom stick just the right length to enable Chuck to close the latch. It's all in Tom Woolfe's book 'The Right Stuff', so it must be true. (Brilliant film, too)

Cheers,
The Odd One

[Genghis the Engineer]

All true, but equally applicable to any other method of fuel gauging - the +10% for the wife and kids is fair, as is the 2 hours fuel. (Actually that all comes down to "it depends" - but you're unlikely to go wrong that way).

I've heard Chuck Yeager mention the broomstick story himself, so I'm pretty sure it is true, or as reliable as anything he says, it's hard to tell.

G

[CherokeeDriver]

I almost fell off my seat when you said the guages on PA-28 are accurate. They are not. The only time they "legally" have to be accurate is when the tank is empty. A situation best avoided in mid-air I think you'd agree!

Basic rules for fule management on the PA-28 are: Fuel Management - you have to do it on a PA-28. Switch between the left and right tanks every 30 mins. You don't have to do this on a gravity fed cross suplied Cessna. Remeber to switch the fuel pump ON before you switch tanks, check pressure, switch tanks, switch pump off, check pressure again.

The "tabs" on the tanks show 17 Gallons. If both tanks are "at the tabs" you have 34 gallons, of which 32 will be useable. 32 gallons is 3 hours endurance with a margin of safety built in for diverts etc.

A hint I was given when I was training was to always fly with full tanks - can make 'experimental' landings less "kangaroo" like ;-)

[B Fraser]

I have a PA-28 wooden dipstick which is also calibrated for spamcans on the reverse side . If you are ever at Booker, PM me so we can meet. Bring a stick and a pen.

[Lowtimer]

CherokeeDriver,
If you have found a way of always flying with full tanks, do tell. We Yak pilots would be especially grateful for help in this regard as our tanks go from "full" to "empty" in as little as an hour or two, but I am sure operators of other types would also welcome the range improvements and reduction in hourly cost.
Seriously, if full tanks help your landings it is probably because you are flying at an approach speed based on max gross weight and not factoring it appropriately for the weight you are actually flying at when you make the approach., This causes a lot of PA-28s to float a few hundred metres along the runway, especially if it is a bit downhill.

[d192049d]

Guys {hope no girls if so sorry]

Thanks for your feedback, clearly I have more to learn about "believing everything an instructor tells me"

Until I get a calibrated dip stick, its full tanks for me.

Mike

[fireflybob]

It really amazes me that in this day and age of technology that we are still flying around with such crude measurements of remaining fuel on board - surely better systems are available or are they just expensive?

Many large public transport aircraft have integrators which measure (very accurately) the amount of fuel which has gone through each engine since they were last zeroed. I believe that you can have such a system fitted to GA aircraft but have no idea of the price.

A friend recently took me for a drive in his recently purchased (new) car (sorry cant remember what type - cars are not my scene!) fitted with a system which shows "miles remaining" to dry tank based on current consumption. Lots of other data available via the system - surely this should be fitted as standard to new light aircraft instead of the mickey mouse gauges?

[TheOddOne]

fireflybob,

We had a C150 we hired in from an outfit that did aerial photograhy and it had a fuel flow computer, presumably so that they could maximise their sortie times. We never did get the hang of it for the short time we had the a/c but it seemd an expensive option for non-specialist work. We're just stuck with the 1940s technology, I guess.

Do any of these 'modern' plastic type aeroplanes like the Diamond or Grob ranges come with anything better?

Cheers,

The Odd One

[Genghis the Engineer]

Many large public transport aircraft have integrators which measure (very accurately) the amount of fuel which has gone through each engine since they were last zeroed. I believe that you can have such a system fitted to GA aircraft but have no idea of the price.

A friend recently took me for a drive in his recently purchased (new) car (sorry cant remember what type - cars are not my scene!) fitted with a system which shows "miles remaining" to dry tank based on current consumption. Lots of other data available via the system - surely this should be fitted as standard to new light aircraft instead of the mickey mouse gauges?

Truckie aircraft, which need that degree of accuracy have them.

Microlights and homebuilts, which aren't subject to the full nausea of GA certification practices have them.

Certified light aircraft sadly, are stuck in the middle and don't!



I can't speak for any other make, but I have a newish Citroen Picasso which has such a device, and very useful it is too! Mind you, at 20 miles remaining, it refuses to give any further opinion and gives up :}

G

[Chilli Monster]

I'm flying a TB20 at the moment with a JPI EDM-700 (http://www.jpinstruments.com/edm_700.html) . Once calibrated they're incredibly accurate, giving fuel quantities accurate to the litre.

(The other day - showed 57 litres burned / 268 remaining. Fuel put in to re-fill tanks - 57 litres :) )

That plus the engine indications that come with the unit mean real savings in fuel consumption due to more accurate leaning. I'm definitely a fan.

[Say again s l o w l y]

The diesel DA40 certainly has a fuel flow meter. How accurate it is I haven't found out yet. The figures it gives are pretty fantastic however! 7.9 gal/hr at 100% power! Certainly alot better than our 172 XP, with full power the fuel flow is above 18 gal/hr! Fuel costs a bit more as well.

Totalisers are very useful, but they aren't always 100% accurate. I've used some that have been out completely and others that have even counted the wrong way. Ahh the joys of commercial aviation!

[foxmoth]

A hint I was given when I was training was to always fly with full tanks

Great if you only want to fly a couple of people round the local area but you will be a bit overweight if you want to go somewhere with 4 up and bags!
From my memory of the Pa28 there are 3 positions where you get a pretty accurate visual fuel indication, Full, Tabs, fuel to the bottom of the outboard of the tank (can't remember the amount but it is still a fair bit due to the dihedral) and of course you also can tell if its empty when the donk stops - but I don't think you can actually see when its empty due to the dihedral. If I remember rightly fuel to bottom of the outboard of the tank would give enough for about an hour if it was a nice day and you did not need full reserve capability, also of course, if it was at this level you could then work out how much to put in for what you wanted to fly (though this would probably put you up to 'tabs' anyway).:ok:

[aerobatic_dude]

I'll never rely on the gauges of my clubs 161, it will often tell you that you've got full tanks when there is clearly 1/4 tanks in it from eye checking. Even doing steep turns with 1/2 tanks both gauges still register full, the whole time.

[Another_CFI]

Having flown over 6000 hours on various Piper aircraft I would sooner trust a politician to tell the truth than trust most of the fuel guages.

The best method that I have found, which works even on aircraft such as the Seneca and Saratoga where you cannot dip the tanks, is to produce a fuel burn sheet for each individual aircraft. After a few iterations of measuring fuel burnt versus time flown these can be very accurate.

[wombat13]

Cherokeedriver wrote:

The "tabs" on the tanks show 17 Gallons. If both tanks are "at the tabs" you have 34 gallons, of which 32 will be useable. 32 gallons is 3 hours endurance with a margin of safety built in for diverts etc.

I have been flying a club Archer for the last 7 months and was told both tanks on the tabs 28 gallons (40 full) with 7gph burn.

Is the fuel capacity / burn of the Archer really so different to the Cherokee? Are our figures wrong?

[Brooklands]

Wombat13,
I have been flying a club Archer for the last 7 months and was told both tanks on the tabs 28 gallons (40 full) with 7gph burn
Its probably the difference between US and Imperial gallons. 34US gallons is approximately 28 Imperial gallons. Since Pipers (and Cessnas) are American, their gauges and tanks tend to be claibrated in US gallons rather than Imperial gallons

Brooklands

[Genghis the Engineer]

An aside here, since we seem to fly mostly American spamcans (with manuals and gauges in US gallons), and fuel is supplied in the UK in litres, I personally take care NEVER to use imperial gallons for aircraft purposes.

The odds of confusing litres and either gallon are pretty small, but US and imperial, the risk is high enough to worry me.

G

[wombat13]

f@*k.

I should have known that. Back to school for The Wombat.