Jabiru J170/J160 Fuel Capacity Management

[Eric McCandless]

My understanding is that fuel tanks should be filled after flight to minimise water condensation due to ingress of moisture laden air. The only reference I could find relating to Jabiru is JTM001-1 Aircraft Service Manual section 4.9 FUEL SYSTEM 100-HOURLY which says "The fuel tanks should be filled immediately after flight to lessen condensation of moisture". There is nothing in the POH.

 

Given:

 

J170 MTOW = 600kg

 

less

 

My aircraft empty weight = 323kg

 

Baggage (assumed but max is 36kg) = 10kg

 

full tanks of 135L fuel (0.72kg/L) = 97.2kg.

 

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Max pilot & passenger weight = 169.8kg

 

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I weigh 88 kg, so I cannot have an instructor/passenger more than 81.8 kg with full fuel and a nominal 10 kg baggage. A check of the trim sheet (my aircraft index =67.7) shows that this is within allowable CoG margins.

 

If I happen to travel regularly with an instructor/passenger greater than 81.8 kg, then I would need to remove fuel before each flight if I always fill the tank. All good, but a real hassle to remove fuel, but that is what I would do (but not sure how at this stage - siphon hose?) to meet the weight limitations.

 

If I had a J160 with 540 kg MTOW with the same 135 L fuel tanks, I could only have a capacity of 132.8 kg for pilot plus passenger or with my weight, an instructor/passenger of no more than 44.8 kg with full fuel and 10 kg baggage. Alternatively I would need to remove fuel prior to every flight with a passenger weighing more than 44.8 kg, which is most likely with most flying schools for example.

 

This got me thinking. Do Jabiru J170/160 owners really fill their fuel tanks after every flight and then drain before each flight? Is it really necessary to fill the tanks as long as you do fuel drains to check for water?

 

P.S. I am in no way suggesting that the weight limit should ever be exceeded by not removing fuel if overweight.

 

 

[facthunter]

It is a good principle but not practical on every occasion. You may be away from home and the fuel not available all hours and you may not have the containers. The instruction says "should", not MUST. Some aircraft are hard to get all the water out of a tank so prevention is a good thing. Are you running on avgas? and if so are you filling it from a bowser?

 

Most of your flying would require a careful filling/removal to get the right figure anyhow which you would only know when your plans to fly are formulated.

 

Since an adjustment is generally required I would use a graduated large plastic bottle and remove fuel by a syphon to your required amount, just prior to flying, when you know what your situation is for weight. Nev

 

 

[old man emu]

Eric,

 

The MUST in fuel management is that you MUST have sufficient for the intended flight plus a reserve. If, at the moment, you are flying with an instructor on a one hour training flight, then you'll need about 20 litres of fuel for that flight. Therfore, you can have a fatter instructor. Same goes for taking a friend on a joyflight.

 

Once you start going on longer flights, then you have to start accounting for minimum fuel requirements as part of your load. You might have to look at intermediate refuelling stops if you are going long distances.

 

As for water contamination overnight. If the plane kept out of the rain, then you won't get buckets of water in a daily fuel drain. If you can't hangar your plane, throw a tarp over the centre section where the filler caps are. That should fix rain in flow.

 

Coming to terms with the reality of a maximum MTOW being affected by pilot/passenger weight and then this weight affecting the amount of fuel you can carry is one of the joys of flying any ariplane. There is one waqy that you can get more fuel in, and that is to throw out all the unnecessary crap you are carrying, like tie-down pegs, spare oil, tools etc, etc. that are not needed for the particular flight. I think that the ability to carry necessary maps, ERSA etc in digital format on an iPad will be of great advantage to those who fly the planes we do.

 

Old Man Emu

 

 

[frank marriott]

Eric

 

Fuel cap seals are important on any aircraft.

 

I have over 400hrs on a Jab 230 and have never got a drop of water in a fuel drain yet.

 

In many GA aircraft with metal tanks I cannot make the same claim. Before I get slammed yes I do know of the problems with 'bag' type fuel cells in GA aircraft but the water has got to get in somewhere.

 

My unqualified opion is that cold metal is more likely to form condensation then other forms of fuel bladders.

 

The preflight water check is the safety net - and if you have a bladder type fuel cell [i.e. 182 style] then you rock the wings before doing the water check in case there is some water collected between possible ripples on the fuel cell floor.

 

FrankM

 

 

[Gnarly Gnu]

My understanding is that fuel tanks should be filled after flight to minimise water condensation due to ingress of moisture laden air.

Hmm, in an ideal world I guess but where would that be?

 

I've never flown a Jabiru with full tanks and one of the strips I fly from you would likely be unable to do this and survive with two POB. Unless you are taking a long trip and it is necessary I suggest the safety risks of full tanks* may outweigh the small water condensation ingress advantage if there is one in a Jabiru. But you need to weigh the risks and decide for yourself of course, YMMV Canberra being cold and all.

 

* Lots of extra weight = longer roll, slower climb & potential for stale fuel if you are not burning good quantities regularly.

 

 

[Dieselten]

For a J160 in a flying-school, having between 60-80 litres onboard allows a reasonable crew weight to be carried. If the crew is heavy, carry no more than 65 litres for normal training and circuit-flying. Most training-flights are about an hour or so in duration. Two heavy pilots and a long nav will dictate loading a maximum of no more than 80 litres, and a possible fuel-stop as part of the nav. The 160 needs to remain below 540Kg...it isn't a 544Kg MTOW aircraft. If you've got really heavy crew, the 170 is a better aeroplane to use.

 

When to put fuel in the aircraft? When it needs it! Dip the tanks, look at the last uplift and how many hours it has flown since then and decide. If you're going to fly for an hour and you're not sure, then put an hour's fuel in to cover your intended flight. As the US Navy says "there are no negative numbers in fuel calculations".