Fuel Guages

I have a Jab 170c. Before the knockers start I love my aircraft. The only frustration I have is knowing how much fuel is in the tanks. I dont even look at the electric gauges. I check the wing gauges but even these are no where near right. i put 80 ltrs in yesterday and after take off the guages showed empty on the right and full on the left. I cant use a dip stick in flight so if I am venting fuel i have no way of knowing. i am starting to do some trips now and need to know what is in the wings. do any Jab owners have anything they have done to help.

 

 

I could be wrong here but if one tank was turned off and the other flowing fuel, wouldn't you have no venting? Providing each tank had a valve of course.

 

I thought venting only occured when both tanks were on/open.

 

 

You would have to have venting available under all circumstances. Some (most) planes will vent fuel turning on the ground, parked on a slope sideways or flown wing low when fuel is near full. It is possible to build a better vent system which will reduce the likelihood. Nev

 

 

I have a Jab 170c. Before the knockers start I love my aircraft. The only frustration I have is knowing how much fuel is in the tanks. I dont even look at the electric gauges. I check the wing gauges but even these are no where near right. i put 80 ltrs in yesterday and after take off the guages showed empty on the right and full on the left. I cant use a dip stick in flight so if I am venting fuel i have no way of knowing. i am starting to do some trips now and need to know what is in the wings. do any Jab owners have anything they have done to help.

Most fuel gauges in aircraft are unreliable . I use a dipstick that has been calibrated on level ground , and check before and after filling to establish average consumption . I estimate 20 l/hr for my J160 , which more than covers the additional fuel used , around 30 l/hr , to get to cruise altitude .It is unlikely you would be venting if the fuel caps are fitting correctly ie. O rings etc. and the vents facing forward to pressurise tank . Having said that Ihave seen older Jabs venting in flight ,when flying wing down with full tanks ,but these were fitted with the older type vent .

 

Bob

 

 

A perennial problem with thin, flat wing tanks, Compulsion. I installed sight tubes, but they are difficult to see (maybe AvGas needs a darker dye). I rely on pre-flight dipstick and the Fuel MiZer during flight. Swapping tanks every 30 minutes also gives some security.

 

 

You need a well calibrated dipstick as noted. In flight, turn the aircraft 'cross sun' - which will reveal any fuel venting overboard - look at the trailing edge of each flap and if happening - it shows as a thin wisp of white. On the ground - provided that you keep the upper wing surface, (aft of the fuel cap), scrupulously clean - any leakage will show as streaking and a pooling of discolouration on the flap trailing edge.

 

I've done several long distance ferry flights in 160's and 170's - and never used more than 16 LPH for a single leg. At 2800 rpm you'd expect more like 14-15 LPH in cruise, and perhaps 16+ at 2900 rpm. You need to fill your tanks, and do a couple 2 hr flights with a refuel at the same location. This will likely pickup any venting of fuel because it's most likely from full tanks.

 

You might obtain an optical tacho and check your aircraft's tacho. Not knowing this isn't a good start to engine management!

 

happy days,

 

 

Downunder I have re read your post. Fuel transfer can occur with BOTH tanks selected and THAT may overfill one and vent it but that would be like one wing low effect or the other two situations I described. You CAN vent a tank without it being selected. To avoid confusion I should say "flow fuel from the vent of a tank". or put fuel overboard.. Nev

 

 

I understand capacitive fuel gauges / senders can be very accurate for the full range of the tank (i.e full to empty), if properly calibrated. The calibration is potentially an issue if you use different types of fuel, as you will get a different reading between mogas and 100LL. You'll also get a different reading if there is etheanol present in the fuel. I've heard of one with a "tanks known full - calibrate me" option, which figures it all out for you.

 

I havn't heard of any being fitted to a J170.

 

I guess it would depend on if you've got a factory J170 or a kit as to whether or not you can fit one yourself.

 

The usual experts can, no doubt, provide guidance on the rules.

 

 

The thin wing section on the Jabs make any kind of gauge inaccurate. You are not allowed to trust gauges alone even though they are supposed to be calibrated to a standard. Work to a (generous) fuel flow rate and record your times and fuel onloaded. The only two occasions you really know how much fuel you have on board is when it is full or empty and the empty means consider usable only. If you have a flowmeter fine, but it doesn't account for leaks or overnight thieves. Nev

 

 

Firstly, a factory built Jabiru does not allow left or right tank selection. My 230 had the same issue when I picked it up from new, I was apparently using more fuel from the starboard tank. I have a Dynon EFIS and a steam guage skid ball, they do not read the same. I trust the Dynon and when flown in balance according to this electronic gauge I get even flow from both tanks.. maybe a source of your issue.

 

 

Firstly, a factory built Jabiru does not allow left or right tank selection. My 230 had the same issue when I picked it up from new, I was apparently using more fuel from the starboard tank. I have a Dynon EFIS and a steam guage skid ball, they do not read the same. I trust the Dynon and when flown in balance according to this electronic gauge I get even flow from both tanks.. maybe a source of your issue.

Interesting point you make comparing the Dynon to the skid ball . I always try to fly balanced at all times but find that the starboard tank still empties first . I suspect that the inst. panel may ,in fact ,not be precisely 90 degrees to the longitudinal axis . Will do a check soon . It may be the reason many Jabs suffer from the same problem .

 

Bob

 

 

Compulsion, have a word with the CFI Karl Faeth as your aircraft is ex flying school and he should have all the info you need.

 

Alan.

 

 

I find on level ground I have about 11ltrs more then the gauge shows when near empty.

 

To level in flight just fly half a ball out of balance and the tanks will level in less then a minute.

 

I find it impossible to get even flow other then in smooth air - Even then you have to be self critical about keeping a/c perfectly balanced.

 

Bob, I don't follow how the ball can be wrong - if it is correct when the plane is on the ground, then as it is a spirit level using only gravity - I fail to see how it can give false indications?

 

 

Wings warped?

 

 

I find on level ground I have about 11ltrs more then the gauge shows when near empty.To level in flight just fly half a ball out of balance and the tanks will level in less then a minute.

 

I find it impossible to get even flow other then in smooth air - Even then you have to be self critical about keeping a/c perfectly balanced.

 

Bob, I don't follow how the ball can be wrong - if it is correct when the plane is on the ground, then as it is a spirit level using only gravity - I fail to see how it can give false indications?

Frank

 

The way I see it is that the ball may well be centred when the aircraft on level ground ,as it is only responding to lateral tilt ,however it can be also off to one side when the aircraft is flying unbalanced with the wings are level . It seems to me that it is a little more than a simple inclinometer .

 

Bob

 

 

Bob, I should have used the term weight instead of gravity I.e. ball in centre in a balanced turn. But,heh, I am no instrument or maths guru, just my understanding of it as a simple spirit level, nothing complex about it. (Someone may well prove me wrong)

 

 

It might as well be a pendulum. Not being exactly at right angles to the fore and aft axis, should not make a lot of difference. Check it during the glide. Engine propwash on one side of the fin can make the ball go off centre. Nev

 

 

Check if the balls in the middle with wings level in the cruise ,still air ,and fly it hands free , and check that the balls still level , if it goes out ,even a little , it's a rigging issue .

 

Might be the ruder needs tweeking , or maybe a flap ,

 

It's a bit of a" think it through "situation ,but you can get it set spot on and I've found this helps no end to having balanced tanks .

 

Cheers Mike

 

 

Engine offset can be used too. Out of balance of fuel load will make an error as does any rigging error. You will always need a bit of rudder pressure on climb if you go for no pedal pressure in cruise. ( where you spend more time) Nev

 

 

Guess it's time to recalibrate my fuel flow meter. Remove the float bowl and pump a measured amount out of the tanks.

 

 

When I fit a T&B I use a sprit level across the seat rails and match the skid ball to the level. It's the only way you can get it set properly.

 

Cheers

 

Dale

 

 

Watch the skid ball on take off, often way off generally pilots concentrating of other stuff and naturally trying to fly level with the ground and straight with the runway, not necessarily balanced. Fuel skids to outer/inner edge of tanks, making one read over full one near empty. I reckon theres an small airlock problem in the Jab setup too, never effected fuel flow but gauges rarely right except in long level flight or on the ground.

 

Using electric pump seems to average fuel feed out a bit.

 

 

Getting near 500 hours now. I occasionally have the right hand lead light gauge drop to red. Correcting is ok, just a tiny bit of rudder will correct in less than a minute. It is impossible in my opinion for the fuel to transfer from one tank to the other in this time. My assumption is that the fuel in the RED gauge is away from the sender, ie slightly out of balance.

 

Two instructors that I know ferried a Jab back for the owner, they landed when one tank lead light indicated red, phone call to Jab who said all ok

 

Phil

 

 

Jab knew it was OK as you had been able to make the phone call.

 

I just hate it when one tank shows empty and you are feeding from both. How can you really know it is alright?. The only gauges I like are direct "sight' ones or something installed on a Boeing.(or such). no matter how good, you are never legal to trust them by themselves. You need fuel usage data, fuel onloads. Tank status ( Full or empty) is the only time you really know what you have there or if you remove or add a fixed amount from either.( as appropriate). A clear plastic tank ( behind you) with graduated marks on it would have to be allowed as reliable. Perfect engines don't run on NO fuel. they all need fuel to work, so don't run out of it. Nev

 

 

Jab knew it was OK as you had been able to make the phone call.I just hate it when one tank shows empty and you are feeding from both. How can you really know it is alright?. The only gauges I like are direct "sight' ones or something installed on a Boeing.(or such). no matter how good, you are never legal to trust them by themselves. You need fuel usage data, fuel onloads. Tank status ( Full or empty) is the only time you really know what you have there or if you remove or add a fixed amount from either.( as appropriate). A clear plastic tank ( behind you) with graduated marks on it would have to be allowed as reliable. Perfect engines don't run on NO fuel. they all need fuel to work, so don't run out of it. Nev

Nev , my J160 kit , and I believe all other Jab's , were originally fitted with sight glasses . I'm not sure about later kits , but certainly the ' factory completed ' aircraft , later changed to a float arrangement driving a display of LEDs . The sight glasses are not truly " direct ", as they are not directly connected to the tanks , but are mounted to the inside of the fuselage , near the pilot and passengers head , requiring separate fuel line connections back to the tank . The space between the wing root and the fuse is minimal , making it difficult for the fuel / vent lines to be connected without some degree of bending and this ,together with the low tank profile , may contribute to unreliable readings .I think the move to the float driven LEDs was designed to overcome the problem .

 

Bob