jabiru down brisbane

[Dafydd Llewellyn]

Are Jabiru wing tanks of constant chord, or do they taper? In level flight the wing will slope down a little at the back, so if the aft edge of the tank tapers up towards the wingtip, it would take significant out-of-balance flight to prevent fuel from reaching the outlet.

If they were tapered, the total fuel capacity would be reduced. If you make a totally foolproof aircraft, only a fool will fly it.

If you comprehend that fuel will flow from the wing tank to the collector tank only if the wing tank is higher - which is not really all that enormous a concept, surely? Then it would follow that it's not a bad idea to regularly raise each wingtip in turn a little, when you are getting low on fuel.

 

So the philosophy of the consumer society that it's always somebody else's fault and products should be such that no thought at all is needed to operate them, will ultimately result in products that are so limited in capability, in order to be foolproof, that nobody will want to use them.

 

I've just been watching Attenborough explaining that the dominance of the human race is due to the use of intelligence. If you want to gain an advantage, it pays to use your intelligence.

 

The penalty for stupidity, in nature, is death.

 

 

[Teckair]

If you make a totally foolproof aircraft,

Probably not possible.

 

If you make a totally foolproof aircraft, only a fool will fly it

Why? I would have thought if it was possible smart people may want to fly it as well. Why do you think they put nose wheels on aircraft?

 

Many aircraft with wing tanks drain one tank faster than the other but they normally do not suffer from fuel exhaustion with 15 litres left in the tank unless you do prolonged side slipping when nearly empty.

 

 

[Dafydd Llewellyn]

Probably not possible.

 

Why? I would have thought if it was possible smart people may want to fly it as well. Why do you think they put nose wheels on aircraft?

 

Many aircraft with wing tanks drain one tank faster than the other but they normally do not suffer from fuel exhaustion with 15 litres left in the tank unless you do prolonged side slipping when nearly empty.

Well, no, every step towards "fool proof" generates a new class of fool.

In Cessna's case, they put the nosewheel on to create the "flying Chevrolet" ("one in every garage"). The C172 was a step backwards from the C170 in almost every regard except the ability to be used by pilots who never learned to use their feet.

 

Re wing tanks, you're not quite correct; aircraft with wing tanks from which the engine can draw simultaneously, often drain one tank faster than the other. The engine will suck air from any wing tank, even with left/right selection, if it's selected to the low tank and flown with sufficient slip to overcome the dihedral. The Jabs do not have a lot* of dihedral, so the amount of slip required is not great. The normal tests for unusable fuel - see my post #334 - mean that aircraft that have long wing tanks and a "both" selector option or an "all on" system, will have enormous unusable fuel unless they have a collector which will keep the engine running for a 30 second slip, and be replenished in one minute of coordinated flight afterwards.

 

My point is that unless people understand the basis for things like unusable fuel, etc, they will not understand how to operate the aircraft correctly. It's something else that needs to be taught, I guess.

 

*The amount of dihedral an aircraft needs is controlled by its lateral/directional stability; one cannot arbitrarily increase the dihedral to assist fuel drainage.

 

 

[Guest Andys@coffs]

The relatively low amount of dihedral on jabs leads to another issue with parking. If you park so that one wing is lower than the other (easy to do, doesn't take much of a slope) and the tanks are full then the high side will drain to the low side and overboard, in my case from the filler cap. (yeah I recon I need to replace the O rings)

 

Almost worth having one of those cheap plastic spirit levels so that you can put it across the wings and turn the plane until the wings are relatively level....Alternately if you have wing tank taps you can turn them off....but then run the risk of forgetting to turn them on!

 

 

[Dafydd Llewellyn]

The relatively low amount of dihedral on jabs leads to another issue with parking. If you park so that one wing is lower than the other (easy to do, doesn't take much of a slope) and the tanks are full then the high side will drain to the low side and overboard, in my case from the filler cap. (yeah I recon I need to replace the O rings)Almost worth having one of those cheap plastic spirit levels so that you can put it across the wings and turn the plane until the wings are relatively level....Alternately if you have wing tank taps you can turn them off....but then run the risk of forgetting to turn them on!

That also happened on my PA 28 - and it had plenty of dihedral, and short tanks. It's not really an issue of dihedral; it will happen in any aircraft unless the fuel shut-off valve isolates the tanks when in the "off" position - and many of them don't. The alternative way to stop that is to use a "cross-over" vent system; but you end up with a multitude of drain points to check every morning, because the low points in the vent plumbing must have drains to remove any water that may collect there.

 

 

[M61A1]

Is it feasible to have a pickup both inboard and outboard on each tank with a simple inexpensive facet type pump on each one (the pumps have check valves)? That way there is very little unusable fuel, if you were so inclined you could put a pressure switch in line on each pump, driving a LED to indicate , bit like an F111 wing tank system. Can't be any more difficult than some of the whiz bang instrumentation some of them have.

 

 

[Teckair]

Well, no, every step towards "fool proof" generates a new class of fool.

Yes that is interfering with the Darwin theory.

 

aircraft with wing tanks from which the engine can draw simultaneously, often drain one tank faster than the other.

Yes that is what I meant.

 

My point is that unless people understand the basis for things like unusable fuel, etc, they will not understand how to operate the aircraft correctly. It's something else that needs to be taught, I guess.

Yes again I agree I have to admit I do not make a habit of running my fuel supply down to 15 litres.

 

 

[Dafydd Llewellyn]

Is it feasible to have a pickup both inboard and outboard on each tank with a simple inexpensive facet type pump on each one (the pumps have check valves)? That way there is very little unusable fuel, if you were so inclined you could put a pressure switch in line on each pump, driving a LED to indicate , bit like an F111 wing tank system. Can't be any more difficult than some of the whiz bang instrumentation some of them have.

Provided one could arrange matters so the pump only ran when there was fuel at the outboard end of the tank - a mercury switch, perhaps? Because those pumps wear out pretty fast if you run them dry.

 

 

[Oscar]

Is it feasible to have a pickup both inboard and outboard on each tank with a simple inexpensive facet type pump on each one (the pumps have check valves)? That way there is very little unusable fuel, if you were so inclined you could put a pressure switch in line on each pump, driving a LED to indicate , bit like an F111 wing tank system. Can't be any more difficult than some of the whiz bang instrumentation some of them have.

Jeez, a hard call. Add three pumps with attendant power drain, two lines, four more things to watch on the panel, four check valves to possibly malfunction.. or teach people to fly a bit more accurately and to be aware of the implications of having low fuel in one or both tanks?

 

 

[Dafydd Llewellyn]

Simplicate and add lightness . . .

 

 

[M61A1]

Jeez, a hard call. Add three pumps with attendant power drain, two lines, four more things to watch on the panel, four check valves to possibly malfunction.. or teach people to fly a bit more accurately and to be aware of the implications of having low fuel in one or both tanks?

Agreed that it's not the simplest option, but it's not what I'd call complex. It's certainly not foolproof, but it would make a lot of that 15 litres of unusable fuel available.

The Facet pumps, are a simple pump that copes with running dry for reasonable periods (they should only run dry for a few seconds in any case), also the check valves are part of the pumps. At 1.4 amps per pump, that's not really a significant load.

 

The indication system, is nothing more than an idiot light system( and is not really necessary anyway)), so full time monitoring is not required.

 

A reasonable proportion of Jab drivers I've met seem to like to add more stuff, to their panel, so something actually useful might be a bonus.

 

I only put it out there, as there seems to be a lot of discussion on how to fix it, and possibly some forced landings because of it's mismanagement. I'll put it this way...If I had long flat tanks, that's how I'd ensure constant fuel flow regardless of attitude. I do like the mercury switch idea though.

 

 

[Dafydd Llewellyn]

Be careful how much mass you add to the wingtips; and keep it as far forward in the wing as possible, otherwise it will adversely affect the flutter margins of the wing.

 

If the pump has a reasonable suction head capability, (and it wouldn't need much - half a metre woulfd be ample) I'd be inclined to locate it in a modified lift-strut fairing.

 

 

[M61A1]

Be careful how much mass you add to the wingtips; and keep it as far forward in the wing as possible, otherwise it will adversely affect the flutter margins of the wing.If the pump has a reasonable suction head capability, (and it wouldn't need much - half a metre woulfd be ample) I'd be inclined to locate it in a modified lift-strut fairing.

Realistically, the pumps don't actually have to mounted outboard, just pick up from there. According to the Facet data sheet, they have the capability to dry lift from 12- 36" depending on the model.

 

 

[Keenaviator]

May be the SK, SP and J120 aren't too bad after all with their very simple fuel system - tank behind the seats (where the later model header tank is).

 

Laurie

 

 

[Dafydd Llewellyn]

Yes, it's a very effective fuel system - but you don't get 8 hours endurance out of it.

 

 

[Guest Andys@coffs]

bit like my bladder then....I don't get 8hrs endurance from it either........and lets not even talk about how uncomfortable it would be sitting in a jab for 8hrs straight!!!!

 

 

[geoffreywh]

some people are not getting the intended irony in my post. I said that the 230 MUST have had at least 15 ltrs left (otherwise he would have been operating illegally) -- You should have 45 minutes reserve in the tank when you land...... For all I know he had none, very little or lots, probably NOT exactly 15 litres!!!

 

 

[SDQDI]

some people are not getting the intended irony in my post. I said that the 230 MUST have had at least 15 ltrs left (otherwise he would have been operating illegally) -- You should have 45 minutes reserve in the tank when you land...... For all I know he had none, very little or lots, probably NOT exactly 15 litres!!!

Don't let the facts get in the way of a good story Geoffrey:wink:

 

 

 

[Dafydd Llewellyn]

bit like my bladder then....I don't get 8hrs endurance from it either........and lets not even talk about how uncomfortable it would be sitting in a jab for 8hrs straight!!!!

You miss the point, Andy; that much endurance allows you to fly to a site , say 300 miles away; (with a piddle-stop on the way if you need it); and after you have dome whatever you needed to there, fly home again. A short endurance means you have to fly to where there is fuel. A long one allows you to get fuel where you want to.

 

 

[Russ]

bit like my bladder then....I don't get 8hrs endurance from it either........and lets not even talk about how uncomfortable it would be sitting in a jab for 8hrs straight!!!!

Do 6 plus hrs easy in my 160, lambs wool seat covers, trim setup properly, tea coffee, snacks.....and a pee bottle.....all's good

 

 

[frank marriott]

The J230 has around 600nm range with reserves.

 

I regularly do 500nm (YBTL - YHBA) with over 60 min remaining (in the mains, forget the header tank)

 

If weight limited, YBRK is a convenient mid way point to stretch the legs and refuel.

 

Fly "in balance" and get an even fuel burn from both tanks.

 

 

[rankamateur]

........and lets not even talk about how uncomfortable it would be sitting in a jab for 8hrs straight!!!!

Has it ever occurred to you that they were designed by someones wife. If they were too comfortable some women would never get their lawn mowed.

 

 

[Oscar]

Surely, a simpler idea than four fuel pumps, is to have a header tank and if you want, inboard feeds from both in the normal location plus outboard feeds that come down the lift struts (they have to have fall from the end of the tank to the header tank so that no point of them is above the tank-end with that wing low, obviously).

 

 

[Dafydd Llewellyn]

Surely, a simpler idea than four fuel pumps, is to have a header tank and if you want, inboard feeds from both in the normal location plus outboard feeds that come down the lift struts (they have to have fall from the end of the tank to the header tank so that no point of them is above the tank-end with that wing low, obviously).

I think you'll find the tanks go all the way to the wingtips; they did on the prototype. However I suppose an outlet at the tip than ran inboard to the lift strut and then down inside the strut might siphon.

 

 

[Oscar]

Yep, that's what I thought, the fillers are at about 40% span, so if the tanks extend much beyond that, how would you fill them?