flying dog

GUYS! Hello!? This is getting a wee bit "off thread". I am asking about Jabirus and the increased fuel flow when the electric fuel pump is turned on. Not other aircraft. Not centrifical pumps. Not fuel injection systems. I appreciate there is a bit of lattitude, but this is just getting WAY OFF the original question.

Rocketdriver, I can't argue with that, but the "increase in pressure" is another thing. Can anyone say - definitivley - how much more pressure the electric pump put in/on the fuel? A car's electric fuel pump - as an analogy: Most blokes can pi$$ faster/harder than the pump. The needle/seat in the carb should negate the extra pressure - unless we are talking about going from (example) 2 PSI to 20 PSI. It would be foolish to add a fuel pump to the system which (by default) puts too much pressure for the carby to handle. Fuel injection systems as you mentioned are another kettle of fish and do have the extra things, so really theyy aren't applicable to this. Are they? Now to something you posted: This is because the float has to push harder to close the valve, which can only happen if the fuel level in the float chamber increases. Sorry? The float level doesn't change irrispective of the pressure. When the fuel is at "level x" the needle pokes into the seat and bloks the fuel flow. (Again, this is with normal pressures. If you push the pressure into another set of figures, the needle/seat won't work.) So I can't understand what you are wanting to say here. P.S. (via edit). And you mentioned "COMPETITION ENGINES". I agree that they have special tricks they do to optimise their systems. But again: How does this relate to Jab' engines? And how much "richer" will all this make? less than 10%, less than 20%, 30, 40...? A small increase of mixture would be "ok" and this would need quantative testing to see what really happens to fuel consumption. Also EGT's would need to be measured. (And/or CHT)

Bilby, Yes, I am saying that having the electric fuel pump turned on (always) should not/will not change the fuel used by the engine. RE post 12: Can't say. Insufficient details.

I'm laughing all the way to the bank. I weigh 40-50 Kg nominal. I don't own scales. (I'm not a fish - sorry.)

Bilby, Well I have asked, asked and done research. What I have found - and belive to be true: The fuel pump is in the wrong place and it is interfering with the sensor. The sensor SHOULD be as far away from the pump as possible, OR: BEFORE the pump. Leaving the electric fuel pump on does NOT change the fuel consumed by the engine. There is a slot/slit/groove in the pump's piston which allows the fuel to back flow once pressure is reached.

No worries. I am just asking. Live and learn!

David, I agree, but "they" say there is no "return line" from the carb'. I should have mentioned the problem with the explination but I wasn't wanting to put him off-side. He was on the spot and was only sumising - he actually admitted he didn't know and I am kind of respectful of him for admiting that. Not many people can admit they don't know something, especially if it is to do with something they should know about. Anyway, I'm still stuck on what is going on with the extra fuel.

Just spoke to Jab (won't say the person's name.... - parly because I've already forgotten it) He offered the possibility that with the electric fuel pump on, the mixture is increased and so the engine would be running with a higher fuel/air mixture. And.... As the butterfly isn't any more opened, the revs won't increase. Makes sense I guess, but he wasn't 100% sure. Anyone with thoughts on that?

Ooops, dislexia. Yeah, the Newcastle club...... Sorry.

Thanks. So, riddle me this: (wink wink) The reves on the engine are determined by the ammount of fuel. The ammount of fuel governs the ammount of fuel/hour the engine uses. After I start the engine I get a Litres/hour figure shown. Swithing on the electric fuel pump the number increases BUT the revs don't. There has to be a return line: Otherwise the "extra" fuel flow is not being burnt/combusted/used. Or am I missing something?

Though not at Maitland, but a few miles to the west, there is going to be a bit of a get together at Luskintyre airport that weekend. Contact RNFC for more details. Ask for Phil (Lucky).

Yeah, the radio is one of those small round things which are the "norm" for Jabs. Alas a lot of testing will have to wait until next time I am down that part of the world - it is 1.5 hours driving - so it is not every day I am close to it.

Yeah, I've seen that a long time ago. Would love to know how to download and save it. Tried, tried and tried. Failed, failed and failed.

The term "motorboating" was used by another person to discribe the voltage dropping below usable while the unit it trying to transmit. Maybe not the "accepted" meaning, but that is how he discribed it.

Yeah, I am not bagging the people who rent the plane. I shall have to try and find time myself to try and work out where/what the fault/problem is. But as the plane is 1.6 hours away from me, it is not something I can do just any time.

Well, I have my headset. I don't like snogging everyone else who have flown the plane. Ok, it is a cheapy, but it has worked on other Jab's - but that may not be saying much. First time I have flown that one and transmitting when in the circuit (or turning base/final) with no revs, is basically pointless as the CHARGE light is glowing quite brightly and pusing the TX button bascailly the radio fails.

Only the Asian market would crash. And only for the two/three months leading up to December. :(

Andy, Ok, I left my self open there. The other stations are reporting the distortion. I can "squelsh out" any muck I hear from myself. I am asking for Sydney QNH and need to ask more than once and Sydney radar are informing me of broken transmission with background noise. There are no other headphones plugged in at the time and the intercom is also set to ISOLATE. The voltage reading I am getting if from the Dynon EFIS.

And the weirdest part is that "they" still don't know how tranquilisers work. (skewz the spelling if wrong.)

Skyfox, Well no not yet. It only started happening the other day. I'll post updates, but was interested in people's thoughts on anything else which could be causing the problem.

Thanks, Nev. Shall try maybe one day. But it is a rental. So I can't just do these things at will. Also don't know if the battery voltage is good enough. I shall try it next time with engine not running and see what happens. I guess the only "trick" is getting someone to monitor me while parked. Then start engine and see if it makes any difference.

Ok, another question. Though I should probably ask Jabiru....... but here goes: Ok, start up for the Jab' is basically: Master on, fuel pump for a few seconds, then off. Mags on, and start. Take off, is fuel pump on and take off. In flight turn fuel pump off - to help with fuel flow / litres/hour calcs. Granted. But this is where I am stuck: Reading about fuel systems in planes - which may or may not include Jab's - there is the main fuel line to the carb'/injectors, going via an "optional" electric fuel pump. There is also a RETURN line for "excess fuel" to return to the tank. As a worded sequence would go it would read: Fuel tank - fuel pump - fuel flow gauge - carb' -(split to) engine and return line. (or something like that.) Isn't there a fuel PRESSURE gauge in there somewhere? Anyway..... I would have thought it would be "smarter" to have the fuel flow AFTER the return line? Then, when you get in you turn on the master, and turn on the fuel pump. You would see the fuel pressre go up, so you have established the fuel line is ok. Zero fuel flow - or you have a leak. Turn off fuel pump. Start engine. Monitor fuel flow. Turning on the pump would/SHOULD not alter the fuel flow, ONLY the pressure. Again: Am I missing something here? I'm only asking with the hope of learning.

Ok, I have asked and been given AN explination, but in thinking about it: What was said doesn't quite work for me. No offence to the person who said it. Scenario: Jab' with radio. My head set. When in flight and I talk, it is distorted with a lot of background noise and "pulsing". It was said this is called "motor boating" and it is because the altermeter is not big/strong enogh to handle the load. Sounds plausible. But let's look at some things which I feel/think fail that idea: I am flying, not idling. The revs are at about 2700, the voltage is 14.4 and there is little else on. IE: No landing lights, no NAV lights, no beacon, no strobes. Just the radio, Xponder, EFIS and HSI. Oh, ok, and my GPS plugged in the AUX socket. Now, fair enough voltage and current are different things, but if the alternator wasn't cutting it, wouldn't the voltage also be fluctuating? And there is a battery in the equation to "fill in the gaps" if the alternator wasn't producing enough output. Of course throughout this the CHARGE light is NOT glowing. It does at idle. So who has any other ideas? Yes, I know that usually with that kind of problem the power supply is the first and major suspect. But given the voltage (inndicated) is 14.4 at the time, it sort of shoots that idea dead. At idle, the voltage goes down to 11.9/what ever. I can clearly see that with revs/power the voltage increases, which makes sense. Anyone?

Facthunter, Thanks. Live and learn.

Glint, Possibily part of the reason the plane pulled left could be torque. However, others have explained what you need to do - and even you said you worked it out. There is no harm in what you did. We make mistakes. And the reason we do is to learn by them (Batman, Alfred to Bruce as a child.) One question for you though is: Why flaps up? From what I understand, you keep flaps down until you have established a positive rate of climb and are high enough to be safe. Lifting the flaps kills lift, and that close to the ground CAN be dangerous. So I was told to keep them down until things are sorted out. Am I wrong? Anyway, safe flying. Keep learning and keep enjoying yourself.