Engine burping

[shumway76]

During preflight of an aircraft using the Rotax912UL engine, it requires the engine to be burped. Why is it?

1. It's only to return the oil back to the oil tank so that proper oil level can be checked?

2. Or is it also to circulate the and remove air from the oil system to facilitate easier starting?

Also does burping apply to all dry sump piston engines or just this particular Rotax model?

Cheers!

[ifitaintboeing]

It's called "gurgling": the process is to return oil back to the tank so you can check the oil level. See towards the end of this document:

http://www.lightaircraftassociation.co.uk/engineering/Maintenance/Rotax%20Service%20Interval%20Guide%20%20April%202011.pdf

ifitaint...

[Jan Olieslagers]

And if the oil reservoir is well below the engine, as it is on my Apollo Fox, you will not get it to burp no matter how much you turn the prop - the oil will already have trickled down by the extremely reliable force of gravity.

Still I do hand turn the prop before starting, two or three revolutions, to activate ("wake up") both the oil circuit and the fuel circuit.

[Pirke]

I've been taught to never hand turn the prop. If there's a grinding problem in the mags it could start.

[Rod1]

Standard procedure in a Rotax 91X or you have no real clue as to the oil level. Overfilling is very bad for the engine.

The Rotax does not have magnetos.

Rod1

[Jan Olieslagers]

If there's a grinding problem in the mags it could start. I reckon you mean a _grounding_ problem? But it is extremely unlikely. If you could stop the engine after your last flight by short-circuiting both circuits (and Rod1 is right, there are no magnetos properly speaking) then the grounding circuit is all right. And even if there is a fault, it is very hard to start a 912 by hand propping, due to the gearbox working against it.

You want to ressaure yourself? Try handpropping your Rotax - you'll have a hard time, and small chance of success. Especially if it is cold.

Last, but not least: gurgling is indeed standard practice for 912'ers, can be found in all engine/airframe handbooks. Whoever told you not to do it (by which I mean: specifically on a Rotax 4-stroker) is, err, less than sufficiently familiar with this type of engine (to put it as politely as I could).

[gasax]

Just to add that in some installations some of the oil can drain into the crankcase from the tank. In those cases, gurgling becomes very important to avoid potential damage.

Dry sumped engines of all varieties will have differing procedures depending on the relative locations of tank, cooler and crankcase. The majority of these engines have much higher capacity scavenge sumps than supply, to try and avoid oil build-up in the engine.

[cockney steve]

there is a thread on this very subject, over on "the light side" (Well, this forum's referred to as "the dark side:O ) I learrned from it!

[Cusco]

I've been taught to never hand turn the prop. If there's a grinding problem in the mags it could start.

Not to mention the 'dry' pistons scraping up and down the cylinders, bereft of lubrication.

[Jan Olieslagers]

...and which will be a thousand times worse when starting the engine with the electric starter - because the engine speed will be much higher. Turning the prop by hand is a way of distributing a tiny bit of oil around the engine at a very gentle speed.

[KandiFloss]

Hi Shumway76,

Not sure which aircraft you fly, Technam P2002? If so, I recently had a lesson with an instructor and am part way through conversion onto the Technam. I was surprised about the gurgling aspect too! I find it hard to pick up on the 'gurgling' sound.

I was also surprised at what a nose low attitude the aircraft has inflight compared to the PA-28 / C-152. I kept having to remind myself to push the stick forward to lower the nose :ugh:

[Jan Olieslagers]

Dear Kandi,

If you find it hard to discern the gurgling sound you have never properly heard it - but, as I already said, on some types it simply doesn't occur. You do have to remove the oil filler cap, though, and better remove the dipstick too. One problem is to find a convenient place for both, where they won't fall off at the merest movement, yet be sufficiently conspicuous that you don't forget to put them back in place before starting.

As for pushing the nose down, isn't your issue with using a stick for the first time, having only used yokes before? You'll soon get used to it. But really, if that must be discussed further, it would be better done in a separate thread - this one is about gurgling a Rotax 4-stroker.

PS and forget about Technam, these fine but slightly overweight craft are called Tecnam.

[smarthawke]

Just so as there is no doubt - the Rotax is very different to other aircraft engines, so those going on about not gurgling as it's potentially harmful to yourself or the engine are unfortunately incorrect.

That said, the 91x will start by hand (search this forum and others for links to AAIB reports), so treat the propeller with due respect.

Finally, the gurgling process works much more efficiently when the engine is at operating temperature. We gurgle after flight then if the oil is on the dipstick flat on the pre-flight then you're good to go.

[BackPacker]

Just so as there is no doubt - the Rotax is very different to other aircraft engines, so those going on about not gurgling as it's potentially harmful to yourself or the engine are unfortunately incorrect.

Agree. And the other misconception aired on this thread is about the magnetos being or not being properly grounded. Apart from the fact that the Rotax doesn't use traditional magnetos like a Lycosaurus, the Rotax also doesn't have a mixture control. So you don't shut down the engine by pulling the mixture to ICO, but you shut it down by grounding the "magnetos" (word loosely used here). This means that every shutdown of the engine is an implicit check of the grounding of the "magnetos". If they don't ground, the engine won't stop and you have to use drastic measures like shutting the fuel valve.

So in that respect rotating the prop of a Rotax is about as safe as rotating the prop of a Lycosaurus - it should not be a problem since there should not be a spark (Rotax) or fuel (Lycosaurus) if the engine was properly shutdown. But you treat the prop with respect anyway.

[Jan Olieslagers]

Thank you, BackPacker, you neatly confirmed what I already stated in #06

If you could stop the engine after your last flight by short-circuiting both circuits (and Rod1 is right, there are no magnetos properly speaking) then the grounding circuit is all right.

[Lone_Ranger]

No mice in mainland Europe??? Never assume anything when dealing with loud whirly things (and yes I own a 912 powered aircraft and know how hard (nearly impossible but not quite) to hand prop they are, but that's no reason to assume your wiring is intact)

[Piper.Classique]

There is also the option of cranking the engine on the starter, ignition off, if that configuration is available. Yes, I know this means you have to get in and out of the aircraft, but your choice. The engine will still gurgle with the filler cap on, but you won't hear it over the noise of the starter motor. Personally, I just pull the prop through, without offering my head up as a sacrifice. It's a Pioneer, so the height is a bit low for comfort.

[KandiFloss]

Dear Jan Olieslagers, thank you for pointing out my incorrect spelling of the Tecnam, I am of course aware of the correct spelling ... Tecnam and not Technam. I was just following your advice about throwing in a few spelling mistakes here and there ... ;)

Re: Flying the Tecnam ... as you said, maybe it's the fact that i'm not used to flying with a stick (as opposed to a yoke) that I need to get used to ... I hadn't considered that

[Butchersboy]

Rod1 - Why is overfilling a Rotax 912/4 so bad? It has a separate oil tank with an over flow . The oil pump sucks the oil from this tank into the engine, and the blow by crankcase pressure pumps it back. Any excess is discharged into the airstream.

BB

[BackPacker]

Environmental concerns? Cost of oil? Having to wash the fuselage more often because of the oil streaks?

In addition to those, keeping track of oil consumption is one of the things you do to keep track of the overall engine health. After a break-in period the oil consumption of an engine should stabilize at some low number. If that number starts to rise all of a sudden it's time for some TLC.

If you regularly overfill the engine you can't keep track of what was consumed and what was blown overboard.

[Butchersboy]

Rod 1 said:

Overfilling is very bad for the engine. Not the environment

BB

[Rod1]

Butchersboy

When I installed my Engine I remembered a warning about "overfilling could cause engine damage". I am away from home so do not have my original paper documentation but I have failed to find any reference to this in the current documentation. Conclusion - I am losing it or the documentation has changed in the last 13 years!

Rod1

[BackPacker]

Rod 1 said:

Overfilling is very bad for the engine. Not the environment

BB

Reminds me of a joke.

ATC: XX flight XX, turn left 10 degrees for noise abatement.
XX: Noise abatement? We're at FL300 and no one can hear us up here.
ATC: Have you ever heard the massive boom when two airplanes collide at FL300?

Anyway, back to overfilling. I'm not quite sure about dry sump engines that are properly burped, but wet sump engines that are overfilled may have the oil level higher than the bottom cylinder walls. So the pistons are banging against the oil. This may cause sloshing, foaming and whatnot, and may even cause hydraulic lock. All are pretty bad for the engine.

In addition to that, a crash because of engine failure is an environmental concern in addition to a whole slew of other concerns. When I landed at a grass field after having suffered a bird strike against the wing, the first thing that the airport manager looked at was the location of the bird strike relative to the fuel tank, to make sure there was no chance of a fuel spill.

[Kregster]

Don't want to overstate the obvious, but I also use this time to "feel" the compression during each of the strokes of the engine. Turning the Prop and listening for the "gurgle" or "burp" is also just one more exercise in the pre-flight.