Primarily for general aviation discussion, but other aviation topics are also welcome.
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By carlmeek
#1786647
I have recently heard of an accident with someone being injured as a rotax engine fired during gurgling.

Traditionally, props are live and scary and taught as such, but rotax with the gurgle makes people feel more relaxed around props.

My understanding is that we gurgle to purge oil in order to check level. So why dont rotax suggest turning it on the starter motor, then checking level? Safer surely.
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By Miscellaneous
#1786653
carlmeek wrote:So why dont rotax suggest turning it on the starter motor, then checking level? Safer surely.

That's a worry to hear. :(

I'd suggest the reason is that to gurgle (and not pump) it is necessary to turn the engine slowly.
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By Marvin
#1786658
Turning on the starter motor means the oil pump is putting more oil in the sump. The idea is to pull a blade though slowly, about 5 sec though a compression, so the sump pressure sends oil back though return and the oil pump is not sending oil round system. Then check oil tank level.

Concerned if someone has managed to get a cylinder to fire.
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By lobstaboy
#1786689
Assuming this is the same incident, then I believe that the switch was indeed faulty and one "mag" was live. But I think the engine was turned over rapidly - by hand but still fast enough to get it to fire. As mentioned above, gurgling needs to be done slowly.
This was talked about in a fairly recent Safety Spot in Microlight Flying magazine (within the last six months iirc) and used to stress the importance of doing a proper "mag" check as part of the shutdown routine, rather than just switching off.
I have heard of at least one previous incident.
By Big Dex
#1786700
lobstaboy wrote:Assuming this is the same incident, then I believe that the switch was indeed faulty and one "mag" was live. But I think the engine was turned over rapidly - by hand but still fast enough to get it to fire. As mentioned above, gurgling needs to be done slowly.
This was talked about in a fairly recent Safety Spot in Microlight Flying magazine (within the last six months iirc) and used to stress the importance of doing a proper "mag" check as part of the shutdown routine, rather than just switching off.
I have heard of at least one previous incident.

I would assume that if the engine has been shut down on the mag switches, it has correctly passed the relevant element of a mag check?
By Aerials
#1786705
In the Rotax 912 Series Operating Manual it states under Cold Weather Operation; Cold start • Be aware, no spark below crankshaft speed of 220 rpm (pro-peller speed of 90 rpm). I have seen some people turning the prop far too quickly to be effective in gurgling so this may be another case and with a faulty ignition circuit.

There isn't any specific procedure for stopping the engine. The Operating Manual merely says Engine shut-off - Normally the cooling down of the engine during descending and taxiing will be sufficient to allow the engine to be shut off as soon as the aircraft is stopped. At increased operating temperatures make an engine cooling run of at least minimum 2 minutes.

My self-invented procedure to shut down is to carry out the magneto checks as laid down in my POH then, following the second switch being made live again, I pull the throttle to idle. As the rpm decays, I switch one magneto off then as the engine just begins to find it a struggle to keep going, I put the remaining switch off. This is to reduce the possibility of gearbox wear etc during the sudden stop if both mags are made off together.
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By allout
#1786712
"So why dont rotax suggest turning it on the starter motor, then checking level? Safer surely."

They do.
From the Flight Manual of my Club's 912S:
"para 4. .... Caution. Run the engine for about half a minute before checking the oil ..."

My understanding is that hand cranking is gentler on a cold engine, so that is what we do.
BUT
From beginning to end we treat the prop as though equipped with a 'normal', ie fail-dangerous magneto.

For shut down we simply switch off: a live ignition will show itself by the engine continuing to run.
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By lobstaboy
#1786720
allout wrote:For shut down we simply switch off: a live ignition will show itself by the engine continuing to run.


Bigdex (above) says the same thing and I would agree also. It seems logical to me too.
When I made this point to John Teesdale who wrote the article in MF, his explanation was that it was possible to stop the engine by switching off on tick over, maybe if tickover was adjusted to be very slow, even though one "mag" was live, and then if it was hand spun very fast it would fire.
This seems pretty improbable to me, but it's the "official" explanation of what happened.

Moral: don't hand crank the engine quickly.

(I've never seen a POH that tells you to crank it on the starter motor before checking the oil - as Marvin says this will pump oil round the engine rather than back into the reservoir so there's no chance of getting a good reading on the dipstick. It is normal as part of the engine start procedure, however, to run the starter motor with the switches off to check that the oil pressure gauge shows a reading before engine start - but this is a different thing to the gurgle check )
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By Miscellaneous
#1786724
allout wrote:"So why dont rotax suggest turning it on the starter
They do.
From the Flight Manual of my Club's 912S:
"para 4. .... Caution. Run the engine for about half a minute before checking the oil ...

That's not what @carlmeek is asking. He's asking why not crank without starting, rather than turning the prop by hand.
User avatar
By lobstaboy
#1786736
Miscellaneous wrote:
allout wrote:"So why dont rotax suggest turning it on the starter
They do.
From the Flight Manual of my Club's 912S:
"para 4. .... Caution. Run the engine for about half a minute before checking the oil ...

That's not what @carlmeek is asking. He's asking why not crank without starting, rather than turning the prop by hand.


The answer to that has already been given, i.e. cranking on the starter motor before checking the oil on the dipstick is too fast and circulates oil all round the engine. Turning SLOWLY by hand causes a rise in pressure in the crankcase due to leakage past the rings. This pushes oil from the sump up into the reservoir can where the dipstick is. Turning until the gurgle is heard ensures that all the oil has got to the reservoir (the engine is blowing bubbles!)and the dipstick will read accurately.

It's possible to turn too fast by hand, both for the oil and for the potential risk of getting the engine to fire (allegedly).

The gurgle check is done once a day at the beginning of the day as part of the daily inspection.

Every time the engine is about to be started and with pilot and passenger aboard, the engine is cranked with the starter to check that a reading is shown on the oil pressure gauge. If no reading- don't start.

The 912 is a very different engine to Lycomings and Continentals etc...
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By carlmeek
#1786737
I can't see how a slow turn (hand), versus a fast turn (starter motor) would make any difference to what's happening with the oil - there will be some pumped around the engine, and most scavenged to the tank.
We're debating a club safety notice to say either crank, or start and run, the engine before checking the oil. Obviously there's a 99.9% probability oil level is good, so the risk of running it dry is virtually non-existent, and if so, there may be a puddle under the aircraft!

Better than losing one's arm.
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By lobstaboy
#1786744
carlmeek wrote:I can't see how a slow turn (hand), versus a fast turn (starter motor) would make any difference to what's happening with the oil - there will be some pumped around the engine, and most scavenged to the tank.
We're debating a club safety notice to say either crank, or start and run, the engine before checking the oil. Obviously there's a 99.9% probability oil level is good, so the risk of running it dry is virtually non-existent, and if so, there may be a puddle under the aircraft!

Better than losing one's arm.


But you will overfill with oil. It's easy to see that the two methods will give you different oil levels on the dipstick. Just do a trial to compare them. First do it slowly by hand and see where the oil is. Don't put the dipstick back in - and turn the engine on the starter for 30 seconds. Now put the dipstick in and measure it again. When I tried this there was a definite difference.

Why don't you contact John Teesdale the BMAA Safety Officer?
https://www.airsportstraining.co.uk/about/
He knows properly the original story that you are reacting to and will be happy to help I'm sure. He's one of the good guys (he must be - he's the FIE who passed me as a micro instructor).
Last edited by lobstaboy on Tue Jul 28, 2020 6:54 pm, edited 1 time in total.
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By RichJordan
#1786747
Interestingly, (and I've not thought about it before) I don't think I can crank my Rotax without it attempting to start.

My ignition key sequence goes OFF - MAG1 - MAG2 - BOTH - STARTER.

I gurgle mine very carefully, having previously owned G-CCXM, a Skyranger which a previous owner hand started, it jumped it's chocks and nearly cut his arm off.
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