Can the modern 912 fire while turning the prop slowly to check oil or compression.

[DrZoos]

1. With key off

 

2. With key on

 

My understanding was

 

1. No unless there was a fault and you achieved a certain rpm

 

2. No unless you achieved a certain rpm

 

 

[fly_tornado]

CDI ignition

 

 

[DrZoos]

CDI ignition

So whats the rpm required to produce lightning should a fault occur???

 

 

[kaz3g]

I was taught to ALWAYS treat a prop as live. I was also taught to check both the mags earthed just before shutdown in case an earth wire had broken.

 

I think these are good habits to develop irrespective of the particular aircraft you are flying.

 

Kaz

 

 

[facthunter]

Pulling it through to "burp" the oil return is normal procedure, so that means it is regarded as safe. BUT... I like to treat all props as potentially alive. I heard 400 rpm somewhere but don't trust things like that. Relying on earthing to kill a mag is not a guarantee when there are remote switches and wires involved. Nev

 

 

[Head in the clouds]

I agree absolutely with Kaz's comment above, in exactly the same way that all guns should always be considered to be loaded.

 

To answer the OP question though, IIRC the manual says you need 800rpm to trigger the ignition circuitry.

 

It has often been said that it's impossible to hand-prop start the 912 but there's a well-known YouTube video showing it being done successfully with an energetic swing.

 

Of course there are skeptics that also say it's faked. Looks genuine enough to me. A search on YouTube should find it easily enough.

 

 

[facthunter]

The engine goes two revs for the props one. I believe you CAN start them. If an engine can idle reliably it must be able to be started. Nev

 

 

[DrZoos]

Go straight to 3 minutes

 

Absolutely that is a real video...the shadowing gives it away as real and there is no editing

 

I cant verify what all the leads are for , or if they help, but undoubtedly he started that by hand, with or without electrical help via those black leads.

 

 

[Nobody]

 

The "leads" are ropes to the chocks so he can pull them out one he is strapped in the aircraft so as to prevent this:

 

 

[DrZoos]

How do you possibly explain that to the owner... umm , David, i bumped into KBZ with my prop, ya better come take a look... oh, might be best if you go via the hospital and take a few valium on the way...

 

 

[Head in the clouds]

How do you possibly explain that to the owner... umm , David, i bumped into KBZ with my prop, ya better come take a look... oh, might be best if you go via the hospital and take a few valium on the way...

Yes, we'll it's not nearly uncommon enough, I must have seen 50 similar photos of different aircraft. Gladly only one was a fatality.

 

The saddest similar one was on a whale-watching trip ... Whale watching vessels should be compelled to have protective rings around their props like surf lifesaving boats have.

 

 

[Downunder]

So whats the rpm required to produce lightning should a fault occur???

I heard 200rpm. 800 sounds awfully high and I'm sure mine starts well below that..............

 

This is why a good battery and cables are required........ seen a few 912's turned over with a low battery. The owner hoping it'll fire but of course it won't.

 

Potential damage to the sprag clutch can occur too which is a very pricey fix.

 

Lots of aircraft, factory and otherwise out there with substandard cabling too......beware....

 

 

[kaz3g]

That was just one part of the damage account...

 

http://www.check-six.com/Crash_Sites/VH-KBZ-ShreddedSeminole.htm

 

I also remember a LAME's large toolbox being shredded and its Sidchrome contents being flung to all corners of the RVAC maintenance hangar at Morrabbin a number of years ago.

 

Kaz

 

 

[DrZoos]

LOL thats a great read.... angry wife...got sued, got off... poor silly fella...just goes to show you can have an extremely high IQ and be dumb as a post all at once.

 

That was one expensive flight , makes the $100 burger look cheap

 

 

[facthunter]

Very evenly sliced. Quick reactions NOT. A TBM chopped up a small plane in the US. Fatal unfortunately. I was taught to "S" turn taxiing in high/long nosed T/W planes. Don't see it being done always . Think safety. Nev

 

 

[kasper]

Oh its less than 200rpm to spark a 912 up. I have hand propped them and there is no way I can spin a 912 prop at 90rpm - that's 200rpm engine speed. I prop the 912 about the same prop speed as a breaker points 503 or 447 and the gear ratio measn its sparking up at lower engine rpm - the CDI on the 912 seems to fire up much easier than the CDI on the 503 or 582 that I always hate trying to prop start because they usually refuse to start before I am knackered.

 

 

[DrZoos]

So how hard is it in terms of hand propping... Would it be 75% of your best efort? 100% ?

 

Given that experience do you think its at all possible to accidently start a 912 while purging or compression testing..

 

 

[Geoff13]

If you purge as per the book it shouldn't start. As I read it the idea is to turn her over very slowly holding the compression to allow the oil to be forced back into the reservoir.

 

If you do that you are not going to have enough revs. As for compression testing you are feeling for the compression so again slow turning.

 

But as has been already said. Check switches and treat it as live anyway.

 

 

[DrZoos]

Yeh i always double check... I have had several old guys comment that its too dangerous and shouldnt be done, despite the manuals saying to do it...so was wondering if anyone actually had any experiences in recent times about actual rpms or effort needed rather than just fear mongering or reference to old stories....

 

Im all for standing in a very safe position and turning it slow, but just wanted to know from others of any recent experience with one firing... Sounds like everyone is cautious, but none have fired recently??

 

 

[kasper]

So how hard is it in terms of hand propping... Would it be 75% of your best efort? 100% ?Given that experience do you think its at all possible to accidently start a 912 while purging or compression testing..

I gurgle the engine - its as described it is turning the engine at maybe 3-10rpm - no error in typing its REALLY slow and you are holding the compression to pump the oil.

To start its fast turning - as fast as I can fling the prop and thats nothing like a gurgle. There is really not a risk of prop firing on the CDI with a gurgle test.

 

And for anyone thinking of hand proping a 912 (or any engine) the trailing edge of composite props are not that strong and if you break it by dragging your hand as you pull through you are in for an expensive repair - having a charged battery is much better than propping - my excuse was that in a french field at 7am and 1 of the trikes has a 70yo pilot and flat battery it was that or wait hours to get a charge.

 

 

[pylon500]

While caution, and maybe a good dose of natural fear, is healthy around props, a cold, non primed 912 is pretty safe.

 

The possible worry is when turning a geared prop is the sudden 'ramp up' of compression, for a relatively slow turn of the prop, that tends to create a quick 'over compression', right at the point that the CDI pickups can energize.

 

The history of treating props as 'live' stems from the introduction of the 'Impulse' magneto.

 

Here the core of the magneto is held back via a spring until the prop passes 'top dead centre', where upon the core then spins rapidly back to position, moving the magnets quickly, thus energizing the plugs.

 

Thus, with an engine primed and ready to run, the prop only had to be pulled up to, and then just past, top dead centre, and the engine would fire.

 

Not a great deal of effort required to get started.

 

You can hear the impulse system working, if you stand near some brave soul as they turn over most of the old GA engines, as a loud 'clack' as the engine goes over TDC.

 

 

[Downunder]

I think we need to quantify what 912 we are talking about here.

 

The lower capacity and compression 80hp is more likely to be prop started but a 10:1, 100 hp much less so I think.

 

And these days I imagine a 100 horse outsells the 80 at least a few times over.....

 

 

[facthunter]

Revisiting the "original" Phrasing of the question. Who can give a DEFINATE answer? You can hand prop a 912. this seems to be obvious but you have to put a lot of effort into it. It's the momentary rotational speed that provides the spark Ie at the point of firing and the compression usually slows the motors rotational speed at the point where firing occurs.

 

As stated above the purging of the oil is done by turning SLOWLY to allow the gases leaking past the rings to push the oil back to the tank. The Technique is not as effective if the engine is turned quickly.

 

Magneto's with "impulse" mechanisms can fire at virtually NO RPM as the mechanism "trips" on a pin and the tensioned spring gives a sudden part turn at the right time to fire a full sized spark. This is the reason for the "care" most older pilots show for ALL props. Everyone still should, as you never know if the starter may be engaged even by a spanner falling on a terminal. Nev

 

 

[kasper]

I think we need to quantify what 912 we are talking about here.The lower capacity and compression 80hp is more likely to be prop started but a 10:1, 100 hp much less so I think.

And these days I imagine a 100 horse outsells the 80 at least a few times over.....

I have hand prop started both the 80hp in a Medway Raven with a delicate Arplast eco prop and the 100hp in a P&M Quik with the hard as nails Warpdrive - not a real difference in pull to get them started - the real difference was in the prop trailing edge - Warpdrive is blunt, strong and cuts fingers if not careful with little risk of breaking the edge, the Arplast is delicate and can break really easy ... but is a nicer prop and to my ear quieter both in the plane and from the ground ... but poisonously expensive.

 

 

[DGL Fox]

I watching these old videos yesterday and when I read this thread it reminded me of the stories main character and his sons near serious injury when he turned over the prop with everything turned off....but it seems he didn't figure on the hot engine after his flight dieseling back into life for one revolution of the engine when he turned the prop...he and his son were very lucky not to be seriously hurt or killed...I wonder with all of our new technology it could be possible for a modern engine to do just the same things as his did...here is a link to the videos...not sure which episode it was in...

 

 

David