Burping Rotax 912 with the starter motor

[fatsportpilot]

My shoulders hurt when I burp the engine but I know it must be done because it's a dry sump system.

Then I thought wouldn't it be nice if there was an electric motor that could turn the prop for me? And there is! The starter motor. I don't think it would be difficult for me to add a button that engages the starter motor (without also turning on the magnetos) at half or quarter power so the motor doesn't overheat.

Why hasn't anyone done this yet? Is there some reason that it wouldn't work? Just sit in the plane and hold down a button for a few seconds until you hear a burp, then get out and check the oil level. Is that a worthwhile thing to do for someone who doesn't like to burp it manually?

[Warmi]

You mean like this red button labeled Start ?

5CCE98C4-4D81-4CD0-856E-7D05920BBBB4.jpeg (150.37 KiB) Viewed 5469 times

[fatsportpilot]

That doesn't burp the engine though, that just starts it right? I have a 912ULS with a key that I have to turn to the start position (which engages starter and mags) while pulling the choke so I can already start the engine of course but burping still is done manually.

[Warmi]

That doesn't burp the engine though, that just starts it right? I have a 912ULS so I have a key that I have to turn to the start position (which engages starter and mags) while pulling the choke so I can already start the engine of course but burping still is done manually.

It starts the engine only if two separate switches for magnetos are on - if these are off , this red button just engages the starter and rotates the prop.

[fatsportpilot]

Does it turn it slow enough that it burps? I heard that the engine oil pump shouldn't be moved too fast when burping or it won't work correctly but since everyone just turns the prop manually, it's never an issue. I always thought the starter at full power was too fast.

[Warmi]

Does it turn it slow enough that it burps? I heard that the engine oil pump shouldn't be moved too fast when burping or it won't work correctly but since everyone just turns the prop manually, it's never an issue. I always thought the starter at full power was too fast.

I don’t know , I rotate my prop manually after each flight ( which is much easier than before the flight when the engine is cold ) - I used the button once or twice after oil purge procedure but that’s about it.
In other words, I don’t find rotating the prop on a warm engine cumbersome enough to even bother with using the starter button - interesting idea though.

[fatsportpilot]

It's possible to damage a dry sump propeller engine if it sat too long and the oil settled and you start it without burping it first so I always burp it during my engine preflight before the first flight of the day. I also heard advice that it's not good to burp the engine right after it stops. Then again I'm pretty new to this and my only source of Rotax information has been the internet (not classes) so far so I might be full of it.

To me it's not cumbersome but it hurts my shoulders after the first few rotations that let me "feel" the compression. I wish I had a start button like yours that just engaged the motor. My ignition looks like this (it's of this type) so there's no "starter without mags" option.

[Warmi]

It's possible to damage a dry sump propeller engine if it sat too long and the oil settled and you start it without burping it first so I always burp it during my engine preflight before the first flight of the day.

To me it's not cumbersome but it hurts my shoulders after the first few rotations. I wish I had a start button like yours that just engaged the motor. My ignition looks like this (it's of this type) so there's no "starter without mags" option.

It is not that I don’t burp before the flight - I look for oil, and if it is not within limits I do burp. It is just it takes fewer rotations on the cold engine if you pre-burp after each flight ( which normally takes only a few blades on the warm engine )

I am familiar with your ignition - I have trained and flown on many planes with this type of ignition and never really liked it mostly because I find separate explicit magneto buttons much more user friendly.
Also, I remember during my Rotax training a few years back at Leading Edge , the instructor mentioning that these ignitions are pretty unreliable and advising not to install them ( most of the folks in that class were builders)

[fatsportpilot]

I am familiar with your ignition - I have trained and flown on many planes with this type of ignition and never really liked it mostly because I find separate explicit magneto buttons much more user friendly.
Also, I remember during my Rotax training a few years back at Leading Edge , the instructor mentioning that these ignitions are pretty unreliable and advising not to install them ( most of the folks in that class were builders)

Yes they are very unreliable. The one I fly in is not working properly and the mags don't ground, so I have to pull the throttle far back to kill the engine, and I can't check each mag separately. A new one will be installed soon. It's my CFI's plane which he has available for rent so I can't expedite repairs as much as I want to. When I (one day) get to building my own I'll be happier with a fuel injected engine (either Rotax 912iS or maybe the wet sump ULPower UL350iS which doesn't need burping). Then I can play with lanes instead of mags.

[3Dreaming]

The purpose of burping the engine is to get an accurate check of the oil level. If you pull the dipstick out and the oil level is on the flat you are good to go. If it is not then you need to burp. Even if the oil is on the flat I like to pull through 4 compressions just to make sure the engine is not hydrolocked. Another trick to burping is to pull the propeller though compression slowly. The process of pushing the oil back into the tank comes from air moving past the piston rings during the compression stroke. The longer you leave the pressure to move past the rings with each compression the less work burping the engine will be. I burped one today that had been setting for a couple weeks, and it only took 5 compressions. The oil was just below the flat when I started.

[ShawnM]

I agree with Tom and it's how I was also taught. Pull the prop SLOWLY and the burp will happen faster. Slow and steady wins the race.

Besides, trying to burp the engine with the starter humming away won't really work, you'll NEVER hear it burp sitting in the cockpit over the noise of the starter and the prop spinning.

[fatsportpilot]

Besides, trying to burp the engine with the starter humming away won't really work, you'll NEVER hear it burp sitting in the cockpit over the noise of the starter and the prop spinning.

What I was thinking of was have the starter spin it a few times and then I would do the last turn or two manually to hear it and feel the engine etc. But I asked on a dedicated Rotax forum to make sure and they said that it's necessary to stop after each compression which the starter wouldn't do so I guess that's it for this idea.

[Wm.Ince]

Ya' gotta' ask yourself, what is the purpose of "burping the engine" in the first place?

Then . . . second question is . . . is there an alternative way of accomplishing what burping does . . without turning the engine over?

Using the starter for this purpose is a non-starter for me. That would be just asking for trouble. Very hard on the starter (think about starter cycles) and would probably decrease its longevity. No thank you.

[3Dreaming]

Besides, trying to burp the engine with the starter humming away won't really work, you'll NEVER hear it burp sitting in the cockpit over the noise of the starter and the prop spinning.

What I was thinking of was have the starter spin it a few times and then I would do the last turn or two manually to hear it and feel the engine etc. But I asked on a dedicated Rotax forum to make sure and they said that it's necessary to stop after each compression which the starter wouldn't do so I guess that's it for this idea.

You don't want to stop after the compression. You want to stop as compression is building, the move a little more a couple times, then on the the next compression. I would be afraid to hit the starter without pulling it through by hand at least 4 compression strokes first. I have never had a hydraulic lock, but I have an airplane in the shop that last year filled one bank of cylinders twice with fuel. If they had hit the starter they would have bent a rod ruining the engine.

PS: I had not been maintaining the aircraft at the time of the issue.

[3Dreaming]

You could always remove the cowling and a spark plug, and use a compression tester to burp the engine.