Rotax 912 ULS Engine Oil Level

[alf jessup]

Hi Alf - Not sure that Rotax would agree with the post flight burp, but I am actually more interested in the heat soaked engine & the the baked ignition modules.My aircraft does not facilitate the opening of engine cowl (multiple fixings must be removed) however I have long been concerned with the unnecessary containment of engine heat after shutdown. In my case the contained heat may be contributing to fuel vaporisation, making subsequent hot starts (failures) embarrassing. To mitigate this I open my oil/coolant inspection hatch to allow the heat to dissipate more readily. Seems to work, at least some of the time.

 

What makes you think the ignition modules are not designed to withstand the heat emanating from a hot engine?

 

Going back to the post flight burp - by checking your oil level outside the accepted regime, you may introducing variables that Rotax designers/engineers may have not allowed for. I am not an engineer but I do know that in land based engines, allowing the oil to flow back into the sump usually gives a better measure of oil quantity, than when the engine has been recently run. Hence the advise to check the oil level before the first start of the day or at least after a suitable cooling off/drain down period.

Skippydiesel

Rotax being a dry sump what oil in the canister is the oil level

 

I always check it again before flight in any case

 

As for the modules, we'll my take on it is less heat the better post shutdown, yes they probably are designed for heat soak but I am figuring if I let the latent heat dissipate by opening the cowl hatches I'm doing the modules a favour by not letting them soak up the heat

 

Plus opening the cowl hatches takes all of 2 seconds a side.

 

Cheers

 

Alf

 

 

[facthunter]

I believe stick to the makers procedures but there's no harm in understanding what is going on. I noticed a new motor took ages to get it to Burp and was improved by turning over REAL slow, giving it time for the compressed gas to leak past the rings. This works well and also safer than turning it faster. You hold the blade as you turn it and can feel the resisting force diminishing. There's no direct relation between the number of rotations and how effectively the oil returns. Going faster can be less effective. Since the return pipe is not large when the oil is colder (and thicker) it returns more slowly, so you have to give it time for the gas pressure to push it back.

 

When you shut down a motor, oil drains down to the lower parts with time. If you check it soon after stopping more will drain down later.

 

Re the heat after shutdown, this is more a problem with aircooled motors where the heads are very much hotter than the core, and the equalising effect if the motor has delivered a lot of power on approach needs time after landing, idling into wind with cowl gills open, or you cook magnetos seals etc Some cowls aggravate the problem. Nev

 

 

[skippydiesel]

Hi Nev - Agree with all your comments and would add one more:

 

My 912 (& I assume all others) has the fuel line, from tank to the mechanical pump (located front right of gearbox/engine) and from the pump to the carbi distributer, passing over the crankcase. Classic case of designed in fuel vapourisation. I don't usually have any problems until the air temp rises to about the mid thirties. When in this situation & I have to do a "hot" start I have a range of strategies to get the fan to run & stay running ( I may not use all). Strategies include, prolonged fast idle before shutdown, opening inspection hatch on top of cowling & facing aircraft into wind after shutdown (both to assist in dissipation of heat). On start up, prolonged use of fuel boost pump before start, use of boost pump immediately after start up, gradual application of throttle, prolonged engine run up, monitoring of fuel pressure gauge (wavering needle/sudden drops indicate gaseous state still present) and most important a plan for "aborting" takeoff. I have always managed to get her to start but sometimes there is an embarrassing "conk out" requiring a second start. The main thing is to get the engine delivering smooth continuose power before starting my takeoff run - once achieved I have no problems maintaining normal engine function.