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rotax 4-stroke - fuel system
912UL, 912A, 912F, 912ULS, 912S, 914UL and 914F Engines
Always operate the engine on the fuels as detailed in the aircraft manuals and in accordance with local regulations.
Both Avgas & Mogas are approved by Rotax for use in their engines. Rotax engines prefer unleaded Mogas as the lead in Avgas causes maintenance issues such as fouled piston rings, deposits on spark plugs, deposits in the combustion chamber and exhaust port and can sometimes cause sticking valves. The lead can also accumulate in the slipper clutch and sprag clutch, which can prevent them from functioning correctly.
912UL / 912A / 912F: European standard: min ROZ 90 (EN228 Normal, EN228 Super, EN228 Super Plus) or AVGAS 100 LL. Due to higher lead content in AVGAS, the wear and deposits in the combustion chamber will increase. Therefore only use AVGAS if you encounter problems with vapour locks or if other fuel types are not available. Note that the service life of the oil and spark plugs is reduced if AVGAS is used, see Rotax maintenance schedules for details.
912ULS / 912S / 914UL / 914F: European standard: min ROZ 95 (EN228 Super, EN228 Super Plus) or AVGAS 100 LL. Due to higher lead content in AVGAS, the wear and deposits in the combustion chamber will increase. Therefore only use AVGAS if you encounter problems with vapour locks or if other fuel types are not available. Note that the service life of the oil and spark plugs is reduced if AVGAS is used, see Rotax maintenance schedules for details. We would suggest that all operators of 912 100hp engines or 914 engines use at least super plus 97 octane fuel.
All information provided here is correct at the time of publishing to the best of our knowledge, but Rotax recommendations may change at any time without our knowledge. It is the engine owners responsibility to ensure that the engine is fit for flight at all times. The information is provided here free of charge and with no obligation from us to the consumer. To ensure that you have the correct and most up to date information, you should refer to the current Installation, Operators and Maintenance manuals for your engine. The information provided here may not be valid for aircraft outside the UK. Click here for ConAir SportsTerms& Conditions, including website usage policy.
Experience has shown that ethanol does not harm the engine components and the engine performs well with it. The main concern is the ability to capture and hide water within the fuel. Proper storage and water detection are critical for ethanol use.
Carb icing when using ethanol fuels should not be a problem if an effective carb heat is fitted and most problems with vapour locks should be avoided if a fuel system is designed to the Rotax guidelines. Protecting hoses with heat sleeving helps prevent vapour locking. Particularly avoid restrictions and tight bends on the suction side of the fuel pump.
Yes. But the lead in Avgas causes maintenance issues such as fouled piston rings, deposits on spark plugs, deposits in the combustion chamber and exhaust port and can sometimes cause sticking valves. The lead can also accumulate in the slipper clutch and sprag clutch, which can prevent them from functioning correctly, as well as gumming up the wastegate on 914 series engines. Please note the following for Avgas use:
- Change the oil every 25 hours
- use a semi synthetic oil
|
Fuel Consumption in l/hour |
912 UL / A / F |
912 ULS / S |
914 UL / F |
|
At take-off performance |
24 |
27.5 |
33 |
|
At max. Continuous performance |
22.6 |
25 |
27.2 |
|
At 75% continuous performance |
16.2 |
18.5 |
20.4 |
|
Specific consumption at max. continuous performance |
285 g/kWh |
285 g/kWh |
276 g/kWh |
With engine running and with any back up pump turned off, bleed off fuel between pump and carbs, restricting bleed off to maintain minimum 0.15 bar pressure at carb inlet. Measure bleed off at full throttle. This bleed off must be at least 25% of published full throttle fuel consumption.
Full throttle fuel consumption 912UL = 24 l/h, 912ULS = 27.5 l/h, 914 = 33 l/h
Backup electric pump:
With engines stopped, run backup electric pump. Bleed off fuel between mechanical pump and carbs, restricting bleed off to maintain minimum 0.15 bar pressure at carb inlet. Measure bleed off, which should be at least 125% of published full throttle fuel consumption.
See additional information on 914 on the LAA website which requires a pressure to be applied to the airbox to simulate the turbo boost pressure.
Useful information on fuel flow testing can be found on the LAA website in TL2.20, click here.
The single most likely cause of an engine failure must be fuel starvation - yet it is one of the least popular gauges on a pilots wish list. If you are focused on engine reliability, make sure you get a fuel pressure gauge, see here.
If installing an electric backup pump, the fuel flowand pressure requirements must be met. Experience shows that the 40106-K Facet pump is a good choice.
Any pump that does not free flow when switched off must have a bypass check valve fitted.
The mechanical fuel pump should be replaced at overhaul (or every 5 years if fitted with integral hoses).
The 914 uses 2 rotary valve pumps which should be connected in series with check valves in parallel. The main pump should be replaced every 1000 hours and both pumps replaced at TBO.