rlborger(at)mac.com
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 Posted: Wed Feb 05, 2014 4:35 pm Post subject: Some data points and pictures from my Rotax 91X School |
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Bob & others out there in aeroelectric land,
I have some pictures from the Rotax 91X school I attended back in 2006. They are posted on my Europa build web site. You can go directly to the school pictures with this URL: http://www.europaowners.org/main.php?g2_itemId=64472
The first set of pictures of a piston/con-rod are from that engine in which the gentleman reversed the in/out fittings to the oil reservoir.
The next set of pictures are of the engine which had the oil pressure sender mounted out on the extension to allow for a pressure switch. You can see the broken brass fitting in the housing of the oil pump, a couple pictures of the holes in the crankcase that the thrown rods made and an overview of the engine. Which is now the demo engine used in the course.
As I said, I don’t know if the engine seized in 10 seconds or 10 minutes, but Dean said that if you interrupt the lubrication of the Rotax 91X engine it will usually seize like that in 10 to 30 seconds. It does not tolerate loss of lube at all well. And I’m not going to test it on my engine. You can have a total loss of the coolant and the engine will continue to run and will usually get you to a safe landing at a reasonably close airstrip. It may never run again after it gets you there, but it will get you there. You loose oil pressure and you better find a flat spot quick because the engine is going to stop very soon.
The Rotax 91X engine has much more in common with motor cycle engines than it does with your normal Lycoming or Continental. The 914 turbo is 74 cu.in. and produces 115 HP (at) 5800 rpm. It is recommended that you limit this power setting to 5 minutes max on take off. It uses a gearbox with a 2.43:1 gear ratio to drive the propeller. The gearbox has a slipper clutch to protect the engine in case of a prop strike. Because the engine and gearbox share the lube system special oil is required. Most of the recommended oils are motorcycle oils. But Shell does make an oil specifically for the Rotax 91X engine. The engine has a dual Capacitive Discharge ignition, no mags. Normal operating range of the engine is 5000 to 5500 rpm and you must keep the idle above 1400 rpm, preferably above 1800 if you can. This saves wear on the gearbox. It has air cooled cylinders and liquid cooled heads. It is a dry sump engine with separate oil reservoir and oil cooler. Oil is returned from the engine directly to the reservoir. From the reservoir it goes through the cooler on its way to the oil pump. Purge the oil system after every oil/filter change. Never turn the prop backward more than half a turn or you stand a chance of ingesting air into the oil system and into the hydraulic valve lifts. This could trash your valves. Always “burp” the engine before starting. (Open the oil reservoir, turn the prop forward slowly to get compression on each cylinder, continue till all the residual oil has been forced from the crank case into the reservoir. You will get a distinct gurgle or “burp” when all the oil is back in the reservoir.) This allows an accurate determination of the actual oil in the system and provides some oil into the engine so you don’t get a “dry” start. It has dual carburetors which must be balanced for the engine to run smoothly. When the carbs are properly balanced, the engine is extremely smooth with almost no vibration. Almost like an electric motor.
All in all, it is a very good little engine. Lots of power for the size and weight of the engine. I don’t think anything out there can match the power to installed weight ratio. A very efficient engine with a fuel consumption of about 4.5 gph at a 130 kt cruise in my Europa tri-gear. 5.0 gph will get you to 140 kts. You just can not treat it like your daddy’s Ly/Co. If you do, you will probably hurt it.
I HIGHLY-HIGHLY recommend anyone flying behind a Rotax 91X engine attend one of the Rotax operators schools. They are available from several Rotax shops in the US and Canada.
Blue skies & tailwinds,
Bob Borger
Europa XS Tri, Rotax 914, Airmaster C/S Prop (50 hrs).
Little Toot Sport Biplane, Lycoming Thunderbolt AEIO-320 EXP
3705 Lynchburg Dr.
Corinth, TX 76208-5331
Cel: 817-992-1117
rlborger(at)mac.com
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