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Rotax 912 History...

Piper J3

Well Known Member
There are a lot of new folks on the forum these days so I thought I’d mention a little Rotax history…

When I bought my RV-12 back in 2015 I was curious why Rotax called their 4 cylinder horizontally opposed engine a 912. I pretty much know Lycoming and Continental nomenclature: IO-360 is opposed, fuel-injected, 360 cubic inch displacement. I asked the question over in the RotaxOwner Forum…

Christian Wilfling asked Hans Paierl, "The father of the 912" concerning this question, he laughed and said: back in 1989 Rotax were building engines with less than 1000cm3 and because our account department could not handle more than three numerics back then,
he decided to choose the niner for Aircraft Engines and the 12 for 1200cm3 cubic capacity of the first 80 HP Rotax 912.
 
Another little Rotax 912 tidbit is that it's total engine displacement is approximately equal to the displacement of one Lycoming O-320/O-360 cylinder:

Rotax 912 engine = 82.5 cu. in.
Lyc O-320= @ 320 cu. in., therefore one cylinder = @ 80 cu. in.
Lyc O-360-A = @ 360 cu. in., therefore one cylinder = @ 90 cu. in..

That's @ 100 hp out of four tiny Rotax cylinders -- not too shabby.
 
What's even more incredible is the those 4 small cylinders hold up better than the typical Lycoming or Contenential types as far as compression and oil consumption and wear...this is what I've heard.
 
Think about this;

The Rotax 912 has a TBO of 2000 hours the same as a Lycoming 0-360. That is saying the manufacturer expects the engine to last 2000 hours before needing a major overhaul.

The Rotax can run all day at 5400 RPM where the Lycoming is 2700 RPM. The Rotax will turn twice as many revolutions in it's expected lifetime than the Lycoming.
 
Ask a Rotax heavy line repairman what the bore wear and ring end gap measurements are on a 912 ULS after 2000 hours and if the bores and pistons are reused in the rebuild.

How often does a Lycoming make it to 1000 or 1200 hours and need a new jug and piston?

How do you break in a Lycoming engine, and how do you break in a Rotax engine?

Technology and material advancements are a wonderful thing.
 
Is it true that, worldwide, Rotax has sold more aircraft engines than all of the other manufactures COMBINED?
 
Another little Rotax 912 tidbit is that it's total engine displacement is approximately equal to the displacement of one Lycoming O-320/O-360 cylinder:

Rotax 912 engine = 82.5 cu. in.
Lyc O-320= @ 320 cu. in., therefore one cylinder = @ 80 cu. in.
Lyc O-360-A = @ 360 cu. in., therefore one cylinder = @ 90 cu. in..

That's @ 100 hp out of four tiny Rotax cylinders -- not too shabby.

OK 0320 has about twice the horsepower, and 1/2 the RPM. So this equates (ironically) to 1/4 the displacement for the Rotax. It all fits. Seems like horsepower per (displacement * RPM) is similar.
 
I think some of the design features of the 9-series engine that allow long service life include roller bearing crankshaft, camshaft positioned below crank, sealed crankcase with remote oil tank, water-cooled heads and heavy cast cylinders.

As compared to Cont or Lyc, the cast cylinders on the 9-series engine have extremely heavy fins. This feature, in conjunction with small bore, keeps the cylinder geometry truly round with temperature cycles. Shock cooling is not a concern on 9-series because of water-cooled heads and heavy cast cylinders. Cont and Lyc use “choke” bore that approximates a true cylinder shape at elevated temperature. Cylinders go out-of-round because of uneven cooling on bottom side and front Vs. rear cylinder position within a pressure cowling.

It’s very common for 9-series engines to consume less than one liter of oil between oil change intervals. Lycoming uses the following formula to determine maximum oil consumption: (. 006 x BHP x 4 )/ 7.4 = maximum quart/hour consumption. This means that, for a typical 180-horsepower engine, using one-half quart per hour is acceptable to the manufacturer.
 
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