Difference between Rotax's
Jon N. Steiger
I think a big factor in Rotax "unreliability" is the fact that they
are a 2 stroke engine. (Well, the ones on most ultralights, anyway.)
2 strokes need more maintinence and have to be watched more carefully
than their 4 stroke counterparts. I think that, behind most
tempermental engines, you'll find a pilot who isn't as dedicated
to maintenence as much as he/she should be. Plus, when the engine
goes out on your ultralight, you'll care a lot more than when it
goes out on your dirt bike... (And the memory will stick longer.)
I think the unreliability of the Rotax (and 2 stroke engines in
general) is a myth, and has probably been blown out of proportion...
From what I've seen, the Rotax is one of, if not the best engine
for ultralight applications. I know instructors and dealers who
swear by it, and would never consider an alternative engine.
Like the original poster, I don't have any personal experince with
Rotax engines, just minimal experience with a 250cc Yamaha 2-stroke. I'm
just regurgitating the opinions of the people I've encountered. YMMV.
-Jon-
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Paul Kevin Buller
that were basically the same size, but with minor changes in
displacement, compression ratio, etc. that make them different
models. I've heard of the 377, is that related to either the 277
or the 447? What about the 503? Are any of them basically the
same core with different piston arrangements?
I also heard that some people complain that the rotax
engines have a bad habit of quiting for no reason (ie. not man
induced like fuel startvation). Could people tell me why they
have a bad reliability record, and what can be done about it.
Please understand, I am not complaining about the engines, I'm
just regurgitating what I've heard. I'm building a plane, and
considering a rotax as a power source. Thanks
Sam Buchanan
>
> I was just wondering if there were any two rotax models
> that were basically the same size, but with minor changes in
> displacement, compression ratio, etc. that make them different
> models. I've heard of the 377, is that related to either the 277
> or the 447?
Yes Paul, the 377 is practically identical to the 447 except the bore is
smaller. Matter of fact, the 377 is very close to being a "square" engine (bore
and stroke being equal) which means it is one of the smoothest running of the
air-cooled Rotaxes. Alas, it is no longer imported, but used ones are available
and all spare parts are stocked. (I have a 377 in my MiniMax).
>What about the 503?
The 503 has proven to be a VERY reliable engine.
> Are any of them basically the
> same core with different piston arrangements?
All the aircooled Rotaxes (except the single cylinder 277 which I believe is
no longer imported) are "basically the same core", ie. piston port, twin
in-line engines
> I also heard that some people complain that the rotax
> engines have a bad habit of quiting for no reason (ie. not man
> induced like fuel startvation).
No engine quits "for no reason". It can be difficult sometimes, however, to pin
down exactly why an engine seizes. With aircooled two-strokes, it is almost
always a problem with cooling, fuel mixture, or ignition timing.
>Could people tell me why they
> have a bad reliability record, and what can be done about it.
> Please understand, I am not complaining about the engines, I'm
> just regurgitating what I've heard. I'm building a plane, and
> considering a rotax as a power source. Thanks
Yes, if a four-cycle engine with the same power-to-weight ratio of the Rotax
was available, we all would be flying it (if cost wasn't a factor); However,
such an engine is not available...
DON KINNEY
pauc> Subject: Difference between Rotax's
pauc> Organization: The University of Calgary
pauc> I was just wondering if there were any two rotax models
pauc> that were basically the same size, but with minor changes in
pauc> displacement, compression ratio, etc. that make them
pauc> different models. I've heard of the 377, is that related to
pauc> either the 277 or the 447? What about the 503? Are any of
pauc> them basically the same core with different piston
pauc> arrangements?
The 377 is a 477 with smaller bore... I think but its not made
for ul anymore so dosnt relly matter
pauc> I also heard that some people complain that the rotax
pauc> engines have a bad habit of quiting for no reason (ie. not
pauc> man induced like fuel startvation). Could people tell me
pauc> why they have a bad reliability record, and what can be done
pauc> about it. Please understand, I am not complaining about the
pauc> engines, I'm just regurgitating what I've heard. I'm
pauc> building a plane, and considering a rotax as a power source.
pauc> Thanks
Its not that ROTAX engines are finikey, its that way with all 2-stroke
engines. Different models have different degrees of being finikey. I
used to use a CUYUNA and that when you idel it back too far to land
would cool down and want choke and not getting it would/did many times
quit on final. So I learned from the school of hard knocks (knees
knocking together) to keep 4000-5000 rpm and just dive a little to
keep the glide slope the same (in case it does quit).
My 277 dosnt do that but I dont take chances BUT it does vibrate
ALOT! On 1 flight it ripped the rubber connector 1/3 the way round that
connects carb to engine in abt 30 min, but still worked cause air
pressure kept the rip closed. Another trip the bolts worked out of
the top of carb. Everyone was standing arround after i landed and
someone asked me "do you fly with your carb like this?". Embarrassing!
Another time the plug cap fell off. Others told me to wire it on.
LISTEN TO OTHERS! I said "Nah ...I have 40 hrs with no prob" WIRE
YOUR PLUG CAPS! the engine quit and had to dead stick it. The mag
ignition cutoff wires have broke... good thing it wasnt to the coil
but i learned to coat solder joints with silicon to hold em rigid.
Ive had cracks appear all over an air scoop I built.
True you wouldnt have this vibration with a 4 stroke and they idel
nicer... on a 254 ul your stuck with 2 strokes. A 4 stroke weighs
alot more, for the same cc produces less power, and cost ALOT more.
Rotax, as far as 2 strokes go make very good engines.
SO one learns the proper rituals and is super finikey about gas and
worships the oil and keeps the cht below 400 and eventually WILL
reach the enlightment that comes from not having the engine stop
for over 100 houres or maby even 300!
The true enlightened 2 stroker will find himself/herself
going arround unlandable terrane.... scan the ground and say "I
could land there, and there"... Always poking the engine.... the
gas station attendents know you cause you get the best from the same
place all the time unless forced otherwise .... discusses brands
of oil and oil/gas mixture at meetings and tries to convert everyone
else who is trying to convert you (and you think religious discussions
are bad?) ..... and maby now and then just says a little prayer to the
great god of all rotax engines "DONT LET ME DOWN!!!"
DENNIS CLARK
reliability is in four stroke engines. GM and Ford have spent millions
of dollars on two stroke research. They got the emissions to an
acceptable level but the reliability was not there. That's why you don't
see them in automobiles. A company imports a smooth four stroke that is
converted to aircraft. It has the power of a rtx 582 but the weight of a
ready to fly rtx 503. The U S military uses them in arial recon vehicle,
with good reliability. The company is D&D 130 Ebenezer Dr. Newnan GA
30265 They have a free info packet.