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lstavenhagen(at)hotmail.c Guest
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Posted: Sun Jan 01, 2006 6:54 am Post subject: 2 Stroke VS 4 Stroke |
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Quote: | Men...on the 2cycle Vs 4cycle engine issure, I have been following this
thread, and
in reading I sometimes wonder if some might be confuseing...or better said,
interchangeing, the meaning of the word relilable with durability?
Working for the largest manufacturer of 4 cycle engines in the world, I
am
very familiar with the commonly misunderstood comparision of these 2
engines.
A 2 cycle can easily be built as reliable as a 4 cycle...but it is almost
impossible to build one as "durable"...I say "almost" because someone who
works for Detroit Deisel might be reading here and take issue with the
statement.
So remember in your reading of the posts...are we debateing a durability
problem..or a dependability problem. Sometimes both I think..and they
shouldnt be confused.
Could we agree that a certain Rotax 2 cycle might be as dependable as a
certain 4 stroke....but it just wont last for as long? With that might come
the admission that it wont be as "dependable" for as long......
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I'll go along with this 100% - this is unquestionably true....
In fact, ironically, this is one of the main improvements in terms of
reliability of 2-strokes over the years - a very good knowledge of the
limits in terms of how long things last in the motor and what kind of
operation they're NOT tolerant of.......
This is what I mean when I say knowledge is the key to reliable operation of
any engine including 2-strokes. And the reason I can confidently say that
the Rotax 2-strokes ARE quite reliable.
For example, some operational things that tweak 2-stroke weaknesses are:
- extended full throttle operation. I.e. running at max or very near max all
the time. This is where the 300 hour TBO listed in the manual came from .
The usual cause here is underpowering the airplane to cut costs - putting a
503 on a big 2-place and flying it dual a lot of the time (where really the
582 or something bigger is required). Generally, aviation 4-strokes can
handle this all the way out to TBO (some of the continental/lycoming
aviation motors are literally designed to run at full throttle just about
all the time), but a 2-stroke due to its design is simply not as durable
when run this hard.
- low MOI limits on the Rotax gearboxes, particularly the B box. Some of the
most popular props on the market (like the IVO in 3-blades and the warp
drive) are 50% or more over the MOI limits of the B box. They can take it
and regularly do, but the stresses they put on the crank and other moving
parts inside the motor and gearbox itself are outside of the design limits.
This can lead to premature damage and wear, and sometimes catastrophic
failure.
- mag end electric starters. The 2-stroke Rotaxen's weak spots are generally
the cranks (especially with the 582) and the ME electric starts can do a lot
of damage (especially the GPL starter, but even the Rotax model) - you have
that bendix flying out and smacking the starter gear which is like taking a
hammer to the edge of it. This puts a heavy side-loading shock on the mag
end of the crank, which can knock the journals out of alignment. Also, they
have to instantly get the entire moving system - crank and prop - up to 300
rpm, which puts a lot of stress on the crank (much moreso than the pull
start). You have no such problem at all on the bigger 4-strokes, since
their cranks are MUCH beefier even if they are press-fit designs.
- over or under propping. Here is where the 4-stroke shines and the 2-stroke
just makes you pull your hair out in aggravation. In particular, 2-strokes
are extremely susceptible to high-rpm/low throttle opening situations due to
their design (this leads to poor lubrication and cooling). So too small of a
load, such as a fast descent with the throttle reduced or too small/too fine
of a prop, is a hazardous situation to be in with a 2-stroke. With a
4-stroke there's no such concern at all, since the lubrication circuit is
completely independent. Just keep it below redline and you're ok basically
. Overpropping is less bad on a 2-stroke but still bad since their torque
curves tend to be fairly peaky. 4-strokes - no problem or very little
problem....
Last but not least:
- simply lower TBO generally due to higher specific output, more maintenance
required. These are just facts of life of 2-stroke operation and these have
to be paid attention to. The crank seals on the Rotax simply start to leak
at 100 hours or so and there's nothing that can be done about it. They also
simply wear out faster (400 to 500 hours on the aircooled) and just simply
need to be rebuilt after that time. The 4-strokes just simply last longer,
i.e. the 912 has a TBO more than 4 times longer than the 2-stroke! That's
just a fact of life (and certainly nothing I ever debated against).
So, while these are definite limitations of the 2-stroke, they're KNOWN
limitations - that allows us to work around them and avoid the reliability
problems they can introduce.
Indeed, the most dangerous thing in aviation is the unknown. The Rotax
2-strokes aren't as reliable as they are because they're so fantastically
good quality (they're basically just beefed up snomo engines), but it's
because we KNOW so much about operating and maintaining them.
Incidentally, this is true of the 4-stroke designs as well. Knowledge is the
key there too...
Ok, nuff said....
LS
N646F
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kfackler(at)ameritech.net Guest
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Posted: Sun Jan 01, 2006 8:04 am Post subject: 2 Stroke VS 4 Stroke |
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Quote: | - low MOI limits on the Rotax gearboxes, particularly the B box. Some of
the |
Quote: | most popular props on the market (like the IVO in 3-blades and the warp
drive) are 50% or more over the MOI limits of the B box.
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What does this mean, i.e., what is MOI?
-Ken Fackler
Kolb Mark II / A722KWF
Rochester MI
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lstavenhagen(at)hotmail.c Guest
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Posted: Sun Jan 01, 2006 8:26 am Post subject: 2 Stroke VS 4 Stroke |
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Quote: | What does this mean, i.e., what is MOI?
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Oops, sorry. MOI means moment of inertia, the rotational mass of the
prop....
LS
N646F
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jhauck(at)elmore.rr.com Guest
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Posted: Sun Jan 01, 2006 9:40 am Post subject: 2 Stroke VS 4 Stroke |
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| - mag end electric starters. The 2-stroke Rotaxen's weak spots are
generally
| the cranks (especially with the 582) and the ME electric starts can
do a lot
| of damage (especially the GPL starter, but even the Rotax model) -
you have
| that bendix flying out and smacking the starter gear which is like
taking a
| hammer to the edge of it. This puts a heavy side-loading shock on
the mag
| end of the crank, which can knock the journals out of alignment.
Also, they
| have to instantly get the entire moving system - crank and prop - up
to 300
| rpm, which puts a lot of stress on the crank (much moreso than the
pull
| start). You have no such problem at all on the bigger 4-strokes,
since
| their cranks are MUCH beefier even if they are press-fit designs.
|
| LS
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LS/Gang:
What is the solution for the above? Do you think super glue would
help keep the cranks from twisting as the result of the electric "self
commencer" ???
Take care,
john h
Thinking the electric starter was one of the most significant safety
factors of the two stroke ultralight/light plane engine.............
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lstavenhagen(at)hotmail.c Guest
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Posted: Sun Jan 01, 2006 3:01 pm Post subject: 2 Stroke VS 4 Stroke |
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Quote: | LS/Gang:
What is the solution for the above?
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The model "E" gearbox.
This one does the electric start the right way - it cranks the motor at the
PTO end off the drive gear. This way the inertia of the prop isn't
transmitted through the crank during starting.
More importantly, there's no side loading perpendicular to the crank due to
the hammering action of a bendix on the gear as there is on the mag end
starters.
The E box is also lighter by a few lbs and cheaper than a C box + mag end
starter...
Do you think super glue would
Quote: | help keep the cranks from twisting as the result of the electric "self
commencer" ???
|
Personally, I won't buy any airplane with a 2-stroke that has a mag end
starter fitted to it, unless the motor is already runout or nearly so and
needs rebuilding (new crank) anyway.
E box, though, is ok.....
LS
N646F
Quote: | Take care,
john h
Thinking the electric starter was one of the most significant safety
factors of the two stroke ultralight/light plane engine.............
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Kolbdriver(at)bellsouth.n Guest
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Posted: Sun Jan 01, 2006 4:47 pm Post subject: 2 Stroke VS 4 Stroke |
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lstavenhagen(at)hotmail.c Guest
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Posted: Sun Jan 01, 2006 5:19 pm Post subject: 2 Stroke VS 4 Stroke |
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Quote: | Do you have data from Rotax concerning the above statement?
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Most of this comes from field experience. Mark Smith, for example, is a good
source of information on this as well (he does a couple of motors a week and
is pretty familiar with this). Most guys who've done a lot of motor work
will tell you similar things.
Quote: | I find it hard to believe that the electric starter, powerful as it is, has
enough torque to twist the crank. The starter drive (Bendix) is engaged in
the ring gear before the starter motor makes one full revolution so the
engine is pretty much accelerating to cranking speed along with the starter
motor. I don't see how it is hammered.
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It's the action of the starter gear flying out to hit/engage the gear that
does it. After a whole bunch of times, it eventually can do damage to the
mag end of the crank. Typically, it shows up as higher than normal runout on
the mag end.
The mag end starter thing is a lot like running the high MOI props on the B
box - kind of a crapshoot. Most of the time it can take it and there isn't a
problem. But it's still definitely a mode of operation outside the limits
and does increase the liklihood of damage.
For what it's worth, the Rotax mag end starter isn't as bad as the GPL
starter (but you're still much better off with the E box).
As for accelerating the crankshaft
Quote: | form 0 -300 rpm with the starter motor, what about 300 to 2200 when the
engine fires? Every power stroke on each cylinder also side loads the
crank
much more than the starter does.
The crank is even accelerating and
decelerating two times per revolution for an inline 2 cyl. 2 stroke.
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The crank is designed to take these kinds of loads in these areas.
Quote: | As for reliability of 2 stroke engines, I have had 350 hours of reliable
service and only about 60 seconds of unreliable flying with them. (pto end
rod bearing failure at 210 hrs TTSN 582)
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I've never had a mechanical failure of any kind with any of my Rotaxen (one
electrical problem with my 447 and that was it). I attribute that success
partly to, among other things, running props that meet the inertia limits of
the gearboxes I run (or using the clutch in case the prop is too heavy like
on my current plane) and not using mag-end electric starters on any of my
engines.
Also, with the E box available, I've never understood why anyone would use
anything else. It is set up the correct way, weighs less and is
cheaper.......
LS
N646F
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blackbird754(at)alltel.ne Guest
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Posted: Sun Jan 01, 2006 5:20 pm Post subject: 2 Stroke VS 4 Stroke |
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Aha......yes ..Rotax does know about the crank twist problem......My new
blue head 582 with an "E" box has the starter mounted to the gearbox and
pull rope on the mag end........I have read all of the info on the new
bluehead and ....it seems Rotax has done their homework with this new
motor....
Time will tell.............
Wayne McCullough
Kolbra 4
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lstavenhagen(at)hotmail.c Guest
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Posted: Sun Jan 01, 2006 5:50 pm Post subject: 2 Stroke VS 4 Stroke |
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Quote: | From: "Wayne T. McCullough" <blackbird754(at)alltel.net>
Reply-To: kolb-list(at)matronics.com
To: <kolb-list(at)matronics.com>
Subject: Re: Kolb-List: 2 Stroke VS 4 Stroke
Date: Sun, 1 Jan 2006 20:22:33 -0500
<blackbird754(at)alltel.net>
Aha......yes ..Rotax does know about the crank twist problem......My new
blue head 582 with an "E" box has the starter mounted to the gearbox and
pull rope on the mag end........I have read all of the info on the new
bluehead and ....it seems Rotax has done their homework with this new
motor....
Time will tell.............
|
I'm tellin' ya'll I'm not making all this stuff up .. Quite a few guys
have already spent a lot of money learning about this and I for one prefer
to just learn from their experience...
The E box is the best deal all around if you need electric start. Sure it's
1400 bucks, but it can't damage your crank and it works really well....
Personally, I think I'll always find a way to use a pull start if I run a
2-stroke if for no other reason than the weight savings. The only thing I
wish I could do with my firestar is pull the rope after getting into the
plane (my trike was setup this way and it was heaven). As it is, I have to
start outside the plane and there're obvious safety concerns with that. The
clutch helps with this a good bit though....
LS
N646F
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frank-margie(at)worldnet. Guest
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Posted: Sun Jan 01, 2006 8:05 pm Post subject: 2 Stroke vs 4 Stroke |
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Don,
I understand there is a single cyl, 4 stroke Honda, used in Motocross bikes-----and evidently it's about bulletproof, despite being really abused, at very high RPM's, under very tough conditions. The guy who told me about them thought they would make a good U/L engine-----are you familiar with anything fitting that description?
Also, in the Dan Johnson article on the Hawk Ultra, in the Jan '06 U/L Flying, he talks about a 2 cyl Jabiru in the developement stage. Supposed to be 45 HP (at) 85 lbs. Sure sounds interesting if it comes to pass.
Frank Clyma
-------------------------------
From: "Don Gherardini" <donghe(at)one-eleven.net>
Subject: Re: Kolb-List: 2 Stroke VS 4 Stroke
HI Will,
Hehe...ya pard...I would brag on how good the 447 has treated me on the
Flagfly...but then it would probably quit me on the very next flight too!
I think I understand you perfectly Will, and I believe you are very likely
correct...that your 503 has been...and is a very dependable engine, much
like most of them.
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donghe(at)one-eleven.net Guest
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Posted: Sun Jan 01, 2006 8:43 pm Post subject: 2 Stroke vs 4 Stroke |
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Frank,
Yes I am very familiar with the Honda engines in the motocross bikes....and
yes, they are about bullet proof...but as an ultralite engine, I dont think
they are suitable at all due to the transmission built into the lower
crankcase...adds a ton of weight.
I have Looked at every single motorcycle engine Honda makes with an eye
towards light aircraft power, and I have found none suitable to be easily
dismembered from the transmission and adapted to a reduction drive
configuration.
If some ever does find out how to do this economically..they will have given
the light aircraft world a whole new and wonderful source of powerplants, as
the mass-production of Motorcycle engine makes them so much cheaper ...not
to mention the availability of wrecked bikes for super low prices.
Now I have NOT heard of the 2 cyl Jab....and it surely excites me......I am
going to head for their website right n ow as I dont subscribe to UL flying
anymore..
thx for the tip!
Don Gherardini
FireFly 098
http://www.geocities.com/dagger369th/my firefly.htm
DO NOT ARCHIVE
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frank-margie(at)worldnet. Guest
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Posted: Mon Jan 02, 2006 11:32 am Post subject: 2 Stroke vs 4 Stroke |
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Yes I am very familiar with the Honda engines in the motocross bikes....and
yes, they are about bullet proof...but as an ultralite engine, I dont think
they are suitable at all due to the transmission built into the lower
crankcase...adds a ton of weight.
I have Looked at every single motorcycle engine Honda makes with an eye
towards light aircraft power, and I have found none suitable to be easily
dismembered from the transmission and adapted to a reduction drive
configuration.
------------------------------------
Don,
Back in the early 80's, a friend put a Honda Oddesy ATV engine on a Weedhopper, and it worked very well (it was a 2 stroke). He chose it because it did not have a built in gearbox. You know where I'm going with this, and I know you've already been there, but I'd like to hear what you did/didn't find. It's hard not to be impressed with any Honda motor, and they build lots of them without gearboxes---and today, most are 4 cycle. Sure would be nice if something off a snowmobile/seamobile/genset/pump/whatever might work for a legal U/L.
I've also seen pics of a larger bike engine (not a Honda) installed in a light plane, with the gearbox serving as the reduction unit. This list has had postings on BMW conversions, and there is a Harley based demo at Sun 'n Fun (on a test stand). How much does a Honda motocross motor weigh incl the trans? Can it be lightened by removing some of the gears? Might the gearing hold up if used as an RDU?
I for one really enjoy the info you have shared with this list----can I get you to expound on the above?
Frank Clyma
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jbhart(at)onlyinternet.ne Guest
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Posted: Mon Jan 02, 2006 12:05 pm Post subject: 2 Stroke vs 4 Stroke |
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Don & Frank,
Just before leaving for the holidays, I was Googling and I ran across a
fellow down in South America that had put a small Honda motorcycle engine on
a trike. After reading Don's post, I spent a couple of hours trying to
rediscover the page as I did not bookmark it. I failed. But as I recall it
was running some where around 12,000 rpm. The fellow used the gear box and
modified it so that he could mount the propeller.
May be in another day or two I can recall what I was originally looking for
and search again. It is amazing what people are doing.
Jack B. Hart FF004
Winchester, IN
do not archive
02:30 PM 1/2/06 -0500, you wrote:
Yes I am very familiar with the Honda engines in the motocross bikes....and
yes, they are about bullet proof...but as an ultralite engine, I dont think
they are suitable at all due to the transmission built into the lower
crankcase...adds a ton of weight.
I have Looked at every single motorcycle engine Honda makes with an eye
towards light aircraft power, and I have found none suitable to be easily
dismembered from the transmission and adapted to a reduction drive
configuration.
------------------------------------
Don,
Back in the early 80's, a friend put a Honda Oddesy ATV engine on a Weedhopper, and it worked very well (it was a 2 stroke). He chose it because it did not have a built in gearbox. You know where I'm going with this, and I know you've already been there, but I'd like to hear what you did/didn't find. It's hard not to be impressed with any Honda motor, and they build lots of them without gearboxes---and today, most are 4 cycle. Sure would be nice if something off a snowmobile/seamobile/genset/pump/whatever might work for a legal U/L.
I've also seen pics of a larger bike engine (not a Honda) installed in a light plane, with the gearbox serving as the reduction unit. This list has had postings on BMW conversions, and there is a Harley based demo at Sun 'n Fun (on a test stand). How much does a Honda motocross motor weigh incl the trans? Can it be lightened by removing some of the gears? Might the gearing hold up if used as an RDU?
I for one really enjoy the info you have shared with this list----can I get you to expound on the above?
Frank Clyma
do not archive
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herbgh(at)juno.com Guest
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Posted: Mon Jan 02, 2006 2:52 pm Post subject: 2 Stroke vs 4 Stroke |
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Jack and all
I ran across a CBR600 powered tandem seater at Lucedale Miss fly in
three years ago.. The guy use the whole engine.. He had the gear shift
and clutch levers in the cockpit.. Used a roller chain and when I called
him, he said that he has several hundred hours on the combo.. He lives
south of Lucedale as I recall. Said that he was installing a cbr 900 in
a Pulsar.
Ronnie Smith gave me his phone number.. Herb
do not archive
On Mon, 02 Jan 2006 15:12:26 -0500 "Jack B. Hart"
<jbhart(at)onlyinternet.net> writes:
<jbhart(at)onlyinternet.net>
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ceengland(at)bellsouth.ne Guest
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Posted: Mon Jan 02, 2006 5:10 pm Post subject: 2 Stroke vs 4 Stroke |
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Herb Gayheart wrote:
Jack and all
I ran across a CBR600 powered tandem seater at Lucedale Miss fly in
three years ago.. The guy use the whole engine.. He had the gear shift
and clutch levers in the cockpit.. Used a roller chain and when I called
him, he said that he has several hundred hours on the combo.. He lives
south of Lucedale as I recall. Said that he was installing a cbr 900 in
a Pulsar.
Ronnie Smith gave me his phone number.. Herb
do not archive
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I've seen what had to be the same a/c at a flyin N/E of Jackson MS,
about 100-125 mi north of Lucedale, so he obviously isn't afraid to
travel with it. He told me that the shifter was so he could use a lower
gear when carrying passengers.
Charlie
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