From: jlw@world.std.com (James L Walker)
Subject: Re: 2 stroke vs. 4 stroke engines
Organization: The World Public Access UNIX, Brookline, MA
Date: Wed, 15 Apr 1992 13:01:52 GMT

In article <51470014@hprnd.rose.hp.com> jahr@hprnd.rose.hp.com (Steve Jahr) writes:
>In rec.models.rc, santo@pictel.com (Santo Wiryaman) writes:
>
>> 4-stroke
>> --------
>>  - Operates with larger prop at lower RPM which gives a pleasant
>>    (scale) putt..putt..putt sound.
>>  - More fuel efficient than 2-stroke
>>  - Lower power/weight ratio than a 2-stroke
>>  - Leave considerably less oil on fuselage
>
>I have to somewhat disagree with this one.  I have admired four strokes
>but after watching a couple of flying buddies get thumpers, I am having
>second thoughts.
>
>One reason is that while there is less exhaust residue on the general
>fuselage, there is *tons* more in and around the engine compartment.
>The reason for this is that four strokes "breath" in and out of the
>front bearing.  On piston down strokes semi-burnt fuel and oil are
>blown/sprayed out of the front bearing and on up strokes whatever
>happens to be around is sucked in... including dirt and other
>abrasive engine unfriendlies.
>

My O.S. 4cyc has a breather valve underneath.  I run a tube from this
valve to a Formost bulkhead fitting on the bottom of the fuse.  The
amount of junk/stuff/gunk that sticks to my plane is alot less than
with a 2cyc. and my engine compartment is pretty clean of oil.  I will
be on the lookout from now on for four-cycles that breath through the
bearing.

Sucking in dirt is a nonissue.  All engines want to suck in dirt and
there are standard ways of dealing with this.

>The other thing that has soured me on 4 strokes is the power output.
>In order to get equal power to a .40 sized 2 stroke, you need to go
>up considerably in displacement and cost.  I think I'll just stick
>with muffled tuned piped 2 strokers.
>

This is an interesting issue that warrants more discussion.  There is
no doubt that four-strokes are more expensive... period.  On the other
hand the performance gap is narrowing.  4cyc engines may not have the
screaming RPMs of the high-performance 2cyc engines, but thier torque
can pull a sport or pattern ship through vertical manuvers more
smoothly -- just my opinion, flames welcomed.  BTW: by torque I mean
the force normal to the prop surface acting on the air... or something
like that.  I've been burned on this before so don't bother burning me
again.

>It's too bad that the knee jerk reaction to sound complaints it to just
>*prohibit* certain classes of engines.  The mufflers that come on most
>engines, both 2 and 4 stroke, are close to useless.  On the other hand
>the *stock* extra baffle on my OS FP 15 makes it so quiet I can hear
>the air whistling over the plane.  It is much quieter than *any* four
>stroke I have ever hear... almost as quiet as an electric... and yet I
>couldn't fly it at the Pioneer field because it's a 2 stroke ):
>

IMO the sound advantage to 4cyc engines is their tone, not noise
level.  Can you really make your engine quieter than an appropriately
matched 4 cyc.  If so, then perhaps the assumption that 4 cyc engines
is going the same way as the assumption that 2 cyc engines are more
powerful.

-- Les Walker
-- High Flyers