I think you missed the point???


Rich Gillen
 

No Pat, I didn't miss the point. Fast in level flight, is fast. We weren't
taking about Rapid Decents. As long as you stay with in the recommended
RPM range, you should be OK. One plane with say a Rotax 50hp 2 stroke will do
one speed, while another plane with less drag, will do another speed with
the same 50hp. The more slippery a plane is, usually the faster it will be,
less drag.

Any plane, making a Rapid Decent, can exceed it's Vne, where the throttle
needs to be reduced rather far. That's where knowing, what type of
engine/plane you are using comes into play. You are correct though, " When the
throttle is reduced, so is the oil supply to the bearings, rings, and piston
skirt (since the oil is mixed with the fuel) however the engine is still
turning, creating friction, requiring oil." On Rotax, 2 strokes, with oil
injection a 50:1 ratio is required, but the oil ratio is way less at idle,
something like 70:1. I have never read anywhere, at what RPM, does it actually
put out the Full 50:1 ratio they require. So someone making a rapid decent,
and a rapid throtle down to idle, may go from the 50:1 ratio to a 70:1
ratio. Since Rapid decents, is known as one of the cause's of seizure's in 2
strokes for many years, then why, would any pilot with a 2 stroke, even make
one? Like I said, some people like to push the envelope. Some just don't
know any better, and they learn the hard way. Since Rotax's, seem to also have
a lot of crank & rod bearing problems, maybe a 40:1 ratio, would be a
better choice. Kawasaki 2 strokes use 40:1.

Just My Opinion
Rich Gillen


============================================================================
===
2b. Re: 2 strokes are prone to seizing
Posted by: "Patrick Panzera" editor@... pat_panzera
Date: Fri Mar 23, 2012 8:28 am ((PDT))

On Fri, Mar 23, 2012 at 4:06 AM, <Armilite@...> wrote:

Allan:
So your 2 stroke engine knows how fast(MPH) it's going? Wish mine did, I
wouldn't need a Speedo.
I think you missed the point. The concern with " fast/slippery" airframes
is that in order to descend, without exceeding Vne, the throttle needs to
be reduced rather far. When the throttle is reduced, so is the oil supply
to the bearings, rings, and piston skirt (since the oil is mixed with the
fuel) however the engine is still turning, creating friction, requiring
oil.

Pat


If you stay within the acceptable RPMs, recommended
by Rotax, you should be OK. Some people tend to push the envelope. That's
6500rpm MAX for most Rotax 2 stroke engines, I have read. Only the 618UL
was
rated for 6800rpm, and those RPMs, are only for takeoff, 1 minute, 30
seconds. Then their throttled back. Most people fly between 4000rpms -
6250rpms
MAX.

Most seizures are caused by what I stated below.
"Seizures are caused by many different situations, Heat (lack of proper
cooling), lack of proper lubrication (Oil Mix), or not using the Proper
Type
of Oil, Over Revving the engine with no load, are the main reasons."<

Just my opinion.
Rich Gillen

Join main@Q-List.groups.io to automatically receive all group messages.