Dear Group:

I was looking at Mick Duckt's web page on his ducted fan long ez, and
noticed that the 13b is capable of producing between 80hp to 120hp in the
3500rpm to 4000rpm range. Considering the orginal long ez was designed for
the 0-235, and the plane achieves good performance with the 0-235. My
question is why not get rid of the psru and save the weight and

complexity?

How much would the engine efficiency suffer to operate at the lower rpm?
Interested to hear any thoughts.

 Andrew Shaw

David Leonard wrote:

Andrew,

Since everyone else seems to be busy playing with their computers instead of
building I will throw in my 2 cents.  Perry is doing a great and reasonable
thing.  He is meeting the goals he set out to achieve but you should
consider a few points.

Most importantly, the thrust bearings in the 13B were not designed to take
prop loads - or any significant amount of thrust for that matter.  I believe
perry has replaced them once but otherwise they seem to be holding up OK.
It is possible to replace them without doing a complete re-build, but it
does require removing engine from the plane.

If you are only hoping for 80-120 hp. you could get that from an aircraft
engine for probably less weight and much more simple installation.

3500-4000 RPM is still too fast for most props without going to very short
and inefficient blades.

As far as 'efficiency' goes (shaft h.p. per pound of fuel), slowing the
engine will imporve efficiency somewhat, but what you gain there is more
than lost in reduced prop efficiency.

All that said, Perry's plane FLIES, is RELIABLE, and INEXPENSIVE to operate
and maintain.  What more do you really need?

JMHO,
Dave Leonard

If you can stay with a redrive you will be better off overall.
The weight aside, the engine will just do you a better job at the higher revs.
The rotary is a high rev engine, and is happy there.  True it will run ok at lower
revs, it just loves to turn.
I think a lower weight redrive is much needed. Haven't had the opportunity to work
on that much, too much to do to build a single rotor, which I work on in the day
time, and write computer programs in the evening/night.
Perry's plane can do ok at lower rpm because of the prop he uses.
Royce

 
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