The primary problem with the PFM was the increased cooling drag over
a ram-air cooled Lyc.  The Porsche engine used a fan, which is fine for a

car

which must cool at idle in traffic, but unnecessary and even detrimental

in

a vehicle like an airplane which MUST maintain a fairly high speed.  The
very low velocity of the cooling exit air was not accelerated back up to
even a modest fraction of free stream velocity, causing substantial

cooling

drag.  The fan took power, too.  Net results?  A *very* automated,

modern,

simple-to-operate engine which cost the same or more than an 'antiquated'
Lyc, and was 5-10 kts slower in cruise and burned the same or more fuel.
Nobody wanted them.   Very good technology, just not well optimized for
an aircraft.

Back to my previous comment that while modern automotive computerized
engine controls are interesting, a very dumb carb or extremely simple
mechanical fuel injection can be pretty easily tuned (leaned) to a very
efficient fuel burn by a slightly skilled pilot, who then leaves the

throttle

and mixture untouched for hours.  VERY different than the load cycle on
a car.  So, unless we are willing to pay (money and complexity) for the
'technology' solution, it will not happen.   It turns out that the

Continental

type simple fuel injection is 'good enough', and even the Bendix style,
which is more complex and expensive is still good enough, altho costs

more.

I get a bit sick of hearing how crummy and outdated existing aircraft
engines are.   PFM flopped.   LAZER flopped.   Apparently we are
unwilling to actually PAY for these technological advances when we
find out how small (or even negative) the actual performance gains are.

The rotary is worthwhile because it is mechanically MUCH, MUCH
simpler- not because we need to have complex, automotive gee whiz
systems to adjust the spark and mixture 10 times per second.   I maintain
that the advantage to a system like Tracy's system is in affordability,
flexibility and tunability, not it's capability to adjust itself at a

high

frequency and
the "modernity" of it.  Affordable, tunable and flexible mechanical fuel
injection (Hillborn?) will work very well,too.

Bill
Long EZ builder & pilot
mechanical engineer

I agree with the simplicity issue but I would not run magnetos
on a rotary.

Klause maintains the reason the LAZER flopped was they were unwilling to
use automotive spark plugs in air-cooled aircraft engines and gap them

around

0.050 instead of the certified aircraft spark plugs gapped at 0.016. Many
people are now using electronic CD ignition systems with automotive spark
plugs in their air-cooled aircraft engines and they swear they are paying
off in lower fuel burn with more power. They are also using back up

batteries.

Paul Lamar

tommayer wrote:

What's wrong with mags for a rotary in an airplane?  Are you not going to
run the rotary at a fairly constant rpm, just the way you would a Lyc? Is
that mags are inherently unreliable at 5000 to 6000 rpm?  Tom Mayer

A rotary takes a lot of juice to fire the plugs properly.
CD ignitions work the best. A mag does not have much juice or voltage.

Paul Lamar
 
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