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Posted for "richard titsworth" <rtitsworth@mindspring.com>:
A personal view on auto conversions.. I love airplane engines (read
lyco/cont), but it's based on my personal value "tradeoff", not based on OWT
(Old Wise Tale) of engine capabilities.
It is certainly true that normal family car engine performance/usage/duty
profile is quite different that a typical GA aircraft (even for Corvette's -
unless perhaps you live at Bonneville). However, to use a typical auto
engine duty cycle to compare the "capability" of aircraft and auto engines
is a bit misleading (i.e. OWT vs fact/engineering). Selectively, auto
engines are "capable" of much more than driving to the grocery or grandma's
(especially if/when setup for a specific application). Likewise, attempting
to use a NASCAR/racing engine as an comparative basis aero/auto engine
capability is also pretty misleading - they're, designed for "ultimate" HP
and aren't intended for extended durability (beyond perhaps 600 miles). For
comparison purposes, the "capability" of a (properly setup) auto engine (in
an aircraft sense) is somewhere in BETWEEN "workday commute" and "winners
circle".
While not at all perfect, other analogies exist which provide a better basis
for comparing "capabilities" and advantages/disadvantages of auto and
aircraft engines. For example, my LT1 (corvette motor) based ski boat
spends most of its life around 4000+ RPM with an ungodly number of full
throttle starts - probably more "take-offs" than a normal Lyc/Cont ever sees
(perhaps some C152 "pattern zombie" trainers that can top it). This is much
more analogous to a typical GA aero engine and demonstrates the potential
for similar aero/auto engine capabilities. Additionally, It runs with V8
smoothness, but is subject to constant vibration from waves and my
unbalanced "dinged" prop, through a geared drive unit. It spends most it's
life in a wet/humid environment. It spends winter months just sitting
(never fogged it) and it still re-starts each spring. Any idiot can start
it - just turn the key - no need to touch anything else. It doesn't need
special (overly toxic and expensive) fuel - it's electronic control unit
adjusts for the operating conditions and octane used (knock detection). It
doesn't get oil changes every 25-50 hours. It's spark plugs last virtually
forever (hence doesn't need two per cylinder) and can be purchased at
Walmart for a few $. It doesn't benefit from enhanced engine gauges (CHT,
EGT, etc) to allow intelligent operation - in fact in the hands of some of
my "lake friends" it gets rather rough treatment. It once ran without any
cooling water (hose was disconnected), momentarily overheated, and still
runs fine. It once had a fuel pump failure and still got home in "limp
home" mode. (Those events due tend to highlight the danger of complexity
and the need for redundancy in an aircraft application). It provides well
over 300 HP in the stock/factory configuration. HP performance improvements
can add 50-100% to that. Personal/anecdotal experience aside - this is
typical usage/capability for auto engines in marine applications. Aside
from lake water vs radiator for cooling, some added redundancies, and
attention to a few high weight components, an aircraft auto conversion could
be similar.
Have to add one OWT, since I am also not immune to their fun. A former (4
cylinder auto engine) boat of mine run fine after being "totally submerged"
for a few days (don't ask). I left it in the boat, drained and replaced the
oil (milky watery mess), dried out the distributor, and purged the water
from the cylinders by cranking it with the sparkplugs removed. Presto, it
ran fine till the day I sold it (forgot to provide that part of it's history
to the new owner - oh well). Perhaps not a great analogy - but an
interesting OWT on the potential for extreme durability.
Commercial trucks/busses typically run for "several" thousand hours (way
over 2,000 TBO) and I was once told that diesel locomotives (some of which
are over 30 years old) run for months without ever being shut off, sometimes
in high HP uphill routes, (unverified - any locomotive experts out there?).
Those are poor analogies, but do provide some awareness of the potential
range of operating envelopes of various piston engines.
Auto and aircraft engines have been engineered/set-up for different
applications and thus provide different advantages/benefits and
limitations/drawbacks. It's not that either is simply any better/worst
overall. Both have been improved over time through creativity, science, and
testing on the part of "teams" of professionals (there is no "magic" in
either). Autos benefit from the economics of relatively high production
volume, a highly competitive global marketplace, the desire for idiot-proof
operation, and relatively benign "land based" failure scenarios. Aircraft
benefit from the "assumption" of a relatively intelligent/competent pilot
(trading increased operator workload for mechanical simplicity/durability -
i.e. mixture and temp monitoring), acknowledgement of efficient prop RPM's
limitations, designed-in redundancy on critical items (mags), and a
heightened economic payback for weight reduction. History has demonstrated
successful liquid cooled engines in (production) aircraft and successful air
cooled engines in cars, when setup/engineered accordingly.
Likewise, there have been good (and bad) conversions/installations of auto
engines for experimental aircraft. In all cases, it implies a
knowledgeable/factual acceptance of the tradeoffs. Those are ultimately
personal and the purview of those in the "experimental" world with the
time/energy/values to pursue them. For those traveling that path, I respect
their motivation and dedication, more power to them - pun intended :-)
Rick
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