Engines and Reliability

Things that make you go 'hmm'.

The accepted wisdom is that aviation engines are tough, because they can
be run at full rated power for hours on end, and auto engines are
fragile, and must not be thrashed or they won't last very long. It was
even mentioned in a thread in the last couple of weeks - I don't
remember who said it, but they said "operate your car engine like that
and it wouldn't last half an hour".

I've never really thought about it, but this weekend I learned how to
drive the winch at the glider club. After a few launches it got me
thinking - this thing about aero engines vs car engines is probably an
old wives tale, possibly promulgated so people don't feel so bad about
spending so much money on aircraft engine parts when yet another
cylinder is cracked.

The winch. Basically, the winch is a method of launching gliders. At one
end of the runway, you have the glider. At the other end, attached to
the best part of a mile of steel cable is the winch. This consists of a
take-up drum which reels the cable in, and a power plant and
transmission of some sort. Our winch is a 'homebuilt'. The power plant
and transmission came straight off a car - a mid-70s Jaguar XJ6.

In this era, Jaguar quality was at its worst. Jaguar was part of British
Leyland, a nationalised car making monstrosity, beset by problems with
trade unions and appaling quality control. The engine is a 4.2 litre
inline six with dual overhead camshafts, and dual SU carburettors. The
transmission is the standard 3-speed automatic.

Winching a glider means you go from idle, rapidly increase the power,
then as you see the glider pitch up to about 45-50 degrees nose up,
floor it. The glider rockets skywards. Wide-open throttle is held, with
the transmission in drive which will select the appropriate speed for
the drum. As the glider starts getting towards the top, power is eased
back, eventually reaching idle. The cable then comes down on a
parachute. A little power is required (especially if there's a
crosswind) to bring the chute and cable in and make sure it lands on the
runway.

The engine is tortured by this idle - wide open - idle cycle maybe 30
times a day when we're operating. Since 4-star leaded fuel (98 octane)
which the engine was designed for is no longer available,
the engine is now run on regular unleaded. The engine and transmission
is nearly 30 years old, it's been in the winch for a few years and it
hasn't missed a beat. It starts easily, and runs sweetly despite the
abuse it gets - and it was built during Jaguar's worst years.

Perhaps auto engines aren't as feeble as people like to make out?

--
Dylan Smith, Castletown, Isle of Man
Flying: http://www.dylansmith.net
Frontier Elite Universe: http://www.alioth.net
"Maintain thine airspeed, lest the ground come up and smite thee"