|
Takeoff check: Mixture set to full rich
As most pilots know when taking off from lower altitude
airports - usually at or below 3000' MSL our handbooks tell us
to set the fuel mixture to full rich. Every wonder why? Well, in
order to keep our engines from serious detonation our fuel
delivery systems are calibrated to provide a super rich mixture
when we set the mixture control to full rich. Those of us with
fuel delivery instrumentation can watch a typical O-360 engine guzzle
upwards of 18 gallons of fuel per hour in the full rich position
with the throttle wide open.
We are using substantial amounts of fuel to cool our engines
during periods of high power settings at low altitude and we are
not only getting nothing back for this (other than keeping our
engines from blowing up) but we are also losing power! Yes, a
super rich mixture causes a considerable amount of power loss.
Why? Quite simply because we are cooling and absorbing a
significant amount of the heat produced by combustion. There is
less heat available to be converted into mechanical force.
Now what if you could pickup an extra 5 to 7 HP on a typical
O-360, 180HP engine during takeoff and use as little as
12 GPH during takeoff and high power operations below 3000' MSL?
Well you can as soon as you convert your air-cooled O-360 or
O-540 to water cooling.
Peak lean EGT or 50F lean of peak EGT at all
times
Yes, it is possible. Imagine that you set your mixture to
peak lean EGT on takeoff and keep it set to peak lean EGT at all
times. Instead of burning upwards of 18 GPH at sea level you are
now burning 12 GPH or less and making more power! Our dynamometer
testing has shown that a liquid cooled, 180HP, O-360 engine will
produce 187HP at peak lean EGT at sea level using about 12GPH
without any sign of detonation. In fact we tried everything we
could to make the engine detonate and we couldn't! We even
lugged the engine down to 1600 RPM at wide open throttle (28
in/Hg manifold pressure) at peak lean EGT and left it there for
30 minutes. It was quite happily producing 355 ft/lbs of torque
at 1600 rpm (108HP) as smoothly as it produced 365 ft/lbs of
torque at 2700 rpm (187HP). At full rich the same engine fell to
about 180HP at 2700 rpm and guzzled fuel at the rate of around
18GPH.
So you can have your cake and eat it too
Lets see - more power on less fuel - that's hard to believe -
but its true! Water cooling so significantly reduces the
temperatures of the combustion chamber that the engine can
safely be run at full power at peak EGT, 50F to the lean side
of peak EGT or even leaner! During our dyno runs we regularly
brought the mixture back to such lean levels that the engine
would barely run and yet we never had any detonation. Peak EGT
and 50F lean of peak EGT mixture settings are not recommended
for the air-cooled O-360 engines and with good reason. There
is the high probability that detonation will occur and the distinct
possibility of engine failure as a result of detonation.
1600 RPM at wide open throttle (28 in/Hg manifold pressure)
at peak lean EGT! I'd never do that to my engine! Yes we know
- that's because quite simply your air-cooled engine would self
destruct if you did that. We did it to prove a point. That even
the most mismanaged water cooled engine would still continue
to operate safely and reliably. Now we are not suggesting that all
water cooled engines would behave this well - we have only
proven this on a typical O-360 engine. However, we believe that
we will achieve similar results with other engines as our test
program continues.
|
