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Fili:
It is common for an IV to climb from sea level to the flight levels without
leveling off to cool. I do it frequently. I have the old style cowl outlets
(not the enlarged ducts) and no gills. I do have a very tight upper plenum
on my Lycoming and I use an extended climb speed of 180 KIAS which gives a
ROC of about 1000 FPM (depending on load). Climb fuel flow is 28-30 GPM at
75% power, compared to a cruse flow of 21 GPH (150 degrees rich of peak TIT)
af FL270. The thermal limit for climbing too fast from a hot environment is
the from the fuel. Hot fuel has a higher vapor pressure and I have had to
level off to let the fuel chill.
IMHO, the reason that the enlarged outlets and gills worked is that the
original baffling on the Continentals leaked a lot. The inlet to outlet area
ratio is about right without the modifications IF all the air is going
through the engine and not around it.
Regarding cabin cooling, I used to operate out of the Central Valley of
California where the afternoon temperatures were frequently above 100. I
would taxi with the door open and latch it just before taking the active.
Leaving the door seal off until about 8000 MSL would provide plenty of air
flow from the tail to keep the cabin tolerable. By that time (<10 minutes)
the OAT is cool enough to seal and pressurize the cabin.
I have never liked air conditioning systems and can't see the benefit of
carrying all that weight all the time for such a small percentage of flight
time. JMHO. Some installations I have seen feature a pod slung under the
belly, reportedly costing 10+- Kts and causing the engine to run hotter
(lower airspeed for a given power setting = less cooling). Not an acceptable
trade in my mind.
If you are operating in a humid climate, don't expect an evaporative cooler
to work very well and ice may be difficult to procure and keep until needed.
If I had to add a cabin cooling system, I would add a second 28V 100A
alternator and array 36 Peltier (70 watt) modules (solid state heat pumps)
on an aluminum plate that is mounted in the upper portion of the aft
pressure bulkhead. The Peltier modules would pump heat into the baggage
compartment/ tail and the cabin fan would blow cool air on the faces of the
passengers. A flick of a switch would turn this system into a heater and the
alternator can act as a standby power source (add a couple of resistors on
the regulator sense line and a switch to get 14 volts). Parts cost would be
around $1,500. Heat flux would be about 6,100 BTU, which compares favorably
with automotive systems that are designed for ~20,000 BTU (a much larger
cabin).
Just might work ;)
Regards
Brent Regan
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