Dico,
I’ll
answer via the LML as this may be of interest to other Lancair
owners/operators.
First
the disclaimer: The description below covers Lancair IV-Ps built using the
parts provided by Lancair, and following the building manual. I have seen
a couple of other configurations out there…the product of “individualism,”
and occasionally better ideas… So check to be sure your system is plumbed
as described below before trying these things.
The
IV-P uses bleed air from the engine turbochargers to both pressurize and
heat the cockpit. The compressed air pipe exiting each turbocharger has a
port added to tap off some of the air for the cabin. (By the way, this air
has run through the turbochargers, but does not yet have any fuel added,
so is breathable.) This port should have a “sonic nozzle” either welded to
the port itself, or installed in the SCAT/SCEET line that’s attached. The
sonic nozzle provides a relative constant flow of air to the cabin
heating/pressurization system over the typical range of pressure in the
turbocharger system (typically 25”-38” MP at cruise power settings).
Depending on the power setting (MP), this compressed air is near ambient
temperature to quite hot (200+ degrees), and is the “hot” feed for the
cabin heating/pressurization system. It is routed via SCAT/SCEET ducting
to a flow controller (a gold-anodized round canister a bit smaller than a
coffee can) mounted to the top engine-side of the
firewall.
The
cabin heating/pressurization system has a second “cool” feed that starts
with an additional port welded to the engine inlet air ducting downstream
of the large intercoolers on each side of the engine. These ports are
connected with SCAT tubing to a third intercooler on the forward left chin
of the engine, opposite the alternator. For the “cool” feed, compressed
air passes through the side intercoolers, then through this third
intercooler and then via a single SCAT tube to the flow controller. Note
that both hot and cool feeds are “relative.” The hot side can
yield luke-warm air if the engine power is
low, and the cool side is, at best, a few degrees above ambient; usually
not cool at all in Florida in the summertime.
The
above compressed air is fed into the cabin directly from the flow
controller on the firewall. With the cabin temperature control in the cold
position, flow from the hot side (above) is completely blocked and all
pressurization air is being fed into the cockpit from the cool side. With
the temperature control in the hot position, the cool side feed is blocked
and the hot side feed is fully opened. As a side note, the flow controller
has a second function that’s important. The “pressurization control” in
the cockpit is connected to a flapper valve in the flow controller that
alternatively opens a port allowing pressurized air to flow into the
cockpit (normal operation) and closes a “dump port” that feeds air, via a
SCAT tube, down the forward side of the firewall to the engine exhaust
area. When in the dump position, this valve opens the dump port and closes
the port into the cabin, dumping the pressurized air overboard. This might
be useful in the case of an engine fire or other contamination of the
inlet air…not common, but could really ruin your day if it happened at
altitude.
So
why no heat? If you haven’t done so,
it would be very beneficial to verify that the controls/components
discussed work as described above. IF there are leaks or the system is not
connected/configured correctly, all bets are
off.
The
next task, assuming the system is plumbed and operating correctly, is
actually generating some heat…especially up where Dico lives… At low power
settings, the air coming directly off the turbochargers is not hot. Your
choices (via the cabin temperature control) of compressed air for
pressurization are cool and cold. 25” of MP is about the minimum that will
maintain cabin pressurization, and the compressed air off
the turbos is just a bit
above ambient temperature. Above 32” of MP, the exit air is approaching
200 degrees and will keep the cockpit toasty in any conditions I’ve seen
to date…but I don’t like to run my engine at that high a power setting. So
to answer your specific question, heat the cabin
by:
1) Ensuring
the cabin pressure dump control is closed, and not leaking air/heat out
the dump vent.
2) Set
the cabin temperature control to full hot
3) Increase
engine power (MP), with care to the engine, to get the needed
heat.
Note: I’ve
actually taken to running the MP between 29-30” during the winter time
just to keep Judy warm and happy. A good investment…
<grin>
Just
a last bit of information to “polish off” the system: The flow of high
pressure air into the cockpit is “unregulated” as long as the dump control
is closed, and although relatively constant, is subject to changes in both
pressure and flow rate depending on engine power setting. The cockpit
pressure is maintained by controlling the outflow (controlled leakage) of
air through the Dukes controller mounted in a “bucket” under the rear
seat. This is an electrically-controlled exhaust valve and takes some time
to adjust to flow and pressure changes. It’s therefore easy to “get ahead”
of the pressurization system by rapidly changing the engine power setting.
Most of us have learned to compensate for this, but if you’re getting a
lot of ear-popping and complaints from your passengers, try changing the
engine power more gradually, especially at level-off and start of descent.
…And I’m sure you’ve all discovered by now what happens if you pull the
engine back to below 25” MP or so while at altitude? The air in the cabin
actually back-flows through the engine and the cabin altitude goes quickly
to the outside pressure altitude. Solution: Keep the MP above 25” until
you’re down out of the flight levels; then slowly bring it back more if
needed…
Hope
this helps!
Bob