It is normal to fly with ac on.
Jeff
Sent from my iPad Dear subscribers, Since we are talking about cabin heat I got another question. What cabin temperature do you get from your turbos on the cool side (after the intercoolers and the additional heat exchanger in the front)? I put my cool air supply hose in an additional fireproof jacket that has additional insulation inside (see picture) – the intension was to insulate against engine heat and get nice cool cabin air. At higher power settings (32 MAP, TIT1620) the cool cabin air is about 100F. This means flying in the sun even in the high teens with OAT around 20F it still gets really warm in the cabin and I turn on the AC every now and then. Is this normal? Any input is appreciated. Ralf From: Jack Morgan [mailto:jmorgan1023@comcast.net]
Sent: Friday, November 09, 2012 8:45 AM
To: lml@lancaironline.net
Subject: Dukes pressurization controller Just a quick note on the controller. Bob's excellent description below is all good. The Dukes controller is an "aneroid" controller which needs no electric power to operate once the airport elevation is set. The electrical control for altitude setting in the cabin controls an electric motor in the controller which sets the aneroid so that it controls cabin pressure to just above the set airport altitude. This insures no pressurization is present at landing. Once set, an electrical failure will not cause any problem for the cabin pressurization system. On Nov 9, 2012, at 6:01 AM, Lancair Mailing List wrote:
Subject: RE: [LML] IVP cabin heat Date: November 8, 2012 3:16:51 PM EST 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…
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