Return-Path: Received: from [65.33.162.219] (account marv@lancaironline.net) by logan.com (CommuniGate Pro WebUser 4.2.8) with HTTP id 611082 for flyrotary@lancaironline.net; Mon, 17 Jan 2005 22:55:45 -0500 From: "Marvin Kaye" Subject: Re: [FlyRotary] Re: Switching to Evans NPG+ To: "Rotary motors in aircraft" X-Mailer: CommuniGate Pro WebUser Interface v.4.2.8 Date: Mon, 17 Jan 2005 22:55:45 -0500 Message-ID: In-Reply-To: References: MIME-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1"; format="flowed" Content-Transfer-Encoding: 8bit Try and remember that the rules for what happens inside an engine at sea level are different than what goes on at 15,000 feet. While the NPG+ may not boil until 396*F at sea level, I'm certain that it's a different beast at altitude. The guy who engineered the Eagle was livid when we told him that Evans recommended a pressureless system... part of the reason for the pressure is to keep the coolant pressed firmly against the metal surfaces it's trying to cool. Even if you have a high boiling point, when the metal temperatures exceed it the boiling will happen and without the pressure to insure coolant contact, pretty soon everything is surrounded by a cloud of PG steam (well, maybe not a "cloud", but all the hotspots will be working overtime keeping the coolant boiling next to them). Those metal temps quickly build, the areas where the coolant has turned to vapor grow, and the problem feeds on itself until the system goes completely out of control. At this point your pressureless system vents itself, throwing out what's left of the coolant and the engine is toast. The point here is that there are more reasons for having a pressurized system in an airplane than meets the eye. One more thing... with a pressurized system you can alarm it for a low pressure situation. If something goes wrong with the coolant system (like you spring a leak) the pressure will likely go down before you see a rise in temps. If the system is setup to run at 20psi and you alarm it at 15, when you see that master warning you know that pretty soon you're probably going to overheat. Just another chance to get a jump on things that you pass up without pressure.