An Adroit Aeronautics, Inc. STC for cooling the engine driven vacuum pump and battery on the Cirrus Design SR20 was approved on March 25th. The proofing aircraft was 262BM (Michael Burke & Brian Abeel). Inspection and approval of the STC was carried out by Jeff Morfitt of the Seattle ACO. The STC uses a RAPCO cooling shroud and other off-the-shelf parts
The first line installation was on 365DP (Del Fadden, Peter Morton, Daniel Wiseheart). Before installation of the STC, an electronic temperature probe was installed on the vacuum pump housing surface near the exhaust port to measure the pumpÂ’s operating temperature. The probeÂ’s lead was taped to the side of the fuselage and led into the cabin through the door seal, allowing recording of the vacuum pump housing temperatures during verification flights.
Two flights were made on Saturday, April 20th out of Boeing Field in Seattle, WA. Del Fadden was the pilot, Vince Roux recorded the data during the flight. All data related to cooling of the engine driven vacuum pump was recorded at regular intervals including: Pump housing temperature, OAT, Airspeed, Altitude, and Engine RPM. Both flights took a little less than 30 minutes and followed the same profile closely, a “Vashon Departure” out of Boeing Field, with several minutes to stabilize the pump temperature over Puget Sound at 1900 feet, and a direct approach from the north back to Boeing Field. Weather conditions and temperatures remained constant during the two-hour period of the first flight, installation of the STC and the second flight.
The data from the flight shows a marked drop in the vacuum pump housing temperatures after installation of the cooling STC during all phases of aircraft operation and flight. After reaching test altitude a difference of as much as 22 degrees Celsius was observed. This preliminary data is very encouraging, given the high rate of failure of engine driven vacuum pumps on Cirrus Design SR20Â’s.
Other problems addressed by this STC include the tendency of the batteries to overheat and dehydrate The Master Control Units have also had various problems that have been attributed to the same heat. This excess heat is addressed by adding a second duct to direct cooling air around the battery and upper portion of the area aft of the engine.
365DP is an especially good test subject to use for this application as it has had very regular engine driven vacuum pump failures, all close to the 100 hour point of pump use. The installation of the STC was at approximately 80 hours of the current pumpÂ’s life. At installation, the heat indication sticker on the pump cooling vanes was still white, indicating that it had not yet over-temped. We will be watching the vacuum pumpÂ’s performance closely and publish any observed trends.
The copyrighted STC is immediately available from Adroit Aeronautics, Inc. for $125.00 per aircraft and uses all off-the-shelf parts that are purchased by the owner. The STC can be installed by any A&P, installation time is approximately 2 hours.