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#11
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Some systems ARE designed to work off of pressure. Depending on the system
designer. John If the carbon vanes in a vacuum pump fail, any debris will be blown overboard. If the pump pressurizes the instruments, the debris will be blown into the instruments, ruining them. The Piper PA 31 Navajos for one use a pressure system with a filter between the pumps and the instruments. John Dupre' |
#12
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Originally, at least, the vacuum came from a venturi in the
slipstream. It was a natural to use a vacuum pump with the same instruments. Posted Via Usenet.com Premium Usenet Newsgroup Services ---------------------------------------------------------- ** SPEED ** RETENTION ** COMPLETION ** ANONYMITY ** ---------------------------------------------------------- http://www.usenet.com |
#13
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Don Hammer wrote:
Originally, at least, the vacuum came from a venturi in the slipstream. It was a natural to use a vacuum pump with the same instruments. Right. I've seen a venturi on an old aircraft. You can still buy them. They cost about as much as beer money, and are pretty reliable unless a bird hits them or they ice up. I understand from the designer's point of view the drag they create hurts performance much more than an engine driven pump... Thanks to all who provided examples of current aircraft that use pressure pumps. Looking more closeley in my Aircraft Spruce catalog, it has a couple pumps with separate part numbers- for "vacuum system" and "pressure system." Most everything else is simply described as vacuum. Also, thanks to the two or three guys who gave short physics lessons without being condescending, although I already understood that "push here" = "pull over there" Lots of good help on this group. Keep the fender washer jokes coming. |
#14
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Jim Carriere wrote: Don Hammer wrote: Originally, at least, the vacuum came from a venturi in the slipstream. It was a natural to use a vacuum pump with the same instruments. Right. I've seen a venturi on an old aircraft. You can still buy them. They cost about as much as beer money, and are pretty reliable unless a bird hits them or they ice up. I understand from the designer's point of view the drag they create hurts performance much more than an engine driven pump...Thas Right! A venturi doesn't add much, percentage wise, to a slow,draggy, wire-braced biplane---but on a modern fast streamlined job would cause a significant speed loss. Thanks to all who provided examples of current aircraft that use pressure pumps. Looking more closeley in my Aircraft Spruce catalog, it has a couple pumps with separate part numbers- for "vacuum system" and "pressure system." Most everything else is simply described as vacuum. Also, thanks to the two or three guys who gave short physics lessons without being condescending, although I already understood that "push here" = "pull over there" Lots of good help on this group. Keep the fender washer jokes coming. |
#15
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Jim Carriere wrote:
Right. I've seen a venturi on an old aircraft. You can still buy them. They cost about as much as beer money, and are pretty reliable unless a bird hits them or they ice up. I understand from the designer's point of view the drag they create hurts performance much more than an engine driven pump... Yes they hurt performance but if you don't have an engine with a vacuum pump and/or don't have an electrical system (and we all know how much more electrical gauges cost!) them really there is not much choice. Venturis work and hey they look cool! John |
#16
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Most airplanes that have de-icing boots use a pressure system. Even some
Bonanza even without the boots. "JDupre5762" wrote in message ... Some systems ARE designed to work off of pressure. Depending on the system designer. John If the carbon vanes in a vacuum pump fail, any debris will be blown overboard. If the pump pressurizes the instruments, the debris will be blown into the instruments, ruining them. The Piper PA 31 Navajos for one use a pressure system with a filter between the pumps and the instruments. John Dupre' |
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