Vacuum Gyro Question

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'

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.


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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.

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.

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

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'