Ed Rasimus wrote:

[snipped for brevity]


Third, the much earlier assertions that pitot tubes were somehow
relevant only to jet engine powered aircraft is absurd. Conventional
(i.e. piston-driven) aircraft has just as much of a requirement for
measurement of pitot pressure. And, even sailplanes, with no engine at
all, use a pitot tube for airspeed indication.

Yep, we even have 'em on our trikes. Of course, they're not the
complicated (and more accurate) flush type "Y" static systems with
vents on the fuselage as you described, however, they're reasonably
accurate for our purposes (e.g: low & slow in the 25-95 kt. range).

For an ASI that uses a pitot tube to measure the difference between
ram pressure and static pressure, all you need is a pitot tube with
it's opening facing straight into the oncoming air. We found that the
size of the hole is not critical. Usually it's just a short length of
1/4-inch aluminum tubing that can be inserted into plastic tubing
and routed to the fitting on the back of the instrument.

For static pressure, we simply use the "static" fitting which is also
on the back of the ASI guage itself, which can be left open as long
as the instrument is protected from the airstream. Sometimes the
forward edge of the pitot tube is rounded a bit to smooth the flow,
but I doubt that it makes much difference at typical trike speeds.

The main concern for getting accurate readings from a pitot tube
airspeed indicator (as opposed to the even more simple but
accurate "Hall" type ASI that looks like a rain guage) is locating
the tube. It needs to face straight into the flow at cruising speed
(which often means a downward angle when the craft is sitting on the
ground) and it needs to be in "clean air" meaning as far forward as
possible and not in the wake of any obstructions.

For an altimeter, we don't need a pitot tube and just a "static" port
is fine. Again, if the altimeter is in a pod (that's not hermetically
sealed) there's usually no need to connect anything to that little
brass fitting on the back of the altimeter in order to get a decent
altitude reading.

Poor Henri, he probably never would have believed what his invention
has wrought on Usenet.

I'm wondering if Henri would think this neverending, silly thread is
as amusing and entertaining as I think it is.