Piers,
I guess I have to go back to my roots as an aerodynamicist to explain what
seems to be a common misconception. The pitot tube is a forward-facing tube
that accepts "ram air" as the aircraft moves through the air. The faster
the aircraft, at a given altitude, the higher this ram pressure becomes. It
is combined with a static orifice, either on the side of the pitot tube
installation or on the side of the aircraft, in order to provide the two
pressures necessary for an airspeed indicator to function. The static
orifice also connects to the altimeter.
The venturi seen on older aircraft that have no powered vacuum pump merely
serves to provide a vacuum source to power the vacuum-driven gyro
instruments. Many of these instruments are now powered electrically, or
from an engine-driven pump, so the venturi is basically a thing of the past.
And then there are the venturis that drain the relief tube, also a thing of
the past.
Jim Nichols
Tullahoma, TN USA
----- Original Message -----
From: "Piers Hemy" <piers@xxxxxxxx>
To: "'Olympus Camera Discussion'" <olympus@xxxxxxxxxxxxxxxxx>
Sent: Tuesday, December 15, 2009 9:52 AM
Subject: Re: [OM] IMG: 1929 Gulf Hawk Seen in 1972
> And I also thought of pitot tubes when reading Jim's message. But I
> assumed
> I had misunderstood the application of pitot tubes all these years, and
> that
> they had always been, indeed, "pee to" tubes.
>
> Piers
>
> -----Original Message-----
> From: Chris Barker [mailto:ftog@xxxxxxxxxxxxxx]
> Sent: 15 December 2009 06:09
> To: Olympus Camera Discussion
> Subject: Re: [OM] IMG: 1929 Gulf Hawk Seen in 1972
>
> I must admit that I had never realised that the venturi below aircraft
> like
> that was a "relief" tube. I had always thought it to be a pitot system.
> I'll try to remember to look when I next visit Duxford, which is just to
> the
> south of me.
>
> Chris
>
> On 15 Dec 2009, at 06:04, Jim Nichols wrote:
>
>>
>> Yes, those were a real challenge to control properly. Thanks for
>> looking.
>
>> When I saw the venturi beneath the cockpit, I couldn't help but think
>> of the earlier thread.
>
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