Warbird Information Exchange

Just tapping into the collective knowledge base...

I have what appears to be a 1940s-early 1950s vintage Radar Pressure Indicator, 0-25 PSI Absolute, made by US Gauge pn AW 1 7/8-31-B2F29. I'm speculating that the pressure measurement was pneumatic vs hydraulic, given its range. The markings painted in munsell green seem to indicate usage by aircraft of the US Navy from that era.

I've been researching the airborne radar systems of that era (USN or other services) and have yet to find a clue as to the system that used pneumatics (perhaps for gyro stabilization or even antenna rotation?).

Photos below. Any ideas? I'd love to figure out what radar system used it and what aircraft used the radar system (thanks in advance!)

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JT
AeroAntique
"Preserving Warbird History...one artifact at a time"
http://aeroantique.com/
"All right, Striker, you listen, and listen close. Flying a plane is no different from riding a bicycle; it's just a lot harder to put baseball cards in the spokes."

I believe a number of early RADARs had pressurized transmitters.
My guess is the APS-20. Used on many Navy aircraft.

Thanks AlohaDave. I'm chasing that lead in my documentation and online but haven't come up with anything.

Any specific document references are appreciated. Would you think the indicator is mounted on the transmitter itself, the radar operators panel, or the pilots panel?

An old boss use to say to me "one idiot can ask more questions than 20 professors can answer". I've not learned my lesson yet.

_________________
JT
AeroAntique
"Preserving Warbird History...one artifact at a time"
http://aeroantique.com/
"All right, Striker, you listen, and listen close. Flying a plane is no different from riding a bicycle; it's just a lot harder to put baseball cards in the spokes."

Maybe mounted on the Navigator's panel?

I recall a pressure gauge being part of the C-130 weather radar panel (APN-59). A look at the NMUSAF photo essay confirms I did remember it correctly, however the gauge is of a different scale. The APN-59 was used on a number of aircraft and was a 50's or 60's vintage unit.

http://www.nationalmuseum.af.mil/Visit/ ... -hercules/

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"Take care of the little things and the big things will take care of themselves."

gauge would be mounted on the RADAR operators station.

I shared this thread with a buddy who was a senior Flight Examiner Navigator in my old unit. His comments are:

"The radar pressure gauge measures the pressure in the radar's waveguide. The waveguide is a hollow metal tube which directs the radar energy from the radar's R/T to the antenna. It is pressurized to prevent arcing.

On the C-130 there was a pump which could increase the pressure, and a bleed valve to reduce it. There was also an automatic feature, controlled by a switch, which was normally on. There was a light which illuminated when the pump was operating.

We had to test it for leaks during pre-flight by pumping it up to 40 in Hg, and timing for 10 minutes. It was supposed to keep at least 38 in Hg if I recall. The older airplanes usually failed the test, but the pump would keep the pressure in the normal mode in flight, it just might have to work harder.

The normal range for the APN-59 was about 30 in Hg, or normal sea level pressure. So the system needed the sealed waveguide and the pump when flying at altitude. The photo on the Warbirds site seems like it is for a radar which operates at a lower waveguide pressure, which suggests it was not intended for low-level operations. My guess is the waveguide pressure may correlate to the radar frequency.

Also, on the APN-59, it seemed like the the higher the pressure in the waveguide, the better the radar picture. So sometimes old heads would "pump up the radar" when encountering weather to get a better picture."

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"Take care of the little things and the big things will take care of themselves."

Fascinating Ken! So it operated in a similar fashion to pressurized magnetos and for the same purpose.

Many thanks to all for the insightful information! Thanks for tapping into some outside expertise.

I've found the panel from the C-130B Flight Manual dated Dec 1962 which illustrates the pressure indicator described by Ken's colleague, and it is different than this one (up to 45 psi). So at least we've confirmed the purpose of a pressure indicator on a radar system.

The original question remains: What radar system used this gauge and what aircraft had the system installed?

AlohaDave's original guess of the AN/APN-20 may be on the mark. I've seen photos of the console itself, but not of the entire radar operators station which may have displayed the pressure indicator. Late/postWW2 TBM's, early P2V's, or recon AD-1's?

Perhaps I'm pondering the imponderable...

_________________
JT
AeroAntique
"Preserving Warbird History...one artifact at a time"
http://aeroantique.com/
"All right, Striker, you listen, and listen close. Flying a plane is no different from riding a bicycle; it's just a lot harder to put baseball cards in the spokes."