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1. 10:54 AM - Re: Re: Re:Dynon pitot (Leland)
2. 07:59 PM - Re: Re: Re: Re:Dynon pitot (Bob Kelly)
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| Subject: | Re: Re: Re:Dynon pitot |
--> RV9-List message posted by: Leland <Federigo@pacbell.net>
Steve, when I tested my Dynon it was without the pitot tube in the
circuit. I simply pressurized the line going to the control panel. I
also wondered if the Dynon accounted for the air leak in the pitot, and
that is one reason why I did the pressure test. I noticed that the Dynon
and my Van's analogue gauge differed in readings. I called Dynon and was
assured that everything would work out, but I am not yet reassured.
Van's gauge reads some 4-8 mph high over the range of 117 to 199 mph,
and the Dynon reads low by 4-5 mph over the same range. It seems that a
leaky pitot tube would read even lower.
And yes, my manometer was simply the tubing leading to the Dynon. (When
I started pressure testing, I found a lot of leaks in the connections,
and in the static system too. Upon advice from two different
pitot/static calibration shops, I used the high quality threaded
connectors from the likes of Wick's and ACS rather than the cheap barbed
connectors sold by Van's. There was a fatal accident due to a
low-altitude stall in an RV6 in Florida some two years ago. The
builder's friend conjectured that this accident occurred because the RV
had a leaky pitot/static system.)
Bob, assuming the airspeed gauges were calibrated at 29.92 inches of
mercury and 20 degrees Celsius, the airspeed in mph can be calculated by
multiplying the square root of the difference in meniscus height,
measured in inches, by the value 45.43. For other conditions, the
airspeed can be calculated by the formula:
AirSpeed
=SquareRoot[2*WaterMassDensity*Gravity*WaterColumnHeightDifference/AirMassDensity],
where the value of AirMassDensity can be gotten from the CRC Handbook of
Chemistry and Physics. If you want more detail, I could email you a copy
of my Excel spreadsheet.
Leland
Installing the empennage and elevator control tubes (getting the washers
in is a bitch)
>
>
Message 2
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| Subject: | Re: Re: Re:Dynon pitot |
--> RV9-List message posted by: Bob Kelly <mmpi@missionmedia.org>
Leland,
Thanks for the formula. I knew 5" H2O was around 100 mph and have used a
monometer to compare instruments in the past, but didn't know anything
beyond that. The spreadsheet should be a help if it isn't too much
trouble. mmpi at missionmedia.org
I used REALLY stiff grease to hold the washers in place on the control
tubes. Almost tar-like. You might try something like that, safer I feel
than the super-glue I hear some people use while assembling them. Still,
it is trial and error. If you don't have any really stiff grease, try
sitting a tub of wheel bearing grease on the top shelf with the top ajar
for 15 years or so. Don't ask how I know!
Thanks,
Bob Kelly, 90854
> Bob, assuming the airspeed gauges were calibrated at 29.92 inches of
> mercury and 20 degrees Celsius, the airspeed in mph can be calculated by
> multiplying the square root of the difference in meniscus height, measured
> in inches, by the value 45.43. For other conditions, the airspeed can be
> calculated by the formula: AirSpeed
>
=SquareRoot[2*WaterMassDensity*Gravity*WaterColumnHeightDifference/AirMassDensity],
> where the value of AirMassDensity can be gotten from the CRC Handbook of
> Chemistry and Physics. If you want more detail, I could email you a copy
> of my Excel spreadsheet.
>
> Leland
> Installing the empennage and elevator control tubes (getting the washers
> in is a bitch)
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