Air Data Sources - DA42

Any DA42 related topics.

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Pmurphy
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Air Data Sources - DA42

Post by Pmurphy »

I have a question that I have been unable to answer from the POH or web and would appreciate if anyone could assist. The G1000’s Air Data Computer receives air pressure data from a single source (I believe...) - the aircraft’s pitot on the port wing which, unusually, measures both static and dynamic pressure in one combined instrument (from what I can gather). I have been unable to confirm where the standby ASI and Altimeter receive their information from. Does it come from the same source?/? I hope not, but I’m just trying to confirm that all air pressure data on a DA42 does not come from a single source - the pitot probe under the port wing. Appreciate any wiser views.
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Re: Air Data Sources - DA42

Post by Boatguy »

The DA42 has two static ports, one on either side, just aft of the passenger door/window. You can see the little round circles of the static port if you look closely in photos of the plane.

And the alternate static port valve on the underside of the panel to the left of the pilot opens a port in the cabin. So there are three static ports. But only one pitot tube.
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Re: Air Data Sources - DA42

Post by Rich »

According to the AFM for the original DA42, these did have the same pitot-static setup as the DA40, with that single blade under the left wing providing both. There is an advantage to this, though. It means both the pitot and static ports are heated when the pitot heat is activated, as that entire blade gets hot.
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Re: Air Data Sources - DA42

Post by chili4way »

The pitot and static pressure sources for the standby and G1000 instruments are the same (as described by Russ above). There is no separate source redundancy between the G1000 and the standby instruments. Also: only ram air pressure is provided from the pitot tube.

You can find more specifics in the DA42 Maintenance Manual available at:
http://support.diamond-air.at/

34-00-00 page 2 (1516/2339 PDF page count) has a text description
34-10-00 page 2 (1520) has a nice illustration of the 'plumbing'
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Rich
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Re: Air Data Sources - DA42

Post by Rich »

chili4way wrote: Sat Jan 30, 2021 7:14 pm The pitot and static pressure sources for the standby and G1000 instruments are the same (as described by Russ above). There is no separate source redundancy between the G1000 and the standby instruments. Also: only ram air pressure is provided from the pitot tube.

You can find more specifics in the DA42 Maintenance Manual available at:
http://support.diamond-air.at/

34-00-00 page 2 (1516/2339 PDF page count) has a text description
34-10-00 page 2 (1520) has a nice illustration of the 'plumbing'
True for the NG and VI versions. The old TDI Flight manual and AMM say otherwise. From the latter, section 34-10:

The DA 42 has the usual flight environment data systems. It has a Pitot static system. The Pitot
static system has a Pitot static probe located under the left wing. The Pitot probe has an electric
heater. The heater is controlled by a switch on the left side of the instrument panel, at the bottom.
Flexible plastic hoses connect the Pitot static probe to the airplane instruments.
The airplane has a static system. The normal static vents are integral with the Pitot probe. If
OÄM 42-102 (GFC 700) is installed, the static ports are on the rear fuselage. An alternate static
vent is located in the cockpit, under the instrument panel, on the left side. The pilot opens the
alternate static vent by turning a valve on the vent.
The Pitot static system connects to these flight instruments and systems:
) Altimeter.
) Airspeed indicator.
) Integrated cockpit system.

The older ones also have provision for optionally having the dedicated, separate static ports for the autopilot. I bring this all up to help clarify possible confusion. Be sure you have the right documents for your bird.
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Re: Air Data Sources - DA42

Post by Pmurphy »

Many thanks. What I’m really getting at; is that there is a single point of failure on air pressure data when flying a DA42. If, say a large insect gets caught in the dynamic pitot tube, then the effect will impact both the G1000 flight displays AND the standby instruments. Am I correct?
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Re: Air Data Sources - DA42

Post by Rich »

Pmurphy wrote: Sat Jan 30, 2021 10:07 pm Many thanks. What I’m really getting at; is that there is a single point of failure on air pressure data when flying a DA42. If, say a large insect gets caught in the dynamic pitot tube, then the effect will impact both the G1000 flight displays AND the standby instruments. Am I correct?
For the pitot tube (i.e., the dynamic pressure port) that is true. But I can not think of a single plane I have piloted over 55 years that does not have this weakness. The reality is ice-clogging is much more likely than to suddenly have an insect meet its maker while in flight, hence pitot heat. These days our backup is to use ground speed. Prior to that we had no backup, just deducing by the net effect of power settings and "feel". Most of us have had at least a bit of training flying with an INOP airspeed indicator (and no GPS).

BTW, in those 55 years I have never had an actual INOP AS indicator. However in one night flight I lost all electrical so I could not see any perfectly usable steam gauges.
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Re: Air Data Sources - DA42

Post by Pmurphy »

Many thanks. Very useful forum.
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Re: Air Data Sources - DA42

Post by Rich »

Just a comment. As I've stated, I've never had a pitot or static port blocked by an insect. This is kind of amazing given how many thousands of these critters I've smashed with the rest of the airplanes' parts over the years. :D
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Re: Air Data Sources - DA42

Post by Paul »

Rich wrote: Sun Jan 31, 2021 12:02 am
Pmurphy wrote: Sat Jan 30, 2021 10:07 pm Many thanks. What I’m really getting at; is that there is a single point of failure on air pressure data when flying a DA42. If, say a large insect gets caught in the dynamic pitot tube, then the effect will impact both the G1000 flight displays AND the standby instruments. Am I correct?
BTW, in those 55 years I have never had an actual INOP AS indicator. However in one night flight I lost all electrical so I could not see any perfectly usable steam gauges.
I have. Pitot heat failure climbing out at night in IMC and the tube froze and airspeed rolled back to zero. This was in a Meridian. I was happy to have a second pitot tube and second PFD but pitch, power and groundspeed work just as well so one pitot in a DA42 would not be concerning to me. I do wish they had the opportunity to add a second ADC and AHRS.
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