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12-26-2016, 09:04 PM
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Join Date: Nov 2014
Location: Concord, NH
Posts: 215
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Two Engines?
I've been reading all of the posts regarding multiple ADAHARS and the worry of losing one or two and not being able to complete the IFR flight.
I've only got a single IFR G3X/GTN625 installation. I would be more concerned about losing the engine due to mechanical failure than losing the electronics. I've flown in actual IFR with only needle ball and airspeed in the past, before the days of ipads and Foreflights, and Garmin Pilots. If I had had these tools years ago I would have felt blessed. To anyone who has not flown actual IFR using only the needle ball and airspeed, I recommend it as a great confidence builder. You'll stop worrying about your backup ADAHRS agreeing.
Steve
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Steve Briggs. RV9, G3x, G5, VPX, GTN625, PMags, A&P, IA, ATP-CFII
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12-26-2016, 11:34 PM
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Join Date: Mar 2008
Location: Anacortes, WA
Posts: 823
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Single screen ifr
Ken
Thanks for your question. I'm contemplating same scenario. My engine install is almost done then I'll be doing avionics. I fly IFR regularly in 6-pack Cherokee. I'm thinking for my RV7 I'll do Dynon Skyview plus a Dynon D2 pocket EFIS. But I'm also thinking and electrical Attutude Indicator-maybe. Plus I'll probably have Garmin 430 or equivalent. And I'll use VP-X but the AI would be wired outside of VP-X.
With my 6-pack if I loose vacuum pump I lose AI, DG and autopilot. Turn and bank is almost worthless backup gauge because it is too wiggly. But compass and Garmin 430 tells me if there is a direction change. Altimeter and GPS tells me if there is a pitch change. So I think there is a lot of backup in using the GPS, and the compass such that a third EFIS isn't necessary. And also plenty of info to decide if a gauge is wrong.
And iPAD with Garmin Pilot gives a lot of functionality that is working very reliably for me.
PS I'm in Anacortes.
__________________
Steve Lynn
RV-7A
Flying Phase I
Anacortes, WA
www.mykitlog.com/sglynn
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12-27-2016, 02:11 PM
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Join Date: Mar 2010
Location: KSGJ / TJBQ
Posts: 2,039
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Quote:
Originally Posted by sibriggs
I've been reading all of the posts regarding multiple ADAHARS and the worry of losing one or two and not being able to complete the IFR flight.
I've only got a single IFR G3X/GTN625 installation. I would be more concerned about losing the engine due to mechanical failure than losing the electronics. I've flown in actual IFR with only needle ball and airspeed in the past, before the days of ipads and Foreflights, and Garmin Pilots. If I had had these tools years ago I would have felt blessed. To anyone who has not flown actual IFR using only the needle ball and airspeed, I recommend it as a great confidence builder. You'll stop worrying about your backup ADAHRS agreeing.
Steve
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FWIW Confidence is no good and can be deadly if you don't maintain proficiency. Most GA pilots I know maintain basic IFR currency, not proficiency. For those current but not proficient, the majority of GA pilots, having redundant systems to get them out of an IFR emergency is important. YMMV
Quote:
Originally Posted by BobTurner
Since you have an all-Dynon system, I'd be curious as to how it reacts to a partial pitot clog - bad enough to lose attitude reference, not bad enough to auto-switch to GPS (a failure like this has been reported here on VAF). Would both instruments look exactly the same (but both incorrect)?
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Pitot indications are based solely on air pressure, air doesn't flow within the system. So a partial clog might affect how fast the indicator reacts to an airspeed change, but once the pressure builds up it will indicate correctly. That is why you can use different size lines (small line is the same as a "partial clog") with no major effect. No different than putting a flow restrictor (partial clog) on oil, fuel or manifold pressure gauge lines. They react slower, but still indicate correctly.

__________________
Galin
CP-ASEL-AMEL-IR
FCC Radiotelephone (PG) with Radar Endorsement
2020 Donation made
www.PuertoRicoFlyer.com
Last edited by GalinHdz : 12-27-2016 at 03:08 PM.
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12-27-2016, 03:20 PM
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Join Date: Jul 2013
Location: US
Posts: 2,251
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Quote:
Originally Posted by GalinHdz
Pitot indications are based solely on air pressure, air doesn't flow within the system. So a partial clog might affect how fast the indicator reacts to an airspeed change, but once the pressure builds up it will indicate correctly. That is why you can use different size lines (small line is the same as a "partial clog") with no major effect. No different than putting a flow restrictor (partial clog) on oil, fuel or manifold pressure gauge lines. They react slower, but still indicate correctly.

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He's asking about the effect of a partial pitot blockage on the attitude computation, since Dynon (and presumably other EFISes) use air data in the computations for attitude. I assume the failure mode postulated here is something blocking it in such a way that, at least for a period of time, the airspeed (dynamic pressure) is jacked up somehow. Although you're right, it *should* stabilize at some value and then the airspeed AND attitude should recover.
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12-27-2016, 04:34 PM
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Join Date: Mar 2010
Location: KSGJ / TJBQ
Posts: 2,039
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Quote:
Originally Posted by RV7A Flyer
He's asking about the effect of a partial pitot blockage on the attitude computation, since Dynon (and presumably other EFISes) use air data in the computations for attitude. I assume the failure mode postulated here is something blocking it in such a way that, at least for a period of time, the airspeed (dynamic pressure) is jacked up somehow. Although you're right, it *should* stabilize at some value and then the airspeed AND attitude should recover.
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AFAIK for the attitude algorithms, Garmin units use GPS speed as primary with Pitot as backup but the GX guys can confirm. Dynon uses Pitot as primary with GPS as backup for the same. Either way it "shouldn't" cause a serious situation with a partial block since the indication will eventually be correct.

__________________
Galin
CP-ASEL-AMEL-IR
FCC Radiotelephone (PG) with Radar Endorsement
2020 Donation made
www.PuertoRicoFlyer.com
Last edited by GalinHdz : 12-27-2016 at 04:39 PM.
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12-27-2016, 05:03 PM
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Join Date: Nov 2005
Location: AUSTRALIA
Posts: 749
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Can't comment on a blocked/partially blocked pitot but an intermittently blocked static port (rain/water) will cause an erratic pitch display on the Skyview.
Fin.
9A
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12-27-2016, 10:16 PM
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Join Date: Dec 2011
Location: Livermore, CA
Posts: 6,797
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Air does flow in the pitot tube - because of the drain hole. As the pitot opening gets reduced (bug, ice) down close to the size of the drain hole, the line pressure drops. And the airspeed reads low but not zero.
I know the GRT Horzon EFIS will show the horizon correctly without either airspeed or GPS data.
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12-28-2016, 01:42 AM
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Join Date: Mar 2010
Location: KSGJ / TJBQ
Posts: 2,039
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Quote:
Originally Posted by BobTurner
Air does flow in the pitot tube - because of the drain hole. As the pitot opening gets reduced (bug, ice) down close to the size of the drain hole, the line pressure drops. And the airspeed reads low but not zero.
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As I remember it; as a partial pitot clog develops, changes in airspeed take longer and longer to change the pressure in the system making the display slow to react. As long as the partial clog size stays greater than the drain size, the system stays pressurized and the new airspeed eventually displays correctly. When the partial clog becomes equal or smaller than the drain, then there is no pressure in the system (excluding venturi effect) and for all practical purposes you have a complete clog. Drain holes are tiny!
IMHO this makes for great theoretical discussion(s), but not much for a practical application.

__________________
Galin
CP-ASEL-AMEL-IR
FCC Radiotelephone (PG) with Radar Endorsement
2020 Donation made
www.PuertoRicoFlyer.com
Last edited by GalinHdz : 12-28-2016 at 01:52 AM.
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12-28-2016, 10:01 AM
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Join Date: Jul 2013
Location: US
Posts: 2,251
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Quote:
Originally Posted by GalinHdz
As I remember it; as a partial pitot clog develops, changes in airspeed take longer and longer to change the pressure in the system making the display slow to react. As long as the partial clog size stays greater than the drain size, the system stays pressurized and the new airspeed eventually displays correctly. When the partial clog becomes equal or smaller than the drain, then there is no pressure in the system (excluding venturi effect) and for all practical purposes you have a complete clog. Drain holes are tiny!
IMHO this makes for great theoretical discussion(s), but not much for a practical application.

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So we're back where we started  . A partial clog *may* have some temporary impact on the attitude display (and airspeed), but we don't really know what or how much of an effect it is (need manufacturers to weigh in here). But it should eventually clear. A complete clog...system goes to GPS assist, attitude shown is correct.
OK, that's *one* branch down the failure tree...still looking for inputs on likelihood of the failure modes for an ADAHRS itself.
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12-28-2016, 10:12 AM
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Join Date: Jul 2009
Location: Mojave
Posts: 4,652
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I've had one experience with an airspeed malfunction while flying through rain. D10A with AoA in cruise flight the airpeed suddenly jumped to 500 knots and AoA display went nuts. Attitude remained stable throughout - until the display went black a few minutes later (unrelated failures).
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WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.
Michael Robinson
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Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C
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