Jawed
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GPS As Pitot Tube Backup?

Sun Jun 07, 2009 9:35 pm

If the pitot tubes are plugged up with ice or whatever, why don't modern airliners use GPS as a backup option to measure their aircraft's current speed? Wouldn't a GPS-estimated speed be a lot better than no information at all?
 
A10WARTHOG
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RE: GPS As Pitot Tube Backup?

Sun Jun 07, 2009 9:47 pm

Well the chances of all 3 pitot tubes being inop, I think is very slim. You are more likely to lose your GPS data.
 
Jawed
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RE: GPS As Pitot Tube Backup?

Sun Jun 07, 2009 9:51 pm

It sounds like a lot of recent problems have been caused by inaccurate pitot tube readings. I would imagine that some kind of sanity-check against GPS would be useful, at least in these emergency situations when the pilot doesn't know what data to trust.
 
JoeCanuck
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RE: GPS As Pitot Tube Backup?

Sun Jun 07, 2009 10:12 pm

GPS only shows ground speed, though combined with other information, (such as power settings and heading), it could be used to estimate airspeed.
What the...?
 
AirframeAS
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RE: GPS As Pitot Tube Backup?

Sun Jun 07, 2009 10:33 pm

While the GPS technology is a really neat and cool fad, it is not totally 100% reliable.

Case in point: I have a GPS for my car and the speed that my GPS tells me is not the same as what my car's speedometer says. GPS is not 100% accurate.
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DescendVia
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RE: GPS As Pitot Tube Backup?

Sun Jun 07, 2009 10:45 pm

Raw GPS is not very useful for altitude and stuff. Plus it would take a major modification to the ADC (Air Data Computer) plus some time of augmentation system to be able to tie GPS in.
 
Fly2HMO
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RE: GPS As Pitot Tube Backup?

Sun Jun 07, 2009 11:30 pm

Quoting Jawed (Thread starter):
ouldn't a GPS-estimated speed be a lot better than no information at all?

Yes. IIRC the Garmin 430 GPS has a function where you can calculate your TAS knowing your pressure altitude and temp. IAS need not be known.

Quoting AirframeAS (Reply 4):
GPS is not 100% accurate.

Far from the truth. GPS is extremely accurate, more so than any speedometer out there. My handheld Garmin has a speed accuracy of better than .0001 of a mi, position accuracy is 3ft or better. And it's just a cheap WAAS enabled handheld. Aviation GPSs are much much more accurate and reliable.

Also, your speedo is wrong. No car (other than calibrated police cruiser speedos) has an accurate speedo and its on purpose by design. Typically speedos will show a speed up to 3mph than what you're actually doing. Also changing the dia. of your tires will also affect readings.

[Edited 2009-06-07 16:31:31]
 
lowrider
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RE: GPS As Pitot Tube Backup?

Sun Jun 07, 2009 11:35 pm

This has been done well before the advent of GPS. In the event that both airspeed indicators become inop for any reason DME or INS groundspeed along with pitch and power information can be used to approximate airspeed.
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N353SK
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RE: GPS As Pitot Tube Backup?

Sun Jun 07, 2009 11:47 pm



Quoting FLY2HMO (Reply 6):

Yes. IIRC the Garmin 430 GPS has a function where you can calculate your TAS knowing your pressure altitude and temp. IAS need not be known.

Take a look at your E6-B. In order to calculate true airspeed you need to know your calibrated airspeed. Calibrated airspeed is based off of indicated airspeed, which can only be ascertained from the pitot-static system.
 
dw747400
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RE: GPS As Pitot Tube Backup?

Mon Jun 08, 2009 12:07 am

In theory, Sat WX with winds aloft could be linked to the GPS in order to compute a rough approximation of TAS/IAS. Of course, this would depend on the reliability of the wind forecasts. I'm not sure how useful this would be when winds are rapidly shifting, though newer GPS has impressive refresh rates.

As others have mentioned GPS reliability isn't perfect, but there is no reason not to use it as a backup when all other options fail.
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Starlionblue
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RE: GPS As Pitot Tube Backup?

Mon Jun 08, 2009 1:26 am

Would there be an issue with altitude? That is, does GPS assume you are moving at ground level and base speed measurements on this?

Quoting AirframeAS (Reply 4):
Case in point: I have a GPS for my car and the speed that my GPS tells me is not the same as what my car's speedometer says. GPS is not 100% accurate.

As mentioned, it's not the GPS. Your speedometer is inaccurate. The method of measurement (based on the wheels) introduces all sorts of inaccuracies.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
AirframeAS
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RE: GPS As Pitot Tube Backup?

Mon Jun 08, 2009 1:40 am



Quoting FLY2HMO (Reply 6):
GPS is extremely accurate, more so than any speedometer out there.

My readings comeout totally different from each other.

Quoting FLY2HMO (Reply 6):
Also, your speedo is wrong.

I disagree. My car is pretty brand new, the speedometer was calibrated by the manufacturer.

Quoting Starlionblue (Reply 10):
As mentioned, it's not the GPS. Your speedometer is inaccurate. The method of measurement (based on the wheels) introduces all sorts of inaccuracies.

See above.
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Fly2HMO
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RE: GPS As Pitot Tube Backup?

Mon Jun 08, 2009 2:19 am



Quoting AirframeAS (Reply 11):
My readings comeout totally different from each other.

And your GPS is correct, not the speedo.

Quoting AirframeAS (Reply 11):
I disagree. My car is pretty brand new, the speedometer was calibrated by the manufacturer.

There is ALWAYS some error in it, it's impossible to avoid, and manufacturers lean towards a faster reading if there is an error. So your speedo will always read slower than what you're going.

http://en.wikipedia.org/wiki/Speedometer
 
AirframeAS
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RE: GPS As Pitot Tube Backup?

Mon Jun 08, 2009 2:23 am



Quoting FLY2HMO (Reply 12):
There is ALWAYS some error in it...

Same with the GPS. If the speed on cars was not correct, then we would be seeing so many folks being pulled over for speeding maybe?  sarcastic 
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mandala499
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RE: GPS As Pitot Tube Backup?

Mon Jun 08, 2009 2:25 am



Quoting FLY2HMO (Reply 6):
Yes. IIRC the Garmin 430 GPS has a function where you can calculate your TAS knowing your pressure altitude and temp. IAS need not be known.

And wind...

Quoting FLY2HMO (Reply 6):
Far from the truth. GPS is extremely accurate, more so than any speedometer out there. My handheld Garmin has a speed accuracy of better than .0001 of a mi, position accuracy is 3ft or better. And it's just a cheap WAAS enabled handheld. Aviation GPSs are much much more accurate and reliable.

In fairness, GPS is only good when used in conjunction with other stuff and backup when it comes to aviation.
If you've descended based on your GPS expecting a coastline only to find that once U're below the clouds you found NOTHING but water, U'd start wishing you got something else other than your GPS. This happened to a friend and luckily, he only had to wait for 15 mins until the local VOR switched on on schedule... and guess what, the GPS threw him 40NM off course. The airline later sent back the GPS and antennae back to the shop and they found nothing wrong. Another friend felt something was not right on his 777 one day and decided to look at the POS page in his FMC and saw that 1 GPS detected his position about 30NM away from his position. That gave him cold sweat for a couple of hours.

As a backup or used in conjunction with other stuff, GPS is wonderful... but, it is not all the hype people believe it to be... but it is very useful... no doubt.
When losing situational awareness, pray Cumulus Granitus isn't nearby !
 
AirframeAS
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RE: GPS As Pitot Tube Backup?

Mon Jun 08, 2009 2:29 am



Quoting Mandala499 (Reply 14):
As a backup or used in conjunction with other stuff, GPS is wonderful... but, it is not all the hype people believe it to be... but it is very useful... no doubt.

 checkmark  You said it better than I could. Thanks!  Smile
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nomadd22
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RE: GPS As Pitot Tube Backup?

Mon Jun 08, 2009 2:40 am

With flying through storms and in and out of the jet stream you air speed can be more than 140 knots off your ground speed.
Saying that, GPS can be a lot more useful than most people realize. A three antenna system with a tiny little gyro for temp loss of signal backup and attitude information is a whole different animal than a K-Mart handheld.
My Iphone map keeps showing me in Vietnam. Dumb thing confuses west latitude with east.
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tdscanuck
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RE: GPS As Pitot Tube Backup?

Mon Jun 08, 2009 3:13 am



Quoting Jawed (Thread starter):
why don't modern airliners use GPS as a backup option to measure their aircraft's current speed?

I'm pretty sure some do.

Quoting Starlionblue (Reply 10):
Would there be an issue with altitude?

Nope. As long as you've got 5+ satellites, you can get coordinates in 3D. You can technically do that with 4 for pure geometry, but then you don't get accurate time.

Quoting Starlionblue (Reply 10):
That is, does GPS assume you are moving at ground level and base speed measurements on this?

Aeronautical GPS's shouldn't do this. Some handhelds might.

Tom.
 
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Starlionblue
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RE: GPS As Pitot Tube Backup?

Mon Jun 08, 2009 4:29 am



Quoting AirframeAS (Reply 11):
Quoting FLY2HMO (Reply 6):
Also, your speedo is wrong.

I disagree. My car is pretty brand new, the speedometer was calibrated by the manufacturer.

Quoting Starlionblue (Reply 10):
As mentioned, it's not the GPS. Your speedometer is inaccurate. The method of measurement (based on the wheels) introduces all sorts of inaccuracies.

See above.

Just to cite one example, your tires change size with changes in temperature. So after driving for a while, your tires have heated up and the circumference of the tires has changes. This results in a small error.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
L-188
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RE: GPS As Pitot Tube Backup?

Mon Jun 08, 2009 6:15 am

I have a Boeing anti-ash video and they talk about the possiblity of loosing all three pitots in the advent of a volcanic ash encounter.

They do mention using groundspeed readings from ATC to compute airspeed. No reason why those readings have to come from ATC radar vs. GPS.
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PhilSquares
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RE: GPS As Pitot Tube Backup?

Mon Jun 08, 2009 6:37 am



Quoting L-188 (Reply 19):
I have a Boeing anti-ash video and they talk about the possiblity of loosing all three pitots in the advent of a volcanic ash encounter.

They do mention using groundspeed readings from ATC to compute airspeed. No reason why those readings have to come from ATC radar vs. GPS.

I am sure the 330, like every other transport aircraft, has in it's QRH an abnormal procedure that will cover flight with unreliable airspeed indications. The procedure would have each pilot check their airspeed and ADC to try to determine which airspeed indicator is the most reliable. Absent that, there is a listing of "typical" pitch and thrust settings that the crew can use. With those you can then get the GS from the FMC which has a GPS input.
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star_world
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RE: GPS As Pitot Tube Backup?

Mon Jun 08, 2009 11:13 am



Quoting AirframeAS (Reply 11):

I disagree. My car is pretty brand new, the speedometer was calibrated by the manufacturer.

As other have said already, this is completely incorrect - the speedometer is wrong, and the GPS is correct. If you want to add some doubt to the conclusion you have come to, try driving with 2 GPS devices in the car, from 2 different manufacturers. I think you will eventually agree  Smile
 
nomadd22
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RE: GPS As Pitot Tube Backup?

Mon Jun 08, 2009 11:32 am



Quoting Nomadd22 (Reply 16):
Dumb thing confuses west latitude with east.

Dumb poster confuses latitude with longitude.

The biggest single difference between good GPS and cheap GPS is probably receivers that scan channels compared to receivers that monitor channels simultaneously. Good ones with real multi channel capability can compare data streams real time and discard one that doesn't add up with the others. Errors on cheap ones can affect all channels and not get caught. The technology is extremely reliable. Some of the hardware isn't.
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trex8
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RE: GPS As Pitot Tube Backup?

Mon Jun 08, 2009 2:04 pm



Quoting AirframeAS (Reply 11):
Quoting FLY2HMO (Reply 6):
Also, your speedo is wrong.

I disagree. My car is pretty brand new, the speedometer was calibrated by the manufacturer.

car manufacturers are allowed a certain inaccuracy in their speedos, no more than a few mph either way for US and Japanese manufacturers and the Europeans never allow the indicated speed to be under the true speed (so your porsche is never going100mph when the speedo says it is, by EU law the true speed will have to be at best just under!)

there's a reason the Europeans are developing Galileo GPS, do you really trust the Pentagon in a wartime to keep Navstar GPS transmissions accurate for everyone all the time? let alone the paranoia the Chinese and Russians have for keeping or developing their own GPS constellations.
 
WPIAeroGuy
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RE: GPS As Pitot Tube Backup?

Mon Jun 08, 2009 3:21 pm



Quoting Tdscanuck (Reply 17):
Nope. As long as you've got 5+ satellites, you can get coordinates in 3D. You can technically do that with 4 for pure geometry, but then you don't get accurate time.

Aren't only four satellites needed, with the fourth being the for the time calibration?
-WPIAeroGuy
 
Phoenix9
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RE: GPS As Pitot Tube Backup?

Mon Jun 08, 2009 3:39 pm

I took these pictures last year on an AC flight. The ground speed readings on the IFE unit and my GPS unit were fairly consistent (just have to convert b/w mph and kph)

Big version: Width: 864 Height: 576 File size: 60kb
Big version: Width: 864 Height: 576 File size: 52kb
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N353SK
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RE: GPS As Pitot Tube Backup?

Mon Jun 08, 2009 5:26 pm



Quoting WPIAeroGuy (Reply 24):
Aren't only four satellites needed, with the fourth being the for the time calibration?

Not for aviation. At least five are needed, and six is ideal.

Take a look at this if you'd like: http://en.wikipedia.org/wiki/RAIM
 
DescendVia
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RE: GPS As Pitot Tube Backup?

Mon Jun 08, 2009 8:57 pm



Quoting WPIAeroGuy (Reply 24):

Aren't only four satellites needed, with the fourth being the for the time calibration?



Quoting N353sk (Reply 26):

Not for aviation. At least five are needed, and six is ideal.

4 or 3 and a Baro altimeter for basic RAIM. That in turn allows LNAV MDA approaches and terminal capability if the database is kept current. 5 or 4 with a Baro altimeter are required for vertical guidance. WAAS trumps it all though.
 
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zeke
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RE: GPS As Pitot Tube Backup?

Tue Jun 09, 2009 2:15 am

Airbus have a backup speed tape on new aircraft these days that replaces the airspeed information with an angle of attack fast/slow indicator, the altitude indicator will also show the GPS altitude.

Need to remember that GPS altitude is based on a mathematical model of earth, the altitude readout does not represent the altitude above terrain or seal level.

Due to wind, GPS is not suitable in the real world for airspeed indicator replacement.
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Flighty
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RE: GPS As Pitot Tube Backup?

Tue Jun 09, 2009 2:25 am



Quoting DescendVia (Reply 5):
Plus it would take a major modification to the ADC (Air Data Computer) plus some time of augmentation system to be able to tie GPS in.

Yup, that seems to be exactly what the thread starter had in mind... it would require some revision of the information systems on the plane. But the plane should have multiple verifications of speed, especially if it is making life-threatening decisions based on that info.. JMO. Especially since the sensor hardware is already onboard.
 
L-188
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RE: GPS As Pitot Tube Backup?

Tue Jun 09, 2009 2:58 am



Quoting N353sk (Reply 26):
Quoting WPIAeroGuy (Reply 24):
Aren't only four satellites needed, with the fourth being the for the time calibration?

Not for aviation. At least five are needed, and six is ideal.

And that is why GPS isn't great, There are spots north of the Brooks Range where you can't get 4 birds.

GPS is good, but it isn't infallible.
OBAMA-WORST PRESIDENT EVER....Even SKOORB would be better.
 
WPIAeroGuy
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RE: GPS As Pitot Tube Backup?

Tue Jun 09, 2009 6:25 pm



Quoting N353sk (Reply 26):
Not for aviation. At least five are needed, and six is ideal.

I'm not familiar with RAIM (I've never heard of it until now) but from the article the 5th or 6th satellite seems to only be needed as a backup, and that fault detection won't work with less than 5 but I'd assume navigation would still be possible? (I'm talking about lateral navigation, you'd still need the baro altimeter or RA for vertial navigation.)
-WPIAeroGuy
 
nomadd22
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RE: GPS As Pitot Tube Backup?

Tue Jun 09, 2009 6:47 pm



Quoting L-188 (Reply 30):
And that is why GPS isn't great, There are spots north of the Brooks Range where you can't get 4 birds.

I can't really make any sense out of that. GPS sats are at a 55 degree inclination. There should be more available at the poles than at the equator.
Anon
 
TSS
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RE: GPS As Pitot Tube Backup?

Tue Jun 09, 2009 7:49 pm



Quoting AirframeAS (Reply 4):
Case in point: I have a GPS for my car and the speed that my GPS tells me is not the same as what my car's speedometer says. GPS is not 100% accurate.



Quoting FLY2HMO (Reply 6):
Also, your speedo is wrong. No car (other than calibrated police cruiser speedos) has an accurate speedo and its on purpose by design. Typically speedos will show a speed up to 3mph than what you're actually doing. Also changing the dia. of your tires will also affect readings.

 checkmark   checkmark   checkmark 

One of the car magazines (Car And Driver, I believe) used to post a "speedometer error" table in their road test results. Most cars showed a percentage error (example- 20 mph indicated = 19 mph actual, 60 mph indicated = 57 mph actual, etc.), but Fords of that period tended to show a flat, across-the-board error (20 mph indicated = 15 mph actual, 60 mph indicated = 55 mph actual, etc.). While the technology for displaying the speed on a speedometer has advanced somewhat over the years, the initial speed data is still extrapolated from the rotational speed of the tires which can vary greatly depending on a number of factors.
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PPVRA
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RE: GPS As Pitot Tube Backup?

Tue Jun 09, 2009 8:27 pm

Why not also use the RAT as an emergency air speed sensor? Shouldn't be too complicated, no?
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mandala499
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RE: GPS As Pitot Tube Backup?

Tue Jun 09, 2009 9:34 pm



Quoting PPVRA (Reply 34):
Why not also use the RAT as an emergency air speed sensor? Shouldn't be too complicated, no?

Better still, have deployable pitot static tubes for backup !  Smile
When losing situational awareness, pray Cumulus Granitus isn't nearby !
 
osiris30
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RE: GPS As Pitot Tube Backup?

Tue Jun 09, 2009 9:39 pm



Quoting PPVRA (Reply 34):
Why not also use the RAT as an emergency air speed sensor? Shouldn't be too complicated, no?

Apart from drag, that's brilliant.
I don't care what you think of my opinion. It's my opinion, so have a nice day :)
 
DaBuzzard
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RE: GPS As Pitot Tube Backup?

Tue Jun 09, 2009 9:40 pm



Quoting PPVRA (Reply 34):
Why not also use the RAT as an emergency air speed sensor? Shouldn't be too complicated, no?

Hmmm, now that just might be doable.
Would be working off air flow, so as long as you know the load and rpm, you could work a system out.

Would it be worth it (development, certification, and installation cost) is another question.
 
tdscanuck
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RE: GPS As Pitot Tube Backup?

Tue Jun 09, 2009 11:59 pm



Quoting Nomadd22 (Reply 32):
GPS sats are at a 55 degree inclination. There should be more available at the poles than at the equator.

An orbit at 55 degree inclination means the satellite loops between 55 N and 55 S latitude. If you're below those latitudes, the satellites will go directly overhead at some point. Above those latitudes, the satellites never get overhead, they're always lower in the horizon. Hence, as you move away from the equator, your view gets progressively obstructed by terrain and atmosphere.

Quoting PPVRA (Reply 34):
hy not also use the RAT as an emergency air speed sensor? Shouldn't be too complicated, no?

Possible, not not simple.

Quoting DaBuzzard (Reply 37):
Would be working off air flow, so as long as you know the load and rpm, you could work a system out.

And the air density. Measuring the electric load isn't too hard, but measuring the hydraulic load could be tricky, especially with sufficient accuracy to back out airspeed. You also really don't want to drop the RAT unless you have to...doing it just to get airspeed is a bit of overkill when there are better ways to do it. I suspect backing it out of the FBW system would probably be more accurate, and certainly less draggy.

Tom.
 
N353SK
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RE: GPS As Pitot Tube Backup?

Wed Jun 10, 2009 3:48 am



Quoting WPIAeroGuy (Reply 31):
I'm not familiar with RAIM (I've never heard of it until now) but from the article the 5th or 6th satellite seems to only be needed as a backup, and that fault detection won't work with less than 5 but I'd assume navigation would still be possible? (I'm talking about lateral navigation, you'd still need the baro altimeter or RA for vertial navigation.)

All I can tell you is that you need at least 5 to have RAIM and that you need to have RAIM to use your GPS under IFR.
 
DiamondFlyer
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RE: GPS As Pitot Tube Backup?

Wed Jun 10, 2009 4:19 am



Quoting N353SK (Reply 39):
All I can tell you is that you need at least 5 to have RAIM and that you need to have RAIM to use your GPS under IFR.

Or WAAS, as was previously stated. Ultimately it comes down to if your GPS box is installed to the TSO 129 standard versus the TSO 146 standard.

But, would the pilots really need an estimation of airspeed. With a groundspeed, and a decent weather report with them, they could stay within the operating zone comfortably, I would think, could they not?

-DiamondFlyer
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DescendVia
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RE: GPS As Pitot Tube Backup?

Wed Jun 10, 2009 5:12 am



Quoting N353SK (Reply 39):
All I can tell you is that you need at least 5 to have RAIM

5 or 4 with a baro altimeter setting for RAIM and 6 or 5 with a baro altimeter setting to have RAIM delete corrupt signals.
 
tietkej
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RE: GPS As Pitot Tube Backup?

Wed Jun 10, 2009 7:49 am



Quoting AirframeAS (Reply 4):
Case in point: I have a GPS for my car and the speed that my GPS tells me is not the same as what my car's speedometer says. GPS is not 100% accurate.

Hate to be naggy, but your GPS speed is more likely to be correct than your speedometer in the car (provided you are going straight on flat land). Manufacturers tend to build in roughly a 5km/h buffer into car speedometers. On the ground that means more safety - obviously not good in the air though  Smile

Cheers.
 
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Faro
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RE: GPS As Pitot Tube Backup?

Wed Jun 10, 2009 11:23 am

How about pressure-sensitive sensor pads on the wing leading edges? I would imagine that these can be made pretty sensitive these days. After all, for indicated airspeed (which is what the pitot measures), you are looking to detect i) static pressure and ii) dynamic pressure. The sensor pads would take care of ii), you just need a couple of extra static ports spread along the fuselage to detect i)...

Faro

[Edited 2009-06-10 04:58:29]
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nomadd22
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RE: GPS As Pitot Tube Backup?

Wed Jun 10, 2009 11:43 am



Quoting Tdscanuck (Reply 38):
An orbit at 55 degree inclination means the satellite loops between 55 N and 55 S latitude. If you're below those latitudes, the satellites will go directly overhead at some point. Above those latitudes, the satellites never get overhead, they're always lower in the horizon. Hence, as you move away from the equator, your view gets progressively obstructed by terrain and atmosphere.

Satellites directly overhead are acutally the least usefull, since they have the smallest movement compared to your position.
The satellites are around 12,000 miles altitude in six orbital planes. That means that at the equator the highest sat could be as much as 30 degrees off vertical. Also means you will only see birds in two of the planes at once. Maybe three if you're right under one and have a clear view of the adjacent two. But at the pole you're in view of all six planes at once and the satellites have greater velocity relative to your position, which means more precise data.
Anon
 
zappbrannigan
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RE: GPS As Pitot Tube Backup?

Wed Jun 10, 2009 11:57 am



Quoting Tietkej (Reply 42):
Hate to be naggy, but your GPS speed is more likely to be correct than your speedometer in the car (provided you are going straight on flat land). Manufacturers tend to build in roughly a 5km/h buffer into car speedometers. On the ground that means more safety - obviously not good in the air though

Yep, I've checked my car speedo with good handheld units, and it overreads by around 3 km/h at just about every point on the dial I tested, up to around 120 km/h. This is deliberate.

The GPS is correct (or very very close to it). The car is not.
 
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glen
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RE: GPS As Pitot Tube Backup?

Wed Jun 10, 2009 1:03 pm



Quoting PPVRA (Reply 34):
Why not also use the RAT as an emergency air speed sensor



Quoting Faro (Reply 43):
How about pressure-sensitive sensor pads

To get your indicated airspeed you need the difference between dynamic air pressure (from pitot) and static air pressure (from static source). With both solutions mentioned above you only can derive dynamic pressure from an electrical signal. So you need again some kind of computer to calculate your indicated speed by taking into account static pressure. Which means all you get is only a 4th source of information (which isn't fail save either) in addition to the three normal pitot/static systems. If I wanted an additional system, I would prefer again a "simple" pitot/static system without any kind of computer in between.
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nomadd22
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RE: GPS As Pitot Tube Backup?

Wed Jun 10, 2009 1:10 pm

GPS doesn't have tires that change diameter throughout their life, manufacturers who think 5% off is accuracy enough, different size tires than the factory put on or perspective problems with looking at the analog display at an angle.
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Faro
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RE: GPS As Pitot Tube Backup?

Wed Jun 10, 2009 1:27 pm



Quoting GLEN (Reply 46):
If I wanted an additional system, I would prefer again a "simple" pitot/static system without any kind of computer in between.

Quite the item, yes, I would prefer that too but then that would also be susceptible to extreme icing/contamination conditions if we -very very tentatively- take the tragic case of AF 447 as potential reference.

I recall that certain turbine engines have a centrifugal facility built into the inlets to disperse sand and avoid it being ingested into the compressor. Perhaps the same type of gizmo can be adapted to pitot tubes to disperse extreme levels of snow/ice particles or supercooled droplets impacting the pitot inlet? You would have to rework the mechanics of the airspeed indication apparatus to take into account the pressure effect of the device though, just an idea off the top of me head.

Faro
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mandala499
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RE: GPS As Pitot Tube Backup?

Wed Jun 10, 2009 2:28 pm



Quoting Faro (Reply 48):
Quite the item, yes, I would prefer that too but then that would also be susceptible to extreme icing/contamination conditions if we -very very tentatively- take the tragic case of AF 447 as potential reference.

Well, with all this talk about GPS as Pitot Tube Backup...
Why not the BUSS/BackUpSpeedtapeSystem that's available on the Airbus?
It will allow you to fly using power, AoA and GPS altitude... no longer dependent on the Pitot Static System...
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