The day all my performance was stolen

[Browncbr1]

Well, I usually fly LOP, but this day I knew I had big head winds to deal with as well as low temperatures.   I was also carrying a ~700lb payload, so I decided to go ROP.  I shot this video to show how a normally 2 hour flight became 3 hours.  At one point before making the video, the winds were 68kts 20 degrees right of coarse.     G5 says 183mph tas (~159ktas), but gtn calculates 156ktas.  Any idea how there is error between the gtn and G5 calculations?  ASI calibration error is about 1-2mph, which I manually input into the gtn..   is there a way to program calibrated airspeed to the G5 computations?
 

 

[A64Pilot]

So your saying it was 3 kts off? I’d say that’s within tolerance, TAS calculations aren’t as accurate as we would like them to be in my experience, not sure why.

Your comparing on to the other, each could be slightly off

[Browncbr1]

11 minutes ago, A64Pilot said:

So your saying it was 3 kts off? I’d say that’s within tolerance, TAS calculations aren’t as accurate as we would like them to be in my experience, not sure why.

Your comparing on to the other, each could be slightly off

I was mainly wondering why the two units would display different info, while being on the same canbus backbone.  In typing this, I just realized jPI probe OAT is going into the gtn, while the G5 is getting OAT from its own probe.   Doh!   I guess I need to calibrate the two probes.  

[A64Pilot]

27 minutes ago, Browncbr1 said:

I was mainly wondering why the two units would display different info, while being on the same canbus backbone.  In typing this, I just realized jPI probe OAT is going into the gtn, while the G5 is getting OAT from its own probe.   Doh!   I guess I need to calibrate the two probes.  

How are you going to calibrate the probe? adjust it so the two read the same? That’s a single point calibration and therefore the probes will agree at that one temp, without a multi point calibration which you may not be able to do they may drift apart as temps vary significantly.

Plus and I may be wrong here but I think algorithms vary slightly, I know it’s simple math and math is of course a constant but I can’t explain it any other way

Other than perhaps they are analog devices but display digitally.

Enjoy your instruments of course just don’t get upset if they both don’t agree to a single digit, that level of accuracy just isn’t needed, a pet peeve of mine is that it seems many instruments display to a much finer degree than they are accurate to measure, some multimeters that display voltage to three digits for example.

[flyboy0681]

I have the same 3 degree issue between the same two probes and explanations given here on MS mention that the Garmin probe "may be" calibrated to account for ram rise while cruising. Also, where the two probes are located can have a significant impact on the readings.

[M20F]

I would do a 3 way gps test and see what it details.  

[Shadrach]

67 was a great vintage for Mooneys.  That a fine running machine you have there. Do you know if your airplane's ignition timing is set to 20° or 25°? 

[carusoam]

Aaaaaah….

A man with two different OAT sensors doesn’t know his real TAS….!

A version of having two watches… 

OAT sensors are very sensitive to location…

The more modern ones are just a bump, hiding from the sun, and avoiding being in line with warm air sources…

 

Exactness of OAT sensors is mostly for avoiding ice buildup or getting to warm air to melt an ice problem…

It was probably mr. Fahrenheit that decided that 32.0000° was a good temperature for pure water to freeze

 

PP thoughts only, not a weatherman…

Best regards,

-a-

[Shadrach]

The delta between probes must be significant to make a 3kt difference in TAS

[Browncbr1]

3 hours ago, Shadrach said:

67 was a great vintage for Mooneys.  That a fine running machine you have there. Do you know if your airplane's ignition timing is set to 20° or 25°? 

Thank you.  It’s got ~70 hours on the major overhaul.  Compressions last week were all 80/80.   Believe it or not, I picked up a few more kts when I balanced the top prop to .00.   Ignition is 25deg..   

[Browncbr1]

3 hours ago, carusoam said:

Aaaaaah….

A man with two different OAT sensors doesn’t know his real TAS….!

A version of having two watches… 

OAT sensors are very sensitive to location…

The more modern ones are just a bump, hiding from the sun, and avoiding being in line with warm air sources…

 

Exactness of OAT sensors is mostly for avoiding ice buildup or getting to warm air to melt an ice problem…

It was probably mr. Fahrenheit that decided that 32.0000° was a good temperature for pure water to freeze

 

PP thoughts only, not a weatherman…

Best regards,

-a-

Well, the two probes are both installed side by side in the pilot side naca duct.   I recall years ago, I had fiddled with the jpi oat temp offset a little.  I never touched the G5 OAT settings.    Seems like I remember atis was reporting 32degrees one day, so I adjusted the jpi to match.   Maybe that is why they are a bit off….  As winter comes, I’ll monitor atis and awos temps to see how close my indications are on each unit.  

Edited October 16, 2022 by Browncbr1

[Shadrach]

23 minutes ago, Browncbr1 said:

Thank you.  It’s got ~70 hours on the major overhaul.  Compressions last week were all 80/80.   Believe it or not, I picked up a few more kts when I balanced the top prop to .00.   Ignition is 25deg..   

Mine has 1300smh and also runs quite well. Mine is also timed to 25° and runs as cool as yours. Had you been LOP at that altitude, I don’t think you’d have had a CHT over 300°.

[jetdriven]

That’s part of the problem, the Naca duct is inside the prop arc and exposed to the sun. And different probes will vary different amounts because of this. I know for certain Davtron  says to mount the probe outside the prop arc and in the shade. I think JPI does too.

[Ragsf15e]

14 hours ago, Browncbr1 said:

Well, I usually fly LOP, but this day I knew I had big head winds to deal with as well as low temperatures.   I was also carrying a ~700lb payload, so I decided to go ROP.  I shot this video to show how a normally 2 hour flight became 3 hours.  At one point before making the video, the winds were 68kts 20 degrees right of coarse.     G5 says 183mph tas (~159ktas), but gtn calculates 156ktas.  Any idea how there is error between the gtn and G5 calculations?  ASI calibration error is about 1-2mph, which I manually input into the gtn..   is there a way to program calibrated airspeed to the G5 computations?
 

 

Regardless of the couple knots TAS error, that’s a fast F!  My 68 F isn’t that fast.  The cold probably helped, density altitude probably around 7,000’.  Im actually surprised your ff wasn’t higher. Was that around 100 ROP?

[Browncbr1]

11 hours ago, Shadrach said:

Mine has 1300smh and also runs quite well. Mine is also timed to 25° and runs as cool as yours. Had you been LOP at that altitude, I don’t think you’d have had a CHT over 300°.

You’re correct.  That’s a big reason I ran ROP that day.  I even have aluminum tape all over #4 and a little on 1 and 2

[Browncbr1]

8 hours ago, Ragsf15e said:

Regardless of the couple knots TAS error, that’s a fast F!  My 68 F isn’t that fast.  The cold probably helped, density altitude probably around 7,000’.  Im actually surprised your ff wasn’t higher. Was that around 100 ROP?

DA was about 8300ft.  These planes seem to do best 8-9000’.   That’s about 100 ROP for #3 and 4.   It’s about 135 ROP for 1 and 2.  My FF transducers is slightly calibrate to totalize more fuel burned than actual.  (Only maybe a couple gallons of I’ve burned 40 gallons.).  I got it fairly close, then left it there figuring a little safety error is not a bad thing.  Im guessing that means actual flow is maybe .2-.3 less than indicated.  
 

I have the 201 windshield and brake caliper reversal.   OEM guppy mouth cowl though.   Been waiting for David’s cowl, but may sell this plane before that ever happens.  

Edited October 16, 2022 by Browncbr1