TE probe installation

At 19:03 07 December 2014, Dave Nadler wrote:
On Sunday, December 7, 2014 1:56:25 PM UTC-5, wrote:
Looking at my decade old code for a transducer based variometer,
I see that I went to a bit of trouble to convert pressure to ISA
altitude before differentiating to get rate of climb.

Good, but its much easier just to correct by one_over_sigma ;-)

For even more amusement, consider the relationships between
"altitude corrected" rate of climb, IAS, TAS, calculated total
energy compensation, and speed to fly...

Right, proper instruments consider MC as a 'true' input as
well as correcting vario, IAS-TAS, and of course polar.

Discuss amongst yourselves ;-)

Seems to me that this discussion is about a complete non problem. When we
"read" a vario we are not really interested in the arbitrary figure it
displays but more in the fact of whether the value is higher or lower than
the previous value.
In other words if 4kts is really 2kts at 10,000 ft it does not matter a jot
to us. What does matter is that 4kts will always be greater than 2kts. We
search for better lift not some arbitrary figure.

On Sunday, December 7, 2014 12:00:08 PM UTC-8, Dan Marotta wrote:
...And it's not even officially winter yet...

Well, it's raining here in northern California, I can't even work on our winch 8^(

OK, I understand about correcting the transducer based altitude,
corrected for ISA, so I guess you're using your static and OAT inputs to
calculate altitude before calculating and displaying the rate of change.

Actually, OAT isn't used to convert pressure to ISA altitude, as what matters is the mean temperature of the column of air between your altitude and sea level, not OAT at that altitude. So, one would need to drop periodic sounding probes to correct for "true" altitude, but just applying a basic mapping from pressure to ISA altitude (or one_over_sigma as Dave indicated) is "good enough" for our purposes (if one wants to know the actual altitude, as such, applying a QNH or QFF setting gets you closer, yet). Likewise, for a transducer variometer hooked to a TE probe, static pressure is typically not used, instead one ends up with effectively "total energy altitude" (where you would end up if you could convert all (?) of your airspeed to altitude), which is again "good enough".


So am I to understand, then, that my mechanical vario is displaying
*indicated* rate of lift/sink while my electronic vario is displaying
*true* rate of lift/sink? I guess I'll take a close look on my next
wave flight.

I think it may be a bit more complicated than that, but I've never really thought about what a mechanical flow-based variometer actually measures...

Marc

On Sunday, December 7, 2014 3:30:05 PM UTC-5, Don Johnstone wrote:
Seems to me that this discussion is about a complete non problem. When we
"read" a vario we are not really interested in the arbitrary figure it
displays but more in the fact of whether the value is higher or lower than
the previous value.
In other words if 4kts is really 2kts at 10,000 ft it does not matter a jot
to us. What does matter is that 4kts will always be greater than 2kts. We
search for better lift not some arbitrary figure.

No, it is important to know climb strength to accurately set
speed-to-fly, MC or otherwise derived, for both inter-thermal
cruise and final glide.

All this is well-covered in Reichmann...

What I meant to say concerning OAT is that it's used in computing TAS
(horizontal or vertical).

I also agree with Don in that I'm really only concerned with "more"
rather than "how much".

Still, just for jollies, I'm going to compare my mechanical vs
electronic varios just to see if the difference between the two
increases with altitude.

On 12/7/2014 1:25 PM, wrote:
On Sunday, December 7, 2014 12:00:08 PM UTC-8, Dan Marotta wrote:
...And it's not even officially winter yet...

Well, it's raining here in northern California, I can't even work on our winch 8^(

OK, I understand about correcting the transducer based altitude,
corrected for ISA, so I guess you're using your static and OAT inputs to
calculate altitude before calculating and displaying the rate of change.

Actually, OAT isn't used to convert pressure to ISA altitude, as what matters is the mean temperature of the column of air between your altitude and sea level, not OAT at that altitude. So, one would need to drop periodic sounding probes to correct for "true" altitude, but just applying a basic mapping from pressure to ISA altitude (or one_over_sigma as Dave indicated) is "good enough" for our purposes (if one wants to know the actual altitude, as such, applying a QNH or QFF setting gets you closer, yet). Likewise, for a transducer variometer hooked to a TE probe, static pressure is typically not used, instead one ends up with effectively "total energy altitude" (where you would end up if you could convert all (?) of your airspeed to altitude), which is again "good enough".


So am I to understand, then, that my mechanical vario is displaying
*indicated* rate of lift/sink while my electronic vario is displaying
*true* rate of lift/sink? I guess I'll take a close look on my next
wave flight.

I think it may be a bit more complicated than that, but I've never really thought about what a mechanical flow-based variometer actually measures...

Marc


--
---
Dan Marotta

On Sunday, 7 December 2014 00:59:38 UTC+2, Dave Nadler wrote:
On Saturday, December 6, 2014 12:27:42 AM UTC-5, krasw wrote:
... variometer does not care about the absolute pressure.

Really? What happens at 10,000 feet vs. sea level?

Since the variometer flask contains same 10000 feet air, the speed of airflow trough variometer would be exactly same, in that sence it does not care. Depending on vario design, the force turning variometer vane could be less.. All of this (incl. temperature) is easily compensated in electric vario.

Discuss amongst yourselves...

Seems to me that you are participating this a lot, after all.

On Monday, December 8, 2014 5:01:59 AM UTC-5, krasw wrote:
On Sunday, 7 December 2014 00:59:38 UTC+2, Dave Nadler wrote:
On Saturday, December 6, 2014 12:27:42 AM UTC-5, krasw wrote:
... variometer does not care about the absolute pressure.

Really? What happens at 10,000 feet vs. sea level?

Since the variometer flask contains same 10000 feet air...

Really? Isn't the air less dense at 10,000 feet than at sea level??

Discuss amongst yourselves...

maanantai, 8. joulukuuta 2014 15.04.33 UTC+2 Dave Nadler kirjoitti:
On Monday, December 8, 2014 5:01:59 AM UTC-5, krasw wrote:
On Sunday, 7 December 2014 00:59:38 UTC+2, Dave Nadler wrote:
On Saturday, December 6, 2014 12:27:42 AM UTC-5, krasw wrote:
... variometer does not care about the absolute pressure.

Really? What happens at 10,000 feet vs. sea level?

Since the variometer flask contains same 10000 feet air...

Really? Isn't the air less dense at 10,000 feet than at sea level??

Discuss amongst yourselves...

Are you aware that you are clinging on a detail that is quite irrevelant when talking about the very basics of TE probe? What's next, shall we go trough air density vs. humidity relation? Isn't it annoying that every sentence I write is a question?

On Thursday, December 4, 2014 2:02:55 PM UTC-5, Jim Lewis wrote:
I have been trying to understand just how a TE probe functions.

Hi Jim - I hope the RAS nonsense has not discouraged your quest
for knowledge! Get yourself a copy of Helmut Reichmann's "Cross-
Country Soaring". Instrumentation functions are covered in a
practical and readable fashion, including of course TE probes.
The book is also a fabulous overview of XC soaring basics.
Enjoy!
Best Regards, Dave

PS: Beware answers you get on RAS! Way too many people happy
to provide incomplete and/or incorrect answers with a solemn
tone of authority...

PPS: If you want to dig into the math, beware that early editions
of Reichmann's book have the terms for some of the equations
translated incorrectly (equations are correct but explanations
of the terms are not).

On Wednesday, December 10, 2014 10:57:08 AM UTC-5, Dave Nadler wrote:
On Thursday, December 4, 2014 2:02:55 PM UTC-5, Jim Lewis wrote:
I have been trying to understand just how a TE probe functions.

Hi Jim - I hope the RAS nonsense has not discouraged your quest
for knowledge! Get yourself a copy of Helmut Reichmann's "Cross-
Country Soaring". Instrumentation functions are covered in a
practical and readable fashion, including of course TE probes.
The book is also a fabulous overview of XC soaring basics.
Enjoy!
Best Regards, Dave

PS: Beware answers you get on RAS! Way too many people happy
to provide incomplete and/or incorrect answers with a solemn
tone of authority...

PPS: If you want to dig into the math, beware that early editions
of Reichmann's book have the terms for some of the equations
translated incorrectly (equations are correct but explanations
of the terms are not).

Now you warn me! Today I replaced the venturi style TE probe with an ILEC fin mounted probe in fashionable blue anodized color. I measured thrice and cut once based on this thread's info. You guys better be right!

Lane
XF

Hi Dave,

I'm not at all discouraged! I've learned a lot and I think I now actually understand the TE system.
I have Reichmann's books and many others too. Sometimes I'm too thick to understand what is being discussed but I keep trying. Thank you for your help.

Jim