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Tim Olson
Joined: 25 Jan 2007
Posts: 2872
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 Posted: Tue Jun 19, 2007 6:13 am Post subject: Instrument Calibration |
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Ok, here's the promised rant that I'll try to keep short.
It's frustrating for me to see people who don't do diligence in
their avionics calibration and flight testing. I think we all
owe it to our hard work to get flying to make our systems as good
as we can, and I really can't fathom some of the lack of follow-through
that I sometimes hear. Let me give you 2 examples that are even
RV-10 specific...
One RV-10 I know of, built for sale, not for personal use, had
been flown THROUGH it's flyoff period, and had over 50 hours on
it with this issue: The GRT EIS is very nice, but the manual takes
some focus to actually read and perform the proper calibrations of
some probes. You need to enter scale factors and offsets for
various probes that are factor known numbers, and some like fuel
calibrations you have to do a little simple math. Well, this
particular RV-10 builder didn't enter scale factors and offsets
for the oil and fuel pressure sensors, among others. They told
me how the "Oil pressure was running too high so I cranked it
down about 20psi to get it into the proper range." Well, that
doesn't seem to be such a brilliant move, given the transducer
calibration numbers were never entered....now that plane is
flying with a false reading, with pressure adjusted to show
as good....all due to lack of diligence. The same plane had
CONSTANT alarms for fuel flow (or maybe it was pressure) due
to a similar problem, and I personally saw fuel pressure (or
was it flow) readings of 65,000. Hmmm....makes you wonder. Good
thing it wasn't built to keep, but built to sell, right? Doesn't
make a damn bit of difference to me, because it's still in my
freaking insurance pool.
Next, there's the RV-10 that exhibits physics-defying fuel flows.
Burns something like 11 or 12gph at 25 squared. Takeoff flows
are down in that range too. Seems a bit strange to me, given
the Lycoming power chart
(see http://www.myrv10.com/files/engines/IO540/Lyc-540-Power.pdf)
clearly showing that this isn't possible. 25 squared should
yield something like 18-19gph. Takeoff flows will be 24-29gph
approx. But, the flyoff period is ended, and there's no obligation
on anyone's part to perform any calibrations necessary to get
accurate readings.
I'm just hoping that this perhaps encourages you as builders
to try to obtain at least safe, and accurate instrument
calibrations for your equipment. You can't do it without
reading the manuals, and you probably will have questions
and have to ask the manufacturer. Even a pre-built panel
from a panel maker will NOT have all of these calibrations
performed....we're EXPERIMENTAL, and it's up to the BUILDER
to do these things. Why does this matter to me? Because I
pay the same insurance company (AIG) to cover my plane as many
other builders do, and if someone else has a loss, it affects
me. Not to mention the fact that is even bigger...these
people are RV-10 building friends, and when we finally lose
our first one, which is a statistical inevitability, it's
going to be a sad day for all. Let's at least try to get
a few good years out of it before this happens so we don't
give homebuilding, or RV-10's a bad name. Do your diligence.
--
Tim Olson - RV-10 N104CD - Flying 245+
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Jack.Phillips(at)cardinal
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| Posted: Tue Jun 19, 2007 6:31 am Post subject: Instrument Calibration |
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Good post, as usual, Tim
Jack Phillips
Finally riveting the tailcone on #40610
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pitts_pilot(at)bellsouth.
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rnewman(at)lutron.com
Guest
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| Posted: Tue Jun 19, 2007 8:03 am Post subject: Instrument Calibration |
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In my case, (with the glastar) I put the OAT probe sticking out of the
bottom of the gear leg fairing, I don't yet have a place picked for my
rv-10.
-bob
<pitts_pilot(at)bellsouth.net>
Tim Olson wrote:
| Quote: |
Ok, here's the promised rant that I'll try to keep short.
|
snip!
Short? 
But, you still haven't told me where you found the 'proper' (or good)
place to put the temp probe!!!
Linn
do not archive
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ddddsp1(at)juno.com
Guest
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| Posted: Tue Jun 19, 2007 8:50 am Post subject: Instrument Calibration |
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Next, there's the RV-10 that exhibits physics-defying fuel flows.
Burns something like 11 or 12gph at 25 squared. Takeoff flows
are down in that range too. Seems a bit strange to me, given
the Lycoming power chart
(see http://www.myrv10.com/files/engines/IO540/Lyc-540-Power.pdf)
clearly showing that this isn't possible. 25 squared should
yield something like 18-19gph. Takeoff flows will be 24-29gph
approx. But, the flyoff period is ended, and there's no obligation
on anyone's part to perform any calibrations necessary to get
accurate readings.
Tim is talking about my O-540 in the above paragraph. I have talked to other people about these numbers and they have seen numbers close to mine but not nearly as high as Tim suggests. I have not ENDED my testing or calibrating as Tim states...........I consider every flight a test flight and continue to fine tune the aircraft. I am only reporting the actual numbers/Gallons/etc that I am seeing on my plane so far. If it bothers people that I do that I will cease posting.
Safe flying,
DEAN
_____________________________________________________________
Click to find anyone's secrets with an instant background check
[quote][b]
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Tim Olson
Joined: 25 Jan 2007
Posts: 2872
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| Posted: Tue Jun 19, 2007 9:06 am Post subject: Instrument Calibration |
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Sorry, I didn't add that part because I don't think there is any
ONE good place to put it. But, if you eliminate all of the areas
that could be affected by propwash, engine heat, exhaust and
such, you're basically talking about being 3-4' out from the
wing roots at a minimum, and the by the selection process it
becomes much easier. Then eliminate the TOP of the wings, and
you're down to locating it somewhere on the underside of your
wings, with about 2/3 of your wing length to play with. Putting
it by or in an inspection cover is a handy step for the future.
The innermost inspection cover might be just a little inboard
for the best results...make sure it's outside of your prop
diameter a bit. The real anal people would put it way out
near a wingtip, but once you get out of the affected areas
you're doing great. You want as few external effects on it
as possible, other than just the raw temperature.
My preference? One of the 2 outbard wing inspection panels.
Mine is actually next to the panel, so I can easily remove the
panel to inspect, but don't have to remove the probe to
completely remove the inspection panel.
There isn't just one good spot, but there are far more poor
locations than good ones.
Tim Olson - RV-10 N104CD - Flying
do not archive
linn Walters wrote:
| Quote: |
Tim Olson wrote:
>
>
> Ok, here's the promised rant that I'll try to keep short.
snip!
Short?
But, you still haven't told me where you found the 'proper' (or good)
place to put the temp probe!!!
Linn
do not archive
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rene(at)felker.com
Guest
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| Posted: Tue Jun 19, 2007 9:30 am Post subject: Instrument Calibration |
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Tim, are you just mounting the probe with no external exposure? Or, did you
drill a hole in the skin and project the end of the probe out into the slip
stream? I wouldn't think it would make much of a difference, but I am sure
the inside of the wing heats up in the sunshine and does not cool off all
that quickly
Rene' Felker
N423CF
40322
801-721-6080
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Tim Olson
Joined: 25 Jan 2007
Posts: 2872
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| Posted: Tue Jun 19, 2007 9:41 am Post subject: Instrument Calibration |
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It does need to be out in the airflow...not just in the wing.
Holes involved.
Tim Olson - RV-10 N104CD - Flying
Rene Felker wrote:
[quote]
Tim, are you just mounting the probe with no external exposure? Or, did you
drill a hole in the skin and project the end of the probe out into the slip
stream? I wouldn't think it would make much of a difference, but I am sure
the inside of the wing heats up in the sunshine and does not cool off all
that quickly
Rene' Felker
N423CF
40322
801-721-6080
--
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bcondrey
Joined: 03 Apr 2006
Posts: 580
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| Posted: Tue Jun 19, 2007 9:49 am Post subject: Instrument Calibration |
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Regardless of instrumentation, gallons needed to top off the tank, etc. a Lycoming engine has a BSFC (brake specific fuel comsumption) of around .43-.48 depending on leaning and exact RPM. A fuel injected engine with electronic ignition and a balanced set of GAMI injectors will do a bit better – maybe getting down around .40. This fuel consumption rate is driven by the physics of the engine design. This BSFC is specified as pounds of fuel per horsepower per hour. This is horsepower being produced, not the rated horsepower. As an example, a 260 HP engine at 75% (rough performance at 8000 feet) is producing only 195 HP. Using the low end of the BSFC range we get: 195 HP * .43 = 83.85 pounds per hour. That divided by 6 (avgas weight per gallon) equals 13.975 gallons per hour which very closely matches a Lycoming power chart. Producing more HP (lower altitude for example) would burn more fuel. Obviously doing something like running lean of peak you’ll do better but it’s not likely to be something you’re going to be doing down low.
For reference, below is an extract from an article on proper leaning of an engine and expected fuel consumption results. Note that the Aztec with a 250 HP engine is very close to what we’re dealing with. Also note that if you use the above formula you wind up with a BSFC of .4352 when leaned for best economy:
Leaning the normally aspirated, direct drive Lycoming engine at cruise vs. full rich at 4,000 feet density altitude, 75% power
Engine Model
Airplane Model
300 HP
Piper Cherokee 300
Full Rich
Best Economy (Peak EGT)
Hours Rich
Hours Lean
19+ gals
15.6 gals.
4.2 hrs.
5.1 hrs.
Engine Model
Airplane Model
250 HP
Piper Aztec
Full Rich
Best Economy (Peak EGT)
Hours Rich
Hours Lean
16.2 gals
13.6 gals.
4.3 hrs.
5.1 hrs.
Engine Model
Airplane Model
180 HP
Cessna Cardinal
Full Rich
Best Economy (Peak EGT)
Hours Rich
Hours Lean
11.9 gals
9.7 gals.
4.1 hrs.
5.1 hrs.
There are a lot of possibilities but none of them include modifying the engine physics. So what are the possibilities? Maybe not producing expected horsepower for a variety of reasons (compression issue, tach reading high, etc), fuel flow not calibrated, bad measurement of fuel to top off tank, etc.
Hopefully Dean will post the results of his additional testing so we can all learn from it so when it’s time for our own testing we’ll be better prepared with real life examples.
Bob #40105
STILL finishing up – wishing all I had left to do was resolve issues like this…
From: owner-rv10-list-server(at)matronics.com [mailto:owner-rv10-list-server(at)matronics.com] On Behalf Of ddddsp1(at)juno.com
Sent: Tuesday, June 19, 2007 11:49 AM
To: rv10-list(at)matronics.com
Subject: Re: Instrument Calibration
Next, there's the RV-10 that exhibits physics-defying fuel flows.
Burns something like 11 or 12gph at 25 squared. Takeoff flows
are down in that range too. Seems a bit strange to me, given
the Lycoming power chart
(see http://www.myrv10.com/files/engines/IO540/Lyc-540-Power.pdf)
clearly showing that this isn't possible. 25 squared should
yield something like 18-19gph. Takeoff flows will be 24-29gph
approx. But, the flyoff period is ended, and there's no obligation
on anyone's part to perform any calibrations necessary to get
accurate readings.
Tim is talking about my O-540 in the above paragraph. I have talked to other people about these numbers and they have seen numbers close to mine but not nearly as high as Tim suggests. I have not ENDED my testing or calibrating as Tim states...........I consider every flight a test flight and continue to fine tune the aircraft. I am only reporting the actual numbers/Gallons/etc that I am seeing on my plane so far. If it bothers people that I do that I will cease posting.
Safe flying,
DEAN
_____________________________________________________________
Click to find anyone's secrets with an instant background check | Quote: | | http://www.matronics.com/Navigator?RV10-List |
01234
[quote][b]
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pitts_pilot(at)bellsouth.
Guest
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| Posted: Tue Jun 19, 2007 11:19 am Post subject: Instrument Calibration |
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Thanks Tim. I had occasion to work on my wifes Lincoln Towncar (I hate
paying someone to do what I can still do) and was searching for the mass
airflow sensor. I found it, and I also found the OAT sensor. Both are
located close to each other in the incoming air ducting for the engine.
I'm not sure that the air intake for our engines wouldn't be a bad place
for a temp sensor, but I have a lot of time to do some research. On the
Lincold the ducting sits near the hood, kinda beside the engine Vs. over
it, and after sitting and getting heat soaked ...... the sensor reads
the same before and after starting the engine. Kinda flies in the face
of reason, but the temp readout in the panel just doesn't change! Go
figure!
Linn
do not archive
Tim Olson wrote:
| Quote: |
Sorry, I didn't add that part because I don't think there is any
ONE good place to put it. But, if you eliminate all of the areas
that could be affected by propwash, engine heat, exhaust and
such, you're basically talking about being 3-4' out from the
wing roots at a minimum, and the by the selection process it
becomes much easier. Then eliminate the TOP of the wings, and
you're down to locating it somewhere on the underside of your
wings, with about 2/3 of your wing length to play with. Putting
it by or in an inspection cover is a handy step for the future.
The innermost inspection cover might be just a little inboard
for the best results...make sure it's outside of your prop
diameter a bit. The real anal people would put it way out
near a wingtip, but once you get out of the affected areas
you're doing great. You want as few external effects on it
as possible, other than just the raw temperature.
My preference? One of the 2 outbard wing inspection panels.
Mine is actually next to the panel, so I can easily remove the
panel to inspect, but don't have to remove the probe to
completely remove the inspection panel.
There isn't just one good spot, but there are far more poor
locations than good ones.
Tim Olson - RV-10 N104CD - Flying
do not archive
linn Walters wrote:
>
> <pitts_pilot(at)bellsouth.net>
>
> Tim Olson wrote:
>
>>
>>
>> Ok, here's the promised rant that I'll try to keep short.
> snip!
>
> Short?
>
> But, you still haven't told me where you found the 'proper' (or good)
> place to put the temp probe!!!
> Linn
> do not archive
>
|
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etekberg(at)gmail.com
Guest
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| Posted: Tue Jun 19, 2007 11:35 am Post subject: Instrument Calibration |
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Hi,
Not often I can chime in with potentially helpful info, so I'm taking the opportunity. The temp sensor for a car engine and your aircraft serve two different purposes. The temp sensor for the car is for the purpose of the engine computer to calculate the mass of air entering the engine. In that case the car cares about what is actually going in the engine and less about the air outside of the car. The pupose of the aircraft OAT (outisde air temp) is to determine the temperature of the air mass you are moving through, not necessarily the temperature of the air entering the engine.
Eric. do not archive
On 6/19/07, linn Walters <pitts_pilot(at)bellsouth.net (pitts_pilot(at)bellsouth.net)> wrote: [quote]--> RV10-List message posted by: linn Walters <pitts_pilot(at)bellsouth.net (pitts_pilot(at)bellsouth.net)>
Thanks Tim. I had occasion to work on my wifes Lincoln Towncar (I hate
paying someone to do what I can still do) and was searching for the mass
airflow sensor. I found it, and I also found the OAT sensor. Both are
located close to each other in the incoming air ducting for the engine.
I'm not sure that the air intake for our engines wouldn't be a bad place
for a temp sensor, but I have a lot of time to do some research. On the
Lincold the ducting sits near the hood, kinda beside the engine Vs. over
it, and after sitting and getting heat soaked ...... the sensor reads
the same before and after starting the engine. Kinda flies in the face
of reason, but the temp readout in the panel just doesn't change! Go
figure!
Linn
do not archive
Tim Olson wrote:
| Quote: | --> RV10-List message posted by: Tim Olson < Tim(at)MyRV10.com (Tim(at)MyRV10.com)>
Sorry, I didn't add that part because I don't think there is any
ONE good place to put it. But, if you eliminate all of the areas
that could be affected by propwash, engine heat, exhaust and
such, you're basically talking about being 3-4' out from the
wing roots at a minimum, and the by the selection process it
becomes much easier. Then eliminate the TOP of the wings, and
> you're down to locating it somewhere on the underside of your
|
| Quote: | wings, with about 2/3 of your wing length to play with. Putting
it by or in an inspection cover is a handy step for the future.
The innermost inspection cover might be just a little inboard
for the best results...make sure it's outside of your prop
diameter a bit. The real anal people would put it way out
near a wingtip, but once you get out of the affected areas
you're doing great. You want as few external effects on it
as possible, other than just the raw temperature.
My preference? One of the 2 outbard wing inspection panels.
Mine is actually next to the panel, so I can easily remove the
panel to inspect, but don't have to remove the probe to
completely remove the inspection panel.
There isn't just one good spot, but there are far more poor
locations than good ones.
Tim Olson - RV-10 N104CD - Flying
do not archive
linn Walters wrote:
> --> RV10-List message posted by: linn Walters
> <pitts_pilot(at)bellsouth.net (pitts_pilot(at)bellsouth.net)>
>
>> Tim Olson wrote:
|
| Quote: | >
>> --> RV10-List message posted by: Tim Olson <Tim(at)MyRV10.com (Tim(at)MyRV10.com)>
>>
>> Ok, here's the promised rant that I'll try to keep short.
> snip!
>
> Short?
>
> But, you still haven't told me where you found the 'proper' (or good)
> place to put the temp probe!!!
|
[b]
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pitts_pilot(at)bellsouth.
Guest
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| Posted: Tue Jun 19, 2007 11:49 am Post subject: Instrument Calibration |
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|
Eric, there are three sensors in the ducting. Two are called the 'mass airflow sensor' and one separate one (OAT) for air temperature. The mass airflow sensors are made up of one heated sensor and one unheated. From their construction, I'd say the mass airflow sensors are far more sensitive than the separate temperature sensor ..... which from my tests only go the the air conditioning system and the OAT display there. Engine operation wasn't affected by the unplugging of the OAT sensor (my term), but unplugging the MAF really makes it run crappy! 
FWIW, the car had a stalling problem when it came up to a stop sign. Yup, I know ... I hate them too  . Mileage was also suffering. The problem was soot that had collected on the MAF sensors. I brushed them off (carefully) and all is well in the world again.
Linn
do not archive
Eric Ekberg wrote:
[quote] Hi,
Not often I can chime in with potentially helpful info, so I'm taking the opportunity. The temp sensor for a car engine and your aircraft serve two different purposes. The temp sensor for the car is for the purpose of the engine computer to calculate the mass of air entering the engine. In that case the car cares about what is actually going in the engine and less about the air outside of the car. The pupose of the aircraft OAT (outisde air temp) is to determine the temperature of the air mass you are moving through, not necessarily the temperature of the air entering the engine.
Eric. do not archive
On 6/19/07, linn Walters <pitts_pilot(at)bellsouth.net (pitts_pilot(at)bellsouth.net)> wrote: | Quote: | --> RV10-List message posted by: linn Walters <pitts_pilot(at)bellsouth.net (pitts_pilot(at)bellsouth.net)>
Thanks Tim. I had occasion to work on my wifes Lincoln Towncar (I hate
paying someone to do what I can still do) and was searching for the mass
airflow sensor. I found it, and I also found the OAT sensor. Both are
located close to each other in the incoming air ducting for the engine.
I'm not sure that the air intake for our engines wouldn't be a bad place
for a temp sensor, but I have a lot of time to do some research. On the
Lincold the ducting sits near the hood, kinda beside the engine Vs. over
it, and after sitting and getting heat soaked ...... the sensor reads
the same before and after starting the engine. Kinda flies in the face
of reason, but the temp readout in the panel just doesn't change! Go
figure!
Linn
do not archive
Tim Olson wrote:
> --> RV10-List message posted by: Tim Olson < Tim(at)MyRV10.com (Tim(at)MyRV10.com)>
>
> Sorry, I didn't add that part because I don't think there is any
> ONE good place to put it. But, if you eliminate all of the areas
> that could be affected by propwash, engine heat, exhaust and
> such, you're basically talking about being 3-4' out from the
> wing roots at a minimum, and the by the selection process it
> becomes much easier. Then eliminate the TOP of the wings, and
> you're down to locating it somewhere on the underside of your
> wings, with about 2/3 of your wing length to play with. Putting
> it by or in an inspection cover is a handy step for the future.
> The innermost inspection cover might be just a little inboard
> for the best results...make sure it's outside of your prop
> diameter a bit. The real anal people would put it way out
> near a wingtip, but once you get out of the affected areas
> you're doing great. You want as few external effects on it
> as possible, other than just the raw temperature.
>
> My preference? One of the 2 outbard wing inspection panels.
> Mine is actually next to the panel, so I can easily remove the
> panel to inspect, but don't have to remove the probe to
> completely remove the inspection panel.
>
> There isn't just one good spot, but there are far more poor
> locations than good ones.
>
> Tim Olson - RV-10 N104CD - Flying
> do not archive
>
>
> linn Walters wrote:
>
>> --> RV10-List message posted by: linn Walters
>> <pitts_pilot(at)bellsouth.net (pitts_pilot(at)bellsouth.net)>
>>
>> Tim Olson wrote:
>>
>>> --> RV10-List message posted by: Tim Olson <Tim(at)MyRV10.com (Tim(at)MyRV10.com)>
>>>
>>> Ok, here's the promised rant that I'll try to keep short.
>>
>>
>> snip!
>>
>> Short?
>>
>> But, you still haven't told me where you found the 'proper' (or good)
>> place to put the temp probe!!!
|
[b]
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Tim Olson
Joined: 25 Jan 2007
Posts: 2872
|
| Posted: Tue Jun 19, 2007 11:58 am Post subject: Instrument Calibration |
|
|
And, to add to Eric's, being off by 1 degree in a cloud can mean ice, or
no ice, so it's kind of something that you'd like to have very accurate.
If you weren't flying IFR, then you really don't need any OAT probe
at all...but if you're flying IFR, you'd not only want one, but one
that will warn you of impending icing conditions before you
see it build on the wings.
Tim Olson - RV-10 N104CD - Flying
Eric Ekberg wrote:
| Quote: | Hi,
Not often I can chime in with potentially helpful info, so I'm taking
the opportunity. The temp sensor for a car engine and your aircraft
serve two different purposes. The temp sensor for the car is for the
purpose of the engine computer to calculate the mass of air entering the
engine. In that case the car cares about what is actually going in the
engine and less about the air outside of the car. The pupose of the
aircraft OAT (outisde air temp) is to determine the temperature of the
air mass you are moving through, not necessarily the temperature of the
air entering the engine.
Eric. do not archive
On 6/19/07, *linn Walters* <pitts_pilot(at)bellsouth.net
<mailto:pitts_pilot(at)bellsouth.net>> wrote:
<pitts_pilot(at)bellsouth.net <mailto:pitts_pilot(at)bellsouth.net>>
Thanks Tim. I had occasion to work on my wifes Lincoln Towncar (I hate
paying someone to do what I can still do) and was searching for the mass
airflow sensor. I found it, and I also found the OAT sensor. Both are
located close to each other in the incoming air ducting for the engine.
I'm not sure that the air intake for our engines wouldn't be a bad place
for a temp sensor, but I have a lot of time to do some research. On
the
Lincold the ducting sits near the hood, kinda beside the engine Vs. over
it, and after sitting and getting heat soaked ...... the sensor reads
the same before and after starting the engine. Kinda flies in the face
of reason, but the temp readout in the panel just doesn't change! Go
figure!
Linn
do not archive
Tim Olson wrote:
>
<mailto:Tim(at)MyRV10.com>>
>
> Sorry, I didn't add that part because I don't think there is any
> ONE good place to put it. But, if you eliminate all of the areas
> that could be affected by propwash, engine heat, exhaust and
> such, you're basically talking about being 3-4' out from the
> wing roots at a minimum, and the by the selection process it
> becomes much easier. Then eliminate the TOP of the wings, and
> you're down to locating it somewhere on the underside of your
> wings, with about 2/3 of your wing length to play with. Putting
> it by or in an inspection cover is a handy step for the future.
> The innermost inspection cover might be just a little inboard
> for the best results...make sure it's outside of your prop
> diameter a bit. The real anal people would put it way out
> near a wingtip, but once you get out of the affected areas
> you're doing great. You want as few external effects on it
> as possible, other than just the raw temperature.
>
> My preference? One of the 2 outbard wing inspection panels.
> Mine is actually next to the panel, so I can easily remove the
> panel to inspect, but don't have to remove the probe to
> completely remove the inspection panel.
>
> There isn't just one good spot, but there are far more poor
> locations than good ones.
>
> Tim Olson - RV-10 N104CD - Flying
> do not archive
>
>
> linn Walters wrote:
>
>>
>> <pitts_pilot(at)bellsouth.net <mailto:pitts_pilot(at)bellsouth.net>>
>>
>> Tim Olson wrote:
>>
>>>
<mailto:Tim(at)MyRV10.com>>
>>>
>>> Ok, here's the promised rant that I'll try to keep short.
>>
>>
>> snip!
>>
>> Short?
>>
>> But, you still haven't told me where you found the 'proper' (or
good)
>> place to put the temp probe!!!
*
*
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pitts_pilot(at)bellsouth.
Guest
|
| Posted: Tue Jun 19, 2007 12:24 pm Post subject: Instrument Calibration |
|
|
Good point. I, for one, can't see the value in paying big bucks for a
state-of-the-art electronics package ..... and not have it tell ya the
truth. In our hobby, what you don't know CAN hurt you! The only reason
to add the car to the mix was to show a commonality (the intake) and
bring up the possibility that the intake ducting on our engines might be
a possible place for an OAT sensor. It sure gets enough air flow!!!
Linn ..... just thinking out loud
do not archive
Tim Olson wrote:
| Quote: |
And, to add to Eric's, being off by 1 degree in a cloud can mean ice, or
no ice, so it's kind of something that you'd like to have very accurate.
If you weren't flying IFR, then you really don't need any OAT probe
at all...but if you're flying IFR, you'd not only want one, but one
that will warn you of impending icing conditions before you
see it build on the wings.
Tim Olson - RV-10 N104CD - Flying
Eric Ekberg wrote:
> Hi,
>
> Not often I can chime in with potentially helpful info, so I'm taking
> the opportunity. The temp sensor for a car engine and your aircraft
> serve two different purposes. The temp sensor for the car is for the
> purpose of the engine computer to calculate the mass of air entering
> the engine. In that case the car cares about what is actually going
> in the engine and less about the air outside of the car. The pupose
> of the aircraft OAT (outisde air temp) is to determine the
> temperature of the air mass you are moving through, not necessarily
> the temperature of the air entering the engine.
> Eric. do not archive
>
>
> On 6/19/07, *linn Walters* <pitts_pilot(at)bellsouth.net
> <mailto:pitts_pilot(at)bellsouth.net>> wrote:
>
>
> <pitts_pilot(at)bellsouth.net <mailto:pitts_pilot(at)bellsouth.net>>
>
> Thanks Tim. I had occasion to work on my wifes Lincoln Towncar
> (I hate
> paying someone to do what I can still do) and was searching for
> the mass
> airflow sensor. I found it, and I also found the OAT sensor.
> Both are
> located close to each other in the incoming air ducting for the
> engine.
> I'm not sure that the air intake for our engines wouldn't be a
> bad place
> for a temp sensor, but I have a lot of time to do some research. On
> the
> Lincold the ducting sits near the hood, kinda beside the engine
> Vs. over
> it, and after sitting and getting heat soaked ...... the sensor
> reads
> the same before and after starting the engine. Kinda flies in
> the face
> of reason, but the temp readout in the panel just doesn't
> change! Go
> figure!
> Linn
> do not archive
>
> Tim Olson wrote:
>
> >
> <mailto:Tim(at)MyRV10.com>>
> >
> > Sorry, I didn't add that part because I don't think there is any
> > ONE good place to put it. But, if you eliminate all of the areas
> > that could be affected by propwash, engine heat, exhaust and
> > such, you're basically talking about being 3-4' out from the
> > wing roots at a minimum, and the by the selection process it
> > becomes much easier. Then eliminate the TOP of the wings, and
> > you're down to locating it somewhere on the underside of your
> > wings, with about 2/3 of your wing length to play with. Putting
> > it by or in an inspection cover is a handy step for the future.
> > The innermost inspection cover might be just a little inboard
> > for the best results...make sure it's outside of your prop
> > diameter a bit. The real anal people would put it way out
> > near a wingtip, but once you get out of the affected areas
> > you're doing great. You want as few external effects on it
> > as possible, other than just the raw temperature.
> >
> > My preference? One of the 2 outbard wing inspection panels.
> > Mine is actually next to the panel, so I can easily remove the
> > panel to inspect, but don't have to remove the probe to
> > completely remove the inspection panel.
> >
> > There isn't just one good spot, but there are far more poor
> > locations than good ones.
> >
> > Tim Olson - RV-10 N104CD - Flying
> > do not archive
> >
> >
> > linn Walters wrote:
> >
> >>
> >> <pitts_pilot(at)bellsouth.net <mailto:pitts_pilot(at)bellsouth.net>>
> >>
> >> Tim Olson wrote:
> >>
> >>>
> <mailto:Tim(at)MyRV10.com>>
> >>>
> >>> Ok, here's the promised rant that I'll try to keep short.
> >>
> >>
> >> snip!
> >>
> >> Short?
> >>
> >> But, you still haven't told me where you found the 'proper' (or
> good)
> >> place to put the temp probe!!!
>
> *
> *
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toaster73(at)earthlink.ne
Guest
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| Posted: Tue Jun 19, 2007 6:46 pm Post subject: Instrument Calibration |
|
|
One has to be careful of accuracy and repeatability when it comes to
thermocouple and instrument calibration. What does the company qoute as the
thermocouple type that will be used to take the measurement? Is it a K type
thermocouple which could be off as much as 1.5 degrees C. or other common
types which would be similar in accuracy. How well is the tip standing up
to the elements/corrosion/moisture? This can change the voltage across the
circuit and lead to further error over time. Just because you have it
mounted in the "best" spot doesn't mean you are reading with any better
accuracy than the instrument capability. Is 1.5 deg C going to be good
enough - the capability of your device?
I ask the question to all the EFIS types...what are your probe/transducer
types and there response and accuracy, and are they traced to a calibration
standard and back to NIS??? How often should transducers and temps be
calibrated or does it need calibrating?
Hopefully, your reading 1.5 degree C wrong such that when it is really 0 C
you are reading -1.5 C so as to give you concern. Best to check it in an ice
bath, and boiling water too on occasion, or stick it under your tongue.
-Chris
#40072
---
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james.k.hovis(at)gmail.co
Guest
|
| Posted: Wed Jun 20, 2007 5:48 am Post subject: Instrument Calibration |
|
|
OAT readings are affected by whether the air is compressed. Compressed
air heats up. Now, air in an engine inlet duct will compress somewhat
compared to the free-stream (also depends on the suction of the
engine) but shouldn't be compressed that much to severely impact the
accuracy of a probe reading. Different placements on the exterior of
an aircraft may affect the reading too. Some areas that have higher or
lower pressures will increase or decrease the temperature but again to
only a slight degree at the speeds we're talking about. Best place to
me is anywhere on the airplane not close to a heat source (i.e. in the
engine compartment or aft of the cooling air outlet.). My old Grumman
had the OAT probe in the windshield. Somewhere on top of the airplane
(or maybe the vertical tail leading edge) would be my optimum choice.
Kevin H.
On 6/19/07, Chris <toaster73(at)earthlink.net> wrote:
[quote]
One has to be careful of accuracy and repeatability when it comes to
thermocouple and instrument calibration. What does the company qoute as the
thermocouple type that will be used to take the measurement? Is it a K type
thermocouple which could be off as much as 1.5 degrees C. or other common
types which would be similar in accuracy. How well is the tip standing up
to the elements/corrosion/moisture? This can change the voltage across the
circuit and lead to further error over time. Just because you have it
mounted in the "best" spot doesn't mean you are reading with any better
accuracy than the instrument capability. Is 1.5 deg C going to be good
enough - the capability of your device?
I ask the question to all the EFIS types...what are your probe/transducer
types and there response and accuracy, and are they traced to a calibration
standard and back to NIS??? How often should transducers and temps be
calibrated or does it need calibrating?
Hopefully, your reading 1.5 degree C wrong such that when it is really 0 C
you are reading -1.5 C so as to give you concern. Best to check it in an ice
bath, and boiling water too on occasion, or stick it under your tongue.
-Chris
#40072
---
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