Verification that Heated Pitot is working

Of course that is another way of doing it, but it involves bonding the diode
thermally to the pitot tube, putting a reference diode somewhere in the same
general vicinity of the pitot tube to sense ambient temperature, insuring an
ambient airflow over the reference diode, an opamp to sense the 2.5
millivolts/°C change, and all of that stuff. I prefer dumb when I can get
away with it.

As I recall, the pitot heater gets about 50°C above ambient, so you are
messing around trying to detect a little over a tenth of a volt change,
which isn't rocket science, but trying to explain it in this newsgroup is.

Jim




"Richard Lamb" wrote in message
oups.com...
Hi Jim,

Question..

Why put the diode in series with the pitot heater power.
(Ok, it senses that power if flowing in the heater circuit, but is that
necessary?)

Couldn't the same thing be accomplished by using the diode as a
temperture
sensor (thermometer) to decide if the pitot tube was above a certain
temperature?

No self-heating on the part of the sense diode, and no pitot heat
failure if the diode
opens up (burns up?).

Richard

"Dave S" wrote ...
Why would you have a heated pitot on a Cessna 172 or a piper arrow then?
Neither of THEM are certified for entry into known icing conditions, but
its nice to have the ability to safely fly OUT of them if you get INTO
them.

Dave,

A 172 can take a bit of icing and get away with it. Trust me and please
don't ask any questions I won't answer. In selecting a canard type
aircraft, the owner has to realize that there are some huge differences in
the way the horizontal controls react to airflow disturbances. In the case
of icing, he needs to take extreme measures to avoid those conditions. Even
if that means grounding the airplane for an extended period. That's what he
bought into when he got the airplane.

Having said that, if anyone knows of a canard icing study that says
differently please point me to it.

Rich

Nothing wrong with an old-fashioned ammeter. Dead simple, and tells you
everything
you want to know. I have one that was used for prop de-icer amps (not
that I use it for that - I actually use it to test solar panels).

David Johnson

The easiest way is a glass encased reed switch that turns on a LED in
series with a resistor. Wrap a large enough wire to carry 8 amps
around the reed switch enough times until it will close the contacts
at about 5 amps. Total of 4 parts required: wire, reed sw, LED, and
resistor of about 560 ohms.
PS Do not mount this near the compass.

I think it would be easer and weigh less to check the heater with your
hand as a pre flight item.
John


On 19 Oct 2005 11:20:01 -0700, "iflycozy"
wrote:

Question to you electrical designer gurus:

Here is what I would like to do and Jim Wier suggested that I post this
here. I want an indicator on my Cozy homebuilt airplane to show me
that my heated pitot is actually working when I turn on the switch on
the instrument panel. So, the light will go out (with the switch still
in the on position) if the heated pitot stops working for some reasons
(but not because it tripped the circuit breaker). So, how can I build
such a device or circuit? I would appreciate specific parts or
identification of parts as I am an amateur. This is a 12 volt DC
system and the heating element draws 7 amps. I know I can not use a
LED in series because it would blow the milli-second I turned the unit
on. I know I can't use a light or lamp in parallel because it would
not indicate if the heated pitot was on or off. So that is my dilemma.
Please help.

Reply to:

Richard Isakson wrote:

Having said that, if anyone knows of a canard icing study that says
differently please point me to it.

While I won't disagree with you that icing conditions are certainly to
be avoided in canard aircraft, probably more than in conventional
aircraft, I will say that I know two folks that have flown in icing
conditions, collected some ice on the canard, and had minor issues.

One of those people is me, during my instrument lessons near
Schenectady, NY in April of this year. I got about 1/16" - 1/8" of ice
on the canard, and my stall speed went up about 10 Kts. I flew around
under the clouds for one circle of the pattern, the ice melted, and we
landed. Of course, having the stall speed go up and not realizing it is
far less dangerous in a canard, since I can't stall the whole plane or
spin it - I noticed the speed difference because the nose started
bobbing at 90 mph in the downwind to base turn.

Another aquaintance with a COZY has had ice up to 1/8" - 1/4" on his
canard, and he says about the same thing.

That being said, I still agree that icing conditions are to be
strenuously avoided - 1/8" of ice is certainly not a lot, and I wouldn't
want to be experimenting with more.

--
Marc J. Zeitlin
http://www.cozybuilders.org/
Copyright (c) 2005

click this link,
http://www.tpub.com/aviation1.htm
u might find this one useful. i hope that one helps! they got infos
there regarding electrical and aviation and more!. try visiting it!






iflycozy wrote:
Question to you electrical designer gurus:

Here is what I would like to do and Jim Wier suggested that I post this
here. I want an indicator on my Cozy homebuilt airplane to show me
that my heated pitot is actually working when I turn on the switch on
the instrument panel. So, the light will go out (with the switch still
in the on position) if the heated pitot stops working for some reasons
(but not because it tripped the circuit breaker). So, how can I build
such a device or circuit? I would appreciate specific parts or
identification of parts as I am an amateur. This is a 12 volt DC
system and the heating element draws 7 amps. I know I can not use a
LED in series because it would blow the milli-second I turned the unit
on. I know I can't use a light or lamp in parallel because it would
not indicate if the heated pitot was on or off. So that is my dilemma.
Please help.

Reply to:

On 19 Oct 2005 11:20:01 -0700, "iflycozy"
wrote:

Question to you electrical designer gurus:

Here is what I would like to do and Jim Wier suggested that I post this
here. I want an indicator on my Cozy homebuilt airplane to show me
that my heated pitot is actually working when I turn on the switch on
the instrument panel. So, the light will go out (with the switch still
in the on position) if the heated pitot stops working for some reasons
(but not because it tripped the circuit breaker). So, how can I build
such a device or circuit? I would appreciate specific parts or
identification of parts as I am an amateur. This is a 12 volt DC
system and the heating element draws 7 amps. I know I can not use a
LED in series because it would blow the milli-second I turned the unit
on. I know I can't use a light or lamp in parallel because it would
not indicate if the heated pitot was on or off. So that is my dilemma.
Please help.

Find one of those out door thermometers with a remote read out. Some
of the older ones had a meter. The newer ones have a battery powered
digital read out which could probably be adapted to the plane's
electrical system, but you wanted simple.

Just drill s small hole into the pitot tube metal where is it thick,
preferably from the inside of the mount. (stay away from the heaters
and the actual tube) Put a little heat sink compound in the hole,
stick the remote sensor in, clamp it in place and run the wires to the
inside where they hook to the sensor. Neat, easy, simple.

As a side note, you don't need accuracy. Fire up see what it reads.
Go flying and see what it reads. It won't be near as hot on cold day
and even less so in rain, but I doubt you'll be flying the cozy in the
rain. Put a sticker or just a piece of tape above, below, or beside
the read out with what you'd expect to see for normal readings.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

Reply to:

Roger

Find one of those out door thermometers with a remote read out. Some
of the older ones had a meter. The newer ones have a battery powered
digital read out which could probably be adapted to the plane's
electrical system, but you wanted simple.


KISS, the best approach........

It will even tell you if the heater is not up to the job regardless of it's
on or off state.

Peter

system and the heating element draws 7 amps. I know I can not use a
LED in series because it would blow the milli-second I turned the unit
on. I know I can't use a light or lamp in parallel because it would
not indicate if the heated pitot was on or off. So that is my dilemma.

You should be all set if you put an LED in parallel with a resistor
in series with the heater. Basically you're making a high-current
ammeter. The values of the LED and resistor depend most on what's
available at your local Radio Shack or equivalent.

Find one of those out door thermometers with a remote read out.

You'd mount that out on the pitot tube?! That seems a bit extreme.

--kyler

On Fri, 21 Oct 2005 14:17:02 GMT, Kyler Laird
wrote:

system and the heating element draws 7 amps. I know I can not use a
LED in series because it would blow the milli-second I turned the unit
on. I know I can't use a light or lamp in parallel because it would
not indicate if the heated pitot was on or off. So that is my dilemma.

You should be all set if you put an LED in parallel with a resistor
in series with the heater. Basically you're making a high-current
ammeter. The values of the LED and resistor depend most on what's
available at your local Radio Shack or equivalent.

Find one of those out door thermometers with a remote read out.

You'd mount that out on the pitot tube?! That seems a bit extreme.

Inserting a second wire into the assembly is extreme? In addition it
lets you know how well the system is working, particularly if it's one
of those two heater types.

The Deb has a digital read out for a number of parameters (Includes
temp in F and C, Density altitude, battery voltage, etc...). All I'd
need to do with something like that would be hook up the TC leads.

Any time I'm in rain, or visible moisture the pitot heat is on.

BTW, I've flown loose formation to Oshkosh with a Cozy a number of
times. One day there were scattered showers all along the path. I
thought I was going to wear out the vernier throttle on the Deb trying
to stay in position.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

--kyler