Today's Message Index:
----------------------
1. 05:44 AM - Re: Piper Arrow Pitot Mast (Robert L. Nuckolls, III)
2. 05:46 AM - Re: ov warning light (Robert L. Nuckolls, III)
3. 05:56 AM - Re: Magnetometer wiring (Rick Beebe)
4. 06:21 AM - Re: Piper Arrow Pitot Mast (Alec Myers)
5. 06:22 AM - Re: ov warning light (Alec Myers)
6. 07:13 AM - Re: Piper Arrow Pitot Mast (Pat Little)
7. 07:38 AM - Re: Piper Arrow Pitot Mast (William Hunter)
8. 07:42 AM - Re: Piper Arrow Pitot Mast (R Adams)
9. 11:22 AM - Re: ov warning light (Robert L. Nuckolls, III)
10. 11:32 AM - Re: Piper Arrow Pitot Mast (Robert L. Nuckolls, III)
11. 12:58 PM - Re: Piper Arrow Pitot Mast (Robert L. Nuckolls, III)
Message 1
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| Subject: | Re: Piper Arrow Pitot Mast |
At 11:40 PM 4/1/2019, you wrote:
>Bob,
>If I measure the resistance of my pitot heater
>elements at room temperature and calculate the
>current thru each of these two resistances in
>parallel when driven by a 14V supply, how far
>off am I for deducing peak inrush current in
>each circuit and thus wire size and breaker rating?=C2
Two resistances? Is this a 12/24v
device? I've never seen one but that
would kind of make sense.
Yes, but they are LOW resistances.
You need to do the 4-wire method
to measure them accurately. I think
you're fine with 20A/12AWG . . . plenty
robust, not overkill.
Bob . . .
Message 2
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| Subject: | Re: ov warning light |
At 08:42 PM 4/1/2019, you wrote:
>
>Unfortunately for me I have a TC aircraft (it
>has at least three type certificates from EASA,
>the FAA and Transport Canada) with a Bosch 28V
>automotive alternator with built-in regulation.
>There is _no_ off-board OV regulation.
>
>The Approved Flight Manual (I stress
>_approved_!) procedure for an =9Cexcessive
>charging" condition is =9CAlternator Circuit Breaker - PULL=9D
>
>So, I=99m looking for a mitigation strategy for
>me (and for my ab initial students!) who will be flying the aircraft.
I'm astounded . . . . what can I say?
Bob . . .
Message 3
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| Subject: | Re: Magnetometer wiring |
I don't know about "common" but I would test it before you get things
bundled up too tightly. Closely follow the manufacturer's
recommendations on shielding and if they have diagnostics, use them. I
had a lot of trouble with my LED strobes interfering with the
magnetometer even though my magnetometer is in the tail. My plane was
built with standard Whelen strobes and I replaced those with Aveo LED. I
imagined LEDs would be electrically quieter but they're not. When I
installed the magnetometer I ended up having to replace all the strobe
wire and being very careful to make sure everything was securely
grounded as the manufacturers said to. The magnetometer still registers
every pulse but it's within allowable tolerances now.
--Rick
On 4/1/2019 7:07 PM, bcone1381 wrote:
>
> I will placing a magnetometer, LED Navigation lights, and LED Strobe Lights in
my wings. Is it common and necessary to separate the Magnetometer wire bundle
from all other wiring or can all of these be run together in one bundle?
Message 4
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| Subject: | Re: Piper Arrow Pitot Mast |
Do you think the weather might make a difference?
Inrush current when switched on at -20C might be higher than inrush current at
room temperature.
On Apr 2, 2019, at 8:43 AM, Robert L. Nuckolls, III <nuckolls.bob@aeroelectric.com>
wrote:
At 11:40 PM 4/1/2019, you wrote:
> Bob,
> If I measure the resistance of my pitot heater elements at room temperature and
calculate the current thru each of these two resistances in parallel when driven
by a 14V supply, how far off am I for deducing peak inrush current in each
circuit and thus wire size and breaker rating?
Two resistances? Is this a 12/24v
device? I've never seen one but that
would kind of make sense.
Yes, but they are LOW resistances.
You need to do the 4-wire method
to measure them accurately. I think
you're fine with 20A/12AWG . . . plenty
robust, not overkill.
Bob . . .
Message 5
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| Subject: | Re: ov warning light |
I dont know!
But Im keeping my ear open for an easy retro-fit (and easily approved) mitigation.
Replacing the B-lead breaker with one that has built-in OV protection seemed
an easy half-win.
On Apr 2, 2019, at 8:45 AM, Robert L. Nuckolls, III <nuckolls.bob@aeroelectric.com>
wrote:
At 08:42 PM 4/1/2019, you wrote:
>
> Unfortunately for me I have a TC aircraft (it has at least three type certificates
from EASA, the FAA and Transport Canada) with a Bosch 28V automotive alternator
with built-in regulation. There is _no_ off-board OV regulation.
>
> The Approved Flight Manual (I stress _approved_!) procedure for an excessive
charging" condition is Alternator Circuit Breaker - PULL
>
> So, Im looking for a mitigation strategy for me (and for my ab initial students!)
who will be flying the aircraft.
I'm astounded . . . . what can I say?
Bob . . .
Message 6
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| Subject: | Re: Piper Arrow Pitot Mast |
The pitot head is from a Cherokee, looks like this
[image: pitot mast DSCN0049.JPG]
Here's a picture of the wiring inside the wing during construction
[image: pitot heat DSCN0053.JPG]
which looks possibly like two circuits in parallel.
The wing is closed up now, so I can only investigate at the wing root where
there are two wires for pitot heat, let's call them A and B. The
resistances I measure (with a multimeter) are
A to ground 2.9 Ohm
B to ground 3.7 Ohm
A to B (i.e., in series) 6.4 Ohm
In trying to understand what is going on I dug into the internet and found
a PA-28 service manual (don't know if this is the same model of pitot mast
or not) which had this diagram
[image: image.png]
which shows two resistors in parallel, although only one circuit supplying
their current.
So, my deduction is I have two parallel resistors and two wires to feed
them - the wires in the wing are 18AWG.
My room-temperature resistance readings may not be accurate (not 4-wire) or
relevant (per Alec's comment about turn on at low temps) but doing a simple
calculation I would have 14/2.9 = 5A and 14/3.7 = 4A for a total of 9A
at
room temp.
I can see that designing for 20A 12AWG (for the wires I'll be adding inside
the fuselage) would give me a good margin. I wonder about the 18AWG wires
in the wing though.
Pat
On Tue, Apr 2, 2019 at 6:49 AM Robert L. Nuckolls, III <
nuckolls.bob@aeroelectric.com> wrote:
> At 11:40 PM 4/1/2019, you wrote:
>
> Bob,
> If I measure the resistance of my pitot heater elements at room
> temperature and calculate the current thru each of these two resistances
in
> parallel when driven by a 14V supply, how far off am I for deducing peak
> inrush current in each circuit and thus wire size and breaker rating?=C3
=82
>
>
> Two resistances? Is this a 12/24v
> device? I've never seen one but that
> would kind of make sense.
>
> Yes, but they are LOW resistances.
> You need to do the 4-wire method
> to measure them accurately. I think
> you're fine with 20A/12AWG . . . plenty
> robust, not overkill.
>
>
> Bob . . .
>
Message 7
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| Subject: | Re: Piper Arrow Pitot Mast |
Pat, that is precisely the pitot mast that I have installed on my airplane
except mine does not have the duct tape upgrade.
Thank you for the shot of the service manual and thanks so much everybody
for all your help!
Thanks,
Bill Hunter
On Tue, Apr 2, 2019, 07:21 Pat Little <roughleg@gmail.com> wrote:
> The pitot head is from a Cherokee, looks like this
> [image: pitot mast DSCN0049.JPG]
> Here's a picture of the wiring inside the wing during construction
> [image: pitot heat DSCN0053.JPG]
> which looks possibly like two circuits in parallel.
> The wing is closed up now, so I can only investigate at the wing root
> where there are two wires for pitot heat, let's call them A and B. The
> resistances I measure (with a multimeter) are
> A to ground 2.9 Ohm
> B to ground 3.7 Ohm
> A to B (i.e., in series) 6.4 Ohm
> In trying to understand what is going on I dug into the internet and foun
d
> a PA-28 service manual (don't know if this is the same model of pitot mas
t
> or not) which had this diagram
> [image: image.png]
> which shows two resistors in parallel, although only one circuit supplyin
g
> their current.
>
> So, my deduction is I have two parallel resistors and two wires to feed
> them - the wires in the wing are 18AWG.
>
> My room-temperature resistance readings may not be accurate (not 4-wire)
> or relevant (per Alec's comment about turn on at low temps) but doing a
> simple calculation I would have 14/2.9 = 5A and 14/3.7 = 4A for a tot
al of
> 9A at room temp.
> I can see that designing for 20A 12AWG (for the wires I'll be adding
> inside the fuselage) would give me a good margin. I wonder about the 18AW
G
> wires in the wing though.
>
> Pat
>
>
> On Tue, Apr 2, 2019 at 6:49 AM Robert L. Nuckolls, III <
> nuckolls.bob@aeroelectric.com> wrote:
>
>> At 11:40 PM 4/1/2019, you wrote:
>>
>> Bob,
>> If I measure the resistance of my pitot heater elements at room
>> temperature and calculate the current thru each of these two resistances
in
>> parallel when driven by a 14V supply, how far off am I for deducing peak
>> inrush current in each circuit and thus wire size and breaker rating?=C3
=82
>>
>>
>> Two resistances? Is this a 12/24v
>> device? I've never seen one but that
>> would kind of make sense.
>>
>> Yes, but they are LOW resistances.
>> You need to do the 4-wire method
>> to measure them accurately. I think
>> you're fine with 20A/12AWG . . . plenty
>> robust, not overkill.
>>
>>
>> Bob . . .
>>
>
Message 8
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| Subject: | Re: Piper Arrow Pitot Mast |
Hey Pat
I used to fly one of these on a Seneca
Every time I got into ice it froze over and I lost the airspeed indicator
(which made it quite handy as an ice detector)
Was told it was a design flaw... it didn=99t have enough capacity to
heat the
mass of the probe sufficiently
All the best!
Ron
On Tue, Apr 2, 2019 at 10:21 AM Pat Little <roughleg@gmail.com> wrote:
> The pitot head is from a Cherokee, looks like this
> [image: pitot mast DSCN0049.JPG]
> Here's a picture of the wiring inside the wing during construction
> [image: pitot heat DSCN0053.JPG]
> which looks possibly like two circuits in parallel.
> The wing is closed up now, so I can only investigate at the wing root
> where there are two wires for pitot heat, let's call them A and B. The
> resistances I measure (with a multimeter) are
> A to ground 2.9 Ohm
> B to ground 3.7 Ohm
> A to B (i.e., in series) 6.4 Ohm
> In trying to understand what is going on I dug into the internet and foun
d
> a PA-28 service manual (don't know if this is the same model of pitot mas
t
> or not) which had this diagram
> [image: image.png]
> which shows two resistors in parallel, although only one circuit supplyin
g
> their current.
>
> So, my deduction is I have two parallel resistors and two wires to feed
> them - the wires in the wing are 18AWG.
>
> My room-temperature resistance readings may not be accurate (not 4-wire)
> or relevant (per Alec's comment about turn on at low temps) but doing a
> simple calculation I would have 14/2.9 = 5A and 14/3.7 = 4A for a tot
al of
> 9A at room temp.
> I can see that designing for 20A 12AWG (for the wires I'll be adding
> inside the fuselage) would give me a good margin. I wonder about the 18AW
G
> wires in the wing though.
>
> Pat
>
>
> On Tue, Apr 2, 2019 at 6:49 AM Robert L. Nuckolls, III <
> nuckolls.bob@aeroelectric.com> wrote:
>
>> At 11:40 PM 4/1/2019, you wrote:
>>
>> Bob,
>> If I measure the resistance of my pitot heater elements at room
>> temperature and calculate the current thru each of these two resistances
in
>> parallel when driven by a 14V supply, how far off am I for deducing peak
>> inrush current in each circuit and thus wire size and breaker rating?=C3
=82
>>
>>
>> Two resistances? Is this a 12/24v
>> device? I've never seen one but that
>> would kind of make sense.
>>
>> Yes, but they are LOW resistances.
>> You need to do the 4-wire method
>> to measure them accurately. I think
>> you're fine with 20A/12AWG . . . plenty
>> robust, not overkill.
>>
>>
>> Bob . . .
>>
>
Message 9
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| Subject: | Re: ov warning light |
At 08:22 AM 4/2/2019, you wrote:
>
>I don=99t know!
>
>But I=99m keeping my ear open for an easy
>retro-fit (and easily approved) mitigation.
>Replacing the B-lead breaker with one that has
>built-in OV protection seemed an easy half-win.
You're not going to find a
light-footed breaker that will
fit into the same slot. There
are remote-trip breakers that
can be triggered by an external
ov sensor . . . but that's
not going to be any less
complicated than Z-14 (interim).
What kind of airplane are we
talking about? How tightly
is it bound to the TC/STC/
Field Approval processes?
Bob . . .
Message 10
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| Subject: | Re: Piper Arrow Pitot Mast |
At 08:20 AM 4/2/2019, you wrote:
>
>Do you think the weather might make a difference?
>Inrush current when switched on at -20C might be higher than inrush
>current at room temperature.
Sure. The document I cited speaks to
the heater temperature coefficient of
resistance for an exemplar pitot tube.
Emacs!
In the instance illustrated, resistance
will vary over a 4:1 range between 0C and
the 270C operation during a max-ice
condition. You can check your heater on
the bench but do it will the tube
submerged in water to avoid still-air,
room-temperature overheat. Without
the heat rejecting qualities of ram-
air in near-icing conditions, the tube
will easily heat up to cherry red!
Bob . . .
Message 11
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| Subject: | Re: Piper Arrow Pitot Mast |
A
>which shows two resistors in parallel, although only one circuit
>supplying their current.
>
>So, my deduction is I have two parallel resistors and two wires to
>feed them - the wires in the wing are 18AWG.
The wires will be fine . . . tie them together
at some convenient point you can reach, then
extend on to switch with the 12AWG wire.
The drawing shows 15A breaker which is also
fine.
>My room-temperature resistance readings may not be accurate (not
>4-wire) or relevant (per Alec's comment about turn on at low temps)
>but doing a simple calculation I would have 14/2.9 = 5A and 14/3.7 =
>4A for a total of 9A at room temp.
>I can see that designing for 20A 12AWG (for the wires I'll be adding
>inside the fuselage) would give me a good margin. I wonder about the
>18AWG wires in the wing though.
Yeah . . . 9A at room temp will
go lower at operating temperature
unless melting ice. Sounds like
not much of a heater . . . which
sorta agrees with other folks
experiences with poor performance.
Pitot heat really isn't much of
a hedge against a bad day in the
cockpit. If you're collecting
ice, airspeed is probably the least
of your worries. I could tell
you a tale or two about that.
Wire it up but don't let its
existence dissuade you from due
diligence with the weather-guys
while you're still on the ground.
Bob . . .
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