---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Tue 04/02/19: 11 ---------------------------------------------------------- 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 _____________________________________ Time: 05:44:17 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: 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 _____________________________________ Time: 05:46:20 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: 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 _____________________________________ Time: 05:56:05 AM PST US Subject: Re: AeroElectric-List: Magnetometer wiring From: Rick Beebe 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 _____________________________________ Time: 06:21:03 AM PST US From: Alec Myers Subject: Re: AeroElectric-List: 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 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 _____________________________________ Time: 06:22:33 AM PST US From: Alec Myers Subject: Re: AeroElectric-List: 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 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 _____________________________________ Time: 07:13:17 AM PST US From: Pat Little Subject: Re: AeroElectric-List: 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 _____________________________________ Time: 07:38:13 AM PST US From: William Hunter Subject: Re: AeroElectric-List: 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 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 _____________________________________ Time: 07:42:18 AM PST US From: R Adams Subject: Re: AeroElectric-List: 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 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 _____________________________________ Time: 11:22:33 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: 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 ____________________________________ Time: 11:32:17 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: 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 ____________________________________ Time: 12:58:30 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: 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 . . . ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message aeroelectric-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/AeroElectric-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/aeroelectric-list Browse Digests http://www.matronics.com/digest/aeroelectric-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.