Which Radios to Switch On?
Keygrip
What can I say
- would you believe it was a deliberate mistake? 'thought not! 
Benix
That's not what I'm saying. DFC told us that the electrically induced deviation had to be less than 5 degrees. I simply made the point that there could therefore be an error of up to 5 degrees. Try looking at the compass when you turn things on and off; it moves noticeably in many aircraft although I'd admit the most I've seen is probably 5-7 degrees.
Personally I don't switch on pitot heat as a matter of course for VFR trips but it's part of my line-up checklist for IFR departures.
DFC
The "right hand grip rule" illustrates the direction of the field around a current. The magnetic field around a pair of long wires with equal and opposite currents varies directly with both the current and the separation of the wires and inversely with the square of the distance between the centre of the pair and the victim. The answer to disturbance from leakage fields is to keep the wires very close (coaxial would be good), the current low and the distance maximised.
"Why do the radios get special treatment? - Simple - many sources of alternating voltages and currents as various frequencies" You seem to think that alternating currents cause more compass deviation than direct currents; this is not correct. The compass cannot respond to alternating fields above a few Hz so effectively only static or half wave rectified fields are an issue. Therefore any significant load may have an effect.
I'm surprised that it's legit to swing with electrics off, do you have a link to where the rules are defined?
HFD
What can I say
- would you believe it was a deliberate mistake? 'thought not! Benix
That's not what I'm saying. DFC told us that the electrically induced deviation had to be less than 5 degrees. I simply made the point that there could therefore be an error of up to 5 degrees. Try looking at the compass when you turn things on and off; it moves noticeably in many aircraft although I'd admit the most I've seen is probably 5-7 degrees.
Personally I don't switch on pitot heat as a matter of course for VFR trips but it's part of my line-up checklist for IFR departures.
DFC
The "right hand grip rule" illustrates the direction of the field around a current. The magnetic field around a pair of long wires with equal and opposite currents varies directly with both the current and the separation of the wires and inversely with the square of the distance between the centre of the pair and the victim. The answer to disturbance from leakage fields is to keep the wires very close (coaxial would be good), the current low and the distance maximised.
"Why do the radios get special treatment? - Simple - many sources of alternating voltages and currents as various frequencies" You seem to think that alternating currents cause more compass deviation than direct currents; this is not correct. The compass cannot respond to alternating fields above a few Hz so effectively only static or half wave rectified fields are an issue. Therefore any significant load may have an effect.
I'm surprised that it's legit to swing with electrics off, do you have a link to where the rules are defined?
HFD
Last edited by hugh flung_dung; 15th Dec 2005 at 11:38.
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The compass swing does not garrantee that the compass will give a true reading / deviation with all states of electrical load.
Again its this old cherry of read the POH it will specify what it is swung using. And usually there is 2 bulbs in a compass linked in series, one either side which cancel each other out. They are in series so it fails safe ie if one bulb goes it stops the other one working so the whole lot still gives the correct reading.
My day job type needs for you to get a resonable reading all sorts of stuff turned off. And normally sits with about 30 degrees error on it. And the most use it gets is for jamming a chart behined when the sun is in you face. And the stuff you do require to turn off means that you are flying on standby instrument power and you will have gone onto timed turns from ATC.
And the point on re-racking is to be honest bordering on dangerous. Re-racking even in the hands of an avionics engineer must be the quickest way of shagging sevicable equipment ever invented. Bent pins, wear and tear. Turn everything on and dry it out is by far the safest way to both yourself (less chance of slashing your hand open on sheet metal) and to the plane of not bending delicate connections.
The pitot heater is one of personal preferance persoanlly now I would have it on all the time. When instructing I had it on at night or IMC.
And the DME argument is very nice but. In reality most modern area nav equip planes will be using and speaking to 6 if not 10 different DME stations. And the likes of TLA or POL can accept over a thousand requests per cycle. A terminal ILS DME must be nearly 500. In the UK i wouldn't worry about it leave it on if you want. If the big boys use a DME slot when they arn't even using it for primary nav so can a SEP. If you don't get a reading inside the DOC NATS need to know so they can upgrade the installation as required. If they don't know they can't fix it.
Turn the whole lot on leave it on would be my advice and if you really don't want the DME just tune it to a freq which isn't used.
MJ
Again its this old cherry of read the POH it will specify what it is swung using. And usually there is 2 bulbs in a compass linked in series, one either side which cancel each other out. They are in series so it fails safe ie if one bulb goes it stops the other one working so the whole lot still gives the correct reading.
My day job type needs for you to get a resonable reading all sorts of stuff turned off. And normally sits with about 30 degrees error on it. And the most use it gets is for jamming a chart behined when the sun is in you face. And the stuff you do require to turn off means that you are flying on standby instrument power and you will have gone onto timed turns from ATC.
And the point on re-racking is to be honest bordering on dangerous. Re-racking even in the hands of an avionics engineer must be the quickest way of shagging sevicable equipment ever invented. Bent pins, wear and tear. Turn everything on and dry it out is by far the safest way to both yourself (less chance of slashing your hand open on sheet metal) and to the plane of not bending delicate connections.
The pitot heater is one of personal preferance persoanlly now I would have it on all the time. When instructing I had it on at night or IMC.
And the DME argument is very nice but. In reality most modern area nav equip planes will be using and speaking to 6 if not 10 different DME stations. And the likes of TLA or POL can accept over a thousand requests per cycle. A terminal ILS DME must be nearly 500. In the UK i wouldn't worry about it leave it on if you want. If the big boys use a DME slot when they arn't even using it for primary nav so can a SEP. If you don't get a reading inside the DOC NATS need to know so they can upgrade the installation as required. If they don't know they can't fix it.
Turn the whole lot on leave it on would be my advice and if you really don't want the DME just tune it to a freq which isn't used.
MJ
Last edited by mad_jock; 15th Dec 2005 at 10:42.
Thanks for all the replies - I never imagined my query would generate so many answers!
I have to declare I am in favour of switching all radios on after start.
Happy Christmas to all and safe landings in 2005.
I have to declare I am in favour of switching all radios on after start.
Happy Christmas to all and safe landings in 2005.
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DFC
I agree that it does not make sense to have things like pitot heat on when not needed (unnecessary electrical drain on system)
where I disagree is with your following comment....
When it comes to drying out the avionics - turn up the heater!
Carbon monoxide poisoning is a real and ever present threat so makes more sense to turn on radios and other low current essential services.
I agree that it does not make sense to have things like pitot heat on when not needed (unnecessary electrical drain on system)
where I disagree is with your following comment....
When it comes to drying out the avionics - turn up the heater!
Carbon monoxide poisoning is a real and ever present threat so makes more sense to turn on radios and other low current essential services.
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HFD,
The place to go for info is the CAAIP - CAP562
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Mad Jock,
If something is U/S. The Avionics Engineer can a) Re-rack the box or b) Replace the box or in some cases swap the #1 and #2 boxes. Each of the options involves removing a box from the rack and putting a box back into the rack. Replacing unserviceable items is not dangerous. Re-racking done properly is a common standard maintenence procedure.
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unfazed,
Ask yourself - if the radios kept the cockpit nice and toasty why would they have installed a heater?
If you never use the heater for fear of Co I would recomend that you get yourself one of those Co detectors and watch out for a black dot while you and your equipment enjoy the heat.
You are correct about Co but hypothermia can be just as deadly!
Regards,
DFC
The place to go for info is the CAAIP - CAP562
-------
Mad Jock,
If something is U/S. The Avionics Engineer can a) Re-rack the box or b) Replace the box or in some cases swap the #1 and #2 boxes. Each of the options involves removing a box from the rack and putting a box back into the rack. Replacing unserviceable items is not dangerous. Re-racking done properly is a common standard maintenence procedure.
-----
unfazed,
Ask yourself - if the radios kept the cockpit nice and toasty why would they have installed a heater?
If you never use the heater for fear of Co I would recomend that you get yourself one of those Co detectors and watch out for a black dot while you and your equipment enjoy the heat.
You are correct about Co but hypothermia can be just as deadly!
Regards,
DFC
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re-racking is a con merchants way of getting the plane online again and very rarely actually fixes anything apart from allows the engineer to sign off the fault and usually means you re-start the deffered defect sheet the next flight or the next. The potential damage which can be done usually far out ways the benefit. And if its being done day in day out just to get the thing working it will lead to damage.
Replacing I have no problem with but re-racking is a easy sign off when you don't know or can't be arsed fixing it properly. Also the avionics might not actually have the moisture where the heater air can get to it. And the working temp of most avionics is way in excess of the heater air so the kit will dry out faster with use than with just cabin heat. If you re-rack once and the problem occurs again the next day its the seals on your connectors you need looking at not a constant re-rack.
MJ
Replacing I have no problem with but re-racking is a easy sign off when you don't know or can't be arsed fixing it properly. Also the avionics might not actually have the moisture where the heater air can get to it. And the working temp of most avionics is way in excess of the heater air so the kit will dry out faster with use than with just cabin heat. If you re-rack once and the problem occurs again the next day its the seals on your connectors you need looking at not a constant re-rack.
MJ
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And if its being done day in day out just to get the thing working it will lead to damage.
Agree with that. Re-racking is not done as an isolated fix and some related checks need to be done. I have experience of a modern aircraft where two boxes had to swapped on a regular basis. This was an approved maintenance procedure until the software engineers could make a more long term fix!
Regards,
DFC
Agree with that. Re-racking is not done as an isolated fix and some related checks need to be done. I have experience of a modern aircraft where two boxes had to swapped on a regular basis. This was an approved maintenance procedure until the software engineers could make a more long term fix!
Regards,
DFC
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A lot of talk about keeping the damp at bay and I think that this has some merit at this time of year but the biggest "killer" of avionics is heat build up and therefore overheating, this is not my opinion but that of Bendix/King and is clearly stated in most of that companys instalation manuals.
So I have to ask BEagle if "his" aircraft have avionics cooling fans fitted ?
So I have to ask BEagle if "his" aircraft have avionics cooling fans fitted ?
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I've had more avionics problems due to corrosion and damp, than for anyother reason. In the U.K I've never had anything overheat, but I also wouldn't turn everything on if the ambient temperature was high.
Like most things in flying, just use a little common-sense, If the weather is cold and miserable, then turning on all the avionics will be a benefit, but during a hot summer when everything will be dry anyway, what's the point.
Horses for courses.
Like most things in flying, just use a little common-sense, If the weather is cold and miserable, then turning on all the avionics will be a benefit, but during a hot summer when everything will be dry anyway, what's the point.
Horses for courses.
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Re: Which Radios to Switch On?
As you say you have not had a radio overheat in the UK but you dont have to go to far south in the summer to get the radios very hot.
Put your hand on one of your radios at the end of an hours flying and you will find it walm , when one of your aircraft flys to the south of France or Spain in the summer the OAT on the ground may well be up towards +40C.
Add the heat that you are feeling from an hours flying and the radio could hit the +55C that most avionic companys state as the upper limit for the radio.
I have no doubt that the radio will continue to work at that heat level but that is when the damage is done that surfaces months later, perhaps mistaken for damage from damp conditions ?.
The cost of a radio cooling fan would be covered by the first radio repair that you DONT have to do. In all of my aircraft that have more than a NAV/COMM & transponder I have radio cooling fitted and the low level of radio problems is I think entirly due to the fact that the radios dont suffer from heat build up but not swiching on some of the equipment is simply not an option in some airspace enviroments that my aircraft fly.
Put your hand on one of your radios at the end of an hours flying and you will find it walm , when one of your aircraft flys to the south of France or Spain in the summer the OAT on the ground may well be up towards +40C.
Add the heat that you are feeling from an hours flying and the radio could hit the +55C that most avionic companys state as the upper limit for the radio.
I have no doubt that the radio will continue to work at that heat level but that is when the damage is done that surfaces months later, perhaps mistaken for damage from damp conditions ?.
The cost of a radio cooling fan would be covered by the first radio repair that you DONT have to do. In all of my aircraft that have more than a NAV/COMM & transponder I have radio cooling fitted and the low level of radio problems is I think entirly due to the fact that the radios dont suffer from heat build up but not swiching on some of the equipment is simply not an option in some airspace enviroments that my aircraft fly.
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Re: Which Radios to Switch On?
DFC.....
I know the answer to this question.
" which direction the aircraft is pointing in the event of a total electrical failure"
...............forwards.
Sorry
I know the answer to this question.
" which direction the aircraft is pointing in the event of a total electrical failure"
...............forwards.
Sorry
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Re: Which Radios to Switch On?
Originally Posted by A and C
the low level of radio problems is I think entirly due to the fact that the radios dont suffer from heat build up but not swiching on some of the equipment is simply not an option in some airspace enviroments that my aircraft fly.
Re: Which Radios to Switch On?
FWIW (which may not be terribly much) I recall from a previous existence that the thermally-induced failure rate of electronic components was given by the Arrhenius equation. The broad result is that the failure rate will roughly double for every increase in temperature of 10 degrees (the detail is far too tedious to type here but a quick Google will probably reveal chapter and verse if you are feeling masochistic). The bottom line is that a fan is good if it's outside the equipment and you can tolerate the noise but bad if it's internal because it has a large impact on the MTBF.
HFD
HFD
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Re: Which Radios to Switch On?
[B]Noise.. What Noise ?
I can hardly tell if the avionic cooling fan is running when the engine is not so noise in flight or for that matter when taxing is not an issue.
If it is electrical noise that you are thinking of that is not a problem with the Ameri-King unit that I have fitted.
I cant see a down side to fitting avionic cooling, In my opinion the reason that cooling is not fitted is the same as the reason that DME remote channeling & GPS/Encoder interface is not fitted ...... That is the avionic companys have entirely to compeat on cost and the price of a cooling fan and some of the other functions that a lot of the owners dont understand will blunt the avionic shops compeditive edge.
The irony is that six months down the line the owner wishes that he had all the functions of the equipment fitted but now it will cost twice as much to fit the equipment to enable all the functions.
I can hardly tell if the avionic cooling fan is running when the engine is not so noise in flight or for that matter when taxing is not an issue.
If it is electrical noise that you are thinking of that is not a problem with the Ameri-King unit that I have fitted.
I cant see a down side to fitting avionic cooling, In my opinion the reason that cooling is not fitted is the same as the reason that DME remote channeling & GPS/Encoder interface is not fitted ...... That is the avionic companys have entirely to compeat on cost and the price of a cooling fan and some of the other functions that a lot of the owners dont understand will blunt the avionic shops compeditive edge.
The irony is that six months down the line the owner wishes that he had all the functions of the equipment fitted but now it will cost twice as much to fit the equipment to enable all the functions.
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Re: Which Radios to Switch On?
Different aircraft have different requirements (electrically speaking) to get the most accurate reading on the standby compass, so there is no hard and fast rule about that.
Regarding switching pitot heaters on, remember that venturi effect will provide cooling. It costs nothing to switch it on (unless you're stationary on the ground for hours while the stude goes through the run-up checks), and will cost lots if it gets iced up in the air. Besides, it's a good habit to get into.
Finally, on the use of the transponder, if you turn it on, for heavens' sake make sure you're squawking Mode C. Nothing gets the heart rate up if you're trogging along at altitude and you get the "Traffic - Traffic" callout and no Mode C info to tell you where to look. I have known instructors who tell studes to sqawk only Mode A on the grounds that they can't get done for straying into controlled airspace. And yet they call themselves professionals!
Regarding switching pitot heaters on, remember that venturi effect will provide cooling. It costs nothing to switch it on (unless you're stationary on the ground for hours while the stude goes through the run-up checks), and will cost lots if it gets iced up in the air. Besides, it's a good habit to get into.
Finally, on the use of the transponder, if you turn it on, for heavens' sake make sure you're squawking Mode C. Nothing gets the heart rate up if you're trogging along at altitude and you get the "Traffic - Traffic" callout and no Mode C info to tell you where to look. I have known instructors who tell studes to sqawk only Mode A on the grounds that they can't get done for straying into controlled airspace. And yet they call themselves professionals!
