If the pitot heat results in only “slightly warm” during the preflight check, due to an end of life battery, there is probably no safety of flight concern about pitot heat, as the battery probably lacks the energy required to get the engine running to go flying at all! If the pitot heat does not become too hot to touch after having time to warm up, something is not airworthy.
A_and_C wrote:
Slightly warm is usualy a good indication that the battery is at the end of its life not problems with the pitot heater.
No matter what the power source is, the pitot will be “slightly warm” before it is “very warm”. As Pilot_DAR writes, there is no need to wait until it is hot.
Peter wrote:
I wonder if there are different grades of pitot heaters.
Yes, there is. E.g. for Cessna P210, there are two P/N. One is the “high temperature” one, and is installed on the ones that are/were certified as FIKI from the factory. The other is the “normal” one.
Peter wrote:
I wonder if there are different grades of pitot heaters. Mine draws 5A at 24V which is obviously a lot more heat than 5A at 12V.
AFAIK, there are different versions with one (2-wire) or two (3-wire) heater coils.
@Ultranomad yes I tried your suggestion on ground/air, I get a change of Ammeter reading on battery only from pitot ON/OFF but it is so low that it will be hard to detect in rough air but would work on smooth air…
Probably the only reliable alternatives are from aircraft attitude/power performance
Ibra, yes, on conventional needle ammeters it may be just a slight move. On the other hand, on digital ones (e.g. on a G1000, which shows battery current with 0.1 A resolution) it’s very obvious.
Ibra wrote:
Probably the only reliable alternatives are from aircraft attitude/power performance
??
On the other hand, on digital ones (e.g. on a G1000, which shows battery current with 0.1 A resolution) it’s very obvious.
Yes, provided you understand how the ammeter is wired into the electrical system, and interpret the indication in the context of how it’s wired. Pages 4 and 5 of the Electronics International manual below describe the different ways to wire a digital ammeter in, and how to operate it depending on its connection. Understanding this will assure that a “no indication” on a digital ammeter is not mistaken for a non functioning electrical consumer, because the observer is misunderstanding the wiring.
Ibra wrote:
How one does check the pitot heatIt’s part of the daily preflight check on our PA28s.
It warms up to really hot if you wait, but you usually don’t wait that much so as not to drain the battery…or fry the heating element. The pitot heat is set to be hot enough at cruising speed, one the ground it gets too hot to touch.
one method that would work … is comparing ammeterThat’s actually how we check the alternator is working. At idle on the ground the pitot heat is the single largest electric load you can easily turn on and off. The needle moves more than a little.
As mentioned, unless it is capable of getting very hot, it’s not going to be much use in anger.
If there was a poor connection that may affect performance.
If a battery is in good condition there should be zero risk of leaving the Pitot heat on to check it gets hot, not just warm.
When I check ours, it’s done in isolation to other checks. The switch goes on and I check it constantly, waiting to ensure it will get too hot to hold…… I dont actually wait to that point, but close to it.
It’s quite obvious by the rate of change toward the end of the check.
This will not damage it. If it would, that would be a really daft design.
It’s out of propwash and would be turned on before take off, any delay, extra check or ATC hold would not and should not require me to remember to lean down and turn it off.
Once I’m happy it works well, subsequent checks, over the next weeks/months will be the usual ‘is it getting warm’. Unless of course I’m definitely expecting to enter cloud, then it would be a ‘big’ check again.
In 18 years, I’ve never flattened a battery this way.
@Pilot_DAR assuming you fly level, you can get you IAS from GPS ground speed, wind and density altitude down to instrument calibration errors (+/-5% ?) or from power and density altitude given POH data and you know how far that aircraft is from those numbers (+/-30% ?)
Large deviations from those estimmates probably indicate issues with pitot tube (or airframe), in my case I was expecting 120kts ASI that did read 80kts with +/-10kts rapid fluctuations (there was no icing but few rain around), pitot heat was ON in the air but it was not working: on the ground it was just cold…
