Hot Prop

[chrisk]

My M20K came with a hot prop.  How does one tell if this is working?  When I turn it on, I don't see the ammeter move.   Does it have a thermostat that would require colder temperatures?  Anyway, its questionable until proven otherwise.

 

I've also heard hot props are difficult to keep working.  What typically goes wrong with them?

 

 

 

[DonMuncy]

I'm no expert, but there  is a disc behind the prop with brass rings on the back side. These contact a "box like" affair with what I assume are brushes that contact the brass rings. That brush to ring contact is where they fail. Since they are in contact with the spinning prop plate at all times, I assume they wear whether you have the switch on or not. There is no thermostat. If the ammeter doesn't jump when the switch is turned on, it is not working. After having mine worked on at annual for several years, I gave up and disabled it. Since I don't fly in ice, I haven't missed it.

[RocketAviator]

I have hot prop on my M20K Rocket & there is no thermostat. One can easily see a significant current draw when active. You can also feel each heating boot they warm very quickly... Caution prop electrucal power people are recipe for possible accident... You can also check voltage at the prop ring that Don mentioned. Mine has always worked perfectly but like Don I plan & hope to never need it....but it came in the plane &I have it if I should need it.

[carusoam]

Expect to have to find and clean the contacts behind the prop. If they haven't been used in a while, a light corrosion could be expected.

This is my engineering experience more than aviation experience,

-a-

[Jerry 5TJ]

Most electric hot prop systems have more than one zone.   There is a controller or sequencer which sends current to the heaters in turn.  For example, on the 4 blade PA46 hot prop there are inner and outer boot regions, each is cycled on and off for 34 seconds at a time when the system is energized.   There is an ampere meter on the panel which monitors the prop current; if one boot section is out or if the slip rings for that zone are not working the pilot will see different current readings during the different cycles.  There is no thermostat.   In some systems the power is inhibited by the squat switch to prevent overheating on the ground.

 

For discussion and some nice diagrams of all this, have a look at

http://www.vravionics.com/downloads/PDC_Spec_Sheet.pdf