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What is your tidbit that can be placed here??? E-mail me and I will add it to this site. |
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THE HEATING SYSTEM
Getting heat into the cabin has been an ongoing challenge. My first discovery was that the 6" butterfly valve that closes with the "pull heat" lever that is located in the cockpit to turn off the outside air was a very poor fit. I was able to trim the edges to attain a good seal.
There are two fans that "suck" air out of the heat exchanger on the fire wall. The first vent fan came as original equipment with the airplane and is used to boost the airflow into the cabin, or to the front windows when the vent knob is pulled out. Jetprop added a heater fan under the rear seat. This fan sucks air from the heat exchanger through both the left and right side inlets. On the pilots side the air passes through the original fan and then into the cabin where it also goes directly to the front windows vent if the vent knob is pulled out. If the knob is pushed in it is then channeled back to between the seats where it is plumed with a 2" hose under the floor to the heat channel on the co-pilots side. A 2" hose comes out of the channel at the far back seat and goes directly into the rear fan. The output of the fan feeds 2 nozzles under the rear seats and the 2 each nozzles on each side under the front windows. Since the fan "sucks" the heated air out of the heat exchanger it is crucial that there be no leaks on the low pressure side between the firewall and the rear fan. Jetprop tells you to close the heater levers at the feet up front. If they are open then the fan draws in air from the cabin instead of the heat exchanger. These are reed valves and leak even when closed. I ended up taking out the co-pilot side and replacing it with a plate. (Very easy, just 2 screws you can get to from the outside) I removed the 2" hose by the co-pilot's right knee and hooked up a vacuum cleaner (pressure side) to the 2" inlet that goes to the fan in the back. I was able to identify leaks by placing the system under pressure. It helps to put the vacuum cleaner outside the airplane so you can hear the leaks. (Run the hose through the window and close the door) I found a major leak between the front and center seats on the co-pilot side where the front and rear channel boxes attach. There were several other small leaks that were fixed with caulking.
On the output side, I found a large leak under the heat nozzles on the pilots side where the pipe comes into the top section of the box. You can see this by removing the nozzles.
After all of this effort the heater only works if it is turned on immediately into the flight. Once the cabin starts pressurizing it will not get going on it's own. There are still major problems with the windows frosting up. The last few thousand feet of altitude seems to make a big difference.
Please e-mail me if you have any additional input or better yet, solutions. JetProp is coming out with an inline heater placed under the back seat in 2003. That should be a big help. |
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Fog/Vent Fan
The JetProp hot air through the fan motor is much hotter than with the piston engine. The grease in the bearings dries out faster and the bearings burn up. The first clue is that the fan starts making a loud noise because it is hitting the housing. This is the time to replace the bearings. As it gets worse and the fan blade digs into the housing it will eventually stick and blow the circuit breaker.
To repair, take apart (see picture) and clean. I used a Drumall Tool to smooth out the fan blades and groves in the housing. The bearings are easily replaced and available at your local bearings store. Be sure to reseal the wires since the housing is under pressure. |
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Flap Motor Blowing Circuit Breaker
My flap motor started blowing the circuit breaker on landings when I put in the third notch (30o) of flaps. Measured the current under load = 15 amps. Cleaned the worm gear with a solvent and thinly lubed with lithium grease = 5 amps. I now clean and lube the worm gear at each annual. |
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Pitch Servo
Located in the tail, I have had two problems. At times, when the autopilot is disconnected, there is a strong pitch change. This can be caused by the up or down arm that pushes against micro switches that turn the trim wheel to take the pressure off the pitch servo. To test this, push on the yoke with the auto pilot connected and the trim wheel should turn. Pull, and it should turn in the opposite direction. An arm is broken if the trim wheel will turn only in one direction.
The second problem deals with how much pressure you need to put on the yoke in order to get the servo to turn. If the auto pilot calls for a pitch change the servo should turn before you can notice any deviation on the FD. When the servo gets cold it takes more deviation for it to start turning. In the JetProp the servo gets colder than before because of the higher altitude. If bad enough, the servo will lock up and not turn. The auto pilot will keep working, but not hold altitude. The big clue is that it will start working again when you descend to warmer temperatures. The servo has planetary gears that get hard to turn when the grease hardens. The best way to test the servo is to remove it and use a variable power supply directly across the servo motor. The motor should start to turn at .3 to .7 volts. If it is higher, you can carefully take the planetary gears out laying them in a row and clean them with a solvent. Put a light coat of lithium grease on the gears as your put them back in. This is very tricky, so you must take the gear box apart and put it back together with the precision of a jeweler. |
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