I completed the modifications by added -10 straight fittings for the gearbox drain and rotor housing foot. These were sealed and JB welded in place and provided a lower profile than NPT fittings. For the drain to clear the starter, the gearbox housing was rotated one set of holes placing the drain at the 5 o'clock position as viewed from the prop. For hose routing, I initially added the -4 vent at the 11 o'clock position so rotating the house place the vent at the 10 o'clock position. The drain hose routing keeps the gearbox minimum oil level about 1/2 full if the hose size is adequate and the vent is working. So I ended up with a minimum oil level at the 3/9 o'clock position and the -4 vent at the 10 o'clock position. Not very much space. The -4 vent line is also connected to the rotor housing foot and may have the same problem that Steve identified. I plan to installed a clear tube in the vent line to see if its acting as another drain. I do believe my drain oil temperature has been reduced but need to install a new sensor to verify. Since the modification, my gearbox oil temperature sensor has not provided a steady temperature. If the sensor is correct for the high side them my drain oil temperature has been reduced by 10-15F in cruise. I'll report back once the new sensor is installed and flown for a few hours.
Dennis H and I installed bushings to repair the input shaft damage caused by the thrust bearing stack. We installed a single 5mm thrust bearing and added the preload pins and springs to lock rotation of the rear 3.5mm thrust washer. I have about 14 hours of flight after the modifications.
Bobby Hughes
-----Original Message-----
Sent: Tuesday, May 07, 2019 12:32 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Venting the Reduction Drive
If the original return line was not enlarged, the "vent" line simply acted as an additional return line and my gearboxes operated completely filled with oil.
Steve Boese
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> Hi Steve, is the enlarging of the oil return necessary?
> I thought you first tried enlarging the return line expecting it to improve draining, only to find no improvement until the vent line was added.
> Jeff
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> Jeff,
> At this point I have only 3 hr of flight time on the gearbox with the modified drain and vent. I have not observed a significant effect with respect to power absorption or heat generation.
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> Connecting the vent line to the foot of the rotor housing was ineffective even though this location was above the oil level. Connecting the vent line to the area of the oil filler opening at the top of the center iron allowed the gearbox to drain as intended.
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> The most troublesome part of the modification was enlarging the oil return to 1/2" NPT in the rotor housing foot.
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> Steve Boese
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