Skeeter Jr.

HobbyCAD

Homebuilt Heli Enthusiast
Joined
Jul 8, 2008
Messages
1,615
Location
Hervey Bay, QLD, Australia
Has anyone measured/recorded the Mini-500 or CH-7's main transmission oil temperature during normal operations? I need to determine what the red line needs to be set to on the trans temp gauge.

Thanks, Francois.
 

Chuck Roberg

Gyro's are more fun
Joined
Oct 30, 2003
Messages
3,542
Location
Naperville, IL
Aircraft
SnoBird Tandem Gyro, Robinson R-22, Assorted Fixed Wing
Total Flight Time
2200
This is what the temps are for the Mosquito Helicopter.

90degree Gearbox Temperatures
Maximum 190 F
Operating 120 - 140 F
 

HobbyCAD

Homebuilt Heli Enthusiast
Joined
Jul 8, 2008
Messages
1,615
Location
Hervey Bay, QLD, Australia
Thanks Chuck, much appreciated.

I vaguely recalling someone stating their Mini-500 transmission was running around 200F to 220F. Was this seen as normal temp? Seems a bit high to me, but feedback on previous experience from others would help me a lot.

Cheers, Francois.
 
Last edited:

bryancobb

Junior Member
Joined
Aug 2, 2010
Messages
5,071
Location
Cartersville, GA
Aircraft
Owned Brantly B-2b/Fly Kitfox III/Mini-500b
Total Flight Time
1350
Thanks Chuck, much appreciated.

I vaguely recalling someone stating their Mini-500 transmission was running around 200F to 220F. Was this seen as normal temp? Seems a bit high to me, but feedback on previous experience from others would help me a lot.

Cheers, Francois.
My goal was to get it down to less than 200. I was never comfortable at 220 but that's where it ran without cooler.
 

HobbyCAD

Homebuilt Heli Enthusiast
Joined
Jul 8, 2008
Messages
1,615
Location
Hervey Bay, QLD, Australia
Brian, with a stock Mini transmission, am I assuming correctly that the oil mainly remains in the lower transmission area below the crown gear, not a lot splashes up past the crown gear up onto the casing sides, as the oil flung off the pinion is shielded from going upwards by the crown gear shielding it? I'm hoping that seeing I'm pumping the oil out the rear of the pinion space, and pumping in back into the transmission at the upper bearing, the oil then passing through the bearing and flung to the sides up there will run down the transmission casing sides, acting as a heatsink, cooling it down, before it settles down in the lower half of the transmission casing. Hopefully then it would have dropped in temp. If not, I will have to put in a radiator between coming out of the pinion area, and going back into the top of the transmission.

Time will tell.
 

bryancobb

Junior Member
Joined
Aug 2, 2010
Messages
5,071
Location
Cartersville, GA
Aircraft
Owned Brantly B-2b/Fly Kitfox III/Mini-500b
Total Flight Time
1350
Brian, with a stock Mini transmission, am I assuming correctly that the oil mainly remains in the lower transmission area below the crown gear, not a lot splashes up past the crown gear up onto the casing sides, as the oil flung off the pinion is shielded from going upwards by the crown gear shielding it? I'm hoping that seeing I'm pumping the oil out the rear of the pinion space, and pumping in back into the transmission at the upper bearing, the oil then passing through the bearing and flung to the sides up there will run down the transmission casing sides, acting as a heatsink, cooling it down, before it settles down in the lower half of the transmission casing. Hopefully then it would have dropped in temp. If not, I will have to put in a radiator between coming out of the pinion area, and going back into the top of the transmission.

Time will tell.
In my experience, pumping oil to the upper bearing is important but it doesn't help cooling very much. I suggest having a transmission oil temperature gauge on the instrument panel.
 

HobbyCAD

Homebuilt Heli Enthusiast
Joined
Jul 8, 2008
Messages
1,615
Location
Hervey Bay, QLD, Australia
Hi Bryan, I have one. This is why I needed the operating temp range, the custom markings are a special order from Westach. Instrument was dispatched last week, hopefully here soon.

Cheers, F.
 

HobbyCAD

Homebuilt Heli Enthusiast
Joined
Jul 8, 2008
Messages
1,615
Location
Hervey Bay, QLD, Australia
Bryan, it seems from my research that I'll shoot for 50 in.lb mast preload, 35 in.lb pinion preload, 006" backlash, set up at 200F case temp. How does this sound to you?

Cheers, Francois
 

HobbyCAD

Homebuilt Heli Enthusiast
Joined
Jul 8, 2008
Messages
1,615
Location
Hervey Bay, QLD, Australia
It seems that measuring bearing preload is in itself a debatable topic. For measuring transmission tapered roller bearing preload, does one need to measure the "breakout" torque, or the "turning" torque? I would interpret we are after the "turning" toque value.

For breakout torque, this is simple enough, one can use a conventional old-school non-clicking beam and pointer type torque wrench, 0-80in.lb range. One can even use a lever arm and a pull-scale.

For turning torque, this method is not possible, for at the moment of measurement, the shaft either has to be stopped, or in a steady state of rotation. Seems the best way to measure turning torque is to wrap a cord around the shaft a couple of times, attach the pull-scale, pull until the turning RPM is steady or the reading stabilises, take the tension value in pounds, multiply by the shaft radius in inches, and you should have the in.lb turning torque value.

Anyone see an error in my way of thinking?

Cheers, F.
 
Top