Skeeter Jr.

bryancobb

Junior Member
Joined
Aug 2, 2010
Messages
5,063
Location
Cartersville, GA
Aircraft
Owned Brantly B-2b/Fly Kitfox III/Mini-500b
Total Flight Time
1350
Back to the clutch. Once engaged and up to RPM, the clutch will eventually get heat saturated with the engine crankshaft and everything will stabilize thermally at engine RPM. If you manage to ALWAYS GET THERE without letting it get hot so the Fwd and Mid Bearings spin in the aluminum cog, THEN YOU ARE GOOD AND YOUR CLUTCH WILL LAST A LONG TIME!

If you have spun those two bearings, even once, then you will have several problems. The things in Set B above will now be off-center and spinning at 6200. This vibration will make everything wear out prematurely. You need to do all you can to avoid ever spinning the bearings, even once.

My way of preventing this, in addition to adjusting my rotor engagement technique like I describe above...is to aerate my brand new clutch before any damage from bearing spinning happened. In short, I made "swiss cheese" out of the clutch parts so air could flow through and then "super-balanced" each component and clocked them at assembly to limit runout of the assembly to 0.001" max. I had 50 hours of flying on it when I sold the helicopter and I had not needed to replace a single rod-end from wear.

Dennis told me I had basically ruined a new clutch, unnecessarily but I call the experiment a great success. Another thing I did was to remove the INNER seals only from the Aft and Mid bearings and packed the entire space between them with red synthetic hi-temp grease.

May be overkill but my opinion is...this fixed something that needed fixing.
 

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btd1982

Gold Supporter
Joined
Jan 28, 2021
Messages
89
Location
Devon
Aircraft
Home built helicopter
Total Flight Time
0
Great info Bryan, thanks for sharing!

If you like a laugh, I decided it would be a good idea to make an Aluminium version.
 

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HobbyCAD

Homebuilt Heli Enthusiast
Joined
Jul 8, 2008
Messages
1,602
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
3,536
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
1,602
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
5,063
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
1,602
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.
 
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