Aeromatic operation in the cold

[dtreid]

I took the Cruisiar up for a flight today in -10 degrees C weather.

The prop seemed like it didn't want to coarsen up very easily in cruise. I am wondering if this is a result of the cold weather and thick oil in the prop.

Has anyone else had similar experiences?

 

[ronm]

The regular Aeromatic lube was some kind of special snake oil. If it got old enough and gummy enough, it might congeal at -10c I suppose. I usually flew at 11 or 12 thousand where it is quite brisk and never noticed any pitch lag though.

If backing off on the power in cruise reduces the RPM considerably, the prop isn't stuck.
Also, since RPM tends to change with altitude for a given throttle setting, cold = lower density altitude and a little higher RPM would be expected for that pressure altitude.

 

[blimpy]

FYI Kent Tarver recommends 80/90W gear oil for the hub.

Makes sense to change/ flush the hub and renew the goop.

This is widely available at National Airplane Parts Association ( Napa auto parts )

:wink:

 

[blimpy]

It's pretty darn easy to drain and flush the old oil from the hub.
Manual shows how to "fill" it. Which really isn't full at all.

max rpm decreases 20 rpm/1000 feet.

this is normal.

so at 10,000 feet max rpm is going to be 200 less than sea level ( seal level ? ) :wink:

 

[gjordan]

In all of my junk, I found a can of original Aeromatic oil, and it seemed pretty light, like maybe 10 or 20 weight. I have doubts about 80 or 90 weight. I wonder if the original specs can be located. It is probably some old MIL spec? ____Grant.

 

[Larry Lowenkron]

I have often wondered about the wt of Aeromatic oil. When I got my first one in 1980, I was told that I could use (and did) Marvel Mystery Oil. Later owners of the TC told me to use 90 wt gear oil (which I did on a different prop) Did not see any difference in operation! I have no idea why, but all original hubs that were reworked.

 

[twheel47]

I concur with Larry. I never saw any difference in prop performance usin MMO, light gear oil or with Kent's suggested heavier weight. I think it's really just used to dampen the hub movement, not really control as in a constant speed.