KenSandyEggo
Platinum Member
- Joined
- Mar 29, 2004
- Messages
- 3,657
- Location
- Charlotte, NC
- Aircraft
- McCulloch J2
- Total Flight Time
- approx. 1400+
I put the shortened cable on today after a good lube job, snugged up the disk to the pucks very closely and took her to the runup area. Winds were light and variable. Spun her up and got up to 181 rrpm on the first try. Couldn't get a pic at that speed. I had to settle for 163. Each subsequent spinup was a little less, and I think I know why.
This has been mentioned several times, and I don't know why all of us former and current RAF-ers have had our heads stuck up our butts for so long. I'm not sure about everyone else, but when I squeeze the handle, it's always been mushy feeling and after a little usage, the handle squeezes up to the hand-grip on the stick. Now, forgetting what had been said before, I'm always assuming that the cable is stretching and causing this. The cable is not actuating the lever on the lower unit. The outer casing (sheath) is. The cable is fastened to a fixed bolt, so when you yank your handle, the sheath is sliding along the cable and pushes on the lever to activate the clutch.
This has to be inefficient. That outer casing must compress some. It is not meant to be the part that actually does the work on a Bowden cable. It is designed so that the inner cable pulls. We're just not getting enough pressure to prevent slipping, especially after heat buildup and by using the cable housing to exert the force needed.
I see 2 solutions. One is using a hydraulic system to exert more force on the lever. This will be expensive. The 2 main components (actuator handle and slave unit) cost around $200. That's not counting the cost of a good, metal-sheathed hydraulic cable. When he finally gets off his ass, the first machined bracket for the slave will cost me about $200 with the designing. Of course, subsequent ones will be less expensive. I'm sure that replacing the spongy system with a hydraulic system will more than attain the 19 rrpm.
The other solution would be to rearrange the outer cable-housing (sheath) end at the lower unit so that it is anchored in a bracket before the lever. The inner-cable would then go past the lever, around a small pulley and back to the lever, where the inner cable will be pulling the lever to actuate the clutch instead of a crunching outer housing. I'll see if I can get this done also for a tryout. I can probably work on it while the machinist is picking his butt and scratching his head.
When spinning up to 181 rrpm, I was surprised how smoothly everything was spinning. The upper control rods were perfectly still. Following are some photos, including one of the lower housing. The first one shows the shortened cable, eliminating the sharp bend I originally had. It's now a smooth curve to the top. The photo was taken with the sticks all the way forward, so this is as tight as it gets. I had it shortened by 7 inches.
So the solution as I see it, is to reduce the prerotator cable and housing as much as practicable to elminate friction; face the rear plate with a good clutch/brake material; and get those last few pounds of pressure to the actuating arm to prevent any slipping via a modified U-turn cable system or hydraulic system. 181 is still pretty good....I think.
This has been mentioned several times, and I don't know why all of us former and current RAF-ers have had our heads stuck up our butts for so long. I'm not sure about everyone else, but when I squeeze the handle, it's always been mushy feeling and after a little usage, the handle squeezes up to the hand-grip on the stick. Now, forgetting what had been said before, I'm always assuming that the cable is stretching and causing this. The cable is not actuating the lever on the lower unit. The outer casing (sheath) is. The cable is fastened to a fixed bolt, so when you yank your handle, the sheath is sliding along the cable and pushes on the lever to activate the clutch.
This has to be inefficient. That outer casing must compress some. It is not meant to be the part that actually does the work on a Bowden cable. It is designed so that the inner cable pulls. We're just not getting enough pressure to prevent slipping, especially after heat buildup and by using the cable housing to exert the force needed.
I see 2 solutions. One is using a hydraulic system to exert more force on the lever. This will be expensive. The 2 main components (actuator handle and slave unit) cost around $200. That's not counting the cost of a good, metal-sheathed hydraulic cable. When he finally gets off his ass, the first machined bracket for the slave will cost me about $200 with the designing. Of course, subsequent ones will be less expensive. I'm sure that replacing the spongy system with a hydraulic system will more than attain the 19 rrpm.
The other solution would be to rearrange the outer cable-housing (sheath) end at the lower unit so that it is anchored in a bracket before the lever. The inner-cable would then go past the lever, around a small pulley and back to the lever, where the inner cable will be pulling the lever to actuate the clutch instead of a crunching outer housing. I'll see if I can get this done also for a tryout. I can probably work on it while the machinist is picking his butt and scratching his head.
When spinning up to 181 rrpm, I was surprised how smoothly everything was spinning. The upper control rods were perfectly still. Following are some photos, including one of the lower housing. The first one shows the shortened cable, eliminating the sharp bend I originally had. It's now a smooth curve to the top. The photo was taken with the sticks all the way forward, so this is as tight as it gets. I had it shortened by 7 inches.
So the solution as I see it, is to reduce the prerotator cable and housing as much as practicable to elminate friction; face the rear plate with a good clutch/brake material; and get those last few pounds of pressure to the actuating arm to prevent any slipping via a modified U-turn cable system or hydraulic system. 181 is still pretty good....I think.
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