Goal: 200 Short by 19!

[KenSandyEggo]

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.

[KenSandyEggo]

This shot shows 133 rrpm and you'll notice that the tachs are showing 1,050 engine rpm, just about idle speed.

[KenSandyEggo]

Here's 168 rrpm and the engine tach to the left of the rotor tach is showing 1500 engine rpm.

[KenSandyEggo]

This is a shot of the top of the control rods at around 160 rrpm. Notice the lack of any blurring.......except by the low-resolution setting I was using. There's no motion blurring.

[KenSandyEggo]

Here's what happens to the grip-handle, no matter how well-adjusted everything else is.

[KenSandyEggo]

Here's the lower unit I was talking about that uses the outer cable to apply pressure to the lever.

[rgraffeo]

Ken,
One of my PRA chapter members devised a system of pulleys to help pull tension on the clutch of his pre-rotator. I have to look to see if I still have the pictures he sent me, it looked like a good system. I don't know if he tried it since he's still building his RAF.

The cable I'm using is galvanized. I was told by a cable supplier that galvanized was stronger & would not stretch as much as stainless steel. When I change my cable next time, I'm going to coat the cable with anti-sieze as I put it in the sheath.

[CLS447]

Ken, how about a Morse cable like my new machine uses for the rudder cables & the High Torque prerotator? There is no casing squash with these! It uses a lever instead of a clutch handle.

[quadrirotor]

Is the mast twisting wildly?

[KenSandyEggo]

Andre, it's not twisting at all. It probably does a little with the initial startup as it would no matter how you were doing your prerotation, but once she's spinning, it's not. The trick of course is to add power in very small increments. Too much too soon would probably assist in it twisting.

Chris and Rudy, I have a Morse cable for my throttle, but I would still prefer having the inner cable doing the actual work. I was thinkink that one small pulley at the cable-attach bolt on the lower unit would do it. Of course the cable-end would have to be anchored somewhere other than the moveable lever.

[Caribean_gyro]

Ken do you engange and hold it there? Or you engage release enage, release rev up and continued?

I noticed in hy hydraulic system I have to do this if not the load the the pump is too much and it slow down the time to get at 100 RPM. But if I go slowly in and out like 3 times I get faster spin up time. my max is 120 with 2,000 rpm and my max rpm is 2700.

ChuckP

[KenSandyEggo]

Chuck, I kind of engage about halfway and/or engage/release a couple times until she reaches about 50 rrpm, but it gets there very quickly now.

Andre, once I get it set, I'll see if my buddy can shoot a video and me go crazy trying to post it somehow.

[rehler]

Ken,

Can you figure a way to make your lever longer. I changed mine for about 1" (stock Wunderlich) to 10" long (see photo). The force applied to the clutch (in your case) would be 10 times as much. This makes it very easy to operate and takes very little squeeze pressure.

Even if you could only make it twice as long it would still be twice as much pressure at the clutch.

[KenSandyEggo]

Hmmmmmmmmm.

[KenSandyEggo]

I tried something different today. I went and bought a longer inner-cable for my prerotator and replaced the old one inside the outer-cable. I attached one end to my Harley lever on my stick and Mickey Moused a bracket at the other end. I used a part from the old RAF axel. This locked the end of the cable in the bracket instead of to the clutch-engagement arm.

I kept getting a mushy feeling and I kept tightening up the cable at the clutch end. I'd get it snug and then when I engaged it, it would be sloppy. Finally, the cable came all the way out from the Harley handle. It has a barrel-type connector that squeezes the cable. I guess with all the pressure for prerotating, it was too much and began slipping out. I need to put a Nicropress on it tomorrow to secure it in the handle and start over again.

Here are 2 pics of what I was trying. Instead of the cable-housing pushing against the arm, I wanted the inner-cable to actually be pulling the arm into position, which means a 180 turn of the cable. I just ran the cable around the large bolt on top of the lower unit and back to the arm. If I get favorable results, I'll make a good bracket for the cable-end and install some sort of spool or pulley to the bolt and line everything up. This rough test should at least let me know if it's going to work any better. I think it will, but won't know until I secure the cable in the stick-lever. I left the excess cable wrapped around the bracket for the time being to have some extra to work with. The cable is slack looking, because I took the pics after the cable let loose from the Harley handle.