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.

[KenSandyEggo]

Second photo. I'm kind of thinking that eventually I'll wind up with the hydraulic line and slave to push the arm and find that's the best setup.

[mceagle]

Ken,
Technically there is no difference which way the cable works, all the actions and loads/forces are the same. The best way would be the most direct route for the cable, which I gather in your case was the origonal setup (no 180 degree bend).

[KenSandyEggo]

But Tim, the end of the inner cable is attached to a bolt on top of the lower unit. The cable doesn't actually pull the arm, the outer cable-housing does, and this is what I see as a weak point. This is the best I can explain it. Maybe someone else can explain it better than me. The inner cable can't pull into the outer housing because it's attached to the bolt. The outer cable-housing then slides along the inner cable instead and pushes against the arm. The end of the outer cable is attached to the moveable arm and pushes against it. The lever on the stick is pushing the outer-cable rearwards to apply pressure to the lever at the clutch. (Wish I could draw). The cable-end shown attached into my Mickey Mouse bracket, originally is screwed into the top of the moveable clutch-arm and there is no bracket for the cables. The inner-cable passes through the arm and is locked onto that big bolt.

With a 180 turn and the cable end fixed in place with a bracket, the inner cable is actually pulled into the cable-housing and pulls the clutch-lever. Clear as mud?

[Aussie_Paul]

It makes no difference Ken, pushing or pulling. Try this with the standard Raf set up.

Put a pulley on the "large bolt" and bring the cable back and attach it to the bolt that you used for your "mickey mouse" bracket. That will give you twice as much pull, but the handle will move twice as far.

Am I right Tim?

A number of Raf owners have done that. I think it was Lisa DeVries(sp) that had it on her gyro at Bensen Days 1999 when I was in the Raf camp!!!!

Aussie Paul.

[KenSandyEggo]

I guess I'm thick or something, Paul. Isn't it the outer cable pushing against the lever in the original setup? If so, doesn't the outer cable compress? It doesn't seem to me to be as strong as the inner cable pulling. I'm really getting P.O.-ed at the guy that's supposed to make my bracket for the hydraulic activation. I'll bug the heck out of him this coming week until he starts having nightmares about me.

[Harry_S.]

Curtiss Patton had that pulley set-up on his RAF that I flew in '97. I have pics of it around somewhere. I was thinking of setting mine that way, but after building mine per the factory set-up and flying it, I could see no need for the change.

I have no problem with getting around 200 from my P/R...dependent on what wind is available...and I try to keep the engine below 1700, but when I reach runway centerline and release the stick grip, I lose 30-40 rrpm before the eng. gets to 3500 on take-off roll.

I'm interested in what Ken comes up with as regards the main cable routing to the Bendix. I've replaced the inner cable 2 (two) times now because it has shredded...I think due to the "severe" bend. I'm tinkering with a slight change right now and will let you know how it goes. Yes, the cable has always been well greased...maybe too much grease??

[KenSandyEggo]

Harry, what frustrates me is that the RAF where the guy let me fly his Sportcopter blades a few years ago was able to get up to 200 on pre-rotate. What gets me is that the guy has no idea whatsover why he is able to. He never tinkered with anything and that's just the way it came out. He wasn't even a very careful builder and I had to show him some things to correct. I examined his system and it didn't look a whit different than mine. Grrrrr. Go 'figger.'

That's another frustration I have, Harry. I'm at a busy towered airfield, so I can't sit on the runway and start my prerotate. I have to do it in the runup area, and when the tower clears me for take-off, I better get my butt out there and go. This usually means losing some of the builtup speed on the rotor while I'm taxiing into position to take-off. I was dreaming of being able to get up to 200 and go to full throttle quickly and leap off the ground. If this happened, I would ask the tower to allow me to take off from the ramp or taxiway, like the helis. I can see me doing a 300 foot take-off roll on the apron. :eek:

[Aussie_Paul]

"I guess I'm thick or something, Paul. Isn't it the outer cable pushing against the lever in the original setup? If so, doesn't the outer cable compress?"

It doesn't matter which way Ken, both inner and outer have to carry the load.

Ken, When it comes to neatness, a flair for artistic work etc, I am thick!!!!

You are almost as bad with mechanics!!!!!!!!!!!! LOL :D To each their own :D

If I had a Raf I would fit the pulley idea in a couple of hours. ;) Well that would end up being a day, now wouldn't It? Does that mean I am thick when it comes to time management? Actually it does, I am afraid.

Another way to get leverage is as Ken R said. Extend the lever that the outer cable pushes up against, and the bolt that the inner cable attaches to. Just bolt a 1/4" thick piece of steel, approx 1 and a half" long and 1" wide, to the lever that the outer cable pushes up against. Wind out the bolt that the inner cable attaches to, and buy a longer one.

Actually I have a spare lever, so I will make one for a guy who has a Raf, and we can test it. I always wanted to make the mod, but I have never really had pre rotator problems with any of our Rafs, and the ones we did were fixed with the facing of the 3 pads.

Aussie "Thick in a lot of ways" Paul :eek:

[Aussie_Paul]

Ken, have you tried holding the pre rotator on as you taxy? You can keep the rrpm up that way particularly if there is a little wind. In a tightish situation I keep the pre rotator going almost until the nose comes up.

Aussie Paul.

[mceagle]

Ken,
The cable actuation system can be likened to a pair of scissors. It does not matter which side is "floating" and which side is "stationary", they will still cut the same with the same pressure. Some small disc brake units have the inner cable hooked to a lever on one puk and the outer cable hooked to a lever on the other, and they supply even pressure to both pads.
The potential pull measured at either the inner cable or the outer cable is the same.

[KenSandyEggo]

%$#@&!!*!!!

I hate when I type a post that rivals War and Peace and then somehow hit the backspace button and it all erases!

Here I go again. O.K., you Aussie nags, I get it now......finally. I went back to the original hookup as I couldn't get a solid stick-lever feel no matter what adjustments I made. I then went to the runup area for the X-runway several times to play around. I had the clutch a little too snug and the Bendix wouldn't completely disengage when I let go, so I had to loosen it up a little.

Eventually I was able to get into the 150s, 160s and even into the 170s a few times after some adjustments to the cable and big clutch-nut. When advancing the throttle, it really has to be done smoothly. Give it a little spurt and she starts slipping. I've gotten pretty good when that happens. I can hear it with a very slight engine rpm increase and the upper control-tubes start vibrating. I can feel it in the stick.

I believe the only barrier right now is getting just a little more pressure on the plates to keep them from slipping. The clutch facing and shorter prerotator-cable helps a lot, because I never saw over about 140 rrpm whenever I previously prerotated, and that was very rare. My usual was 110-130. I can't come up with anything better than the hydraulic actuating system that I hope to have to try out this coming week. Oh wait....I forgot. Bigger clutch areas would most likely help. Below is the template I'm using to have some bigger ones made. ;)

[mceagle]

Your proposed hydraulic setup may be the answer to your problems.
If not, there are better quality cables cables that compress or stretch a lot less than cheaper ones - should solve your problem. I had the same problem on a nose wheel brake at one stage so that when it was fully adjusted, it would not lock the wheel and felt spongy. When I changed it to a Honda Bike cable, it would lock the wheel with only about 1/2" movement at the lever, and it felt free and solid.

[Aussie_Paul]

Ken, I think that you should go bigger with the clutch plates!!!!!!!!!!!!!!!

We are ganging up on you now Ken!!!!!

Aussie Paul. :)

[TomCarlisle]

Get really sophistacated and use a proportional selonoid with a reostat on the handle and do it with electricity.

[KenSandyEggo]

Tom, I didn't have the verbiage down, but the thought of something electrical crossed my mind, but I don't have the knowledge to monkey with that. I also thought of a vernier control, but then we'd need 3 arms and hands. I also was trying to think of something that would lock the 2 plates together mechanically after they were spun up sufficiently with the clutch.....like a pin that would go through holes in both plates, but I can't think of how that could be accomplished because of the spinning. The pin would then be disengaged when ready to take off.

Tim, I was also looking at my bicycle brakes yesterday and was marveling at how efficiently they grab with a minimum of movement and no sponginess. The only thing is that they looked a little flimsy for what I'm working with, but maybe not. Oh wait. You said Honda. I did stop in at a Harley shop the other day, but all their cables are made to fit and they have to be ordered. It wasn't a dealer, just an independent shop. Because of all the time and expense I have in the hydraulic setup, I'm really anxious to give that a go.

[Harry_S.]

Ken: Was that picture taken before or after your clean-up for the hangar inspection? :D

[KenSandyEggo]

Harry, I hate to admit it, but after. I took 2 sacks of trash to the dumpster and you couldn't even tell. I am a crappy housekeeper. I feel like I'm wasting time when I clean the hangar, because I could be driving myself nuts with prerotators and the other stuff floating around in my head......or be flying. I was seriously thinking of calling a trash service to haul a lot of stuff to the dump for me. I have the molds for the stab I used to make on the floor and they weigh a ton and take up a lot of space. I'm not a pack rat, just sloppy when it comes to chores like that.

I have a nice little tool chest, but after I'm done using a tool, I just drop it in a box on the floor and continue working. Pretty soon all my tools are in 2 boxes on the floor. I get inspired one day and put them all back in the tool box and then the ritual starts all over again. :o

[Harry_S.]

I know where you're coming from Ken. Just joshin' ya.


Cheers