206 RRPM....for awhile

[KenSandyEggo]

I got the hydraulic activator bled properly with my buddy Reis Evans assisting....actually, he did most of the work because he knew what he was doing. The $52 piece-of-crap suction pump sat on the floor after it wouldn't work properly and we used the handy oil squirt-can. Put lock nuts on the activator bolt as it started slipping through the pre-drilled hole without them. Pulled her outside and started her up and let the engine warm up a little. I pulled the handle on the stick and that thing grabbed like it suddenly welded the clutch-face to the plate. I let go and began easing her in, but it takes a light touch (and some more practice) to get her going without lugging it and twisting the mast. I finally locked it in around 75 rrpm and started adding power as needed. Got up to 206 at 2000 engine rpm and stayed there.

After I stopped, Reis told me that he thought the mast was twisting too much and to let him do it so I could watch. Weeeeel, Reis didn't have the feel of it and locked it in too soon and the mast twisted some and pulled the lower end of the prerotator cable out of it's metal sheath. The inner cable wound into a ball and then it sprayed grease all over the engine, prop and tail.

That was one of my ideas that didn't work too well. Remember, I had my cable shortened as much as possible to eliminate as much bend and friction as I could? If it were a couple inches longer, it would have been O.K. Reis suggested that the upper mast (cheek plates) be strengthened to counteract all the torque. We can install more aluminum squares, or as Reis suggested, fill the space with oak as the lower mast is. The options are to fill in the existing spaces between the aluminum channels or take them out and use one solid piece of wood. It would take a little ingenuity at the bottom, as the cheek plates spread out to about 2.25 inches to fit around the lower mast. Some aluminum wedges would probably do the trick. The rest is 2 inches, so it would have to be tapered at the bottom 2 or 3 inches, probably with the wedges. Adding doublers to the cheek plates was another idea, but Reis thought the wood would work best.

Below are some pictures of the event. That's Reis (the big guy) and my friend Pat that I used to share an Ercoupe and hangar with. So anyway, everything worked great....until it broke. Back to the drawing board, but we're getting close.

I had a brainstorm on the way home in my car for a prerotator system using the best features of a cable drive and solid-shaft drive with no universal joints. I have to look up some components to see if they're affordable, like when did that ever stop me before? This will be great if it's doable, and I don't see why not. It'll eliminate the drawbacks of the cable system and the solid-shaft system. Igor! Where's my sandwich?

 

[KenSandyEggo]

Additionally, I forgot to tell Reis to undo the gust lock, which keeps the stick all the way forward and the prerotator cable as taut as it can be. If the stick were moved back, there probably would have been enough slack to prevent the pullout. With the stick all the way forward, there is no slack at all in the cable.

I'm extremely lucky that the inner cable didn't zoom into the prop. That would have really ruined my day.

 

[scott heger]

Ken, why do you want to pre-rotate so fast? Seems like you are going to alot of time and expense for a guy that flys out of 5341 foot long airport runway. I flew on friday, and it was a dead calm wind day after the storm(which was unusual). I rarely prerotate to more than 90-100 RRPM so the blades don't bump, and let the wind do the rest. No wind takeoff was about 500-600 feet. Why beat the prerotator system up by going much faster. My gyro's 5 years old, and have yet to replace a moving part other than a 50 cent brass bushing that wore. A soft engagement will save the system, and maybe you could rig a partial bypass to it. I am sure you have thought about all these things already. Just trying to make a gyro play helicopter on the ground always seems strange to me.

Scott Heger, Laguna Niguel, Ca N86SH

 

[KenSandyEggo]

I just have these thoughts of landing at some small dirt strips or fields in the mountains and being able to get out. Will I ever do it? Who knows, but I just enjoy monkeying with stuff like this. I want to see how quickly I can break ground by being able to prerotate above 200. Make sense?........I didn't think so. I've been meaning to take some photos of these places. There are even a few model airplane strips I could pop into. They always wave to me when I fly by, so it must be O.K. with them.

 

[scott heger]

Kenny, I think what those people are waving at you are guns!!! Since I know you always fly into good airports....Remember that those sandy dirt stips tend to chew up props badly if not really careful. That is what I would worry about. Given a chioce, I would find a nice county paved road to take back off from...I know , I know,...rules, etc.. But if you can see someone that close anyways , you shouldn't be taking off. There are plenty of good out of the way places to land without putting yourself in a short strip. Come up to Corona and practice some good (and legal) airport grass strip landings and takeoffs. I will challange you to some spot helipad landings there for a cold beverage. The only problem if you miss, you run into a 3,000 fuel truck. Not for the weak at heart, but I will still come to the (memorial)"service". Hey , what a guy I am, right? Get that thing running, and lets meet.


Scott Heger, Laguna Niguel, Ca N86SH

 

[CLS447]

Ken, sorry to hear about that but it seems that you definately got something going there! It's great coming up with good new ideas, why doesn't someone else do this stuff for us?

Where will you be getting your new cable? How is the flex shaft converted from round to square?

I know what you mean about the longer shaft friction, mine needs to be shortened also but hate to mess with the squared ends. I actually have to force my aluminum outer casing ends into the upper drive but I know my shaft is fully engaged then, but then you have the inner rubbing going on.

My AC high torque prerotator will get me to 200 but it is alot of stress on things, but it's just nice knowing that you can do it. I now settle for 150. My rubber drive wheel engages very well & is tuff to "feather". So it takes a beating. Starting those SC blades is like starting a freight train , but try to stop one!

 

[Jerseywing]

I may be wrong but I was taught that a longer shaft will handle torque better than a short shaft. Reduction gears were " folded" on each other to increase the length of the shaft to allow for better torque capabilities.

 

[Mike Hook]

Ken

Keep up the good work, I have been follwoing this thread closely. There is some of us out there that has to come in and out of short strips if we want to fly from this area.

Mike

 

[Harry_S.]

I agree with Heger...if plenty of good runway is available, you can monkey your rrpm up with no problem and it's easy on the equipment. I can get my rrpm up to 200 before I'm on the center line but, I take it slow and easy and reach centerline between 150 and 180 before I release the p/r and am airborne within 3-400 ft. This is on hard surface of course.

I also agree with Ken...I admire his vision, his tenacity, his seemingly *deep pockets*...as he strives to improve on the mechanics of his machine; for himself as well as his fellow gyronuts.

Personally, I like my machine as is; it serves my purpose, relative to recreation. Some improvements I think about, like a bigger engine, silky smooth ride, better prop, etc. would be nice but, I think in another 10-15 yrs. I'll hang it up anyway??


Cheers

 

[KenSandyEggo]

Got my new prerotator housing and cable yesterday and hooked it up while waiting for the trash truck to arrive to take the hangar trash away. Everything fit well and secure. We're almost there folks.

After the trash was hauled away I got her ready for a flight. At the run-up area, after all my preflight stuff, I started to prerotate. This time, I just tapped the handle slightly to get the blades moving, and kept doing that. It picks up speed very rapidly. I kept watching the top of the mast and there was no chattering or wobbling. The only thing that happens is the mast twists noticeably from all the torque and stays twisted. All that's at the top half of the mast are the cheek-plates, and now these appear pretty flimsy to me. Anyway, she easily got over 200 rrpm and as soon as I turned onto the runway, I was able to go full throttle and was off in the shortest run I've ever experienced. I don't have the number of feet layed out yet.

I have several ideas for stopping the cheek-plates from twisting. I already bought some components today to experiment with. It appears from hand-twisting the cheek-plates that the twist mainly comes about 3 inches up the plates. I bought some chunks of 2 by 4 inch by 1/8th thick aluminum channel today at a metal supply place. They have everything there. I had them cut one piece 5 inches in length and I'm going to place it and secure it between the plates at the very bottom. This may be enough to counter the torque and that'll be it. If not, the next step is to drill out the 3, 2 by 2inch existing braces between the cheek-plates and replace them from top to bottom with a 23.5 inch piece of 2 by 4 channel. This'll run from just below the rotorhead to just above the bottom, solid mast. I'll have to drill a couple holes for the radiator expansion-bottle mounting or maybe move it somewhere else.

Now, there's no guarantee that all this will work, as it may still twist at the very bottom, as the cheek-plates aren't really braced there to anything or to each other. There's a 5.5 inch gap between the bottom mast and the first channel insert that comes with the kit. I already have a design in my head for a brace that encompasses the cheek-plates on each side and then anchors to the top strut-bar on my gyro (AAI upgrade). The unmodified RAFs wouldn't have this top-piece. I'll use some channel to completely sandwich the sides of the plates (2 and 3/8 inches wide) and run the brace to the top-bar of the gyro, which is 2 inches wide. I'll use some doublers to thicken this part up to fit the 2 and 3/8 inch channel. I'll have to work on some sort of rubber grommets at some point in the brace, so that the top-mast can still flex forward and rearward with the "magic donut."

I also bought some steel plates that are 4" by 4" from the cut-off bin. They already have 4 holes drilled in the corners. If the first 5 inch insert works fairly well, I may use these plates as doublers for the bottoms of the cheek-plates, or later down the road. If I isolate the section that twists most, I may place them there. It appears to be near the bottom and that the 3 channel inserts do a pretty good job of keeping the rest of the cheek-plates aligned.

Here are some pics of today's monkeying around. One shows 205 rrpm at 1,900 rpm while prerotating, and the other one shows me in cruise at 3600 engine rpm and 72 m.p.h. indicated. I had a little more than 1/4 tank on board, actually between 1/4 and 1/2, but I thought that was pretty impressive, a 1,000 engine rpm drop to maintain the same speed as with the fixed-pitch prop, which is a great prop. The prerotating photo really blows up large when you click the enlarge button at the bottom right of the photo after you click on it the first time for some reason. Gives a good magnified view of my panel.

 

[KenSandyEggo]

Chris, I got my new cable from AAI. The ends of the outer cable look the same as Wunderlich's. I guess they grind the ends down to make them square.

 

[CLS447]

Thanks, Ken. Air Command seems to crush them square & then finish grind them also. I'm not real crazy about this. I wish there was a better way.

I am really happy for you with your new high speed prerotator!

I have a 4" rubber wheel hitting a 9" prop hub wheel. For me to get 200 RRPM my engine would have to be spinning at 3000 RPM's.

200 RRPM's at 1900 engine RPM's ! Wow that's some torque, no wonder the clutch plates slip !

 

[KenSandyEggo]

Chris, the pulley for the prerotator is smaller than the drive pulley, but I don't know by how much and what the actual ratio is. By the way, I see I have a Magellan GPS, not Garmin as I posted a couple days ago in the GPS thread.

 

[Harry_S.]

Ken:

I'm certainally no engineer but I wouldn't try to eliminate that initial *wobbiling* at the upper mast area. I think the enormous amount of torque on a 30 Ft. rotor at pre-rotation has to be dissipated somewhere and somehow. Maybe better at the upper mast than down on the airframe.

On my machine, I have a discernible *wobble* between 80-90 rrpm and then it disappears. I think the RAF design of the 2x2's between the cheek plates makes sense. If the 2x2's start cracking, you have a problem. That's better than a stiff mast. I check my 2x2's every pre-flight.

Does your AAI mod still have the 2x2's?

 

[lanichol]

The only thing that happens is the mast twists noticeably from all the torque and stays twisted. All that's at the top half of the mast are the cheek-plates, and now these appear pretty flimsy to me. Anyway, she easily got over 200 rrpm and as soon as I turned onto the runway, I was able to go full throttle and was off in the shortest run I've ever experienced. I don't have the number of feet layed out yet.

My-oh-my. To have such problems as a twisting mast.

At 200 rpms, has weight been taken off the wheels? Would this be an analogy to a soft field takeoff?

Great job on both the pre-rotor and the variable pitch prop!

What surprises me is the pre-rotator at 200 rpm has not been resolved on the RAF style gyros years ago.

Ken everytime you design a better mouse trap or write a journal entry, I end up waiting weeks or months for the final results.

For example, I am sure there is some fuel benefit to the variable pitch prop at cruise speed [comparable to OD in an automobile]. But now I have to wait for you to find some method to measure the fuel, and then fly 10s of hours to find the sweet spot.

Again Great job.

 

[KenSandyEggo]

I still have the wood-packed lower mast as supplied by RAF. The twisting of the cheek-plates concerns me more than dissipating the torque. The torque of a prop isn't dissipated by a wobbly engine......hey, that's all I could think of. Maybe some real engineers can pipe in here about this. When the rotorhead twists about 15 degrees to the right (per one witness), that seems more dangerous to me. I don't see where a solidly braced upper mast would be a detriment, but mine still does have the fore-aft movement of the rubber-bushing. Don't some of the other gyros have a solid upper-mast as opposed to twisty cheek-plates.....or not? Question: Once the rotor-head twists along with the cheek-plates as far as they're going to twist during prerotation, isn't all of the torque going to be taken up by the lower mast anyway?

Anyway, I removed the 3, 2 by 2 by 4 inch rectangular tubes supplied with the kit that are spaced within the cheek-plates today. WARNING. THE BOTTOM 2 HAD CRACKS IN THEM! ONE OF THEM HAD CRACKS AT 5 OF THE 8 CORNERS. You can't see the cracks when the tubes are in place. Most were sandwiched between the piece and the cheek-plates. Anyway, I installed a 23.5 by 2 by 4 inch rectangular piece of aluminum between the cheek-plates after drilling out the small riveted in-place ones. I redrilled all the rivet holes to 1/4" and replaced the rivets with nuts and bolts. The cheek-plates do not twist anymore, but by pushing very hard, I could get a little movement at the very bottom of the cheek-plates and at the top of the lower mast. Maybe this will absorb any undue torsional loads. I am making it a point to gently start my prerotation with my new hydraulic actuator. It got to late to try even a prerotation today. An unknown factor is whether stiffening up of the cheek-plates to lessen twisting will affect the ride. I'll try to take her around the pattern tomorrow if I have time after finishing up the expansion bottle reinstall. Have to be at work at 2:30 p.m. Grrrrr.

I have a fuel-flow gauge on order which should be here Monday. 3 pics are attached. One shows the piece I installed, one shows it partially installed and the last shows it in place, with one of the holes drilled for the radiator expansion "can."

 

[Jerseywing]

Be careful how stiff you make it... That energy needs to be dissipated somewhere. If you stiffen one place it'll just transfer that torque to another, maybe someplace that won't be as forgiving. Also the stiffer you get the mast the more vibration will be transmitted down to the rest of the airframe. Along with that can be the deterioration of parts that may be more sensitive to vibration. Let us know how you fare and when you do the first jump takeoff

 

[KenSandyEggo]

The torque from the cheek-plates is transferred to the lower mast which is solidly connected to the keel with massive cheek-plates and a ton of stainless steel rivets. This lower mast is also solidly imbedded with a piece of hardwood running the full length of the lower mast. So I'm guessing that's where it went anyway. Once the cheek-plates twisted to their maximum deflection, they stayed there as long as she was prerotating. One good thing, if I have it too stiff, I can always incrementally remove parts of the new cheek-plate stiffener I inserted. I'll get in a pattern flight this morning and see how she does.

 

[Harry_S.]

You da man, Ken.


But fly safe. I mean it!!!

 

[Brent_Brown]

He said wood