Stick Shake

[David Bliss]

Side to Side Stick Shake

Side to Side Stick Shake

Either I missed it or there was no mention of the cause and or solution for Side to Side Stick Shake. My gyrobee has just presented me with this situation. the blades have been checked and are in string. i will be videoing the rotor disk tomarrow to check for tip track. any advise will be appreciated.

 

[down under]

David, check the teeter bushes - bearings as a possible cause.

 

[CLS447]

Gerg, It's is nice to have an assistant, but you need to share some photos of the assistant, in & around the gyro.

Thanks

 

[NoWingsAttached]

Well...all ya gotta do is ask, Chris.

 

[NoWingsAttached]

OK. I'm gonna start a new thread for fun pictures. It's gonna be (inspired by this thread) "Good Stick Shake"

Will anyone be offended?

 

[CLS447]

Gerg, WOW !!!!...... Thanks for sharing !

Now please tell me where you find them. Is she a local girl ?

Oh, & by the way.......the gyro looks real good , too !

 

[NoWingsAttached]

I live out in the boonies. All the females here are too young, too old, or married. I went to Match.com. and met her. This gal owns a Kitchen cabinet and granite counter top shop about an hour away up in Marietta.

 

[CLS447]

Well, good for you ! Are you gonna get a new kitchen, now ?

Side note.....when I was a Class 3 gun dealer, I would order these direct from the factory, in Marietta. My cost was $318 for the gun & they would throw in a suppressor(silencer) for an extra 100 bucks ! I sold quite a few !

Look what they are bringing NOW !!!! They ain't THAT good !

http://www.tacticalinc.com/cobray-m....html?osCsid=469990c208c1b4aa19cb36f9494e97c9

 

[NoWingsAttached]

wow, 5k? A bit rich for my blood..I gotta save for retirement after my 401k disppeared. The ATL detective we have Thanksgiving dinner with has already been elected as the "Supplier" for the dinner club of full auto if the need arises, LOL. He a has a nice AK47, some other stuff.

 

[Mike Schallmann]

Well I can see that htis thread has been hijacked to hell and back!

 

[NoWingsAttached]

ok. BACK to the original design of the damper then.

I seem to recall we were talking about this:
Advancing blade loads the hub bar more, then as it becomes the retreating blade, it unloads, and SPRINGS back to a less loaded coefficient working against the hub bar and the opposite blade. As this occurs we experience a twice per rev stick shake, as each of the 2 blades goes through this cycle per rotation.

The only answer to reducing this springy loading and unloading against the hub bar is to beef it up outside the towers. Like the difference between using a 2x4 floor joist, jumping up and down on it, and using a 2x8 floor joist and jumping up and down on it. Both will take the stress, but the 2x4 is too damn springy, and is a terribly insufficient piece of lumber to use as a floor joist.

That being said, I can't see why you would need to bend the dampening bars at all. Kinda defeats the purpose, as they will not be as efficient in their application.

I can't see where solid, heavier round stock would be any better than a hollow tube. Ever look at a steel building with trusses made of top and bottom girders tied together by triangulated cross ties? Same deal. The middle does absolutely nothing. It is the distance between top and bottom that determines stiffness.

Porsche used round torsion bar suspension in the 911 and 914 cars. We gun-drilled em to lighten em up when we built our track mods. Later, you could buy em that way from the parts shops. Of course, that is torsional, around the radius, and this app is longitude, along the length, but it still works in a similar way.

BUT - the machined coning angle of the hub bar makes it very difficult to built a straight stiffener, so...bend it to match the angle of the hub bar, right?

I think I understand how this works. If I am wrong, please set me straight. I want to try and make one of these for my AC. IT is a fantastic mod in my worthless opinion. I have heard about these from a few people, but couldn't picture it in my mind. This is a big help.

I can't see much need for it on the little bitty 1-foot hub bars, on a light single place, but, MAN, on a huge tandem with a 4-foot hub bar? Abso-frikkin-lutely man!.

 

[down under]

A couple of thoughts for you NoWings. If you are using DWs the hubbar may be stiffer than the blades so the stiffening rods would do very little. Worth checking on.

Also when you are flying next try a couple of manoeuvers to test for shake. First a hard banking left turn. The stick may hammer a bit.
Next try a nose over and right roll, just a bit of forward stick plus some right stick. Should be no shake on this one.
I think you will find the shake is a kick from the rear left.
If both these happen then the blade tips are pulling to the front or front right of the machine, not to the rear as would be the case if drag and resonance are causing the shake.

 

[Mike Schallmann]

Had I not put in the bend it would have been impossible to put in the teeter bolt. Also I had the solid stock on hand -tubes would probably work. This mod is most effective on HEAVY blades with a long thin hubbar. It would have little effect on DW's as they are light blades. Also the Hubbar dosent need to be rock solid (like a McCutchen) it only needs to be stiff enough to alter its resonance charecteristics to a point that is well above the operating Rotor RPM range --in my case this is above 420 RPM --This allows high altitude flight as my regular RPM is about 350/360--at my normal cruise altitude of 2500-4000 ft MSL

In retrospect I just reread CB's post (#21). I also reviewed some of my notes. On several occasions I did achieve near Zero airspeed in a verticle descent and noted that my stick shake was significantly less. This factor along with several other comments by CB over the years led me on the path to stiffening the hubbar--In short this mod works for me and that is ALL I really care about. If youve got stick shake issues and you have tried ALL other remedies -give this a try --it may work for you! If not your only out a few bucks and a little time --one thing for sure it wont HARM you or degrade performance in any way--

 

[CLS447]

Another thing to discuss with stick shake is tower height.

How tall are your towers ?

Which hole in the block are you using ?

Have you experimented with this ?

A member here is trying everything on his tandem Air Command with EJ22. I think he needs taller towers & maybe a slider head ! He seems reluctant to spend his own money.

I want him to be happy so I can get my stuff back from him !

My SxS AC has flown with 28' SC blades & 28' DW blades......both flew with very little stick shake. I was starting to blame the tandem design. My teeter bolt height is 4 1/4" from bearing block to center of bolt hole. My SC blades were built for this height. I think I was using the middle hole on the DW block.

 

[Mike Schallmann]

IMHO The towers have squat to do with stick shake--the height of the tower is calculated to provide sufficient clearance to allow teetering action - PERIOD! -In my quest to solve my problem I made six sets of towers in a futile attempt to solve the problems. There was ABSOLUTELY no inprovement or difference in the amount of stick shake when different towers were installed. It was one of those good ideas that wasnt worth a damn!

 

[CLS447]

So Mike ....Undersling has no affect ? Interesting!

 

[Mike Schallmann]

You have totally missed the point-- I SAID "-the height of the tower is calculated to provide sufficient clearance to allow teetering action - PERIOD! "

I always thought ( in simplistic terms) that undersling was the distance between the rotorblades and the teeter bolt. Now using that definition my above statement is valid.

The height of the towers is determined by the length of the rotorblades ---the longer the blades ,the taller the teeter block ,the taller the towers. It REALLY is as simple as that--

Dont make this harder than it has to be--

 

[CLS447]

Mike , I am sorry....don't get mad at me !

What is the proper clearance for the blade teeter ?

I also thought that undersling is based on rotor blade loading & coning. The more coning , the more undersling ?

Are you using Dragon wings ? Which hole do you use for your teeter bolt ?

When you made the different height towers did you try different holes in your Dragon Wings ?

Thank You.

 

[Mike Schallmann]

Chris -Im not mad Im frustrated--I use Vortech Blades (see post # 20)

1.IIRC The "proper" clearance is to allow approx (+/- ) 10 degrees tilt movement --

2. Well sorta--you actually get about 5 degrees cone in SL flight -- increase "G" load it you get a little more --decrease "G" load and you get a little less--that is why you can never totally eliminate stick shake under ALL conditions. IMHO The best you can achieve is to eliminate it in straight and level flight

3.See post # 20

4. I dont fly d DW's --I tried them and didnt like them --on a lighter gyro they are probably OK --but on this lead sled I didnt like the feel of them--I know this is subjective -but that the way it is!

 

[NoWingsAttached]

Tracking Ills

Tracking Ills

I set up a camera and took high-speed, high-quality video of prerotation up to 150 RRPM, let the rotor coast down from there. At 3 - 4 seconds after releasing the prerotator, I got 5 good shots of the black-tipped rotor and the white-tipped rotor at the same spot in the frame, and found out the black rotor is tracking an inch or more higher than the white.

At just under 150 RRPM, these frames are about 0.20 seconds apart, four frames. I had to keep playing with the Windows Movie maker to get the "in-between" frames, as I clicked on the button it only wanted to give me frame spacing of .07 seconds. After I chopped the video into a smaller piece, I was able to get the slider to produce frames just 0.03 - 0.04 seconds apart. This worked REALLY well.

I used Micrographix Picture Publisher (c1996 - 12 YEARS OLD!!!) to justapose the images, and blended to about 57% to get both blades to shade about the same density. IT is difficult to tell here which is tipped with black electrical tape, and which one has the white super-reflective tape, but I can tell in a better grain, higher pixel original.

I painted the hub bar on one side to tell which is which also. GLAD i did, or I would have to do this routine again - I peeled off the tape before I went flying again right after this was done!