Jekyll 60 elevator pushrod bushing???
 

Could someone show or explain exactly how Chip Hyde designed this elevator pushrod bushing at the tail end of the aircraft?

It seems as if a brass sleeve is glued onto the end of a pushrod. I think it is slid into another brass sleeve that is secured into the tail end of the airplane. The brass sleeve is inserted into a sleeve at the tail end of the airplane and slides back and forth inside this sleeve.

Is this correct? What materials are used in this bushing assembly?

I stole this picture in another thread from Scott Anderson (PatternPilot) with Performance Model Aviation. I hope this is okay.

RE: Jekyll 60 elevator pushrod bushing???
 

Your thinking is correct. I don't remember mine using brass tubes, but any two tubes that fit slop free yet smoothly will work. It makes for an amazing tight pushrod setup.

RE: Jekyll 60 elevator pushrod bushing???
 

Brian,

I think that several classics of the late 80's used this approach to supporting the elevator pushrod. I have to plans of Kristensen's Summit 3 and Piorun's Eclipse and both of them show the exact same setup as the Jekyll. They probably all just copied one another or the molding companies drew them into their "2-view" plans. It is a clever idea to embed the shaft into the tail post.

David.

RE: Jekyll 60 elevator pushrod bushing???
 

What material is commonly used? In my mind, I am thinking that brass or alluminum might be heavy. Would a person look for nylon or plastic?

For some reason, I am thinking that brass against brass or alluminum could be a problem and pit, then bind, if debris entered the assembly at all. Was this ever an issue with this design?

I am seriously considering this approach to another build I am currently finishing. This would solve the geometry problems I've been wrapping my brain around.

I've been modeling for almost 18 years and I have never run across this set-up before. (Probably because I am just entering this avenue of aircraft recently!)

I love the fact that I am learning new ways to think things through!

Brian

RE: Jekyll 60 elevator pushrod bushing???
 

Brian,

the setup is simple enough. Basically you use a FG arrow shaft such as those from Dave Brown which have been around since he used them on his Tipo's and Illusions. The forked steel pushrods that go to the elevators are bent and attached to the shaft where appropriate. They are then bound to the shaft with some nylon or kevlar string and epoxy or JB weld. The rear of the shaft is cut to length so that when the elevators are in full up deflection, the end of the shaft is shy of hitting the tail post. The shaft itself is supported in the rear by a short length of metal tube that is embedded into the balsa tail post. The section is quite short since the shaft only moves back and forth a small amount. Provided the outer alum tube is short enough, weight and friction are not an issue.

The moment I saw that, I figured that was the way to go since typically the shafts are not supported by anything other than the servo wheel and the elevator control horns. The nince thing about centering the shaft in the rear with the above technique is that it helps to produce a more linear movement along the fuse centerline resulting in more uniform elevator deflections on both sides of the stab. This in turn allows you to be less critical about the location or orientation of installation of the elevator servo. I often place the elevator servo on it's side actuating on the fuse centerline which avoids lateral movement of the pushrod due to the rotation of the servo arm. Using the above approach allows you to more safely install the servo in a conventional upright fashion since the actuation in the rear is held on the fuse centerline by the metal section.

David.

RE: Jekyll 60 elevator pushrod bushing???
 

Guys when I get home next week, I will look at the instruction books for the building of the pushrod and scan it and post it.. I should be home mid week.

This system works great.


scott

RE: Jekyll 60 elevator pushrod bushing???
 

I found this setup to be less stable than other methods. Heavier as well. Much harder to install.

I prefer to run a normal Y push rod with bushings where the push rods exit the fuse. This approach keeps the push rod centered in the plane and imparts the exact movement to the Elevators without any side to side or up and down flexing. I used short piece of inner and outer Ny rod as the bearings. The outer is glued to the fuse side, the inner is glued to the push rod. Simple, cheap and light, easy to install even on an airplane that's fully built. I've fixed many airplane tracking problems with this method, even those with the afore mentioned push rod set up. Think of it as a early version of the Deps setup.

Tim

RE: Jekyll 60 elevator pushrod bushing???
 

Thanks Scott.

Brian

RE: Jekyll 60 elevator pushrod bushing???
 

mastertech that is the exact system I used on my contest planes in the 70's for rudder and elev and you are correct it works very well (the key is glue the bearing tube to the fuse so it cant move). I will be trying the Dual Elevator System from Central Hobbies on one of my Phoenix 7s.

RE: Jekyll 60 elevator pushrod bushing???
 

I've never quite understood all the mystique there is about the "DEPS" system. Not that I'm putting it down, on the contrary, but aren't we really talking about a couple of CF pushrods in sleeves bound together. I don't understand what is so specialized about it.

I guess there are a few different ways to skin the cat.

David.

RE: Jekyll 60 elevator pushrod bushing???
 

David,

Deps is supper light and hardly any trim change , the lightness is the biggest key..

Back to the push rod in thread.. the bearing as such and the sleeve is mounted in the vertical tail post to keep it in line and will not let it move side to side..

I'm still in the north and should be home mid week and will get a set of plans and scan it and post it and the instructions.

Scott

RE: Jekyll 60 elevator pushrod bushing???
 

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RE: Jekyll 60 elevator pushrod bushing???
 

The pushrod in this thread will allow the elev control rods to move and cause elev tracking to change.

Tim

RE: Jekyll 60 elevator pushrod bushing???
 

I disagree completely. The bushing at the tail will maintain the pushrod shaft through any high G maneuver, as is it's intended purpose. Remove the pushrod bushing at the tail, and this will allow for flex.

I have always used the method without the bushing. Honestly, I do not fly well enough to tell if there is actually any flex or not. The engineering is sound, regarding the bushing method.

I do not have any doubts this bushing method is foolproof- so long as it gets properly installed.

And if I am wrong, then it is my price I am willing to pay.

Brian

RE: Jekyll 60 elevator pushrod bushing???
 

I saw Chip using 2 small servos mounted on the side of the fuse....so that's what I did on my Jekyll.
It worked well and was super easy...and I didnt have a problem with the c/g.
Today I would do the same thing except I would use one of those 4 wire extensions for both servos.....saves the weight of 2 heavy duty wires.

RE: Jekyll 60 elevator pushrod bushing???
 

Not so!! I've installed every style pushrod and even invented a couple new ways myself over the many years of doing this and I weighed almost every one. The dual elevator carbon rods are practically the same weight as twin 3421's in the stab, believe it or not.

The lightest by a wide margin is pull-pull kevlar cables. Compare around 1/2 ounce (pull-pull) with about 2 ounces for twin push rods, assuming and excluding the same servo in the fuse. The single push rod with two rods is heavier than these 3 methods. The heaviest is the MK belcrank ...... Why this silly thing EVER became popular is beyond me.

Don't forget there's weight in the support ladder this twin carbon rod set-up needs. The teflon tubes should be changed to thin walled PE. Teflon is about the densest plastic we have. PE is one of the least dense. Slipperiness is practically identical. After all, poly-tetrafluoro-ethylene (teflon) is first and foremost polyethylene (PE)

And BTW, as memory serves, the single pushrod with twin rods with the aft support was first observed in Ivan Kristensen models in the early 80's. But it may have been Ron Chidgey that actually invented it

RE: Jekyll 60 elevator pushrod bushing???
 

Matt,

These are interesting points.

I think the MK bellcrank became popular because it allowed classic pattern ships to use one servo and accomplish essentially the same thing that dual elevator servos in the fuse rear or in the stab do. On the other hand, DEPS seems like an alternative when building a wood fuse but not so tangible with classic glass fuses.

Tim seems to think that the tail post arrow shaft positional locking causes elevator differential. It seems to me that the only way that this can occur is if the steel elevator rods themselves flex, or, if the positional locking of the shaft causes the elevators to bow it upon heavy loads. I know that a great number of forked arrow shaft pushrods are merely supported by the servo in the fuse. In time, people like Dick Hanson, started to show a support system for the servo end pushrod length to avoid the servo from carrying the weight of the pushrod at that end.

While heavy, perhaps the use of the tail post bearing in combination with either 4-40 elevator rods or fuse exit supported 2-56 rods might accomplish the best zero slop setup for classic glass fuses.

Any thoughts?

David.

P.S. Tim, what is your thinking behind your comments.

RE: Jekyll 60 elevator pushrod bushing???
 

My observations,

On the single push rod Y support only at the rear will allow the metal rods to twist and bow between where they join the push rod and the control horn, this is why most used 4-40 rods to try and solve this and also adds weight to the rear of the fuse. Also once the aft support tube is in it must be perfectly aligned with the servo or binding occurs, this can also happen in high G situations. Easy to change a servo.

The shorter Y with the bearings in the fuse sides is lighter and places the bearing surface much wider and therefore more stable. Easy to change a servo.

I do like the deps system and if building a wood Fuse is the one I'd most likely use. It is a major PITA to get true in a built fuse. It is also fussy to get right. Changing a servo is cake.

The best overall system for stiffness is twin servos in the tail, only draw back is that much weight that far back and the fact you have to re trim the elevators if you have to change a servo. This system while a PITA to change a servo has saved me one plane so far when one elev servo died.

I've used the pull-pull on elev and while it is the lightest, it's far fussier to setup and can change as time goes by. Easy to change a servo if need be. Not one I'd ever use again.

Twin push rods using twin servos at the front is easy to install but redundant. Heavy as well.

The MK bell crank is not even a player in my book, this syetm has the most slop of any system in my exp.

All in all every system has it's plus and minus. Pick what works for you.

RE: Jekyll 60 elevator pushrod bushing???
 

My two cents:

My best overall system IMO is the single pushrod and single lever.

Servo’s can experience a lot of vibration in the tail. I never did have a servo of the elevator failed as far as I remember. (Old School!)
Second point is, drag of all the levers, links and iron works visible on the tail, impressive but a source of drag and only commercial interesting.

Last profit, both elevator halves are always exactly synchronized and that’s important for me.
I did show a picture with 2,2 kg (cilindrical piece of steel) hanged on the TE of the elevators of my plane and the position left and right is still symmetrical.

The plane you are talking about is an ideal example to use a single lever system, see my drawing.

Cees

RE: Jekyll 60 elevator pushrod bushing???
 

I agree on the Y with bearings through the fuse being the best overall. But the twin servos in the tail are the stiffest as far as linkage goes.

The one I had fail was on a YS powered bird. Electrics don't have that vibration. When I had that happen on my YS powered ship I replaced the twin servos with a Y push rod and bearings on the push rods where they exit the fuse. Rock solid system.

Tim

RE: Jekyll 60 elevator pushrod bushing???
 

Mastertech.
I do show a single lever single pushrod system, the system has nothing to do with any Y with bearings. People often do have a surge to make things impressive and needless complicated. We are not making a steam engines.
Because you did make a summery I did show the system because it is forgotten. The principle of this system is more than 50 years old and used by pilots in the period they also were engineer, applied in the most famous classic pattern planes of the USA. Astro Hog, Smog Hog, Orion , Taurus etc.
Only challenge is, you have to make the system yourself, but when made it is the best system you can have. Stiffness of the (wood of the) elevator halves is a problem and not this system. Do a test with your own plane and add a weight with the use of strong tape on the TE of the elevator halves generating a total torque of 8,8 kgf cm = 7,6 pound force inch total and check deformation left and right. When you see a difference the plane fails in contruction and during flight IMO.

I did not tell another pro of this system.
The single main pivot bearing of the pushrod is encapsulated in the fuselage, protected against rainwater and dust just as the crankpin bearing is protected in the crankcase of the glow engine. When made with the right plain bearing material and dimensions this system holds its accuracy for many many hundreds of flights.
Cees

RE: Jekyll 60 elevator pushrod bushing???
 

Here is another solution for keeping the elevator pushrods aligned. I’ve been using the nylon exit guides for decades and they do a great job. The flat angle that the metal pushrods pass through the guides keeps the side play under control and the back end of the main push rod centered. Works well on a single rod rudder push rod too.

RE: Jekyll 60 elevator pushrod bushing???
 

Sorry, I miss understood your response. I think I know of what you're talking about. Yes that was old school for sure, seemed to work well.

RE: Jekyll 60 elevator pushrod bushing???
 

Mastertech,

No problem, I am the historyprotector so we do not forget they did design for us.
You cannot post a message in classic pattern flying and forget the past, then we send you back to RC pattern flying.

Cees

RE: Jekyll 60 elevator pushrod bushing???
 

Cees,

the single center actuated system where the elevator halves are joined (CL flap style) is an elegant solution in some cases. This of course, is for those who desire no independent trim adjustment.

The main problem I see with this system though is that with glass fuses, maintenance is basically non-existent. Because the installation of this system requires you to first pass the joined elevators through the stab opening, then link up and finally followed by the stab itself, once you lock the stab in position there is no access to the linkage. I suppose one can argue that if done properly one needs no access to the linkage but if for whatever reason you did - you would find yourself in one of those [:-] situations - if you know what I mean.

For wood fuses, it would be simple enough to build in a maintenance hatch as is done on several scale models using this system.

David.