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Author Topic: Sullivan Flexible Pushrods?  (Read 3991 times)

Offline Avaiojet

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Sullivan Flexible Pushrods?
« on: February 16, 2017, 07:31:24 AM »
Flexible Pushrods.

 I was wondering if anyone has ever used Sullivan Flexible Pushrods for an application?

 They are flexible and can go around corners with a radius. Flexible tube in a tube.

 Fixed in place properly, there is no play.

 I've only used them in R/C.

 Has anyone ever used them in CL with success?

 Thanks in advance.

 Charles

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Offline Mark Scarborough

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Re: Sullivan Flexible Pushrods?
« Reply #1 on: February 16, 2017, 08:35:58 AM »
no not for CL and they are not a good fit, way to much friction and without a servo to center, they would lack repeatablilty In my experience

also they change length with temperature, I found out with my RC stuff, they are not good at holding trim  because the length changes,, so the short answer, use them if you want, but not if you are serious about flying something with them in it.
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Offline john e. holliday

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Re: Sullivan Flexible Pushrods?
« Reply #2 on: February 16, 2017, 09:46:05 AM »
For just plain sport flying they will work.  For the changes in length because of temp changes we used a bell crank type device mid way between wing and elevator. H^^
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Offline Trostle

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Re: Sullivan Flexible Pushrods?
« Reply #3 on: February 16, 2017, 12:41:32 PM »
Hi Charles,

I have not used the flexible pushrods for CL stunt.  I do not think they would give the feel and response of a "hard connection" set up provided by arrow shaft or music wire pushrods typically used on the CLPA models.

However, I have found that the flexible pushrods with the cable cores have been useful for a number of applications used on my small CL profile scale models built to the Tucson rules for 1/2A multi-engine profile scale.  It certainly simplified getting the throttle connection on my Ju 88/Bf 109 Mistel model to get the throttle hooked up to the top mounted Bf 109.  Also, saved a lot of linkage problems getting the elevator control to the high location of the stabilizer/elevators on the Westland Whirlwind.  I have used the flexible pushrods on any number of other scale models, both for throttle control as well as elevator control, simply for the simplification they offer for certain situations.  These scale applications do not require the response as well as the "feel sensitivity" and "temperature insensitivity" that CL stunt models need.

On the Mistel, the flexible pushrod is connected to the transfer bellcrank that controls the Ju 88 engines from the 3-line Roberts bellcrank.  That flexible pushrod then was imbedded in one of the support braces between the two airplanes and then on to the throttle of the Bf 109.  (All of that was done in relatively constrained areas.)  The Whirlwind was built to the St Louis Multi-Engine Scale rules which require the control system to be exposed.  The photo does not show but a circular bellcrank was on the bottom of the wing and the flexible pushrod was imbedded but exposed on the left side of the fuselage and could be seen all the way to the elevator horn.

Keith
« Last Edit: February 19, 2017, 01:25:44 PM by Trostle »
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Offline Target

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Re: Sullivan Flexible Pushrods?
« Reply #4 on: February 18, 2017, 04:42:40 PM »
From my RC sailplane experience, I would (generally) avoid these.
I would (for a straight run) much prefer a .060" CF rod in an etched Teflon tube housing.
The ones that you showed usually have "hysteresis" problems, a fancy way of saying slop between the inner and outer parts.
The first thing that happens with that on a curved run is that the inner moves laterally in the housing at the bend, before any movement occurs at the end of the rod where you want it.
On a servo driven application, you can alleviate that a bit by spring loading the surface with a light simple music wire spring. That takes the free play out of the system.

I have also use the Sullivan housings with the .032 or .062 stranded cable. These work OK, but are heavy, and since in an RC glider application are normally going to the tail, that is bad (extra weight behind the CG on a long moment arm).
That is where the etched Teflon tube, fully secured, and the solid carbon Fiber rods come into play.
Additionally, the larger sizes of etched Teflon tube are basically "one size fits all" since you can warm them, and stretch them out, reducing the ID to be just a few thousandth's over the CF rod, all but eliminating "hysteresis" in that system.
Yes, I really am a glider geek.
Some of it does have applications for U/C though. All of the "new" CF tubular push rods with ends are pretty commonplace in the glider community, for instance. MPJet sells a boat-load of different sized threaded ends, and ball linkages, for example. So many sizes and options there.

If I were to use this type of system, it would be supported full length alongside a profile fuse, where it would be easily replaced if you didn't like the results.
I like the out of the box thinking, though!

R,
Chris
« Last Edit: February 19, 2017, 08:56:45 AM by Chris Behm »
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Offline Steve Helmick

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Re: Sullivan Flexible Pushrods?
« Reply #5 on: February 18, 2017, 08:49:00 PM »
We had a club member who built a test model using the Sullivan Flexible Pushrods. It was a failure, so there you have another answer.  D>K Steve
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Online Dan McEntee

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Re: Sullivan Flexible Pushrods?
« Reply #6 on: February 19, 2017, 12:05:19 AM »
   These have been around for about 40 years. If they were an acceptable option, don't you think you would have seen them used in some ones construction article or in a major kit offering by now? If they worked like we need, people would be using them. Sometimes they create more problems than the one or two they were intended to solve. I'm like Chris, my experience with them came from 15 years of R/C sailplane competition. There were some designs where you had to use them. The worst ones were the Golden Rods, as they tended to really expand or contract as it has already been mentioned. When the cable push rods came out, then you had to be careful with running your receiver antennae wire to avoid possible interference and you couldn't have any metal chattering against each other as that may cause problems. As higher performance sailplanes came about, then newer more precise pushrods had to be developed. Not so much for thermaling, but for the speeds these models hit when pushing to the next thermal or streaking back to the spot landing circle. Control surface flutter could cause you to loose an airplane. FAI competition called for speed and distance tasks, and you were talking speeds of 100 miles an hour or more. Wood, paper and iron on coverings were out, and composite structures were necessary. That was about the time I got into stunt. I couldn't afford the 500 dollars air frames and the 600 dollar radios it took to control them!
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Offline Trostle

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Re: Sullivan Flexible Pushrods?
« Reply #7 on: February 19, 2017, 11:21:18 AM »
Duplicate post removed.
« Last Edit: February 19, 2017, 01:22:29 PM by Trostle »
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Offline Avaiojet

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Re: Sullivan Flexible Pushrods?
« Reply #8 on: February 25, 2017, 07:08:47 AM »
Gentlemen,

Thank you for the great suggestions and for the kind replies. I've been giving plenty of thought to your input.

Keith,

You always seem to come up with class act models and interesting projects.  H^^  Be nice to see more of that.

You reminded me of something, so I went digging through my old R/C stuff and found two brass cables that I have inside the yellow inserts. I have use them for retracts but the ones I found haven't been cut or used.

I'll put up a photo, (charging the camera battery at the moment,) and you could possibly let me know if you are referring to this application used on your above model.

Thanks again guys.

Charles 
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Offline Trostle

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Re: Sullivan Flexible Pushrods?
« Reply #9 on: February 25, 2017, 09:00:29 AM »
Quote from: Avaiojet on February 25, 2017, 07:08:47 AM

(Clip)

found two brass cables that I have inside the yellow inserts.

(Clip)

Charles 

The only ones I have used on these 1/2 A models are the ones with brass cables in the yellow tubes.  As mentioned before, I would not use any of these as a substitute for music wire or carbon shafts for pushrods on any kind of stunt ship.

Keith
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Offline Avaiojet

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Re: Sullivan Flexible Pushrods?
« Reply #10 on: February 25, 2017, 10:00:06 AM »
Quote from: Trostle on February 25, 2017, 09:00:29 AM
The only ones I have used on these 1/2 A models are the ones with brass cables in the yellow tubes.  As mentioned before, I would not use any of these as a substitute for music wire or carbon shafts for pushrods on any kind of stunt ship.

Keith

Keith,

Understandable and thanks for the comment.

I'll place the photo anyway and you'll see what it is.

The brass cable is thick and it slides well in the yellow tube. I'm not the only one that used these for retracts.

I was thinking of tossing the plastic tip for an upgrade and running two of these. One for each side of the elevator.

I really don't want to change the design.

Thanks again for the reply.

Charles

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Offline Avaiojet

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Re: Sullivan Flexible Pushrods?
« Reply #11 on: February 26, 2017, 02:37:33 PM »
Quote from: Motorman on February 26, 2017, 12:12:38 PM
I got one in a buy out deal and cut the yellow splined tubing into 3/4" pieces for lead out guides. I think I used the cable for a handle.

MM

MM,

Some guys would cut the yellow up into short pieces and space them inches apart over solid threaded rods then slip them into the red sleeve. Less resistance I guess?

I never did this. I always used Dave Brown arrow shafts like most of the guys flying pattern. I still have some hanging around.

Charles
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