View Full Version : Elevator to jackscrew cable and spring.

12-28-2005, 11:34 PM
I would like to know the purpose of the cable connecting the elevator horn and jackscrew and what the spring constant is?
Any help would be appreciated.

Dave Calkins
12-29-2005, 09:31 PM
Glenn, Hi. I'm surprised no one got back to you on this.

As far as "spring constant", if you will define what you mean, (I could guess) someone will probably give an answer.

As far as what the cable and spring connecting the jackscrew yoke to the 'up' side of the elevator horn: It would seem that the idea is that when nose-up pitch trim is given, the leading edge of the Stab goes down, and pulls on the cable. This pull is transferred to the 'up' side of the elevator horn, causing 'up' elevator to be given.

I'm sure that the short answer is something like: the cable and spring give 'up' elevator when 'up' pitch trim is selected

If the spring wasn't in there, you wouldn't be able to give any 'down' elevator.

Any one with a better story??? :drinking:

12-30-2005, 07:45 AM
You will like your plane alot better if its missing and you are planning on installing it. Generally boils down to lighter stick forces at at slow speeds. All the parts can be bought at univair.

12-30-2005, 10:33 AM
Interesting note:

With this cable installed on the j-5 it gives you a wider CG range. Anybody know why this is?

I - Model J5A (Army L-4F), Model J5A-80, Model J5B (Army L-4G) (cont'd)
C. G. Range
(+12.2) to (+21.0) or
(+9.6) to (+21.0) when elevator bungee per Piper Dwg. C-40 is installed.

Dave Calkins
12-30-2005, 04:31 PM
because with the 'bungee' you have more nose-up pitch trim authority, therefore, can deal with a more-forward CG.

12-30-2005, 10:19 PM
Hi Dave
The spring constant I am interested in is the spring rating in pounds or ounces per inch of extension. Or I guess knowing the wire diameter and spring coil diameter would work also. I would like to know what spring I need. The reason this all came up was I know someone who is building a cub , has not put that cable in unfortunately the fabric is on and retro fitting it would be a lot of work. I asked why he didn't put it on and his answer was he didn' think he needed it. I surmised that it would help reduce stick forces but was not sure so asked the question. The next question is how do you know how much to preload the spring when the stab is trimmed neutral while on the ground?

Steve Pierce
12-31-2005, 08:54 AM
You can buy the spring from Univair. I can measure the cable if you want. I have installed with the fabric on, a pain but doable.

12-31-2005, 12:17 PM
Thanks for the offer Steve. I'll have a good look at all my PA 18 drawings and see what they say. If I am stuck I'll get back to you on cable length. Any comment on how critical the cable length is? A slight change in pulley position and cable attachment point I imagine could change the effective cable length by an 1/8th" or so?

bob turner
12-31-2005, 02:50 PM
My experience with Super Cubs indicates that the spring /bungee on the elevator makes them harder to control in pitch. One that I fly regularly cannot be flown in the pattern without significant trim changes, flaps up to flaps down. Another can be flown like a J-3, ignoring the trim. I believe that one has a "stretched" spring. Either that, or they simply forgot to put it in.

I asked the local gurus in a previous thread about all this - I got good answers, including the one that says you are in serious peril if you leave this spring out. I think the reason for the spring was the Super Cub had a more rigorous type certification process than did the J-3.

01-01-2006, 06:31 PM
You mean they fly better without the spring and cable???

01-02-2006, 12:24 AM
Found all the drawings and pertinent info for the bungees.
Thanks for your input.

01-02-2006, 01:04 AM
The last time I bought one from Univair it was $32.00. :o Crash