Control cable tensioning

[sfGnome]

For all you Savannah/Zenith/etc builders out there, how did you measure the control cable tension? Tension meters at Aircraft Spruce start at >$1k, but fear of flutter doesn’t want me to just wing it either. Is there a good way that doesn’t require spending lots of dollars for a once a year measurement?

[Marty_d]

Hey sfGnome,

Groups

ZENITH.AERO

---

Builders and flyers of the the original STOL Sky Jeep . You must be a member of this group to view and participate.

 

Discussion on the 701 forum about this seems to indicate there's a lack of information. One poster said the factory told him "around 20 lbs on the rudder cables and around 30 lbs on the elevator" and a few have measured it, but they don't say how.

I like the one from the guy who's put 1100 hours on his, he said for the gauge to even measure it feels too tight. 

Maybe Savannah have better instructions - recommend asking @Kyle Communications

[440032]

I would suggest not to go with any generic cable tension value from "I read it on the internet" to "some guy said" or a double act, "some guy on the internet said" 

Some designs just have no cable tension value at all. My aircraft doesn't, it's done by feel, not too loose, not too tight, very unscientific, but designed that way by an aeronautical engineer. Not even a generic value or procedure employed.

My rudder cables for example cannot be tensioned, even if you wanted to. Rudder pedal (free floating) direct to rudder. With no feet on them they are floppy. Your feet apply variable tension.

Some tensions are, I gather, expressed as a deflection value - eg for XX load applied to the side of the cable, the cable deflects XXX distance, and also depends on cable length.

For example, half an inch deflection over 20 feet of cable might be the number specified, but half an inch deflection over 5 feet is a whole different animal.

Then comes into play, 1/8" cable or 3/16", there's too many variables for a one size fits all answer it seems.

It would seem to me that there's no point having a fancy cable tension meter without rock solid design specific data and procedure to follow.

Edited 17 hours ago by 440032

[rodgerc]

Only If you’re keen….you can buy online a low cost tension gauge that is used to tension balustrade cables.
The spring it is supplied with is too strong, so you can make a lighter spring from piano (spring) wire. (Hobby shops supply)

Then calibrate it with the required preload (22 lb +/- 2lb in my case) using a bucket containing steel scrap and water.
Put your mark on the scale and bingo, you have a calibrated gauge for about 50 bucks. 
I use it at every annual to check. 

[Neil_S]

Hi sfG,

 

I bought a second hand Pacific Scientific T60-1001-C8-1A tensiometer on eBay for a few hundred dollars and have it calibrated by Northside Calibrations in Narangba QLD when I need to use it. Works out cheaper than buying a new one (which would need to be calibrated after a year anyway). 

 

According to the most recent Savannah S Maintenance manual (Revision 11 June 2024) the tension for the elevator cable should be 18-24lbs (9-12kg) and the rudder cables 11-15 lbs (5-7kg).

Note that recent manuals have a reduced tension for the rudder cables, older manuals (eg the original 2015) had it at 18-24 lbs, a significant reduction. 

 

HTH,

Neil

Edited 16 hours ago by Neil_S
clarification

[sfGnome]

Thanks. Yes, the Ventura specs are the same as the Savannah ones, so I know what I need to achieve as per the designer. I appreciate the suggestions for methods thus far. Please keep them coming. 🙂

[Kyle Communications]

My Savannahs have always been adjusted by feel. Not very scientific but practical.

I recently did a few hours in a factory built pretty new sav at a flying school. What a terrible aircraft to fly to what I was used to in my aircraft. I thought it may have just been me and not being in the pilot seat for a while. My mate who used to fly my sav also did a few hrs in this same aircraft for his BFR as well. I asked him if he thought the aircraft was crap to fly and not like mine was. He looked at me and said..yep..I thought it may have just been me. So we both compared notes and yes he hated it as well.

I setup my aircraft by making the cables the tensions I thought would be fine. I never used a gauge. Its pretty easy to do when using your brain.

The complaints we both had on this training school aircraft was the rudder was way too tight and the same with the ailerons. The ailerons the bolts in the hinges were too tight..the bushes were rotating and not the bolts inside the bushes rotating. This is a mistake made by a lot of builders. The bushes need to be fixed in the hangers and never rotate. The elevator wasnt too bad but the stick was adjusted way too far forward it wasnt a natural position. I am a tall guy and it was a little bit of a strect for me. It was quite uncomfortable.

 

The cables should not be like guitar strings. The tension needs to be enough so there is no slop in the system The cable needs to be a little firm in tension not tight. I tried the cables on the rudders on the training aircraft and they were very tight by feel at the rudder. Couldnt really try the elevator cables unless I climbed into the hole of death but the elevator is pretty heavy compared to the rudder so the tension could be a bit more and it wouldnt be that noticable. But having the nosewheel rods and the rudder cables all connected to the same point it was just way to tight.

 

Yes there is a manual to go by but sometimes common sense is a better solution

Mark

 

[rgmwa]

Variations in ambient temperature also affect the tension. Checks are supposed to be done at the temperature the manufacturer specifies.