Bay 2 Neg and Pos. Cables Tension

[Thruster87]

Would like to know what is the allowable slack on the Bay 2 Negative and Positive cables [compression struts in place]when trying to concertina the wing. In other words how much play or movement is OK with respect to front and rear spars longitudinally[ when not attached to aircraft]. Thank you

 

 

[Guest TOSGcentral]

Awwww Allan! You have couched your question in a somewhat contradictory way that may confuse mate! Let us break it down into some components and then give a little bit of background info.

 

 

• Bay 2 bracing wire tensions. I am discussing a situation where the aircraft is rigged and you are doing a pre-flight inspection. These cables should be “taut†when the aircraft is static at rest. That does not mean either should be drooping and neither do they need to be drawn up like violin strings – they just need to be firmly there in a straight line so they take negative or positive torsional loads as soon as these come on but otherwise are just sitting there waiting for it.
   
  

 

 

2. When “concertinaing†the wing (or as it usually referred to as Racking the wing) then tensions do not matter. One cable has to be disconnected at one end and the other is fixed in position but instantly goes slack.

 

 

Now here are a few curly bits. In my experience most Thrusters were produced ex factory with slightly over-length cables (the dismountable one) while the other remains fixed and is usually the correct length.

 

 

The addition length in the dismountable cable “may†be simply down to the fact that they are pricks of things to get on when rigging – hence the generous sized zip opening at the trailing edge so you can get both hands and a couple of pairs of pliars in there!

 

 

I seriously suggest that you go the full yards and put up with the angst – rig the thing properly and if the detactchable cable is slack then wind it up a bit (but no more than four twists) and if that does not fix it then change the cable.

 

 

Not also that different model Thruster wings are a little different although very similar.

 

 

On the Gemini the two bay 2 cables are in contact at the cross over point and need plastic protection. On the T300 the two cables have different top and bottom mounting points so remain separated when connected correctly. But it is possible to get one cable under the other when it should be over the top giving an artificial impression of tension that is not there. It is all pretty obvious if you look at it. The bottom mounted cable should go underneath.

 

 

On the TST this is essentially the same wing as the Gemini but the bay two cable routings could have been changed to T300 design. Just take a look inside the zip openings and see where the cables terminate and work it out from there.

 

 

Note also that slack Bay 2 cables is the single most common fault on the Thruster and in my early days I never found one which had correct installation. It has been a lot better for quite a few years as I have kept pushing the point in TOSG and word gets around.

 

 

Aye

 

 

Tony

 

 

[Thruster87]

I've not yet put the wing skins on, but just had the open frame attached to the a/c and I was checking for excessive movement in all the points and it seems one wing is pretty good with the bay 2 cables but the other not so good[to be reasonably tight would have to shorten by 3/16th"].I had no idea what happens to these when under load [if a bit of slack was required or not]. It also appears one wing is new [spars + inserts] and the other original which also does not have the wing tip inserts installed [seems the factory made some with and others not] but I will put them in as per the drawings for the T300 Cheers Alan [forgot all the wing cables are non adjustable no turnbuckles.]

 

 

[Guest TOSGcentral]

Good point that I also meant to cover.

 

One initial problem with those cables is getting them right. Once the skins are on and tensioned correctly the cable tension changes - sometimes quite a bit. So it can be quite a performance getting the cables to the correct length with the skins off (as you have to do) then racking the wing so you can get the skins on, then tensioning up and finding out how well you actually did.

 

What are you referring to by the "wing tip inserts" Both wings should be the same and symmetrical!

 

Tony

 

 

[Thruster87]

The STB wing is new and appears to have all the reinforcing wing spar sleeving as per the T300 drawing/spec,but the other original wing has all but the wing tip ones installed.That's what I was referring to and should have said spar sleeving rather then inserts. Cheers Alan

 

 

[Guest TOSGcentral]

Ok then you have one bodgy wing!

 

All the two seaters from the TST onwards should be sleeved. The Geminis were not because they used much thicker walls.

 

You can get sleeving material from Wade Air and it is not a difficult job to do - just a pain in the butt taking every nut and bolt out each of the two spars affected so you can press in the new inserts.

 

Take out and keep your tip sleeves as you will be able to use these again either by realigning them or turning them 90 degrees and re-drill.

 

Secure the new sleeving as per the T300 sleeving drawing and use the existing spar holes to drill the new sleeves. Ensure that you are careful, line drill the through bolt holes and especially de-burr the drilled edges (including the spar again in case yoi have stirred it up a bit).

 

Tony