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Flight Control Cable Spacing

Flight Control Cable Spacing

(OP)
Does anyone know any guidelines or regs regarding minimum distance required between control cables? My project is to modify a biz jet to accept a big camera unit. Flight control cables are in the way and need to be rerouted. The most efficient method requires bringing cables that are normally 1.5" apart down to 0.5".

If you know of any examples in transport category aircraft that would also be helpful.

Thanks!
LD

RE: Flight Control Cable Spacing

You might start with FAR 23.689. Also take a look at AC 43.13-1B section 8.

You should also look at the control cable installation from end to end. While the current 1.5" spacing between the cable runs may seem excessive, the spacing may be based on other components in the system such as fairleads, guides, cable end fittings, etc.

RE: Flight Control Cable Spacing

When re-routing control cables, don't forget to mind the spacing to all other components (wire bundles, hydraulic lines, air ducts, etc).
Also consider the stiffness of the new control system, once you add a number of new angles to it, which will probably be lower than it was before, unless you take measures to make the new pulleys/fairleads very rigid.

STF

RE: Flight Control Cable Spacing

I don't really see anything about cable proximity to other cables. There are things that say that splices aren't supposed to come any closer than 2" to pulleys and fairleads. Each time you make a bend, the drag on the cable system will increase, so you may end up with heavier control feel. Likewise, watch your cable tension, with a different cable run you may need a different cable tension for a given control.

RE: Flight Control Cable Spacing

(OP)
Forgot to mention that 23.689 & 43.13 do not specifically mention spacing minimums.

RE: Flight Control Cable Spacing

LuckyDuc,

You are correct that the references I linked don't specifically mention minimum spacing of control cables. But they do describe other requirements that will help you determine what your minimum spacing should be.

For example, FAR 23.689(b) states, "(b) Each kind and size of pulley must correspond to the cable with which it is used. Each pulley must have closely fitted guards to prevent the cables from being misplaced or fouled, even when slack. Each pulley must lie in the plane passing through the cable so that the cable does not rub against the pulley flange." If your system has pulleys, the width of the pulley and guard would determine your minimum spacing at that location. And FAR 23.689(c) states, "(c) Fairleads must be installed so that they do not cause a change in cable direction of more than three degrees.". If you need to add fairleads to re-route your cables closer together, then this requirement would be a consideration.

Many cable end fittings, such as this clevis, must be installed in a specific orientation and may require greater spacing than .50" when installed. So you need to consider each control cable installation from end to end.

RE: Flight Control Cable Spacing

LuckyDuc...

Here are some 'specs' that may help You find answers to Your question.

NOTE.
I originally intended to copy/paste info from each spec: however, there are MANY factors to consider that made this impractical. For this reason, I suggest reviewing each spec for the obvious spacing/clearance discussion... and the practical mitigating factors to be wary of, such as: installation and maintenance, routing variations/issues; affects of operational and natural environment such as temperature and moisture affects, cable tension/vibration, load-induced deflections [cables and bracket strains, flexing of wire harnesses, flexing of fluid tubing, etc]; and real-world operational testing for system friction and binding, flutter, wear-and tear, electrical bonding/isolation, etc, etc.

MIL-F-18372 [CX, 1955] FLIGHT CONTROL SYSTEMS: DESIGN, INSTALLATION AND TEST OF, AIRCRAFT (GENERAL SPECIFICATION FOR)
... replaced by...
SAE AS94900 Aerospace - Flight Control Systems - Design, Installation and Test of Piloted Military Aircraft, General Specification For

AFGS-87242 AIR FORCE GUIDE SPECIFICATION - FLIGHT CONTROL SYSTEM GENERAL SPECIFICATION FOR
...replaced by...
JSSG-2008 VEHICLE CONTROL AND MANAGEMENT SYSTEMS [controlled distribution]







JSSG-

JSSG-2009 AIR VEHICLE SUBSYSTEMS

Regards, Wil Taylor

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