ETLB Squawk Forums — Archive

Since we already use cables to actuate the rudder, I was wondering why not use a cable system for elevators too ?  ..  Is it very difficult to set this up ??

Keith1100,

I have two 3 axis planes, one is my Minimax, and the other is a Spectrum. My Spectrum has a similar set up for the elevators to your diagram. It looks like this;

As you can see, it has two cables going aft to a pivoted lever arm at the tail, that then has a solid aluminium rod going back to the single elevator horn.

The system works quite well, and is not particularly heavy, and allows removal and replacement of either cable without having to dismantle the whole tail end of the plane. Furthermore, the Spectrum has a ladder type fuselage, so all the cables are exposed, and it allows me to examine and lubricate all the cables on a regular basis.

Obviously in a Minimax the rear lever arm would be in the fuselage, so the cables would be kept out of the weather and only the solid rod would exit the rear of the fuselage to go to the elevator horn. Also, in a Minimax the control stick pivot is at the base, so the 'up' elevator cable (orange in your diagram, yellow in mine) would need to be routed as you've shown in your diagram, but other than that, I think it would be quite simple to modify the 'max to use separate cables. After all, the tail wheel uses just such a system, with a pivoting arm in the fuselage and a single rod to the wheel assembly.

Just so you can see what I mean about the Spectrum, here's a picture of it with me at the controls just after I'd landed at a fly-in last year. In the photo you can clearly see the solid rod going from the lever arm to the single elevator horn.

When I use cable operated control surfaces I get distracted by the difference from the MiniMax and it takes me a while to ignore just how much better cables are.

On the other hand Teleflex is very simple, and when flying the MiniMax I never think about the bit of stiction in the stick. I just imagine what I want  - and the MiniMax does it.

If you decide to go for cable control bear in mind that if something goes wrong - maybe a 'Spaniard in the Works' it should not break even if you use your whole strength on the stick. That would take some thought when designing such a control system.

Or you could do this:

Bob , thanks for your response and the pictures.

Personally I trust the teleflex cable ( even a single cable, without a back-up ).
My cable is still almost new and I expect it to give many years of service.

However, the challenge arises when you have an old teleflex cable and you are not sure if that old cable is good enough or not. How do you inspect it ?

I found it very easy to rig my rudder cables, and that is what led me to probe further about using the similar cables for elevator.  Using these cables may also turn out to be a tad lighter than using a teleflex cable.

The downside I visualize is -  something getting entangled in the cables leading to a stuck elevator. But that could happen presently for the rudder cables too.

Routing the cable in the cockpit may also present a bit of a challenge, but still do-able.

Remember the Teleflex type cables cost between $95 and $155 from TEAM.  If, on inspection, a cable doesn't look absolutely perfect, the benefit in peace of mind measured against the cost would seem to favor just replacing the cable.  Just a thought.

Tom

As Tom said, being able to see each cable along its length just like the rudder cables, makes it much easier to see if there is any corrosion. Also, if you do need to replace a cable they will be easy to replace, just keep a spare of each (1 x up and 1 x down) for just such an occasion. You could even keep them in a bag under the seat if you wanted to, so that you'd have instant and easy access to them if needed. Galvanised cable is cheap to buy (in comparison with a teleflex), easy to cut and fit ends to, and you can easily adjust the cable length if you need to in order to make life easier for any trimming you need to do.

I think the cable idea is a great alternative IF DESIGNED CORRECTLY.
Inspectability being top of the list why. cost & ease of R&R probably second.
Not having small pieces of plastic tube & clamps on the ends of the teleflex because.....That's just the frosting on the cake!
Hey Bruce, Did the cable idea ever come to mind when you were designing your impressive system?
Would have loved to see how you would have designed it with cables.                                              TTT

Surly someone has implemented a cable control system for a Minimax at sometime or another. the control system from the Legal Eagle would be easy to adapt.

Quoted from toliver66 The control system from the Legal Eagle would be easy to adapt.

True, the stick on the Legal Eagle as well as in the picture Bob Hood provided above are pivoted slightly different to the Max. But surely adaptable.

Agreed. The elevator would be relatively simple to rig. The ailerons would be the real challenge. Perhaps something similar to the Affordaplane aileron rig?

A rugh elevator control system design.

Possible Legal Eagle adaptation.

I didn't realize I had the floorboard in the wrong place until I had already posted the pics.

Wow, that looks incredible! Your model of a max is way more complete then my own.  

Yes, that is a nice set up.

Attachment of the cable to the stick needs to be at a height
which moves the cable just enough, so as to mimic the elevator deflection
which the present teleflex cable generates.

If attached too low on the stick, we may need to move the stick by
a larger degree to achieve comparable elevator deflection.

We can refine that by trial and error.

Thanks ITman496. I use Adobe Invener pro.

I drew it so the cable will attach to the stick in the same hole as the teleflex cable. That will give the same amount of movement as the teleflex unless Im missing something. But like you said, the stick attachment could easily be made adjustable. Or leave the stick attachment alone and make all adjustments at the rear bell crank to pushrod transition. But then you would have to remove the tailfeathers to make any adjustments. Unless you put in a strategically placed inspection ring.