Dual control Aircraft with different inputs at the same time

[diddy1234]

I was wondering what would happen on :-

1: light dual control aircraft
2. passenger aircraft
3. fly by wire type of aircraft

If the pilot and co pilot put different control inputs at the same time.

for example, pilot pushes stick forward while co pilot pulls stick backwards.

Its probably a stupid question, but I just wondered what the resultant would be.

[Chris Scott]

Hi, diddy1234,

Will try to kep it simple.

1) On most light aircraft, I think, the 2 sticks (or 2 control columns) are effectively cabled ("boot-strapped") together, so different stick positions are not normally possible.

2) The same applies on most non-FBW passenger aircraft. However, in order to cover the situation where one pilot's control cable gets jammed (and the other is not), there is usually a "break out" system, which allows the other pilot to take control if he/she tries hard enough.

3) FBW. Don't know the B777, but suspect that, because Boeing have retained control columns, it may be similar to the "break-out" system in (2). [Perhaps a B777 pilot/engineer can help?] As far as Airbus FBW is concerned, the side-sticks are not cabled together. The normal situation would be that the 2 pilot's inputs would be algebraically summed. That means that, if one stick is fully forward and the other fully back, the net result is a zero input. However, it is possible for one pilot to give his/her stick full "priority", by pressing a button on his stick.

RUDDER
In (1) and (2), the same situation applies. In the FBW airliners, I'm not so confident. The Airbus rudder is not fully FBW, but it does receive certain inputs from the FBW system: e.g., turn co-ordination. The B777 probably does as well. [For about 40 years (i.e., well before FBW), automatic yaw-damping inputs to the rudder have not normally been fed back to the rudder pedals.]
However, my understanding is that there must be a "break-out" system on B777 and the Airbus FBW-types. Even on the Airbus, the L/H pilot's rudder pedals are cabled ("boot-strapped") to mimic the movement of the R/H pilot's pedals, and vice-versa; so the situation where one pilot's pedals get jammed has to be catered for.

Hope this helps.

[Chris Scott]

Not sure diddy1234 ever saw the answer to his question, but for the interest of the 100-or-so others that viewed it, another couple of thoughts have come to me since.

In (2): the "break-out system is, I think, sometimes called a "spring strut". The spring stretches suddenly, once a pre-chosen load has been exceeded.

Also in (2): The VC10 has a completely different concept. A cockpit lever can be operated to disconnect the 2 control columns from each other. Interestingly, the L/H control wheel is linked to the aileron PCU's feel-units (electric); the R/H to the roll-spoilers (hydraulic). In the absence of any failure, disconnecting control wheels in this way allows them to be turned to full travel in opposition to each other. When this was done in my day (1971), the roll-spoilers used to win, so the bloke in the copilot seat "had the con".

Sorry, just remembered that the queen of the skies is still in RAF service, and at least one of the pilots is female. :O