How is flight envelope protection implemented in Dassault Falcons?

Question

In normal laws, envelope protection is implemented differently on Boeing and Airbus fly-by-wire systems, as highlighted in this question. I don't want to reopen a debate about which one is better (both have been proven to be good), I'm looking for information about another manufacturer's implementation.

If I understand correctly, Airbus won't allow the pilot to exceed limitations (such as load factor) while Boeing will make them really hard to exceed them.

Dassault Falcon jets (after the 7X) are fitted with fly-by-wire implementing flight envelope protections (as mentioned in this article.

I would like to know what happen if the pilot's input tend to exceed flight envelope limits (high-G maneuver -both negative and positive G-, high angle of attack, over-speed, high bank angle).

On a fully functional Dassault Falcon 7X (or newer) in normal laws, can the pilot put the aircraft outside its flight envelope? Can the pilot make the aircraft stall (excessive AoA), perform high-G maneuver (excessive load factor), put the aircraft in inverted flight (bank angle > 90°)? Will the aircraft refuse pilot's input or just make them hard ? In short, how is flight envelope protection implemented on Dassault falcon jets?

Answer 1

My information on the Falcon 7x and 8x comes from Aviation Week and Flying Magazine pilot-reports.

It would appear that the Dassault FBW philosophy is very closely aligned with that of Airbus. Namely,

• It employs a C* control law without speed stability;
• It uses passive sidestick instead of control column;
• It employs 3-axis envelope protection, complete with bank angle protection (via positive spiral stability beyond 35 deg), load factor protection, AOA protection and high speed protection;
• It even has a control-by-wire backup system similar to the mechanical backup available in the A320 and A330.

The fact that it has a C* control law, which provides flight path stability and not speed stability, and that it has a passive sidestick without force feedback, the envelope protection would appear to be a must-have for certification, rather than nice-to-have. By all indications, the limitations are hard constraints that cannot be overridden by pilot inputs in Normal Law.

Answer 2

The 7X in normal law will attenuate sidestick inputs to prevent excessive AOA (getting too close to the stall), or excessive load factors.

As a practical example (I've done this in the 7X simulator, not in the actual aircraft), if in level flight you pull the sidestick quickly back past the soft stop, all the way to the hard stop and hold it there, the nose will initially rise, but the G-loading will not exceed limits. As the 7X then approaches stalling angle, the aircraft will start to pitch down - at a fairly gentle rate - even if you hold the stick full aft, to prevent getting too close to the stall.

During our sim training, the instructor did something very interesting: Made us fly a 63-degree bank turn (we HAD to keep it above 60 degrees) with slats and flaps extended, at 300 feet AGL. This requires constant fine bank inputs to the sidestick, as the aircraft is always trying to roll back to 30 degrees. The flap configuration meant that the G limit was now +2.0. Well, it was impossible to maintain level flight! Of course, perfectly logical, since you would need to pull more than 2G to stay level. But I'm still not sure how I feel about this "protection feature".

I agree that there is practically zero documentation about the Dassault or any other FBW systems. Might be due to FBW's military origins...

But, it would be nice to have a bit more info. A hard-landing accident on an Airbus was investigated, and if memory serves me well it revealed that below a height of 50 feet their FBW system changes in the way it reacts. I was very curious to find out if Dassault also does this, but never found anything in writing.