In planes where the stick is mechanically connected to control surfaces pilot can feel in the stick how the plane behaves. But in fly-by-wire systems where the stick isn’t mechanically connected to anything there are no forces passed. So are there devices used to simulate that forces?
Depends on the aircraft. Most don’t but some do. For example, the first airliner with fly by fire (albeit a primitive one with backup) was concorde, which did. None of the airbuses do though.
Also many even non-fly by wire airliners have something called a stick shaker which is designed to simulate the feedback of a stall on the controls in a pre-stall condition. It was invented with T tailed aircraft where a stall could be unrecoverable and so it was very important that it wasn’t allowed to occur. This was usually combined with a stick pusher, which as its name suggests pushes the stick forward unless it was intervened with.
One could ask the same question about airplane flight simulators that pilots train with. I think I’ve heard that good simulators would have this.
So the real in-the-cockpit flight controls with power steering could have this too, in theory at least. Think of it as just a seriously realistic flight simulator that just happens to be surrounded by an actual airplane.
You can buy joystick with force feedback since ages…
In fact that’s what made me think about the question in the first place ;).
Yes but if your force-feedback joystick fails, 400 people don’t die.
I imagine that introducing another point of failure in a complicated system is not judged to be worth the risk for any benefits it may bring, in those planes that lack force-feedback.
Fly-by-wire is not synonymous with controls that aren’t physically connected to the control surfaces. Most if not all modern airliners have at least some of their controls powered by hydraulics. You move the controls which signals the hydraulic system to move the control surface the required amount. All of the controls on a Boeing 737 are hydraulically actuated. The smaller B717 has hydraulic rudder but mechanical ailerons and elevator. Even though they are mechanical, they still need artificial feel because you don’t actually move the control surface directly, you wouldn’t be strong enough, instead you move a small servo tab on the control surface that then aerodynamically causes the control surface to move.
Feedback systems are very important not only so the pilot has a feeling for what is happening but also to prevent the pilot from putting excessive forces on the controls. Most control systems have some sort of “q-feel” device which artificially increases the forces felt at the controls in proportion to how fast the aircraft is flying. The BAe-146 has q-feel systems for the rudder and the elevator. The elevator control system also has a g weight that increases the elevator control forces with increasing g forces. The rudder also has a limiter that reduces the rudder movement available as speed increases. The rudder and elevator are both very powerful controls and without this type of artificial restriction it would be easy for a ham-fisted pilot to break the aeroplane.
So there is already a lot of artificial feel in non fly-by-wire aircraft. Whether or not fly-by-wire aircraft have artificial feel depends on the philosophy of the manufacturer. Airbus aircraft have the sidesticks springloaded to neutral and don’t have any of the artificial feel that other aircraft have. The reason they can do this is that in normal operations the flight computer won’t allow any control surface to be moved in a way that would stress the aeroplane, so ham-fisted pilots are taken out of the equation.
Boeing fly-by-wire aircraft, on the other hand, use conventional looking controls that provide conventional feedback to the pilot. Boeing aircraft will also allow you to do stupid things if you want to, so they need to provide you with feedback so you can tell when you are doing something stupid.
Simulators try to simulate the control feel of the aircraft they are simulating.
The F-16 stick is (for lack of a better term) welded to the airplane at the pilot’s side. It doesn’t move* at all. A set of strain sensors near the base detect any effort by the pilot to “bend” it, and these are translated to control surface movements. I guess this is a sort of force feedback. I have around 2000 hours in F-16 simulators** and I found the stick odd at first, but surprisingly easy to get used to.
*There is a very slight amount of movement allowed in the mounting. I’m told the original design was disliked by the test pilots and a tiny amount of play was added at their request.
**These were developmental sims, but had full cockpits with real hardware for the controls. With the slower, less capable computers in the 80’s, it was necessary to put a guy in the cockpit to fly the thing all day in order to prove/test targeting algorithms. I got to be that guy for a couple of years. Best job ever.
Sorry, but I can’t let this typo pass…
Passengers that flew on the Concorde fly by fire system found it to be the ultimate flight experience, but the backup system did not work at all. :smack:
Si
As a side note, this history of the development of digital fly by wire systems is pretty fascinating. The NASA work started in the early 70’s and used flight computers built for Apollo , as these were the only systems small, light enough, and flight rated, with enough compute power, that were available. The production line for the rope memory used in the computers due to close at the end of the Apollo programme so the fly by wire team had to have their programming done by then so they could have the code woven into ropes. Even better, an actual flown control panel (a DSKY) was lifted from the returned Apollo 15 capsule and used for years in the F-8C test plane because the research team blew up the unit they were first given.
The solid sidestick cited above for the F-16 was tested on the F-8 as part of this work. Early tests used control sticks built for the Lunar lander.
What are the benefits of a solid stick? Less movement = quicker aircraft reaction?
“Rope memory”? That’s a new one on me…
Try this little video.