Control input delay
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Control input delay
Hi,
Have a question that might be a bit difficult to answer, but
I would appreciate any thoughts on this.
When moving the yoke, the control surface will move - offcourse.
Now, my problem is that there will always be some sort of DELAY
from you make the INPUT on the yoke until the surface MOVES to the
selected position. Depending on aircraft, this is due to hydraulic
delays, stretching wires, old bearings, bending levers, twisting
wings, bending control surface etc etc.
So, the big question is how long is this delay in time?
e.g. if you make a full elevator input (in flight), how long
would it takke for the elevator to actually move to full deflection?
(No one probably tried this I know
)
Are FBW aircraft more responsive than non FBW?
I ask because I make aircraft for a flight simulator.
The longer the time delay, the "heavier" the aircraft will "feel".
I don't wan't my Boeings to snap roll like an F16.
Any ideas?
Cheers,
M
Have a question that might be a bit difficult to answer, but
I would appreciate any thoughts on this.
When moving the yoke, the control surface will move - offcourse.
Now, my problem is that there will always be some sort of DELAY
from you make the INPUT on the yoke until the surface MOVES to the
selected position. Depending on aircraft, this is due to hydraulic
delays, stretching wires, old bearings, bending levers, twisting
wings, bending control surface etc etc.
So, the big question is how long is this delay in time?
e.g. if you make a full elevator input (in flight), how long
would it takke for the elevator to actually move to full deflection?
(No one probably tried this I know
)Are FBW aircraft more responsive than non FBW?
I ask because I make aircraft for a flight simulator.
The longer the time delay, the "heavier" the aircraft will "feel".
I don't wan't my Boeings to snap roll like an F16.
Any ideas?
Cheers,
M
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Sim Latency
If you're looking at simulation, there are latency and transport delay tests that are run as part of the initial certification. IIRC you get 150ms from a step input to the controls to get a response from your visual and from the PFD.
Try AC120-40C if you want the exact figures.
Hope that helps
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Try AC120-40C if you want the exact figures.
Hope that helps
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AC120-40C won't give aircraft system hardware delay times; it gives simulation delay acceptable levels.
It's actually possible for a simulator to be faster than an aircraft in terms of delays, depending upon the characteristics of the prototype and the simulator.
In terms of control surface motions - assuming you aren't hitting hinge moment limiting of any significance, a good rule of thumb would be to assume that the controls will move stop-to-stop in one second, and take that as the rate limit for the controls. That's only for primary flight controls. Secondary controls - like a trimming stab, flap, etc - will be significantly slower; stab rates typically of the order of 1 deg/sec, flaps maybe 2 or 3 deg/sec.
One of the factors that makes a big airliner feel more sluggish is the control forces; by regulation you're required to have deterrent levels of stick force at the limit load factor - say 50lbf pull at 2.5'g', which equates to about 30lbf/'g' in terms of stick force per 'g'. Fighter type aircraft will have values almost an order of magnitude lower, since their limit load factor is MUCH higher. Thus an airliner will always 'feel' heavy. You could make a fighter 'feel' heavy just by changing the feel force characteristics.
It's actually possible for a simulator to be faster than an aircraft in terms of delays, depending upon the characteristics of the prototype and the simulator.
In terms of control surface motions - assuming you aren't hitting hinge moment limiting of any significance, a good rule of thumb would be to assume that the controls will move stop-to-stop in one second, and take that as the rate limit for the controls. That's only for primary flight controls. Secondary controls - like a trimming stab, flap, etc - will be significantly slower; stab rates typically of the order of 1 deg/sec, flaps maybe 2 or 3 deg/sec.
One of the factors that makes a big airliner feel more sluggish is the control forces; by regulation you're required to have deterrent levels of stick force at the limit load factor - say 50lbf pull at 2.5'g', which equates to about 30lbf/'g' in terms of stick force per 'g'. Fighter type aircraft will have values almost an order of magnitude lower, since their limit load factor is MUCH higher. Thus an airliner will always 'feel' heavy. You could make a fighter 'feel' heavy just by changing the feel force characteristics.
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Thanks guy's 
I will try delays in that region for the primary controls then.
Would you say rudder/elevator/aileron all have similar times?
From a pilot perspective, does e.g a 747 "feel" heavier and
more sluggish to handfly than a 737 in calm conditions?
Cheers,
M
I will try delays in that region for the primary controls then.
Would you say rudder/elevator/aileron all have similar times?
From a pilot perspective, does e.g a 747 "feel" heavier and
more sluggish to handfly than a 737 in calm conditions?
Cheers,
M
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Since it's pretty much just a rule-of-thub, yes. If I had to guess I'd say aileron's would be faster than elevators (since ailerons are usually smaller surfaces, so less inerta and airloads) which in turn would be faster than the rudder (which is also the "least primary" of the three surfaces in many ways). But there might not be much between the surfaces (and other factors, such as design constraints for weight and space, might constrain actuator sizing in each case)
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The actual term for the delay is HYSTERSIS.
On the L-1011 we used Tension Regulators in the Pitch and Throttle systems. These regulators keep constant tension on the cables and reduced the hystersis. Why only in those to systems, as I use to tell the students in my flight control class. If you break out of a cloud and right in front of you is a mountain, you don't want any hesitation in the pitch or throttle cables. Because the first thing you are going to do is pull back on the column and push forward on the throttles.
On the L-1011 we used Tension Regulators in the Pitch and Throttle systems. These regulators keep constant tension on the cables and reduced the hystersis. Why only in those to systems, as I use to tell the students in my flight control class. If you break out of a cloud and right in front of you is a mountain, you don't want any hesitation in the pitch or throttle cables. Because the first thing you are going to do is pull back on the column and push forward on the throttles.
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Hysteresis is only one of the component contributors to delays between pilot inputs and control surface 9and hence aircraft) response. It's really a pseudo-static characteristic - you'll see hysteresis on a slow control sweep if you cross-plot input versus output; there's a pronounced 'circuit' whereby the control input-to-output relationship is not a single straight line, but rather goes 'out' along one line and back along a different (usually roughly parallel) line. Hysteresis is mainly a result of backlash in a circuit, such that there is a deadband between input and output. It can also arise due to circuit compliance.
Dynamic characteristics are more likely to be governed by both the mechanical response of the control system and, perhaps more importantly, but rate limiting and response times within actuators (for a powered system). Hinge memoent limiting can in some cases further complicate the actuator responses.
It gets more complex if you're building a simulator (as opposed to a simulation) because the flight control system on the sim has its own control dynamics, so it's a case of trying to match one with the other over the range of pilot input scenarios.
Dynamic characteristics are more likely to be governed by both the mechanical response of the control system and, perhaps more importantly, but rate limiting and response times within actuators (for a powered system). Hinge memoent limiting can in some cases further complicate the actuator responses.
It gets more complex if you're building a simulator (as opposed to a simulation) because the flight control system on the sim has its own control dynamics, so it's a case of trying to match one with the other over the range of pilot input scenarios.
