Trim for Autopilot Development - Flight Control Fundamentals - Section 1.7
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- เผยแพร่เมื่อ 29 เม.ย. 2023
- In this lesson we discuss the role of aircraft trim in flight control or autopilot development. Topics include the idea of trim, why trim is important for flight control and aircraft modeling and simulation, how trim is used for flight control, a definition of trim in the longitudinal plane, solving for a trimmed state. Three examples of trim for a transport aircraft are provided.
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You’re videos are awesome! Thank you!
Thanks Jonathan!
Sincerely, your videos are the best GNC lessons out there; Clear and concise explanations. By the way, what programming language did you use for your simulations ??
Thank you Preston! The code is in Octave, an open source package like Matlab.
I'm more familiar with C/ C++, however I'll sign up on your patreon page later today. . . Looking forward to learning more from you. Thank you !!!
Fantastic! I expect Octave will be very easy for you to grasp.
If J cannot be forced to zero, is the aircraft really in a trimmed state? Intuitively, I'm a bit surprised that "true" trim wasn't achieved across a wider array of states.
Hi Andrew,
By how trim was defined in this video, technically, no. If J is not 0 the vehicle is not perfectly trimmed. However, a nearly trimmed vehicle may be good enough for linearization of the dynamics for control.
We could redefine what we mean by trim (i.e. the trim problem statement) to get a better result. This usually means adding constraints or "trim with" variables.
In our problem statement, we are essentially trying to find the roots of three equations with two variables, an underdetermined problem, which leads to the "best fit" solution.
I'm considering a Section 1.7.2 citing the poor trim results (note \dot{alpha} values as they pop up in the command window) with the last trim array example and reposing the trim problem.
Last thing, there could be a bug in my code, but I did verify my routine with examples in Stevens and Lewis.
Good question.
Hi sir,
Is it possible to trim an unstable aircraft in longitudinal axis?
Absolutely! Trim is a question of whether an aircraft can hold an equilibrium at a flight condition. About that equilibrium condition, the system can be stable or unstable.
@@LearnGandC I have a nonlinear aircraft model. When I trim the aircraft for stable case (Cg ahead of the neutral point) there is no problem, but when I move Cg behind the neutral point again I can find a trim point but aircraft cannot maintain its trim condition. Even I run the simulation for 1-2 seconds, aoa increases by 2-3 degrees for example (system has no disturbance or perturbation). Also, I used simulink for this simulation. Do you have any idea what should be the reason sir?
Yes, what you are experiencing is normal and expected. First, note that you have an unstable dynamic system. Second, note that you are attempting to simulate that system with an initial condition about its equilibrium point. However, ask yourself, do you know exactly the equilibrium (trim) condition? If your system diverges its because your off the equilibrium condition. The difference between your approximated trim condition and the exact trim condition may be small, but that small difference will grow according to the severity of the instability.
@@LearnGandCI understand what you mean. Thank you very much for your answer and videos.
You're welcome
Hi, which book are you using?
book called "20 years industry experience"
At the end of the video, I list three references. The most relevant is Stevens and Lewis.