"Why is there a need for external sensors? Won't the IMU be sufficient for stabilzation?
If it can stabilize a stable aircraft why shouldn't it be able to stabilize a (moderately) unstable aircraft.
I think you should try the stock APM…"
kcaldwel's Discussions
Pitch stabilization of an unstable airplane without the autopilot functions
Started this discussion. Last reply by Martin Jul 28, 2012. 11 Replies 0 Likes
Hi,I'm trying to stabilize an airplane in pitch with CG deliberately placed well aft of the aircraft neutral point, but I want control over the angle of attack with the elevator control like a stable…Continue
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Martin replied to kcaldwel's discussion Pitch stabilization of an unstable airplane without the autopilot functionskcaldwel replied to kcaldwel's discussion Pitch stabilization of an unstable airplane without the autopilot functions"Sam,
For some reason there is no "Reply" button under your post, so I'll have to reply to myself. Maybe a bad sign...
I'm ver interested in what you are saying about Dr. Drela's AoA measurement technique. I really…"
Sam replied to kcaldwel's discussion Pitch stabilization of an unstable airplane without the autopilot functions"Jack,
I have not read through all your posts, but in this case we need to use AoA directly, the IMU data won't be sufficient. We also need a high baud rate, at least 20 Hz. Your thought of putting the accelerometer inside a vane…"
kcaldwel replied to kcaldwel's discussion Pitch stabilization of an unstable airplane without the autopilot functions"Thanks Jack.I had seen the airspeed sensor, and was hoping to use it to measure the pressure differential between the top and bottom of the wing as well as airspeed. Getting some files of the outputs is a good idea.
I am working away on a plank…"
Jake Stew replied to kcaldwel's discussion Pitch stabilization of an unstable airplane without the autopilot functions"Sorry I couldn't be more help. The accelerometers could probably be used to sense the G-forces and calculate the rising or falling acceleration. So you might be able to figure out if you're in an up or down draft.
If you want…"
kcaldwel replied to kcaldwel's discussion Pitch stabilization of an unstable airplane without the autopilot functions"Jack,
Airspeed for best sink rate will depend on the bank angle, altitude (air density), and barometric pressure to a small degree. Airspeed at a given bank angle will be dependent on the airplane weight. I don't want to have to reprogram if I…"
Jake Stew replied to kcaldwel's discussion Pitch stabilization of an unstable airplane without the autopilot functions"We'll have to agree to disagree, but lifting tails are well known for being unstable. Anytime the CG is away from the lift vector(s) it makes the plane…"
kcaldwel replied to kcaldwel's discussion Pitch stabilization of an unstable airplane without the autopilot functions"Jack,
Every time you apply down elevator to a hinged stab, you create a cambered tail airfoil. It only changes the trim speed, not the stability. Tandem wing airplanes work quite well with the CG between the wings.
This is getting off topic, but…"
Jake Stew replied to kcaldwel's discussion Pitch stabilization of an unstable airplane without the autopilot functions"A lifting tail can certainly make things unstable. Anytime your CG is not directly under your lift you are making things less stable. Putting your CG in the middle of the aircraft means it's not under any of the lift, but supported…"
kcaldwel replied to kcaldwel's discussion Pitch stabilization of an unstable airplane without the autopilot functions"I want to do this in a sailplane application, where it will spend a lot of time flying tight circles near stall, in rising and descending air, without a motor.
I want an autopilot to provide the missing pitch stability of an unstable airplane. But…"
Jake Stew replied to kcaldwel's discussion Pitch stabilization of an unstable airplane without the autopilot functions"I don't follow what you're saying.
If the actual CG is behind the design CG you have an unstable plane. This is exactly when you would want autopilot stabilization, otherwise you're not going to be able to fly it.
If you want to…"
kcaldwel posted a discussionPitch stabilization of an unstable airplane without the autopilot functions
Hi,I'm trying to stabilize an airplane in pitch with CG deliberately placed well aft of the aircraft neutral point, but I want control over the angle of attack with the elevator control like a stable airplane. I don't want autopilot functions leveling the airplane, or controlling the airspeed.I have been through the past discussions in the DIY forums, and on RCGroups, Charles River, and Steve Morris's electronically stabilized plank. The Steve Morris plank approach is basically what I would…See More
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