Re: [Paparazzi-devel] handle high speed jet

[Michal Podhradsky]

Hi Markus,

I will make a promo for imho a very good book about advanced controls for UAVs, as it might benefit others.
Lawretsky E., Wise K.: Robust and adaptive control with aerospace applications
http://www.springer.com/engineering/control/book/978-1-4471-4395-6

It came out in 2013 and describes optimal, robust and eventually adaptive control strategies for UAVs and manned airplanes. With lots of practical examples. You will find there more information about gain scheduling too.

I guess you are right and I should correct myself - the RC jet plane will be stable so it is possible to fly it manually, and for autopilot you can linearize the flight dynamics equations around some operation point, so you'll be able to get the right gains for a given part of flight envelope. And if you are lucky enough you might be able to fly just with one set of gains (even though the performance wont be great).

There is some gain scheduling implemented for Quadshot from Transition Robotics, but I don't know the details (you can check the code though).

M

On Mon, Sep 23, 2013 at 11:34 AM, Markus Bina <address@hidden> wrote:

Hi Michal, Russel,

> I assume there will be lots of vibrations due to jet engine, so you will need higher quality sensors for start.

That might be a problem. Maybe the influence on the acceleration sensors and gyros can be minimized by cushening the IMU
such that the most dominant frequencies get attenuated (just enough)!?
Also I'd use an airflow sensor to improve the control loops.
Another way around the vibrations would be to use filters or even adaptive filters.
Anyway imho the plane should be designed such, that any vibrations or flutter is minimized.

> so a simple PID control might not be sufficient in auto1/2 mode

Imho: It should be well tuned.
I think auto 1 (attitude control) should work just fine as long as the aircraft is dynamically stable.
Although at 300 km/h one will surely loose the line of sight to the aircraft pretty soon.
Thus I'd be more concerned about the telemetry, since most of the radios for RC-craft (I've used and seen)
are made for reliable transmissions in a line of sight.

> Gain scheduling should help though.

I was also thinking of this, but I'm lacking experience on this matter.

> Also at this speed you might get easily out of the linear flight envelope during maneuvers (somebody who knows more about aerodynamics might correct me)

Well afaik even the simplest system of equations describing fixed-wing UAVs or MAVs are non-linear.
Imho that's why the control loops are normally split into two loops (horizontal and vertical).
In case the "flight mechanics" of this model plane are truely "grossly non-linear", it would be - in my opinion - a waste of money to
even buy it as an RC craft since as a human being you are surely unable to fly it well without any autopilot.
On youtube there are quite a few - imho genuine - videos of (experienced?) people flying RC jetplanes manually:
  eg.: http://www.youtube.com/watch?v=cqCo9QZKy80

@ Russel
If you are a beginner when it comes to ppz, I'd suggest that you start with a slower aircraft.
I recommend the Bixler/EasyJet :)
It is very robust, mine still flies well although I introduced it to quite a number of trees.

Cheers,
  Markus

Am 23.09.2013 18:49, schrieb Michal Podhradsky:

Hi Russell,

I will be delighted to hear what others think, but putting Paparazzi based AP on such a jet sounds pretty risky to me. I assume there will be lots of vibrations due to jet engine, so you will need higher quality sensors for start. Also at this speed you might get easily out of the linear flight envelope during maneuvers (somebody who knows more about aerodynamics might correct me), so a simple PID control might not be sufficient in auto1/2 mode. Gain scheduling should help though.

Also I am not sure if the current AHRS algorithms can handle such velocities and accelerations.

Besides, if this plane looses control, it might be difficult to ever find it again...

What jet model are you using?

Regards
Michal

On Mon, Sep 23, 2013 at 3:04 AM, russell neemo <address@hidden> wrote:

i want to handle my jet model by kroozSD . my jet goes over 350 km/h 

what kind of servos,airspeed sensors and AHRS sensors is compatible for my model.

if it possible please give me some example. 

thanks in  advance

Russell nimo

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