Pitch up/climb to slow the plane down

ArduPlane
1

Hello all,

This is my first post in this forum. So please go easy on me if this topic was already discussed.

I am running SITL simulations to define a tight survey mission with the the “simple grid” pattern produced with the mission planner. In the mission, the plane makes a 180 degree / U turn on each leg and I am trying to reduce the radius of these turns. Beyond the standard tuning parameters that affect the bank angle, waypoint radius, nall1_period, etc, reducing the velocity of the plane ahead of each turn should be the more effective, physics driven approach (R~ v^2).

My issues are:

  1. I set the turn velocity to a low value, some diameter lengths in advance of the turn, but the plane hardly slows down. Is there a way to activate air-brakes on SITL in auto mode? How to configure it? This is probably a bad approach as the plane will waste energy this way…

  2. A more energy conserving way would be to reduce K.E in exchange for P.E. So I (try to) cut off the throttle and put the plane on a climb before the turn to slow it down, However the throttle seems to be compensating and actually accelerating the plane. How do I disable/reduce this seeming throttle compensation?

  3. Alternatively, I set an elevated waypoint for the apex of the turn to see if I can bleed off the airspeed during the simultaneous turn and climb, but still the throttle seems to be kicking in. I lowered TECS_RLL2TAR all the way to its minimum, but I did not see much effect.

Any ideas?

Thanks

2

@Albcem, before getting into more complex solutions, have you tried the following:

  • using a interleaved grid pattern, so you do even grid lines one way, then odd grid lines the other, doubling the available turn radius
  • add more rudder using KFF_RDDRMIX
3

Thanks Tridge!

  • Yes, in fact I have my own custom gridding method where I am able to increase the turn radii of each leg arbitrarily, which creates a similar effect as your first suggestion. However, this or your suggested approach have some detriments on the overall distance flown in the mission (twice as much in turns in your case, if I am not mistaken), so I am giving it less priority.

  • I will look at KFF_RDDMIX, which I never thought off - I will let you know of the results.

4

Back on my original topic, I would appreciate other ideas in here - it looks like the autopilot prioritizes a climb and turn command over set low throttle / velocity command. When I set the throttle low and ask the plane to climb and turn, it actually increases the throttle back up. Not my desired behavior…

Tridge´s idea is well appreciated as it is a form of applying air brakes, but it is not energy conserving therefore not the direction I would like to go.

Thanks

5

In case you didn’t think of this already, low throttle + request-to-climb = ripe conditions for stalling.

I don’t think you want to autopilot to stall, so maybe investigate how to avoid that risk while still executing your desired behavior?

6

Fair point, but the target velocity to slow down to will still be way above the stalling speed.