What is the currently recommended auto-takeoff method for a flying wing?

Hi, I’m about to maiden a pusher-type flying wing and would like to ask about the recommended takeoff method?

TL:DR

Frisbee-like wing toss seems too risky and throwing it traditionally is out of question because there is nothing to grab onto.

I’ve seen a couple of videos, mostly with INAV, where shake-to-wake together with an overhead throw is recommended.

That approach seems feasible but with Arduplane I noticed some caveats.

  1. Shake-to-wake seems to be incompatible with crash detection by design.
  1. Throwing it overhead and hoping it starts the motor also seems to be a recipe for crash unless safety checks are disabled.

OK,
lessons learned after a beyond repair maiden:

  • no reflex for an over the head throw
  • less throttle
  • no tarmac within 50m

I use shake-to-wake on all my hand launch planes. On my AR-900 I would use the Frisbee style throw because I didn’t like the over the head launch. I know lots of people do it, it just doesn’t work for me. And the EBee style forward throw puts a spinning propeller way to close to critical parts of my body.

What worked for me

  • Set the shake to wake so the motor started slowly before I threw it. This way I knew it was ready to go.
  • Set the slew rate so I could hear the motor speeding up. I would time my throw so the motor was ~3/4 of max when I threw it. My AR900 was only on 3S so there wasn’t much power to spare. YMMV.
  • The throw needs to be much flatter than you think. Not too hard with the frisbee method. But really critical for a good launch.
  • The throw needs to be as straight as possible. This I found to be the hardest part of the frisbee method. Holding the plane on the leading edge it was really hard to not give it some back-spin.
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After some crash analysis, it seems I experienced the famous stall and torque roll on the AR Pro.
Over-the-head throw with takeoff mission item, no conditions set, motor running at 85%.
Let go too early, pitch 60deg, no impulse visible on yaw and roll from the throw, managed 25-30m/s² acceleration.
Instead of nose-down due to the CG, it nose-up again by motor thrust after the throw, then stalled, torque rolled to the left, changed direction completely and turned for the tarmac.

QED: too much pitch, too much throttle, too much tarmac

I was able to salvage and move almost all of the electronics to another KIT.
Just had to order a new analog camera because that was hit directly before it split the main fuselage diagonally. Surprisingly not even a scratch on motor and prop. Wings are also ok except that the winglets came off where factory glued them.

I’m preparing to maiden the next iteration of that plane and I believe I found out what effectively crashed the first one. Insufficient throws for elevator down.
With the default FF and P for pitch, the elevons barely move in elevator down direction when I pitch it up in FBWA. I can move it part of the remaining deflection with the stick.

I had to double the values to make the plane move the elevons in full deflection without me touching the stick and I assume if I would have had the radio in my hands at that moment, I would have been able to save the plane by pushing elevator down.

This must be addressed in the wiki IMO, otherwise it’s a recipe for disaster.

Did you turn up the MIXING_GAIN at all? I seem to remember the default is low for some planes.

Nope, I left it at 0.5 and was going to adjust it later if necessary. Have to be once in the air, trimmed and at least half-way tuned for that decision to make.

The thing is that having 1-2mm reflex up takes those 1-2mm from elevator down and with default FF and P, it moved maybe 3mm of the 12mm+reflex it should have in that direction.
I practiced throwing over-the-head in FBWA and I can see that the elevons follow and deflect enough to pitch down, even if I throw it at 60deg pitch again.

I also set CG to balance at the front end of the CG marking with 120g (50g more) of lead in the nose as a last line of defense against this sort of stall.

Just curious, what about strong wind?
Is it beneficiary for a flying-wing maiden or suicide?
Spinning the numbers, forecast shows 8m/s wind coming up in the next days in a favorable direction / location. Expected stall speed is 12m/s .

I guess that would be up to your comfort level. I’ve been looking at a similar forecast except the direction is wrong. Is the wind smooth where you are? Or does it get gusty and turbulent?

If you nail the throw, maybe even go a little closer to flat then it could be fine. You’d be at flying speed by the time you let go. But if it goes wrong, it will be harder and faster.

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Possible takeoff location is a field encased by trees in a U-shape, means the wind is caught in there with 300m of free straight. Vegetation is a little low but at least no tarmac anywhere.
Guess I’ll practice throwing over-the-head there first to check for trimming issues.

I too recomend to add these to wiki as it might be a common problem faced by the model

Concerning your question about parameters.

I have not flown yet but these are the PID values that I took from a log of @stefymtb , a fellow AR Pro pilot.

PTCH_RATE_D,0.000624
PTCH_RATE_FF,0.6931329
PTCH_RATE_I,0.6931329
PTCH_RATE_P,0.1161929

RLL_RATE_D,0.0017829
RLL_RATE_FF,0.2870134
RLL_RATE_I,0.113869
RLL_RATE_P,0.113869

I’ll also go for MIXING_GAIN,0.7 .

I’m running Emax ES08MD on my second plane, so the throws may vary quite a bit from the standard analog servos.

SERVO1_FUNCTION,77
SERVO1_MAX,1750
SERVO1_MIN,1100
SERVO1_REVERSED,0
SERVO1_TRIM,1500
SERVO2_FUNCTION,78
SERVO2_MAX,1900
SERVO2_MIN,1250
SERVO2_REVERSED,1
SERVO2_TRIM,1500

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Thankyou for sharing these
I too have the same servo and I have already setted up the throws somewhat good

So I can directly write these ptch and rcl params right regardless of fc board

And im going for a testing today itself

Wait!

I use a stock PNP ar wing pro. Liion battery 4S.
CG is just a bit back of cg marks. (10 mm)
1400g AUW

First flight was on stock arduplane. Than autotune and than added a bit more of agility for auto flight and fbwa.

I always use auto take off. Max throttle 100%, 25° pitch (i think) and that’s it.

I launch above head. I throw it almost horizontal and it will pitch up almost immediatly.

I use 9x6 propeller.

Here is a video of maiden launch:

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Thank you for the message

I will test the setup and you update it soon
Thanks

Thanks, but you can confirm that the stock FF and P values are insufficient, yes?

I saw this on the second plane while settings throws and in retrospective remembered a similar experience with my ZOHD Drift that did not manage auto-takeoff but did a belly landing instead.

With 0.7 FF and 0.11 P and 0.7 Mix, they now deflect almost 8mm on pitch instead of 3mm without touching the sticks.

9x6 may be a little bit harsh. Sunnysky recommended 8x6 or 9x4.5 . I’ll go with a balanced Aeronaut CamCarbonLight 9x4.5 after the maiden if everything goes right for once.

I can confirm that i use stock wing and stock value from arduplane.

Than autotuned it at first flight.

First flight was auto takeoff.

Update
Day before yesterday I went to test it and take off was fairly good and it flew well but since the weather was getting worse I just immediately landed it and im gonna go fly tommorow

One of the thing I noticed is as soon as throw it in auto takeoff mode there was some oscillations kind of thing in it but it suddenly disappeared when I turn it to auto tone mode

Will update shortly thankyou