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Copter Tailsitters

@kd0aij @lorbass congratulations, the model fly. The sound is very realistic as we can hear differential thrust working exactly like with my biwing.

Nice to hear. This is called “Reverse engineering” at first the real model and then the Simulation :wink:
May be, for your next Project I’m faster.
It would be intersting to compare the Params Real to SITL in order to know if later the SITL Params could help at the beginnig for a real Model.

I defined 8 servos with mappings to receiver channels 1-8 as in @losawing’s setup:

SERVO1_FUNCTION  77.000000
SERVO2_FUNCTION  78.000000
SERVO3_FUNCTION  77.000000
SERVO4_FUNCTION  78.000000
SERVO5_FUNCTION  33.000000
SERVO6_FUNCTION  34.000000
SERVO7_FUNCTION  35.000000
SERVO8_FUNCTION  36.000000

At one point, I had the flaperon servos assigned to RX channels 3 and 4 instead of 1,2 but the effect is the same as mapping servos 1,3 and 2,4 to left/right elevons as above.

I now run both SITL and RF8 on my Win10 laptop, with SITL running in WSL, and that works well. It’s a quad-core i7 with Nvidia GTX1050 graphics.

There’s definitely something wrong with the motor torque. It looks like the torque control is fighting the ailerons. This is left/right elevon and motors 1/3 while hovering:

So I’ll see if I can reverse all the motors…

Did you swap the prop directions as already realized in Post 124?
As I wrote in my File they where wrong.
How does that look in the real model?

After the reverse engineering, the benchmark…
nice model but 3D printing is a little bit heavy, 50% more weight with same battery.The autopilot is KK2 board. I do not see any transition, the flight looks like q_stabilise mode.

@lorbass I finally got the rotations correct; RFX and params uploaded as BiWing9_swapLR JWL-065 backTorque_AV.RFX here:

video here:

@losawing I guess the BlackFly design’s large fuselage has the advantage of serving as landing gear and, of course a streamlined enclosure for a big payload. Plus it’s amphibious…

I thought first, it’s already your next project which doesn’t fly correct yet.:wink:
And advantage I can see is; It can’t tip over in a windy landing.

Congratulation, a perfect demo flight.
@tridge Unfortunatly can’t reproduce it because SITL and RF8 can’t link.
In the Dev Wiki RF8 ist not explained.
RF9 needs a new InterLink-XD Box and with my experience with RF8 Edit issues I do not trust animore if it will work as described.
And I do not want to install Ubuntu for this one application only.
It is to complicate compared with my FSX from Microsoft which works on 5 PC’s over a simple MS Net.
A simple additional Text-Line in the Application.ini File was enoughe and it works without fighting.

The way the model fly is very close to the real one. That’s impressive.
When flying level, are control surfaces deflected ? Is it complicated to change relative wing pitch and airfoil ?

Elevons are neutral at about 20m/sec 50% throttle and 0 deg pitch


It’s fairly easy to change the airfoil in RealFlight; just have to set the root and tip airfoils for each wing. Incidence should also be straightforward, although I’ve never tried it:

Well, they have made it pretty easy to install Ubuntu on Windows 10:

…and it’s free.

Interesting, no deflection at 50% throttle, downward deflection when speed increase as the autopilot compensate for a tendency to climb and upward deflection when speed decrease. I think it looks like to the behavior of a stable plane, I mean a plane with a right CG position.

@losawing I moved the CG back 2cm with the JWL-065 airfoil:

and it’s still controllable in manual mode, inverted flight still requires some down elevator and it still pitches up as speed increases in level flight.

I also tried the MH-106 13% airfoil with -1 degree incidence on both wings, and that shows less tendency to pitch up but is still stable. I pushed the CG back another 2cm with that wing, and it is still stable with a lot more down elevator authority than the JWL airfoil.

I’m not sure whether those CG adjustments (Z is tailsitter body-frame X) are directly comparable, since the change in airfoil probably moves the calculated CG.

I forget whether you use RealFlight yourself?

No, I do not have RealFlight. I have had always more fun making things, testing and sometime craching…
The first time I made a transition to FBWA, the CG was about 2 cm backward, and the biwing unstable. I think, it had resulted in a crash without the pixhauk help. I will test more…
When I made the design of the biwing, I made it in a very conservative way so I choose the JWL065 for the Cm stability. This is a link to a similar airfoil PW51. You can see that the Cm is almost 0 whatever the reynold number and incidence. This is what we want for a tailless airplane as we dont want the pitch moment to change with speed.
But I think now the biwing is not tailless. It has a very large stabiliser instead, the rear wing. Ecalc allow also to calculate the stabiliser volume and the biwing configuration gives a stabiliser volume of 0.5 which is a normal value and, I think, allow for a more cambered front wing airfoil with higher lift coefficient. As a consequence this airfoil would have a higher Cm with higher variation but the rear wing is there to compensate like a stabiliser would do.
Wings incidence relatively to fuselage does nor really matter but incidence between front and rear matter. I am not able to calculate what should be the angle betwwen wings but obviously it depends on CG position, respective wing surface and airfoils and probably speed target. But at least you showed with RF8 that the relative incidence with the actual CG is good at 20m/s. Nice result…

I’m seeing a strong pitch-up moment at high airspeeds with the JWL-065 airfoil, and am not able to do an outside loop in RF8, even with increased values for GSCMIN. Setting the upper wing incidence to +2.5 degrees relative to the lower wing improves that situation, and there is then very little pitch response to throttle.

With the MH-106 airfoil and top wing relative incidence at +1.0 degrees the pitch response is much faster in manual and qacro and throttle to pitch coupling is not noticeable.

I wonder if these results with RealFlight are accurate enough to be useful.

I have not tested the outside loop but I will try tomorrow with enough altitude… I guess your test was in q_acro mode. I am surprised the outside loop fail, because the differential thrust between top and bottom motors is strong. Your test with increased top wing incidence may suggest there is strong interaction between wing in that specific attitude. Did you try to disable bottom wing elevon ?

Disabling the elevons on the bottom wing didn’t seem to make much difference, but I haven’t looked at the log yet. And I still haven’t figured out why flaperons don’t work. When I assign flaperons, the surfaces don’t even move in the right directions.

Try to follow your motivation. Already installed Win 10.
Do you need to do a command or to enable something in RF8 after starting like discribed in the Wiki for RF9 to connect like this:
On RealFlight 9 go to Settings->Physics and enable the FlightAxis option then restart RealFlight.

And as in RF8, in the manual of RF9 is nothing (FligthAxis) to enable at this place (Settings>Phyics)

Thanks for your link for Ubuntu at MS I got it ready to start and with exit to get off again.

Real Flight VS RF8 won by 5-0 :slightly_smiling_face: As the plane was happy, he made just for you a new figure, a kind of edge loop from hover to hover. The video quality is not great.

Maybe the simulated drag is too low? I’ll see if I can increase it.
Perhaps also comparing a simulation log to the real log would tell us something.
I’ll put a simulated log up in the SITL_models repo.

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