ObliX_neo: redesign of multirotor-blimp-drone

We have been silently working for a long time and now it is here: 

A complete redesign of ObliX! [http://danielwibbing.wix.com/oblix]
Since I posted the first design for our airship, many experts have contacted me, explaining to me why a lenticular shaped airship would not have very desirable flight characteristics. Their main concerns were:

 

  • Lenticular airships are not stable concerning their pitch angle and straight flight (Munk Moment). Consequently the airship will easily pitch up and down.
  • An oblate spheroid does not have a defined break-off point for the air stream. Instead the break-off point changes position frequently causing a Kármán vortex street, trying to throw the airship off course.
  • Lenticular airships have a big coefficient of drag.

 

I especially want to say thank you to Johannes Eißing, Andreas Burkart, Peter Hanickel and Jodoc Elmiger for their valuable advice. Based on their feedback and calculation tools, we started again from scratch. After numerous air-flow simulations, this is the first rough design for the new version "ObliX_neo" we ended up with. The CAD model on ObliX’s homepage will be given a lot more details soon.

 

We would be very happy to get your advice, questions or any other comments to be able to improve this new design. 
Maybe you would even like to join our team? Then feel free to contact me e.g. here.
 
Best regards,
Daniel
P.S. Have a look at our outdoor test flight with the silent_runner.

Views: 1544


MR60
Comment by Hugues on November 28, 2014 at 2:54pm

I had contact with Andreas from Stuttgart. He proposed me also his balloon but at the time I asked him if he could integrate an APM on it. He said he was working on it but no news since then (almost a year ago if i'm not wrong). Do you use some kind of autopilot / flight controller ?

Comment by Daniel Wibbing on November 28, 2014 at 3:37pm

Hey Hugues,
yes, we intend to use an autopilot. It might be Arduino-based or Pixhawk-based, but we are not yet sure about it. With  the detailed design coming up next, we will have to make up our mind about that. Any recommendations?

Comment by Daniel Lukonis on November 28, 2014 at 6:53pm

Very nice design! I especially like the camera on the bottom.


MR60
Comment by Hugues on November 29, 2014 at 3:28am

Daniel, I would certainly recommend to use pixhawk in place of APM as it is powered by a stronger CPU, more connections possibilities (such as the future CAN bus) and more memory to run any software you can think of right now (8k APM versus 256k Pixhawk). Pixhawk might be a bit heavier by a few grams...

Comment by Daniel Wibbing on November 29, 2014 at 3:57am

@ Daniel Lukonis: Happy you like it! The camera ball on the bottom is only a place holder at the moment, for any kind of sensor you would like to mount on the payload bay.

@ Hugues: Thank you for your recommendation! So far I was considering and Arduino DUE with ist 84 MHz and 96 KB SRAM, but the Pixhawk really looks even more powerful. :)

Comment by Petr Hubacek on November 30, 2014 at 2:41pm

@ Daniel Lukonis: excelent idea. Just you have at least four redundant propellers (two on each side) that add unnecessary weight to the blimp. The weight increases also due to necessary motor & propeller fixation. Good luck.

Comment by Andrew Rabbitt on November 30, 2014 at 9:10pm

Interesting design Daniel. I think Petr is onto something with the number of motors, but also I think you have too many fins too.  The forward fins cancel out the effect of the rearward fins generating a net-zero pitch / yaw stability moment.

Comment by Daniel Wibbing on December 1, 2014 at 1:23am

@ Petr: You are of course right by saying that I have redundant propellers. I decided for this reduncancy to improve maneuverability and stability against gusts of side wind. The number of propellers is indeed the no.1 criticism experts like you have given me so far. Do you have a specific suggestion for how a better rotor arragement would look like?

@Andrew: Could you explain a little more what you mean? I thought, to be able to fly fowards and backwards in the same manner, I would need a symmetrical arragement of fins. With this fin arrangement, if I wanted ObliX to go right, I would move the front and rear rudders to the right and would thus cause a momentum of rotation around the vertical center axis in clockwise direction. Here is a little draft in which I drew the wind force as black arrows and the resulting forces on the rudders as red arrows. Do you think that is wrong?

Comment by Andrew Rabbitt on December 1, 2014 at 2:27am

Yes Daniel, it will probably yaw, but ask yourself where the centripetal force is going to come from if you (presumably) want to execute a turn (i.e. follow an arc) rather than just a yaw about the centre of gravity?  What happens in a slip or a skid?

If you want to be able to fly reversibly, then you might have to ditch passive stability that fins will give you and just fly it as a quadcopter tipped through 90° and use differential thrust for roll, pitch and altogether now for forward thrust

Comment by Daniel Wibbing on December 1, 2014 at 2:57am

@ Andrew: You are certainly right that a yaw around the center of gravity does not cause a change in the direction of flight yet. But as the body yaws about an angle, the bow and stern propellers also rotate and face into a new direction. This is where the centripteal force comes from ... at least that's how I imagine it. :)

I added the fins because they are much more effective in causing a change in direction than propellers would be during fast forward flight. Why do you think I would have to ditch this passive stability?

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