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.
Comments
Rai, by the way, what are you currently doing in Koeln?
Hi Rai, I'm very happy to read your comment!
I just watched your blog post Dayaks and Drones - The Movie and thought that this might be a great application for ObliX. I would love to hear your stories from the field and what kind of challenges you met. ObliX is still in the design and calculation phase, so I would be very happy to take your requirements into consideration. :)
Daniel, first of all amazing idea! That's what we need in the field monitoring and mapping the forest and other ecosystem, the combination of endurance and autonomous flight. ObliX has the big potentials for our research. I myself is a newbie here and have never been trained as an aeronautics engineer, however I would love to support in any ways I can (probably story from the fields, challenges etc.) the development of ObliX. Plus, I am also based in Germany (Koeln) at the moment. Congratulations and let's do keep in contact!
Andrew, of course the rudders alone don't cause a turn in flight direction.They only cause a yaw movement. But this yaw movement causes the front and rear propellers to point into a new direction (blue arrows). This is what will cause ObliX to move into a different direction as long as the rudders are deflected out of the direction of movement. Like this ObliX will be able to fly a turn. It works much in the same way as the spaceship in the game Asteroids.
Have fun playing! ;)
You have no net centripetal force, Daniel. The lateral forces that you show cancel each other out, although they do produce a yaw moment, but no net force to execute a turn.
http://en.wikipedia.org/wiki/Free_body_diagram
Andrew, I don’t know if this is what you meant by the „free body diagram“, but this is how I imagine ObliX would do a turn in 2D in an indoor setting.
blue arrows: thrust vectors of bow and stern propellers,
black arrows: vector of relative wind direction
red arrows: vector components resulting from wind to rudder interaction
Where did I make a mistake here?
I think you'll understand things better if you sit down and draw out a free body diagram for the system. Start in two dimensions, keep your vector sign convention clear in your head, model your fins as (symmetric) aerofoils with flaps and start adding up all the forces and moments.
It will become obvious very quickly.
Andrew, that sounds quite interesting. Sorry for being such a newbie, but could you explain this a little more, please?
Daniel, your bow and stern propellers aren't going to produce any significant centripetal force unless the aircraft is in a huge skid.
Regarding passive stability, with fins fore and aft, you don't actually have any. If you want some, you'll have to delete (or stow) the fins at the bow
@ 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?
-
1
-
2
of 2 Next