Hello,
This blog will serve to record my progress in the development of a new type of aircraft. This aircraft will combine the efficiency of low disk loading vertical flight with efficient, long range horizontal flight. I plan to design and build a functioning model using composites and electric powered RC components. Future designs will be of a larger scale and utilize more efficient components such as a heavy fuel power system and digital flight control systems.
The original concept for this vehicle came from noticing how some birds, like the kestrel hawk, can soar effortlessly for hours yet are also able to hover over a target with great precision This is a difficult problem in aircraft since hovering and flying require two totally different mechanics and one often makes the other much less efficient. I am developing this new technology with a focus on flying wing designs and the modern need for vertical takeoff and landing in our ever more congested operating environments. I plan to focus on UAV missions since the technology I am proposing does not bode well for human passengers. (more to come on that later)
I am a professional engineer in the field of UAV design and development, as well as composite structures manufacturing. I look forward to seeing this idea really take flight.
I have completed a preliminary design. The model is built in CATIA V5 R19.
The wing has a 6 degree dihedral and a 22 degree sweep. The wingspan is 24 inches and the chord is 6 inches at the root and 2 inches at the tip. There is a 6 degree twist to the wings after the midpoint as well. I went with winglets to reduce washout and induced drag as well as to add directional stability. I used a NACA 2415 airfoil for several reasons.
1) It has a high L/D
2) It has all positive surfaces (it does not cut in on itself) which makes tooling a lot easier
3) It has a forward moment which will help stabilize the aircraft in pitch since a flying wing has limited elevator control.
The rest of the design factors were determined using a lot of research into previous designs and some intuition.
Comments
The inspiration came from several images I saw of 1950s era clipper ships imagined without tails.
As for the prop location design change...
I was looking for a way to move the props more outboard tin increase the moment they have on the wing during VTOL mode. having them too far inboard doesnt give you and moment, and putting them too far outboard causes a lot of other problems such as controlling the twist of the wing from aeroelastic effects, and putting mass to far out might put outboard load on the motor mass (potentially pulling it right off the wing!) Ultimatley, the middle of the wing sounds like a good place to start, Testing will show if that gives me the umph needed to get it into the air.
The asymmetrical airfoil issue is a big concern. I have mapped out the lift gradients and I believe there is a balance between differential elevon input that will give a stable configuration. I will put up a post about that next. Further, some testing with a "wing on a stick" might do the trick in nailing down the actual alpha value for the stability sweet spot. Ill have to video tape that and put it on the web if it goes well.
As for the models, this project is still "for profit" so I don't want to give away the goods for free just yet. If all goes well, I will be able to sell the airframe for a great price since filament winding the wing is actually a very low cost process.
Thanks for you questions.
This is a wild looking wing. Any inspiration from the Horten H.IV? It's one of my favorite designs.
I see you've moved the Props closer to center-line of the vehicle from some ealier concept images. What inspire this change if you don't mind me asking?
How parametric are you going with the CAD model? I found this document inspiring, maybe of interest: http://srl.gatech.edu/Members/ashah/ME%206104%20project%20report.pdf
Are you concerned at all about the difference in lift using an asymetrical airfoil inverted during VTOL? I'm trying to picture how wing twist will interact with that.
Final question: Are you willing to share solid models and/or .sldcrv files for the NACA 2415? :P
will be interesting to see how it progresses.