Several people have been asking about the ability of a wing to generate lift when upside down. The answer is yes, an upside down wing will create lift if the angle of attack is high enough. Now being in a rotor configuration further complicates things, but the same principles of physics apply. There is a distributed lift along the wing based on velocity (v) and angle of attack (alpha).

When the sum forces of each wing are added, a single vector is produced for each wing. That vector will determine the stability of the wing (the moment force) and the total lift force generated. It is no different for a flying wing than a spinning rotor, the rotor just has a different load distribution due the the non-linear, radially distributed velocity along the span. These moment diagrams should hold true independent of factor such as wing twist and airfoil discontinuity. At any speed of rotation there will be a combination of left/right alpha which will result in a stable rotation in hover. This also holds true that there is a combination of alphas which will provide a stable rotation at any amount of lift for climb while at any power level. This relationship will most likely not be linear however, which means that as the controller adds power, the ratios of left and right alpha may have to change. this means that the vehicle may not be able to be "trimmed out" to stable but rather adjusted for stability depending on power level.This all sums up to "i may need a computer control system to incorporate a trim coefficient based on power input and collective control, if not a complete gyro stabilization system with a feedback loop. Either way, it can be done, and so help me, it will be. 

I have taken a couple measures to help enlarge the stability bucket to try to make a stable VTOL ascent/decent possible with manual controls. I have added a generous dihedral of 12 degrees to help compensate for dis-symmetry in the wing lifts, and I have put the cg in front of the control surfaces for each wing.  The wing is structurally very sound, made mostly from carbon fiber, so aero-elacticity should be minimized. To ensure that the design is in the ballpark, I will make a test stand to allow it to rotate at low speeds (below flight rotational speed) in order to inspect for any stability issues before full flight testing. 

This complexity begs the question, "why not just use a symmetric airfoil???" Well, the answer is that fine tuning the aircraft for improved performance is what takes it from proof of concept, to a viable tool. I have been getting emails about an Air Hogs toy called a Switchblade. It is pretty much the same concept, but without any of the elegance or performance. The old saying, you can make a washing machine fly if you put a big enough motor on it comes to mind. Air hogs is known for making some really cool, really fun, really unique, and really low cost toys. Although the Switchblade meets all those standards, it doesn't fly very well, or for very long. It would not make the cut for a military or even commercial UAV system, and from the ratings I've seen online, it didn't sell very well as a toy either. 

At the end of the day, creative people will always try to push the limit. Some people will be neigh-sayers and rant about how an idea will never work, and other will be inspired, and take the technology to the next level. I'd rather be the later than the former. Besides, people aren't remembered for being dismissive and correct, they are remembered for breaking convention and proving the "dismissers" wrong. 

Thank you all for your comments and advice. Keep 'em coming!

The first day of testing is complete. I noted several flaws inherent in the design as well as a few ideas for making the vehicle stronger, lighter, and easier to build. There are a lot of changes that need to occur.

1) After completing the airframe I noticed that some of the materials were not strong enough to hold the fastener heads from pulling through (depron). I reinforced the parts with epoxy and re-drilled them to add bearing strength. 

2) The airframe is a bit heavier than I wanted. I think this is due to the center spar being carbon laminates with balsa. there is a lot of excess glue in the mix which could be eliminated by making the spar a single ply of carbon with tow on the upper and lower cap for stiffness. 

3) The way the wings join in this test model was waaaayy overbuilt. I figured that since it was the center spar joiner that it has to be as strong as the wing, but it only needs to carry load from one spar to the other. I think i can cut the material down by 80% and still have a reliable joint between the wings. 

4) A DIYdrones user noted to me that one of the stability issues is that spinning a flying wing causes an oscillation due to the blades not generating an equal amount of lift. This would normally be corrected by having a heavy body down below the rotor to stabilize the vehicle using a low CG. I think the dihedral will compensate for that to some degree. 

5) The aft mounted motors were vector thrust controlled to remove the need for elevons (and all control surfaces in general. This may have been a good idea on paper as it increased the responsiveness of the input at low speeds, but it has some very nasty stability effects on the vehicle in VTOL mode. That whole section will have to be redesigned. I think I can fix the issue by mounting the engines forward of the wing and extending the elevons aft using a nacelle structure off the motors. This will give me support, stability, and a good mounting point for the servo. Win, win, win. 

6) The mesh structure was sufficient but there was some FWD-AFT bending in the wing since there were no ribs to keep the aft trailing edge form becoming compressed into the spar. I will change the mesh design a little to add stiffness along the chord direction as well as include a few fwd/aft stiffening members at the root, nacelle, and tip. 

7) I may have over estimated the amount of Electric Speed Controller (ESC) I needed. I am using two small motors, and two ESCs. I purchased 30A ESCs, but that was way overkill. I have 8A ESCs coming from hobbyking now. 

The new design is below. In theory this should offer enough stability to solve my VTOL issues. In practice, I may need a gyro to actually make it work the way I want. 

The new wings went together in a snap. Thank you auto-winder!

I struggled with weather or not to post this idea. I determined that there is a big gap between an idea and a flyable aircraft. (even an RC one) That being said, there is a lot of value in expressing ideas and getting feedback. I have decided to think of this project as an "open-source" project. After all, what good is an idea if one just keeps it to themselves?

I have included an overview Vertical-to-Horizontal flight system to make the transformation from one mode to the other. Some refinement will be needed as the design matures. I can already tell that stability and control during the flight transformation process will be less than graceful. 

Here are some photos of other transforming VTOL aircraft. (Most of which are UAV systems due to the difficulty in moving a person around inside something with so much flight instability). These vehicles were chosen because they have all been flow in in prototype form. There is a huge gap in credibility between making a computer model, and a flying prototype. 

This is called the FlexRotor by Aerovel. It has a large propeller to lift it vertically from the tail-sitting position. The little props on the wing tips act as anti-torque rotors. It has a high disk loading since it is supporting its weight on a propeller and its cruise efficiency is somewhat reduced by the fact that the prop and engine are over sized to allow for VTOL. This means the weight is higher than it would be if it only flew horizontally. 

These vehicles, the S-25, D-150 and K-200 UAVs by AERIE, are similar in concept to my design. They utilize a flipping wing with rotors on them. The wings can face opposite directions and the propellers will cause the plane to spin. the wings then generate lift. Once in flight the wings can flip back to aligned and the vehicle can fly like a traditional twin propeller airplane. AERIA claims they can get 24 hours out of these vehicles.

This is the Navy Research Labs "Stop-Rotor". This helicopter has a wing that flips over and locks in place to go from a helicopter to an airplane. The propeller in the back has a rudder behind it to act as an anti-torque rotor during horizontal flight. 

This cool vehicle is the "Dos Samara", named after the Samara seed which spins as it falls from its parent tree. This plane is similar to the stop rotor in that the props act as lifting rotors (like a helicopter) then lock to act as lifting wings in horizontal flight. This (more elegant IMO) design has counter-weighted single-bladed rotors on the tip of each wing. This means that there is no flipping of wings. The blades simply stop rotating and add lift in forward flight. The blades spin in opposite directions which means no anti-torque is required either. The downsides here are that you have to transfer a lot of power into two rotating structures. That little propeller in the back must use a lot less power than the lifting rotors. That means you have to carry around a lot of unusable engine and transmission weight when in horizontal flight. 

There are several "high risk" features of this aircraft design project. Not the least of which is the wing manufacturing process. I will be making fiberglass male tools and wrapping them with prepreg carbon tow (ribbon). This will create a thin mesh in the shape of the wing which will be covered with plastic film. A spar will add the structural support. The wing tool is made larger than the actual wing to allow for excess material. Tool Edge of Part dimensions here:. http://j.mp/WX9az0

The wing tool was made from CATIA generated sections of the wing which were cut out of thin foam. A balsa spar and trailing edge held it all together while I covered it with strips of packing tape. This created a smooth and stable surface to start adding fiberglass veil plys. 10 plys later the wing is pretty sturdy, fairly smooth, and actually quite light.

Bondo time. For those who don't know the joy of fixing old cars or motorcycles, Bondo is a paste like filler which hardens in about 5 minutes to a wood like hard sand-able surface. If you love sanding, this is your wheelhouse. For me however, I would have worn a bunny suit if I had one. That stuff got everywhere. There was a layer of dust in my garage so thick, it looked like it had snowed.

It was worth the trouble however, as I created a great mold for my wings. I will use my home-made filament winder and resin-ator to get the job done.

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.