Here is a video of an inherently pitch-unstable tailless design that I built to investigate the interaction between aerodynamic performance and relaxed pitch stability in tailless aircraft. It’s best to watch this full -screen or you might miss some of the details. The video shows the model flying with computer stabilization and with the feedback control turned off which results in immediate pitch divergence. The active control system is based on modified dRehmFlight open-source software and is explained at the end of the video. Placing the CG behind the neutral point allows this design to trim with nearly optimal flap deflection for low drag at each lift coefficient, whereas the inherently stable design trims with flap deflection that produces increased drag and reduced maximum lift. This idea is not new, it was first proposed in the 1940’s, and I flew an unstable tailless demonstrator 36 years ago to test the idea. This model is a smaller, much simpler version of my original demonstrator.
Is this video available in downloadable form?
Steve, you always do the coolest things. I really enjoy seeing your amazing projects!
Henry Rebbeck you've gotta follow Steve.
I was just talking about this the other day with a colleague. I had pointed them to your project from the '90s. With all the miniaturization and widespread automation, even in little RC toys, I'm a little surprised we haven't seen more unstable products in the uas space. I guess my first suspicion is that the AOA sensor can present fieldability challenges. I saw some very small three-hole and five hole probes at auvsi that would be interesting to explore.
Amazing Steve!
Thanks for sharing
Love this article.
Awesome Steve. For a long time it’s been clear that the drag cost of stability can be excessive, but the consequence of instability is a deal breaker. Are you familiar with my 2004 breakthrough? Instead of stability through drag increase, we achieved exceptional stability and efficient control through drag reduction! Depending on the mission, in many cases, adding flight surfaces actually reduced total drag and induced drag by huge amounts. I flight tested it for years to wrap my head around it, but after I got the patents filed I got good numbers out of panel codes and awesome ones out of LES. Your test platform would be an excellent lab to see that interaction and resulting span efficiency as we did.
Sr. Aerospace Engineer & UAS SME
1yI assume this onr jas a symmetric airfoil, otherwise it would need a constant "reflex" by upward flap deflection. If this is the case, how do you trim at a positive alpha when Cm0 is zero?