Flying Wing for Search and Rescue
Hey Guys,
I've been working on designing a flying wing UAV since 2 months now. Human search and rescue using an autonomous drone is the prime objective of this project.
First Prototype.
One of the major aim of our project is to show how a visual human detection system that uses images from a normal camera can be implemented in software. The system would fit into the larger context of disaster management and more specifically how it can benefit search and rescue operations.
So the first prototype was made but it couldn't fly all that well. The tips stalled while rolling(probably because of no twist and less sweep) and led to a disastrous crash. As soon as our first prototype failed we got down to designing the second version.
I need some advice with the design of the second air-frame.
So I'm pretty satisfied with the numbers Xflr is churning up for the second prototype. But I'm unhappy with the kind of performance I'm getting.
Also I'm a bit skeptical about the amount of twist I've to give to prevent my wing tips from stalling. I'm using the Pankin twist formula and it gives approximately -9 degrees of twist. I'm not sure if this is usual for flying wings or not. I was told anything between 4-15 is normal.
So my doubts about the design are :
1) Is the twist alright or should i reduce it a bit ?
2) What can I do to improve my max Cl/Cd ?
3) Any other design faults you guys see in the design ?
Also some updates on the Image processing part.
HOG detector was successfully tested on a sample camera feed.
Thank you for your time and consideration.
Cheers,
Karan
Comments
Hey @Karan, great work. Am the founder of the Humanitarian UAV Network (UAViators.org) which is publicly endorsed by the United Nations. I'd like to learn more about your human detection software as we've been looking into this to estimate refugee populations, etc. Any chance you can send some info my way? patrick@iRevolution.net
@Karan - Yes - flying wings need airfoils with a very low or positive pitching moment which is one that has a reflex shape. The reflexed part is really the tailplane of a normal aircraft stuck on the back of the wing.
A normal airfoil with a negative pitching moment needs twist to fly in a flying wing. Low or positive moment airfoils can be used without twist or a very small amount.
The MH series of airfoils are very widely used http://www.mh-aerotools.de/airfoils/ and sometimes you can use the thicker higher Cl wing on the tip so it stalls later than the root.
The main point is that most wings on the market use any old airfoil with the elevons set upward to give a positive pitching moment as the designers know that the any old airfoil will work probably just as well in foam as the super special one and be much easier to make. I may also have a wider and easier flight envelope and be generally easier to fly. Some of the super special ones have some really nasty vices.
Yes, you have understood everything correctly.
Okay so correct me if I'm wrong, stability is entirely dependent on CG location and only performance is dependent on the airfoils used.
So for Stephen his elevons would be slightly deflected upwards(say 1/8th inch) in level flight, is this what he meant with "elevons give reflex".
Meanwhile I've started my work on the CAD files for the design. Will be putting them up soon.
Karan, you are confusing trim and stability.Reflex is needed to trim the flying wing without having to deflect the elevons upwards all the time. The last one really hurts performance.
Stability does not depend on the airfoils used.
If you have enough sweep you can use conventional airfoils without twist or having to use the elevons for reflex.
@Stephen That's true we'll never get the exact profile. I have read about aerodynamic twist. Thanks for the link. Are you getting a better performance by using conventional airfoils ?
From what I've read they've a lot of negative pitching moment and ultimately longitudinal stability becomes a huge problem.
Dunno if you have seen this:
http://www.mh-aerotools.de/airfoils/flywing1.htm
It is a pretty good tutorial on wing design. The idea is to use a tip airfoil with a different zero lift angle to achieve a aerodynamic twist and reduce the amount of twist required.
The other problem is that it is very very unlikely that with foam wings the airfoil will be anything like what you plot no matter how good your cutter and templates are. The only way to get anything near is to mould the wings in fibreglass in CNC moulds. A 1 or 2% difference in shape can completely destroy the lift/drag parameters in your polars.
The wing I am building at the moment just seems to have a Clark Y and the elevons give the reflex - go figure...
You should use as little twist as possible. With 30 deg of sweep it should be possible to use no twist at all.
Please also plot the CL distribution.
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