Full Scale Quad - Composite Rotor Blade

Here are some photos of my progress on the rotors for my full scale quad.  This quad design targets a 200 kg gross wt with 4 rotors of 2.5m diameter.  It's mot much progress, but if you're interested here are the pics.

Rotor Tip Weights

Rotor Tip Weight against leading edge (fiberglass) rod.

Layup of leading edge portion of airfoil.  Wrapped with 2 layers of 6 oz cloth at 45 deg angle to provide torsional rigidity,

Also, the back end of this section (or this whole assembly) creates a spar which gives rigidity to the blade.

Preparing to glass the tip portion of the leading edge spar section.  This will envelope the lead tip weight in glass.

Attaching the rotor tips (shaped wood pieces that rounds the sharp edges to reduce corner stresses on the fiberglass cloth skin.Main foam core placed in position behind the leading edge spar section.  Trailing edge is 3/4 x 1/16" aluminum strip with very thin tapered wood strips to give correct taper.

Glassed rotor (tip end).  You can see rotor tip cap (wood) and foam core with body filler in areas to smooth the surface.

Flashing of excess fiberglass skin has not been trimmed from trailing edge yet.  This glass was wrapped from end to end so as to give strength along the length of the rotor and support the centrifugal loads.  Tension in the glass skin is transferred to the inboard tip cap which rests against a composite beam, which in turn is bonded to the FlexElement bearingless hub element.

This is the FlexElement end.  Quilted blanket is part of my curing tent setup which allows me to cure the slow-set epoxy at 55C without melting the styrene foam core.

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Comment by HyperGuy on March 4, 2016 at 6:38pm

Umm.. as an aerostructures engineer myself, can I ask what testing you are going to do to verify structural integrity? Is this to carry a person?

Comment by Hector Garcia de Marina on March 5, 2016 at 2:01am

How are you going to control it?

Comment by Randy Sonnicksen on March 5, 2016 at 9:06am

Hyper - My approach so far has been destructive testing, but obviously I won't destructively test a whole aircraft.

If this project gets that far, it will start as A pair of rotors on a pivoting test stand (to test how heavy rotor reacts to gyro effects, Then as a teathered drone.  Then as a free drone, Then as a fully loaded drone.  I will also do some cycle testing of main structural elements to verify fatigue life.  I'm open to suggestions.  

Comment by Randy Sonnicksen on March 5, 2016 at 9:11am

@Hector

Control will be with a typical quad-copter flight controller such as ArduCopter.  I will test large scale RC servos for the pitch control.  I will also need to write some custom code for an Arduino to work as a speed controller, and to monitor each rotors speed to detect a transmission failure.  Haven't worked on that too much yet.  Just thoughts.I might have to go back to rotor design if CG/CL of rotor not correct and pitch forces are too large for servo.

Comment by Hector Garcia de Marina on March 5, 2016 at 10:37am

@Randy

There are not many quadcopters around with such a big scale. Among other reasons, one very important is that the physics model gets complicated. In other words, aerodynamics. I am not aware of the current status of the control loops in ArduCopter, but I can tell you very certainly that standard PIDs controller will not work as they do with their small brothers. Keep that in mind. 

It is a nice project but very difficult one! Good luck!

Comment by James Downing on March 7, 2016 at 11:23am

Randy, are you putting any blade twist into your design?  I'm not sure how much analysis you've done on your airfoil and AOA, but I've noticed that sometimes the blades have a large incidence angle near the rotor head, and practically none at the tips to account for the various radial airspeeds that the sections of the blade will encounter.  It looks like your blade is uniform throughout and untwisted?

Comment by Randy Sonnicksen on March 7, 2016 at 12:06pm

@James,

I've got a model in Excel that analyzes the aerodynamics of the airfoil from root to tip.  My design has no twist, and that is primarily because I plan for this design to be able to auto-rotate.  My simple calcs tell me that anything inside the 35 cm radius will not produce lift, which is why my FlexElement is 14" long.

At the tip of the rotor the pitch is 15.2 deg which yields a 9 degree AOA with downwash factored in.

Probably biggest error from inability to model tip vortice effects. Tip airspeed is mach 0.228 (somewhat arbitrary to put my AOA in a comfy zone.) Rotor RPM=600. 

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