I have looked around the forums and have seen several discussions about variable pitch. Most revolve around construction and configuration.
What I want to know, is does it make the quad fly any better?
If I go the route of variable pitch, I will use tail booms and tail rotors from a T-rex 450 going to a single main gear in the center and one or two drive motors. Obviously, this set up would cost more that a conventional quad with four prop/motor/speed control arms.
Anyone flown both types (fixed and variable)? What did you think?
Keshka
Replies
I'm a big fan of Helis and don't have any quads, so you might think I'd be a proponent of this idea. But I'm not.
There are a number of things going on here.
1. Lifting efficiency. Is it better to use flat helicopter blades or propellers? If you use relatively long rotors spinning at a low speed, you will gain efficiency. But, most helicopter blades on the market are made for 3D, and are thus less efficient at lifting than a single-direction profile. I think that propellers will get back some efficiency advantage because the blade angles along it's length to maintain a true pitch value.
2. Complexity. Obviously it's more complex. It's more complex than a quad, and probably more complex than a heli. Depending on how you do it, it could be much more complex than a heli. So what really is the point? If you are OK with the complexity of a heli, why not just fly a heli, and benefit from the longer flight time and payload resulting from the massive rotorspan?
3. Stability. The servo system will have slop. Period. I think any benefit you get from quickness of response will be lost in servo mechanics. Plus, I've seen quads so stable you could probably balance a ball on their nose. I've also seen quads incredibly responsive and acrobatic. I really don't see room for improvement?
I'd be much more interested in seeing somebody work on a tandem helicopter or tilt-rotor airframe instead. Both of those offer significant advantages and are worth pursuing.
I think it would help make it much more complicated...
...and increase the frequency response of your thrust vectoring controller
Adding variable pitch means you have twice as many actuators now - one speed controller and one pitch controller for each motor/propellor. You can begin to see why most like the simplicity of a fixed pitch quad instead...
We too looked into doing this. There was a company I saw was starting to make one doing it as you mention, which is the easiest starting point (Design wise). I think what pushes most into doing it the traditional way is because of less parts count, less tweeking etc doing it direct drive. If it were gas ran I would believe that having a steady RPM like that of using a governor would be a huge bennie as you could set pitch curves to match max economy/power etc. unlike the insane rpm needed to fly using direct drive. I am no PHD on this and many here are.
Dave
22,000 members and no one has done this? Share! pretty please!