PPRuNe Forums - slowrotor ~ this thread's for you

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Dave, i hate to break it to you but the dinosaurs are extinct. My own theory is that they died out due to mechanical complexity and poor payload-range performance. :E

Actually, a peculiar fact of nature is that it never evolved any rotating systems (outside of several microscopic examples). So if birds had evolved rotors instead of wings what would they look like?

Slowrotor, i'm still trying to figure out what the typical mission profile of your machine is? Are you trying to achieve fixed wing efficiency/range but with limited endurance VTOL landing? Even with a turbo-piston engine you will struggle to get much speed. :confused:

Basically i don't understand why you are rejecting the rotor as a main source of lift? Why not go the other way and design a rotor with large enough blade sections to handle lift at zero RPM. Then you can play with variable rpm counterrotators without any fear of rotor resonance...

Mart.

What is neat about the Microrapter is the functional association between the location of the feathered feet and the flight attitude.

Quote:

a peculiar fact of nature is that it never evolved any rotating systems

http://www.zylex.geek.nz/tumbleweed.jpg :E :)

Dave

Hehehe - that picture made me chuckle!

the only other I can think of is the sycamore seed

Hmmm, didn't think of that.

Perhaps what i should have said is that nature never evolved any stator-rotator systems. This includes wheels, rotors, propellers, motors and in fact anything which requires roller bearings and seals to work.

Even here there are some single cell examples of chemically driven rotating motors.
http://ourworld.compuserve.com/homep.../flagellum.jpg
http://www.allaboutthejourney.org/mi...-organisms.htm

Quote:

The so-called "bacterial flagellum" is what propels a bacterium through its microscopic world. The bacterial flagellum consists of about 40 different protein parts, including a stator, rotor, drive shaft, U-joint, and propeller. Through 21st century magnification technology, we now understand that a simple bacterium has a microscopic outboard motor! The individual parts come into focus when magnified 50,000 times using electron micrographs. These microscopic motors can run at 100,000 rpm. Nevertheless, they can stop on a microscopic dime. In fact, it takes only a quarter turn for them to stop, shift gears and start spinning 100,000 rpm in the other direction! The flagellar motor is water-cooled and hardwired into a sensory mechanism that allows the bacterium to get feedback from its environment!

http://en.wikipedia.org/wiki/Flagellum

Graviman,
To address your question:"Slowrotor, i'm still trying to figure out what the typical mission profile of your machine is? Are you trying to achieve fixed wing efficiency/range but with limited endurance VTOL landing? Even with a turbo-piston engine you will struggle to get much speed."

I think the bird flight discussion here is a good start.
Consider the hummingbird to be the natural world equivalent of the helicopter. The hummingbird burns more fuel than a seagull because it stays in rotary wing mode. The seagull can maintain forward flight with occasional power strokes between energy saving glides and is more efficient. The seagull cannot hover for more than a second, I think, but this brief hover ability is all the seagull really needs to land on a rock perch.

A brief hover is all that is needed for a fixed wing. And if a hover is not possible in the first edition, direct lift is still useful in that the landing run could be as short as a few feet. In fact, it might be better to forgo attempts at hover as this requires additional complex control ability.

I was in a Pilatus Porter turboprop fixed wing that landed on the muddy tundra of Alaska in an area about the size of a tennis court. The pilot locked the wheels to eliminate mud flinging and applied full reverse and we stopped in about 50 feet it seemed.
The seagull lands in a similar manner, gliding in with a burst of reverse thrust just before touchdown the same as the STOL airplane. But the seagull also has brief LIFT added with reverse thrust and is therefor capable of a shorter landing. This extra lift, directed up and rearward is what I seek to provide, only needed for a few seconds. Turned forward and upward these lift fans would provide a quick launch.

Does this make sense?
slowrotor