Should we be using different bearings for our high-speed rotor blades which are used on the most common drone types like the Quadcopter designs? I believe so, as these drones need to be very reliable, long range, and will have important cargo onboard as part of their important missions whether on the battlefield, commercial application or delivering you a very important pizza or Amazon package.
Not long ago, I was listening to an interesting NASA podcast on rotorcraft air bearings and foil bearings:
NASA Aeronautics Research Technical Seminar Podcast Series:
“Technical Seminar 16: Oil-Free Turbomachinery Technology for Rotorcraft Propulsion and Advanced Aerospace Propulsion and Power 1:14:33 11/24/2008. Oil-Free Turbomachinery Technology for Rotorcraft Propulsion and Advanced Aerospace Propulsion and Power”
This got me thinking that not only is this relevant to today’s military aircraft, space flight propulsion, future jet engines, but also relevant for high-speed little motors that spin well over 10,000 RPM. If we want these motors to last and if there are multiple motors per flying craft; MAV – Micro Air Vehicle, UAS – Unmanned Aerial System, or PFC – Personal Flying Craft (Air Taxi) then it makes sense to use such technology.
You see, I was thinking that it would sure be nice to lighten-up the motors on such future VTOL (vertical take-off and landing) aircraft concept designs since there are often 3-4 motors or more. Some of the benefits are very apropos:
1.) Nearly Maintenance Free Bearing Assembly
2.) Reduced Weight
3.) More even friction heat
This is a very good thing due to the geometry and weight distribution that Quadcopters have. Lower weight means more payload, less fuel and/or longer range.
Perhaps the weight savings of lube oil, (2-types needed in normal current helicopter technology) on each of the four motors could also give weight space for electromagnetic bearings with a thrust bearing combination around the outer ring on the rotorblades to control vibration and free-wheel free of drag, and easy start. If the motors happen to be electric, even better in this case. If high speed gas turbines we save weight and add safety to a nearly maintenance free design.
Some of the NASA tests have concluded 60,000 hours with no damage or need to replace parts or bearings. For a rotorcraft this is nearly unheard of due to the harsh environment they fly and the fact that the motors are under so significant load all the time the aircraft is airborne.
Now then, for the outer assembly – more safety is garnered by outer bearings, but reduced friction is the key, thus, electromagnetic system makes sense, but due to weight perhaps not 100% magnetic. This article explains the concept of Thrust Bearings and the combinations I propose we employ.
“Design, Fabrication, and Performance of Foil Gas Thrust Bearings for Microturbomachinery Applications,” by Brian Dykas, Robert Bruckner, Christopher DellaCorte, Brian Edmonds, and Joseph Prahl. (NASA/TM-2008-215062, January 2008; GT2008-50377).
Currently, we know that the quadcopter design is probably one of the most stable designs yet, but most quadcopters are only toys, small drones, and have a limited payload. If we want these types of designs to fly around people, heavy weight, or become our future flying cars and air taxis, commuter shuttles, we’ll need near 100% safety, that means current rotorcraft components may not be viable. Please think about the future, maybe you can have a flying car after all?
*Additional Cites to Consider When Evaluating This Concept:
A.) “Preliminary Analysis for an Optimized Oil-Free Rotorcraft Engine Concept,” by Samuel A. Howard, Robert J. Bruckner, Christopher, Kevin C. Radil. (NASA/TM-2008-215064 March 2008; ARL-TR-4398).
B.) “Tribology: Principles and Design Applications,” by R. D. Arnell, P. B. Davies, J. Halling, T. L. Whomes.
C.) “Measurements of Drag Torque, Lift-Off Journal Speed and Temperature in a Metal Mesh Foil Bearing,” by Luis San Andres, T. A. Chirathadam, Keun Ryu, and Tae Ho Kim (J. Eng. Gas Turbines Power 132(11), 112503 (Aug 11, 2010) (7 pages)doi:10.1115/1.4000863).
D.) “Thermohydrodynamic Model Predictions and Performance Measurements of Bump-Type Foil Bearing for Oil-Free Turboshaft Engines in Rotorcraft Propulsion Systems,” by Tae Ho Kim and Luis San Andres. (J. Tribol 132(1), 011701 (Nov 11, 2009) (11 pages)doi:10.1115/1.4000279).
E.) “Foil Bearing Starting Considerations and Requirements for Rotorcraft Engine Applications,” by K. C. Radil (Army Research Lab) and C. Della Corte (NASA). August 2009, Doc # 201200112857, (ARL-TR-4873, E-18263).