Should we use different bearings for our high speed rotor blades which are used in the most common drone types like Quadcopter designs? I think so, as these drones need to be very reliable, long-range, and will have a significant cargo on board as part of their important missions, be it on the battlefield, in a commercial application, or delivering you a very important pizza or a Amazon package.
Not long ago, I was listening to an interesting NASA podcast about air bearings and aluminum bearings:
NASA Aeronautical Research Technical Seminar Podcast Series:
“Technical Seminar 16: Oil-free turbomachinery technology for helicopter propulsion and advanced aerospace propulsion and power 1:14:33 11/24/2008. Oil-free turbomachinery technology for helicopter propulsion and advanced aerospace propulsion and power”
This got me thinking that this is not only relevant for today’s military aircraft, spaceflight propulsion, future jet engines, but also for small high-speed engines spinning at over 10,000 RPM. If we want these engines to last and if there are several engines per flying ship; 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 surely be nice to lighten the engines in such future VTOL (vertical take-off and landing) concept aircraft designs as there are often 3-4 engines or more. Some of the benefits are very relevant:
1.) Virtually maintenance-free bearing assembly
2.) Reduced weight
3.) More uniform 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 greater range.
Perhaps the weight savings of the lubricating oil (2 types needed in normal current helicopter technology) in each of the four engines could also give weight room for the electromagnetic bearings with a combination of thrust bearings around the outer ring in the Rotor blades to control vibration and release – Free wheel drag and easy start. If the motors are electric, better in this case. When it comes to high speed gas turbines, we save weight and add safety to a design that requires almost no maintenance.
Some of NASA’s tests have completed 60,000 hours without damage or the need to replace parts or bearings. For a helicopter this is almost unheard of due to the harsh environment in which they fly and the fact that the engines are subjected to such a significant load the entire time the aircraft is in the air.
Now for the outer assembly, the outer bearings get more safety, but reduced friction is the key, therefore the electromagnetic system makes sense, but due to the weight it may not be 100% magnetic. This article explains the concept of Thrust Bearings and the combinations that I propose we employ.
“Design, Manufacture, and Performance of Reed Gas Thrust Bearings for Microturbomachine 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 just toys, small drones, and have a limited payload. If we want these types of designs to fly around people, heavyweights or become our future flying cars and air taxis, commuter shuttles, we will need close to 100% safety, which means that current helicopter components they may not be viable. Please think ahead, maybe you can have a flying car after all?
* Additional quotes to consider when evaluating this concept:
A.) “Preliminary Analysis for an Optimized Oil-Free Rotor 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 applications of design”, by RD Arnell, PB Davies, J. Halling, TL Whomes.
C.) “Measurements of drag torque, takeoff journal speed and temperature in a metal mesh sheet bearing”, by Luis San Andrés, TA Chirathadam, Keun Ryu and Tae Ho Kim (J. Eng. Gas Turbines Power 132 (11), 112503 (August 11, 2010) (7 pages) doi: 10.1115 / 1.4000863).
D.) “Predictions of thermohydrodynamic models and performance measurements of bump-type reed bearings for oil-free turboshaft engines in aircraft propulsion systems”, by Tae Ho Kim and Luis San Andrés. (J. Tribol 132 (1), 011701 (November 11, 2009) (11 pages) doi: 10.1115 / 1.4000279).
E.) “Sheet Bearing Startup Considerations and Requirements for Aircraft Engine Applications”, by KC Radil (Army Research Laboratory) and C. Della Corte (NASA). August 2009, Doc # 201200112857, (ARL-TR-4873, E-18263).