EVTOL Propellers complete guide

aircraft propellers there are so many types High bladed low blade high-pitched low pitched ducted non-ducted coaxial Contra rotating and core rotating Q-tip toroidals edfs but which ones are the best what are the breakthroughs in propeller technology what are the fundamentals of selecting the best propeller how can I make my aircraft more efficient all of this will be covered in the video so do watch it till the end the types of propellers we will be covering in the video are being used in the upcoming EV toll aircraft so anyone who's looking to design or dissect the design of an evtool would find this video very informative let's begin with the four basic facts that apply to all propeller types the limiting factor of a propeller is the tip speed the speed at which the propeller cuts through the air increases as we go from the root to the tip of the propeller the tip speed of a propeller is kept subsonic that is below Mark 0.8 and this is to avoid the formation of shock waves which significantly increase drag and Noise in most cases it's kept around 480 miles per hour or 770 kilometers per hour which is about Mach 0.6 having said that there are certain propellers which are capable of achieving supersonic tip speeds such as the ones in the Tuple of tu-95 it's an aircraft that can reach speeds of up to 575 miles per hour or 925 kilometers per hour the speed at which the propeller will achieve its peak efficiency depends upon the shape and the angle of the propeller blades therefore it's important to take into consideration the speed of the aircraft at which it will be traveling for most of the time and design its propeller accordingly second thing we have to learn is that if the number of blades are increased then we get more purchase that is more thrust from the propeller for the same RPM the motor however will draw more power from from the energy source as the blades will meet more resistance for cutting through the air it should be understood that doubling the number of blades on the propeller would not double the thrust the addition of each single blade follows the law of diminishing returns therefore adding more blades to an existing propeller for higher thrust is a less efficient process compared to adding a new propeller in simple words more blades equal more thrust with more drag which reduces efficiency on the other hand less blades equals less thrust with less drag thereby increasing efficiency longer blades instead of more blades would be the ideal choice but we are limited by both tip speed and the length of the landing gear sometimes because we are cramped for space or limited by weight adding more blades to increase the thrust is the only way forward the third fact to know about propellers is that there is no such thing as a single propeller that is ideal for all flow regimes at low speeds for higher efficiency we require a propeller that has a lower pitch or low angle of attack for better acceleration and Power on the other hand at higher speeds we require a propeller with a higher pitch it is also for this reason that to provide an ideal angle of attack along the entire Blade the blade has a Twist to it which varies the pitch angle of the blade from the low at the root too high at the tip so the pitch of the propeller is like the gearbox in a car and in an ideal case should change according to the flow conditions evitols have three distinct operational regimes one is a vertical takeoff or Landing followed by transition to horizontal flight and then finally there is a cruise to design an ideal propeller for each of these distinct phases of flight we have two different approaches in EV tools we can either have separate propellers for lift and Crews or we can have propellers that can change their pitch based on the flight mode this is because for hovering we require propellers with a higher pitch but for forward flight we require propellers with a lower pitch the fourth point that we must understand is that as the propeller spins there's a region of low pressure created at the top while there is a portion of high pressure at the bottom the blade itself serves as a barrier between the two the tendency of the high pressure air is to find a way into the low pressure region as the air in the vicinity of the propeller spins it is not only pushed away from the propeller along the axis of propeller spin but also pushed out towards the tip of the rotor the tip of the row motor is an important Zone because this is where the barrier between the high and the low pressure Zone ends if the high pressure zone of air does find a way to mix with the low pressure Zone then it creates a Vortex there is a loss of thrust and the efficiency of the propeller drops the noise also increases because of the resulting vortices now that we have learned a few Basics let's look at the different type of propellers to understand their advantages and disadvantages but before we do that I would like to mention that this video is sponsored by brilliant.org the making of these videos require honing your analytical skills and there's no better platform to do that than brilliant.org if you have ever visited a science museum you'll find that one learns very effectively through interactive exhibits the beauty of brilliant is that it places all those exhibits in the palm of your hand you learn through puzzles and challenges you understand the real meaning of the equation rather than just seeing them as numbers and alphabets brilliant has thousands of lessons from foundational to advancements to AI data science neural networks and more and new lessons are added every month what's great is that to try everything brilliant has to offer free for a full 30 days just visit brilliant.org electric Aviation or click on the link in the description the first 200 of you will get 20 of Brilliance annual premium subscription okay back to our video we will start with the most common type of propeller namely the open propeller the advantage is that it is lightweight simple and less expensive the absence of any duct means that low drag overall for open propellers forward flight isn't a problem even when the propeller is nearly horizontal to the ground they allow us higher maneuverability compared to ducted counterparts open propellers do have a few disadvantages though they are noisy vulnerable to debris and hazardous at low speeds they're also less efficient than ducted propellers the very best contemporary propellers can approach 90 Peak conversion efficiency but as with any propeller the efficiency drops very rapidly as the tip speed velocity exceeds its optimal value open propellers have been the choice of many evitol aircraft in most designs we notice low pitch propellers installed just to provide lift and variable pitch propellers for cruise it is interesting to note that the Joby S4 midnight by Archer and vertical Aerospace VX4 have five bladed variable pitch propellers for their tilting rotors in the S4 and the midnight the blades have a Q-tip this is similar to winglets on an aircraft wing and serves the same purpose the Q-tip creates a barrier between the high and the low pressure zones and separates them from mixing Q-tips have been used in gyrocopters and they make the aircraft quieter more recently there has been a lot of hype about toroidal propellers toroidals have been used successfully in Marine industry research in aircraft applications still ongoing it's difficult to make a toroidal propeller as it requires a three-axis CNC machine or a 3D printer a recent study at the MIT has shown that the noise signature can be lowered using these steroidal propellers those who have tried it on drones claim they also provide a much higher grip and better control now let's move on to the coaxial propellers which are also quite commonly used in EV tools jetson1 being the prime example the main reason coaxial propellers are used is that they can provide higher thrust in a compact space thus reducing the aircraft footprint coaxial propellers provide more control and maneuverability than a single main rotor or two separate rotors by varying the speed and pitch of each of the propeller independently the aircraft can be controlled more precisely the disadvantage is the lower efficiency to generate the same amount of trust as two separate propellers a coaxial propeller would consume 15 to 22 percent more power one get half both Co and Contra rotating configuration for the coaxial propellers there are two advantages of the coaxial counter rotating propellers over the co-rotating propellers first is that the net torque is zero the second is that content rotating configuration is less susceptible to disturbance from longitudinal gas compared to co-rotating propellers let's now move on to a very interesting topic the ducted propellers there was a time when tilting ducted fan technology was seen as the way for producing the highly demanded and Elusive compound aircraft that is an aircraft that is a perfect cross between a helicopter and a fixed Wing the Bell x22 demonstrated this capability but unfortunately was shelled this is despite it being the best aircraft of its type at the time there were others too like the Ryan xv5 vertifan Vanguard omniplane and the doke vz4 the power for the fans came from jet engines that were mounted away from the fans hence a power transmission system was needed which added to complexity and lowered the efficiency now ducted propellers Are Back In the Mix thanks to the relatively small and yet powerful electric motors that can be directly attached to the fans this is the main reason for the renewed interest and many new aircraft designs are adopting them ducted propellers after all provide much higher thrust per watt of power spent compared to the Baseline open rotor the shrouded or the ducted rotor can increase the thrust by up to 94 percent for the same power consumption or reduced Power by up to 62 percent for the same thrust level the reason it achieves this Superior performance is because of two separate phenomenons first is by eliminating the tip vortices the Shroud prevents the low pressure zone of air from merging with the high pressure Zone this improves the trust by up to 15 percent the bulk of the Improvement comes from making the duct into a Venturi tube by having an annular lip more fluid is entrained and accelerated this leads to a much higher thrust compared to an open propeller of similar size so the question is why don't we see this used more often provided that the battery energy is very limited the reasons are the additional weight of the duct and a few aerodynamic issues the greatest advantage of the duck comes during the phase of vertical takeoff but the body of the duct becomes susceptible to Crosswinds during this phase another problem is while moving forward the ducts add to the drag nonetheless all of these issues can be minimized for example by using composite material the text can be made very lightweight to reduce use the problem of drag a design called the adapted ducted fan can be used adapted ducted fan changes its geometry and more specifically the diameter at the mouth of the duct and ADF can increase the thrust efficiency up to 80 percent and can operate in all weather conditions furthermore when it's tilted the fans can reduce its profile to a retracted configuration which reduces drag to eliminate the problem of susceptibility to Crosswinds a tilting or a gimbal mechanism for two axes can be added one for tilting the rotor from vertical to horizontal the other axis for adding Kimber to counter the Crosswinds this requirement of tilting an Adaptive geometry mechanism can be weighed against the ducted fans compared to the open propellers which are very simple take the example of the Jetson one all the maneuverability comes from just changing the RPM of the propellers over version of ducted fans that have become quite popular recently are the smaller scale edfs they were produced mainly for hobbyists who design model planes the high requirement of trust necessitated a higher number of blades in the edfs the ducted found that lilium uses is similar to EDF but has more blades and a section of stator veins behind the fan these veins remove the swell component from the outflow of the fan thereby reducing the losses the Adaptive nozzle shape not at the mouth of the duct but Downstream end helps lilium jet increase the truss by 40 percent compared to open blade propellers of the same size the nozzle detects during the cruise phase the acoustic liners inside the duct reduce the overall noise produced let's now look at coaxial ducted fans coaxial ducted fans are also being looked at as a means of propulsion they are present in the upcoming evitol such as the lauderhspider mark IV and the vrco xb4 it can be seen from both these designs that they do not employ a large duck with annular Wings the duct size is much smaller from studies it has been shown that the Contra rotating ducted mechanism can significantly augment the lift Force production while still being lower than twice of the force from a single ducted propeller a two-stage EDF has been proposed that would have two fans and two Motors the second fan with a different pitch would accelerate the air from the first fan to an even higher velocity theoretically this way higher trust can be achieved from a smaller diameter power unit allowing for a narrower aircraft overall and with this the video is concluded we hope you would have learned a thing or two about propellers if you did then please do give this video a thumbs up thank you for your attention

Channel: Electric Aviation

Views: 48,075

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Id: 0au2IA4uUok

Length: 15min 38sec (938 seconds)

Published: Mon Apr 24 2023