Human Powered Helicopter

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Human Powered Helicopter - Mechanical Drive-Train - Images Human Powered Helicopter - Electric  Drive-Train, Phase I - Images Human Powered Helicopter - Electric  Drive-Train, Phase II - Images  
 

History of the Human Powered Helicopter

 In May 1980, the American Helicopter Society (AHS) announced the Igor. I. Sikorsky Human-Powered Helicopter Competition. The flight requirements shall consist of hovering for one minute while maintaining flight within a 10-meter square. Once during this time the lowest part of the machine shall exceed 3 meters above the ground.  It is much harder to get airborne using rotating wings rather than with fixed wings. A dozen or so HPH have been built and tested indoors, usually in sports halls. Some of the important attempts are listed below. The only serious UK machine was experienced helicopter engineer Andrew Cranfield’s 4-bladed Vertigo, which had a rotor diameter of 24m (79ft) and structure typical of a fixed wing Human Powered Aircraft. Occasionally, it has been claimed that a HPH has hovered. Nihon University named one of their machines ‘A Day Fly’ because it was thought that one day in December 1985 it did fly.

 Since the mid-1980s, students at California Polytechnic State University at San Luis Obispo, with project manager Neal Saiki, have been working on the Da Vinci helicopter project. On December 10, 1989, the Da Vinci 3 took off and hovered for 7s, reaching a height of 200mm, powered by pilot Greg McNeil, an Olympic-standard cyclist. One-rotor operation was made possible by the propulsion system, which consisted of a small propeller on each helicopter blade that pulled the blade around. The propellers were spool driven which put a limit on the duration of the pilot effort. The weight of the craft was 44kg.

 Toshio Kataoka and Kouichi Nakamura have been working on their 24m, 36kg Mitsubachi HPH since 1988. The rotors, which revolve once every 12s, are driven by legs and hands via chain and chord. Later Nihon University HPHs have been the 1985 Papillion A, Papillion B and Papillion C, the first two having counter-rotating concentric rotors like those of ‘A Day Fly’. All were supervised by Dr. Akira Naito, who since his retirement in 1991, has been personally developing a four-rotor HPH, YURI I, with each rotor at one end of a girder. Each 10m rotor has a Daedalus design airfoil, DAE 11, which revolves once every 5s. On March 7, 1994, with Norikatsu Ikeuchi piloting, YURI I was officially observed hovering above the Nihon University for 19.46s. Since then, the YURI I has hovered several times. Ward Griffiths, an American woman with no special training, became the first female HPH pilot with her August 1994 flight in YURI I. On her second attempt, she hovered the YURI I for 8.6s, observed by delegates at a Human Powered Flight symposium.

 University of British Columbia’s Thunderbird Project (http://batman.mech.ubc.ca/~hph/index2.html) is a HPH with 2 concentric counter-rotating rotors, mounted above the cockpit. Each rotor has 2 blades. The span of the upper rotor is 36m (118') and the span of the lower rotor is 28m (91ft). The craft weighs 66kg (145 lb) without the pilot and 140 kg (308 lb) with the pilot. They attempted to fly on August 10, 2004 but were unsuccessful. 

 

Phoenix HPH Project

 The Phoenix HPH project was founded in the summer of 1999 at the University of Michigan, Ann Arbor by David Hornick who conceived the original design. In the same summer, the founding members of the project performed preliminary research, created a computer model and established the Phoenix Project as a student team at the Wilson Student Team Project Center in the College of Engineering.  

The design is centered on ground effect. Like hovercrafts and hydrofoils, known as ground-effect-machines, the success and limitations of the craft hinge about this phenomena. To harness this effect, the blades are located close to the ground and a duct is used to increase the lift of the inner blades by reducing the pressure equalization at the blade tips. The duct also acts as a hub for the outer counter-rotating set of blades. Counter-rotation was chosen as the method of torque balancing because unlike the tail rotors, no power is wasted. The following figure (fig.1) shows the 3-D CAD view of the HPH during each phase of the project, since I joined the team. The first image is the HPH, our team designed in the Winter 2004 semester, which has a mechanical drive-train. The second image is the HPH, I designed at the beginning of the Fall 2004 semester, which was modeled around an electric drive-train. The third image is the final model, I made for this project which has the actual electro-motive units and was enhanced to optimize the performance of the “human engine”. The fourth image is an enlarged view of the third image. 

fig.1

 Though this report focuses mainly on the Electro-Motive design, I would like to explain the design of the mechanical drive-train and its limitations which necessitated the development of an electric drive-train.

 

Mechanical Drive Train

 In the HPH using a mechanical drive-train, the pilot would be riding a bicycle (cockpit), mounted above the blades as shown in the first image of fig.2. The pedals, attached to the chainwheel would drive the sprockets by a chain. The sprockets would be mounted below the bike frame, at the front of the craft. Using standard chainwheels and sprockets, we were able to obtain 12 fixed speed ratios on the bike. This would be useful when starting the bicycle, since the inertia of the blades would be too high for the pilot to overcome without a reduction mechanism. The shaft on which the front sprocket is mounted will also have a pulley for a belt, as shown in the second image in fig.2. This belt would drive the main drive-shaft which is mounted vertically, below the cockpit. The belt would need to twist since the 2 shafts are oriented perpendicular to each other. The upper portion of the drive-shaft is shown in the third image in fig.2. This shaft would have a square rod running along its length, inside, to maintain the orientation of the gearbox to the bike frame. The upper hub for the outer blades would be attached to this shaft using an octagonal hub. A bevel gear is attached to the lower portion of this shaft. The fourth image shows the gearbox. The bevel gear on the upper drive-shaft would drive a smaller bevel gear on the upper horizontal shaft which would drive a large chainwheel, as shown in the first image in fig.3. The large chainwheel would drive a smaller chainwheel, through a chain. These chainwheels were chosen appropriately to achieve the 7:1 ratio for the speed of the inner blades to the speed of the outer blades.  

fig.2

 The smaller chainwheel would drive a large bevel gear which is mounted on the lower horizontal shaft (second image in fig.3) which would drive the smaller bevel gear mounted on the lower vertical drive-shaft. The gearbox frame (third image in fig.3) would preserve the relative orientation of the shafts and would serve as a reservoir for lubricating oil, if the gears need lubrication. The fourth image of fig.3 shows the 3-D view of the lower drive-shaft. This shaft has the lower floating octagonal hub of the outer blades. The lower portion of this shaft would be attached to the hubs for the inner blades. 

fig.3

 The first image in fig.4 shows the inner hub and blades. The second image shows the enlarged view of the inner hub. The hub consists of an outer octagonal hollow unit and a square hollow inner unit. We needed the 2 units to prevent the bending of the inner blade-spars. The 2 spars on each blade would go through the outer and inner hubs. The upper plate on the inner hub has a flange which is rigidly attached to the lower driveshaft. The third image shows the inner blade which has the DAE51 airfoil profile. The fourth image shows the duct and the spars for the outer blades. The duct is shaped like a fenestron, to ensure that the flow reaching the tip of the inner set of blades remains laminar. 

fig.4

 Advantages:

Disadvantages:

 

Electro - Motive Design

 The earlier mechanical designs had a lot of moving parts, like belts, chains & gears. The failure of the University of British Columbia’s Thunderbird HPH, which had a mechanical drive-train, necessitated the introduction of an electric drive-train. The new electro - motive design has fewer moving parts. It was inspired by the GE AC6000 CW & the GM-EMD SD90MAC diesel-electric locomotives. Fig.5 shows the 3-D view of the entire HPH (first image on the left), the enlarged side view, the enlarged front view and the enlarged top view of the HPH. 

fig.5

 On this helicopter the pilot would be powering a D.C. generator, which is located between the pedals. The electrical energy generated, would drive the 2 counter-rotating blades through 2 D.C brushless motors. Unlike conventional motors in which the housing remains stationary, here the shaft will remain fixed and the housing will be rotating. The hubs for the inner and outer blades would be attached to lower motor and upper motor respectively. Depending of the polarity of the electrical input to the motors, the motors can me made to rotate in opposite directions. As per the competition rules, there will not be any energy storage device, on-board like a flywheel or a battery. Unlike a mechanical gearbox in which the ratio of the speeds of the blades will be fixed, an electric drive train allows this ratio to be varied infinitely. A D.C. motor was chosen because it can start under load which eliminates the need for a clutch. The brushless designs were the lightest motors available for the required torque & speed.

 The images in fig.6 show the different views of the cockpit. The first image is the rear 3-D view of the initial cockpit, which I modeled just to explain the concept of an Electro-Motive Design. The second is the front 3-D view of the latest design which has detailed mass properties for each of the components and a layout to increase the output of the pilot. The third image is the side view of the cockpit and the fourth image is the front view of the cockpit.  

fig.6

 The changes in the layout of the craft were based on the information available in the book – “Human-Powered Vehicles” by Allan V. Abbott and David Gordon Wilson. The nearly upright cycling position (75 from the horizontal plane) was chosen because it allows the pilot to provide the maximum power output. I chose the Serfas Terazzo saddle because it is one of the lightest commercially-available saddles, weighing 280gms (0.62lb). The saddle features include leather top and manganese rails. The first image in fig.7 shows this saddle. The second image shows the saddle and the seatpost. The seatpost is similar to Easton Carbon Rail Seatpost, weighing 155gms (0.342lb). The holes on the side of the seatpost allow the riding position to be raised in increments of 0.254m (1”), depending on the height and comfort of the pilot. The total weight of the cockpit (without the pilot) would be 12kg (26.5lb).  

fig.7

 The third image in fig.7 shows the D.C. generator and pedals. The fourth image shows the D.C. generator. It has 2 ports on the side for the sensor (feedback) cable connector (upper port) and the power cable connector. A D.C. motor can be used a generator by supplying mechanical rotary input, which is converted to electrical energy. Hence the generator is based on an Aerotech D.C brushless motor-BM 800E, which had the desired specifications and capacity to run the 2 D.C motors driving the two sets of blades. The generator would weigh 6.6 kg (14.6lb). It would need to run at a speed as low as 80-100 rpm. Though this speed is low for a commercially available generator/motor, it is a reasonable estimate for the maximum capacity of a well-conditioned athlete, piloting the craft.

 The first image in fig.8 is the 3-D view of the cockpit and the motors, mounted on the drive-shaft. The second image is the front view of the same assembly. The third image is the 3-D view of the drive-shaft, motors and hubs for the blades. The transparent shade for the circular inner blades hub was chosen solely for giving a better view of the hidden components. The fourth image in fig.8 shows the side view of the driveshaft and motors. The smaller upper motor would drive the outer set of blades and the larger lower motor would drive the inner set of blades. 

fig.8

 Fig.9 shows the drive-shafts and the motors. The first image is the 3-D view of the drive-shaft. It would be 0.75m (30”) tall. It consists of 5 separate components, all made of steel. The first part shown in a lighter color would be attached to the lowest region on the cockpit. It has a slot on its cylindrical surface for the power cable and control circuit cable for the 2 motors. The lower portion of this shaft has a flange for the tapered-roller bearing which arrests the upward axial movement of the upper motor and outer blades. The second part, shown in a darker color, serves as the shaft inside the motor. It is hollow along its length to accommodate the cables for the lower motor. The third shaft (lighter color) is used to connect the 2 motor shafts together (shown in a darker color). This hollow shaft has 2 flanges for 2 tapered-roller bearings which arrest the downward axial movement of the upper motor and the outer blades and the upward axial movement of the lower motor and inner blades. The fourth part, shown in a darker color, is the shaft inside the lower motor. It doesn’t need an axial hole along its length like the shaft inside the upper motor. The lowest part serves as the feet for the entire craft. The upper portion of this shaft has a flange for the tapered-roller bearing which arrests the downward axial movement of the lower motor and inner blades. The second image in fig.9 shows the upper D.C brushless motor and the octagonal mounting flanges for the outer blades and the duct, which is shaped like a fenestron. Unlike the mechanical drive-train, in this design, the lower hub of the outer blades is rigidly attached to the lower surface of this motor and this eliminates the need for a heavier floating hub. The flanges on the motors house the tapered roller bearings. There are 4 identical bearings used in this design, two for each of the motors. The bearings specifications are NSK 32203 with an inner diameter of 17mm (0.67”), outer diameter of 40mm (1.58”), thickness of 17.25mm (0.68”) and they weigh 0.105kg (0.68lb), each. 

fig.9

  The third image in fig.9 shows the upper D.C. brushless motor. It is based on the Aerotech BM200E motor. It weighs 2kg (4.3lb) and is 0.196m (7.7”) tall. It would need to spin at a constant speed of 25.5rpm. It would also need 63.2 watts to rotate the outer blades and the duct (data obtained from an older HPH project report). The fourth image shows the inner blade hub and the lower D.C. brushless motor. Unlike the heavier twin-hub design in the mechanical drive-train, this hub consists of 2 aluminum circular disks, 0.56m (22”) in diameter, the thickness of each disk being 2.54mm (0.1”). These plates weigh 1.65kg (3.6lb), each. There are wedges mounted on these plates which decide the angle of attack (AOA) of the inner blades. The AOA chosen for this design was 7. The spars for the inner blades would be sandwiched between the wedges (2 wedges for a blade), as shown in the first image in fig.10. The spars would have flanges which would resist the radial outward motion of the inner blades due to the centrifugal force, when rotating. The 2 circular plates would be bolted together, using the 32 holes provided on each of the plates. This set will serve as the hub for the inner blades and this hub will be rigidly attached to the upper surface of the lower D.C. brushless motor.

 The second image in fig.10 shows the entire view of the inner blades, hub and lower motor. The third image shows the side view of the same assembly. The fourth image is the lower D.C brushless motor. It is based on the Aerotech BM500E motor. It weighs 5kg (11lb) and is 0.247m (9.74”) tall. It would need to spin at a constant speed of 178.5rpm. It would also need 542.97 watts to rotate the inner blades. 

fig.10

 The competition rules require one person on the craft to remain stationary. Since it will be impossible to ensure that the torque of the 2 sets of counter-rotating blades are balanced, a control mechanism would be required which would automatically direct more power to the slower set of blades without any intervention from the pilot. The generators and motors support feedback control circuits, using appropriate hardware. This is necessary since the pilot has to focus all his/her efforts on powering the HPH and stabilizing it by shifting his weight.  

Advantages:

Disadvantages:

 

 Acknowledgments:

 I would like to thank my advisor Prof. C. William Kauffman for this support, guidance and help in locating the resources I needed to learn more about the Electric Propulsion. I would also like to thank the HPH Project Leaders – Karen Kotzan, Greg McCabe, the Blades team, the Drive-Train & Cockpit team, Webpage team and the CAD team for their support and assistance in refining the design. I would also like to thank former team member Brianna Gieleghem, who helped me a lot in designing the mechanical drive-train. I would like to thank Prof. Jeff Horowitz, Prof. Daniel Ferris and Allison Alt in the Movement Science group in the Division of Kinesiology at the University of Michigan, Ann Arbor for assisting me with the Human Performance issues. I would also like to thank Mr. Roger Burg, Senior Sales and Applications Engineer, Aerotech, Inc. for his help in choosing the suitable motors for the electric drive-train. I would like to thank the librarian, Leela Lalwani at the Art, Architecture & Engineering Library for her help in obtaining the relevant standards and technical papers.

 

Conclusions:

 The electro-motive design for the HPH drive-train is a new concept and looks promising. I came up with this idea only at the end of August 2004 and since it took some time for the HPH Competition Coordinator at the American Helicopter Society to approve the concept, I didn’t have the time to perform a detailed analysis of the components. But I have chosen a large number of commercially available components, after reviewing their specifications and assessing their suitability for the project. I have built the virtual prototype of the HPH in Pro/Engineer (Wildfire 2.0) & CATIA (V5R12) and used DMU Kinematics Simulator in CATIA to define mechanisms for digital mock-ups & manipulation in order to validate the mechanisms. I analyzed mechanism motion by checking interferences and computing minimal distances. I generated the swept volume of the moving parts to drive further design optimization. I briefly used the Human Builder module in CATIA to create and manipulate a digital human (male cyclist) to analyze human-product interactions. The tools, I used within the Human Builder module were manikin generation, gender and percentile specification, manikin manipulation and vision simulation. Though the motors and generators seem heavier, if the weight elsewhere in the craft is reduced by using lighter metals or composite structures, the motor sizes required to drive the blades would also be reduced.

  

HPH Specifications: 

Empty Weight

90kg (198lb)

Height (to the top of saddle)

1.5m (4.91ft)

Diameter of the HPH

10.16m (33.34ft)

Diameter of inner blades set

5.4m (17.7ft)

 

References: