Category Archives: Biomimicry
This is part 2 of the Ornithopter project . In part 1 , we managed to build a flapping wing ornithopter using straws , foams , wires and tapes . The ornithopter could not achieve flight though . We identified the problems and continue to work to improve the ornithopter in part 2 . And this is the report for part 2 . And yes , we manage to get little “ORNY” flying .. well a good few seconds of flight !! Its a lot better than previous . Tough project though , but we made it !!
Ornithopter | The problems in part 1
In part 1 we identified 2 major problems . Though we very much wanted to use recycled material , but to get a flying ornithopter , we have to get the right material in order to achieve flight . So here is the list of problems we had earlier on part 1 and the recommendations or solutions that we have in part 2 of this ornithopter project
- Straws . They are just not strong enough though we used tougher straws from Yakult , the Japanese probiotic milk drink products . With normal household rubberbands , the straws bend under severe stress when we wound up the rubberbands . So we have to explore balsa wood which we did . We use different dimension balsa wood for different areas of the ornithopter .
- Household rubberbands . They are not thick enough and therefore may not be able to provide sufficient force to turn the crank and to move the “wings” of the ornithopter . Some hobby shops do sell special rubberbands but those that we used , we have to trim the thickness of the rubberbands by half. Alternatively , we can also source rubberbands used on trousers .
Ornithopter | Parts , material and dimensions
Here is the list of parts and their dimensions used on part 2 of the ornithopter .
Ornithopter | The problems in part 2
As we start to build a flying ornithopter , more problems surface . Here are some of them
- Choice of glue . Putting the balsa wood together was tough as not only was the wood thin with small surface area , it also has to withstand the stresses imposed by the rubberbands and also the crashes . So choose a glue that is strong enough that can hold the wood together . In our case , we also had aluminium tubing , used for the crank , that we need to stick onto the balsa wood . So type of glue used is important .
- Balsa wood . We use balsa wood because it is light and stronger than straws . We have to use different dimension balsa wood though . For the motor shaft , its needs to be thicker for its needs to withstand the stress caused by the wound up rubberband . The front connector is thicker to allow more surface area to glue and to secure the aluminium tubing . The wing spars balsa wood are specially selected to be as light as possible but present enough area to stick the foam onto it . As for the back connector , we tried a design without this back connector to save some weight , but with the wings mounted onto the top wing shaft , the wing shaft just could not take the stress alone . So we had to have this back connector to spread the stress .
- Rubberbands. Household bands will not do and to create sufficient force to move the crank and the wings , the rubberbands needs to be thicker . But thicker rubberband may not allow us to wind many turns and in our design , it allows a maximum of about 30 turns . This means that the ornithopter will have a very short flight duration lasting less than 30 flaps . More than 30 turns , the balsa wood and the aluminium tubing holding the crank would experience severe stress
- Wing flaps . We taped and glued different types of plastic , paper and foam thickness onto the wing spars to create the wing flaps . Foam of 0.7mm thickness was best because it can retain the shape and form of the wings better than any other material . A 1.0mm foam was simply too tight for the ornithopter and does not allow the crank to turn freely . It is very important to ensure that the wing flaps is not stressed too tightly especially during the downward movement
- Wing root . There are 2 ways to secure the wing root . Its either at the top or at the sides of the wing top shaft . We prefer securing the wing root using Yakult straws at the side so that the “Z” shaped wire does not interfere and damaged the foam during flight . This also allows us to glue the entire middle section of the wing flap onto the top wing shift .
- Aluminium tubing and the metal wire crank . We choose aluminium for the tubing for it is light . Plastic tubing may not last as it will be constantly being rubbed by the metal crank . This aluminium tubing is a important piece of the ornithopter because the crank at one end will be pulled by the rubberband leaving the “bend” area of the crank rotating and rubbing against the tubing . If there is a lot of friction in this area , then the crank will not turn smoothly . It is a good practice to add some lubrication to this area to allow the smoother turning of the crank . Also maintain parallel or perpendicular of the crank relative to the other areas of the ornithopter to minimise stress build up . The crank is also the area that will be easily bend due to crashes or head on collisions experienced by the ornithopter .
- Conrods . The conrods dimensions are dependent very much on the 2 metal Z-shaped wires “bend length” of the crank and the wings spars . In our case , we find that 1.5cm and 2.0cm works well and the conrod must be able to prop the wings up , above its horizontal wing top shaft
Ornithopter | how to achieve longer flight ?
To achieve longer flight duration , we will need a longer rubber band and therefore a longer motor shaft . This means more back weight added to the ornithopter . We will also need to increase the wing span to create more lift but we need to ensure that the rubber band is able to propel the wings sufficiently . What this means is that we need to ensure that the ornithopter is able to create sufficient lift over its entire weight .
Ornithopter | What else needs improvement ?
We certainly would like to add a rudder so that the ornithopter can achieve a straight line flight . We believe that we need to improve the wing design by having a sturdy structure to shape the wings . Well , that’s about it for the ornithopter for the time being !!
This is our first attempt to design and build an Ornithopter . But first , what exactly in an Ornithopter ? Well an ornithopter is any machine that mimic the flying mechanism of birds by flapping its wings . Ornithopter derives it name from the Greeks (from Greek ornithos “bird” and pteron “wing”) . Guess who was also fascinated by bird flight ? Yes , Leonardo Da Vinci was also a great fan of this flapping wing machine way back in the 15th century
Ornithopter | What material do we use
Most people would use balsa wood , but we will use straws to build our models instead . It is important to understand the design and mechanical constraints using models before we build one that can fly . So for our first model , the material needed will be
- Galvanised wires
Ornithopter | Observation and findings
Now we will need to build a bigger model to see things clearer . Since we know from the small model , things aren’t exactly symmetrical and this could pose severe challenges to the final design of a flying ornithopter .Here we focus on the turning radius and its impact to the flapping action of the wings
It seems that the smaller the radius , the smoother the flapping actions . With a larger radius , from the videos below , note how furious is the downward wing movement . It probably can create a lot more lift with such forceful downward movement but being a larger radius would also mean less symmetry , leading to more problems with balancing and flight . So we will need to strike a good balance between these 2 conflicting parameters .
Ornithopter | Design and assembly
In this design , we connect the conrods directly to the wing spars . This makes the design simpler and require less mechanical parts , unlike the previous design . This will also make the ornithopter more efficient . We still make use of straws , foams , galvanized wires and tapes for our models . Now the ornithopter is completed , with a wing and a tail added to it . Note that it is not symmetry in nature due to the V-shape conrods and the circular crankshaft assembly .
To reduce the degree of non symmetry , we use thinner straws , those that we get from Yakult drinks for kids . We added some beads at critical areas to reduce stress build up and a smaller diameter galvanized wire thickness
Ornithopter | what else is needed ?
The current ornithopter will not be able to fly . There are 2 major obstacles that we need to overcome . First is the speed of the flapping wings powered by the rubber bands . The addition of the foam wing reduced the flapping wing speed tremendously , due to its added weight and stress . Second is getting the ornithopter to glide due to the imbalanced in its construction and design . So though we have some ideas how an ornithopter works , we still have a long way to go to get a flying ornithopter up in the air
The “wow it works” program has a close relevancy to the syllabus dictated by MOE Singapore . We will use the “walkalong glider” as an example how this project can be fitted into MOE Singapore requirements as “Inquiry based education” for kids .