Blogs and information for various projects.
Magnus Effect Plane Project
Have you ever managed to curl a football in flight, or swung a cricket ball? This is the Magnus effect. The ability for a symmetrical object to produce lift by spinning it.
This project is to make a Magnus effect aircraft, and we have a few experiments already done.
Browsing through YouTube, we can see that this has been tried before:-
The initial plan:-
So, in order to work out the weights and force vectors we needed data on the lift and drag that the rotor generates. Finley had the idea of approaching FAST and use their wind tunnel. An Email to Brian Luff the manager brought a swift affirmative to the request, so Finley started to design a test jig to measure lift and drag.
This first jig used springs to measure forces. The hope was that we could measure deflection of the spring and determine the forces from that. Design complete, it was constructed from 3D printed parts and wood.
Assembled on the coffee table
Then off to FAST where we got an enthusiastic welcome. They were only too happy to start up the wind tunnel, which incidentally was liberated from Germany at the end of WW2
Short video of the jig in motion
The jig ran very well until the wind speed got to about 3m/s where it started to oscillate. The springs were also contributing to the general instability.
So, from this test we resolved to make a stiffer jig and change the measurement system away from springs to a weight system. Inspiration came from a model of a test jig for full size planes in the big wind tunnel in the Q121 building.
At that point we got a fantastic exclusive tour of the shipping containers out the back. Only 2% of what they have is on show in the actual museum.
The second Jig was completed and taken to FAST for testing. This time it used weights to determine the lift and drag.
Designed in 3D CAD - CREO.From this image you can see the location where calibrating weights are put to balance the jig. In use, weights are put on the front positions to counter the lift and drag generated by the rotor.
This time at FAST we had an accurate anemometer.
The results were as follows:-
The full size wing will be scaled by 2. The lift and drag can therefore be scaled by 4.
The results were not what Brian Luff was expecting.
So, using this data we can start to design the plane, knowing what weight we need to aim at for a given speed, and the thrust needed from the EDF.
We think it will fly in this sort of attitude:-
Here is the working design of the machine...
- The rotor is twice the size of the test rotor.
- Each end of the rotor will have a ball bearing.
- The power source has changed from an EDF to a prop since it fits, and for weight, and efficiency reasons.
- Motor is a 1500kV 25g 150W.
- The frame will be laminated balsa.
- Battery is an 800-3S, which seems large but the weight helps to counter the offset between the thrust and drag vectors.
- Fin and rudder are Balsa.
Looks fragile so we think the best way to land it is to catch it.
Next stage is to get the bits and make it..
The image above shows the flight rotor (above) compared to the test rotor (below).
Compared to the test rotor, it's a bit bigger, twice as big.
The test rotor weighed 16g. The flying rotor is 65g.
... Much later ...
After a long respite (8 months) where Finley built a pipe organ,
( https://bryher3.wixsite.com/pipeorgan-1/organ ) we finally got back onto this project.
It did not take long, about a week, and its finished. The result is at the end of this post.
After the rotor, the frame was next. The frame is a laminated balsa construction. We made some moulds from chipboard to hold the frame correctly while he laminations dried. We used Gorilla wood glue.
The gluing jig.
The frame arm gluing jig.
Then, before I knew it, the frame was together.
The main shaft is again laminated from 12 layers of balsa. Some extra carbon bracing was needed since laminating the balsa still was not stiff enough.
The rotor runs on two miniature ball bearings on the carbon shaft. The outside of the bearings are held in a nylon turning.
The model weighed around 335g wet. So according to the wind tunnel results, we would have to fly at 15mph for the
rotor to fully support the weight of the aircraft. Up to that point we will need the prop to pull with an upward vector to compensate.
Ready to go...
So....
Not to spoil the surprise, the video below has the story of the first flight attempts.
Lots of repairs were needed between these flights, so it was getting quite dark by the end.
Anyway. Here is the result.
Project complete.
Post Script.
Finley won this years concours trophy at the flying club for this innovative and well researched design.
We also had a local Internet celebrity video one of Finleys flights.
Turned out to be a very popular video.