Nice solution Claudio, with this approach there would not be any ambiguity as to what you were measuring.
Jim.
Mji,
more simple, just a small spring and you mark the index position. Changing sail or wind direction you can see the variation what ever will be.
You can also use only half number of ball bearings to make it cheaper
ClaudioD
A simplification of your design could use stretched wires rather than a track with tubes (possibly teflon) sliding on the wires and attached to the sail platform?
A fairly major problem that appears to have been overlooked is that of your wind source.
If one were to look at a professional wind tunnel the ‘lengths’ the designers go to to achieve an accurate and measurable airflow is phenomenal. Using just a fan presents many problems of its own, most notably the pattern of the airflow. It’s all well and good setting up different designs of hard or soft sails in the ‘airflow’ but you can never be sure if you’re going to compare apples with apples. General airflow from a fan is of a swirling nature and so even if the sail models to be trialed are set with the same apparent angle of incidence there is no way of really knowing whether or not they truly do have the same.
I only mention this as I have distant memories of a school friend developing a wind tunnel for testing scale models as a design project - the single biggest headache was that of achieving smooth and repeatable airflows. If memory serves the final design utilised fans ‘sucking’ the air through a chamber with long straight tubes bundled together at the inlet and outlet (but before the fans) to give the required flow patterns.
Food for thought if nothing else…
Regards,
Row
Row,
I think that Claudio is proposing that we do the testing outside in a real wind and test on different days to test different wind conditions. Without making a wind tunnel this might be the best we can achieve in terms of testing under appropriate conditions. I agree that a fan alone will not produce a suitable air flow.
Jim
Mji
wires are too flexible and probably ruining the set up repeatability.
The system do not pretend to achieve precise data as a real instrumentation with wind tunnel and electrical gauges to measure the wind force on the sail, but to obtain a repeatable check. The error being constant, different sails will be presenting relatively different results also using an air blower !.
ClaudioD
Claudio,
I don’t quite understand your latest image. Is it the same as the previous configuration using bearings? Could you please provide a side view?
I can see that two rails will be necessary, but should they be in the same vertical plane or horizontal plane? Or would it be better to have 3 or 4 rails?
Jim.
Claudio,
It occurred to me that the movement of the mast may be quite small depending on the spring selected. With this in mind, could a wheel (I’m imagining a racing bike wheel) be utilised, with the mast mounted on the rim (see image below):
The advantage of this arrangement is that the alignment of the bearings has already been done (and if you have a wheel there is less building required).
Jim.
It may work with a large sail surface. Just try !
The inertia of the wheel is probably too high to respond rapidly
ClaudioD
I do not think inertia would be as much as a problem as gravity. If the wheel is vertical, having the rig on top gravity will change the measurement depending on the cg of the mast/sail position above the axel. If the wheel is horizontal, it should take gravity out of the equation. Use a bubble level to make sure the wheel is level. You could also put a counter weight on the opposite side of the wheel to help minimize leveling errors.
Since you already have a scale, using the measuring method in post # 26 may work better with the wheel instead of the spring. Easy enough to try both and see which works better. Just have the string go through a ball bearing pulley to minimize friction.
iom_noob,
Good point. The arrangement would also be more stable and easier to to operate.
Jim.
Hi,
i would like to present you my wing projekt for an Mini40 AC45:cool:
It is designed for the Mini40 Class in Germany and Europe.
Note, it isn´t a scale modell of a AC45 or AC72, because the aero- and hydrodynamics of an AC45 are not compareable and did not scaleable in a model in this size.
Special features were realizied in this project and are different from the original AC45 and AC72!
For example: i developed a moveable foilersystem like the KIWI foiler system. I hope to foil with this boat astimatated at 2.5 - 3 m/s!
The wing is like the 3-flap system as the AC45 are equiped. The wing is full controlabel with 2 servos. So wing is easy to build with styrofoam and very efficency and light as possible.
If you like to get more informations about my Mini40 - foiler projekt, please visit my tread at the forum and at youtube
http://www.rc-network.de/forum/showthread.php/357334-AC45-im-Mini40-Format
[video=youtube_share;bhHOVIBHdiw]http://youtu.be/bhHOVIBHdiw[/video]
If you have any questions about the project do not effort to contact me;)
so long and have a good flight
Hydroptere,
Very impressive project. For those of us who don’t speak German, could you give a run down on how you went about designing your wing sail?
Jim.
Modified test system design. Do these arrangements measure what I am suggesting they measure (lift and drag)?
View from above.
If scaled-up, this so-called “blade-less fan” should produce better air flow than a conventional fan:
Commercial version with better explanation - see the short film (I know I shouldn’t be linking to a commercial product, but the explanation is quite good):
http://www.dyson.com.au/technology/airmultiplier.asp
Perhaps an entrained air flow fan system like this, with the fan only along the top edge of a box, could be used to mimic the flow of wind over water (as described in Alan’s post #27 in this thread):
Cross-section of box, from side.
Ok, either I’m making no sense, or you are all to polite to correct me :). I’ve been thinking about this test arrangement and I think that the setup entitled “Lift measurement” is actually measuring only the component of lift perpendicular to the wind (F[SUB]Lx[/SUB]), while the setup entitled “Drag measurement” is actually measuring the combined drag force (F[SUB]D[/SUB]) and the component of the lift force in the direction of the wind (F[SUB]Ly[/SUB]). With the test system I can’t see a way of separating F[SUB]D[/SUB] and F[SUB]Ly[/SUB].
[LEFT]Does this make any sense, or am I completely off-track?
[/LEFT]
Test of method (still just using a fan, and no pulley yet) - note slightly different configuration to previous diagrams:
The method seemed to work quite nicely. However, I need to test it on a better sail, the profile of the sail tested is about what you would expect for a flat plate.
I actually found a similar test system on a NASA page, although they use a fulcrum rather than a wheel:
http://www.grc.nasa.gov/WWW/k-12/airplane/tunbal.html
It looks like much more complex test systems are required to measure drag and the other component of the lift force.
Some footage of a test hard/soft wing sail:
With this sail I’ve tried to make it like a hard wing sail, but with the flaps replaced by the soft sail. The advantage I hoped for is that the soft section would provide twist (as Alan suggested in an earlier post). This arrangement should be more practical for a rc boat as it won’t need control over multiple flaps. I think that I need to put this sail on a boat to assess how successful it is.
I’ve also tried to make the top close to elliptical to minimise tip vortices (and because I like the shape). Probably won’t ever know if this has worked.
The profile is similar to one that was developed for an autonomous wing sail catamaran (http://users.soe.ucsc.edu/~elkaim/Documents/ElkaimDesignCat.pdf).
Better profile than for previous sail.
Ready for testing on my old boat:
Setup as a swing wing, with sheeting control from the leading edge of the wing (due to the position of the mast).
Weight of wing: 89 g (a bit heavier that my previous attempts due to servo in wing).