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Final Testing

This version was saved 12 years, 9 months ago View current version     Page history
Saved by Nikolas Osvalds
on May 13, 2011 at 10:01:21 pm
 

Back to Third Prototype Page

 

Final Testing

 

The first goal of the final testing was to see if the shrink wrapped balsa wing would meet the performance requirements that I set. I also wanted to get data on what angle of attack and flap angle produced the best results at each apparent wind angle. This data could then be used by the person sailing the boat as a basic trimming guide.

 

Final Performance Requirements

  • For apparent wind angles of 0-90deg (0 deg is in the direction of motion of the cart), the wing sail should create at least 50% more forward pulling force on the cart than the soft sail.

 

  • The wing sail should be able to create forward pulling force on the cart at closer apparent wind angles than the soft sail.

 

After the first round of testing I thought more about how the wing should perform. I decided that the performance of the wing versus the soft sail was the most comparable at apparent wind angles of less than 90deg. At any larger angle than this the soft sail is not creating lift, and will naturally produce more force than the wing because of its larger sail area. The wing however should still out perform the soft sail while on the water. The reason for this has to do with the apparent wind. Apparent wind is the wind that is felt by the sail when moving through the water and takes into account the velocity of the vessel as well. The true wind is what is felt by a person standing on land or not moving on the water.

    So taking this phenomenon into account, as soon as the catamaran with the wing starts moving forward quickly the apparent wind angle will move forward as well. Therefore as long as the wing outperforms the soft sail at less than 90deg apparent wind, it should technically outperform it at most points of sail.

     Since the apparent wind angle moves forward when going forward it is also important that the boat can sail at close apparent wind angles. This is why I set the second requirement that the wing be able to create forward force at closer angles to the wind than the soft sail.

 

Testing Set-up

 

     The set up was basically identical to the second prototype testing. One difference was that I wrapped the wheels of the cart with a strip of duct tape to prevent side slipping, which seemed to work better than the masking tape and rubber bands I tried before. I also used a different scale, which could not read negative values. Therefore I took the reading on the scale once the fans were on an subtracted it from the original mass of the weight. Additionally since I was only testing apparent wind angles of 90deg and less, I added an extra testing angle at 65 degrees (and got rid of the 120deg).

                                                                                                                           

Procedure

 

For each set up I tried to keep the fans running as long as possible so that any fluctuations in voltage or motor temperature wouldn't skew my data.

 

Shrink wrap covered balsa wing

 

     For the balsa wing at each apparent wind angle I played around with the angle of attack and the flap angle to find the maximum lifting force. I wrote down the scale reading at each of the different trims. After I determined which one of those trims performed the best, I set the wing up that way again and tried recreate the results. If it was within an acceptable error range (5-10g) I took it as the maximum force.

 

Soft Sail

 

     For the soft sail I basically just played with the trim of the main and jib at each apparent wind angle until I found what created the most lift force. I didn't need to worry much about the effects that each change in the trim made because I'm not trying to write a trimming guide for the soft sail.

 

Results and Discussion

 

Table of results, foam wing data from previous testing added for comparison.

 

Apparent wind angle (deg) 30 45 65 90
Maximum mass lifted (g)
       
Soft Sail 0 46 72 152
Balsa Wing 56 99 142 239
Percent more force (balsa over soft) N/A 115% 97% 57%
         
Foam Wing 43 78   180
Percent more force(balsa over foam) 30% 27%   33%

 

Plot of results

 

 

     As can be seen in the table above the shrink wrapped balsa wing sail met my first final requirement of creating at least 50% more forward pulling force than the soft sail. It just made the cut off for 90deg and far exceeded the requirement at 65 and 45 degrees. This trend in the data shows that the wing sail creates an increasingly greater amount of pulling force as the apparent wind angle decreases. 

     The data also meets my secondary requirement that the wing sail would create forward pulling force at an apparent wind angle closer than the soft sail. This is shown by the fact that the wing sail created about 56g of pulling force at 30deg while the soft sail produced none.

 

Videos

 

I took video of the max lift force for the wing and soft sail at each angle of attack, for documentation that I completed the requirements. The first two videos are the wing and soft sails at 90 deg angle of attack.

 

 

 

 

 

 

     

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