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11 September 2011

Update: Interesting SAWDIS Kite Project to promote science and technology

Constructing the PICAVET.

I received several e-mails from blog readers wanting to know what a PICAVET is. The Picavet is named after a French inventor in the early 20 th century. I will attach the payload to the kite line and not the kite. The angle of the line to the kite is constantly changing. To provide a level platform for the payload I will use the Picavet. The payload hangs beneath the Picavet cross from a bolt that is fastened through a hole at the center of the cross. The Picavet has an inherent dampening effect as part of its design. As the kite line changes angles a Picavet moves to the new level position and stops. The lines of the Picavet also provide dampening of wind induced vibrations on the kite line. The diagrams below show the major parts of the Picavet.

I constructed a 150mm x 40mm x 1.6mm Picavet Cross and used 5 eyebolts, 1.5mm line, small washer and two keyholder rings. To prevent the eyebolts from loosening in the wind I used lock nuts on both sides of the cross.

I contacted Johan ZS2I and we decided to go ahead with the testflight. Myself , Johan ZS2I and Sewes set out to the "airfield". We first decided to let the kite fly without the picavet. I took the kite to approx. 100 meters. It flew beautifully and just "sit" up there. Very little movement. The wind at that stage was blowing between 10 and 18 km/h. The next test was to attach the picavet. The picavet was tied to the kite line about 4 meters from the kite and two fishing sinkers were attached to the picavet. Needless to say that the distance from the kite to the picavet was to short. The "payload" swinged fiercely from side to side. We hauled the kite in and added another sinker and lengthened the distance between the kite and picavet to about 10 meters. The wind took the kite and it just went up and up. Johan ZS2I : "Die kite wil net op en op, gee hom lyn, laat hom gaan. All in the name of science! "

It went up to about 35 meters but then disaster struck, the wind was not strong enough to carry the payload (348g) and line any higher. Not deterred by the light wind, we decided to do another experiment. We removed the sinkers and attach a portable anemometer and temperature sensor to the picavet. The kite went up again to about 40 meters. The anemometer was adjusted to give us the maximum strength of the wind and temperature. After about 15 minutes the kite was lowered and the measurement showed the maximum wind speed as 31,3 km/h and temperature as 17.7 Degrees Celsius. These measurements were taken 35 meters above the ground. The kite was again send up to about 35 meters with the sinker payload. Then disaster struck a second time. With the approaching cold front the wind suddenly picked up in strength. It got so strong that it was impossible to hold onto and I decided to give it line to release the pressure. The wind increased in strength and the kite shot up to approx 300 meters. It entered the "Stratosphere". You don't believe me. Looking at the photo (taken from a light aircraft), you can just see the earth at the bottom of the photo.

Photo: Kite flying above the clouds in the "Stratosphere". Earth visible at the bottom of the picture.

Yep, we then hit the Statosphere. The wind suddenly decreased and the kite glided through the clouds back to the "airfield". (Note: Just kidding about the Stratosphere and flight above clouds but a light aircraft did explore the strange object in the sky. Luckily it is red and white obviously noticeable from quite high up. We flew for another 15 minutes and called it a day after the wind decreased even further.

What did we learn:

1. The wind speed to carry a 557g payload must be between 35 and 45 km/h.
2. The size of the kite in light wind (10- 18 km/h) should be at least 5 meters from tip to tip.
3. The 2.5 mm kite line that is currently used, is to thick and to heavy for the 2.8 meter Delta Conyne.
4. There is a need for at least three different sizes of kites to fly in different wind strengths.
5. Leave enough line length between the kite and the picavet to ensure a steady flight.

Although this flight might sound dull and useless, we learn from experience, something we definitely will need when the time comes to fly the real payload.
We once again had great fun. Many thanks once again to Johan van Aarde ZS2I who took photo's during the flight.

Next Activity:  Testing the PICAVET in stronger wind.

Previous posts:

1. New!! - Interesting SAWDIS Kite Project

2. Update: Interesting SAWDIS Kite Project to promote science and technology - Building the Kite.