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 Post subject: Comparative measurements of mast flex and torsional stiffnes
PostPosted: Thu Nov 07, 2013 10:35 pm 
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Joined: Wed Mar 01, 2006 7:51 pm
Posts: 241
Based on Franckite (the Sword father) method on the kitefoil Forum:

Comparative measurements for mast flex and torsional stiffness

Purpose of the method: investigate what makes a fast ? comfortable ? kitefoil .... using a method as reproductible and scientific as possible ... though cheap.

A very straight forward protocol:
1- a cantilever beam test with 5kg applied at a 85 cm distance from the "wall"
2- torsional stiffness test : 5kg applied at a 30cm distance from the mast

Measurements taken at 85cm and 30 cm in each case with respect to the initial position without weight

Attachment:
Flex and Torsion Protocol.jpg
Flex and Torsion Protocol.jpg [ 65.33 KIB | Viewed 881 times ]

Metric to Imperial conversion: 5 kg = 11 pounds at
1 - 85 cm = 2.79 feet (2 feet 9 15⁄32 inches)
2 - 30 cm = 11.81 in - 0.984 foot (11 13⁄16 inches) - 25cm = 9.84 in

The results will be updated with your values and the Kitefoil Forum ones (Spotz, Ketos, Zeeko, Carafino and MHL measurements are missing).
Results expressed in mm would be an advantage.

Click on the table below to expand ...


Attachments:
Flex Comparative Table.jpg
Flex Comparative Table.jpg [ 53.07 KIB | Viewed 892 times ]
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 Post subject: Re: Comparative measurements of mast flex and torsional stif
PostPosted: Fri Nov 08, 2013 7:26 pm 
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Joined: Tue Jul 19, 2011 5:26 pm
Posts: 194
Location: Langebaan (Cape Town)
I think these will be very useful data once the table gets filled. I must make some effort to measure the foils I have. I can add an MHL Lift, and two of my own designs.

I think for foils with a keel of less than 85cm, we should just measure the bending at the end of the keel.

In fact, I think we should maybe measure all the foils at the end of the keel. A longer keel would require a stiffer keel, and I think the data will be more useful to compare how stiff a foil feels for its given design versus how good the construction is irrespective of the design?

I also think we should measure the bending from the wing tips somehow. A low aspect foil might require less torsional stiffness than a high aspect foil?

What do you guys think?


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 Post subject: Re: Comparative measurements of mast flex and torsional stif
PostPosted: Sat Nov 09, 2013 2:40 am 
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Joined: Wed Nov 20, 2002 1:00 am
Posts: 880
Location: rhode island
Excellent..
Thanks

@christoff
I understand your reasoning and it makes sense.
One number may not suit everyone.
But, any deflection value should scale easily if both the moment arm and load are provided.
The same procedure will also help standardize comparisons between fuselage and foils.
-Bill


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