Ultrafoil 15 mods for stability part 2

It occurred to me Ray Merry has a design signature: the meshed slot is a nice detail on the original Flexifoil and he has used a similar feature on the Ultrafoil. It’s a neat way of getting air into the cell whilst maintaining structural strength and avoiding awkward hole cutting in manufacture.

The Flexifoil stacker is perhaps Ray’s masterpiece: it has endured as a tough traction kite that is a thrill to fly. It’s a 2 line stunter designed take a lot of stress and, if scaled up, as a tractor for power kiting.


The leading edge meshed slot is such a strong feature it’s become a trademark, and it’s printed with the brand ID on Flexifoil kites. For a ram air parafoil the narrow meshed inlet works really well, the Flexifoil Stacker inflates, stays inflated and produces great traction when swung sideways accros the flow, it’s a great high speed wing. You can really feel the power of it as it speeds up and gets the low pressure suction over its top skin.

When Ray looked at designing a single line flowform for ITW he brought the same philosophy to it: strength and speed ideas can be clearly seen it it : it has a compactness, even with a deep areofoil profile, it looks sleek.


A flowform is almost the oposite to the Flexifoil: it’s a slow speed wing, it needs drag and lift in balance, it will not gain lift by acceleration across the wind window, it is reliant on coping with the flow as presented to it.

Viewed along the flow axis the classic Sutton is almost more air than fabric: BKT-FF16

The Utlrafoil is tighter and less ‘breathy’ than the classic so getting more air through it might improve its stability. The next step is the venting of the centre cells on the top skin:


With 4 big holes in the top skin it holds its shape and there is no discernible loss of power. There is some improvement in stability but it’s still moving a great deal more than its reference: the Didak Explorer 16. Wind speed is down to 10.2 mph peak.

Next I shall experiment with bridle length and then vent the side keels Becot style.

looking back through Kappers comments on this kite from 2013 onward I can see a common thread:

  • darts around in dirty wind
  • responds very fast to gust which gives a darty effect
  • The Uf did move around a bit
  • did spend a lot of time going from one side of the window to the other
  • There was a lot of side to side movement but no diving and it flew at a higher angle then most parafoil kites I used.




About billboyheritagesurvey

Heritage worker
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2 Responses to Ultrafoil 15 mods for stability part 2

  1. Piotr Mądry says:

    Hi Bill,

    How to watch a movie of your FF, I think that my copy of FF16 is very stable in the range of 8 – 20mph. All today’s attempts were in a very dirty wind. I think that the increase in air ducting inside the kite can help. Attempts at sea breeze is very deceptive, in the middle of the land the wind likes to play tricks. Flying on the beach, is a great boundless pleasure!


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