The last one of these I did was for the HQ Flowform2.0 which uses a much heavier grade of fabric. For the Ufoil which I think is 31g/m Icarex I used a No.60 needle and a fine polyester thread. Tulle is horrible stuff to stitch as it stretches as it feeds through the foot.
The whole kite has to pass through the machine…
The keel cut-outs are scaled off the Becotised flowform and are filled with a light weight tulle mesh to maintain strength and shape to the keel. This is about as far as I can go following the Becot method: the only remaining stabilisation mods are to develop down wind drag effects from tail and drogue. These can be very effective but require lot of space to deploy and recover. The trees, hedgerows and barbed wire fences of the county await.
A response from ITW. As I work through the Becot method I have let ITW know about it and Mary Ann at ITW took the trouble to seek advice from Ray Merry (designer) and George Emmons (ITW proprietor) who are involved with the production of the kite. They suggest I’m flying the Ultrafoil at too close to its maximum wind-speed for stability. They looked at the video footage and noted the wind-speed at the height of the kite may well be close to the 30mph upper limit for it and the weaving behaviour is because of this. 2 suggestions to improve stability were offered:
- 1. Fly higher to get to a smoother flow
- 2. Add a longer tail
Unfortunately fly higher is not an option here in the UK as I’m limited to 60m. Short line oscillation is a problem for many kites and it appears ‘short line’ for the unmodified Ultrafoil in Bft 5 is longer than my flying height.
Duh! Adding more tail is perhaps what I should have done to begin with. I have been far too influenced by my experience with the Sutton, HQ2.0 and Explorer, which are stable flowforms without a tail, to consider this. I keep forgetting a tail is not a preference for many kites it is essential for stability in some designs. The Ufoil is clearly designed to work with a tail as it’s supplied with one but, sadly, too short to stabilise the kite throughout its declared wind range.
Ralf Beutnagel says: “The tail should be seven-times the length of the kite for best efficiency.” The Ufoil 15 is 1.5m long so a suggested length is 10.5m. The kite is supplied with a colourful 4.2m tail, so I need to find at least another 6.3m.
ITW stand by the 30mph upper wind-speed for the kite despite my experience to the contrary. I suppose you could say it will fly in a 30mph flow although it will wallow across the sky drunkenly as the wind speed approaches the limit for the kite.
The mods work well. I doubled the tail. I am unsure as to which are the most effective or whether they work together a whole but at a peak flow of 25.2 mph (recorded at the kite, it was a mere 13mph on the ground) the weaving was absent and the kite at last kept a steady station in the sky.
I shot a short clip as I hauled the kite down:
It was a relief to see the kite move gently even in the low down rough stuff. The stable wind range is now increased to at least 25mph (Bft5)
At 60m it was good as gold and I was so happy I hitched a camera to the line and walked from Denver to Downham with the kite leading the way.
The stabilisation is a great credit to Christian Becot’s work on the Sutton Flowform I’m grateful it works on the Ultrafoil too!