Line-pull ratios

After recording line-pull with 4 KAP kites in Bft 1 to 5 (2 to 18kn) I have worked out a rough estimate of line-pull ratios. The ratios are expressed as line-pull (lb) to wind strength (kn)

Line-pull Ratios (lb:kn)
7ft Pirate Rok              1:1
ITW Levitation Delta    1:2
Peter Lynn 2m2 Pilot   2:5
PFK Nighthawk            1:3

Which means the line-pull (in pounds) of the Rok roughly equals the wind strength (in knots). The Levi delta pulls half as much as the Rok and the PFK one third as much.

For example: In 12kn the Rok pulls at 12lb, the Levi pulls at 6lb, the PL pilot pulls at 5lb and the PFK pulls at 4lb. 

Rok and PFK in Bft 1-2. Insufficient wind for the Levi delta and PL 2m2 Pilot.

Four kites in Bft 3 

Line-pull measurements

The amount of pull on the line dictates which KAP rig can be used. I have started recording line-pull using an electronic luggage scale ($9 on ebay) to help with kite selection.

I have found that line-pull of about 3 times the rig weight is enough to safely lift the rig. So I need 7lb pull to lift my 1.1kg SLR rig. (Apologies for the mixed units, must start measuring pull in kg!)

Here is a clever interactive lift/pull calculator from Kaper e-zine. Plug in rig weights and see line pull and angles.

Of course line angle also matters. Deltas can fly almost directly overhead. At times the delta and rig can be in perfect balance leaving next to no tension on the line in your hand and zero movement of the rig. Perfect for sharp KAP shots. It's a magical moment, hard to believe it's possible.

My intention is to build up data for each kite in a range of wind strengths.
It's early days but it seems with the 7ft Rokkaku line-pull in pounds is pretty close to wind strength in knots. For example I would expect line-pull of 7lb in a 7kn breeze.

Here are two video compilations of kites compared in Bft 4 and Bft 2.
I'll do Bft 3 and Bft 5 when the conditions permit. I have tried Bft 1-2 but the Rok was the only kite capable of staying up.

Three kites compared in Bft 2

Four kites compared in Bft 4

Eventually I'll put together videos and publish a line-pull table for each kite separately in the full range of wind strengths.

Beaufort Wind Scale
Bft 1     1-2kn          Calm - Not enough to fly. Go diving
Bft 2     3-6kn          Light breeze - Rok will fly, others maybe.
Bft 3     7-10kn        Nice breeze - All kites will fly. Need to match kite to rig.
Bft 4     11-15kn      Decent breeze - All kites will lift rigs easily. Upper range for the Rok.
Bft 5     16-20kn      Strong wind - Too much for the Rok and Levi
Bft 6     21-26kn      Howling - Only the PFK will survive.