Bft 5 fly off.

The beefy westerlies have kept up this week so I have been able to to to grips with Bft 5  (19-24mph) and see how 2 ‘high speed’ KAP contenders fare.

Windspeed 19052015To get an idea of the comparative performance of the Dan Leigh/ITW Trooper and the dynamic spar (DS) modified Levitation I flew them both back to back in the wide Fen sky in the same wind and on the same line, lifting the same load.

PFK will go all the way. I know the PFK Nighthawk will fly fine in Bft5 (and beyond) but I have come to dread lofting it because it pulls so hard and can really hurl itself around the sky. It will not invert and will take the pressure but its not a comfortable thing to fly at all. It is something of a last resort. Flying it in a fresh breeze is both exhilarating and frightening. It’s a jarring experience that needs strong ground anchor and an athletically demanding haul down.

Mike Le Ducs’s Dynamic Spreader spar. After a wonderful display of international co-operation I now have one of Mike LeDucs beautiful dynamic spars for the Levitation 9′ Delta and this raises the top wind speed for it well into Bft 5. The delivery from Iowa was by personal arrangement involving 4 Kappers in USA, France, Yorkshire and Suffolk (Mike Le Duc, Jim Powers, Sue Storey and Tim Carter) without the precious carbon ever exposed to the vagaries of international airmail. I count myself lucky as Mike is a busy man and the time it takes to put the spar together is not trivial. He has supplied it ‘at cost’ and his experience in making these is a summation of careful iterative development. As a DIY project I failed to get reliable results with a ‘knock off’ copy so I know how difficult these are to make. Balance is all and that is where I failed- I just couldn’t get it to work in the higher wind-speeds where it should benefit the kite the most. From Iowa to Cambridgeshire by hand my spar is No 10. Drilling that hole in the P300 carbon is beyond the capacity of my shed workshop!DS detail 2DS Detail-1The wind in the heart of the Fens. The wind in the Fens can be cruel and I wanted the cleanest flow I could find, despite our big skies the Fens are cluttered with overhead wires, bird reserves and airfields, finding a clear reach is not easy but it can be done. A public footpath on a raised bank and the fun can begin. Minimum wind-speed was recorded at ground level at 10.3 – and a max of 18.5mph, this is the tame end of Bft5. AnenometerDan Leigh’s Trooper deals with the force of the wind by spilling much of it under a carefully designed shallow angle of attack so that it almost ‘skids’ across the face of the wind. This produces a gentle pull on the line in exchange for reduced lift. It is happy in Bft5 provided it has a tail to dampen its skittish behavior: the bigger the wind the bigger the tail it needs. DLT Lifting 600g in 15mph_01Finding how much the Trooper will lift has been interesting, unlike any other kite I have this one is load-shy, it has very little power so I have been flying it in gradually stronger winds to see what works.  Lifting a 600g payload works in at least 10mph provided there is downwind space for it. The Trooper needs a tail. Everybody that flies one flies it with a tail. Now I know. At 15mph it needs more tail than I expected, 5m was not enough to steady it at launch so this was doubled to 10m which has the required effect. Line handling was comfortable and at no point did the line ‘sing’ as the deep catenary kept the tension low as the camera was hauled upwards. With the fixed length of line all out I left the rig in the sky as the clouds raced across the sun. The kite was steady, the line almost continuously slack and rig movement gentle with little vibration detected on the line. From the photographic point of view the reach to height ratio for the Trooper is low when lifting the load. The down wind distance is something like 1/3rd greater than the height achieved. This is an important consideration as, if the kite was to be used to pin point a shot positioning it needs a lot of space. It is stable but it is far away with a great ‘J’ curve of line between the anchor and the kite. It is almost magical to see the kite and camera float through the sky in a smooth, gentle sweep as the wind raced clouds to the horizon. Recovery was straight forward and I achieved (for the fist time in many attempts) lowering the kite to my hand thanks to the action of the tail, the line tension was easy to manage. _DSC0001Mike LeDuc’s ‘DS’ modded Levitation. The DS Levitation behaved as advertised, no tail required and a clean lift of the load on a fairly tight line. The pull with the DS is smooth as buffet is dampened by the elastic. The big surface generates plenty of power and handing is ‘physical’ but nothing like the ‘iron bar’ PFK experience. The kite had a tendency to heel as the line came under sudden tension during pay out but centred quickly once the line was taken up. The steepness of the line compared to the Trooper was noticeable: the kite gained more height with a shorter down wind range. I estimate the ratio to be almost opposite the Trooper: the height is about 1/3rd greater than the down wind distance. Recovering the kite required a fairly energetic walk-down compared to the Trooper but nothing like the struggles I have had with the PFK. The descent was smooth and without the yawing the Trooper is prone to.

Comparative performance.

  • Line angle: the Trooper does not fly as high as the Levi, the angle of the line is much steeper for the Levi.
  • Line tension: the Trooper flies on a near slack line even at Bft5. In the same wind speeds the Levi can pull hard requiring effort to recover it. The DS helps smooth the tension (less jerking in gust/lull cycles) and accelerates walk down procedure as the tension is balanced as the line is steepened by shortening it, the DS helps prevent ‘topping’.
  • Lift capacity: the Trooper will not lift 600g reliably until the wind speed exceeds 10mph, the Levi is much more powerful, lifting 600g at around 7mph.
  • Stability: the DS Levi is more stable over a wider wind range than the Trooper but once tail length is matched to wind speed the Trooper keeps its line in wind speeds which can force the Levi to heel. The Levi can glide and hold up the load in lull the Trooper cannot. The sink rate for a rig under the Trooper can be alarming compared to the hang glider effect of the Levi.

An indicative height/reach diagram of the the 2 kites lifting 600g on 200m of line looks something like this (not to scale): Levi vs Trooper The photography.

Trooper

  • Shots taken: 238
  • Rejects*: 68
  • Sharp shot/reject ratio 1:0.28
  • Approx down wind distance at apex: 150m
  • Approx height at apex:40m
  • Approx height variation: 5m

DS Levitation

  • Shots taken:122
  • Rejects*: 53
  • Sharp shot/reject ratio 1:0.43
  • Approx down wind distance at apex: 140m
  • Approx height at apex: 60m
  • Approx height variation: 10m

*rejected as ‘not sharp’ due to motion blur. No image or gyro stabilisation used. The kites were tied off to the same point and flown on the same length of line lifting a Canon EosM with a 22mm STM ‘pancake’ lens on an AutoKAP rig weighing 600g. The camera is set to auto with the ISO fixed at 800. Shutter speeds varied from 1/80th to 1/800th in variable light.

Dan Leigh Trooper Canon Eos M clickPan Pro: _MG_6782DS Levitation _MG_6970Conclusions : the Trooper gives the camera a smoother ride on a line that is easy to handle but at the price of balancing it on just the right airflow. The DS modded Levitation is a reliable lifter with an extended wind-range, it flies without drama and copes with load lifting, compared to Trooper its harder work but its superior sink rate in lull and easy launch characteristic make it a go to kite for most work. Mike LeDuc reports 35mph is possible with the DS. The great strength of the Trooper is the slack line, even in gust the pull is modest making extended flight possible without fear of stretched line or fabric damage.

I will continue exploring the Bft5 envelope….now I can fly there without razor tight line!

B

About billboyheritagesurvey

Heritage worker
Gallery | This entry was posted in KAP, Kites and tagged , , . Bookmark the permalink.

2 Responses to Bft 5 fly off.

  1. Sue Storey says:

    Interesting comparisons Bill.
    Re the last photo….I thought that horses were supposed to be spooked by kites. I know from experience that cows are very interested in them.

    Fly High

    Sue

    • Hi Sue,
      I’m pleased the DS Levitation acts as a replacement for the PFK, I find it too powerful in Bft5.
      Horses are spooked by kites. They hate them… but only if they can see it. The trick is to keep the kite out of their line of sight while you launch. I believe they can’t look up and I have found getting the kite well up before you approach them works well. I launched about 500m upwind of them and walked the kite in. Cows are similar and many birds too. In the nadir shot the white spots are 2 swans rearing signets..they weren’t bothered at all.

      B

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