Trevor Jack kiteboats in Australia

[Baptiste LABAT]

Hi, I copy below the very interesting converstation I had with Trevor Jack

Hi,

I've just looked at the videos in your project.  I'm very interested.  Congratulations on what you've done so far.  I've also read most of the github wiki....I will read the rest later.

I'd be very interested to use some of your work and hopefully contribute to further development.  

Although I have a long standing interest in renewable energy development, my primary interest is in kite propulsion of boats.  I have used kites on several boats, all manually controlled.  Here are some example videos:

• Semi foiling proa
  
• Outrigger stabilised tandem surf ski
• Nacra 5.8 catamaran

I will launch a 15m proa in a few weeks. It will be a very unusual boat! It is very light and will initially be propelled by manually operated kites no larger than those we've used on smaller catamarans and the smaller proa.  But we will eventually need larger kites and different control systems.

 

Although the videos mostly show LEI kites, I have been using single skin (SS) bridled foils - the video of the nacra catamaran shows a high aspect ratio 12m SS foil.  Extraordinary kites - though with many challenges.  I have a 16m 2 line version of this kite, with a slightly lower aspect ratio.  It has pulled me along the beach in 3.5knots of wind.  These kites are scalable - so when we get the 16sqm version working on the big proa and control systems developed, we will be having larger kites made.

My initial interest in the project was remote control.  That is, the objective was to have short control lines with a control unit near the kite then a single line from the control unit to the boat.  Although that may still be possible at some stage, with a 2 line kite, the advantages of going to a single line are much less.  And having all electronics on the boat is considerably simpler.  The most advanced remote control system I developed was a very efficient (low power consumption) controller on the wingtip of a Peter Lynn Arc (16sqm Venom).  The Arc geometry (specifically the wing tip strut) allowed for a very mechanically efficient control system.  That test was done with (as I recall) a 60W outrunner motor and was quite successful.

Although arc kites have their advantages, SS foils have many attractions.  So that's what I propose to use, at least in the medium term (short term, for testing the boat, we'll use LEI kites and ram air inflatable race kites which are easier to launch by floating).  As SS kites can be rigged to fly on 2 lines and dynamic depowering on a boat, at least in controlled circumstances, is not so important, I plan to use 2 line control systems - this primarily makes it easier to launch and retrieve (ie without floating the kite away from the boat).  Here is a recent test of launching a 2 line SS kite from a short mast - the sock should be discarded, see the launch at about 25 seconds.  It should be possible to do this from the proa with the 16sqm kite then reel out the lines to a good flying height.  I have a pair of highly geared and braked winches which, when coupled, reel out or retrieve both lines but are easily decoupled so that one can be driven, either direction, and thereby steer the kite.  Bigger versions of these spooling winches will be adequate for the large proa.  Eventually I plan to drive the winch with an automated controller.

So, my interest in automated control is primarily to provide for stable flight if on a given tack.  The kite will be controlled manually for changing direction.  At least in good winds, SS kites are very stable.  Although I'm not an engineer, I did some study of control theory more than 30 years ago but have only read small amounts since then.  I am an actuary by profession - but prefer working with kites and boats than finances these days!  I expect that a relatively simple PID controller could be applicable.  The objective will be to simply maintain elevation.  

Although the winch arrangements I plan to use, with separate but coupled winches for the 2 lines, has many advantages, a significant disadvantage is that since steering will be by decoupling and reeling or releasing one line, that line will have full (half) kite load - so a relatively powerful winch will be required.  The winch gearing will allow manual control initially.  And electronic/automated control will be developed on much smaller kites.  I have a linear actuator largely developed, but not implemented to fly a kite, that uses a drill as you've used.  Particularly with the gear box and torque control, they are very cheap/suitable motors/systems to use, at least for prototyping.  I have used Arduino and standard RC radio control systems.

Although I have experimented with reading IMU and elevation, with the expectation that these might be installed on a kite, these experiments have been quite rudimentary.  I'm very interested in your use of video systems - that seems to be a relatively simple way to proceed, if the vision recognition systems are good (note some of my kite boating video has the kite right in front of the sun....how would such a system cope?).  As it happens, my son is doing a PhD in artificial intelligence, specifically recognising poses (ie positions of arms/legs/knees/elbows/head etc) with no markers on the joints etc.  I'm sure he would help me with any coding, but could be particularly helpful in integrating a vision component.

I've written too much, and all in English - my apologies. I hope we might be able to collaborate.  Please let me know if you'd like to talk and if you are now working on robokite. 

Regards,

 

Trevor Jack
+61 408 152 414

Skype: TrevorBernardJack 
www.MoretonBayKiting.com.au

[Baptiste LABAT]

Hi Trevor,

Thanks a lot for sharing your thoughts and progress. If you agree, we can copy and paste this discussion on the forum to share it with others?

Congratulation for the wing tip strut actuation, but I didn't fully  understand how it works. Is it playing on the bridle length from the kite?

What do you call dynamic depowering? Is this by moving the kite to the side of the flight windows, or by bearing away to reduce the apparent wind, or by reeling out the two lines?

I am currently working for French America's cup team, and will probably work on this project till June. but hope to be able to work on kiteboats from June (I have more and more people getting in touch with me for more or less open projects). I am starting to organize a gathering of kiteboat enthusiasts for next summer/autumn.

I did not really make advance on the project for a while and have never succeeded in having all the pieces for the close loop control working together...

However, I witnessed lots of progress from others, for example from Beyond The Sea project by Yves Parlier (very secret), or in Airborne Wind Energy field.

I have not read it yet, but I am sure Uwe Fechner thesis can give good insights for accessible real world automation.

I think your coupled winches is a very good base, but maybe you could add a control stage which would save power and add reactivity. I joined a sketch I did some times ago. Tell me if it is not comprehensible!

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Baptiste

[Baptiste LABAT]

I copy below the response from Trevor

Hi Baptiste,

Thanks for replying.

If you think it would be useful to paste this discussion elsewhere, feel free to do so.

The description and diagram below show the arrangement for my arc wing tip controller.  You ask about the bridle length.  In case you are not familiar with Peter Lynn Arcs, there is no bridle as such, just a front and rear line on each wing tip going to the ends of a strut in the wing tip.  The arrangement below was “inspired” by a Delft design that moved the tow point along the strut on a rail (as I understand).  So there was only one line going to each wing tip and it’s position of attachment, effectively, could be moved fore and aft.  I understand that although it showed some promise it was considered impractical.  My design essentially aims to take most of the load on a single line, at a fixed point on the strut, but pivot the angle of the strut around this point by tensioning either the front or rear line by use of the winch.  With appropriate purchase systems/pulleys, the whole system stays tight through a fair change in pitch angle.  The tensioner, from G1 to G2 is probably not necessary.  Although it showed good promise and such kites are largely scalable, I found them very difficult to use ….the single skin kites I’m now trialling show great promise…though they are not, unfortunately, amenable to such a control system.

 

By “dynamic depowering” I simply mean changing the angle of attack while flying – exactly as a kiter does by letting the bar out or pulling it in.  This is clearly not possible with a 2 line control system.  But 2 line control systems have considerable attraction for launching and retrieving (if they are not to be drift launched).

What is your role with the America’s Cup team?  Must be fascinating work? 

I’m happy for any of my work to be shared.  A gathering of kite boat enthusiasts next summer/autumn (northern hemisphere?) could be very interesting.  Please keep me informed.  Unfortunately, to either Europe or North America is a long way from Australia – but I might be able to travel.

You mention that the Beyond the Sea project is “very secret”.  I had wondered why I didn’t see more about this.  I’m a little surprised there hasn’t been more progress on airborne wind energy – I would have expected bigger demonstration sites at least to be working near full time (at least at reasonable capacity factor) by now.

I like your winch design.  Very good to keep only steering loads on the middle winch, albeit doubled up due to the pulley.  My concern with this would be if you were perhaps looping downwind where almost all the load can be on one line.  With the pulley doubling the load, that would imply that the holding torque of the steering winch would need to be very high – but for most beating/reaching, it should be fine.  Unless a boat is very fast, downwind is quite problematic.

Regards,

Trevor

[Baptiste LABAT]

Thanks a lot for your diagram, I struggled a bit to understand even with it, but I got it now.
I thought about the same 2:1 ratio thing for the depower when acting from ground.

I am working on the stability of the boat and control systems of the foil. Yes, that's a great experience to work with such a team.

I will try to keep you inform for the gathering.

Yes, I agree everything is going slower than we think! I think many projects start from scratch without joining their efforts. The few succesful ones are the ambitious ones which get fundings to go big and secrete, whereas I think we should first go as small as possible.

Good remark for the looping kite


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Baptiste