High Performance MPX Foil/Self-righting Trimaran-The Test Model

Resin

Hi Doug, Sorry I may hove forgotten to send you what happened

We have come to the conclusion that it is epoxy but we are still being very careful. We mixed it at 12:1 and it was fine and gave us quite a bit of working time so we will probably do the 8:1 mix next time like they gave us. It did not react when we put it on an off cut from the hull edges what so ever and it was very strong. I don't know why it was pink because I know from using epoxy before that it doesn't usually come in those colours but hey when you live here that's nothing. :!:

It does seem to smell a bit more than usual but not as bad as Magnus described so its all very confusing but it didn't react with the other epoxy or the glad wrap and the ratio of 8:1 I think says something so yeah, that's what happened.

I finished the flap servo mount in foam last weekend and fixed my mast issues (that's a long story) so yeah everything is going well and I plan to have a float hull mold thing glad wrapped and ready and half the 'cross wing thing' with no name!

Regards
-Curtis

 

MPX System

Hi Doug,

I was reading through the forum again the other day and I just cant get my head around how your main foil creates down force at a certain point and how the wand affects this. I may be looking at this in a silly way but it is really confusing me. Also is there a specific reason why you have 2 wands or is it just to keep the drag even? :?:

The only reason I’m asking is because I love to be able to have input and help with these types of designs and I’m generally interested in all of your amazing concepts.


Kind regards
Curtis

 

MPX Test Model

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Curtis, see the animation below to see how a wand works. The wand is set up with shock cord or a spring attached on a rocker arm that is attached to the wand axle so that the tension pulls the wand down to the water.
On my boat, the wand is all the way back as the hull starts to move forward. When the wand is in this starting position the flap on the main foil is maximum down(30 degrees) so that the foil develops maximum lift. As the boat begins to lift the bottom of the wand moves forward and down. And the flap starts to move up decreasing lift until the flap reaches the neutral position(in line with the foil-neither up or down). The foil is still developing lift because it is set at a positive angle of incidence. On my boat, if the force of wind on the rig is enough the main hull will still want to rise and as it does so the lower end of the wand moves forward with the flap begining to move up. At about 5 -8 degrees up flap the foil no longer is developing any lift and if the boat continues to rise the end of the wand moves further forward and down which causes the flap to move to it's maximum up position which causes the foil to develop downforce. It will be possible to "turn off" downforce by physically preventing the wand from moving the flap beyond the no lift position so it cannot develop downforce.
In that circumstance, altitude would be controlled by the sails-depowering them to reduce altitude(like on a "normal" multihull).
An important note: as soon as the main hull lifts off speed increases and the boat rapidly reaches the point where it is the sail heeling moment holding up the main hull and not foil lift. This is critical because it ensures that there is no leeward force vector resulting from the main foil AND it eliminates most of the induced drag(drag due to lift) of the mainfoil. As this point is reached most of the lift is automatically created by the lee ama foil.
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My boat uses two "midship wands" because of the beam of the boat and because it is designed to sail at an angle of heel of around 10 degrees to around 17 degrees. Only the lee wand is in contact with the water once the boat reaches it's designed angle of heel.
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This system has advantages mentioned before:
1) it allows an over square trimaran to fly the main hull in light air, drastically increasing performance,
2) while the system increases performance in light air it also increases performance in heavier air due to the great righting moment of an oversquare trimaran, and due to the down force from the main foil, if used for that purpose.
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Don't hesitate to ask any questions...

http://www.youtube.com/watch?v=yuFwDm8t3IM&list=PL42F2DD938047A54C&index=5

 

MPX Test Model

Sails at last! I think Scott did a really good job-can't wait to see how well they work. The white sail is the Code Zero made with Dimension Polyant's lightest code zero material. All sail material is Dimension Polyant. Main design by Sandy Goodall, Jib and Code Zero design by Scott Morgan.
Main + Jib + mast=3455.88sq.in. / 24 sq.ft.
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Main + Code Zero + mast= 4245.6sq.in. / 29.5 sq.ft.
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The reefing protocol on the new boat is:

1) to remove the Code Zero and add the jib,

2) to roll a reef into the main and leave the jib

3) to remove the jib, and leave the full main and move mast step slightly forward,

4) to roll a reef into the main and leave the mast step forward.





Picture four shows the reefed foot for the main--

 

One problem I can see with the wand system is that it reacts to each wave it encounters, when you actually want it to react just to waves over a certain wave length. This continuous movement of the wand will cause an erratic movement of the flap too, and that adds more drag because of the increased rate of vortex creation by the flaps (respect to a slow movement case).

So you should try to devise some kind of low-pass filter for your system, which will discard shorter waves and will react to just longer ones. For example, a degree of controlled elasticity of the control system, or some (wand) motion-damping device.

Cheers

 

No go pogo?

 

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I think thats what the flexible, planing paddle does, Slavi. But on this boat it makes no difference: the F3 used straight carbon wands, eventually sanded flat on one side to stop the high pitch noise and vibration. Either way she took off in a 5mph wind and did close to 19-20 mph top speed. These wands will work much better than those did and will be satisfactory for this boat, at least initially.
The Rave foiler started out with square rods and no attempt to make the wand plane. The video, above, shows the final configuration of the planing wand on the Rave. Interestingly, the new Osprey is using just square rods with no mod for planing, probably due to running out of time. The planing wand "evens out" the wand response and has been adopted on most Moths.
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One note on this boat: after takeoff the no-lift portion of the flap position is reached pretty quickly and it would be possible to retract the wand completely at that point.(as well as to "shift-gears" by reducing the angle of incidence of the main foil when heeling moment is lifting the main hull and mainfoil lift is no longer required-----if not using downforce from the main foil-all stuff to be experimented with!) The wand is not necessarily required all the time-just in light air takeoff. Thats a big difference with a "normal" wand system.
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The flexible, planing wand paddle for this boat:

 

I was thinking along these ideas the other day... but now that you said "low-pass filter" it popped on my mind!!! My idea:

Use a damper/spring combination to slow down the movement (same as a car suspension system). You can get these parts from hobbyking (example: http://www.hobbyking.com/hobbyking/...er_Set_complete_2pcs_bag_A2030_and_A2031.html)

No idea how to get the proper one, thou.

 

Just for general info, there's a nice introductory article about wands and how they work here: http://www.teknologika.com/mothblog/wp-content/uploads/2009/10/Magic-Wands.pdf

 

Yes, suspensions for land vehicles are exactly that - low-pass filters.
The fast-changing casual road bumps and distributed asperities are absorbed mainly by the spring and the inertia of the wheel, while the bigger bumps which build up more slowly (hills, for example ) are transmitted to the rest of the car body - which will so be able to conform to the average height variations of the road.
The dissipator (gas or hydraulic) controls the speed of spring compression/extension, while the spring rigidity controls the amount of force which will be transmitted to the car body. Combined together, the suspension mass, it's rigidity and the dissipation characteristics determine the frequency response of the suspension. In other words, they determine which part of forces and frequencies shall the shock absorber pass to the vehicle and which part shall it absorb and dissipate.

Something similar is imo necessary for the foil-control system, like the wand-based shown before. An elastic wand combined with the water in the role of energy-dissipator can do the job (like the planing wand in Doug's previous picture), though it is nearly impossible to reliably control the frequency response of such a simple system. There is also an additional difficulty in deciding where to position the wand along the boats' length. Forward, mid or aft? And exactly how much forward, mid or aft? It should imo have some variable-positioning system, because each longitudinal position will likely react well just to a narrow range of wave-encounter frequencies, and will be a potential cause of instabilities outside of its working boundaries.

Cheers

 

MPX Test Model

The Rave, Osprey and Skat all use midship wands. The Hobie Trifoiler uses forward surface sensors("feelers") that stick out in front of the boat instead of trailing wands, and most Moths use forward planing wands.
I've always thought that for best speed, controlling altitude using manual control and totally eliminating the wands would be fastest. That was proved out in the Rave class racing. To my knowledge, it hasn't been tried in the Moth.
On the test model, manual control would be a piece of cake and will be tested-in fact it is less complicated than the dual wands and about the same weight.

 

Could be. In that way you would eliminate all the induced drag associated to the erratic-flap motions. But you would then need other means for controlling the stability of the boat, like moving CoG (the crew, in the case of manned foilers) or active tensioning and easing of sheets (by the crew again). Perhaps you could place a call to the seven dwarfs, while waiting for your sails to arrive. Maybe a couple of them would be interested in taking a ride on your boat.

 

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I asked Dr. Bradfield about using manual control on a Rave or on a monofoiler-he said a humans' ability to respond was too slow and it wouldn't work. A few months after that the guys in Gainesville modified their Raves and successfully raced them.
A year or so after that I sailed and foiled my 16 footer with a twist grip to control the main foil flap. The little time I sailed it proved to me that such a control system could be made to work well.

 

In the previous message of yours, I had wrongly read "totally eliminating flaps" (intended as movable lifting surfaces) instead of "totally eliminating wands" - hence my last reply. My mistake, evidently it's time to go to bed.
Cheers.

 

Was someone calling me?!! I'll take a ride anytime!!!!