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

Impressive! Can't wait to see her step up on it.

 

Happy Birthday

Happy Birthday Doug, congratulations on the maiden sail. I can't wait for the foiling videos!!!

 

MPX Testing and Development----First Sail!

Thanks guys! It was a great birthday and I'm ready to fly. Got a problem with the radio box switch: it won't turn off but that won't matter if thats all it is.
Gary, the leach twistoff was mostly fixed on the second video using the vang , but the biggest part of the problem was the gaff tensioning line not tight enough. Adding the jib or code zero will add lots of power.
Next flight tomorrow EXCEPT that the forcast is for rain-we'll see. Absolutely have to go when Dan is available which is tomorrow or next Tuesday as far as I know now. And I may find another video crew....
-----
>>>Last night I had youtube "fix" the shakiness but the fix totally screwed up the audio so I'm having it undone now.UPDATE- now its the worst of both worlds: got the shakiness back though there is not much anyway, but the screwed up audio remains.

 

Could be some water infiltration creating a contact?

 

MPX Testing and Development

==================
I've written Rob Guyatt about the problem. The switch is competely sealed.
It's stuck "on" showing the red LED. I don't care about it unless it's trying to tell me something I don't understand. I have to unplug the battery every time anyway. I re-read the manual and no failure modes are mentioned. We'll see what Rob says-I just don't want it to fail when I'm sailing. It's more than a switch it has a BEC circuit(battery eliminator) and supplies the receiver and winch with power at different voltages. The battery is connected directly to the switch. We'll see.
PS-the radio box is 100% sealed underway(I hope) but, in any case, it didn't go fast enough yesterday to have water on deck or the box.
==================
Whups! Just discovered another problem caused by the boatyard help: the rigger got the jib sheet twisted around the main sheet and if I had the jib yesterday it wouldn't have been controllable! Fixed and ready to go. I'll have to speak to the yard foreman........

 

Congratulations on the maiden and happy birthday!
Now for a nice 10mph wind day. Fingers crossed.

 

MPX Testing and Development

Thanks, Jim!

 

MPX Testing and Development

Lessons from light air test sail:
1) modification of the main hull ,increasing the L/B ratio, was an advantage since the transom is no longer submerged. Another example of L/B trumping wetted surface. Notable very small wake . Light air speed gets the boat to take off quicker. Approx. 3mph speed in 3mph wind(3mph=2.61 knots).
a. weight is 21.13lb all up which is 4.4lb over the orignal target of 16.688 lbs.
including the aft hull mods. Weight is primarily due to the fact that I finished the thing to a fairly high level which is weight intensive when I do it. I'm very good at doing tooling to a high level of finish(when weight doesn't matter) but every time I've done a one off to a finish I consider good to very good I wind up going over the weight budget. I just can't bring myself to do something that I'm not proud to look at and claim having done the finish on-just isn't in me.
---
This is a scale model of a 19.5' boat(up from 18' originally) and the extra weight is equal to one 175lb crew and 26lb of beer or diet coke and ice, giving a total of three 175lb crew plus refreshments. This is a satisfactory test weight for this boat. I would have liked to be able to add weight if required or maybe make a movable ballast system but the conception of the full size version is that the crew only has to move from one side of the cockpit to the other(about 3') and only if they want to. For comparison this is approximately same weight as the Flying Phantom with one extra crew. But the comparitive sail area of this boat is significantly higher than the Phantom. Scaled up the model rig is 300sq.ft. main + jib. The actual boat would have 350 sq.ft. compared to the 247sq.ft(main + jib) of the Phantom. Model SA is reduced compared to the full size sail plan. Righting moment of the Phantom with two guys on trapezes is about 6380ft.lbs. RM for the MPX with two people sitting to one side of the cockpit drinking a diet coke is 9300 ft. lb.. More sail area and more power to carry sail which is a direct result of the oversquare platform*. So this is a good test and the boat should perform well. If her light air performance is any indication she'll do just fine.
* This is one of the main advantages of the MPX foil system. An over square trimaran like this has tremendous righting moment and w/o the main foil the main hull wouldn't fly until 15+ knots of wind; with the main foil +rudder foil, the main hull should lift off at about 5 knots of wind for both the model and fullsize boat sailing three up.
--
2) Tacking with main only in light air was very good. Manouverability on the whole was excellent. Crisp response to rudder movement. Slight weather helm
with mast in same position it would be in with the jib. Mast stepped two holes fwd: neutral to extremely slight weather helm.
--
3) Main is extremely controllable using a combination of gaff control line and vang. Significant ability to reef main by twisting off. Boat very responsive to
proper set up-boat was faster in vid 2 in same wind after most excessive twist was removed.
--
4) Every component worked well except on-off switch when I tried to turn it off after sailing. Don't know the nature of the problem yet.
--
5) The igotU tracker mounted above the rudder is just flat excellent!
--
6) Mainsheet winch worked perfectly and was very quick-could carry out a gybe like you would by grabbing a mid boom mainsheet and slinging the boom over.
--
7) Checklists don't work unless you read them. duh

 

MPX Testing and Development

No go today-next chance is Tuesday. The main problem is the switch-nothing definitive from the manufacturer yet. Weather doesn't look good for later but right this minute it's perfect.

 

What a fantastic start for a new design.

Very encouraging as there's lots of innovations here that will apply in many other situations.

I agree, if it's good in light air...

Congrats Doug, well earned!

 

MPX Test Model

================
Thank you ,Tom! My schedule revolves around the weather and now my friend Dans schedule. His next free day is Tuesday and I wouldn't under any circumstances sail w/o my video man there. This next video may be really something!

 

MPX Testing and Development-------AOI problem discovered

Since, I had some time before the next test, I decided to get the boat up on the table and use my long red straightedge to measure the angle of incidence of the main foil and rudder foil, again. I use the straight edge to measure from the waterline intersection with the bow to the bottom of the transom(intersection of transom and bottom) to get the boat exactly level fore and aft as it sits in the water(static). Then I measure from the straightedge to the trailing edge of the foil* and then to the center of the leading edge, this measurement is slightly to one side of each foil. The rudder foil was perfect at zero degrees AOI. But the main foil was a surprise-it was at 1.5 degrees when it should have been at 2.5-3 degrees. It is now at 3 degrees and I'm making a physical lock so that the wand plate can't move forward. Sometime from when when I last checked this something must have hit the foil or the plate and moved it. Even with a good wind it is unlikely that the thing would fly at 1.5 degrees!
* This isn't so easy since the flap has to be precisely at neutral for the measurement to have any meaning. Today it fought me, but I won.
The lock will be a carbon tube with a slit in it front and back to wedge in between the back of the mast step and front of the wand plate. The daggerboard is attached to the wand plate and it's possible that the foil may have hit bottom and changed the AOI-now that will be impossible. If the AOI has to be changed again, I'll make a new lock. The lock is not yet shown below:
click---

 

MPX Testing and Development

Here are a before(no lock) and after(lock installed) shot of the wand plate mentioned earlier(post 1377). Its function is to prevent the wand plate and the daggerboard/mainfoil from moving forward(about the lower pivot axis at the bottom of the trunk).

 

MPX Testing and Development----Speed

<Note added>
Link to corrected post here:
http://www.boatdesign.net/forums/mu...trimaran-test-model-36058-112.html#post701967


Comparing an RC model to the fullsize in terms of speed is likely very inaccurate because the model is likely to have close to laminar flow and the fullsize turbulent flow.
That said there have been questions about scale speed/fullsize speed(remember the first paragraph).
=========
1) If you know the full size boats speed:
a. Divide the full size length by the model length in ft..
b.multiply the full size speed(in knots or mph) by the square root of the ratio found in "a."
=========
2) If you know the model speed:
a. Divide the full size length by the model length in ft..
b."X" = full size boat speed. Solve the equation: [X divided by the square root of the the ratio between the two lengths=model speed] (works for knots or mph)
=========
Model to full size examples:
-----------
Example one: the 5.42' Mpx was clocked at a max speed of 3 mph by the tracker. What would the speed of the 19.5' full size version be?
X divided by the square root of 3.6=3 Therefore, full size boat speed = 5.7mph( not accurate but fun)
-----------
Example two: the 4.67' F3 foiler that I designed built and produced 14 years ago was clocked ,over a measured course, at 18 mph in a 22mph wind.
How fast would that be in a 19.5' version of the F3?
X divided by the square root of 4.18=18, Therefore, full size boat speed would have been 36.7 mph(31.9 knots). Like I said,not accurate but fun!
========================================
I don't care about scale speed-I only care about actual speed of the test model. And right now the record is 3 mph in about the same amount of wind(which is excellent).
Note: I use mph mostly because the lift formula uses mph and the wind pressures shown in Skenes are in mph.

 

MPX Testing and Development-------Wing Tip

Got the Wing Tip from Sails by Morgan this morning. He and I knocked it out in no time. The idea is that it will prevent the boat from turtleing in a pitchpole or capsize, thereby reducing the chances of ruining the radio equipment. This thing will also act like a vertical endplate, effectively increasing the span and ,therefore, the power of the rig.

Pictures,L to R, 1) Gaff Control Device(GDC-discussed in detail earlier-changes the point of rotation of the gaff),Wing Tip support strut(with rounded plastic tip), Gaff tensioner-accesible when Wing Tip is in position-fully adjustable*, 2) Shows the foam(for buoyancy) sliding into the Wing Tip, 3) Velcro straps, 4) All the Wing Tip components together, 5) The sail with the Wing Tip:

*On the first sail I forgot to adjust this and consequently there was too much twist even when I adjusted the vang.