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

MPX Testing and Development----First Flight!

Technical Analysis of the First Foil Assist Video*

Some interesting facts: based on the boat sailing in 9-11mph wind
and flying the main hull. Boat is an oversquare platform and the full size boat would require about 17mph of wind to fly the main hull w/o the main foil-which will allow the main hull to fly in as little as 5mph of boat speed(6-7 mph wind speed ,estimated). One of the main functions of this design is to use the mainfoil to fly the main hull BEFORE it would on the basis of just wind pressure.
MPX Test Model:
1) Heeling moment(HM) at 11mph wind about 45.2 ft.lb.( .48lb/sq.ft pressure on 23.54 sq.ft @ 4' )
--
2) Heeling moment(HM) at 9mph wind about 29.2ft.lb. (.31lb/sq.ft. pressure on 23.54 sq.ft @ 4' HA )
--
3) Heeling Arm(HA)= 4'
--
4) Righting arm(RA) with both the ama and the ama foil supporting some of the weight= 3.04'.
--
5) MAX RM(Righting Moment) of boat with ama and the ama foil supporting the weight required to fly the main hull: 3.04' X 21.13lb= 64.24 ft.lb
--
6) Ama buoyancy 7lb
=====================
Conclusions:

A) At 11mph wind and boat weight of 21.13(discounting rudder foil loading) :
--1-Vertical lift required of ama + foil for this HM= 45.2ft.lb divided by 3.04'=14.86lb (so even with ama submerged ama foil would have to generate 7.86lb of vertical lift).
---
--2) Vertical lift required of main foil at this wind speed=[21.13-14.86]= 6.27lb
------------------
B) At 9mph wind speed and boat weight of 21.13(discounting rudder foil loading) :
--1-Vertical lift required of ama + foil for this HM= 29.2 divided by 3.04'= 9.6lb (with submerged ama ,foil would have to generate 2.6lb of vertical lift)
---
--2) Vertical lift required of main foil at this wind speed =[21.13-9.6]= 11.53lb.

====================
This, coupled with the video is conclusive proof, beyond a shadow of a doubt, that the foils worked* in arduous conditions and that they allowed the boat to fly the main hull in conditions where it would not have been able to do so otherwise due to its oversquare beam. Which was and is the central rationale for the MPX foil system.

*I didn't realize it wasn't caught on video but both Dan and I saw daylight under the lee ama with the main hull flying about 2-3" up just after we started sailing and when the wind was the lightest of the whole 20+ minutes of sailing. Dan was having trouble with the camera and caught the last 4+ minutes of a 20 minute session with the wind increasing the whole time.

--- From the original MPX foil page(p 88) : "6) Speed- Top end speed is NOT the priority of the MPX Foil System-light air speed resulting from the unique ability to fly the main hull in light air is. The MPX Foil System's main claim to relevance are the two lifting foils on the main hull which allow an oversquare platform to fly the main hull when a wide trimaran,particularly 20' or under, w/o these foils would not. To make a 1.2-1.3 oversquare tri fly the main hull (without foils) requires excessive sail area(or wind) and impairs the pitch stability of such a boat . The two main foils work together to provide pitch stability way in excess of any "normal" trimaran and control the running angle of the planing ama and ama foil. The system should work well with a planing ama using foil assist and/or using an ama foil that allows the ama to fly when the main hull does(the current test model configuration).5/1/14


---I use mph because its convenient and used in the lift formula and the wind pressure tables. If you want knots, divide mph by 1.15.


https://www.youtube.com/watch?v=LmXCdAlo4mk&feature=youtu.be

 

"I tend to use mph and not knots because the wind pressure table I have is in mph and the foil lift formula uses mph(ft/per second). If you want knots divide mph by 1.15."

Doug, could you please post a picture of that table , it would be very helpful to me, and maybe others as well.

It may help answer some questions for me in terms of what speed/ heeling moment I can expect from my boat.

Thanks
-Curtis

 

Doug.
Just my humble opinion, but I think you need less dihedral on the Akas and more lift on your Ama foils. Otherwise looking good.

 

Doug, excuse me, but here is some useless advice (because I know you won't agree); there is too much lift on your central hull main foil ... better to make it a conventional dagger, no vertical lift ... because as soon as the boat gets any decent speed; it rears back on its arse, because of too much lift forward, stalls out etc. Whereas for a few seconds it is riding on the lee float foil before the imbalance occurs. And without that T main foil, less drag, better equilibrium, better speed. Just imo of course.

 

Gary, I have the distinct feeling that you and I are going to be in trouble if we keep on being Gadflies.

 

MPX Testing and Development----First Flight!

I hope you guys will read my last post. This was the first time in foiling conditions but the boat was overpowered. If you read and understand that post you will see that the wind was not strong enough to fly the main hull without the main foil lift. And you'll see that the boat would simply have rolled over w/o the lift from the ama foils. Of course the foils need adjustment and the next sail will be at a site with no waves to facilitate that.
Either this Thursday or a week from Tuesday.

 

Wind Pressures-Skenes

------------------------------------
Here you go, Curtis-if you want me to e-mail it just let me know. Keep in mind that these pressures are basically flat plate pressures that have been used over many years-they do not represent any sort of lift/drag for the rig. They allow estimates of the force on the rig but the real value is in the difference between one wind speed pressure and another(pressure varies as the square of speed). I've found good correlation over the years so they're definitely helpful.
click:

 

MPX Testing and Development----First Flight!

I had a brainstorm last night thinking about the almost pitchpole around 2:40+ into the video. I explained how the rudder caused the pitch-ups when turning too hard in post 1414 on the previous page. Now I realize the opposite is also true: if you try to gybe in too much pressure the rudder can force the lee bow down as well with all the power that is capable of throwing a 21lb boat clear of the water(!)*-except in this case it creates a down-force instead of an up-force. Dennis's dual rate suggestion is looking better all the time. So I watched that segment a bunch of times and you can see that the rudder is hard to port as the stern comes out of the water-exactly the way it would have to be turned to precipitate a pitchpole. Contributing factors were the loose shrouds that allowed the top of the rig to go too far forward, the over twist of the main due to the failed vang, the malfunctioning sheeting system and the waves.
*See the picture below of the pitch-up resulting from a hard turn to stb:

 

MPX Testing and Development----First Flight!

==================
Hey, I appreciate your comments even if you won't read the technical stuff!
And ah.....you can't get in trouble for being wrong-at least here....... if you'd p-l-e-a-s-e read the technical stuff in post 1426 you might understand better whats going on.
So we've sailed in 3-4mph(flat water) and in 9-mph(biggish waves for this size model*) next will be 5-7(flat water).........God willing and the creek don't rise.
* equivalent to 7' waves for an AC 72

 

MPX Testing and Development----First Flight!

This screen shot from the video was apparently taken by an individual hoping to ridicule the performance of the boat. As in most places, people go with their "surface" impressions-facts be damned. Anyway, far from ridicule I think this picture is cool! What it shows is the dynamic pitch-up I described in a previous post* and, despite having looked at the video quite a few times,I never realized that that rudder movement completely launched the boat out of the water with the mainfoil , rudder, rudder foil and the radius portion of the port ama foil the only parts still in the water! She wants to fly........
Thanks go to "lost in translation": *(what you see here was explained in post 1414)

Click for best view--

 

Doug,

I do not see the waves that you state made the boat uncontrollable. The water looks much flatter than where I sail my boat.

-RB

 

MPX Testing and Development----First Flight!

I never said the waves made her uncontrollable!! That's something you just made up!
The waves that were there were about 6" from trough to crest and that translates to about 2' for the full size version of the model or 7' for an AC 72.
The waves did not, in any way, make the boat "uncontrollable"-she handled them fine. They were big enough to make any foil adjustments in those conditions( sailwinch/sheeting problems, vang failure, too much wind for the rig,operator error ) impossible. We'll sail in flat water next and get the foils properly adjusted. We'll get a smaller rig at some point. With just a bit less SA she would have done even better.

 

Doug. It's just teething problems.
Persistence will get you there.

 

MPX Testing and Development

==============
You're right Paddy! Just don't understand the reluctance by some to look at the technical facts that explain so much-kinda frustrating.
Just got back from the sailmaker where he added a grommet for the new downhaul(cunningham) and cut down the Wing Tip a little bit. Fixed the vang last night-don't expect any further problems with vang related sail twist. The sail winch is ok-still have to add a block and spring to one side of the lines coming off the drum. Going to adjust the mainfoil down to 2.5 degrees AOI-I think I was wrong to go up to 3. And I'm going to take a careful look at the length of the wands-could be they're too long. We'll sail in flat water with wind between 5-7mph-hopefully.
Looks like Thursday is out so next sailing next Tuesday.

PS-talked to the sailmaker about a #2 rig-I can't afford it now but we've got it figured out.

 

MPX Testing and Development----First Flight!

In my continuing watching of the video there are two pitch-ups and one pitchpole largely explained by excessive rudder movement but there are two other "small" pitch-ups that I don't understand. I know I was probably wrong to set the main foil at an AOI of 3 degrees when 2.5 worked perfectly for Bradfields boats, so that will be corrected before the next sail.That will reduce maximum mainfoil lift(30 degree flap down) by about 20%. No basis for changing the AOI of the ama foils at this point. We'll continue the testing until it is as near perfect as possible.