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

Fire Arrow Foiler / MPX Foil System Testing and Development---Drag Reduction

Thanks Dennis! It's much more foil shaped than you give it credit for. The foam is only a quarter inch thick and sort of "bends out" the black cover into a streamlined shape-definitely not a "block". When I can I'll take close up pictures. As you say, I'm convinced that, for the job it does, it's a better shape than any other masthead flotation I've seen.

 

I'm quoting this post because I still need help:

 

Respectfully:
I don't think you should worry too much about reducing the aero drag at this time.
You have not demonstrated, at least as far as I can see, the type of consistent and controlled foiling that say, Ian Holt, has achieved on his small trimarans. I would posit that this is the standard you need to reach before you can claim real success. Your frame captures paint a rosier picture than the videos. Capture the first objective before adding features and complications.

As a second point, I'm not sure that aero drag is significant at this scale. The boundary layer does not scale. So the actual velocities this close to the surface are pretty low. A foiling moth hull is at your masthead! Drag is a second order function of velocity, and within 6" of the water that velocity is pretty damn low.
SHC

 

Fire Arrow Foiler / MPX Foil System Testing and Development---Drag Reduction

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Thanks Steve. As to foiling I respectfully disagree BUT the boat has only started full flying foiling in the last video for about ten minutes total-so there's a lot of refining to do. To my eye, and having been there, the boat was very stable and under complete control flying in a 5 mph breeze. Other foilers I have seen are foiling in a lot of breeze and flat water and I haven't seen one yet that is 100% stable though Ian Holts are the best Mini 40 foilers I've seen anywhere. I had a tacking problem caused by an overreaction to the previous video on my part: I set the Dual Rate/ Expo up so I couldn't turn it off which was a dumb mistake. The other big problem was the over twist of the main-I'd imagine the boat was short 30-50% on power because of the excessive twist. Thats been fixed and several full length battens have been added to reduce the wrinkles induced in the sail by peak halyard tensioning(and the fancy cut).
The next video will show a lot more foiling.
PS-in the long video below you can compare the waves that the boat sailed in with the waves in the Mini 40 video on the previous page. The waves were "bigger" than the wind was. I measured it before and during sailing at 5 mph max but the wind had been blowing 10-15 from the south all night over a 20 mile fetch. Even though the wind almost died the waves were still bending through the bridge close to where we were.

https://www.youtube.com/watch?v=4YBOEolFqiE


The short version. Notice the boat foiling as it sails away from the camera in close to the first scene-rock stable in pitch and roll. On the reach in crossing a swell generated by a power boat she rolls the port ama into the trough. That could be fixed by longer ama foils but that isn't going to happen on the model. She was steady in pitch in both instances. Pay close attention to :23 to :31
https://www.youtube.com/watch?v=7Mok3d4KiMI

 

I agree with the above, including the note about the aerodynamic drag. The biggest part of drag is very likely coming from the underwater parts, in particular those which work at the air-water boundary.

I would make one step at a time, Doug. You are at risk of dispersing your efforts and time into subtleties which are of very little importance at this point. Make it fly consistently and in a stable manner for long periods of time, before setting up higher-level goals. IMO.

Cheers

 

Fire Arrow Foiler / MPX Foil System Testing and Development

Thanks, Slavi. Unfortunately, I disagree with Steves assessment of the foiling in the videos. But these are early times and there's a lot more to come.
As to aerodynamic drag and its importance, here is a quote from Bill Beavers study of the Moth:
Currently, hydrofoil Moth speeds have been clocked
in the 28 knot range but that is only off the wind. When
beating upwind, typical sailors hit speeds of 10-14 knots
and top sailors reach 15 knots. At 15 knots, Table 3 shows
an aerodynamic drag of 17 lbs. This is about 70% of the
total hydrofoil drag, so it appears that the aerodynamics of
the boat are now nearly as important as the hydrodynamics.

And the whole paper is below:

 

Fire Arrow

I've been a fan of Fred Monsonnec's blog "Foilers!" for years and he just notified me that the article he has done on me and the Fire Arrow is up: http://foils.wordpress.com/

Thanks, Fred!

 

Missed the point.
Some things scale, others do not.
The structure of the wind does not.
Normal models of boundary layer show that it increases in speed exponentially with height.
http://www.onemetre.net/design/Gradient/CarrGrad.gif
As drag increases at the square of the velocity, being low is good from a drag point of view. Note how steep the increase in wind speed is between 0 and 2 meters
Bill's tests quantifies the aero drag of the Moth platform, which is traveling in a region where the wind speed is much much higher and therefore much much more significant. It is common practice in all high performance boats to sail up wind with the crew as close to the water as practically possible. This is not just for righting moment, but to get the crew in that slower moving air and reduce their contribution to total drag.
So my suggestion, respectfully submitted as requested, is that you ignore the streamlining of your platform at this time and at this scale because my estimation of the potential gains does not justify the effort. Instead I recommend you do more testing to document the full performance of the model.
SHC

 

Fire Arrow Foiler / MPX Foil System Testing and Development

Steve, I'm going to take your advice and sail a lot more before doing any other mods. Thanks for the help!
What has been done since the last sail: (see previous posts)
1) Remove the GCD and add a mast extension to support the peak halyard,
2) Increased the purchase on the peak halyard,
3) Added a diagonal batten in the pocket already sewed into the sail plus three other full length battens. I've used the gaff on numerous models before with good results and one of the advantages was not needing full length battens. But, the fancy cut of this sail causes odd wrinkles that the battens mostly remove.
4) Reduced the wand paddle size about 25%.
5) Added the reefing system which works by removing a section of the mast.
6) About to paint white area on side of hull to improve wand visibility in the video.

Here is the image from Steves post:

 

Fire Arrow Foiler / MPX Foil System Testing and Development--UptiP Ama Foils

This is one of the most important successes documented in the first foiling video.It's been mentioned before as part of another post but it's worth repeating. While getting the boat foiling stably was important and shown in the last video, perhaps of equal importance is the fact that the UptiP foils I designed, based on a lot of research on the basic foil invented by TNZ, worked perfectly.
Nothing illustrates that better(except the video!) than these two pictures.
"A" shows the boat with the main hull still seahugging but with the lee ama flying. "B" shows the whole boat flying but with the ama still at the same altitude as it had in "A". So the intrinsic altitude control of the the UptiP foil is shown working in two different speed and load cases-which is really cool because it's maintaining altitude with no wands or other moving parts:

 

Fire Arrow Foiler / MPX Foil System Testing and Development

Here is the before and after of the paint job on the hull to help the wand position to be more visible in the video:

 

Fire Arrow Foiler / MPX Foil System Testing and Development

I adjusted the amount of tension on the wand system tonight . The idea is that the spring has the least force on the wand paddle(@ 90 degrees to the paddle face) at takeoff and maximum force (pulling the wand forward @ 90 degrees to the paddle face) when max downforce is required. The changes today improved how the system works:
click for best view:

 

doug,

all the respect in the world for your design and pushing it, but seriously man, stop posting on the forum and go sail the stupid thing. you sound like all those old wannabes in every marina Ive visited under sail. "yea, just waiting for a.b.c.d.e.f.g. to be ready then its off over the horizon for me". blah blah blah.

you have totally jacked the normal model of hypothesis at this point by literally messing with every variable you can touch without any more testing. STOP WORKING ON IT, AND SAIL IT.

jesus, why do I always have to state the obvious?

I mean this in nothing but a good way. Im looking out for you Doug.

 

Fire Arrow

2F2, you may have missed the part where my friend and videographer had to go back to coaching a high school football team. I've talked to a bunch of people to try to get help with no luck. I can't fit every thing in the car anymore with the new stand and longer ama foils and I can't lift the boat alone. Also,I won't sail unless I get video. I'm working on a solution-there's a remote possibility that Dan and I can go over the Labor Day weekend-we'll see if that works out.
Recent comments on this forum have me really anxious to take a long foiling video since the boat is 100%* now-so I'll get it done as soon as possible.

* One ama foil has no i-flap and one does but that shouldn't cause any significant problem with a long foiling video......

 

Fire Arrow Foiler / MPX Foil System Testing and Development

I'm putting together a chronology of the development of the boat since it's very first sail. It will help(maybe) to put things in proper context.