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

FKS-RC / Dominion 2-HW

While I'm waiting to be able to test the Fire Arrow(and D4Z), I'm building a Foiling Keelboat Scow with a foil system based on Hugh Welbourn's Quant 23 and and a hull based on "Dominion" the first(as far as I know) tunnel hulled scow. Just started building today after several weeks of design work:
(The design and build log is here: http://www.rcgroups.com/forums/showthread.php?t=2434531&page=6 )

 

RC Trimarans

Follow up on Ian Holts Skyfall from previous pages* where the boat was equipped with wand controlled main foils. In this video, the foils have been changed to surface piercers:
*post 2144,p143; posts 2147,2149 and 2156, page 144

https://www.youtube.com/watch?v=JfidwefEW6I

 

3 Mini40s in action on the estuary in a decent breeze. C rigs for most of the time though we did try B rigs for a while. Really good comparison of the conventional fixed V foil configuration versus the wand controlled T foil with flap. The latter is more docile and . . slow! The fixed v foil needs concentration upwind and exactly the right amount of lift, but can be fine. I think we need sets of foils of different lengths, as you can see that we have more than enough lift from the V foils. Number 59 especially demonstrates this by rearing its bows when heeled upwind.

The wand controlled foils may one day work but there is still so much to test, and I am not sure that I have the patience for the trial and error here - too many variables to sort out: size of fixed element of the foil; size of flap; angle of fixed element; depth of foil; wand length; gearing between wand and lever on top of foil, etc. This is my second set of T foils and, whilst better, and noticeably more docile upwind are still nowhere near as fast as the v foils. It could be as simple as the fact that they have almost twice the drag, plus when the flap is in the "hold down" position drag is further increased. The T foils are also wider than the rules permit in the Mini40 class so this is purely an experiment right now.

.... And it is impossible to keep a boat up on its foils through a tack. As soon as it goes head to wind the inertia is lost

A great day by the water!

Video is here:
https://youtu.be/Y51VnXzVgbM

 

F3

Ian, instead of reinventing the wheel you should consider copying the details of the F3 so you could start from a well proven design. The wand system develops all the RM for the boat and works very well-and is not slow. The F3 was 56"(1.42m) LOA and 60"(1.52m) wide CL of foil to CL of foil(72" wide overall). It weighed 8lb(3.64kg). A mini 40 version would work if you kept the cl of the foils equal to the LOA apart. Closer overloads the foils, further apart unloads the foils and is faster. I've posted most of the details here and would be glad to help.

 

Unfortunately I cannot see the dimensions of the fixed part of the foil or the size of the flaps on your F3, nor can I see how you attached the wand to the top of the fin, or how long it is, or how you pin join the push-pull rod to the flap, or how deep the fin is.

 

F3

Ian there are two rough illustrations on page 144, post 2146 showing the wand system and the one below. The wand can be set as shown(32 degrees) or even at 45 degrees for flap neutral. The rocker arm set up should be as shown. The wand system uses a 5/32" SS rod bent to take the wand. So the SS rod serves as an axle to mount the rocker arm. On the F3 there was a ss bearing on either side of the rocker arm but you could probably use brass tubes.
You can set wand length for the flight altitude you want and even make the wand length adjustable. The nominal flight altitude should be with the main foils 2 chords below the surface. The top of the rocker arm should be attached to a spring that tends to hold the wand against the water and should be set up so that as the wand moves forward the tension on the spring increases.
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My foils used partial span flaps that were 20% of the total area. The flap can be up to 30 % of the foil area.
The F3 was 8lb(3.64kg) of which 80%(6.4 lb/2.9kg)) was supported by the two mainfoils.
The main foil area was 17 sq. in(109.68sq.cm), including the flap. The foil loading was .188lb per sq.in.(.013kg/sq.cm). Don't use use the same area but match the foil loading to your boats weight.(see next post) It is very important that the mainfoils lift 80% of the total weight.
The mainfoils (flap neutral) should be set up with a +2.5 degree angle of incidence with the rudder T-foil set at zero degrees relative to the static waterline(roughly parallel to the flight waterline after takeoff).
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I used very thin mylar as a hinge with holes punched either side of the hinge line of the flap. The mylar was laminated into the foil during layup in a split mold.
If you're using wood you could sandwich the mylar between two pieces. It's not critical that the hinge line is smooth(though it wouldn't hurt).

click-

 

=============================
To be proportionately the same as the F3:
1) main foil loading=.013kg/sq.centimeter
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2) main foil area=129.23 sq.centimeters(20 sq.in)
a. flap area at 20%=25.846 sq.centimeters
b. flap area at 30%=38.77 sq.centimeters
c. mainfoils set at +2.5 degrees
d. foil section must be symmetrical
---
3) Rudder foil=same area as one main foil or slightly larger
a. rudder foil set at zero degrees
======================
Wands should be directly connected to the flap as described in previous post and shown in sketches. This will give you the maximum possible righting moment from the foils.
You can use a rectangular planform with full span flaps if you want for the sake of simplicity but don't fudge the area.On a multihull where you are using the foils to develop all the Righting Moment for the boat it's probably not a good idea to have the point of contact of the wand with the water much,if any, ahead of the longitudinal CG of the boat. Multies that are using wands ahead of the foil like the Vampire and the Stunt 9 also use movable ballast-you don't- so keep the wand as shown for the F3.
The F3 used the planform below with a partial span flap at 20% of total area.(see and click on picture below sketch)
It used a nominally 9% thickness/chord ratio.
Keep in mind: the phenomenal ability to generate righting moment will allow these foils to be very fast even though their immersed area when foiling may be greater than a surface piercer. Reducing the foil area will be a mistake because doing that reduces the ability of the foil to generate RM. Just because these foils can generate their own RM doesn't mean they can take any amount of sail in any wind-the sail area will still have to be reduced as the wind picks up-testing will tell you when and how much. I had a little pamphlet- that I can't find- that described exactly when and how much to reef the F3 sails.
If you have any questions don't hesitate to post here or e-mail me. I'd like to help in any way I can.
===========

The rough sketch below shows the exact position of the mainfoil quarter chord for the boat weight specified above. The CG was a guestimates as was the position of the rudder quarter chord.
To find the exact points on your boat for a main foil loading of 80%:
1) find the longitudinal CG of your ready to sail boat,
2) the distance between the CG and the quarter chord of your rudder foil will be 80% of the distance between the rudder quarter chord and the main foils quarter chord. So divide that distance by 8 and multiply it by 10 and that will be the total distance between the rudder quarter chord and the mainfoil quarter chord for a main foil loading of 80% of the total weight.
3) you may have to juggle things a bit to get this right but it's worth the effort.
NOTE-"quarter chord" is used because it is the nominal center of lift of the foil



click on picture for larger:

 

Ian, a couple of observations;

1. It doesn't look like your foils are providing ANY down force, Doug says this is because
the elastic tension isn't strong enough.
2. The wands are always way out of the water which should mean they should be producing max. DF which leads back to #1.
3. Once you are producing DF after putting more tension on the elastic the wand are probably going to be too short, find a tube that fits over your wand rod so you can slide it up or down to adjust your wand length. This is the primary adjustment for ride height in a Moth which uses the same system.

 

Nightmare Mrk VIII

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Hello, Ian
I have just begun working on a Nightmare Mk VIII which I was just informed has been discontinued in favor of the Fire Dragon. I have spent many (many) days redrawing the plans I downloaded as they were unusable as received. I will send the patterns out for laser cutting next week.
But the questions just keep coming... sorry.
Where does the mast go?
Thailand says, "typically the mast is about 650mm from bow while the foils are about 550mm from bow"
Can I use this or do you have other thoughts.
I am also following a lot of discussion about foils and how to control them. Attached is something that came to me this morning whilst showering.

 

Nightmare Mk VIII

Hello there.
Don't worry about the Nightmare being discontinued. The Firedragon is Roland's own design so it is natural that he should want to promote this. It also has more rocker in the hulls so is better for light winds, but if you - like myself - are after fun sailing at high speeds then this is irrelevant.

If by "steerable" foils you mean "adjustable" foils then we are in complete agreement. I am about to lend one of my trimarans to a person at our club whop also has experience with rc helicopters and he is going to try adapting it to have a gyro connected to the foil control, which will be either as you have sketched it, or with two servos, one per foil. And he will revert back to the more conventional foils with a shaft in them. This is semi-balanced so the loading on the servos is much less then when we tried to control the angle on my kinked foils. Video of these is here
https://www.youtube.com/watch?v=Tjy8zr1fRig
The loading on the servos was very high and I burnt out 2 servos before removing this system from the boat

Mast position: I believe that the rigging instructions form Ernst were probably written before T foils on rudders were being used, so the instruction was to put the mast as far back in the boat as possible to prevent cartwheels. T foils have changed all that. My T foils on the rudder are 24cm wide. The UK guys say that this is way too big, but they are not foiling, and they still cartwheel. I recommend you start with this but be prepared to reduce them down a cm at a time in width as you get bolder with controlling the boat.

Positions: Mine are:
1/ Front of mast tube is 56cm back from bow (or 58 cm from front of bumper)
2/ BACK of foil is 47cm back from bow (or 49cm from front of bumper)

Hope this helps

 

Hi Jim yes you are correct, clearly the foils are producing minimal downforce. I must be getting a little otherwise it would have been going airborne briefly, but anyway, it is obviously not enough. I purposely made the wands of 10mm diam tube so I could slide slimmer longer wands into them, and that, plus stronger elastic, will be the next step, but first I am going to cut off the T foils and reduce the fixed angle of attack. Just not enough spare time to make all the changes . . . .

 

On the fixed angle of attack, can you trim the front edge of the foil in the trunk and get your angle change that way? It should take very little to get 1/2 to 1 degree reduction in angle and you could use shims to fine tune the angle. If foil are thin at the front use a small price of scrap to re seal the front. Should be easier and adjustable.

 

Thanks, Ian
What is the cord length of the rudder and bent foils. The foils look rather shorter than the rudder's cord.

 

Fire Arrow Foiling System Testing and Development

On the very first test sail in any wind the wands were too long which caused the boat to want to jump -especially when combined with hard rudder movement. Some pictures showing the midship dual wand system. The midship wand was pioneered by Dr. Bradfield and used on the Rave,Skat and Osprey trimarans. The advantage it has is that the wand makes contact with the water at the F & A CG so that its sole function is altitude control. Some wands are mounted forward of the foil and make contact with the water in such a way that they can change altitude when the boat pitches. This shows up poorly in some cases in rough water where the wand causes unwarranted altitude changes.

Pictures- L-R-1), 3),4) the wand and the "paddle", whose concept was invented by Dr. Sam Bradfield-the idea being to smooth out wand input by allowing the wand a degree of planing.The MPX paddles are made of thin carbon that can flex under load. Paddles of different shapes and sizes are common on Moth foilers. On the F3, when it was first launched we heard this very loud buzzing sound from over 50' away: turns out it was the dual independent mainfoil wands. They were circular and as soon as they were squared off the noise and high frequency vibration stopped. These first MPX wands are set for a main hull altitude of about 6" corresponding to an angle of heel of about 10.75 degrees. They are not yet adjustable but will be for an 8-12" altitude(angle of heel up to 17-20 degrees for testing) or they can be disconnected to allow manual control. The plate that supports the wand axle can slide slightly fore and aft to change the angle of incidence of the main foil which is attached at point "A". Point "B" is where the pushrod from the main foil flap is attached. Point "C" is where a line to the tension spring is attached-this spring holds the wand against the water so it can provide altitude feedback.Points "B-C" are on the rocker arm that transmits wand altitude feedback to the mainfoil flap so that the preset altitude(+angle of heel on this boat) is maintained. Point "D" shows the rotating axle to which the dual wands are attached., 2)-wand plate supporting the axle for the dual wands and the rocker arm directly connected to the main foil flap, 4) Jump related to wands that were too long.

 

Fire Arrow Foiling System Testing and Development

Way back in May, I think it was, I was told by the condo association that they were going to put in a seawall where we now have big slippery rocks.And that the seawall would have steps so we could walk down into the shallow water. Well, its been delay after delay and I was just told by one of the owners that it will be another 5 weeks! Everybody put their assessment up in June so it will be right on 6 months if this proves to be accurate.
When this thing gets done I'll be able to sail right here some of the time which will be just terrific.
Dan doesn't live too far from here and instead of us having to drive 10-20 miles to test we'll be able to do it right here and sit in the shade on the dock and get video.

sunset and the dock........