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

[Doug Lord]

Fire Arrow Foiler / MPX Foil System Testing and Development

More on the new surface piercing main foil(with downforce) : I'm thinking that it could have an application on a racing version of the Fire Arrow even w/o intrinsic downforce because it would drastically reduce the wetted surface of the main foil. And on a racing version, if downforce was wanted you could include a flap on the center section that you would simply "shift" to begin downforce.

More on the automatic main foil: I'm designing the model version now and the way to set it up follows, based on the last sketch of the last post:
1) the sections of the foil outboard of the fences will twist(washin) from a nominal AOI(angle of incidence) of 2.5 degrees to an AOI close to the tip of +6 degrees,
--
2) the center section consisting of an inverted asymmetrical section will be set up with the nose up 2.5 degrees.
--
3) this is based on an expected(will be measured exactly in our next tests) 2.5 degree pitch down at speed, which will:
a.cause the inboard half(the immersed portion) of the outboardsections to have an an angle of attack of zero degrees, and,
b. cause the nose of the asymmetrical center section to operate at an AOA of zero degrees, which, if a similar foil to a 63412 is used, cause downforce to be developed with a section lift coefficient of about .3.
======
The viability of this concept depends on, among other things, knowing the exact pitchdown of the boat at speed. This is where the damn no good go pro would come in handy or one of the cheaper versions-- to be able to watch the wand lever to tell exactly when the foil begins to develop downforce. It's probably not possible to see the wand with sufficient accuracy to tell that this has just started.

click---

Thanks, Paul. The main foil, with dual wand controlled flap, is unquestionably the best for performance. But since this is a scale model of a "sport" boat and not a scale model of a race boat, I've been trying to see if I could come up with a surface piercing main foil that could somehow be designed to produce downforce before the main foil flys due to heeling force- to further simplify the foil system.
Right after takeoff, whether the main foil is a surface piercing foil or fully submerged wand controlled foil, it begins to unload with more and more of the load taken by the ama foil. That's all automatic. And the characteristic of the boat as it speeds up is to pitch down. My use of the asymmetric center section is to take advantage of the fact that an upside down asymmetrical foil will generate vertical lift(an airplane with an asy wing can fly upside down) with the right angle of attack and that while upside down it will generate downforce with a low positive angle of attack or zero positive AOA, while the inboard sections* of the symmetrical foil are at zero degrees angle of attack producing no vertical lift-all this when the boat is at max pitch down.
Whats hard in studying this is to remember that the heeling force is increasing as the boat speeds up and pitches down. And that the heeling force unloads the main foil.
---
At max pitch down there is a symmetrical foil and asymmetrical foil cruising along right next to each other ,separated by fences. The symmetrical foil is at zero degrees AOA and so is the inverted asymmetrical foil. Because an asymmetrical foil can generate vertical lift at zero degrees AOA, it can generate downforce when inverted at the same angle of attack!
So I guess I think it's ,at least, worth a test.....
*which are the only portions of the symmetrical foils that are immersed at that point.

 

[Doug Lord]

Fire Arrow Foiler / MPX Foil System Testing and Development

While I'm waiting for my crew to be ready, I'm working on the prototype for the AC 62RC(see the Projects and Proposals forum here or go to rcgroups and the AC 62RC thread).
One of the big successes so far with the Fire Arrow is how well the UptiP foils worked-they required no adjustment while sailing-none-zero.
BUT-when you start to plan how to use them effectively on an rc cat its a whole 'nother story! The UptiP foils on a cat MUST be retractable so you can sail with the windward foil retracted-I took care of that on the Fire Arrow by having high dihedral to the crossarms so the windward foil is just clear of the water with the main hull not flying-and clear of waves when the main hull does fly.
But not only that: you have to have a servo to adjust the angle of incidence of the foils as well. For instance, to take off the foil must be raked about 6+ degrees and right after takeoff the foil AOI must be reduced(raked) to 2-3 degrees.
That's not necessary on the Fire Arrow because of the i-Flap and/or twist added to the uptip portion of the foil.
All this radio adjustment on the cat can be pretty expensive not to mention adding a bunch to the foiling workload. So on my AC 55RC Proto(the AC 45 to the AC 62RC Class!) I'm going to be using wands on the mainfoils and I've decided to use two separate rudders to allow me to experiment with retracting the windward foil. Using a wand system means that retraction is pretty simple(though not real cheap) and a wand based T-foil system is likely to be almost as fast as an UptiP foil system with the windward wand T-foil retracted.
In the meantime the Fire Arrow sits forlornly waiting,waiting.........

 

[Doug Lord]

D4Z AC 62 Prototype / rudder(s)

I posted this question in the aero-hydro forum as well because I feel it is as applicable there as it is here:
-----
I'd like some input on the two choices I have:
1) place the rudder under or behind each hull-on an rc boat ventilation is not the problem it is on full size boats but loss of pitch control is so the better position on an RC boat having two rudders seems to be behind the hull because:
a. it's simpler to adjust rake angle for the rudder hydrofoil,
b.it increases the "footprint"( distance between the quarter chord of the main foil and quarter chord of the rudder foil).
==============
2) hang the rudder in the center of the boat behind the rear crossbeam. This reduces drag a bit but weight probably isn't less than #1 because of needing to build the structure to mount the rudder.
Retracting the windward foil is likely to be the fastest solution but on an rc cat it is expensive requiring a top of the line, fast (RMG/Guyatt) winch to do the job and would require a rudder t-foil in each hull like the AC 72's, GC32's and Flying Phantom.
On the other hand if the two main foils are wand controlled and left in the water, it seems that the center rudder would work fine. It would be the same configuration(but narrower overall) as my F3 foiler.
-------
I'd appreciate any thoughts on this to help me think it out.....

==============================
Decision: I'm going with two rudders each with a T-foil. The mainfoil will take 80% of the load and the two rudders together 20% of the load. The area of the two rudders together will equal about 33% of the total foil area. So the rudder foil loading will be less than the mainfoil loading.
The deciding factor was my desire to experiment with retracting the windward main foil. If I had a single centered rudder and retracted the windward main foil there would be a new uncontrolled "axis of instability" formed between the central rudder and the lee main foil. With two rudders and the windward main foil retracted the pitch stability is excellent-no new "axis of instability".

 

[Doug Lord]

Fire Arrow Foiler / MPX Foil System Testing and Development

Ordered the sails today from Scott Morgan for the D4Z cat. They will be the same sails used on the Fire Arrow II (48" X 6' wide). Same material used on the Fire Arrow-Dimension Polyant ODL Technora-- 2.2 oz/sq/yd. The sail material is based on the fact that the new boats will do twice windspeed in a 5mph breeze and not normally sail below that.

 

[oldsailor7]

Great stuff Doug.
Your pioneering work is taking model boat sailing into another dimension.
I notice that the rear main rudder foil is raised a little above the level of the main foil. Is that enough for it to avoid the turbulent wake from the main foil ?

 

[Doug Lord]

Fire Arrow Foiler / MPX Foil System Testing and Development

Great stuff Doug.
Your pioneering work is taking model boat sailing into another dimension.
I notice that the rear main rudder foil is raised a little above the level of the main foil. Is that enough for it to avoid the turbulent wake from the main foil ?

===================
I crosses mine fingas and hope so! That kinda of wake turbulence can lead to ventilation but it's not so much of a worry on a model-probably something to do with Reynolds numbers. I patterned the mainfoil/rudder foil relationship after what was learned on the Moth and so far so good. When we get in stronger wind and start really moving we're likely to have a problem if we ever are. I'm not really concerned about it....
PS-Paddy, I hope it goes beyond models before its all over.....
PS2- The sail design for the D4Z/Fire Arrow II will use a large sock luff to make up for not having a wingmast-mainly to save money-the Fire Arrow wing mast made by Forte cost $300 and I already had the carbon tubes for this mast. We'll see how it works out.

 

[Doug Lord]

Fire Arrow Foiler / MPX Foil System Testing and Development

The surface piercing mainfoil with downforce(SPuD) needs to have a way to adjust the center upside-down asymmetric section independently of the outboard twisted sections. This is not a "mature" idea yet, but basically the hollow daggerboard will be fixed to the center section so the AOI of the center section can be varied by angling the daggerboard fore and aft(moving the bottom fore and aft for testing. Then the outside , twisted sections will be adjusted when the boat is set up on the table or maybe I can make a jig to allow adjustment at the sailing site. I'm leaning toward refining the concept so that the whole foil is laid up at one time, including the fences and pivot rods.
I think I can do it-we'll see.

click-

 

[Doug Lord]

D4Z proto(AC 55RC)

==============================
Decision: I'm going with two rudders each with a T-foil. The mainfoil will take 80% of the load and the two rudders together 20% of the load. The area of the two rudders together will equal about 33% of the total foil area. So the rudder foil loading will be less than the mainfoil loading.
The deciding factor was my desire to experiment with retracting the windward main foil. If I had a single centered rudder and retracted the windward main foil there would be a new uncontrolled "axis of instability" formed between the central rudder and the lee main foil. With two rudders and the windward main foil retracted the pitch stability is excellent-no new "axis of instability".

====================
And this means I need to understand Ackerman rudder compensation ,specifically when both rudders are turned max for a tack or gybe, what are the degrees of difference between them. If the rudder on the inside of the turn is moved 38 degrees ,how many degrees should the outside rudder be turned? The reason the degrees are important is that each rudder will be hooked up to its own servo and I will program the Ackerman compensation into them both.

 

[Marmoset]

Next thing you'll be messing with tail/eleven mix? Haha


Barry

 

[Jim Caldwell]

In car, you point the steering arm to middle of the other axel or in our case the middle point between the bows, just do it with the arms not programing.

 

[Doug Lord]

AC 55RC-the "AC45" of the AC 62RC Class

Thanks, Jim.

 

[Doug Lord]

AC 55RC-the "AC45" of the AC 62RC Class

Next thing you'll be messing with tail/eleven mix? Haha


Barry

==================
Barry, there are all kinds of mixes possible on one of these RC cats-lots of possibilities.

 

[Doug Lord]

D4Z /AC 62RC Prototype

====================
And this means I need to understand Ackerman rudder compensation ,specifically when both rudders are turned max for a tack or gybe, what are the degrees of difference between them. If the rudder on the inside of the turn is moved 38 degrees ,how many degrees should the outside rudder be turned? The reason the degrees are important is that each rudder will be hooked up to its own servo and I will program the Ackerman compensation into them both.

=======================
More on Ackerman here: http://www.boatdesign.net/forums/multihulls/ackerman-steering-set-up-tips-racing-cat-51795.html
I've decided that on my cat the Ackerman will be adjusted on site for the conditions that day-even between races. The super radio I'm using on the Fire Arrow will be used on the cat. Problem is the "touch sensor" is the worst programming interface I've ever run into-I had a Futaba 8 channel "computerized" radio in 1985 that was easier to program! But maybe I'll get the hang of it when I do it more often.....

 

[Doug Lord]

Fire Arrow Foiler / MPX Foil System Testing and Development / D4Z

This is something I learned a long time ago and it works real well on RC monos, in my experience. It is something I'm going to address later on the Fire Arrow-probably with a carbon Hoyt jib boom. I mention it here because I'm working on the D4Z AC 55(proto for the AC 62RC) and am going to incorporate either a sliding jib pivot or a Hoyt jib boom.
Here is a sketch of the idea applied to a cat but the principle is the same for any RC boat and makes a noticeable difference in pointing ability:

 

[Doug Lord]

D4Z /AC 55RC--proto for AC 62RC

Heres the boat with some black paint/primer in selected areas:

UPDATE-11/11/14---Curved Twisted Surface Piercing T-Foil---A potentially significant breakthough in RC model foils happened accidentally when I took a sketch of the new experimental Fire Arrow foil(post 1837 and others) and laid it out on a full size drawing off the D4Z: for use on the cat the foil would not have the fences or downforce section the Fire Arrow version has and I found tonight that if the foil is canted 10 degrees outboard the windward foil will clear the water with about a 6 degree angle of heel. What this means is that instead of using wands or UptiP foils with a retraction and rake servo for each foil, the new foil will automatically "retract" when the boat heels just a little and not need rake adjustment by radio(maybe). The potential is incredible and I will use this system on the cat.

click--