High Lift Rudders

High Lift Rudders i.e. Articulated Rudders Sometimes referred to as Flap Rudders. Mostly seen on Tugs and other workboats. In case you need an example try http://www.hatlapa.de/bms/flap_rudder.html or a simple text doc explaining the principle http://www.pilotmag.co.uk/Rudders%20txt.pdf

Question… Has anybody ever heard of this style of rudder used on a model yacht?

Has some advantages that might transfer to small yachts in reducing rudder stresses. Thinking about playing with a simple design.

Any input?



I think that Herreshoff (Nathaniel J.) tried this one in about 1895-1900. Did not persist with it. In the 1970s there was an Italian whose name I cannot remember who produced a multi-panel articulated rudder but nothing came of it (the fact that the rule makers penalised it like crazy probably did not help).

I suspect that the designs shown are most effective at maonouvering speeds just aft of a big propellor - but I may well be wrong.

Hope this helps.

Bugger you mean the motor is banned… :lol:

Seriously though outside of Racing do you think this would be of any benefit on a model yacht?

I’m on my way out and will reply in greater detail later, but I suspect not. In my youth I held a provisional patent for a flexible bladed rudder steered from the trailing edge. It was very difficult to engineer and didn’t seem to do much good.

Looks to me like the general intention is to delay stalling at high angles of attack. Right now I don’t see that the advantages of being able to use a higher angle of attack will offset the disadavantage of the complex mechanism required to articulate the rudder.

Although - you could probably accomplish everything needed by simple steering cables that run through fairleads on the large forward portion of the rudder, terminating on the shorter aft portion of the rudder. In this case, the mechanism is pretty simple. Would take some care in the design to keep the drag of the fairleads, etc. from more than offsetting any advantage from the articulated rudder.

I understand that B17 bombers of WW II fame used articulated rudders. The principle there was reversed, however. The pilot steered what looked more like a trim tab on the aft portion of the rudder. The rudder itself was free to rotate on its shaft. So when the pilot shoved on the rudder pedal for a turn to the right, the “trim tab” pivoted for a turn to the left. Because the “trim tab” stuck out to the left, the bulk of the rudder moved to the right, to zero the total moment about the rudder shaft. What the plane felt, though, was influenced more by the rudder than by the “trim tab,” so the plane yawed to the right, as the pilot intended. Thus the pilot was able to apply sufficient force to yaw the very large plane, and without using any hydraulics. Or something like that.

The same scheme would work with boats, of course, but with boats there may be a problem. Planes don’t fly at all unless there is forward speed, so there is no problem at very low speeds. Articulating a sailboat’s rudder in the manner described might produce a boat unusually difficult to get out of irons.

With the balanced rudders we use most of the time, it isn’t clear that there is any great need to further reduce the load on a rudder servo. However, the articulated design described (the one like on the B17, not the “high lift” design) might allow a tiny servo to control a large boat.

Someone else do it first.

Mike Biggs

The Mechanism isn’t as complex as you would first think.

I have an example under one of my Tugboats and it dawned on me that maybe something similar could be used on yachts.

Two flat bars with a cental pivot and the mechanism works incrementally as the rudder turns. Very Ingenious

I’ll see if I can get a photo of the rudder system I’m thinking of modifying/copying for a Yacht.

could the mechanism be adapted in a micro scale, and applied to a micro solid rig, like on a c-cat?

Not sure how well it will transfer down in micro scale but I have done something similar to a very small tugboat (450mm). Copied from a larger model tugboat and easy to fabricate from sheet metal and simple cast.

Mine was from Cast Bronze & Flat Brass Rod/Tubing etc, but I can’t see a problem with doing something lighter. A small Heli Blade might work for the rudder with a little ingenuity.

I have posted some old photos on the US Footy Forum @ http://ph.groups.yahoo.com/group/FootyUSA/photos/browse/80c9
which might explain it better.

There is also a guy here in Perth WA who does carbon fibre foils for dingys & Kayaks and some of his shapes look promising, ie for the Flap attacment.


Anyway, photos do more justice than my ramblings.

Hope these explain my idea.

Nigel if I get your drift I assume you mean a Trailing edge Solid Sail?

Not overly sure what you mean as I am a power boater by Gene Pool.

Like I say. Boats are cars without wheels and Planes without wings. I Suppose a yacht could be seen as a plane with One wing in the water… :lol:

I think it could be done and would be an interesting model. Side stays would be almost a necessity and would have to be built into the mechanism.

I tried a rotating Turbine (solid sail of sorts) on a boat many years ago as a science project and let the wind generate a charge to a battery which we used to run a small motor. Quite a successful novelty but wasn’t very fast. Motor took more than it could generate. Got an “A” for ingenuity as the task was to charge a battery by wind. We went one step further merely to prove it could be done.

As an upside down Rudder (Large Soild Sail) I could see it working or at least worth a Giggle or two merely by trying. :devil3:


John :zbeer:

I remain sceptical about the dersirability of a high-lift rudder.It may be high lift, but it is also high drag. This is fine for a powerboat manouvering: it does not make much sense for a sailiing boat.

The yaw inertia of a Footy (or virtually any other model yacht) is so low that a normal spade rudder will generally do everything you want. A high lift rudder miht be marginally less prone to straling, but that is easily dealt with by not treating the helm as an on/off switch!

john, ya, i stiil want to muck about with the wing idea. it’s a litte on the back burner for now, but when it’s time, gonna bug mr. lemke, (no insults intended by adding “mr.”, just some pirate talk, “yar mr. christian”.) about some of his stuff. i like your mechanism for moving the trim. i never would have thought of that.


Just to keep up a bit of “interest” and the backburner “warmed up” ! :wink:

Oh yes - by the way …“Heavy” on the “MR.” please :smiley:

yarrr. thanks.

It also comes down to the size and effectiveness of the Spade Rudder and whether it is suitable to the Model in Question. A footy is by default a poor example of Hydro Design. Far too many compromioses need to be made to allow for anything resembeling a real yacht. Too Fat and Chubby for my taste but Cute for my Neice to play with…

As is always the case in Models, Water Molecules cannot be scaled nor can Wind or Barometric Pressure. These have to be interpreted and accounted for.

Unless one is prepared to try new innovations and designs we are all destined to be left in the dark ages. Perhaps the current big boat designs don’t warrrant investigation in modelling? Why push the Paradigm Envelope when we are content to sail floating corks… Bob Bob Bob…

As always I bow to the greater expertise of the Hydro Gods and their drafting pencils. I prefer to push the envelope a little so, no what Angus is attempting to say is not quite right. All I would seek is the evidence to prove it wrong on a conceptual level. May I ask what current model Test Tank is being used to discredit the design motif?

Incorporated with slender keel concave shadows and Trim Tabs this is even of further benefit in design. Might not fit the footy but other sailing enthusiast who pass through might find it beneficial in a development clas swith more scope for innovation… Who Knows…

Not restricted by a box that in my mind is only imaginery anyway. Has no construction info so can only be used on paper. I’ve got digital calipers to prove my boat and not some old vege box…

All a boat has to do to comply is that “it can fit”, it doesn’t have to be physically tested. Calipers don’t lie… Boxes do…

The rules don’t say how a measurement is to be officially carried out. Perhaps issueing Rating Certificates woudl be approrpiate, after initial measurement should be incorporated…

B.1 With the exceptions listed below in B.2, B.3 and B.4, the boat in racing trim shall be
capable of fitting into an open-topped rectangular measurement box
of internal dimensions
305mm long, 305mm deep, 153mm wide, with 6.3mm wide slots for projecting spars and rudder, as shown in the diagram.

Notice how it does not say that the Boat to be certified must pass a physical test but merely that it must be CAPABLE of FITTING

Perhaps another Rule Interpretation is brewing? Pandora is loose and dancing freely with the rules…

Far to Loose these Rules especially when the boys want to limit and control design concepts.

Don’t care if it doesn’t match the current Ideas… as it will out-perform any current stick on a tiller twigs we have now… especially now that it weighs less than ten grams including the tiller arm and post…

Saved that by taking away the servo shells.

Remember Though…

FOOTY CLASS RULES for radio sailing
These are open class rules in which anything not specifically restricted or prohibited is permitted.

Luv these composites. sooo strong…

Then why don’t you find another class to browbeat and bully?


Coz the Guru’s keep slamming every design innovation put forward for discussion. Go back months it’s the same offender…

My Niece Likes them but more the scale versions that look like real boats…

You asked… and please quote me fully. It’s rude not to… Complete the sentence and I’m OK with that…

I think that one of the useful things remaining from this thread is the pros and cons of articulated versus simple spade rudder.

Articulated (or flap) rudders are widely used on commercial ships that need manoeuverability at low speeds such as tugs, rig supply vessels, buoy lifters, etc. The articulated rudder enables tghem to apply a lot of power (such vessels are invariably highly powered for their size) to the rudder from a big propellor mounted immediately ahead of it. The flap means that you can turn the jet of water further sideways more efficiently without the rudder stalling. However, it needs a lot of power and the drag is very high.

A yacht rudder (real or model) is a completely different kettle of fish. Masses and energies are much lower. In particular the polar moment of inertia (the force you have to overcome if you try to twist a dumbell in your wrist) is tiny. This means that as soon as you apply the rudder, the stern starts to swing - quite fast. Because the stern is swinging, the flow angle over it changes. This means that you can add more helm angle (relative to the hull) which maintains the angle of attack or increases it. You can stall the rudder by using the steering as an on-off switch (why people by fancy transmitters) but there is no practical problem in turning as fast as you can react with a normal spade rudder - without the additional comlication, weight, cost or drag of an articulated one.