What's the go? Tailfins and wing for modern hydro?

[hughb]

I've got myself an MHZ Miss Excide 650mm hydroplane. It comes with 2 vertical tails that can be added to the stern, but no horizontal wing to go between the tails.

I like the scale look of having this rear wing, but notice many smaller model hydroplanes don't have this. What's the reasoning? The chance of breaking off in a flip? Redundant extra drag? Too much lift in the stern?

Is it possible to make an adjustable wing? Not on the fly, but rather before putting the boat in the water.

[Jesse J]

Given the size, I would speculate that there is no horizontal wing due to logistical issues. If it comes off in a wipe out, way before any performance concerns. I would be looking at that foam poster board to construct me a wing. I would use shoe goo to secure the wing to the fins.

Adjustable fin possible? Yes. It depends on your creativity and building skills as to whether it will be how you want.

[hughb]

Thanks Jesse. Next silly question, should it be a wing for lift, or an "inverse wing" for downforce?

[Fluid]

Not all full-scale hydros have horizontal wings...or fins either. The Unlimiteds are big heavy boats and the rear wing does help to control the boat’s attitude. Many limited hydros just have fins for directional stability, the smaller classes have none. The fins and wings are really just decoration on most FE hydros. Sport hydros run great without them.


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[Jesse J]

I like the looks of the wing too. I would go for as horizontal as possible; as Jay says, it will run fine without.
Setting the hull on a table, the strut will lift the rear to assume the riding attitude it will have on plane.
Then make it parallel to the table.

[hughb]

Thanks for the response guys. Jesse your talk of riding on the strut leads me to my next question. The hydro hull I have has ride pads at the stern. I have bought a Speedmaster 21 flat bottom strut, but this will lift the stern up leaving the rear ride pads about 1cm above the setup board. Is this acceptable? What would the purpose of the rear ride pads be?

[Jesse J]

Hugh, can you post a pic and tell us the depth of the ride pads and the sponsons at the trailing edge?
This will help us answer you better.

[hughb]

Yes that would make things much easier to understand. I can in a few days when back at home

[Fluid]

Most hydros with rear pads are from the pre-LiPo days when boats were heavier and slower - I put them on several of my old designs. The pads were used to keep the tunnel above the water in the turns since the prop/strut often didn?t have enough lift to keep the transom dry, the prop would otherwise run too deep which slowed the hydros even more. Many riggers use them for the same reason.

Most recent hydro designs don?t have them because of the much greater power we have today, but they usually do no harm as long as they don?t touch the water on the straights. I assume this is your hydro.





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[NativePaul]

Back in the NiCad days I built a 12 cell semi scale hydro with a lot of tunnel, and fitted a horizontal but cambered wing to reduce blowovers in windy conditions and cut a elevator into ito it of 1/3rd chord and a linkage from the rudder to it so it kept the arse end out of the water in the turns, it worked really well and allowed it to compete on even terms with riggers in most conditions.

These days I would make it trap less air as it is easy to get too much lift in the tunnel, I would make the wing horizontal, fixed and symmetrical in section so it only provides any lift if the nose rises. I haven't made one in the LiPo era though, as we don't have seperate classes and without lift being an advantage they lose to modern riggers down the straights as well as in the turns, and in all conditions.

[hughb]

Thanks Fluid that explains the rear pads. And yes that red boat you pictured looks to be the same as my hydro. I notice some mods have been made to the front ride pads, what would be the reason for that?

Paul thankful for your input regarding the rear wing, your methodology sounds good and that's what I'll do.

[Ch.Lucas]

Hi,
i have run hydroplanes with and without rear hoizontal wing. For real it does help only a little to rise the propeller . On the other hand it can give some down foorce and if i run a gliding pad at the propeller strut or a rektangular strut that has a flat surface to run on . This allowe a set up with with less load on the propeller and the down force of the wing help that the propeller is not jumping on the water. The propeller strut is like reading the waves of the watersurface , like a needle on an old turntable reading the music.
At last a big flat wing at the transom is allways a damping system a shock absorber. You can make a test with a bigger plate. If you trow it up and down the air will slow your action.
This happen also to the propeller , the wing will prevent the hull from dancing , jumping on the watersurface . A smoother run is a win. Der rear wing is not only a good show it is a need for cool smooth highspeed runs.

Happy Amps Christian

[Dr. Jet]

I have that hull's little sister; the Miss Madison. MHZ includes the vertical fins as a matter of courtesy for the builder that wants a scale-looking model (as opposed to adding speed or handling improvements). They omit the horizontal wing as they assume most reasonably skilled builders can make a short section of wing to fit, and in reality, no two horizontal wings will be exactly the same length, depending on the installation of the vertical fins. I am re-building my Miss Madison as a scale version of the 1999 Miss Madison (all white with yellow-ish graphics) and it will have removable fins and a wing. I'll run it with wing/fins just to look cool doing a few solo laps with it. Were I to seriously race it against other competitors, the wing/fins would remain safely in the carrying case.

I built a box around the tabs of the fin out of really thin (0.020" or so) carbon fiber sheet. After the box had cured, I sanded the overhanging edges to make the box square and flush on the outside, then cut square holes in the hull and epoxied the box into place. I made sure the box was long enough to contact the bottom of the hull for structural reasons.

EDIT: Added Photos and discussion.

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[Mike Cathey]

Well, the original use of the horizontal wing on unlimited boats was as an anti-blow over device. As the nose of the boat pitched up more of the bottom of the rear wing would be exposed to the air lifting the back of the boat and then dropping it back into the water (hopefully) horizontally. Remember with the hull riding on, and being supported by an air cushion the boat doesn't have the same dynamic weight as the static weight it would sitting on water or the trailer so that pressure under the wing has a lot of leverage.

Yes, you can use the wing and canards to tune to tune the boat ride. However, our model boats have something the big boats don't have-an adjustable strut with cable or wire drive. The best place to start with wings is to zero them out to the same angle of the bottom of the boat and adjust the strut to get the boat ride where you want it. Adjustable front canards can be very handy on windy days to keep the nose down. Some of the 1/8th scale guys in RCU when they first started running the FE boats had slaved the front canards to a servo and piezo gyro that moved them up and down to whatever their baseline setting was based on angle of attack. It looked kind of weird because the canards were flipping up and down so quickly. It must not have been worth the trouble because I haven't seen that set up for a number of years.

The problem with putting either positive or negative angle on the horizontal wings is that it's mostly going to take effect when the boat is completely out of the water. If you look at slow motion video, you will see the model boats traveling several feet completely out of the water in rough water. Too much positive angle and it will drive the stern down and the nose up-blow over. Too much negative angle and it pushes the nose of the boat towards the water and it's a recipe for stuffing the boat into the water most likely taking off the cowling, wings, turbine tube and uprights.

No matter what if you run winged boats you are going to lose/damage them if you race. When I do a winged boat I build extra uprights and wings and get them painted when I paint the rest of the hull. If you use 4-40 nylon screws to assemble them then if you are lucky you just shear those off and not damage the wings. To remove the sheared off screws if you are using 4-40 inserts, grind down a small blade type screwdriver and then heat with a torch and plunge it into the plastic, let it cool and back the sheared off screws out.