Three Point Hydroplane Questions

Great info, gonna have to shove the engine in the hydro tub somehow. Might make a fiberglass cowl.

 

Once you made a working shape that works why not make the whole thing from Glass !! or better still carbon fibre !

 

Been reading a lot and have a better grasp. Thanks to Jim Russell for his articles. I have a few questions,,,

The angle of attack is measured from the water surface to the mean camber line. If the camber line curves up from the aft most edge of the sponson. I end up with way more than 3 degrees. What am I doing wrong?

The sponson deck surface is the top area of the sponson? The area as seen from an "aerial view"?

If the middle section carrying the engine is supposed to be parallel with the water surface, how to do you know how high to raise it off the water so only the aft most part of the sponson is touching the water?

 

not touching !! almost touching !! touching is drag the compression of air on the underside should be able to hold the boat up off the water . MAKE IT FLY !!!!
The very end of the back for can make an adjustable flap to raise and lower the hull at speed . With a 3 bladed prop one blade is leaving the water as one is entering ,only half of the prop needs to be in the water at any one time , its why you have a rudder with you water pick up going down the back and along the bottom of the blade .

all wings sections have a centre line fore and aft that the 3 degrees of angle of attach to work at . The same can be done with the sponsons and the rods or pipes holding the sponsons to the main body as well trail the thread in many places and shift the angle of the boat in relation to the air flow and watch and see what happens
The motor sticking out the top !!,stream line it make the pod over the top aerodynamic . make the air flow smooth round and over it .The round cylinder head is not a good shape its all about making the boat go throught the air with the least amount of effort to push it . lowering wind resistance !! make things a better shape . round is not good !! give it a better shape !! look at the nose of the wing some have a slight point . Look at the tips of wings and see what happens to the airflow . same thing will happen with the side of the main body of the Boat . how to fix it .
You can make a simple wind tunnel of your own just with some thick card board and a house hold fan and light black thread attached to the surface and watch the trails of the tread as the wind blows it ! see how it goes round and over things and what happens at the back where thers a square end !! turbulance and disturbed air flow that in some cases finds its way up onto the top surface and kills the lift you are working at trying to get !
Got a video camera run it while all this is happening .
I tried the net to find some model boat and aircraft sites that have been and done lots of this kind of work but China blocks lots of thing and i cant get in to them from here . .

Have you found any wing sections ???? and had a good look at them !!

 

Can you access this site? http://www.fastelectrics.net/hydroplanes.php

This shows angle of attack from water surface to bottom of sponson, not to the mean camber line. So is this correct?


I'm not understanding what you are saying about angle of attack. Also, how far should the middle section be off the water?

 

Rcgroups.com or whatever it is.

Google it, you'll do fine there.

 

To me the whole of that shape is wrong its hydrodynamic but not aerodynamic It has no choice but create lift to the surface of the water but whats after that ??? it wont fly !! flying is what its all about i feel !!
The fuslage of a aircraft has a angle of attach the wings have an angle of attach that is mostly differant to the fuslage and the motors also can be cambered inwards or in some cases outwards to help with nose up or nose down everything is set at a angle everso slightly to everything else
Its the same designing a boat design the boat and getting the plaining attatude that you want for the boat to look good when its going and of cause at rest as well .
if the body is parralell with the water surface at the center to rear there is no lift being created at all .
I can tell when i go to Tunnel boats racing which boats could be the fastest in the straight away becasue the tunnel roof will have shape built into it ever so slight in some cases . its sometimes a very shallow flattens S shape so i watch during the racing to see where and what part of the course it likes the best . some try just a gental curve from front to back and other just flat , Each one is differant each one does differant things . Just a quick look at the pictures in the fast electics and what i been trying to say is there in picture form and black and white near the end .

I have a son thats into model electics but he likes planes not boats !!!
Use to have a flying wing but going up high and swooping down at high speed the wings used to fold and break and bury its self in the ground . so i got him some light weigth carbon fibre and very ligth glass and we skinned the thing with glass and stiffened it with carbon under the glass skin and it absolutely howls coming out of a high dive and pulling out at the bottom for a speed check, its reall fast . cant remember the kms but its almost double what it used to do before the wings used to break before .

 

If you mount prop up close (bottom picture), not trim it up, when the hull is in the water won't the center part become not parallel to make lift?

 

The tub needsto be wing shape those pictures are just to show thats all !! The bottom picture is where its at but with a better designed tub and better designed sponsons . Only the tip os the sponson and half the prop in the water thats where you need to be headed . I will look and read that before i ened this day .

 

Air Trap

This drag boat is an example of a hydroplane with no air trap, depending only on hydrodynamic lift. No aerodynamic lift is more stable but requires more power to be successful because it has more hydrodynamic drag.

 

What feature made the boat posted above only rely on hydrodynamic weight?

Tunnels, are you saying the bottom of the sponsons should not only be an upwards U shape, but have an extra curve in it to "trap" some of the air flow underneath?

I think the sponson top surface should be as flat as possible?

 

An air trap is a wing-like extension between the hull and the sponson that traps air underneath it. These photos show examples of air trap hulls.

 

Good shape?

 

I see, so when designing using metal tubes to connect the sponsons, you cannot rely on much aerodynamic lift?

 

Correct.