Making a lifting wing

[Andrew Gilchrist]

I am searching for a wing design for a boat hull

it is for a centre hull on an outrigger

the baot will run at 140 mph top speed so minimal drag to that speed would be good.

The boat will weigh 7.5 lbs so I am looking at generating around 6lbs (I think)

the speed means it should not stall easily at high speed

The wing/hull will be 26" long and 6"wide it needs to be 3inches in thickness to enable the motor to be mounted in side it.

Can you suggest where i go from here or could any one assist me?

[Kwok_Yu]

Andrew,
Even though you provide alot of details, your basic idea is still very unclear. Most raceboats have planing hulls. Is that what you want? Or are you making a hydrofoil, where the boat is actually supported by a water wing? Or a surface effects ship where the boat is actually flying in ground effect. 140mph sounds a very high. It would probably be hard to get half that speed. The length seems too short. I would think 2X the length is more reasonable.

[Andrew Gilchrist]

Kwok Yu

thankyou for your reply

The model is an outrigger hydroplane. It runs on sponson tips and the prop blades, rather than the hull. The hull runs clear of the water.

The length is only for the hull which is functionally like the fuse in a plane - primarily an equipment box to which the wings (or sponsons in our case are attached.

there is a pic here showing the mono hull i think you were thinking of and an outrigger hydroplane - foreground two types of hull
http://electron.cs.uwindsor.ca/~bernyk1/rigger%20and%20monohull.jpg

you can see a video of one running here -
http://www.casrecprop.com/videos/2002lasawvideos/videos/shydro-crowe.AVI

As shown in the pic the fuse or hull is just a pencil box with rudimentary streamlining. Hull lift in these hulls was induced by angling the pencil box - other wise they were still pencil boxes.

In recent times hydro designers have been using wing section shaped hulls to generate lift with low levels of drag. The result has been the breaking of the outright marine speed records by electrics. The current record is 120.7 mph set with boat on its first run off the bench. Testing is rumoured to have indicated this year the record will rise to 130mph. 140 looks more like 140 future proofing.

Looking at pics taken during record runs and attempts with gas and electric hulls - the water surface (the attemtps are usual made on mirror smooth water) show little if any effect from hull turblence on the water the gap being about 1".

The key to these speeds have been brushless motors; high power controllers (the prototype for schulzes 157 amp 32 cell controller was made by the JAGS team to enable them to fully exploit GP3300's') and the wing profiles.

Photos suggest in practice successful riggers run with the sponsons not touching the water and only 1/2 the prop (surface piercing) and a short section of rudder immersed

I have looked a modelling programs but cannot for the life of me figure out how to calculate the lift. With the current equipment 600gm motor and 32 cells 6lbs is required.

Looking at the latest boats the chord is 24" on some hulls with 30" the max. ( the fastest boats use the tub and extend the afterplane (wheelbase) between the trailing edge of sponsons and prop by using external frames to move the sponsons forward of the hull.

The thickness seems to be around 9% - enough to allow the motor (lehner 2250) to be angle in the hull. The underneath of the tub shows camber (I had thought they were flat).

[Kwok_Yu]

This calculation should help you get started. So basically you need to pick an airfoil. This is the equation for lift:

L=q*S*CL

L=Lift=weight= 6lb
q=dynamic pressure= (1/2) * density of air * velocity^2
S=planform area of wing= 26" * 6"
CL= coefficient of lift, its found experimentally and normally presented in a graph (CL vs angle of attack) for each airfoil, Normally it between 0 and 2

Well, its been a while since I have done this, but I get a value of 0.00000000002 for CL, which is extremely small. So if this is right, it doesn't matter what airfoil you pick. You are going so fast that you easily get th 6 lb lift. Most airfoil have a CL of 1 at zero angle of attack. Someone can verify the calculation?

[edit]
I think as a first step you could plot how CL varies from velocity = 0 to 140mph. That should point out any critical points. If CL is >>2 at any point then that may be a problem.

[Andrew Gilchrist]

Kwok Yu

Thankyou very much - I appreciate your guidance

I returned to all the pics i have of the latest wing section style rigger hulls and notice most of them run a very neutral angle of attack which accords with what you say

regards
Andrew .

[Kwok_Yu]

Glad to help,

A few other thoughts I have. So lift is not important at high speed, but it will be important for the low speed acceleration. I think you should choose an airfoil for low drag. The drag can be calculated using the same equation and the Coefficent of Drag. You can calculate the moment the same way, for stability considerations.

[edit]
Actually I want to design something similar, a suface effect boat/plane. Except I want it to stay at a constant height and never touch the water again after airborne, even at extreme banking. So it should be able to run across blacktop, too.

[Andrew Gilchrist]

Kwok Yu

are you looking at an ekroplane?

I have an article here on a series of models

[Kwok_Yu]

Yes, I am taking about a ekroplane. It's alot like you hydro outrigger when going forward. What article do you have? Is it digitized?

[Andrew Gilchrist]

The article is from Marine Modelling international - a british modelling mag. I have a feeling the boats were also on the web.