mike hockswell

Thought you guys looking for more speed might be interested in the hydrofoils I'm adding to my twin engined hydroplane airboat (a little unusual, I know). The front foils double as turn fins and are mounted to the rear of the front sponsons.

The rear foils will be mounted to the rear sponsons, but for first experiments I tried a single foil on the transom - this worked but was pretty unstable directionally as any roll gives an exaggerated turn.

The foils are hinged and sprung with rubber bands, so are easy to lift if you want to run on land.

Attached photos show the general arrangement and the boat running without foils.

(The engines are SC 15's and the all-up weight is approx 5 lbs).

I reckon it would be interesting to add foils to a 'seed tray' style swamp boat if anyone runs in clean water... (the foils like to pick up weeds/ crisp packets etc)

mike hockswell

PS, Greetings everybody- this is my first posting here.

b16a2sir

My Feedback: (3)

That looks awsome and like a good quality build. I have also thought about hydrofoils but not seen anything in the RC scene yet.

Very cool, Love to see the hydro-foils in action!

mike hockswell

Thanks, the new rear foils are in production today, so should get to run them next week! I'll try to get a video posted soon...

Depth Charge

Nice one Mike! I'm building an airboat hydroplane at the moment. The boat uses a single Irvine 40 running on a tunnel hydro set-up. She is 1 metre long and about 2 weeks from completion if my wife will give me permission to disappear to the workshop.
How have you calculated the foil sizes? I presume you have calculated them or selected from the standards. The profile at least could be selected from lists but the dimensions are critical. What did you use as your base speed for the calcs? I recon your boat must be shifting if you have a total of 30 engine size and you only weigh in at 5 lbs. Now that is a proper power to weight ratio; you must be British.

mike hockswell

Hi Depth Charge!

I calculated the foil dimensions from standard lift theory equations for a given speed, aspect ratio and foil depth assuming a basic flat surfaced foil with no camber. I weighed my boat at the foil locations to find out the required lift, then guessed at a foil-borne speed of 10m/sec (approx 20 knots). With a range of adjustment on the angle of attack between 3 - 10 degrees you can cover any errors in your assumptions quite easily... Once the boat lifts clear of the water the speed rises way above this 10m/sec point - the lift is self-regulating to some extent as the faster it goes, the closer it rides to the surface and the poorer the coefficient of lift becomes.

The foils are 2mm aluminium, lovingly filed to a smooth leading edge/ sharp trailing edge shape - they create very little (if any) noticeable wake, so I think the lift/drag is good.

This is very much work in progress, however, so watch this space!

Mike

Depth Charge

Being an airscrew driven boat, I assume makes your hydrofoil system work very effectively as the exponential drag of marine screws and assosiated running gear is immeadiately removed. Once "on-foil", top speed drag acting on your hull could indeed be greater from the air than the water if your foil blades are filed as you say. Do you yet have an estimated top speed?
Looking at the photos of you hull design, I pressume you do not suffer any flipping at high speed? (also known as blow-over). With your very fancy looking profiled rear sponsons I also pressume you don't suffer on fast turns?
Will it need water brakes now?

mike hockswell

[link=http://www.youtube.com/watch?v=nBYRC49OhWs]Scorpion MK3[/link]

Here is video of the boat prior to adding the hydrofoils...

Depth Charge

That is the most amazing thing I've ever seen. Are you a proffesional builder?

biteme

Nice!
If ever you're on this side of the Pond, lemmie know. We should get to gether and watch crowds to gawk.
My boat, just over 4lbs, powerd by a .36: http://www.youtube.com/watch?v=RZDZEs5nFWg

Trombe

My Feedback: (1)

Looks like an aircraft-builder's work. The two .15's make me think Mike is a combat pilot?
Maybe/Maybe not, I'm probably way off the mark..

b16a2sir

My Feedback: (3)

VERY IMPRESSIVE,. Thats awsome. Good work. Now wheres the plans for that one!! (hook me up!!)

Selph-Inflicted

Excellent build!

The only negative thing I can say is.....I wish the video had sound.

The boat looks very stable and controllable. I'm sure your having alot of fun with it! Once again, nice job!!

jasperrc

Very nice running boat!

Now I want to see how it runs with the foils in place