My thundercat

[Steve509926]

I didn't realise Ciara was in there until I took a second look! Brave indeed.

[GuyC]

Originally Posted by Roflhat

Maybe the best photo yet, cover photo material. She was extremely brave, couldn't even look where we were going!

I've edited for you.

An excellent pic.

[Roflhat]

Originally Posted by Steve509926

I didn't realise Ciara was in there until I took a second look! Brave indeed.

Not sure if she'll ever set foot in a thundercat again right enough

Originally Posted by GuyC

I've edited for you.

An excellent pic.

Thanks. Trimmed to perfection there

[Roflhat]

Got out for a spin on saturday, didn't want to wait too long. Boat and engine both performing beautifully, the engine seems even better after a good flush out!

[vitalspark]

You had nice conditions in the harbour for it. Good to see you 'back on the horse' after Coniston.

[GuyC]

Originally Posted by Roflhat

Got out for a spin on saturday, didn't want to wait too long. Boat and engine both performing beautifully, the engine seems even better after a good flush out!

Well done - how is the back?

[Steve509926]

And how's your poor traumatised cousin? Are you now looking for a new copilot or have you persuaded her to give it another try?

[Roflhat]

Back is improving all the time now, avoiding heavy lifting but almost back to normal

Ciara announced the other day that she would be up for going back down! I'm well impressed, although I think our Granny would have a heart attack

To be honest if I go back to Coniston I'm thinking I'd go just myself, don't mind putting myself at risk

[Steve509926]

Well good on you for getting back on the water so quickly.

[Roflhat]

Latest idea, have actually been thinking about it for a few years but never looked into it.
Plan is to make an active front wing, positioned in front of the nose cone. Using Arduino board as a controller, gyro/accelerometer as input then servos to adjust the angle of the wing. So during normal running the wing will have 0 angle of attack, may actually improve the airflow over the nose cone. Then if the bow starts to rise too much it will point downwards, to bring the boat back level.
If it all works then I could possibly have the two sections seperate and use them individually to aid cornering



going to try foam wings first then if it works try some carbon fibre ones

[Matt]

Yeah, I researched this a fair bit for my hydrolift cr24 a few years ago.

In my case, I wanted to increase the lifting area by extending the tunnel and also try and pack more air (more pressure) into the tunnel since that would help retain balance.

In addition, I wanted a leading edge that would stall at a well predicted angle of attack. I felt that response time of any active foil would not be fast enough to control a blow over event.

(Have a look at the unlimited hydroplanes though, they do have an active wing)

So for a passive foil I was heading towards a heavily undercambered section with a sharp leading edge that would stall of its own accord if the AoA became to great. So I was heading towards something a little like the leading edge slats on an aircraft wing, but obviously configured very differently. I was hoping that I could then get addition lift from the wing, plus also pack more air into the tunnel by using the undercamber in the wing with laminar flow on the top surface to pack more air in.

One of your challenges is in your hull design to. There might be an argument to modify your hull running surface too so that you can move the cg forwards. This would mean you can run a more stable configuration at less risk of blow over. The hull as it is need you to run it right in its heel which is never going to be dynamically stable. (Although I can see you are able to run flatter than many do already)

I got as far as mocking up a couple of different designs and then Class 3 fell apart, so I couldn’t be bothered with it any more

[Roflhat]

That's a good idea having a wing that would stall, ideally a fixed wing would be a neater solution. Although I have to admit I'm quite excited about the active wing as a fun project.

Didn't know the unlimited hydroplanes had active wings, I'd done some google searching for powerboats with active aero.

Really I'd like to change a few things about the hull design, flatter deck relative to the running surfaces, stepped hulls at the rear to reduce wetted area.

Made up some flaps from an old bodyboard, they're thick but so is the leading edge of the nose cone anyway so shouldn't have much more drag. Just waiting on parts to arriving, need to learn how to program an Arduino board now!

[vitalspark]

need to learn how to program an Arduino board now!

If you pm me Seamus I'll put you onto someone local that should be able to help

[GuyC]

There is quite an interesting book by Abbott and von Doenhoff on the Theory of Wing Sections that gives you lift and drag figures for different sections.

I'd be nervous as to whether an active aerofoil could react quickly enough to compensate for what happened on Coniston but motorcycles now have electronics that react to changes of grip and meter the throttle sufficiently to avoid you being spat off so the technology is there.

Looking at some of the pictures of your boat, the main bit in the water is the outboard leg. Thinking aloud, do you put your trim control on the outboard leg or have something that would only come into play once the bow started to lift e.g. a foil that is just above the water in normal trim but touches the water surface as the trim increases.

[Roflhat]

Cheers, just ordered it. Had quite a few good notes from uni on various different shaped sections but can't find them now.

The sites selling the servo's claim they can rotate 60 degrees in 0.13 seconds, which would be perfect. Shouldn't have to rotate much more than that if at all, to get a change in wing angle of 50 odd degrees.

So far invested about £85 in all the parts. Hopefully using a carbon fibre plate to mount it all, which I'll glue to the underside of the nose cone then add rubber patches over the top.
At 75mph with the wing at 60 degrees the total force is equivelent to 5kg (each side). at 45 degrees which is likely the max I'll require the total force is 3.5kg

[Matt]

If you have power trim and can catch it quick enough, full throttle and trim in can sometimes save it. I thought about ballistic parachutes too - but you don’t want the bow to come down too fast either or you get a stuff.

My conclusion was that stability was just as important as lift. So steps and notches on the hull running surface to allow you to to move the CG forward, and aerodynamic devices to move lift backwards and stall at a positive AoA I thought was the way forward.

There’s also some good tunnel hull design software.

I assume you’re already running the bullet surfacing, with remote water pickup and suitable props - at the speed he’s running it must be a pretty well optimised setup already.

Can you show us some pics of your running surfaces?

Which uni and degree please? Just being nosey

[Roflhat]

No power trim, in fact no trim at all. I've spoken to Jim at tunnel boat design, clever guy certainly knows his stuff. But essentially the thundercat's speed comes from being so light and unstable, using aerodynamic lift rather than hydrodynamic.

Everything is a compromise, even adding wings etc. obviously takes away from the simplicity of the boat. Yeh already running LWP with the engine fairly high. I think I'm getting the most or close to it from the setup.

At full speed the only bits in the water are maybe 10cm of the back of the hijackers if that and the gearbox. Hijackers are not quite flat, slight outward slope maybe 10 deg.

[Matt]

Could be worth playing with the hull form then, <10 degrees, possibly even wedged further forward. And remote water pickup so you can jack the motor even higher (the bullet is inefficient). I assume it’s already a noseconed/long bullet? Is it high enough that your at least getting good lift off the bullet rather than pure drag?

Also, how straight does it track? Have you investigated a torque tab on the skeg?

[Roflhat]

Just hard to experiment with the hull with it being fully inflatable, Jacques at Ceasar says they have been playing with the hulls in the last year or so, moving the nose cone down and transom up so you have less lift from the hull. Sounds like just what I need, that or he's just trying to sell me yet another boat!

I've played with the motor height, going higher gives more rpm but no more speed. It's at the optimum where it is I would say. Yeh LWP nose cone on it

[Matt]

I’m not sure how current Jims work is? It was certainly excellent back
In the day, but I also feel hull design has evolved a fair bit. So while I think all the aero work still applies, I reckon the application of it has moved on and I’ve got no idea if he’s been keeping current.

What are you doing on the top surface of the boat to improve aerodynamics? Have you got a tonneau cover you use for top speed runs?