My thundercat - Page 21

Roflhat · 19 February 2020, 08:25

Quote:

Originally Posted by jeffstevens763@g

is it only picking up in the gudgeon pin area or in line with as in the photo

It looks like it, near the top of the piston

Roflhat · 29 March 2020, 11:08

Right here we go, the last rebuild

Doesn't look like I'll be able to test for a while because the airport is shut and I need Avgas 100LL.

Roflhat · 10 May 2020, 10:42

Rebuild didn't last long, got the engine break in done then about 10 minutes of use before it went bang. On my last set of pistons now

My trophy shelf, most of them I'd rather weren't there...

Got some footage during engine break in
https://www.facebook.com/seumas.macl...91852507522692

Engine is now rebuilt again with the timing backed right off, pretty hopeful that was the problem. Also running the tell tale over my tiller hand so I can be a temperature gauge

Roflhat · 23 May 2020, 09:17

Engine is running well with less timing, lots of testing done. Rebuilding again now though, due to one of the wee bolts from the choke flaps coming loose...

Tested the motorbike windscreen, worth about 0.57 knots. Modelling the boat on CAD too to try do some CFD aerodynamic tests. Not something I know much about

Allye · 23 May 2020, 10:16

Seriously unlucky with the motor. Did you spec the boat without carry handles?

GuyC · 23 May 2020, 11:07

Impressive stuff.

The CFD will be interesting.

Are you allowed to wear aerodynamic clothing? One of those aero helmets that cyclists wear might be of benefit.

Roflhat · 23 May 2020, 12:02

Quote:

Originally Posted by Allye

Seriously unlucky with the motor. Did you spec the boat without carry handles?

Yeh, more aerodynamic, few other bits removed too, copilot rope moved down so it was below the nose cone line etc.

Quote:

Originally Posted by GuyC

Impressive stuff.

The CFD will be interesting.

Are you allowed to wear aerodynamic clothing? One of those aero helmets that cyclists wear might be of benefit.

A lot of work but got plenty time at the moment anyway!

Helmets have to be road approved, motorbike standard but I was thinking about adding a tail section like the olympic riders have as you say. I removed the visor cap from my helmet already.

Was also thinking of making an extension of the nose cone to smooth air over the boat, but hopefully the CFD testing will show how much difference these changes would make

Roflhat · 26 May 2020, 13:40

Finally getting somwhere with the CFD. Took a long time to get a solid model in Rhino which I could use. Cd, drag coefficient is around 0.438, now to try and reduce it

GuyC · 26 May 2020, 17:48

That's very interesting.

Sadly I'm not clever enough to make sense of the various factors but I did note from Wikipedia it appears to be slightly less aerodynamic than a Ford Transit (0.37) which I'm struggling a bit with. Are you allowed to change the shape of the outboard cowl?

Having said that, if you streamlined the cowl, it might create more lift and I'm guessing once the lift coefficient becomes positive, you become unstable (or something).

Even if the actual figures are incorrect it should allow you to do some relative stuff.

Roflhat · 07 June 2020, 17:44

Not really "allowed" to do a lot of stuff, but I might do it anyway. Now thinking simply rounding the front of the cowl a bit would help more than the windscreen I was using. Shape of the screen would generate downforce, which I don't need.
Backed the timing right off to 13 degrees, which seems to agree more with the pistons. Been out in the boat a lot since the lockdown was eased, no issues so far.

Ordered a 53L fuel tank as the 21L doesn't last long! Still plenty of testing to do, just waiting for dead calm conditions, going to test the 90hp carbs again
Carbon cowling is coming along nicely, should be 3kg lighter than the original which was 5kg

Allye · 07 June 2020, 18:23

Madman solo helming that thing! Tank up the front or keep ot reward for speed?

Roflhat · 07 June 2020, 19:27

Quote:

Originally Posted by Allye

Madman solo helming that thing! Tank up the front or keep ot reward for speed?

Fuel tank was at the back, had an anchor bag up front but takes some getting used to the lack of ballast!

Jokomane · 08 September 2020, 23:49

What a phenomenal thread this is!
I’m new here and just read the whole thread from beginning to the end and learned a lot

))
I’m expecting a new Thunderbolt to be delivered in 2-3 months.
Plan is to put a tiller-steered Yamie F115B or VF115 on it with a hydraulic jackplate, 100l fuel tank, battery, etc.

Which fuel tank did you just get?

Roflhat · 09 September 2020, 10:57

Thanks, glad you enjoyed it!

Would love to try a tiller control 5.3, think it would be great fun. Definitely have performance potential in them, should be more stable than the 4.1m too. I bought a 53L tank, plastic but not sure what the make is, similar to a "new era" one. Please keep us updated on how your maxi goes

Roflhat · 18 December 2020, 10:32

Bits and pieces done to the boat, got more props to try just need some decent weather. Gearbox is getting a nose cone added on so will have to re test props anyway

Roflhat · 09 January 2021, 20:07

Engine sadly didn't last long with the modified gear box...
Thinking it lifted too high, lost water pressure and cooked the top piston. Fortunately didn't damage the block so will get it back together soon enough. Going to remove the nose cone from the gear box, have ordered a low water pickup version which should solve the issue. Whos stupid idea was that anyway

Managed to quickly test the Forge V2 before the engine blew, very happy with how it went. Still got 5 more props to try but will have to wait a while. Going to do a couple other jobs on the engine while it's apart. Cleaned up the cylinder head, printing some new velocity stacks for the 90hp carbs. Might get some nylon engine mounts made up for it, and maybe a lick of paint for the leg.

Roflhat · 15 January 2021, 09:25

Doing some more bits and pieces, the play in the engine was from the swivel tube bushes. Getting some brass ones made up which should last longer. New stacks are made up, also designed some reed block stuffers. Took a few days and 7 versions to get them how I wanted but they're a really good fit.

Also cut down the air intakes on the cowling.

Going for 185/195/195 main jets to start with, playing it safe! Also drilled out the needle valve seats, they were 1.6mm now 1.8mm. Ordered a bigger fuel pump, from the Yamaha v6 two stroke.

Flowed the exhaust and sandwich plate, removed some restrictions from there. This does mean the engine isnt UIM legal any more but I don't mind. If I go to Coniston again it will likely just be for a performance certificate rather than a record. Would prefer to go for the worlds fastest thundercat.

Roflhat · 10 March 2021, 13:57

Engine is now back together bar the gearbox with new LWP which should hopefully be done next week. This kit seems to fit the 70hp gearbox better too

Got new nylon engine mounts made up and brass swivel tube bushings. Everything went back together nice and snug, far nicer than the old plastic ones. I did machine grooves in the brass sleeves like the plastic ones for the grease

jwalker · 10 March 2021, 14:21

Spring is in the air!...

I thought you'd decided not to run a nose cone?

Roflhat · 10 March 2021, 19:01

Quote:

Originally Posted by jwalker

Spring is in the air!...

I thought you'd decided not to run a nose cone?

Originally I thought I wouldn’t need one but according to the melted piston I do... every day is a school day