Author Topic: 2.5cc tether car  (Read 1885 times)

Offline lohring

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Re: 2.5cc tether car
« Reply #15 on: March 28, 2020, 02:33:26 PM »
We ran water injection on a 35 cc CMB engine.  It's easy on a boat since there's water everywhere.  The RC cars run 2 and even 3 speed transmissions.  The gears have one way bearings and are selected by pawls that open by centrifugal force at preset rpm.  Something like that should work with tether cars, though there would be a little power loss in the gearing. See
and similar videos.

Lohring Miller

Offline lohring

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Re: 2.5cc tether car
« Reply #16 on: March 28, 2020, 02:46:59 PM »
On the other hand, this is the 21st century.  Why aren't tether cars electric powered?  In RC boats electric power has pushed the speeds to 185 mph.  The best nitro IC powered boat has only gone 135. 

Lohring Miller
PS Since the links don't work, replace "link" in the below with .com

 https://www.youtube "link"/watch?time_continue=8&v=Fr7D9_V4UZs&feature=emb_logo
 https://www.youtube "link"/watch?time_continue=2&v=YUUshUaITqc&feature=emb_logo
« Last Edit: March 28, 2020, 02:57:45 PM by lohring »

Online Vixen

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Re: 2.5cc tether car
« Reply #17 on: March 28, 2020, 03:28:32 PM »
It looks like there is a fine line between either being airborne or a submarine. Incredible machines

Mike
It is the journey that matters, not the destination

Offline Old School

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Re: 2.5cc tether car
« Reply #18 on: March 28, 2020, 03:33:05 PM »
Yes I do make my own pipes.

The American build and run some fast electric tether cars 200mph, but their is nothing like a piston engine going flat out.
For me I race in Europe and have to fly you cannot take the batteries on a plane. Fuel is supplied at the track for ic engines.

Online Vixen

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Re: 2.5cc tether car
« Reply #19 on: March 28, 2020, 03:38:06 PM »
Are power valves like the Yamaha YPVS or Kawasaki KIPS permitted to switch in a larger pipe resonator volume at the lower speeds?

Mike
« Last Edit: March 28, 2020, 04:06:07 PM by Vixen »
It is the journey that matters, not the destination

Offline Old School

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Re: 2.5cc tether car
« Reply #20 on: March 28, 2020, 05:54:45 PM »
Yes they are I have something similar on my 10cc car but I have not managed to make one that works for a 2.5cc car. Need track time to do it as it works on centrifugal force.

Online Vixen

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Re: 2.5cc tether car
« Reply #21 on: March 28, 2020, 06:32:26 PM »
Yes they are I have something similar on my 10cc car but I have not managed to make one that works for a 2.5cc car. Need track time to do it as it works on centrifugal force.

Using centrifugal force to operate a power valve sounds like a neat trick. However, getting something to work on a tiny 2.5cc engine is bound to be difficult even with unlimited track time. When do they weigh the car, before or after a run? Is it dry weight or wet weight?

Mike
It is the journey that matters, not the destination

Offline Old School

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Re: 2.5cc tether car
« Reply #22 on: March 28, 2020, 08:30:00 PM »
The car is weighed ready to run lubricated and fuled ready to run. No top ups allowed on the track.

Online Vixen

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Re: 2.5cc tether car
« Reply #23 on: March 28, 2020, 08:42:08 PM »
The car is weighed ready to run lubricated and fueled ready to run. No top ups allowed on the track.

That is a good, strict regulation. No room for maneuver.

Is the problem one of achieving the maximum possible power or to broaden the power band to get 'on the pipe' quicker?

What is the temperature rise in the pipe from first lap to end of run. Can anything be gained by thermally insulating the pipe to maximise the thermal difference and so widen the power band.

Mike
It is the journey that matters, not the destination

Offline Old School

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Re: 2.5cc tether car
« Reply #24 on: March 28, 2020, 09:01:44 PM »
The engine has a few seconds warm up the flat out run time is about 10 seconds or less for the 500 metres plus getting on the pipe and run down. By then it’s hot you wouldn’t t want to touch engine and pipe. No cooling in the cars.

Online Vixen

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Re: 2.5cc tether car
« Reply #25 on: March 29, 2020, 10:16:16 AM »
Thanks for this fascinating insight into the world of tether car racing.

So you build a car with the most powerful engine possible, that may last 10 runs before a complete rebuild. You have a run time of ten seconds or less to go from zero to a British Record Speed and back. But, you have to do as many runs as possible in the hope of getting in a 'lucky' run to push the maximum speed up a small amount. Even a 0.5% improvement in engine performance may make the difference.

You have my admiration for your dedication and perseverance in the sport you obviously love.

Stay in, Stay safe

Mike

PS can you make advantage of wheel diameter growth to change effective gear ratio, as the speed increases. Like a dragster's donut tyres.
« Last Edit: March 29, 2020, 10:20:48 AM by Vixen »
It is the journey that matters, not the destination

Offline Old School

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Re: 2.5cc tether car
« Reply #26 on: March 29, 2020, 12:05:26 PM »
I just like the engineering challenge of racing the cars and making as much as I can, it took me two years to perfect making pistons that perform.

Tyre size is critical to going fast, tyres grow the most on the first run after that growth is minimal.

Offline Hugh

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Re: 2.5cc tether car
« Reply #27 on: April 11, 2020, 10:04:43 PM »
This is one of my modern tether cars powered by a 2.5cc glow plug engine with a tuned pipe. Fuel is 80% methanol 20% castor oil. Engine revs to around 40,000.

Could you provide a few more details on the engine? Is it home-built or something bought? How does it differ to engines used in e.g. F2A?

I once had the opportunity to see a car in this class run a couple of years ago - super impressive stuff. Bizarrely, the guy running it lived about 5 doors down from where my wife grew up in Norway. Small world, I guess...


Offline Old School

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Re: 2.5cc tether car
« Reply #28 on: May 23, 2020, 02:02:50 PM »
Sorry I have only just seen your post. The engine is Stelling made in Lithuania by Edvard Stelling it is one on the most used tether car engines it is quite old but spares are available from the cottage industries that support tether car racing.
It is very similar to F2A engines two main differences the exhaust is over the crankshaft and they are a much heavier engine, power output is similar as are the rpm around 40,000.

Offline Muzzer

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Re: 2.5cc tether car
« Reply #29 on: May 23, 2020, 03:34:26 PM »
My first self-propelled vehicle was a tether car that I made when I was 10. It had a CI (not glow plug) 2 stoke and a propeller, mounted on a wooden pillar, sitting on a wooden trolley with 4 wheels. The only place I could find to run it was in the playground at school, where I tethered it to a nail in the tarmac. No propeller guard or anything sensible and you had to grab hold of it to stop it. It was exciting and fun. Following on from that I made an electric go kart thing from 2"x6" joist, pushchair wheels with a dynamo as a motor running from an old car battery. That was big enough to sit on.

Not sure you'd get away with that nowadays but this would be the late 60s when teachers probably had a different outlook than today.