Author Topic: 2.5cc tether car  (Read 6870 times)

Offline Old School

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2.5cc tether car
« on: March 26, 2020, 09:24:12 PM »
You liked the Mercedes this is something modern also from my workshop.
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. Hold the British record at 262kph.

Offline awake

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Re: 2.5cc tether car
« Reply #1 on: March 27, 2020, 12:06:52 AM »
40,000 rpm ... 262 kph ... I'm having trouble wrapping my head around either of those numbers. Wow!
Andy

Offline Old School

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Re: 2.5cc tether car
« Reply #2 on: March 27, 2020, 06:56:04 AM »
The engines have a short life about 10 fast runs, then they need a new piston making and fitting.

Offline nj111

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Re: 2.5cc tether car
« Reply #3 on: March 27, 2020, 11:01:58 AM »
Wow that's insane! My father told me a bit about tether car racing as he had some involvement I think in the 1950's.  Is there much club activity these days? (or I should say was there - prior to the current lockdown situation)
Nick

Offline Old School

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Re: 2.5cc tether car
« Reply #4 on: March 27, 2020, 11:19:22 AM »
I do most of my racing in Europe with the modern cars, there is a track in Lincolnshire but only suitable for old timer cars.
We have almost finished a track at the BMFA ( model aircraft) Buckminster site but the virus has beat us to having trial runs to prove it’s ok for the modern cars. Picture of track attached.

Offline Vixen

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Re: 2.5cc tether car
« Reply #5 on: March 27, 2020, 11:53:26 AM »
When I was a lad, there was a tether car track a few miles away. They had cleared out a disused sewage settlement tank, still with a circular wall all round. Very bumpy surface so speeds were low, no record breakers there.

Mike
It is the journey that matters, not the destination

Sometimes, it can be a long and winding road

Offline cnr6400

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Re: 2.5cc tether car
« Reply #6 on: March 27, 2020, 12:57:15 PM »
GB010 looks like a screamer! Thanks for sharing the pics!  :ThumbsUp: :ThumbsUp: :ThumbsUp:
"I've cut that stock three times, and it's still too short!"

Offline JC54

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Re: 2.5cc tether car
« Reply #7 on: March 27, 2020, 01:42:26 PM »
Good afternoon Old School, I live only about 4 miles from buckminster track so will have a look when racing/flying resumes.   John  :old: :DrinkPint:
When the Fun Stops,, Stop!

Offline Rick Doane

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Re: 2.5cc tether car
« Reply #8 on: March 27, 2020, 02:50:22 PM »
That is a very nice car Old School and I like the tuned pipe also.  Did you make that one?  Mr. Jack ODonnell in the USA and Mr. G. Picco in Milano built some fast cars and were always great advocates for model engine building.  The speeds you guys obtain are fascinating especially keeping fuel flowing to the engine.  I would expect that there is little taper in the pistons considering only 10 runs per piston/liner.

Regards.....Rick

Offline Admiral_dk

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Re: 2.5cc tether car
« Reply #9 on: March 27, 2020, 03:13:27 PM »
While your handle "Old School" matches the "Mercedes" just fine - it isn't really a for for this one, where the only hint is British Racing Green  :praise2:

Record holder  :praise2: well you are not alone here (not me) - there are a few very fast boat guys here too.

I read that the current state of affairs with model car speed records - there is a problem to get the engine "on the pipe" ..... I do not see any attempts at changing exhaust timing / length, nor throttle to help with flow through the carb ....  :thinking:

Per

Offline Old School

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Re: 2.5cc tether car
« Reply #10 on: March 27, 2020, 05:51:22 PM »
Yes getting them onto the pipe requires a young fit horser that knows what he is doing the problem is no one is getting any younger.
My care runs very moderate exhaust timing of 195 degrees and a pipe length to match it.
To go really fast some of the racers are using in excess of 200 degrees of exhaust and short pipes.
Something has to change in the way the engines are set up so that they can be got onto the pipe a lot easier than what is happening at the moment. The challenge is what to change and keep the speed. You can only do so much on a test rig, the cars need to be run on the track.

Offline Admiral_dk

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Re: 2.5cc tether car
« Reply #11 on: March 27, 2020, 08:23:23 PM »
The Boaters inject water into the exhaust as this moves the peak power of the pipe down to lower RPM's and this works perfectly - then again they have a very "convenient water tank" at hand (or more correct at the rudder) .....

Being an Electronic Technician, I had thought about a very small control unit for a variable exhaust timing several times - but it hit me just now, that you only need this for a few times round the track at the beginning of the run ...!!... So why not have a small water tank onboard, that starts spraying water into the exhaust just after the engine fires ????
This could probably be done with pressure from the exhaust itself (or the crankcase) as it is two different places in the system with different pressure + a one-way valve would help. The extra weight should not have much influence as the tank will be empty before the car reaches the really high speeds and the engine will produce much more torque @ lower RPM's just after starting ....  :thinking:

Per

Offline Old School

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Re: 2.5cc tether car
« Reply #12 on: March 27, 2020, 09:09:53 PM »
I would struggle to find space for a water tank, plus most of us are close to maximum weight.
We control the initial acceleration by the vent pipe in the fuel tank at the start of the run the vent is submerged giving a lean setting as the fuel is burnt off the vent comes out of the fuel giving a richer setting also helped by centrifugal force.
The car still needs the help of a horser to get it on the pipe.

Offline Vixen

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Re: 2.5cc tether car
« Reply #13 on: March 27, 2020, 10:39:50 PM »
Didn't strictlybusiness1 discuss water injection into the tuned pipe a few weeks back? If I remember correctly, the organisers outlawed it by classing the injection water as illegal fuel.

Water injection must have worked if it was outlawed. It may be worth a search through the strictlybusiness1 posts.

Mike
It is the journey that matters, not the destination

Sometimes, it can be a long and winding road

Offline Admiral_dk

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Re: 2.5cc tether car
« Reply #14 on: March 28, 2020, 11:13:32 AM »
I'm pretty sure that it is Lohring Miller who has most experince with water Injection in the exhaust, as he even wrote a Tech Paper on the subject (that has been shared here a few times) - but I'm sure you're right that Jim was punished for using it as you mention Mike.

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 <a href="https://www.youtube.com/watch?v=oLLSnx86dig" target="_blank">http://www.youtube.com/watch?v=oLLSnx86dig</a> 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 »

Offline 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
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Sometimes, it can be a long and winding road

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.

Offline 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

Sometimes, it can be a long and winding road

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.

Offline 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

Sometimes, it can be a long and winding road

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.

Offline 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

Sometimes, it can be a long and winding road

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.

Offline 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

Sometimes, it can be a long and winding road

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.

 

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