Chasing that extra mph

[WindyParticipant @windy30762]

As I am always trying to find that extra mph from my 14cc two stroke flash steam engine (122.91mph) there was a speedway engine piston that triggered the thought processes.

I was being shown a JRM (JAWA) 499cc 90mm bore 78.5mm stroke 4 stroke methonal burning speedway engine piston.

It was very short with a compression ring and a oil control about 1 mm from the top of the gudgeon pin hole (piston land known to break at that point).

The rpm of that engine and the flash steamer are about the same 11,000 to 12,000.

Was told some other racing engine pistons have a shorter length to bore ratio and if the cylinder to piston clearance is excessive the piston can turn sideways on the gudgeon pin and ruin the engine.

My flash steamer piston is cast iron with a single dykes ring and thinking can I shorten it to reduce weight and friction or should it be left as it is.

There are Forum members that have been involved in full size as well as model engine racing development and any comments about the pitfalls or benefits of shortening my piston would be welcome.

JRM 499cc Piston

Paul

[WindyParticipant @windy30762]

[JasonBModerator @jasonb]

Similar thread currently on HMEM

[Ian PParticipant @ianp]

Paul

I dont know what your existing piston is like but if it a conventional cylinder you could make it lighter and possibly reduce friction slightly by removing quite a chunk of the skirt.

You need to keep a reasonable amount intact to guide the piston in the 'slap' direction, but the side of the skirt below the gudgeon pin does not normally even come into contact with the cylinder walls so you could make the lower edge of the skirt a nice 'wave' shape.

Ian

[_Paul_Participant @_paul_]

I dont know anything about flash steamers but a cast iron piston at 11-12,000 rpm wont the loading be rather high particularly on things like the crank/pin gudgeon pin etc?

In my days of 2 stroke tuning even the better forged alloy pistons (Wiseco) used to pull themselves to bits at that rpm.

Regards

Paul

[Sub MandrelParticipant @submandrel]

Paul,

Windy is one of the strange breed of flash steamers. They shed no tears if the entire boat disintegrates into tiny fragments – as long as the record has been broken first!

Neil

[WindyParticipant @windy30762]

If you watch the top drag racers with the Blown Nitro Burning monsters after every run a complete engine strip down and replacement of worn parts by a team of engineers for the next run is done in an extremely short time.

Reliability is not required as long as it lasts the 1/4 mile or 1000yds course similar to my steamer runs over 500metres.

If the fuel and water pumps were set differently the hydro would reliably do 100mph time after time but we experiment to push the limits and if something fails you find out why.

In the few meetings I had last year a number of runs over 120mph were achieved reliably with no problems to the engine so a fellow flash steam competitor and myself are hopefully going to achieve 130mph?

If conditions are right this year my fellow flash steamer and I should be trying to achieve personal bests as we are equally as fast as each other at the present time.

Competition is good for development and ideas are freely exchanged.

Paul

 

Edited By Windy on 12/02/2013 21:52:10

[jason udallParticipant @jasonudall57142]

In no way wishing to be argumentative but …

Why such high rpm?

High rpm leads to ,in reciprocating engins, very high accelerations on pistons and hence forces for the pistons and linkages long with huge "centrifugal" forces on crank components.

Are turbines allowed?

If you need high shaft speeds ..Gears or toothed pulleys?..

Just wondering..
also what sort of hp is required?

Is water freely available or is fixed mass required?

Look at some of the pre electric torpedo propulsion designs..in particular the ww2 steam turbine designs..water spray through flame onto turbine…also exhaust into water…

[WindyParticipant @windy30762]

 

Hello Jason,

Regarding my flash steam engine the high rpm are required to develop the HP.

The engine is a very simple design with uniflow ports to let the exhaust out and a poppet valve operated by a cam to let steam in (car exhaust valve machined down to size).

There is a weight limit on this hydroplane 16lbs dry so it is very difficult to be a legal weight for competition.

Gearing is unnecessary due to weight and power loss the service piercing propeller has to rotate fast to be efficient, it is a prop rider only one blade in the water when at speed.

The water is carried on board, as any contamination will stop the pumps.

The HP is debatable and there are various formulae but I only no the Time it takes to do a certain Speed over 500metres, a rough guess comparing IC engines to mine might be around 6bhp at 10,500rpm?

The IC glow plug engines rpm is higher than mine.

Turbines are allowed but weight again raises its head and I am in the process of finishing one as an exercise.

On my photo album there is my steam generator testing nozzles for the turbine.

But you need a great amount of steam to be as fast as my piston engine.

Steam generated by chemicals would do as some of the small fuel pump turbines fitted to one of our past rockets developed vast amounts of HP.

Paul

 

Edited By Windy on 13/02/2013 12:55:15

Edited By Windy on 13/02/2013 13:00:44

[jason udallParticipant @jasonudall57142]

Thanks for that Windy..

So super cavitating prop….my guess slip at 10 % or lower..so about 14.4" pitch..(12.9" at 0 %)..

 

edit..

Just a thought. what rpm do you get with engin "un loaded"…for IC engins you usally chose prop with max pitch that limits ( on water)  rpm to 80 -95 % of off-load rpm..how far down is a matter of bottle ..and trade off against accelleration…

Used to check WOT rpm will prop replaced with "flywheel" for offload testing..flywheel provided some drag but much reduced load for testing but enough to limit " runaway"…

 

.

Edited By jason udall on 13/02/2013 23:29:43

Edited By jason udall on 13/02/2013 23:35:32

[WindyParticipant @windy30762]

 

Your guess not too far out used to use 14" pitch but for my fastest runs last year increased pitch but reduced blade area and better shape plus other mods to stop aerobatics.

RPM without load has been frightening in the past it will not run long without load as excess water and fuel cools the generator.

15,000rpm for a very short time but replaced burner fuel with propane for another static test and the rpm became like a musical scale 20,000rpm at a guess very nervous time.

Do not run at home now do not want to upset the neighbours.

There are so many variables that can effect speed on water so one thing at a time now it has got this far.

Paul

Edited By Windy on 14/02/2013 00:24:09

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