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Amazing flash steamer
Posted by: Mike Clark (
Date: November 11, 2005 06:12PM

Ok I know it's not a car but today I spoke to a chap who is involved with the revived sport of model flash steam boat racing. These things either run in a straight line so you have to catch them at the other end of the pond or they are tethered to a pole on a 15 meter length of wire and go round and round.

The speed record for a round and round one is 120mph! - this boat is about 4 feet long, weighs 15 kg and has a petrol fired burner with a monotube generator of about 12 ft of 1/4" titanium tube. It works at 1200C and 1500psi. Get this - the engine is a single cylinder piston inlet/uniflow exhaust which runs at 26,000 rpm - yes twenty six thousand.

The prop is 3 inch diameter and has been a major headache because only one blade is in the water at any instant and there are huge bending forces at the root of the blades. They are made from EN24 - anything else fatigues.

And I thought we were bonkers!


Edited 1 times. Last edit at 11/11/05 06:13PM by Mike Clark.

Re: Amazing flash steamer
Posted by: (
Date: November 16, 2005 04:56PM

Yes Mike that is amazing. I think it was Sir Nigel Gresley who said that 'any fool can get the steam in---it is getting it out that is the problem'. High revs. of those you quoted are made possible with the unrestricted initial exhaust that a uniflow can provide,an additional benificial byproduct of uniflow is to have high compression.
The other thing is piston speed. Just as a rough (very) comparison a piston travelling 6" (similar to some Stanley engines) at 2000rpm is no different to a small engine like the one you described having a 1/2" stroke turning at 24000rpm.
I am not suggesting that a Stanley turns at 2000 normally, but I am sure engines of that size could.
I understand that Formula 1 racing cars have an exceptionally short stroke to keep their piston speeds within acceptable limits even though the rpm are very high.


Re: Amazing flash steamer
Posted by: henry (217.136.171.---)
Date: January 12, 2006 07:37AM

I've just found the site and stumbled on your letters: couldn't resist asking for some more info on these small powerplants.
Can you recommend a site or address where I can find out about flash-boilers in general?

I agree with the reasoning of Jack, but even so, 26000rpm is a huge frequency: do these engine have any form of inlet valving and internal expansion or is the piston driven over the whole stroke by boiler pressure steam?


Re: Amazing flash steamer
Posted by: Mike Clark (
Date: January 13, 2006 05:27PM

Henry are you in the UK?

There are a couple of very out of date books about flash steam dating from the 1970ís but now reprinted and available from Tee Publishing

These are:- Flash Steam by Edgar T Westbury, and Experimental Flash steam by JH Benson and AA Rayman. These will give you the basics but things have moved on a lot since then.

The expert in this country is Phil Abbot who is the person I mentioned at the start of this thread. He gave a good talk at the International Model Boat Show in the midlands in October. I donít have a contact address for him but he is a member of the Blackheath Model Boat Club.

The main place where steam hydroplane racing, both tethered and free, goes on seems to be Kingsbury Water Park which is near Tamworth. []

The current engines have a poppet type inlet valve with uniflo exhaust and do expand steam - however economy is not their aim - just speed.


Re: Amazing flash steamer
Posted by: Rick Benson (
Date: January 30, 2006 04:05PM

Hi Everyone,

I have just stumbled across your excellent web site and forum and "wow" there is someone talking about model hydroplanes.

My father, John Benson was the co author of the book mentioned above
Experimental Flash steam, he is now 89 but still making these stange model craft. (Only "model" in terms of size they do not resemble anything full size.)

He and Alan Rayman wrote the book in 1973 and there are chapters refering to transport and steam cars.

By the way, as mentioned this book is now published by TEE Publishing who made a one off payment for the rights. So we can plug it with a completely clear conscience.

My father is always extolling the performace of the Doble and to discover there are examples of Dobles owned and run in the UK is great. Please excuse my ignorance to this fact. I will investigate the website further as we would love to get along to an event to see one.

With regard to the models I am not a real expert but I can add the follwing. I think 26 000 rpm is a bit optimistic on Phil's part but 15,000 is being obtained. Although we do not try to measure RPM whilst running know the propellor pitch and guessing slip 15000 is realistic. Certainly expansion is taking place. There was a suberb series of 5 Articles in Model Engineer starting 19th Oct 1990 by Mr Bob Kirtley who is the current record holder and a very fine engineer. I think it should be possible to get reprints of this, it practically tells how to make it.

In this article he gives 7deg of advance 54 deg steam admission , 81 deg of expansion , 102 deg exhaust and 123 deg of compression. It sounds very similar to an I.C. engine when running. The water and fuel are pumped geared down from the engine. Actually the design is not very different to previous but the succesful pumping of the fuel has been of great importance and Bob has led the way in obtaining these very high speeds.

Interesting comment on piston speeds, We make I.C engines for these model Hydros and my father and me have often discussed why we don't get the same piston speed as full size practice. Inertia? gas flow limits?

If anyone wants any more info please contact me, I have some pictures, perhaps I could send them for posting on the site or is there a procedure?

Best Regards

Rick Benson

Edited 1 times. Last edit at 01/31/06 07:56PM by Jeff Theobald.

Re: Amazing flash steamer
Posted by: William Gatlin (
Date: January 31, 2006 02:27PM

Hello Rick,

Your fathers book is a good one, glad to hear that he is still active.

Interesting that the numbers on the "model" engine are similar to the first stage of my compound design.

I imagine that the piston speed limits might be caused by boundary layer phenomina. This would make flow through little ports and valves much more restricted for the area than otherwise.

Also with such small pistons the circumference to area ratio is much greater. Here the boundary layers are more significant at higher speeds as they have to be scraped off when the piston moves. A domed piston might agravate the situation moving up the cylinder like a wedge, packing more gases around the periphery of the piston. Similar considerations for the bottom end of the piston. I would make the bottom of the skirt sharp like a wood chisel.

Just some thoughts on the subject, no substitute for real world experiments.

Wishing you the best ------------ Bill G.

Re: Amazing flash steamer
Posted by: Rick Benson (
Date: January 31, 2006 03:27PM

Hi Bill,

I am sure what you saying is on the way to the truth. The famous model Loco man who wrote in the Model Engineer under the title "LBSC" often wrote that nature cannot be scaled and that is really what we coming up against.

By the way I coppied the timing figures from Bob's article but I think there is typo, I think the expansion period should be 81 deg , in this way we maintain the convention of 360 deg for one revolution.

Best Regards


Re: Amazing flash steamer
Posted by: Mike Clark (
Date: January 31, 2006 04:41PM

Rick - Glad you found us and to hear that your Dad is still on the go - breathing steam must be good for us! Do send the pictures to Jeff - he has a classic flash steam hydroplane moored on his office desk so I am sure he'll find a spot for them.

Hi Bill good to see you read this forum too!


Re: Amazing flash steamer
Posted by: (
Date: January 31, 2006 05:28PM

Hello Rick,

I have had a copy of the book since it was first published and found it most informative. Yes it is mainly concerned with small high speed engines and 'model' boats but there is plenty of info. on feed pump and lubrication pump design that I have found very useful for application to any steam plant.Flash steam as applied to steam cars,locomotives and even a short section on steam powered aircraft are all included in this informative book.
Perhaps your father could be the co-author of a new version of the book?

ps. nice to know that LBSC can still be remembered!!

Re: Amazing flash steamer
Posted by: terry Weston (
Date: March 23, 2006 05:43PM

I want to build a steam car from scratch, but using an off-the-shelf engine, and a few years' ago found details on the internet of a 4 cylinder "1 stroke" steam engine being made in Tasmania and costing £16,000 (?) fob Tasmania. It was being used for boats and generators, and had a flash boiler, generating steam to 1200psi and had a 6 litre water tank. It could be adapted to use various fuels. Can anyone help in locating the maker, or a maker of a similar engine.


Terry Weston

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