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[KBIO]

Hello !

Winter being what it is, he keeps the Vaporist in the workshop, but this one  has to keep busy.
That's why , with two members of my forum we have set up this test bench to estimate the power of our little machines.
It's not quite perfected yet, but we're working on it.
My friend Rookie has even drawn up a spreadsheet, but as the software costs €150, we'll stick to simulated and approximate calculations when it's operational.
Any suggestions are welcome.


Just for info :
- the vertical boiler need 6/7 min to reach 3 b when 2/3 full.
- the compound is an old one save from the landfill !
- and we'll see that there is difference between two identical engine ;
The few tests I did are not very accurate and I am not sure that this method is the good one for such small engines.
.... but it keep me busy with my dog beside me! And you what ! That dog knows more than I concernig steam !

https://youtu.be/i-05W4zhwws?si=MM84JNma4LbdTL84

https://youtube.com/shorts/ZwnLjoFtlTE?si=AmpbnefwUpmR8Slp

[1967Brutus]

That set-up sets high demands on how true the flywheel turns. You get a usable reading from that?

If so: Kudos!

[DBS88]

Well done, your latest development of the brake for testing engine power is looking like the changes are working well. It would be nice to compare the power outputs you achieve with manufacturers data as a verification of the results you are achieving. I am not sure about other manufacturers, but know that Saito published power outputs for their engines, so maybe running a Saito on your test rig will help confirm the accuracy of the results you are getting. The Saito T2DR has a published power output of 22 watts or 0.03hp, the T3DR is given as 28 watts and 0.038 hp. Good luck with the experiments, it will be nice to see how much power the different engines deliver

[KBIO]

Hello !
Good informations that I keep under my elbow. I still have the T2DR , so I should be able to compare. I have the big one too (23cc) .


You get a usable reading from that?
To be honest , I need to improve the brake itself. The reading by pressing the wooden pads against the flywhell are still a bit eratic from one reding to the other. Even if I oil it.Maybe an hydraulic brake to be considered. Still working on it...]
Cheers !

[DBS88]

Its good to hear you have both those Saito engines, it will be great to see your results compared to the published results, for info the Big One T2GR has a claimed power output of 75 watts or 0.1 HP with a max torque of 3000g/cm or 2.6lbs/inch with a max rpm of 3600
Here is a photo of the T2DR next to Big One for comparison 

[rhavrane]

Bonjour,
Does someone know the power of a Stuart D10 ?

[DBS88]

The power of the Stuart D10 is likely to be similar, probably a bit less,  than the T2Gr, The T2GR has a bore and stroke of 20mm, the D10 a bore and stroke of 19mm. Here is a photo of the T2GR alongside a Stuart 10v (Obviously the D10 has two cylinders) for size comparison.

[rhavrane]

Bonjour Dave,
Thank you for this quick reply ! I am a little bit disappointed because I thought it was about 1/4 CV - 180 W 

[1967Brutus]

Hello !
Good informations that I keep under my elbow. I still have the T2DR , so I should be able to compare. I have the big one too (23cc) .


You get a usable reading from that?
To be honest , I need to improve the brake itself. The reading by pressing the wooden pads against the flywhell are still a bit eratic from one reding to the other. Even if I oil it.Maybe an hydraulic brake to be considered. Still working on it...]
Cheers !

If I may suggest:

Make a separate saddle with a disc with the beam attached to it. Stick a bunch of magnets to the disc (the stronger the better).
Of course the disc and beam need to be supported in bearings so they can otherwise move freely, only held by the scale.
Place the saddle in front of the flywheel. The not moving magnets will generate eddy-currents in the flywheel (this will happen regardless of the material of the flywheel, as long as it is a conductive metal). These eddycurrents by virtue of Lenz's Law, will brake the flywheel, and the exact same braking force will be excerted on the disc, pushing the beam down on the scale.


By varying the distance between magnets and flywheel, the braking effect can be varied/adjusted.

Since disc and beam are not making any physical contact to the engine, the braking force should be 100% smooth and even, and it should be usable regardless of engine, no need to modify flywheel or build a specialized teststand.

For a visual demonstration of the principle, take a cylindrical magnet (say, 3 mm diameter), and drop it first through a plastic tube of 4 mm inner diameter, then through a non-ferro metal tube (does not matter if it is copper, brass or aluminium) and watch the speed with which it falls through...

[1967Brutus]

Bonjour,
Does someone know the power of a Stuart D10 ?

Bonjour Dave,
Thank you for this quick reply ! I am a little bit disappointed because I thought it was about 1/4 CV - 180 W 

A rough estimate of the power (more precise, a calculation of the theoretically max possible power) can be found as follows:

Determine boiler pressure, and convert from Bar to Pascal (1 bar is 100.000 Pa)
Determine total cylinder displacement and convert that to cubic metres (1 cc = 0,000001 m3)
Determine RPM in revolutions per second.

Power is pressur in Pa x volume in m3 x rotations per second. Outcome is in Watt.

Example:
Stuart D1, bore x stroke 19 mm, 2 cylinders. Displacement (assuming pistonrod is 4 mm) is approx 21 cc or 0,000021 m3
Pressure, assume 4 bar=400000 Pa
Max specced RPM is 2000, which is 33,3 revs per second.



0,000021 x 400000 x 33,3 = appr 280W or 0,38 hp.

Mind you, this is extremely theoretical, because 2000 RPM typically is a free running engine, and due to the pressure loss over the valve chests and steam ports, cylinder pressure is very unlikely to be identical to boilerpressure. The above formula also does not take into account the labour used for discharging the spent steam from the cylinders.

But at 4 bar, and loaded with a prop to turn,say 1000 RPM, 0,10~15 hp could be realistic.

[DBS88]

Have just researched the D10 a bit more and the specification for it is Bore 3/4 inch, Stroke 3/4 inch  max rpm 2000, and a power output of 1/10th BHP Obviously this will vary considerably in the downwards direction rather than upwards, depending on how well the engine has been machined and fitted together.


I have not yet found any power figures for the Stuart Twin Compound engine that KBIO is using, although it's likely to be less than the Stuart Twin Launch engine. Maybe it can be worked out from the HP Cylinder dimensions which are 3/4 bore and 7/8 inch stroke - for completeness the Low Pressure cylinder is  1 1/4 inch bore and 7/8 stroke.


The Stuart Sirius engine, 1 inch bore and 1 inch stroke, single acting twin, is claimed by Stuarts (In an old catalogue) to deliver 0.4 BHP at 2800 rpm with a steam pressure of 80psi or 5.6 kg cm moderately superheated.

[1967Brutus]

Have just researched the D10 a bit more and the specification for it is Bore 3/4 inch, Stroke 3/4 inch  max rpm 2000, and a power output of 1/10th BHP Obviously this will vary considerably in the downwards direction rather than upwards, depending on how well the engine has been machined and fitted together.


I have not yet found any power figures for the Stuart Twin Compound engine that KBIO is using, although it's likely to be less than the Stuart Twin Launch engine. Maybe it can be worked out from the HP Cylinder dimensions which are 3/4 bore and 7/8 inch stroke - for completeness the Low Pressure cylinder is  1 1/4 inch bore and 7/8 stroke.

Compounds are very difficult to work out, since the pressure in the 2nd stage is very hard to determine, too many factors. But it is most definitely lower than a normal twin. If I had to estimate, about the steam consumption of a single, with about 3/4 the power of a twin.

I wasn't too far off with my estimate on the D10, apparently

[KBIO]

Hello !
At our scale , I agree that a compound develops less power than a a bi-cylinder , as the steam enters in the L.P with some back pressure remaining in the opposite side of the piston. Very hard setting of the sliding sleeve , but even so...
We did some test on  triple expansion (Stuart , Reeves ) and it appears that the third cylinder is "useless" when it is not acting as a break .
The advantage of a multi expansion is a lower steam consumption but no gain of power.
At the end , it's all fun as I doubt that I can get reliable numbers with my set up.
Though life for us !

[roycv]

Hi all, I remember doing some experiments with power o/p from a steam engine before we all had computers at home.  That would be back in 1986 or so.  I made a Meccano frame with a 1 inch diameter drum created on a lathe as the brake drum.  I had a very accurate gram gauge, which tripped at adjustable pre-set points.  The steam engine was connected and run up to speed, it was all very messy and difficult to get reliable readings.

I remember there was a lot of arithmetic to do after each measurement!  We were checking a 3/8ths bore and stroke D/A engine running on 20 lbs pressure and I believe it all worked out to about 30 watts.  By back tracking the performance of the boat the installation was in, we had found that the boat planed for a short time at 20 lbs pressure and then the the boiler could not maintain the steam o/p and she slowed down.

Using a home made rev counter, the 2 inch dia prop of unknown pitch was checked out in a small pool at 2000 rpm. This was the fastest that the steam plant could go.   Later the steam plant was removed and an electric motor installed and set up to produce 2000 rpm under load.  When tested in a small lake the boat planed nicely.
For the testing mentioned we had a gas blow lamp.  Lots of fun was had and I found out how fast I could run when I started to sense danger, much to my friends amusment!  We were playing with French blowlamps at the time and they can have a very spectacular start before settling down!
Regards
Roy 

   

[1967Brutus]

Hello !
At our scale , I agree that a compound develops less power than a a bi-cylinder , as the steam enters in the L.P with some back pressure remaining in the opposite side of the piston. Very hard setting of the sliding sleeve , but even so...
We did some test on  triple expansion (Stuart , Reeves ) and it appears that the third cylinder is "useless" when it is not acting as a break .
The advantage of a multi expansion is a lower steam consumption but no gain of power.
At the end , it's all fun as I doubt that I can get reliable numbers with my set up.
Though life for us !

In small scale steam, and at the low pressures we work with, principles like "expansion" have no practical application. They are done for the technical appeal.
In order to benefit from the efficiency gains of "expansion", you need at least 10, perhaps even 15 bar steam pressure, and expansion all the way down to 0,1 bar absolute (-0,9 bar vacuum) or so, or it is utter pointless.
The economics of scale cause that achieving this kind of condenser vacuum in model scale more energy consuming than any efficiency gain.

Having said that, power measurements are always fun to do and interesting in the sense that you can check the effect (intended or unintended) after modifications or repairs.

[GG]

Having decided to build another steam powered model, I find these posts very interesting.  The subject of the output power of these engines puzzled me and, in the absence of suitable testing equipment I just has to make an educated guess based on what electric motor power I'd need for the same performance in an equivalent model.  This has proven "good enough" when using my three modest oscillating engines (2 single 1 twin cylinders).  Hence my interest!


This did allow me to approach this subject from the point of view of their efficiency, that is the amount of the fuels energy they were turning into usable mechanical power.  This was simply comparing the rate at which the fuels energy was being used by the engine to my output power estimate.  Yes, very much an "Engineers Back of the Envelope" calculation but usually good enough to get a sensible answer.


At first I was shocked at the results, did the obvious rechecking in case a decimal point had gone adrift, but still came up with a value of around 1% efficiency!!!  This seemed awfully low but then I recalled that even full size steam engines could struggle to better a thermal efficiency of 10%.


It would be interesting if other modellers have every tried similar calculations and there findings?
Glynn Guest

[1967Brutus]

At first I was shocked at the results, did the obvious rechecking in case a decimal point had gone adrift, but still came up with a value of around 1% efficiency!!!  This seemed awfully low but then I recalled that even full size steam engines could struggle to better a thermal efficiency of 10%.


It would be interesting if other modellers have every tried similar calculations and there findings?
Glynn Guest

Yes, I did, and I usually do (I am autistic, AND a marine chief engineer, power and efficiency calculations used to be part of my routine jobs on board). so yeah, and still do, just out of interest.
Overall efficiency (fuel tank to end of propshaft) of a model steam plant indeed is in the rough vincinity of between 1 and 2% sadly enough, but there's not much that can be done about it.
My IC powered boat https://www.modelboatmayhem.co.uk/forum/index.php/topic,69665.0.html gets in the vincinity of 3~4%.
My petrol powered RC airplane engines are usually in the neighbourhood of 10~15% (with the exception of the Wankel that struggles to exceed 6%).

It's not that I care about it, I simply just want to know, because that is what I do, "wanting to know"...

[rhavrane]

Bonjour Glyn,
I like reading all the experiences made on my passion, Yves/Kbio, among other members, has a great knowledge and never hesitates to share it with us in French videos
Personally, for my use, I have another approach of the power which is "Is this machine powerful enough for this hull and with witch propeller" ?
Most of my model boat are too fast and our tugs never enough.
As I like using 2 bar / 30 PSI working pressure, the autonomy of my boats depends on the boiler, its possible coupled pump and the RPM of the machine.
Steam machines, even our small ones, have torque and finding the appropriate four blade steam propeller is my question to make them operate at low RPM.
I admit that with more than 50 boats, I have now an idea, for example 5 cm3/2,5"-62mm but I have never found any theoretical demonstration of my approach.   

[KBIO]

Hello Hello !
Yes ! When I learnt what was the efficiency on the first steam machines = 5 % , I cried !
When we realize that the best efficiency on a CESNA plane is about 20% . Gas jet  turbine can achieve 70/75 % = the top with a tremendous consomption of energy. And what about a car , a lorry , ...?
Things are improving , our engineer are working hard , but I guess that there is an unachievable limit untill now
!
[/size][size=0px]for example 5 cm3/2,5"-62mm but I have never found any theoretical demonstration of my approach.   [/size][/size][size=0px] [/size][/size]Yes Rhavrane , we are mostly working in the same size & range with our boats. So the expérience avoid us to make(too much)  mistakes.
[/size]Still , it is interesting to understand , or at least try to understand how behave our littles machines.
[/size]Not obvious though and I get stucked real easy in this thermodynamic science.


DS88 can eventually lead you toward a spread sheet in english to allow you to calculate the needs in a model boat , from the burner to the propeller passing by the hull and its shape.


For my test , I decided that I  shall do them with compressed air @ 2 & 3 bar. A lot more handy that with steam , above all with this winter temp. It's about 5 °C in my work shop.
that is just to have an idea of comparaison between engines.
Let's wait a bit .
Cheers !

[roycv]

Hi all, When I first got interested in steam power in a model boat my last thought was about efficiency!   Having played with  Mamod toy steam etc I wondered if there was enough power to drive anything at all.  That was in my Meccano days and later I played with a small oscillator and meths burner in a small boat and found that going into wind was problematical.

I joined a club who also ran round the pole hydroplanes and was impressed by the steam powered boats that could notch up 70 mph.  This was the first time I had seen flash steam driven boats, Impressive yes, but not for me.  As mentioned before steam has its attractions and the commercial, Cheddar and the like are amazingly effective, we have a club tug 'Resolve' with a twin installation, loads of power, and behaves like an electric driven model.

Quite a while ago now I developed the electronics for the boiler water level automatic control.  Offered at first to Cheddar Models but rejected as 'no one wants to have automatic control'!  His words not mine.  Low and behold within 12 months he had the Cheddar ABC system.

In the non-boat field a club member has a Mamod / Wilesco set of accessories driven by 2 stationary engines which can drive the chain and band driven toys on no more than 5 pounds indicated steam pressure.  A blowlamp powered large boiler with an automatic mechanical water feed to the boiler.  Works most of the time!


With all the above I never once worried about efficiency, just 'Will it work'? 
In any case the heading for the thread is Power, much more useful to know.

Roy

[1967Brutus]

I don't think anyone "worried" about it... It's just a very simple calculation, once you know fuel going in and power coming out.
It's one of those "nice to know" things, but no one in his right mind is now trying to improve on it, or leave his boat on the shelf for budgetary reasons, I guess...

OK... OK... I'll fess'up... I make use of a feedwater preheater... The gains are humongous... I went from 1% to 1,05% efficiency... :p

[roycv]

Hi Brutus During some experiments we went through heating the gas supply, this was a camping stove size one.  All experiments were in a home made copy of the Bassett-lowke Streamlinia a 40 inch loa model boat. 

The first attempt was a large plate curved to fit the can and the gas pressure in the can really built up and the neoprene feed to the burner blew up like a balloon.  There was a fire as well which was easily put out.  Previously the gas can had iced up due to the extraction rate.
Eventually a compromise was worked out. 

The next idea was to use a steam pressure feed to adjust the gas rate down so as the boiler reached optimum pressure the gas flame was reduced to keep it on the boil but not blowing the exhaust valve.  When the steam pressure reduced the flame was turned back up again.

The model was on show at the Model engineering exhibition in 1989.
Regards
Roy
 

[1967Brutus]

Hi Brutus During some experiments we went through heating the gas supply,

The next idea was to use a steam pressure feed to adjust the gas rate down so as the boiler reached optimum pressure the gas flame was reduced to keep it on the boil but not blowing the exhaust valve.  When the steam pressure reduced the flame was turned back up again.

I used electric heat elements to heat the gastank of my boat until recently, controlled by thermostat keeping temperature at 20 deg C. but since two weeks ago rebuilt the system for liquid phase feed...
No need to heat the gastank anymore.

https://www.modelboatmayhem.co.uk/forum/index.php/topic,70510.0.html

But that has little to do with power, fuel consumption or efficiency. It's more a method to enhance system stability and control.

I have used a boiler pressure control system from the get-go. It works via a pressure transducer in the boat, sending data back to my TX over telemetry, the TX converting that data automatically in a control signal for the burner. Works a treat, boiler pressure is maintained within 0,1 bar of setpoint. Pretty fast response, burner control reacts within 1~2 sec of shifting the steam throttle valve.

I also use full condensate recovery back to feedwatertank, and contiuous proportional feedwater pumping (as opposed to on/off).

[KBIO]

Hello !


I started air testing with the old Compound. As I suspected, and despite the equipment's lack of precision and reliability, the measurements speak for themselves, giving an error of 5 or 6%.
Pressure is practically the same in both cylinders, without expansion, and given the LP setting, this should logically slow down the HP and reduce power accordingly. It's well known that a compound will be much less powerful than a Twin for the same displacement, and that's logical. The advantage lies in the difference in steam consumption. We also know that you need a minimum of 5 b to be able to benefit from relaxation and work on the BP.
Don't forget that +/- 900 l of steam at 2 b entering the machine will give +/- 1.1 l of condensate leaving = A drop of water!
Refer to the Excel steam table
I may to continue my comparisons with air, but I'll have to do these tests more seriously with steam.
Nevertheless, these tests show that 3 identical engines have different engine speeds due to drawer settings and sliding sleeve overlap sizes.
Contrary to what I thought, it turns out that the speed of the machine with the two cylinders: HP & LP have the same speed as with the HP alone (the BP being disconnected) and this despite the dead weight and the friction of the BP cylinder and the sliding sleeve.
Amazing, isn't it?


Below, data supplied by Stuart. We can see that even with their equipment, the power developed by these machines is not lightning fast.
HP diameter: 19 mm HP displacement: 17.76 cc
BP diameter: 22.00 mm “ BP: 24.40 cc   
Stroke: 22.20 mm TOTAL: 42.16 ccRated power @ 5.6 B & 1500RPM = 1/16 HP 46 w

Saito lists the power output as 0.1 HP at 3600 RPM, with 30 PSIG steam pressure (2 atmospheres gauge pressure).

I prepared 2x D10 and 1 xTwin Launch but I'm not satisfied with their performance. The D10 in the photo is a Stuart factory machine and does not exceed 700 rpm, whereas a well-tuned D10 pushes up to 2000 rpm.
Cogetimus , cogetimus !!! No servat occupatus !

[DBS88]

Thank you for sharing the results of your experiments, the extra power provided by raising the pressure from 2 to 3 Bar is impressive, it would be interesting to also see the power at 4Bar?
If you get a chance to run the Saito machines that would be great, since they are only supplied factory finished so hopefully the numbers achieved will provide an idea of how accurate the results are that the test rig is delivering. Whereas the Stuart machines performance relies heavily on the abilities of the person machining, assembling and timing the finished machine, so more room for errors