Welland 2019 Dyno test of Boadicea

[steamfly3535]

Having seen the YouTube videos, it reinforces the reality that you can't hide from things when they go wrong these days. The evidence is available for all to see. Someone will always be recording it on their smart phones, in some ways it has finally proved the non existence of nonsenses like UFOs, but of course it would also be difficult to argue your version of events at an inquiry.

[tenor]

What are the risks of a dyno test?

Is it more dangerous than any other steam engine activity?

Taking the practice as seen on the videos, and some rather crazy stuff at Tallington in around 1988 (approx.):

There doesn't appear to be a governor in use. Any steam engine will race away uncontrolled after a belt loss- especially with regulator wide open. How quick can you shut things down or "Are you feeling lucky, punk?". Potential ending is a burst flywheel.

The engine is clearly putting out very large powers - well beyond what the makers suggest. Potential for siezed bearings, broken con rod / valve gear with associated flying debris.

The belt is obviously taking power well beyond design point for that width of belt. Failure mode well illustrated. How much further debris could have been thrown and who gets hit is entirely down to chance - potential outcome fatal.

Driving a threshing box or sawing is what engines (and their belts) were designed for. With dyno testing, the stresses are much greater and the chances of failure similarly increased.

I notice the chatter on Youtube is less than complimentary - is this really where we want our hobby to go?

Martin

[David Powell]

Search though I might I have failed to find a definitive formula, I do remember that every inch of width of flatbelt will safely transmit a given horsepower depending on the surface speed of the driving pulley. with a maximum limit.
My small Southbend lathe has a 1inch wide flatbelt driving it and it will , providing it is fairly tight, transmit all my I hp motor will put out.
I seem to remember that a rule of thumb for 4 ft 6 flywheels at about 150 rpm is that one inch width of belt will safely transmit up to 10 brake horse power.
It is over 50 years since I saw Boadicea. I seem to remember she had about 8inches of belt width on the flywheel.
Please can anyone give more information about this formula.
Regards David Powell.

[windmiller78]

Originally Posted by David Powell

Search though I might I have failed to find a definitive formula, I do remember that every inch of width of flatbelt will safely transmit a given horsepower depending on the surface speed of the driving pulley. with a maximum limit.
My small Southbend lathe has a 1inch wide flatbelt driving it and it will , providing it is fairly tight, transmit all my I hp motor will put out.
I seem to remember that a rule of thumb for 4 ft 6 flywheels at about 150 rpm is that one inch width of belt will safely transmit up to 10 brake horse power.
It is over 50 years since I saw Boadicea. I seem to remember she had about 8inches of belt width on the flywheel.
Please can anyone give more information about this formula.
Regards David Powell.

rule of thumb for flat belts i was told was 10hp per inch width hence a 5 inch belt 50bhp, 6 inch 60bhp etc, giving a saftey factor built in when you look at a large showmans like the leader with an 8 inch belt putting out 500 amps at max chat.
sawing on a large rack bench would be considerably more hard work than a steady load like threshing which a 54 inch would be about 25 bhp, with a baler or chaff cutter added that would run up to 35 or 40 bhp but again on the belt and well within the normal working limit of the engine.

[tenor]

Thanks for the rule of thumb on belt power, Adam. I checked my own source and found a slightly more conservative value, but not enough to warrant a discussion. One of the Youtube comments reckons the engine recorded a torque of 3554 ft lb, but that was presumably somewhat before the belt loss, certainly 3554 ft lb on a pulley approximately the same diameter as the engine flywheel at an estimated 190 rpm (using a musical tempo meter) gives 125 horsepower - quite a lot!

Looking back at the video from the flywheel side again; Shortly before the incident, the belt is oscillating at the same frequency as the chuffs. That to me suggests a resonance between the belt natural frequency and engine running speed. The brake is then wound further down and the engine starts to lose the battle with revs. dropping dramatically, I think the video also shows that the belt is slipping by that stage. Then the inevitable happens.

If the engine revs are dropping and the belt is slipping you are clearly way past the optimum point for transmitting useable power from the engine. Does that not tell you something?

Martin

[Northburrell]

I think for me it's nice to see this stuff going on at rallies but as Martin said there needs to be a limit. this could have ended very badly for the driver and crowd and then we would ALL be penalized for it.
I've watched the video over and over and it's the way the belt is almost suspended in mid air then gets whipped back into the flywheel.
I was wondering if some sort of catching arm could be employed and be placed through the space in the belt nearer the dyno to catch the belt if it were to fall off.
Governors should also be used, can i ask if the engine would have stopped or slowed faster using the governor to shut off steam than the human response time of the driver to get it into mid gear and shut the regulator?

A comment above about coal being unloaded behind the fly wheel is very valid! this should not have happened and imagine the state that guy would have been in if he was there at that moment!

At the end of the day the limit needs to be set and it adhered to. It's great fun seeing this stuff and it's good for engine owners and public to see but we certainly need to be safe and not see this sort of accident again.

[steamshovel]

Dear all,
so far I have never written in this forum. I am operating a steam shovel here in Northern Germany, which definitely is something different to the majority of traction-talk threads.

Please let me give you an engineer´s comment on Boadicea´s belt-issue. For 20 years now I am working as an application engineer for the Forbo Siegling Company. We are manufacturing flat belts in Germany since 100 years. On our English website you can also find contact data:
https://www.forbo.com/movement/en-uk/
Forbo Siegling (UK) Ltd.
Unit 4, Fifth Avenue
Tameside Park
Dukinfield
GB-Cheshire SK16 4PP

Until 1943 we made flat belts from chrome leather, after that date only with a tension member made of Polyamide, covered with leather on both sides for friction. These belts are available in a big range, the effective beltpull can be between 45 lbs/inch and 450 lbs per inch belt width (I calculated from metric dimensions). One of my jobs is to calculate and understand belt drives, mostly the heavy ones, which today can reach up to 1500 kW (2000 hp) in waterpowerstations, steel mills or wood-chipping machines. The belt width can reach more than 3 ft. One of the problems we have to avoid are vibrations of the belt strands. Every free tensioned belt part ist like a tensioned string on the guitar, having a resonance frequency, which can be altered by the tension (like you tune the guitar).

In the video you see the upper belt strand, which is transmitting the effective beltpull, running stable and calm. But the bottom strand shakes heavily. This means, that the bottom belt part is in resonance with an external excitation, possibly coming from the uneven torque of the steam engine (compare the belt movement with the engine chuffs!).

You need the pretension force in the bottom strand to build up the effective beltpull when the belt is going around the drive pulley. When you have a big arc of contact, you can transmit more beltpull than a smaller arc of contact with the same pretension.

But when the belt is shaking, the pretension oscillates, which can lead to short-time but frequent complete slippage of the belt on either pulley. When the belts slips in longitudinal direction, there is also no force to hold it in transverse direction, not even on crowned pulleys. So it can easily be pulled off sideways by the belt forces, if the pulleys are not aligned perfectly. I assume it is not possible to align them perfectly in reality. Maybe one of the machines moved on the ground due to vibrations or unsufficient anchors.

There is only one solution to shaking belts: increase tension (=increase the distance between the pulleys), reduce effective belt load or change the speed. They should have stopped the test or reduce the power after the first heavy shaking of the belt. You can see, that it was not possible to come beyond the resonance point, and this is dangerous.

When you watch a belt drive speeding up on a saw bench or similar, in most cases you will see that each belt strand has its shaky seconds when going through resonance. But as long as resonance does not persist in normal operation, this is ok.

We should be glad that no person was injured, there is a lot of energy stored in a tensioned belt. Even with smaller belts that might have a wire-hook-splice there is a risk – do not stand in line with the pulleys, because belt ends with disintegrating wire hooks can produce some nasty scratches.

English is not my native language, so please apologize if some expressions are not 100% correct. But I hope that I could explain some of the theory behind. We should leave resonance to string instruments, and listen to the smokebox rhythm! Have a save steaming!!

Peter

You may also contact me by my company-email: peter.meyer@forbo.com

[Dazzla]

Originally Posted by Northburrell

Governors should also be used, can i ask if the engine would have stopped or slowed faster using the governor to shut off steam than the human response time of the driver to get it into mid gear and shut the regulator?

The governor would have had the opposite effect of the driver when the belt came off as it would have tried to maintain the engine speed.

Dazzla

[marshall8hp]

It would stop an engine over revving and the chaos that that would cause. The driver wasn’t injured, but suppose he was. I understand the steersman’s seat was destroyed. Assume he was sitting on it or standing next to it at the time. He is on the floor with a great gash to his head or his thigh sliced open and the engine is speeding out of control until someone can get onto the footplate and shuts it down, or the motion disintegrates. As can be seen in the video, if a belt breaks on a loaded steam engine, the engine goes straight up, so to speak.

[Dazzla]

Agreed, the governor would have stopped the engine racing away, but the question was whether it would have shut the engine down quicker than the driver.

Dazzla