Class 47 Acceleration and Braking

[Railperf]

The engines would be practically cremated because, my friend:
The top speed on level track is 95mph. 10% overspeed - 104.5 mph. Engines are probably screaming hot.
117mph is a 23.5% overspeed of course the engines won't handle it that's over double the "intended" overspeed the loco was meant to handle

Loco engines are massively detuned compared to a car engine. A HST engine for example at full power is only running at 1500rpm. Not sure what Class 47 engines max speed was.
The engine is turning a generator shaft. The generator supplies electricity to the motors. Therefore whether you are running at 5mph or 95mph, the actual engine is running at the same maximum speed. The only difference is the higher back EMF from the traction motors and it is working against the current coming from the generator. That's why there is a balancing speed on level track. But downhill the balancing speed is higher due to the effects of gravity aiding the loco - despite increased aerodynamic resistance. Give the 47 a more aerodynamic pointed nose, and it would probably go faster than 117mph downhill.
At seriously high speeds the motors, wheel axles, wheel bearings and other equipment starts to move beyond design limits and are more likely to fail due to overheating and stresses. The engine and generator seem to be the least likely items to fail at higher than designed speeds.

 

[Richard Scott]

Loco engines are massively detuned compared to a car engine. A HST engine for example at full power is only running at 1500rpm. Not sure what Class 47 engines max speed was.
The engine is turning a generator shaft. The generator supplies electricity to the motors. Therefore whether you are running at 5mph or 95mph, the actual engine is running at the same maximum speed. The only difference is the higher back EMF from the traction motors and it is working against the current coming from the generator. That's why there is a balancing speed on level track. But downhill the balancing speed is higher due to the effects of gravity aiding the loco - despite increased aerodynamic resistance. Give the 47 a more aerodynamic pointed nose, and it would probably go faster than 117mph downhill.
At seriously high speeds the motors, wheel axles, wheel bearings and other equipment starts to move beyond design limits and are more likely to fail due to overheating and stresses. The engine and generator seem to be the least likely items to fail at higher than designed speeds.

There is a chance of generator failure at higher speeds due to higher output voltage, this is usual cause of flashover, hence reason why locos intended for freight use in latter years had maximum speed reduced (know this was just a paper exercise and difficult to impose if loco was pinched for passenger work). The other risk, which hasn't been mentioned, is the higher centripetal forces being experienced by the traction motors can cause banding to lift and hence end up with armature damage if coils also lift. One of the highest overspreads I know of is a pair of 60s reaching 97mph, an overspeed in excess of 50%, surprised traction motors survived.

 

[47827]

The engines would be practically cremated because, my friend:
The top speed on level track is 95mph. 10% overspeed - 104.5 mph. Engines are probably screaming hot.
117mph is a 23.5% overspeed of course the engines won't handle it that's over double the "intended" overspeed the loco was meant to handle

All 47s were OK for 100mph on shorter trains. 95mph was just the speed BR was happy with and regarded as fitting with standard maintenance. Revised maintenance regimes and a few minor modifications saw the 47/7 as a Scottish push pull loco cleared for the 100mph on a daily basis and quite happy doing it on their shorter rakes of mk2 and mk3 stock. Trust me and other posters they could and did cook sometimes and other major injuries but having spent many 10,000s of journeys on them, often fast routes, they were capable of going a wee lot more in limited circumstances mostly on shorter trains or when the hills were favourable downwards and didn't automatically self combust or similar.

And yes to Railperf. In my experience 47827 pre zombie conversion was a fastun and its a shame it got into the conversion programme. Even managed to get some out and back Shap and Beattock action plus over its final weeks too (finally travel tally of over 21,000 miles). The ultimate day near the end - October ish 2001 Liverpool to New St then up to Edinburgh and back down to New St after the 86 burst in the early hours and I found out in time. Shame I was too elated to notice its timekeeping that day. Not many days later after a number of further more modest days out with it, I was off on V50 Preston to Penzance, with a pear shaped overnight on the sleepers for M56 back to Manchester (it's pre planned final service - since it was dragged to New St behind an 86 then to work an ECS to Derby).

 

[big all]

The engines would be practically cremated because, my friend:
The top speed on level track is 95mph. 10% overspeed - 104.5 mph. Engines are probably screaming hot.
117mph is a 23.5% ****ing overspeed of course the engines won't handle it that's over double the "intended" overspeed the loco was meant to handle

you seem to misunderstand how a 47 works ??
an engine under full load will give out full power [about 2580 hp] at i think it was 750 rpm this will be constant from about 15mph up to whatever speed that how its designed and will happily go on for days on end with no strain .
when you talk about "hot screaming engins " perhaps you are refering to the traction motors ??
at 95+ miles the engine is happy the motors are cool because back emf is lowering the actual load so the only actual mechanical strain is the chance off disbanding the motors when centrifugal force exceeds the level off grip holding the electrical winding in place then one or more traction motor will lock up as the wire gets jammed up ??

 

[SolomonSouth]

There is a chance of generator failure at higher speeds due to higher output voltage, this is usual cause of flashover, hence reason why locos intended for freight use in latter years had maximum speed reduced (know this was just a paper exercise and difficult to impose if loco was pinched for passenger work). The other risk, which hasn't been mentioned, is the higher centripetal forces being experienced by the traction motors can cause banding to lift and hence end up with armature damage if coils also lift. One of the highest overspreads I know of is a pair of 60s reaching 97mph, an overspeed in excess of 50%, surprised traction motors survived.

Woah that's absurd, how did the 60s bogies and suspension not fail?

Loco engines are massively detuned compared to a car engine. A HST engine for example at full power is only running at 1500rpm. Not sure what Class 47 engines max speed was.
The engine is turning a generator shaft. The generator supplies electricity to the motors. Therefore whether you are running at 5mph or 95mph, the actual engine is running at the same maximum speed. The only difference is the higher back EMF from the traction motors and it is working against the current coming from the generator. That's why there is a balancing speed on level track. But downhill the balancing speed is higher due to the effects of gravity aiding the loco - despite increased aerodynamic resistance. Give the 47 a more aerodynamic pointed nose, and it would probably go faster than 117mph downhill.
At seriously high speeds the motors, wheel axles, wheel bearings and other equipment starts to move beyond design limits and are more likely to fail due to overheating and stresses. The engine and generator seem to be the least likely items to fail at higher than designed speeds.

Ok

 

[43096]

Woah that's absurd, how did the 60s bogies and suspension not fail?

They’re derived from the Class 89, I believe.

 

[SolomonSouth]

They’re derived from the Class 89, I believe.

Some of the electronics from the 89 are shared with the 92, not the 60, according to wikipedia. Besides, the 89 is a prototype and no-one really knows much or even anything about it, so the wikipedia page could be pure guesswork and could easily be wrong

 

[43096]

Some of the electronics from the 89 are shared with the 92, not the 60, according to wikipedia. Besides, the 89 is a prototype and no-one really knows much or even anything about it, so the wikipedia page could be pure guesswork and could easily be wrong

Who mentioned electronics?

My response was specifically about bogies, in response to your original comment. As the Class 89 was 125mph capable, the bogies probably aren’t much of a concern.

As for your statement that “no one really knows much or even anything about” the Class 89, I think you’ll find the AC Loco Group know plenty about it.

 

[SolomonSouth]

Who mentioned electronics?

My response was specifically about bogies, in response to your original comment. As the Class 89 was 125mph capable, the bogies probably aren’t much of a concern.

As for your statement that “no one really knows much or even anything about” the Class 89, I think you’ll find the AC Loco Group know plenty about it.

Oh bogies weren't mentioned sorry.
The 89 is undergoing an overhaul since January that will return it to the main line btw. Where will it go on the mainline once it is overhauled?

 

[ac6000cw]

Some of the electronics from the 89 are shared with the 92, not the 60, according to wikipedia. Besides, the 89 is a prototype and no-one really knows much or even anything about it, so the wikipedia page could be pure guesswork and could easily be wrong

The 89 traction system uses DC-motors fed from a thyristor bridge rectifier plus individual motor field control (SEPEX), whereas the cl.92 uses AC-motors fed from 3-phase inverters (supplied by ABB), so I suspect the amount of electronics shared between the 89 & 92 is not a high proportion of the total. Also the 89 & 92 are roughly seven years apart in design terms.

The cl.60 probably shares more with the 89, as it also uses SEPEX control of DC-motors.

 

[hexagon789]

All 47s were OK for 100mph on shorter trains. 95mph was just the speed BR was happy with and regarded as fitting with standard maintenance. Revised maintenance regimes and a few minor modifications saw the 47/7 as a Scottish push pull loco cleared for the 100mph on a daily basis and quite happy doing it on their shorter rakes of mk2 and mk3 stock.

They were 95mph locos - geared for such, rather than being a peculiar whimy of BR. Falcon which was very similar to a 47 had slightly higher gearing and officially a 100mph maximum.

The 47/7s were only permitted 100mph (and only from May 1984 onwards) in very controlled circumstances, with a few modifications to said locos and with a special maintenance regime. If the maintenance regime lapsed for whatever reason they returned to being 95mph locos. They were also only officially allowed 100mph on the Edinburgh & Glasgow, a plate affixed to the cab door made specific note of this.

I appreciate much of that being '95mph locos' is academic at best but that was the 'official' situation.

 

[Railperf]

Oh bogies weren't mentioned sorry.
The 89 is undergoing an overhaul since January that will return it to the main line btw. Where will it go on the mainline once it is overhauled?

It was originally cleared for the ECML and tested on parts of the WCML. So I'm guessing that it could be used for rail tours on those lines...

 

[47827]

They were 95mph locos - geared for such, rather than being a peculiar whimy of BR. Falcon which was very similar to a 47 had slightly higher gearing and officially a 100mph maximum.

The 47/7s were only permitted 100mph (and only from May 1984 onwards) in very controlled circumstances, with a few modifications to said locos and with a special maintenance regime. If the maintenance regime lapsed for whatever reason they returned to being 95mph locos. They were also only officially allowed 100mph on the Edinburgh & Glasgow, a plate affixed to the cab door made specific note of this.

I appreciate much of that being '95mph locos' is academic at best but that was the 'official' situation.

Yes. I wasn't towing the "official line" other than regarding maintenance being 95mph save for 75mph freight locos and 47/6 sub classes latterly. If gearing had prevented the 47/7 (which you correctly explain its reasons and caveats to being cleared for 100mph) then it wouldn't have come about itself nor would every other 47 hit post 100mph happily on the flat on shorter trains at some point (some regularly) most probably. Anyway I'm probably just being technically pedantic knowing full well what the design speed and gearing design was and BR's line on the matter!

 

[hexagon789]

Yes. I wasn't towing the "official line" other than regarding maintenance being 95mph save for 75mph freight locos and 47/6 sub classes latterly. If gearing had prevented the 47/7 (which you correctly explain its reasons and caveats to being cleared for 100mph) then it wouldn't have come about itself nor would every other 47 hit post 100mph happily on the flat on shorter trains at some point (some regularly) most probably. Anyway I'm probably just being technically pedantic knowing full well what the design speed and gearing design was and BR's line on the matter!

No problem, I mean plenty of trains can and have exceeded their 'geared' maximum I just wanted to point out that they were designed as 95mph locos rather than that being set as an arbitrary figure.

There are references to the 95 being due to track loadings that wouldn't allow the full 100 but there are several good sources which agree that 95 was the intended maximum as peculiar a figure as it may be.