Power:Weight Ratio Class 221 Voyagers

[XCTurbostar]

Just had a thought about Voyagers in general.

On level ground. If you were to take a Class 221 4 Coach Super Voyager and accelerate from a stand to 100MPH and then take a Class 221 5 Coach Super Voyager on the same test on the same track. How would the results of acceleration times fair?

Does the weight of the extra coach reduce the acceleration because the extra engine does not complement the weight?

Stats;
Class 221 4 Coach Weight: 227 t (Reference Wikipedia)
Class 221 5 Coach Weight: 282 t (Reference Wikipedia)
Engine Power: 750 HP (Reference Wikipedia)

Thanks,
Ross

 

[eastwestdivide]

As 282/227 is about 1.24 and 5/4 is 1.25, i.e. within 1%, I'd guess they'd fare about the same.

 

[Yew]

Hi Ross,

remember that the 750hp figure is for each coach. So, using those figures we get.

4 Coach

(750 x 4)/227 = 13.21hp/t

5 Coach

(750 x 5)/282 = 13.29hp/t

Now these figures are roughly similar, the main effect is going to be due to aerodynamic drag. Adding an extra coach, will not result in a 25% increase in drag, as most of the drag is formed from the front coach of the rake moving the air out of the way of the train. The increase is probably closer to 10%. Therefore, Sicne we have 25% more power, but 10% more drag, it would be expected that, at least at higher speeds were there is a large amount of drag (lets say from 100 - 125mph), the 5 Coach would be able to out accelerate a 4 coach. At lower speeds, the magnetude of drag is smaller, so the difference between the two trains would be less.

 

[455driver]

They would accelerate at the same rate until about 60mph(ish) when the wind resistance against the front would start to have a slight effect and then the 5 coach would accelerate very slightly quicker. Its the frontal area wind resistance which although it remains the same the 5 coach train has more horsepower to overcome that resistance.

 

[notadriver]

In the real world differences in the condition of the engines would affect performance more and the engines have been derated to 700 bhp.

 

[Minilad]

In practise the 4 car 221s "feel" slower. I have never tested it scientifically (stopwatch) mind you. 220s feel much quicker than both. Although you have to get a 221 with all engines running first!!

 

[notadriver]

221s are heavier than 220s as they have their tilt equipment and so are slower as a result.

 

[Moonshark]

As Class 220s have all 4 engines working and 221s only have 4 working, the 221s will have less power because of the extra un-powered coach.

 

[broadgage]

With all engines working, and all producing the same output, the 5 car train would have better acceleration due to having very slightly more HP per ton, and due to the wind resistance being a little less per vehicle or per ton on a 5 car train.

The difference would be small and in practice probably would be swamped by minor variations in actual achieved engine HP, variations in the weight of passengers/luggage, and variations in engine power used for heating or air conditioning.

 

[455driver]

As Class 220s have all 4 engines working and 221s only have 4 working, the 221s will have less power because of the extra un-powered coach.

Since when have 221s only had 4 engines working?
What about the 4 coach 221s?

 

[Moonshark]

Since when have 221s only had 4 engines working?
What about the 4 coach 221s?

I did read that Crosscountry Class 221s have one engine disabled on each unit (I think on this forum). There is a 4 car Class 221 (slipped my mind) with Crosscountry. Also, Virgin on occasions have 4 car Voyagers (due to coaches being removed in the depot).

 

[455driver]

I havent noticed any 221s with engines off lately although I dont see them very often.

 

[Moonshark]

I havent noticed any 221s with engines off lately although I dont see them very often.

Could anyone confirm whether or not (XC) Class 221s have an engine disabled please?

 

[Rich McLean]

Could anyone confirm whether or not (XC) Class 221s have an engine disabled please?

This used to be the case, but not anymore. All engines should be operating, but if there is an engine that requires attention, it can leave the depot with only 4 engines running.

 

[XCTurbostar]

I think that this is the case for most modern units. However, some, namely 2/3 coach units would suffer the most. Then you've also got newer units like Class 185s which are designed to turn an engine off when it's not required.

There are a few Voyager variations running around at the minute. Virgin have 5 Coach Voyagers only. CrossCountry have 4 and 5 Coach Class 221s and 4 Coach Class 220s as well as 220007 which has one tilting coach from 221135 because of fire damage.

As a side note, I have travelled in a voyager coach from Crewe to Birmingham New Street a few months ago in a coach with no engine running and it was actually surprisingly quiet for a voyager!
Thanks,
Ross

 

[Minilad]

The XC 221s went though a trial a while back whereby one engine would be isolated in rotation to see if any cost savings would be made. The trial has now ended and all should have all engines running in service. Of course engines can be isolated for various faults throughout the day so it's not uncommon to get a 221 or 220 for that matter to run round with an engine out. Generally it doesn't cause problems with timekeeping when an engine is out

 

[Martin_1981]

Given that the Voyagers have 750hp per coach, they can probably just about cope with two engines being down, although the acceleration would obviously be considerably slower, probably similar to that of a HST with one dead power car.

 

[455driver]

Given that the Voyagers have 750hp per coach, they can probably just about cope with two engines being down, although the acceleration would obviously be considerably slower, probably similar to that of a HST with one dead power car.

700hp per coach, they were derated a few years ago!

I take it the switching engines off was a fuel saving measure?
It wont work because the other engines will just be worked harder for longer to achieve the same thing, it would have been a totally pointless idea thought up by some plank in an office who hasnt got a clue!

 

[Moonshark]

700hp per coach, they were derated a few years ago!

I take it the switching engines off was a fuel saving measure?
It wont work because the other engines will just be worked harder for longer to achieve the same thing, it would have been a totally pointless idea thought up by some plank in an office who hasnt got a clue!

The Class 220/221s were NOT derated a few years ago. It was the Class 222s. The Voyagers need full horsepower for climbing hills such as The Lickey.

 

[455driver]

The Class 220/221s were NOT derated a few years ago. It was the Class 222s. The Voyagers need full horsepower for climbing hills such as The Lickey.

So the various XC drivers I know are wrong, I will tell them next time I see them.

 

[Moonshark]

Below are some figures from Wikipedia about the Class 221.

Prime mover(s)
Cummins QSK19 of 560 kW (750 hp) at 1800rpm[1]

 

[455driver]

Below are some figures from Wikipedia about the Class 221.

Prime mover(s)
Cummins QSK19 of 560 kW (750 hp) at 1800rpm[1]

Ah wikepedia, the font of truth!

 

[Moonshark]

Ah wikepedia, the font of truth!

As it is so detailed, it is likely that the article was written by a driver or an engineer.

 

[455driver]

As it is so detailed, it is likely that the article was written by a driver or an engineer.

Yeah of course! :roll:

You believe what you read, and I will believe what I am told by the staff who deal with these trains every day.

 

[edwin_m]

7
I take it the switching engines off was a fuel saving measure?
It wont work because the other engines will just be worked harder for longer to achieve the same thing, it would have been a totally pointless idea thought up by some plank in an office who hasnt got a clue!

It depends.

A diesel engine is most fuel-efficient around the middle of its output power range. The engines and transmissions on the Voyager are sized to provide enough power for high acceleration of a heavy unit. The power needed to sustain a constant speed is much less, so the engines may well be in a less efficient operating mode for much of the time. In which case three engines running close to maximum efficiency might use less fuel in total than four each delivering less power. Reduced hours on each engine should also reduce engine maintenance, unless outweighed by the extra wear from more stopping and starting.

 

[notadriver]

Also to add to that trains spend a lot of their time coasting - so having an engine shutdown instead of idling will save fuel.

 

[Minilad]

The Class 220/221s were NOT derated a few years ago. It was the Class 222s. The Voyagers need full horsepower for climbing hills such as The Lickey.

Yes they were.

 

[455driver]

Yes they were.

Dont argue with him, he got the facts off Wikipedia!
And because they used some long words

it is likely the article was written by a driver or an engineer

 

[notadriver]

Of course 185s have an Eco-mode and can and do run on 2 out of 3 engines.

 

[O L Leigh]

The Class 220/221s were NOT derated a few years ago. It was the Class 222s. The Voyagers need full horsepower for climbing hills such as The Lickey.

Voyagers do not need full power to get up Bromsgrove Bank. They have an excess of power and can manage that feat quite nicely thank you. Even a Cl150 with approximately 8bhp/ton empty has enough grunt to get up the hill, even from a standing start at Bromsgrove station, whereas a derated Voyager has more than 15bhp/ton empty.

O L Leigh