The GPS data is interesting, but unfortunately not particularly reliable. There are too many variables, such as the driving style of the driver, the load factor of the vehicles, OHL / third rail voltage during the acceleration, gradient, the amount of power drawn from other trains in the area etc.
A comparison would therefore require a series of tests under almost identical conditions. Or you could use a tractive effort diagram like the one in the attachment and do some calculations. I couldn't find any for the 701 or 720 though.
View attachment 155528
When talking about "reliable' im reffering to the fact that its a good refrence for performance when compared to other units. Its like an indication of what units seem to perform better towards higher speeds when we account for repeated analysis of the same trains over time.
.Factors like driving style can be accounted for based on repeated footage and feel of the trajn upon acceleration and making a judgement. Its not perfect though
.Taking footage of the same trains in other areas that may vary in gradient
. Assessing how fast the starting acceleration usually is to gauge if drivers are using full power or not ( its more an educated guess with that one)
When comparing a class 701 to class 465/1s, majority of the GPS footage of the class 465/1s usually put them in the 75 + second range when hitting 60mph , vs footage of class 701s hitting 57 mph in under 60 seconds perhaps indicating it will hit 60 mph in much less than 75seconds , although in this case the class 701s haven't really been demonstrated to hit 60mph in any footage thus far, but we can gauge how multiple filmed takes of GPS footage at lower speeds may affect the long term acceleration towards higher speeds until we actually see it. With experience of other units being filmed also.
Is it a reliable variable for gauging why the traim accelerates the way they do? No, youd have to consider the factors you mentioned prior. Esspecially weight and software programmming etc of the units themselves and so on. GPS cant predict that. But it just gives you an idea.
But when we look at GPS , it can show (if multiple different takes are done in different places on the same train types) how they perform as compared to other units. With the aventra fleet , the GPS footage shows so far that they repeatedly hit mid speed faster than most footage of other third rail trains, meaning they likely have a much better weight to power ratio than other subsequent units.
That being said i absolutely dont think GPS is the proffesional way to determine a trains output at the wheels etc. Its just a laymens way of comparing trains for fun but making speculative guesses over time.
Class 701s are new on the block so who knows how valid the videos we have seen so far are from a non drivers perspective until more footage is released or other data sourves gathered etc.
As previous mentioned EMUs are adhesion rather than power limited at lower speeds, above the threshold speed the reduced power on DC results in lower TE, below that threshold speed it doesn't - power draw rises from very low when almost stationery to max at the threshold speed.
No "fatigue" involved you are confusing Power (kW) and Force /Tractive effort (KN), acceleration is all about TE not power (F=m*a). TE (kN) = Power at rail (kW) / velocity (ms^-1). The power draw remains high but the TE reduces naturally (newtonian mechanics) with increasing speed as the energy dissipation per unit distance reduces.
Interesting, interesting. This adhesion thing is a new thing i had never thought of. Inwill need to research or get more info on it.
www.realtimetrains.co.uk
