Acela Speeds

ApproachMedium wrote:You can't see a train hunting from the wayside. I have watched many HHP-8s go by, and been in the rear cab of many in the duties of my job. Almost every one of them hunts above 70MPH at the end facing the train. Its something you can definitely feel sitting in one but not something you can see as the train passes by. At that speed its going too fast.

You could see hunting on the E60s; it was unmistakable. How would it be invisible on HHP-8s?

ThirdRail7 wrote:

MBTA F40PH-2C 1050 wrote:how is the transportation and mechanical dept. able to conduct these tests? are they cutting out the ACSES and SPEED control on the lead locomotives?

They did exactly what I said earlier in the thread and gave an extensive Line 13 to go with it!

amtrakowitz wrote:

Jishnu wrote:

Matt Johnson wrote:What's the limiting factor on the Acela's top speed, and could it be overcome with rocket assisted propulsion?

Stability on track. They are notorious hunters.

Didn't seem to be any hunting during those tests.

What are you basing your statement on, Mr Amtrakowitz?

Oscillations from truck hunting would get worse the faster the speed, yes? And then a derailment would happen, one can say without being too presumptuous?

amtrakowitz wrote:

ApproachMedium wrote:You can't see a train hunting from the wayside. I have watched many HHP-8s go by, and been in the rear cab of many in the duties of my job. Almost every one of them hunts above 70MPH at the end facing the train. Its something you can definitely feel sitting in one but not something you can see as the train passes by. At that speed its going too fast.

You could see hunting on the E60s; it was unmistakable. How would it be invisible on HHP-8s?

Can you hear hunting from trackside? I always assumed that when I heard a wubba-wubba sort of sound that it was hunting (as opposed to the clatter of flatspots, for example)

Arlington wrote:

amtrakowitz wrote:

ApproachMedium wrote:You can't see a train hunting from the wayside. I have watched many HHP-8s go by, and been in the rear cab of many in the duties of my job. Almost every one of them hunts above 70MPH at the end facing the train. Its something you can definitely feel sitting in one but not something you can see as the train passes by. At that speed its going too fast.

You could see hunting on the E60s; it was unmistakable. How would it be invisible on HHP-8s?

Can you hear hunting from trackside? I always assumed that when I heard a wubba-wubba sort of sound that it was hunting (as opposed to the clatter of flatspots, for example)

You may be able to hear some artifact of hunting, but there can be serious hunting without you hearing or seeing anything from trackside.

There can be other insidious effects of hunting that is not otherwise visible such as premature cracking of yaw damper brackets causing them to have to be strengthened etc.

amtrakowitz wrote:

ApproachMedium wrote:You can't see a train hunting from the wayside. I have watched many HHP-8s go by, and been in the rear cab of many in the duties of my job. Almost every one of them hunts above 70MPH at the end facing the train. Its something you can definitely feel sitting in one but not something you can see as the train passes by. At that speed its going too fast.

You could see hunting on the E60s; it was unmistakable. How would it be invisible on HHP-8s?

HHPs are different, its not really so much the truck that has the sway its the body. I know almost every one of them does this and any of the times I have been trackside I have not been able to make it out. It seems like its more of an aerodynamic effect of the rear body up against the coaches and not so much a truck hunting issue. If it was the truck, both ends would do it. This is only the trailing end up against the cars.

amtrakowitz wrote:Oscillations from truck hunting would get worse the faster the speed, yes? And then a derailment would happen, one can say without being too presumptuous?

Seems a little bit too presumptuous to me, given that this is a complex, dynamic system we're talking about. I guess we will see what the tests reveal.

Just because HH8 trucks oscillates, doesn't mean Acela trainsets do too. They're using two entirely different types of couplers and vestibules between cars, which can have an effect on the rear trucks of the power cars/locomotives.

amtrakowitz wrote:

ThirdRail7 wrote:

MBTA F40PH-2C 1050 wrote:how is the transportation and mechanical dept. able to conduct these tests? are they cutting out the ACSES and SPEED control on the lead locomotives?

They did exactly what I said earlier in the thread and gave an extensive Line 13 to go with it!

amtrakowitz wrote:

Jishnu wrote:

Matt Johnson wrote:What's the limiting factor on the Acela's top speed, and could it be overcome with rocket assisted propulsion?

Stability on track. They are notorious hunters.

Didn't seem to be any hunting during those tests.

What are you basing your statement on, Mr Amtrakowitz?

Oscillations from truck hunting would get worse the faster the speed, yes? And then a derailment would happen, one can say without being too presumptuous?

The HHP-8s and Acela sets are equipped with a monitoring system that sounds an alarm before that point, which would cause you to reduce speed. So, the only sure way to know if there was a truck hunting issue is to know that the alarm didn't sound during the tests.

This is why I asked what you were basing your statement on.

http://www.youtube.com/watch?v=ahBlfzUj5sg

25Hz wrote:http://www.youtube.com/watch?v=ahBlfzUj5sg

Yikes . . . you're going to spill that drink!

Since this is my video I have watched it a few times. Anyway, after reading ApproachMedium's post about the swaying being worse in the back I concentrated on the rear of the HHP-8 while I watched it. YIKES!

bostontrainguy wrote:

25Hz wrote:http://www.youtube.com/watch?v=ahBlfzUj5sg

Yikes . . . you're going to spill that drink!

We started a discussion about this particular video in this thread HHP-8/Acela Power Car Ride Quality(?). Notice the difference between the Acela, HHP and the AEM-7.

I'm sure Amtakowitz wasn't referring to this because what you're seeing isn't truck hunting. There is a huge difference between excessive lateral motion of the body of the vehicle (which can be caused by many things) and actual truck hunting. Take a closer look at the trucks in that video, 25hz.

At any rate, we're stuck with it for a little while longer....which reminds me. I have answer to something in another thread.
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One of the railfan videos posted in sections from VHS on youtube has an E60 accelerating, and yes it does hunt quite a bit. If i find the clip i'll post the link here. It's notable in that it's on a stretch of straight track that is in pretty good shape.

As far as the HHP8 in that video, clearly the momentum going through the curve was causing the sway, not the trucks.

Given that the Acela power car and HHP8 are somewhat similar, and only the HHP experiences rear-truck hunting, could it be a function of aerodynamics? The rear of an HHP is shaped in an aerodynamics nightmare - similar to Porsche 911 or Audi TT, both of which are equipped with a aerofoil or "spoiler" to reduce lift at higher speed. Does the shape of the HHP create lift, leading to hunting?

Tadman wrote:Given that the Acela power car and HHP8 are somewhat similar, and only the HHP experiences rear-truck hunting, could it be a function of aerodynamics? The rear of an HHP is shaped in an aerodynamics nightmare - similar to Porsche 911 or Audi TT, both of which are equipped with a aerofoil or "spoiler" to reduce lift at higher speed. Does the shape of the HHP create lift, leading to hunting?

This is exactly what I have been trying to convey, except its NOT truck hunting thats causing this problem it is an aerodynamics issue of the HHP curved nose body going up against the absolute flat face of the Amfleet car. Have you ever seen what air does when it travels over something like that and hits a wall? It has to go somewhere. The air is pushing the carbody of the HHP left and right because it has no place to go and gets caught up between the two machines. There really should be some kind of spoilers on the HHP that come out on the end facing the cars. This would redirect the air over the cars, create less drag and eliminate this body hunting issue.

If it was a truck hunting issue, both ends of the locomotive would have this problem and so would power cars. Power cars do not have this problem at all because they are aerodynamically part of the train.