Acceleration out of the turn?

A snowHead

Ok if anyone has the time, I'd really like to work this one through as I'm bored of being told different things....

With the exception of leaning on the tails of the ski so they go faster, is it actually possible to increase my speed coming out of the turn? or is it all imaginary acceleration?

MATT

A snowHead

dulcamara, my perception is that if you are really locked into your edges and carving "properly" you can apply the energy locked into your bent ski into accelerating you forward.

Or indeed, upward.

I'm sure it works on my SLs, not so sure about GSs.

Well, the person's real but it's just a made up name, see?

what are the different things you've been told and were they by different instructors in separate lessons or by "mates" at the side of the slope?

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dulcamara, is it a question if "increasing your acceleration" or "decreasing your deceleration"? In long radius turns I tend to think of it as the latter, by making sure you do most of the turn above the gate (high edge angles, appropriate amount of pressure management) so by the time you get to the gate you can come out of the turn smoothly and with a fairly direct line so you minimise any speed loss (leaning on the ski tails will make you come out of the turn more smoothly as you gradually unload the pressure from teh front of the ski and your turn radius begins to open up). If you look at the ruts left when the training lanes have been pulled in pre-season training all the better skiers leave much more pronounced ruts above the gate than below the gate. Slower skiers leave big ruts below the gate because they are doing more of the turn there, consequently losing more speed.

In short radius turns I think you can "juice" the turn by putting lots of energy in to the skis which will in return pop at the end of the turn. As under a new name said, you can use that to accelerate forward or pop upwards depending on how skilled you are.

All IMO and limited experience, and happy to be put right on this.

Anyway, snowHeads is much more fun if you do.

Now then. Thinking hat on.

As you come out of a turn (on the legendary frictionless, constant gradient snow and performing exactly the same turns every time; as needed for theories), your skis will probably be going at their slowest, as at that point they'll be facing accross the hill at the greatest angle. They'll be accelerating hardest half way through the turn when pointing directly downhill.

But at the end of the turn, you will/may of course be launching your body down the fall line to start the next turn.

Is that accelaration on your body (no skis) greater then than at the fall line moment? No idea.

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I'm not sure where you would store the energy and assuming you are heading perpendicular to the fall line then you would be going the same speed (ignoring friction). Unless moving your body upwards adds a little momentum, I can't believe the spring in the ski does much either

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dulcamara, Yes you can 'pump' your turns... all to do with timing the release/initiation properly. Takes a bit of practice. You can chase another skier and work at getting closer - ski the same line and see if you can close on them. Have them ski consistent turns and you can see where you get it right. A good way to work on it is carving long turns on the flats - you can work at generating that little 'ooomph' out of the turns and it is more obvious due to not huge speed otherwise.

A friend, who's a proffesor of Physics, once explained it to me and it got very complicated and longwinded. Then he said it's like a kid standing on a swing in a playground; By pumping thier legs at the right moment the swing goes higher and faster, but the kid doesn't have to understand the science, just practice the timing.

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Easy, just buy some HEAD skis with KERS built in and they take care of all that for you. wink

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under a new name, rob@rar, and little tiger have it right here dulcamara. It's a learned skill, much involving good timing of release. When you get it, you know it. If you do what little tiger said you can prove it works. I use it when I'm in a rather flat race course,,, I pump the turn. In a dual format course you can pull away from the racer at your side by doing this. little tiger has seen me do it. It's work though.

In a more subtle application, a well timed and executed release will simply allow rebound to move you fluidly into the exit line of the turn, rather than popping you up in the air.

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FastMan, but popping into the air rather fun, and can be surprising to companions who aren't expecting it... Twisted Evil

I don't like this, already we have a lot of different answers. For clarification, Im happy with the how its just the why, can get lots of kick out of a ski but am i actually getting faster in my direction of travel.

The standard thinking says that if you load the ski and release onto the tails at the end of the turn it will then accelerate you out of the turn.

My thinking as under a new name, kind of joked and tiffin, stated, is that bending a ski is applying force perpendicular to the direction of travel, how will releasing this accelerate me anything other than upwards? does it help me get up the "virtual bump" or does it just feel like im going faster?

rob@rar, 's point is undoubtably true, and it is the more recently vocalised point that the acceleration is imaginary as you have bent the ski early to set yourself in the fall line and controlled the grip out keeping your speed increasing so it feels like you are accelerating compared to a normal.

adithorp, has the most intruiging point which I have never truly considered, using the swing thought experiment, though I would assume that would only work if you were then to travel back in the opposite direction, otherwise you would be making energy/acceleration out of nothing and we aren't allowed to do that yet. One would have to slow down the same amount after the turn hmmmmm.... or is all this balls, i'm pretty sure i can kick myself along on my wheely desk chair in the direction of the muffins.

You know it makes sense.

Otherwise you'll just go on seeing the one name:

Has everyone forgot about the "GRAVITY"

The imaginary acceleration is actually real at approx 9.81 m/s2 (take some due to above sea level and not directly down)

I guess going into a turn you are slowing your speed and when you come out the turn its like releasing the brakes.

Also...

As mentioned you can generate some speed

I thought about a skater on ice, You can replicate carving turn motion to a small degree and without lifting skates off ice you can "pump" the turn as fastman said, You are putting you energy into the turn by bending and straightening legs(popping?)

A snowHead

Ok, we can take gravity as a given, the point is, do you accelerate faster in a normal turn or by driving the ski?

I have done all the races and stuff that FastMan, and little tiger, describe, but it leads to the same question, is it the release of the ski speeding me up? if so why? or does it just form a more efficient turn like rob@rar, says?

A snowHead

It could be that unweighting the ski reduces friction, but that won't accelerate, just decelerate less

Well, the person's real but it's just a made up name, see?

dulcamara, gravity is a constant, so that's not going to change no matter what you do in the turn. So if you are looking to add to the constant acceleration you get from gravity the question is are you able to create a force which momentarily pushes you down the hill? Even if you are able to do that I'd say it's going to have a relatively small effect on your overall speed compared to making effective turns which minimise your speed loss.

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rob@rar, PERFECT

Thats the question i am trying to raise after a bottle of 2 euro wine, there is a split down the thread of "yes you can squirt/drive/pump to generate more speed" or "no you can only decrease the amount you slow down".

An interesting point stuck in my head at this point is, if you generate acceleration perpendicular to your movement will it help you up or over the "virtual bump" as LeMaster likes to call it., so is that actually going to result in a net acceleration?

Anyway, snowHeads is much more fun if you do.

dulcamara, If one person pumps and the other does not and both do the same quality of turn except for one adding the pump and one not what do you find happens? Both are releasing the turn and initiating the new one so what is the difference if you see one? I see a clear acceleration each turn from the 'pump' person versus the 'no pump'

Try video of yourself skiing a set line - do it once with no pump and once without. (You will need to be mounting video on a tripod) You will be able to then 'race' yourself on teh video when you overlay them.

If you are making turns that are NOT clean you will not notice as the slowing from the bad initiation will be much greater as rob@rar, says. However when making clean turns there is a noticable difference when you 'pump' versus not pump. I know - I play chasing FastMan, a bit to work on the timing in an attempt to improve my skill at this. Without the pump I stay constant distance with the pump I start to catch up. Same deal when FastMan, actually decides to race in the race course versus 'demo race'. I've watched him race old team buddies and you can see the acceleration from the pump as he works to get ahead. This is not the same as his 'clean run' runs.

BTW a clean run with a decent start alone will get him a VERY low handicap. Most of the population simply don't ski the gates clean - I can do the less tight gates but not the tighter ones clean. When he is working for time though you can see him pump as well.

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I will 'try' and explain what I think I mean...

If you are traveling straight down a slope and the maximum speed you can get to is 30mph then you introduce turns which slow you down to 20mph as you "turn"

As you are at the very last moment before you release the ski your body will continue to travel in a straigh line while your skis move under you. At this point you must be subject to 9m/s2 of gravity (even if you say 5m due to the slope angle or 2.5m) and that must feel like acceleration.

so, 2.5m is equal to roughly 5mph (0-60 in 12 seconds) - in the second or so in the middle of the turn your speed will increase 5mph, I think you can make it feel faster or maybe help it along by loading the ski and pushing off through the turn

There is probably some massive error in calculation but hopefully it explans what I was trying to say.

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daehwons, Try it on the flats you are not deviating from falline by that much...

You are using flexion/extension/edge angle to increase ski flex momentarily - but also releasing the ski. You have one edge angle as you flex ski and a different angle as you release it. That is how I think it feels(sorry it has been 5 months since snow time).

My earlier instructor described it as 'working' the ski.

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Are we talking speed or velocity?

Your velocity across the slope goes from zero in the fall line to maximum of whatever. Your velocity down the slope reduces, maybe to zero, possibly negative.

Your senses tell you there is acceleration, measurement may give another story.

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dulcamara, "...otherwise you would be making energy/acceleration out of nothing and we aren't allowed to do that yet..."

You're not getting something for nothing as you're putting energy into the system.

The long explanation went something like... When an object rotates around a point (turning skier) it is experiencing an acceleration towards the centre of rotation through out that turn. This acceleration is caused by the centripital force (presure on the skis) and that force is governed by the velocity of the object and the radius of the turn. Increase the force (pump the skis), maintain the turn radius and the velocity has to increase... Of course my Prof' friend could do the maths to prove it..

It's the same thing on a swing or spinning a weight around on a string. The effect is minimal compared to gravity when the slope is steeper but relatively more significant on shallower slopes.

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adithorp

Sounds like orbiting satellites sort of thing.

Low orbit satellites go really fast, tight circle, high ones go slow.

The skier is orbitting around some sort fo centre albeit a variable one if you move about a bit, tighten the turn and the circular velocity must increase to maintain the balance.

So to rocket out of the turn roll the skis right over into a tight turn and then shoot off like a probe going past Jupiter.

Is that the sort of thing ?

We're speaking of two different speed generation mechanisms here. One is pumping, which loses it's effectiveness as the slope steepens. The other is a well timed and executed release, which works to maximize speed in all situations.

The sensation of the latter, the release version, is that of bouncing on a trampoline. The turn is the landing and sinking of the tramp, and the release is the launching. It's hard to describe precisely how it's done, but I said before, when you feel it happen you know you got it right. Being able to do this is one of the things that separates the winners from the also rans on the World Cup. It's very clear to a trained eye the guys/gals who are coming out of their turns dead, the energy they carried through the turn just dissipating into nothingness, and those who know how to use it to rocket themselves out of the turn.

It's predominantly a timing thing. Knowing when to release, and how to direct the energy forward. Getting off the front of the ski, and letting them squirt forward and take you with them. The skiers who miss the boat with this look very flat and slow coming out of their turns, kind of like they are just hanging there, waiting to get across the slope to begin the new turn. The guys who nail it rocket across the slope towards the new turn.

So big picture, what's it worth? For the recreational racer, executing a clean turn will provide the most bang for the buck. After that, line will be the next most important thing. Straight while carving clean is generally faster than round while carving clean. Only after those primary speed generating factors are intact will a powerful turn exit make a meaningful difference.

You know it makes sense.

FastMan, and it's not a new thing, google "Stenmark Charge"

Don't bother, just check this out
http://youtube.com/v/-lpFWjOFe8w n.b. not every turn, some of them he's actively braking (I mean, he's right on the limit...)

poetry in motion

Otherwise you'll just go on seeing the one name:

adithorp, that's a new idea on me, its actually quite interesting (i am a physicist, ski instructor who owns a cat suit, i am allowed to be this sad). Assuming that is the case, why then do the racing stock, as FastMan, and little tiger have described, have to then rock onto the back of the ski to feel the effect. Surely, with the exception of the slight loss of friction you get by hitting the tails, you would get the same effect by staying forward... Surely by throwing your skis forward you body will move back the same amount, stopping you getting faster?

A snowHead

under a new name, I love that film.

Before people start pointing at his tips shouting ACCELERATION. lets get one thing straight, you will always be kicked back at the end of the turn, as you go from a steep slope in the fall line to essentially on the flat while traversing, the harder and tighter the turn is the more exegerated the effect will be. My question is, does allowing this to kick to you back to your tails actually make you go faster in the direction your tips are pointing.

A snowHead

Well, the person's real but it's just a made up name, see?

my point exactly, but racers swear by it, as i used to

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under a new name, he's the guy I modeled my skiing after when I was in my prime, so many years ago. A visionary, he showed us how to ride clean edges on skis that carved arc to arc tracks that could be seen from the moon. King of the diverging power step, he was an artist on skis.

dulcamara, you figured out your own question. Shovel pressure is slow, like riding the front brakes on a bike. Working a ski from tip to tail through the course of a turn is a long practiced tactic in racing circles. The tips get the turn initiated aggressively, then getting off the tips releases the brakes and lets the skis accelerate through the body and exit of the turn. Static centered fore/aft though the turn is safe, and efficient. Working tip to tail is riskier, and more work, but can juice the turn, and promote the sling shot effect I've been describing. Bode used it extensively, to the point of detriment at times. He used to advocate working the tails to kids coming up.

Used in moderation, working the ski from tip to tail can provide a nice flow into and out of turns. It's a pleasant sensation. In comparison, remaining static at center feels more boringly blah, similar to park and ride. On steep terrain, at least moving from fore to center is advisable. It keeps a skier proactive, with an aggressive attitude to the pitch, which helps the skis do their thing and crank out strong turns.

Anyway, snowHeads is much more fun if you do.

I think we need to ask ourselves how skating on skis works, and then it will explain the popping effect when used with 2 skis in the turn. Popping/pushing in the turn is energy from your body being dissipated into acceleration, hence the reason it is tiring.
However most of the time I have to agree with rob@rar, that the sensatation is really.

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cool, we are shifting our weight distribution backwards to reduce friction after the turn, so the question remains, preferably from a forces point of view. How does pressing down and bending a ski from one dierction result in the slingshot effect in a completely different direction. i.e. how does releasing the ski generate forward acceleration or is it just lifting us up?

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After thought for you, dulcamara. Just to be clear, the sling shot turn exit can be done without aggressively going to the tail, too. Even when staying centered, a well timed and executed release can result in forward energy taken into the exit line. The fore to aft thing is just something some use at times to accentuate it.

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Acceleration out of the turn?

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