What does the term "Platform Angle" mean to you?

[LiquidFeet]

What do you understand this term to mean?
Do you use this concept in your skiing in any way?
Have you encountered instructors or coaches or writers using this term?

 

[Steve]

Since my question in the Edging thread started this, and there were already a couple of replies in that thread I'll pick it up here.

We all use the term "edge angle" and distinguishing the meaning of that from "platform angle" is what's important.

As LF pointed out in the Edging thread, you can have low edge angles and still have good grip and be able to carve pure arc-to-arc turns. Railroad tracks.

So to me "platform angle" is the combination of "edge angle" and other factors.

It would be good to pursue these other factors in order to understand how to use them to control the skis grip and ability to carve.

Angulation
Inclination
Speed
Steepness

What else? What about the above can some of you expand on please?

 

[François Pugh]

It is the angle between the plane of the snow platform created by the ski's base and the net force exerted by the snow on the ski/skier. This ground reaction force must be must be 90 degrees to the platform, or pointing more up than sideways than a 90 degree angle in order for the ski to not slide sideways.

 

[Tony S]

I was thinking, "poorly chosen tent site." You never quite realize, until you lie down, that what looks level sometimes ain't.

 

[geepers]

I was thinking, "poorly chosen tent site." You never quite realize, until you lie down, that what looks level sometimes ain't.

If you angulate the right amount you won't slip out of bed. Assuming your fore-aft balance is good...

 

[geepers]

What do you understand this term to mean?
Do you use this concept in your skiing in any way?
Have you encountered instructors or coaches or writers using this term?

This. Which must have been posted so many times.

I prefer to think about it in terms of the force the skier experiences (perceived gravity for want of a better term) as it is more intuitive for understanding how that results in the ski being held in the groove cut in the snow.

Yes, think about this in skiing. No. 1 in that it help me understand how a skier executes a carving turn at high angle turn without skidding out. No. 2 as being encapsulated inside the CSIA Technical Reference #3 "Upper and lower body separation allows for angulation to provide grip".

First met this term on pugski. And again in Ultimate Skiing by Ron le Master. And again in Section 8 vids. Not heard the term in a CSIA course however I've heard plenty about the Tech Ref #3.

 

[LiquidFeet]

I posted about platform angle in another thread the other day. Here's that post reformulated for this thread.

Platform angle measures the spatial relationship of the skier to the outside ski. It consists of two imaginary lines that meet at an angle. The first line extends across the surface of the ski from side to side. That line starts where the tipped ski's inside edge contacts hard snow - and extends to the other edge, the outside edge, of the ski. The second line starts at that same point where the tipped ski contacts hard snow - and travels up to the body's center of mass. The angle created by these two lines needs to be less-than-or-equal-to-90º for the ski to grip on hard snow. See the image by Bob Barnes that @geepers just posted above for a visual.

Platform angle is independent of edge angle. Low edge angle skis can cleanly grip the snow and produce pencil-thin tracks if appropriate platform angle is maintained (railroad tracks). The relationship of the body to the ski defines whether the ski will grip, not slip, and whether it will produce narrow tracks or wide skidded tracks on hard snow. This assumes the skier does not rotate the skis and is balanced fore-aft over the skis.

What skiers actually need to know about platform angle is simple. If the ski is slipping/skidding even though it was tipped without being rotated and even though the skier is balanced fore-aft on the ski, the problem may be that the platform angle is too large. To reduce that angle, the skier can
--move the upper body farther out over the outside ski, or
--bring the outside ski closer up under the body.
Either of these, or both together, can reduce the platform angle to enable grip.

Common skiing problems make it difficult to maintain a small enough platform angle.
----Leaning in/banking/bracing puts the body too far inside the turn. Angulate instead of leaning the shoulders into the turn.
----Hip-dumping puts the body too far inside the turn. Shorten the inside leg and roll its knee into the turn instead of dropping the hip.
----Pushing the outside ski to an edge puts the body too far inside the turn. Tip the skis without pushing on the outside ski by flexing the inside leg instead.
----Skiing square makes angulation more difficult, and lack of angulation puts the body too far inside the turn. Ski with separation and angulation instead.

Platform angle gets mixed up with edge angle. There are functional reasons for that. If the skier knows to increase edge angle by flexing the inside leg, that flexion can indirectly result in an effective platform angle. That's because flexing that inside leg keeps the inside foot/ski up under the body, which in turn discourages pushing the outside ski outward. Flexing that inside leg also discourages hip dumping since dropping the hip isn't being used to develop edge angle. And inside leg flexion is usually paired with angulation, not with banking, since leaning the whole body is not being used to create the edge angle. The resulting angulation positions the body farther out toward the outside ski. All of these reduce the platform angle. So three of the impediments to maintaining a small enough platform angle listed above can be indirectly eliminated by flexing that inside leg to get the edge angle. Skiers who know to use inside leg flexion for edge angles may not be thinking about adjusting platform angle to get and hold grip, but they are.

 

[oldschoolskier]

I love technical discussions, but some days question why we try to over define everything and fall back onto K.I.S.S.

Just ski.

Or as Master Yoda would say “Do. Or do not. There is no try.”

 

[karlo]

If the skis don’t hold, assuming sufficient edge sharpness, it’s because angulation was insufficient?

 

[François Pugh]

I love technical discussions, but some days question why we try to over define everything and fall back onto K.I.S.S.

Just ski.

Or as Master Yoda would say “Do. Or do not. There is no try.”

I find it fascinating how different backgrounds bring about different ways of looking at platform angle. As an over-educated engineer and former physics teacher, I see it mainly in terms of where the forces are applied and the direction of those forces with respect to the geometry. It appears that @LiquidFeet and some other ski instructors see it mainly in terms of body position and angulation with respect to the geometry. We all experience it (when skiing) the same way though.

 

[karlo]

see it mainly in terms of where the forces are applied and the direction of those forces with respect to the geometry

see it mainly in terms of body position and angulation with respect to the geometry.

How are those different. Assuming fore aft balance is good, what else besides body position and angulation affects forces, as they relate to platform angle?

Angulation
Inclination
Speed
Steepness

What else? What about the above can some of you expand on please?

IMO speed affects what edge angle is possible, but doesn’t directly relate to platform angle. Neither does edge angle. To me, you have whatever edge angle you choose, within limits of what gravity allows. After that, it’s only a matter of inclination and angulation that determines one’s platform angle.

 

[geepers]

I posted about platform angle in another thread the other day. Here's that post reformulated for this thread.

Platform angle measures the spatial relationship of the skier to the outside ski. It consists of two imaginary lines that meet at an angle. The first line extends across the surface of the ski from side to side. That line starts where the tipped ski's inside edge contacts hard snow - and extends to the other edge, the outside edge, of the ski. The second line starts at that same point where the tipped ski contacts hard snow - and travels up to the body's center of mass. The angle created by these two lines needs to be less-than-or-equal-to-90º for the ski to grip on hard snow. See the image by Bob Barnes that @geepers just posted above for a visual.

Platform angle is independent of edge angle. Low edge angle skis can cleanly grip the snow and produce pencil-thin tracks if appropriate platform angle is maintained (railroad tracks). The relationship of the body to the ski defines whether the ski will grip, not slip, and whether it will produce narrow tracks or wide skidded tracks. This assumes the skier does not rotate the skis and is balanced fore-aft over the skis.

What skiers actually need to know about platform angle is simple. If the ski is slipping/skidding even though it was tipped without being rotated and even though the skier is balanced fore-aft on the ski, the problem may be that the platform angle is too large. To reduce that angle, the skier can move the upper body farther out over the outside ski, or bring the outside ski closer up under the body. Either of these, or both together, will reduce the platform angle to enable grip.

Common skiing problems make it difficult to maintain a small enough platform angle.
----Leaning in/banking/bracing puts the body too far inside the turn. Angulate instead of leaning the shoulders into the turn.
----Hip-dumping puts the body too far inside the turn. Shorten the inside leg and roll its knee into the turn instead of dropping the hip.
----Pushing the outside ski to an edge puts the body too far inside the turn. Tip the skis without pushing on the outside ski by flexing the inside leg instead.
----Skiing square makes angulation more difficult, and lack of angulation puts the body too far inside the turn. Ski with separation and angulation instead.

Platform angle gets mixed up with edge angle. There are functional reasons for that. If the skier knows to increase edge angle by flexing the inside leg, that flexion can indirectly result in an effective platform angle. That's because flexing that inside leg keeps the inside foot/ski up under the body, which in turn discourages pushing the outside ski outward. Flexing that inside leg also discourages hip dumping since dropping the hip isn't being used to develop edge angle. And inside leg flexion is usually paired with angulation, not with banking, since leaning the whole body is not being used to create the edge angle. The resulting angulation moves the body farther out toward the outside ski. All of these reduce the platform angle. So three of the impediments to maintaining a small enough platform angle listed above can be indirectly eliminated by flexing that inside leg to get the edge angle. Skiers who know to use inside leg flexion for edge angles may not be thinking about adjusting platform angle to get and hold grip, but they are.

Nice post.

Something I may see somewhat differently is that inclination is not a bad thing. As long as there is sufficient angulation to maintain appropriate platform angle. But I may be reading too much into the words.

If the skis don’t hold, assuming sufficient edge sharpness, it’s because angulation was insufficient?

There's other issues that may result in lack of grip - fore/aft balance is a biggie.

I find it fascinating how different backgrounds bring about different ways of looking at platform angle. As an over-educated engineer and former physics teacher, I see it mainly in terms of where the forces are applied and the direction of those forces with respect to the geometry. It appears that @LiquidFeet and some other ski instructors see it mainly in terms of body position and angulation with respect to the geometry. We all experience it (when skiing) the same way though.

Well, I'm an engineer too and I see it purely as management of forces as a result of position of the body. Please share if there's another way to manipulate the position of the CoM so that the ski's edge angle is (slightly) more than the edge angle would need to be to balance gravitational and centripetal forces (for a given radius turn at a given speed) if we skiers were a point mass on a rigid pole perpendicularly mounted on the ski.

 

[François Pugh]

Forces and body positions, they are two things, but they go together; you can't change one without the changing the other. I naturally focus on manipulating the forces and angles; it's the way I think. Ski instructors, I observe, focus on what the skier needs to do with his/her body in order to manipulate the forces and angles. I guess, maybe, that's the habit of thought that ski instructors have.

 

[oldschoolskier]

Sorry I have to agree with @François Pugh, but then again engineering back ground.

 

[oldschoolskier]

If the skis don’t hold, assuming sufficient edge sharpness, it’s because angulation was insufficient?

Not necessarily, it could be poor technique preventing forces to be directed correctly.

Correct body position does not always mean correct/effective technique.

 

[karlo]

Forces and body positions, they are two things, but they go together; you can't change one without the changing the other. I naturally focus on manipulating the forces and angles; it's the way I think. Ski instructors, I observe, focus on what the skier needs to do with his/her body in order to manipulate the forces and angles. I guess, maybe, that's the habit of thought that ski instructors have.

Ski instructor: “Use the force.“

 

[karlo]

If the skis don’t hold, assuming sufficient edge sharpness, it’s because angulation was insufficient?

There's other issues that may result in lack of grip - fore/aft balance is a biggie.

Yes, but assuming for/aft balance is good...

For the engineers here, what I’m thinking is that, if it’s possible to land a Falcon with pin point accuracy, it should be possible to design and build a seated mono-ski, like those that parapalegics use, that automatically angulate, the rider controlling fore-aft balance of course.

Lower the volume of your earbuds or headphones.

 

[geepers]

Yes, but assuming for/aft balance is good...

For the engineers here, what I’m thinking is that, if it’s possible to land a Falcon with pin point accuracy, it should be possible to design and build a seated mono-ski, like those that parapalegics use, that automatically angulate, the rider controlling fore-aft balance of course.

Lower the volume of your earbuds or headphones.

 

[karlo]

Not saying there wouldn’t be some trial and error in developing a self-angulating sir ski. But, having looked at it more, seems like no problem angulating to achieve appropriate platform angle. See 0:35 of this

 

[geepers]

Not saying there wouldn’t be some trial and error in developing a self-angulating sir ski. But, having looked at it more, seems like no problem angulating to achieve appropriate platform angle. See 0:35 of this

The booster landing "learning" attempts was just for the laughs. I almost posted it elsewhere.

With the sit ski the ski is directly under the rider's CoM so there's a natural advantage for platform angle vs bipedal skiers who have more than 1/2 our body on one side of our outside ski's inside edge unless we angulate.