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Thread: Planing

  1. #41
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    Default Re: Planing

    We’re all good Zank, but thanks.

    Re: racing cars, etc. – with such hi frequency power delivery I don’t see an analogous situation as it relates to propulsion. Bicycles have low frequency power delivery with very distinct times of power, vs. no power. I think that’s what opens the door to the possibility of power smoothing and max muscle fiber tension reduction from strain energy flow. Ultimately I think it resolves to some sort of spring/mass/inertial system with different spring constants (the frame), different masses (bike + rider) and different forcing functions (rider power delivery). As I noted earlier – the flexural modes that could influence the drivetrain aren’t as intuitively obvious as for, say, a golf club. If you're a serious golfer or fisherperson, you're probably aware of the degree to which strain energy affects performance. If not, try out the stiffest club or rod you can find.

    I mentally resolve the main triangle as a single beam (a spring that flexes in all three Cartesian planes); BB at on end, handlebars at the other. Rider, out of the saddle, honks down on the power and you can imagine the deflection, a deviation ‘twixt chainwheel and the frame that increases with increasing force by the rider, with the chain being the constraint. You've experienced it. It’s a simplified notion, but it allows me to imagine a way in which power pulses and deflections, at a particular frequency for a particular system comprised of all of those parts, could apply the strain energy back into the chain in a way that would reduce peak chain tension while broadening the crank-angle/period of delivery. For the same amount of energy (and power delivery), lower max chain tension but delivered over a longer period of time. Seems a physically reasonable proposition to me, and if it does exist it would have to alter the power delivery characteristics in ways that should be beneficial.

    Imagine an ancient one lung IC engine with something like one power cycle every second, connected to a stretchless cable, hauling a boulder up in the air. The cable is going to see high peak tensions corresponding to the power cycles. Now stick a spring in-between the rock and cable, and ignore the harmonics that would probably cause havoc (or else give the air a meaningful viscosity); intuitively you can tell that the maximum loads on the cable (our cyclist’s legs) would be much reduced. Intuitively, the efficiency with which the boulder was hauled up into the air would have to be more efficient since energy isn’t being wasted on constantly accelerating the rock after each non-power cycle. Spring systems were used for power smoothing in industrial drive applications like this back when motors were crude.

    But: It’s a spring that’s operating over a relatively small range of deflections, so one would expect small results, nothing enormously obvious.

    I played lots of paddle ball, with a (essentially non deforming) wooden paddle, a long time ago. When I switched to racquet ball I wasn't any stronger by by gawd the ball went a hell of a lot faster. It was hugely obvious, and totally down to the strain energy of the strings and racquet acting on the ball.

  2. #42
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    Default Re: Planing

    Quote Originally Posted by Jonathan View Post
    I'd be curious to know if similar theories have been proposed and sorted for other performance vehicles. I'm particularly thinking sailboats, but wonder about motorcycles and racing cars too.
    For not quite the same reasons, fins for Formula* windsurfing boards which are 70 cm long (yes, they look like a small sword and will cut open a watermelon accordingly) were found to be much faster if not quite as stiff. It's a rather complicated explanation so I won't bore the non-windsurfing public - it involves twist and bend. But the idea is that the windsurfer will plane earlier and go faster.

    Riding in flat water with steady wind the fin can have a very constant load, but as the water gets rougher the load on the fin begins to pulse with periods of relatively constant loads followed by low and high loa d spikes. The overall stiffness, flex and twist pattern will affect the load on the fin and the load on the rider; a rider using a very stiff fin may get tired early and thus start to sail slower.
    http://www.kashyfins.com/resources/K...-Brief-7_0.pdf

    The best fins are shaped by hand by just a few select shapers out of carbon fiber; and very, very expensive: $800+ and a wait time of months.

    So, yeah, there is that "planing"



    484658.jpg
     

  3. #43
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    Default Re: Planing

    Quote Originally Posted by Jonathan View Post
    I'd be curious to know if similar theories have been proposed and sorted for other performance vehicles. I'm particularly thinking sailboats, but wonder about motorcycles and racing cars too.
    At the high end (at least) of motorcycle racing, the suspension is not very active as the bikes get leaned over (lean angles close to 60 degrees are common) and the teams/manufacturers have worked a lot to incorporate chassis flex tailored to particular riders' feel preferences to keep the tires in contact with the pavement at these lean angles.

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    Default Re: Planing

    Quote Originally Posted by Mark Kelly View Post
    As the state of instrumentation improves we will probably see the application of good empirical evidence to this theory. My money says that the measurments will show that some energy is lost and some is returned. Debate will continue.

    * As I see it, the theory is that strain energy is stored in frame deformation and returned to the drivetrain and that this can be beneficial to the rider in certain circumstances.
    it's not clear to me how you could prove or disprove this with instrumentation. Interestingly enough, I first heard this theory back in the '70s. I put it in the same category as the theory that kept racers from using derailleurs for a long time because they caused the chainline to not be straight.

    One thing that seems to escape notice in most discussions about frames is that the headset is a hinge with very little stiffness. Bike design is such that stiffness is added through head angle and trail. A sideways force on the pedals causes this hinge to rotate. This is the dominating element of just about anything to do with bike performance and dynamics. And Jan's preferred low-trail forks provide a lower restoring force.
     

  5. #45
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    Default Re: Planing

    ok, here goes. i've not read every word in this thread but saw enough to make some comments. i think i understand that some of you are associating Jans likes with a bike that is torsionally lacking stiffness? lets look at this simplified answer form my desk.

    i'm gonna suggest there are 3 primary... ah, directions of bending forces on the complete bicycle as it may pertain to this discussion.

    ---- vertical: lets call it Z axis, earth. the mass of the combined rider and bike, up and down over lumps and bumps of all frequencies/sizes. might be associated with comfort. and other stuff

    ---- lateral: bending stiffness in X axis(perpendicular to BB spindle) and Y axis(parallel top BB spindle). my feeling is the biggest contributor to this bending is pedaling forces.

    ---- torsion: twisting from end to end. wheels not maintaining parallel.

    i think most are not separating lateral from torsion and assuming a torsion noodle is what Jan desires. the OPs own comments regarding less fatigue on leg muscles suggests less stiffness in the lateral X axis is desired.

    Jan reviewed a frame i built some years back that in my opinion was as torsionally stiff as I could do at the time while lacking in lateral stiffness. as I recall Jan loved the bike. so did i.

    i'm gonna leave the muscle fatigue behind as I have no theory or evidence but i'll suggest that in a road bike, regardless of discipline, high torsional stiffness and lower lateral wins my vote every time.

    i think thats what Jan really wants regardless of how it is being communicated.

    make the bike as soft as you want just keep those wheel parallel and in plane!

    flame on!
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    Default Re: Planing

    I'm open to new data points and expanded discussion. Are elite level rowing shells built for rower weight or strength beyond just needing more displacement? And are we mainly just regurgitating the same arguments we made back in 2007 or whenever? Has there been any new work on this by Jan or others.

    I'm surprised Jan is not here, I though he had an alarm that rang when his name is mentioned somewhere.

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    Default Re: Planing

    This is a kind of thing that is very hard to measure, but really easy to get a theoretical upper bound of. To know the ammount of energy saved by the frame we should know how much it deflects.
    Knowing this is not as hard as it may seem. Just fix your rear wheel from moving and stand on one of your pedals. I doubt the pedal deflects more than 5mm or so. And lets say that you push with 100kg(sounds like a tough sprint to me =). Well, the amount of energy is 0.005m*100kg*10N/kg /2 = 2.5J. This is only about 2-3 joules of energy that your frame saves per each crank rotation. If you go 120rpm/min this is only 5Watts.
    Only 5Watts. And these are not 5W that you lose or get for free. These are 5W by which the system smoothes your power output given that you output around 1000kW. This is nothing.
    Evgeniy Vodolazskiy (Eugene for English-speaking =)

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    Quote Originally Posted by Too Tall View Post
    Ok Jan, it is safe to swim in our water again.
    Shake it off,
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  9. #49
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    Default Re: Planing

    Quote Originally Posted by waterlaz View Post
    This is a kind of thing that is very hard to measure, but really easy to get a theoretical upper bound of. To know the ammount of energy saved by the frame we should know how much it deflects.
    Knowing this is not as hard as it may seem. Just fix your rear wheel from moving and stand on one of your pedals. I doubt the pedal deflects more than 5mm or so. And lets say that you push with 100kg(sounds like a tough sprint to me =). Well, the amount of energy is 0.005m*100kg*10N/kg /2 = 2.5J. This is only about 2-3 joules of energy that your frame saves per each crank rotation. If you go 120rpm/min this is only 5Watts.
    Only 5Watts. And these are not 5W that you lose or get for free. These are 5W by which the system smoothes your power output given that you output around 1000kW. This is nothing.
    That's real good thinking Evgeniy. A couple of things come to mind.

    1) I just clamped a piece of wood into my shop vise, snugged the head tube of my bike (9/6 conventional tubing) up to it and applied what a scale told me was 100 kg. The HT didn't move detectably. With both hands occupied it was pretty fiddly and I couldn't measure pedal spindle movement but it was a lot more than 5mm and, due to the frameI flexing, it wasn't in a straight line. I'm estimating 20mm between the end points. The curved path travelled was greater but I take your larger point.

    2) This may not be a good analog, but in the world of variable frequency drives seemingly minor motor lead differences can cause extremely short duration, high transient voltages such that a difference of 2x between two otherwise identical systems can exist. That can be the difference between a long lived system and one that fails in a short time. In a similar vein, might remarkably small differences in frame flex have a surprising effect on maximum, instantaneous muscle fiber stresses and therefore fatigue.

  10. #50
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    Default Re: Planing

    I think the mind of the rider is one of the largest variables. And with that you can't dismiss knowing you're on a xxx color bike, or you have xxx wheels, or knowing xxx built it. For pure performance I agree with Craig G., stiffness is king. For me and all the others out on recreational rides it's not the same.
     

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    Default Re: Planing

    Quote Originally Posted by waterlaz View Post
    I doubt the pedal deflects more than 5mm or so. And lets say that you push with 100kg(sounds like a tough sprint to me =). Well, the amount of energy is 0.005m*100kg*10N/kg /2 = 2.5J.
    Two problems with that analysis but they work in opposite directions so the result is near enough.

    Firstly, the formula you used is incorrect, the strain energy is 1/2 k. x^2 where k is the stiffness and x is the displacement.

    Your value of stiffness is probably too high: this source has frame stiffness clustering between 50 and 100 N/mm at the BB, your estimate used a value of 200.

    Using 1 kN at the pedal and 100 N/mm stiffness, x is 10 mm and the resultant energy stored is 1/2* 1 *10^5 * (1x 10^-2)^2 = 5J per stroke.

    Using 50N/mm, the result is 10J per stroke.

    Your conclusion is valid: it's a small percentage of total effort.
     

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    Default Re: Planing

    Quote Originally Posted by Mark Kelly View Post
    Firstly, the formula you used is incorrect, the strain energy is 1/2 k. x^2 where k is the stiffness and x is the displacement.
    Sure, E = 1/2 k x^2, but the force F necessary to deflect by x is F = kx. Therefore, E = 1/2 k x x = 1/2 F x.
    Evgeniy Vodolazskiy (Eugene for English-speaking =)

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    Default Re: Planing

    The instrumentation has been in use and available for ages. Ten years ago we were hooking riders up to a cart that monitored specific muscle activity and intensity. Each muscle was displayed as a graph and numerically. This data combined with an SRM would tell me how rider position (scoot up or back in the saddle or heels up vs down) during hard tempo (for instance) would resolve in terms of efficiency.

    Take that and a bike that has been wired for strain and we are "there".

    (laughing) I can't be far off on this WAG but who the eff has the $$ and time to pull it off????

    Quote Originally Posted by EricKeller View Post
    it's not clear to me how you could prove or disprove this with instrumentation. Interestingly enough, I first heard this theory back in the '70s. I put it in the same category as the theory that kept racers from using derailleurs for a long time because they caused the chainline to not be straight.

    One thing that seems to escape notice in most discussions about frames is that the headset is a hinge with very little stiffness. Bike design is such that stiffness is added through head angle and trail. A sideways force on the pedals causes this hinge to rotate. This is the dominating element of just about anything to do with bike performance and dynamics. And Jan's preferred low-trail forks provide a lower restoring force.

  14. #54
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    Default Re: Planing

    What about the rider kickassness factor? Measurable?
    T.o.m. K.o.h.l.

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    Default Re: Planing

    T.o.m. K.o.h.l.

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    Default Re: Planing

    Quote Originally Posted by EricKeller View Post
    it's not clear to me how you could prove or disprove this with instrumentation.
    With a power meter ride at XXX watts and see what your speed and HR are ?
    I think BQ did something like this road surfaces/tire interactions.
     

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    Default Re: Planing

    ^^^ So many variables in that though. Change any one component in the chain from rider through to road surface and you are going to get a diiferent outcome. The cost, both time and money, would be huge for a few watts advantage, if any.

    Other than sticking with a frame setup that feels good you are chasing something that IMO just does not matter.
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    Default Re: Planing

    Quote Originally Posted by waterlaz View Post
    This is only about 2-3 joules of energy that your frame saves per each crank rotation.
    What makes you think this energy is simply saved and not dissipated? Somehow it can't store energy forever and I don't see how a frame would have any mean of giving back that energy to propel the crank or wheel. I know that in magazines so called journalist try to make us think that this energy is stored then redelivered to the rear wheel at some point but it is simply not true or I can't think of a way it could be true. Did someone check the temperatures variations of a frame ? Could it really be measured ?

    My opinion is that a rider may find a very stiff/uncomfortable bike enjoyable when he is killing it but it will just become unbearable when a rider is tired. But it is just about comfort, not about the way the frame react at specific power outputs / rpms, etc. Do you react the same to the bad roads and potholes in the first 10km and after a century ? I don't. It's not about planing, energy transfers, oscillations or things like that.
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    Default Re: Planing

    I think my Hampsten planed today but it might have been the whiskey.
    steve cortez

    FNG

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    Default Re: Planing

    Quote Originally Posted by waterlaz View Post
    Sure, E = 1/2 k x^2, but the force F necessary to deflect by x is F = kx. Therefore, E = 1/2 k x x = 1/2 F x.
    My bad, I completely missed the "/2" in your calculation. As you were.
     

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