you said better. better is better. the human engine has a fixed amount of power. energy is not coming from anywhere else. are you saying it’s better for some of that energy (obviously not all :rolleyes: ) to be used to flex the frame rather than turn the cranks? maybe because different muscles are used, at different points in the motion? and that the return of that energy is as efficient as just turning the wheel?

Well, I used the example of a throwing device that allows you to accelerate your arm more quickly than a rigid one because it decreases peak torque, which is sometimes beyond the ability of human muscles. So we're back to why people buy and like oval chainrings - distributes peak torque across a greater amount of the pedal stroke. Since people aren't electric motors, "energy is not energy", it is whatever we can put out in different body positions. Again - no one makes oval gears to address the limitations of electric motors.

The second part you are implying is a problem is the fact that I'm suggesting frame flex would be a good way to do that. And that's probably because flex is a dirty word in cycling. But in engineering it is well understood that springs are some of the most efficient devices for storing and returning energy. Steel, ti and carbon frames are composed of excellent spring materials, and the fact that all of this flexing can happen without the addition of extra linkages, bearings and hardware means that there aren't additional energy losses due to friction.

And as I mentioned, bike flex provides the same sort of pedaling smoothing as oval chainrings, but has perfect feedback since it isn't prescheduled like a machined oval chainring is. Bike flex happens instantaneously and at exactly the same level as the pedaling input force.

So while you are trying to make it sound stupid that very efficient spring flex might be better than less efficient pedaling motion - that is exactly what I'm saying. Maybe trying to get a person to emulate a motor on rigid mount is a little stupid.

I'm not a smart man. But I know what Google is.
I typed the phrase "cyclical addition of forces" into my favorite Internet sort engine. The top 2 useful results are linked here:


https://eng.libretexts.org/Bookshelv...ector_Addition

https://www.physicsclassroom.com/cla...tion-of-Forces

What do they mean? Well, they mean that at the right combination of inputs to a system, a new output can be achieved in a reliable & predictable manner.

As to all this talk of professional this, professional that...I have no doubt that the bikes ridden by professionals are optimized for the 350 watts at 85-95 rpm that professional tend to ride at. And also true, there is nothing to be gained and a lot to be lost for even letting the mention of the term "planing" to be heard outside the confines of the engineers desk. Why even mention it at all? None of us, the bike buying public, have the strength to take advantage of such a property even if we wanted to. Those that can? They have their bikes at the track or on the course with huge race winning smiles on their faces. Simply happy with the engineering of their race winning bike however it got them there.

The old mantra of "stiffer is always faster" has fallen by the wayside with better, more comprehensive modeling. Curious.

I see no reason that so called "planing" should be dismissed out of hand. Bikes suffer all kinds of oscillating forces that do not necessarily "cancel out." Whose to say they can not be additive as well? Indeed, the speed wobble shimmies is one such example.

These "planing" frames are still available from Radio Flyer. There must be something to it. I don't see any pedals on that thing.

Bikes are already "inchworming" because they are driven by two pistons that have short power strokes.

I've taught both undergrads and graduates. I tell them that as undergrads, we teach them the simple models; as graduates, we teach them the full-on, detailed, obsessive models; and as professors we spend the rest of our careers figuring out when we have to do the detailed full-on exhaustive and exhausting thing and when we can get away with the simple thing.

I've had some conversations with Mark and Jim about Jan's experiments. Jim said something along the lines of, "I've tried." Mark was pretty skeptical that field tests could be used to estimate some of the things that Jan says they can. I think they have less influence on Jan's experiments and write-ups than that excerpt suggests.

[Edited to add:] That may have sounded harsher than I intended. In my first post in this thread, I said that Jan has interesting ideas, lots of them, but doesn't do good experiments; and that I give him credit for interesting ideas but not dispositive proof. There's a place in this world for people who have interesting ideas, even if not all of them pan out. I'm not very imaginative so I like it when people with imagination contribute. The world would be duller without them.

Carbon fiber! In the bat world, they use the term "composite".

So why did this work?

https://cimg3.ibsrv.net/gimg/bikefor...795c30e14f.jpg

By Nick Webb. - Flickr: Oscar Pistorius., CC BY 2.0, https://commons.wikimedia.org/w/inde...curid=21029911

A tennis racquet benefits from the stiff frame supporting the trampoline effect of the strings. String tension is adjustable to tune the desired trampoline effect. Hollow baseball/softball bats (aluminum, composite) also tune trampoline effect for performance. To reduce injuries, there are limits on exit velocities. Manufacturers control this with adjustment of the trampoline effect.

In addition to the additional length for an effectively longer arm (and an additional hinge point in the system), the ball-chucker benefits from the unloading of stored energy in the flex of the shaft, similar to a hockey stick.

My comments were about a chuck-it, not prosthetic limbs. They are different.

This is true, but it misses the point. In this particular case, a stiff carbon fiber racquet frame makes the racquet more efficient, but this doesn't mean every system benefits from higher stiffness. Likewise, you can't conclude all systems benefit from more flexibility, just because some other simple systems benefit from more flexibility. You have to analyze the system of interest itself, and not blindly make analogies with simple systems that are inherently different.

Yep. In physics, the reasons you teach simple models to undergrads are 1) simple models usually have closed-form solutions 2) simple models sometimes more clearly convey the basic underlying principles and 3) undergrads rarely possess the mathematical tools required to solve complex models. As you mentioned, once you acquire the ability to handle complex models, the game is determining when you need the complex model and when you can get away with a simple model.

The disappointing thing about the Chuck-it is that it's only half as complex as an atlatl

How so? There seems to be a lot of similarities, although my example is probably more relevant.

You said the only difference was that it was a limb extension. This one is a limb replacement, yet he was disqualified because it gave a mechanical advantage. Why would that be? I am genuinely stumped.

*Groan*

For me, the complexity of the atlatl is in the name. Is it "At-Lattle" or "Attle-Attle"?

Worth the cost of entry on this thread, right there.

I see you and raise you:

Yeah, but Nirvana was from Seattle.

If you honestly cannot see the difference in how a chuck-it and prosthetic legs work, I can't help you.

Have you ever used one to throw a tennis ball to a dog (the chuck it, not Oscar's leg)?

A safe trampoline? :foo:

It is much less elastic. You jump on it and it absorbs a lot of the energy.

I didn’t say “FTP.” I said “power,” because that’s what Jan Heine said. I’m quoting Heine directly because I’m trying to take his idea seriously and to respond to the specific parts that I think are wrong. Other people in the thread have said FTP, but I’m not one of them. You’re saying that this claim of a 12% power increase is an anecdote about a single rider, and that’s great! I agree completely! But Jan Heine says that this anecdote proves planing, a phenomenon he defines as allowing riders to produce more power, is real. Meanwhile, another of the interlocutors in this thread has been lambasting me for rejecting this isolated data point. I get that you all aren’t coordinating, but no one here seems to agree on terms or even to be defending Jan’s actual definition of planing, instead selecting a definition that makes sense to the person writing the post. So I’ll lay out the three major categories of planing people seem to be arguing for.

1. Planing is real, strong form. This is Jan Heine’s idea that a bike that planes allows the rider to produce significantly more power, over essentially all durations. This is the idea I think is basically unsupportable given everything we know about physiology and material properties.

2. Planing is real, weak form. This is the idea that frame flex is beneficial and a flexible bike can be faster than a stiffer bike due to factors like a stiff bike causing the tires to skip about. I think this idea is very plausible but the range of circumstances where a bike could have too much drivetrain stiffness is probably pretty narrow. British Cycling has been brought up in this context, and since British Cycling is mostly concerned with track bikes, which have very short chainstays and very skinny tires, that makes sense to me. I don’t really believe that any bikes being used in professional road racing are losing power due to excessive stiffness. With 28 and 30 mm tires now standardized in pro racing, I don’t think a bike in the style of the French constructeurs can plausibly be faster than a carbon fiber superbike on this basis.

3. Not even planing. This is just about the ineffable and romantic qualities of a bike with a really magical ride quality. It’s the feeling of floating over the road while still feeling connected to it, of the mix of comfort and liveliness that the best steel and titanium frames are renowned for. This is definitely a thing and bikes like this feel great irrespective of how fast they are. They’re a joy to ride. It’s just not at all what Jan Heine means by “planing.”

It seems like you’re arguing point number 2, and as I said I don’t really have much of a beef with it. I just a) think the real world circumstances where a bike could be too stiff in the driveline are very rare and b) don’t really think this is the key idea of “planing” as described by Jan Heine.