Re: Fw: Dinosaurs and birds

[don ohmes <d_ohmes@yahoo.com>]

Yeah, nobody argues that humans or any biped are going to double their speed... 
what is your point there? Are you implying I did?

Care to hazard a guess as to how close is "close"? 1% of max running speed? 2%? 
3%? Mike says it is zero...


Care to decree what the level of minimum advantage is? 

----- Original Message ----
From: David Marjanovic <david.marjanovic@gmx.at>
To: DML <dinosaur@usc.edu>
Sent: Sunday, April 15, 2007 6:24:22 AM
Subject: Re: Fw: Dinosaurs and birds

> To sum: in theory, a biped that can sprint at a given velocity can exceed 
> that velocity, w/out falling down, by applying appropriate thrust to the 
> upper body. This is because the stride frequency at maximum unassisted 
> running speed is NOT the maximum stride frequency attainable by the hind 
> legs.

But almost.

Try it yourself: lie down on your back and make running motions. You'll soon 
find the speed at which you can move your legs is limited even in the 
absence of any resistance (other than drag in air).

In other words, when the wings produce too much thrust, the legs can't keep 
up, and the animal either flies or trips over its own feet, inevitably. Make 
a thought experiment: if you were tied to a car on a highway, could you stay 
upright?

> The maximum speed a biped can generate through unassisted use of the hind 
> limbs does NOT constitute some magical theoretical barrier that cannot be 
> exceeded.

I'd bet money it's very close to that barrier, which is not magic at all but 
depends on length and mass of the hindlimbs in total and the arrangement and 
size of the muscles that move them.

> =======================================
> 2). Total power relative to forward motion is not coming from the hind 
> limbs in this situation, yet evidently there is a term in your equation 
> that "...requires higher hind limb power (that we've already limited)". 
> [???] Why is that? In fact, relative to the theoretical situation as 
> posited, NO forward thrust is required from the hind limbs... nor is any 
> aerodynamic lift required, as the legs serve to counteract gravity. Note, 
> that can be done mechanically, w/out thrust generation other than that 
> required to pull a given leg forward into the front of the stride cycle...
> =======================================

...fast enough, wherein the rub lies.