[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

[Fwd: nostrils & dynamic ram pressure]



This was sent on to the list with Jame's permission

James R. Cunningham wrote:
> snipped
> 
> > I've been wondering if it developed because of the "bow wave' that a
> > bird or plane or other flying object develops in the front.  You
> > wouldn't put in-take valves in the absolute front of a plane unless you
> > have a processing area to handle the high impact air, right?
> 
> Hi Betty,
> When I'm not piddling with pterosaurs, I do the same with induction
> systems for air racing.  At first impression, I didn't think dynamic
> pressure would be high enough to matter in bird or pterosaurs
> respiration, but your post made me decide to look.  The fastest extended
> duration flight I'm aware of was a desperation effort by a male whooper
> swan designated JAP, who held an average airspeed of 60 mph (ground
> speed roughly 19 mph) for a bit over 4 hours in an effort to make the
> southwest coast of Iceland against gale winds (as an aside, his top
> speed is about 62 mph, and there is at least one female a couple of mph
> faster than he).
> 
> I didn't go back to check the temperature and barometric pressure for
> that day, but at this low airspeed, in terms of overpressure percentage,
> it won't make too much difference.  I've assumed he was flying at a TAS
> of 60 mph, 20 feet above the ocean, and with a standard atmosphere.
> 
> Under these conditions, for hypothetical nostrils on the front of the
> snout, facing directly forward, he would generate an impact pressure of
> 9.204 psf (0.0639 psi) or about 0.4% overpressure.  His recovery
> efficiency would probably be 80-85%, so optimistically using 90% (yeah,
> and I believe in the tooth fairy too), he would have recovered 8.28 psf
> (0.058 psi), still only about 0.4% overpressure, roughly 1/8" Hg.  So,
> for most birds, bats, and pterosaurs, I doubt that dynamic ram pressure
> drove the position of the nostrils (this may not hold true for peregrine
> falcons).
> 
> > Whatever the face is made of, whether beak or bone or a combination
> > even, it seems to me that the make up won't affect the major silhoette
> > much.  Pterasaurs seem to share the same facial layout as modern birds
> > and they used bone.  Birds use a combination of bone and beak.  I think
> > it's an example of convergent evolution.  (we still are avoiding
> > bats-any species that has a member that can take it's chin, wrap it up
> > over it's head and look through the 'eyeholes' in it's chin is just
> > plain wierd)
> >
> > So the nostrils may have moved as flight became more important to these
> > animals.  Better flying capabilities=nostrils to the aft of the leading
> > edge.
> 
> Maybe the more important effect was shortening the length of the
> breathing passages to reduce head losses (friction, no pun
> intended--well, maybe) due to the length of the passages.  I haven't
> checked required oxygen consumption for JAP at maximum exertion, and
> don't know if he had the capability of mouth breathing or not, or if he
> needed to.
> 
> > So maybe birds were ALL lousy flyers like Archie when they
> > started out.
> 
> I wonder how bad he/she really was?
> 
>                         All the best,
>                                 Jim Cunningham

----------------the followup from James after requesting permission to
post to the list.....

> can I post this to the list-pretty please with sugar on it?
> -Betty

Sure, if you think anyone'd be interested.  Do you want me to check on
the date of the event and use better numbers for the temperature and air
pressure?  They would still be just approximations, because the weather
chart wasn't quite current for that part of the flight.  I was also
guessing on the altitude, but whoopers often fly low to get a ground
effect boost, and he was quite desperate so would most likely have been 
low to minimise the headwind and pick up some help from ground effect
(above wave height though).  He was on his way from Scotland, and it has
been estimated that he made landfall with about an hour and a half fuel
reserve(fat).  If I do redo the numbers, it won't change the results
much.  Whatever you decide is fine with me.      JimC