View previous topic | View next topic

How geese can fly thousands of miles with little effort

Page 1 of 1

Andrew420
1190540.  Tue May 03, 2016 5:31 pm Reply with quote

Imagine yourself driving along a motorway/highway at speed and you encounter a large lorrey/truck in the lane directly in front of you.

>>IF<< you decide to "tailgate" this large vehicle and you actually follow it at the very dangerous distance of less than twenty feet behind (more like ten feet), you will discover that there exists: a partial vacuum created directly behind the lorrey/truck and you can use this area of low air pressure to simply glide along behind the lorrey/truck with little or no effort on the part of your vehicle's engine.

Geese do something quite similar: they fly in a "V" formation, with the leader or their second calling the cadence of wing flaps. The lead goose, flying through the air, does all the work and the following geese get to enjoy a much easier flight because they are riding the lead goose's vortices and are, essentially, pulled along by the partial vacuum created by the flapping of the lead geese' wings...and the other geese in front of them...the effect is magnified as you go further back in the "V" formation.

When the goose in the lead grows weary, he or she falls back to the last place and their lead position is asssumed by their second.

Now, when the lead goose falls back, they usually do so by cutting immediately left or right and they ride/buffet the "wash" until they get to the back of the formation, where they will cut back into the "V".

"Wash" is what you encounter, as the driver of a car, when you are overtaking a lorrey/truck. The "wash" is the air which has been suddenly displaced by the sheer mass of the lorrey/truck and it forms as a wave of oncoming air resistance in the face of any and all vehicles which seek to overtake the lorrey/truck.

Once the front of your car has past the front of the lorrey/truck,
the effect [extra wind resistance] disappears behind you and your car then accellerates ahead of the lorrey/truck without you needing to apply the accelerator.

-it has been proven that JUST LIKE your car saving a fortune in fuel by tailgating a lorrey/truck and proceeding down the motorway with very little effort; geese do the very same thing, aerodynamically, to travell thousands of miles with little effort.

[-five points please ;) ]

 
14-11-2014
1190561.  Tue May 03, 2016 10:23 pm Reply with quote

Quote:
it has been proven that JUST LIKE your car saving a fortune in fuel by tailgating a lorrey/truck and proceeding down the motorway with very little effort; geese do the very same thing, aerodynamically, to travell thousands of miles with little effort.

Less effort? The Mythbusters have tested drafting too. On the road and in the air.

Perhaps it's more interesting that the lorry/truck, the leader, will drive faster too.

 
crissdee
1190577.  Wed May 04, 2016 2:35 am Reply with quote

When I was at college, a lot of the lads had 50cc mopeds. To make the most of the limited power they would "tailgate" the artics on the dual carriageway. One day, a lorry braked suddenly.............

The practice ceased overnight.

 
PDR
1190593.  Wed May 04, 2016 3:50 am Reply with quote

I think "little" effort is putting it a bit strongly. There is certainly a benefit, and this has been known & understood for many decades. If you do an academic search you'll find many papers, theses and dissertations on the subject, not to mention the reports of practical trials.

One of the issues for air use is that it doesn't just reduce the drag; it reduces the lift coefficient as well and this offsets the benefit. Not so much of an issue for birds, but aircraft on long-range cruise flights generally look to operate in a "sweet spot" of lift coefficient and mach number which produces the optimum fuel consumption, and this sweet spot is very small - to the point where long-range airliners will often "cruise climb" so that the lift coefficient remains the same for a given mach number as the fuel burns off and the weight reduces. So if you set up a close-formation "convoy" like the birds do only one of the aircraft can actually operate within its sweet spot because the conditions will be different for each of the others.

This is less true of "extended formation" convoys which are "wave-riding" so only the induced drag is reduced, but it's actually very hard to predict where the wave-riding positions will be and so station-keeping in the formation becomes a challenge.

A lot of work has been done on the benefits of running close-convoys of trucks, and recent announcements about running "driverless truck" trials are mainly concerned with this, the idea being that a convoy of a couple of dozen driverless trucks spaced only a couple of feet apart at constant speed well consume a lot less fuel and produce a lot less pollution (this is kinda how trains work). But the real challenge for this in the UK and Europe is that it needs motorways which actually allow long periods of constant-speed running; in the stop-start congestion that characterise most of the UK motorway network it delivers no benefit at all.

PDR

 
Jenny
1190766.  Wed May 04, 2016 3:43 pm Reply with quote

Close convoy driverless trucks sounds like a good idea. Maybe there could be some kind of special track for them to run on. Or maybe we could just use the rail network.

 
PDR
1190775.  Wed May 04, 2016 4:12 pm Reply with quote

Indeed. In fact I believe I mentioned that parallel...

:0)

PDR

 

Page 1 of 1

All times are GMT - 5 Hours


Display posts from previous:   

Search Search Forums

Powered by phpBB © 2001, 2002 phpBB Group