10-01-2013, 09:06 AM
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#601 (permalink)
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Thanks for that, I still need to play with this equation a bit more.
I've been reading a variety of things from Semi-Truck aero through to Belbouth design for engine air intakes, but one thing that struck a chord was rocket nozzle theory.
A perfect rocket nozzle will have maximum efficiency when gass departing is at the same pressure as the surrounding atmosphere, if it is higher it is wasted energy, when it is lower pressure it creates drag.
From this, in an abstract way I started to look at template theory as an inverted rocket nozzle, the ultimate goal is to leave the air behind the vehicle completely stationary, as if the vehicle had never been there.
This equation with the kick in the tail may well be in the vicinity, the rate of change in angle is ever decreasing and then reverses at the end so departure angle at the tail tip is 0, this goes in line with having 0 velocity and ambient pressure at that point.
Although most of us will never build a full perfect boattail, but understanding what one is will help us to build an effective Kammback or trailer canopy.
We know that perfection lies in the vicinity of the paramaters aerohead has provided, 2.5:1 total ratio, 1.78:1 tail ratio, 22-23° max angle etc., this has been proven experimentally numerous times, so this is the ballpark we need to play in. I think the final equation will incorporate natural constants of growth and decay and be completly logical when we find out what it is, till then keep discussing and debating to get ourselves closer.
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10-03-2013, 04:56 PM
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#602 (permalink)
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never been there
Quote:
Originally Posted by Tesla
Thanks for that, I still need to play with this equation a bit more.
I've been reading a variety of things from Semi-Truck aero through to Belbouth design for engine air intakes, but one thing that struck a chord was rocket nozzle theory.
A perfect rocket nozzle will have maximum efficiency when gass departing is at the same pressure as the surrounding atmosphere, if it is higher it is wasted energy, when it is lower pressure it creates drag.
From this, in an abstract way I started to look at template theory as an inverted rocket nozzle, the ultimate goal is to leave the air behind the vehicle completely stationary, as if the vehicle had never been there.
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That's it in a nutshell.
If you string-line the streamline half body you'll notice that the pathway length of the tail is twice that of the forebody.
Which suggests that the deceleration ramp necessary for attached flow must provide an aerodynamic residence time over the aft-body which is twice the dwell time as that over the nose.
It's the premise for the area rule/sectional density.
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10-14-2013, 10:20 PM
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#603 (permalink)
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10-14-2013, 10:38 PM
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#605 (permalink)
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If the "smoke" is coming from the right, are we to believe that the folks doing the test thought the "aerofoil" would be better with the pointed end into the wind?????
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10-14-2013, 11:07 PM
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#606 (permalink)
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I'm sure they put both models in both ways just to see what would happen.
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10-15-2013, 04:00 PM
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#607 (permalink)
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Schl'o'rwagen backwards
Quote:
Originally Posted by kach22i
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It may be intentional,but the Schl'o'rwagen model is backwards in the tunnel.
Ooops! I should have scrolled down first.Obviously everyone sees the same thing.
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Last edited by aerohead; 10-15-2013 at 04:13 PM..
Reason: add oops!
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10-15-2013, 04:15 PM
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#608 (permalink)
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'67 Lotus Europa
Did they publish a Cd for the Lotus CFD modeling? The car was originally reported at Cd 0.29.
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10-15-2013, 04:42 PM
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#609 (permalink)
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Quote:
Originally Posted by aerohead
Did they publish a Cd for the Lotus CFD modeling? The car was originally reported at Cd 0.29.
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I did not see it at first glance, but it might be buried in there somewhere.
Overlay-image004_zpsd67536fb.jpg Photo by kach22i | Photobucket
One of the more interesting aero-template overlay's I've done to date.
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10-26-2013, 04:00 PM
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#610 (permalink)
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1967 Lotus
Quote:
Originally Posted by kach22i
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I believe Colin Chapman is responsible for the Europa.There are stories about him being strapped to the outside of a Lotus while it was driven so he could observe the airflow (presumably with a tuft wand) over the cars body.
He's also known for his low mass construction.
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