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Old 02-14-2014, 06:03 PM   #1 (permalink)
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Canopy drag

I expanded and modified a graphic for canopy drag published in Goro Tamai's "THE LEADING EDGE".
What's unique about the data concerns 'reversed' bodies.Since 1974 I've seen less than a handful of images depicting drag measurements of 'reversed' teardrops.They're dramatic in that the significance of losing the boat tail really shows up no matter how slick the nose is.
All seven images,when viewed from above (plan view)are teardrops,with aft-body plan-taper to a point.
All Cds are approximations,as they vary as a function of where they're positioned on a body,and the quality of the boundary layer at any given location.The numbers were generated in MIT's wind tunnel.

Here is a drag table for aircraft canopies from Hoener's book,'AERODYNAMIC DRAG',

Here are some armaments enclosures:

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Last edited by aerohead; 02-19-2014 at 07:05 PM.. Reason: add 2nd Hoerner table
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Old 02-14-2014, 06:54 PM   #2 (permalink)
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Hmmm, what does the clear advantage Shape 1 enjoys over Shapes 2 and 3 say about the unimportance of the leading edge shape?
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Old 02-14-2014, 07:27 PM   #3 (permalink)
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advantage

Quote:
Originally Posted by Frank Lee View Post
Hmmm, what does the clear advantage Shape 1 enjoys over Shapes 2 and 3 say about the unimportance of the leading edge shape?
The numbers are what they are.What the automakers will say,including Hucho,is that we'd never be able to see out of it due to internal reflections.With safety vehicles fore and aft on a race course we might be able to suffer through,but for a daily driver it looks like a non-starter.
If we try to use the shape for a body,it's impossibly long and with no ramp clearance.It can't be altered in any way without sacrificing the 0.045.
Oskar Teitgens got Cd 0.08 out of a self-propelled passenger rail car in 1933 or so with a body kinda like this.
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Old 02-14-2014, 09:13 PM   #4 (permalink)
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I was a little bugged that the only image of this railcar was a tiny drawing (second Image). So I did some digging and found this patent (first Image) from 1932 which does not mention Oskar. I believe its one and the same though, only the nose appears to be missing in side view to show the underworkings of the engine.
Patent US2051073 - Rail car - Google Patents

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Old 02-15-2014, 04:22 PM   #5 (permalink)
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Quote:
Originally Posted by aerohead View Post
All seven images,when viewed from above (plan view)are teardrops,with aft-body plan-taper to a point.
A 3D illustration of these shapes would be interesting, be it unnatural for some.

Quote:
Originally Posted by Frank Lee View Post
Hmmm, what does the clear advantage Shape 1 enjoys over Shapes 2 and 3 say about the unimportance of the leading edge shape?
Unimportance?

I don't want the aero-template shape which is without a canopy to be confused with these studies, do you? I just want to take a moment to clarify and avoid false or inaccurate transference of old quotes to these unique conditions.

The only previous discussions I recall on canopies have dealt with the length ratio being doubled from the aero-template 5:1 to an elongated 10:1 (length/width).

There have been many warnings by Aerohead about intersecting planes and their unpredictability on the final outcome regarding canopies and wheel bulges/blisters.

I'm going to assume no fillet or rounded corners with these canopies illustrated , plus they are on a flat plane or deck - similar to some solar cars.

Symmetrical blisters are certainly in the minority, how long has this data been out there?

Example below of a WWII cannon blister (like a canopy on a flat plane).
Spitfire Vc by Ian Robertson (Tamiya 1/48)


Below, very large plane fillets and closer to being symmetrical than the cannon blister above.

XB-17 blister turret (pre-WWII)
http://commons.wikimedia.org/wiki/Fi...ter_turret.jpg


A slightly older blister than the other two above - from a PBY seaplane.
http://www.warbirdphotographs.com/WBP/f2k1.htm


The F-16 glass canopy and nose blister (early/mid 1970's) are different from each other. The glass being more symmetrical, the small blister half of our aero-template?
http://commons.wikimedia.org/wiki/Fi...e_20110813.jpg


All of the F-18 canopy (below) and multiple blisters (early/mid 1970's) are close to symmetrical. Click on link for greater detail. Many of these blisters could have been applied to later variants of the craft, thereby illustrating a knowledge of systematical blisters as being more aerodynamic.
http://texasmilitaryaviationjournal....liance_13.html


Later jet aircraft just don't have blisters, not very stealthy. I'm sure there are exceptions and retrofitted equipment which may lead to evidence of an information base.
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Old 02-22-2014, 04:05 PM   #6 (permalink)
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fillets / how long

The drag reported is for the images as depicted,and the only canopy with 'fillets' is the top image with its reflexed contour.The solar teams might place the canopy within the 1st 30% of body length where the boundary layer was minimal in thickness and they'd have a shot at laminar boundary layer there.
The fillet would address 'junction' drag and associated hook vortices which can form at this intersection between canopy and body.If you look at the canopy for the 1957 MG EX 181 Cd 0.12 land speed record car,you'll notice the fillets at the base of the canopy to address the hook-vortice junction drag.
Junction drag is addressed by Tamai in a different section and he cites Hoerner's work in this area.
----------------------------------------------------------------------------The time period would be from before 1995,when Tamai and team mates were conducting wind tunnel tests to determine their MIT plan of attack on drag.
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Old 07-07-2014, 04:51 PM   #7 (permalink)
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Is this right? It is the first profile shape with a NACA 0040 plan.
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Old 07-07-2014, 06:58 PM   #8 (permalink)
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Old 07-07-2014, 07:15 PM   #9 (permalink)
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Old 07-08-2014, 03:01 PM   #10 (permalink)
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...gradually perturb the air, followed by gradually un-perturbing the air.

...ease into, ease out of...

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