If The Profile Is Good For Depasrture Angle...
 

Could a double ended profile be better for approach angle?

As I understand it, the pressure build up at the nose enhances air attachment on the latter half.

If the pressure is not built up at the bow, it may not cling in the aft sections, and then it becomes detached, and therefore causes turbulence - right?

Good questions.

I think this has been reviewed before, but I'm blurry on the answer - sorry that I cannot be more definitive.

Your influencing factors:

1. Speed

2. Angle of attack (cross winds and turns)

3. Deceleration including abrupt braking.

The optimum shape might be influenced by one of the above or all of the above, don't you think?

Also the center of mass could be a weighted factor....haha, but seriously.

EDIT:

I once posted on aircraft canopy shapes (blisters) after some images Aerohead posted. That thread may contain more information, look it up.

double-end
 

The short answer is no.The template has the shortest low-drag nose which also respects SAE approach geometry.
Also,the template is at the 'sweet-spot',in the 'bucket' of the drag curve,with respect to surface drag and pressure drag.
If the body is any longer,or any shorter,the drag will be higher.
The other thing about the double-ended form is forward visibility.The windshield angle is so extreme,that we suffer light refraction through it,and internal reflections below it,such that you can't see out of the car.Hucho makes special mention of this problem in his text.

Challenge accepted:

https://ecomodder.com/forum/showthre...rag-28206.html

Thank you for finding it, that was a good thread.

Brings to mind a new question though; when a car is lowered so much and chin spoilered so much that it almost behaves like a surface blister, does the pressure wave change enough to warrant an optimized shape change?

That is to say, the lower you go, the more slope you need at the front?

index
http://www.highway99hotrods.com/Blis...140016_JPG.jpg

And in the same vein of thought; the higher you go the more important it is to curve the chin inward and not have an abrupt splitter-like "cut-off" that could cause turbulence below it.

Or are these two different phenomena?

[shrug] One is above the stagnation point, the other below.

This becomes true at transonic air speed.

I can see the symmetrical center profile lifting at speed.

As for the windshield, do away with all windows, put a pair of video cameras on a three axis swivel in a bubble atop the roof, and wear stereoscopic display Glasses. The cameras move with the driver's head.

To what point? [no pun]. The space in those pointy ends isn't really as usable as a blunter end.

To the end of lowering CD

What is the point of lowering the Cd? Top speed? Moving a volume of space through free air? Moving a volume of space down a traffic lane? Moving pianos or marbles?

Bragging rights?

High MPG transportation.

https://ecomodder.com/forum/member-f...e6244-gaps.jpg

It's better to convoy brick-shaped vehicles.

I don't need to pull that much weight. Interesting point, though.NASCAR teams have been doing that for a few years. (Makes for a dull race!)

pressure wave/slope
 

I'm not certain that I fully understand the question,but I'll throw this out.
*The bulbous nose,as on the Template is ideal.There's nothing you can do to lower the drag.All you're trying to do is provide for the approach angle and achieve attached flow.If you extend the nose further forward it won't improve flow attachment (you're already there),and the added surface friction will increase drag.With around 40mm of radius under the chin spoiler,you're golden.
*Ground clearance doesn't change the flow,other than the consideration that,you've got to have ground clearance around town so you don't tear the front and rear end off the car,or high center in the middle.
*On a perfectly smooth highway,with no road kill laying in the lane,you could drop the car 'into the weeds' and get closer to the drag minimum,or just leave the clearance alone and do full wheel fairings.
*The only pressure you're concerned with is that produced by separation.With the template,there is no separation and there's no lift.The high pressure at the nose and tail cancels any Bernoulli lift due to flow acceleration.

lowering
 

It won't lower a thing.Really! It will add drag.

It is obvious that the profile is optimized for passing through air at a certain airspeed. If the airspeed is doubled, would the profile need to be stretched horizontally in the direction of travel to prevent laminar flow separation? If the profile were applied to a taller, or lower vehicle, would it need to be stretched, or shortened to maintain attachment?

Reread Permalink #6.

https://ecomodder.com/forum/member-f...1264438870.jpg

airspeed
 

The body's drag coefficient is constant between 20-mph and 250-mph.Above that,compressability effects begin to come into play as shockwave-dependent transonic flow begins to initiate.
The length of the body is a function of height and all proportions remain the same.(just as if you put it in a copy machine and enlarged or shrunk it)
You could 'stretch' the body simply by adding to the very center,and pay for the added skin friction,as limousines are done.

Thank you.

I have to give this some more thought.

I somehow believed there was a great deal of lift with the Aero-template.

The airfoil myth
The airfoil myth
http://warp.povusers.org/grrr/images..._incorrect.png
http://warp.povusers.org/grrr/images...il_correct.png

http://warp.povusers.org/grrr/images/flat_wing.png
I'm not sure how mainstream the blog above is, perhaps some sort of radical or heretic?

The Template is simply an edge case for Mair:

https://ecomodder.com/forum/member-f...1215134663.jpg

...a 'stretch' of zero length.

lift
 

All wing sections have an angle of attack of zero lift.It is referred to as the 'bottom of the 'bucket.'' A look at Abbott and von Doenhoff's book on wing sections will illustrate it.
Half-bodies of revolution are similar to wing sections when viewed from the side,however,in no way resemble a wing in plan view (looking from the top down).There's no 'span.'
Since a streamlined body of revolution is streamlined,the rearward stagnation pressure is nearly identical to the forward stagnation pressure,with only a loss in energy,equal to what is lost with skin friction,which is the absolute minimum with the template,on account of it's specific fineness ratio.
Lift IS produced over the maximum cross-section on top,but is cancelled at the nose and tail.As long as angle of attack is not introduced.
At 135-mph,Spirit's nose produces negative 30-pounds (downforce),and the tail produces positive 22-pounds of (lift).For a 4,200-pound vehicle this lift is 'meaningless At legal speeds lift is unmeasureable.
We can't use the lift data for the baby template car due to how it was fashioned to the load cells but according to Kamm and Fachsenfeld, these half-bodies are incapable of producing lift.
Now if you get the car sideways at high speed,that's another matter all together!
I used to have graphics to share from Photobucket,but I've lost the use of all of them.

I always think of a comparison to the wing tip, sticking out of the ground.

Like this:

https://o.aolcdn.com/images/dims3/GL...-lsr-crash.jpg

Could have been mitigated/solved with a fence or two running longitudinally over the roof, which this car did not have:

http://vtec.academy/wp-content/uploa...521.jpg?ver=30

My understanding of lift from body shape partly comes from an early childhood fascination with the so-called NASA Lifting Body aircraft of the mid-1960's thru mid-1970's.

Lifting body
https://en.wikipedia.org/wiki/Lifting_body
https://upload.wikimedia.org/wikiped...tingBodies.jpg
These "aircraft" were falling rocks (gliders) at a high angle of attack using air-ground compression to land. However the later X-24B flew at powered level flight.

technology of lifting bodies
http://www.century-of-flight.net/new...mages18/20.jpg
http://www.century-of-flight.net/new...mages18/17.jpg
http://www.century-of-flight.net/new...mages18/19.gif

I'm taking Aerohead at his word, but I need time to integrate his information with other things that I'm familiar with. Being familiar may not be the same as understanding, but I'm always trying to improve.

lifting bodies
 

the lifting bodies evolved from a 'nose' form with a portion slashed away in a diagonal chop,which produced delta-wing-like attached vortices for generating lift.It was discovered by accident around 1958.
They came in real 'hot',with very high stall speeds,since they didn't have a lot of wing area.
The Space Shuttle was a variation on the design,and in some landing footage,you can discern the over-wing vortices as they touch down.Landings were computer-controlled and in the event of a system failure,chase plane pilots could talk the Shuttle pilots down,as is done with the U-2 and Camaro-based spotter,so visibility wasn't as big an issue.
The Concorde utilized this also,and had to incorporate the drop-nose for takeoff and landing,as the angle-of-attack required for lift would have otherwise made visibility from the cockpit impossible.

As seen in the opening scene of Six Million Dollar Man

https://www.youtube.com/watch?v=3jvGJhJINlc
It drops like a steerable rock.

Cool, I've never seen the unique canopy in operation before.

Similar video, but with highly informative audio:
https://www.youtube.com/watch?v=50dDWT48b9M

Aerohead, I've never read a description of lift before on these craft as "delta-wing-like attached vortices for generating lift". Reminds me of F-117 Nighthawk Stealth Fighter flight/lift descriptions. Thank you for the description.

These "over-wing vortices" are something I'd like to see a wind tunnel video of, I may have to look that up one day.

Such a video may answer why the early lifting bodies were upside down foil shapes, and the latter ones just the opposite with curve on top not the bottom. Part of the mystery that my brain has never been able to fully process. The key must be these over the body/wing vortices combined with the ridiculous angle of attack.

EDIT: Freebird soundtrack, and you know this bird cannot change aaaaaaaaaa change............

At the 6:00 mark you can see the landing speed is similar to the Douglas Skyray chase plane's stall speed.

https://www.youtube.com/watch?v=D4iZw3ui5Uw

Good footage otherwise, much of it seen already in the other two videos but very crisp.

IIRRC, lifting bodies were more aligned with kasper theory of attached tip votrices, but could be wrong. They were attempting to make spacecraft recovery better without deploying external devices like chutes.

Also Facetmobile. https://en.m.wikipedia.org/wiki/Wainfan_Facetmobile

[waves lighter in air]

The compound curved skin should be an inspiration to ecomodders everywhere.

Nothing you can't accomplish with sanding, putty, and fabric overlay. 1/32 to 1/16 aircraft ply is really malleable after it sat in your swimmimg pool overnight.

Those old timers were skilled with wood structure

You could never get there with coroplast. :)

https://ecomodder.com/forum/member-f...hes-dinghy.jpg

Howard Hughes made these the same way as the 'Spruce' Goose. aerohead is a fan of reinforced concrete forms.

You are saying the skins are built up in layers? Coroplast does heat soften

https://i.imgur.com/K4KOu.jpg

The dinghy and this display case are under the wing of the Spruce Goose in the Evergreen museum (last I checked). I don't know the technique, possibly vacuum bagging like carbon fiber. The result is essentially compound curved plywood. No sanding or putty.

compound
 

The fuselage of the DeHavilland Mosquito was formed from streamed strips of wood and adhesive,laid up inside a concrete mold, with a balloon at the center,which forced all the loose plies against the mold until the glue went off.It made a beautiful,lightweight,composite,compound skin.Very cool!

Clingenpeel told me how they made the Hercules wings, but I was young and didnt pay close attention. I do recall they were built, installed then covered. I suspected a combo of vacuum bagging and sandbags. Really hard to seal the underside.

In OZ they made them on the outside of concrete plugs, then strapped the wood down.