Failed segmented boattail experiment using drawer slides

[freebeard]

Wheelie bars?

[Cd]

Originally Posted by freebeard

Wheelie bars?

Lol - seriously not a bad idea except of the additional rolling resistance.
I thought of having a single small tail wheel.
It would go with the plane theme.

However, I'm just too O.C.D. over the additional rolling resistance.

As far as your pantograph idea, I remember you mentioned it when I started this project.

The problem is weight and cost.

I'll still look into it.

BTW, the drawer slides I was using had 24 " of travel, and I stacked one above the other, so that the first extended, and then the top one extended.
They are rated at 100 lbs + IIRC.

[freebeard]

The whole assembly wants to slide downward on the bumper, no matter how tight I have the ratchet strap.

Buy a scond bumper so you won't feel bad about drilling holes through this one?

[aerohead]

Originally Posted by Cd

This is a mock up of how the finished car was going to look :

From my vantage point, what you've envisioned could be one of the most significant contributions to road vehicle aerodynamics since the mid-1930s.
Depending on the belly, and cooling system, the car is clearly in Cd 0.15 territory or better.
Everyone at the FORUM ought to think of all we can to facilitate safe, zero-anxiety testing.
If you were closer, I'd take you up to the Lindsey Municipal Airport, west of Gainesville. There's an inactive runway where dedicated testing could be done, away from traffic and morons.
And Highway 82, which it sits astride, I've used for road testing without incident.
Good Barbecue too if you're into that. Or great German food in Muenster, further west.

[aerohead]

My greatest fear has always been shock-loading due to killer pot-holes, even on the interstate highways.
In engineering parlance, its 'jerk', which is an instantaneous acceleration.
If there isn't sufficient rigid triangulation in some tension member, spanning from the top of the car's rear, angled down to the tip of the extended stinger, if the car strikes some nasty road hazard, the car 'must' undergo a sudden change in position, however, if there's 'slop' in the structure, it can allow the tail to 'remain' where it 'was', because of its inertia and momentum. It's now become 'elastic'.
And if the stress or strain exceeds even one attachment point, anywhere along that pathway, the thing can begin to unravel and separate.
Sum of all fears!
Given that there are 'three' sections, there just needs to be some inelastic member ( maybe just section of woven steel cable ) which achieves a level of pre-tension ( preload ) as each nested section locks into it's fully-extended position.
The first main cavity will have to pickup and carry the load of the two traveling cavities.
After that, I don't see any major impediment.
Crosswind will be acting on a diminishing and rounded weathervane. The further the moment ( wind-induced torque ) is acting from the center of gravity, the smaller it's transverse aerodynamic footprint becomes.
It would be blowing on the pointed end of an ice cream cone.
You should have essentially zero rear lift. The pressure at the tip is equal to the forwards stagnation point, minus the skin-friction component associated with the turbulent boundary-layer.
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Your high conspicuity paint scheme will alert the un-anointed that your car is 'LONG" and don't hit it! (reminds me of Korean War-era US Sabre Jet fighters ).

[freebeard]

Tensegrity
Tensegrity, tensional integrity or floating compression is a structural principle based on a system of isolated components under compression inside a network of continuous tension, and arranged in such a way that the compressed members do not touch each other while the prestressed tensioned members delineate the system spatially. Wikipedia

Fuller experimented with collapsible tensergity domes in the 1950s. The design problem becomes to collapse a prolated sphere along it's longest axis.

en.wikipedia.org/wiki/Kinematics_of_the_cuboctahedron

https://en.wikipedia.org/wiki/Kinema..._cuboctahedron

Those four vertexes in the middle move in an X shape.

[Piwoslaw]

Fellow forumers, we need to coerce Cd to remove the word 'Failed' from the title of this thread.

Or just ask the mods, explaining it is misleading.:P

[Cd]

As far as keeping the structure all together when the vehicle hit a pothole, I planned to have each segment attached to the following structure by cables attached to the inner stricture
It would be allowed to flex , rather than have all the force transfered to one or two areas that could snap.
My only concern, is that the cables would tangle when the segments retracted.

BTW, I drove around the apartment driveway with the tail extended fully.* I tested it over a set of speedbumps.
The test went well, but I had to stop because I don't have lights hooked up.
The segments did not have any attachments to the following segment during the test.
* I retracted the tail around corners of coarse lol.

Regarding the sleekness of the design, I expect between .28 and .25 cD with the tail fully extended.

[kach22i]

Originally Posted by Cd

https://youtube.com/shorts/ZyWfZoQZKGI?feature=share

Awesome work, it's projects like this that keep me coming back to the forum all the time.

Kind of quirky that it actually sounds like drawers opening and closing.

[kach22i]

Originally Posted by Cd

https://youtube.com/shorts/_8jlq2eCInE?feature=share

Reminds me of something I've seen before.

Sigourney Weaver Alien Gif GIF
https://giphy.com/gifs/alien-sigourn...dYjwEQuR1J7dte