Solution to boat tail dragging On Ramps

[kach22i]

I know this thread has been scrubbed, but it brought up some interesting issues.

Explain to me again how this design below can stray from the 2.8 degree rule.

Aptera Comes Back from The Dead | Design Engine


Just eyeballing underbody looks to be plus or minus 15 degree average.

Bottom of rear wheel faring almost an 30 degree tangent.

[freebeard]

...2.8 degree rule...

It's what you get from reducing to a single parameter a complex, dynamic 3-dimensional situation. Another example is the cabin of the GM EV-1.

[kach22i]

Originally Posted by freebeard

It's what you get from reducing to a single parameter a complex, dynamic 3-dimensional situation. Another example is the cabin of the GM EV-1.

Good example because the greenhouse canopy is very 3D as well.

EV1


https://en.wikipedia.org/wiki/General_Motors_EV1

To boost efficiency, the EV1 possessed a very low drag coefficient of Cd=0.19 and a drag area of CdA=3.95 sq ft (0.367 m2).[1][60]

[aerohead]

Originally Posted by kach22i

I know this thread has been scrubbed, but it brought up some interesting issues.

Explain to me again how this design below can stray from the 2.8 degree rule.

Aptera Comes Back from The Dead | Design Engine


Just eyeballing underbody looks to be plus or minus 15 degree average.

Bottom of rear wheel faring almost an 30 degree tangent.

It's the 1947 NACA 2-D numerical/Morelli shape,which is a special structure.
As a reflexed airfoil in ground proximity it could do Cd 0.05,compared to Cd 0.08 for a streamline half-body.
As more of a 'car' body,Morelli could get it to Cd 0.171 with the small truncation,but it swelled to Cd 0.35 when wheels were added.
Only wheel integration,via wheel fairings got a viable passenger car variant to Cd 0.205.
As the Aptera,at the X-Prize competition she was Cd 0.15(?),requiring the optimized (high) ground clearance.
I'll never know why it failed to attract more of a following.And with wheels,I'm uncertain that it has any drag advantage compared to more 'conventional' low drag forms.
The cost of producing a DOT-rated, laminated safety glass windshield alone,may have have scared people off.Hucho discusses this issue in his book.

[kach22i]

Originally Posted by aerohead

It's the 1947 NACA 2-D numerical/Morelli shape,which is a special structure..............

I'll never know why it failed to attract more of a following.

Thank you for the information.

I think that shape has a strong following in this forum if that counts for anything.

[BamZipPow]

If yer gonna stay with a single wheel, non-swivelling wheel, you could go with the back end of a scooter as part of yer initial build. Just rip the motor and transmission off and you have the suspension and wheel setup to weld the rest of the connecting pieces!

Here's a scooter fer $50!
https://houston.craigslist.org/mcy/d...476136536.html

Heck...you could even use the back end of a kid's bicycle as yer initial build as a test.

[freebeard]

I'll never know why it failed to attract more of a following.
vs
And with wheels,I'm uncertain that it has any drag advantage compared to more 'conventional' low drag forms.

What are your thoughts on the plus/minus you found with the reflex tail on Babby Template at Darko?

[aerohead]

Originally Posted by freebeard

What are your thoughts on the plus/minus you found with the reflex tail on Babby Template at Darko?

*Since I was trying to reflect a 'real',DOT-friendly,street-legal body,intentionally mutilated to allow for wide-spaced tail lamps and license plate,I knew, going into the project, that I'd have to settle for whatever turned up.
*During the smoke-flow session,even though she was at sub-critical Reynolds number,she exhibited zero reverse flow,indicating a robust turbulent boundary layer for the entire length of the aft-body,with fully-attached flow.That couldn't have been better!
*I'm not comfortable at all with the DARKO lift measurements due to how Baby's ground-board was attached to only a single set of load cell uprights.Since Spirit does not produce lift,I'm confident,that properly measured,Baby won't generate lift as well.Technically,it's impossible for a streamline half-body to produce lift,as long as angle-of-attack is not introduced.The dynamic pressure on the nose,along with the high pressure over the tail,cancels any lift-due-to camber (Bernoulli-effect).They sit at the bottom of the drag 'bucket',with minimum drag,and zero lift.
*Since she came in at an averaged Cd 0.1209,when the actual frontal area was introduced into the raw data,I can't really ask for better.Had she had more plan-taper,and come to a knife-edge,as Cambridge University's Eco Racer (CUER),we'd probably have seen Cd 0.11 or better.
*Enlarged to match the frontal area of,and replacing the body, of a 1994 Honda Accord,the Honda would see an MPG increase on the highway,from 32,to 100 simply by changing the shape.You can read this right off Honda R&D's test data, published by the Japanese Society of Automotive Engineers.
*I suspect,that over time,as artificial intelligence improves,and CFD is further refined,we may discover a few new tweaks for car bodies;but in the meantime,the evidence suggests that we can take Jaray's 1922 aero technology and produce 100-mpg I.C.E vehicles left and right.EVs will do even better,since they've got the equivalent of an adiabatic engine,getting 3X the mpg of the typical ICE car,on a Btu basis.
*Personally,I couldn't be more pleased with the Baby project.I didn't invent a single thing.All I had to do,was do the 'monkey see,monkey do' routine.Mike Turner's one of the few people smart enough to connect all the dots,and just mimic what aerodynamic devotees have advocated for nearly a hundred years now.

[freebeard]

Made me look: Mike Turner = Basjoos.

just mimic what aerodynamic devotees have advocated for nearly a hundred years now.

Tropfenwagen for the win. I look for the edge cases. One example is this offroad vehicle shaped like a dolphins head:



Granted it needs wheel pants, but wouldn't the reverse tumblehome produce a jet of air down the sides?

[aerohead]

Originally Posted by freebeard

Made me look: Mike Turner = Basjoos.


Tropfenwagen for the win. I look for the edge cases. One example is this offroad vehicle shaped like a dolphins head:



Granted it needs wheel pants, but wouldn't the reverse tumblehome produce a jet of air down the sides?

It's hard to know without actually being with it.
'seems like the hard edge,over the roof might cause separation,precluding the formation of a jet,but otherwise I can see what you're talking about.That side flow would be captured in there like a fence.
Texas Tech Alumni, Scott Funderburk, might caution us to be wary of vortice formation off those hard edges.During his stint on Project Tailwind,he experienced high-drag,attached,longitudinal vortices wherever hard intersections were present.I suspect that NASA saw the same thing on Project Shoebox,their modified Ford Econoline.(nature abhors right-angles)