Full-boat-tail trailer with gap-fillers for Toyota T-100 pickup

[slowmover]

Gonna think of this as the Skyking dilemma, or, "how tall will be my pickup truck and fifth wheel combination". One giant aero template in height. And, length, ha! Full-time living quarters sure presents some challenges. But the road is clear for cargo configurations!

Thanks, again. (I imagine I'll be posting those two words in the future as well).

.

[drmiller100]

make it as tall as you want, but it can only be 104 inches wide.

which means your tail only has to be about 6 feet long to get most of the advantages.

[climbinghalfdome]

Nice!! I can't wait to try this.
Kevin

[aerohead]

Originally Posted by Sven7

Okay, so can we say turbulence acts similarly to wake? Are they different words for the same thing?

I didn't look close enough to recognize PRK Nice job- I thought it was out of a textbook. It's nice to see that (if I'm reading this right) as long as the trailer form fits inside the "template", it will reduce drag, without factoring in RR and such.

'Wake' is short for 'turbulent wake' or 'wake turbulence' and many use the two words interchangeably.
Whatever we want to call it,it is the region of separated flow behind the vehicle which possesses a 'base pressure' which is equal to the pressure at the point of separation.
A proper boat tail allows for a deceleration and pressure rise of the flow while preventing the separation.
A full boat tail allows for zero separation and maximum pressure recovery,swapping static pressure for velocity(dynamic)pressure.
The truly low drag vehicle has zero separation and full pressure regain and no kinetic energy is lost to eddies and turbulence which cannot be converted back to static pressure.
-------------------------------------------------------------------------
From the table which has the bus dragging the boat-tailed railroad tail car,you can see that with the 'trailer' at about the same length as the bus,the drag for the bus/trailer is almost the same as for the solo bus; Cd 0.51 vs Cd 0.50.
As the trailer is shortened from about 12-meters in length,surface friction drag begins to fall and the drag of the bus/trailer is actually LESS than for the bus by itself.
When all the trailer is erased with exception to the boat tail itself,the Cd 0.05 surface friction of the tail car has been eliminated completely,leaving only 0.05 for the tail,its own friction,and any remnant of base pressure acting upon it.
------------------------------------------------------------------------
So actually,you could pull a rather long trailer and still have lower overall drag than of the 'tug' by itself.
The drag minimum does occur with just the tail,and it offers the greatest promise in a range-extender trailer application.

[aerohead]

I've added four new tables up at at permalink #248 on page 25 which will keep the images together for easier comparison.

[aerohead]

I've added 5 more pages of tables for Cd comparisons.
The data was presented by General Motors researchers in 1962 in the SAE Paper identified and I've put it in pictorial form based on their tabular descriptions.
The second image on page-1 reflects photograph from tuft-testing for the chamfered-nose trailer van which I imposed upon the line drawing of the semi-trailer.
The data reflect Cd values as they are impacted by tractor or trailer leading edge radii,or lack thereof,and the effect of tractor height and gaps.
Again,I'm putting them on page-25 at permalink#248.

[eco_generator]

So leading edge is vastly important if you are starting with a completely flat face...

[KamperBob]

Originally Posted by eco_generator

So leading edge is vastly important if you are starting with a completely flat face...

That is my understanding.

Unlike most passenger cars and trucks today that early 60s semi tractor trailer example had high initial Cd (0.88) due to poor onset. I expect quantitative analysis (CFD, wind tunnel smoke) would show a lot of bow splash from initially stingy/small leading edge radii and turbulence from a large gap between the tractor and trailer. Cd reduced a lot by addressing those problem areas with modest treatments.

Originally Posted by aerohead

After initial gains the difference between modest and massive rounding of trailer front edges (shadowed by the tractor) provided marginal return.

Originally Posted by aerohead

Radical front redesign of the tractor was needed to further reduce the Cd to 0.46.

Originally Posted by aerohead

Much better ... and yet still worse than most passenger vehicles. because the large flat rear of the trailer acts like a drag chute. Hoerner showed this. Clean onset creates good attachment. Which also increases base drag. And thereby limits return on front investment. A boat tail is all the more important for a holistic solution and ultimate aero slippery.

Phil, thanks again for sharing all this research!

[aerohead]

Originally Posted by eco_generator

So leading edge is vastly important if you are starting with a completely flat face...

I really respect Wolf Hucho and all he is doing, so bear this in mind,when I say that unless you read every chapter of his books,you may get stuck with a 'rule' which is actually contextual and could lead to losses.
In the sections on automobiles Hucho discounts leading edge radii,essentially saying that at some degree of rounding,with further rounding you'll see no further appreciable gain in drag reduction.
In his sections on commercial vehicles,he presents drag tables which reflect the variation in Cd as a function of yaw.And it's clearly apparent that a full convex hemispherical nose has the lowest drag when in a crosswind environment.
And crosswind is so prevalent in some geographical locations that crosswind effects should be considered as significant enough to engineer for.
If you want to see some minimums,check out the U.S.Mk 46,and Mk 50 torpedo,and also the Whitehead Motofides A244 torpedo.You'll be shocked at the bluntness of their noses but these fish can really haul -ss through the water and for quite some range.
Then compare them to he Alpha I and Akula class Soviet nuclear submarines.These were the world's fastest subs up until maybe the new Virginia class.

[eco_generator]

I get what you are saying. I knew the general rule that "rear aero is more important", but did not know that a flat face up front is a giant hindrance. Good to know. Thanks for all the info you have researched so far!