[Xist]

Your post is definitely shorter than many I have made, but I need to get back to staying in grad school, so I asked Gemini to summarize #1:

The Goal:

Improve fuel efficiency (currently 26 MPG at 62 MPH) on a 450-mile daily bread delivery route, saving on $58 daily fuel costs.
The driver wants to implement a folding "trailer tail" on their Sprinter van.
Challenges:

Frequent cargo access (9 stops) prevents a fixed boat tail.
Difficulty visualizing and designing the folding mechanism for the trailer tail.
Limited metalworking resources, leading to a plan to use marine-grade plywood.
Adapting a trailer tail design to a van's tapered rear profile.
Addressing potential gaps between the van's body and the trailer tail.
Figuring out the proper angle for the tail (12-15 degrees?).
Needing to keep the doors able to open, and lock into the open position.
Proposed Solution:

Construct a folding trailer tail from 3/8-inch marine-grade plywood.
Use existing hinge holes on the van's doors, possibly reinforced with metal stock and piano hinges.
Utilize all-thread and clevis ends for movable connections.
Address door opening limitations with cargo trailer hardware or modified magnetic door holders.
Consider vortex generators before the tail.
Key Questions:

How to design and build the folding and locking mechanism?
Is marine-grade plywood suitable?
How to adapt the design to the van's tapered rear profile?
How to minimize the impact of gaps between the van and the tail?
Is 12-15 degrees the optimal angle?
Are vortex generators beneficial?

#6

Key Points:

Door Folding Necessity:
The user folds the van's rear doors flat against the sides for space efficiency at delivery stops, especially in tight parking situations.
Simply opening the doors 90 degrees or having a fixed boat tail would obstruct roadways and sidewalks.
Parallel Parking Challenges:
A fixed boat tail would significantly hinder parallel parking due to increased vehicle length.
This reinforces the need for a foldable design.
Van Size:
The user primarily uses a longer Sprinter van for increased cargo capacity, making deliveries more efficient.
Alternative Aerodynamic System:
The user discovered a "utility aerodynamic tail 2" system, which involves a small ramp-like structure at the rear of the vehicle.
The user is unsure how this ramp reduces drag, but the company claims it improves aerodynamics.
The user is considering this as a potentially simpler alternative to a full trailer tail.
The user is skeptical of the ramp system, due to lack of use, and the proven benifits of a trailer tail.
Picture Reference:
The user mentions providing a picture of the "utility aerodynamic tail 2" system.

and #7

Alternative Vehicle Considerations:

Volkswagen Jetta Station Wagon with Trailer:
The user considered using their Jetta, which achieves up to 53 MPG unloaded, to tow a 6x12 enclosed trailer.
They acknowledge uncertainties about the trailer's weight and the impact on fuel efficiency when towing.
They need to calculate the weight of the bread cargo.
The Jetta currently needs a head gasket repair and a trailer hitch installation.
There are also concerns about the Jetta's towing capacity in the USA, as opposed to European models.
Minivan:
The user's minivan, which achieves 24 MPG unloaded, is deemed unsuitable as towing would further decrease fuel efficiency, making it less efficient than the Sprinter van.
Other Vehicles:
The user struggles to identify other vehicles that would offer competitive fuel efficiency.
Sprinter Van Advantage:
The user already owns the Sprinter van, which simplifies the situation.
Key Points:

The user is actively trying to find the most fuel-efficient solution.
The Jetta with a trailer is the most promising alternative, but it involves significant modifications and uncertainties.
The user is aware of the convenience of using the Sprinter van that they already own.
The user is trying to find a balance between fuel efficiency and practicality

Would heavy-duty drawer slides work for extending the tail? Hopefully, sheet rubber could help seal the gap.
Members on here used to experiment with conveyor belts.
The point about the gaps on the corners of trailer tails is interesting.
It shouldn't have been too difficult to create fold-down flaps to seal the gaps.
What about a trailer tail on your trailer?

I worked for a bakery 10 years ago and talked about delivering bread in my Forester--after I replaced the head gasket.