Heinkel Cars, Kabines and Cabin Scooters: Camping and Picnic Trailer

Here's something I finished during the Covid pandemic for my Heinkel Scooter: a single-wheeled trailer to tow my stuff. I had to cancel two big trips because of Covid. I'm not going anywhere this summer because of the pandemic, so I can take little picnicking, camping beer/food pickup or beach trips. It's based very loosely on an East German "Campi" design that my friend Werner in Germany built. Since I'm also a woodworker I chose to make the storage area out of wood, reminiscent of a "woody" station wagon or wooden boat.

Travel Trailer and Heinkel Tourist Scooter

13 Feet of Scooter and Trailer!

Trailer with access hatch

This was a very challenging project- almost every piece is curved, bent or angled. From now on right-angled woodworking will be boring!

The trailer weighs about 80 lbs and runs on a single 4.80x8 tire. I've added some pictures below and a description of how I made it.

Design:
My friend Werner gave me some detailed measurements of his trailer and I used them as a place to start. I started scouring the internet for design ideas and found a lot of videos, but this one in particular was really helpful: Single Wheeled Trailer. This gentleman provided good sources for the wheel and design for the U-joint.

Prototyping the metal frame of the Heinkel trailer

Learning:
I learned some new and improved metal and woodworking skills. My welding is much better. Here's the trailer hitch I built for the scooter, which lets me keep the rack and spare tire:

Trailer Hitch with U-Joint

It bolts directly into the frame of the scooter using the existing holes. I raised the rack by topping the existing spare tire mount bolts with coupling nuts, and covered that assembly with 7/8" black water supply tube, which I left slightly long to act like a lock washer when I bolted down the rack:

I also learned to better cut and rout channels in complex shapes. I had to build several helper jigs to get the curves and channels correct:

Various routed and curved custom shapes

I added a kickstand so the trailer could stand on it's own and not have the woodwork damaged, since a one wheel trailer is not stable:

Kickstand, based on the Heinkel Scooter Kickstand

Kickstand in the Up position with return spring and toe grab

Finishing:
The trailer is made of Ash and Okume, Ash was the first choice of car body makers in the US for wooden station wagons. It is light in color and very strong. I used Okume for the rest since it looks like mahogany, is waterproof and can bend. Okume's natural color is boring so I used a Walnut stain to darken it:

Staining the pieces

Example of the color contrast on the hatch

I finished it with 8 coats of spar urethane. Spar urethane is flexible and contains UV protection. I could have achieved a glass-like finish with a few more coats, but I was afraid the wood would end up looking like the cheap plastic imitations you see in car interiors. This level of finish highlights the woodgrain nicely.

Next Steps:
I just got my license plate. It is registered as a "homemade" trailer, costs $20 per year and is covered under my homeowner's insurance. The total length is over 13 feet so it is not as nimble as a regular scooter. I've gone up to 35 miles per hour in my test rides to determine how it reacts at faster speed. I'm learning how to load it to avoid swaying, and checking the welded joints to make sure they don't crack under stress.

I hope you like it. I've attached some other pictures of the build in progress below: