Closable NACA Duct for the DF

After noticing how much more air is passed by the Milan’s small NACA duct than the DF’s, I took a long look at the larger duct on the DF. One of the main differences was the depth of the ducts. The floor of DF’s duct seemed to rise so that there was a section of the duct that was very shallow. My guess is that this reduced area was causing some turbulence which reduced the air flow. I came up with this deeper duct. I also added an extension to the duct to feed the air closer to the rider. The air flow was improved greatly by these pieces.

I showed these changes to my friend Doug (the gentleman who sold me the Milan SL). He thought that it would be nice to make the duct closable with a flush flap of some sort. There are 3D printed NACA ducts sold in Germany for the Milan that have a closable flap. However, these NACA ducts won’t work directly on the DF due to the flat shape of the Milan’s top panel vs the curvy, recessed shape of the DF’s access panel.

I took Doug’s suggestion as a challenge and this is what I came up with. I first laid up a new NACA duct and extension duct as shown above. Then I laid up 2 new DF access panels – one to house the NACA duct shown above. The other panel was used as the donor for the flap. The flap needed to have the same curvature as the duct panel in order to perfectly fill the opening when closed. Extensions were added to the tip and trailing edge of the flap to allow it to lie flush with the top of the duct panel. The tip extension of the flap inserts into a loose slot in the front of the NACA duct to form a sort of hinge. All of the pieces in their rough, unpainted form are shown below.

To operate the flap, I needed a mechanism to push it up flush with the panel and down to touch the floor of the duct. The solution that I came up with was a simple stick screwed to a carbon fiber clevis (not shown) on the bottom of the flap and protruding through the floor of the duct. I 3D printed a piece to attach to the bottom of the duct to provide a rigid slot for the stick to ride in. The stick could easily be reached by the rider. I used a small piece of 5mm bungee attached to the stick to force it and the flap up and back. To lower the flap, the stick just needed to be pulled down. The friction caused by the bungee pulling the stick back against the 3D printed slot holds the flap in the down position. If needed, I can grind several notches in the stick to hold it more firmly in some in between positions. Below you can see the stick exiting the plastic slot attachment and the model of that slot attachment.

So how did it turn out? It works surprisingly well. I replaced the wooden stick with a nicer carbon fiber piece. I added a couple of very thin magnets to the bottom side of the panel and to the rear flange of the flap to locate the flap more precisely when being closed. Was it worth the trouble and complexity? Maybe. For the most part, I just ride with an open duct. So it would be a rare occasion that I’d want to be able to open and close the flap. That said… it was a fun exercise.

Here are some photos of the “finished” duct panel.

Milan Hood Version 3

The second version of my Milan hood was pretty successful. However, it still had a small problem that I should have addressed in an earlier version. Since I barely fit in the Milan SL, my knees can touch the inside surface of the knee bumps from time to time. Over a long ride, this can get a bit irritating. So I decided to make one more version of my hood with taller knee bumps.

Rather than build a new plug, I decided to modify the previous (V2) plug by adding more volume to its knee bumps. To do this, I laid up some knee bumps from the V2 mold and grafted them on to the V2 plug. Here is the progression of cutting and shaping the bumps.

Here you see the V3 plug, set up with flanges, before making the new mold. This time around I decided to incorporate the pesky leading edge lip into the main mold rather than as a separate mold and part as I had done on the previous 2 molds.

It’s difficult to notice the enhanced knee humps visually on the V3 hood. After all the work, I gained about 3/4″ of extra clearance for my knees.

Another New Hood For the Milan SL

After completing the new aero hood for the Milan SL, I began taking a more critical look at the way it fits. You’d think that I would have been more tuned into the fit as I was making the plug, but it didn’t really strike me until I was photographing the finished part installed on the Milan.

There is a large gap between the trailing edge of the hood and the head fairing on the main body. This gap is there in the stock hood that mine is based on. But, it just didn’t look right to me.

I thought about modifying the actual hood to close that gap. But that would leave me with a one-off hood that couldn’t easily be reproduced. So I decided to make another plug, mold and part to close the gap.

To do this, I made a fiberglass copy of my aero hood from my mold. Since this would end up being my new plug, it made sense to use the much cheaper fiberglass materials rather than carbon fiber. I then cut an approximately 180 deg slit around the base of the visor area. I then taped this sliced hood onto the Milan with the trailing edge taped down to the head fairing and the leading edge to its normal location on the front area of the body. This opened that slit along the base of the visor area. By filling that gap with layers of fiberglass and body filler, I was able to produce the plug, mold and hood with the proper gap along the trailing edge.

Compare the gap on the trailing edge of the old hood to that of the new hood shown below…

During a short shakedown run, I noticed that the airflow from the front NACA duct was reduced from what was produced by the NACA duct on the previous hood. The NACA ducts are identical and positioned in the same place on the hood. My hunch is that the smaller gap at the trailing edge of the hood is restricting air exiting the cockpit. I may try to improve the air flow out of the cockpit by adding an exit duct to the low pressure area of the top of the hood similar to the duct on my aero hood for the DF.

New Hood for the Milan SL

I’ve been thinking about getting a replacement for the stock hood/manhole cover for my Milan SL. I’ve always thought that it was a bit clunky looking. Also, I wondered if it couldn’t have been made a little bit more aerodynamic. Also, there are some pretty large gaps between the sides of the hood and the main body. There is a beautiful new hood from Velomobile World that looks much nicer aesthetically and more efficient aerodynamically. Unfortunately, they don’t seem to be available for sale at this time. I’ll just have to wait to get one when they’re available. In the meantime, I decided to make my own hood.

The goals for my hood were to improve the aerodynamics, improve the aesthetics and if possible, provide a little more head space so that I can fit with a helmet. In making my own hood, I didn’t want to modify or damage my stock hood and manhole cover. They’re very hard to come by. Also, I didn’t want to make any modifications to the Milan that would prevent me from using the stock parts in the future. The photo on the left below shows the stock hood and cover. The photoshopped image on the right below shows the changes I had in mind.

I made molds of the stock hood and manhole cover so that I could make copies that could be modified as a starting point for the pattern or plug. I made those copies, then joined them together to form a single part. To change the angle and shape of the visor area, I blended a piece from my DF hood mold (shown in orange below).

There is another small issue with the stock manhole that has always bothered me. The leading edge of the manhole cover of the Canadian Milan was extended forward to overlap with the body. This causes the cover to no longer remain flush with the body. I decided to remove this overlap and fit the cover to be flush with the body (as is the case with the European Milans).

Progress on the plug.

Once the plug was in decent shape, I made the main mold. I also made a small mold for the lip of the leading edge of the cover to fit in the gutter of the body. Neither mold is shown. Shown below is the front lip that fits into the gutter of the body. Also shown is the carbon fiber hook used with the stock bungee hold down.

I built a NACA duct, similar to the stock duct, by first sculpting it in clay, then making a female mold and from that a male mold. I constructed the duct (on the right) using the male mold (on the left) below.

Here’s the first hood from my mold. I used the same type of simple magnet-Lexan visor as I used on my DF hood. I painted it in RAL 9010 Pure White which is the same white as used by most European velomobile manufacturers. It surprisingly matched the white gelcoat of the Canadian Milan pretty well.

Some shots of the new hood side by side with the stock setup.

Some photos from the first ride with the new hood.

Some later photos of the hood…

Front & Back Polaroid Cube Holder

I had a tough time finding a good place to mount my front and rear facing Polaroid Cube cameras on the Milan SL so I came up with this temporary back to back camera mount. I’ll use this until I can come up with something better. This mount is attached to the left side window. Here are some views of the design in Fusion 360.

Each camera has its own microUSB cable that is fed to a battery pack / charger. Here it is in real life on the Milan SL. I didn’t spend a lot of time smoothing and painting it since I consider it a temporary solution.

I’ve since gotten rid of the Polaroid Cube cameras in favor of a dedicated motorcycle dash cam system. This required re-designing the camera holder for the smaller, lipstick shaped cameras.

Flip Down Fan for the DF

I’ve come up with a useful gadget for the DF that I thought I’d share here. It’s a small USB fan that’s attached under the front cowling that can be flipped down to provide a small breeze when I find that I’m not moving fast enough to get decent airflow into the cockpit. The important pieces are the cheap fan bought on Amazon, a cabinet hinge, some magnets, E6000 glue to attach the magnets, a 3D printed hinged holder for the fan, velcro and a USB charger/battery pack.

Here’s the fan in the down and up positions.

This the fan that I bought on Amazon. If you look closely in the other pictures, you can see that I cut off part of the external plastic ring below the pivots.

Here’s the fan and hinged holder. It’s mounted to the cowling with strong velcro. The Magnets are used to hold it in the up and down positions.

Here’s a better look at the design of the 3D printed hinged fan holder.

This is the cabinet hinge. I don’t know the model number. It’s one of many that I’ve replaced in my kitchen due to a broken return spring.

This is the battery pack that I’m using to power the fan and 2 video cameras.

Here are some links for the items mentioned above:

DF 141 Has a Cracked Boom

The other day, I was messing around with the chain rings on DF 141 when I noticed a long crack in the top surface of the carbon fiber boom. It wasn’t obvious visually, but I could feel it with my finger. I was a bit surprised since I hadn’t detected any movement of the boom while pedaling. Probably a stronger rider would have caused the boom to deflect more. I removed the bottom bracket holder to expose the cracked area of the boom. It appeared that the crack was due to over-tightening the bottom bracket mount clamps. It was about 12″ long.

I emailed Ymte at IntercityBike and purchased a replacement carbon fiber boom. He warned me that swapping out the boom was a lot of work. The old boom was bonded into the DF and I’d have to use a chisel and hammer to remove it. While I was waiting for the new boom to arrive, I decided to see if I could fix the old boom as a learning exercise. I came up with a plan and it seems to have worked so far. Here’s how I went about repairing the crack.

I first found the ends of the crack and ground round holes at the ends to prevent the crack from elongating. I then ground out the crack leaving a beveled groove on the top surface to provide some surface area to add carbon reinforcement.

I also wanted to lay 4 plies of carbon fiber twill on the under side of the top surface. I needed a way to laminate the carbon fiber and hold it in position, fighting gravity. Ideally, I’d also bevel the edges of the groove on the underside, but I couldn’t come up with a solution for that. I came up with a tool to apply the patch. It consists of an aluminum paddle of the correct length and width and an old bicycle inner tube. I covered the paddle with some pvc tape as a mold release. I then saturated the 4 plies onto the paddle forming the patch. After cleaning out the boom with Acetone, I ran the paddle into the boom, positioning the patch under the ground out crack. I slid the deflated inner tube under the paddle with the valve stem still accessible outside of the boom. I then inflated the tube which forced the patch upward to bond to the underside of the top surface of the boom. The pressure of the inflated tube force some resin out of the patch, filling the ground out crack.

While the resin filling the ground out crack was still in the uncured state, I filled the crack with long strands of carbon fiber. On top of the strands, I filled the ground out beveled area with chopped carbon fibers.

When the resin had cured, I deflated the inner tube, removed the paddle tool and ground the exterior patch flush with the top surface of the boom.

I’ve got about 50 miles on the DF since I made the repair and it seems OK. There are no re-appearing or new cracks. Also I can’t feel any flex in the boom so far. I’m hoping that I can leave the new boom on the shelf and live with the repaired boom for a while.


I’m back down to owning 2 velomobiles again. My friend David L has bought my DFXL. The DFXL was my first velomobile and the test bed for all of my custom parts. I decided to sell it after determining that I could comfortably squeeze into my recently purchased standard DF. It just so happens that David was in the market for his first commercially produced velomobile and the deal was done quickly. I’m so glad that there will be another velomobile rider in town to share this strange hobby with.

David is the grand daddy of recumbent trike riding in Santa Barbara. He’s the guy that got me interested in trikes. He was one of Wizwheelz’s first customers in the 1990s when he bought one of their first generation TerraTrike recumbent trikes. David is no stranger to velomobiles. He’s been tinkering with home made coroplast bodied Terratrikes since those early days. Now he’s finally got the velomobile that he’s been wanting for all these years.

Greenspeed X5 – SOLD

I recently met a fellow retiree at the local dog park. During a short conversation, he mentioned that he has had a tricycle hanging in his garage for years. He had bought it from Dana at Bent Up Cycles to use to walk his dog. It seems that idea didn’t work out very well so he put it away and never used it again. I went by his place to have a look and was surprised to find a pristine Greenspeed X5. It looks like it just rolled off of the Bent Up Cycles showroom floor. There’s not a scratch or sign of any wear. It looks like it was never used. The tires still have the center seam.

I failed to convince him to take it back out on the road. He was more interested in getting the trike in the hands of someone who would make good use of it. So I offered to help him find a new home for the X5.

Price: SOLD $1800 plus Shipping via Shipbikes to Continental USA. Expect $100 – maximum $150 depending on destination. (We will pick up anything over $150).

Here are the details:

  • Frame Color – dark metallic gray (unusual color for a Greenspeed)
  • Seat Color – dark blue
  • Crankset – 165mm Shimano 105 triple
  • Brake Calipers and Levers- Gatorbrake hydraulic (mirrored)
  • Brake lines – stainless braid shielded
  • Front Derailleur – Shimano 105 9 speed
  • Wheels – 349 Greenspeed (unmarked)
  • Tires – Scorchers
  • Shifters – Shimano 9 speed bar end
  • Chain – stock 9 speed
  • Idlers and Chain Tubes – Greenspeed factory set up
  • Rear Derailleur – Shimano 105 9 speed long cage
  • Rear Hub – Shimano Capreo 9-26

Additional Features

  • Greenspeed factory headrest
  • Greenspeed factory rear fender
  • Cateye Wireless computer