Wheel Pant Suspenders

Home shop machinist.

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The SQ2000 sans wheel pants (left) and owner Kevin King (right).

Across from my hangar is Kevin King, the proud owner of a Glassic Composites SQ2000. If you’ve never seen one, don’t feel bad. They only sold a handful of kits, and after at least two changes of ownership by the mid-2000s, had pretty much disappeared.

When Kevin purchased the airplane from the widow of the builder in 2018, it was airworthy and flying, but needed some cosmetic work. Like many builders, this one did not install the wheel pants. Builders often choose to keep the landing gear, brakes and tires naked during the 40-hour Phase I testing to facilitate the inspection regime that goes with breaking in a new plane. Others leave off the wheel pants simply because they are anxious to start—and keep—flying. Whatever the reason, the wheel pants were never installed on Kevin’s SQ2000. As he racked up hours on the plane (including a Florida to California cross-county trip), it became clear that not having wheel pants was holding back the cruising speed.

Images taken with a smartphone (left) were downloaded into Photoshop (right). Photoshop allows you to combine different images as separate layers within one file. By adjusting the transparency of the top layer (or layers), you can see through to the background and position the layer however you want.

After so many months of staring at the wheel pants and researching how to best mount them, including going to the Rutan Reunion in 2019 and talking to every canard-type owner he could find, Kevin was still unsure.

All the while, I was having fun with old Kev. Back in 2014, when I bought my Jabiru, the circumstances were nearly identical. Like Kevin, I purchased my Jabiru from the widow of the builder and the wheel pants had never been installed (see “To Launch a Light Sport—Redux,” May 2015). Not a week went by that Kevin or his hangar mate, Donnie Eubank, wouldn’t ask, “I wonder how that Jabiru would look with wheel pants?”

I eventually got tired of hearing it and got around to mounting the wheel pants. As you might guess, I regretted not having done it sooner. My cruise speed increased from 112 to 117 knots!

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By merging the Photoshop images into a 2D CAD program, it is possible to estimate dimensions with somewhat better accuracy than guessing.

So when Kevin bought the SQ, it was my turn: “Hey Kevin, I sure would like to see how the SQ looks with wheel pants,” to which I added, “I bet you’re losing 10, 15 or even 20 knots with those naked wheels.”

Then, when word got out that AirVenture was on for the end of July 2021, we started talking plans to fly the SQ to Oshkosh. But I told Kevin, “We have to put the wheel pants on first.”

After some discussion, we agreed the wheel pants he got when he bought the plane (generic catalog items called “gel-coated fiberglass wheel pants”) probably wouldn’t work for the mains, but might work for the nose gear. The challenge was where to mount it, and how.

Sketch of the final bracket for attaching the nose gear wheel pant.

I remembered a while back a “see-through” composite Photoshop image created by a builder to visualize the relationship between the engine and his custom cowling. This seemed like an extremely useful technique to “fit up” curvy parts with other curvy parts that otherwise have no physical plane or straight face to take reference measurements. So, borrowing that idea, I used my smartphone to take side-view photos of both the nose gear and the wheel pant. Back home, I opened the images using Photoshop and combined them using the “layers” feature.

After fly cutting the 1×1-inch square to 1×3/4 inch, the mounting holes and slot ends were roughed out on the drill press.

Once an image or a part of an image is a layer, you can control the level of transparency and “float” it over the background to position it wherever you want. After a few minutes of experimenting, I had the wheel pant positioned more or less in the right spot.

A 3/8-inch end mill was used to create the slots between the pre-drilled holes.

I saved the resulting composite image as a JPEG image and loaded it into my CAD software (Solid Edge). By scaling the photo, I was able to make a dimensionally accurate 2D view. This allowed me to get a more precise idea where and how the front half of the wheel pant could be attached to the fork. With the composite imagery in hand and dimensional estimates from the CAD program, I sketched out a bracket to bolt to the fork and provide the correct spacing and support for the wheel pant.

A self-centering Vix bit was used to mark the precise location for drilling and tapping 10-32 threads in the fork (left). With both brackets attached to the fork, the pointy-end 8-32 cap screws (red arrows) were used to locate the holes in the wheel pant (right).

To save weight, I selected thick-wall 1-inch aluminum square tubing. A box section makes for a strong and lightweight structure, which I made even lighter by milling slots between the mounting holes (refer to the sketch).

A strip of painter’s tape was stuck to the inside of the wheel pant and then the wheel pant was positioned on the fork. A light tap on the outside face with a rubber mallet created the center marks on the tape (left). An angle-head drill attachment was used to get inside the tight quarters of the wheel pant to drill the locating holes (right).

Please note the 8-32 threaded holes in the bracket. These were eventually drilled out in favor of floating nut plates for the actual fixing of the wheel pant to the bracket. But they served a useful purpose for marking the holes to be drilled in the wheel pant. I took two 8-32×1/2-inch cap screws and ground a sharp point on the end of the threads. When threaded into the brackets, these served as locating punches for marking where to drill the wheel pants.

The test fit proved the bracket to be a rock-solid mount for the wheel pant. The 8-32 threaded holes in the bracket were later drilled out and replaced by 8-32 nut plates riveted to the bracket (left). The final fit came pretty close to the Photoshop plan (right). Additional trimming for ground clearance and some glass work still needs to be done. But the main task of mounting was all in a day’s work for the home shop machinist!

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