Everything You Wanted To Know About The Radial-Powered Pickup on Jay Leno’s Garage

We have a lot in common with Jay Leno. Well, at least as far as taste in cars go. Sadly, not so much in disposable income. Leno may be a rich guy, but he gets a kick out of homebuilts and freaky projects, so we shouldn’t be surprised to see Gary Corn’s Jacobs radial-powered Plymouth truck featured in a recent episode of JLG. It’s pretty funny to see that Bonneville salt shot and know that we were standing directly to the side of Leno’s videographer! Leno does a good interview with Gary, and the build shots are neat to see. If you want even more info about the airplane-Plymouth, keep reading after the video.

There’s quite the backstory to the Corns family’s love affair with airplanes. When the younger Corns, Adam, was about 13, he was obsessed with flying. For his birthday, his parents, Gary and Alice, got him a ride in a stunt plane. Seems pretty sweet, right? But it all went horribly wrong when the plane clipped some power lines and crash-landed right in front of Adam’s terrified parents. Incredibly, Adam wasn’t even hurt and the pilot only suffered a black eye—Adam joked that even that was only from his mom punching him. She didn’t, of course, but she probably wanted to. Still, the Corns liked airplanes, but decided to keep them on the ground in the form of aviation-inspired cars.

Using a combination of hand-built parts and junkyard finds, the Corns family fit a radial engine into a 1939 Plymouth truck for an airplane-inspired custom.
Using a combination of hand-built parts and junkyard finds, the Corns family fit a radial engine into a 1939 Plymouth truck for an airplane-inspired custom.
The Plymouth has been chopped and tubbed, and there are hand-formed details all over the place, from the custom bedcover to the fuel tank beneath it. The little keg tank behind the cab is the remote oil pan. Fat 29x18.5/15 Mickey Ts put the power to the ground.
The Plymouth has been chopped and tubbed, and there are hand-formed details all over the place, from the custom bedcover to the fuel tank beneath it. The little keg tank behind the cab is the remote oil pan. Fat 29×18.5/15 Mickey Ts put the power to the ground.

Adam Corns is now 27 and works with his brother, Eric, and his parents at a family-run salvage yard in Englewood, Colorado. The yard has been in Alice’s family since 1959, and the whole family is super into collector cars and wacky wrenching—so when cool stuff comes in, it’s more likely to go in the project pile than the crusher. Cool stuff comes in often when you work in a wrecking yard, and the project queue can get pretty long. “We have a group of friends who come by on Wednesday nights, and instead of playing poker, we build cars,” says Alice, and Gary adds that the rules for joining this weekly wrench-o-rama are: “Love cars, bring beer, and have a sense of humor.”

The mile-high theme continues inside the truck, with dual leather-wrapped airplane steering consoles and a double brake, making the truck perfect for driver training. Would time spent in this cockpit qualify towards pilot hours?
The mile-high theme continues inside the truck, with dual leather-wrapped airplane steering consoles and a double brake, making the truck perfect for driver training. Would time spent in this cockpit qualify towards pilot hours?

It’s obvious Gary and Alice have a sense of humor the second you see their 1939 Plymouth pickup. Its pockmarked, raw-steel body is dotted with rivets, and rising out of the open engine bay is a halo of finned cylinders—an airplane radial engine shoved back against the firewall. The joke’s on you, though, if you think it’s all for show. When Gary starts it up, there’s a wheeze and then a rat-a-tat-tat in the bare-metal engine bay. Smoke billows around the Plymouth and it disappears before you can comprehend what you’re looking at.

Because of their design, radial engines tend to leak a bunch of oil into their lower cylinders when they aren’t running. Gary says each start up requires pulling the bottom two spark plugs—there are two per cylinder—and draining the oil before trying to fire it up.
Because of their design, radial engines tend to leak a bunch of oil into their lower cylinders when they aren’t running. Gary says each start up requires pulling the bottom two spark plugs—there are two per cylinder—and draining the oil before trying to fire it up.

The Plymouth started as just an old truck, one that Gary picked up from a customer for a couple hundred bucks, and then sat around for almost 30 years. He wasn’t quite sure what he wanted to do with it, but he knew that inspiration would come. “One day, my dad said we needed another project,” Adam says. “He went over to an airplane wrecking yard and the next thing you know, this 1950s seaplane shows up on a trailer, and he says we’re gonna use the 300hp Jacobs radial engine for the truck. Growing up around metal, you never question if it will work, you just start welding.”

Gary likes to put on a full show when he brings the Plymouth out to play. Not only does the radial engine make plenty of smoke on its own, but the Corns have added a stunt smoke tank, and acquired a real military airplane tug to accompany the truck to events.
Gary likes to put on a full show when he brings the Plymouth out to play. Not only does the radial engine make plenty of smoke on its own, but the Corns have added a stunt smoke tank, and acquired a real military airplane tug to accompany the truck to events.

Before breaking out the welder, the Corns had to see if their aircraft powerplant was still in sky-high condition. A customer offered the use of a radial-engine runstand—because the Corns are the kind of people who know people who just happen to have 1950s radial engine run stands sitting around. “It fired up and we couldn’t believe it!” Gary says. Eric tracked down a new single-barrel updraft carb on eBay, and the fun of fitting the round peg in the square truck began.

The engine is a dry-sump, 7-cylinder, 757ci, Jacobs R755 radial out of a 1959 Cessna seaplane.
The engine is a dry-sump, 7-cylinder, 757ci, Jacobs R755 radial out of a 1959 Cessna seaplane.

Welding, bending, cutting, and inventing—often in the wee hours of the morning—the group made short work of removing the truck body from the stock chassis and stripping it to bare metal. The top was chopped, the rear was tubbed, and more than 1,000 hand-bucked solid rivets now trace lines around the pickup’s panels. The original framework was ditched in favor of a custom tube chassis, which extended the front end of the truck to make room for the seven-cylinder Jacobs radial. Since the airplane engine was designed to turn a propeller, getting the power back to the Turbo 400 automatic trans and narrowed Franklin quick-change rearend took some engineering, with most of the components either scavenged from the yard or handbuilt in the shop. The propeller shaft is connected to a custom cogged pulley that runs down to a boat V-drive with a 3-inch Kevlar blower belt. A custom driveshaft heads back from the bottom of the V-drive flange to the front of the transmission, where a clever assembly made of a 1970 Chevelle pinion and various old Ford bearings spins the 12-inch torque convertor. “In the end, the transmission thinks it’s connected to a small-block Chevy,” Gary says.

Because the engine was originally intended to drive a propeller, fabricator, and family friend, Curt Garner had to come up with a method of bringing the power back to the Turbo 400 transmission. “Curt was up all night working on the problem,” says Gary. “Finally designed the bearing and shaft assembly leading back from the Casale V-drive at 4:00 am.”
Because the engine was originally intended to drive a propeller, fabricator, and family friend, Curt Garner had to come up with a method of bringing the power back to the Turbo 400 transmission. “Curt was up all night working on the problem,” says Gary. “Finally designed the bearing and shaft assembly leading back from the Casale V-drive at 4:00 am.”

The transmission may think everything is copacetic, but inside and out, the truck thinks it’s a plane. Pitot tubes and aircraft lights dot the exterior, and in the interior, leather aircraft seats face dual steering yokes and an array of gauges intended to soar above the clouds. Airplane geeks will get a kick out of the cartridge shells and “shotgun” starter in the handbuilt console. Early radial engines used what were basically shotgun blanks to send a gust of high-pressure gas into the cylinder to start the engine. Even though the Jacobs engine is started with a more modern electric method, Gary always loved the scene in Flight of the Phoenix where Jimmy Stewart has to start a plane while lost in the desert with a limited number of cartridges. “I just built what I thought it might look like,” he says about that little touch of cinematic drama.

When the Corns started on the air truck, they were planning to run it on the Bonneville salt flats, but then the race got canceled—and canceled again. While still hopeful about getting out to Utah, Gary and his crew haven’t just been sitting around waiting for Speed Week. Besides making numerous passes—and lots of smoke—for our photographer, the Plymouth “Air Radial” has been flying around the show circuit, picking up awards and even offers of a reality show based around the Corns family business. Gary says one of the coolest things has been the response from the aviation community. “A former CEO of Cessna saw it and liked it so much he brought me parts and signed the console. A VP at Lockheed Martin asked me to explain how we put it together. We must be doing something right when a rocket scientist is asking us how it works.”

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