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ABSTRACT:     Article about the highly-modified, Continental radial tank-engine powered Skybolt built by Kevin Flynn and owned by Vince Grasso of Oak Hill, FL.
Boltin' Skybolt
A round engine gives this Skybolt character
(From Sport Aviation, 12/2002, Page 28)
By Budd Davisson
Photography by Leeann Abrams and Jim Koepnick

Why did I buy the airplane? asks Vincent Grasso of Oak Hill, Florida. That's easy. I was born too late. I should have been born in the era of round-motor biplanes. But I wasn't, so the Skybolt scratches that itch at a price I can afford.

In order to provide ground clearance for the huge 98-inch prop, the gear legs of this round-engined Skybolt needed to be lengthened by 11 inches using stockier steel tube.
In order to provide ground clearance for the huge 98-inch prop, the gear legs of this round-engined Skybolt needed to be lengthened by 11 inches using stockier steel tube.

Grasso was lounging in the distinctively shaped shadow of his distinctively shaped Skybolt at Sun 'N Fun 2002. Mostly, he was enjoying the attention the airplane was getting and answering the inevitable question, What is it? From a distance, we had to ask the same question.

Besides being a good-looking machine, Grasso's Skybolt is part of a new breed that we might call Internet airplanes. I was looking for an airplane, and I knew what I wanted -- a round-motored biplane -- but I also knew I couldn't afford one of the big ones, Grasso says. I was surfing the Net, looking at various airplane websites and ran across They had a bunch of airplanes listed, but the one that instantly caught my eye was the Continental radial-powered Skybolt being offered by Kevin Flynn in Nixa, Missouri. I'd seen a Skybolt with a Russian radial on it, but never one with a Continental. I loved it! Something about it was just different enough that it could have been one of the big airplanes of the golden age.

Grasso isn't a newcomer to sport aviation. He and his twin brother, Vaughn, and their brother, Kurt, are true second-generation aviation addicts. Only brother Darryln, who is heavy into cars, didn't go the aerial route. Their father, Leonard, was a U.S. Army Air Forces pilot during World War II and flew a little of everything available at the time. After the war he established a salvage/restoration operation that handled both cars and airplanes.

When we were growing up, disassembled airplanes were everywhere around our place, Vince Grasso says. Where most kids had a jungle gym, we had a BT-13, and when we got tired of playing in that, we'd go over and climb around in the Kinner Sportster. I can't begin to tell you how many unusual airplanes came and went during our childhood. Man, I wish we had just a couple of those today.

The net result of a childhood surrounded by funky airplanes is that the three Grasso brothers who stayed close to aviation have owned, between them, more than a dozen unusual flying machines. These ranged from Sonerais and Stardusters to a Stinson L-5, a Tailwind, a Tri-Champ, and a couple of airplanes that show the Grassos tend to listen to different drummers.

Before the radial Skybolt joined the clan, a custom-configured S2A Snow ag plane preceded it, and brother Kurt was the first to see the sport aviation potential in the Schweitzer/Grumman Agcat. He stood back and saw a 1930's comic book hero's airplane hiding within the Agcat's hulking outline and modified the 600-hp machine into his idea of a macho biplane. So, Vince was in good company when he went on the search for his own round-motor bipe.

Something about it was just different enough that it could have been one of the big old airplanes of the golden age.
Something about it was just different enough that it could have been one of the big old airplanes of the golden age.

Vince Grasso spent most of his life working in the aerospace industry, most recently at Cape Kennedy. Upon retirement he decided to continue exercising his airframe and powerplant (A&P) ticket while accelerating his search for his dream biplane. Looking back at all of the $400 Stearmans and Wacos we had laying around as kids, it makes me sick. I spent much of my life wanting an airplane just like that, but the prices kept just a little more than an arm's length ahead of my income. It was obvious: I'd never be able to afford what I wanted.

Vince Grasso's Radial Skybolt flying Vince and Eve Grasso at home along the Indian River in Oak Hill, Florida, named for its abundance of trees.
Vince and Eve Grasso at home along the Indian River in Oak Hill, Florida, named for its abundance of trees.

Along the way Grasso bought and sold a bunch of airplanes, and the last one -- a little Russian observation airplane -- is the one that gave him the money to finally get his round-engine bipe. The Russian airplane was one of the few like it in the country, and a doctor had been following the design for some time he says. When I put it up for sale he got ahold of me immediately, and I was suddenly in position to buy a biplane.

Cash in hand, Grasso started surfing the Net. When I saw the pictures of Flynn's Skybolt on the website, I just knew this was the one. Nothing could look that good and not be something special.

Grasso spent quite a bit of time talking to Kevin Flynn about the airplane, and Flynn gave him a good feeling about the modifications he was considering. It wasn't so much What he said, but how he said it. I felt I could trust him, Grasso says. So he arranged to deliver the little Russian bird to its new owner in Meridian, Mississippi, and Kevin met him there with the Skybolt.

The Skybolt panel is super-simple VFR. Grasso wings over his home field, Blue Ridge Flight Park, a fly-in community in east central Florida. The Skybolt's 250 horses help to convey him swiftly off the grass strip at some 3000 fpm.
The Skybolt panel is super-simple VFR. Grasso wings over his home field, Blue Ridge Flight Park, a fly-in community in east central Florida. The Skybolt's 250 horses help to convey him swiftly off the grass strip at some 3000 fpm.

I've got to be honest about it: assuming a wing didn't fall off when I looked at it, I was going to buy that airplane. I parked at the FBO, took a quick lap around the airplane, went back inside, and we filled out the paperwork. Just like that.

The next time Grasso saw the airplane he was its new owner and hadn't even sat in it yet. I was going to take it back to Florida, he says. I was wearing a T-shirt, shorts, and flip-flops -- typical Florida airport bum clothes. Kevin told me how to start it and gave me some numbers to fly it by, and I was on my way.

Grasso had started flying as a teenager and had plenty of tailwheel time, hut nothing had prepared him for the Skybolt. On the ground, it was entirely normal, but it sits at a really steep deck angle, like an old Waco, which is something I like about the airplane. It has a great stance, but that also makes it quite blind. Still, on that first takeoff it didn't feel that strange. Besides, as it started accelerating down the runway, I started grinning because it was obvious the airplane was a rocket ship.

Kevin Flynn, who built the airplane, says that of the many aircraft he's owned, the Continental-powered Skybolt is the one he wishes he hadn't sold because he, too, has a soft spot for radial-engine biplanes. Like Grasso, however, he flies and builds on a budget.

My dad, Van, is the original homebuilder of the family, and we built the Skybolt together, Flynn says. When we started looking at engines, we decided to use one of the tank versions of the W-670, the 220-hp Continentals usually seen on Stearmans, the 38-year-old airplane builder explains. This engine, however, actually puts out 250 horses, according to the book. The tank engines are called that because they were used in the early versions of the M-3 Stuart light tank, as well as a couple of landing craft. They use a different crankshaft that has external rather than internal splines, so you need a special hub to mount a prop. When we got the engine it still had all the extra shrouding and the little cooling fan that was part of the tank installation.

Tank engines don't need to be light, so they have a lot of details -- like internal gears with no lightening holes -- that add weight, and they weigh about 75 pounds more than a stock 220-hp Continental. To keep the weight down, Flynn says, we didn't put a generator on it. We would have preferred to use a regular aircraft engine, but the tank engine was only $2,800 -- pretty hard to turn down. The engine was basically new, having been overhauled by the military in 1944 and was still in the crate. We took it apart, checked everything, replaced a few gaskets, and put it back together.

Another builder had started the Skybolt airframe, and Flynn and his dad got it at a good price. The airplane also had the shorter 22-foot wings, which made it a more attractive project to the pair.

When they started work, they sought the advice of the late Hale Wallace of Steen Aero Lab who, at the time, sold the plans and components for the Skybolt. Kevin Flynn laughs when he says, Hale wasn't crazy about us mounting the big radial, but when it became obvious we were going to do it anyway, he pointed out a few areas to beef up. This included sliding tubing down inside the longerons and rosette welding it in place.

On a conversion as radical as this one, the center of gravity (CG) always presents a major obstacle to be conquered. According to Flynn, the round engine weighs 75 to 100 pounds more than a flat Lycoming, so they had to make some adjustments. We moved the pilot's seat back 7 inches and mounted the battery as far back as we could get it, he says. That balanced everything nicely. When we were finished and put it on the scales, it came right at 1,300 pounds, which isn't particularly light for a Skybolt, but it's not really heavy either.

Getting the CG in the right place was only one challenge. The Continental was swinging a huge 98-inch prop, and the stock gear wasn't long enough to keep it out of the dirt. We extended the gear 11 inches, which means me had to make new gear legs out of tubing that was both bigger in diameter and thicker in wall thickness. We used standard 600-by-6-inch wheels and brakes. That big, slow-turning prop is one reason for the airplane's performance. It really puts out the thrust.

The long gear and radial engine make it hard enough for a lot of people to identify the airplane, but there were other subtle changes that do even more to hide its Skybolt lineage. When we did the fuselage, we used a UC-78 cowl and built a round firewall to match it, Flynn says. Then we just faired back to the tail with stringers, which gave the fuselage a definite rounded appearance. During the '30s I think they used to refer to that as a barreled' fuselage.

Flynn says he didn't want to sell the airplane, but they had too many airplanes and something had to go. But, at least it went to an owner who appreciates it.

Vince Grasso describes his first takeoff: As it blasted off the ground, I knew the best rate of climb was somewhere around 95 mph, but at that speed it was going up at such a steep angle that it was unnerving. I flattened it out a little, and it was still going up at better than 2,000 fpm. Flat out, with that prop, it indicated about 150 miles per hour and was only turning 1800 rpm.

After putting more than 80 hours on the airplane, Grasso is more enthusiastic than ever. With a prop change from 98-by-72 to 96-by-60 to increase takeoff performance, I'm now feeling most of those 250 horses and seeing 3,000 fpm at max climb speed. Flat out is now about 140 mph indicated, which is right at its 2400 rpm redline. At usual cruise settings it indicates 128 mph, and I've verified it to be accurate. At that speed it's burning about 13 gallons of gas and about a quart of oil. What's even more amazing is that in all that time there has only been one tiny oil leak, knock on wood, and he leans over to tap on part of the airplane.

The Grasso family has a tradition of going through airplanes the way most people go through laundry, so it would be logical to think the Skybolt might eventually be replaced by yet another flying machine. But, don't count on it. I've been waiting for this airplane my entire life, and I'm not going to let it go as long as I'm still able to crawl into the cockpit.

NOTE: You can view more articles by Budd Davisson on his website:

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