Article from Sport Aviation July 2003:
Harmon Rocket III This One Will Get Your Attention!
Zowie! 258 mph cruise! Red lined at 373 mph! There, now you don’t need to read any further. Your most obvious questions are answered. And if those numbers don’t make you want to know more, you have more will power than most of us.
We were driving down Knapp Rd, one of the local streets that when captured in the net of AirVenture becomes a north-south artery right through the fly-in. That’s when we saw it. It was snuggled in between a couple of RVs and Rockets, which it bore a vague resemblance to but was somehow wildly different. We braked to a hard stop: “What is that!!!”
We were late for a meeting but there was absolutely no way we could keep going and not spend a few minutes salivating over this unknown beauty. It was familiar but it wasn’t. It was the very embodiment of speed. Sitting on the ground, silent as a stone, it still looked as if it was pushing 250 knots. The name on the side explained it all: Harmon Rocket III. We should have known.
John Harmon is to RV’s what Roy LoPresti is to things with wings and Roger Penske is to things with wheels. He starts with one idea, in this case the RV concept, and mulls it over in his high-speed mind until a wholly different and much faster product rolls out. The last time it was the Rocket II, the well known two-place that borrows heavily on the RV-4 and scoots around the sky with a 260 Lycoming in the nose.
The Rocket III takes the Rocket II and moves it one or two notches futher up the performance scale.
John Harmon lives in Bakersfield, California, but where he apparently really lives is in his workshop. He comes from a long line of people who make things. His dad developed a sulpher dioxide generator, which helps California farmers stave off soil problems caused by carbonation of their water supplies. This built into quite a business and aviation was always right there.
Harmon says, “My dad had a number of airplanes on the ranch including a Stinson and he bought the very first 1946 Luscombe sold.”
John went into the business but didn’t learn to fly until he was 23 years old. It was only a few years later that he got into sport aviation.
“I was attracted to the RV-3 when it came out and bought a set of plans. I wound up building the first RV-3 to fly in California.”
That first airplane took him only thirteen months to finish. This was before any component kits were available, which is an indication not only of his skills, but the level of his commitment and his shop capabilities. However, he wasn’t satisfied with that airplane, so he built another RV-3. Then another, and another. Eventually, in addition to the first one, he built the fifth RV-3 to fly, the twenty-second and the thirty-fourth ones. By that time it was taking him an incredibly short 600 hours to crank one out. ‘Almost seems impossible doesn’t it?
In 1982, he built an RV-4 so he could take his wife along with him. It was set up with a 200 hp Lycoming and constant speed prop so he could cover some serious territory.
“That airplane was pretty fast, but we’d be barely an hour into a trip before I’d hear her asking from the back seat, ‘Are we there yet?’. She didn’t like taking so long. However, I finally put a GPS back there so at least she’d didn’t have to ask the usual question. Still, it was taking too long, so we were always talking about going faster. ”
“The Rocket I started out as a sexy drawing of an RV-3 with a raised turtle deck and 200 hp. My friend, Jim Ewing, said, ‘Let’s build it,” so we did. That airplane was basically built with one purpose in mind. He wanted to race it in the C.A.F.E..”
The RV-4 took him exactly a year to build but he built two Rocket I’s in only nine months! He was definitely starting to figure RV’s out.
So, what’s the logical next move after pushing the basic RV as hard as possible with four-cylinders? That’s right, six cylinders. He wanted an 0-540 powered RV, and he knew that wasn’t going to be a bolt-on affair.
“Right from the beginning, I knew it was going to require some re-engineering and, while I was at it, I thought I’d change a few of the things I thought the RV-4 needed. For one thing, I felt it needed more room so I pushed the fuselage sides four inches further apart to make it a full thirty inches wide. At the same time, I lengthened the fuselage by four inches to help balance the heavier weight of the 540.”
The fuselage received .040 skins in place of the .032 and the wings were shortened a total of fifteen inches with the ribs re-pitched closer together. Some of the wing skins went up to .032 but the spar remained true to its RV lineage.
“I had the airplane professionally engineered and stressed to six G’s at a weight of 1550 pounds versus an RV-4 at 1350 pounds. The Rocket II landing gear is a machined titanium rod with flats milled in it. It’s quite a big longer then the RV and puts the nose another six to eight inches in the air.”
Incidentally, from the time he chalked the outline for the Rocket II on the shop floor to its first flight was nine months. If he wasn’t such a nice guy, John Harmon could start to get irritating, couldn’t he? Nine months!
“The Rocket II is pretty fast, but is anything really fast enough?” he asks, with a grin. “I decided I wanted something that was not only faster, but had ‘that’ look to it.”
Enter the Rocket III.
“The Rocket III is built for speed, so I narrowed the fuselage back down to the same as an RV-4 but I sat the pilot where the back seat is in a –4. This took care of most of the CG problems. Many of the fuselage skins are now .040 and there’s a single piece of skin that runs from the instrument panel to the firewall with a couple of stiffeners to make it even stronger.
“I took the traditional floor-mounted rudder pedals and eliminated them entirely. I hung them from an overhead bar going across the fuselage similar to the way some military airplanes do it. That gave me an uninterrupted floor.
“To beef the wings up, I just shortened them a full forty inches from the original RV-4 length, which makes them just a little under twenty feet long. I tossed one rib out entirely and re-pitched the rest with the widest space being about ten inches.”
Most of the tail surfaces received heavier skins to eliminate any flexing both chordwise and spanwise.
“I wanted a canopy that was a particular shape,” says Harmon, “so I made up some drawings and patterns and went to Gee Bee Canopies and had them blow one to my specifications.”
In front of the firewall, John hung a Lycoming 0-540-XXXX parallel valve (“…angle valve engines are too heavy…”) engine pumping out XXX horses. That’s swings a counterweighted Hartzell scimitar prop that’s seventy-eight inches in diameter.
When the airplane was completely finshed and he put it on the scales he came up awith an empty weight of 1084 pounds compared to an RV-4 at 960 pounds and a Rocket II at 1134 pounds.
The obvious question every one asks (next to “How fast is it?”) is how does it fly?
“On takeoff it naturally accelerates like a shot but it tracks perfectly straight with no effort on my part. That’s just the way the airplane is. Because you sit so far back in the fuselage, it’s a little blinder than most of the RV’s, but it’s off the ground in seconds.
“Climbing out at 110 knots is fun because it’s climbing at 4,500 feet per minute at sea level. It really gets with the program!”
Once at altitude, which doesn’t take long, John says full power at 11,000 feet gives him about 265 knots TAS, which is 305 mph TAS (!) for those of us who are nautically challenged.
“On cross countries I flight plan for a cruise of 225 knots (258 mph) at a little less than fourteen gallons per hour.
“It has a real honest, RV type of stall, even though the wing loading is quite a bit heavier. There is nothing about its stall that’s not predicable. With the flaps down, it stalls at 56 mph, which I don’t think is bad at all.”
“I’ve spun the airplane both left and right a full three turns and it’s absolutely normal. Just like an RV. That’s probably because the CG on all Rockets is a little forward. Most Rocket II’s are at thirteen to fourteen percent and the Rocket III is nineteen percent. I can put one-hundred ninety pounds of baggage in it and still be within limits.”
In addition to the spins, John has flutter tested it in three knot increments all the way up to 320 knots.
It looks like a hot rod, but he says that in the pattern it’s a pussy cat, largely because of the braking effect of the big prop and the flaps.
“Depending on traffic, I usually fly downwind at 160-170 knots and when I hit 140 knots I start the flaps out. They are electric. The prop helps slow it down so I plan the approach to put the airplane over the fence at 80 knots.
“Because of the visibility, I usually wheel it on, which is really easy. It almost does it on it’s own although it does float a little and you can’t get in a hurry about it.”