The Legacy of the Spitfire and the Evolution of the RV-15
Legend has it that when the British Spitfire returned from its first test flight, Captain Joseph "Mutt" Summers climbed out of the cockpit, hopped off the wing, and told the waiting engineers, "Don't change a thing—it's perfect!" If true, then the Spitfire was a rare bird—almost never does a new aircraft live up to its design team's hopes and dreams right out of the box. An airplane's first flight is really a new starting point in the development process—the refining of the design to become everything it was intended to be. This is as true in the experimental aircraft world as it is in the factories of the great production aircraft.
I thought about Summers as I flew my RV-8 over the Cascades and descended into Oregon's lush Willamette Valley to fly the RV-15 once again. Although we'd been sworn to secrecy until now, I had been given the opportunity to sample and comment on the RV-15's handling qualities several times during its development. Now I was looking forward to seeing—and feeling—the improvements in the latest version, the version Van's was finally happy enough to make public. After my last flight in the airplane, I smiled at Rian Johnson, chief engineer for Van's, when I said, "I'd buy this one!" His response was, "Well, we're going to make it better still!" I was looking forward to seeing how they'd do that.
The Vision Behind the RV-15
When Van's Aircraft set out to create a clean-sheet design with a high wing—a major departure from the many successful designs making Van's the largest kit manufacturer in the world—they had a number of performance targets. The airplane had to be rugged for backcountry operations and it had to carry 1000 pounds of payload, be able to operate off of typical backcountry strips, and carry two people with a significant amount of equipment and other cargo. Importantly, it had to be fast enough to simply get to the backcountry from the flatlands where most people live. But primarily, it had to fly like an RV—balanced, responsive, stable yet maneuverable—and leave the pilot with a smile of satisfaction. No matter how much it carried or how fast it went, if it didn't "fly like an RV," it wasn't finished.
The story of the refinement of the original RV-15 prototype is the story of how aircraft development really works. In reality, companies never get lucky and have the perfect airplane the first time, the Supermarine 1930s legend notwithstanding. It takes many hours of flying and many thousands of hours of creative engineering to tune an airplane to fly the way the designers want.
Original Requirements and Market Niche
There is always speculation when any successful company undertakes to deliver a new product. Van's hasn't released a new model—the RV-14—in close to a decade, choosing instead to refine designs, kits, and production processes while thinking hard and talking to current and potential customers about what they might want in the RV-15. When the news finally broke in 2020, the RV-15 was going to be a high wing, the internet forums lit up with excited builders demanding Van's "take their money!" But Van's is nothing if not thorough in scrubbing through requirements and wanted to target a niche that was not already occupied by an existing design—at least one that wasn't already in series production.
As Van's embarked on the RV-15 journey, the LSA class of high-wing bush planes had been selling like hotcakes for years. These give two seats for people and enough camping gear to enjoy the backcountry for a couple of days, an attractive proposition. But for many, these lightweight bush planes weren't enough. You can't bring a mountain bike with you nor haul game back out. You can't carry enough gear to set up a base camp for a week, and while these smaller airplanes are decidedly nimble, some of them lacked ruggedness. That's fine for operating at LSA weights, but add more equipment and you need a heavy-duty pickup, not an economy-minded runabout.
So the RV-15 was sized for generous weight-carrying capability even though it was built around two seats. Many have asked if they could add small seats in the back, and while the answer is certainly "you could," the people sitting in them would have to be small and short because the baggage compartment was not designed for height. This was a conscious decision to reduce cross-section area; RVs are supposed to be faster than their counterparts and "big" is "slow." As a result, the RV-15 is closer to a Cessna 170 than to a Cub or Kitfox at the small end or a Cessna 180 at the big end of the scale.
Early Flights and Development Challenges
It was late spring of 2022 when the RV-15 made its first flight, cloaked in secrecy until a security camera from the hangar next to Van's "skunk works" captured the airplane for the internet to see. Van's made a few attempts to hide the airplane, registering it as an "RV-8X" just to have a little fun with those trying to unravel the secret. The N-number "N7357" sort of translates into the letters "TEST" if you squint hard enough, according to Van's marketing vice president at the time, Greg Hughes. And facilities were obtained at a nearby private field for much of the early flight testing to avoid curious onlookers with cameras crowding the fence line at Aurora State Airport.
The first flight was made by test pilot Axel Alvarez, with early reports filtering out about a cautiously optimistic team. The RV-15 was a single-seater at the time because the developmental wings had no fuel tanks; instead, a boxy 20 gallons of fuel was strapped roughly on the CG in the passenger seat location. This gave the added advantage of a built-in excuse why no one got to ride along to see how it flew, but eventually, a new tank was built that fit behind the seats and a right seat appeared.
The prototype was thoroughly test flown, with much data gathered on handling qualities, performance, and stability. Potential improvements in roll, pitch, and yaw were discussed early on, but there was tremendous satisfaction with the completely new landing gear designed by Brian Hickman. No engineer is ever completely pleased, however, and refinements to make the gear more compact were on the drawing board before the initial testing was complete.
Refinement After Oshkosh
While the prototype did fine getting to and from Oshkosh, there was still much work to do. Most importantly, it didn't yet completely "fly like an RV." The team spent months working on the ailerons, chopped a foot or two off each wing, experimented with control system gearing, and tightened up control runs all to make it more RV-like with positive, harmonious control in all axes. These were learning experiences for the team as they prepared to design the final wing, fuselage, and tail, items that would be similar to the original test article but differing enough they couldn't just be "scabbed on."
The new wing, by now perfected in shape and area, needed integral fuel tanks. The fuselage had to accommodate moving the wing back 4 inches—helping with center of gravity location as well as giving the windshield more rake. The new fuselage would also accommodate a more compact version of the landing gear, making the floor area less deep. Controls were constantly modified in the search for more precision and reducing slop and to move the flap lever low between the seats. The engine mount was changed to tune the thrust line, and investigations were planned into tail designs for improved handling.
There was much to do—and then Van's experienced financial difficulties leading to a reorganization. That delayed development significantly, but the RV-15 was never in danger of cancellation. Customer demand was too great and the team had made too much progress to walk away.
How It Flew on Our First Trial
It was early September of 2024 when I received a phone call from chief engineer Rian Johnson asking if I'd be interested in popping up to Aurora for a little flying. Rian had been promising a chance to fly the restored RV-5 for several years, and I had been kidding him mercilessly while hearing things about the RV-15 testing and how I was hoping to fly an airplane that started in "RV" and ended in a "5" before the year was out. Naturally, I had to ask how the single-seater was flying. "Well, it's still hanging from the ceiling, so I guess you'll have to fly the other one that ends in 5," Rian said, and I quickly canceled my schedule for the next day, jumped in my RV-8, and headed across the Cascades without further delay.
Rian Johnson met me with the RV-15 at Independence Airpark, a quiet field away from the bustle of Aurora's towered, student pilot environment. There we adjusted the seat cushions to give me the view he designed the pilot to have. Honestly, the view over the nose was excellent, despite me feeling like I was sitting in the cab of an Air Tractor. I found this made the view over the nose different enough for a longtime taildragger pilot such as myself that getting the right attitude at the end of the flare took some time to learn. When I flew the updated RV-15 later I used fewer cushions and had better results, but this seat height is still a matter of debate… and personal preference.
The cockpit was utilitarian—this was not a production prototype but rather a proof-of-concept study. But effort had been put into getting sight lines the same as intended for the final airplane to keep reach and visibility the same, and I found the cockpit fit well. At that time, the flap lever was hanging from the ceiling between the two seats, a location that frankly I enjoy.
The airplane was on 6.00×6 tires, quite appropriate for pavement operations and a good match for the airplane when not dedicated to backcountry operations (where 26-inch tires are intended for the design). My flights that day were to baseline the -15 before a major change was made to the empennage. The tail surfaces with the then current stabilator were being replaced with a conventional tail from an RV-10 to evaluate potential handling improvements.
The aircraft as tested had recently gained new ailerons to improve roll handling, and the entire roll channel mechanism had been gone through to remove free play and friction. While it was readily apparent on the ground by pushing on control surfaces and sticks that there is still play in the system, the in-flight handling was quite good.
We flew the airplane twice that day, concentrating first on air work and then on numerous landings to judge the final flare characteristics. Here is an excerpt from my report to Van's:
"My overall impression is that this is a good aircraft that will benefit from the additional development work and tuning that the design team is currently engaged in. Roll control currently feels quite natural for an aircraft of this configuration and size and is neutrally stable in turns. It is significantly lighter than typical high-wing aircraft in this category, but not so light as to make the aircraft twitchy—it is, in my opinion, at a good point on the stability/sensitivity curve. Stick forces feel appropriate in roll.
"Yaw is good—it requires rudder input for turns (unlike the low-wing RVs in general) but not significantly so, and it felt both sensitive and well-damped—I did not overshoot or oscillate trying to find the right amount of rudder.
"Pitch is still going to require some work and is the target of the team at this point, which is why they will be changing the tail. While the airplane flies fine in cruise and is stable on approach, any change in configuration of the flaps that requires a re-trim, or the beginning of the landing flare, causes an oscillation (it feels almost like a bob-weight oscillation) in the stabilator, which makes it difficult to be smooth in the flare. I would therefore give the pitch channel a C/H rating of 6 for the flare."
Refining the Design
Van's engineering staff was aware of the issues the airplane had in pitch. In fact, the reason we were called to fly it when we did was because they were about to change the tail, and they wanted me to get a feel for why they were changing the tail. The stabilator approach was tried initially to give better tail power in slow flight for short-field operations, but stabilators are notoriously difficult to get right. The plan was to swap it out for what amounted to an RV-10 conventional tail.
Along with the new tail, the team had other changes in mind. The second prototype wing would, of course, have fuel tanks (the plan all along), and in response to numerous inputs from customers and within the team, it was decided to make them hold 60 gallons. While no one has to fill the tanks for every flight, having lots of tankage makes it easier to stay in the backcountry without coming out to civilization for fuel. Then there were the already noted changes to the landing gear to make it more compact, moving the wing back, re-lofting the entire fuselage, adjusting the thrust line, and moving the flap handle to the floor.
The beauty of a concept prototype is everyone involved expected to make changes and therefore everyone was open to ripping things apart and trying new ideas. Good engineering is to make changes one at a time, evaluate the results, and then make another change—and the team worked methodically through this process. They had already spent considerable time getting the roll feel right, and while they continued this work, their concentration on pitch was apparent when we flew the airplane again.
Improvements Proved
I was pleasantly surprised when I received a text message from chief engineer Johnson barely a month later on October 24, 2024. They had just flown the airplane with the new tail and other improvements, and the text was accompanied by a picture of a can of grease… meaning landings were now "greasers" with the new tail. Excellent! Johnson said I needed to fly it, but the weather was closing in and I had some travel planned the following week. "Could I come up tomorrow before noon, fly it, and skedaddle back before the storms hit?" I asked. "Sure," Johnson said, "We'll be ready for you!"
And so, after a two-hour trip in my RV-8, I settled into the left seat with project engineer Brian Hickman on October 25, 2024, for approximately 1.2 hours. The purpose of the flight was to evaluate significant changes made to the aircraft since my previous flight. These changes include:
- An entirely new conventional tail (to replace the original stabilator-based tail)
- Reductions in roll control system friction
- Stiffening of the flap control system
- Changes to the aileron airfoil
- Aileron hinge position (% MAC) change
- Increase in aileron throw
- Rudder changes, including gearing changes and a bump on the trailing edge
- Thrust line revisions
In our flight test report, we wrote the following:
"The change in pitch control was apparent the moment I slowed it to approach speed and nibbled at a few stalls. A quick trip to a practice field proved that landings were indeed now easy to grease it on. The previous deficiency had been completely resolved with the change to a conventional tail—pitch is predictable and stable, and the landing task is very intuitive no matter if you are wheel landing, three-pointing, or landing from an approach with power or gliding."
The Amazing, Forgiving Landing Gear
Why would you want a forgiving landing gear on your backcountry airplane? Well, sometimes the terrain is unforgiving, sometimes the air is unforgiving—and sometimes the population of pilots observing your landing is… well, you get the picture!
The RV-15 landing gear is unique enough that Van's Brian Hickman was awarded a patent on the design. "Leverage-reducing landing gear system, a constant angle suspension landing gear system, or a combination of both systems" (patent #US12330774B1) is a fancy title, but in the end—for a pilot—it means a landing gear that absorbs excess vertical energy, preventing a bounce that throws you back in the air. Stiff, spring-style gear tends to reward high-sink-rate arrivals with a second chance to land—but with lower airspeed, poorer control, and the very real possibility of a bad outcome.
Pilots are taught bouncing back into the air is usually cause for adding power and going around, but in a lot of backcountry strips this just isn't possible. With rising terrain, tall trees, and poor visibility, many of the mountain strips put the decision point out on the approach long before you get to the runway. In other words, once beyond that point, you have to land—or crash. Having a gear that helps you arrive safely makes the crash option less likely.
Many popular STOL aircraft have landing gear with enough shock absorbers and travel to impress an advanced motocross racer. But all those shocks, springs, bungees, and telescoping tubes hang out in the breeze; they make sure you can get into very short strips—and that it'll take all day to get there because of the drag. The RV-15 gear, on the other hand, has similar shock-absorbing capability, but the mechanicals are hidden between the cabin floor and the bottom skin of the fuselage. Keeping the draggy stuff out of the breeze helps you to go faster—and the RV-15 is intended to land slow and fly fast.
A cutaway view of the gear mechanism (from the front) shows part of the secret—the shocks are oriented almost horizontally, while the tops of the gear legs (above the hinge point) curve upward. They are connected to two links that effectively turn the sideways motion of the shocks into an up/down motion of the wheels. Students of lever arms might look at it and wonder where the mechanical advantage comes from, but skipping the math, I just took the airplane flying to find out.
The original tail I flew on the RV-15 made landings a bit of a challenge, especially when you were flying slowly and trying to hit a spot on a short runway. The pitch feel had an oscillation (induced by the stabilator) causing what amounted to a "gallop" down the runway. It really made it difficult to time your touchdown with a low sink rate. This is where the Hickman gear saved my bacon again and again. Oh, we weren't in danger of losing the airplane, but the landings weren't very pretty. Yet the gear absorbed the excess vertical energy and prevented a bounce back into the air every time. Impressive!
Because the patent and gear design have been revealed, I've seen pilots on message boards complaining it looks more complicated than spring steel gear, and sure enough, it is. But the complicated gear on other STOL planes isn't any simpler and has as many moving parts, and they seem to be lasting out in the field just fine. I'd suggest that for the dubious, a flight with the RV-15 gear is advised before you make a judgment one way or another. This pilot is sold on the concept—I'll take anything that gets me back on the ground surely and safely.
