The Rihn DR-107 One Design is an American aerobatic homebuilt aircraft that was designed by Dan Rihn and first flown in 1993. The aircraft is supplied by Aircraft Spruce & Specialty of Corona, California in the form of plans and a materials kit for amateur construction.
The DR-107 was designed as a low-cost one design aircraft for competition and sport basic to advanced aerobatics, including International Aerobatic Club Class One competitions. For this role it is stressed to +/-10g.
Design and development
The DR-107 is a monoplane that features a cantilever mid-wing, a single-seat enclosed cockpit under a bubble canopy, fixed conventional landing gear with wheel pants and a single engine in tractor configuration.
The aircraft is predominantly made from wood, with some steel parts and doped aircraft fabric. Its 19.50 ft (5.9 m) span wing employs a Wainfan 16% symmetrical airfoil and has a wing area of 75.55 sq ft (7.019 m2). The wing has almost full-span ailerons that produce rolls of 360° per second. The wing has no flaps. Other features include a low-mounted cable-braced tailplane and a 24 in (61.0 cm) wide cockpit.
The DR-107 can accept engines of 160 to 180 hp (119 to 134 kW). The standard engines used are the 180 hp (134 kW) Lycoming O-360, modified with high compression pistons, an inverted oil system and fuel injection or the 160 hp (119 kW) Lycoming AEIO-320 powerplant.
The aircraft has an empty weight of 740 lb (340 kg) and a gross weight of 1,150 lb (520 kg), giving a useful load of 410 lb (190 kg). With full fuel of 19 U.S. gallons (72 L; 16 imp gal) the payload is 296 lb (134 kg).
The designer estimates the construction time from the supplied materials kit as 2000 hours.
Operational history
By 1998 the company reported that 355 kits had been sold and five aircraft were flying.
In November 2013 33 examples were registered in the United States with the Federal Aviation Administration, with another 11 previously registered and now removed. Also in November 2013 there were two registered with Transport Canada and ten in the United Kingdom with the Civil Aviation Authority.
Specifications DR-107
General characteristics
Crew: one
Length: 17 ft 0 in (5.18 m)
Wingspan: 19 ft 6 in (5.94 m)
Wing area: 75.55 sq ft (7.019 m2)
Airfoil: Wainfan 16% symmetrical
Empty weight: 740 lb (336 kg)
Gross weight: 1,150 lb (522 kg)
Fuel capacity: 19 U.S. gallons (72 L; 16 imp gal)
Powerplant: 1 × Lycoming AEIO-320 four cylinder, air-cooled, four stroke aircraft engine, 160 hp (120 kW)
Propellers: 2-bladed constant speed propeller
Performance
Maximum speed: 184 mph (296 km/h; 160 kn)
Cruise speed: 160 mph (257 km/h; 139 kn)
Stall speed: 63 mph (101 km/h; 55 kn)
Range: 375 mi (326 nmi; 604 km)
Service ceiling: 22,000 ft (6,700 m)
g limits: +/-10 g
Rate of climb: 2,000 ft/min (10 m/s)
Wing loading: 15.22 lb/sq ft (74.3 kg/m2)
Pirep: One Design
EAA/Sport Aviation, February 1994
Let’s get one thing straight from the git-go. The little Dan Rihn designed One Design is a lot more airplane than I am pilot. But then, most specialized aerobatic airplanes are more airplane than most pilots. There aren’t, for instance, but a handful of pilots in the world that can utilize everything a Pitts S-1S has to offer.
But, the One Design isn’t aimed at that top handful of unlimited pilots. It is aimed at guys like me who are serious about aerobatics, but can’t afford to play in the big leagues because of the horrific cost of the current big guns. Most of us don’t have the time to go unlimited anyway. There are, however, uncounted hundreds of us who would love to compete, if we didn’t have to get caught-up in the dollar-race competition usually turns into.
The One Design is an effort to stop that.
The IAC One Design class is an International Race of Champions (IROC) approach to aerobatics. To compete, you must fly this one design (clever name!) and it must conform to specifics as laid down by the IAC tech committee. This includes things like engine displacement, wing span and shape, wieght minimum, etc. An interesting part of the qualifications is that a photo is required of the instrument panel in flight showing the airspeed and tachometer at full throttle. The goal is to have everyone flying airplanes so similar, the pilot becomes the only variable in the equation.
The one design concept has been bashed around in a lot of late night bull sessions by a lot of folks, but the one that finally got something accomplished was between Lewis Shaw of Dallas and Dan Rihn of Long Beach, Ca. A long time competitor and akro supporter, Shaw finally drew the line in the sand and told Rihn, who’s an aeroengineer and akro pilot, it was time to stop talking and start building. He’d fund it and toss in his two-cents on design parameters, when asked.
That was late in 1992. The prototype flew 9 months later, a tribute to the building capabilities of Jon Staudacher, who did the wing, and Doug Dodge of Acro Specialties, Inc in Bay City, Michigan, who did the rest. Dodge actually started cutting metal in March ’93 and flew the airplane in late August, losing two weeks for Oshkosh. During this time Dan Rihn had to design the airplane and produce drawings for the builders to build from. There was a tanker load of mid-night oil burned by a lot of folks, during 1993!
The IAC Board of Directors has given the green light to the One Design class concept and the exact rules are being refined, even as we speak, er, write. So, One Design, the airplane, has a home in One Design, the aerobatic competition class.
As I was strapping into the airplane on Scottsdale, Arizona’s ramp, I felt secure, if nothing else because, although the airplane had only about 85 hours on it, they had been at the hands of over 75 different pilots and almost all of them had been hard aerobatics. If it was going to break, it would have already broken. Besides, the airplane had just come out of Lewis Shaw’s shop being completely inspected and freshened up.
Everyone’s first impression of the airplane is the same, “Boy, is that thing small.” It looked miniscule out there on that big Scottsdale ramp and with only 19.5 foot of wing (tips included) and 75.5 square feet of wing area, it was small. A single-hole Pitts ihas only a 17 foot span, but 98 square feet of wing area, for comparison.
The wing looks short because it is so fat and it feels like a gymnasium floor, it is so solid, when stepping up on it to board. Sliding down in to the cockpit, the wing tips seem to get closer, but this is feeling that disappears almost as soon as the engine cranks.
Chris Gardner was sheparding the airplane around for Lewis and Dan, and he was a good choice. Besides being a mechanic, he personally built the 0-320 Lycoming that had been lifted right out of a C-172. The engine was essentially stock except for an Airflow Performance injection system and slightly higher compression pistons which Chris feels makes it good for about 160 hp. The prop is a 74″ diameter, 60″ pitch, metal Sensenich.
The first impression on boarding is that this thing is really wide and not just when compared to a Pitts. I’m an FAA-standard pilot in every dimension and the longerons were at least 2-3 inches outboard of my shoulders, when wearing only a light jacket. At 24 inches, it is one of the widest monoplane cockpits around.
The huge spar ran under my knees and the seat angle approached the so-called semi-supine configuration. This means your feet are really out in front of you and higher than on most aircraft. This supposedly makes it easier to tolerate “G” forces.
Looking around, I couldn’t see a thing on the ramp if it was smaller than a JetStar, so we cranked the seat back forward to give me as much height as I could get inside the glass. The prototype uses a canopy which Dan Rihn says, “…we just happened to have laying around and don’t know what it is for…” and is several inches lower than that which is in the drawings or which will be available for the airplane. That is important because, as I flew it, the airplane is too blind for a monoplane. Because of it’s width and low seating position, the airplane is much blinder than a Pitts during ramp operations. It makes a wide runway seem narrow and two more inches of sitting hieght should fix that.
I have a bad back (doesn’t every body?),. so I wadded up a spare jacket and put it behind my back as a lumbar support. More on that, later.
Locking the canopy down (Dan says a sliding version is designed and in the plans), I toggled the primer and hit the start button, immediately being rewarded with a throaty roar from the region down by my feet. One of Shaw’s contributions is an unusual offset control stick arrangement he first had on his Swiss Akrostar. It looks wierd, but, as I wrapped my hand around it to taxi, I was surprised how natural it felt. The throttle, however would have benefitted from being relocated forward an inch or so.
The tailwheel ratios are dead nuts on. The Aviation Products 4″ tailwheel is small enough, cracks in the pavement are felt, but, otherwise it is delightful in the way it lets the pilot control the airplane. Most airplanes fall in a range, when it comes to tailwheel steering, with none of them being bad. However, when a good one comes along like this, it points out how much further the rest have to go.
On Scottsdale’s 50 foot taxiways, I had to really exaggerate my “S” turns to see ahead. Even in a Pitts, a gentle turn opens up a sight window straight down the taxiway. Not so the One Design. Dan is aware of this. Since the airplane is going to a wide variety of pilots on different types of airports, the assumption has to be it will see its share of narrow runways and green pilots, so the vis has to be fixed.
Cleared, I rolled out on what I estimated to be the runway centerline and gently brought the power up. ‘Sure felt like a 180 pulling out there! As we rocketed down the runway, I eased the tailwheel off the ground and kept increasing backpressure on the stick to hold a slightly nose high attitude. I never did let the tail get high enough I could see over the nose. At some point, the airplane skipped once and a little more pressure put it off the ground and climbing.
It was instantly obvious there was no reason to drop the nose and let the airpseed build. The challenge was keeping the speed down and that meant increasing the deck angle by a bunch. A big bunch! Chris had said 100 knots was a comfortable climb speed but I hadn’t paid any attention to the airspeed at all until I had it established in a climb that seemed to look and feel good. It was indicating 115 knots! I pulled up to 100 knots and found myself pointing up at a rediculous angle. At the end of the runway I had an easy 1,000 feet and by the time I was ready to change frequency, I was going through 4,000 feet.
I had been told the airplane had a tremendously high roll rate, so I was very conscious not to tweak the ailerons and I kept looking for the “balanced on the head of a pin” feel, but never found it. On climb-out I could feel a lightish pitch input, but the ailerons felt fairly natural, especially if I rested my hand on my knee and finger-tipped the stick below the stick grip.
A Decathalon or Citabria pilot might be well advised to take a ride in something like a two-hole Pitts or Extra 300, just to get themselves introduced to the world of light, quick controls. As it happens, the One Design presents absolutely no problems in those areas, as long as the pilot is prepared for light controls and can control his movements. If he is ham handed and prone to panic, he could possibly get a PIO going on his first flight. If he does, the fix is obvious…let go, the airplane will damp-out and take care of itself.
I wanted to get a stop watch on the climb rates, but I was already so high, I dropped the nose and twisted around in a diving spiral, to get rid of a couple thousand feet. In the spiral, I could see I would have to watch the prop since it was fine enough the rpm built fast, when nose down. The speed, on the other hand, was easy to keep in check.
I found at 100 knots, the airplane climbed at about 1,400 fpm, and reducing the speed to 90 knots put it right at 2,000 fpm. I didn’t go any slower because the angle gets so steep it is dangerously blind.
Level, I slowly pushed the throttle to the stop and watched as the speed and rpm built up. It was still accelerating through 160 knots and and the tach was pegged at 3100 rpm and I was unwilling to push someone else’s engine any faster. Obviously, it could stand to have a couple inches of pitch put in it, although the serious akro types are happy as clams putting 3,200-3,300 rpm and up on their engines.
The initial part of the flight had been done under great duress because it had all been right side up. I fixed that at the end of the speed run by pulling hard upward, watching as the nose whipped into the vertical, as indicated by the wingtip attitude indicators. At this point, I had yet to do anything with the ailerons other than normal flight maneuvers, so, I wasn’t ready for the world to disappear, when I hammered in what I thought was full left aileron. With absolutly no hesitation whatsoever, the wings ripped, absolutly ripped, around the horizon screwing up any form of planning I had in mind.
Since I had entered out of level flight with no extra speed in the bank, I had planned on doing only a half vertical roll and hammerheading out, but to this day, I don’t have the slightest idea how far I went around, but it was more than once. When I saw what was happening, I held it in for a second, then centered the ailerons instantly. The airplane stopped so quickly, again, I wasn’t ready for it.
At that point, I felt suitably humbled and pulled over the top, doing a half roll on a downline, while building speed.
On the way out to the practice area I had played with the controlls and found the airplane to have absolutely no decernable adverse yaw, so rudders were redundant in aileron rolls. With that in mind, I let the speed build to 160 knots and brought the nose up high intending to do two full-deflection aileron rolls. Stick to the side, I was amazed at how fast it went around. It was significantly faster than even a Pitts snaps. Dan says it has been timed at 420 degrees a second, where an S-1S is about 180 degrees. Wow!
I did the same thing again, this time leaving the ailerons in for four rolls and, when I snapped the stick back into center, causing the airplane to stop just as quickly, my brain did at least two more circuits before it stopped. Serious roll rate! What makes the ailerons even neater is that besides being fast, there is no inertia at all. When the ailerons are poked, the wings immediately respond, and when the ailerons are released there is absolutely no tendency for the wings to keep on moving. Point rolls are so precise and easy its hard to keep your eyeballs in their gymbals!
After doing some investigation of the controls, I realized the airplane is really unusual in that unless the pilot asks for a high roll rate, he’ll never know it is there. The stick ratios, break-out forces and travel are such that a pilot could fly the airplane for years in a normal fashion and never have an inkling the airplane has such phenonomal roll available.
This is not true of the elevator forces. The stick gradient for the elevator force in positive flight is flat enough that it gives the impression of falling off slightly. As “G” is applied, it feels as if it gets progressively easier to add the next “G”. Again, this is no problem except for the “non-sensitive” (read: ham handed) pilot. The first few times a Decathlon pilot loops the One Design, there is a high probability he will make himself a lot shorter unless he lightens up on the stick.
Later on, in doing outside work, I found the outside elevator forces to be out of balance with those inside. In otherwords, it was much easier to pull than it was to push. Dan says this has been a common comment and has a fix in mind.
The first time I rolled upside down I was first surprised at how much forward stick it took, but wasn’t surprised at how effortless the airplane flew with the wheels pointed up. With the stick pressures as they were, it was easy to drop the nose a little and get a few extra numbers, which naturally led into a healthy push, up and around. I was watching the airspeed, as the nose went up and trying to connect that to what I was feeling in my hand. I initially pushed 3.5 negative, since I knew a Pitts would easly motor over the top with that load, but I was pushing so hard to get it, I didn’t want the speed to fall off and me not feel the “G” availability go away. Doing outside loops, most airplanes telegraph how much G they have available through the stick by building and lightening pressures. The One Design didn’t lose nearly the speed I had expected and motored over the top with something like 80 knots showing, when I only started at 145 knots.
I then went ahead and pushed, again aware of the extra pressure. I just treated it like a Pitts, getting as much pitch rotation as felt good at the top and played the “G” load to give 150 knots at the bottom. It went around like it was a mechanical toy, with only minor inputs from me. I have no idea whether it was actually round, but it sure felt good.
I noticed the airplane didn’t accelerate as quickly as I had expected, when going down on the outside loop, so I pulled nose high and slowed it down, planning on doing a split “S”, so I could hold a vertical downline and watch the drag rise. At 60 knots, I resorted to habit and banged a lot of aileron in, since most airplanes need it at that speed. Again, the One Design tweaked my nose and went around so fast, I almost missed inverted. There is no speed at which the airplane doesn’t have lots and lots of roll left!
Letting the nose point straight at the ground power-off, I watched the speed build and found it very similar to a biplane, which both surprised and delighted me. At about 160-170 knots it begins to get draggy and doesn’t want to run away from the pilot. Since so many of the pilots building this airplane won’t be experienced in high performance monoplanes, that’s probably a good feature, although it might limit the energy available to the guy wanting to work into higher aerobatic classes. I know some folks have flown the unlimited known in the airplane with no problems, so the drag rise must not present a serious problem.
Almost everyone who flies the airplane comments on a super pronounced root-stall buffet, when pulling “G”. It’s hard not to comment, since, when the airflow separates at the root it really gets your attention. The airplane doesn’t react by doing something stupid. In fact, it normally doesn’t do anything, but it feels as if there is a mechanical shaker beating on the airplane in the vacinity of your feet. I got it in some vertical pulls and in some screwed up snap rolls, but otherwise didn’t feel it to be a problem. Dan says he was trying to get by without any fairings in that area, but obviously will have to add them.
In normal stalls, the airplane comes down to about 50 knots, shudders a bit and starts mushing. In accerlated stalls in turns, it does the same thing, but rather than rolling to the outside, like most airplanes would, it simply holds the bank and mushes.
The airplanes has so little dihedral effect in any situation that you can sit in level flight and walk the nose back and forth with the rudders and not have either wingtip leave level flight. Later, when I was coming back to the airport and wanted to pull my jacket-lumbar support under my butt for more height, it proved a real challenge because I couldn’t bring up a down wing with just my feet. Interesting!
We were working within a fairly tight time constraint and I only had 45 minutes to play with the airplane, not nearly enough to delve into many secrets of its soul. For instance, I found my snapping techniques and the One Design’s were not necessarily the same. I had a tendencey to bury the stick too much, when all it took was a tweak back followed by unloading the stick. Given a few more minutes, it was obvious the airplane would snap clean and stop even cleaner.
The same thing was true of the spins. I did inside three turn spins right and left and noticed it was fairly assymetric, with them being noticeably different, one being more on-axis than the other. It was the inverted spins I wanted to work with. Someone had told me to do a flat spin, which I normally won’t do in a strange airplane without more assurances. But, they said I wouldn’t believe it. I hadn’t planned on doing an inverted spin, but I was in the process of screwing up a hammerhead, so I went ahead and pushed, keeping the left rudder in and about quarter power. The airplane snapped into the spin so cleanly and stablized so quickly there was practically no transitional spin at all. Then I played with the power, watching the nose go up and down.
When I killed the power to recover and initiated rudder and stick movements, the airplane stopped spinning so quickly, I found myself in an inverted, glide before I got the controls fully reversed and had to neutralize everything. I hate to make blanket statements, but the airplane appears as if it will recover cleanly all by itself hands-off.
The airplane does everything I know how to do so easily and cleanly, it could have been an Extra 300S. It obviously doesn’t have the speed or the vertical, but for the audience it is aimed at, they’ll be hard pressed to see the difference and it’s a darned sight cheaper.
When I came in to land I lucked out and was cleared to land from five miles out, so I motored right in and set up for a power-off approach. I shut things down opposite the end of the runway and yanked the trim full up, since it ran out of trim at 80 knots and I wanted about 75 knots. As it was, it takes a little time to get it to slow down below about 110 knots.
I flew a Pitts-type circling pattern, turning all the way to the threshhold and the airplane felt as if it liked that kind of approach, since it stayed on speed and profile like it had been there before. As I rolled out in ground effect and on centerline, most of the runway disappeared and I concentrated on keeping my head back so I could see both sides in my peripheral vision. I didn’t know for sure where the ground was so I gingerly flaired and felt at the same time.
I felt the mains kiss off the pavement and mentally chastised myself for setting up a bounce and kept working to hold a three point so the airplane would come down out of the bounce straight. I worked for what seemed like a long time, then I realized I wasn’t coming down because the airplane was rolling on the pavement. I had originally planned on a touch and go, but called the tower and said I’d take that one. I’m no fool.
The foot work required during takeoff and landing was Citabria-simple, but the lack of visibility made the landings much, much more difficult than necessary, and that’s coming from a long-time Pitts pilot.
One thing everyone should keep in mind about the One Design: It isn’t fair to compare the airplane to any other, if only because it isn’t designed to compete with other airplanes. If the One Design class concept works, its primary competition will be itself. So the question of how it flies should be in relation to the pilot audience it is meant to address, not in relation to the hottest or newest designs out there.
One of the intriguing side notes to the One Design is the adaptability it offers to other kinds of pilots and homebuilders. Although it was designed as a bargain basement Sukhoi-killer, what it also offers is a tremendous amount of fun and performance in an airframe that is basic and simple to build. This is also one of the few airplanes that can actually be built right from the plans utilizing no pre-made components, if so desired, which makes it a real boon to the budget minded. In all probability, the material costs alone of the airframe are well under $5,000, if no pre-made components are used.
At this time Aircraft Spruce is ramping up to be the exclusive supplier as well as the plans seller for the IAC. Although they may be the exclusive plans seller, as soon as the plans get out in the hands of builders, suppliers will pop up who are ready and able to crank out tails or wings, landing gears, etc.
I also predict the airplane will become the basis for all sorts of hotrod modifications, the 180 Lyc being the first and some sort of six cylinder bomb won’t be far behind. Dan is already getting pressure to do a two-place, but that’s such a massive project, that’s not a modification, that’s a new airplane.
If, as anticipated, a huge number of builders get into this project, the economies of scale are going to result in tooling being available that will take the fear out of some of the harder processes, like drilling the main wing spar bolt holes. That process alone has always terrified Laser builders.
The One Design is exciting, if nothing else because it offers serious monoplane performance for sport pilot and akronut alike. Also, whether the One Design class concept takes off or not, the airplane gives homebuilding a new plansbuilt design that’s within the reach of many possible competitors who were previously financially grounded. Now they can get in there and mix it up with the big guys.
As I look back at what I’ve written, I think its necessary to make one more comment. We’ve all become so accustomed to Sukhois and Extras, Lasers and Staudachers that we’re guilty of being a little too blaze’ about what makes outstanding performance. We’re measuring performance against airplanes that are available to a select few and I’ve got to tell you, the margin between the One Design and the super machines is so small that only the established unlimited top dogs are going to be able to tell the difference. So who cares. That’s not us little guys.
The first time a Citabria pilot pulls vertical and hammers the airplane into a double vertical roll, his mind is going to throw off blue sparks as it yells, “It can’t possibly get any better than this!” And I’ll tell you something, in the real world most of us live in, it doesn’t get any better.
Now if Dan could just put another wing on it for us old guys.
