Reprint of: DR-109 Flight Test Report
by:Clive Davidson
DR-109 Flight test Report
I was very fortunate to be introduced to Dan Rihn designer of the DR-107 "One
Design" and the two place DR-109 at the annual Sun 'n' Fun fly in. Later, I was
invited to fly with him. It is often said that you sum up the person you meet in the first
few seconds and I summed Dan up as a well built, relaxed, friendly and very
knowledgeable fellow. The immediate impression of his polished red and white
machine trimmed with twin slim blue lines was that it too was well built, with
particular attention to detail.
Dan has been immersed in aviation from the word go, even before he was aware of
it, through osmosis. Of the more formal and measurable yardsticks he soloed a
glider at 14 and a J-3 Cub at 16. His PPL was in his hand by 17 and a year later Dan
had a CPL/IR. He studied Aeronautical Engineering at Northrop University where he
also built a Pitts and qualified as an A&P (Aircraft and Powerplant) engineer. He now
works for the Northrop Corporation (no relative) as head of a think tank who consider
new aircraft designs. Of the projects that can be mentioned are; the F-18, F-5X,
"Tacit Blue", B-2 and the YF-23. I expect in time we will learn of other publicity shy
and retiring aircraft he has been involved with.
Away from the office and in his spare time he has designed several aerobatic
aircraft; three biplanes; the Sun Bird, (marks I and II), plus the Phoenix and the
Goshawk. A mid wing monoplane called Sabre which was later put into production
as the Edge 540 built by Zivko. These aircraft were designed and built before the
personally initialed and century series aircraft arrived; first the single seat DR-107
and now his latest creation bearing a strong family resemblance and character, the
larger, two-seat DR-109. (By the way, there is an aircraft designation in that
numerical gap between the 107 and the 109, the yet to be built 108, a single-seat
version of the 109.)
In actuality the DR-109 was sketched up much earlier than the One Design. Here is
how Dan tells the gestation of the DR-109- "When I attended the 1988 World
Aerobatic Contest in Red Deer, Alberta Canada, I saw the mid wing Extra 300 which
made its public debut. I was very impressed with the Extra. Here was a true
Unlimited aircraft capable of carrying two people and had good cross country speed
and range. A really incredible package. The only problem for me owning one was
that it was going to be built as a certified production aircraft and therefore very
expensive. The solution for me was to design and build my own version using
typical homebuilt materials and methods. I came home and drew up my two place
aerobatic monoplane. The big difference I made was to design it with a low wing
design from the start to ease (note the Extra 300 now has a low wing and is known
as the 300L). At the time I was competing in Unlimited and did not have the time or
money to build it. I shelved it and chalked it up to another dream. Several years
later after I designed the DR-107 One Design several people asked me about the
possibility of making a two place One Design. I resurrected the original drawing and
got busy with the detailed design."
The DR-109 is a two-seat, dual controlled, unlimited aerobatics competition aircraft
of scintillating performance. In a thumbnail sketch it can cruise at 178 mph (154.1
knots, 186.4 km/h), has a climb rate of 2,800 fpm, a roll rate of 360? a second and is
stressed to +/-10g when solo, or +/-8g when dual. Quite a portrait - and it is available
as a kit!
This is a niche market in which I can only think of two other real contenders; the
Giles 202 (now out of production) and the Velox Revolution Mk.II. All three have a
remarkably similar resemblance to each other. They are, of course, related by intent
and convergent design.
Dan briefed me on the cockpit and opened the lightly smoked canopy to the right so
that I could see and compare the tandem seating and facilities. The welded steel
truss frame was immediately apparent but the item I was drawn to was what would
normally be termed the rear instrument panel. It is just a slim and functional grey bar
holding the minimum of conventional dials and gauges, plus a small screen on the
right. Entry is effortless and it is easy to settle into the cockpit, its dimensions being
generous. Both front and back cockpits are 24" wide (a whisker under 61cm), and
pilots of up to 6 feet 5 inches (1.95m), weighing 240lbs (109kg) have flown the DR-
109 and all had ample room. The view is excellent. I could move my head and
shoulders around within the cockpit and no optical distortion was apparent through
the canopy. The latching arrangement is sturdy and simple, operable from the rear
seat. The seat backs are adjustable to an inclination of 30?, which allows good g-
tolerance. The rear set of rudder pedals could not be sited too high, as there are
limits that the front seat can endure; too high would place them in his armpits. I very
much liked the protective rear pilot rudder pedal shrouds that are sited either side of
the front pilots' seat and hips. It has been more than a few times while flying from
the front seat of a Pitts, I have ended up with my flight suit dirtied by the insteps of
the rear pilots shoes, despite dire warnings about bringing mud into the cockpit.
These shrouds also prevent the slim possibility of the front seat belts becoming
entangled with the rear rudder pedals. The straps in the 109 can be further tidied
and held clear of the seat by a taut elastic octopus on each cockpit side. The rear
seat back can be removed so that the inner rear fuselage may be inspected
internally. There is an ELT under the wooden and very firm seat - very practical.
Nothing extravagant or technically tricky here.
I eased the control column to the extremities of the box and cockpit. It was near
frictionless in its smooth operation with no backlash. The elevators and ailerons are
rod operated. Let go of the control column and it centres itself - beautifully balanced.
I hoped the expected promise and the actual reality of smooth and effective control
were close cousins!
The rudder and steerable tail wheel are cable operated with toe brakes fitted. It is
fortunate that the front set of rudder pedals have now been modified on production
kits, as in this prototype they were awkward to operate being mounted so low. That
in itself was not a problem, but as the spar passes under the front pilot's knees and
"the heel was above the pivot point so the rudder bar was in the arch of the foot, it
was not real easy to get good leverage" commented Rihn. The front cockpit has
since been slightly modified; the internal fuel tank now being both wider and
shallower. Subsequently there is more room in the front well and the rudder pedals
have been raised higher as in the single-seat One Design.
Instrumentation was minimal, just as one might expect in clean efficiency. On the
right of the ASI, altimeter and compass and above the minimum of service switches
was a green screen of the EIS (engine information system). There was one in the
front cockpit as well, which could be scrolled independently. Linked to a computer,
there was a choice of six pages covering all that should be required to monitor the
engine functions and state; oil temperature and pressure, CHT through to manifold
pressure, fuel flow and voltage were but a few of the measured parameters. Should
a problem arise, a separately mounted red warning light flashes and the system
automatically selects the page that shows the problem. Once acknowledged the
operating pilot may still choose any other display required. The screen is easy to
read in direct sunlight using a reflective mode and in poor light yellow-green LED-
backlighting illuminates the display. The system is manufactured by Grand Rapids
Technologies Inc. and condenses the engine condition display to a 4½" by 2¾"
screen, (11.43cm by 6.98cm). From a practical point of view it is thought that the
system will outlast many of the standard instruments that it replaces and at a similar
price.
The throttle fell easily to hand and included a PTT button on the top. The propeller
pitch lever is similar to the Pitts' lift and push rod type, while a simple lever operates
the elevator trim. Only the elevators have a trim. Excluding an aileron and rudder
trim means a less complicated aircraft and a faster build time. It also indicates that
the forces through the aircraft controls are manageable.
Out of the cockpit and standing by the left wing root, the mix of construction is clear.
The fuselage has a welded tube truss and from the firewall aft of the cockpit is
covered by sheet metal, as is the turtle deck, all secured by stainless screws. Each
panel is removable for inspection. The one piece symmetrical wing is all wood,
although at first I had to check this, as I thought it to be composite, being so well
finished. The leading edge is rather bulbous and with 16% thickness is capable of
generating lift at high angles of attack during slow flight, erect or inverted. The main
box and secondary spars are of Douglas Fir and Sitka Spruce, the ribs are of a
Mahogany ply and the whole wing is covered with Okume plywood. On the
underside of each wing there are two circular, clear view panels so that the aileron
circuitry and rods can be inspected - a nice touch. The ailerons are constant chord
and extend for 75% of the wing. These are constructed in the same manner and are
mass balanced and aerodynamically counter balanced. Spades, or balance surfaces
hang below each aileron. The tailplane, elevator, fin and rudder all have steel tube
spars and sheet metal ribs. These are fabric covered and double wire braced. I had
to admit to being comforted by the fact that each elevator is attached to the tailplane
by three hinges, nice to know if you are engaged in a tail slide. As standard, the
rudder and tail wheel steering cables exit the rear fuselage and are, of course,
examined prior to each flight.
At the sharp end of the airframe the design can accept four-cylinder, 200hp right up
to the six-cylinder smoothness of 300hp units. But like all things, you would pay for
entering that higher performance bracket. New, the 200hp Lycoming engine can be
bought for just under $27,000 (around £16,550 @ $1.63). To acquire the next 100hp
and if it were to be bought pro rata, it would cost $169.41 (£103.93) for each horse
power! This makes the 300hp Lycoming price $43,920 ( £26,945). N109RD is fitted
with a six-cylinder 260hp, "...and that engine sir, retails at $36,945 ( £22,665)".
The main fuel tank of 20 US gallons (16.67 Imp. Gallons or 75.8 litres) rests in the
front fuselage above a header tank of 10 US gallons capacity. Along with two
optional auxiliary wing tanks of 8 US gallons, it brings the cross country tankage up
to 46 US gallons (38.3 Imp gallons or 174.4 litres). Fuel consumption figures
supplied by Dan suggest a range of around 550 statute miles (465nm or 860km),
with a 45 minute reserve and an endurance of 3 hours 45 minutes at 55% power,
indicating a fuel burn of 12 US gallons per hour (10 Imp. or 45.5 litres an hour). If the
optional auxiliary tanks were not filled or incorporated in the first place, the
endurance would drop to 2 hours and 25 minutes, but the last thing you require while
engaged in aerobatics is extra weight that may prejudice the stress calculations and
almost certainly degrade performance. What do you require, range or vertical
performance? What is an acceptable compromise?
The engine is neatly cowled with a two-piece fibreglass unit and confirms the design
as a multi-medium build project utilising wood, metal, ceconite and fibreglass. There
is something here to stretch every builder on the ground and in the workshop. A
composite three-blade constant speed MTV-9 propeller completes the front end.
The fuel drains are located just aft of where the one piece aluminium sprung
undercarriage legs meet the fuselage. The wheels are neatly spatted 500 by 5s and
tie down eyes are on the inboard hubs. While these items are being checked it is
possible to look up through the lexan floor for any loose cockpit items that may be
resting under the web of welded tube. The underbelly was clean and free of oil, the
drain that is now very much a standard fitting on aerobatics aircraft, which carries
the oil thrown out through the breather during negative g, exits just far enough ahead
of the tail wheel so as not to lubricate it too liberally.
Having been immersed in the individual items of the aircraft it is pleasant to stand
back and view the whole. I liked the manner of this man's project. We would see
early the following morning how all the details dove-tailed in their operation and
flight, when cooler and calmer air would be available at nearby Lake Wales airport.
As I was once told by my mentor, a former Royal Air Force pilot of the 1920's who
first soloed an Avro 504, "If you cannot do aerobatics, then the next best thing is to
learn its manners and behavior in the circuit – don't just bumble about straight and
level on a cross country if you wish to learn, go do lots of landings!" Fortunately, I
had the opportunity of both aerobatics and circuits in the DR-109, the latter while
waiting for the camera ship to arrive.
Seated and strapped in, the rear seat is comfortable and the view excellent. The
one-piece smoked canopy had little apparent distortion and no frame members to
obscure the view ahead. Dan's head and shoulders were obviously in front of me
and admittedly he blocked the immediate view ahead. With engine started the
steerable tail wheel and a good pair of brakes allowed the swinging of the nose from
side to side in S-turns, clearing the area ahead. With Mag' checks at 1800rpm and
the prop cycled we were almost ready.
When in Rome……CIGAR - a new check.
Controls; cant column all around the box ensuring no restrictions, ailerons and
elevators rising and dropping, rudder pivoting as it should without any friction or
slack (whiplash).
Instruments; not many here but all checked during the taxy, T 's & P's were all within
limits.
Gas – fuel tank selected, contents and pressure satisfactory.
Attitude; elevator trim to neutral.
Radio check; still on field frequency, intercom and squelch set.
A scan up the hill to finals and both bases, a radio clearance and we lined up. With
the tail on the ground and the right foot ready to counter the swing the power was
brought on smoothly and the acceleration brisk! T's and P's good, full power. With
increased rudder holding the nose easily without the need for brakes, I eased the
control column forward and the tail wheel lifted smoothly off the runway. With the
runway centre line flashing beneath and direction easy to maintain, we were
airborne within 200 yards and accelerating briskly in ground effect up to 100mph. By
the time the nose was in the climbing attitude we were indicating 120 mph. There
was no VSI but, by inspection, the rate of climb was around 1,900fpm.
The trick within the circuit is to make things as easy as possible. In the climb out,
trim for 120mph and use the same speed in the downwind leg before reducing
power and rpm (remember throttle back and rpm up), 21 inches and 2,500rpm being
appropriate. Another new check – GUMPS.
Gas; on and sufficient. Undercarriage; welded. Manifold. Prop'. Switches and
security.
Descending in a curving arc with a constant aspect approach, the view was
unobstructed. Speed reducing and my more familiar and normal litany - PUFA. Pitch;
fully free, throttle already fully aft so the unit is no longer constant speeding and with
the propeller lever pushed forward we wouldn't wake everybody in the next county
with the awful wowar! That would have made us so distinctive and unpopular.
Undercarriage; yes! Flaps; nil. Altimeter; set.
There was an audible swish of air around the airframe as we crossed the threshold
at 70mph and touched down at around 60. I had the control column fully aft and the
tail wheel met terra firma first, a slight unbading. It was not quite a three pointer,
more like a one, two (onto the mains) and then three-pointer! With power on we
continued back into the circuit. I tried a variety of slipping approaches and with a
conscious effort flared without the control column reaching the aft stop - they were
all three pointers. On the runway she ran straight, not skittish, directional control
through the steerable tail wheel was light and effective. The wind had initially been
straight down runway 35 at 10-12 knots but increased to 18 knots and veered 60º off
the runway. Of the seven landings I tried, four from the rear and three from the front
cockpit, all were handled easily by this capable machine's generous rudder. No
awkward manners were apparent, peg the speed and trim accurately – oh, and
restrict the stick aft movement for a perfect three-pointer.
Away from the circuit I was given the opportunity to learn more about the 109's
character. From the cruise at 160 mph, trimmed hands and feet clear, the slip ball
stationery and in balance, I pushed the control forward 10º nose down. The speed
rose by 10 knots and I release the control column, letting it float, stick free. The trim
overcame the dive and we pitched up into the first part of a recovering phugoid.
After 3 cycles of rising and falling these were only slightly damped, no bad thing for a
seriously maneuverable aeroplane but it exhibited no problems in straight and level.
From the same speed I rolled left to 45º, right to 45º and back again without any
balancing rudder, looking for the nose to swing or yaw away from the direction of the
roll. No discernable adverse aileron yaw at all.
The roll rate was impressive, from around 300 to 360º a second, depending on
airspeed and of course airflow. Breakout forces were light aided by the spades. The
wing lacks inertia so can be zapped into a roll and stopped with complete control, as
long as you are used to their rapid roll, of course! Four-pointers or hesitation rolls
were easy. Zap to right knife edge, zap to the inverted, zap, zap to left knife edge
and back to straight and level.
Perhaps there is a flaw here. In a timed four-point roll, the pause should be as long
as the roll itself. This means each 90º of roll only takes a quarter of one second and
the pause before the next quarter rotation should be of the same length. If the
judge/observer on the ground blinks, she may miss the hesitations as the whole
manoeuvre would only take two seconds. In the cockpit you would be in no doubt
you had started and stopped several, well to be exact four, times. Who are we
doing this for anyway? Above 200 mph the force required to apply the ailerons grew,
although this is bad thing as it provides another speed cue.
N109RD responded predictably in both directional and lateral axis. From a glide at
72 knots (1.2 times stall speed), in a cross controlled condition, the wing rose when
the aileron and control column was released. Again, from the same cross-controlled
flight, when the rudder was released the nose swung to its 'correct' position, aligning
us in the direction of flight. The results were encouragingly the same from a right
wing-low slip. As the wings have no dihedral and that small looking fin I didn't
expect such a good yaw/roll couple. To confirm the fin's correct size the aircraft was
placed in a straight side-slip, as opposed to a slipping turn where aileron overcomes
rudder. With 20° left wing low the nose could be held on the horizon with right
rudder. The good yaw/roll couple ensures she can be flown hands-off, to write a
play, a letter, note new frequencies or fold a chart (sectional…..sorry).
Stalls are accomplished without any wailing horn, bells, or flashing red lights. The
standard cue of the air separating from the wing and striking the full travel elevator,
whether up during erect flight and up again in inverted flight, is transmitted through
the control column as a juddering vibration. Erect and inverted, straight and level,
power at idle, stalls are at 60 mph, with the ailerons functioning right down and into
the stall. Climbing and descending turning departures were easily countered, back-
off the control column pressure and if it hasn't rolled to the nearest horizon on its
own, use those lovely ailerons to bring it back.
Stall plus yaw equals spin. The rotation was fast but could be stopped with
precision. Both the standard and Muller recovery worked well. Inverted appeared
easier to exit because the fin and rudder were in clean undisturbed air.
To give some idea of its clean lines and excessive power, from 180 mph, with a 5g
pitch-up, we climbed 1800 feet vertically so its possible to squeeze in 3½ vertical
rolls. With two-up I was happy slowing them down using half aileron with a pause in
between. Then another pause, into a stall turn (hammerhead) and from the next
vertical a bunt, a push over the top with wings level.
Maximum flick speed is 150 mph and I still cannot decide which has a faster
rotation; the standard zapping rate of roll or the flick. Logic tells me that with all
things being equal, the rate of roll increases with airspeed but the flick requires a
slight releasing of the control column to prevent too much drag slowing the rotation
down. Both are fast and controllable in the inverted as well.
Dan commented that "the goal of the DR-109 was to provide the home builder with a
world class aerobatic performance at less than a 1/3 of the cost of a certified
equivalent". The DR-109 is an extremely laudable concept. The better the build
quality and the greater the power unit, coupled with the determination of its
pilot/constructor, then the closer Dan's goal is to becoming reality. The enjoyment of
my flights were complimented by Dan's open attitude and relaxed manner; there is
nothing like flying with a man who has designed and built his own capable machine.
The DR-109 is truly a joy to fly, with great agility and manageable stability.
I had four flights in the DR-109, totaling 1 hour 55 minutes including the air-to-air
photographic sortie. I was greedy and wanted more. I have an insatiable appetite
for this type of machine but Dan's father, Dick Rihn had a deadline and a twelve
hour ferry flight back to California. I couldn't really just play and delay him further,
could I? Another interesting note here was that Dick Rihn, the past President of the
IAC, (International Aerobatics Club) and at the age of 73 is the World's oldest
competing unlimited aerobatics pilot. Additionally he built and flies an aircraft
designed by his son Dan, the DR-107 "One Design" is a single-seat aircraft intended
for a single class of aerobatics competition – unlimited!