Hangar 9 Arrow RTF Aerobatic Trainer
Hangar 9 Arrow RTF Aerobatic Trainer
Buy One – Get One Free?
A Dual Personality
Fortunately for model aviation, more and more companies today are manufacturing high quality, Ready-To-Fly (RTF) trainers. These model aircraft arrive with the on-board radio system, the engine and the fuel system installed and tested. The new modeler needs only a screwdriver to complete what little assembly remains. These basic trainers fly as well, or even better than, most of the famous kit-built trainers of just a decade past.
Although ARF model aircraft are available in many types, most RTF model aircraft are designed as basic trainers. The wing is usually very large for the plane in order to provide the extra lift that slows take-off and landing airspeeds. The airfoil is flat on the bottom for even more lift to help the student pilot learn turns. The wing has extra dihedral; the wing tips are higher than the wing’s center section. Dihedral diverts some of the wing’s lifting force toward the center of the fuselage. Aircraft with large dihedrals are the most stable whenever the aircraft is flying straight, upright and level. All these design factors make for a perfect basic trainer.
But once the student pilot solos and wants to try basic aerobatics, these very design factors inhibit their RTF trainer’s performance. The large wing adds both the weight and extra air drag that limit an aircraft’s vertical performance. The flat-bottom airfoil produces less lift once the aircraft is rolled inverted. Many times, the pilot must apply all the available negative elevator (known as “down elevator”) just to maintain level, inverted flight. Outside loops, sharp inverted turns and other negative aerobatic maneuvers are impossible.
Even worse, dihedral tries to roll the aircraft back to upright flight during inverted flying. Dihedral also prevents the model from making attractive rolls. Most rolling maneuvers involve the trainer’s fuselage roaming the sky as if it were sliding along the inside of a barrel (called barrel rolls for this reason). During good rolls, the fuselage should rotate along the same straight line of flight it was on before the roll began. This is known as axial rolling and is not possible with basic trainer airframes.
How about an aircraft that can do both? Wouldn’t it be great if someone designed a basic, RTF trainer that taught student pilots the basic model-flying skills and would then go on to win the National Aerobatic Championship? Yes it would be, but that is an aerodynamic impossibility. However, Hangar 9’s new Arrow RTF Aerobatic Trainer is not all that far away from achieving major portions of this goal.
The Arrow is designed to function both as a basic trainer and as an outstanding aerobatic trainer as well. The Arrow has the wing mounted on top of the fuselage, called a “high wing”, to improve level flight stability like a trainer. But this high wing has a semi-symmetrical airfoil instead of a basic trainer’s flat-bottomed wing. Having part of the airfoil on the wing’s bottom, as well as on the top means, that the Arrow has good inverted flight abilities.
The bottom airfoil is not an exact replica of the top airfoil; the wing would be fully symmetrical if it were. Instead, it is a mix of airfoil and flat bottom shapes. The result is a wing that has almost as much lift as would a flat-bottom one but has good inverted flight performance, which a flat-bottom wing definitely does not.
The wing has less dihedral than most basic trainers to improve rolling ability. Yet enough dihedral remains to provide easy, stable flight when the Arrow is flying in basic trainer mode. Finally, the fuselage is highly streamlined to reduce frontal drag. We understand this shape helps keep drag to a minimum when performing vertical maneuvers, but we like the racy look this streamlining adds to the Arrow.
Photo 1
Putting It All Together
Inside this box is a RTF model aircraft with above average performance. As shown in photo 2, the radio is JR’s Quattro 4-channel system with JR 527 sport servos. These servos produce 43 in. oz. of torque through their steel-bushing supported output arms. The engine is the new Evolution 40 powerhouse and is pre-run by the manufacturer. The box includes a complete accessory kit as well. There are just four major assembly steps, each clearly explained and illustrated in the photo assembly manual.
Photo 2 Photo 3
Photo 4
The easiest place to start assembly is the wing. Both wing halves slide onto a lightweight, hollow aluminum tube (photo 4). This system is lighter than most RTFs’ solid steel bars yet strong enough for any possible stress. There is an anti-rotation pin near the wing’s trailing edge to lock everything firmly in place. After the wing halves are joined, the assembly is sealed in place using clear adhesive tape (photo 5). The tape passes over the wood aileron servo mount on the underside of the wing. Trim the tape around the mount (photo 6) to provide maximum wing contact.
Photo 5 Photo 6
After the wings are permanently joined with the tape, remove the excess tape after overlapping it onto the wing’s trailing edge (photo 7). The last wing assembly step is to connect the aileron control rods (photo 8). Total wing assembly time was 9 minutes.
Photo 7 Photo 8
Assembling the fuselage involves a screwdriver and a hobby knife or rotary grinding tool. The nose wheel strut is factory installed. But the main landing gear needs to be mounted. The main gear is made from steel wire. One end has a short bend that inserts into the fuselage to prevent rotation (photo 9). As is common in most RTF aircraft, the landing gear mounting hole is drilled perfectly straight into the wood. However, the landing gear has a slightly round bend. This bend prevents the gear leg from sliding all the way into the straight mounting hole. As a result, the gear leg is raised slightly above the fuselage (photo 10). This weakens the gear’s mounting strength.
Photo 9 Photo 10
To fix this small problem, just use a knife or grinding tool to “round out” the inside of the hole just enough to clear the bend and to let the gear leg sit completely flat in the fuselage mounting slot as shown photos 11 and 12. Do the same for the other main gear leg. The main gear legs are secured in place with two plastic tabs (photo 13). The tabs’ screw holes are pre-drilled.
Photo 11 Photo 12
Photo 13 Photo 14
The Arrow’s wing is held in place using the supplied #64 rubber bands. These rubber bands connect to two wing dowels as shown in photo 14 above. The dowels are simply inserted into the fuselage. In flight, the dowels are held firmly in place by the bands’ tension. However, to prevent their falling out during transport, you may wish to add a dab of wood glue to the dowels inside the fuselage.
Photo 15 Photo 16
Four bolts firmly mount the vertical fin (fin) and horizontal stabilizer (stab) to the fuselage. The entire assembly is clearly pictured in the instruction manual (photo 15). The two threaded rods from the vertical fin are inserted into the stab’s matching holes (photo 16). Apply a liberal amount of thread locking compound (photo 17) and install the wing nuts to hold the fin onto the stab. Make sure the wing nut ends are aligned as shown in photo 18. If not properly aligned, they will interfere with the fuselage sides as the stab/fin assembly is attached to the fuselage.
Photo 17 Photo 18
The entire tail assembly bolts onto the fuselage. Apply thread-locking compound to the two blind nuts located in the stab. Position the tail assembly and secure it by inserting one bolt into the most rearward blind nut. The rear blind nut is easy to see, as it is right under the elevator pushrod (photo 19). The forward bolt is accessed through a hole in the fuselage. Using a magnetic screw holder is a good idea here (photo 20). This simple tool that you will use forever in your modeling career costs just a few dollars and may be found in any hardware or home improvement store.
Photo 19 Photo 20
Use a small screwdriver to spread the plastic elevator clevis and attach it to the top most hole in the elevator control horn (photo21). Lock the clevis in place and slide the silicone lock ring into place. Install the rudder control rod in the same manner. Turn on the transmitter, trims in neutral, and receiver battery (you did charge both the night before beginning assembly) then make sure the elevator and rudder are centered. For more information on this, see the Sport Aviator article, “RTF?…Maybe” in the Flight-Tech section.
Photo 21 Photo 22
The last assembly step is mounting the propeller. It does matter which side of the propeller is mounted against the spinner’s back plate. The side pictured in photo 22 is mounted against the spinner, towards the engine. Last year, a basic trainer showed up at the field with a similar propeller that no one could get to fly well until one sharp eye noticed that the student pilot had reverse mounted the propeller.
Photo 23 Photo 24
Place the propeller inside the spinner with the trailing edge positioned against the spinner cone mounting holes. Tighten the propeller firmly using a wrench or modeling spanner (photo 23). When properly installed, the propeller assembly should look like photo 24. Attach the spinner cone as in photo 25.
Photo 25
We will almost guarantee that it took longer for you to read this assembly section than it will take you to actually assemble the Arrow. Total assembly time, without pre-flight checks, was just 18 minutes. After your Arrow is assembled, make sure everything is ready to fly by performing the checks outlined in “Ready-To-Fly? Maybe” in Sport Aviator’s Flight-Tech Section.
Time To Fly, Gently At First
Because the Arrow is able to perform two radically separate missions, the aircraft does have a split personality. As it arrives from the manufacturer, the ailerons, elevator and rudder controls are set for minimum effectiveness. This is the basic trainer personality. The elevator, aileron and rudder control rods are connected to the innermost holes in the servo arms (photo 26). The directions state that the control rods should be connected to the outermost holes on the control horns (photo 27).
Photo 26 Photo 27
The inner hole in the servo control arm rotates less distance than does the outer hole. This means that the control rod itself has less movement than if it were connected to the outer most hole in the servo arm. Since the top hole in the control horn is the furthest away from the surface, the control rod imparts the least amount of movement to the surface itself. This setup insures a gentle response to transmitter inputs.
We fueled the Arrow with Magnum sport fuel containing 15% Nitromethane and 20% oil. It was cold, about thirty- five degrees F, and windy. We primed the Evolution 40 engine, connected the glow starter and tried the electric starter just once. The engine really did fire immediately and settled into a high idle of 3,500 rpm. We had advanced the throttle some to insure the new engine would run. It did, and remained steady as the glow starter was removed. Hangar 9 says the engine is test run at the factory and set for most conditions.
We applied full throttle and the engine accelerated to 11,700 rpm. Even though the engine was pre-set, Hangar 9 probably did not have a thirty-five degree air temperature in mind when they set the high-speed mixture. We felt the engine was running just slightly lean for break-in, so we added more fuel to the mixture (richened it) by rotating the high-speed needle valve counter-clockwise 3 clicks until the engine turned a maximum of 11,450. Raw fuel was spitting out the muffler and the engine held this rpm for several minutes with no adverse reactions. There was no sagging, no rpm changes.
We reduced the engine to idle and found that the Evolution 40 idled well at 2,400 rpm. Again the outside temperature was colder than the manufacturer planned. The idle mixture was slightly too rich making for a hesitant engine acceleration rate when full throttle was applied. We leaned the idle mixture and the hesitation disappeared.
The Evolution 40 has several features making it an ideal engine for new fliers. First, both needle valves may only be moved within a limited range. This prevents lean engine runs that could damage the engine due to excessive heat and too little oil in the air/fuel mixture. But it is interesting to note that Hangar 9 has designed a sufficient adjustment range into the mixture controls to handle temperatures as low as 35 degrees F.
The Evolution 40 also has a flywheel. I don’t know why sport engine manufacturers did not think of this sooner. The flywheel helps the engine to maintain a reliable idle. The extra rotational energy helps to keep the engine “turning through” low speed rough spots or stumbles that might cause an engine without a flywheel to stop. Once this engine is broken-in and adjusted, we think a reliable idle near 2,200 rpm will be possible. The only downside to a flywheel is that the engine must overcome the flywheel’s inertia when accelerating. But the time lag is very small and not a factor when sport flying.
The lower a reliable idle can be set, the slower the final landing and touchdown speeds can be, depending on the stall speed of course. As for airspeed, the Evolution 40 is supplied already fitted with a wide blade, very stiff, 3-bladed propeller. Although 3-bladed model propellers on 40-60-size engines are less efficient than 2-bladed ones, 3 bladed propellers are better at maintaining constant airspeeds. In theory, a 3 bladed propeller helps to prevent airspeed gain during descents while keeping high-speed and climb-speed within the same limited range. We were looking forward to testing this theory.
There was a strong wind, with gusts to around 20 mph, as we placed the Arrow on the runway. Right after a gust ended, we hit the throttle and the Arrow started to roll forward. The airplane accelerated fairly rapidly and reached liftoff speed in about 50 feet. We judged this distance to be about 10 feet more than a flat-bottomed winged trainer would have used. As photo 28 shows, we were holding full up elevator and yet the aircraft rotated cleanly with no tendency to drop a wing. Of course, right at liftoff, a strong, 90-degree wind gust hit us from behind. The Arrow started to wingover to the right since the mains were still on the ground when the gust hit (photo 29).
Photo 28 Photo 29
Even though the controls were set to minimum movements, a little aileron immediately righted the Arrow and it climbed cleanly into the bright blue sky. Almost no trim was needed, just two clicks of right aileron and one of up elevator. We were surprised that the Arrow penetrated the heavy winds with little effort. The constant gusts from varied directions would have made flying a true basic trainer a task requiring both rudder and ailerons. But the Arrow did not need rudder input despite the heavy, changing winds.
It is true that, once in the air, an aircraft is part of the airstream and does not react to steady winds except in relation to its ground path (we will cover this in a separate article). However, constantly changing wind speeds, with upwards and downwards components, do affect an aircraft in flight. The aircraft needs a few fractions of a second to adjust to the speed change and new wind direction. During these periods, an airplane can be difficult to keep in level flight. The Arrow however, had little trouble flying level and straight despite the winds.
Several factors helped the Arrow handle the wind better than the usual basic trainer. The Arrow has a slightly higher wing loading than would a basic trainer. The semi-symmetrical airfoil is less sensitive to wind gusts. The fuselage also has a smaller frontal area. Whatever the reason, we liked the Arrow’s wind and gust handling abilities.
During flight, the Arrow responded like a basic trainer, even in turns. The 3-bladed propeller functioned as planned, keeping the airspeed within a narrow range, especially during descents. The aircraft was stable in level flight, showed no bad habits, and had an aerobatic capability far above that of a basic trainer (photo 30). Even slow flybys were easy in the high wind. Note the wing tilted into the wind in photo 31 to keep the ground path straight along with slight right rudder.
Photo 30 Photo 31
Holding this type of wind correction is more difficult with a basic trainer than it was with the Arrow. We also liked the way the sharp nose, low-dihedral wing and sharply raked vertical fin looked on this aircraft.
Just as every bomb ever dropped from any airplane in history was always 100% successful, the bomb always hit the ground (water) somewhere, so too must any successful flight end in a successful landing. We lined the Arrow up for the runway and held a little wind correction (little?) as shown in photo 32. We noticed that the Arrow had a higher airspeed than a basic trainer during the approach, but was otherwise as easy to handle.
Photo 32 Photo 33
As the Arrow flew closer we noticed that it was easy to control the descent rate with the throttle. Even when nose high (photo 33), a little throttle slowed the rate of descent like magic. The Arrow maintained its nose-high glide path right to the ground (photo 34), even when the wind died for a short time. The nose-high, main gear touchdown was automatic (photo 35).
Photo 34 Photo 35
The flight data results are interesting. Takeoff, cruise, climb, stall approach and landing speeds are all slightly higher than most basic trainers we have tested so far. But the difference is minor, usually only a few miles per hour and suitable for a basic trainer. The climb rate is much lower, but we think the 3-bladed propeller may be the cause.
What The Arrow Is Really Meant For
We proved to our satisfaction that the Arrow would make a good basic trainer as delivered. But the box says “Aerobatic Trainer” so we needed to give the Arrow its head through all the basic maneuvers. First, we adjusted all the control surfaces for maximum deflection. The control rods were moved to the outside of the servo arms. The clevises were relocated into the control horn hole nearest the control surface. The aileron connectors were screwed inwards 15 turns as well. All adjustments were reset to insure the control surfaces remained neutral.
Full elevator was no longer required for takeoff. The Arrow rolled only about 25 feet and took off with authority. The liftoff speed was 5-6 mph slower than with the trainer settings but climb out speed and rate of climb were the same. The Arrow felt completely different in the air. The aircraft was responsive, lively and obeyed the slightest control input. The heavy wind became even less of a factor as the Arrow seemed to compensate immediately for gusts and direction changes. We like the handling of this aircraft.
Photo 36 Photo 37
It was time for some fun flying. The first maneuver we tried was a slow roll. We turned the airplane into the wind and started a slow right roll (photos 36-40). The airplane responded just right, but we noticed the first thing about the Arrow that will need some work. The beautifully covered dark blue wings were a little hard for these old eyes to see against the bright blue sky. We think a white stripe on one side would make everything visible again. The roll continued and used about 200 feet to finish. That is a nice slow roll for a high wing aerobatic trainer. The aircraft rolled well in both directions.
Photo 38 Photo 39
Photo 40 Photo 41
Next, we pulled vertical and did a Stall Turn. Surprisingly, the Arrow rotated in its own wingspan and showed little tendency to roll with full rudder input, as most other trainers would do. Photo 41 shows the Arrow on the way down from the Stall Turn. No aileron correction was held and yet the wings are only about 10-15 degrees from level.
Inverted maneuvers were even better than with the more gentle settings. Outside loops were about 100 feet in diameter and required only half the available “down” elevator input. As we have mentioned before, it is a Herculean task to outside loop most standard trainers but the Arrow made it a pleasure. The Evolution 40 pulled well in all vertical maneuvers. Standard inside loops were also about 100 feet in diameter. The Arrow would loop consecutively without dropping a wing. We should mention however that we had laterally balanced the wing as discussed in “RTF…Maybe” so that might have helped this performance aspect.
We tried snap rolls and found that, while the Arrow had no trouble performing these easy-to-do but attractive maneuvers, the snap rolls were slower than we would like. A little experimenting showed that the Arrow would snap rapidly if the maneuver were entered with the nose held about 45 degrees above the horizon.
The Arrow will teach all the basic maneuvers: loops, multiple rolls, slow rolls stall turns, snap rolls, outside maneuvers and many others. The Arrow performs these maneuvers more slowly and more easily than would most aerobatic sport aircraft, yet the Arrow maintained both altitude and flight path as would an aerobatic airplane.
There is only one aerobatic maneuver that the Arrow will not fly well. Like most high-wing airplanes, knife-edge flight (the wings are vertical to the ground and sky) is very difficult. In true, 90-degree knife-edge flight, the Arrow attempts to pull the aircraft’s nose upwards towards the wing as the rudder is used to hold the airplane’s nose level. In aerobatic terms, this is known as “walking towards the canopy.” The Arrow walked enough that nearly half of the available down elevator was required to correct the walking. But then the Arrow would start to dive away from the roll. In addition, the Arrow’s frontal fuselage side area is not large enough to maintain level flight.
However, the Arrow is so well balanced that 4-point rolls were not a problem. Even at the two vertical points in the 4-point roll, the Arrow did not require much “top rudder.” As long as the points were not prolonged, the Arrow had no problems during excellent 4-point rolls.
We must stress that prolonged knife-edge flight is nearly impossible with any high-wing aerobatic aircraft, not only the Arrow, and is not even conceived of by standard trainers. The Arrow’s real advantage to newer aerobatic fliers is its outstanding ability to perform almost all the basic classes of aerobatic maneuvers honestly, with style and with grace, but without the touchiness, tip stalling or jerky quickness of advanced aerobatic performance aircraft.
There is one last Arrow capability that truly endeared itself to this old instructor. The Arrow will teach the newer pilot how to really land advanced model aircraft. Standard basic trainers almost land themselves, automatically compensating for poor throttle and attitude control. The Arrow can be landed this way in the basic trainer stage of a new pilot’s learning. But model aircraft above the basic trainer stage require throttle to control altitude and elevator to control airspeed (see “Basic Landing Techniques”). Unless the standard trainer is weighted with lead, this landing technique is hard to learn. The Arrow will respond to this advanced landing technique, as would a high-performance model aircraft.
A new RC pilot can learn to fly using the Arrow. After soloing, the pilot can also learn basic aerobatic maneuvers on the Arrow without having to deal with the usual aerobatic aircraft’s handling problems. While it will never be able to win the World Aerobatic Championship, the Arrow could be flown well in either IMAC Basic or Pattern Sportsman classes. For a 2 inr 1 aircraft, we don’t think any new RC model pilot could ask for more.
In fact, we think enough of the Hangar 9 Arrow that we are going to make a few changes to see if we can improve its performance even more. The supplied 3-bladed propeller may be the best available for the Evolution 40. But we suspect this engine has hidden power reserves yet to be tapped. We are going to try several high-performance propellers, install a bolt-on wing mounting system, seal the control surface gaps, and install a larger fuel tank. We’ll report what, if any, improvements result in this already fine aircraft as soon as the weather warms up just a little.
For more information on the Hangar 9 Arrow, please go to: www.horizonhobby.com or to www.hangar-9.com
Q
Photo 42 Photo 43
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Additional Aircraft SpecificationsManufacturer: Hangar 9 Length: 52.5 in.Cost: $350.00 Wingspan: 63 in. Radio: JR Quattro 4-channel Wing Area: 710 sq. in. Servos: 4 x JR 527 Wing Loading: 18.3 oz./sq. ft. Engine: Evolution 40 Weight: 6.63 lb. Airfoil: Semi-SymmetricalSpecial Airframe Features: Semi-Symmetrical Wing, 3-Bladed Propeller, Quick Assembly. |
| Notable Positives Excellent aerobatic abilities Extremely fast assembly Very good looks Light flying weight Good basic trainer performance Pre-Run, factory-adjusted engine Notable Negatives |
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Posted by Frank Granelli
on Filed under Advanced Trainers.
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