Hobbico HobbiStar 60Mk III

 

MOVIE FILES

Ron Farkas reviewed Hobbico’s HobbiStar 60 Select in Sport Aviator’s “On the Flight Line” Section. In Hobbico’s lexicon, “Select” means the airplane is supplied as a Ready-To-Fly (RTF) model. The on-board radio system, engine, fuel tank, and wheels are installed. Ron finished assembling the HobbiStar 60 Select in about an hour or so. After doing all the preflight checks detailed in Sport Aviator’s article, “RTF? … Maybe,” Ron flew the HobbiStar 60 and found it to be an excellent airplane.

But it just so happens that there is another HobbiStar 60 kit available, the Almost-Ready-To-Fly (ARF) Mk III version. It also just so happens that the HobbiStar 60 Mk III ARF model is being used to illustrate some modifications that can be made to most ARF aircraft for Model Aviation’s “From The Ground Up” article series. Here was a chance to really find out how the HobbiStar 60 can really perform. This was too good an opportunity to resist. Actually, I didn’t even try.

So in went the Eagle Tree Systems Flight Data Recorder. This faithful device has allowed Sport Aviator to quantify many aircrafts’ performance. It also made possible an objective evaluation of the various modifications that we did on the ARF version. Some of the results were very interesting.

Just A Few Changes

Photo 1

The HobbiStar 60 used in this Test Report has a few durability and performance enhancements not found in the factory “stock” ARF version. How and why they were done is the subject of Model Aviation’s “From The Ground Up” ARF No. 4 article. As soon as this article is published in Model Aviation, a link to the article will also appear here. The performance improvements are our subject here.

The major performance modifications were done on the wing. Look at photo 1, click on it to enlarge it for a better view, and you might notice that there seems to be a servo sticking out of the wing. This servo controls only the right aileron. There is another identical servo controlling the left wing’s aileron. The “stock” ARF HobbiStar 60 normally uses just one servo, mounted at wing center, to control both ailerons.

Why make this modification? Having two aileron servos permits a modern computer radio to transform the ailerons into flaperons. Flaperons perform all an aileron’s usual duties but can also be lowered to act as flaps. Flaps increase the wing’s lifting power and add drag. With flaps deployed, descent angles are steeper making the landing approach easier to control. Flaps also reduce the landing approach airspeed, lower the airplane’s stall speed and stabilize slow flight at high angles of attack.

Computer radios also allow flaperons to be adjusted to reduce or eliminate adverse yaw. Using the computer transmitter, the pilot can adjust the aileron differential as required to compensate for the aircraft’s adverse yaw tendencies. As an added bonus, the flaperons can be mixed to the elevator so they function identically to the flaps on a Control Line Stunt model. The flaps are lowered when “up” elevator is applied, increasing the wing’s lift even more than does the elevator alone. The flaps raise above the wing to reduce lift when “down” elevator is inputted. This control surface combination produces some outstanding aerobatics.

 
Photo 2    Photo 3

Finally, the two-servo system makes for short, very direct control rods (photo 2). The torque rod system used with single aileron servo systems (photo 3), with all its slop and flutter potential, is eliminated. Servo force applied to the ailerons is doubled, providing more control and a tighter “feel” for the pilot. Control surface vibration, called flutter, that can lead to lost ailerons is virtually eliminated.

The extra servo and covering costs plus the hour or so required installing the two-servo system are more than worth it. The extra performance is permanent, the inconvenience very temporary.

 
Photo 4    Photo 5

Look closely at the above photos and you may note that something seems to be missing. The fuselage has a cleaner, more realistic, appearance. That is because it is “cleaner” (has less aerodynamic drag) since there are no rubber bands over the wing and no dowels sticking out of the fuselage. The wing is firmly held in place by three nylon bolts. Compare the appearance difference between the HobbiStar 60 Select, with its rubber bands, to the modified ARF in photo 5 to see the difference.

Besides looking better, the bolt-on wing does have a performance advantage, but probably not the one that would first come to mind. Yes, there is less drag using wing bolts so top speed should be faster. But this is a trainer after all and is not designed for pylon racing or for setting world speed records. Whatever speed increase there is must be so small, I didn’t notice it.

But, the bolt-on wing mounting system does insure that the wing is always in the same position from one flying session to the next. The trim settings do not change. The aircraft does not require resetting the trims during the first flight every time the pilot gets to the field. It is always easier to learn piloting when an aircraft has constant trim settings. It’s a bit safer too, as that first takeoff with a misaligned wing can be exciting.

The nose wheel has been replaced with a twin-strut system for extra durability. The firewall has been reinforced to resist the stresses imposed by hard student, or occasionally my own, landings. The fuselage servo tray has been reinforced to stay in place over the thousand or so hours this aircraft will fly as has the servo screw mountings. All the fuselage former joints have also been reinforced with glue fillets.

 
Photo 6     Photo 7

Performing all these modifications are detailed in the Model Aviation articles. But a quick view of how it is done is shown in photos 6 and 7. Photo 6 shows the three maple blocks drilled and tapped for the nylon ¼-20 bolts. Nylon bolts are used to allow the wing to separate from the fuselage with minimal damage, there always is some, during really hard landings. The maple blocks are reinforced with spruce triangle stock. Balsa stock reinforces the servo tray joint to the fuselage sides. There are additional spruce reinforcements below the servo tray as well.

Photo 7 shows the twin-strut nose gear. The mounting blocks must be drilled out to accommodate the thicker metal strut and a different nylon steering arm, provided with the new nose gear, is also used. The spring absorbs landing shocks but the twin struts do not permanently deform after a hard landing as do single strut systems.

Radio and Engine

RTF models are very convenient and can be in the air just minutes after the box is opened. ARF models require a few evening’s work and some building skills. But ARF’ models allow the pilot to chose the radio system and engine to be used. RTF models make that decision for the pilot.

To motivate the HobbiStar 60, we picked a classic powerhouse. The O.S. Max 61 FSR we used is an older model and has been flying since the 1980’s. The FSR features a ball bearing supported crankshaft, a very reliable idle and some powerful top end. One of modeling’s Engine Gurus, Richard Black, rebuilt this engine three years ago but this is its first aircraft installation since the rebuild.

The 61 FSR reaches a top end of 11,900 rpm when turning an APC 12 x 6 in. propeller. Since all top ends must be set about 3-400 rpm rich to protect the engine, the FSR’s useable top end was set at 11,500 rpm. This is more than respectable for a 20+ year old engine and rivals most of today’s engines. The idle proved reliable at 2,200 rpm.

My limited experience with the O.S. Max 65 LA provided with the HobbiStar 60 Select RTF has been that this engine’s useable top end with this propeller is about 11,200 rpm. Both engines’ performance is close, but the edge goes to the FSR and will probably show up in the climb.

The radio is Futaba’s new 7CAP 7-channel system. The T7CAP transmitter uses PCM for extra signal discrimination and a “tight” feel from pilot to airplane. The servos are Futaba’s digital sport servo, the S3151 on everything except the ailerons. Two S3003 analog sport servos work those surfaces. The digital servos provide better control response so the analog aileron servos will be replaced with the superior digital ones as soon as my piggy bank gets a little fatter. (Ok I heard that! The bank, not me OK?)

The computer transmitter allows full flaperon use and, with a little finagling, coupled elevator/aileron mixing on the same switch. The flaps lowered 35 degrees for all the test flights. The Center of Gravity (CG) was set exactly per instructions. This aircraft weighed 7 lb. 14 oz versus the RTF version’s 7 lb. 13 oz. weight.

This is somewhat amazing since the ARF aircraft is carrying an extra servo, longer servo wires, wing mounting blocks, servo tray strengtheners and a heavier nose gear. Rubber bands and wood dowels must be heavier than most pilots think! Actually, the FSR is lighter than the 65 LA and the R7CAP receiver might be slightly lighter than the sport receiver in the Select version. The RTF’s stabilizer/vertical fin bolts are replaced by much lighter epoxy adhesive as well. Even so, the ARF kit must have some wood that was lighter than the RTF version to allow the weights to be nearly identical.

Let’s Get To The Flying Part

Photo 8

Since this is a Test Pilot Report we should not be discussing building, radios and engines too much. Ron did that very well and the HobbiStar 60 ARF builds much like any other ARF reviewed in Sport Aviator. As photo 8 shows, this is a standard ARF kit with all the standard ARF parts. So how about getting to the Test Pilot part?

 
Photo 9     Photo 10

Great! Bolt on the wing (photo 9) and let’s start with the Takeoff. The runway was grass, cut a little too long, and the wind was about half crosswind, half down the runway. Call it a 45 degree crosswind. With full power, the aircraft accelerated down the runway then lifted off at 40 mph (photo 10). The HobbiStar 60 has a semi-symmetrical wing. While this wing provides excellent inverted performance, it will sacrifice lift to get it. The lower lift figures show up in higher airspeeds across the entire performance range.

After liftoff, the HobbiStar climbed out at 1,700 fpm, flying at 50 mph. This excellent climb rate is due to the airplanes large, “Hershey Bar” wing, (wide, constant cord wings like those found on the Piper 140 series resemble this famous candy’s shape, raising the nickname to the level of a technical term), and the powerful FSR engine. Climb out was steady in the cross wind. The elevator was sensitive on high rate as were the ailerons. But the high rate was set very high (see the specification page) for the fun aerobatics to come later.

Photo 11

Once reaching 250 ft. (photo 11), power was reduced until a comfortable airspeed was reached. At about 56 mph, the HobbiStar 60 flew like a basic trainer, just faster. With low rates set at 60%, flight was very trainer-like. Control response was positive but not overly quick. A new student pilot would be very comfortable flying the HobbiStar 60 in this configuration. The HobbiStar’s large, 71-inch wingspan and long fuselage made it very easy to see at all attitudes. In a normal, full-power, in-flight climb, the HobbiStar 60 went up at a respectable 1,900 fpm flying at 50 mph.

 
Photo 12    Photo 13

The airplane did not lose much altitude in a turn even without adding additional “up” elevator (photo 12). This is good since it makes turning easier to master for the student. However, if over-banked past 60 degrees (photo 13), the airplane will drop quickly and require the pilot to initiate recovery. The HobbiStar has enough wing dihedral to maintain stable flight and to lighten the pilot’s workload. But it does not have enough to recover from unusual attitudes without pilot input. The dihedral is a compromise between the large amount of a basic trainer and the smaller amount used for sport aircraft.

But the overall trainer handling was satisfactory. The airplane has absolutely no bad habits. It is honest, warning the pilot as the stall approaches and will not snap stall, (rotate fast, then drop a wingtip and the nose while heading fast for the dirt), for any reason.

The HobbiStar 60 can easily function as a basic trainer. There is plenty of pilot “think time” for the student but not as much as there is with a true basic trainer. This is only because the HobbiStar’s airspeeds are higher than those of a basic trainer. Basic trainers in this size range usually liftoff and climb at around 30 mph with a training speed about 40 mph. The HobbiStar 60 is just a little faster.

 
Photo 14    Photo 15

Similarly, the HobbiStar 60 has a best landing approach speed of about 46 mph. During the approach, its descent rate, no flaps, is about 1,000 fpm. Touchdown speed slows to 41 mph, on average. While higher than a true basic trainer, these speeds are not truly fast and can be handled with ease by most student pilots after a few flights. Touchdowns can be nicely flaired, nose high, by using just a little throttle (photo 15). Lowering touchdown speeds closer to the stall results in “arrivals” rather than landings as the HobbiStar 60 quickly runs out of elevator authority at slow airspeeds. Fortunately, the heavy duty, 3/16 in. landing gear and twin-strut nose gear easily handled the extra stress.

 
Photo 16    Photo 17

The wing-level stall, power off, breaks at 30 mph (photo 16). Banking the wings to about 60 degrees raises the power-off stall speed to 36 mph (photo 17). This is not a large difference and illustrates this airplane’s gentle habits. Like most aircraft of this type, the HobbiStar 60 stalls are non-events. Unless the nose is forced up to very high attack angles, the aircraft refuses to really stall. It just “mush’s” around, losing a little altitude in the process at about 800 fpm.

Even steeply banked stalls don’t truly happen. The airplane flies in a tight circle while descending at about 1,000 fpm. Even tiny amounts of engine power stop the fall and the airplane flies out of the turn.

Speaking of turns, with 18% differential dialed into the transmitter, there is very little adverse yaw on this aircraft. Without differential, adverse yaw is most evident just before the stall and is moderate. But the ailerons remain effective throughout the stall and recovery. This is better aileron performance than most trainers and is probably due to the semi-symmetrical wing, which reduces adverse yaw effects, and to the higher airspeed, 30 mph, at which the stall occurs.

Having the ailerons still effective in bank control throughout the stall reduces the pilot’s “rudder workload”. In normal speech, the pilot doesn’t need to level the wings using the rudder because the ailerons have fallen asleep during the stall. This makes slow flight a whole lot easier on the student, and experienced, pilot.

Photo 18

But this HobbiStar 60 has a few tricks to play. Remember those flaperons? What happens when they are lowered into the air stream as in photo 18? First, the aircraft becomes more docile and predictable during slow flight, approaches and landings. Both climb and descent angles become steeper.

With flaperons deployed, the HobbiStar 60 lifts off at the same 40 mph as it does without them. This is most likely because of the high grass that kept trying to enfold the airplane into its misty clutches, keeping it forever earthbound. Once in the air, climb out speed dropped to 46 mph, down from 50 mph, while the climb rate lost 200 fpm, dropping to 1,500 fpm. The extra lift provided by the flaperons is not free, the price is increased drag and decreased climb rate.

But once in cruise flight, the flaperons become the student’s friend. Best training speed drops to 51 mph. It is surprising how much extra time the pilot has to think when the airspeed is just 5 mph slower. It is only 7.5 ft. per second slower, but that little bit of extra time seems to make a big difference.

The power-off stall speed also drops, to 26 mph. This brings the HobbiStar 60’s level stall speed right into the same 24 mph range of the basic trainers. The 60-degree stall speed with the flaperons deployed is 31 mph, again almost equal to the average basic trainer’s 29 mph.

Because of these reduced airspeeds, there is some adverse yaw at the stall and the ailerons lose almost all their effectiveness. This is common to all aircraft stalling at low airspeeds and very high attack angles. I think the Futaba 7CAP allows the pilot to change the amount of aileron differential when flaps are deployed. I haven’t done that adjustment yet. It should reduce the flaps-down adverse yaw once the adjustment is made.

We should note that there is no pitch change, the aircraft suddenly points up or downwards when the flaperons are deployed. Regardless of the airspeed, deploying or raising the flaps is a non-event. The aircraft is so stable in design that it has enough reserve pitch stability to overcome any trim changes caused by flaperon deployment.

Lowered during the approach, the flaperons again work in the pilot’s favor. Approach speed drops down 42 mph, instead of 48 mph, and the aircraft touches down around 32 mph. Touchdown speed is a full 9 mph lower than without the flaperons (photo 19).

Once the airplane gets within half its wingspan from the ground, about 35 inches, it encounters ground effect. Ground effect produces extra lift since the air deflected from the wing’s leading edge rebounds from the ground striking the wing and “pushing” it upwards. This grossly over-simplified explanation is all we need to understand that any airplane’s wing produces more lift very close to the ground.

Photo 19

But the flaperons seem to magnify ground effect, keeping the airplane floating on a cushion of air. In fact, the HobbiStar 60 wanted to float right past the runway at times, making it necessary to hurry the touchdown, or the average touchdown speed might have been even lower. This was unexpected since flaperons are supposed to produce extra drag and should slow the aircraft faster. Maybe an Aeronautical Engineer can explain this but for now, this performance just makes flying the HobbiStar 60 a whole lot easier for the student pilot and lots more fun for the more experienced one.

The Real Flying Part

 
Photo 20   Photo 21

As we have discovered, the HobbiStar 60 sacrifices ideal basic trainer performance to gain some aerobatic abilities. Its semi-symmetrical airfoil gives the HobbiStar 60 good inverted performance. Photo 20 shows the HobbiStar 60 in a cruise speed inverted fly-by. Enlarge photo 20 by clicking on it and you can see that the airplane does not require much “down” elevator to maintain level inverted flight.

For photo 21, we tried a very slow speed inverted fly-by. More down elevator was required for the slow speed, high attack angle pass but not all that much as to be troublesome. There was plenty of reserve elevator control to pull the airplane out of any trouble. The HobbiStar 60 was rock steady at this very slow airspeed and more controllable than many sport aerobatic aircraft would be. The flight data recorder does not record airspeed while inverted but my guess is that the aircraft was flying less than 35 mph. This is excellent inverted performance for this class airplane.

 
Photo 22    Photo 23

Now that inverted fly-bys are good, how about flying an outside loop? Every basic trainer we tested, except for Lanier’s Explorer 40, has failed this maneuver. While basic trainers with flat bottom airfoils can fly inverted, so much “down” elevator is required that there is little reserve lift for the inverted loop. This is not a problem with this aircraft.

With just a little more “down” elevator and full throttle, The HobbiStar 60 started into a fairly large outside loop from the bottom (photo 22). The airplane tracked well, requiring about 30% left rudder to maintain its flight path through the first half of the loop (photo 23).

 
Photo 24     Photo 25

The airplane went over the top of the loop about 150 ft. higher than the entry point (photo 24). The old Max FSR was doing a great job pulling the airplane up and around. Rudder input was not required coming down the “back” side of the loop. After completing a good, round inverted loop, the HobbiStar 60 pulled out (photo 25) with plenty of reserve elevator control remaining.

The HobbiStar 60 flew the inverted loops so well that there could not be a problem with upright ones. Regular inside loops could be stretched to diameters around 250 ft. before the aircraft had lost so much airspeed that the controls became too “soft” to maintain good flight control. Some right rudder was required in the first half of the loop and could be released completely as the airplane rode down the backside of the maneuver.

Photo 26

Straight vertical climbs required about 30% right rudder for the first half of the climb. The HobbiStar 60 never ran out of rudder control but did require about 60% right rudder near the climb’s top end. The airplane could fly vertically for about 300 feet before running out of airspeed. Stall turns were easy as the rudder has considerable control authority.

As do all high-wing airplanes with dihedral, The HobbiStar 60 has considerable “rudder coupling.” This means that applying rudder also banks the wings in the same direction as the rudder was applied. Excess coupling is the price the aircraft pays for all the good things that dihedral does. Since the HobbiStar 60 has less dihedral than most basic trainers, the coupling effect is also less.

Some opposite aileron control must be used to counter the rudder’s rolling effect during the stall turn. Not much is required but some definitely is. Opposite aileron must also be used during knife-edge flight when the wing is pointing straight at the ground.

Single and multiple rolls are very straight forward with this aircraft. The airplane rolls on line, maintaining its flight direction. The roll is not truly axial, meaning the fuselage rotates exactly along the line of flight, but it is not all that far from it. There is some “barrel roll” tendency, but not enough to worry about inputting corrections.

Slow rolls are good but limited to about three seconds duration. Rolls slower than 3 seconds spend too much time in knife-edge flight making direction control difficult. There is no need to raise the nose before rolling as the semi-symmetrical wing has lots of inverted lift. Just a little “down” elevator keeps the nose level during multiple rolls.

Knife edge flight with any high-wing aircraft is always difficult as the airplane does not maintain direction. Instead, it tries to fly sideways; usually in the direction its bottom is pointed. This is called “walking” and the HobbiStar 60 walks to the bottom with authority.

Photo 27

About 20% “up” elevator is required for straight knife-edge flight. This means that the pilot is holding full top rudder, while inputting 20% up elevator to fly a straight line and also applying some left aileron to stop the role. This is a lot of work for a simple maneuver and all high-wing aircraft require the same control inputs. But since the HobbiStar 60, like all the high-wing aircraft we have tested, can not maintain level knife-edge flight anyway, this problem is somewhat academic. However, the airplane will maintain level knife-edge flight long enough to perform a reasonable 4-point roll. That is really all any pilot can reasonably ask of a high-wing advanced trainer and the HobbiStar 60 meets this requirement very well.

Using the flaperons during knife-edge results in the need for extreme corrective inputs so that is not even close to an answer. But the flaperons do some amazing things for other aerobatic maneuvers. Coupling the flaperons to the elevator, as do Control Line Stunt aircraft, lets the HobbiStar 60 perform sharp cornered square loops less than 20 feet in diameter.

The HobbiStar 60 performs slow snap rolls in either direction. At least the first snap roll is slow, taking about 1.5 seconds to complete. However, hold the controls in for a second snap roll and the airplane will rotate around its CG in about 0.5 seconds. A third rotation is not recommended near the ground as the airplane starts heading quickly in that direction.

Deploying the coupled flaperons during a snap roll actually slows the first rotation to about 2 seconds. Subsequent snap rotations still speed up, but never get as fast as the no-flaperon ones. Spins without flaperons are hard to induce requiring very high attack angles at entry. But once in a spin, the HobbiStar 60 rotates quickly in a nearly full nose-down attitude. There is no danger of the dreaded flat spin, where controls are nearly useless and recovery difficult, with this airplane.

Because of the steep spin attitude, recovery is simple and very fast. Let go of the controls and the airplane immediately stops spinning. No opposite rudder control is required. Just apply a little up elevator and the airplane is flying happily along once more. Inverted spins are also a non-event but easier to enter as they require about half the attack angle. Still recovery is automatic once the controls are released. Using the mixed flaperons results only in a less steep nose-down attitude during the spin but the airplane never even approaches a flat spin attitude.

Even without flaperons, the HobbiStar 60 ARF is a capable, fun aircraft that can get in the air in a few days. This airplane can function as a basic trainer but it does so at slightly higher airspeeds than would a true basic trainer. However, the airplane’s aerobatic performance can take a new pilot into realms forever barred to basic trainers. My own opinion, and it is just that, is that the tradeoff with this particular airplane is worth it.

But adding the flaperons lowers landing and training speeds while improving the airplane’s self-righting abilities so much, that the flaperon equipped version does rival basic trainers in pilot-friendliness. Raise the flaps and the aerobatic HobbiStar 60 returns with all its exciting performance. The flaperon equipped HobbiStar 60 is the best of both worlds. Spend the extra hour installing them and this airplane will take a brand new pilot from the first glimpses of the sky through tumbles and flight routines destined to keep RC flying exciting for several seasons.

Q

Flight Data Results*                                              w/o Flaps       w/ Flaps *Take Off Speed:               40 mph           40 mph Climb Out Speed:                50 mph           46 mph Best Training Speed:          56 mph          52 mph Top Speed:                          70+ mph        67 mph Sustained Climb Rate:       1,900 fpm      1,700 fpm Range:                                20 minutes      N/A Dive Speed:                        70+ mph        70+ mph Best Glide Speed:              40 mph           38 mph Gliding Descent Rate:       1,200 fpm      1,400 fpm 400’ Glide Distance:          1,200 ft.         970 ft. Level Stall Speed:              30 mph          26 mph 60-deg. Bank Stall Speed: 36 mph          31 mph Landing App. Speed:          46 mph         42 mph Touch Down Speed:           41 mph          32 mph *All results are an average of 3 flight tests Aircraft Specifications Type: Advanced Trainer Engine Used: O.S. Max 61 FSR Propeller: APC 12 x 6 in. Top RPM: 11,500 rpm Idle RPM: 2,200 rpm Test Weight: 7 lb. 14 oz. CG Location: as directed Elevator Movement*: 7/8 up; 5/8”dn Aileron Movement: 7/16 up; 3/8 dwn Rudder Movement: 1 ¼ in. Weather Data Temp 72 deg F. Wind: 10-12 mph Alt: 250 ft. * In inches

Short URL: http://masportaviator.com/?p=226