Hangar 9 Pulse 125 XT ARF

Hangar 9

Pulse 125 XT ARF

By: Frank Granelli

Hangar 9 first introduced this Mike McConville designed sport/advanced trainer airplane in 40-and 60-sized versions. Sport Aviator has already reviewed the 40-sized Pulse XT in this section under “Advanced Trainers”. Since they proved popular and great flyers, Hangar 9 added an electric-powered 25-sized version. Now, the newest Pulse ARF is the Big One – The 125 XT.

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The Pulse XT aircraft combine exciting performance with gentle handling and ease of flight. There are four “secrets” to achieving this winning combination. All the Pulse aircraft share these features:

ª Each airframe is “all wing”. Their wings have lots of extra wingspan; 76 inches for this airplane, 70 inches for the 60 Pulse XT and over 60 inches for the 40-size version. Such wingspans are about 10% longer than is usual for each size range sport airplane. In addition to the extra wing span, the wing chords are very wide. The longer wingspans and extra wide chords make for huge wing areas; 1,050 sq. in. for this Pulse XT 125. The end results are very low wing loadings for their class. In fact, the Pulse XT 125’s wing loading may be a bit on the too low side as we will see a little later on.

ª In addition to all that extra wing area, the airfoil is semi-symmetrical. This shape airfoil has much of a flat-bottom airfoil’s extra lift while also having much of a symmetrical airfoil’s excellent inverted aerobatic abilities. If a sport airplane has “enough wing”, this type airfoil provides an excellent compromise between gentle flight characteristics and exciting performance. As we have already seen, all the Pulse XT aircraft have lots of “wing”.

ª Having so much wing span and area does, however, create extra drag that can hinder an aircraft’s performance (called Induced Drag); especially in the vertical and knife edge. Pulse XT aircraft minimize the drag effect with a sleek, low-drag fuselage and a drag-reducing landing gear design that combine to help reduce the Parasitic Drag usually caused by these surfaces and the long leading edge of the wing.

ª While not much of a secret in these 3-D days, the over-sized elevator and rudder help maintain control authority even at slow airspeeds. In the years before transmitters with exponential, such large control surfaces made an aircraft overly sensitive. But with exponential, full surface deflection can be used at slow airspeeds for maximum control while the exponential will smooth out the high-speed performance envelope.

In short, the Pulse XT design is a modern design that best utilizes a computer transmitter’s abilities. Exponential, differential (lots), throttle/rudder mixing and flaperons all play an important part in the Pulse XT’s wide performance envelope. But before we can start tearing up the lower atmosphere, we have to assemble the airplane.

Assembling the Big Pulse XT

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Everything required to become airborne is in the box. Photo 4 shows the main airframe components. The vertical fin is enlarged to show that the fairing is built from wood, not from plastic, covered and already attached to the vertical fin. The rear of the fin uses a fin post that glues to the fuselage for extra strength and durability.

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All the hardware needed is high quality and useable. Both glow and electric engine/motor mounts are included as well as a large fuel tank for glow or gasoline use. The wheel pants are complete and finished. The painted metal landing gear already has the blind nuts used to hold the wheel pants in place installed and glued in place. The 40-page photo instruction booklet doesn’t miss a step and is clear and unambiguous (unlike some we have seen).

Despite its large size, there isn’t much work required to assemble the Pulse XT 125 for flight. That is, if you plan to build it exactly according to the directions. But this is a very special second airplane and is capable of some great performance, so it might be worth a little extra work to make two suggested changes. These changes are not totally necessary but one adds to the airplane’s appearance and the other to the pilot’s piece of mind. Both will be detailed in the fuselage section.

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Compare photos 5 and 6. Both are side views of the Pulse XT 125. The first is courtesy of Hangar 9 because we did not build the airplane this way and so had to “borrow” this photo from their website (if you don’t tell them they will never know). The second is of this review airplane. Can you spot the difference? From the side, this is a very sleek and attractive airplane.

The fuselage side view is reminiscent of an early WW II fighter such as the P-51B Mustang or the British Spitfire. It is long, sleek and has a turtle deck behind the canopy. Its looks fantastic until you get to the engine compartment. What is that “thing” sticking out of the cowl of this beautiful airplane? Could that be the engine? I guess it is. With all that room in the lower cowling, why would Hangar 9 stick an upright engine right out in the open like that?

Even more than being terminally ugly, the upright engine position places the needle valve too high in relation to the fuel tank; possibly reducing engine power when inverted or even flooding out the engine. If you are using electric power, all the parts are included for that conversion, you don’t have to worry about the ugly engine. If you are using a 4-stroke engine, you can’t eliminate the upright engine as bigger 4-strokes do not like idling when inverted unless the glow plug is electrically lit in flight.

But if you plan to take maximum advantage of the Pulse XT 125’s performance and use a powerful 2-stroke engine such as the reliable Evolution 1.20 NX, the suggestion is that you consider mounting the engine inverted. We’ll cover how to do this easily while assembling the fuselage.

But first, there is one note in Hangar 9’s defense. An upright engine is easier to start, to keep running and to tune. But our thoughts are that this is a second or third airplane. If a pilot already knows how to tune an inverted engine, mounting it that way is no problem. If the pilot does not yet know how to make an inverted engine start, run and not drip fuel while sitting idle, it is a good time to learn as many scale and high performance airplanes utilize an inverted engine.

The Wing:

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The wing assembly is simplicity itself. The only work is to install the aileron servos and connect the linkages. Even that is easy as the linkages are factory made. Photo 7 shows all the parts used in the wing “construction”.

The aileron servos are the new JR DS 821 Sport Digital servos. These servos have precise centering and positioning plus are extra strong. They produce 72 in. oz. of torque as opposed to the more common ~45 in. oz. torque of most sport servos. In addition to their precision, they are fast, needing only 0.19 seconds to move 60 degrees. Yet the DS 821 servos won’t break the bank as they cost less than $30 each. An aircraft with the Pulse’s performance makes good use of the digital servos’ extra power, precision and speed.

Connect and then tie in place a 12-inch servo extension before installing the aileron servo into the wing. Use the installed thread to pull the servo wire assembly through the wing and out the hole in the top of the wing center section (photo 10). Mount the servo. Thread the clevis, tubing “keeper” and lock nut onto the control rod and adjust for length. Connect the rod onto the outside of the long servo arm that comes with the DS 821. Then adjust for length to achieve neutral centering.

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After connecting the ailerons, put some 5-minute epoxy into the hole in the wing leading edge near wing center. Then insert, wood end first, one of the metal reinforced wing hold down dowels. Push the dowel all the way into the hole until the metal reinforcement sits flush against the wing. You might want to test fit this first before applying the adhesive. Ours was a perfect fit. The metal reinforcement is a nice feature not usually seen in ARF aircraft.

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After the dowels and ailerons are installed, slide both wing halves over the metal spar tubing. The instructions say the wing is now finished. But my suggestion would be to install a spare “landing gear strap” purchased at the hobby shop as shown in photo 10 if you intend to keep the wing as a one piece unit.

While there is no play in the wing spar tubing, the wing halves do slide easily onto the spar. During transport, they tend to slide apart as they are being carried or packed into the travel vehicle. The landing strap keeps everything connected. However, if your transport vehicle is too small for the one-piece wing (and many are too short for the 76-inch span Pulse XT 125 wing) then just transport the wing in two halves. But once joined at the field, be careful to remember that one wing half can slide off the spar tubing before it is mounted onto the fuselage.

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There is a wing hold-down bolt reinforcement plate on the Pulse XT 125. This covered plate is not glued to the wing. One side has a slight crease under the covering. The “creased” side goes towards the wing and helps the plate to conform to the wing’s dihedral.

For storage between flying sessions, just keep it and the bolts in position on the fuselage. I imagine that some of the wing covering under the plate and on the plate underside could be removed and the plate epoxied in place, with the wing mounted of course. But the need for this has not yet been apparent so the directions are fine as written.

That is it for the wing. Make sure the ailerons are centered when the transmitter trims are also in their center. Trial fit the wing to the fuselage but it should fit fine. This is a precisely made ARF. While the control surfaces are all hinged and installed, now would be a good time to apply a little extra thin CAA to each hinge just to be sure. Also tighten slightly all the control horn mounting bolts. Three were a little too loose on this airplane. Put the wing aside for now.

The Front Fuselage:

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Photo 12 shows all the items needed for finishing the fuselage front end. There are some items here not normally found in most ARF aircraft. The glow motor mount is there but so are the four octagon metal spacers for mounting an electric motor. The large fuel tank is also present as is all the necessary hardware.

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A very unique item is the plywood template for the firewall. This unique tool has mounting bolt holes pre-drilled into it for all three powerplant options. One set of mounting holes are for the upright Evolution 1.20 NX two-stroke engine mount spacing. A second set of mounting holes are for installing an upright Saito 1.25 engine. The final set marks the drill points for the electric motor mounts.

If you plan to use a different glow engine than one of those marked on the template, my suggestion would be to drill and mount the engine to the supplied mounts on a vertical board (See “Engines 101 Part Two” for an example of such a board in operation). Then transfer the mounted engine to the template aligning the thrust lines to the thrust line marks on the template. Once the new drill holes are marked, just hang the template in front of the firewall and transfer the marked holes as discussed below.

Note that the thrust line holes are slightly to the left of dead center on the template to allow for right thrust. When the engine is given right thrust, it is built into the true firewall on the Pulse XT, the center of the crankshaft naturally moves slightly to the right of center. The marked thrust line offset corrects for this and centers the crankshaft in the cowling.

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While I plan to use the Evolution 1.20 NX engine in this Pulse XT 125, it will not be mounted upright. The template’s existing mounting holes will be the correct width. However, their height position will be incorrect. This is easy to fix. Draw a straight line, as shown in photo 14, connecting the two template holes on each side on the template. These lines mark the “width” location of the new drill holes.

Then align each of the mounting beams with the vertical thrust line on the template as shown in photo 15. If your eyes are as old as mine, you might wish to put a little white chalk on the mounting beam’s raised scribe mark (photo 15 also). Once the beam is properly positioned, drill the new hole into the template. Do the same for the other beam.

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Photo 16 shows the completed template with the new drill holes for the inverted engine position circled in red. The new holes are 0.54 inches (17/32 in.) higher than the factory drilled upright engine holes. Then hang the template on the front of the firewall and drill the new mounting holes (photo 17). That is all there is to keeping the sleek fuselage looking trim and fast.

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Install the supplied blind nuts behind the holes just drilled. Of course, as required by Murphy’s Law (which is always strictly enforced for all aircraft regardless of size), the top two blind nuts must fall right within the narrow plywood hatch floor. Just relieve this area as shown in photo 19. Try not to remove all the cross member brace. Just cut as shown. You may also have to relieve this area on the hatch itself.

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Now install and mount the engine. While Hangar 9 has installed the throttle rod guide tubing, you will note that it is now out of position for an inverted engine. Twist the guide tube slightly to release it from the adhesive and pull it out of the fuselage. Drill the new 1/16 in. throttle rod hole in the firewall even with the engine’s throttle but outside the mount (photo 20).

Insert the rod without the guide tube into the new firewall hole. Push it into the fuselage until it meets the middle former that had the factory guide tube installed in it. Mark that location (photo 21). Click on any photo to enlarge it for better detail. Drill a 1/16 in. pilot hole here also.

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Push the throttle rod further into the fuselage until it contacts the former just in front of the throttle servo. Drill a new pilot hole just inside the factory tubing hole (photo 23). After checking that everything is straight, withdraw the throttle rod and enlarge the holes to hold the guide tubing.

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Enlarge the servo output arm’s outer hole using a 1/16 in. drill (photo 24). Then install the adjustable servo arm connector and the throttle servo. Hangar 9 has already drilled the servo mounting holes for you. Adjust the throttle so that at full throttle the carburetor is fully open, slightly open at half throttle trim with the stick all the way down and fully closed when the trim is also moved all the way down.

It took me four hours to write and document this short section on inverting the engine. Actually doing it only took two hours. I consider both time investments to be well spent. My flight experience to date has proven that.

Not only is the airplane’s appearance much better, but the engine’s needle valve is now the proper 3/8 in. below the fuel tank’s centerline when the aircraft is upright. The choice is yours. If you use the upright engine, expect to need only about 30 minutes for engine installation. Most of that time will be spent drilling the engine mount. Again, “Engines 101 – Part Two” shows how to accomplish this task.

The instructions say to mount the engine so that the propeller thrust washer is 5.5 inches out from the firewall. This allows for about a 1/4 inch spacing between the spinner’s backplate and the cowling. It you wish, you can mount the engine 5.25 inches out to achieve the more traditional 1/8 inch spacing normally used for a fixed (non-flexible) mounted engine. This airplane used the stock spacing and it looks and works fine.

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Once the engine is installed, it is time to make the cowling cutouts. Do this as always using card stock and low-tack masking tape. Tape the card stock to the fuselage located to the rear of the cowling, flip the card stock over onto the engine and make the cutouts in the card stock. Photo 25 shows this operation for the muffler exit hole.

Remove the engine, mount the cowling (the mounting bolt holes and blind nuts are factory installed) and flip the card back into place over the cowling. Mark the cutouts onto the cowling. Photo 26 shows this step for the engine head space.

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Repeat this process for all the needed cutouts – Needle valve, engine head and muffler, using a high speed rotary tool. The final fittings are a bit laborious involving several engine mountings, cowl trimmings and re-mountings until the engine head fit allows for cowl removal without removing the engine but remains tight enough for good appearance and sufficient cooling.

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Photo 29 shows the final product. Note the extra space behind the engine head to allow cooling air to escape which lowers the air pressure inside the cowling enough for new cooling air to enter from the front. Without this air escape “hatch” little cooling air will enter from the front causing engine overheating. Do not forget to allow clearance for the throttle arm to rotate without moving the idle mixture needle valve extension that all Evolution engines have. (That’s why there is the little notch in the cowl around the lower throttle arm.

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Hangar 9 includes complete fuel tank parts for both gasoline and glow tank versions. The tank installs using two tie wraps and has a piece of vibration insulating foam under it. Accessing the tank is easy using the Pulse XT’s unique giant hatch.

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The top hatch is gigantic and allows complete access to the entire front top of the airplane. The hatch is easily removable as it is designed for easy, no-tool access for changing the flight batteries in an electric-powered Pulse XT 125. The flight batteries (two 4-cell 4500 mAh) sit where the fuel tank does in the glow version. The hatch front is held in place by two pieces of plywood (photo 32) while the rear is held down by two super magnets (photo 33). Just slide the hatch forward and lift from the up rear.

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If you are going to convert your Pulse XT 125 to an inverted glow engine, remember to loop the fuel feed line over the top of the engine mount and then run the connection to the needle valve inlet (photo 34).

When the airplane is upright, the fuel must first travel a small distance uphill to leave the tank and enter into the engine fuel inlet. While this extra “uphill” travel does not affect the engine’s fuel draw when running, it does prevent any fuel feed into the carburetor when the engine is not running. Without this simple trick, inverted engines sometimes become flooded with fuel if left for a while with the tank full. Sometimes fuel even drips slowly from the carburetor without the uphill travel.

Assembling the Tail:

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Photo 35 shows everything necessary to finish the tail section. As was the case with the Hangar 9 Saratoga ARF, the Pulse XT 125 truly simplifies this normally difficult task. Proper stabilizer and vertical fin alignments are critical. If the stabilizer is not parallel to the wing, the airplane wants to roll every time elevator is inputted. If the vertical fin is not perfectly in line with the fuselage, the airplane flies in a crab or constant side slip.

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But the Pulse makes either of these problems impossible. The stabilizer and vertical fin, complete with the tail fairing that blends into the fuselage rear, are bolted into position. Improper alignment is impossible.

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Before bolting the vertical fin / stabilizer assembly into place, install the rudder onto the vertical fin. The rudder is not installed at the factory, unlike all the other control surfaces which are, to allow for the tail wheel installation. Note the bare wood post extending below the vertical fin in photo 37. This post should be epoxied onto the fuselage during installation. This provides extra strength and is good durability insurance.

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The tail wheel assembly is glued into the rudder using 5-minute epoxy. Make sure to put a little plastic-safe oil into the nylon tail wheel bearing to prevent its sticking should some adhesive find its way in to the bearing (photo 38). Be certain to insert some epoxy into the rudder steering arm hole in the rudder. This reinforces the wood so that steering stresses do not crack the rudder in this area.

After the epoxy cures, mount the rudder to the vertical fin using the included Mylar® style hinges and thin CAA. For complete hinge installation, read the Sport Aviator Flight-Tech article “Installing Mylar Hinges in ARF Trainers”.

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Harden the two holes in the stabilizer and the matching holes in the fuselage stabilizer “seat” with some thin CAA first. After that has dried, insert the twin rudder bolts through the horizontal stabilizer. Notice how the fin and fairings will sit tight against the stabilizer. Test that yours do as the fit is tight to insure a good fitting, well-aligned assembly. This airplane’s fit was perfect.

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If your Pulse XT is as well fitting and tight in this area as was the test airplane’s fit, you might have to lift the vertical fin / fairing slightly away from the stabilizer during installation to clear the rear turtle deck end of the fuselage. Once the stabilizer is in, then the fin assembly slips right in place, tight against the fuselage as in photo 41. Bolt the assembly in place using the supplied lock nuts. Do not crush the wood, but do insure they are snug.

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Take this opportunity to tighten the six control horn mounting bolts in the elevator and rudder. After that, it is time to install the rudder and elevator control rods. This is the other change we talked about in the introduction. The Pulse XT 125 arrives with 2 mm control rods for those giant elevators and that big rudder.

These are very large control surfaces on a rather large airplane. My planned extensive aerobatics will be putting heavy loads on these control rods. For myself, I just didn’t feel comfortable using such thin control rods. Also, there appeared to be too much flexing in the stock elevator rod to enjoy the extra control response that using the JR DS 821 digital servos combined with the Spektrum 2.4 GHz radio system provides.

Hangar 9 must have realized that many more experienced pilots might feel the same way. They made the plastic rod guide tubing large enough to accommodate and work well with the stronger 4-40 control rods (4-40 here means that the threaded portion is cut to 4-40 threads). I very strongly suggest that you purchase two 48 in. long 4-40 size rods and cut to size. Also purchase two packages (2 ea.) of metal 4-40 locking clevises, a package (4 ea.) of Du-Bro 4-40 solder couplers and two 12 in. long 4-40 control rods.

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Insert the threaded rod end into the guide tubing from the rear. Attach a 4-40 clevis and lock nut to the rod and then attach the clevis to the servo. Center the servo and control surface and then cut the rods about half way between the fuselage outlet and the control horn. Install another clevis on the 12-in. control rod and install into the control horn keeping the control surface neutral. Then cut the 12–in. rod to match against the long rod from the servo.

Apply flux to both rods, slide on the solder coupler and, with everything still clamped in neutral, solder the rods inside the coupler. This is a standard method for attaching control rods on most larger kit-built aircraft. The solder joint must be good and tight. No dull, “cold solder” joints allowed here.

The larger rods fit well inside the guide tubes and provide solid control authority. They also make me feel better about that all-important elevator control hook up.

Landing Gear:

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Photo 47 shows that Hangar 9 did not leave anything out of the landing gear package. The wheel pants are tough fiberglass painted to match the Pulse XT’s orange UltraCote® covering while providing the large, 3.35 in. light-weight wheels plenty of rolling room.

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Assembling the landing gear is pretty straight forward. About the only “trick” to remember is to not completely tighten the axle mounting nut before sliding the wheel pant over the nut and aligning the two wheel pant mounting holes over the installed blind nuts. Once the bolt holes are aligned, remove the wheel pant and firmly tighten the axle nut.

Apply thread locking compound to the two blind nuts, Install one wheel collar on the axle, slide the wheel in place and attach the outside wheel collar. Center the wheel and then tighten the inside wheel collar nut. Mark the outside wheel collar position, remove the wheel collar, grind a flat in the axle (procedure is well illustrated in the manual) and reinstall everything and tighten it all down.

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The landing gear adds much to the Pulse XT’s looks. However, there is a lot of rearward sweep to them. The wheels are slightly behind the wing’s leading edge. When flying from grass longer than about 2 inches, the airplane has a definite nose-over tendency when taxiing. It does not bother the takeoff as the elevator becomes immediately effective when high-throttle is applied and besides, the Pulse XT 125 lifts off in less than 15 feet anyway.

However, taxiing into position can be a problem; especially if nose weight must be added (this airplane required 2 ounces on the spinner). Maybe if the nose weight was inside the fuselage instead of so far out on the propeller then taxiing would be better.

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In any case, the simple solution is to place a 1/4 in. wide x 3-in. long piece of 1/16-inch thick plywood, again from your hobby shop, under the rear of the landing gear mount where it bolts to the fuselage. We tried a 1/32 in. shim and it helped reduce the nose over tendency but not enough for taxiing purposes. But the 1/16 inch spacer does tilt the wheel pants at a funny angle. If this bothers you, you will have to enlarge the holes in the landing gear legs to compensate. Or, relocate the blind nuts inside the wheel pants.

This moves the main wheels nearly 1/2-inch forward. This wheel re-positioning is enough to help stop any nose-over tendencies that the airplane might have on longish grass. If you always fly from a paved runway well, then… Never Mind!

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Finally, mount the switch on the side opposite the muffler. Two spaces are provided. One is for the standard switch and the other for the JR Heavy Duty switch incorporating the charging jack. Since this airplane will be flying a lot, I want to have an external charge jack that will allow me to check the battery’s voltage and/or charge it during a flying session. If the field is not crowded, I might be putting in a dozen flights each day and must be able to keep track of the voltages and recharge as required. Whatever switch setup you chose, install it from the top front.

Getting Ready to Fly:

Many pilots use both high and low rates, switchable maximum control surface movements, on their airplanes. Competition and long experience has proven that this system does not always work best for me. Somehow, I always seem to be in the wrong “rate” mode for the next maneuver.

Instead, I use only maximum high-rate control movements and then exponential to lower the airplane’s control sensitivity. Sometimes my “high” rate” is more than is recommended based upon flight experience with the airplane. Using only high rate with sufficient exponential has proven best for my style of flying. This way, I don’t have to be smart enough to always remember what switch to change.

Keeping that in mind, here are this Pulse XT 125’s control setups:

Surface This Airplane Rec. Movement Exponential

Elevator 1 inch 0.75 inch 40%

Rudder 2.75 inch *0.75 inch 70%

Ailerons 0.75 inch 0.75 inch 43%

(*While I didn’t check this with Hangar 9, this could possibly be a manual misprint. 3/4 inch rudder travel is almost totally ineffective at low speed; and for stall turns and knife-edge flight.)

The recommended Center of Gravity (CG) starting point is 3 11/16 inch back from the wing leading edge. Flight tests revealed that this is a truly excellent start point. At this CG point, the airplane has absolutely no tricks to play on a newer pilot and will fly much like an Advanced Trainer.

Hangar 9 lists a CG range from 3 1/2 inch to 3 7/8 inch. Do not go to the rearward most CG point at the start. No, the Pulse XT 125 doesn’t become a treacherous death ship at its rearward CG. It remains an honest, tractable airplane regardless of the CG location within its range.

But its habits and trimming do change as the CG moves towards the tail. Landings become less positive and more dependent on the pilot’s skill levels. At the starting CG point, the Pulse XT 125 lands itself once the approach is properly set. At the rearward CG, the pilot can’t just stand there admiring the landing approach while the airplane does all the work. The approach attitude must be managed and the descent rate monitored with throttle to get those “squeaker” type landings.

But this airplane is more than an Advanced Trainer and gradually working the CG aft has its performance advantages. The more rearward CG improved ground handling, made trimming knife-edge flight easier, improved rudder response and quickened the snap roll (still not overly quick). Spins became more positive and had a faster spin rate. Stall Turns became less “flop” prone (nose over instead of stall turning). Keeping multiple rolls on track required less “down” elevator input and the input timing became less critical.

This Pulse XT 125 never flew at the most forward CG point of 3.5 inches. Having the CG at this point will probably make landing this airplane even more extremely easy but could require more “up” elevator at the flair point than many pilots would be prepared to apply. Ground handling, especially nosing-over, might become more difficult.

Many pilots also may not realize that moving the CG far forward increases the airplane’s stall speed. As the weight shifts forward, more elevator force is required to keep the nose “up” during the slow flight. Therefore, the airspeed at which there is no longer sufficient elevator force available to keep the nose above the horizon increases.

While this is not a true stall (the wing is actually still capable of supporting the airplane if it could be held at a high enough attack angle), the effect at low altitude is the same from the pilot’s perspective. The airplane’s nose drops fast and is quickly ground bound.

The moral of all this discussion? Start at the recommended CG point and gradually work aft. But, now you know why!

This is a big airplane with a lot of wing span. It is critical to laterally balance this airplane. Doing so will make you smile during those perfect loops while not doing so will teach you new words you are probably not old enough to know as the airplane tracks a cork-screw path.

If you are not familiar with lateral balance, read the Sport Aviator article “RTF Ready To Fly? Well … Maybe. This airplane needed two 3 inch finishing nails in the right wing to balance the large, 1.20-size muffler. Electric powered airplanes usually require little lateral balance weight as there is no muffler sticking out on one side. But remember that wood weights vary even for electrics so check the lateral balance and make the adjustments even on electrics.

Center all the control surfaces, especially the rudder. Set the throttle for top speed and the proper idle (2,200 rpm). Check that all controls move in the proper directions. Charge the batteries. Drive to the flying field.

Flying the Pulse XT 125:

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There is no way around it. The Pulse XT 125 has to be one of the best looking large sport airplanes available.

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That long nose and sloping “glare” panel really look great. This view makes me glad I spent the extra time installing the inverted engine. The inverted engine has not caused any starting, running or operational problems at all.

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(Photo 54 courtesy aviation-history.com; Photo 55 courtesy MustangsMustang.com)

Its fuselage, with its long nose, slim cross section and the rear turtle deck is shaped much like the early WW II fighters. Just compare the above photos to photo 52. These warplanes have always been modeling favorites partly due to their looks. The Pulse XT 125 does not disappoint in the looks department.

But what about flying it? No disappointments here either. In fact, there are a few pleasant surprises here.

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The takeoff is nearly instantaneous. There is so much lift in this big wing that the Pulse XT 125 lifts off after about a 15-20 foot ground roll after full throttle is applied. What short ground roll there is remains straight and easy to manage.

The climb out with the Evolution 1.20 engine can be steep if desired but the airspeed stays manageable in the 25 mph range. Hold less of a climb angle and the Pulse XT gains very little airspeed while still holding a respectable climb rate. Reaching flying altitude happens in about 10-15 seconds at a very gentle climb angle.

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The Pulse XT 125’s underside is composed of alternating sliver and white stripes. The bottom of the wing’s leading edge is bright orange. The stabilizer’s underside is also bright orange as is the fuselage bottom. This airplane has no visibility problems once airborne.

Before getting into this airplane’s aerobatic capabilities, let’s check out its slow speed performance (always a good idea on an airplane’s first flight). Slow flight in the all the Pulse XT variants usually means very slow.

But in the Pulse XT 125, slow means so slow as to be nearly stopped. At its actual 9.57 pound weight, this Pulse XT 125’s wing loading is only 14.5 ounces per square foot! 14.5 oz. / sq. ft? That is lower than almost all the 40-sized Basic Trainers Sport Aviator has ever tested. No wonder this airplane will loaf along near single-digit airspeeds!

In fact, it is possible that the extra elevator movement, installed on this airplane to provide a flair cushion at very slow landing speeds, might be reducing the stall speed so much that some slow-speed control annoyances do occur. These are minor but are annoying.

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When flown just above stall speed for example, The Pulse XT 125 exhibits a lot of adverse yaw. The ailerons are large and extend all the way out to just short of the wingtips. There is little wonder the airplane has some adverse yaw. However, it is only at such very slow airspeeds that the adverse yaw is evident to most pilots.

For the more advanced aerobatic pilot, slight adverse yaw occurs in cruise flight and vertical lines but only requires about 15% differential to remove. Extreme slow flight’s adverse yaw can not, of course, be trimmed away in this or any other airplane. But a little bit of rudder solves that problem. The Pulse XT 125 does have a moderately powerful rudder that is very effective.

When slowed down and into the stall, the ailerons become almost totally ineffective. Without rudder input, the airplane’s adverse yaw actually results in a bank in the opposite direction to the aileron input. Again, the effective rudder easily picks up a down wing and guides the airplane even through the deepest of stalls (continued full “up” elevator is kept in through the entire stall event).

The lack of aileron effectiveness in the stall itself is most likely due to the 1/4 inch extra elevator movement installed in this airplane. The reason for the extra movement is that, with the extra elevator authority, the Pulse XT can touch down at single digit airspeeds without fear of the airplane’s falling out of the sky. Having full aileron control at the stall is little required when the airplane is just about touching the ground.

Photo 59

Inverted flight and maneuvers was surprisingly very good. The semi-symmetrical airfoil provides excellent inverted flight characteristics. Multiple outside side loops remain on track without requiring much rudder input and without unduly slowing the airplane. Remember that time spent laterally balancing the airplane? The airplane’s great tracking performance is the payoff for that extra effort.

Inverted multiple rolls (stopping inverted) remain on track and need almost no “up” elevator when upright to maintain the flight track. Inverted Immelmanns and half loops are fun but do not require any different piloting techniques than the same maneuvers would require when flown upright.

Photo 60

During prolonged knife-edge flight with the CG set at the 3 11/16 in. point, the airplane has a definite pull towards the canopy in either rudder direction. Prolonged knife-edge flight is possible but only just. Before the roll coupling is trimmed away, the pilot will have to hold a little opposite aileron to prevent the airplane from rolling out of the knife-edge.

With the CG moved rearward after flight testing, the rudder now has sufficient power to easily hold knife-edge and maybe even exhibit a little climbing ability. The tendency to “walk” toward the canopy is reduced and now can be easily trimmed away with a little down elevator mixed to the rudder in either direction. However, roll coupling does increase some with the aft CG but is very easily trimmed out with just a few “points” of opposite aileron mixed with rudder input.

Photo 61

Snap rolls are slow but precise at the starting CG. At the rearward CG, the snap rolls do quicken and the airplane recovers more on track. Regardless of the CG position, the snap rolls are never too fast and always remain extremely controllable. Spins are slow and very nose-down at various CG locations.

At the starting CG, this is a difficult airplane to make spin at all. About the only way to spin the airplane, even with the excess rudder movement, is to pitch up to about 50 degrees, hold a little throttle into the stall and then to move everything into one corner or another.

Inverted spins do happen at more regular stall attitudes. But the rotation rate remains slow and recovery can be had instantly by just releasing the controls. Remember to pull out of the resultant dive!

At the rearward CG, the Pulse XT 125 excels at rolling circles. In fact, the airplane flies this maneuver better than I do! (That last quarter circle remains a killer for me.) No sport airplane that has a non-airfoil vertical fin and rudder will fly complete one-roll rolling loops (they usually lack the ability to perform the knife-edge pull-out during the last quarter of the loop) but the Pulse XT 125 comes very close. Just quicken the last quarter’s roll rate so that the final pull to horizontal becomes an elevator maneuver.

A great pilot like the Pulse’s designer, Mike McConville, can probably perform this maneuver with the Pulse XT 125, but regular stick jockeys like you and I will have to cheat during that last quarter loop. Still, not many other sport airplanes can even come close to matching the Pulse XT 125’s performance here.

This is probably the Pulse XT 125’s greatest benefit. Since it can fly so much better than I, it is going to teach me a lot of maneuvers that I do not yet fly well. This airplane is going to make me a much better Pattern pilot. It is designed for those smooth, precision Pattern-style maneuvers, not for 3-D flight.

Photo 62

Getting back to more common maneuvers designed to not scare pilots out of their minds, the Pulse XT 125 is terrific at flying large concentric loops. The airplane’s small dihedral aids the pilot in keeping the airplane on track when things get slow over the top of a very large loop. This airplane can fly pretty loops as large as about 200 ft. diameter but the pilot will need to input some rudder to stay perfectly on track. Slightly smaller diameter loops, say about 150 ft., fly themselves without rudder input (that ole` time dihedral at work again).

Speaking of rudder input, most sport airplanes with propellers in the 15-inch range, this airplane uses a 15 x 6 inch propeller, usually require a fair amount of right rudder in a vertical climb. However, the Pulse XT 125’s thrust line is just about perfect so very little right rudder is needed until the airplane gets very slow near the top of the vertical line. A hands-off vertical line on this airplane (each aircraft is always different in this area) required only 3 points of right rudder mixing with throttle and then only when full-throttle was used in the vertical climb.

In order to trim this, you will need a transmitter like the JR 8103 that allows “step” mixing. If your transmitter does not have this function, that is not a problem. So little right rudder is needed that no-rudder vertical climbs are so close to straight that few of us will notice it anyway. This is a well designed aerobatic aircraft.

Rolls are fairly axial for a sport airplane and on the slow side. Maximum roll rate is about 1 roll per two seconds. Increasing the aileron deflections might speed up the roll rate but that will greatly increase adverse yaw. Instead, try sealing the aileron gaps with clear packing tape or covering. That speeds the roll just a little to around 3 rolls in 5 seconds. Perfect!

Considering the large rudder and with the powerful Evolution 125 NX engine to pull the airplane straight up, stall turns are this aircraft’s favorite maneuver. It is very hard to flop a stall turn with this airplane. Multiple climbs and stall turns, such as those in the Figure “M” maneuvers are a true pilot’s delight.

With its semi-symmetrical airfoil, the Pulse XT 125 seems to love inverted maneuvers and outside loops, Bunts (a push from the top into an outside half loop and half roll out), outside snap rolls, inverted and regular Avalanches and Top Hats (inverted across the top).

If you have wanted to learn some of these more complex maneuvers, this is one good-looking airplane that can safely teach you to fly them and even more.

Photo 63

It’s a shame, but even the best flights must finally end. It is a little heart breaking to have to land this airplane because you will be having so much fun. You will never want it to end. But end it does and the Pulse XT 125 makes even this maneuver low-stress.

Like a good Pattern airplane, the Pulse XT 125 will make you look like a great pilot. The mix between high lift, slow airspeed and moderate drag makes approach control one of the easiest tasks ever. The near single-digit touchdown airspeeds allow the pilot to be so far ahead of the airplane that point landings right in front of the pilot become routine.

This airplane’s combination of aerobatic capabilities and high-lift, slow flight removes all the stress of flying. The pilot always has plenty of time to plan ahead, fly the maneuver and then to recover exactly as planned. At no time will this airplane scare its pilot or present sudden surprises. Maneuvers, though precise, seem to be flown in slow motion (one advantage of the Pulse XT 125’s large size). It is nearly impossible to get “behind” this aircraft even if you nearly fall asleep (well, not quite but you know what I mean).

Summary:

Photo 64

This great-looking airplane performs several important missions for its pilot:

ª If you are a newer pilot, this airplane will teach you everything you need to know about aerobatic flying without being demanding. Despite many piloting mistakes, it will stay with you and keep encouraging you to learn without scaring you. This is great second airplane for anyone just out of Basic Trainers.

ª If you are a more experienced pilot, this aircraft will take you into those far off flight realms you always wanted to try. Plus, it will do so without stress and concern. While remaining aerobatic, it is also gentle and non-demanding of its pilot.

ª The large size and great, sleek appearance make a statement at any flying field. This is one airplane that you will be proud to fly.

This airplane looks so great and flies so well, that we have two suggestions for Hangar 9 to consider. First, insert inverted two-stroke engine details on the firewall template.

Second, how about offering us a fully symmetrical airfoil wing as an add-on item? Keep the top airfoil shape the same so the new wing will mount easily on the fuselage. Just match it on the bottom. While the airplane flies very well as is, a fully symmetrical airfoil can only make better inverted and snap maneuvers. That is just a thought but one worth considering.

For more information on this large and stress-free airplane, go to: http://www.horizonhobby.com/Products/Default.aspx?ProdID=HAN5170

Additional Aircraft Specifications Manufacturer: Hangar 9 Length: 62.5 in. Cost: $270.00 Wingspan: 76 in. Radio: JR 8103 2.4 GHz Wing Area: 1050 sq. in. Servos: 5 x JR 821 Wing Loading: 14.6 oz./sq. ft. Engine: Evolution 1.20 NX Weight: 9.57 lb. Airfoil: Semi-Symmetrical Special Airframe Features: Semi-Symmetrical Wing, Loads of Extra Lift. Great Appearance, Designed for Low Stress Aerobatics.

Notable Positives Excellent aerobatic abilities Extremely fast assembly Very good looks Light flying weight Good advanced trainer performance Low Pilot Stress Flight Extra light wing loading Very easy to fly well Notable Negatives Elevator/rudder push rods light

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