Review and Photos by: Adrian Martinez

Form Follows Function in Aircraft Design

Just a couple of years ago, modelers interested in extreme aerobatics had few capable planes to choose from.  Early profile and fun fly planes could do some amazing things, but they were very specialized and did not have the all around performance some pilots were looking for.  The Harrier 3D 90 is Seagull Models expression of the state of the art.  Some planes can hover well, but are not so good at high alpha knife edge.  Others can knife edge, but suffer from wing rock in harriers.  The designers at Seagull have come up with a plane than can do it all, and do it well.

The Harrier 3D is covered in transparent yellow and blue Hanger 9 Ultracote.  You can not hide flaws in construction with transparent covering and the Harrier has nothing to hide.  The more you look, the more you are impressed by the quality of the laser cut light ply and balsa parts.  As a guy that really likes to build kits, I can really appreciate the care and craftsmanship that went into the construction of this model.

As with most ARFs today, this kit includes a full suite of parts required for the completion of a model.  The only unusual omission was the lack of a spinner.  However, as this model may be powered by two or four stroke engines, this is not too bad.  For safety, I prefer to equip my four stroke models with an aluminum spinner, and I really did not need another addition to my unused kit spinner collection!  The only changes I felt I needed to make were in the areas of control horns and linkages.  While the included gear would be fine for low rate sport flying, the 2mm push rods and standard control horns are not really up to the task of serious 3D thrashing.  Du-Bro heavy duty threaded control horns and homemade carbon push rods (more on that later) are solid, light weight alternatives that allow pilots to max out the throws with confidence.

The recommended engines were .61 to 1.00 two strokes or .91 to 1.10 four strokes.  This kind of plane really needs the torque and instantaneous throttle response of a four stroke, so I chose a Saito 100.  For really extreme flying, a plane like this  needs high torque servos.  The surfaces are large and while standard servos would be okay, stronger servos add greatly to the crispness and precision of all maneuvers.  I used  five Airtronics 94731 high torque/high speed coreless servos for the flight surfaces and a 94102 standard servo for the throttle.  The instructions call for a computer radio to really get the most out of this plane.  My Airtronics Stylus Radio and 8ch receiver allow direct connections to all servos with no Y-harnesses.  While this really is not necessary, it does allow me to center and set end points for each individual servo for max precision and unlimited mixing freedom.

PLANE: Harrier 3D 90
MANUFACTURER: Seagull Models
DISTRIBUTOR: Horizon Hobby
PRICE: $174.99
TYPE: Unlimited 3D Aerobatics
FOR: Intermediate Pilots
WINGSPAN: 60.5 in.
WING AREA: 948.4 sq. in.
WEIGHT:
WING LOADING: 32.8 oz./sq. in.
LENGTH: 66 in.
RADIO: 6-channel Computer Radio with 6 servos required; flown with Airtronics Stylus transmitter, Airtronics 94731 Servos (ailerons (2), elevator (2), Rudder (1)) and 94120 Standard Servo for throttle
ENGINE RANGE: (.61-1.00) 2S, (.91-1.10) 4S Glow

ENGINE USED: Saito 100 from Horizon Hobby
Specs: 1-cylinder, 1.0 ci displacement, 4 Stroke, 15-30% Nitro, 1900-10,000pm range, 20.8 oz. with muffler)

PROPELLER/SPINNER: APC 15x6 and 16x4W, Tru-Turn 2 1/4 in Wide Cut Spinner

FUEL USED: Morgan Cool Power 30% Heli-Fuel

FUEL TANK USED: Kit Standard

ONBOARD BATTERY: Power Racing 6v 1000Mah

I am a builder, I love to spend months turning a box of sticks into a flying machine.  I have always been a little wary about the build quality of ARFs.  However, unwrapping the Harrier was an eye opening experience.  "Wow" was the most common word choice during unpacking.  As I unwrapped every part, I could see well thought out detail after detail through the transparent blue and yellow Ultracote Lite.

The manual features nice step by step instruction with plenty of images to clarify key assemblies.  As always, it is a good idea to read through it a few times, inventorying the kit contents and rounding up all the accessories you need before starting.

GETTING STARTED

Assembly begins with hinging the ailerons and elevator.  The kit includes a set of very nice CA hinges.  I installed an Airtronics 94731 high-speed/high-torque servos in each wing panel.  Be sure to put a drop of CA in the servo mounting holes to toughen up the threads.  I put a drop on the tip of a T-pin to do this.  The instructions say to use 12" servo extenders on each aileron servo.  It appears the authors expect you to plug into the receiver every time you install or remove the wings.  I preferred to use 2-6" extenders per side.  This makes plugging this in at the field a much easier proposition.  I like to label the female leads coming from the receiver to make sure I can clearly identify which one is for the left or right wing panel.  As always, be sure to secure the servo to extender connections in the wings.  I used heat shrink tubing for this purpose.

SETTING UP LINKAGES

Linkage geometry is very important in a 3D model.  The instructions say to install the control horns so that with the servo horn centered the rod is perpendicular to the servo horn and hinge line.  This method has been in instruction books for years but it was, is and forever will be wrong.  Setting up links like this will result in a falling rate actuation of the control surface.  You get the most movement right off center and as you reach the limit of travel you get less and less movement.  This is all due to the servo horn's rotation.  I locate the control horn on the flying surface so the rod is perpendicular to the hinge line at maximum servo throw.  This way the flying surfaces travel is more linear from neutral to maximum throw.

The manual shows the installation of the kit hardware.  While the included hardware would certainly be fine for a 40 size sport model, I was leery of using 2mm metric rods (a bit smaller than 2-56 rod) to control this planes gigantic flying surfaces. I used Du-Bro No.912 heavy-duty control horns which feature a base that can articulate to match the angle of air foiled surfaces like the Harrier 3D's ailerons.  I drilled the appropriate size hole for the control horns 6-32 center bolt and hardened the hole with thin CA before installing the horn.

Making Carbon Control Rods

Extreme control throws are necessary to make 3D flying possible.  Maintaining control of your flying surfaces requires stiff control rods.  Traditionally this meant heavy steel 4-40 rods.  Recently, several sources have popped up for very nice carbon tube control rods.  This was exactly what I wanted, stiff and light.  After a few minutes of research on RCU, I found that the carbon control rods were made from the same tube I have been using for months as spars in my 3D foamy planes!  3/16" pull-truded carbon tube has an ID that allows for a slip fit with the non-threaded portion of 4-40 steel rods.  To make a rod, cut the carbon tube to the length you need with a cut off wheel.  Be sure to wear safety goggles and a filter mask, carbon is nasty stuff.  I used Sullivan S494 assorted 4-40 rods to make the threaded ends.  I cut them so I had a 3/4" smooth portion and a 3/4" threaded portion.  With a cut off wheel, nick up the smooth part of the rod to give the glue something to bite onto.  Mix up some 30 minute epoxy.  Use .032" wire to put some epoxy in the end of the carbon tube.  Put some epoxy on the smooth part of the steel rod and insert it into the carbon tube.  Wipe off the excess epoxy and set it aside for 2 hours.  That's it!  I have hammered completed rods into 2x4's, attached one end to a board and pulled as hard as I could, and so far, I have not been able to get a rod I have assemble to fail.  My assembly method is the same as the commercially available rods, so I am very confident in them.

The Fuel Tank

The next step in assemble deals with the fuel tank.  The Harriers tanks uses plastic molded tubes instead of the traditional brass tubes found on most tanks.  I used them as instructed, and have had no problems at all.  The kit tanks was of a generous size and allows for 8-10 minute flight with a good reserve.

LANDING GEAR

Wheel pants and landing gear were next.  The pants are very nice and very light fiberglass pieces. Since I fly off of a grass field, I decided to use some 1/16" aircraft ply to reinforce the inside of the pants where the axle goes through (see picture).  I glued them in with thick CA and fuel proofed the bare wood with thin CA.  After a few weeks of flying, the modified pants win the honor of being the only intact wheel pants on any of my planes!  The landing gear is mounted with 4 large steel screws into blind nuts anchored to well reinforced hardwood blocks in the fuse.  Once again, a good example of Seagull's top notch construction.

INSTALLING THE ENGINE

I installed a Saito 100 using the included white plastic motor mounts.  A Great Planes dead center hole locator make short work of the process.  The pre drilled throttle push rod hole was a bit too low to line up with the carburetor.  It would have been fine on a 2 stroke but not on 4 stroke.  I drilled a new opening closer to the carb.  Due to the engines close proximity to the firewall, it was necessary to bend a "U" into the throttle push rod.  This allows for a no strain connection to the carb.  The included push rod wire was of the perfect diameter and springiness to allow for this.  For this plane, speed is not a major requirement, so I ran an APC 16x4W prop. A 15x4W would be best if you plan to run 15% Nitro.  I usually run 30% in my 4 strokes so I had to run a 16x4W so the engine would not over-rev.  There are lots of choices in spinners out there.  For 4 strokes, I like to stick to aluminum units for safety reasons.  Backfires are a possibility and nothing stays together under that type of strain better than an alloy spinner.  I chose a new Tru-Turn 2 1/4" wide cut spinner.  Wide cut spinners have openings that allow you to run wide blade, low pitch 3D props.

The Cowl

The cowl has the same high quality fiberglass construction as the wheel pants.  I made a couple of card stock templates to determine where the muffler and needle valve would need to exit the cowl, and using a Dremel tool, I carefully made the openings.  Start small and keep test fitting the cowl until you get the clearance you need.    I took a few extra minutes to open all of the intake holes in the front of the cowl.  Originally I mounted the cowl as instructed.  However after my first day of flying I found that the holes in the cowl for the mounting screws had become oblong due to vibration.  To fix this I made four 3/4" square plates out of 1/16" aircraft ply.  I glued them in with thick CA and covered them with strips of .56oz glass cloth and thin CA.  It has been more than a few weeks of flying and the cowl is rock solid.

TAIL SERVOS AND REAR STABILIZER

I installed three Airtronics 94731 servos to control each elevator half and the rudder.  Be sure to put a drop of CA in the servo mounting hole to toughen up the wood.  At this point, you need to mount the horizontal stabilizer.  Cut away the covering from the stab slot in the fuselage.  Test fit the stab.  Measure with the span to make sure it is centered in the fuse then install the wings and measure from each wing tip back to the stab to make sure it is perpendicular to the planes center line.  Mark the stab for where the covering need to be cut away.  I always use a soldering iron to cut away covering on flying surfaces.  You never want to use a knife as if you cut into the wood you could be in big trouble down the line.  Glue the stab in place with 30 minute epoxy.  Once it is in place measure, just as before, to make sure it is placed properly then pin in place until the epoxy sets.

As with the ailerons, I used Dubro control horns, but since the elevator and rudder were flat, I used No.867 Heavy duty .40-.91 horns.  These are of a more basic design, and are meant to be used on flat control surfaces.  I drilled the appropriate size hole for the control horns 6-32 center bolt and hardened the hole with thin CA before installing the horn.

Installing the stab bracing wires is next on the list.  The manual shows step by step pictures of this process.  It goes smoothly due to the high quality coated stainless wire and crimps included in the kit.  I found it was best to install all the terminals in the fuse and stab first.  I then attached the eight wires to the eight brass threaded turnbuckles and crimped them in place.  I threaded the turnbuckles into the included clevises and snapped them onto the terminals on the stab.  Thread the wires through the terminals in the fuse and crimp them in place.  All that is left to do is to take up the slack in the support wires.  Remember, all you need to do is take up the slack...you are not stringing up a guitar! When its all done take a step back and look to make sure there is no twist or bow in the stab.  If so, go back and adjust the tension of the support wires.

RADIO INSTALL

There is not much left to do at this point.  The throttle servo is the only one inside the fuselage.  The instructions suggested putting the battery under the fuel tank.  I used a 5 cell 1000Mah NiMh pack to make the servos even faster and more powerful.  I attached the receiver next to the throttle servo by gluing a 1/16" aircraft ply plate across the servo rails and used a hook and loop strap and some foam to hold it to the plate.  I cut some of the hook and loop strap material to make smaller straps to bundle up all the servo extensions, switch leads and  charging jack.  I attached the bundle of wires to the rear wing tube.  This functions as a strain relief.  There is about six feet of wire inside the fuselage.  The last thing you want to have is that whipping around during a blender and having a lead pull out of the servo.

The fuselage is topped off with a large canopy/hatch.  It extends from the fire wall to the turtle deck.  During the first day of flying, I notice vibration noise coming from the hatch while running the engine up in the pits.  To fix this I applied a few coats of thin CA to the tongue at the front of the hatch until it was a tight fit into its slot.  Make sure the CA is dry before test fitting the hatch!  No more vibration!  After the first flight, I noticed that one of the M4 cap head bolts that hold the canopy in place had parted company with the plane.  Get some lock washers to prevent this from happening to you.  8-32 units fit just fine.

CG LOCATION
To check the CG, I made two marks on the wing tips at 170mm and 180mm from the leading edge of the wing. With the battery under the tank and the receiver next to the throttle servo, the plane balanced right behind the forward CG point.  Just fine for the first flight.

I set up all the control throws according to the manual.  I added 50% expo to the ailerons  and elevators at High rate and 35% to the rudder at high rate.  For Low and Mid rate, I used 25% expo in all surfaces.  That's it...time to fly!

Slow Flight and Landings

Landing approaches were smooth and stable.  Three-point landings are a cinch. Most landing turn into harriers with the tail wheel touching down first followed by the mains!  I tested the stall characteristics only to find there were none.  Instead of a stall, you get a sort of a flat elevator with moderately steep glide path. Adding power at any time gets you back to normal forward flight. 

Aerobatics and 3D

At half throttle and medium rates, the Harrier 3D is a well-mannered sport plane capable of any aerobatics maneuver the pilot can input.  Loops, Stall turns, Spins, Cuban-8's, you name it and it can do it and look good.  Previous 3D models I have flown did not do so well at conventional aerobatics.  Flip on the high rates, and the plane transforms.  It may not be much of a surprise, but the Harrier 3D Harriers well....really well!  Entry into high AOA flight is just full elevator and a blip of throttle away.  There is just a hint of wing rock, which disappeared completely when I set up a 50% elevator-spoiler mix in my radio.  On my second tank of fuel, I was doing rock solid Harrier figure 8's twenty feet off the deck.  The Harrier is a big 3D plane.  The massive wing area and fuselage side area combine to give this plane a real graceful sit in the air.  This plane makes falling out of a hover into a beautiful maneuver.  All sorts of snaps and spins can be done in what seems to be slow motion.  No matter what ham fisted input you give this plane it will never do anything unexpected.  You can truly fly this plane out of any attitude.  Waterfalls, blenders, walls, parachutes and Knife edge...knife edge is another big WOW!!  The Harrier has side area in spades.  At half throttle and higher, knife edge flight requires minimal rudder input.  Knife edge loops are easy and can be any size from big and graceful to almost like knife edge waterfalls.  Lower the throttle and add rudder and you will find yourself in a rock solid high AOA knife edge attitude.  The Harrier tucks to the gear very slightly when in knife edge.  A five percent up elevator to rudder mix fixed it entirely.  Over the course of testing this plane  I have moved the battery at total of eighteen inches back from it original position under the tank.  It now resides in the turtle deck behind the canopy.  The plane now requires zero down elevator to maintain inverted flight.  However, it is still completely docile

Hovering was no problem at all.  With the combination of the Saito 100, 30% fuel and the 16x4W prop it could be done easily at about half throttle with a solid punch out at any time.  Vertical was absolutely unlimited.

WOW...The Seagull Harrier 3D has become one of my favorite planes!  From its brilliant construction and finish to its to its flight characteristics, it is truly an outstanding plane.  It is perfectly comfortable putting around on a Sunday morning or ripping up the sky.  I have owned and flown several 3D planes. This one by far is the best of the bunch.  It has no bad habits and it an do anything its pilot asks of it.  Seagull has taken the latest knowledge about the design of 3D optimized models and applied it in the Harrier 3D.  This one is a keeper!