A Giant-Scale Thermal Hunter

giant-scale-thermal
Written by Fitz Walker
Hobby Club Leprechaun
As seen in the February 2022 issue of Model Aviation.
Review
 

At a Glance

Specifications

Wingspan: 102 inches

Length: 80 inches

Wing area: 1,705 sq. in.

Wing loading: 6 ounces/square feet

Weight (as flown): 71 ounces

Motor: 1,000 Kv brushless Suppo 2814/8

ESC: Avian 45-amp brushless Smart

Battery: Spektrum 3S 4,000 mAh Smart

Receiver: Spektrum AR637T

Servos: Hitec HS-82MG; Hitec HS-85BB

Radio: Spektrum NX6

Price: $199.99

Pluses

  • Unique styling.
  • Wonderful flying qualities.
  • Extremely light wing loading.

Minuses

  • Manual too simplistic.
  • Could use an extra piece of 2mm balsa sheeting.

Manufacturer

ValuePlanes

http://www.valueplanes.com

Importer/Distributer

Hobby Club

(949) 425-1362

www.hobbyclub.com

Access additional content by visiting www.ModelAviation.com/bonuscontent.

THE ORIGINAL LEPRECHAUN GLIDER design dates back to the early 1950s. It was a Free Flight model by Dick Twomey that was known for its large size and low-aspect-ratio elliptical wings. Dick’s design features undercambered wings and a lifting tail. It’s an undeniably vintage model from Hobby Club that has been updated for modern radio control and utilizes laser-cutting technology. You also have the option of building it as a pure glider or electric-powered, self-launching aircraft.

The box was quite heavy because there were apparently a lot of various trees that gave their lives to make this model. Expect copious amounts of wing ribs and balsa sticks to work with. In fact, I counted 62 pieces of wood sticks and parts sheets. The wood quality is good, with only a slight variation in wood density of some of the balsa sticks.

The wing ribs are cut not from balsa but from 3mm light plywood. The laser cutting is good, and most of the parts can be easily popped out of their sheets, with the thicker ones needing a little encouragement from a hobby knife.

The assembly manual is adequate, with numerous color photos of the various construction steps, but it’s obvious that the text was written by a non-native English speaker and some of the steps are slightly vague. The model can be built powered or nonpowered, but the manual only gives guidance for a powered version. There are two large sheets of plans—one for the fuselage and tail parts, with the other squeezing in the two wing halves on one modest-size sheet with a clever, overlapping outline.

Build

Construction starts with the fuselage, which is made up of balsa sticks that must be cut and sanded to size (a miter saw comes in handy for this part). Because of the long length of the fuselage, it is necessary to splice several of the sticks together to lengthen them. Some of the balsa sticks were stiffer than others, so I was careful to choose the softer ones for the tighter bends that form the nose section. When building up the aft end of the fuselage, I noticed a missing line on the plans. Fortunately, the picture in the manual shows correct wood placement.

After the fuselage sides are complete, a series of laser-cut triangular pieces is used as a jig to vertically align the sides while the crossmembers are glued into place. These jig pieces worked quite well, and after the core fuselage was built, I couldn’t see any warping or crookedness. I should mention again that the fuselage is long! Fully built, it will stretch to roughly 80 inches in length.

The plywood firewall in the nose has two sets of holes for a variety of motor-mounting options. Thick, balsa side pieces comprise the front of the nose fairing, which must be sanded to shape. A battery-mounting plate that also doubles as the rudder servo mount is held in place with screws under a hinged access hatch. Magnets are included to hold down the hatch.

Wing construction also requires splicing balsa sticks to make wing stringers the proper length. Much of the wing is made of light plywood, including all of the ribs, which have been thoroughly lightened to save weight. Three sets of spars, along with leading edge (LE) balsa sheeting, provide a strong, lightweight wing structure with a C-tube LE. Wing boxes at the wing roots allow the wing halves to slide onto the wing spar joints protruding from the fuselage. I did run out of 2mm balsa sheeting and needed to substitute a small piece of 1/16-inch balsa sheet from my personal stash.

The all-balsa tail components are completely built-up for lightness. In what appears to be a carryover of the design’s heritage, the horizontal stabilizer is attached to the fuselage with rubber bands. This allows the rather large elevator to be removed for transportation if vehicle space is tight.

A little care must be taken in building the rudder because the trailing edge (TE) needs to be lifted slightly to center on the ribs. String for connecting the rudder to the servo is included in the kit, but I elected to use Du-Bro 4-40 pull-pull metal cabling. This allows for better adjustability while remaining a light setup.

The elevator servo is mounted in the tail beneath the removable horizontal stabilizer, so I chose a slightly lighter-weight servo for that function. With such a long fuselage, it is prudent to keep the tail as light as possible. Elevator control is connected to the servo via a relatively short control rod. All of the control surfaces used CA hinges that were supplied with the kit.

The wing halves are also held in place with rubber bands tied together by wrapping them around screws in the LEs and TEs. I wasn’t terribly confident in this method of keeping the wing halves on, so I also used a couple of strips of clear tape on the wing/fuselage joints.

I elected to use a combination of transparent blue and opaque white Hangar 9 UltraCote for covering. You will need a lot of covering. I went through five rolls of blue and one roll of the white. I’ve never used that much covering on a model before! (I guess I need to get out more often.) The results, however, were quite satisfactory, with a rather striking look that allows admiration of the underlying structure.

the framed up fuselage
The framed-up fuselage is held in place and aligned via laser-cut triangular jigs.
an abundance of laser cut parts
An abundance of laser-cut parts is included in the kit. Basic hardware is also included.
the battery hatch allows easy access
The battery hatch allows easy access to electrical components and is held in place by included magnets.

The recommended motor size is deceptively small on paper, but I happened to have one in my motor drawer that matched the specifications. It was a 1,000 Kv Suppo 2814/8 motor that aligned perfectly with the precut holes in the firewall; however, I needed to fabricate some 20mm standoffs from aluminum tubing in order to move it forward enough for the spinner to fit.

The ESC is an Avian 45 Amp Brushless Smart ESC, which provides battery-voltage telemetry. A Spektrum AR637T receiver also has a built-in variometer and altimeter as part of its telemetry stream. Both are perfect for this glider application.

Flight

I initially planned to use a 3S 2,200 mAh LiPo battery pack for power, but because the aircraft was slightly tail-heavy, I upsized to a 3S 4,000 mAh pack. Even with the heavier pack, 3 ounces of lead weight was needed to balance the model. A Maxx Products folding propeller aluminum spinner, with several sizes of Aeronaut propeller blades, gave me options to control the power draw. After some static power measurements, I settled on a 12 × 6 folding propeller.

Flight day was in the mid-70s with a slight breeze. It was nearly perfect except for some cloud cover, so I didn’t expect much in thermal activity. With some trepidation, I overhand launched the Leprechaun at roughly half throttle into the wind. The large model leaped out of my hand with ease and settled into a slow, stable climb. Some down-elevator was needed under power, but not as much as I had expected.

Handling in the air is very sedate. It’s a large model, so don’t expect an instant response to control inputs. You don’t fly it as much as guide it; however, I found it quite stable and could fly it for extended periods of time, hands-off, while in the glide. The Leprechaun will settle into a nice, flat glide that is almost mesmerizing to watch. Stalls are sedate, with no tendency to drop a wing. Elevator authority is good, but the rudder control is noticeably milder.

I tried working some light lift and was easily able to stay in some zero sink fairly close to the ground. You can crank it into a reasonably tight circle for working thermals, so I have no doubts that on a better day, you can ride thermals to speck it out. On the other hand, it’s probably not a model for windy days, although it does handle light breezes surprisingly well.

rubber bands and is removable for transportation
The tail is held on by rubber bands and is removable for transportation.
despite its size hand launching
Despite its size, hand launching is easy, and the Leprechaun practically leaps out of your hand.

While flying the Leprechaun, I had a nice sense of awe because it’s a large model. It’s not just its size that’s impressive, but also its shape and presence in the air. The wide-chord, elliptical wing is a unique profile for a glider, but there is no doubt that a lot of lift is being generated by it because it can fly so slowly that at times it seems to defy gravity.

The Leprechaun is almost an anti-high-performance glider in a sense, but it has so much charm and character that each flight is high performance in feeling. The only thing that could be better would be if there were a pot of gold at the end of each flight.

SOURCES:

Spektrum

(800) 338-4639

www.spektrumrc.com

Hitec RCD USA

(858) 748-6948

www.hitecrcd.com

Du-Bro

(800) 848-9411

www.dubro.com

Hangar 9

(800) 338-4639

www.horizonhobby.com

the leprechauns profile
The Leprechaun’s profile in the air is a delight to look at. Thanks to its size, it’s easy to see.

By Fitz Walker | flying_fitz@yahoo.com Photos by Lee Ray and the author

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