Graham's Hobby Website

RC Flying Wings

After some dubious attempts at RC slope soaring in the 1980's, after thirty years procrastination I finally got round to joining a local club in 2015 and sending off for some 21st century kit.

Building the Ninjas

The Ninja SL is sold by Flying Wings as a robust slope soarer with sufficient inertia to cope with aerobatics and collisions. It has a deep chord wing section and is able to fly in stronger wind strengths. There also is a lighter weight version the Ninja Lite.

The Ninja SL wing is in black EPP foam with a GRP tube spar, balsa elevons and correx wingtips. It requires a battery, receiver, two servos and covering materials.

Heavyweight Ninja SL at top, Ninja Lite at bottom

The construction involves joining the wing halves and spar with UHU Por adhesive, then excavating slots in the foam for the radio equipment and nose weight. To keep the upper airfoil section clean I put the battery bay on the underside of the wing. The leading edges of the elevons are chamfered to shape.

The build utilised 2 no. Futaba S3003 standard servos (37gm each) with a Futaba R617FS receiver (at 20gm) and a 3300mah 4.8v flat Nimh battery (at 225gm). After fitting the RC equipment, the wing is sprayed up and wrapped in strapping tape with suitable overlaps, before being covered in coloured tape, again overlapped. Foam hatches are made for the battery and radio bays. The elevons are attached with strapping tape hinges.

Servo installation, pushrod connections and servo/radio programming required the elevons to be set up for correct elevator and aileron responses, using the Futaba 6EX radio transmitter's elevon mixing facility. The flying wing requires a small amount of airfoil reflex (i.e. "up"elevator) to provide a trimming moment for level flight, in the absence of a fuselage/tailplane.

With beefy RC gear and probably excessive glued linings to the bays, the flying weight came out at 1245gm rather than the suggested 700-800gm. This included 142gm nose weight, made with mild steel strip, cut up in to convenient lengths, stacked to suit and hot-glued in place. In practice, the chunky airfoil is tolerant of added weight.

Ninja SL set (lash!) up on bench for determining nose weight for correct CofG

The Ninja Lite has the same wing geometry but is in a lighter white EPP foam. The concept was to extend the range of lower wind strengths I was able to fly in, whilst retaining the basic flight behaviour of the ninja design.

To further keep the weight down I was also careful specifying the other components. It utilised 2 no. Hitec HS82MG servos (19gm each), 2mm carbon push rods, a Futaba R617FS receiver again and a 2600 mah 4.8v Nimh battery (at 115gm). The same covering system as the Ninja SL was used. The flying weight came out at 785gm, including a nose balance weight of 122gm.

Ninja Lite with strapping tape covering & rough RC layout

These two slope soarers were built in winter/spring 2015 and flown many times during the summer, mainly at LMMGA's Staffordshire Moorlands sites at The Mermaid-Gate, Edgetop and Elkstone. After that I got bogged down at my workbench with two more involved builds.

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Flying the Ninjas 2015

I should mention that the Ninja manual recommends control throws of +/- 10mm for elevon control movements (both elevator and aileron sense). From experience at the slope and with advice from club members, I altered the elevon throws to +/- 8mm (elevator function) and +/- 15mm (aileron function). This avoids excessive elevator effect, whilst giving good roll authority.

Maiden outing at The Gate. Wind measured as 10-12mph at head height, using a Silva wind meter. The Ninja SL was flown without trims, exponential or dual rates set up on the transmitter. It flew well "out of the box", turning smoothly and climbing strongly. I was easily able to make fine adjustments to attitude and flight path. The plane was very planted in flight but responsive as well & it manoeuvred "on rails". Even as a beginner with minimal experience I was able to fly it it well out from slope at height and also from low on the slope work it back to height, progressing cross-wind. A small amount of backstick/up elevator was needed to be held on, so the reflex setting needed to be adjusted subsequently. Below 10mph it flew "like a drunkard".

Wintry view westwards from LMMGA The Gate flying site

Two weeks on at The Gate. A flight with revised reflex settings saw both the Ninja and the Ninja Lite head skywards and stall spectacularly on launch. The morals are: a) don't over-complicate the reflex issue, b) put the servos in the right way round (Lite version). The reflex setting solution amounts to dropping the elevon onto a straight edge applied to the rear part of the airfoil underside. The servo reversal was amenable to a software setting in the transmitter, with relief.

Up at The Gate again. A few days later it was 13-15mph gusting 18mph and it was a relief to find that the "straight-edge" reflex setting was nearly spot-on. Pretty cold, so some issues with watering eyes and running nose. Some good circuits out on the right, but also some stall crashes owing to fiddling with transmitter ancillaries.

A good development day at Edgetop. Both planes flown in gusty 15mph wind conditions, out from the slope and back, in left and right hand circuits. One notable moment was heading out from the slope on the right and being caught "low & slow". The Ninja was sucked down by a rotor behind a dry-stone wall, which it hit head on. Some minor nose creases resulted but no worse surprisingly. By the way, a further gotcha is trying to launch with the wrong transmitter model invoked. On a more positive note, started working on "crest-hopping", making cross-slope progress at low height and low speed. Further notes to self - Avoid circuit passes directly overhead, as it gets disorienting! and Avoid being blown downwind in the circuit, especially getting near/over the road! Generally keep forward of the projected flight line.

A spring day at The Gate. 20-25mph gusting 29mph. Flying in boisterous conditions and working on figure eights at varying distances out. Left and right circuit passes. Able to do my first loop. Some major no-no's encountered as: Overhead passes = DISORIENTATION and Don't fly too close / fast near the flight line! I was able to benefit from some help with trimming the Ninja in flight. These settings I was able to incorporate in to the basic set up. Improvement was identified as needed with: the crosswind leg parallel to road (feeding in down elevator); landing smoothly / closer; better launching technique.

A fine late-spring day at Elkstone. At 7-12mph a good day for Ninja Lite flying. Plenty of circuits, but holes in the lift. Needing some up elevator to trim in the light winds.

Scale RC slope soarers at LMMGA Elkstone

A summers day at The Gate. Wind high teens to low teens later. After previous launch problems, 100% successful launches from head today. Sounds silly, but rest plane on head holding it near it's nose then flick it off and down to launch. This technique carries the weight pre-launch and controls the initial attitude of the plane. Someone showed me, so I am not making this up. First mid-air collision. The Ninja Lite had low energy, hanging stable in lift, when the other plane came at me from below in loop, written off. No damage to Ninja Lite. Notes to self: Be more aware of nearby plane dynamics; Square up the approach circuit with definite turns; Work on cross-wind up-slope approaches. Good things about today: Ninja Lite trimmed fine from launch; Making LHS & RHS circuits in stiff wind conditions; Getting a feel for turns in circuit.

Lovely mid-summer day at Elkstone. Wind 5-10mph variable. Flying the Ninja Lite. Lot of drop outs, but some nice left & right circuits in 5-8mph. More lift after lunch. Loops and rolls. Some thermals passing through. Then holes in lift and lots of walking. Best spot: a thermalling seagull.

Bracing summer day at Elkstone. Wind 12mph gust 17mph, typically mid/low teens, 18mph max., stonking lift in middle of day. Broken cloud, blue sky patches. Good Stuff - Reasonable loops & rolls; Some great lift - pushing well out towards visual limit; Bigger model = better visibility; From height into wind: 1/2 roll, loop regain height, 1/2 loop to finish. Poor Stuff - Aerobatics too close in with poor alignment / discipline; Getting blown back like a paper bag in the "compression zone"; Twitchy landing approach (half rates helps); Not marking fall line for crash at a distance; Lack of Ninja penetration, despite weight, consider some ballast; High landing speeds!!

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