David Ashby fills his pandemic lockdown hours completing a modern update of a classic glider
The Super-Sinbad was designed in the early 1940s by Henry Struck and kitted by Berkeley Models in the USA. Spanning 62″ and weighing less than 20 ounces all up it was a tow line glider equipped with a clever method of staying straight on the line.
‘Tow-control’ linked the tow hook to the rudder via a push rod and an elastic band made sure the rudder returned to neutral, correcting deviations on the way up. Sounds simple, but how well the system worked is another matter.
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Now a design classic, the Sinbad has returned to the skies over the last few years, particularly thanks to the prolific John Woodfield via his social media channels. John’s enlarged 93” span machine retains the original’s pleasing simplicity by using rudder/elevator control, so retaining the dihedral.
Pichler, perhaps in order to broaden its appeal and versatility, has pushed the span to 2.5m (98”), replacing the original’s distinctly under-cambered section with a semi-symmetrical profile while adding ailerons, a motor and folding prop. An outrunner isn’t compulsory though, so the model could be built as a pure soarer should you prefer.
This is a traditional kit, complete with two full-size plan sheets, laser cut parts, sheet and strip balsa, a pre-cut clear cockpit screen and some hardware. The main structure is 3mm ply and the standard of cutting is excellent.
Retained by bands, the wing is two-piece, so helping with transportation and storage. Bolts retain the horizontal stabiliser, so it’s also removable and the fin forms part of the fuselage structure.
The illustrated instruction manual acts as a guide and anyone with a bit of balsa crafting under their belt should manage without too many problems. I did encounter a few puzzling moments along the way and, in truth, the plan should really offer more help by way of notation and section diagrams. So, it’s important to number the parts, then really study the plan and manual before committing the glue.
I prefer aliphatic to cyano and I used this throughout. It dries quickly but also allows time to re-position parts. Although the manual suggests building the fuselage first, it’s not critical, so my tail feathers were for starters, quickly done and set aside.
The horizontal stabiliser is surprisingly large but while the wings and fuselage must be built over the plan, the fin and stab can be done without thanks to the interlocking ribs, trailing edge and false leading edge sections.
Adding the ribs vertically to false leading edges works well before the section is laid flat and the trailing edge added. I used some of the laser cut 14 x 6mm balsa strip for the elevator and rudder leading edges, profiled to allow control surface movement
Theoretically you could build the wings without the plan, again thanks to an interlocking structure. But it’s sensible to build them over the plan, so making sure that everything really lines up. My only deviation was to add the lower 6 x 8mm balsa spar to the lower L.E. D-box sheeting first before placing the ribs down over the spar. This had the effect of levelling the ribs over the building board.
Both sheet and strip pieces must be joined to provide the reach required and while the manual illustrates butt joined sections, plain scarf joints will be stronger and look better. Like the tail feathers, the aileron ribs can be fixed vertically before the sections are completed flat over the plan.
My plan didn’t mention the root rib angle and although the box pic indicates there’s practically none, the track of the rib holes through which the clear plastic joiner tube passes confirms that a degree or so is intended, not least to negate the appearance of anhedral that a straight wing can confer.
A root rib template is needed but, in its absence, I added the root rib, using the tube end to guide the angle – that sounds crude, but it worked.
Although it may appear complex, when taken steadily the fuselage structure comes together easily enough. The lower fuselage comes first, built inverted flat over the plan, before the structure is removed and the upper formers and stringers added. You’ll appreciate the sense in numbering the parts first before starting these stages. The captive nuts and bolts that retain the stab were not included, but my spares box produced some replacements.
The instructions suggest assembling the fin as part of the fuselage process, but that’s a bit awkward, especially if you’re having trouble keeping the keel structure straight and upright on the building board. There’s no reason why this section can’t be built separately and added as one piece, and that’s what I did.
If you plan to add a motor then the design calls for an outrunner with a shaft extension that passes through, and extends beyond, the balsa block nose. It’s easier to add the motor’s captive retention nuts to former A3 before that part is added to the structure.
If Pichler’s bespoke motor is difficult to source then, with some ingenuity, the nose could be altered to accommodate a shorter shaft alternative and a shaft extension could be created, perhaps with the help of a friend with a lathe.
With the basic structure complete, embellishments can be added; the rear sheeting, rear wing supports, cockpit coaming and battery hatch cover. All require the careful application of sheet balsa, where the ‘measure twice, cut once’ maxim is worth remembering.
Like most models I found that creating the big structures over the plan was a pretty speedy task. The final bits and bobs seemed to take forever, although the UK’s third Covid lockdown provided no shortage of bench time.
Four servos are required, Pichler suggesting two of their Master 19g DS3012 digital metal gear minis for rudder and elevator, with a 22g slim profile DS3010s each moving an aileron. Arm yourself with two 1000mm servo extension leads too, one for each for each wing.
Pichler’s bespoke motor, a Boost 40LS, is an 890kV 35mm diameter unit weighing 200g and the shaft extends 84mm beyond the case. The two ball bearings supplied with it support the shaft as it passes through the nose block. Care is needed to ensure the bearings aren’t pushed back inside the nose at the fitting stage. UHU Por held mine in place.
My worries that the long shaft would introduce some unwanted vibration were unfounded. The 40LS seems well made and, in use, is very smooth, although that would be unlikely without the bearing supports.
That it has to be the clear stuff is unquestionable. After all, who’d want to hide that lovely structure? It’s a big thing though, so no surprise that it just devours covering film. Not helped by the fact that I’m terribly wasteful and always seem to throw away as much material as goes on the model. The 12” wing cord doesn’t help either, meaning that a standard roll isn’t quite wide enough to finish both sides of the wing. Given the quantity needed, I thought I’d try some of the clear orange stuff from Hobbyking, which was easy to apply, producing a nice result.
A little trim helps to break up the acres of yellow and my pal, Ray, a very clever and skilful man (who just happens to own a vinyl cutter) produced the lettering.
At a smidgeon over 200g, Pichler’s LemonRc 3300mAh 3S pack isn’t heavy enough to get the C of G forward to the recommended point. Another 200g was needed. The solution is to add nose weight; perhaps use two smaller LiPos in parallel or a larger battery, a 5500mAh 3S LiPo in my case – there’s enough power to keep the model up all day in the right conditions. A power system trial with the wattmeter recorded 235W and 21A peak, a fairly modest 45W/lb.
Pichler’s suggested C of G is fine though. I don’t think experimentation is needed beyond moving it a couple of millimetres either way to suit your flying feel. Control surface movements are German language but translate to:
Elevator: 20mm +/-
Rudder: 40mm +/-
Ailerons: 25mm up and 15mm down
Despite the large deflections I don’t think exponential is required so fly without it first before you decide.
Although the Sinbad appealed as a relaxing hillside soarer, events and calmer conditions conspired to make my power flying field the test flight venue. The V-shaped fuselage provides a good, safe hold when launching and the power system, while modest on paper, has enough urge to pull it up at a steady pace.
As it climbed out into the 9mph headwind my first instinct was to add rudder to supplement the slightly sluggish ailerons. Was it a little tail heavy or did the aileron differential need a tweak? With some turbulence coming from the trees nearby it was probably too early to say.
A stall test came first and revealed a benign model that mushed and nodded but refused to drop a wing. I circled for the camera, made some low passes and brought it home for an easy landing.
It was a bright but chilly day, with little evidence of thermal activity. But the breeze had got up, so the second flight demonstrated how the model’s large wing area was susceptible to sudden gusts, especially below the tree line when taking off or landing.
A day on the hill came next, leaving the impression that the model had found its natural flying home. Being lightly loaded meant it needed little effort to launch, but I wondered if that might translate into a model that wouldn’t make decent headway in the 12mph breeze. Penetrate it did though, surprisingly well.
I’d added an aileron-to-rudder mix at the transmitter, allocated to a switch, just in case the model needed some assistance through turns. While this did help, the model behaved far better in the smoother breeze, so using the coupled aileron/rudder mix wasn’t the necessity I thought it would be.
In many respects it felt like a vintage scale glider – which is no great surprise – but with a positive and predictable feel that some scale subjects don’t possess. It’s hardly surprising that the aerobatic repertoire is limited. Loops are straightforward when you’ve some energy to spare, but rolls, despite the large deflections, aren’t really on the menu. It’ll turn a tight circle to make use of passing thermals and heads up impressively when the stronger lift comes through.
Slope landings should be drama free. The ailerons can catch a wing if the model finds turbulence behind the edge and it’ll make headway on finals, providing you haven’t drifted too far back.
I must mention the wing incidence. The plan notes +0.5 degrees compared to the stab and, judging by the plan, the kit’s laser cut integrity takes care of this. It’s not far off the original’s set up and although I should’ve measured my model, I’m a ‘fly it and see’ chap, so I flew it to see. So doing left the impression that ‘0.5’ is compromise that lends the model a good all-round performance wherever it’s flown.
Sinbad is lovely and I’m very pleased. Unsurprisingly, this isn’t a machine for gusty days at the flat field. Save it for the warm evenings and calmer conditions, where it should hook a passing thermal without any trouble. Smoother conditions suit it better on the hill too.
You can get yours direct from Pichler in Germany, but Sussex Model Centre are Pichler stockists, so orders can be placed there too. Arriving last December my kit was an early production sample and the plan has been updated since this time. Construction has been very satisfying, although not without a few niggles along the way. It’s not a project for tyro balsa bashers but if you’ve glued a few sticks together then, with a bit of care, you’ll have a fine vintage motor glider that’ll fly well and draw plenty of admiring glances.
Model Type: Vintage motor glider
Manufactured by: Pichler
Distributed by: shop.pichler.de or www.sussex-model-centre.co.uk
Wingspan: 2500mm (98.4”)
Length: 1525mm (60”)
Wing area: 2133.7 sq.in.
Wing loading: 5oz / sq.ft.
Weight: 2350g (5lbs 3oz)
Power system: Boost 40 890kV outrunner, 12 x 6” folding prop, 3S 3300mAh LiPo, 50A ESC
Functions (servos): Ailerons (2), rudder (1), elevator (1), throttle (via ESC)
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