DYNAM PT-17

Dynam are back and quality levels have improved too. David Ashby flies a biplane classic

I don’t know about you, but I do feel a little guilty when I see the great chunks of polystyrene used to protect foam models. It doesn’t bear thinking about how long that stuff will take to break down in landfill, making Dynam’s all-cardboard packaging a welcome sight.

The downside though is that, in the past, Dynam’s foam parts have sometimes arrived with more than a little transit-added hangar rash, but not here. Although the cockpit windshields were knocked off on the way, this PT-17 came out pristine.

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Pretty, isn’t it?

Although it flies well - really well - and I’ve no hesitation in recommending the model to careful foamie assemblers, Dynam’s build quality remains a work in progress and, almost inevitably, some niggles will be encountered when you screw this one together.

This PT-17 is Dynam’s first new release for a while and while it’s clear that some very necessary quality improvement is evident, this isn’t a model that’ll screw together during an evening TV advert break. Rest assured though, a few evenings of careful work will result in a pretty pipe that, as I say, does fly well.

ASSEMBLY
There are no step-by-step instructions, although a large sheet provides information such as control deflections, the C of G setting, a decal location guide and some small assembly diagrams.

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The dummy radial section holds nose weight yet is retained by magnets. It’s the reason why some have improved on the retention method.

Main points of interest are:

Those windshields went back on using canopy glue.

Ten screws hold the undercarriage retention plate and, although not obvious, the short black fixings seemed the most likely items for the task in the absence of guidance.

Screws to retain the elevator horns have insufficient reach so my spares box came to the rescue.

While a very long carbon rod supports and joins the bottom wing halves, the top wing is braced and joined using a smaller rod and an EPO foam joining plate.

Both the plate and wing are moulded with an indent for the spar, although said spar wasn’t supplied with my model. I guess I was just unlucky but, again, the good ol’ spares box again came to the rescue.

The lower wing on the port side was slightly bowed but gluing the spar into position while weighing the assembly down onto a flat surface straightened things out.

My fin and rudder were a tad uneven in cross section. I couldn’t decide whether this was down to a poor mould or a warp, so I left it unaltered and the flying qualities haven’t been affected.

Both motor side and down thrust have been built into the design and shouldn’t be altered.

The main wheels required drilling out a fraction to get a friction-free fit over the axles.

The rudder horn supplied isn’t orientated correctly, calling for a final visit to my spares box for a replacement.

Decals add a finishing touch, although the fuselage registrations aren’t handed to match the red band.

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Although the instruction sheet doesn’t help, these short black screws seemed appropriate here.

The short nose PT-17 needs plenty of weight as far forward as possible and the nose section incorporating the dummy engine is retained by magnets. It’s a heavy part as weights have been added to help with the C of G. Although those magnets do the job intended, it’s easy to appreciate why some builders have added an extra retention mechanism, just to make sure the nose section doesn’t detach in flight. I relied on the decals to do that, the number ‘607’ spanning the join while providing a little extra security.

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The tail wheel is steerable. Screws supplied were too short to retain the rudder horn.

The flying wires, interplane struts and cabane struts are easy to fit, remembering that the retention bolts pass through both the strut attachment points and the wire eyelets. The wing wires looks good but also add some all-important rigidity to the structure. Tension springs hold wires above and below the horizontal stabiliser, although the arrangement is cosmetic.

PRE-FLIGHT
The control surface deflections suggested are fine and the C of G should be achieved using the 4S 2600 mAh LiPo pack recommended. I’ve flown the model using lighter 4S 2200 mAh packs and tend to add a little weight to compensate. All up my model came in at 2120g, a shade under Dynam’s 2150g.

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Large wheels handle grass easily enough. It’s worthwhile filing a ‘flat’ on the axle to help retain the collet. Use thread lock too.

At the wattmeter I’ve recorded 300W and 21A peak, or 64W per lb. That’s a modest figure by some measures although perfectly sufficient to provide the power required for this scale, slow flying model.

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I tweaked the combined elevator pushrods, on the left, to pass through the collet in parallel to improve the collet screw’s purchase. Thread lock use is very wise.

FLYING
I’ve loved the PT-17 since first setting eyes on the dusty crop-duster version ‘flown’ by Telly Savalas in the climactic chase sequence from the film Capricorn One. It’s on YouTube if you want to see one of the most dangerous pre-CGI flying sequences ever filmed. That’s probably the reason why I’ve tested a fair few R/C PT-17s over the years.

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At the front there’s plenty of room for a LiPo battery to slide into position.

While the type always has bags of presence in the air, there’s a distinct ‘feel’ at the sticks too. Some really nice-looking models have been spoilt by horrible flying characteristics. One memorable example left the impression that the wings and fuselage wanted to go in different directions, a trait I put down to dodgy incidences and a lack of down and side thrust. It means a manufacturer really has to get those sums right for a PT-17 to work in foam ready-to-fly form.

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Interplane struts, flying and landing wires fit well. The wires do provide some necessary rigidity.

My first few flights with this one enjoyed calm, bright blue autumn skies; perfect conditions to establish whether Dynam had done their homework. A little elevator keeps the tail down as the model starts to roll and while you can get it up quickly, it’s better to let it rise gradually, tail unsticking first, in a scale-like manner.

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Aileron servos sit on the underside of the lower wing. Horns and clevises have been fine in use.

Some ‘17s need a touch of rudder to make the turns nicer, but not here. The ailerons provide a comfortable, positive response and exponential isn’t really necessary. The same goes for elevator and rudder. Slow speed handling is fine; it comes to a virtual standstill before anything happens, when the stall is revealed as a lethargic wing drop and spiral dive that’s easily managed. It’ll pull a loop from level flight and although rolls aren’t crisp, in the Pitts sense, that’s not what a Stearman is about. Think ‘slow barrel-type rolls’ and ‘lazy wing-overs’ and you’re on the right lines.

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It’s a nice size, yet not too big that it won’t go in the car assembled.

Duration is good. I see a very respectable eight to nine minutes from my 2600 mAh 4S pack and bringing this one home is perfectly straightforward when the timer sounds. The large wheels are untroubled by grass and easing in elevator prevents a nose-over as the model comes to a halt.

WELCOME RETURN
Dynam’s return augurs well for the future. Few can resist a pretty PT-17 and I think those assembly niggles will soon be forgotten when you fly this one. It’s a good size, not too small, yet it should fit in most cars fully assembled.

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Pilots are on the shopping list!

Describing a model as ‘perfect for those long summer evenings' is a bit of an R/C flying cliche, but this is certainly a model for calmer conditions, whatever the season.

DATAFILE
Name: PT-17
Model type: Ready to fly scale
Manufactured by: Dynam
UK distributor: CML Distribution
www.cmldistribution.co.uk
RRP: £209.99
Wingspan: 1300mm (51.2”)
Fuselage length: 995mm (39.2”)
All up weight: 2120g (4.67lbs)
Power system: Detrum BM3527 650kV outrunner, 50A ESC, 13" x 6” prop
Connector type: XT60
Req’d to fly: Receiver and 4S 2600mAh LiPo
Functions (servos): Ailerons (2), elevator (1), rudder (1), throttle (via ESC)

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