PT-17 Stearman

 

Pre-war trainer, latterly a sport aviation classic and conveyor of brave wing walkers. Despite these claims to fame, the PT-17 has always burned itself in my consciousness as star of one of the most exciting and dangerous flying sequences ever committed to celluloid. You might recall the chase from the film Capricorn One where reporter Elliott Gould hires larger-than-life pilot Telly Savallas to find the missing astronauts in a tatty Stearman crop-duster while at the same time evading two Hughes 500 helicopters in close pursuit. In those pre-CGI days, the Stearman pilot was reported as saying the sequence was some of the most dangerous flying he’d ever done a fact that’s easy to appreciate as the bipe skims the ground and weaves between the sides of the desert canyons.

I’ve just loved the Stearman ever since – the all-muscle machine with the huge radial has immense appeal so it’s no surprise that E-flite eventually turned their attention to the iconic 1930s trainer.

This isn’t a new model, it was released some 18 months ago, but it’s still available, pretty as a picture and just the right size if you like to put bipes in the car without first taking them apart. That said, and in the typically thorough E-flite fashion, you’ll find some laser-cut wing transport jigs included. These support the wings near the root so the struts can remain in place so both upper and lower wing assemblies slide into place in one action. Although I haven’t used them, for some this will be a great way of speeding up pre-flight preparation.

The classic US ARMY training colours bedeck the model, which, in that scheme, has something of a slightly cartoonish appearance in miniature although closer inspection reveals great attention to detail, notably the fine engine and cowl – a factory made one-piece item – and those beefy legs, another Stearman trademark. They’re factory finished from aluminium and pre-painted in that classic blue. They’re beautifully made too, just bolt into place and very strong like those on the full-size machine, so sympathies will be hard to find if you bend ‘em on the first flight.

The rest is beautifully constructed from balsa and ply, Oracover coated, supported by fine hardware and bundled with one of E-flite’s thorough instructions manuals.

WING IT
Assembly is perfectly straightforward, the model slipping together as easily as any other well developed ARTF you’ll find. Construction commentary therefore barely warrants a mention – well ok, you could just trim the overly long tail wheel wire that runs down from the rudder but, apart from that horribly minor aside, I really can’t think of anything to say – just follow the instructions and you’ll soon be the proud owner of a pretty bipe. The two cockpits need pilots and none are better than E-flite’s 1/9th scale chaps (EFLA150). While we’re there, a quick internet search soon found some instrument panel dials that I printed, cut and fixed into place.
The dummy radial engine looks a bit plasticky but dry-brushing brings out the details, enhancing the appearance no end. I’ll be adding some bracing wires post review too.

Electric powered models need good battery access a facility that must have initially taxed the designer but the removable top hatch is covert and big enough to slip in a Li-Po while providing comfortable access to the servos and receiver.
It’s a model for four servos, one in each bottom wing half driving ailerons plus one each for rudder and elevator. Ailerons incidentally are just on the lower wing. E-flite suggest JR MC35s, a mini servo type that’s unavailable in the UK but any good minis or powerful micros will be fine. Sometimes I seem to have a set of servos sitting pretty and waiting for a new home but not this time so my PT-17 is filled with a few odds and sods but all are 1.5+ kg torque rated and comfortable in this undemanding airframe.

POWER PLAY
E-flite’s models are designed around their ‘Power’ range of motors. You can’t blame them I suppose but, if you’re keen to fit what’s recommended then you’ll be required to purchase an outrunner that’s notably distant from the budget end of the market. Aside from cost, there are other factors to consider, not least that ‘Power’ range units are very robust, powerful, very well made, ultra-reliable and, as I say, just what the model was designed for.

Now, I’ll just let you into a secret – I went out and bought this review model. Yep, you read that right – bought, purchased, so did I try to save money where the motor was concerned? Well, no I didn’t actually. I played safe, bit the bullet and got a Power 15. I’m glad I did, it's a very fine lump, fits a treat without the need to muck about customising the mount and, twinned with a 12x6 APC prop, flies the aeroplane a treat. System measurements then are 380 watts and 33 amps peak.

BALANCING ACT
We need to talk C of G. This model has been on the market for some time and a good deal of user experience is recorded on the internet forums yet some clarity doesn’t go amiss. The stated C of G range is 3¼ - 3¾” back from the leading edge of the upper wing measured at the root. Added to this, there’s a little line in the manual under the section Flying Your Stearman that alludes to the fact that ‘the model may require a few degrees of "down trim" and another section also mentions that some 2-4oz of weight will need to be added at the nose.

Let’s be frank here - if you balance the model at 3¾” then this PT-17 will do a good Saturn V rocket impression and you’ll rapidly run out of down trim. So don’t. My first flight was carried out with the C of G at the mid-point of the range and even this is too far back. Not to the extent that the model is unflyable, but too far back for comfort non-the-less.

Needless to say, the model’s tail-heaviness has attracted some considerable commentary and solution alternatives. Some have played about with wing incidences but I’m happy now I’ve got the C of G up to the forward end of the range by adding weight to the nose. A few degrees of motor down-thrust too seems to have helped. Said weight is in the form of sick-on lead in the cowl and a big 3200mAh 3S Li-Po shoved as far forward as it’ll go. This extra weight adds a fraction to the wing loading and pushes the AUW up to 4lbs but this isn’t a factor that’ll harm the performance.

The control throw movements suggested are about right when a forward C of G point has been established but bear in mind that the model will be far more pitch sensitive when the C of G is at the mid-point or (perish the thought) further back. I still fly with a good 30% of expo dialled in for elevator although ailerons seems fine without this.

BLAST OFF
The first few flights were spent adjusting the balance point to get that C of G further forward but things were soon comfortable enough. Some bipes can be effortlessly floaty models to fly and while, on paper, the wing loading here would seem low enough for the model to adopt those characteristics, in reality this is one that needs to be ‘flown’ all the time, if you know what I mean.

That’s not to say that things are unpleasant, quite the opposite in fact and despite what I’ve said about the C of G, even at the mid-point, the machine is very forgiving and will never drop a wing or surprise the pilot all the while it’s being flown like the little scale aeroplane it is, so the trick is to keep things smooth and to keep the Stearman moving along, no matter how slow.

Power from the system (about 90 watts / lb) seems just right. There’s urge aplenty when it’s required and what’s available seems to fly the model in an authentic fashion. Some thoughts will turn to fitting a heavier motor as a way of addressing the balance issue but I’m not so sure the machine needs any more grunt than it has.

Let’s talk through a flight. Ground handling is fine, the forward u/c location and big wheels mean the tail should stay down when negotiating bumpier surfaces. Lining up, a slow application of throttle requires just the slightest correction by rudder and the model should rise gracefully with a squeeze of elevator.

The suggested control throw rates don’t really deliver a strong aerobatic performance – for many, aileron travel especially is unlikely to be enough yet it’s mattered little to me. This is one of, what I call, my sight, sound and emotion models – one where raw performance doesn’t seem to matter. It just looks good in the air, as pretty as a picture and flies just fine. I’ve grown to like it the more I’ve flown it. Some gentle aerobatics are perfectly possible but they call for throttle and rudder management of the sort that a standard sport model doesn’t often need which is no bad thing I suppose.

Calmer days, where the wind speed is down to a single figure, are the PT-17’s friend. I’ve flown the model in a 15mph breeze, but only once – it’s a small biplane after all and bipes and windy days can be uncomfortable bedfellows so little surprise it wasn’t enjoyable. Bringing the model down for a gentle landing is straightforward when the C of G is forward, less so when it’s further back. Some may challenge my C of G commentary but it’s here at the landing stage where a tail heavy model significantly increases the workload. Coming into a breeze, you’ll need throttle to manage the descent and, at this point, the last thing the pilot needs is a model that pitches up significantly as throttle is applied.

NICE
I once saw comedian Alexi Sayle tell an audience how he liked to annoy people by using the word ‘nice’ to applaud their efforts. In an age when we’re always seeking to trump the last superlative, it might seem churlish to describe this model as nice, yet somehow and, in the er.. nicest possible way, it’s a word that seems to fit.

This PT-17 is simply a very nice ARTF aeroplane that’s been produced with care and attention to detail. It’s pretty and it flies well. Now all I need are a couple of heli pilots who’ll be happy to risk all in a little low level duel.

DATAFILE
Name: Stearman PT-17 15e
Model type: ARTF scale
Manufactured by: E-flite
UK distributor: Horizon Hobby UK
01279 641097
www.horizonhobby.co.uk
RRP: £169.99
Wingspan: 44” (1117mm)
Fuselage length: 35” (889mm)
Wing area: 608 sq. in.
All-up weight: 4lbs
Wing loading: 15 oz / sq. ft.
Power system req’d: E-flite Power 15, 40-amp ESC, 3S 3200mAh Li-Po, 12x6 prop.
Functions (servos): Ailerons (2), elevator (1), rudder (1), throttle via ESC.

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