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Jan 25, 2013, 11:55 AM
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FMS Stearman PT17

FMS Stearman PT17

Having had the chance to give airrides during a couple of years in the 3 different 220hp Antwerp based Stearmans at the end of previous century, I wanted to fly this charismatic icon in model form as well.

The existing rather expensive wooden E-flite model often got criticized for having bad flying qualities, but when FMS commercialized it as a foam 1 meter span ARF, I jumped at the occasion and soon started to cosmetically change the kit appearance to conform to one of the aircraft I had flown. After opening the box and spreading everything on the table it became clear this model had all the good foundations to further detailing it into a charming little flyer.

I was glad to see FMS finally inserted an extensive spare parts list in the manual, but later orders I placed for reserve spinner shaft etc, took more than half a year to get delivered through the Belgian FMS representative, and wore another number (for common use with 5 other models). That is the reason why when I purchase any kit, I immediately order propblades , propholder, motor shaft and spinner. This is especially important with taildraggers because chances are high it will ever tip over causing damage to the drive train, and then waiting half a year for a part or discovering it cannot be obtained anymore is not what I like. With only a small serial number decal on the nose it became easy to turn that model over to 309, the British registered G-IIIG still operated from Belgium. Instead of removing that decal (taking away a whole blue area) I was able to paint it over after which I could apply my own numbers. I then undertook the easy job of repainting parts of the provided pilot heads, and applied marker corrections to create iris on their eyes, raising the eyebrows, adding a mustache. In the kit they look like nuns straight out of a Closter, but with a few streaks they can look much better. The picture below illustrates the difference between a stock and corrected figure, flanking the unpainted dummy engine. The other figure was later painted to portray a female front seat passenger (for cg reasons pilots fly from the back seat in most early trainers, the front seat either empty or occupied by an instructor or passenger). I later also cut a slice of their lower torso so they sat at the correct height behind the windshields instead of having their heads stick out too much in the wind-stream.

The black plastic engine (7cyl instead of the more common 9cyl) was well detailed but before painting it, I Dremeled out the oil cooler intake and placed a grille in it, allowing more ram air to the ESC and battery compartment. Those previous minor changes made a hell of a difference to the overall appearance of the front fuselage as seen on following distorted picture (because shot too close to the prop).

The top wing is wrapped downwards at the ends but I have no idea if that was intentional or not. The end result is that the outboard portions of the upper wings are the first ones to stall, but because a Stearman has ailerons only on the lower wings it doesnít harm much, and results in gradual stalling of that (front placed) wing, helping the model to pitch down to recover before a full stall develops on both wings. The upper wings also incorporate led navigation lights, but the main portion of the clear plastic has to be painted over with many coats of yellow paint to prevent the strong red and green led lights to shine all over and through the outer wing panel. Leaving only the bulbous protruding mold clear is much more pleasing and realistic. The wires of those lights first run through the bottom of the upper wing towards the outer struts, in which channels are provided to route them towards sticker covered cutout channels in the bottom of the lower wings, towards the fuselage mounted receiver. If done with care the whole thing is almost invisible. Before assembling the wings I first painted the strut loops blue to better blend in with the interplane struts. On the next picture you clearly can see those blue dots, and all the other repainted or further detailed subassemblies ready for mating. Canopy frames were painted aluminum, and solid panel rivets accentuated silver. The instrument panels, although rudimentary, were left untouched because I had no cockpit pictures of our specific aircraft to create better ones. Cockpit side leather stepovers got a brown paint. All this would have been much more difficult if delayed till after the assembly because wires and struts cause insurmountable obstacles for fingers and paint brushes.

So far I havenít seen two identical Stearmans on the airshow circuit, there are always differences in engine (220,300 or 450hp), propeller (wood or metal), engine cowlings or the absence thereof, and various other details. When I had to choose between the 3 Stearmans I flew, the basic layout of the FMS model, overall color and even wheels dictated the way to go. Our 309 had the same wheel covers as the model, just adding paint and red anti slip marks was sufficient to make it near perfect. Slipping the gear assembly to the maximum depth of the fuselage slot has been my greatest problem during final assembly. It all looks right till you try to push down the plastic securing part in the slot. With the model balancing correctly, the placement of the receiver in the roomy fuselage was easy. Individual pushrods coming from separate elevators, rudder and tailwheel steering allow a precise setup, and clear instructions show in which holes to connect everything for adequate initial throws. I used separate channels for each aileron in order to allow differential aileron movements.

Reading the manual I found no instructions how to install the elastic flying wires with the provided springs, but it mentions somewhere fastening them with sticky tapes on the wing! For the tail feathers correct preshaped piano wires are provided that are inserted through spring assemblies at both ends, these being in turn hooked into small plastic loops already in place on the surfaces. I had to look very carefully on the pictures on the manual front picture (plus some I had of the real aircraft) to see how the main wing rigging had to be done. Some of the wires are doubled and run parallel, others are single, but tiny hooks were on the correct places to suggest which are which. I had insufficient spring hooks in my kit to do them all so I reverted to running some twin wires in a loop through the plastic loops. The real aircraft has airfoil shaped wide strong metal strips as wires, and those are sometimes painted, others chromed. Where they cross between the wings they run through guides parallel to the airflow (to minimize vibrating wires because of their length) and I fabricated those out of scratch (paint brush wooden stick remains). With the pictures of the real aircraft on hand, I then painted those plastic elastic wires as per original, with elastic type paint (those wires donít remain rigid in the air). I also added small metal rings at the lower back of the fuselage, which are used as hand holds to steer the aircraft on the ground when is moved by muscle power into a hangar or so. The complete model then got a coat of clear strong wooden floor varnish. The original airplane was kept immaculate and shiny at that time so I used high gloss for that. This made all my touch ups and corrections blend in very well with the factory paint. That model was a head turner when I got it out on the airfield for its maiden.

With a 3S1800mah battery (8 minute flying time) placed vertically from the bottom through a ventilated snap hatch, it weighs just over a kilo and has a wing load of 35gr/dm2, very similar to my Parkzone SE5a biplane. The 11x7 prop gives sufficient pulling power to rapidly get it in the air, but care has to be taken to keep back pressure on the stick for tail wheel friction and steering during the initial takeoff roll. Unfortunately, if unchecked, this often results in a steeper than desired climb angle. Power for that is sufficient, but controllability isnít at such low speeds. With rudder properly trimmed out for taxiing straight, but not for climbout power torque (same servo), my PT17 pulled to the left after liftoff, towards the other pilots in their so called safe box, during the maiden. Instead of correcting with the rudder, my unfortunate reaction was applying right aileron before lowering the nose sufficiently. At least it didnít tip stall, but wasnít effective at all. With the situation going out of hand I then applied too much right rudder which caused a spin entry. I throttled back and neutralized the controls upon which the aircraft responded well by recovering, but unfortunately the nose was in a 45į dive. I didnít dare to apply power and pull up the nose abruptly for fear of entering a secondary spin, and elected to gently reduce the dive angle within the limited altitude available, and allowed it to crashland almost level just 2 meters from a couple of rc pilots with their noses high up in the air, tracking their gliders in a thermal, unaware of a potential hit from my foamy.
Back in the pits I saw no apparent damage and opened the pilot hatch to manually change the rudder angle (slight right rudder) whilst keeping the tail wheel straight on the left stick central point. A more detailed inspection revealed nothing else damaged, thanks to the stopped engine and prop upon impact.

Half an hour later (when my shakes were gone) pilots wisely pulled back behind the green safety wires when I lined up for my second attempt. This time I opened the throttle much slower so I had time to slowly lift the tail before liftoff. This provided me a much more relax time to use rudder inputs for a straight track and straight climb with shallow angle. Only when I deemed I had built up sufficient speed, I raised the nose further, and brought it back overhead with a shallow turn. After trimming it out it became a pleasant aircraft, not as responsive as my SE5a (that is blessed with 4 ailerons instead of 2) but behaving well and predictably. Stall recoveries were straightforward with little tendency for wing drop as long as you kept the wings level with rudder instead of ailerons. It even didnít want to spin properly, transiting by itself into a spiral dive after less than half a turn. After a few low passes I brought it in for landing in 2-point attitude, but directional control after touchdown is very tricky until lower speeds with tailwheel firmly on the ground.

Next flights I made further adjustments and found a good balance with 30% expo on the elevator, 35% on the ailerons and none on the rudder for instant directional control. I dialed 50% aileron differential and that helped reduce the wing drop tendency at low speeds. A 15% aileron to udder mix neutralizes adverse yaw, and 15% throttle to rudder mix (with 50% offset) neutralizes engine torque. Off course with such setup it is not very responsive on the ailerons but it resembles the sloppy behavior and rolling capabilities of a full seize Stearman. At the end of the 2012 season I discovered the slack on the tail wheel steering to become excessive, making it more difficult to handle directionally during all the ground phases. Further looks made me conclude the bellcrank and tail wheel rod had lost their friction, or a bolt was loose, but there was no bolt visible or accessible through the side slit in that portion of the aft fuselage. The fuselage halves had been glued together at the factory, enclosing that whole assembly. Having no drawings of what was in there, and no idea how it was fastened, the only option I had was to take the knife and start cutting through the fake leather bag enclosing the tailwheel system.

Poking deeper I hit something hard where I didnít expect anything. I had hit a kind of nylon baseplate that had been glued into foam slits, and after freeing the back half, was able to pull the front out without further airframe damage (thanks to the infamous never drying FMS glue). With everything exposed it became obvious our Chinese friends didnít sufficiently tighten the bellcrank bolt. I removed it, applied Locktite and securely tightened it in the flat spot on the wire. That slot had prevented the assembly from turning freely, but left excessive play so the tailwheel was allowed to move about 10 degrees either side around the desired servo input. I then reassembled everything and grossly filled the gaps in the foam before painting it flat black. It now looks much more like the irregular leather bag on the original airplane. At that time I also discovered the foam holding the rudder to the vertical tail started to beak and I replaced that with proper nylon hinges. To augment rudder effectiveness I increased the throw by snapping the quicklink in a different bellcrank hole.

This near scale model is extremely attractive, both on the ground and in the air, but is more delicate to fly as the Parkzone SE5a, and therefore not recommended as a first biplane, especially operating from a direction limited hard surface with even a slight crosswind.

After setting up and testflying the model on my new Spectrum DX10 transmitter, I plan to add a Orange3rx gyro stabilizer, only connected to the rudder and elevator because I donít want to lose my differential aileron capability. Stay tuned for an update on that, but only later in spring because I donít fly (open biplanes) in winter temperatures ;-)
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May 12, 2013, 05:40 PM
The sky is the limit
BAF23's Avatar
Thread OP
Spring 2013 I added a Hobby King Orange RX3 flight stabilizer between the receiver and the servos. More info about the this can be found on my dedicated blog page
It now flies much better and flight videos will be made soon. In the meantime compare a recent picture of my model versus the real airplane. Click on the picture to enlarge.
Last edited by BAF23; May 12, 2013 at 05:45 PM.
Nov 07, 2015, 12:30 PM
The sky is the limit
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Thread OP

2015 update

In 2015 I changed all my Sprectrum for Taranis/FrSky electronics. On the Stearman I also substituted a Orange V2 stabilizer for the V1. After about 20 flights the model still looks immaculate and flies better than ever. It looks muuuuch better (more scale) than the e-flite Stearman a fellow member flies on our field. Thanks to the inflight switchable the stabilizer I can fly near perfect scale aerobatics with the gyro off, but also can fly in more than calm winds with the gyro on. Just as with a real stearman, stay away from crosswinds for takeoff and landing.

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