pc21

This is an assembly and customisation article of this popular and sleek military trainer from Sebart.  The model comes in three variations of colours.  The model featured is the third generation, version 3 which has all metal retracts.  The earlier versions were plastic and caused many pilots grief, modifications were mad eon theMKII but many swapped out their retracts for E-flite trike sets with anti-jam feature adding around £120 to the cost of the model. Sebart's third genration has all metal retractsand uses a sequencer circuit to operate the gear. On the sequencer there are two spare pins which  can be used for other items that need to be switched when the gear is triggered. Landing lights?

 However, in this article I am upping the scale looks with a super looking prop just like it's full size counterpart and some customisation.  Some info on the real beast first.

The Pilatus PC-21 is a single-turboprop, low wing swept monoplane advanced trainer with a stepped tandem cockpit manufactured by Pilatus Aircraft of Switzerland. The PC-21 is powered by a single 1,600 shaft horse power  Pratt and Whitney Canada PT6 turbo-prop engine, which drives a five-bladed graphite Hartzell scimitar propeller on the aircraft's nose.

Claimed by Pilatus that the PC-21 possesses speed and climb rates previously normally only performed by jet-powered aircraft. It is also fitted with a high-speed profile wing, rated for maneuvers up to 8G, complete with hyraulically-assisted ailerons and spoilers which enable the execution of fighter-like rates of roll and other maneuvers. In order to make the aircraft easy to fly at low speeds, crucial to the advanced trainer role the PC-21 is furnished with a digital power management system and the horizontal stabilizer is equipped with an automatic yaw compensator/suppression system to compensate for engine power and speed changes.

Sebart's PC21 50E.

The model is superbly built at the factory to  accurate standards.  Covering in my model was tight and clean.  The retracts look the business now!  The wing comes fully asembled and covered with retracts installed. The cockpit is in two parts. The floor and the main bubble.  This is to allow you to fit your pair of pilots of choice before finally gluing the the two components together.  The wings are very slim so you will need low profile servos!  I used Hitec HS77BB.  Rudder and Elevator are standard size and I used Hitec HS5495BH HV servos, the latter a bit overkill but that was all I had to hand.  The nose wheel retract is also pre-installed with a micro servo for steering.  Rudder and elevator servos are rear mounted and close to their control surfaces.

Recommended power is a Hacker A50 14S with a 70amp ESC.  Use with a 16x8 or 16x10 APC-e prop.  Hello!  This sounds like the Angel 50e power set up!

Here is where I deviate.  I used an E-Flite Power 60 400 kv (ex H9 Blue Nose Mustang). This motor is good for 1800 watts or more and can run 6 cells. I used a HobbyWing Platinum Pro 100amp for the ESC.  (Overkill, yes, but I had it to hand)  My Angel uses the 16 inch props and ground clearance is minimal.  Coming off our excellent grass runway on to the rougher grass it makes for a lawn mower.  Looking at the full size with it's five blades - That's what we need!

Vario Prop

Ramoser in Germany makes multi blade set ups for most scale planes and his designs make them variable.  His company is known as Technik & Design in 86916 Kaufering, Germany.  After some emails he says he has the ideal 5 blade kit for the PC21 50e as I am not the only one who has requested five blade set ups. So, after transfering the sum of around £98 to his company's account I received in just a few days the 5 blade kit.  He can supply three/ four blades kits for your scale war birds which are functional as well as scale.

The items are separately packed. The highly machined hub, motor shaft adaptor, 5 composite blades each weighed and verified. (Mine were 17g each) a pitch gauge and a bit over-proced aluminium spinner and back plate.  After studying the information leaflets for some time I finally figured out how to set the blades up. A bit fiddly I think!

The motor shaft adaptor goes on first followed by the rear part of the vario hub.  Then insert the blades ensuring that the spigots are located correctly. Now fit the front of the hub and then gently lock it together with supplied washer and adaptor nut. By slackening the main nut you can rotate a blade to change the pitch and the others will follow.  I set it up for 13 x 8 using the clever little pitch gauge supplied. Pitches available are from 4 to 15.

Fitting the spinner and backing plate.  To get the backplate located you have to carefully cut out slots in line with the machined prop exit holes.  Not a nice job to do but necessary. 

I only had to cut enough out so that the smaller rounded part of the blade just clears the spinner backplate.  With that done the backplate now just slides over the blades roots and sits neatly on the hub.  The spinner is located by a 4mm threaded rod screwed into the motor shaft adaptor, I used loctite blue once I got the right height so that when the spinner is hand tightened on to the hub, just a little of the thread is showing.  Due to the rotation of the prop direction the spinner is self tightening.

Pilots?  These model pilots are just about the right scale and in the blue colours to match the blue and white plane.  These pilots are from Hobbyking and are ready painted and just few dollars from Hong Kong

With that job done it certainly look like the full size.

Power Set Up

For RX and servo power I used a 2100 MAh LiFe the latter switched on by a HD switch/charge receptacle with led lamp (the latter reminds me to switch off) mounted in the fuselage just aft of the trailing edge. I much favour power redundancy in my electric models where I can rather than rely on the main pack. If the main pack gives up I have got the chance of still having control and hopefully get back in "dead stick".  The 5a BEC is not used so the red wire on the throttle lead has had the pin removed from the plug and taped back and insulated.  Main power LiPos are Zippy compacts 6 cell / 60C / 4000mah.  Don't really need 60C but these were purchased a while ago for a project that never materialised. The main pack weighs 693 grams and needs to sat right back on the battery tray which meant moving the RX to another location.

Powering up at a pitch setting of 13 x 8 gave an input of 1200 watts.  Changed the pitch to 13 x 10 and now shows 1795 watts.  It was left at this setting for the maiden flight which was to be arranged weather permitting as Autumn is fast approaching and this is England!  Up to about half throttle there just the usual prop wash sound but as you start to wind it up through the 3/4 to WOT the prop noise is more of small turbine, a high pitched whoosing sound like a 11 blade EDF.  Not loud though!

Maiden Flight

17th September, not an ideal day at Cashmoor field with a Norwesterly 11 mph crosswind, gusting 16mph and grey skies.  Nevertheless, our chief test pilot Jon Tappin took the PC21 up for it's maiden flight.  Minimal trimming was needed.  Jon pushed it around the sky with verticals, rolling circles, stall turns a lot harder than I ever would.  Does not fly as fast I expected but probably comparison scale speed but no problems with pulling power. In the air it is virtually silent.  Landing was a non event too.

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