PILATUS - Flugmodellbau Geitner€¦ · tionately known as ‘Platty’ (as in duck-billed platypus...

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A Pilatus? I can’t quite remember when I was bitten by the Pilatus bug. Friends questioned my sanity at the time and while in some ways that is normal, for once I had to concede that they had a point. In the world of the modern sailplane the Pilatus B4 is thought to be something of an ugly duckling and is affec- tionately known as ‘Platty’ (as in duck-billed platypus - I’m sure you get the picture). A lit- tle research showed that I was spoiled for choice as there are several European kit manufacturers who include the Pilatus B4 in their range. I followed my ‘OCD’ instincts and made up a list and comparison table which ended up with me settling on the Geitner ver- sion. Don’t ask me how, because I couldn’t explain the rationale I used, but I struck lucky. What You Get Geitner is a family business based in Austria, with an advertising strapline of ‘Ausgereifte GfK-Technologie zu fairen Preisen’ (Glass Reinforced Plastic (GRP) technology at a fair price), making a range of models that are mostly of scale sailplane subjects. They were a new supplier to me and placing an order with them was a bit of a step in the dark. It turned out that they were easy to deal with via email and all my queries were answered in English. A good model-maker is likely to have a waiting list and in that respect Geitner was no exception. Delivery was quoted at about 10 weeks, but in fact turned out to be about half that time. My first impressions when the model arrived were of ambivalence. Surface finish was not quite up there with the standard of the best European competition sailplane mak- ers, but then again, you do get a lot of model for the money. I guess I have been spoiled by PILATUS B4 A Classic “All Round” Scale Glider from Flugmodellbau Geitner BENCHMARKS - By Paul Jubb PILATUS 22/7/11 09:50 Page 2

Transcript of PILATUS - Flugmodellbau Geitner€¦ · tionately known as ‘Platty’ (as in duck-billed platypus...

Page 1: PILATUS - Flugmodellbau Geitner€¦ · tionately known as ‘Platty’ (as in duck-billed platypus - I’m sure you get the picture). A lit-tle research showed that I was spoiled

A Pilatus? I can’t quite remember when I was bitten bythe Pilatus bug. Friends questioned my sanityat the time and while in some ways that isnormal, for once I had to concede that theyhad a point. In the world of the modernsailplane the Pilatus B4 is thought to besomething of an ugly duckling and is affec-tionately known as ‘Platty’ (as in duck-billedplatypus - I’m sure you get the picture). A lit-tle research showed that I was spoiled forchoice as there are several European kitmanufacturers who include the Pilatus B4 intheir range. I followed my ‘OCD’ instincts and

made up a list and comparison table whichended up with me settling on the Geitner ver-sion. Don’t ask me how, because I couldn’texplain the rationale I used, but I strucklucky.

What You GetGeitner is a family business based in Austria,with an advertising strapline of ‘AusgereifteGfK-Technologie zu fairen Preisen’ (GlassReinforced Plastic (GRP) technology at a fairprice), making a range of models that aremostly of scale sailplane subjects. They werea new supplier to me and placing an order

with them was a bit of a step in the dark. Itturned out that they were easy to deal withvia email and all my queries were answeredin English. A good model-maker is likely tohave a waiting list and in that respect Geitnerwas no exception. Delivery was quoted atabout 10 weeks, but in fact turned out to beabout half that time.

My first impressions when the modelarrived were of ambivalence. Surface finishwas not quite up there with the standard ofthe best European competition sailplane mak-ers, but then again, you do get a lot of modelfor the money. I guess I have been spoiled by

PILATUS B4A Classic “All Round” Scale Glider from Flugmodellbau Geitner

BENCHMARKS - By Paul Jubb

PILATUS 22/7/11 09:50 Page 2

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the finish of some of my moulded F3F mod-els. The fuselage has been painted in themould and consequently, no external seam isvisible. A first class finish could be created byspray painting, but I decided to leave wellalone, so what you see in the photographs iswhat you get. The full-size Pilatus B4 wasmade from aluminium and most exampleshave an epoxy paint finish on the surface, giv-ing the appearance (as a colleague unkindlyremarked) of an old Kit Kat tin. So maybe thefinish on this model was quite authentic!

Further inspection showed the wings to bevery solid with minimal torsional flex. They’ve

also proved to be quite ‘ding-resistant’. Themain components fit together straightawaywhich gives the promise of a relatively shortbuild time. The supplied wing joiner is madeof 16mm glass and my first thought was thatI would replace it with steel - mistakenly as itturned out as the glass joiner is perfectlymatched to the airframe, as you will readlater (or earlier if you went straight to the fly-ing review).

Some fiddly jobs are already done such asfitting the spoilers and rudder. Geitner alsoinstalled flaps at my request and put in twoservo-wells for driving each flap as they are

quite long compared to the ailerons. Aileronsand flaps have a living hinge and an insideinspection showed that silicon had also beenused to strengthen the hinge. There werequite large gaps between the false trailingedge of the wing and the leading edge of theflaps/ ailerons. A reel of tape was suppliedto be fitted as gap wipers. No control hornswere supplied, so I fabricated my own.

Also included with the kit were A4 sheetswith brief information about trim set-up andan illustration of the proposed elevator servoinstallation, ‘Pilatus’ logo stickers, two vac-formed canopies (one is a spare) and threeplastic bolts for the tail (one installed and twospares!). Again, I thought of replacing theplastic bolt with a steel one, but I still haven’tgot round to doing that and the plastic bolthas survived prolonged and spirited flying.

Fit OutIt’s almost a reflex response now for me tomake a cradle for each new model from poly-styrene foam. It gives a stable platform forworking on the fuselage and helps to providesome protection in the workshop (diningroom) and when the model is being trans-ported in the car.

I’ve also got into the habit of starting workat the rear end of the fuselage and then towork forwards from there. Geitner suggestsmounting the elevator servo at the base ofthe fin post. No horn was supplied so I useda brass one and set it into the elevator usingepoxy. A hole needed to be opened up at thetop of the fin as an exit for the servopushrod. Trial operation showed that thearrangement worked OK, but the geometryneeded to be thought out to give adequatemechanical advantage for down elevator. Iused a Multiplex Micro ‘digi’ servo as it fittedeasily in the fin with good clearance for theservo arm. Dynamic torque of the Micro ‘digi’with 6V supply was quoted at 42 Ncm.Would that be enough for my flying style?There is minimal play in the control run andgood leverage for ‘up’ elevator, so in practiceit has worked very well. Geitner suggeststhat pieces of sandpaper be glued to the topof the fin; there is then no need for anyother locating pins for the tail plane, every-thing being held in place by the main plasticbolt and friction from the sandpaper.

The rudder hinge was already fitted byGeitner. The rudder itself was supplied withKevlar thread for a pull-pull control arrange-ment. This did not prove satisfactory asthere was stretch in the thread that allowedthe rudder to flutter at speed. I have subse-quently replaced the Kevlar thread with steelcable and fitted 3mm brass horns on to therudder to increase leverage. That certainly

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This model handles easily for launching by yourself.

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seems to have done the job as it has not flut-tered since.

WingsFirst job with the wings was to open up thepre-moulded servo wells and to cut the servocovers to size. Before cutting and sandingbegan, I worked out the position of each servoin its well, the alignment of the pushrods toget them perpendicular to the ailerons andflap hinge lines and also where the pushrods

would exit their servo cover shroud to actuatethe horns. All this was sketched on to mask-ing tape on the wing surface to minimise anychance of me making a mistake and it worked!Actually the first job was to decide what ser-vos and horns were to be fitted, because thatdetermined all the geometry.

Each wing panel needed four servos to beinstalled (1x aileron servo, 2x flaps plus 1xspoiler per panel), so there was a fair amountof work (and cost) here. There was 19mm

clear between the top and bottom wing shells,so a mini servo or smaller is required unlessyou want to undertake serious surgery on theservo cases. After a bit of dithering I settledon using Hyperion Atlas 16 digital servos forthe aileron and flaps. These are relatively newservos, so durability has yet to be established,but they have had good ‘press’ so far andseem very well put together. I also went formetal gears to reduce the chance of my strip-ping them with ham-fisted handling. I got myservos from Robotbirds where I could havesaved £6 per servo by going for plastic gearsinstead of metal. Each spoiler is driven by avenerable HS85 servo and I again went formetal gears.

I made up the servo horns from fibreglassPCB board. The horn shape was drawn on tothe board using a cardboard template andeach horn was cut out using a powered fretsaw and thereafter the finish sanding wasdone as a sandwich. Slots for the horns wereopened up in the flap surfaces using a fine drill- a pin vice is an ideal tool for this. The hornswere glued in place using epoxy thickened withmicro fibres. A carbon rod through the twoflap horns was used to keep things alignedwhile the glue set.

Before fitting the servos I applied some car-bon cloth patches, wetted with epoxy, into theservo wells and also inserted some balsasheet to act as a shear web rib between thetop and bottom skins. The main reason I dothis is to try to avoid getting ugly bulges in thetop wing skins, which would otherwise resultfrom blow back of the flaps and ailerons, but italso helps with achieving a crisp controlresponse. I’m in favour of using servo framesin this kind of installation as they allow servosto be removed easily should it be necessary tochange position of the servo arm, or for main-tenance. Unfortunately I couldn’t find anyframes for the Atlas servos, probably becausethey were so new.

So my servos were stuck in using the ‘rusticand resilient’ method of gluing in with pastemade by mixing epoxy resin with micro bal-loons. The paste is lighter than using resinalone. I also sealed the servo with heat-shrinksleeving first as that gives a fighting chance ofbeing able to remove it should I need to later.To get a tidy and tight seal, I removed theservo lugs and cut a slot for the servo wirebefore shrinking. To prevent the sleeve fromtrying to shrink into a random shape Iclamped everything in place between the jawsof a vice or workbench while it was initiallyapplied, and then to final shrink out from theclamp. I also roughened up the shiny heatshrink using glass paper (or Permagrit file) toprovide a key for the epoxy paste to adhere to.

Pushrods were made up from 2.5mmthreaded rod, which I’ve found to be ideal forsailplanes up to the size of this Pilatus. Noteveryone stocks this rod and most modelshops seem to assume that modellers shouldbe using either 2mm or 3mm. I got my latestbatch of 2.5mm rod from ebay. Servo centreand travel was all trialled and clevices weretacked into place using ‘Threadlock’. Thisseems to have removed any play in the

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The main components can be fitted together immediately.

Airbrakes are ready installed by Geitner andwork freely.

I fitted a brass horn to control the elevator.

ABOVE LEFT: My solution for the wing servos was to fit carbon cloth into the servo wells and to bridge theskins with balsa ribs. Note that the home-made PCB horns have also been installed and a carbon rod insert-ed to check the alignment. ABOVE RIGHT: The wing servos were installed by floating on to a paste ofepoxy resin and microballoons.

ABOVE LEFT: Wing root detail showing the servo wiring socket is permanently fixed in place. ABOVE RIGHT: Multiplex green plugs were left on a fly lead.You can also see the cable release for the canopy which exits below the wing root.

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pushrod thread, but if any does appear I willwick solder in between the rod and clevice.Once I was happy that all was working OK andthe rods were the correct length, the epoxypaste was mixed and spread on to the nowdry carbon cloth patches and the servos low-ered on to this to create their own bowl.

Each flap is driven by two servos, so I usedthe following procedure to match the move-ments and reduce the chances that the ser-vos would work against each other. Theinboard servo was set up and glued in asdescribed above. When the glue was set thepushrod assembly was removed and an identi-cal pushrod assembly made up for the out-board servo. The outboard flap servo wasthen installed using the same method as theinboard servo. Operation of each servo wastested independently with the flap connectedand the other servo running free. A final checkwas made to ensure that the servo armswere working in unison by running a carbonrod between the servo arms and operatingthem as a gang (either using a y-lead, or witheach channel having identical settings for cen-tre, travel end points and volume. Once thischecked out OK, the pushrod assembly forboth servos could be attached to the hornsfor testing of the ganged servo drive. I guessit worked out OK as there has been no‘buzzing’ to indicate any resistance. I’m sure Icould use a more high-tech solution for match-ing the servo movements and for load testing,but my crude method has worked out OK.

The flaps were set to work with a neutralcentre, because I wanted to be able to couplethem with the ailerons and I didn’t need to setup large downward deflection for crow brakingas the wings have spoiler brakes.

Front EndA retractable wheel is very handy for aerotow, but as my flying is almost exclusively atslope sites, you might wonder why I decidedto fit a retract unit. My rationale was that itwould provide some ballast to help bring thewing section on step and help with resalevalue if I ever decide to move the model on. Imanaged to get my retract unit from an oldcontact - Neil at Spire Models in Salisbury.When positioning the unit in the fuselage, thewheel needs to be in front of the CG, but notso far forward that the unit encroaches intothe cockpit. So I did some maths and meas-urements to check the size of the aperturethat needed to be made in the fuselage andmarked that up using masking tape. Cutswere made using a knife rather than aDremel, to keep the gaps between the fuse-lage and doors as neat as possible. I alsodecided to mount the rudder servo on thechassis of the retract unit and to incorporatea bell crank for the rudder closed loop intothe formers for the chassis. Hopefully thepictures will help to explain the arrangement.After all this effort the retract doors weretaped up to avoid any chance of snaggingduring a landing at the slope!

By ganging the flaps I was able to get awaywith a 9-channel receiver (three channels perwing, two for the tail and one for the retractunit). The latest generation of 2.4GHzreceivers will cope with a higher voltage than35MHz receivers, so I have settled on using2S LIFE battery packs to power the on-boardradio control equipment. The voltage is wellwithin operating range for the receiver and isbelow that of a freshly charged 5-cell nickelpack, so the servos I used can cope withoutthe need for voltage regulation. The largerLIFE cells have plenty of capacity for a fullday’s flying so I also decided to avoid thecomplication of twin packs and a batterybacker unit. I did want the convenience of aswitch so I wouldn’t have to clear out thecockpit at the beginning and end of eachflight. Multiplex has a new range of ‘safety’switches and the 12HV unit seemed ideal formy application as it had a healthy 12 ampcurrent capacity without a direct mechanicallink between the battery and receiver.

The instrument panel was fitted directly onto the canopy frame. When the canopy wasremoved it allowed good access into thefront of the fuselage for tweaking the noseballast and for charging the battery. I madethe panel by laminating two thin pieces of plyand recessing printed dials on to the backpiece. Closed-loop cable was fitted to thecanopy latch and exits the fuselage below thewing root - so the canopy release mechanismis well hidden when the model is rigged.

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TOP LEFT: Formers were made up to support the retract unit. TOP RIGHT: Retract doors were cutout using a craft knife. ABOVE LEFT: The rudder servo is mounted on the retract unit and the rud-der pull-pull mechanism is supported on the retract former. ABOVE RIGHT: More detail of theretract unit. You can also see the bracing rod at the leading edge of the wing root and the canopyrelease cable. RIGHT: I made a compartment for the receiver battery which also supports the noseballast.

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DecorationI quite like a sailplane that is coloured plainold appliance white and was more than con-tent to campaign my Pilatus with minimalistmarkings, until I was eventually shamed bysome of the great and the good of our hobbyinto adding decoration. The starburstscheme shown in the photographs was sim-ply applied using coloured vinyl. I also invent-ed some personalised registration markings,so my Pilatus is not based on a full size sub-ject and not likely to win favour at the localscale meeting, but I’m quite sure that with abit of research, any modeller with morepatience than me could indeed turn theirGeitner Pilatus into a prize winner.

The Flying BitThe maiden flight was so free from drama

that I cannot remember much, other than ittook place on a beautiful and warm summerevening. It was one of those perfectmoments when the wind was light and thelift was extensive. The Pilatus was able tohug the contours of the slope and to fly asfar as I could see. That really seems to havecast the die and most of my flights with thePilatus since then have left me with a rosyfeeing.

I hope that the photographs convey someof the wonderful character of this model.You see, it seems to have multiple personali-ties. One moment it’s a stubby aerobat, thenext it’s an elegant high aspect ratio alpinesoarer and then the very next moment it’s aclassic standard class racing sailplane.That’s certainly the visual impression that itgives depending on which face it’s showing,but it also reflects the broad range of flying

qualities.Geitner has made

an airframe with awell balanced mixof stiffness andflex. The wings canbe loaded andunloaded during aloop in a most satis-factory way, withwhat looks to be anelliptical distribution offlex across the span andit’s likely that the glass join-er plays its part in this.There’s never a feeling that theflex is going to lead to softening ofthe controls, or that the airframe will failand so the model can be happily flown with

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Nicely controlled landing approaches areeasy to achieve due to the combination offlaps and spoilers.

Retractable wheel unit is optimally located to be forward of the CG while still allowing space for thepilot.

I shaped a dashboard from polystyrene foam

and the instruments were mounted on thin ply.

The cockpit is reasonably convincing with only

minimal effort on detailing.

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some abandon. Theflexible nature is alsoof benefit when land-ing at the slope -any shock loadsseem to dissipatethrough the airframeto cushion each land-ing. The additional

weight with the retractunit has also worked

out just right for my fly-ing style; the model always

seems to be able to pene-trate into wind, yet flying

speed seems to be easy to con-trol. I have not felt tempted to use

the steel joiner for additional ballast, but itmight have been handy if the retract unithad been omitted.

The optional flaps have definitely provedtheir worth. Roll rate with aileron only feels

a bit sluggish, so I almost always fly with theflaps coupled in. The flaps are relativelylarge, so it’s important to set up asymmetricmovements in order to minimise adverseyaw. I’ve also programmed in a touch of flapto help control speed when using spoilerbrakes and that’s resulted in a nicelybehaved model throughout landing approach-es and touch down.

This model is an excellent all-rounder, butis never going to be able to compete at theextreme end of aerobatics with a specialistglider such as the Swift. Axial rolls requireelevator and rudder movements to be co-ordinated with the aileron, which may be aresult of the Pilatus having a high-mountedmain wing and high-mounted tail plane. Itusually takes me a few moments to adjustafter flying a sport model, but it is veryrewarding on standard aerobatic figures.Inverted flight is easy to hold in good liftwithout losing too much momentum. The CG

is just right for my flying style, but it mightbe a little rearward because the model feelslike it wants to tuck when starting downfrom a stall turn. That could also be due tothe pendulum effect with a T-tail, but in anyevent it’s easy to correct once you’re readyfor it.

I’ve already had a lot of fun and I’m goingto have a lot more flying time with thismodel. The fuselage shape makes it easy togrip so there’s no problem launching it bymyself at any slope and in any windstrength. It’s a convenient size to have in thecar and for carrying. Geitner has managedto produce a very nicely balanced all-roundsailplane with rewarding and forgiving char-acteristics which makes it perfect for every-day flying. It may not have the ‘bling’ of someand there may be stiffer, bigger and sexierversions of the Pilatus B4 out there, but Iwouldn’t want to swap. Now what else hasGeitner got in that catalogue... ■

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Key Dimensions and Surface MovementsScale 1:4, Span 3.75m, Aspect ratio 1:17.6, Length 1.64m, Wing profile HN950,10.5% max thickness.

These are the movements that I have set up, but I rarely use all the available movement.Aileron, rudder and elevator movements were measured at the tip. Flap movements weremeasured at the root.

Elevator: +11 / -8 mm (+ up, - down)- spoiler compensation 0 mm

Rudder: +50 / 50-mm

Aileron: +10 / -8 mm- spoiler 0 mm- thermal flap -2 mm

Flap: - aileron mix +11 / -5 mm- spoiler -5 mm- thermal flap -4 mm- snap flap -3 mm

Centre of mass: 95 mm from the leading edge at the wing root.Longitudinal dihedral: 1 degreeAll up flying weight: 5.85kg (12lb 10oz)

ResourcesGeitner: http://www.flugmodellbau-geitner.comRobotbirds http://robotbirds.comMultiplex RC http://www.multiplex-rc.deSpire Models 01722 415541

The proud owner wouldn’t wantto swap this with other versionsof the Pilatus B4.

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