RCM&E Magazine **FEBRUARY ISSUE FREE 20 PAGE PREVIEW!**

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SZD FOKA PART ONE VOL.67 NO.2 FEBRUARY 2024

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RADIO CONTROL MODEELS AND D ELECTRONICS

4

Foka BUILD THIS 3.35M SCALE SAILPLANE

CHILLI BREEZE EP PART 2: FINISHING & FLYING

AVANTI! A

FFAST FORWARD WITH ARROWS’ NEW MINI JET

PLUS II SPIRIT OF IVAN - ADAPTING IVAN PETTIGREW PLANS II LMA ROUND UP - LARGE MODEL ACTION FROM 2023

W

Welcome NEVER MISS AN ISSUE

elcome to the February 2024 issue of RCM&E. This will be the first issue to reach you in 2024 so the time is ripe to wish all of our loyal readers and advertisers a very happy and prosperous New Year.

In this issue we are very pleased to bring you the first of a two-part Pro-Plan for the stylish SZD Foka 4 sailplane and an accompanying feature on its build by our classic glider guru Chris Williams.

On test this month we have the Avanti mini sports jet from Arrows models, which is a fabulous looking EDF model. And yours truly dashes out on a rare sunny winters day to clock up maiden flights with the two new XFly Model kits that I reported on in the last issue, the P68 small scale twin and the fast and furious Eagle flying wing with its two wingtip mounted electric ducted fan jets.

Amongst the regular columnists to clock in for this issue are Tim Hooper (Bench Blog) who resumes building a weird and wonderful Waterman Arrowbile flying car. Dave Goodenough (One Man & His Shed) looks at more popular model fixtures and fittings, whilst Chris Williams (Scale Gliding) resumes his regular bi-monthly slot with a visit to the last White Sheet slope scale fly-in of 2023. Next, Keith Jackson (Aerobatic Scene) files a report from the Triple Crown F3A ‘Home International’ event before lending his column to Peter Jenkins, who starts the first of several contributions about how to get started in model aerobatics.

This time we have the conclusion of two features which we started in the January issue, starting with Mike Delacole and Chilli Breeze EP. Mike finishes the build article for his new electric version of his popular aerobatic design, Pro-Plans for which were published in the last issue. In the RCM M&E 4 | RC

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January issue Mike Roach introduced us to the scale plans of Canada based modeller Ivan Pettigrew. Ivan’s designs result in lightweight scale models that are often praised for their scale like flying speeds and appearance when airborne. But his drawings are regularly used as the basis for other scale designs, often multi-engine types, which Mike and other Pettigrew aficionados lovingly refer to as being in the ‘Spirit of Ivan’. Mike presents a few such models in his latest article.

Wrapping things up for this issue is Shaun Garrity who, although best known for his love of all things retro, is also a large model enthusiast. Last year was not kind weather wise to a lot of model shows but participating modellers and pilots did a sterling job of carrying on with their displays, as typified in Shaun’s round-up report on his local LMA events.

I hope you enjoy reading it all.

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Get your digital edition for just £3.99 per issue www.classicmagazines.co.uk/subscription/RCM Editor: Kevin Crozier

Mortons Media Group, Media Centre, Morton Way, Horncastle, Lincs LN9 6JR kcrozier@mortons.co.uk

PRINT AND DIGITAL The whole package – just £5.50 per issue for a printed and digital version www.classicmagazines.co.uk/subscription/RCM www.modelflying.co.uk | February 2024

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10

On the cover Photo: Chris Williams

The Foka 4 was a single-seat sailplane built by the Polish SZD concern in the early 1960s. This new model from Chris Williams, presented as two Pro-Plans over the next two issues, has been built to represent the full-size version at the Glider Heritage Centre at Lasham. However, the design has been simplified to make it easy to build and a joy to operate.

RCM M&E 6 | RC

14 48

22

Contents

Regulars 8

39 82 92

94 95 98

SWITCH ON

Features

28 CHILLI BREEZE EP

Our latest round up of model flying news

COUNTERPOINT

A selection of new gadgets, kits and bits for you to buy ALL WRITE

40

Have your say in RCM&E’s monthly chat room

GOING PLACES

Our updated list of model shows, events and competitions for you to visit over the next few months

MARKETPLACE

64

Sell off your unwanted airframes and engines or maybe buy a few new ones

PARTING SHOT

After celebrating the scale models designed by Ivan Pettigrew, we sign off with a scenic pic of Ivan’s Blackburn Beverley taken by Hal Norrish

22

70

ARROWS AVANTI

David Ashby flies a new EDF ‘grab-n-go’ version of a popular aerobatic sports jet

BENCH BLOG

60

74

86

Dave Goodenough provides more advice on model fixtures and fittings before showing how to mould DIY canopies

SCALE GLIDING

Down Wiltshire way. Chris Williams reports from the fifth White Sheet RFC scale meet of 2023

AEROBATIC SCENE

Keith Jackson reports from the Triple Crown F3A event. But first he hands over to Peter Jenkins who starts the first of several contributions about how to get started in model aerobatics

KICK THE TYRES

As Graham Ashby recounts, success in model aircraft design is as much about grit as it is genius

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LMA - AROUND THE SHOWS

54 ONE MAN & HIS SHED

OVERLANDER E455

Andrew James extols the virtues of a simple, easy to use battery charger

In the last issue Mike Roach discussed model plans designed by Ivan Pettigrew. This time Mike presents a selection of lightweight scale aircraft that have been built using adaptations of Ivan’s drawings

Tim Hooper picks up on his Waterman Arrowbile flying car project

TWO UP FROM XFLY

In the last issue the Editor unboxed a pair of small aircraft from XFly-Model.

This time he takes them to the flying field for their maiden flights

SPIRIT OF IVAN

Columns

14

Reviews 10

Mike Delacole finishes building an electric version of his popular aerobatic design, the Pro-Plan for which was published in the last issue

Shaun Garrity presents a round-up report from his visits to Large Model Association shows in 2023

NEXT ISSUE

Take a look at what’s coming in the March ‘24 issue of RCM&E

Volume 67 | Issue 02

Free Pro-Plan 28

48

SZD FOKA 4

Chris Williams introduces part one of his latest Pro-Plan article describing the build and flying of a 1960s scale sailplane

40 64

February 2024 | www.modelflying.co.uk

RCM RC M&E | 7

Switch All Write on

Our latest round up of model flying news and miscellany

SOUTH MIDLAND INDOOR FLYING EXTRAVAGANZA Brian Seymour writes: Coming up for its third year, the BMFA South Midland Indoor Flying Extravaganza is set to return to Wycombe Leisure Centre (HP11 1UP, just off M40, J4) on Sunday 25th February 2024 from 1 - 7pm. Once again Microaces are sponsoring pre-entry ticket sales with a raffle prize of a £100 Gift Voucher (one strip of raffle tickets are included with each pre-entry ticket purchased). Microaces are also sponsoring a pylon race, open to all 1S models under 80 g, with a £50 voucher for the race winner.

The aim of the event has always been to get as many classes of indoor flying together in the best hall we can find (and afford) and have a great day celebrating indoor models. The venue is excellent, with a 34 m x 60 m floor plan and a ceiling height of just over nine metres, and the first-class facilities make for an exceptionally comfortable event.

The classes supported are small sport and scale R/C models, larger or fast sport and aerobatic R/C models (such as Shockies and pylon racers) and Free Flight.

Helicopters will have their own hovering area and micro drones (with well-guarded props) can fly alongside the R/C models.

Flying time is divided into 20-minute slots,

Picture courtesy of Danny Fenton.

repeated every hour, so that similarly classed models can fly together. The R/C slots will be slightly curtailed to allow for the pylon race, practice and Grand Finale.

Entry fee is £15 and Junior entry is free

with a paying adult. Advance tickets are available at: http://www.ticketsource.co.uk/ bmfa-ife-2024 Event website: http://www.hwdmac. co.uk/indoor-flying-extravaganza-2024

CHILLI BREEZE EP WING SETS

SALE MODEL FLYING CLUB Richard Lines of Sale MFC writes: Sale Model Flying Club is currently looking for new members. Whether you are newcomer or established in the sport you will be welcome at Sale.

The club has been flying on our existing site since 1974 in Sale, Greater Manchester, M33 5UN (Banky Lane). Our members consist of all age groups from ages 8 to 85 (at the last count!).

We fly many types of models including trainers, scale models, aerobatic aircraft, float planes, vintage and helicopters, with a mix of electric, IC and petrol power.

We operate a comprehensive training scheme for newcomers and have registered examiners who can take candidates for their ‘A’ or ‘B’ tests.

Prospective members and visitors from other clubs are always welcome to enjoy our facilities by prior arrangement when a club member is on site. Instruction for newcomers is always free under the supervision of our accredited RCM M&E 8 | RC

flying instructors. Flying takes place Wednesday to Sunday and flying times can be seen on our website: https://salemfc.co.uk/ If you would like any further information or directions to the club, please contact Richard Lines: lrichard@live.co.uk

If you are planning to build a Chilli Breeze EP from our Pro-Plan in the last issue and would like to use foam wings instead of built-up wooden panels, then Bill Manley of Bill Kits fame has sent in the following information: ‘I was contacted by Mike Delacole requesting that I get in touch with information about cutting foam wings for his new Chilli Breeze EP design.

The cost, including UK postage, at the moment is £70.00. The wings are made from medium density white foam veneered in obechi and the fibreglass joining tape is included.

I am also able to produce many other designs from RCM&E plans and prices are available on request.’

You can view the Bill Kits website here: https://www.billkits.com/

Picture courtesy of Mike Delacole.

www.modelflying.co.uk | February 2024

Get in touch kcrozier@mortons.co.uk

COLCHESTER MAC CELEBRATE 75 YEARS Paul Oliver, Development Officer of the Colchester MAC, writes: The Colchester Model Aircraft Club was established in 1949 so it will have been around for 75 years come 2024. When it was formed it was with the aim of promoting the sport of aeromodelling, which it has done for all that time and still does today.

Over the course of the club’s history model flying has evolved massively, along with changes in the complexity of model aircraft and flying, with some aspects becoming easier and others more complex. Members undertake various forms of model flying and several of them have competed regionally, nationally or internationally over the years.

The club is lucky in having the use of three flying sites in the locality and a village hall for indoor flying. Club members undertake a broad range of model flying activities including R/C electric and IC powered fixed wing and helicopters, multi-rotor and drones, electric and conventional thermal soaring and control line flying.

During the winter months indoor flying is undertaken on a weekday afternoon, every week, and once a month an additional evening session is held. Indoor flying boasts a mix of rubber power, electric powered fixed wing, helicopters and multi-rotor models.

The club has an active training programme that has seen several new members undertake training from club instructors and examiners over the years. Despite the impacts of the

pandemic this has continued in the past few years and the club has seen an influx of pilots across all age ranges from juniors upwards undertake training and passing their A tests.

That said, the club is still looking to attract new members, whether total novices or experienced pilots.

It is probably fair to say that whilst the club has seen some new members there has also been a small decline in numbers. Whether caused by the passing of some members, or the fact that there are not the number of local model shops that there once was in the area, and, of course, the fact that there are many other distractions for people, this is all part of the challenge for many clubs these days.

Colchester MAC members have been prolific over the years, whether competing at competitions at all levels or undertaking public displays locally, as well as supporting local community groups or indeed the BMFA’s Mass Record Attempts over the past two years. The club has lived up to its aims over the years and fully intends to for the future. http:/www.webjam2.com/ colchestermac1_colchestermac_intro

DELUXE MATERIALS GLUING TIPS Deluxe Materials, manufacturers of many of the most popular and advanced adhesives and related products used by aeromodellers, have kindly offered to sponsor a ‘Gluing Tips’ section in RCM&E. All you need to do is to send in your suggestions and top tips for using glues and related products when building a flying

February 2024 | www.modelflying.co.uk

model aircraft. Simply describe your gluing tip in a few words and, if possible, send in a sketch or photograph to illustrate it to the Editor: KCrozier@Mortons.co.uk To get things rolling here’s a sample Gluing Tip courtesy of Deluxe Materials to show you what your idea could look like in print.

RCM RC M&E | 9

It’s an Avanti, even down to the colour scheme.

ARROWS AVANTI

David Ashby flies a new EDF ‘grab-n-go’ version of a popular aerobatic sports jet Words & Photos: David Ashby

Y

ou must’ve heard of Sebastiano Silvestri. He’s the man responsible for many highly regarded aerobatic designs through his the SebArt model range. His Avanti S, originally a 2m span turbine model, has been reproduced under licence in several sizes over the years, FMS’ regularly updated 70mm EDF version being a particular favourite.

It seems strange that a smaller version hasn’t arrived sooner, although perhaps it’s no surprise that Arrows, the mini jet specialists, are first past the post by finding a new home for their ubiquitous 50mm 11-blade fan driven by their 2627-size 4500kV outrunner motor.

Some commentators say that Arrows’ mini jets

all fly the same. But I’ve flown them all and found that each is a little different, especially because while some use a standard 3S 2200mAh LiPo battery, others fly better with a lighter 1800mAh 3S, while one, the recently reviewed L-39, is best with the extra urge provided by a 4S pack.

To this Avanti then. There’s no denying it’s pretty, and if it reminds you of the BAe Hawk then it should because Seb’ based his design on that aeroplane before tweaking away to maximise the aerobatic abilities. Assembly is a five-minute job: glue on the stabiliser, screw down the wing and you’re done. As always, I prefer UHU-Por to the CA suggested as it allows time for adjustment before the glue grabs.

Arrows jets now arrive with a factory-fitted

Vector flight control gyro that sits between the servos and receiver. Allocated to a transmitter switch, it provides three modes - Stability, Dynamic and Direct - that can be changed in flight: Stability Mode – The unit levels the model whenever no control inputs are detected. This is the mode I use for take-off.

Dynamic Mode – Adjustments are made to correct for movements not made by the pilot, such as cross winds, gusts etc.

Direct Mode – ‘off ’ in other words, the unit making no intervention.

“…if it reminds you of the BAe Hawk then it should because Seb based his design on that aeroplane” RCM M&E 10 | RC

www.modelflying.co.uk | February 2024

TESTING, TESTING | EDF sport jet

‘Grab-n-go’ are the words you’re looking for. You need never take this one apart.

A single servo moves a Y-pushrod for elevators.

Cooling air comes in via this small nose inlet.

The finger grips are excellent, but I tend to launch underarm.

DATAFILE Name: Model type: Manufactured by: UK distributor:

Avanti 50mm EDF jet Arrows Hobby J.Perkins Distribution www.jperkins.com RRP: £179.99 Wingspan: 640mm (25.2”) Fuselage length: 750mm (29.5”) Wing area: 8.9dm2 (137 sq.in.)

Wing loading: 51.7g/dm2 (0.11oz/sq.in.)

Flying Weight: 460g Power system: 2627-size 4500kV outrunner, 11- blade fan, 30A ESC, 3S 1300mAh LiPo Required to fly: Receiver, LiPo Connector type: XT60 Functions (servos): Ailerons (2), elevator (1), throttle (via ESC)

The Vector unit sits on a shelf and there’s plenty of room nearby for 4-6 channel receivers.

February 2024 | www.modelflying.co.uk

“Avanti will feel livelier with a lighter 1500-1800mAh LiPo on board” RCM RC M&E | 11

It’s easy to see why these little jets have proven so popular.

This cheater vent behind the wing underside feeds the fan.

3 OR 4S?

So, what’s this one, 3S or 4S? Well, both actually.

If you’re new to EDFs then the popular 3S 2200mAh pack is a good starting point, but this Avanti will feel livelier with a lighter 15001800mAh LiPo on board. As always, it’s a case of trading battery weight with performance.

Experienced pilots should jump straight in with a 4S battery. A 2200mAh would be too heavy, a 1300mAh pack would be fine, but an 1800mAh is my preference and still good for a three minute flight.

Similarities to the BAe Hawk are no accident.

RCM M&E 12 | RC

Plenty of room for a battery. My packs tend to sit towards the rear of this space.

FLYING

Whatever battery I fly with, I find that it needs to be reasonably far back in order to achieve the forward end of the C of G range suggested. Most flyers will be happy with the low rate control surface deflections as a starting point.

It’s best to use Stability mode for take off, just to keep the model level should fingers slip and things go awry at that critical moment.

An underarm lob works fine, although the underside finger grips provide good purchase.

Once up I tend to fly with Dynamic mode which

Covers protect the aileron servo outputs.

isn’t intrusive and, as you’d expect, keeps the model tracking much smoother than Direct mode. I think you’ll stick with Dynamic after you’ve sampled both. In any flying mode the stall is very benign and a wing drop is difficult to provoke.

It’s very nice of course and flies with a speed and smoothness you’d come to expect from an EDF jet. That 11-blade fan delivers the right sort of whooshy jet sound too.

Rolls are effortless, loops from the horizontal

I use Stability mode for landing, just to keep the wings level and make life easier. www.modelflying.co.uk | February 2024

TESTING, TESTING | EDF sport jet

Inverted flight feels safe and solid.

need a little full throttle run up before execution, inverted flight is fuss free and faster point rolls are there for the taking too.

I tend to flick into Stability mode for landing, just to keep the wings level and make life easier for myself. Come in too slow and it’ll feel like there’s insufficient elevator to flare smoothly and the model will have that falling feeling for the last couple of feet.

GOING FORWARD

In the Introduction, the manual whimsically explains that Avanti means ‘going forward’ and how the model should give the inexperienced pilot the confidence to do that. It depends what’s meant by ‘inexperienced’ I suppose;

needless to say this isn’t a beginner’s model but if you’re a competent pilot looking for a costeffective, friendly and forgiving introduction to EDF jets then this one should be at or near the top of your list.

The machine’s aerobatic pedigree means experienced pilots familiar with larger versions will miss the rudder (one I know has decided to add his own rudder servo to this model) but that’s not to detract from an enjoyable little ‘grab-n-go’ EDF sportster. ■

Although not essential, I tend to use Stability mode for take-off and landing.

“It’s very nice and flies with a speed and smoothness you’d come to expect from an EDF jet”

It’s happy with either a 3S or 4S LiPo battery.

February 2024 | www.modelflying.co.uk

RCM RC M&E | 13

Building a flying car Tim Hooper picks up on his Waterman Arrowbile project

R

egular bath-time readers may recall that we’d started on the US-designed Arrowbile flying car a couple of episodes ago. The concept was to have a roadable fuselage pod, topped by a removable wing. With the wing safely stashed at your local hangar, the pod could be driven home on the highway. A clever concept, you’ll agree.

I’d very loosely based this model on the vintage rubber powered model produced by Megow many years ago. Last time out we’d fabricated the swept wing and tip fins, so it was

Words & Photos: Tim Hooper time to make a start on the fuselage.

FUSELAGE POD

Whilst I had followed the Megow plans closely for the wing, the fuselage pod required a different approach. As drawn on the pilfered plan the pod is made of an intricate open structure of skinny strip wood, as properly befits a rubber powered model. Instead, I opted for an all-sheet assembly for our radiocontrolled rendition, using 1/16” sheet panels over a simple floor and former substructure.

I made a tracing of the pod’s flat floor and cut this out of 1/8” sheet, cutting and raising up the front portion by 10 mm. This was pinned down to await the arrival of the fuselage formers, the solid sheet front and rear formers and the strip built intermediate ones. The wedge-shaped rear former sits at 10° away from the vertical, with its pointy end on the rear of the floor.

When all was dry the edges of the floor were gently bevelled to match the formers. I cut two 30 mm wide strips of 1/16” sheet and gently dampened one side of each. These were pinned

Our Waterman Arrowbile ready for its maiden flight.

Maybe not the outcome you’d expect, so read on!

RCM M&E 4 | RC

www.modelflying.co.uk | February 2024

BENCH BLOG | Column

With formers erected, the lower sides are added. All ship-shape so far.

Arrowbile’s fuselage pod starts life as a flat, balsa floor and a couple of balsa formers.

and glued along the sides of the floor, pinning and clamping as I went along, giving the pod the appearance of a flat-bottomed boat.

This marine allusion was heightened by the arrival of the middle sections of the fuselage sides, as they swept upwards at the stern, giving the pod a rather galleonesque appearance. Almost forgotten marine terminology such as ‘transom’ and ‘tumblehome’ reared their archaic heads as I viewed the burgeoning structure. More clamps and pins held it all together.

A simple motor plate was cut from 1/8” ply, drilled to suit the little E-flite Park 370 outrunner that I had in mind, and glued vertically to the top edge of the lower rear former. The fuselage sides are each in three pieces of 1/16” sheet - lower, mid and upper - and this allows the sides to gently bulge around the waistline as they adopt to the shapes of the internal formers.

February 2024 | www.modelflying.co.uk

Mid sides and canopy framing are a logical progression as we move upwards.

As the wing will attach to the top of the cabin I added balsa strip strengtheners around the sides of the windows, together with a ply plate to eventually accept the wing bolts, as well as a bit of soft block at the very rear of the pod.

It seemed like that the proposed 2S 1300 mAh flight pack would have to live in the nose, if only to balance out the rear mounted motor, so it seemed sensible to construct the upper deck of the nose and the windscreen as a removable one-piece item to serve as a battery hatch.

Turning the pod upside down, I added a bit of a platform from balsa and 1/8th ply to serve as a mount for the horizontal main undercarriage, before planking the pod’s underside with 1/16” balsa strips.

Kept separate by a layer of sticky tape during construction, the windscreen and top of the nose form the basis of the battery hatch.

The ply rear former doubles up as the mount for the pusher motor.

Lower planking hides the hardpoint that will accept the main undercarriage leg later.

RCM RC M&E | 15

The nose leg is sandwiched between the nose block laminations. An inset ply plate takes the strain.

TRIKE UNDERCART

The full-size Arrowbile featured a tricycle undercarriage. In road guise the pusher prop was de-clutched from the engine and its drive diverted to the spatted rear wheels, leaving that skinny nose wheel to take the brunt of the steering and braking forces. To a modern driver used to big fat tyres and vented disc brakes this all looks highly dodgy, but I’ve no idea how it felt in the monochrome reality of the 1930s.

Modelling wise the rear axle is just a straight length of 12 SWG piano wire, secured to the bottom of the fuselage pod with a brass saddle

Laminated balsa and lite-ply spats will shroud the tiny tricycle wheels.

clamp. The nose leg is bent from thinner 16 SWG stock and is screwed to a ply plate that is itself sandwiched within the laminated nose block.

The tiny wheels came from the spares box and are all enclosed in the ply and balsa spats.

Little screws pass through brass tabs on each U/C leg and into the ply sides on each spat. As there’s little chance of the model ever being able to lift off from a grass strip, I didn’t spend any effort in retaining the wheels on their axles with collets and let the spats do the work instead.

Cocktail sticks serve to replicate the full-sized glazing bars quite effectively.

RCM M&E 16 | RC

www.modelflying.co.uk | February 2024

BENCH BLOG | Column

FINISHING OFF

The front hatch was built in situ from scraps.

It’s planked in 1/16” thick strips, and there are cocktail sticks to represent the windscreen framing. The pod’s cockpit was glazed with clear plastic after daubing a bit of green paint on the balsa framing to match the chosen tissue that followed. I used wide strips of tissue, brushed on with WBPU varnish, thinned 1:4 with water.

This was followed by a single unthinned coat to fully proof the tissue and to add a bit of a sheen.

For those unfamiliar with the term, WBPU is an abbreviation for water-based polyurethane, and it is sold widely as domestic varnish for woodwork. In my experience it’s as tough as old boots, second only to epoxy for surface hardness, yet dirt cheap in comparison. It’s coloured white in its wet state but quickly dries clear. It also works extremely well in glass clothing applications too.

For the wings and those twin fins, I resorted to my old favourite of tissue over Doculam.

The Doculam is applied as with any other heat shrink film; tack around the edges then nuke in the middle with a hot iron. Getting the overlying tissue to lose its wrinkles is always a challenge and I’ve tried a variety of methods, including pre-damping the tissue, not dampening it all, and dampening it after application. None are perfect (although others have had spectacular results) and, for me, it’s always a bit of a step into the unknown.

The elevons were hinged with sticky tape. I’d originally wanted to use 4.5 g servos to jiggle the elevons, but they just weren’t up to the job.

So, I retrofitted 9 g items instead. Given that the elevons will need a bit of ‘up’ reflex to achieve level flight, I set their neutral position at 6 mm above the wing’s trailing edge. At full down deflection they become level with the rest of the wing. We’d have to see how this panned out in the air.

I’d no intention of going overboard on detailing, so the pod received a single dummy headlight from a little disc of ali and the wing registration was bashed out of tissue paper on the Cricut cutter. With an 8 x 6 slo-fly prop fitted the motor pulled 90 watts from the 2S pack, which should be plenty for the AUW of

After covering in Doculam the yellow tissue was affixed with diluted floor varnish (WPBU).

A little goes a very long way.

15.5 oz, especially given its low 11.5 oz/sq.ft. wing loading.

TRICKY TAILESS

Now, it’s always nice to report that a new model flew ‘straight off the board’. Not so with the Arrowbile, I’m afraid. Being a tailless flying wing, I’d guessed the CG as being cited at around 15 % of the mean aerodynamic chord (MAC), which I remembered from my Zagi flying days of 20 years ago. Well, the theory seemed sound enough but the execution left a lot to be desired.

Luckily, I was able to conduct the first hand-launch over the oh-so-forgiving corn crop that surrounds our strip. Powered up and released nice and level, the Arrowbile literally piled downwards into the ground within a split second. Thankfully, the corn absorbed the shock and there was no damage to the model. I wish I could say the same for my own self esteem!

Back at home, the battery was re-sited around 25 mm further aft, but this didn’t really help much. The model would now acceptably glide from a hand launch, but any application of throttle saw the Arrowbile instantly bury its nose in the crop. Surely, this indicated a thrust line problem.

Several weeks of lousy weather (coupled with my own cold feet, I’ll confess) have kept the Arrowbile in the hangar. During the interim I’ve jacked up the front of the wing with a scrap of balsa, the idea being to give the motor yet more upthrust at the rear.

Balsa faired main undercarriage is screwed to its plate after covering with tissue.

There, for the present, we’ll have to leave it. If the issue is based on the thrust line, then it’ll get sorted. If there’s insufficient reflex in the elevons then perhaps something more fundamental needs to be addressed. I’ll keep you posted…

SPARKIE SILENCER

The previous Bench Blog was devoted entirely to fettling the ancient Ohlsson and Rice engine that had been sent to me by my old mate, Ian Easton, a while back. I’d got the engine, complete with its new ignition, carb, tank and beam mounts, installed in my psuedo vintage Murg airframe and had several successful flights at the club field.

All would be blissful, except for one thing the noise! For such a small engine it generates a howling loud and penetrating crackle that causes even hardened glow fliers to wince and put their fingers in their ears. Hmm, time to think about a silencer methinks.

Back on the bench, I gave the silencer idea more thought. What I wanted was a thin-walled cylindrical type of expansion chamber, but with a flattened inner face to marry up with the end of my existing exhaust stub. Not an easy compromise to achieve so I had to think a bit laterally.

The thick walled ali tube was offset in the lathe’s chuck by adding 1.5 mm of packing under just one of the three jaws.

The silencer for the O&R sparkie called for a bit of lateral thinking in the planning stage. Time to get the crayons out to plan its eccentric bore.

February 2024 | www.modelflying.co.uk

End result of the eccentric boring operation is very marked indeed.

RCM RC M&E | 17

This 2 mm die sits comfortably on a fingertip and was used to thread the silencer’s internal tie rod.

Components of the completed silencer. The pierced internal baffles were intended to break up the flow of the exiting gases.

eBay yielded a short length of 20 mm diameter, thick-walled ali tube and I broke out the graph paper and crayons to sort out some dimensions. I figured that if I eccentrically mounted the 20 mm tube on the lathe’s chuck, using a piece of 1.5 mm thick scrap packing on one of the chuck’s three jaws, then the tube’s central cavity could be bored out, but over to one side.

This was an interesting machining exercise and another new trick learned. It was strange to see the lathe mounted tube revolving so obviously off centre, and then to introduce a miniature boring bar to its central cavity. As the boring bar was gently fed to engage, it started to re-bore the central hole, but off-centre. The finished bore is a circular 15 mm in diameter, but with a chunky 4 mm of wall thickness on one side, but only a skinny 1 mm on the other.

Our new piece of lopsided tubing was now lightly clamped in the mill’s vice, with the thick wall at the top. I could then mill a shallow recess to house the end of the exhaust stub, followed by drilled holes to correspond with the mounting screws and actual gas porting. I had originally hoped to have the mounting bolts screw into tapped holes but there wasn’t enough metal to accept more than a couple of threads,

so I opted to drill clearance holes for through bolts and then settled for having separate nuts inside the silencer instead.

The next step was to turn up the front and rear caps for the silencer, both of which fitted snugly into the ends of the silencer body and use a length of 2 mm threaded rod to hold the ends in place, with an external nut at the rear end.

Luckily, Netty had already decided that I really needed a miniature set of taps and dies in my engineering arsenal, so I was able to cut a thread on a length of suitable mild steel rod.

That’s mild steel – not piano wire! I’d never cut a thread that tiny before, but a drop of 3-in-1 oil made sure the operation all went smoothly.

I’ve no technical knowledge when it comes to the theory of silencing engines, but I guessed that a couple of internal baffles might help in disrupting the pulses of power (i.e. noise) so two pierced discs of aluminium sheet were threaded onto the central rod just aft of the silencer’s inlet slot and secured with 2 mm nuts, just as an experiment in applied over-complication really.

Back at the field, the O&R equipped Murg was fired up and this time it was a lot quieter thanks to the surprisingly effective silencer.

Whether or not the engine had lost any

Strapped onto the engine, the silencer gives an appreciable reduction in the otherwise intrusive crackle of the burning camping fluid/engine oil fuel mix. Doesn’t look too bad, either!

RCM M&E 18 | RC

Assembled silencer ready for mounting on the O&R engine. The exhaust outlet is a plain drilling in the rear cone.

power output is unknown. There’s a short YouTube clip of the engine running here: https://youtu.be/gJNOhTfT0t8 Anyway, the Murg was lined up into the breeze for an ROG and released. It trundled along for an alarming amount of time and distance before I felt confident enough to coax it into the air.

Yes, it’s a bit marginally powered but the thing is, it flies! A couple of flights later saw me with a big smile on my face and the Murg still in one piece, which is always a bonus in itself !

That’s been quite a journey of learning, engineering-wise. All the mods to the engine that you’ve read about in a few minutes actually took several weeks in real life and became something of an enjoyable pre-occupation. I think life can move on now!

WORK ETHIC

Very occasionally I get asked about my work ‘through put’. Despite my workshop being scarily tidy to some, there does appear to be a steady stream of toy aeroplanes reaching completion on a fairly regular basis. This may be due to a couple of factors, I think: 1. One at a time. I’m a single-task kind of bloke so generally I only have one project on the go at any one time. I’ve seen the workshops of other modellers that are festooned with half-built or repaired models in various stages of completion, repair and/or destruction and I just couldn’t work in all that chaos. Sorry and all that.

2. Little and often. My attention span is pretty minimal, so I rarely spend more than an hour or two in the workshop on any single day. The trick to my being being productive is planning; when I go in there for an hour, I have a good idea exactly what I’m going to be doing during that hour. When I’ve achieved the allotted task then it’s time to shut up shop and go and do something else!

3. This damn column. Having to produce a regular update of the workbench traffic, together with reasonable photographs as evidence, gives a point of focus to my efforts and sees projects through to a conclusion usually. This column’s Arrowbile is stalled at the moment (complete but resting in the hangar) and another airframe is already on the blocks.

We’re all different, thankfully. There’s no single way to enjoy this ridiculous hobby of ours, so each to their own! ■ www.modelflying.co.uk | February 2024

RCM M&E 20 | RC

www.modelflying.co.uk | February 2024