Repairing an ARTF Trainer.

[David Davis]

My favourite ARTF trainer is the Boomerang mainly because it's semi-symmetrical wing allows it to penetrate a breeze better than those trainers with flat-bottomed aerofoils. When instructing you reach a phase when you have to allow your trainee to correct his mistakes. However, if the trainee becomes completely disorientated you have to take back control. If you're too slow the model crashes! It's the instructor's fault of course.

 

When the club's Boomerang went in because both pupil and instructor became disorientated downwind in a stiff breeze, the model was comprehesively damaged. A few years ago I would have bought a new ARTF but with current prices I thought I'd have a go at repairing it. To us Greybeards repairing a model is something we've done many times before but it occurred to me that newer modellers who have only ever assembled ARTFs do not have this knowledge so could benefit from this repair blog.

 

I'm also building a Pegasus Models Mystic and a DB Sport & Scale Auster so I won't be rushing its repair. I hope to be able to do a bit every week and will post pictures of progress accordingly. Anyway, this is what we're starting with.

[Cuban8]

One of my flying buddies ia a dab hand at repairing busted AFTFs that are little more than matchwood - far worse than the picture above. I've inspected his work and honestly thought that he'd bought a new model, until I looked inside and saw all the intricate work to piece together the parts that could be recovered and additional  new wood.

Even the covering matched. Some very clever people out there.

[David Davis]

I will recover the fuselage and tail surfaces but I won't attempt to reproduce the paintwork of the Boomerang. Note the orange patches on the tailplane which preceeded the latest crash. The wing is strangely little damaged.

[Jon H]

Thats a nice easy repair. The front has just peeled like a banana 

[JOHN MOSLEY 2]

Quicker to measure and make a new fuselage .

 

[Don Fry]

It’s a trainer.. as Jon says, no big deal, and no brownie pints for looks. Tool to do a job, learn to fly.

Edited December 8, 2023 by Don Fry

[Robin Colbourne]

I've been repairing a few similar ARTF trainers.  By using clear laminating film it was possible to patch over the holes in open structure and attach the split printed covering to the back of the laminating film by carefully working in from the edges of the holes.

[Don Fry]

I’ve found, celebrate the repair. Hole in covering, irregular splodge of film. Area to repair, use a contrasting colour. Live with it. 
accept some stuff with a soul poured into it, gets the repair of Old Master treatment, but a trainer?

[Brian Cooper]

That Boomerang isn't dead yet. 

 

It might need a couple of days in hospital, and a few injections of cyano,  but it can avoid a trip to the morgue.  🤕

[Ernie]

I learned to fly on a flair cub. A fine trainer. It was dark blue. Everytime I repaired it, I finished it with green solartex.

When eventually, I binned it. It was a green cub

ernie

[GrumpyGnome]

Lol. I suppose a benefit of learning on a Cub is that you know how to use the rudder nice and early.....

 

[PDB]

 

After a pretty cool cartwheel and the wing bolts not letting go mine snapped the fuselage behind the wing, as good as new 😁

[David Davis]

The first job was to undo the throttle and steerable nose wheel connections at the servos, to remove the engine and firewall and to put it aside while I repaired the interior fuselage struture. I examined the fuselage formers and the servo plate. They were largely undamaged, mostly only the glue joints had failed in the crash. Each of the formers  is located with little tabs  lining up with slots in the fuselage, so having lined up all of the tabs I clamped the fuselage and applied cyano. We now have a pretty square fuselage.

 

I'm aware that many ARTFers may not have a pair of clamps but a Workmate or even a vice could have been used.

[Geoff S]

It's interesting that there seems to be some damage to the tail - the fin, at least.  Even my most horrendous crashes have usually left me with only an undamaged tail.  Good job, David.

[David Davis]

5 minutes ago, Geoff S said:

It's interesting that there seems to be some damage to the tail - the fin, at least.  Even my most horrendous crashes have usually left me with only an undamaged tail.  Good job, David.

 

It must have gone in inverted or flipped over on its back when it crashed. It was oos anyway, I only heard the crash!

[Arthur Harris]

On 08/12/2023 at 11:24, JOHN MOSLEY 2 said:

Quicker to measure and make a new fuselage .

 

There is a perverse but definite satisfaction from repairing a crashed plane, a bit like tackling a crossword or repairing a shattered ornament that may have no real intrinsic value.

[David Davis]

Progress so far.

 

All fuselage formers where the glue joint had failed were put back into place, clamped and cyanoed into position. Each former had small lugs on the side which fitted into slots on the fuselage side.

 

The firewall, the former to which the engine mount is bolted, also fits into slots in the side. There was excess glue on the side of the fuselage from a previous repair which had to be removed to get a good looking result. I used a Stanley knife, a file and some abrasive paper to achieve this. I may strengthen the joint yet further by glueing some triangular section balsa behind the firewall.

 

Two formers behind the wing's trailing edge had broken so I removed some of the top sheeting to improve access and repaired them using scrap 3mm (1/8") balsa with the grain running across the fuselage. I also fitted some 3mm sq balsa to support the top sheeting when it goes back.

 

The next stage will be to fit the top sheeting then to turn the model upside down to repair the underside sheeting, then I will strip off all of the existing sticky-back plastic covering and re-cover the fuselage in red Solarfilm supplied by my club. While I'm at it I will introduce some 6mm (1/4") plywood to support an improved and more rigid main landing gear.

 

With some reluctance I've decided to replace the Thunder Tiger 46 PRO with my beloved Enya 50. Unlike most trainers the Boomerang has a fully sheeted semi symmetrical wing. Consequently it's rather heavier than most ARTF trainers of its kind and needs a longer take off run to get airborne. While I am capable of achieving take-off speed on my club's 80 metre long runway a novice might run out of space first. The Enya will provide greater thrust.

 

Realising that my building board was typically very untidy I tidied it up a bit for the last picture! Some say that an untidy building board is a sign of a creative personality. 😏.

[David Davis]

Boomerang ARTF Repair Continued.

 

Yesterday I removed the printed sticky-back covering from the fuselage and tail surfaces, fitted a 6mm (1/4") plywood plate to the underside of the fuselage to support the new undercarriage and replaced any damaged sheeting with new 2.5mm (3/32") balsa sheet from my scrap box. Please note that in order to save costs ARTF maufacturers align the balsa on the top and bottom of the fuselage with the grain running along the fuselage. You build a much stronger structure if the grain runs across the fuselage as you may see in the picture below.

 

Today's tasks will include trimming and sanding the new wood and filling any small holes. Some of the fuel has got underneath the original covering and left a sticky mess in one or two places. I will remove this with cellulose thinner before covering can begin.

[Geoff S]

I've been tempted to fit fuselage bottom sheeting with the grain along the length in one piece because it's quicker, easier and sands more neatly, but I've always done it in short grain across the width as kit instructions always state.  I'm not convinced it makes a lot of difference but I do it anyway.  One advantage of the grain across method is that you can use up balsa offcuts effectively, which in a repair like this may be an advantage 🙂

 

Looks like the trainer will live to fly again 👍

[PDB]

2 hours ago, David Davis said:

fitted a 6mm (1/4") plywood plate to the underside of the fuselage to support the new undercarriage

 

Did the same with my Boomerang then used one of these attached with saddle clamps which has proven to be very robust with my less than perfect landings. https://www.modelshopleeds.co.uk/catalog/product_info.php?products_id=29274

 

Also fitted one of these which went straight in https://www.modelshopleeds.co.uk/catalog/product_info.php?products_id=21580

 

Also some larger Dubro wheels helped. 

Edited December 20, 2023 by PDB

[David Davis]

Beginning to take shape.

 

The red covering is old Solarfilm, the white is Chinese film sold by Kavan. It's not the best covering job I've done but it will make the wing look scruffy! The up-rated main landing gear has been installed likewise the Enya 50. I hope that I do not regret my decision to change the engine but on the other hand it's probably better that these much admired items are actually used rather than have them lie about in a box until I die!

 

I have fitted a balsa block across the nose to tie in the nose cheeks. I have done this with many ARTF trainers in the past using either block or sheet, ever since an ARTF trainer I was flying ran out of fuel and landed in a field sown to spuds. The haulms unpeeled the fuselage like a banana!

 

I need to do some repair work to the fin but I should have the model in flying condition by the weekend.

[David Davis]

Twenty days to get the model into flying condition. That's fast by my standards. I flew the model this afternoon. It flew quite quickly because of the larger more powerful engine and the ailerons were very sensitive for the same reason. I'll dial in a little more expo on the ailerons. I may even replace the original engine and just put up with the long take-offs. The landing was rather hot this afternoon and I damaged the propeller. I was running a 12x6 which may have been a little large for the Enya 50.

 

The new covering makes the old wing look scruffy but uniquely amongst ARTF trainers I've seen, the Boomerang II's wing is sheeted top and bottom with balsa. The model is a tool, an advanced trainer for trainee pilots so I'm not too concerened about cosmetics.

Edited December 30, 2023 by David Davis

[Mike Etheridge 1]

A good effort David. I have carried out similar repairs to a Super Air I was given and also a club member's Challenger plane. At present I have not got a car that is ULEZ compliant so I have dropped the hobby for now. What do I do with all my planes?

[David Davis]

How unfortunate for you Mike, but wait a minute! I happen to own a 1974 Rover 2200 SC. It requires a polish but is otherwise very useable. Yours for £4500!

[Mike Etheridge 1]

David,

 

Thanks for the offer of the Rover but the cars I use are also somewhat old but in good condition and both passed MOT's without any work necessary. One is a 1988 MK2 Polo Ranger that my wife bought new and this has been valued at £1200 by Car Wow. My other car that I paid £20K for in 2006 is a Jaguar X TYPE estate XE that is ideal for transporting model planes is only worth under £1K despite only covering 7200 miles. Therefore the Rover value is beyond that of both my cars.  I thought I could avoid the ULEZ cameras but there is one at the top of our road plus three others that would catch me on my way to Bartons Point  MAC in Sheerness and I assume plenty of other cameras on my route to Epsom Downs. So far my ULEZ fines have exceeded £100 and I am sure there will be more. I also got fined £100 for doing 34 MPH on a restricted stretch of the A303 last summer where the speed limit had been dropped to 30MPH near the Royal Navy aircraft museum.