Engineering Matters

Including: Corroded and failing rudder cable, battery retention device specifications, deteriorating fuel cap seals and a reminder about propeller attachment bolt torque

Welcome to Engineering Matters – the section of Light Aviation that is dedicated to discussing all manner of topics concerning both technical and operational aspects of the LAA fleet. We all learn by sharing information, so if you have anything to say that you think would benefit others, or have experienced an interesting technical issue or component failure, then please contact us with a description of what you encountered and include accompanying pictures. Send your submissions to LAA Engineering at engineering@laa.uk.com

At the LAA Popham Grass Roots fly-in, Pulsar builder and flyer Ron Oliver kindly presented me with a failing rudder cable from his aircraft.

The aircraft has been flying since 1998 and this year he removed the multi-strand rudder cables during the annual inspection.

Ron was surprised to find that the cable had corroded badly (to the point the wire strands broke when the cable was flexed) where it runs through a nylon guide tube in the cockpit area.

Obviously, this part of the cable cannot be seen without removing it from the guide tube.

LAA Inspector David Smith was recently carrying out a Permit to Fly revalidation inspection on a Rans S6 Coyote and decided to drain the fuel tanks, as the fuel was possibly over a year old.

Battery retention

During the investigation into a fatal accident involving an LAA administered aircraft, it was found that the battery had been released from its mounting position during the incident. In actual fact, the box that it had been sitting in had failed as well, breaking away from its mounting base.

For LAA administered aircraft, an aircraft design is checked against Certification Specification CS-VLA. In CS-VLA, it is stated that the battery retention device must be able to cope with a forward load of 9g and a sideward load of 1.5g. These requirements are specifically for emergency landing conditions, to ensure that the battery doesn’t become a lethal weapon in an otherwise survivable crash landing.

Of course, CS-VLA also requires the battery retention device be designed to cope with the maximum manoeuvring, gust, and landing load factors of the aircraft, so that it won’t come loose in normal operation.

Although the accident aircraft might well have seen forward loads in excess of 9g in the accident, the battery box appeared very ‘under-engineered’ and likely failed at a much lower load.

It is generally considered that fabric retention straps are not satisfactory, unless they have been called up in the original (accepted) plans or drawings.

Left top and bottom The battery ‘box’ as found following a fatal accident to an LAA aircraft, showing the poor quality of the ‘box’ and a hook and loop retention strap.

The photograph shows what David found inside the tank. The remains of the fuel cap seals, which had degraded sufficiently to be able to fall into the fuel tanks. This aircraft has apparently been run on mogas, but regardless of the fuel type used, it is best to regularly check the condition of the fuel cap seals and avoid allowing them (or anything else) to fall into the tank.

Left The remains of the fuel cap seals as removed from the Rans S6 fuel tanks (the pen gives scale to the bits of the seals – it was not found inside a fuel tank).

Propeller attachment bolt torque

LAA Inspector Ray Harper has reported that he recently looked at an aircraft with a poorly varnished wooden propeller. With the extremes of weather/temperature/humidity, which have recently been experienced in the UK, the poor surface protection allowed the wood to ‘breath’ and expand or contract even more than it would have if properly protected.

In this instance, Ray insisted that the spinner was removed which was fortuitous, as it revealed that the propeller retaining bolts were only finger tight.

It is imperative that propeller retaining bolts are frequently checked to ensure that they are maintained to the correct torque, particularly with large weather variations, be it seasonal or as experienced, in the case of the recent hot weather.

On aircraft which involve wooden airframe structures (such as Tiger Moths, Jodels and Pioneers etc) the various attachments to, or through, the wood must also be closely monitored. When retractable, undercarriage systems are installed to wooden airframes, it is very easy for the adjustments to become ‘out of limits’ due to the airframe effectively changing size relative to the metal undercarriage parts.

Pioneer 300 inboard flap brackets

Ben Davis has reported that during inspections, he has found a number of Pioneer 300 aircraft with a loose inboard flap hinge bracket where it attaches to the wing rear spar.

The wire-locking on the flap bracket attachment bolts has still been present, therefore it is not a case of the attachment bolts working loose by rotation. It may be another occurrence of the effects of seasonal and other weather changes.

Spinner failure

Propeller spinners are easily overlooked when it comes to inspections – both pre-flight and scheduled. The forces imposed on them are immense and when they fail, they can easily cause damage elsewhere as they depart the scene.

Composite spinners may not show obvious signs of damage that may be caused by a bird strike or simply people pushing on them when ground handling the aircraft (not a good idea at any time, but it happens).

Attempts are sometimes made at repairing cracked metal spinner by welding, but these rarely last for long and patches riveted over cracks can upset the balance of the spinner/ propeller assembly, and the same out of balance issue can result from repairs to composite spinners.

It isn’t only the spinner itself but the backplate to which it attaches that can suffer – and it is quite common to find these cracked as well.

Eurofox rudder torque tube failure

As discussed a number of times previously in Engineering Matters, aircraft involved in glider towing operations work hard for their living.

One LAA-administered Eurofox used for towing has suffered a failure in the rudder pedal torque tube. The failure occurred at the base of the pedal support tube where it welded to the torque tube.

Failures of rudder torgue tubes are familiar to experienced Cessna 150/152 engineers and we have had a report some years ago of a similar failure to another Eurofox tug.

The location of the rudder pedal torque tube deep down in the cockpit, does not make inspection easy, and they are inherently dirty from the outside world detritus

LAA Engineering housekeeping

FWR-1 Engine and Propeller Designations LAA Engineering is continuing to check the internal database against what is recorded on an aircraft’s Operating Limitations document and the FWR-1 Permit to Fly revalidation application when they are received.

What is recorded on the FWR-1, is in turn checking the engine and propeller designation of what is actually fitted to the aircraft against what the Operating Limitations document. When there is a discrepancy, it is often reported that what has been recorded on the FWR-1 is what is stated in the applicable logbook.

Inspectors should check that the information recorded in the logbooks are the complete designations and align with the Operating Limitations document, and what the data plate or placard on the engine and propeller state.

LAA Engineering charges

Up to 450kg to 999kg

Four-seat aircraft

Category change being dragged into the cockpit on the soles of shoes worn by the crew. This difficulty in inspection, is compounded by the like of manufacturers to paint components black – exactly the same colour as cracks.

Manufacturers may call up for the rudder pedal assemblies to be lubricated and their specific requirements should be followed. Oiling or greasing rudder pedal assemblies should be done with caution and only if specified by a manufacturer, due to the likelihood of dirt sticking to the lubricant, accelerating wear. Normally, it would be better to use some form of ‘dry’ lubricant in these areas.

Left The failed Eurofox rudder torque tube.

Emails going to spam and junk folders For reasons best known to ‘someone else somewhere’, there still appears to be a higher than normal proportion of emails sent from LAA Engineering that are going straight into recipients’ spam or junk folders.

If you are expecting an email from LAA Engineering and it has not appeared, please check your spam or junk folder, and if you can, add engineering@laa.uk.com to your email providers’ ‘safe address’ list.

Email subject headings It really assists LAA Engineering if emails include the registration of your aircraft in the email subject heading. Some emails we receive never mention the aircraft registration at all in the entire email! ■

Recent Alerts & AILs

Please note the Engineering section of the LAA website has the most current information.

LAA TSB: TSB-001-2022

Applicability: All Europa aircraft

Europa: Door latch system stop

CAA MPD: 2022-003

LAA AIL: MOD/247/012

LAA Alert: LAA/AWA/21/08

£2,000

£50

£150

£150

Change of G-Registration fee

Note: CAA MPD 2022-003 has now been corrected as of 22 June 2022

MT-PROPELLER ENTWICKLUNG GmbH

Applicability: MTV-( ) Variable Pitch Propellers

Subject: Propeller Blade Lag Screw Replacement EASA AD 2022-0134

Note: Please see the MT Propeller TADS P17 link to the ‘EASA AD Safety Publishing Tool’ for further info.

SLING

Factory-built gyroplanes* (all weights) £275

*Gyros note: if the last Renewal wasn’t administered by the LAA, an extra fee of £125 applies

Modification application

Prototype modification minimum £60

Repeat modification minimum £30

Transfer

Replacement Documents

£55

Lost, stolen etc (fee is per document)£20

PLEASE NOTE: When you’re submitting documents using an A4-sized envelope, a first-class stamp is insufficient postage.

Applicability: All Sling aircraft types and serials

Subject: Eyebolt inspection and conditional replacement Sling Service Bulletin #0020

Note: It has been found that the eyebolts fitted in the control system of certain Sling aircraft may fail to meet the manufacturer’s specification in regard to fatigue life. Such eyebolts are identifiable by the narrowness of the neck of the eyebolt above the bolt thread. This service bulletin details the procedures for inspection and replacement of such eyebolts in the various control systems.

ANDAIR FUEL SYSTEM COMPONENTS COMBINE MODULAR DESIGN, SUPERB QUALITY AND THE FLEXIBILITY TO SUIT ANY AIRCRAFT BUILD PROJECT.

Having built a reputation for excellence in the design and manufacture of light aircraft fuel system components within the amateur-build aircraft sector, Andair has now established a significant presence in the commercial aviation market as well.