Mogas Pt II

Hot starts after heat-soaking were an ‘against’ in the Mogas argument, with carburettor icing a minor snag.

The overall points score totted up to something of a decisive win for Mogas. It wasn’t even a TKO, from reports received by AUSTRALIAN AVIATION. It was a complete count-out.

We have since received additional information from the Experimental Aircraft Association in the US, adding further proof to the justification for using mogas in most cases.

With Amoco providing lead-free mogas and a variety of special mixtures with a particularly high Reid vapour pressure, the EAA has now completed 520 hours of test-flying in a Cessna 150 powered by a standard Continental 0-200 motor with a 7:1 compression ratio.

The EAA went about their business in a most thorough manner; the Amocosupplied special brews with Reid vapour pressures up to 16 psi were varied with an experiment using various aromatics percentages – some up to 36 per cent which is ten per cent higher than avgas itself.

Flights were conducted in ambient temperatures up to 30°C. One of the things monitored was exhaust gas temperature (EGT) with comparative graphs being worked out between avgas and mogas.

Mogas proved to be the much cooler burning fuel – a regular 250°F cooler than its rival.

The EAA’s final conclusions were that mogas had no adverse effect on its test aircraft engine’s efficiency. They have put their undeniably authoritative reputation on the line to the extent that they have now applied to the FAA for a supplemental type certificate for its use in this aircraft.

Britain has done more work on mogas in aircraft engines, and the combined US-British test flying using mogas has now hit 750 hours.

In Britain, engines tested with mogas – with no harmful effects so far – have included the Continental 0-200, 115 hp Lycoming 0-235 as supplied in the Tomahawk, a Piper Warrior’s 160 hp 0-320 Continental, and a Seneca brace of 200 hp Continental TSIO-360s.

One of Britain’s engine specialists, Westlake, has since run successful bench tests on a 250 hp Lycoming 0-540 as fitted to eg Aircraft like the Pawnee.

In Australia, the Aircraft Owners and Pilots Association’s expert Bill Abbott has been the prime investigator in the mogas argument. Acting for his Association, Bill has now amassed a pile of answers to AOPA’s mogas questionnaire.

According to AOPA, nearly 40 replies had been received to the end of November last year, with many more coming in since then as word got around that AOPA means business.

So far much more than 20,000 hours of mogas operation have been admitted, on an anonymous basis, in Australia.

AUSTRALIAN AVIATION has continued its own discreet enquiries as a backup to the mogas argument; however, many operators and owners admitting to using mogas on a regular basis told AUSTRALIAN AVIATION they had already given information to AOPA and would thus like to keep all their eggs in one neat and tidy basket. We have no argument with this – it isn’t a case of getting more information than the chap next door, it’s a case of proving a point in the interests of an entire industry.

Mogas companies preferred not to be drawn into any discussion on the quality of their product, merely wishing to point out that if any allegations were to be made on quality control or the end-user product they would be delighted and anxious to argue the case, in or out of a legal environment.

We have taken much of the salient material from Bill Abbott’s articles in AOPA’s magazine, in the knowledge that the Association welcomes any and all support on a non-partisan basis.

Most replies to the AOPA questionnaire came from New South Wales, with Queensland heading Victoria for second place. Surprisingly, Western Australia ran fourth – a State where mogas have been and is being used in relatively significant amounts.

A variety of aircraft types were put on the list, ranging through the Cessna range (150, 172, 180/182), most of them fitted with Continentals, to Piper types from PA20, PA22-160, PA25-235, PA28-140, PA28-160 and PA28 – all Lycoming-fitted.

There were a few one-offs in the list; a Victa, an Auster Beech 23, a Rallye, a Druine, a Tiger and others with a mixture of Continentals and Lycomings.

Most admitted to using mogas fuel of one brand or another. The replies to ‘Standard or Super?’ were hazy, but some operators said they used either, both or a mix. According to Bill’s report, one Piper operator in the Eastern sector wrote that he used BP Zoom – but failed to record if it was the outboard or lawn mower type, Bill added!

How much? One agricultural operator said he used mogas for 8000 hours over the years, but an average – which must pull down the actual amount of hours flown – worked out from those who replied, to 115 hours per aircraft.

The ratio of those who had used it for 12 or 24 months worked out two to one in favour of the longer term.

All are snag-free, apart from one or two minor and non-accident-provoking incidents.

Some replies to Bill’s question of Have you had any abnormal maintenance problems on mogas?’ included:

‘Both engines (Cessna 172 and 150) had only 300 hours to run and both had had a top overhaul. Both engines fouled one plug during the above times (not lead). ‘

‘No noticeable difference (from an agricultural operator in Victoria) – except cheaper.

‘Carburetter needle valve failed after 200 hours since new (from both WA and Victoria). Not known if caused by mogas. The rear seal on Bendix fuel pumps leaked, age unknown, but discussion with mechanic revealed this to be a common failure for the pump type.

A Piper operator in NSW and Queensland replied, ‘No,’ and the operator has flown mogas for 4800 hours.

Bill then asked operators and owners replying to his Association’s questionnaire, ‘Have you had any incidents involving flight safety with mogas?’

Almost a hundred per cent ‘no’ to this one, but there were one or two comments which bear repetition:

‘We have on one occasion had a slight hesitation on throttle opening at very high OAT (outside air temperature) and after heat soak condition. . . ‘ This was from an agricultural operator in Victoria using a PA25-235. ‘Minor engineering mods could easily overcome this. ‘

A Cessna 172G operator in New South Wales commented, ‘Use avgas for take-off, mogas for above 1000 ft. ‘

One Cessna 182 operator commented, ‘I believe a lot of operators in the west use mogas and the only problem I’ve heard of is vapour lock. . .

I believe this did cause an engine failure on take-off but this was in a low-wing aircraft with a fuel pump. I have no trouble with the gravity feed. I have not operated through the hot weather on mogas at this stage, apart from a trip to Charleville – about 33°C and about 5°C at 9000 ft. ‘

Bill, who travelled widely in other countries during his extensive and most authoritative survey, is still cautious about mogas suitability for 40°C operations. ‘We just don’t know for certain,’ he writes.

He says he expects the Gliding Federation of Australia’s coming summer tests on their tugs (PA25) to show what mods could be necessary to permit the absolutely safe use of mogas at high OAT.

The key question have you had any knowledge in the case of vapour lock causing engine failure? Under what conditions? Was it during summer?’ has produced such a high rate of favourable answers that Bill Abbott frankly confesses they worry him.

If asked, as an engineer, if mogas is suitable for operations around the high ambient of around 40°C, Bill’s answer would at this stage be ‘no. ‘

He points out, after detailing such factors as the RVP of the fuel in the tank, fuel temperature in the tank, how much heat the fuel picks up on its way from tank to carburetter, the degree of heat soak the aircraft has had prior to start, and other factors, that the critical and dangerous phase is the take-off and initial climb.

He commends pilots using dual-fuel – avgas for take-off and initial climb out and mogas for cruise.

He backs up his opinion by listing several replies to questions of what was the OAT at which vapour lock occurred; what the maximum temperature/ pressure altitude reached without a problem; and had the aircraft been standing in a heat-soaked condition before vapour locking happened.

The resultant advice from these replies indicates that the adage of, ‘Not above 30°C ambient and 5000 ft’ is a conservative statement. In other words, don’t stretch your luck. . .

Maintenance costs appeared to be no greater when using mogas, according to the questionnaire’s replies. In fact, mogas appear to lead to healthier plugs in most cases.

Bill Abbott goes into some technical detail when considering Transport Australia’s big worry – mogas quality and contamination.

He points out that Transport Australia isn’t as concerned with the product while it’s still in the refinery; it’s what happens to it after it leaves the refinery.

Answers to Bill’s questions of whether users have had any problems with poor quality or contamination are interesting:

‘Very fine sediment – looks like Rust,’ said a Cessna 172 operator.

‘A filter funnel is necessary as some flakes of metal get in from the drums,’ says a PA25 operator.

‘I find some form of filter is essential (823 operators). I have found rust particles and dirt. All have been caught with a filling funnel with a very fine brass mesh filter.

Several other operators reported rust, dust or dirt in the mogas decanted. There was an almost (and expected) total approval of mogas as an alternative fuel to avgas, in the questionnaire.

One operator (Cessna 172) said he didn’t know if he considered mogas a safe and satisfactory fuel; unsafe and should not be used; or could be made safe by aircraft modifications. ‘But I’d like to see it usable legally. . . ‘ he added.

This operator currently operates on a shandy of avgas and mogas.

This comment, says Bill Abbott on behalf of his Association, is the ultimate objective of the AOPA-GFA exercise; to make mogas a legal fuel for either emergency or alternative use, to that fuel currently specified in a specific aircraft’s flight manual.

Most of the replies provide a bank of information on whether or not mogas is a fair substitute for 80/87.

If Italian safely replaces higher rating fuels, 1s another matter. Meanwhile, AUSTRALIAN AVIATION backs AOPA and Bill Abbott to the hilt in urging operators not to become complacent, especially over the fuel vapour lock risk.

As Bill says, ‘One serious accident from it could put the whole program back years . . .