Primarily for general aviation discussion, but other aviation topics are also welcome.
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By leiafee
FLYER Club Member  FLYER Club Member
#1472242
So how much of a correlation between OAT and fuel temp is there all things being equal? Anyone have temp gauges?

Is it more or less risky than using a alternative fuel which my manual says is for desperate measures only?

If I stay below 5000' while sallying off to Devon am I safer because of reduced risk or vapour locking or more at risk because I've given up my gliding height?

I don't want to sound bolshy, but if I frankly if Idon't fly in summer because of mogas temp, and winter because of weather and never above 5000 I might as well get a kite...

Do microlighters just not worry about it because ultimately there's hardly ever a time you can't plonk into a hundred yards of field?

I didn't like the "feel" of the two really hot days we had and stayed down - but carb ice and whopping great cunims in the forecastwas what kept me on the ground.
By patowalker
FLYER Club Member  FLYER Club Member
#1472281
It was 6000', not 5000' in GC 5, but GC 4 applied to microlights and IIRC there was no altitude limitation.

All you have to do is comply with the TADS and engine manual.

http://webarchive.nationalarchives.gov.uk/20141217040056/http://www.caa.co.uk/default.aspx?catid=1407&pageid=16578

Any type of fuel may be used in an aircraft providing it meets the specification(s) set out in the aircraft’s approval documents and any associated operational limitations. ...; for national Permit aircraft this will be found in the Airworthiness Approval Note, Permit Conditions, Permit Operating Limitations or associated referenced documents.
By cockney steve
FLYER Club Member  FLYER Club Member
#1472345
"20*c or 5,000 feet"
Pedant mode on

Shirly , the Dry Adiabatic Lapse -rate would give a temp-drop of 10* at 5000'? Would wind-chill offset the effects of direct sun-radiation ?......If not, how come the big jets suffer from sub-zero chilled fuel .?

OK, i'm still not a pilot... does that make the questions irrelevant? :wink:
User avatar
By SteveC
#1472450
TheFarmer wrote:Good advice, but worth adding some more detail.

It's not directly the OAT that poses the threat. Filling up from the garage and putting sub 20 degree C fuel in, and then going flying is fine in these temps.

The risk lies in aircraft (especially dark coloured ones) sitting out in the heat while their owner stuffs his face in an airfield cafe. The volatilisation at these temps is what's risky, not the actual OAT per se.

A well managed flight with cool fuel going in at both ends of the trip pretty much negates the risks.


That's inaccurate and unsafe indformaton and constradicts all the guidance and advice on the use of MOGAS. I suggest you are a lot more careful with your personal perspective sage advice.

It is very easy to exceed the tank temperatures which create volatility in the fuel and enough to cause vapour lock. The guidelines have been issued the way they are for a reason which is to try and create a blanket safety margin. Your post is irresponsible.
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By MichaelP
FLYER Club Member  FLYER Club Member
#1472453
Are there any statistics about engine failures due to the use of Mogas?

I fly here in Canada, and in hot Thailand, and there's considerable use of Mogas in both places, and as I wrote before I started a school here with Rotax engined Katanas flying year round on Shell V Power.

Why have I not seen an engine failure due to the use of Mogas yet?
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By Charliesixtysix
#1472468
All of this is very interesting and I do appreciate the official advice is pretty clear about use of mogas in warm temps.

Well based explanations here would lead one to conclude that there is a real risk in some aircraft/temp combinations and less of a risk in others.

I would never suggest anyone ignore official advice......But....

Once again, hundreds of flights took place in central UK this weekend with many types of aircraft ( lots of which are known to fall into higher vapour lock risk category ) in temps at well above 20c and ( touch wood) there is no reporting of problems re the dreaded vapour lock....

It is pretty obvious that the offical advice is effectively disregarded, or at least viewed with a degree of scepticism, by many mogas users and they do seem to be able to fly quite happily in summer, without the need to buy a kite.

Genuine question:
Is it time for a review of official quidance notes in light of experience gained over many hundreds ( thousands?) of hours flying of the various engine/ aircraft combinations?
Possibly to include somthing along lines of indiviual risk assement guidance rather than the blanket ban as present?
mick w liked this
User avatar
By Charliesixtysix
#1472562
Agreed, in November 2014.
'Official advice' was a poor choice of words on my part, sorry.

Certainly there is contradictory information within LAA information sheets, at least two versions of which are still found on searching LAA website for Mogas limitations. No wonder confusion abounds.

OPERATING INFORMATION- UNLEADED MOGAS iss8 was published in 2013 and refers to CAP 747 GC5
http://www.lightaircraftassociation.co. ... MATION.pdf

That was superseded by TL2.26 iss 1 in 2015 with more recent information, included permitting use of E5 fuels and explaining removal of CAP747 GCs.
http://www.lightaircraftassociation.co. ... 0Mogas.pdf

I shall drop LAA engineering a line and ask if this could perhaps be tidied up.
User avatar
By MercianMarcus
#1472571
From one of 66s links ...

... if more than 15 litres is stored then there is a legal obligation to inform the
Petroleum Officer who must inspect and approve the premises. He will require the fuel store to
be adequate for the job and to be equipped with a suitable nearby 6 Kg dry powder fire
extinguisher.


Bureaucrats don't do themselves any favours do they! No wonder important matters get missed if they are simply tiny needles in enormous haystacks of utter twaddle like that.
By cockney steve
FLYER Club Member  FLYER Club Member
#1472674
ponder on the fact that 15 litres of petrol will keep a small aircraft and at least one human aloft for about an hour/ 40 miles.
now consider that same energy leaking from a can and the fumes are ignited :shock:

A secure, bunded store is an absolute necessity where fuel is stored at other than a residential, closely monitored site. rhe legal limit and methods of containment are tightly controlled for good reason.
this is one of the few areas where I agree with tight control.