Primarily for general aviation discussion, but other aviation topics are also welcome.
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By Paul_Sengupta
#1770640
riverrock wrote:5-Star had the highest Octane rating of 101 so I suspect its lead content was close to our 100LL.


Don't confuse RON with MON or AKI.

Oh, and the Bulldog, like most fuel injected Lycomings, doesn't have a recirculating fuel system.
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By Flyin'Dutch'
#1770645
Rob L wrote:
Flyin'Dutch' wrote:Ugh, maybe for a lawn mower not too bad but I would not want to inhale AvGas fumes from a chainsaw etc.

The LL is a total misnomer - there is (IIRCC) 10x more TTL in AvGas than there was in 5 Star Leaded for road use.


It's TEL But you are quite right; Low Lead is a relative term.
Think of the 130 octane used for all those bombers & fighters in WWII.
I confess that I always thought 100LL was about the same as five-star in terms of lead content.

Chainsaws are generally 2-stroke, so the above does not apply.


A 2-Stroke can run on AvGas, innit?
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By rf3flyer
#1770646
andytk58 wrote:I still think its criminal that aircraft are designed with fuel systems that suck liquid. Particularly a volatile liquid which will flash vapourise at any excuse!!

IMO mogas systems should always have an 'always on' circulating pump at the lowest point in the system, with a pump failed warning lamp on the instrument panel. Cheap insurance against disaster.

[\rantoff] 8)

Andy

Decades ago I read an article in, I think, Experimental Aviation, or maybe Flying, of a ground trial by Piper where the fuel system on one of their models was built of transparent materials to see what happened with fuel flow. One of the biggest vapour forming features was the inlet, suction side of the fuel pump(s)! That would have been with 100LL so I guess mogas will be worse in that respect.

Not all aircraft are susceptible though. Any with a straightforward gravity fed, high to low, uncomplicated routing, no pump, should be trouble free, IMO.
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By MikeB
#1770676
I've said all this before but apparently it needs saying again.

You won't get vapour lock if you have a Net Positive Suction Head. High or low wing, Mogas or Avgas, NPSH= no vapour lock.

You can't compare RON of Mogas with Avgas. Completely different measurement basis.

As per Raoult's law, ethanol will evaporate slightly faster than some other Mogas components, but there will be more butane lost which is the main reason for both octane loss & starting issues (the latter not connected to the former).

If you drain your tanks and fill with 'fresh' Mogas, the engine will be easier to start but you will be more not less susceptible to vapour lock.
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By Trent772
#1770681
Flyin'Dutch' wrote:


A 2-Stroke can run on AvGas, innit?[/quote]


2 strokes run really well on Avgas !

Start first time, never goes stale - the future.
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By TheFarmer
#1770686
MikeB, that’s a good post.

There is often an overlap of views about MOGAS, and its various downsides.

Therese are,

1. Vapour lock risk - engine fuel starvation issues.
2. Rapid degradation - general running issues.
3. Ethanol - the degradation of non-metal fuel feed lines and carb parts.

The subject title of this thread is about the former, and the risk is poses to us when we want full power and max flow in and out of the carb when the temperature of the fuel rises* The other two are separate issues.

Old fuel won’t increase the risk of vapour lock.

* Aircraft with tanks beneath dark paint schemes running on MOGAS need to be particularly cautious. It’s not directly the OAT that’s the issue, but the fuel temperature itself.
By andytk58
#1770815
riverrock wrote:My understanding is that most injected engines essentially have a circulating pump, pushing fuel around much faster than the engine needs (our Bulldog goes anyway), but can still get vapour lock, although its post common when trying to restart a recently running hot engine.


The issue isn't so much a recirulating pump, but the location of the pump. Engine driven pumps are dangerous as once heatsoaked, any attemot to suck the fuel up from the tanks results in vapour lock.

The pump really has to be at the lowest point on the system so it had net positive suction head under all eventualities.

Andy
By Crash one
#1771493
andytk58 wrote:
riverrock wrote:My understanding is that most injected engines essentially have a circulating pump, pushing fuel around much faster than the engine needs (our Bulldog goes anyway), but can still get vapour lock, although its post common when trying to restart a recently running hot engine.


The issue isn't so much a recirulating pump, but the location of the pump. Engine driven pumps are dangerous as once heatsoaked, any attemot to suck the fuel up from the tanks results in vapour lock.

The pump really has to be at the lowest point on the system so it had net positive suction head under all eventualities.

Andy


I’m led to believe that these engines were initially designed to drive farm tractors which had the fuel tank well above the engine. Not much can be done about it now but the mechanical pump being at the top of the engine and in a low wing aircraft, it’s in about the worst place possible.
By andytk58
#1771521
Crash one wrote:
I’m led to believe that these engines were initially designed to drive farm tractors which had the fuel tank well above the engine. Not much can be done about it now but the mechanical pump being at the top of the engine and in a low wing aircraft, it’s in about the worst place possible.


Ok, now I'm curious, what is it you fly and what engine does it have that was once in a tractor?!

Andy
By Crash one
#1771540
I hope that was tongue in cheek. :D
However. I believe that in the 1930s or thereabouts the Continental engine was designed for farm tractors,
Being very successful and reliable it was adapted for use in aircraft.
Then, aviation being the way it is, very little modifications were performed and they started being built for and fitted to aircraft.
My engine in my Emeraude was never ”once in a tractor”! It was built in 1959 and fitted in the aircraft brand new as were numerous others.
By andytk58
#1771554
Crash one wrote:I hope that was tongue in cheek. :D
However. I believe that in the 1930s or thereabouts the Continental engine was designed for farm tractors,
Being very successful and reliable it was adapted for use in aircraft.
Then, aviation being the way it is, very little modifications were performed and they started being built for and fitted to aircraft.
My engine in my Emeraude was never ”once in a tractor”! It was built in 1959 and fitted in the aircraft brand new as were numerous others.


I was joking, but it had crossed my mind that you might have some odd eastern european straight 4 that had originally graced the front end of a tractor.... :lol:

I know that lycoming made a field irrigation pump from what was essentially an O240 (probably got the model wrong, but it was an air cooled flat 4).
A few of these got converted back to aero use by EAA folk in the states.

I wouldn't be at all surprised to learn that Continental started with farm machinery.

Cheer

Andy
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By Rob L
#1771556
Air-cooled engines were never designed for tractor use.
The first vehicular air-cooled engine was I believe that of the VW Beetle, 1938.

But many ancilliaries, particularly carburettors & magnetos, were developed from turn-of-the-century tractor parts for aviation use.

Case magnetos were produced by the millions for tractors at that time; they were cheap, reliable, easy to start and (relatively) light-weight due to their simplicity. Eisemann and Bendix and many others followed, all following the same basic design.

I have several friends in the US flying 1938 Taylorcraft with Case magnetos. I fly with Eisemanns.
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By Rob L
#1771557
andytk58 wrote:I wouldn't be at all surprised to learn that Continental started with farm machinery.

Cheer

Andy


They started with the A-40 (2 cylinder 4-stroke) 40 hp, developed from the "Kitten" engine (which is why a Cub is called a Cub). Nothing to do with farm machinery.

[Edit: If you can find a copy of "Flying with 40 horses: A history of the Continental A-40 aircraft engine and the planes it flew" by Chet Peek, you'd be surprised how little (and how much) things have changed. I can't find my copy right now to give the ISBN]