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Avgas quality concerns ... helicopters

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Avgas quality concerns ... helicopters

Old 2nd Oct 2018, 13:55
  #41 (permalink)  
 
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TEL (the "lead") is added to a gasoline to increase its octane rating or resistance to detonation. It is not added for any other purpose. The TEL doesn't alter the combustion characteristics of the fuel, it's there to prevent detonation from occurring. The actual amount of TEL in the fuel doesn't matter providing the fuel meets the octane quality specified. (lean rating >100 MON, rich rating >130 P.N. in the case of Avgas 100LL). So if higher octane blendstock is used, less TEL is required for the fuel to meet the octane requirements.
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Old 2nd Oct 2018, 19:29
  #42 (permalink)  
 
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Originally Posted by tio540 View Post
Megan, CASA did not forbid operation above 40 deg C. The correspondence stated "a pilot must not operate an aircraft outside the limits set out in the AFM".

Read CAO 20.7.4 again.
Well, not that's actually not what was said is it? You edited the statement so that your version says something different. Here's what was it actually says:
“ Therefore, unless a declared emergency exists, if ambient conditions exceed the limitations set out in the AFM, including the range for which performance data is provided, the aircraft must be grounded.”
Essentially, they are arbitrarily declaring the extent of the published performance data to be a limitation, when in fact it is not. Witness the fact that many manufacturers will cheerfully provide you with performance charts with temperature range beyond that provided in the standard AFM, which is a pretty clear indication that the manufacturer did not intend that the chart temperature range was a limitation. My own airplane has no takeoff performance data below 15C/59F and no method to adjust. That would mean that in the eyes of CASA my plane would be grounded on ....well, most days here in Alaska where I live, and I could only fly it on the odd summer day.
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Old 2nd Oct 2018, 23:39
  #43 (permalink)  
 
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Major issue with piston engines in our mustering helicopters turns into another diatribe against the regulator.
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Old 3rd Oct 2018, 07:58
  #44 (permalink)  
 
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The TEL doesn't alter the combustion characteristics of the fuel, it's there to prevent detonation from occurring.
Let me fix that for you:

TEL reduces the probabilities of detonation occurring by altering the combustion characteristics of the fuel.

How else could adding TEL to fuel “prevent detonation from occurring” if, as you state, TEL doesn’t alter the combustion characteristics of the fuel?
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Old 3rd Oct 2018, 08:24
  #45 (permalink)  
 
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eddie:
]Major issue with piston engines in our mustering helicopters turns into another diatribe against the regulator.
That is because the regulator claims to have "safety" as their imperative to the point of draconian penalties and capricious enforcement practices.............yet when this obviously safety related event surfaces, they are no where to be found.

Considering that well funded oil companies are involved, rather than relatively poor private citizens, Might one perhaps think that CASA are institutional cowards?
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Old 3rd Oct 2018, 08:43
  #46 (permalink)  
 
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Detonation is the spontaneous combustion of the fuel air mixture ahead of the flame front. The remaining part of the mixture in the combustion chamber explodes prematurely due to the cylinder pressure increase, not as intended via the spark plug. That is what gives the "knocking" or "pinking" (the latter usually known as "pinging" if you're in USA).

In the past I explained it to a rugby playing student by likening it to someone in a match trying to jab him away with a fist, rather than pushing him smoothly out of the way with the palm of a hand. The same energy is expended, but the first one hurts and does physical damage. He understood that.

TEL also forms lead salt deposits on the valve seats and mating surface of the valves themselves. This prevents one or both wearing away prematurely by preventing metal to metal contact. I believe this was a lucky side effect of the initial intention to prevent detonation and wasn't fully understood until some years later when older engines became damaged by the use of the newer, supposedly "greener, low lead" fuels.

The above is also why mag drop checks are done - build up of lead salts can foul spark plug contacts. It's also why car engines needed regular "de-coking" in the days of 4 and 5 star fuel, now a thing of the past. In the 1970s I ran a tuned BSA motorbike with a 12.5 to 1 compression ratio. It needed 4 or 5 star fuel. Decoking the valves on that needed a small chisel - the deposits on them were like toughened glass.
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Old 3rd Oct 2018, 09:19
  #47 (permalink)  
 
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FYI. It is affecting fixed wing aircraft. Not as bad as the R22 but there is damaged engines, in fact i have one back a manufacture now being debated on why it is damaged.
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Old 3rd Oct 2018, 10:15
  #48 (permalink)  
 
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Sunny...no 'perhaps think' about it !!
CAsA most certainly IS a proven 'institutional coward'
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Old 3rd Oct 2018, 15:29
  #49 (permalink)  
 
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A.E.F.R says:
TEL also forms lead salt deposits on the valve seats and mating surface of the valves themselves. This prevents one or both wearing away prematurely by preventing metal to metal contact.
Really? If the lead salt deposit you're talking about is lead oxybromide how does it deposit on those mating surfaces? Lead oxybromide melts at 703.4*F. The engine exhaust is between 750*F and 1,650*F so it is in liquid form. The exhaust gas exits through the open valve at better than 600 km/h The valve head is heated to close to the exhaust gas temperature. Under those conditions I don't think anything would stick to to mating surfaces.

The most convincing argument for me that it is an old wives tale that lead is a lubricant and /or cushion is the result when natural gas or propane gas is used in internal combustion engines instead of leaded fuel. The engines last just as long if not longer and there is not an atom of lead in either gas.
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Old 3rd Oct 2018, 20:55
  #50 (permalink)  
 
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Originally Posted by rutan around View Post
A.E.F.R says:


Really? If the lead salt deposit you're talking about is lead oxybromide how does it deposit on those mating surfaces? Lead oxybromide melts at 703.4*F. The engine exhaust is between 750*F and 1,650*F so it is in liquid form. The exhaust gas exits through the open valve at better than 600 km/h The valve head is heated to close to the exhaust gas temperature. Under those conditions I don't think anything would stick to to mating surfaces.

The most convincing argument for me that it is an old wives tale that lead is a lubricant and /or cushion is the result when natural gas or propane gas is used in internal combustion engines instead of leaded fuel. The engines last just as long if not longer and there is not an atom of lead in either gas.

It's pretty well documented that there were a lot of problems with rapid valve seat recession when lead was removed from gasoline. You're may right that "lubrication" may not be the best word for what the lead was doing something . How would you describe what the lead was doing to prevent that? Because I think you're going to have a pretty tough battle convincing anyone that valve seat recession wasn't a problem when automobiles were switching to unleaded fuel.
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Old 3rd Oct 2018, 22:08
  #51 (permalink)  
 
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You (and many others) confused correlation for causation.

Removing the lead from the fuel meant that the lead was no longer in the fuel. That caused an increase in the probabilities of detonation in engines that were not designed to run on unleaded fuel. Detonation causes a disruption of the boundary layer inside cylinders that usually helps to insulate them from being exposed to all of the heat generated by the combustion event. That’s why ‘heavy’ detonation causes an increase in CHT (and is what is causing the problem in mustering chopper engines).

I think you’ll find that what actually caused the rapid valve seat recession in car engines when lead was removed from MOGAS was detonation/high CHT.
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Old 3rd Oct 2018, 22:26
  #52 (permalink)  
 
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What Lead Balloon said
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Old 3rd Oct 2018, 22:33
  #53 (permalink)  
 
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What Lead Balloon said.
The cylinders and valves are not hurt by natural gas or propane because their octane rating is above 100

Last edited by rutan around; 3rd Oct 2018 at 22:43. Reason: Forgot the last line
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Old 4th Oct 2018, 03:16
  #54 (permalink)  
 
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Originally Posted by Connedrod View Post
FYI. It is affecting fixed wing aircraft. Not as bad as the R22 but there is damaged engines, in fact i have one back a manufacture now being debated on why it is damaged.
Hey mate, which engine aircraft combination was that engine out of. Also what operation was the aircraft carrying out?
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Old 4th Oct 2018, 03:22
  #55 (permalink)  
 
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Originally Posted by Lead Balloon View Post
You (and many others) confused correlation for causation.

Removing the lead from the fuel meant that the lead was no longer in the fuel. That caused an increase in the probabilities of detonation in engines that were not designed to run on unleaded fuel. Detonation causes a disruption of the boundary layer inside cylinders that usually helps to insulate them from being exposed to all of the heat generated by the combustion event. That’s why ‘heavy’ detonation causes an increase in CHT (and is what is causing the problem in mustering chopper engines).

I think you’ll find that what actually caused the rapid valve seat recession in car engines when lead was removed from MOGAS was detonation/high CHT.
Once again not quite true. Whist the boundary layer protects the top of the piston detenation will at the extreme will and can blow down the side and top of the piston. It also damages the small and big end bearings and can even bend the con rod. Light detenation will damage plugs and cause errision in the chamber and top of the piston.
Damage to car engines valve seats when lead was removed was that most cars up to that period didn’t have hardened valve seats as they were part of the head casting and machines out of the parent material.
To get around this problem hardened valve seats were used in both alloy and cast iron heads. It had nothing to do with high cht as the water cooling system in a car is far more efficient than air cooling.
Stick to your day job !!!!!
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Old 4th Oct 2018, 04:40
  #56 (permalink)  
 
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The trouble with your day job is that it has been just about the same day, over and over again, and you’re incapable of learning anything new.

You failed to explain what caused the problem that was solved by using hardened valve seats. It couldn’t have been the absence of lead. As has already been explained, ‘unleaded’ propane or natural gas didn’t cause valve recession.
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Old 4th Oct 2018, 05:37
  #57 (permalink)  
 
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Something old is new again?

https://www.flightglobal.com/pdfarch...0-%202701.html

When leaded fuel was first introduced, associated valve problems using the aluminium bronze inserts then commonly used..

https://www.flightglobal.com/pdfarch...0-%201389.html
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Old 4th Oct 2018, 09:26
  #58 (permalink)  
 
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Removing the lead in the fuel to C441's gives the same engine problems in the north, from what I hear Eddie.
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Old 4th Oct 2018, 09:32
  #59 (permalink)  
 
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Originally Posted by megan View Post
Something old is new again?

https://www.flightglobal.com/pdfarch...0-%202701.html

When leaded fuel was first introduced, associated valve problems using the aluminium bronze inserts then commonly used..

https://www.flightglobal.com/pdfarch...0-%201389.html
I have an old bronze head from a Gipsy Major that I use for a bookend!!
Tootle pip!!
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Old 4th Oct 2018, 12:09
  #60 (permalink)  
 
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Originally Posted by Eddie Dean View Post
Hey mate, which engine aircraft combination was that engine out of. Also what operation was the aircraft carrying out?
unfortunately at this time i cant give out any information on what were why etc as it is before and under the manufacture at this very time. I guess you can get the sensitive nature at what is at risk.
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