Avgas quality concerns ... helicopters

[kaz3g]

Investigation into mid-air engine failures yet to yield answers as pilots fear for their safety - ABC News (Australian Broadcasting Corporation) (http://www.abc.net.au/news/2018-09-30/av-gas-helicopter-aviation-engine-component-casa/10306564)

[LeadSled]

Investigation into mid-air engine failures yet to yield answers as pilots fear for their safety - ABC News (Australian Broadcasting Corporation) (http://www.abc.net.au/news/2018-09-30/av-gas-helicopter-aviation-engine-component-casa/10306564)

Folks,
The reported lack of interest, let alone action, mirrors the Avgas crisis of 1999.
Tootle pip!!

[YPJT]

From memory, Mobil's response at the time was much more proactive than Viva's has been to date.
https://www.wsws.org/en/articles/2000/01/air-j25.html
Can someone explain why they are only saying helicopters are affected?

[Sunfish]

CASA response, as quoted in the ABC article: "We are doing a lot of research in terms of fuel which is an area normally outside of our expertise and jurisdiction to better understand the fuel supply and manufacturing processes," said Peter Gibson from the Civil Aviation Safety Authority (CASA)."If [pilots] do have a rough-running engine in flight they need to be very careful with the handling of that aircraft and get it on the ground as soon as possible."

I totally fail to understand why CASA states that a critical input to aviation safety, fuel, is "an area normally outside of our expertise and jurisdiction". Especially since CASA micro manages virtually every other aspect of aviation safety.

To put that another way, CASA specifies in detail how and how much fuel a pilot must load and carry and manage consumption, yet there is no concern given to the possibility that the fuel itself is substandard???? This defies belief. There is a chain of responsibility leading from the refinery to the aircraft engine combustion chamber, yet CASA only wishes to micromanage part of the chain (complete with draconian penalties for non compliance) but gives the fuel companies a free pass. Why aren't fuel companies and their staff facing criminal penalties right now? It's only fair.

[megan]

an area normally outside of our expertise and jurisdiction Of course it is, we see proof regularly. See how you get on if caught running your non STC'ed engine on mogas. Does CASA actually know anything? Can I fly my lighty if the temp exceeds 40°C yet? CAO 20.93.1 The pilot in command of an aircraft shall ensure that the aircraft is not flown unless the aviation fuel, aircraft engine lubricating oil, aircraft engine power augmentation fluid and aircraft hydraulic system fluid used in connection with the servicing or operation of the aircraft complies with the specification and grade required or approved for the purpose by CASA.

Note 1 In respect of aircraft engine power augmentation fluid and aircraft hydraulic system fluid the specification and grade specified for a particular purpose in a manual or manuals promulgated by the aircraft or aircraft engine manufacturer may be considered as having been approved by CASA.
Note 2 The pilot in command may assume that:

(a) aviation fuel; and
(b) aircraft engine lubricating oil; and
(c) aircraft engine power augmentation fluid; and
(d) aircraft hydraulic system fluid in the aircraft, other than that which he has caused to be delivered into the aircraft, complies with the required specification and grade.

[neville_nobody]

. I totally fail to understand why CASA states that a critical input to aviation safety, fuel, is "an area normally outside of our expertise and jurisdiction". Especially since CASA micro manages virtually every other aspect of aviation safety.

Ah yes but if they entered into fuel regulation they will have to start dealing with very well financed and politically influential Multi National Oil companies who will have the means and the finance to fight CASA at every turn. It will begin with every court case imagineable followed by backroom political pressue. Just have a look at what happens in other industries, when regulators try to regulate Multi Nationals companies.

[Eddie Dean]

It appears at this time to be accelerated wear of piston cylinders. And only on mustering machines.
A CE in the NW tells me that they have been having issues for 12 months or so.
Indications are of high internal temps and erosion, which leads me to suspect something other than just fuel.

YPJT- There has been no issues with fixed wing aircraft operating in the same areas.

FWIW

[Bend alot]

I would expect that a change made to an aviation fuel that has an adverse effect on any aircraft, is part of CAsA's responsibility.

By changing the lead content in the fuel it seems to have had an impact on the safety of helicopters used for mustering operations - I say CAsA has a responsibility to restore the safety.

I further say that to make a statement, to put it down as soon as possible is not a very good safety response from the regulator. But rather than direct the fuel back to the previous lead content until further testing is carried out, CAsA would simply suspend all mustering operations (possibly fixed wing also) until replacement engines that can operate with the new fuel are designed, tested and fitted with silly restrictions such as happened with Jabiru engines.

[megan]

In the previous avgas drama the recalled fuel was off loaded onto the sport/racing car enthusiast, so one of them told me. After blown engines a group got together for a class action, but the lawyers told them you don't have a hope in hell aka big, big multi national, at the time the worlds biggest.

Edited to add: https://www.casa.gov.au/file/203356/download%3Ftoken%3DmKVSloyT&ved=2ahUKEwifmLX35OHdAhVNa94KHXEJDDEQFjAEegQIABAB&usg=AOvVaw0XISAONwNVBXwlewbDwqf3

[swh]

Somewhat mirrors something the FAA put out recently in relation to a Falcon biz jet that suffered an all engine flame out due to the fuel not meeting standards.

Fuel standards are not developed by the regulators.

[LeadSled]

From memory, Mobil's response at the time was much more proactive than Viva's has been to date.
https://www.wsws.org/en/articles/2000/01/air-j25.html
Can someone explain why they are only saying helicopters are affected?

YPJT,
Interesting web site to pull up that information from 1990/2000. However, the article is accurate.
My original comment about CASA involvement was based on CASA's reluctance to get involved, over a period of several years, in what, as I recall, turned out to be a quite long standing problem of EDA contamination.
It was left up to AOPA to recruit the late Prof. David Trimm, from UNSW, as an independent expert on the fuels. He very smartly got to the core of the problem.
As always, CASA is not renowned for "taking on" anybody who has the resources for a legal defense.
Tootle pip!!

[YPJT]

YPJT- There has been no issues with fixed wing aircraft operating in the same areas.
indulge my ignorance but aren't they essentially the same engines?

[Bend alot]

YPJT - yes and very much no.

Choppers don't have the same airflow for cooling.
A fixed wing is cooled during landing, a chopper the opposite - mustering is not high power but not high cooling either.

[A Squared]

indulge my ignorance but aren't they essentially the same engines?

To a large degree, yes.

[rutan around]

Originally Posted by YPJT https://www.pprune.org/images/buttons/viewpost.gif (https://www.pprune.org/pacific-general-aviation-questions/613866-avgas-quality-concerns-helicopters.html#post10262282)
indulge my ignorance but aren't they essentially the same engines?I,m just guessing here but aren't helicopters run pretty hard particularly when mustering. The lead in the fuel is to prevent detonation which is most likely to occur in hot conditions and at high power conditions. Reducing the lead content reduces the octane rating. With helicopters it might have been a tad too far.

[Eddie Dean]

I,m just guessing here but aren't helicopters run pretty hard particularly when mustering. The lead in the fuel is to prevent detonation which is most likely to occur in hot conditions and at high power conditions. Reducing the lead content reduces the octane rating. With helicopters it might have been a tad too far.You have nailed the issue.

[Bend alot]

While I don't fly helicopters nor do mustering I have been told that during mustering mostly it is not high power used. Lots of manoeuvring yes, but cows don't run very fast.

Detonation I would expect would cause damage to the pistons (holes), what seems to be reported is accelerated wear of the cylinders. I assume this wear is the sidewalls and/or piston rings possibly valves, guides and seats could be included.

So I think it is something other than detonation.

Is the issue similar across carburettor and fuel injected engines?

AWB 85-024 Issue 1 - points to exhaust and guide as the area of damage and wear.

[Ascend Charlie]

The other difference, is that in a fixed wing, if the engine coughs and stops momentarily, the windmilling propellor turns the engine over and allows it to fire again.

In an Uptycopter, there is a freewheel unit that does not allow the rotor to drive the engine, so if it coughs and stops, you are on the way down with probably no time to try a restart. You need altitude to establish an autorotation, left hand off the collective, crank the starter switch, with no spare hand to manipulate the throttle, unless you can get the cyclic between your knees. Very unforgiving of fuel contamination, starvation, or poor quality.

[rutan around]

AWB 85-024 Issue 1 - points to exhaust and guide as the area of damage and wear.

This sounds like too much heat to me and lends strength to the idea that the fuel doesn't have enough lead in it. An often misunderstood area of spark ignition combustion is how lead works to prevent / reduce knocking. People think it slows the burn rate down. Actually it slows down the start of burning after the ignition spark.(Ignition lag) Once the burn gets going it burns at the same rate as unleaded fuel.(Think of starting a damp campfire and a dry one. The damp one is slow to start but once going properly it burns the same as the dry one) This reluctance to start burning delays the start of auto ignition we call knocking.

If an engine is timed for fuel with a particular amount of lead and then a new fuel with less lead is used, then the timing will be wrong. The quicker ignition of the low lead fuel will have the same effect as advancing the timing. Advancing the timing means peak cylinder pressure occurs earlier and transfers excessive heat and pressure to the cylinder,piston and valves. If it goes on long enough it will do internal damage.

Some engines are more forgiving than others when it comes to timing range but a hard working one with barely adequate cooling probably not so much.ignition lag. [ig′nish·ən ‚lag] (mechanical engineering) In the internal combustion engine, the time interval between the passage of the spark and the inflammation of the air-fuel mixture. Also known as ignition delay.

[Bend alot]

rutan - I was taught that lead also assisted in heat removal by the unburnt fuel air mixture out of the cylinder.

It appears that for some reason the exhaust valve and its guide area are now getting and remaining hotter than they use to, given that it is not just Lyco' but also PMA cylinders and even TCM's. I can only conclude that it is pilot error in operation of engines. ( I have my AWI interview next week).

[A Squared]

While I don't fly helicopters nor do mustering I have been told that during mustering mostly it is not high power used. Lots of manoeuvring yes, but cows don't run very fast.




Well, I don't fly helicopters or muster cattle either, but that said, I would guess that it would be at high power quite a bit of the time. I would expect that mustering would necessarily involve being in a hover a significant part of the time and hovering tends to require higher power than cruise. And not only would they be hovering but doing a fair amount of maneuvering in a hover which I'd expect to increase the power requirements. But, I haven't been involved in such operations, so I'm speculating here.

[A Squared]

Actually it slows down the start of burning after the ignition spark.(Ignition lag) Once the burn gets going it burns at the same rate as unleaded fuel.

If that is literally true as stated, I've just solved the aviation leaded fuel issue: Simply remove all the lead and retard the ignition on all the engines.

[Bend alot]

From the people that I know that do mustering in R22 they say it is not high power more the noise and slowly moving them forward. If power was indeed used often then the carburettor machines would have long ago been replaced with the fuel injected models.

I guy I know that bent his machine (an owner operator musterer) had the option to go the fuel injected way but could not make a case for the extra cost.

[tio540]

Quote. “Can I fly my lighty if the temp exceeds 40°C yet”?

Megan, 20.7.4 is quite clear on this.

[rutan around]

A squared says
I've just solved the aviation leaded fuel issue: Simply remove all the lead and retard the ignition on all the engines.

You forgot the reason lead is added to fuel. It's to stop detonation during the normal power range of a properly timed engine. You could certainly correct the timing BUT at high power settings combined with a hot day and or a long climb you would get detonation if the octane rating was too low. The lead slows down or stops auto ignition ahead of the flame front. It's a public holiday here in Australia for QE2s birthday. Having toasted her health you're doing my head in answering technical issues this late in the day.:}

[John Eacott]

rutan - I was taught that lead also assisted in heat removal by the unburnt fuel air mixture out of the cylinder.

It appears that for some reason the exhaust valve and its guide area are now getting and remaining hotter than they use to, given that it is not just Lyco' but also PMA cylinders and even TCM's. I can only conclude that it is pilot error in operation of engines. ( I have my AWI interview next week).

I wouldn’t expect an Air Warfare Instructor to know better ( ;) ) but to reef this back as pilot error shows a total lack of understanding of helicopter operation and engine management. This has been extant for some 18 months and change to fuel additives is clearly being associated with the failures: that they are occurring in helicopters can be attributed to the lower cooling available plus the higher power demands, which are not related to airspeed but to handling requirements in a low level environment.

[Bend alot]

Low in hot ambient air temps and constant large power changes in slow moving helicopters mostly seems a large factor.

Sadly not many of these aircraft have multi egt and cht devices fitted, but even then we could be looking at a heat change just 2 inches from the previous point with a new fuel.

[Bend alot]

I wouldn’t expect an Air Warfare Instructor to know better ( ;) ) but to reef this back as pilot error shows a total lack of understanding of helicopter operation and engine management. This has been extant for some 18 months and change to fuel additives is clearly being associated with the failures: that they are occurring in helicopters can be attributed to the lower cooling available plus the higher power demands, which are not related to airspeed but to handling requirements in a low level environment.
I was pullin the bit on the AWI - but that is because CAsA seem to be sitting on the fence on a known decrease in safety on this - so instead of doing something Blame the Pilots!

Again I am told that high power is not a requirement of most muster operations in R22 or R44, power changes and manoeuvrability are attributes of a muster operation in helicopters. This is certainly true in fixed wing that I have been a pax in a 172, would love to see a 210 or even a 208 do a muster.

[rutan around]

but to reef this back as pilot error shows a total lack of understanding of helicopter operation and engine management.

I totally agree. It is a nonsense to think that suddenly a whole bunch of chopper pilots adopted new SOPs that were damaging their engines. If the lead content of their fuel has changed it's a likely culprit. From time to time engine manufacturers make changes to the detriment of owners pockets. High wall pressure rings by Continental and crankshaft material change by Lycoming are two that come to mind. This does not seem to be the case this time because it would have to be very flukey that both companies did something stupid at exactly the same time.

[Lead Balloon]

If that is literally true as stated, I've just solved the aviation leaded fuel issue: Simply remove all the lead and retard the ignition on all the engines.That would work to ‘by pass’ the problem that lead solves.

But, alas, the engines would no longer make their rated power.

There is usually no simple solution to a complex problem.

[A Squared]

You forgot the reason lead is added to fuel. It's to stop detonation during the normal power range of a properly timed engine.

Ahhh, so you agree that lead affects the combustion of the fuel charge beyond merely delaying ignition then. ;)

[Tankengine]

Ahhh, so you agree that lead affects the combustion of the fuel charge beyond merely delaying ignition then. ;)
Does not lead aid in piston-cylinder lubrication as well?

[Eddie Dean]

Does not lead aid in piston-cylinder lubrication as well?
The OWT rears it's ugly head once again. No it does not provide lubrication.
The mustering machines are worked very hard.
The recording of flight hours leaves a lot to be desired.
Low time pilots are the norm for the industry.
If it still flies it must be serviceable.

The damage to the valves is indeed interesting, there doesn't appear to be pounding of the seat or tuliping of the valve head.
The broken/pitted edges seems more mechanical damage rather than over heating.

FWIW

[machtuk]

Does not lead aid in piston-cylinder lubrication as well?






It does indeed have some effect on lubrication whether that be directly or from the result of other factors like cooling.
Piston engine fuel itself is also an aid to lubrication/cooling, a change in the fuel chemistry maybe having an effect as seen.
I think most agree here that IC powered piston Helicopters especially in the mustering role in hot dusty conditions are subject to a multitude of stresses such as high power settings changing constantly with varying operating temps & environmental conditions hence the high maint required on these machines. Perhaps that seeing as there is a perceived increase of late of rapidly deteriorating engines (due whatever actual reason/s) the maint sched needs to be increased?

[Eddie Dean]

Machtuk Perhaps that seeing as there is a perceived increase of late of rapidly deteriorating engines (due whatever actual reason/s) the maint sched needs to be increased?
Perhaps the Lycoming servicing schedule should be adhered to, including the first 100 hour inspection criteria after overhaul/initial fitment.

[megan]

Megan, 20.7.4 is quite clear on this Well, it seems not tio540. CASA issued a letter forbidding operation above 40C, to which I personally replied, with clarification rebutting their argument obtained from the manufacturer (Cessna). That's about twelve months ago, I'm still awaiting a reply.

There is even a thread on the subject.

https://www.pprune.org/pacific-general-aviation-questions/593322-casa-opinion-aircraft-must-grounded-temps-over-40-degrees.html?highlight=40%B0C

[tio540]

Well, it seems not tio540. CASA issued a letter forbidding operation above 40C, to which I personally replied, with clarification rebutting their argument obtained from the manufacturer (Cessna). That's about twelve months ago, I'm still awaiting a reply.

There is even a thread on the subject.

https://www.pprune.org/pacific-general-aviation-questions/593322-casa-opinion-aircraft-must-grounded-temps-over-40-degrees.html?highlight=40%B0C

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.

[ivan ellerbai]

The recording of flight hours leaves a lot to be desired.

Really? That's hard to believe :rolleyes:.

[rutan around]

Machtuk says,
Piston engine fuel itself is also an aid to lubrication/cooling,

Where did you get that idea? Just for starters if it's such a good lubricant why do bores wear if you run far too rich or in a car with the choke on.

As to the current problem wouldn't it be a good idea to look at what has changed in the last 18 months and what hasn't changed. If the same pilots are flying the same choppers in the same way they have been flying them for years it's hardly likely to be an operational problem. Has the fuel changed? Is it only effecting engines overhauled in the last couple of years? Is it effecting engines across the board? If it's only effecting new and fairly recently overhauled engines then maybe the cylinder manufacturers are playing silly buggers and experimenting with new ideas all the while using their customers toe beta test their ideas.

AXA says: Ahhh, so you agree that lead affects the combustion of the fuel charge beyond merely delaying ignition then

Yes of course. It delays the onset of detonation. What should be taken from this is that changing fuels should not be taken lightly and timing varies with different fuels. When you chop and change fuel in a modern car it doesn't matter because they have knock detectors and the cars computer takes care of the problem.I don't personally know of any aircraft engine with a knock detector but there may be some.

[kaz3g]

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.

Glad I fly an aircraft that doesn’t have an afm ( exempt).

[Octane]

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.

[A Squared]

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.

[Eddie Dean]

Major issue with piston engines in our mustering helicopters turns into another diatribe against the regulator.

[Lead Balloon]

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?

[Sunfish]

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?

[Art E. Fischler-Reisen]

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.

[Connedrod]

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.

[aroa]

Sunny...no 'perhaps think' about it !!
CAsA most certainly IS a proven 'institutional coward'

[rutan around]

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.

[A Squared]

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.

[Lead Balloon]

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.

[Eddie Dean]

What Lead Balloon said

[rutan around]

What Lead Balloon said.:D
The cylinders and valves are not hurt by natural gas or propane because their octane rating is above 100

[Eddie Dean]

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?

[Connedrod]

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 !!!!!

[Lead Balloon]

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.

[megan]

Something old is new again?

https://www.flightglobal.com/pdfarchive/view/1975/1975%20-%202701.html

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

https://www.flightglobal.com/pdfarchive/view/1934/1934%20-%201389.html

[Bend alot]

Removing the lead in the fuel to C441's gives the same engine problems in the north, from what I hear Eddie.

[LeadSled]

Something old is new again?

https://www.flightglobal.com/pdfarchive/view/1975/1975%20-%202701.html

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

https://www.flightglobal.com/pdfarchive/view/1934/1934%20-%201389.html

I have an old bronze head from a Gipsy Major that I use for a bookend!!
Tootle pip!!

[Connedrod]

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.

[Eddie Dean]

Removing the lead in the fuel to C441's gives the same engine problems in the north, from what I hear Eddie.
That is good to hear, I was starting to think it is an operator problem

[Bend alot]

Chemistry of things like fuel have benefits and penalties in achieving a target such as a "octane rating"

They are not tabled as such as they are by products of a requirement of the fuel.

Changing any part of the chemistry can keep the same "octane rating" and other performance items like say burn speed.

But can have massive changes on other things due to chemistry change - say more acidic for example, that brings on corrosion in humid conditions on valve faces that accelerates wear.

A single atom can change things dramatically.

Lead seems to have effects on cooling and lubrication in certain applications as a by product.

[LeadSled]

Folks,
Cessna 441 --- leaded fuel, am I missing something here, or has somebody been re-engining Conquests??
Tootle pip!!
PS: Years ago now, but persistent engine/fuel system problems due fuel quality is why Qantas Eastern got rid of Titans, with a policy decision of no more petrol burners. As we found out later the problem was EDA.

[Bend alot]

Folks,
Cessna 441 --- leaded fuel, am I missing something here, or has somebody been re-engining Conquests??
Tootle pip!!
PS: Years ago now, but persistent engine/fuel system problems due fuel quality is why Qantas Eastern got rid of Titans, with a policy decision of no more petrol burners. As we found out later the problem was EDA.

Yep you missed passed comments on a C441 fuel issue witnessed by a poster (here) on another thread that we still await to hear about its fuel issue from the ATSB.

The lack of lead allowed a massive fungal growth in the fuel tanks!!

[Andy_RR]

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.


This is kind of true but not really very illuminating. Knock/detonation excites the resonant frequencies of the gas in the combustion chamber causing the gas to oscillate back and forth in varying patterns at the fundamental and higher order harmonic frequencies. There are many different modes to this oscillating pattern but the pressure wave that is generated needs an associated gas velocity to make it happen so yes, when a pressure peak arrives to one side of the piston crown the gas will be stuffed down the side of the ring land - that's what makes the pressure happen. It's the velocity of the gas that disturbs the boundary layer and causes the increased heat transfer rates associated with symptoms of higher CHTs.

The higher the knock pressure amplitude the faster the gas has to move so heavy knock is associated with high local gas velocities and thus high heat transfer. The local pressure of the wave against the combustion chamber can also fatigue the material (which at higher temperatures also has a lower tensile strength and therefore fatigue strength) causing pitting associated with knock damage.

[LeadSled]

Yep you missed passed comments on a C441 fuel issue witnessed by a poster (here) on another thread that we still await to hear about its fuel issue from the ATSB.

The lack of lead allowed a massive fungal growth in the fuel tanks!!

?? So the Conquest was burning Avgas 100LL (which I assume is an alternative fuel) instead of Jet A. Why would you do that, except when Jet A is not available?
Or am I still missing something ---- how did piston engine problems possibly consequent on a change to Avgas 100LL constituents rope in Conquests??
Tootle pip!!

[megan]

Leadie, the smart asses are commenting on a Conquest that had both motors stop due to lack of fuel. You're not missing anything. :ok:

[Bend alot]

megan - more the comments of an eye witness of the 441 that make me question a posters comments and knowledge.


"There was no fuel uplifted on the highway. Unless of course there is a secret squirrel method of doing this."

[LeadSled]

Leadie, the smart asses are commenting on a Conquest that had both motors stop due to lack of fuel. You're not missing anything. :ok:

Megan,
This gives a whole new meaning to "thread drift".
Tootle pip!!

[Bend alot]

Chemistry of things like fuel have benefits and penalties in achieving a target such as a "octane rating"

They are not tabled as such as they are by products of a requirement of the fuel.

Changing any part of the chemistry can keep the same "octane rating" and other performance items like say burn speed.

But can have massive changes on other things due to chemistry change - say more acidic for example, that brings on corrosion in humid conditions on valve faces that accelerates wear.

A single atom can change things dramatically.

Lead seems to have effects on cooling and lubrication in certain applications as a by product.


Back on track back here - it is very hard to post as a "new here member" when not new member waffle a bit and need to be reminded that even if they "eye witness" they can be wrong and at times admit they are.

So I will say the safety in certain aircraft has been reduced. Hot maybe humid and a reduction in lead can be a factor for this - lead was not added for cooling or anti wear on exhaust valves but it seems to have an effect when reduced - why I don't know. How is aircraft safety regulated in Australia?

Not Shell!

[Art E. Fischler-Reisen]

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.

I find it very strange that you think that. There is plenty of evidence that engines run on LPG need hardened valve seats and those that don't have them are likely to suffer valve seat recession and valve burning.
I first came across this in the early 1970s. My fiance's father had an almost brand new Leyland Mini van that he had professionally converted to LPG. Within weeks it began misfiring. The company who carried out the LPG conversion wouldn't take responsibility. I was asked to take a look. I removed the cylinder head and the valves and seats were already showing damage. The A series engine was one of those that had the seats cut directly in the cast iron head; it became a well known problem in later years on that type and on some other engines.

Valve Seat Recession Explained (http://www.amrautos.co.uk/index.php/lpg-systems/26-valve-seat-recession-explained)

Earlier this year I had to have a new exhaust valve seat fitted to a single cylinder motorcycle engine (Royal Enfield) because it had recessed; the valve was also damaged beyond further use. The only explanation I can think of is that the seat was too soft to be used on unleaded fuel; the exact type was never officially imported to my country (Indian home market bike) and it's possible the fuel formulation is different.

I can't explain the molecular effects because I'm not a chemist but I certainly do know what I've experienced first hand.

[A Squared]

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.


What Lead Balloon said.:D
The cylinders and valves are not hurt by natural gas or propane because their octane rating is above 100

As has already been explained, ‘unleaded’ propane or natural gas didn’t cause valve recession.



Actually, Valve seat recession is a significant, well known and well documented problem with piston engines converted to petroleum gas fuel. You folks probably ought to stop using that as your "most convincing argument" as 30 seconds with Google shows that it's not true.

[Lead Balloon]

Nobody said that valve seat recession wasn’t a problem.

What we said was that the cause of the problem was not the absence of lead.

What we said was that the cause of the problem was heavy detonation and high CHT that resulted from putting lower octane fuel in engines designed for higher octane fuel.

You should spend 30 seconds actually reading what we said.

[A Squared]

Nobody said that valve seat recession wasn’t a problem.

What we said was that the cause of the problem was not the absence of lead.

What we said was that the cause of the problem was heavy detonation and high CHT that resulted from putting lower octane fuel in engines designed for higher octane fuel.

You should spend 30 seconds actually reading what we said.


You probably ought to refrain from saying "nobody" and "we" because the other guy very clearly was claiming that valve recession is not a problem in PG fuel engines. (Which is quite demonstrably not true) I will quote again, his precise words, as you appeared to miss it the first time I quoted them: 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. Now, I will concede that your own repeated references to valve recession in PG fueled engines, in the same discussion, were a little more ambiguous, and that when you said: As has already been explained, ‘unleaded’ propane or natural gas didn’t cause valve recession.
that it could have been just a poor choice of words, that you didn't really mean that valve seat recession is not a problem in PG fueled engines, and you didn't intend to interject that as a means of demonstrating that the lead itself had no direct affect on valve recession, but it certainly appears that way to me. If I misunderstood your purpose for making those statements, I am now left wondering what your point was for those statements? If you now agree that valve seat recession was a problem in PG engines, as it was in the first unleaded gas engines (pre-hardened valve seats) then you must also agree that it doesn't prove that lead was not the factor which prevented valve seat recession? So, what is your purpose of referring to it repeatedly in the discussion?

[Sunfish]

It could be that lead forms some sort of intermetalic layer on the valve and seat that has a protective effect, but we don't know that. the real question to ask is how has the fuel composition changed because the change HAS to be the cause of the damage, no matter the octane rating or performance characteristics.

[Lead Balloon]

What was the octane rating of the “PG fuel” to which you referred, A Squared? I certainly agree that if it wasn’t sufficient for the engines in which it was used, it too would cause detonation and higher CHT and valve seat recession, thus proving (again) that it wasn’t the absence of lead that caused the recession.

PS: My apologies A Squared. I now realise the last bit of the last sentence does not necessarily follow logically.

[rutan around]

AEFR posted:
in the early 1970s. My fiance's father had an almost brand new Leyland Mini van that he had professionally converted to LPG. Within weeks it began misfiring. The company who carried out the LPG conversion wouldn't take responsibility. I was asked to take a look. I removed the cylinder head and the valves and seats were already showing damage.

I'm not disputing that valve recession was a problem. I am disputing why. In the 1970s LPG conversions were not very sophisticated .While I can't vouch for it's accuracy the article below is a possible explanation for your fiance's fathers Mini van problem.

http://www.acl.com.au/web/acl00056.nsf/0/359683e8a538a3e64a2566c0007bb33e?OpenDocument

[andrewr]

What was the octane rating of the “PG fuel” to which you referred, A Squared? I certainly agree that if it wasn’t sufficient for the engines in which it was used, it too would cause detonation and higher CHT and valve seat recession, thus proving (again) that it wasn’t the absence of lead that caused the recession


LPG is much higher octane than petrol. As a rule, lighter fuels are higher octane: diesel = low octane, gasoline = medium octane, gas = high octane. LPG could be as high as 115 octane. Engines designed to run exclusively on gas typically run higher compression ratios than petrol or dual fuel engines e.g. the EcoLPi Falcon had 12:1 compression ratio, the petrol version was 10.3:1.

It would be a strange sort of detonation that only damaged the exhaust valve with none of the other damage typical of detonation.

[Art E. Fischler-Reisen]

Rutan,

No I don't think so. I've been building and tuning engines (and modifying the advance curves of Lucas distributors) for well over 40 years. My bedside bookshelf is full of engine tuning manuals from a whole range of authors. I also used to teach piston engine theory to RAF student pilots. I've never seen any evidence that a less than optimum ignition timing setting causes valve seat wear. If ignition timing were drastically incorrect, i.e. too far advanced, detonation would be the immediate result. If too little advance, the result is less than optimum engine performance. Generally speaking, a higher octane fuel can tolerate a more advanced ignition setting.

On the other hand there is a great deal of evidence that the removal of TEL from petrol for environmental reasons resulted in rapid valve seat recession on many older engines. Many of them had to be retro-fitted with good quality, hardened steel valve seats (as did my old design motorcycle engine a few months ago). LPG obviously contains no TEL.

AVGAS contains a relatively large amount of TEL, even the advertised "Low Lead" (LL) quality (a reduced amount compared to that from years gone by, but still about five times the amount that the old 4 star road fuel had). Some years ago I experimented with an unleaded / LL AVGAS mix in a very high compression competition engine I had built (it was quite common to do this). I researched this and was surprised to learn that I only needed about 1 gallon in 5 of unleaded to bring the octane rating up to the desired level. The engine loved it. What surprised me was that the colour of the inside of the tail pipe went from black to grey with just one tankful, as did the plug colour, just as in the old days of "proper" leaded fuel.

LPG naturally has a very good octane rating but is known to cause valve problems on some engines (see the list in the link below) because it is generally seen as a "dry" fuel. I have a brand, old stock Lucas distributor originally intended for an LPG engine (Land Rover) in my garage. I used to collect new old stock to dismantle them for parts or just use the bodies to build on. I stripped it down but I soon discovered that it has considerably more total advance (taking into account both mechanical and vacuum) than those required for any petrol engine I've come across.

Valve Seat Recession Explained (http://www.amrautos.co.uk/index.php/lpg-systems/26-valve-seat-recession-explained)

Here's another interesting link:
LPG Problems (http://www.amrautos.co.uk/index.php/lpg-systems)

[rutan around]

AEFR
If ignition timing were drastically incorrect, i.e. too far advanced, detonation would be the immediate result.

Not necessarily. If the octane rating of the fuel is high enough it won't detonate. However if the timing is too far advanced ie the fire is lit too early all the fuel will be burnt at or even before top dead centre. This means peak pressure occurs early and, at first, is doing negative work until the piston is past TDC and can begin to move down and do some useful work. The lengthy time (relatively) that peak pressure (and high heat) are in the cylinder's head transfers much more heat to the enclosing metal before the valve opens and dumps the exhaust gas and cooling can begin. It is the heat doing the damage.

How did you address the problem of different flame front speeds for the different fuels?

[Bend alot]

Rutan!

"However if the timing is too far advanced ie the fire is lit too early all the fuel will be burnt at or even before top dead centre."

Name the Chopper that runs lean mixtures? - never is all fuel burnt any place near TDC or much later at BDC - they run a rich mixture in every case I am aware (no LOP).

[rutan around]

Bendy,
never is all fuel burnt any place near TDC or much later at BDC

My post wasn't about rich or lean mixtures. It was about incorrect timing for a particular fuel and how the head could get hot enough to cause valve recession. Without good data relating to where peak pressure occurred at various revs, what that pressure was and the actual CHTs at different revs it's drawing a long bow to blame lack of lead in LNG or propane for internal damage to heads. Taxi cab owners aren't noted for being silly with their money yet they continued to do gas conversions until gas became too expensive and hybrids became available.

[andrewr]

Taxi cab owners aren't noted for being silly with their money yet they continued to do gas conversions until gas became too expensive and hybrids became available.

And it is well known that gas conversions need hardened valve seats to avoid valve recession. If the engine doesn't have suitable seats installed from the factory, there are people who will build special cylinder heads or install hardened seats into an existing head.

Advanced timing is more likely to damage other components (e.g. the piston, which has much less cooling than the head) than the valve. The exhaust valve is much more likely to be damaged by retarded timing, because there is more heat in the gas while the valve is off its seat. When the valve is closed it is cooled through the seat, when it is open is the time when heat can be a problem.

It is hard to imagine an (advanced) timing or detonation problem that would damage the valve before the much less robust piston.

[Bend alot]

Bendy,


My post wasn't about rich or lean mixtures. It was about incorrect timing for a particular fuel and how the head could get hot enough to cause valve recession. Without good data relating to where peak pressure occurred at various revs, what that pressure was and the actual CHTs at different revs it's drawing a long bow to blame lack of lead in LNG or propane for internal damage to heads. Taxi cab owners aren't noted for being silly with their money yet they continued to do gas conversions until gas became too expensive and hybrids became available.

Just state at what part of the cycle (rough degrees 0-360) that this comment of yours is possible.

"However if the timing is too far advanced ie the fire is lit too early all the fuel will be burnt at or even before top dead centre."

[Eddie Dean]

Rutan!

"However if the timing is too far advanced ie the fire is lit too early all the fuel will be burnt at or even before top dead centre."

Name the Chopper that runs lean mixtures? - never is all fuel burnt any place near TDC or much later at BDC - they run a rich mixture in every case I am aware (no LOP).Are you sure that "chopper" engines run rich mixtures? Rootin around is correct about too far advanced timing causing the fuel to be consumed too early. FWIW.
And BTW if you re read my comments in the Broome incident, I said ONLY that whilst I was stopped beside the aircraft the bloke with the wings and stuff on his shirt said hadn't loaded any fuel and while I waited saw no fuel being loaded.
You seem to regard any discussion as a reason to start willy wagging, in that case you win I have a little one.

[Ascend Charlie]

Eddie, choppers like the R22 and R44 have a collar placed over the mixture control to prevent it being inadvertently pulled away from Full Rich while applying cyclic trim, and also to stop people leaning the mixture.

In your plank you can lean the mixture until it runs rough and then advance it a bit - the prop keeps the engine turning over if you go a bit far.
In a chopper if the engine coughs it will stop and will not restart unless the pilot takes specific actions which consume time and altitude.

[megan]

In a chopper if the engine coughs it will stop and will not restart unless the pilot takes specific actions which consume time and altitude Tell me about it, rich cuts while doing autos, likely you too AC.

[Eddie Dean]

Eddie, choppers like the R22 and R44 have a collar placed over the mixture control to prevent it being inadvertently pulled away from Full Rich while applying cyclic trim, and also to stop people leaning the mixture.

In your plank you can lean the mixture until it runs rough and then advance it a bit - the prop keeps the engine turning over if you go a bit far.
In a chopper if the engine coughs it will stop and will not restart unless the pilot takes specific actions which consume time and altitude.Wasn't talking about manual mixture control or cutoff was referring to the Carburettor internal settings which closer to stoichiometric than rich.

[rutan around]

Bendy asks:-
Just state at what part of the cycle (rough degrees 0-360) that this comment of yours is possible.

My answer is "I don't know" However if you supply all the factors listed below and shout me a weekend in the USA with George Braly I'll have a stab.:E
I will guess it wouldn't take too many degrees of advance from the optimum setting to cause trouble because pressure and heat have a big effect on flame speed. It becomes a vicious circle. The spark is early so the fire starts early and the pressure builds sooner than it should. The higher pressure speeds up the flame front and so peak pressure occurs many degrees before the desirable 10* to 15* after top dead centre.https://qph.fs.quoracdn.net/main-thumb-197897587-50-hpborklgkjxttofntmszqvzwyfcgtlrg.jpeg (https://www.quora.com/profile/Krishnamani-Selvaraj)Krishnamani Selvaraj (https://www.quora.com/profile/Krishnamani-Selvaraj), M.E Internal Combustion Engines, College of Engineering Guindy, Tamil Nadu, India (2007
The combustion characteristics of an I.C engine(petrol and diesel) significantly depends on the ignition delay. In the petrol engine ignition delay or lag is the time between initiation of spark and the time of ignition. Whereas in the diesel engine, it is the time between start of fuel injection and the time of ignition. Since the combustion is heterogeneous in the diesel engine, the delay period is long as compared to the petrol engine.The delay period is the main factor influences the flame speed in the I.C. engine. some of the factors determine the flame speed are:

compression ratio 2. Engine speed 3. Engine load 4. Spark timing in petrol engine and Fuel injection timing in diesel engine. 5. Fuel injection pressure in diesel engine 6. properties of fuel like viscosity, volatility, octane number for petrol ,cetane number for diesel and surface tension 7. type of combustion chamber in the engine. 8. properties of coolant. The engine knocking mainly occurs due the presence of higher flame speed. The delay period should be as long as possible for petrol engine for smooth engine operation and for diesel engine the delay period should be as short as possible.

[Art E. Fischler-Reisen]

AEFR


Not necessarily. If the octane rating of the fuel is high enough it won't detonate. However if the timing is too far advanced ie the fire is lit too early all the fuel will be burnt at or even before top dead centre. This means peak pressure occurs early and, at first, is doing negative work until the piston is past TDC and can begin to move down and do some useful work. The lengthy time (relatively) that peak pressure (and high heat) are in the cylinder's head transfers much more heat to the enclosing metal before the valve opens and dumps the exhaust gas and cooling can begin. It is the heat doing the damage.

How did you address the problem of different flame front speeds for the different fuels?

I adjusted the ignition timing. Have you never tuned an engine?
A higher octane fuel can tolerate more ignition advance and/or a higher compression ratio. The best output of a spark ignition engine is obtained by experimentation with the timing; it's by no means unusual for the limiting factor on engine performance to be detonation. Retarding the timing is the easiest way to alleviate that problem but obviously it can be solved by use of a higher octane rated fuel where available; it is still possible to buy TEL in the form of an additive. It can also be done by richening the mixture, or in extreme cases by reducing the compression ratio, such as by fitting a decompression plate.

[Bend alot]

I don't think any of these choppers pilots or engineers are experimenting or "tuning" the affected engines any different than they have been.

They also don't run any place near stico - THEY RUN RICH!

Full rich during the mustering 100% for sure as 3 armed pilots are not common, many power changes.

[LeadSled]

----3 armed pilots are not common, many power changes.
Just as well, I wonder does CASA know about any number of armed pilots, they take a particularly dim view of firearms airborne.
Tootle pip!!

[A Squared]

So, tell me again how mustering is a docile activity that doesn't use much power ...

[Bend alot]

Just as well, I wonder does CASA know about any number of armed pilots, they take a particularly dim view of firearms airborne.
Tootle pip!!

I think you will find that it is CASA that supply's the letters to pilots to fast track being able to buy and carry single handed cannons around and many/most mustering helicopters and even fixed wing aircraft pilots carry the hand guns.

Some property owners request the pilots to cap the stubborn bulls so they don't teach the other cattle - that takes a fair calibre gun. I also know a chopper charter company that the pilot carried a pistol in a holster on his belt for his and passenger safety.

Thats it! it is the carriage of the lead around that effects the Top End aircraft! - carry the spare bullets in the fuel tank and problem solved.

[LeadSled]

Bend A Lot,
A bit of thread drift, but I was having a go, via a bit of an in joke, re. various attempts, over the years, for CASA to legislate against fitting up your Drifter or C-150 as some kind of a flying gun platform. When asked, repeatedly every time it appears in a draft, where this problem has been encountered, complete silence, and claims of preemptive legislation for an emerging threat??, I have always had a bit of a chuckle.
And a further chuckle about the likelihood of airborne stockperX in their R-22 Gunship strafing rogue bulls.
Tootle pip!!

[Bend alot]

The drifter is a great gun platform, just I was not a great shot. As for the 150, only seen results of it being a gun target.

Yes the old thread drift!

It will be interesting to find out the cause (more the science behind the cause) of this engine wear - but that may not happen.

[LeadSled]

The drifter is a great gun platform, just I was not a great shot. As for the 150, only seen results of it being a gun target.

Yes the old thread drift!

It will be interesting to find out the cause (more the science behind the cause) of this engine wear - but that may not happen.

Bend a lot,
My apologies for more thread drift --- I should have made it clearer, the CASA "serious concern" was guns fixed to the airframe, remotely fired by the pilot, hence my reference to "gunships".
Tootle pip!!
PS: Many, many years ago, there was an attempt to fire a Bren gun from the front seat of a Tiger Moth, the "target" was a very big eagle that had been savaging new born lambs around Gunnedah. The eagle was quite safe, which is more than could be said for the LH aileron at the first and only attempt.

[Frontal Lobotomy]

Tried to imagine during a flight this morning what it would be like if the pax in the front had a bren gun hanging out the side. Reckon they were lucky all they took out was the LH aileron. Only fired one once but I seem to remember the recoil was forward.

[A Squared]

v Only fired one once but I seem to remember the recoil was forward.


Oh yeah? Bullets must have been flying out of he back of the gun then ... or Newton was mistaken. One or the other.

[Frontal Lobotomy]

A Squared Yes it sounds like garbage but: "the recoil of the weapon tended to pull the weapon forward, when firing on automatic it would "walk" away from the firer".

Apologies for the thread drift.