Avgas quality concerns ... helicopters
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).
"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).
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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.
never is all fuel burnt any place near TDC or much later at BDC
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Originally Posted by rutan around
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.
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.
Originally Posted by rutan around
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.
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.
"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."
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Originally Posted by 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).
"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).
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.
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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.
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.
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
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Originally Posted by 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.
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.
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Bendy asks:-
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.
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.
Just state at what part of the cycle (rough degrees 0-360) that this comment of yours is possible.
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.
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:
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.
Originally Posted by rutan around
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?
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?
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.
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.
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.
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Originally Posted by Bend alot
----3 armed pilots are not common, many power changes.
Tootle pip!!
Originally Posted by LeadSled
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!!
Tootle pip!!
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.
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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!!
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!!
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.
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.
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Originally Posted by 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.
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.
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.
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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.
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Originally Posted by Frontal Lobotomy
v Only fired one once but I seem to remember the recoil was forward.
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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.
Apologies for the thread drift.
