Idle power & it's effects
Joined: Apr 2009
Posts: 247
Likes: 0
From: New Zealand
Flybymike, despite your instructor's experience being far greater than my own, in my opinion the phrase
is not a smart one.
There are pages and pages of good discussion regarding leaning on Pprune, and many more elsewhere (Avweb being excellent). Too much fuel fouls plugs and valve guides, possibly leading to gliding! Likewise running out of fuel leads to gliding! I've developed a dislike for 'cute' phrases like the above because it often over simplifies an important subject.
Anyway, sorry for hijacking, this be about idle and taxi (but you can/should still lean on the ground!), but my childlike fascination with leaning and engine management takes over.
"Fuel is cheaper than engines."
There are pages and pages of good discussion regarding leaning on Pprune, and many more elsewhere (Avweb being excellent). Too much fuel fouls plugs and valve guides, possibly leading to gliding! Likewise running out of fuel leads to gliding! I've developed a dislike for 'cute' phrases like the above because it often over simplifies an important subject.
Anyway, sorry for hijacking, this be about idle and taxi (but you can/should still lean on the ground!), but my childlike fascination with leaning and engine management takes over.
Joined: Jan 2001
Posts: 5,982
Likes: 1
From: In the boot of my car!
Torque tonight
I was really making a point that brakes are there to be used when required!
When you land on a fairly short strip a pilot will be fairly hard on the brakes.
There is a mindset that taxiing the brakes are some sort of delicate contraption that should be avoided at all costs which is rubbish,
Obviously you don't ride the brakes with high power settings any more than you would drive your car with one foot on the accelerator and one on the brake,
It is not equally good practice to design your engine management to avoid use of brakes,
The brakes on landing will be used far far harder than anything you will do taxiing,
Pace
I was really making a point that brakes are there to be used when required!
When you land on a fairly short strip a pilot will be fairly hard on the brakes.
There is a mindset that taxiing the brakes are some sort of delicate contraption that should be avoided at all costs which is rubbish,
Obviously you don't ride the brakes with high power settings any more than you would drive your car with one foot on the accelerator and one on the brake,
It is not equally good practice to design your engine management to avoid use of brakes,
The brakes on landing will be used far far harder than anything you will do taxiing,
Pace
Joined: Dec 2007
Posts: 160
Likes: 0
From: UK
700 rpm is the recommended idle setting for a warm small aero engine.
After prolonged running at this rpm, carb icing is a probable cause for stoppage with the throttle closed. The Lycoming 0235 is particularly susceptible to this problem.
After prolonged running at this rpm, carb icing is a probable cause for stoppage with the throttle closed. The Lycoming 0235 is particularly susceptible to this problem.
Joined: Feb 2002
Posts: 2,547
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From: Dublin
700 rpm is the recommended idle setting for a warm small aero engine
Joined: Jan 1999
Posts: 6,209
Likes: 2
From: north of barlu
Flybymikes stupid instructor
It is not often that I come across such stupid statements, to deal with brakes being used to keep control of the speed when the engine is set to 1200 RPM I only have to think of the badly burnt Extra 300 that I inspected in Florida, overheating brakes had set fire to the spats, the resultant fire had resulted in the aircraft being written off.
The fuel cheaper than engines statement also fails to hold water, assuming that the leaning of the engine is carried out badly and that you write off a set of cylinders at half life it much cheaper to change four cylinders that except a 20 % higher fuel burn. Using a Lycoming O-360 as an example over 1000 hours you can save £12960 in fuel costs by leaning the engine rather than running it full rich, a set of new cylinders in is will cost you IRO £ 5500 and fitting will cost IRO £ 800.
This assumes poor engine. Management I am sure that those of you with engine monitoring equipment could run the cylinders to 2000 hours without damage.
The fuel cheaper than engines statement also fails to hold water, assuming that the leaning of the engine is carried out badly and that you write off a set of cylinders at half life it much cheaper to change four cylinders that except a 20 % higher fuel burn. Using a Lycoming O-360 as an example over 1000 hours you can save £12960 in fuel costs by leaning the engine rather than running it full rich, a set of new cylinders in is will cost you IRO £ 5500 and fitting will cost IRO £ 800.
This assumes poor engine. Management I am sure that those of you with engine monitoring equipment could run the cylinders to 2000 hours without damage.
Joined: Jan 2001
Posts: 5,982
Likes: 1
From: In the boot of my car!
A and C
I am sure nobody including Mikes instructor is recommending more than idle power and using brakes to control speed.
Obviously brakes against power for prolonged periods will lead to overheating and fade.
What I thought we were discussing was residual thrust at idle power setting?
I gave an example of a Citation which I fly which does not have thrust reversers.
On level ground with thrust levers at Idle the aircraft will accelerate with residual thrust which means you will have to stab the brakes every so often to keep the speed where you want it.
It is not a fault with this particular Citation but a known common trait.
The same goes for light GA I see nothing wrong with using the brakes to help control speed in the sense of gentle sporadic pressure as required.
That is very different to having a highish idle setting and keeping your foot planted till they overheat and fade.
Pace
I am sure nobody including Mikes instructor is recommending more than idle power and using brakes to control speed.
Obviously brakes against power for prolonged periods will lead to overheating and fade.
What I thought we were discussing was residual thrust at idle power setting?
I gave an example of a Citation which I fly which does not have thrust reversers.
On level ground with thrust levers at Idle the aircraft will accelerate with residual thrust which means you will have to stab the brakes every so often to keep the speed where you want it.
It is not a fault with this particular Citation but a known common trait.
The same goes for light GA I see nothing wrong with using the brakes to help control speed in the sense of gentle sporadic pressure as required.
That is very different to having a highish idle setting and keeping your foot planted till they overheat and fade.
Pace
Fleet Manager
Joined: Aug 2006
Aviation Qualifications: CPL
Posts: 7,090
Likes: 2,952
From: Ontario, Canada
aircraft POH (as I hadn't read through it in full for some years) to find that it recommended warming that engine at 1400-1500rpm, and if a hold was encountered while waiting, to use the same rpm setting.
Joined: Jan 1999
Posts: 6,209
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From: north of barlu
Pace
I don't think that most of the people on this forum fly aircraft that will require more than reducing the power to control the taxi speed on level ground, riding the brakes is usually unnecessary on the types of aircraft that most of this forum readers fly.
The high residual thrust that is exhibited by some turbine types is usually due to the minimum engine RPM required to keep the CSD or IDG on line, the correct way to control the taxi speed in this case is to brake the aircraft almost to a stop and then release the brakes and let the speed build until the taxi speed is such that you need to repeat the process, no doubt instructions will differ between aircraft manufacturers but this seems to be the norm for most of the turbine aircraft that I have flown.
The high residual thrust that is exhibited by some turbine types is usually due to the minimum engine RPM required to keep the CSD or IDG on line, the correct way to control the taxi speed in this case is to brake the aircraft almost to a stop and then release the brakes and let the speed build until the taxi speed is such that you need to repeat the process, no doubt instructions will differ between aircraft manufacturers but this seems to be the norm for most of the turbine aircraft that I have flown.
Joined: Dec 2007
Posts: 160
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From: UK
Idle rpm is when the throttle is fully closed.
Thiis setting is determined by the engineer on engine installation.
This figure is around 500 to 700 rpm and is set to a figure which gives the minimum vibration. This setting allows the engine to continue to run at the end of the landing roll, prior to opening the throttle for taxy.
Thiis setting is determined by the engineer on engine installation.
This figure is around 500 to 700 rpm and is set to a figure which gives the minimum vibration. This setting allows the engine to continue to run at the end of the landing roll, prior to opening the throttle for taxy.
Joined: Jan 2008
Posts: 517
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From: London UK
Going back to the OP:
But at least if does not quit while the aircraft is stationary, it is even less likely to do so while airflow is driving the prop blades. At least, that's what I comfort myself with as I listen to it splutter.
I noticed that when throttle is physically pulled back all the way, the engine doesn't sound "good", as though it's on the verge of quitting.
Joined: Oct 2007
Posts: 120
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From: purley
I find that with my RV6, that even 1000rpm and the aircraft is taxiing too fast, so it is the usual practice of going along then throttling back until slow enough then opening up a bit again and so on. In the Lycoming flyer manual it says that stationary the engine should be run at 1200rpm to keep enough cold air over the cylinders and 1000rpm taxyiing. In my aircraft, I am in the situation where on start up the cylinder head temps get very high before the oil is warm. So I have to be very careful with the gradual warm up of the engine, especially in the winter. This is due to tight cowlings and no cowl flaps like some aircraft for example a Mooney or Beech Bonanza.
Joined: Dec 2007
Posts: 160
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From: UK
500 to 700 rpm is the recommended idle setting for a warm small aero engine.
WARMING is allowing it to reach normal operating temperature, around 1,000 to 1,200 rpm. POH will give the exact figure for specific type.
Joined: May 2001
Posts: 2,118
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Idle rpm is when the throttle is fully closed.
Thiis setting is determined by the engineer on engine installation.
This figure is around 500 to 700 rpm and is set to a figure which gives the minimum vibration. This setting allows the engine to continue to run at the end of the landing roll, prior to opening the throttle for taxy.
Thiis setting is determined by the engineer on engine installation.
This figure is around 500 to 700 rpm and is set to a figure which gives the minimum vibration. This setting allows the engine to continue to run at the end of the landing roll, prior to opening the throttle for taxy.
You must not open the throttle above 700rpm for taxi lest thee burst into flames and perish!Like Pace I simply cannot understand all the angst generated by this stuff. Pootling along at 3 knots and 1200rpm with the occasional dab on the brakes is not going to kill anyone. In 28 years of multi aircraft ownership I can only recall, a couple of pad renewals anyway, and I cannot understand why road vehicles are not exploding all over the place on a daily basis. Their brakes get far more use at far higher speeds than the average puddle jumper. Get a life folks.
