Power/RPM on CSP to fly like a boy racer
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Power/RPM on CSP to fly like a boy racer
I was out flying today and wondered what would be the best power and rpm settings to fly with complete disregard to how much fuel I was burning, i.e. flat out at low level at about 1000 AMSL, like a teenager in a suped up Corsa?
The power chart for the plane lists in graphic detail the plethora of pwr/rpm settings for best economy for 55%,65% and 75% power at different altitudes and RPM settings, but how do I achieve flat-out balls to the wall performance over say a 5 minute period (without shagging the engine of course) if indeed that is possible.
Are the following assumptions correct?
1. As I plan on using more than 75% power (its a Lycoming 360) the factory recommends not leaning above this power level, so the mixture is going to stay full rich.
2. I want max power so the throttle is going to be firewalled, say about 29 inches + on a standard day at that level.
3.I want the prop being as efficient as it can be at that power setting so I assume with its rated red line of 2700 RPM I'll want it lower than that so its grabbing more air in level flight, perhaps about 2400 RPM (a higher gear if you will).
This configuration assuming its the best for achieving top speed would leave me in breach of the old unwritten law of never being over square on your your MAP v. RPM although I have also heard this is an old wives tale and you can exceed it within reason (I assume fixed pitch aircraft exceed the MAP v RPM over-square rule all the time on take off)
So am I looking in the wrong end of the telescope or over-thinking this one and the answer is simply red, black and blue knobs firewalled or does anyone have any opposing views or tips on how I might best satisfy my "boy racer" urges?
The power chart for the plane lists in graphic detail the plethora of pwr/rpm settings for best economy for 55%,65% and 75% power at different altitudes and RPM settings, but how do I achieve flat-out balls to the wall performance over say a 5 minute period (without shagging the engine of course) if indeed that is possible.
Are the following assumptions correct?
1. As I plan on using more than 75% power (its a Lycoming 360) the factory recommends not leaning above this power level, so the mixture is going to stay full rich.
2. I want max power so the throttle is going to be firewalled, say about 29 inches + on a standard day at that level.
3.I want the prop being as efficient as it can be at that power setting so I assume with its rated red line of 2700 RPM I'll want it lower than that so its grabbing more air in level flight, perhaps about 2400 RPM (a higher gear if you will).
This configuration assuming its the best for achieving top speed would leave me in breach of the old unwritten law of never being over square on your your MAP v. RPM although I have also heard this is an old wives tale and you can exceed it within reason (I assume fixed pitch aircraft exceed the MAP v RPM over-square rule all the time on take off)
So am I looking in the wrong end of the telescope or over-thinking this one and the answer is simply red, black and blue knobs firewalled or does anyone have any opposing views or tips on how I might best satisfy my "boy racer" urges?
Hi PB.
Assuming there is nothing to the contrary in the POH, you should get maximum speed at full throttle/max rpm, and mixture adjusted just enough for smooth running(if necessary) Most normally aspirated Lycomings can run at these settings until the fuel runs out.
Although it is conventional to run with square power settings, this is just a convention, and you can run most normally aspirated Lycomings with up to 4 units 'oversquare' eg. 29"/2500rpm.
The fuel flow in USgph at full throttle and max rpm should be about equal to the max horsepower divided by 10. eg. 200hp = 20 USgph.
Do check the limitationms in your POH though!.
MJ
Assuming there is nothing to the contrary in the POH, you should get maximum speed at full throttle/max rpm, and mixture adjusted just enough for smooth running(if necessary) Most normally aspirated Lycomings can run at these settings until the fuel runs out.
Although it is conventional to run with square power settings, this is just a convention, and you can run most normally aspirated Lycomings with up to 4 units 'oversquare' eg. 29"/2500rpm.
The fuel flow in USgph at full throttle and max rpm should be about equal to the max horsepower divided by 10. eg. 200hp = 20 USgph.
Do check the limitationms in your POH though!.
MJ
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Be cautious if its turbocharged as some were time limited at max and there is also the danger of overboost
In a Seneca I used to experiment and on a very long runway set climb power for take off then didn't touch it for takeoff, climb, or cruise.
It was quite smooth for the PAX as there were no power noise changes But it was just experimenting and not a realistic way of operating.
On a normally aspirated engine always be aware of leaning some high altitude airfields you need to lean for takeoff so always lean as it will always find its level even if leaning ends up as full rich
I think there has always been a reluctance to Lean probably from training days when instructors were scared students might stop the engine and scare themselves or overleen and damage it!
Pace
In a Seneca I used to experiment and on a very long runway set climb power for take off then didn't touch it for takeoff, climb, or cruise.
It was quite smooth for the PAX as there were no power noise changes
But it was just experimenting and not a realistic way of operating.On a normally aspirated engine always be aware of leaning some high altitude airfields you need to lean for takeoff so always lean as it will always find its level even if leaning ends up as full rich
I think there has always been a reluctance to Lean probably from training days when instructors were scared students might stop the engine and scare themselves or overleen and damage it!
Pace
Last edited by Pace; 21st Nov 2015 at 09:12.
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The DA40-180 has an IO360, and our SOP on that for takeoff is:
1) Full throttle, prop full fine, mixture (normally) full rich. This usually involves the RPM indicator showing between 2550-2700 RPM (I must confess that I don't normally spend the takeoff roll staring at the RPM indications
).
2) Once airborne, and established in the climbout, reduce pitch to settle the RPM at 2400, continue like that until at cruise alt and then adjust to whatever power setting you want.
On the few occasions I've needed to get from A to B quickly, I've just flown it at the climbout setting of full throttle, 2400 RPM, and full rich (this was in the UK at around 1500' so no real air density issues).
Paul.
1) Full throttle, prop full fine, mixture (normally) full rich. This usually involves the RPM indicator showing between 2550-2700 RPM (I must confess that I don't normally spend the takeoff roll staring at the RPM indications
).2) Once airborne, and established in the climbout, reduce pitch to settle the RPM at 2400, continue like that until at cruise alt and then adjust to whatever power setting you want.
On the few occasions I've needed to get from A to B quickly, I've just flown it at the climbout setting of full throttle, 2400 RPM, and full rich (this was in the UK at around 1500' so no real air density issues).
Paul.
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I think there has always been a reluctance to Lean probably from training days when instructors were scared students might stop the engine and scare themselves or overleen and damage it!
HOWEVER, for injected engines, I've always leaned at any altitude (against the EGT) and with the Continental, for instance, in the Reims Rocket, on the ground, too. Friends with a Beech 33 have a clever gismo which enables them to operate 'lean of peak'. The oil after 50 hours looks as fresh as when it was put in. The engine is 'on condition' at nearly 3,000 hours and seems in fantastic condition.
TOO
The POH of our Archer specifically states that the 'normally' aspirated O360 should be operated full rich at anything below 5,000', so that's what we teach the students.
The mixture should be leaned during cruising operation above 5000 ft.
altitude and at pilot’s discretion at lower altitudes when 75% power or less is being used.
altitude and at pilot’s discretion at lower altitudes when 75% power or less is being used.
Para 4.14
