Less than full power takeoffs?
Is there a temperature producing a very low density altitude at which full throttle will produce too much power, over stressing some engines?
PS Adding power as you turn onto the runway, with no stop on the runway - soft ground?
PS Adding power as you turn onto the runway, with no stop on the runway - soft ground?
My first flight deck ride in a Tristar, I noticed they set the thrust at 80% for takeoff and never went above that. '146s have a computer which calculates how much thrust you need according to auw and limited the thrust accordingly.
The generally accepted definition of a "reduced power takeoff" is one where the pilot deliberately chooses to not set the power/engine controls to produce the maximum power available.
Last edited by Big Pistons Forever; 3rd Jun 2015 at 18:25.
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The Spitfire was like that you had two settings on takeoff one reduced for the initial roll and a higher setting when there was more control authority
The Spitfire was like that you had two settings on takeoff one reduced for the initial roll and a higher setting when there was more control authority
Sometimes in the past there has been an aircraft on finals! ATC ask you to expedite your departure as you enter the runway from the taxiway! Do you taxi out stop and line up on the numbers, hit the brakes and build to max power or start your takeoff slowly increasing power while in a turn to the centreline? to assist separation to the landing aircraft?
i have seen that done by more experienced pilots many times in large jet aircraft as well as small aircraft too! To be shunned on ? accelerating on the turn to the centreline? i.e. do you ever start your takeoff roll while entering the runway from the taxiway? Not advisable with max power so theoretically a reduced power takeoff
i have seen that done by more experienced pilots many times in large jet aircraft as well as small aircraft too! To be shunned on ? accelerating on the turn to the centreline? i.e. do you ever start your takeoff roll while entering the runway from the taxiway? Not advisable with max power so theoretically a reduced power takeoff
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Where is the fun ?
I think many of us have experienced the extremes in flying from severe turbulence to storm penetration to severe weather landings, go arounds from missed approaches etc.
Carrying PAX and you have a different challenge as most PAX are nervous of flying or want as smooth a flight as possible and that then becomes the challenge.
You avoid the lumps of cumulus, change levels to get out of upper air turbulence and do everything possible given the conditions to make the flight seamless.
building to maximum power against the brakes and then being pinned to the seats by the acceleration might be great for us but not so great for nervous PAX
Ok short runway you have to do that but do you have to do that on a Heathrow type runway.
Hence that " experiment " on a very long runway with a Seneca Five and a takeoff with cruise climb setting. the takeoff roll was smooth the climb smooth with no power changes until cruise altitude . Ok it was just an experiment and not a modus operandae
I think many of us have experienced the extremes in flying from severe turbulence to storm penetration to severe weather landings, go arounds from missed approaches etc.Carrying PAX and you have a different challenge as most PAX are nervous of flying or want as smooth a flight as possible and that then becomes the challenge.
You avoid the lumps of cumulus, change levels to get out of upper air turbulence and do everything possible given the conditions to make the flight seamless.
building to maximum power against the brakes and then being pinned to the seats by the acceleration might be great for us but not so great for nervous PAX
Ok short runway you have to do that but do you have to do that on a Heathrow type runway.
Hence that " experiment " on a very long runway with a Seneca Five and a takeoff with cruise climb setting. the takeoff roll was smooth the climb smooth with no power changes until cruise altitude . Ok it was just an experiment and not a modus operandae
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For big planes, typically anything much larger than mid-size business jet right through to 747/A380 size, there will exist a fairly healthy margin between the engine thrust/power needed to get airborne and climb out and a healthy rate, and what the engines can deliver with the power levers wide open (for most conditions!). In those circumstances it doesn't make a great deal of sense to thrash the engines, and can indeed make life safer all around if you use just enough engine-ooomph to get up and away.
For those scenarios there is a fairly well trodden path, and it goes something like this...
As a previous poster alludes to, quite often an aircraft will happily take-off from a runway for a large range of ambient temperatures. However when the ambient temperature increases, a number of things happen: the engines typically generate less thrust, the density altitude increases, the IAS/TAS split becomes larger, and so on.
When a large aircraft manufacturer certifies an aircraft, they will conduct a large number of take-off and climbs for a large range of conditions. They will then further in the background take that data, identify trends, and sensibly extrapolate out until you now have a data-set which can tell you exactly how an aircraft will behave for any given runway, OAT, wind, slope etc.
So, back to the day where we're sat in the cockpit, we don't have many passengers, the aircraft is light, and we have a really long runway to take-off from. How much thrust/power is just enough? Well we can play a little thought experiment here: If I used the runway I'm on today, what in theory is the hottest ambient temperature I can successfully take-off with? Fortunately my voluminous data set from the aircraft manufacturer can go through all of those factors and arrive at answer: ASI, you could take-off today up to 45 degrees celsius, say.
What I can then do is consult my engine data and ask; at 45 degC, what engine setting am I going to get? Typically for jet engines this is measured by engine fan-speed (N1), or engine pressure ratio (EPR). I might find out that on a 45 degC day with the throttles wide open, the engine will give me 91% N1.
But it's actually really cold out today, say only 10 degC at the airport, what good does that nugget of knowledge do for me? Well what it means is I can push my throttle forward to get the 91% N1, and the engines will give me just enough thrust to get off the runway and climb away. I have in effect lied to myself about the temperature, and set the engines to a lesser thrust than they could otherwise achieve with full power in today's colder weather.
This approach all in all is called a FLEX derate, and is relatively common amongst Boeing and Airbus (barring differences in terminology). The success of this approach is based on the following things: A really expansive and well validated set of data from the manufacturer, some very accurate engine gauging and predictable engine behaviour, and a rigorous set of SOPs to make sure that the soft and squidgy chaps up front input the right numbers, get the right numbers out, and apply them correctly.
Coming back to the average light aircraft...well, you're basically out of luck on the first two counts straight away...
For those scenarios there is a fairly well trodden path, and it goes something like this...
As a previous poster alludes to, quite often an aircraft will happily take-off from a runway for a large range of ambient temperatures. However when the ambient temperature increases, a number of things happen: the engines typically generate less thrust, the density altitude increases, the IAS/TAS split becomes larger, and so on.
When a large aircraft manufacturer certifies an aircraft, they will conduct a large number of take-off and climbs for a large range of conditions. They will then further in the background take that data, identify trends, and sensibly extrapolate out until you now have a data-set which can tell you exactly how an aircraft will behave for any given runway, OAT, wind, slope etc.
So, back to the day where we're sat in the cockpit, we don't have many passengers, the aircraft is light, and we have a really long runway to take-off from. How much thrust/power is just enough? Well we can play a little thought experiment here: If I used the runway I'm on today, what in theory is the hottest ambient temperature I can successfully take-off with? Fortunately my voluminous data set from the aircraft manufacturer can go through all of those factors and arrive at answer: ASI, you could take-off today up to 45 degrees celsius, say.
What I can then do is consult my engine data and ask; at 45 degC, what engine setting am I going to get? Typically for jet engines this is measured by engine fan-speed (N1), or engine pressure ratio (EPR). I might find out that on a 45 degC day with the throttles wide open, the engine will give me 91% N1.
But it's actually really cold out today, say only 10 degC at the airport, what good does that nugget of knowledge do for me? Well what it means is I can push my throttle forward to get the 91% N1, and the engines will give me just enough thrust to get off the runway and climb away. I have in effect lied to myself about the temperature, and set the engines to a lesser thrust than they could otherwise achieve with full power in today's colder weather.
This approach all in all is called a FLEX derate, and is relatively common amongst Boeing and Airbus (barring differences in terminology). The success of this approach is based on the following things: A really expansive and well validated set of data from the manufacturer, some very accurate engine gauging and predictable engine behaviour, and a rigorous set of SOPs to make sure that the soft and squidgy chaps up front input the right numbers, get the right numbers out, and apply them correctly.
Coming back to the average light aircraft...well, you're basically out of luck on the first two counts straight away...
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Carrying PAX and you have a different challenge as most PAX are nervous of flying or want as smooth a flight as possible and that then becomes the challenge......
building to maximum power against the brakes and then being pinned to the seats by the acceleration might be great for us but not so great for nervous PAX. Ok short runway you have to do that but do you have to do that on a Heathrow type runway.
building to maximum power against the brakes and then being pinned to the seats by the acceleration might be great for us but not so great for nervous PAX. Ok short runway you have to do that but do you have to do that on a Heathrow type runway.
When I started right seat in the Cheyenne in the '80's, I was sharply told by my Captain: "Hey, the people back there are paying for this ride, they want a smooth one!"
In the last two days I have been doing the initial proving flying for a new amateur built "Cessna 172" taildragger, with 180HP, and extended STOL kitted wings. The first takeoff I eased the power in, and found I was airborne before I had eased it all in! Apparently it did not need full power to get airborne in a few hundred feet! I did learn to use full power though, and found a sustained 1300 FPM rate of climb - certainly a first for me in a 180 HP 172!
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A very well and informative response. I fly business jets and agree totally with you.
We check the temp and airfield elevation and take the N1 setting from the book normally in the Citation about 97.4% N1.
Yesterday at the airfield I departed 28 C and 1000 ft ASL it was 96.2 N1. You can build on the brakes to that thrust setting and let go or apply that thrust setting progressively which is smoother and not so greyhound out of a trap departure. Jet engines do not have the torque effect that piston and turbine singles can display.
Obviously that then meets the takeoff performance charts. Anything less and you are in the relatively unknown.
Changes in jet engine thrust are not so noticeable to PAX as they would be in a piston single or twin where RPM and manifold changes are more noticeable especially in twins where out of sync can mean an alarming sound to unknowing PAX.
Maybe Paid to fly and flying PAX your goals change? As few turns as possible as smooth air as possible as slick and time saving as possible? Etc
That becomes the challenge not the excitement factor.
But that emphasis can be the challenge flying PAX in light singles and twins to make the operation as smooth and slick as can be.
My experiment was just that! An experiment on a long runway and have to say it was very smooth
But not something i am advising.
We are so conditioned to go MAX and that brings in other considerations where going MAX can be fatal. you only have to go and look at the stall spin accidents on high powered single turbines like the TBM series or aircraft on go around or low and slow or look at high powered singles which will not take MAX on takeoff so in a way maybe this is just to be aware that Our training on low powered pistons is not the best on higher powered aircraft.
How many accidents have occurred where pilots are so brainwashed to max power that approaching VMCA in a twin they do not consider reducing power on the one live engine because they are brainwashed to MAX is best
A very well and informative response. I fly business jets and agree totally with you.
We check the temp and airfield elevation and take the N1 setting from the book normally in the Citation about 97.4% N1.
Yesterday at the airfield I departed 28 C and 1000 ft ASL it was 96.2 N1. You can build on the brakes to that thrust setting and let go or apply that thrust setting progressively which is smoother and not so greyhound out of a trap departure. Jet engines do not have the torque effect that piston and turbine singles can display.
Obviously that then meets the takeoff performance charts. Anything less and you are in the relatively unknown.
Changes in jet engine thrust are not so noticeable to PAX as they would be in a piston single or twin where RPM and manifold changes are more noticeable especially in twins where out of sync can mean an alarming sound to unknowing PAX.
Maybe Paid to fly and flying PAX your goals change? As few turns as possible as smooth air as possible as slick and time saving as possible? Etc
That becomes the challenge not the excitement factor.
But that emphasis can be the challenge flying PAX in light singles and twins to make the operation as smooth and slick as can be.
My experiment was just that! An experiment on a long runway and have to say it was very smooth
But not something i am advising.We are so conditioned to go MAX and that brings in other considerations where going MAX can be fatal. you only have to go and look at the stall spin accidents on high powered single turbines like the TBM series or aircraft on go around or low and slow or look at high powered singles which will not take MAX on takeoff so in a way maybe this is just to be aware that Our training on low powered pistons is not the best on higher powered aircraft.
How many accidents have occurred where pilots are so brainwashed to max power that approaching VMCA in a twin they do not consider reducing power on the one live engine because they are brainwashed to MAX is best
