Increase in Weight demands an increase in Power
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The concept that carrying more weight will require more power being applied may be an over simplification. Yes, adding the proportionate increase in power will keep everything else more or less in line, but it's not the only way.
For a certified aircraft, the handling and performance information you are provided, will be applicable at the maximum permitted weight, unless it says otherwise. Of course, in most cases, the performance charts allow the pilot to select information with weight as a factor. But, if in doubt, keep it within the weight and C of G limits, and you'll be fine.
The maximum certified weight will be based on one or both of structural capacity or performance. An efficiently designed aircraft will limit at both very close to each other. Or else, you have more of one of those than you really need.
For aircraft where performance was in excess, sometimes a small structural improvement will allow a higher gross weight - a C 182 can have a higher gross weight when an STC'd wingstrut change is installed.
For aircraft with excess structure, like the venerable C 150, if you increase performance (with.... yes, more power) a heavier gross weight is possible - hence the C 152 with 70 pound heavier gross weight, because it's about 10 HP more powerful.
But otherwise, all other things being equal, if you want to carry more weight in a power plane, some more power will be your best solution - more fuel burn...
For a certified aircraft, the handling and performance information you are provided, will be applicable at the maximum permitted weight, unless it says otherwise. Of course, in most cases, the performance charts allow the pilot to select information with weight as a factor. But, if in doubt, keep it within the weight and C of G limits, and you'll be fine.
The maximum certified weight will be based on one or both of structural capacity or performance. An efficiently designed aircraft will limit at both very close to each other. Or else, you have more of one of those than you really need.
For aircraft where performance was in excess, sometimes a small structural improvement will allow a higher gross weight - a C 182 can have a higher gross weight when an STC'd wingstrut change is installed.
For aircraft with excess structure, like the venerable C 150, if you increase performance (with.... yes, more power) a heavier gross weight is possible - hence the C 152 with 70 pound heavier gross weight, because it's about 10 HP more powerful.
But otherwise, all other things being equal, if you want to carry more weight in a power plane, some more power will be your best solution - more fuel burn...
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I am a tid surprised. Even aircraft have to obey the basic principles of physics, or?
We all learned during our very first lessons on the physics of flying about the different forces enabling flight. One of the most prominent force pairs is a recall from school physics, called "Weight&Lift" and governed by gravitational forces down. Some may remember that an almost ancient guy with a second good application for an apple, Newton, came up with the grandiose idea, that Force equals mass times acceleration (the best idea for an apple use came from a snake, just to be complete and indeed ignoring Steve Jobs).
A Plane needs to overcome gravity to fly, or (hard to imagine different)?, where the acceleration is equal to earth gravitational acceleration. Even our little planes do not get their force from The Force, but simple from the power drawn from the engine. So, to keep a plane up in the sky when it gathered weight, it has to use more force = power, or am I oversimplifying? (Of course I am talking status within flying envelope)
We all learned during our very first lessons on the physics of flying about the different forces enabling flight. One of the most prominent force pairs is a recall from school physics, called "Weight&Lift" and governed by gravitational forces down. Some may remember that an almost ancient guy with a second good application for an apple, Newton, came up with the grandiose idea, that Force equals mass times acceleration (the best idea for an apple use came from a snake, just to be complete and indeed ignoring Steve Jobs).
A Plane needs to overcome gravity to fly, or (hard to imagine different)?, where the acceleration is equal to earth gravitational acceleration. Even our little planes do not get their force from The Force, but simple from the power drawn from the engine. So, to keep a plane up in the sky when it gathered weight, it has to use more force = power, or am I oversimplifying? (Of course I am talking status within flying envelope)
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This seems to be surprisingly complex !
As an example (using the Cessna Graph and some guessed weights)
IF 2000 lbs and 100 knots is 'typical', this will probably have an angle of attack of 5 and CD of 0.05
IF one adds 400 pounds (which is a lot in to an aircraft previously 2000 all up), you will need to increase the angle of attack to 6 at a constant airspeed) and increase the Cd to 0.06 (20%) which will result (if we keep the power constant) in a speed reduction of 6% (cube root of 1.2). It will be slightly less because we always cruise above our minimum drag speed, so the Cd will be somewhat reduced due to our slower speed reducing parasitic drag more than the increase in induced drag from the higher angle of attack needed at slower speed (vs the above calculated effect of the higher AoA needed for increased weight).
HOWEVER, In many planes the increase in weight will also result in the CG moving aft, which as previously discussed reduces the drag due to the reduced downward force on the tail. So for many aircraft, the difference between light+forward CG and heavy+aft CG could be negligible.
As an example (using the Cessna Graph and some guessed weights)
IF 2000 lbs and 100 knots is 'typical', this will probably have an angle of attack of 5 and CD of 0.05
IF one adds 400 pounds (which is a lot in to an aircraft previously 2000 all up), you will need to increase the angle of attack to 6 at a constant airspeed) and increase the Cd to 0.06 (20%) which will result (if we keep the power constant) in a speed reduction of 6% (cube root of 1.2). It will be slightly less because we always cruise above our minimum drag speed, so the Cd will be somewhat reduced due to our slower speed reducing parasitic drag more than the increase in induced drag from the higher angle of attack needed at slower speed (vs the above calculated effect of the higher AoA needed for increased weight).
HOWEVER, In many planes the increase in weight will also result in the CG moving aft, which as previously discussed reduces the drag due to the reduced downward force on the tail. So for many aircraft, the difference between light+forward CG and heavy+aft CG could be negligible.
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@Chickenhouse
Exactly, (again) Chickenhouse has got it as have some other learned folk here - - as chickenhouse and porterhouse have correctly declared without the academia thereof
Load your 172 or PA28 or 152, A320, A330, B747, DC10 chocka block with weight - up to the max perameters etc - or not, just for this academic experiment and try to fly as you would if you were with full tanks and no payload and no other baggage, with same power setting
~and
You would notice a decrease in airspeed in the heavier aircraft. Assuming then that you could actually fly the heavier aircraft at that power setting (and speed) - assuming you could control the aircraft and that it did not feel too sloshy you would be grappling for speed, never mind the handling.
Now, if you apply full power AND hope for the best, in this experiment, for we are experimenting here guys (and fair maidens
then, you might, might get an increase in airspeed and with a lower angle of attack, (providing you are not too heavy, baby) and hopefully the handling characteristics would be perhaps tighter affording greater flying control of the aircraft. [if not then land the bloody thing and consider you got away with it]
In short -
For a substantial increase in weight - you need an increase in power.
The manuals of all of the above aircraft give you the graphs and the tables so you can all go and work it out for yourself before you fly - which is what you do.
But, as we all train in an aeroplane with no payload apart from the instructor or flight crew but no pax or payload - and we already know what is written in the performance tables - and even though we know that weight is opposite to lift and the less weight you have the more lift you get - in short.
No one stands there in front of you all in class, and announces that for an (a substantial) increase in weight you WILL need an (a substantial) increase in power.
Nor is it writ, in them there books like you say on the first pages either. Obvious - simple and true.
Load your 172 or PA28 or 152, A320, A330, B747, DC10 chocka block with weight - up to the max perameters etc - or not, just for this academic experiment and try to fly as you would if you were with full tanks and no payload and no other baggage, with same power setting
~and
You would notice a decrease in airspeed in the heavier aircraft. Assuming then that you could actually fly the heavier aircraft at that power setting (and speed) - assuming you could control the aircraft and that it did not feel too sloshy you would be grappling for speed, never mind the handling.
Now, if you apply full power AND hope for the best, in this experiment, for we are experimenting here guys (and fair maidens
then, you might, might get an increase in airspeed and with a lower angle of attack, (providing you are not too heavy, baby) and hopefully the handling characteristics would be perhaps tighter affording greater flying control of the aircraft. [if not then land the bloody thing and consider you got away with it]In short -
For a substantial increase in weight - you need an increase in power.
The manuals of all of the above aircraft give you the graphs and the tables so you can all go and work it out for yourself before you fly - which is what you do.
But, as we all train in an aeroplane with no payload apart from the instructor or flight crew but no pax or payload - and we already know what is written in the performance tables - and even though we know that weight is opposite to lift and the less weight you have the more lift you get - in short.
No one stands there in front of you all in class, and announces that for an (a substantial) increase in weight you WILL need an (a substantial) increase in power.
Nor is it writ, in them there books like you say on the first pages either. Obvious - simple and true.
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No one stands there in front of you all in class, and announces that for an (a substantial) increase in weight you WILL need an (a substantial) increase in power.
I will not need an increase on power, if I will accept a decrease in performance.
I have flown many aircraft at weights greater that the certified gross weight, as much as 130%, without the benefit of more power. I just expected less performance, (and I limited G) in accordance with the overweight authority for the flight.
So, no, I will not stand in front of class and assert that more weight requires more power - it just requires a "trade back" of something.
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Yes, you are right. An increase in weight requires an increase in power or you will lose something like, controllability, performance, predicted attitude, stall perf, therefore turning perf - and somewhere in all of this is dangerousness - just flying along having traded speed, performance, stall speed, to see what happens - else why fly in that config?
I thought we flew to a performance figure/parameter rather than "see watcha got"
That being said - if you don`t get what you want . . . .with say . . .full power plus the attitude you want then it is time reconsider your options. Power + Attitude = Performance.
I remember one sad time at a touring air show departure event thang - this single engined aircraft took of from the UK and climbed out turned left and promptly went side ways into the ground from about 200 feet - heavy and full of fuel.
Step Turn - I don`t know why (because I am not very intelligent) anyone would want to fly with a trade off rather than go for a perf. Once we went heavy and there was no trade off or power increase (can`t have been that heavy then . . maybe not) once we went heavy and there was a big trade off. Why trundle along like that - I landed back on - some mother else took it. Flying slow and slushy (not mushy) on purpose to demonstrate is one thing, flying slow and slushy because that is all you`ve got is not a place to be. I am not talking about commercial operations stuffed full of mail - even so I have been there too and whilst my nose was comfortably pressed onto the windscreen (joking . . ) there was no deficit in performance, admittedly it was a twin turbo-prop - I am talking about flight training SEP here.
I thought we flew to a performance figure/parameter rather than "see watcha got"
That being said - if you don`t get what you want . . . .with say . . .full power plus the attitude you want then it is time reconsider your options. Power + Attitude = Performance.
I remember one sad time at a touring air show departure event thang - this single engined aircraft took of from the UK and climbed out turned left and promptly went side ways into the ground from about 200 feet - heavy and full of fuel.
Step Turn - I don`t know why (because I am not very intelligent) anyone would want to fly with a trade off rather than go for a perf. Once we went heavy and there was no trade off or power increase (can`t have been that heavy then . . maybe not) once we went heavy and there was a big trade off. Why trundle along like that - I landed back on - some mother else took it. Flying slow and slushy (not mushy) on purpose to demonstrate is one thing, flying slow and slushy because that is all you`ve got is not a place to be. I am not talking about commercial operations stuffed full of mail - even so I have been there too and whilst my nose was comfortably pressed onto the windscreen (joking . . ) there was no deficit in performance, admittedly it was a twin turbo-prop - I am talking about flight training SEP here.
Last edited by Natstrackalpha; 2nd Apr 2015 at 12:47.
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and somewhere in all of this is dangerousness - just flying along having traded speed, performance, stall speed, to see what happens - else why fly in that config?
I don`t know why ... anyone would want to fly with a trade off rather than go for a perf.
to see what happens
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@ Step Turn
@ Dubbleyew 8
Yer not lost - I stuffed a large tool kit in the back (which put my back out for a year in physio) took 3 pax did the working out in the charts - WAT and all - and got up there. In the 172 I used 2350 RPM and whereas I would often get 102 knots or more indicated - on this day I barely got 82 knots flat out - waiting for the airspeed to increase and it did not. So, I landed back on - sod that. (the highest power setting I have used in my life to maintain the approach profile - interesting)
Yes, although clean I was stuck with that airspeed.
========================================================
@ Step Turn Yes. Step Turn I see you point and this is precisely my point when you mention design compliance. Well, Design Compliance is not the issue - because it does not state the airspeed you will achieve if heavy.
They DO say, on the charts that at a certain altitutde and temp and a certain power setting you will achieve an average of . . . Xknots . . . (an often lower figure with significant altitude increase and also a recommended Full Throttle setting0.
My point was to demonstrate that there is not one maxim of more weight equals more power. There is an examiner around who is not light in weight at all. In the 150 and with top fuel we are on the edge and, depending on the day (WAT) we might not even load max fuel.
My point was demonstrated in the above example of the 172.
However, as clearly seen - even using full power did nought to . . improve the situtation.
Had I have used normal cruise power - we would not be having this conversation.
Yer not lost - I stuffed a large tool kit in the back (which put my back out for a year in physio) took 3 pax did the working out in the charts - WAT and all - and got up there. In the 172 I used 2350 RPM and whereas I would often get 102 knots or more indicated - on this day I barely got 82 knots flat out - waiting for the airspeed to increase and it did not. So, I landed back on - sod that. (the highest power setting I have used in my life to maintain the approach profile - interesting)
Yes, although clean I was stuck with that airspeed.
========================================================
@ Step Turn Yes. Step Turn I see you point and this is precisely my point when you mention design compliance. Well, Design Compliance is not the issue - because it does not state the airspeed you will achieve if heavy.
They DO say, on the charts that at a certain altitutde and temp and a certain power setting you will achieve an average of . . . Xknots . . . (an often lower figure with significant altitude increase and also a recommended Full Throttle setting0.
My point was to demonstrate that there is not one maxim of more weight equals more power. There is an examiner around who is not light in weight at all. In the 150 and with top fuel we are on the edge and, depending on the day (WAT) we might not even load max fuel.
My point was demonstrated in the above example of the 172.
However, as clearly seen - even using full power did nought to . . improve the situtation.
Had I have used normal cruise power - we would not be having this conversation.
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Nats, I'm not sure of the point you're tring to make. The aircraft either will be within weight limits, or it was overloaded. If within weight limits, it has met the requirements for climb performance, in standard atmoshpere. Yes, you might eventualy find a WAT value, at which a sacrifice must be made. This is why people purchse more powerful aircraft, or turbo equipped aircraft - but that would be comparing apples to oranges here.
Fly the plane within limits, it will give you "book" performance. That's what it was certified to do....
Fly the plane within limits, it will give you "book" performance. That's what it was certified to do....
