Maximum Endurance vs Maximum Range
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Maximum Endurance vs Maximum Range
Hello everyone i have a little question and doubt about Maximum Endurance and Maximum Range because apparently i was wrong for a little while
It has been established that maximum range, as far as the aerodynamics of the airplane is concerned, is a function of a particular coefficient of lift (Cl), the one at which the lift-to-drag ratio is at a maximum. So then if it is like this why cant i draw a graph of Drag vs Velocity on the white board and explain that my MAX range is at my best L;D ration the lowest point on the total drag curve?? Because after my book i have to draw a Horsepower required vs CAS and show where is my best RANGE SPEED. I am a little confused on this one
It has been established that maximum range, as far as the aerodynamics of the airplane is concerned, is a function of a particular coefficient of lift (Cl), the one at which the lift-to-drag ratio is at a maximum. So then if it is like this why cant i draw a graph of Drag vs Velocity on the white board and explain that my MAX range is at my best L;D ration the lowest point on the total drag curve?? Because after my book i have to draw a Horsepower required vs CAS and show where is my best RANGE SPEED. I am a little confused on this one
Re: Maximum Endurance vs Maximum Range
Because a you state, you have to maximize L/D, not just minimize D.
As an AvCanada discussion grows longer:
-the probability of 'entitlement' being mentioned, approaches 1
-one will be accused of using bad airmanship
-the probability of 'entitlement' being mentioned, approaches 1
-one will be accused of using bad airmanship
Re: Maximum Endurance vs Maximum Range
Thanks for the quick reply but i am beginner can you please elaborate more for me please because i understand your statement of you have to maximize not just minimize. But how a bigger like me can minimize that
Re: Maximum Endurance vs Maximum Range
Look at an L/D graph. Those usually have a speed on the horizontal axis. Randomly pick a certain speed and read the value of L and D. If there are no values on your graph, choose or estimate a value that looks right.
Now calculate L/D with your estimated values for that speed.
Repeat the above for different speeds. You will notice that the maximum L/D value is not achieved at the speed that gives you minimum D.
Now calculate L/D with your estimated values for that speed.
Repeat the above for different speeds. You will notice that the maximum L/D value is not achieved at the speed that gives you minimum D.
As an AvCanada discussion grows longer:
-the probability of 'entitlement' being mentioned, approaches 1
-one will be accused of using bad airmanship
-the probability of 'entitlement' being mentioned, approaches 1
-one will be accused of using bad airmanship
Re: Maximum Endurance vs Maximum Range
You can, and it is.Horia1337 wrote: ↑Sat Jun 01, 2019 10:05 am Hello everyone i have a little question and doubt about Maximum Endurance and Maximum Range because apparently i was wrong for a little while
It has been established that maximum range, as far as the aerodynamics of the airplane is concerned, is a function of a particular coefficient of lift (Cl), the one at which the lift-to-drag ratio is at a maximum. So then if it is like this why cant i draw a graph of Drag vs Velocity on the white board and explain that my MAX range is at my best L;D ration the lowest point on the total drag curve??
The “power required for level flight” curve is more useful for consideration of best endurance, but if you want to find “best range” speed on that curve, it’s where the tangent passes through the origin.
On the understanding that weight stays the same, and that lift is equal to weight, and that therefore in the flight in question the lift needed to maintain horizontal flight is fixed, then yes, best L/D is achieved at the speed where the drag is least.
DId you hear the one about the jurisprudence fetishist? He got off on a technicality.
Re: Maximum Endurance vs Maximum Range
You made it more easy and clear for me to understand i appreciate sir. Thanks you
Re: Maximum Endurance vs Maximum Range
Well that was a whole bunch of gibberish that I wrote.
You are of course correct.
Should have known better than to try and beat you to an answer on questions like these!
As an AvCanada discussion grows longer:
-the probability of 'entitlement' being mentioned, approaches 1
-one will be accused of using bad airmanship
-the probability of 'entitlement' being mentioned, approaches 1
-one will be accused of using bad airmanship
Re: Maximum Endurance vs Maximum Range
Don't forget that power is not a force but a force x velocity. In this case, you'd have to plot the Drag x Velocity vs Velocity to find your Max E and Max R speeds. Velocities should be in KTAS which can easily be converted in KCAS at a given pressure altitude, What photofly said about Max R is true in still air. With a headwind or a tailwind, shift your origin by the amount of head/tailwind (in the negative for tailwind, positive for headwind).
Going for the deck at corner
Re: Maximum Endurance vs Maximum Range
It's very easy to get turned around on this topic!
In addition to what AuxBaton added about the wind, a real consideration of best range (or best endurance) has to take into account propeller and engine efficiency, or equivalently the amount of thrust (or power) that the engine or propellor generates for a given fuel flow and at a given airspeed.
Going a little bit faster may result in more drag, but if the prop gains efficiency at the new higher airspeed this could more than make up for it: your fuel flow will increase less than your speed increases, and presto-hey, your real best range speed is now actually faster than the speed at which you get best L/D.
DId you hear the one about the jurisprudence fetishist? He got off on a technicality.
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Re: Maximum Endurance vs Maximum Range
I think it is important that while it is good to understand the theoretical concepts around max range there are a host of practical factors that also apply.
Any discussion about situations where you are trying to get the most range out of the fuel you have, must start with pilot decision making including
- How confident am I in knowing exactly how much fuel I have on-board
- How confident am I in the weather, especially if you are trying to take advantage of a tailwind
- What is my plan B if it looks like I can’t make my destination
- Best Range for piston engines is predicated on optimal learning, a skill that doesn’t seem to be widely understood in newer pilots
The only time I ever actually flew at a max range airspeed was preceded by several really bad decisions and resulted in me landing with about 10 mins of fuel left
Finally an easy real world approximation of best range speed in a piston single is Vy. Flying that speed in no wind/tailwind conditions will get you pretty close to the theoretical least pounds of fuel per nm
Any discussion about situations where you are trying to get the most range out of the fuel you have, must start with pilot decision making including
- How confident am I in knowing exactly how much fuel I have on-board
- How confident am I in the weather, especially if you are trying to take advantage of a tailwind
- What is my plan B if it looks like I can’t make my destination
- Best Range for piston engines is predicated on optimal learning, a skill that doesn’t seem to be widely understood in newer pilots
The only time I ever actually flew at a max range airspeed was preceded by several really bad decisions and resulted in me landing with about 10 mins of fuel left
Finally an easy real world approximation of best range speed in a piston single is Vy. Flying that speed in no wind/tailwind conditions will get you pretty close to the theoretical least pounds of fuel per nm
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Re: Maximum Endurance vs Maximum Range
...all of the above and don't forget to lean the mixture!
"I found that Right Rudder you kept asking for."
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Re: Maximum Endurance vs Maximum Range
I hate auto correct. My last bullet got auto corrected from “leaning” to “learning” ......although in retrospect I guess both apply
Bottom line is you should get in the habit of leaning the mixture for cruise at every altitude on every flight, and the much quoted FTU-ism that you should not lean in cruise below 5000 needs to be stamped out. It is completely totally wrong.
Bottom line is you should get in the habit of leaning the mixture for cruise at every altitude on every flight, and the much quoted FTU-ism that you should not lean in cruise below 5000 needs to be stamped out. It is completely totally wrong.