Angle versus Climb
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Take a look at the units:
rate of climb:
xxxx ft / minute
climb angle:
xxx ft / nm
Thus, best rate will keep time to a minimum while max angle will keep the traveled distance to a minimum.
So, if by quickest you are referring to time, then best rate of climb is your answer.
Regards,
Mark
rate of climb:
xxxx ft / minute
climb angle:
xxx ft / nm
Thus, best rate will keep time to a minimum while max angle will keep the traveled distance to a minimum.
So, if by quickest you are referring to time, then best rate of climb is your answer.
Regards,
Mark
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Flight at the Best Climb Angle Speed will get you to Top of Climb in the shortest possible DISTANCE. Fuel economy is terrible.
Flight at the Best Climb Rate Speed will get you to Top of Climb in the shortest possible TIME. Fuel economy is quite good.
Flight at the Max Range Climb Speed will get you to Top of Climb with the smallest possible FUEL BURN. This speed is slightly above the Best Climb Rate Speed.
Regards,
Old Smokey
Flight at the Best Climb Rate Speed will get you to Top of Climb in the shortest possible TIME. Fuel economy is quite good.
Flight at the Max Range Climb Speed will get you to Top of Climb with the smallest possible FUEL BURN. This speed is slightly above the Best Climb Rate Speed.
Regards,
Old Smokey
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Flight at the Best Climb Angle Speed will get you to Top of Climb in the shortest possible DISTANCE. Fuel economy is terrible.
Flight at the Best Climb Rate Speed will get you to Top of Climb in the shortest possible TIME. Fuel economy is quite good.
Flight at the Max Range Climb Speed will get you to Top of Climb with the smallest possible FUEL BURN. This speed is slightly above the Best Climb Rate Speed.
Regards,
Old Smokey
Flight at the Best Climb Rate Speed will get you to Top of Climb in the shortest possible TIME. Fuel economy is quite good.
Flight at the Max Range Climb Speed will get you to Top of Climb with the smallest possible FUEL BURN. This speed is slightly above the Best Climb Rate Speed.
Regards,
Old Smokey
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The problem with these definitions that I have is that there appears to be a contradiction.
If one operates at best climb rate speed then cruise is acheived in the shortest possible time. However, distance is a function of speed and time and if we just took the shortest time to get up to 390 then it seems sensible to me that we have traveled a short distance.
How a shorter distance can be acheived with best angle of climb speed evades me.
Further clarification appreciated
If one operates at best climb rate speed then cruise is acheived in the shortest possible time. However, distance is a function of speed and time and if we just took the shortest time to get up to 390 then it seems sensible to me that we have traveled a short distance.
How a shorter distance can be acheived with best angle of climb speed evades me.
Further clarification appreciated
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This is exactly correct, and at the best angle of climb speed, the distance traveled is less due to the lower speed.
See above.
..and if we just took the shortest time to get up to 390 then it seems sensible to me that we have traveled a short distance...
How a shorter distance can be acheived with best angle of climb speed evades me...
How a shorter distance can be acheived with best angle of climb speed evades me...
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pstaney,
It's all about incremental cruise. Looking at the first two cases (Best Gradient Climb and Best Rate Climb), the aircraft at Best Gradient speed will get to cruise level in a shorter distance (but in a longer time) than the aircraft at Best Rate Speed. Even if the time to climb and fuel to climb were the same (they're NOT, the aircraft at best rate will get there first and for less fuel), the aircraft at best Gradient Climb now has to cover incremental cruise distance to the point where the aircraft at best rate commenced cruise. This must be added to the climb fuel. Strike out the aircraft at best Gradient for good fuel economics.
To take it one step further, if best rate climb is examined, the rate is attributable to maximum excess Power (whereas the aircraft at best gradient is flying at maximum excess Thrust).
Power = Force (Thrust) X Velocity (TAS). If we examine Power Required (Pr) graphs for a JET aircraft Vs Power Available (Pa), they lie at quite high speed in a region where the Pr is increasing in a gentle curve upwards with increasing speed, but Pa is also in a gentle curve upwards and almost parallel with each other. Small (20 to 25 knots) variation is speed either side of best rate result in only slight change in Pa Vs Pr, i.e. excess Power, with very small impact upon Rate of Climb. The aircraft about 20 knots above best rate speed will suffer only a small penalty in fuel burn during climb, but cover a considerably greater distance for that very slight fuel investment.
If I look at typical B777 figures at high weights, Best Rate comes out at about 300 KIAS (Mean TAS = 425), and Minimum Fuel at about 320 KIAS (Mean TAS = 451). For a 30 minute climb (30.5 minutes at best fuel speed), I have covered an additional 13 miles for an investment of .5 minute of climb fuel. The aircraft at the lower speed (Best Rate) must now cruise for 13 miles (about 1.5 minutes) to catch up to the same point.
Yes, the speed is very similar to, or FASTER than typical Maximum Range Cruise speeds.
Regards,
Old Smokey
It's all about incremental cruise. Looking at the first two cases (Best Gradient Climb and Best Rate Climb), the aircraft at Best Gradient speed will get to cruise level in a shorter distance (but in a longer time) than the aircraft at Best Rate Speed. Even if the time to climb and fuel to climb were the same (they're NOT, the aircraft at best rate will get there first and for less fuel), the aircraft at best Gradient Climb now has to cover incremental cruise distance to the point where the aircraft at best rate commenced cruise. This must be added to the climb fuel. Strike out the aircraft at best Gradient for good fuel economics.
To take it one step further, if best rate climb is examined, the rate is attributable to maximum excess Power (whereas the aircraft at best gradient is flying at maximum excess Thrust).
Power = Force (Thrust) X Velocity (TAS). If we examine Power Required (Pr) graphs for a JET aircraft Vs Power Available (Pa), they lie at quite high speed in a region where the Pr is increasing in a gentle curve upwards with increasing speed, but Pa is also in a gentle curve upwards and almost parallel with each other. Small (20 to 25 knots) variation is speed either side of best rate result in only slight change in Pa Vs Pr, i.e. excess Power, with very small impact upon Rate of Climb. The aircraft about 20 knots above best rate speed will suffer only a small penalty in fuel burn during climb, but cover a considerably greater distance for that very slight fuel investment.
If I look at typical B777 figures at high weights, Best Rate comes out at about 300 KIAS (Mean TAS = 425), and Minimum Fuel at about 320 KIAS (Mean TAS = 451). For a 30 minute climb (30.5 minutes at best fuel speed), I have covered an additional 13 miles for an investment of .5 minute of climb fuel. The aircraft at the lower speed (Best Rate) must now cruise for 13 miles (about 1.5 minutes) to catch up to the same point.
Yes, the speed is very similar to, or FASTER than typical Maximum Range Cruise speeds.
Regards,
Old Smokey
Last edited by Old Smokey; 28th Nov 2006 at 17:50. Reason: I forgot an important bit
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Bobmij,
Perhaps some examples will help.
Take a typical jet with a best angle climb speed of about 220 knots and a best rate climb speed of about 290 knots.
Climb at 220Kts to FL390 might take 25 minutes with an average climb rate of about 1,560 FPM and average TAS of about 300 knots covering lets say about 120 miles.
Climb at 290 Kts (eventually becoming a particular Mach Number) might only take 21 minutes with higher average rate of climb of 1,860 FPM but with a much higher average speed of say 400 knots. This means we will have covered about 140 miles. So it took less time but covered more distance. The reason really being that the average speed is so much higher than that achieved when flying at best angle.
Although these numbers are made up, they are fairly realistic. Hope it helps!
CP
Perhaps some examples will help.
Take a typical jet with a best angle climb speed of about 220 knots and a best rate climb speed of about 290 knots.
Climb at 220Kts to FL390 might take 25 minutes with an average climb rate of about 1,560 FPM and average TAS of about 300 knots covering lets say about 120 miles.
Climb at 290 Kts (eventually becoming a particular Mach Number) might only take 21 minutes with higher average rate of climb of 1,860 FPM but with a much higher average speed of say 400 knots. This means we will have covered about 140 miles. So it took less time but covered more distance. The reason really being that the average speed is so much higher than that achieved when flying at best angle.
Although these numbers are made up, they are fairly realistic. Hope it helps!
CP
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Would it be correct to say:
Best Angle Climb speed (Vx) is used to clear obstacles or for short runways intially. Then once commencing the next segment, Vy is used for economy etc.
Best Angle Climb speed (Vx) is used to clear obstacles or for short runways intially. Then once commencing the next segment, Vy is used for economy etc.
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We have a lot of good CRM going on on these Pprune pages boeingbus2002, everybody checks on everybody else. That's exactly the way that it should be.
Regards,
Old Smokey
Regards,
Old Smokey
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And....if he's using cost index, where cost other than fuel is considered, then the climb speed would be even higher.
I'm just wrestling with the concept of cruising at the mach where maximum excess POWER is AVAILABLE. How close is this to LRC?
