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sekos

difference between max. rate and max. angle

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Max angle versus max rate, in an over-simplified nutshell:Best Rate of Climb (Vy) will get you to a particular altitude within the shortest amount of time.Best Angle of Climb (Vx) will get you to a particular altitude within the shortest distance.Stated differently:Vy will get you to a particular altitude in the least amount of time, but will take more distance over the ground than would Vx.Vx will get you to the altitude with the least distance over the ground, but will take more time than would Vy.Initially that may not make a lot of sense. Why would you want to climb at Vx if Vy is quicker to that same altitude? Vx means you cover less distance over the ground, which is important for obstacle clearance. Your rate of climb isn't as good as Vy, but again, you're travelling more feet vertically for each foot horizontally at Vx, so you can clear that obstacle sooner than you would at Vy.


Kyle Rodgers

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Vx and Vy speeds:Vx is the indicated airspeed for best angle of climb. Vy is the indicated airspeed for best rate of climb. Vx is slower than Vy.Climbing at Vx allows pilots to maximize the altitude gain per unit ground distance. That is, Vx allows pilots to maximize their climb while sacrificing the least amount of ground distance. This occurs at the speed for which the difference between thrust and drag is the greatest (maximum excess thrust). In a jet airplane, this is approximately minimum drag speed, or the bottom of the drag vs. speed curve.Climbing at Vy allows pilots to maximize the altitude gain per unit time. That is, Vy, allows pilots to maximize their climb while sacrificing the least amount of time. This occurs at the speed for which the difference between engine power and the power required to overcome the aircraft's drag is the greatest (maximum excess power). Climb rate is proportional to excess power.Vx increases with altitude and Vy decreases with altitude. Vx = Vy at the airplane's absolute ceiling, the altitude above which it cannot climb using just its own lift.Source: Wikipedia(MOD EDIT: It's your first post here so we'll cut you some slack. Please sign all posts with your full, real name in the PMDG forum. Forum rules can be found here)


Sergio Silva

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to add... You would generally climb at Vx, unless there in an obstacle to clear.


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Mike Murawski

 

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to add... You would generally climb at Vx, unless there in an obstacle to clear.
You mean Vy?

Kimo

 

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to add... You would generally climb at Vx, unless there in an obstacle to clear.
Not in a heavy jet you wouldn't. Here we got a set speed schedule for climb out. Just after lift off we are at about V2 +10kts. For a given weight the higher the V2 the better the climb gradient. Hence we use optimized V-speeds. V2 is 1.13x Vsr. This speed is much less than Vx which is less than Vy Then at accel hight we increase the speed to 250kts below FL100 and then upto ECON climb speed. This is the FMGS calculated climb speed for best economy and time to climb. varying the speed with wind/temp and weight and CI.hope this helps,

Martin Dahlerup

My rig contains a random selection of computer parts working in perfect harmony....

 

I hold a EASA fATPL + A320 SIC rating and a FAA CPL with CFI rating.

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Vx and Vy and any other V-speeds are definitions of SAFE speeds for a given set of conditions. Sometimes they are calculated and sometimes they are obtained by practical testing, sometimes even both are required and sometimes they are just approximated because no testing beyond a given point has been made either for safety reasons or practicality.Those definitions can and will change from airplane to airplane and the only way to be sure what they mean for the particular airplane you are flying is to read flying handbook. The reason is not only the actual performance is taken into account, but the safety too. For instance: Some light turbocharged twins have an actual Vx much lower than the indicated on their airspeed indicators but the manufacturer limits you as pilot to a higher speed forcing a smaller angle for safety, you might think the manufacturer is crazy, why would you want the airplane you are selling to look worst than it really is? Right?Well.. There is a very good reason for that. If you fly that airplane at the actual Vx for maximum perfomance you will be very close to stall speed and below Vmc. In the event of an engine failure that wing will inmediately stall due to the lack of induced airflow and you wont have enough aerodinamic control to keep the working engine from turning the airplane upside-down and into a wild spin. That was what happened to the Concorde that crashed and the reason why it crashed inverted.So you see.. V-speeds are more than maximum performance indicators. In general the terms Vx and Vy are used in slow airplanes because their simple definitions are enough, but the faster you go the more complex the situations become and therefore other terms more specific are used although to the observer they might look like pretty much the same.Anyway, no matter how they are named there will be a best angle and a best rate speed for every airplane and situation, the main difference being what worries you as the pilot. On takeoff what worries you are the obstacles around the airport so what you want is to gain altitude in the shortest distance so you'll go for Vx. Once cleared what worries you is fuel economy so you'll go for Vy to get higher as fast as possible into thinner air.I'll leave it here for simplicity.


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Jose M Garcia

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Vx and Vy and any other V-speeds are definitions of SAFE speeds for a given set of conditions.
No, Vx and Vy, as already stated, are the speeds that give maximum rate of climb or maximum angle of climb, respectively.Vx and Vy don't really exist on large transport category aircraft as max rate/angle generally occur at the same point, where lift is greatest and drag is lowest, and the rest is excess thrust.On the MD-82, Max Angle is ~210 kts below 18000 ft, but also equates to max rate, too, as to fly any faster reduces vertical rate, and to fly any slower reduces vertical rate. If you climb at V2+10 at TOGA with optimum flap, you can get a high angle of climb, but the wings lose lift and the engines thrust production reduces forcing you to accelerate, or stall.Vy and Vx only really applies to light aircraft, because drag is so large and thrust so little, there is a split between these two points. You either reduce drag by flying slow and climbing on power (max angle), or increase speed to increase lift thereby climbing faster, but now the attitude is much flatter due to a lack of power, so it takes much greater distance.You'll also be interested to note that best climb speed is also best glide speed.Best regards,Robin.

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You can use best of angle of climb for take off near by mountans, to make climb faster and don't hit the mountan! Batting%20Eyelashes.gif


Volkan

 

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Well.. There is a very good reason for that. If you fly that airplane at the actual Vx for maximum perfomance you will be very close to stall speed and below Vmc. In the event of an engine failure that wing will inmediately stall due to the lack of induced airflow and you wont have enough aerodinamic control to keep the working engine from turning the airplane upside-down and into a wild spin. That was what happened to the Concorde that crashed and the reason why it crashed inverted.
Almost correct on the Vmc stuff. Assuming you are talking about the left wing because on conventional twins in the usa, the left engine is critical, the loss of induced airflow isnt the main reason a twin will spin. Its actually not even recognized by the faa as a reason why the left engine is critical. Its p-factor thay really makes a plane violantly yaw towards the critical engine because there is a greater arm for the right engine to act upon. Then since the right wing is traveling faster and the left wing is effectively slowing and therefore having a greatly reduced relative airspeed, they plane starts to roll towards the dead engine. That roll i just mentioned isnt just because you loose accelerated slipstream from the dead engine. Loosing that airflow isnt as bad as the wing itself loosing airspeed from the inital yawing motion. Anywho just wanted to clarify that for ya and go a little deeper. I know its a pain trying to explain things like this on a forum.

FAA: ATP-ME

Matt kubanda

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Well.. There is a very good reason for that. If you fly that airplane at the actual Vx for maximum perfomance you will be very close to stall speed and below Vmc. In the event of an engine failure that wing will inmediately stall due to the lack of induced airflow and you wont have enough aerodinamic control to keep the working engine from turning the airplane upside-down and into a wild spin. That was what happened to the Concorde that crashed and the reason why it crashed inverted.
No. Check your facts. First, Concorde was a jet!!! Second, the WING CAME OFF. It BURNED THROUGH AND DETACHED. That is why the aircraft rolled in the last seconds.Loss of an engine in a twin during low speed high angle climbs results simply in the loss of thrust. What is a climb? Excess thrust. A lot of twins will not even sustain level flight on one engine as it doesn't have the power. As the saying goes: "Twin engine safety *IS* the remaining engine will take you direct to the scene of the accident".@ahsmatt7: Not even close. The critical engine is critical due to p-factor. That part is correct. The result of losing the critical engine is that induced yaw can be so great as to not be able to be countered by the rudder at very low airspeeds (this is why it is critical during the takeoff and landing phases). The other issue is again the (in)ability of the aircraft to sustain at least level flight or even slowly climb on the remaining engine, and for the rudder to compensate for the yaw (particularly at low speeds, ex. takeoff or landing).FYI there is no "in the USA" etc.. regarding the critical engine. Some aircraft have props that turn the same way, some have counter-rotating props, of both orientations. It isn't like helicopters where generally yes, US helis turn the other way to European helis for example.Counter rotating props: neither (left prop anti-clockwise, right prop clockwise) OR both engines are critical (opposite of neither).Both props rotate clockwise (as viewed from behind): LEFT engine critical.Both props rotate anti-clockwise (as viewed from behind): RIGHT engine critical.The critical engine is the engine LEAST desired to fail, and its failure would result in very difficult handling.Best regards,Robin.

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No. Check your facts. First, Concorde was a jet!!! Second, the WING CAME OFF. It BURNED THROUGH AND DETACHED. That is why the aircraft rolled in the last seconds.Loss of an engine in a twin during low speed high angle climbs results simply in the loss of thrust. What is a climb? Excess thrust. A lot of twins will not even sustain level flight on one engine as it doesn't have the power. As the saying goes: "Twin engine safety *IS* the remaining engine will take you direct to the scene of the accident".@ahsmatt7: Not even close. The critical engine is critical due to p-factor. That part is correct. The result of losing the critical engine is that induced yaw can be so great as to not be able to be countered by the rudder at very low airspeeds (this is why it is critical during the takeoff and landing phases). The other issue is again the (in)ability of the aircraft to sustain at least level flight or even slowly climb on the remaining engine, and for the rudder to compensate for the yaw (particularly at low speeds, ex. takeoff or landing).FYI there is no "in the USA" etc.. regarding the critical engine. Some aircraft have props that turn the same way, some have counter-rotating props, of both orientations. It isn't like helicopters where generally yes, US helis turn the other way to European helis for example.Counter rotating props: neither (left prop anti-clockwise, right prop clockwise) OR both engines are critical (opposite of neither).Both props rotate clockwise (as viewed from behind): LEFT engine critical.Both props rotate anti-clockwise (as viewed from behind): RIGHT engine critical.The critical engine is the engine LEAST desired to fail, and its failure would result in very difficult handling.Best regards,Robin.
you took my explainatiom and elaborated...i wasnt going to get deeply in to vmc. I wasnt trying to explain vmc. I was just sayin how induced airflow is just one of the reasons why an airplane will start to roll and could eventually stall. Not thee sole reason why it stalls. I did mention yaw in my explination but didnt go into how the low airspeed cant give the control surfaces enough authority to overcome all the thrust being put out by the right engine. I assumed he grasped that concept along with the concept of vmc.No worries though. I may not be well versed in high altittude aerodynamics but im on top of my multi aerodynamics.....just had my chckride so this stuff is pretty fresh. I will admit though that i get lazy when explaining things like this on forums. In turn i leave a lot out. Going through this topic would involve going over vmc and what it means to us as pilots. Then going over the critical engine and what it is. Then combining the two and disesceting an engine failure and what forces are acting on the airplane immidiately as the engine fails......assumin we are talkig about the critical engine.

FAA: ATP-ME

Matt kubanda

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Okay guys, not that I'm a mod, but this has nothing to do with the original topic. You've both proven you know more about the information than does the average simmer.Just sayin'...


Kyle Rodgers

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Okay guys, not that I'm a mod, but this has nothing to do with the original topic. You've both proven you know more about the information than does the average simmer.Just sayin'...
I dont see anything wrong with that. I myself have learned an immense amount of stuff because a user corrected another user. I think people correcting others is what fosters a learning environment. Now we must all do it in a professional manner of course. I bet a fellow simmer who may have read this thread and could have thought...."so thats what a critical engine is....or i have always what vmc really does and now i know." There are probably simmers who just started real world stuff and are consistently picking up new info on these forums...whether they like it or not. We all who have the knkwledge would be doing the new student pilots a disservice if we didnt correct erronous info. The people who are corrected learn aswell. I myself thought i knew about high alttitude and high speed aerodynamics. I was corrected and i axtually gsined more workijg knowledge on the subject.

FAA: ATP-ME

Matt kubanda

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