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  1. #1
    Lnewqban's Avatar
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    Question for commercial pilots

    This question is about angle of attack during take off, for the commercial pilots at there.

    The extreme angle of take off amazes me each time that I fly in an airliner, or watch one taking off.

    It seems that they are very close to the critical AOA during the first seconds of take off.

    I understand that flaps are half deployed, and also the LE slots, and that the wing has more lift and area during take off; however, it seems to me that some of the total lift comes from the vertical component of the engines' thrust.

    I would love to read some explanations of the physics, as well as of the purpose, of such "extreme" maneuver in commercial airliners.
    Lnewqban - "God will not look you over for medals, degrees or diplomas, but for scars. He has achieved success who has worked well, laughed often, and loved much." - Elbert Hubbard

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    RE: Question for commercial pilots

    Hi L; You are correct; the engine has enough thrust to put the plane on its upward trajectory. When you first rotate, even if its a Tcraft or the like, the initial aoa is raggedly near the stall, but as soon as the plane assumes its desired flight path, that AOA reduces to a proper amount. If it didn'*** could spoil your whole day! Remember the airliner some years back (I think it was in Canada) where it took off, and the "brain" suddenly thought it was in landing mode, and REDUCED power! It quit climbing and simply settled into the trees! Definitely a bad day! Lee Robinson W. Palm Beach

  3. #3
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    RE: Question for commercial pilots

    On another note....what is so "Magic" about climbing to 10,000'? Landing lights go off, flight attendants start doing their thing and now we can use those electronic 'goodies' that (supposedly) would cause the plane to activate the wing detachment bolts and everyone would have a REAL bad day....just wondering.....

    Jerry
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    RE: Question for commercial pilots

    The take off and initial climb out, and final descent and landing are considered the most critical phase of flight and the potential harm that could come from an electronic device is the main concern. The odds that any device could cause interference is slim to none but legally each and every manufacturer, chipset, and device with even the smallest difference would have to be rigorously tested and as you have seen by the near infinite number of different devices out there it is easier to just prohibit their use.
    The three most useless things to a pilot, the sky above you, the runway behind you, and the fuel on the ground.

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    RE: Question for commercial pilots

    The biggest reason airliners have such steep climbouts is for noise abatement. People like to build their houses near airports and then complain about the noise.
    Dry white toast.

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    RE: Question for commercial pilots

    I know John Wayne in Orange County CA suffers from the above noise laws.
    Very cool to fly out of there feeling like your climbing at a 45 degree angle.

  7. #7
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    RE: Question for commercial pilots

    Thank you gentlemen; all great responses.
    Lnewqban - "God will not look you over for medals, degrees or diplomas, but for scars. He has achieved success who has worked well, laughed often, and loved much." - Elbert Hubbard

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    RE: Question for commercial pilots


    ORIGINAL: pkevinb

    The biggest reason airliners have such steep climbouts is for noise abatement. People like to build their houses near airports and then complain about the noise.
    Mostly not true. Some airports do require noise abatement but the major airports do not. Also, if there is a noise abatement policy in effect at an airport the procedure is to reduce thrust immediately after takeoff (usually 400') and do a slow climb. Steep climb and full power like you are thinking puts the exhaust pointing directly at the sensors on the ground.

    To the OP.... the critical AoA is not really as close as you might think during rotation. I have kept an eye occasionally on the AoA gauge in the cockpit and you go trhough the critical area (less than .6 AoA for us) very quickly. The steep climb (it is not as steep as you might imagine.... about 20 degrees of pitch) harks back to the old addage about "altitude is your friend". The acceleration is very quick and without a significant pitch attitude the speed would build very quickly.

    Normal phase is V1, VR, V2 sooooo..... V1 is decision speed where anything after that you are committed to fly, VR is of course rotation speed and V2 is basically single engine safety speed. If an engine is lost during initial climb, the SOP at our company is to trend back to V2 (because you most likely be above it) and set the bug speed for V2 for the remainder of the climb while the aircraft is cleaned up and checklists are run (at no lower than Minimum Safe Altitude (MSA) which for us is never lower than 1500AGL).

    I know it seems like that if an engine were to quit during that climb it seems like the aircraft should fall out of the sky at that angle but remember there is a lot of mass there that takes a little bit to decelerate..


  9. #9
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    RE: Question for commercial pilots

    What aircraft do you fly? And what are your numbers for V1 VR etc?
    # 93 in Club Saito; Carl Goldberg Ultimate Brotherhood # 12; Pulse brother # 2;Hellcat Brotherhood #8;P-47 Thunderbolt Brotherhood #18

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    RE: Question for commercial pilots

    I fly a mid sized buisiness jet. It is a Hawker 800XP. The theory is the same however, regardless of size of jet (except maybe the real little ones like the Eclipse...dont know much about those).

    The numbers for the Hawker are as follows....for a 22,000 lb takeoff (pretty light) on a 15 degree C day at sea level. V1 - 116kts VR - 116 (sometimes numbers are that same) and V2 - 126. Now, if we load it up to max gross takeoff wt of 28,000 the numbers for a 15C degree day at sea level are V1-125, VR-133, V2-140. I have done takeoffs close to max gross a lot and you definately know it.... Vr at 26,000lbs is still 128. 128kts=147mph

    All of those numbers are for flaps at 0 degrees. We can do flaps 15 degree takeoffs for a little lower numbers but the second segment climb performance on one engine with 15 degrees of flaps SUCKS!

    Hope that helps..

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    RE: Question for commercial pilots

    On take off roll, how fast do those numbers change, let's say between V1 and V2? I know from my PPL days it took a long time to go from 60 to 64 or what ever, but what do you expect from a 4 banger?
    # 93 in Club Saito; Carl Goldberg Ultimate Brotherhood # 12; Pulse brother # 2;Hellcat Brotherhood #8;P-47 Thunderbolt Brotherhood #18

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    RE: Question for commercial pilots


    ORIGINAL: tailskid

    On take off roll, how fast do those numbers change, let's say between V1 and V2? I know from my PPL days it took a long time to go from 60 to 64 or what ever, but what do you expect from a 4 banger?
    Generally we like to see about 1 knot per second.acceleration up in that speed region...... so yeah, it happens rather quickly. Usually when you are calling out the numbers it is one right after another... Vee One........... Rotate......... Vee Two........ Positive rate, gear up....
    and then after that the "flows" start.


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    RE: Question for commercial pilots

    Thanks, JurassicJet

    A private jet may take-off with more reserve of speed than a heavy airliner.

    I just think of the energy that is needed to elevate 150 tons at that height that fast.

    A crane couldn't do it!!
    Lnewqban - "God will not look you over for medals, degrees or diplomas, but for scars. He has achieved success who has worked well, laughed often, and loved much." - Elbert Hubbard

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    RE: Question for commercial pilots


    ORIGINAL: Lnewqban

    Thanks, JurassicJet

    A private jet may take-off with more reserve of speed than a heavy airliner.

    I just think of the energy that is needed to elevate 150 tons at that height that fast.

    A crane couldn't do it!!
    I understand what you are saying however if you look at a Boeing 757 for example it is very close to what we do.

    My aircraft weighs 28,000 at max gross takeoff. We have two Garrett TFE731-5BR engines developing 4660lbs of thrust each. soooo......28,000/(4660*2)=3.004. So, 3.004lbs of aircraft for 1 lb of thrust.

    The Boeing 757-200 (the most common variant). 255,000 lbs max gross takeoff. They have three options of engines but lets say we take the smallest of the three, which develops 36,000lbs of thrust each. 255,000/(36,000*2)=3.542. So the 757 has 3.542 lbs of aircraft for each pound of thrust. If you take their powerful engine which develops 46,000lbs of thrust. 255,000/(43,000*2)=2.965 lbs of aircraft per pound of thrust, which is a better thrust to weight ratio than us.

    Just throwing some numbers out there for thought....


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    RE: Question for commercial pilots


    ORIGINAL: JurassicJet

    I fly a mid sized buisiness jet.Â* It is a Hawker 800XP.Â* The theory is the same however, regardless of size of jet (except maybe the real little ones like the Eclipse...dont know much about those).

    The numbers for the Hawker are as follows....for a 22,000 lb takeoff (pretty light) on a 15 degree C day at sea level.Â* V1 - 116kts VR - 116 (sometimes numbers are that same) and V2 - 126.Â*Â*Â* Now, if we load it up to max gross takeoff wt of 28,000 the numbers for a 15C degree day at sea level are V1-125, VR-133, V2-140.Â* I have done takeoffs close to max gross a lot and you definately know it.... Vr at 26,000lbs is still 128.Â* 128kts=147mphÂ* [img][/img]

    All of those numbers are for flaps at 0 degrees.Â* We can do flaps 15 degree takeoffs for a little lower numbers but the second segment climb performance on one engine with 15 degrees of flaps SUCKS!Â*

    Hope that helps..
    So do you do the majority of take-offs at 0 Flaps?

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    RE: Question for commercial pilots


    ORIGINAL: G4guy

    So do you do the majority of take-offs at 0 Flaps?
    Yes.
    When I started to fly the Hawker a decade ago ALL takeoffs were at flaps 15. I told them (training department) that that didn't make sense. The second segment climb at flaps zero is much better than at flaps 15. The takeoff distance numbers usually change very little, maybe 150-200ft at the most. I have even seen certain weight/temp/altitude combinations where flaps 0 had a shorter TO roll than flaps 15.


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    RE: Question for commercial pilots

    Well, I can fill you in about the Eclipse Jet, as I have been flying one for the last three years. First of all (unlike almost anything I have ever flown) we don't have V1 or V2 speed. The computer assigns a Vr (rotate) speed based on weight and weather. The airplane uses half flaps (15 deg) for takeoffs-it uses a whole lot more runway without the flaps which can be hard on tires as well as other things. At Vr we rotate (I'm using the editorial we because it is a single pilot jet) to 10 degrees nose up. This is a bit less than most jets, and a bit more than most high performance piston twins (a Baron will use about 5-7 deg nose up at rotation). At any rate its Vr nose up 10 deg, Positive rate of climb=gear up, then at 400 feet above the runway flaps up, yaw damp on, and (optional depending upon conditions) power to climb, as determined by a mark on a guage which has been predetermined by the computer. As the airplane cleans up, it accelerates, so still with 10 degrees of pitch you accelerate to about 170 knots, which is the speed limit in a control zone. If things are going right you will hit about 170 as you exit the control zone and then you can accelerate to 250 knots, which is the speed limit below 10,000 feet. On something like the afformentioned Hawker, some power reduction may be necessary in the CZ or even below 10K feet, but on the comparitivly underpowered Ecilipse it is all you can do to reach about 220 Knots or so. At light weights on a cold day I can maintin 250 in the climb to about 20,000 feet, but hot and heavy it just won't do it. BTW the computer gives a climb speed that it thinks is the most efficient, but we have learned that it is wrong. The fastest foreward speed you can do with still a good climb rate is best. Cold and light I can do 2000-2500 feet per min till 20K-the Hawker will do much better and a Lear is just fantastic. ANY airplane will climb faster, and better when light and in cold air, much less so hot and heavy. Also as speed increases and you can get rid of drag producers (gear and flaps) the airplane will accelerats very noticably. The more is accelerates the better it performs. Recips are not quite like that in that they don't have the massive power of a jet and they are loosing the ability to make power as they climb into thinner air. All ariplanes however just LOVE cold air-as do the pilots.

  18. #18
    tailskid's Avatar
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    RE: Question for commercial pilots

    Very interesting......anyone else out there wish to share with us?
    # 93 in Club Saito; Carl Goldberg Ultimate Brotherhood # 12; Pulse brother # 2;Hellcat Brotherhood #8;P-47 Thunderbolt Brotherhood #18

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    RE: Question for commercial pilots


    ORIGINAL: tailskid

    Very interesting......anyone else out there wish to share with us?
    What do you want to know?

  20. #20
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    RE: Question for commercial pilots

    I've got about 100+ hours as a pp and felt the only 'exciting' time was when I was shooting touch and goes.....cross-country flights were boring...how do you guys stay sharp on those long cross-county flights?
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    RE: Question for commercial pilots

    ORIGINAL: tailskid

    I've got about 100+ hours as a pp and felt the only 'exciting' time was when I was shooting touch and goes.....cross-country flights were boring...how do you guys stay sharp on those long cross-county flights?
    Staying sharp is our profession, from short hops to 12 hour, 5000 mile legs. It's what we get paid to do!

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    RE: Question for commercial pilots

    RE: staying sharp-I fly mostly up and down the East Coast in the Eclipse Jet, sometimes in a Baron, Citation, or King Air. EVERY flight is on an IFR flight ln. Since I am almost always single pilot, the auto pilot does most of the flying and I direct it. Much of my time is spent dealing with ATC and solving the, fairly regular, navigational challenges of flying in the Northeast. As a single pilot this can, at times, keep you quite busy-a copilot would be a luxury. To maintain motor skills I used to make muself hand fly at least the first 30 mins and the last 30 mins of a flight. That is simply not possile in a jet as you are too busy doing the other "chores" involved in operating and managing the airplane (mostly navigation and communication, plus dealing with time to climb equations as well as descent planning-oftentimes you are told to cross a point at a specific altitude. How fast you descend, where you start your descent is up to the pilot, but it takes planning, and the plan changes a lot. In the Eclipse espically we learn to let the autopilot do all the work, while the human pilot does the planning, co-ordination and directing of the autopilot. There is very little time to sit back and enjoy the ride while flying up and down the East Coast. If I get to go out West things slow down a bit, but it is still busy.

    I used to fly a 4 engined "heavy turboprop" (cl 44) internationally. Hours of boredom seperated by moments of insanely busy work shared by two pilots and an engineer. When it got busy (such as nearing the destination airport) we all had our tasks to do and we worked together to accomplish these. Over the water it was simply maintain the status quo and make a position report every 30 minutes. It can be very hard to keep up the motor skills when flying long distances, but we are trained to do exactaly that and we stay sharp.

  23. #23
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    RE: Question for commercial pilots

    Hi guys,

    I am a regional airline pilot. I fly the CRJ-200 which is based on the Challenger, but is definitely not a great airplane. Having been on the CRJ900, I know what Bombardier could have done, but in the 200, they fell very very short. First off, we have no leading edge slats. We fly a super critical wing as well. Our books say to rotate and pause at 10 degrees nose up on the takeoff because if you don't, you will activate the continuous ignition (this is to prevent flameout at high angles of attack). It is also the first thing the stall protection system does (followed by stick shaker, then stick pusher). Anyhow, that being said, I don't know a CRJ200 pilot who hasn't gotten the continuous ignition light on rotation. It is a side effect of how weight and balance is calculated. It is all averages! I am a small guy, but with my books, my luggage, and my lunch, I weigh over the 190 lbs a crew member is supposed to weigh. Also, this is the average weight a passenger is supposed to weigh in the summer (195 for winter.... Coats I suppose...)... Our flight attendant is tasked with telling us how many passengers are in each "zone" of the airplane and that is used to compute the mac index (Center of gravity) of the airplane. We use that to calculate the take off trim used for each flight. If that doesn't seem crazy enough, bags are also averaged in the cargo compartment. I've heard of times where the plane is overweight (in theory) so bags are moved into the cabin because there they weigh nothing INSIDE THE CABIN, as opposed to bags calculated as an average of 30 lbs or 60 lbs for a heavy bag. This causes a rough discrepancy in the actual take off trim. You sort of have to deal with the airplane either under or over rotating on each take off. It's almost a reflex to change the trim after you've rotated.

    Bombardier designed a feeder airplane... An airplane that is supposed to take passengers from/to smaller airports. It is just a bad design... The 200 has one of the fastest landing speeds of any airliner out there due to the lack of leading edge slats or slots, yet it is supposed to land on short and contaminated runways in the winter. We seriously look like lawn darts on the approach. It's pretty funny to watch actually.

    Anyhow, I guess the reason of this post is to say that, yes, the CRJ200 can be close-ish to critical angle of attack on the rotation, but not anywhere near shaker or pusher! After a few hundred hours of on the plane, pilots learn to cope with the issues, and how pitch sensitive is. A feature that needs to be on the airplane is what the 737 guys have in the glass cockpits... They have the "eyebrows" on their primary flight display (the display with the attitude indicator). The eyebrows show you how high you can pitch at any given time, before reaching the critical angle of attack. Handy! I've observed this as I jumpseated home on Southwest many times. I'd love this feature on any airliner out there. The CRJ has no angle of attack indicator. The stall protection system simply chimes in where it deems necessary.

    Sorry for the longwinded response... Basically, on the 200, it is a design flaw. Most other airplanes, not so much.
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