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  1. #1051

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    RE: Downwind turn Myth

    I fly big airplanes for a living.   This myth appears because once you turn  into a strong headwind i.e. from base to final leg you need more power to maintain the same glide path on final approach.  Thats it. 

    But if you get wind shear you can easily stall a plane without changing the pitch.

    I also hate how rc pilots call a accidental stall a tip stall..........  Its not a tip stall just a stall.  One wing just happens to be more stalled than the other causing one wing to drop more than the other. 

    People are just not ready for the models ground seed to pick up on the downwind leg so they pull the power back hold the nose up and stall.  The airplane's wings don't know they are going faster when they have  a tailwind.



  2. #1052
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    RE: Downwind turn Myth

    RZielin,

    Great explanation!........finally!

    The observed ground track is the culprit. So many times I've seen guys make that turn after takeoff or go-around and roll their toy into a fairly steep bank. When the model slips downwind instead of pivoting through the turn, they steepen the bank to get what they want to see.......a tighter radius......steeper bank, more load factor, less stall margin. Plain and simple. It makes me chuckle when it is written that the plane is "banked 30 degrees".....when was the last time you saw a 30 degree bank turn with a model jet. It is usually 45 to 80 degrees.

    In a 30 degree bank the load factor is 1.2
    In a 45 degree bank the load factor is 1.4

    So, your 30 lb. Toy weighs 36 lbs. in the 30 degree bank and 42 lbs. at 45 degrees....not too bad for the thin wing.

    In a 60 degree bank the load factor is 2.0 !....or 60 lbs.

    In a 75 degree bank the load factor is 3.9!!!.....that's 117 lbs loading up that thin airfoil.

    These load factor numbers assume constant altitude, so if are trying to stay level or climb (which is usually the case) you need to generate more lift, then you need more AOA or speed or both to stay alive which takes thrust....

    Tailwinds,

    John



    Proud to be a rookie!

  3. #1053
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    RE: Downwind turn Myth

    Furthermore, in your original dinner challenge, did you specify that the ground track and turn radii remain the same as in dead calm? I don't think so. You are now re-framing your challenge and your argument because you now know your original concept was somewhat in error. You might benefit from accepting that, and I'm calling you on it (not belittling you).

    rzielin

    You are mistaken, In my original challenge I said that I would define a ground track that I expected the challenger to follow at an altitude of 6 feet high after I had demonstrated the same ground track at a higher altitude. I never changed this, or my original argument, and the offer still stands!

    Jerry
    AMA -922698 Nomal people scare me, but not as much as I scare them...

  4. #1054

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    RE: Downwind turn Myth

    Cactus,

    Yes the increased bank angle duing the turn to make the airplane appear to "turn around a point on the ground like it would with no wind" around during the crosswind to downwind turn is the culperate. But Load factor has nothing to do with a stall.

    The only reason a wing stalls is angle of attack. A wing can stall at any attitude, weight, load factor, speed ect......

    Your explanation should go like this.

    The observed ground track is the culprit. So many times I've seen guys make that turn after takeoff or go-around and roll their toy into a fairly steep bank. When the model slips downwind instead of pivoting through the turn, they steepen the bank to get what they want to see.......a tighter radius......steeper bank, more ANGLEOFATTACK, less stall margin. Plain and simple. It makes me chuckle when it is written that the plane is "banked 30 degrees".....when was the last time you saw a 30 degree bank turn with a model jet. It is usually 45 to 80 degrees.

    To create more lift you either have to increase airspeed over the wing or increase your angle of attack.

    During a turn you loose some of the vertical component of lift to the horizontal component of lift so to not loose altitude you have to increase total lift to get back the vertical component of lift you lost. So the pilot turns steeper....has to pull back on the stick more to maintain altitude.........and exceedes the critical angle of attack. The plane stalls. If the plane is not coordinated one wing will stall more than the other........this will start a spin.

    People turn rc jets faster than prop planes because they are going faster and they are trying to keep their planes close to them. The faster you are going the spteeper the turn you need to keep the same radious in a turn.

    Load factor is simply the result of the airplane acceleraing toward the inside of a turn. The faster you are going the more lift you can create at any given angle of attack. More lift available means you can change the planes direction quicker wich creates more accceleration......and more load factor.











  5. #1055
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    RE: Downwind turn Myth

    OK......fair enough. You need the AOA to overcome the load factor and then then separation thing happens.....Mister Toad's wild ride into the ground!

    Have a great weekend!

    Tailwinds,

    John
    Proud to be a rookie!

  6. #1056
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    RE: Downwind turn Myth


    ORIGINAL: m1morrow

    I fly big airplanes for a living.** This myth appears because once you turn* into a strong headwind i.e. from base to final leg you need more power to maintain the same glide path on final approach.* Thats it.*

    But if you get wind shear you can easily stall a plane without changing the pitch.

    I also hate how rc pilots call a accidental stall a tip stall..........* Its not a tip stall just a stall.* One wing just happens to be more stalled than the other causing one wing to drop more than the other.*

    People are just not ready for the models ground seed to pick up on the downwind leg so they pull the power back hold the nose up and stall.* The airplane's wings don't know they are going faster when they have* a tailwind.


    I too fly big airplanes for a living! With regard to the tip stall comment........Have you ever heard of WASHOUT?

    John
    Proud to be a rookie!

  7. #1057
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    RE: Downwind turn Myth

    ORIGINAL: m1morrow

    Cactus,

    Yes the increased bank angle duing the turn to make the airplane appear to ''turn around a point on the ground like it would with no wind'' around during the crosswind to downwind turn is the culperate.* But Load factor has nothing to do with a stall.**

    The only reason a wing stalls is angle of attack.* A wing can stall at any attitude, weight, load factor, speed ect......

    Your explanation should go like this.

    The observed ground track is the culprit. So many times I've seen guys make that turn after takeoff or go-around and roll their toy into a fairly steep bank. When the model slips downwind instead of pivoting through the turn, they steepen the bank to get what they want to see.......a tighter radius......steeper bank, more ANGLE*OF*ATTACK, less stall margin. Plain and simple. It makes me chuckle when it is written that the plane is ''banked 30 degrees''.....when was the last time you saw a 30 degree bank turn with a model jet. It is usually 45 to 80 degrees.

    To create more lift you either have to increase airspeed over the wing or increase your angle of attack.*

    During a turn you loose some of the vertical component of lift to the horizontal component of lift so to not loose altitude you have to increase total lift to get back the vertical component of lift you lost.* So the pilot turns steeper....has to pull back on the stick more to maintain altitude.........and exceedes the critical angle of attack. The plane stalls.* If the plane is not coordinated one wing will stall more than the other........this will start a spin.

    People turn rc jets faster than prop planes because they are going faster and they are trying to keep their planes close to them.* The faster you are going the spteeper the turn you need to keep the same radious in a turn.*

    Load factor is simply the result of the airplane acceleraing toward the inside of a turn.* The faster you are going the more lift you can create at any given angle of attack.* More lift available means you can change the planes direction quicker wich creates more accceleration......and more load factor.*










    Very well put, however the explanation of load factor is a very pertinant part of this story. As the load factor increases, the stall speed (speed at which the wing reaches the critical AOA) also increases until the point that it meets the current air speed, so while the aircraft may not be slowing (added power?) it will still stall. Just one more reason for the misconception.
    The three most useless things to a pilot, the sky above you, the runway behind you, and the fuel on the ground.

  8. #1058
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    RE: Downwind turn Myth


    ORIGINAL: pflynn73

    Thanks Highhorse for teaching me something very valuable. What is the next lesson? Thanks again Highhorse!
    Holy moly...you are SO welcome.

    You wouldn't believe the frustration this thread has been, and then one post makes it all worth while,
    so thank YOU!

    Don.

    PS: Regarding the next lesson? No, professional wrestling is not real either
    RCU Rocks, I\'\'d hate to be without it !!

  9. #1059

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    RE: Downwind turn Myth


    ORIGINAL: hugger-4641

    *Furthermore, in your original dinner challenge, did you specify that the ground track and turn radii remain the same as in dead calm? I don't think so. You are now re-framing your challenge and your argument because you now know your original concept was somewhat in error. You might benefit from accepting that, and I'm calling you on it (not belittling you).

    rzielin

    You are mistaken, In my original challenge I said that I would define a ground track that I expected the challenger to follow at an altitude of 6 feet high after I had demonstrated the same ground track at a higher altitude. I never changed this, or my original argument, and the offer still stands![img][/img]

    C'mon Hugger, that's just not true. Here's your original post with the challenge:

    ORIGINAL: hugger-4641

    I have an idea to settle this argument for good, at least in my mind:
    Let's take my 1/4 scale Balsa Usa Cub and set my throttle linkage so*it will max out about 2500 to 3000rpm. (just barely enough to fly, but enough for any skilled pilot to be able stay airborn). *I usually take off in my*front yard, but*I have a*paved road with a downhill approach to the*South that should help get enough speed to take off and get over my flying field.*

    *I want to see somebody fly 6 perfect circuits above my field,*following the*exact same tract everytime (give or take 10feet),*MAINTAINING 6 feet agl, in a steady 10 to 15mph wind,* without moving your body from your*position on the field after you make the first circuit.* *If you can do it, I'll buy dinner and I'll post*my confession and admission of my error on this forum , I will also*put the video on Youtube giving full credit to the person who showed me the error of my thinking!******************** ******

    But...............If you crash my plane, you buy dinner and my plane!* Further details such as using pylons or changing the CG can be discussed *and agreed upon beforehand.

    Any takers????*
    Nothing about "defining a ground track after demonstrating it at a higher altitude". The intent from you original challenge was clear, and quite reasonable. It seems pretty clear that you gradually realized that your original challenge would be too easy to accomplish, and would not "settle the issue" the way you hoped. So you're now trying to "beef up" the challenge with unreasonable "match my ground track at a slower speed" demands???

    It seems to me that you're not being very honest, you're not as open to learn as you claim to be, and you're not willing to acknowledge your initial errors. The initial errors are no big deal, (I make them daily) but the stubborness and insincerity you seem to be demonstrating now is really frustrating to those of us who spend a lot of time crafting these posts to help someone learn. Maybe I'm misreading you, (very easy to do in these posts), but I'm just saying that's how it seems, and that's why some members are getting frustrated with you and others.

  10. #1060

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    RE: Downwind turn Myth

    m1morrow

    ORIGINAL: m1morrow

    I fly big airplanes for a living. This myth appears because once you turn into a strong headwind i.e. from base to final leg you need more power to maintain the same glide path on final approach. Thats it.
    Ifind this statement to be very interesting and have a couple of questions. Is the turn from base leg to final leg a 90deg turn? Are you increasing power to increase airspeed to keep the rate of descent (glide path) constant with the base leg?

    Larry

  11. #1061

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    RE: Downwind turn Myth

    hugger-4641

    ORIGINAL: hugger-4641


    ORIGINAL: cfircav8r

    Again you are referencing the ground. If you used exactly the same inputs the aircraft would react the same, no closer to stall, only the turn would be elongated in the direction of the wind.
    So if I understand you correctly, in my example below, if I used the same inputs for turn two, the bottom senario is roughly what the turn should look like?
    Do you actually fly circuits like your example on a regular basis? Just about all the flying at my field consists of 180deg turns with the final turn before landing having a straight leg to get back to an approach to the runway.

    Larry

  12. #1062
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    RE: Downwind turn Myth



    These load factor numbers assume constant altitude, so if are trying to stay level or climb (which is usually the case) you need to generate more lift, then you need more AOA or speed or both to stay alive which takes thrust....





    [/quote]

    Are you sure ? In a climb you need LESS lift than in level flight due to the vertical component of thrust partially balancing weight ! Can't draw the force arrangement here but its true !

    Regards,

    David.



  13. #1063
    cfircav8r's Avatar
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    RE: Downwind turn Myth

    He never said you need more lift to climb than to fly level. His point was if you are flying level or even climbing when you make a turn you will have to increase lift produced by the wing due to the load factor. For what its worth in stabilized flight (not changing speed) the wing will have the same lift regardless of whether you are climbing, descending or in level flight, so if you are climbing at 60 mph or descending at 60 mph your wing is producing the same lift, except in true vertical climbs or descents.

    Regards,

    Robert
    The three most useless things to a pilot, the sky above you, the runway behind you, and the fuel on the ground.

  14. #1064

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    RE: Downwind turn Myth

    I have seen plenty people SNAP ROLL turning downwind in stron g winds because they applied too much elevator in an attempt to maintain altitude. . . .when they should have been adding throttle. I dont think the same applies for a loop. The plane is upside down and attempt to head downwards. . . . not exactly a stall.

    "steps off soap box and runs into the hills"

  15. #1065

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    RE: Downwind turn Myth

    OMG, this thing could go to 2K posts....

  16. #1066
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    RE: Downwind turn Myth

    There are enough misconceptions, faulty science and plain "I know it's true cuz I seen it" ideas to go on forever.
    The three most useless things to a pilot, the sky above you, the runway behind you, and the fuel on the ground.

  17. #1067
    David Gladwin's Avatar
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    RE: Downwind turn Myth

    ORIGINAL: cfircav8r

    . For what its worth in stabilized flight (not changing speed) the wing will have the same lift regardless of whether you are climbing, descending or in level flight, so if you are climbing at 60 mph or descending at 60 mph your wing is producing the same lift, except in true vertical climbs or descents.

    Regards,

    Robert
    Sorry sir, another myth and emphatically not true !

    Try this: A Lightning weighing 30,000 pounds is in level flight at 250k, wing lift is 30,000 pounds.

    The same aircraft is maintaining a stable 250 knots in a straight 45 degree climb, full dry power, 20,000 pounds of thrust how much lift is the wing producing ?

    Answers please, preferably on a £50 note !

    (Hint : not 30,000 pounds and sin 45 is .7071)

    Regards,

    David.

  18. #1068
    cfircav8r's Avatar
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    RE: Downwind turn Myth

    30,000 lbs, the excess power is causing the climb.
    The three most useless things to a pilot, the sky above you, the runway behind you, and the fuel on the ground.

  19. #1069
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    RE: Downwind turn Myth

    Wrong, try again.

    Even Wikpedia gets it right :





    In flight, an aircraft can be considered as being acted on by four forces: lift, weight, thrust, and drag.[2] Thrust is the force generated by the engine and acts along the engine's thrust vector. Lift acts perpendicular to the vector representing the aircraft's velocity relative to the atmosphere. Drag acts parallel to the aircraft's velocity vector, but in the opposite direction because drag resists motion through the air. Weight acts through the aircraft's centre of gravity, towards the centre of the Earth.
    In straight and level flight, lift is approximately equal to weight. In addition, if the aircraft is not accelerating, thrust is approximately equal to drag.[3]
    In straight, climbing flight, lift is less than weight.[4] At first, this seems incorrect because if an aircraft is climbing it seems lift must exceed weight. When an aircraft is climbing at constant speed it is its thrust that enables it to climb and gain extra potential energy. Lift acts perpendicular to the vector representing the velocity of the aircraft relative to the atmosphere, so lift is unable to alter the aircraft's potential energy or kinetic energy. This can be seen by considering an aerobatic aircraft in straight vertical flight - one that is climbing straight upwards (or descending straight downwards). Vertical flight requires no lift! When flying straight upwards the aircraft can reach zero airspeed before falling earthwards - the wing is generating no lift and so does not stall. In straight, climbing flight at constant airspeed, thrust exceeds drag.
    In straight, descending flight, lift is less than weight.[5] In addition, if the aircraft is not ac

  20. #1070

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    RE: Downwind turn Myth


    ORIGINAL: flythesky

    m1morrow

    ORIGINAL: m1morrow

    I fly big airplanes for a living. This myth appears because once you turn into a strong headwind i.e. from base to final leg you need more power to maintain the same glide path on final approach. Thats it.
    Ifind this statement to be very interesting and have a couple of questions. Is the turn from base leg to final leg a 90deg turn? Are you increasing power to increase airspeed to keep the rate of descent (glide path) constant with the base leg?

    In real airplanes in the pattern we try to allways use the same bank angle (somewhere around 30 degrees of bank at the most) especially turning from base to final because this is where you are the lowest and slowest. We call it coffin corner.

    Yes all turns in a pattern are 90 degree turns. I fly RC planes the same way too. Its a Box pattern.

    When I'm flying any airplane from the big Learjet 45 I fly to a small mooney or a cessna or something I'm really only looking at the ground and compensating for wind to make the pattern look like a box. And making nice shallow banks. You dont turn steeper to make it look like a box you turn sooner. The whole time I'making sure I have enough speed not to stall. Especially in a jet because things can happen faster.

    The only compensation you need to make on the base leg is a crab into the wind. Then if there is a large headwind on final as soon as you turn base to final you have to add a little power to maintain a nice glide path.......... otherwise you would keep the same power setting and hold back on the stick more and you would get really slow and possibly stall.

    If you guys have more questions about areodynamics and stuff ask me. Ihave a degree in aviation and teach and fly for a living.




  21. #1071
    cfircav8r's Avatar
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    RE: Downwind turn Myth

    Sorry I couldn't resist. All you had to do is show the simple lift, drag, thrust, weight model to prove me wrong. We have to get to 2000. I do stand by the first part of my post though. In a climbing turn you need more lift than in a straight climb.
    The three most useless things to a pilot, the sky above you, the runway behind you, and the fuel on the ground.

  22. #1072

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    RE: Downwind turn Myth

    Guys dont look on wikipedia.........

    Straight and level flight Lift=Weight and thrust=drag.

    During a climb Lift is momentarily greater than weight (causing an ecceleartion upward...... you feel gforce or load factor or whatever you want to call it) then once the plane is climbing constantly lift=weight......i know its kind of counter intuitive but its ture.

    How does it feel when your in an airliner and its taking off. You feel G's or load factor when the plane rotates but when its climbing out you dont feel any g's.
    If Lift was allways greater then weight in a climb the plane would climb at a higher and higher rate.

    If you are not sowing down during a constant rate climb or descent Lift=weight and Thrust=Drag.

    I remember having this discussion in college. Some guys could not wrap their heads around this. I can pull my text books and and end all these myths right here lol. Fun to talk about though.




  23. #1073
    cfircav8r's Avatar
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    RE: Downwind turn Myth

    As you get closer to vertical drag is joined by gravity and thrust is required to overcome both forces. in normal flight it is near imperceptible but is there. Since some of the gravity is being overcome by thrust less lift is needed from the wing. Thrust can counter drag and gravity, but lift can only counter acceleration whether it be from gravity or centripetal forces due to pitch changes and turns.
    The three most useless things to a pilot, the sky above you, the runway behind you, and the fuel on the ground.

  24. #1074
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    RE: Downwind turn Myth

    Exactly !

    M1morrow: Coffin corner is where Vs = Mcrit, i. e top right of flight envelope. Never heard it used to describe low alt. stall. in the way you suggest.

    It is believed that the AF 330 lost over the Atlantic was operating pretty close to it when control was lost. Been pretty close to it in a Canberra at FL550, speed range (low IAS- Mach no. spread) got VERY small !

    Pelicans don't have the problem, even in Australia !

    Regards,

    David.

    PS answer to earlier question:

    The vertical component of 20 k pounds of thrust in a 45 degree climb is = 14, 000 pounds . A/c weight (mass) 30, 000 pounds , so 30k less 14 k = 16k pounds of wing lift required ! Gets less as climb angle increases !

  25. #1075
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    RE: Downwind turn Myth

    Yet one more partially correct answer. AND way, way off topic besides.
    RCU Rocks, I\'\'d hate to be without it !!


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