Effect of Density Altitude on Crosswinds

Discussion in 'Flight Following' started by ebykowsky, Feb 19, 2015.

  1. CharlieTango

    CharlieTango Line Up and Wait

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    Some people do come out of the crab wings level and manage to get tires on the runway before too much drift develops.

    Others transition to a slip and minimize side-loading.
     
  2. whifferdill

    whifferdill Line Up and Wait

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    For you, "slip" is a red herring in this discussion. Flight path alone cancels drift. You can fly a constant flight path in coordinated flight, slipping left, or slipping right.

    If you think left aileron in a left x-wind is what is cancelling drift, here is what you need to do - Fly crabbed and tracking the runway, and then apply a slip with LEFT rudder and RIGHT aileron. You will still be tracking the runway, and "cancelling" drift, but you will just be even more misaligned with the runway. Flight path still doesn't change. Have you ever considered this? Hint: don't actually touch down this way. ;)

    Post # 396.
     
    Last edited: Feb 24, 2015
  3. CharlieTango

    CharlieTango Line Up and Wait

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    If the handbook wasn't challenged I would still be thinking that steady state crosswind actually impacts my aircraft as I drift into it. I now grasp the physics better.

    Rudder authority produces only so many degrees of yaw before a turn develops and hence the limitation on crosswind capability. Its good to get that, at least for me.
     
  4. vintage cessna

    vintage cessna Cleared for Takeoff

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    Yes the flight path cancels the drift. In slip the airplane has a sideways movement component , that is why you don't drift.

    What I have considered is that in a crosswind you land the airplane properly, you just don't know why you have. So , the discussion is purely academic.
     
  5. whifferdill

    whifferdill Line Up and Wait

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    Did you even read my post above? If the "sideways movement component" of a slip is what is cancelling drift, how is it that you can slip in both directions in a left x-wind, and still not drift off runway track?? Shall I shoot a video of this too? You are getting less argumentative, we must be getting close. :D
     
  6. Vance Breese

    Vance Breese Line Up and Wait

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    In my limited experience in fixed wing aircraft I found I could fly sideways through the air (uncoordinated flight).
    I found the nose was seldom pointed at my destination so I feel I was flying sideways in relation to my ground track.
    I am puzzled by your divergent perspective.
     
  7. vintage cessna

    vintage cessna Cleared for Takeoff

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    You can't slip to the right in a left crosswind and not drift off course.

    Sure, I read your post, I just fundamentally disagree with it. I have posted a reference from a source material, you have not. So we will just agree to disagree.
     
  8. whifferdill

    whifferdill Line Up and Wait

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    Oh man, this one is so easy. Next x-windy day, video will happen - even though you may disagree with what you see on video. :) So far, we have helped one person in this thread. To me, that is worth it.
     
  9. CharlieTango

    CharlieTango Line Up and Wait

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    My nose seldom points at my destination, that is because of WCA not flying sideways through the air mass.

    You are correct you can fly sideways relative to your ground track, that is due to the drifting air mass that you are flying within.
     
  10. vintage cessna

    vintage cessna Cleared for Takeoff

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    Ok, can't wait to see the video. Now that you have done your good deed for the day by helping CT, maybe you can help him with the DA issue.
     
  11. MAKG1

    MAKG1 Touchdown! Greaser!

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    You can fly sideways in no wind at all. It's a good proficiency exercise to adjust position on the runway in a low approach, all while keeping the nose pointed straight ahead.
     
  12. vintage cessna

    vintage cessna Cleared for Takeoff

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    One last thing CT. Do you see a problem with your logic and how you have contradicted what you have said before?

    It is very possible to transition to a slip from a crab and not minimize side load but eliminate it.
     
  13. dtuuri

    dtuuri En-Route

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    Well, you can certainly make a left turn while banked to the right, then after turning a certain amount stop and hold it in a forward slip. I suspect that's all the video will show.

    dtuuri
     
    Last edited: Feb 24, 2015
  14. CharlieTango

    CharlieTango Line Up and Wait

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    When its argued that you can't fly sideways in this thread the meaning isn't that you can't slip the meaning is to adjust your flight path for drift it takes turning, or bending your flight path.
     
  15. CharlieTango

    CharlieTango Line Up and Wait

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    400 posts ago I was confused and this thread has provided carity.

    I agree 100% side load can be eliminated.
     
  16. whifferdill

    whifferdill Line Up and Wait

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    If I had flown these exact same inputs in a left x-wind, only started from crabbed, runway tracking flight, you think I'd drift to the right off track each time I slipped to the right? Why would I need to make a "left turn while banked right"? So if I replicate these inputs in a x-wind, while maintaining runway track, you're going to claim I'm turning the airplane left when I'm banked to the right?

     
  17. Vance Breese

    Vance Breese Line Up and Wait

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    That sir is exactly why I feel using standard aviation terminology has value in avoiding misunderstandings and pointless debate.
    Apparently I missed in this thread where there was agreement that we redefine sideways, turning and bending.
    Thank you for your help.
     
  18. dtuuri

    dtuuri En-Route

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    If you were exactly crabbed the right amount to track the centerline I think (I know) any slip on the same or less of the original difference (crab angle) from the runway heading would drift you to the right.

    Any plane that can be turned with rudder can be banked the other way to cause a lesser offsetting turn resulting in a net turn the "wrong way". So, if you want to continue the runway track you'd have to change your direction (crab angle) to account not only for the wind drift, but also for the drift of the slip--ergo, you'd turn even further away from the runway and thus decieve the video viewer who might not take note of the additional fuselage angle with the runway.

    No because those inputs won't track the runway in a crosswind. You'll have to increase the slip angle on the upwind side compared to the downwind as measured from the initial crab heading.

    dtuuri
     
    Last edited: Feb 24, 2015
  19. vintage cessna

    vintage cessna Cleared for Takeoff

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    You can slip left and the aircraft will move left ( adjust the flight path). Are you saying that in a slip that the plane is turning on a curved path?

    If that were true you could place a plane in a slip and turn 360 degrees without changing your heading. The airplane will move in a straight line at a diagonal angle to the nose.
     
  20. whifferdill

    whifferdill Line Up and Wait

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    OK, I'm looking forward to some stiff x-wind around here. :) Wish I still had the Cub to fly. Its slow speed would show the x-wind even better.
     
  21. CharlieTango

    CharlieTango Line Up and Wait

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    A slip is an attitude, it could be straight or it could be a slipped turn.
     
  22. dtuuri

    dtuuri En-Route

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    Wish I could go with you, to keep you honest of course. :wink2:

    Hey, ever thought of putting a yaw string in your camera angle? A nice big inclinometer would be a good touch too.

    dtuuri
     
  23. whifferdill

    whifferdill Line Up and Wait

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    I would if I had a second seat. :) Just keep in mind that if I'm turning the airplane left while banked right, that it would be impossible to maintain runway track. I can hold the bank indefinitely in each direction if you're suspicious of me rolling back the other way before this "drift" or "turn" can be seen. ;) Most of my videos are of aerobatics, might as well do something different. :)

    Yaw string? Never flown behind a yaw string in a prop plane. Would the prop wash not negate the relative wind indication on the string?
     
    Last edited: Feb 24, 2015
  24. MAKG1

    MAKG1 Touchdown! Greaser!

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    After some time in a glider, I asked a similar question.

    With one prop on the nose, it ain't working, no way.

    With a twin or a pusher prop, that's much better.
     
  25. eetrojan

    eetrojan Pattern Altitude

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    I've read this whole thread and I think that both sides are right and are simply not seeing the other's point of view.

    It's like the old parable of several blind men touching an elephant, feeling different parts (softball for 6PC), and then being in complete disagreement about the characteristics of the elephant. They're experiences are all true, but none of them are totally true. (No insult meant by reference to "blind men").

    From my inexperienced mind -

    The bank angle produces a horizontal component of lift that brings the RW in at an angle that cause the plane, left to its own devices, to "turn" along a curved flight path because the tail will continually try to face the plane into the RW.

    The application of opposite rudder, however, can be used to prevent the tail from weathervaning to face the plane into the RW and, I think this observation is important (and hopefully correct:confused:), also directs the thrust vector at an angle relative to the plane's direction of travel (i.e. at an angle relative to the RW).

    All that said, isn’t it true that the pilot can skillfully control the relative amount of aileron and opposite rudder in a slipping flight condition to do any one of the following?:

    (1) “turn” the plane in either direction, while slipping, in the sense that the plane follows a curved flight path by continuously maintaining an imbalanced force vector in the horizontal plane; or

    (2) “side slip” the plane in either direction, while slipping, in the sense that the plane moves left or right while essentially staying on a parallel flight path, by applying those same horizontal force vectors in a more balanced, more subtle manner; or

    (3) "forward slip" the plane along a continuous course, while slipping, by keeping the horizontal forces that would otherwise "turn" or "side slip" the plane in complete balance?

    Seems to my newbie-mind that all three scenarios are possible just by varying the relative amount of aileron and rudder in a skillful and timely manner.
     
    Last edited: Feb 24, 2015
  26. Bobanna

    Bobanna Line Up and Wait

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    Wow. You're a giver, Whiff. I'm there for you.
     
  27. Silvaire

    Silvaire En-Route

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    Yes I did and I also pointed out that your nose was swinging left and right. Balance your aileron and rudder inputs to hold the nose on the same heading right down the runway and see what happens. It can be done, just start out slow, lead with aileron input and feed in the rudder required to hold the nose on it's current heading.

    Bear in mind I was taught this stuff back in the late 60's and it's just an exercise that has no real use other than to develop coordination in cross controlled flight. It's not a method you normally use, at least not consciously other than maybe when coming out of base turn to short final with a crosswind from left you might just roll out right into the slip and hold the nose on the centerline rather than go all the way into a crab that you'd have to undo anyway.

    The only reason I ever mentioned this was because someone, somewhere along the line in thisw thread made the statement that it was physically impossible and, having done it I knew that not to be the case. I suppose it's very likely that many people have never done it and so are unfamiliar with it. But believe me it does exist and it does what it says it does. When I get the opportunity I'll go up in the Champ with the new iVues and make a video.

    You'll find it not only in FAA H-8083-3A Aircraft Flying Handbook but also in many other sites and publications if you Google "Constant Heading Slip" such as Warbird Notes - section 16-6 which says, in part: (bear in mind they're talking about a DC3 here)



    The other thing I'd add is that there are some semantics issues here as wiff has suggested. My suggestion is that we all keep civil about it and not let it get into a personal tiff. We're all adult pilots here.
     
    Last edited: Feb 24, 2015
  28. dtuuri

    dtuuri En-Route

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    You have to try it to find out. I've had good success, but there were times it didn't work in the first place I taped the string. You might try taping a row of them and marking the best location for future reference. Make sure the strings aren't too long or they'll get sucked into the prop before you taxi to the end of the runway. BTDT. :redface: Once you find the sweet spot they're pretty cool.

    EDIT: I've taped them to the cowling and the windscreen in various places. It's surprising how little the prop affects the string once you find a good spot.

    dtuuri
     
    Last edited: Feb 24, 2015
  29. FastEddieB

    FastEddieB Final Approach

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    With my pusher prop and tandem seating, I could do a yaw string pretty easily.

    Will it show anything beyond what the ball does?
     
  30. CharlieTango

    CharlieTango Line Up and Wait

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    Only if your ball needs calibrated
     
  31. vintage cessna

    vintage cessna Cleared for Takeoff

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    That is a good reference. I made a reference to the FAA Airplane Flying Handbook, but it was a waste of time.

    One fellow said the books explanation of a side slip made it sound like the airplane will move sideways, so that couldn't be right. Another said such book was dumbed down for students and so would not give the whole story, and yet another said it was something a monkey would regurgitate.

    So what is the point? You are going to make a video to prove something that has already been proven. What ever you put up there is going to be contested.Why get wrapped up in this to that extant? I think forums like these are just a way to get a little entrainment and wile away the time when the weather is freezing. Sort of like a coffee shop.
     
  32. dtuuri

    dtuuri En-Route

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    Even if the ball's centered, it might show you climbing out in a... wait for it... a slip. Due to asymmetrical thrust in the climb (like pulling a plane out of the hangar by one side of the prop) and you holding right rudder to compensate, I bet you see the relative wind coming from the left, uh, that is if the prop on your pusher isn't going the wrong way in which case it'll be left rudder and from the right. Let me know what it does.

    dtuuri
     
    Last edited: Feb 24, 2015
  33. Silvaire

    Silvaire En-Route

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    In my case I'm caring for a seriously ill family member, haven't been into work for six months and pretty much sequestered bedside 24/7 for the past three weeks. This laptop is my only portal to the outside world right now, you'd never see me spending this much time here under normal circumstances, nor would I have so much time to ponder things. :nonod:

    The video will be a piece of cake, don't really care much if anyone believes it or not.
     
  34. RotorDude

    RotorDude Pattern Altitude

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    Silvaire, best wishes for your family member, and nice of you to do that.
    RD
     
  35. FastEddieB

    FastEddieB Final Approach

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    Not sure I follow the first part, but I will definitely try a yaw string* on a future flight and video the result.

    My Sky Arrow shows little, if any, p-factor in a climb. But if it did, it should cause a need for left rudder in a climb - the ROTAX turns normally but is mounted "backwards".

    *I may also try a "pitch string". Seems like it could be a poor man's AOA indicator.
     
  36. dtuuri

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    You mean this?
    "Even if the ball's centered, it might show you climbing out in a... wait for it... a slip."​
    "It" would be what the yaw string shows even while the ball is centered.

    dtuuri
     
  37. FastEddieB

    FastEddieB Final Approach

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    That's what seems to be physically impossible, but I'm working on it.

    Anyway, found the image of pusher p-factor I came up with for another thread:

    [​IMG]

    The left blade is the one moving down into the relative wind, with the right one retreating.
     
  38. dtuuri

    dtuuri En-Route

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    It's the same as a twin on one engine--if the wings are level and the ball is centered, it's in a sideslip. By banking toward the good engine the slip goes away, but the ball is displaced from the center. Your pusher would behave like a P-Navajo I used to fly. It had geared engines with non-conventional propeller rotation. Had to hold left rudder on takeoff and climb.

    dtuuri