Anti-Spin Ideas

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by REVAN, Jun 1, 2017.

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  1. Jun 25, 2017 #501

    Aesquire

    Aesquire

    Aesquire

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    Since box canyon turns have come up, I have a question. ( that I think I already have an answer to... so it's a test )

    You are flying in a canyon below the top of the ridges on either side. Right down the middle. You see the ground rising ahead and lack the excess power to rise above it. You think you have enough room to turn around, but not just using half the canyon's width.

    You decide to turn about 30 degrees towards one side with the intent of performing a 210 degree turn back the way you came.

    There's a cross wind in the canyon.

    Which way do you make your "cheating" turn towards the ridge? First downwind then big turn upwind? Or the reverse?
    Why?

    I'm interested in finding out how wrong I might be :)
     
  2. Jun 25, 2017 #502

    BBerson

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    Depends on the crosswind amount and room ahead. With strong crosswind just turn into the wind.
    Almost always best to turn around into wind. (Since you are already tacking into the wind, right?)
    The basic rule is never turn downwind toward a mountain.
    Of course the other basic rule is never fly up the middle. Fly up the windward side with your nose pointed away from the ridge. The windward side is in lift. The lee side is sink. So flying up the lee side in the sink and turning back downwind is the worst possible approach.
     
  3. Jun 25, 2017 #503

    mcrae0104

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    Observation 1: You quoted me, yet you say "neither of you..." Who is the other person you're addressing? Unlike you, ekiMneriB'O/MikeO'Brien/Winginit, I only have one user name.

    Observation 2: Didn't you protest very recently that you didn't want to discuss the magical qualities of the Storch any longer? And yet... There you go again.

    Observation 3: I invited you to carry on the conversation via PM in order not to derail REVAN's thread. Instead you carried on. Let the rest of the readers judge for themselves.

    Luddite? You're too kind. The appropriate adjectives would violate HBA's rules of conduct, so I'll refrain.

    [HR][/HR]
    Those who post ridiculous things should not be surprised when they are ridiculed.
     
  4. Jun 25, 2017 #504

    REVAN

    REVAN

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    I've got to ask this again, because this has been brought up before, and when I asked for a proper defense of the position, I never got a response. Why do people keep making this assertion? Unless folks are just referring to planes with a rudder interconnect like the Ercoupe as the totality of all "planes that resist spins", I can't think of a reason for making this claim.
     
  5. Jun 25, 2017 #505

    Aesquire

    Aesquire

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    I am going to assume that the "windward" side is the downwind wall of the canyon, and the "lee" side is upwind. In reference to the 2 different ridges. Correct? ( makes perfect sense but may be confusing, at least to us easily confused :) )

    You are absolutely correct that you should not fly down the middle but on the downwind side. And that flying on the upwind side and turning down wind is bad.

    In the example and limits of the question, where you foolishly were sight seeing down the middle ;) and need more room to make your turn, you'd "cheat" downwind before the escape turn? ( I would since the lift is there, and strongest at the top of the ridge, while the sink and rotors are strongest in the lee of the upwind ridge near the top. ..... experience tells me lift is in limited locations, but sink goes all the way down. :) )
     
  6. Jun 25, 2017 #506

    Aesquire

    Aesquire

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    The Grumman F3F had undesirable spin recovery characteristics. Navy specs at the time called for recovery after a fully developed 3 turn spin. While prompt action upon beginning a spin worked, after 3 turns it was nearly impossible to recover. It took time, and lives, but the Navy changed the spec.

    I can see that control limited aircraft, like the Ercoupe, would have trouble recovering if you got into a spin. ( The reason the Acro faction here dislikes control limited planes. The "If I tell it to spin sideways, by golly, it better do it!" approach )

    I'm not positive it's a given that cuffs , for example, reduce spin recovery ability... but I could be wrong, please enlighten me.
     
  7. Jun 25, 2017 #507

    BBerson

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    Well, for example from Stowall's book page 326-
    "The irony here is that the same modified leading edge cuff used to delay the stall on the outboard part of the wing could later contribute to delayed recoveries once spinning started."

    So "spin resistant" does not guarantee that a developed spin recovery is possible.
     
  8. Jun 25, 2017 #508

    BBerson

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    Yes, the downwind side is the lift side and less turbulent. But I would avoid the mountain valley completely in any significant wind. Just too unpredictable.
     
  9. Jun 25, 2017 #509

    Aesquire

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    Ah! the safe and sane approach. Like I was taught "Maintain thine airspeed, lest the Earth rise up and Smite thee".
     
  10. Jun 25, 2017 #510

    wsimpso1

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    With regards to spins, a couple of things have long been found to be true:

    Easy in, easy out - This one is very common. Most airplanes with decent flying qualities and acceptable stability and that can be easily spun, can also be easily stopped. This is usually because of several features: foil gives sharp stall, wing is not designed to resist stall progression, and plenty of elevator and rudder. You thus have strong ability pitch up and induce yaw, and can make much of the inside wing go from flying to stalled with small AOA change. Aply full rudder and aileron, the inside wing stalls and the rotation commences. That same big elevator, when neutralized along with reversing that same big rudder stops the rotation, then followed with forward stick drives the airplane back across the thin dividing line between stall and attached flow and the spin transitions to a spiral dive.

    Hard to enter a spin historically comes about from several features: Limited horizontal tail authority, a wing that resists outward stall progression, an airfoil that takes a lot of AOA change to go from flight to fully stalled. You can play a lot to get it to do a spin entry, it gives the pilot lots of warning that it is getting close, and then it does enter the spin, now you have to achieve a big change in AOA to unstall the stalled wing, but you have small ability to pitch down for AOA reduction and small ability to stop rotation. Hard to enter, hard to get back out.

    One other issue is that entry commences with relatively small rotation speed in yaw, but as the spin progresses, the rotation rate increases, the speed difference and, unavoidably, the AOA difference between wings gets larger and more kinetic energy is stored in the rotation rate. So, once the rotation rate has built up, you have to apply more force against rotation for longer to reduce the rotation and break the spin...

    Now, all of this does not mean that it must be this way, there may be ways of making the airframe design that can be tough to enter a spin, but easy to get out, but I do not know of them... It will be a great discovery if it is found.

    Billski
     
  11. Jun 25, 2017 #511

    wsimpso1

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    If you are in a canyon (below the rim), the winds above the rim are usually not in play, you are largely shielded from them by being below the walls. Furthermore, if you are hugging the right side wall, you are even more shielded from the winds above the rim. If there is a fair amount of sunshine, the airflow in the canyon is generally upslope - the sun is causing thermal effect up valley and up wall.

    Exceptions? You bet! In the overnight, particularly a clear overnight, the thermal effect will run down valley and down wall, and it takes sunshine a bit to over come it and get flows running uphill. If sunshine is only showing on one wall, not on the other and not on the floor, you can have down drafts on the shaded side well into the day. Side canyons can allow winds aloft to mess with the winds inside the canyon - worst turbulence I ever experienced happened this way. Forest fires can cause big flows toward the fire regardless of slope, best leave flying close to fires to the pros, and yes, even they get surprises. Storms can really play havoc with the in canyon winds, but you are supposed to be on the ground when there are storms in the valleys.

    Nonentheless, I have been taught to fly right side of canyon or valley to reduce head-on encounters, you are in position to turn immediately to lower terrain or commence a box canyon turnaround. The view straight ahead and toward the wall do dominate your attention in canyons, and you should be showing your landing lights so you increase the odds of being seen by wrong-way-charlies in time to just make it exciting. These things are odds improvers, not gaurantees, so stay sharp in canyons.

    Billski
     
  12. Jun 25, 2017 #512

    wsimpso1

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    Rule of thumb used when I got mountain flying was do not enter the valleys when winds aloft forecast for altitude near the top of the ridges exceed 20 knots. Some folks use 15 knots. Wind around ridges can be much higher than the forecast...

    Billski
     
  13. Jun 25, 2017 #513

    wsimpso1

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    The way I was taught to fly canyons, the right wing is into the rocks and you constantly tread the line between having a speed blur on those rocks to the right and not having it. Got a speed blur? Edge out, no speed blur, edge back in. This has the interesting feature of putting you further away when your ground speed is higher, giving a little more room to maneuver while following the canyon. If you are doing this, you do not dare do a cheat turn, you are already about as close to the right wall as you ever want to be. Any closer and you get a speed blur and can not tell how close you are. Just commence your strong pull and then roll into your bank.

    Billski
     
  14. Jun 25, 2017 #514

    BJC

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    Anyone that wants to see a spin rotation speed increase should start a normal spin in a C152, wait two turns, keep in-spin rudder, and apply nose down elevator.


    BJC
     
  15. Jun 25, 2017 #515

    REVAN

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    It appears that most of the reasons for 'hard to get in, hard to get out' have to do with making it hard to stall the plane, as opposed to hard to spin once stalled. Since this is usually achieved through limits on control authority, I can see the connection that people are making. Though historically there is precedence for the correlation, I think the connection is in error. I see the stall and the spin as two distinctly different things. Limiting control authority is opposite of what I would like to achieve.

    My goal is to develop and inspire aircraft that can fly at will into and out of a deep stall at the pilot's command while maintaining control over roll, pitch and yaw. I think it can be done, but it requires a different airframe architecture to enable this type of control.
     
  16. Jun 25, 2017 #516

    BJC

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    "Hard" is difficult to quantify. It is hard to make a Cessna A152 spin, at least it is for me, but I know pilots who think that it automatically spins out of any full stall.


    BJC
     
  17. Jun 25, 2017 #517

    pictsidhe

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    Your technique must be substandard compared to theirs!
     
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  18. Jun 25, 2017 #518

    Dan Thomas

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    Billski's example was of a 42-knot stall airplane travelling at 50 knots. The Helio Courier's stall spped is 30 MPH, which is 26 knots. That makes a difference in turn radius. A big difference.

    Any pilot knows that.
     
  19. Jun 25, 2017 #519

    Paulie

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    I was doing a BFR is a 172 and we couldn't even get it to stall! Just mushed.
     
  20. Jun 25, 2017 #520

    Toobuilder

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    mcrae0104 likes this.

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