How hard to pull - a scenario

Discussion in 'Flight Following' started by Jaybird180, May 17, 2012.

  1. Jaybird180

    Jaybird180 Final Approach

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    You're in an airplane with lackluster thrust-weight ratio at altitude. You're cruising WOT at 100kts, Va is 85, Vy is 75, Vx is 60kts and Vs1 is 55kts.

    You're stupidly flying a poorly charted mountain pass in IMC when terrain warning radar (late for whatever reason) tells you to pull up. Your max certified ceiling says you'll make it over the terrain, but you don't have much performance margin for your vertical manuever.

    Terrain avoidance has a indication pre-programmed at 60kts telling you to climb at that speed, 60kts. You are aware this is is a software bug, in that it always defaults to Vx.

    If you pull too hard, you'll bleed too much energy and pull into an accelerated stall. At 1g you'll smash into the mountain. Not that it matters, but there is a 9g limit on the airframe.

    Can you calculate or determine the optimum solution on the ideal amount of Gs to pull for this manuever?
     
  2. Skylane81E

    Skylane81E Final Approach

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    2g, 60* steep turn for 180*
     
  3. Jaybird180

    Jaybird180 Final Approach

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    Answer must be in the vertical
     
  4. Jaybird180

    Jaybird180 Final Approach

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    ...or do you know that you will not bleed enough energy and stall at 2g?
     
  5. Skylane81E

    Skylane81E Final Approach

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    I don't care, I'll reduce the g load as needed.

    Rules of mounting flying as taught to me is never try to out climb rising terrain, so I won't.
     
  6. Skylane81E

    Skylane81E Final Approach

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    Odds are answer kills you
     
  7. COFlyBoy

    COFlyBoy Line Up and Wait

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    Yes, I can...but not with the data you provided. Give me the coefficient of lift and coefficient of drag and I can calculate the optimal flight profile to get the max altitude gain in the shortest distance.

    Edit: Hmm, after thinking a bit more the right answer may be pull infinite g's for an infinitesimal time so that you are climbing at Vx. That will give you the most altitude for distance covered.

    OK, if you want the wings to stay on you should pull at 3.8g's (for normal category) until you are established at the correct climb angle for Vx.
     
    Last edited: May 17, 2012
  8. Jaybird180

    Jaybird180 Final Approach

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    The engine will not provide enough energy. You barely have a reserve as it stands, only 45kts above stall at WOT.
     
  9. Larryo

    Larryo Pre-takeoff checklist

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    Jay,

    I can't imagine ever getting in this situation to start with... so my answer would be to avoid this situation all together.

    But yes, you can calculate it... but a moot point. If you had the time to calculate it, you should have been calculating how to avoid it in the first place.
     
  10. Jaybird180

    Jaybird180 Final Approach

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    Hence the
    But the question remains
     
  11. Jaybird180

    Jaybird180 Final Approach

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  12. Clark1961

    Clark1961 Touchdown! Greaser!

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    My, what an imagination you have.

    Terrain warning radar in the aircraft you describe?????????????????
    Terrain avoidance with "pre-programmed" indication?????????????

    May as well speculate on whether the moon is made of cheese (since the moon landings were fake).
     
  13. Fearless Tower

    Fearless Tower Touchdown! Greaser!

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    Jay, I think you need to watch the video of the L-19 stall/spin in the Rockies.

    Unless you really, really, really know what you are doing (ie being able to read the mountains for updrafts/downdrafts...etc) you should never try to outclimb the terrain. And since, in your scenario, you got yourself 'stupidly' into the situation, knowing how to use the mountains in your favor is likely not a tool available.

    You can try all the fancy math you want, but none of that matters when you are dealing with kinds of variables you find in the mountains.
     
  14. Jaybird180

    Jaybird180 Final Approach

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    Link?
     
  15. rottydaddy

    rottydaddy En-Route

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    :yeahthat:

    Plenty of good science in just facing the facts: near service ceiling; terrain ahead higher than present altitude; less and less space ahead to turn around at a manageable altitude. IMHO, It's time to turn around, not time to start calculating. If there's a climb profile that will work, I'd prefer to discover it while going in the opposite direction, then double back if and when I gain enough altitude to clear the terrain. Not very convenient in IMC, but it can be done. Much more do-able than trying what you think will work, then having to attempt an abrupt and desperate turn, very close to high terrain near your service ceiling... in IMC. No thanks.

    Every time I've watched that L19 crash vid, I've said aloud "Why aren't you turning now? Turn!! No, don't go that way!!" :dunno:
    I know they were there to look at trees, but he clearly was trying to get higher by going straight ahead, and waited to turn until he was obviously stuck in a corner.
     
  16. rottydaddy

    rottydaddy En-Route

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    Last edited: May 17, 2012
  17. gismo

    gismo Touchdown! Greaser!

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    Just because you have a question doesn't mean it needs to be answered. One might just as well ask what is the best method to safely recover from a vertical dive at Vne+10% at 300 AGL.
     
  18. Everskyward

    Everskyward Administrator Management Council Member

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    This. Remember you are not flying in a laboratory. You're in the real word where there are up and downdrafts, etc. People like to sharpen their pencils and figure out these theoretical problems but you should really avoid any situation which puts you on the edge like this.
     
  19. Larryo

    Larryo Pre-takeoff checklist

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    Amen!
     
  20. skidoo

    skidoo Line Up and Wait

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    If one continues on stupidly flying in IMC that low, I say don't pull up. Darwin will take care of everything.

    But, if one is wisely flying in IMC, he would be well above terrain anyway, and terrain radar would therefore be faulty. So, again don't pull up.
    :D
     
  21. Hiperbiper

    Hiperbiper Line Up and Wait

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    Wouldn't that make a great shirt?

    "Darwin is my Co-pilot".

    Might be useful to keep the "will you take me flyin'? questions to a minimum...

    Chris
     
  22. 1200AGL

    1200AGL Pre-takeoff checklist

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    +1. It was explained to me that most GA aircraft are, at best, able to hold altitude in the mountains. Downdrafts swamp whatever climb rate you can attain. For all intents and purposes you are flying a glider. It wasn't until i went flying in the Rockies in a 172 that I realized how true that is. You need to quickly get the hell out of sink and work the lift, orographic or otherwise. Go try that, Jaybird (with an instructor), and you'll realize just how hypothetical your question is.
     
  23. Threefingeredjack

    Threefingeredjack En-Route

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    Ding ding ding we have a winner. Even if you had a Cray on board you could not compute our way out of this. I'd do a 180.
     
  24. gismo

    gismo Touchdown! Greaser!

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    I think that with a slight rewording it would make a great epitaph:

    "Darwin was my Co-Pilot".
     
  25. gismo

    gismo Touchdown! Greaser!

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    If you ever encounter the downdraft that's generated over the downwind side of a ridge in moderate winds you'll quickly realize that virtually no propeller driven airplane can outclimb the descending air.
     
  26. bbchien

    bbchien Touchdown! Greaser!

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    If you get into that situation you already belong to Darwin. The induced drag from the 2G turn will cause TAS to deteriorate and you will stall in the turn. You don't have any kinetic energy to trade to maintain altitude for this maneuver.