Announcement

Collapse
No announcement yet.

tick tock tipms topms

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Evan
    replied
    Originally posted by Not_Karl View Post
    Virgin Australia B738 takes-off after overrunning available runway into a closed section.
    https://avherald.com/h?article=502215e7&opt=0
    Methinks this was less a case of performance miscalculations and more a case of not getting (or not reading) the NOTAM.

    Leave a comment:


  • Not_Karl
    replied
    Virgin Australia B738 takes-off after overrunning available runway into a closed section.
    https://avherald.com/h?article=502215e7&opt=0

    Leave a comment:


  • 3WE
    replied
    Originally posted by Gabriel View Post

    Good point, although I was thinking the "almost" more on the line of quite powerful singles that have a relatively slow take-off speed, like a Cessna 182. Especially if lightly loaded, it will get to 60 knots in a rush and by that time, with the positive deck angle that it has on the ground (to avoid prop strike) and flaps 10, the lift will be a good fraction of the weight, leaving not a lot of weight-on-wheels, so I am not sure that you would be able to stop from 60 knots in the same or less distance that it took to get to 60 knots in the first place.
    Complex Gabrielian thought process which is kind of interesting.

    I guess retract the flaps…and use measured pull ups to put what weight you can on the MLG…avoiding a formal rotation.

    Leave a comment:


  • Gabriel
    replied
    Originally posted by 3WE View Post

    Maybe not_on glaze ice.
    Good point, although I was thinking the "almost" more on the line of quite powerful singles that have a relatively slow take-off speed, like a Cessna 182. Especially if lightly loaded, it will get to 60 knots in a rush and by that time, with the positive deck angle that it has on the ground (to avoid prop strike) and flaps 10, the lift will be a good fraction of the weight, leaving not a lot of weight-on-wheels, so I am not sure that you would be able to stop from 60 knots in the same or less distance that it took to get to 60 knots in the first place.

    Leave a comment:


  • 3WE
    replied
    Originally posted by Gabriel View Post

    (almost?) any speed on the ground deceleration due to braking is greater than acceleration due to engine power.
    Maybe not_on glaze ice.

    Leave a comment:


  • Gabriel
    replied
    Originally posted by 3WE View Post
    Good information on the 70-50 rule…Given that acceleration is “actively decaying” I’m thinking Dan Juan’s rule depends on strong braking being available…yes?
    In my limited experience in GA piston singles, at (almost?) any speed on the ground deceleration due to braking is greater than acceleration due to engine power. So if you could accelerate to any given speed in 50% of any given distance, you can stop from that speed in the other 50%.

    Leave a comment:


  • 3WE
    replied
    Originally posted by Gabriel View Post
    Note that V1 is not useful as a go-nogo decision in multi-engine jets either for the case of reduced performance.
    Perhaps I read it differently than your intent.

    I’m thinking a V-1 is calculated for DELIBERATE reduced-performance takeoffs and that it works, as intended, for that scenario.

    If performance is less than ASSUMED, then yep, it’s invalid.

    Good information on the 70-50 rule…Given that acceleration is “actively decaying” I’m thinking Dan Juan’s rule depends on strong braking being available…yes?

    Leave a comment:


  • Gabriel
    replied
    Originally posted by 3WE View Post
    Originally posted by Gabriel
    Note that V1 is not useful as a go-nogo decision in multi-engine jets either for the case of reduced performance.
    Huh?
    The V1 model assumes that the performance is normal until something happen and you make a decision to continue with one engine less (but nothing else affecting performance) or stopping (with a normal stopping performance). It will not prevent you from running out of runway before Vr because the engine thrust was less than it should or because you are dragging your brakes, because there is no single decision event where you would say "ok, now we need to decide if we stop or go: Are we above or below V1?" You actually could run off the end of the runway without ever achieving V1 to begin with.

    Leave a comment:


  • Gabriel
    replied
    Originally posted by 3WE View Post
    I concur that Dan’s rule is BS.

    Light planes need very different rules DEPENDING on the situation.

    For the typical long runway- if your acceleration is off and you miss your liftoff point YOU STOP. The one engine really needs to be working right.

    Now…for truly short fields where accelerate stop is an issue…you need a speed vs distance check THAT ALLOWS YOU TO STOP.

    There’s also a top secret method of a nice check before you are too committed, that was alluded to by a respected airline pilot.

    Of course, Boeing Bobby’s well-trained a$$ and sixth sense is also pretty darn good.

    Footnote: It’s possible that Dan’s rule provides decent protection, but it’s based on nothing concrete. Perhaps the general disdain that one of our friends has for him is well founded?
    Doing some basic physics and math I found out that, with constant acceleration, and starting from rest, you achieve 70% of any speed in 50% of the distance needed to achieve 100% of that speed. I suspect that that's the basis for this "rule" which, in that case, should be in "survivor's" version, not Dan's. You must achieve 70% of the take-off speed in 50% of the take-off run. If not, you stop.

    Something nice about this is that, even if you attempt the take-off in a runway that exactly equal to the take-off run, by the time you decide to abort you still have 50% of the runway remaining. And for sure you will be able to stop the plane from a given speed (especially a general aviation piston single) in less distance that it took to achieve that speed in the first place.

    But there are problems. First, it assumes that the acceleration is constant, which is not. Not only because drag builds up as you gain speed, but also thrust reduces as you gain speed. Second, it assumes no wind. If you have a headwind component, as you would in most take-offs), you would achieve 70% of your liftoff GROUND speed in 50% of the take-off run distance, For example, say that a plane takes 1000ft to accelerate to the take-off speed of 60 knots. Then it should achieve 42 kts (70% of 60 kts) by the 500ft mark. Now say that there is a 18kts headwind. The take off run to achieve 60 kts now is 500 ft. But the decision point should not be stated now as "250 ft to achieve 42kts -70% of 60 kts-". But 250 ft to achieve 47 kts. Why 47 kts? Because that airspeed corresponds to a ground speed of 29 kts, which is 70% of 42 kts, which will be your ground speed when your airspeed reaches 60 kts (due to the 18 kts headwind).

    So the algorithm should be:
    1- Calculate the distance it will take the plane to achieve the take-off airspeed.
    2- Calculate 50% of that distance, that will be the "decision point".
    3- Subtract the headwind from the take-off airspeed to convert it into ground speed
    4- Calculate 70% of that ground speed
    5- Add the headwind to convert that 70% groundspeed into airspeed. That will be your decision criteria.

    Now, again, all of the above is with constant acceleration. I know that acceleration will not be constant, it will decrease as speed increases, but I don't know if it would be significant or negligible.

    Leave a comment:


  • 3WE
    replied
    Originally posted by Gabriel View Post
    Note that V1 is not useful as a go-nogo decision in multi-engine jets either for the case of reduced performance.
    Huh?

    Leave a comment:


  • 3WE
    replied
    I concur that Dan’s rule is BS.

    Light planes need very different rules DEPENDING on the situation.

    For the typical long runway- if your acceleration is off and you miss your liftoff point YOU STOP. The one engine really needs to be working right.

    Now…for truly short fields where accelerate stop is an issue…you need a speed vs distance check THAT ALLOWS YOU TO STOP.

    There’s also a top secret method of a nice check before you are too committed, that was alluded to by a respected airline pilot.

    Of course, Boeing Bobby’s well-trained a$$ and sixth sense is also pretty darn good.

    Footnote: It’s possible that Dan’s rule provides decent protection, but it’s based on nothing concrete. Perhaps the general disdain that one of our friends has for him is well founded?

    Leave a comment:


  • Evan
    replied
    Originally posted by Gabriel View Post

    The accident is very recent, there is no result of the investigation. The pilot reported what was apparently the engine not producing enough power (as shown by it's inability to accelerate to lift-off speed in the distance it should have and then it's inability to accelerate and climb after lift off even when they were basically at sea level and below maximum weight) but according to the pilot, while now in hindsight he realizes he had a feeling that something was not good during the take-off roll, it was not strong or clear enough as to identify a slow acceleration, and all the engine instruments read normal (that is a bit hard to believe: while not impossible, there are very few ways in which the engine can have the right manifold and right RPM and not producing the useful power that it is supposed to be delivering)

    There is no V1 in single-engine planes (and neither in light twins). There is no accelerate-stop distance in the manuals. Accelerate-stop is based on the decision making process around one engine failing. If an engine fails in a single, you stop at whatever speed that happens. Note that V1 is not useful as a go-nogo decision in multi-engine jets either for the case of reduced performance.
    Well, TOPMS would be good for all planes and seems like a no-brainer in this gadget age when your watch can tell you if you are about to drop dead.

    Leave a comment:


  • Gabriel
    replied
    Originally posted by Evan View Post

    So I skimmed through the video. What was the 'probable cause'? Did they ever determine that? If it was degraded engine performance, I suppose another rule could be to watch your engine instruments and reject before V1 if they seem off (assuming your V1 calculation includes stop distance). He seems to have a well-developed instinct for what is normal performance on that plane but he refers to it as 'a feeling', not any actual indication.
    The accident is very recent, there is no result of the investigation. The pilot reported what was apparently the engine not producing enough power (as shown by it's inability to accelerate to lift-off speed in the distance it should have and then it's inability to accelerate and climb after lift off even when they were basically at sea level and below maximum weight) but according to the pilot, while now in hindsight he realizes he had a feeling that something was not good during the take-off roll, it was not strong or clear enough as to identify a slow acceleration, and all the engine instruments read normal (that is a bit hard to believe: while not impossible, there are very few ways in which the engine can have the right manifold and right RPM and not producing the useful power that it is supposed to be delivering)

    There is no V1 in single-engine planes (and neither in light twins). There is no accelerate-stop distance in the manuals. Accelerate-stop is based on the decision making process around one engine failing. If an engine fails in a single, you stop at whatever speed that happens. Note that V1 is not useful as a go-nogo decision in multi-engine jets either for the case of reduced performance.

    Leave a comment:


  • Evan
    replied
    Originally posted by Gabriel View Post
    GA is not immune...

    I will give some thought (engineering thought) to this 70% 50% rule. My instinct says it is not correct neither in the form stated by Dan nor in the form stated by the surviving pilot.

    https://www.youtube.com/watch?v=ZNUvC5IbybQ
    So I skimmed through the video. What was the 'probable cause'? Did they ever determine that? If it was degraded engine performance, I suppose another rule could be to watch your engine instruments and reject before V1 if they seem off (assuming your V1 calculation includes stop distance). He seems to have a well-developed instinct for what is normal performance on that plane but he refers to it as 'a feeling', not any actual indication.

    Leave a comment:


  • Gabriel
    replied
    GA is not immune...

    I will give some thought (engineering thought) to this 70% 50% rule. My instinct says it is not correct neither in the form stated by Dan nor in the form stated by the surviving pilot.

    https://www.youtube.com/watch?v=ZNUvC5IbybQ

    Leave a comment:

Working...
X