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Engine failure video

Old 16th Nov 2021, 16:50
  #141 (permalink)  
 
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Much better to go into the hedge at the end of the runway at 20kts then into the hedge at the beginning of the runway at 60kts...
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Old 18th Nov 2021, 13:28
  #142 (permalink)  
 
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Originally Posted by Pilot DAR View Post
Oh, by the way, from that steeper descent angle, it will require a greater acceleration upward (G) than normal to flare. Slightly greater G requirement means that stall speed goes up when you pull. Cessna test pilots have learned the same lesson I've learned during flight testing, that the ten knot excess speed above stall on approach is just not enough.
A steeper descent angle does not require a greater acceleration to flare. The guy is talking about a steeper descent resulting from lower airspeed to begin with and I'm quite sure about this because it's in all the textbooks - centripetal acceleration = v²/r. Therefore, load factor in the flare is closely approximated with the formula 1 + v²/rg. The load factor reduces as a function of v². Or, for the same load factor you can flare lower with a tighter arc.

Note, I am not saying the margin has not been reduced. What I am saying is your explanation is wrong. It does not follow that the steeper descent angle requires “greater upward G”. That is not the problem. The problem is you have less kinetic energy available for the flare, which becomes a limit in the power off case. As the angles are quite small, the energy you are going to use up can be approximated with D x r x approach gradient, where D is the average drag. So increasing the gradient obviously eats into the energy margin. Your load factor results in a shorter radius (and this wins out over the extra induced drag) so you can save some energy (within the limit of CLmax) by increasing load factor. So in one sense, the steeper angle may lead you to increase load factor – assuming you have a margin to begin with - but that is to shorten the radius to save energy. Nonetheless, in the scenario given, of reduced airspeed, the steeper descent angle does not “require greater acceleration upward”. This stands to reason when you simply consider the fact that you have a lower vertical velocity to start with.

FWIW I think 172 driver's suggestion of reducing the airspeed below best glide is a subtle and efficient way of controlling the glide ratio in the engine out scenario. It's one option to get back to the nominal glide path. I would not be messing about with it on short final, nobody is saying is saying you should persist with some low airspeed like 1.1 Vso right into the flare.
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Old 18th Nov 2021, 14:29
  #143 (permalink)  
 
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Originally Posted by oggers View Post
A steeper descent angle does not require a greater acceleration to flare.
Newtonian mechanics teaches from v = a * t , that for a flare performed in a fixed time, the additional acceleration (above standard 1g) is proportional to the vertical speed to be arrested, which in turn is almost exactly proportional to glide angle (because x = sin(x) for small x).

Similarly, if the flare is performed from the same height, then a = v * v / (2 * S) shows that the acceleration goes up as the square of the descent speed - or descent angle, for small angles.

This supports Pilot DAR’s statement that a greater acceleration is required from a steeper glide angle.
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Old 18th Nov 2021, 16:20
  #144 (permalink)  
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Thanks for the math, it exceeds my math skills. An element for consideration is "...flare performed in a fixed time...". If you're descending at a slower airspeed than recommended for the the airplane, It will slow more quickly as the nose is raised to flare - so the time available to flare will be less. If the pilot is highly skilled, it may work, but it otherwise eats into the margins which most pilots need to do a nice landing. It can be the unexpected slowing in a slightly misjudged flare, which leads the pilot to add a last moment burst of power - if it's available....

The key takeaway is that by gliding at a slower than recommended speed, you are reducing your room for error on several sides at the flare. To achieve an acceptable landing, you'll have to judge your flare altitude with greater precision, as once you begin the flare, you won't have reserve energy to pause it to correct for being too high. And this leads to having to perform the flare all the way through to touchdown as one well judged transition.

The increase in G at flare for a slower than recommended speed is as I said, slight. But, that slight increase one of several elements which result in a reduced margin for error. When you combine reduced margins, the effect is multiplied. On the face of it, if you choose to approach the surface power off with less energy (speed) than recommended, the need for pilot skill increases exponentially. Once you try this non recommended technique at altitude, you'll realize that it's a skill not worth building, when simply flying good power idle approach and landings as recommended is a more appropriate skill to build.
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Old 20th Nov 2021, 18:17
  #145 (permalink)  
 
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Originally Posted by punkalouver View Post
Probably just have not known the proper terminology for the two different maneuvers for decades. No big deal as long as you know the different techniques.

Bottom line for newbies: Be able to perform and do a proper slip if required in the type of scenario that was in the video.
I found that training for slips it is good to have the students go right to the practical slip limit, in order to impart confidence in the maneuver...Of course, it not only works for landing, but side slip can also be used to do an emergency decent for fire or smoke.
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Old 20th Nov 2021, 18:59
  #146 (permalink)  
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but side slip can also be used to do an emergency decent for fire or smoke.
Not only can be used, is recommended!
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Old 20th Nov 2021, 20:22
  #147 (permalink)  
 
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Gentle reminder from my recollection of Cessna high wing series 150 /172 is that slips with flaps extended were not approved, or perhaps this has changed ?
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Old 20th Nov 2021, 23:33
  #148 (permalink)  
 
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Quite a while ago I crunched some numbers using very generous speeds and sink rates for demonstrating the impossible turn and the calculations showed numerically that I would still crash
I was trying to find it here on PPRuNe but so far can't...

Last edited by Pugilistic Animus; 21st Nov 2021 at 00:40.
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Old 21st Nov 2021, 01:21
  #149 (permalink)  
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Cessna high wing series 150 /172 is that slips with flaps extended were not approved
C150/152 have no restriction regarding slips.

Some earlier 172's have an "avoid slips with flap extended" placard, but it's not unapproved. The 172N is an example. Though it also has an amplified procedure under "Crosswind Landing" which says:

When landing in a strong crosswind, use the minimum flap setting required for the field length. If flap settings greater than 20 (degrees) are used in sideslips with full rudder deflection, some elevator oscillation may be felt at normal approach speeds. However, this does not affect control of the airplane. Although the crab or combination method of drift correction may be used, the wing low method gives the best control. .....
The wing low method would be the beginning of a slidslip.

Other 172 models have notes which vary in this regard, but none prohibit slips with flaps extended, or the plane would not be certifiable. For the 172S, it's a recommended procedure for a wing fire in Emergency Procedures.

All Cessnas can be slipped with the flaps retracted, which is a good starting point if you want down, flaps can be extended later.
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Old 21st Nov 2021, 02:22
  #150 (permalink)  
 
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Some earlier 172's have an "avoid slips with flap extended" placard, but it's not unapproved........Other 172 models have notes which vary in this regard, but none prohibit slips with flaps extended, or the plane would not be certifiable
Cessna 172H POH - Slips are prohibited in full flap approaches because of a downward pitch encountered under certain combinations of airspeed and sideslip angle.

My guess is this prohibit clause with 40° flap may have been why later models no longer had 40° selectable.
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Old 21st Nov 2021, 02:47
  #151 (permalink)  
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Yes, Megan, for the 172H, you're right. Though, the note about crosswind landing technique is pretty similar to the one I quoted from the later model 172, so a little inconsistant. That said, the POH for the 172H was written prior to the "GAMA" format (around 1977), where the terminology of "approved", "avoid" and "prohibited" were standardized.

The 172H was certified to the following:

(2) The static lateral stability, as shown by the tendency to raise the low wing in a side-slip, for all flap positions and symmetrical power conditions, shall:
(i) Be positive at the maximum permissible speed.
(ii) Not be negative at a speed equal to 1.2 Vs1.
(3) In straight steady sideslips (unaccelerated forward slips) the aileron and rudder control movements and forces shall increase steadily, but not necessarily in constant proportion, as the angle of sideslip is increased; the rate of increase of the movements and forces shall lie between satisfactory limits up to sideslip angles considered appropriate to the operation of the type. At greater angles, up to that at which the full rudder control is employed or a rudder pedal force of 150 pounds is obtained, the rudder pedal forces shall not reverse and an increased rudder deflection shall produce increased angles of sideslip. Sufficient bank shall accompany sideslipping to indicate adequately any departure from a steady unyawed flight.
(4) Any short period oscillation occurring between stalling speed and maximum permissible speed shall be heavily damped with the primary controls (i)
The present FAA requirement for this reads:

(1) In straight, steady slips at 1.2 VS1 for any landing gear and flap position appropriate to the takeoff, climb, cruise, approach, and landing configurations, and for any symmetrical power conditions up to 50 percent of maximum continuous power, the aileron and rudder control movements and forces must increase steadily, but not necessarily in constant proportion, as the angle of sideslip is increased up to the maximum appropriate to the type of airplane.(2) At larger slip angles, up to the angle at which the full rudder or aileron control is used or a control force limit contained in Sec. 23.143 is reached, the aileron and rudder control movements and forces may not reverse as the angle of sideslip is increased.

(3) Rapid entry into, and recovery from, a maximum sideslip considered appropriate for the airplane may not result in uncontrollable flight characteristics.
I think that this often quoted and discussed "limitation" for certain 172's comes as a result of varying interpretations and phraseology over the decades.

Ultimately, if the model of airplane you're flying says something's "prohibited" it is. Otherwise, "Avoid" is a caution, not a prohibition.
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Old 21st Nov 2021, 04:58
  #152 (permalink)  
 
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Originally Posted by Pilot DAR View Post
Not only can be used, is recommended!
Lol...yes indeed
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Old 21st Nov 2021, 05:46
  #153 (permalink)  
 
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Originally Posted by Rozy1 View Post
Yes they are names, but there is a difference. I think most people, even pilots, intuitively think of the slip as a side slip because the side of the airplane is headed towards the runway, not the spinner/longitudinal axis. Just my guess as to why so many get it backwards.

A lot in aviation is taught incorrectly. Like two molecules leaving the leading edge, then because of a rendezvous they have set up at the trailing edge, the one on the top of the wing goes faster. I have heard lift described thusly from more pilots than I care to admit.
I can guarantee you that's not how I would explain it
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Old 21st Nov 2021, 08:00
  #154 (permalink)  
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Originally Posted by Pugilistic Animus View Post
I can guarantee you that's not how I would explain it
I'm sorry, but I have to flag-up yet another quote from the brilliant radio 4 series, Cabin Pressure. When Arthur asks how an aircraft stays in the air, Martin tries that explanation:


MARTIN: .... Listen carefully, Arthur. The wing is curved on top but flat on the bottom. When it meets the air, it's split in two. The air that goes over the top has further to go, so it has to go faster to keep up with the air underneath, that reduces pressures above the wing, giving us a lift.
ARTHUR: Ah, fantastic! Thanks, Skipper. I, I totally get it now.
MARTIN: You are welcome.
ARTHUR: Except, why does it have to?
MARTIN: Why does it what what?
ARTHUR: Why does the air on the top have to keep up the air at the bottom? Why don't they just..split up?
DOUGLAS: For the sake of the kids?


Last edited by double_barrel; 25th Nov 2021 at 04:42.
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Old 25th Nov 2021, 13:06
  #155 (permalink)  
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Speaking of Old Bridge Airport, here's another incident - well, accident actually - from three days ago...

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Old 25th Nov 2021, 20:01
  #156 (permalink)  
 
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Originally Posted by treadigraph View Post
Speaking of Old Bridge Airport, here's another incident - well, accident actually - from three days ago...
Same machine as the previous video :-(

Interesting software in use to have the camera auto-track the incoming aircraft...
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Old 26th Nov 2021, 19:46
  #157 (permalink)  
 
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Originally Posted by Pugilistic Animus View Post
I can guarantee you that's not how I would explain it
Good on ya mate. You know what you’re doing.
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Old 29th Nov 2021, 22:48
  #158 (permalink)  
 
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Originally Posted by Rozy1 View Post
Good on ya mate. You know what you’re doing.
I try, Rozy1, I really try...thank you
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Old 1st Dec 2021, 01:55
  #159 (permalink)  
 
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Originally Posted by treadigraph View Post
Speaking of Old Bridge Airport, here's another incident - well, accident actually - from three days ago...

https://youtu.be/46Xt2dbbk8I
I don’t normally pay too much attention(as in try to analyze) student accidents as I just put it down to someone who basically doesn’t know how to fly an airplane.

Once the pilot has met a standard, such as a private licence, I seem to take more interest.

I know……bad attitude on my part and I shouldn’t think that way as there is always something to learn. And not all pilots need a license.

Anyways, I suspect this is a case of the student freezing at the controls with a gross over-reaction of full aft control column input trying to ‘get out of there’.


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Old 1st Dec 2021, 12:42
  #160 (permalink)  

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There was a case of an older graduate from my school when the trajectory looked identical. Terribly with 3 casualties, the pilot's chair slid back resulting in a pull on the yoke and his inability to recover the excess pitch.
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