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The Dreaded 180 turn back on Takoff


207WF

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I figure it makes sense to have an altitide in mind on takeoff, above which I will make a hard turn back to the runway if the engine fails, below which I will not try to turn back. After some airborne experimentation, I have chosen 300' agl when I am about 20% below gross, temps are near standard and I am near sea level. I want to refine this further, so I am curious: what critical altitides do others use ? - WF

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I use 400 AGL. I'm adding a little for the "this really isn't happening" thoughts. In practice, my problem hasn't been getting turned around and lined up, it's getting down so I don't run off the end of the runway. This requires full flaps and slips. I have practiced with my usual takeoff flaps, 15 degrees, max 30 degree bank, and holding about 65K. I need to practice a little more to get my comfort level up.

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I think 3-400 ft is too low to safely make it back to the runway. 16:1 glide ratio gives you a bit over 400fpm sink. Assume a standard turn (2 min) and you drop at least 400 feet by the time you make a 180 degree turn and you're still not aligned with the runway. Add another 45 degrees and you've dropped another 100 feet. I think most are going to auger in at less than 500 ft.

 

Go steeper than standard and you lose lift so you drop faster but turn quicker. Same result, though at 400 feet.

 

Remember idle is not the same as engine out so testing glide ratio at idle is probably well into the mid-20s so your results could easily have 50% error. My minimum is 800 ft AGL cause I figure I may not have perfect reactions nor hold best glide at all times.

 

Read this for another view http://www.eaa.org/experimenter/articles/2011-01_editorial.asp.

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s3flyer: I think you can do way better than a standard rate turn. Using a steep turn, 45-60 degrees, entered at 60 knots and flaps 15 from a climb configuration, I have been able to make a 180 with only a 100' altitude loss! Try it and see! WF

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s3flyer: I think you can do way better than a standard rate turn. Using a steep turn, 45-60 degrees, entered at 60 knots and flaps 15 from a climb configuration, I have been able to make a 180 with only a 100' altitude loss! Try it and see! WF

 

Absolutely. A 2-minute turn will never get you there. I've done simulated engine failures at 500' and returned to the runway with 150' feet to spare exactly as WF described, but only after I practiced them at 3000'. Just remember to keep the turn coordinated....

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It's still cold & IFR in NC so continuing to read the POH.

 

FWIW and you probably already know this, I came across the #'s a minute ago.

 

Attempt a return to the airport if above 750' (Sect 3.7)

 

'Chute can be deployed at an altitude of approx 600'. (Sect 3.8)

 

Obviously those are text book #s, your mileage may vary.

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Practice and a pre-takeoff briefing are key. Just don't get so agressive in the turn that you stall. If you are in a skidding turn your inside wing will stall first rolling you to the inside of the turn. Recovery from a low altitude uncoordinated stall would be questionable. Happened to a pilot at our airport a few years ago, slipping turn I think. He lived but he can't walk.

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Interesting discussion on this topic, but I would like to caution anyone with these "supposedly" minimum numbers and would like to argue that it really depends on the conditions of the day.

As an example at my airport where I fly on one west rwy that is just under 4000 ft. If there is a bit of wind at t/o I can be easily be at +400ft over the end of the rwy. Now if I would attempt to turn around here I likely would be succesful to do a 180 but would be flying off the end of the rwy with this tail wind landing. That is a greater risk than trying to pick a landing spot straight ahead due to the much higher ground speed as compared to straight ahead into the wind.

In other words in this case I would have to make an abbreviated circuit (with an oval 360 turn) to end up safely back on pavement and for that I would need >>400ft.

 

So any new pilots reading this thread, please be careful considering this situation and the actual safe numbers depend on the conditions of the day.

My advice would be to make this part of your pre take off checks and consider this situation as to what you would do depending on the conditions of the day prior to t/o.

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I don't doubt the empirical data from practicing the 180 degree turnback at idle RPM. The practice will prepare you for performing the tasks but will not directly equate to the sink rate you will achieve with a true engine out. You can maintain altitude at around 3500 rpm. 1800 rpm (idle) is going to positively impact the lift available, perhaps as much as 50%. This changes the sink rate to closer to 24:1 which is consistent with what is being reported in the above posts. Extrapolating the 50% error in sink rate to altitude gives you a real world minimum number of ~600 ft (from the suggested 400). Add a safety margin and you're right at the Flight Design recommendation -- 750 ft.

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The April 2011 AOPA Pilot Magazine has an in-depth article on this same issue... By Barry Schiff

http://www.aopa.org/.../technique.html You may need to log in to see this.

He agrees that a sharp turn is best, about 45 degrees. With the glide ratio and weight of our LSA, 400 ft seems very reasonable.

Tim

Let's see; according to that excellent article tighter is better so starting at 400' the most effective maneuver would be to push the nose over hard and crank a 60deg turn into the crosswind holding just above stall at 60kts. It would take 7 seconds just to reverse course and you would lose about 200'. I think I had better practice this a bit before putting it to use.

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Here is what I did. Trimmed at 60 knots climbing, flaps 15. Power comes off. I wait a second to simulate thinking - shoot, I just lost the engine, now what? A glance at the airspeed and it is down to about 50 knots. I crank it hard into a 45-60 degree bank. Don't load the wings up, 'cause you don't want to stall. At this point I have applied zero elevator input. Now, the nose starts to fall through on its own in the turn and the airspeed is picking up. At about 65 knots I pull on the elevator to slow to about 60 knots in the steep turn. This speeds up the rate of turn dramatically! In just a few seconds I have swapped ends and only lost about 100 feet! WF

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Just let me add one instructor's viewpoint...

 

There's a reason its "dreaded" - its killed a lot of pilots, some probably a lot more skilled than those of us here typing away.

 

I wait a second to simulate thinking - shoot, I just lost the engine, now what?

 

One second? ONE second??? I have found in real life the "deer in the headlights" phase lasts far longer. Count one-Mississippi-two-Mississippi-three-Mississippi and you're closer to the time lag between the "bang" and the pilot taking action. In that amount of time, with no immediate slamming down of the nose, the airspeed has probably dropped from Vx or Vy or whatever to perilously close to the stall. Yank and bank back towards the airport at that point and you'll likely be in a world of hurt.

 

Add'l points:

 

1) Imagine a 10k headwind and a 39k stall speed. Continue straight ahead or nearly so and you have a chance to mush into the ground (or something) at about 29k. After a 180º turn you'll be landing with a tailwind, and that 20k difference is significant in the amount of energy that needs to be dissipated.

 

2) Survival instincts make it VERY hard to slam the nose down as much as it needs to - the ground is the threat and its unnatural to point the nose at the thing that can hurt you. Most pilots will find themselves with a higher nose and a slower airspeed than they imagine when things get quiet.

 

3) The "siren song" of the airport is strong enough that many pilots will subconsciously try to speed up the turn back with rudder. I've caught myself doing it when overshooting a turn to final - its insidious and subtle. This from Stick and Rudder may help to drive the point home:

 

5576038250_3e5d791718.jpg

 

5576038452_849d13785c.jpg

 

5575451983_f2808b75a0.jpg

 

5576038812_44d3ff172b.jpg

 

Now imagine that sequence with the airspeed already low.

 

Admittedly, with enough training a return to the airport may be possible. But the hazards are so great I instruct students to not even think about it until established on crosswind. Before then, straight ahead or no more than an initial 30º to 45º turn left or right to find the best possible landing area.

 

But, again, That's Just Me™!

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"The 180° turn and downwind landing option should be

used only if the glider is within gliding distance of the

airport or landing area. In ideal conditions, a minimum

altitude of 200 feet above ground level is required to complete

this maneuver safely."

 

Glider Flying Handbook, page 7-6.

 

http://www.faa.gov/library/manuals/aircraft/glider_handbook/media/faa-h-8083-13.pdf

 

A tow break and return is part of the PTS, so every private glider pilot practices this.

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I am thinking another reason to make the turn back a very steep turn is that you end up closer to the runway center line, minimizing the amount of manuvering to line up and land after you roll out of the 180. WF

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But compare the L/D for 2 common 2-place gliders and a CT:

 

L13 Blanik – 28/1

 

Grob Twin II – 36.5/1

 

and a CTLS - 8.5/1

 

Do doubt. My point is that at a certain altitude, a turn-back is not only legitimate but wise. The question is, what is the altitude.? The next question is, has one trained for it? An additional question is, are we going to use science or fear-mongering? I might as well land straight ahead from 10,000' AGL to listen to some.

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Jim,

 

Don't think anyone was saying there isn't a minimum altitude that could be used for the 'dreaded 180 degree turn back'. There are some (me included) who question the relatively low altitudes proposed, steep (and slow) turns to get back to the runway, the real delay factor and the direct applicability of estabilishing the minimum altitude using idle as a reference.

 

I don't know about the CT but my Sting will exceed 20 kts on the ground at idle if I let it. This indicates non-trival thrust. Eric mentioned differences in idle vs. dead stick in another thread. So testing should take this into consideration.

 

Reaction time. 3 Mississippi was mentioned as a minimum to get over the "What the f***" factor. I've had real engine out, with oil spurting onto the windscreen. There was a measurable delay before I estabilished best glide. I was at cruise so alitude loss was trivial. On climb out, this will be a greater loss of altitude and needs to be considered.

 

Steep turns, slow speed, low alitude and pilot anxiety are a potentially deadly combination.

 

Remember this is also called the Impossible Turn: http://www.aopa.org/asf/epilot_acc/lax07la022.html

 

In analyzing real data:

 

Unless the airplane is close to pattern altitude, or you’ve already started a turn when the engine fails, it’s generally safer to land within the area you can see out the windscreen. Statistics bear this out. According to the AOPA Air Safety Foundation’s Nall Report, most maneuvering-related crashes are fatal. By contrast, only about 10 percent of forced landing accidents involve a fatality. Maintaining control of the airplane all the way to the ground, even if landing off airport, greatly increases the chances of walking away from a mishap.

 

The CT manual apparently says 750' AGL which was probably demonstrated by a test pilot who certainly has more skill than me. This is my minimum as well but that's Just Me :)

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  • 1 month later...

I've practiced this many times, and even did it on a BFR (with a pilot who had never done one before). 500ft will work provided you don't turn downwind if there is a stiff x-wind (which I did once and still made it, barely). I would say, in a true emergency, 400 ft could get you close enough to the field to land on a taxiway or grass. This is great practice to learn the limits of the CT. On my field, KADS, power loss at 500 ft leaves me no option but to turn around.

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  • 3 weeks later...

Yet another article on the topic: http://www.avweb.com/blogs/insider/AVwebInsider_LOTOT_204764-1.html

 

Most interesting part is the link at the end to research done by the Navy on the topic. They ran several scenarios with engine out at 500' AGL on takeoff. Main conclusion was that it was possible to make the turn back but it takes training, practice and technique. 45 degree bank is optimal but 30 degrees is almost as good and reduces the risk of stall/spin. 100% of those who landed straight ahead were successful (assuming appropriate terrain). Turn back had varying degrees of success depending on the scenarios.

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Watch your airspeed, yes, but remember that the stall speed varies with the square root of the " G " force.

 

That is...if you pull 2 "g's" in the turn, the square root of 2 is 1.414 so multiply your " normal" stall speed by that factor and come up with the real stall speed.

 

Normal stall speed of 60Kts would become 84.8Kts in a 2G turn ( 60 X 1.414 ) so if you're flying at 68Kts and pull 2 G's in the turn, you're 24.8Kts BELOW stall speed..and if you are turning final at a low altitude you are in BIG trouble.

 

The square root of 3 is 1.732 so your stall speed would be 103.92 in a 3G turn.

 

Just something to think about the next time you overshoot the turn to final and think about horsing it around.

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