Single engine normal climbout: Vx or Vy?
What do you think is best glide speed Sean? I would imagine that would be C/L max.
I misread it as L/D max,...
And I was in a rush earlier when I wrote C/L max. I actually meant L/D max.
Now that we're talking about it and kind of off topic already, would any of you mind explaining why L/D max = Vx in jets but not prop airplanes?
Thrust - Drag = Weight * sin(Flight_Path_Angle)
where Flight_Path_Angle is positive in a climb and negative in a descent.
With zero Thrust, you can simply minimize Drag (as a function of speed) for maximum Flight_Path_Angle (i.e. best glide). So best glide speed is at D/Lmin or L/Dmax
With constant Thrust (as a function of speed), you can still just minimize Drag for maximum Flight_Path_Angle (i.e. best angle of climb). So for a constant-thrust powerplant, Vx is also at L/Dmax.
But if Thrust varies with speed, the maximization is more complex. For example if Thrust decreases with speed, as it usually does, choosing a speed slightly lower than L/Dmax will give you higher Thrust - Drag than at L/Dmax. So Vx is only coincident with L/Dmax in a constant thrust situation.
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A lot of good points made! Thanks for explanations C100driver, werbil and bookworm.
Most of you are all acknowledging that turn backs after engine failures is a complex maneuver with many variables and factors involved. However you constantly fail to realize that even though someone teaches or attempts turn backs, they are also well aware of these factors and might have thought them through way more than you think.
This must be the 100th time I explain this in this thread: just because I recommend or teach turn backs does not mean that I tell my student "any time you have an engine failure after take off turn back", this would just be stupid to assume in my opinion.
Of course the student must be aware of the hazards involved in doing the maneuver, but by all means, when I know for sure 100% that in most conditions (which are explained and discussed with the student) in the C-172 that there is a certain altitude at which you will make it back to the runway, hell, of course I want to let him know about it and see for himself what happens when you try to turn back to the runway on departure. Both at too low of an altitude (so he can see how dangerous it is), and also at an altitude high enough to make it.
As you all know, many accidents have happened because pilots have tried to make it back to the runway after an engine failure shortly after take off. I bet you they would not have been tempted to do so if they had the knowledge discussions like these bring forth in addition to some actual practice with a CFI (or solo). They would have seen instantly that turning back in that aircraft with that load in those conditions just isn't possible. But why do these things happen? My take on it? Bad decision making due to lack of knowledge and lack of experience. I wish for all pilots do have enough knowledge and experience to make good decisions.
And for the billionth time in this thread: if I know I can make it back to the runway if my engine fails at 600 feet (or whatever altitude would be appropriate for that day, some days there might not be a chance to turn back at all), then why on earth shouldn't I do it? Any day and twice on Sundays guys, no matter what argument you come up with this is something I have done a lot and I know it's possible, and therefore nothing can change my mind when it comes to it. But would I do it in any airplane at any airport and in any atmospheric condition? Of course not, and I have never claimed to either teach so or do so.
If you are an instructor and recommending turn backs I hope you have excellent professional indemnity insurance - because if someone stuffs it up and the pilot survives and says 'my instructor told me to' the lawyers for the passengers or their estates will be rubbing their hands with glee.
This must be the 100th time I explain this in this thread: just because I recommend or teach turn backs does not mean that I tell my student "any time you have an engine failure after take off turn back", this would just be stupid to assume in my opinion.
Of course the student must be aware of the hazards involved in doing the maneuver, but by all means, when I know for sure 100% that in most conditions (which are explained and discussed with the student) in the C-172 that there is a certain altitude at which you will make it back to the runway, hell, of course I want to let him know about it and see for himself what happens when you try to turn back to the runway on departure. Both at too low of an altitude (so he can see how dangerous it is), and also at an altitude high enough to make it.
As you all know, many accidents have happened because pilots have tried to make it back to the runway after an engine failure shortly after take off. I bet you they would not have been tempted to do so if they had the knowledge discussions like these bring forth in addition to some actual practice with a CFI (or solo). They would have seen instantly that turning back in that aircraft with that load in those conditions just isn't possible. But why do these things happen? My take on it? Bad decision making due to lack of knowledge and lack of experience. I wish for all pilots do have enough knowledge and experience to make good decisions.
And for the billionth time in this thread: if I know I can make it back to the runway if my engine fails at 600 feet (or whatever altitude would be appropriate for that day, some days there might not be a chance to turn back at all), then why on earth shouldn't I do it? Any day and twice on Sundays guys, no matter what argument you come up with this is something I have done a lot and I know it's possible, and therefore nothing can change my mind when it comes to it. But would I do it in any airplane at any airport and in any atmospheric condition? Of course not, and I have never claimed to either teach so or do so.
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Sean
Some critique. It may be the Internet, but people judge what they read almost instantly, especially re: an attitude. I do this, and I have some feedback for you. You have great energy and an obvious passion for flying. Communicating is not yet your strong suit. Your posts exude a kind of cockiness and know it all that detracts from your message. It may be a language thing, then again, the Internet may be at fault.
When Flight Safety and Emergency procedures come up, there is a need to assume that some who read or hear will take as fact something not considered fully. One example: Many times you refer to a safe altitude without a reference to distance away from the field. An obvious connection, but you neglect it. You have heard some valid criticism from others here, but you treat it defensively. Ego has No place in this discussion. I wish you the best, and I'd like to pass along a final comment from my last Instructor.
The Pilot Certificate is a License to learn. My first instructor, after forty years of flying including F4U's off Carriers for the Navy, busted minimums one night coming home and flew into a Building. Eight people died.
There is always more to flying than you think.
Tailwinds, Airfoil
When Flight Safety and Emergency procedures come up, there is a need to assume that some who read or hear will take as fact something not considered fully. One example: Many times you refer to a safe altitude without a reference to distance away from the field. An obvious connection, but you neglect it. You have heard some valid criticism from others here, but you treat it defensively. Ego has No place in this discussion. I wish you the best, and I'd like to pass along a final comment from my last Instructor.
The Pilot Certificate is a License to learn. My first instructor, after forty years of flying including F4U's off Carriers for the Navy, busted minimums one night coming home and flew into a Building. Eight people died.
There is always more to flying than you think.
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To start with, the primary objective of flying Vx is for obstacle clearance. That is to say; Gain as much height at the least distance. This is achieved at the cost of the following:
1. Slower IAS, thus that much closer to the Vs.
2. Climbing at a higher AoA, thus that much "buffet margin" in a Bank.
3. Climbing at a higher AoA, thus that much less forward visibility.
4. Climbing at slower IAS. thus that much less of kinetic energy.
If, for argument sake, you know that your engine is going to fail at X second after lift off, then if you fly at Vx, you would have gained more altitude that you could have gained at Vy speed, however, being that much closer to Vs, a slight delay in Engine Failure recognition will jeopardize your IAS and perhaps the height gained by Climbing at Vx is insufficient for a successful recovery.
If stall is averted, then you will have lost that much height that will force you to take anything straight ahead anyway, so the advantage of climbing at Vx is therefore gone.
Climbing at that much higher AoA as to gain Vx, will leave you with that much less buffet margin especially during a High Angle Bank that might be required for a turn back to the runway. The risk to stall your aircraft during the turn back is that much greater, because of less airspeed and a higher AoA.
While you may know your area very well, by having less forward visibility, that reduces your chances of finding out if something is suitable for a straight head forced landing, as this is a lot less dangerous than a turn back.
Arguably, during a Low Level engine failure scenario, your kinetic energy will do you more favor by giving that much margin to the above mentioned risk, potential energy (i.e height) does not have significant advantage (because you are low anyway) while poses more risk by having the above mentioned problems.
So, I suggest, unless your specific type of aircraft mention otherwise, Vy will give you more margins for an EFATO.
Safe Flight,
SS
1. Slower IAS, thus that much closer to the Vs.
2. Climbing at a higher AoA, thus that much "buffet margin" in a Bank.
3. Climbing at a higher AoA, thus that much less forward visibility.
4. Climbing at slower IAS. thus that much less of kinetic energy.
If, for argument sake, you know that your engine is going to fail at X second after lift off, then if you fly at Vx, you would have gained more altitude that you could have gained at Vy speed, however, being that much closer to Vs, a slight delay in Engine Failure recognition will jeopardize your IAS and perhaps the height gained by Climbing at Vx is insufficient for a successful recovery.
If stall is averted, then you will have lost that much height that will force you to take anything straight ahead anyway, so the advantage of climbing at Vx is therefore gone.
Climbing at that much higher AoA as to gain Vx, will leave you with that much less buffet margin especially during a High Angle Bank that might be required for a turn back to the runway. The risk to stall your aircraft during the turn back is that much greater, because of less airspeed and a higher AoA.
While you may know your area very well, by having less forward visibility, that reduces your chances of finding out if something is suitable for a straight head forced landing, as this is a lot less dangerous than a turn back.
Arguably, during a Low Level engine failure scenario, your kinetic energy will do you more favor by giving that much margin to the above mentioned risk, potential energy (i.e height) does not have significant advantage (because you are low anyway) while poses more risk by having the above mentioned problems.
So, I suggest, unless your specific type of aircraft mention otherwise, Vy will give you more margins for an EFATO.
Safe Flight,
SS
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Some critique. It may be the Internet, but people judge what they read almost instantly, especially re: an attitude. I do this, and I have some feedback for you. You have great energy and an obvious passion for flying. Communicating is not yet your strong suit. Your posts exude a kind of cockiness and know it all that detracts from your message. It may be a language thing, then again, the Internet may be at fault.
I feel bad when you think of me as "cocky" . I really do not regard myself as a cocky person, and if that is what I seem to be then I obviously have done something wrong because it is not my intention at all. Anyway I have been open to comments and treated you all with great respect in this discussion, even though the discussion went a little off track from what my intentions were.
An obvious connection, but you neglect it. You have heard some valid criticism from others here, but you treat it defensively. Ego has No place in this discussion.
I have been open to a lot of criticism, but you are right that I have treated it defensively sometimes. The reason for this is partially because the discussion moved away from what it was supposed to be about. The purpose of this thread was to discuss advantages of using either Vx or Vy on take off, and I have openly discussed this with many of you and given you my opinion on what is best and explained why (just as many others have done). Now that I am mentioning it I am very happy with getting so many different views and opinions on this (which was the purpose of the thread). However, when people like you call me an idiot for the procedures I use as if you were the god of aviation, and use wording like "if you do that I don't think you're an instructor" then naturally when faced with such childish behaviour I must be allowed to defend myself.
I quote you:
First of all, Sean, if you're in a 172 taking off from a short strip with a tailwind, I don't think you are an instructor. Secondly, an engine failure at rotation makes Vy or Vx quite moot, you're landing straight ahead or you're an idiot. (All due respect). I climb at 70 in the 172, 90 in my Skylane.
AF
AF
Also, people have been constantly saying that turning back in a C172 is not an option after an engine failure on take off, and the discussion has kind of turned to whether this is a smart thing to do or not. That is completely OK, and I have respected many of your comments saying that it is not a wise thing to do and that one should take precations before doing this. I completely agree with this (as I have said before). However, when people argue that it just isn't possible and that it won't do anything else than kill you, naturally I become irritated as I have clearly stated that I have done this several times before and that it is possible. This makes me repeat myself, perhaps in a manner that you think of as "cocky", but I am not sure if that was the case.
Quote from you again:
It is my contention through experience and training (albeit 40 years ago) that by the time you reach 600 feet at any airspeed, you are not able to turn and land back on the airstrip of departure. I hope that isn't confusing, but if I am the only one who gets it, I'll be the one safely on the ground (hopefully) while others are rolled into a ball or on fire. (IMO).
AF clear of the active
AF clear of the active
So, to summarize, I really apologize if I have been regarded as cocky in this discussion, but I hope you can understand where I am coming from as well. I think you should be able to admit that your own attitude judging by these quotes and the other posts you have written are not exactly very "discussion friendly" either..
Now, back on topic:
Silver Spur:
I do not know if you were a little quick on typing there, but remember that Vx gives you the best angle of climb and Vy gives you the best rate, so you will always be at a higher altitude with Vy. I guess that being said you lean even more towards Vy for the purpose of turning back after an engine failure on take off, since Vy gives you both more potential and kinetic energy
Hello Sean:
Perhaps it might be appropriate to take a fairly critical look at the "first principles" that appear to have been accepted without examination as the basis for some of this discussion.
For many years - particularly the time period from the 1950s through to the mid 1980s - a "first principle" that governed much of the decision-making process applicable to emergency and abnormal procedures was "Don't damage the aircraft". Examples of of this include slavish adherence to power limitations, and aircraft checklists that called for engines to be shut down (on multi-engine aircraft) at the first sign of any sniffle or out-of-limit condition from the engine.
For example (please bear with me for a moment whilst I digress and discuss multi-engine issues), in my own experience of over 5,000 hours of instructional experience given in full motion simulators, I very rarely encountered a pilot who would actually firewall the power levers when confronted with severe windshear on final approach. Instead, pilots would advance the power levers until reaching the first redline, and then do their best to cope with the windshear using maximum rated power. The result was very predictable (especially because I had control over the severity of the downdraft) - the aircraft crashed short of the threshold. The only positive outcome was that because the engines had not been overstressed, I suppose (speaking tongue-in-cheek here) they could be removed from the wreckage and used again in another aircraft.
After running this scenario with the above result, I would suggest to the crew that maybe we could try it again, but this time, to heck with the engine limits, just firewall the power levers and do your best. Often - not always, but often - they had enough power to escape the windshear without hitting the ground. The two engines were toast, the repair bill was going to be half a million dollars or more, but everyone was still alive.
Low oil pressure warnings and illuminated chip detectors are another example of incorrect assumption of first principles. For many years, pilots were taught that if a (turboprop) engine on a twin encountered low oil pressure in flight, or if a chip detector light illuminated, that engine should be shut down IMMEDIATELY - right NOW - lest the precious engine be damaged. A scholarly survey of the results of voluntary engine shutdowns in flight vs. actual engine failures in flight carried out by the Flightsafety Foundation in the early 1990s revealed that more accidents were happening as a result of sequela (loss of control, etc.) arising from the voluntary shutdowns than were happening as a result of actual failures of engines. As a result of this, procedures have now evolved - very few turboprop twins are now equipped with chip detectors, and the checklist procedures for those that have them have been changes to read "Monitor the engine, be prepared for a possible failure, otherwise, report to maintenance upon landing and repair before further flight". The very newest aircraft (e.g. a PC-12-47, notably a single) don't even display the chip detector warning if the aircraft is in flight - the aircraft suppresses the message until after landing.
You can see a change in the philosophy of "first principles" here, away from the old conventional wisdom "don't damage the aircraft" toward a new basic principle "don't damage the occupants'.
A similar example - again with multi-engine aircraft, which is where my personal experience lies - has to do with engine failures after takeoff in a twin. For many years, conventional wisdom (CW) was that you beat it around the circuit as quickly as you could and landed back at the departure airport. The result was a rushed procedure, a highly stressed pilot, no time to evaluate options and choose the best alternative - just crank it around the circuit and land, preferably within 3 to 4 minutes.
This CW has now been replaced by procedures that call for the pilot to carry out the necessary memory items (feather failed engine, add power on good engine), then continue to climb straight ahead on runway heading until a safe altitude has been reached - typically several thousand feet AGL - then, to call ATC and request a hold or a vector to no-where while the pilot assesses the situation and determines what the best course of action is. When a decision to land is made, the pilot carries out a full approach to the airport in as normal a manner as possible.
Why did that CW of 'race it around the circuit and land right away' develop? In part, because of a desire to protect precious machinery. But, quite tellingly, also in large part because of an unexpected influence from the ab-initio training industry: It's expensive to rent multi-engine aircraft when a pilot is getting that first multi-engine endorsement. A properly executed engine failure after takeoff in a twin takes about 20 minutes to complete - as can be seen in this video, which is a perfect example of how to do things correctly according to current best practice: Thompson 757 EFTO. How many young pilots who are scraping the bottom of their wallets to pay for aircraft rental would be willing to spend this amount of time demonstrating how to properly handle an EFTO during their ab-initio training? Not many.
So - getting back to your original topic, which was whether to turn back or to land straight ahead following an EFTO in a single - I think you need to critically evaluate what the "first principle" behind your decision making process is. If it is to minimize damage to the aircraft, then trying to get back to the airport makes sense. But, if it is to assure the highest level of safety for the occupants, I think that a very strong argument could be made that landing straight ahead - which eliminates the risk of stall/spin in the turn, running short of potential energy and landing short of the runway, etc. - is the safer alternative.
Michael
Perhaps it might be appropriate to take a fairly critical look at the "first principles" that appear to have been accepted without examination as the basis for some of this discussion.
For many years - particularly the time period from the 1950s through to the mid 1980s - a "first principle" that governed much of the decision-making process applicable to emergency and abnormal procedures was "Don't damage the aircraft". Examples of of this include slavish adherence to power limitations, and aircraft checklists that called for engines to be shut down (on multi-engine aircraft) at the first sign of any sniffle or out-of-limit condition from the engine.
For example (please bear with me for a moment whilst I digress and discuss multi-engine issues), in my own experience of over 5,000 hours of instructional experience given in full motion simulators, I very rarely encountered a pilot who would actually firewall the power levers when confronted with severe windshear on final approach. Instead, pilots would advance the power levers until reaching the first redline, and then do their best to cope with the windshear using maximum rated power. The result was very predictable (especially because I had control over the severity of the downdraft) - the aircraft crashed short of the threshold. The only positive outcome was that because the engines had not been overstressed, I suppose (speaking tongue-in-cheek here) they could be removed from the wreckage and used again in another aircraft.
After running this scenario with the above result, I would suggest to the crew that maybe we could try it again, but this time, to heck with the engine limits, just firewall the power levers and do your best. Often - not always, but often - they had enough power to escape the windshear without hitting the ground. The two engines were toast, the repair bill was going to be half a million dollars or more, but everyone was still alive.
Low oil pressure warnings and illuminated chip detectors are another example of incorrect assumption of first principles. For many years, pilots were taught that if a (turboprop) engine on a twin encountered low oil pressure in flight, or if a chip detector light illuminated, that engine should be shut down IMMEDIATELY - right NOW - lest the precious engine be damaged. A scholarly survey of the results of voluntary engine shutdowns in flight vs. actual engine failures in flight carried out by the Flightsafety Foundation in the early 1990s revealed that more accidents were happening as a result of sequela (loss of control, etc.) arising from the voluntary shutdowns than were happening as a result of actual failures of engines. As a result of this, procedures have now evolved - very few turboprop twins are now equipped with chip detectors, and the checklist procedures for those that have them have been changes to read "Monitor the engine, be prepared for a possible failure, otherwise, report to maintenance upon landing and repair before further flight". The very newest aircraft (e.g. a PC-12-47, notably a single) don't even display the chip detector warning if the aircraft is in flight - the aircraft suppresses the message until after landing.
You can see a change in the philosophy of "first principles" here, away from the old conventional wisdom "don't damage the aircraft" toward a new basic principle "don't damage the occupants'.
A similar example - again with multi-engine aircraft, which is where my personal experience lies - has to do with engine failures after takeoff in a twin. For many years, conventional wisdom (CW) was that you beat it around the circuit as quickly as you could and landed back at the departure airport. The result was a rushed procedure, a highly stressed pilot, no time to evaluate options and choose the best alternative - just crank it around the circuit and land, preferably within 3 to 4 minutes.
This CW has now been replaced by procedures that call for the pilot to carry out the necessary memory items (feather failed engine, add power on good engine), then continue to climb straight ahead on runway heading until a safe altitude has been reached - typically several thousand feet AGL - then, to call ATC and request a hold or a vector to no-where while the pilot assesses the situation and determines what the best course of action is. When a decision to land is made, the pilot carries out a full approach to the airport in as normal a manner as possible.
Why did that CW of 'race it around the circuit and land right away' develop? In part, because of a desire to protect precious machinery. But, quite tellingly, also in large part because of an unexpected influence from the ab-initio training industry: It's expensive to rent multi-engine aircraft when a pilot is getting that first multi-engine endorsement. A properly executed engine failure after takeoff in a twin takes about 20 minutes to complete - as can be seen in this video, which is a perfect example of how to do things correctly according to current best practice: Thompson 757 EFTO. How many young pilots who are scraping the bottom of their wallets to pay for aircraft rental would be willing to spend this amount of time demonstrating how to properly handle an EFTO during their ab-initio training? Not many.
So - getting back to your original topic, which was whether to turn back or to land straight ahead following an EFTO in a single - I think you need to critically evaluate what the "first principle" behind your decision making process is. If it is to minimize damage to the aircraft, then trying to get back to the airport makes sense. But, if it is to assure the highest level of safety for the occupants, I think that a very strong argument could be made that landing straight ahead - which eliminates the risk of stall/spin in the turn, running short of potential energy and landing short of the runway, etc. - is the safer alternative.
Michael
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VX is my suggestion. If you practice the immediate forward stick reaction needed and are confident enough to turn steeply enough....
Aerobatics in California
A good video clip that is worth a full watch.
Aerobatics in California
A good video clip that is worth a full watch.
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Good post Michael! Very interesting read. That video you posted is one of my favorites. Just love the professionalism. It's amazing to see what seemed to be a perfectly executed emergency procedure.
When you talk about the difference in priority between "saving the aircraft" and "saving the passengers" I definitely understand what you mean when it comes to multi-engine airplanes. If an indication shows that something is wrong with an engine, shutting it down will prevent any further damage to it, but obviously jeopardize safety as you'll only have one left.
However, when you relate that to single engine emergency turn backs, I become a little confused to be honest. The way I see it, if the airplane gets damaged then the passengers will most likely be damaged. Also, if the passengers make it without any injury, usually that means that the airplane is in good condition as well. Therefore, both priorities (with safety as the main one of course, always) should lead to the same decision.
bodypilot: why do you suggest Vx?
I did some experimenting with climbing out at Vx and Vy, and surprisingly enough the differences were not too great in terms of altitude gained vs time. At 50 seconds with Vy I made it to 600 feet, 500 with Vx. Then of course this is something that should be tested several times since once is not enough as the execution of the climbout will vary in quality etc.. What also seems to matter a lot is how quicly one accelerates to Vy during the climb.
What I did notice when trying to turn back after pulling the throttle to idle to simulate an emergency turn back at Vx (with a few seconds reaction time), was that it was way easier to stall than what I expected. Since the speed is so low, you can't go directly in to the turn as you could with Vy. You had to pitch forward and build sufficient speed first, and then make the turn. With Vy, since you are way above both the stall speed and the best glide speed you could go directly into the turn and then pitch down to keep the speed up. This will for sure increase the 100 foot advantage Vy had over Vx, even though Vx allowed me to be closer to the runway.
Here is a podcast about the emergency turn back by someone who is supposed to be a well recognized CFI:
http://traffic.libsyn.com/tfpflyingv...urn_tfp_vt.m4v
His name is Jason Miller and has a bunch of instructional videos at Aviation Podcast - The Finer Points
Enjoy!
When you talk about the difference in priority between "saving the aircraft" and "saving the passengers" I definitely understand what you mean when it comes to multi-engine airplanes. If an indication shows that something is wrong with an engine, shutting it down will prevent any further damage to it, but obviously jeopardize safety as you'll only have one left.
However, when you relate that to single engine emergency turn backs, I become a little confused to be honest. The way I see it, if the airplane gets damaged then the passengers will most likely be damaged. Also, if the passengers make it without any injury, usually that means that the airplane is in good condition as well. Therefore, both priorities (with safety as the main one of course, always) should lead to the same decision.
bodypilot: why do you suggest Vx?
I did some experimenting with climbing out at Vx and Vy, and surprisingly enough the differences were not too great in terms of altitude gained vs time. At 50 seconds with Vy I made it to 600 feet, 500 with Vx. Then of course this is something that should be tested several times since once is not enough as the execution of the climbout will vary in quality etc.. What also seems to matter a lot is how quicly one accelerates to Vy during the climb.
What I did notice when trying to turn back after pulling the throttle to idle to simulate an emergency turn back at Vx (with a few seconds reaction time), was that it was way easier to stall than what I expected. Since the speed is so low, you can't go directly in to the turn as you could with Vy. You had to pitch forward and build sufficient speed first, and then make the turn. With Vy, since you are way above both the stall speed and the best glide speed you could go directly into the turn and then pitch down to keep the speed up. This will for sure increase the 100 foot advantage Vy had over Vx, even though Vx allowed me to be closer to the runway.
Here is a podcast about the emergency turn back by someone who is supposed to be a well recognized CFI:
http://traffic.libsyn.com/tfpflyingv...urn_tfp_vt.m4v
His name is Jason Miller and has a bunch of instructional videos at Aviation Podcast - The Finer Points
Enjoy!
Originally Posted by Sean
...when you relate that to single engine emergency turn backs, I become a little confused to be honest. The way I see it, if the airplane gets damaged then the passengers will most likely be damaged. Also, if the passengers make it without any injury, usually that means that the airplane is in good condition as well. Therefore, both priorities (with safety as the main one of course, always) should lead to the same decision.
Consider this: Assuming your departure runway does not point straight out at a large body of water or the urban area of a city, any pilot of average skill could probably successfully carry out a precautionary (off-airport) landing within ±45° of runway heading if they suffered an engine failure in a single at an altitude close to what you think would be the minimum acceptable 'turn-back' altitude. The plane might get a little scuffed up (mud and dirt in the wheels, maybe even a few corn cobs in the air intake), and the consequences of the off-airport landing would be a nuisance (all the work involved in repatriating the aircraft), but it is highly unlikely anyone would be hurt. It's also highly unlikely that the damage to the aircraft would be any more than cosmetic.
On the other hand, turning back and landing at the airport requires considerable knowledge, skill, and mental preparation. Sure, the opportunity exists to avoid all that commotion and embarrassment arising from the off-airport landing... but then again, the risk exists that if even a small error in judgment is made, or something unexpected arises (like the aircraft in the process of taking off from the still-active runway), the consequences could be much more severe than those that come with just landing straight ahead in a cornfield. It's very much a risk-reward issue: You might get the bigger reward (landing back at the airport following a successful low-altitude 180° turn), but you also accept the bigger risk (it might not go as well as you plan).
"Conventional Wisdom" - which is another way of characterizing "first principles", or what elementary school kids call "peer pressure" - suggests that if you turn back to the airport and land on the departure runway after the low-altitude engine failure, hey, you're a hero, you are a skilled pilot, you are to be admired for snatching victory from the jaws of defeat. That same CW also suggests that if you carry out a precautionary landing straight ahead in someone's cornfield, you are a wuss, you wimped out, you didn't try to grab the brass ring.
However - do the math yourself (or, look at the historical records): For every 10 precautionary landings made straight ahead, how many people get hurt? For every 10 low altitude turnbacks, how many people get hurt? Although I don't have the facts and figures at my fingertips, I would venture a guess that very few of the precautionary landings ever result in an injury, but any form of error made during a low altitude turnback has a very high probability of resulting in an injury... because the consequences of the error will be more severe (a low altitude stall, or hitting an obstruction, etc.).
Michael
Originally Posted by Sean
...I did some experimenting with climbing out at Vx and Vy, and surprisingly enough the differences were not too great in terms of altitude gained vs time. At 50 seconds with Vy I made it to 600 feet, 500 with Vx.
You have three possible sources of energy in your aircraft.
1) Kinetic energy (airspeed)
2) Potential energy (altitude beneath you)
3) The engine
If you lose the engine, all you have left is whatever kinetic and potential energy you happen to have at the moment of the engine failure. It is clear from your own independent data collection that climbing at Vy not only accumulates more potential energy in a given period of time, but as an added bonus, it also leaves you with more kinetic energy (a higher airspeed) at the moment the engine fails.
Although it is not directly comparable, observe what large transport aircraft (Boeings, Airbus products) do when they take off: They carry out the initial portion of their climb at what is effectivly Vy (in that class of aircraft, it is called V2, but basically, V2 is Vyse, which is conceptually comparable to Vy in a single).
Michael
depending on what comes after this, I may add more,...looking at that relevant section of the airplne flying handbook, I see the example given is not very encouraging: so I decided to place a more encouraging example but assuming no rwy gradient and no wind but first let me post some figures-:
at 65 KTAS turn radius [feet] at a bank angle[phi]=TuR[phi]
so 1030 feet [20deg] etc 649 [30], 375 [45], 216 [60],
at 75 KTAS:
1372 [20], 865 [30], 500[ 45], 288 [60]
turn rate [deg/sec] [bank angle]
at 65 KTAS:
6.1[20], 9.6 [30,] 16.7 [45], 29 [60]
at 75 [KTAS]
5.2 [20], 8.3 [30], 14.54 [45], 25 [60]
using many aerodynamic assumptions and assuming a 'perfect 180' not a 'pseudo-procedure turn' lets check out a reasonable example aumming vy=v glide and Vx = 65 KTAS all in a standard atmosphere,...
I'll use Vx so that you'll be closer after an engine failure
assuming a 500'/min climb rate and an engine failure occurs 2 minutes after takeoff from 1000' feet,...then immediate recognition,...since 500 feet per min = 470'/nm 65 knots [according to my E6B] you are 2.12 miles away now let say acceleration to Vglide [since there's be no zoom reserves here you lose 100' in accelerating and traveled a negligible distance,...a perfect 180 degree turn at 30 bank from 75 KTAS = has a radius 865' and a rate of 8.3 deg sec so 180 deg takes 21/sec at a ROD of 800'min that =21/60=.35 min so a 400' loss +100 from acceleration at 75 knots and lets add 30 seconds for good measure so you've been decending, lost 400' + 100' so 500' lost in the turn around + 400 feet for error so you've lost 900 feet 1.21 minutes at 75knots you travel 1.25 nm /min and you still have about a mile to go
see not good!!!
because, this is PPRuNE and that's the Airplane flying Handbook,...And I'm
Pugilistic Animus
at 65 KTAS turn radius [feet] at a bank angle[phi]=TuR[phi]
so 1030 feet [20deg] etc 649 [30], 375 [45], 216 [60],
at 75 KTAS:
1372 [20], 865 [30], 500[ 45], 288 [60]
turn rate [deg/sec] [bank angle]
at 65 KTAS:
6.1[20], 9.6 [30,] 16.7 [45], 29 [60]
at 75 [KTAS]
5.2 [20], 8.3 [30], 14.54 [45], 25 [60]
using many aerodynamic assumptions and assuming a 'perfect 180' not a 'pseudo-procedure turn' lets check out a reasonable example aumming vy=v glide and Vx = 65 KTAS all in a standard atmosphere,...
I'll use Vx so that you'll be closer after an engine failure
assuming a 500'/min climb rate and an engine failure occurs 2 minutes after takeoff from 1000' feet,...then immediate recognition,...since 500 feet per min = 470'/nm 65 knots [according to my E6B] you are 2.12 miles away now let say acceleration to Vglide [since there's be no zoom reserves here you lose 100' in accelerating and traveled a negligible distance,...a perfect 180 degree turn at 30 bank from 75 KTAS = has a radius 865' and a rate of 8.3 deg sec so 180 deg takes 21/sec at a ROD of 800'min that =21/60=.35 min so a 400' loss +100 from acceleration at 75 knots and lets add 30 seconds for good measure so you've been decending, lost 400' + 100' so 500' lost in the turn around + 400 feet for error so you've lost 900 feet 1.21 minutes at 75knots you travel 1.25 nm /min and you still have about a mile to go
see not good!!!because, this is PPRuNE and that's the Airplane flying Handbook,...And I'm
Pugilistic Animus
Last edited by Pugilistic Animus; 20th Apr 2009 at 22:17. Reason: bold
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Here's a very simplistic take: I'll use Vy for 'normal' ops 'cos that's what the POH says for normal - it says Vx is for obstacle clearance. I don't personally think the difference between them is significant in terms of /EFATO (gut feel).
As for the turnback - (mostly) NO. Obviously it's very type dependant, your milage may vary. I've played with simulated EFATO & turn at height, and get a 350-400ft loss from a Vy climb for a 180, best technique seemed to be to roll to 45-60 degrees and pull into the stall warner, relaxing back pressure / allowing the nose to fall as necessary. That equates to roughly the same airspeed as level best glide. Pulling into buffet makes things a bit more interesting, and probably not clever close to the ground. Both require excessive back stick, indeed I managed to put the stick on the back stop before it actually began to flick out of the turn.
Disclaimer: This was done in an aerobatic category Robin that I spin regularly, at about 5000+agl, and I'm properly trained, current, and endorsed for aeros. Please don't go and spin something in doing the same.
Conclusion, under 500, I wouldn't even think it. Somewhat over 500, maybe, but it's very dependant on position/ other options; I fly from a large field with long parallel runways where 300ft over the fence is not uncommon and it's surrounded by housing estates. In any case, it won't be a return to the runway, it'll be a hard left/right for an open space - taxiway, grass, whatever.. Equally, the crossing runway may well be an option.
As for the turnback - (mostly) NO. Obviously it's very type dependant, your milage may vary. I've played with simulated EFATO & turn at height, and get a 350-400ft loss from a Vy climb for a 180, best technique seemed to be to roll to 45-60 degrees and pull into the stall warner, relaxing back pressure / allowing the nose to fall as necessary. That equates to roughly the same airspeed as level best glide. Pulling into buffet makes things a bit more interesting, and probably not clever close to the ground. Both require excessive back stick, indeed I managed to put the stick on the back stop before it actually began to flick out of the turn.
Disclaimer: This was done in an aerobatic category Robin that I spin regularly, at about 5000+agl, and I'm properly trained, current, and endorsed for aeros. Please don't go and spin something in doing the same.
Conclusion, under 500, I wouldn't even think it. Somewhat over 500, maybe, but it's very dependant on position/ other options; I fly from a large field with long parallel runways where 300ft over the fence is not uncommon and it's surrounded by housing estates. In any case, it won't be a return to the runway, it'll be a hard left/right for an open space - taxiway, grass, whatever.. Equally, the crossing runway may well be an option.
Last edited by Mark1234; 21st Apr 2009 at 04:02.
Originally Posted by hawk37
...I wouldn't be too quick to say V2 is effectively Vyse.
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Seeing a lot of good posts now
I agree with everything you are saying Michael, it all makes sense. When you're saying that the answer to why Vy is the best option is obvious I completely agree. It will leave you both more potential and kinetic energy, so basically you have more altitude and speed to play with.
However, let's say you choose to turn back above a determined "safe turn back altitude" of 600 feet. At 600 feet in a C172 standard day with lets say a 5000 foot runway, you will make it back no problem. However, lets say you climb at Vy until you reach 1200 feet (straight out departure). Will you then make it back?
Lets say it took you 2 minutes to get to 1200 feet. Since the climb angle is shallower than the glide angle, after a certain amount of time on departure (assuming no winds), you probably won't reach the runway. What if you climbed at Vx for 2 minutes? Would you then make it? You would be lower (maybe 1000 feet), but you would perhaps be close enough to be able to make it back (since 1000 feet is way more than enough to safely make the turn back). Therefore I wonder if above a certain altitude, Vx might be better if you choose to turn back to the runway (again, all depending on atmospheric conditions, which is what makes this so complicated since they are always different). Quick example: two days ago with a student taking off from a 5000 foot runway we were maybe 3000-4000 feet from the runway end when we reached 600 feet. Yesterday with another student taking off from a 6000 foot runway we were right above the runway end when we reached 500 feet. Big difference.
Of course, the problem is that the engine never quits at a certain altitude or above a certain altitude. If I knew that the engine always quit above safe altitude turn back altitude, it might make sense to fly at Vx since we will be closer to the runway. But if the engine quits below safe altitude or in any other case where flying straight ahead is the only option, Vy is obviously the best (for the same reasons you specify: more energy).
PA, I like your calculations! And you are right, at 500 feet per minute there's no way you will make it back to the runway. However, in an airplane that climbs better (C172 will easily do more than 500 ft/min standard atmospheric conditions) or more favorable atmospheric conditions it's a different story.
And Michael, I think what hawk37 meant to say was that V2 approximates Vxse and not Vyse. I guess Venr would be more approximate to Vyse.
I agree with everything you are saying Michael, it all makes sense. When you're saying that the answer to why Vy is the best option is obvious I completely agree. It will leave you both more potential and kinetic energy, so basically you have more altitude and speed to play with.
However, let's say you choose to turn back above a determined "safe turn back altitude" of 600 feet. At 600 feet in a C172 standard day with lets say a 5000 foot runway, you will make it back no problem. However, lets say you climb at Vy until you reach 1200 feet (straight out departure). Will you then make it back?
Lets say it took you 2 minutes to get to 1200 feet. Since the climb angle is shallower than the glide angle, after a certain amount of time on departure (assuming no winds), you probably won't reach the runway. What if you climbed at Vx for 2 minutes? Would you then make it? You would be lower (maybe 1000 feet), but you would perhaps be close enough to be able to make it back (since 1000 feet is way more than enough to safely make the turn back). Therefore I wonder if above a certain altitude, Vx might be better if you choose to turn back to the runway (again, all depending on atmospheric conditions, which is what makes this so complicated since they are always different). Quick example: two days ago with a student taking off from a 5000 foot runway we were maybe 3000-4000 feet from the runway end when we reached 600 feet. Yesterday with another student taking off from a 6000 foot runway we were right above the runway end when we reached 500 feet. Big difference.
Of course, the problem is that the engine never quits at a certain altitude or above a certain altitude. If I knew that the engine always quit above safe altitude turn back altitude, it might make sense to fly at Vx since we will be closer to the runway. But if the engine quits below safe altitude or in any other case where flying straight ahead is the only option, Vy is obviously the best (for the same reasons you specify: more energy).
PA, I like your calculations! And you are right, at 500 feet per minute there's no way you will make it back to the runway. However, in an airplane that climbs better (C172 will easily do more than 500 ft/min standard atmospheric conditions) or more favorable atmospheric conditions it's a different story.
And Michael, I think what hawk37 meant to say was that V2 approximates Vxse and not Vyse. I guess Venr would be more approximate to Vyse.
