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SeanGG
15th Apr 2009, 15:34
I tried to search for a topic regarding this matter, but to no success. If this has been discussed before then I would appreciate a link to the appropriate thread.

In a normal climb out (no obstacles) in a small typical single engine airplane (say a C-172), what is the safest airspeed to use in regards to having an engine failure after rotation: Vx or Vy?

I have always been taught that Vy is the best speed, simply because it will get you to the safe turn-back altitude faster. Therefore, you minimize the "prayer-zone" on the take-off where you have no other choice than flying straight ahead and hope for the best.

Some very experienced fellow instructors of mine argue that Vx is more efficient because it will get you closer to the runway for a given altitude, and that it will therefore be easier to make the runway.


Please share your thoughts!

Intruder
15th Apr 2009, 18:34
A higher airspeed in the climb will give better forward visibility with the less nose-up attitude, and help keep the engine cooler. Vy will also get you to cruising altitude faster, reducing fuel burn.

While Vx might keep you marginally closer to the runway, it also gives you less margin of error when the engine does quit, therefore less time to get the nose down to resume glide speed. You might give up any advantage you had when you push over to regain that speed.

Use Vy, unless the airplane operating manual suggests something different.

V1... Ooops
15th Apr 2009, 23:55
I think that the answer to the question arises more from a 'pure logic' analysis than from an airmanship (aviation specific) analysis.

If you knew ahead of time that you were going to have an engine failure after takeoff - for example, 30 seconds, 60 seconds, or 5 minutes after takeoff - you would want to maximize the amount of energy you had in reserve prior to the engine failing. In an aircraft, we have two types of energy, kinetic (forward speed) and potential (altitude below us). If the engine is working, it provides a third source of energy.

It appears to me that climbing at best rate (Vy) would allow you to put more energy in the bank prior to your engine failure than climbing at Vx.

aditya104
16th Apr 2009, 00:11
Your only concern is about engine failure after take off, the probability of that is very less.
When flying at Vx, and any delay in recognising the engine failure will result in stalling of aircraft and the situation becomes venal.

If u climb at Vy, the chances of making a safe landing after turning back to the runway are higher than Vx(in this case the aircraft will tend to overshoot).

Last week I came across an engine failure of a SE aircraft turning crosswind, at my aerodrome. The pilot turned to the field and landed in the opposite direction, he was able to stop just at the end of the sealed runway. He was too high and had to do sideslip in order to get down. The normal procedure for that aircraft states to climb at Vy. IF they had climbed at Vx, surely they would have overshot.

werbil
16th Apr 2009, 04:48
Assuming no obstacles generally I'd go with Vy for a number of reasons:

Climbing at Vy will have you higher for a given time after take-off, increasing the area of the footprint that you can reach if the engine stops.
If the engine fails at Vx you will have either have to convert height to speed to get to Vg or accept whatever glide performance there is at the speed that you end up at.
Engine coolingTurnbacks are only an option if trained to do them (is usually done for ASEPTA - SE turbine ops). In this case use the speed as per the training.

low n' slow
16th Apr 2009, 11:43
Another point to make in this discussion:

"Some very experienced fellow instructors of mine argue that Vx is more efficient..."

Just because someone is very experienced or "allways has done it that way" doesn't make it right. Especially in flying club environments, some nasty habbits may develop with senior club members without ever being corrected (perhaps because they themselves are the most respected instructors around...).

/LnS

BelArgUSA
16th Apr 2009, 12:52
I fly my own L-21B (an ex-military Super Cub) 150 HP - O-360 engine.
My personal "policy" - really none applies - as I fly in the open country...
Vy initially, to 500 AGL, then Vx+10 max climb power or less.
If in urban areas - Vy to 800/1000 AGL (if no suitable fields straight ahead).
This in case a 180º turn to departure runway is considered.
Obviously - many options - consider your environment and obstacles.
xxx
Super Cubs 150 HP are sometimes operated at "J-3C65" power - Engine economy...?
Seen that note in old PA18-150 owner manuals.
Throttle set to 2200 RPM at takeoff for training.
I think it should not be recommended in urban areas with obstacles.
xxx
:8
Happy contrails

SeanGG
16th Apr 2009, 20:04
Thanks for all the responses guys!

Some things are relevant to this discussion which has not been mentioned by any of you so far.

Normally, depending on atmospheric conditions, the safe altitude in a C-172 is around 500-600 feet. At 500-600 feet I am able to turn the airplane around and land on the opposite runway after a simulated engine failure.

As I already explained earlier, if I fly out at Vy, I will get to this altitude quicker, and therefore I will be "unsafe" a shorter period of time. If my engine fails exactly at safe altitude while climbing at Vy, a climb at Vx would not allow me to safely turn back to the runway. Therefore I would be forced to land straight ahead whereas I would be able to turn back if I would have climbed at Vy.

Some arguments my fellow instructors use to explain how Vx is better is to say that once you get to safe altitude Vx will make you closer to the runway. This is true, but the way I see it having an engine failure is not a function of altitude, but rather a function of time. Either way, unless you take off from a really short runway and with a tailwind, I am fairly certain that safe altitude at Vy will allow you to reach the runway after the turn back (assuming a C-172 or any other light single engine airplane).


Either way what I just wrote and all the other arguments for using Vy rather than Vx obviously makes Vy seem like the best choice.

Any further thoughts or comments to what I just explained, or would you mostly agree?

Cardinal
16th Apr 2009, 23:43
Vy, for many of the above reasons. Also, have you considered how long it would take to get the nose down after an engine failure? If climbing at Vx, airspeed will decay well below Vx before you react / pushover, burning lots of energy in the process.

airfoilmod
17th Apr 2009, 02:12
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

SeanGG
17th Apr 2009, 02:29
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.

AFI'm not sure how to interpret your post, but maybe you should re-read my last post, or perhaps the whole thread.

I have never said that I take off from short strips in tailwinds, neither are we talking about engine failures on rotation. We are talking about engine failures on climb out with no runway remaining.

EDIT: and by the way, one question for you AF:

Why do you cllimb out at 70 in your C172? I am assuming that is somewhere between Vx and Vy, correct?

airfoilmod
17th Apr 2009, 02:42
In post #8 you reference taking off on a short airstrip with a tailwind. Taking off on a short strip is fine, but with a tailwind?

70 is a nice speed for a tight pattern.

If you anticipate an engine out, why are you taking off? What does Rate or Angle have to do with "timing" an engine failure? If you want to be safe and use the runway you just departed as your emergency field, Vx. Plot the glide path for each, including a safe 180. Best glide speed will always favor proximity over altitude. (No Obstacles, Right?).

AF

SeanGG
17th Apr 2009, 03:22
In post #8 you reference taking off on a short airstrip with a tailwind. Taking off on a short strip is fine, but with a tailwind?

If you actually take the time to reread my post and use some common sense, you should be able to realize that the reference I made to the tailwind takeoff was to prove my point that taking off at Vy is superior to Vx simply because one would never take off from a short field in a tailwind, and therefore the scenario where Vx would be superior to Vy would be non-existant. I never said that I have ever taken off with a tailwind from a short strip.



If you anticipate an engine out, why are you taking off?

Obviously you missed the whole point of the thread again....

Let me explain myself (once again):

I do not anticipate an engine out on take off. However, as a professional pilot it is actually my job and also in my greatest interest to always be ready for the worst case scenario. That is why we are discussing what the best procedures are to have the best chance of survival if an engine failure were to happen.


What does Rate or Angle have to do with "timing" an engine failure?

I am not sure exactly what you mean by "timing" an engine failure, but the answer to your question is probably "nothing".

SeanGG
17th Apr 2009, 03:30
If you want to be safe and use the runway you just departed as your emergency field, Vx. Plot the glide path for each, including a safe 180. Best glide speed will always favor proximity over altitude. (No Obstacles, Right?).There you go, that's what I am trying to discuss in this thread.

And I do disagree with what you say for the following reasons (which has been explained previously by myself and also others in this thread):

1. Vy should still be able to get you enough altitude to make it back even though you are further away (unless you have certain atmospheric conditions like strong tailwind on a short runway)

2. With Vx, you might not even reach the safe turn back altitude by the time you would with Vy, and therefore climbing with Vx might force you to have to land straight ahead instead of being able to safely make the turn

3. Vx makes you more susceptible to an inadvertent stall

4. Vy leaves you more both kinetic and potential energy

5. If you lose your engine at Vx, the altitude lost by increasing your speed to best glide speed will most likely equate to an altitude loss equal or greater to the advantage of being closer to the rwy vs Vy.

EDIT: and to answer your question: yes, we are assuming no obstacles for this discussion.

FE Hoppy
17th Apr 2009, 10:33
What do you think is best glide speed Sean?

I would imagine that would be C/L max. Which is also going to be Vx.

bookworm
17th Apr 2009, 12:29
What do you think is best glide speed Sean?

I would imagine that would be C/L max. Which is also going to be Vx.

Only in an engine with a powerplant that delivers constant thrust with changing airspeed. A C172 doesn't quite fit that description, unless you have the turbojet STC. ;)

In practice, the difference in climb angle between Vx and Vy in a C172 is likely to be marginal. The likelihood of that making the difference between reaching the runway or not after a turnback is tiny. I suspect that the optimal policy for long-term safety management in an aeroplane you own is to climb at a speed that keeps your engine running at a moderate temperature, even if that's a little more than Vy

SeanGG
17th Apr 2009, 13:55
What do you think is best glide speed Sean?

I would imagine that would be C/L max. Which is also going to be Vx.


I really do not understand how C/L max would be the best glide speed in any airplane. The lift to drag ratio should be at a maximum (L/D max) to provide the best glide speed. At C/L max, even though parasite drag is low, induced drag is very high, and therefore this does not give you the most lift per amount of drag.

Only in an engine with a powerplant that delivers constant thrust with changing airspeed. A C172 doesn't quite fit that description, unless you have the turbojet STC. http://static.pprune.org/images/smilies/wink2.gif

What did you mean by this bookworm? That in these airplanes that you describe C/L max is the best glide speed, C/L max is Vx, or both like FE hoppy said?

V1... Ooops
17th Apr 2009, 14:32
Hello Sean:

Several posts up, you wrote
Normally, depending on atmospheric conditions, the safe altitude in a C-172 is around 500-600 feet. At 500-600 feet I am able to turn the airplane around and land on the opposite runway after a simulated engine failure.

I'm wondering if this premise - the idea of turning a single engine aircraft around to go back to the runway following an engine failure immediately after takeoff - is a bit of a red herring in this discussion, which originally started off as a question about whether it was best to use Vy or Vx after takeoff in a single engine aircraft.

I've already posted my thoughts about the choice of speed (I favour Vy), however, I'm a bit concerned about your perseverance with the 'turn back to the runway' manouver.

I have not flown singles for a long time, for that reason, I'm not up to date on what present 'best industry practice' suggests if you have an engine failure prior to reaching circuit altitude. I think, though, that you would have much better odds of carrying out an uneventful landing following an engine failure at low altitude if you elected to land the aircraft straight ahead or within perhaps 45° of the runway heading.

This is because the 180° turn required to get back to the reciprocal heading is going to use up quite a bit of your potential energy (the altitude beneath you), and when you roll out from the turn, on the reciprocal of the departure runway heading, you may not have enough altitude left to get you to the threshold - and if that is the case, your options, and your time remaining to choose an option will be very limited.

If, instead, you elect to land more or less straight ahead or ±45° from the runway heading, you will have a great deal more time to properly configure the aircraft, establish your desired glide (and, later, touchdown) speed, and fine-tune your choice of touchdown point as you descend. Obviously, you won't be landing on the runway, but I think you will have a much better chance of walking away from the aircraft without injury.

It's a question of priorities - is your greatest priority to avoid injury to the pilot and passengers, or is your greatest priority to avoid minor damage to the aircraft that might arise from an off-airport landing?

Obviously, my proposal won't make sense if you are taking off over water - something that is not unusual in Norway - but otherwise, I think that the 'land straight ahead' option is the safer choice, especially for a pilot with relatively limited experience on type.

Michael

airfoilmod
17th Apr 2009, 15:35
folks may have figured out by now is that at no speed after takeoff assuming a runway heading departure is it safe to return (in one piece) to the departure runway in this aircraft after OEI. You will always be further away than your glide speed (any) will be able to match the distance you need to return. Under power at any climb is always greater than glide relative to distance covered. Land straight ahead (or at some angle to RH) and walk away, God willing. Keep in mind the "turn back" isn't really a 180. It is more like a 270, considering the distance the turn circle carries you "further away" from the threshold of the reciprocal. Sean, if you insist, I would recommend that you at least try to stay as close to the Departure Field while gaining altitude if your fear is engine loss, perhaps stay in the pattern until you work up the courage to leave it for your destination. That would mean Vx and an immediate xwind pattern turn to stay in tight, while praying for all 4 (or six) to keep banging. I also think that planting in your students' brains the thought of turnback is dangerous.


AF

SeanGG
17th Apr 2009, 17:23
AF and V1, I understand your ways of thinking.

However, I have always been taught that one should make a turn back to the runway providing one has enough altitude to do so. There is a certain altitude at which you can safely make the turn back and land on the opposite runway.

You will always be further away than your glide speed (any) will be able to match the distance you need to return.

This is probably correct, but remember that when you take off (C-172) you take off at around 1000 feet, and lets say the rwy is 6000 feet, you still have another 5000 feet left + overrun area (if applicable) which will make it easy to make the runway on the way back. The main concern is of course that making the turn back to the runway makes us lose a lot of altitude. This is exactly why one should be familiar with the safe turn back altitude of the airplane.

I have practiced a lot of turn backs from 500-600 feet, and unless the atmospheric conditions are very unfavorable it is no problem getting back to the runway. Just immediately roll in to a 35-45 degree bank into the wind and keep the speed up and one should be able to land safely on the opposite runway. Of course one must always consider the atmospheric conditions and adjust the safe altitude accordingly.

But yes, I have done this countless of times and if I know that I can safely make the runway, why would I ever keep going straight ahead? The take-off emergency briefing I was taught always to do by my instructor in the C-152/172 is as follows:

1. If engine failure on take off roll - throttle to idle, brakes apply
2. If engine failure after rotation with remaining runway - full flaps, land on remaining runway
3. If engine failure after rotation with no remaining runway below safe altitude - full throttle, land straight ahead or slightly to the sides
4. If engine failure after rotation with no remaining runway above safe altitude X feet, immediately turn left/right (into the wind), pitch down and land on opposite runway


In airplanes that don't glide too well (like our school's piper arrow) there is no safe altitude. How do I know this? Well, I've experimented with it. It sinks like a rock, so even though you make the turn back you lose so much altitude you won't make it back to the runway. It's all about knowing your airplane.

airfoilmod
17th Apr 2009, 17:35
If straight out departure, there is no "safe return altitude". In your question, you didn't specify 5,000 feet remaining at OEI. If you take-off into the wind, if there is one, you can't "turn into the wind" with any Bank after OEI. You acknowledge that there is no glide distance as great or greater than distance from runway at OEI, yet you say you've practiced it many times. I hope you are at altitude when practicing this, not near the airfield, reading the Altimeter correctly, and solo.

AF

SeanGG
17th Apr 2009, 18:08
Your post is a little confusing to be honest.. of course you can't turn into the wind if you have a straight head wind, that is obvious. Turning into the wind only applies if you have any crosswind. And most often, there will be a slight crosswind from either direction.

About the glide distance, I have not made any calculations or anything to prove/disprove anything when it comes to that. The only thing I know is that if I lose my engine in a C-172 on a standard day I will be able to make it back if I lose my engine at 600 feet. Because I have practiced it before many times. It is certainly not a problem at all, and as I said, when I know I can make it back to the runway, why should I land straight ahead in stead?

airfoilmod
17th Apr 2009, 18:50
Once you are brakes off and rolling in this a/c, you are committed to landing straight ahead, whether on RW or beyond. You continue to say 600 feet is a "safe return" altitude, but you neglect to mention the distance from the departure end. 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

SeanGG
17th Apr 2009, 19:10
Have you tried before? I guess not.

Well I have, and guess what, I made it back to the runway every time from what I determined to be safe turn back altitude. Did you not read what I said?

Arguing against it is just stupid. I am telling you I have done it before several times. But please be my guest, if you choose to rather land in a tree that's fine. If I know I'll make it back then one thing is for sure: I'm landing on that damn runway.

As a side note we had an incident here at the airport where I work just a week ago. A pilot flying solo in a light sport airplane had an engine failure 400 feet on take off. Guess what. He turned back and landed more than half way down the opposite runway from where he departed. That being said I would never make the turn in the 172 from 400 feet (too low to make the turn itself), but this guy made the decision and made it back safely. Better than hitting the city packed with power lines and buildings straight ahead? Oh yes.

bookworm
17th Apr 2009, 19:37
What did you mean by this bookworm? That in these airplanes that you describe C/L max is the best glide speed, C/L max is Vx, or both like FE hoppy said?

I misread it as L/D max, which is equivalent to best angle of glide in all aircraft, and best angle of climb in a constant thrust aircraft (ideal jet).

C/L max, by which I now presume was meant maximum lift coefficient (CLmax), has nothing to do with best angles or rates of climb, unless the stall is limiting angle of climb, which is unusual in a prop and even more unusual in a jet.

SeanGG
17th Apr 2009, 19:52
I misread it as L/D max, which is equivalent to best angle of glide in all aircraft, and best angle of climb in a constant thrust aircraft (ideal jet).

C/L max, by which I now presume was meant maximum lift coefficient (CLmax), has nothing to do with best angles or rates of climb, unless the stall is limiting angle of climb, which is unusual in a prop and even more unusual in a jet.

Thanks, I did not know that :ok:

FE Hoppy
17th Apr 2009, 19:56
And I was in a rush earlier when I wrote C/L max. I actually meant L/D max. Which would infact be at Vx.

SeanGG
17th Apr 2009, 20:16
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?

Would very much appreciate that!

Pugilistic Animus
17th Apr 2009, 22:10
Because at that point in a piston [a constant power variable thrust machine--as Bookworm explained] you have the lowest drag coincident greatest possible lift coincident the only thing affecting climb rate as such is the difference between POWER required and POWER available, however as the power falls off with altitude while drag is always equal to thrust....

But, ROC will decrease so to maintain the highest possible ROC [the condition required of Vx] at less power [from critical altitude] an increase in the lift term and therefore angle of attack is required this action induces drag and requires greater thrust maintain that new AOA at a constant altitude,...i.e there's less actual drag at altitude, but more drag required because more lift is required, so more thrust is required,...READ CAREFULLY THIS!!!

And, since power is thrust X Vtas and increase in velocity is required to maintain the required power for max climb angle,...

so in pistons Vx continually increases until it converges with Vy at the absolute performance altitude, whereas a jet produces constant thrust and a constant the AOA is that which produces the greatest climb rate i.e the AOA for L/Dmax:8



Oh yeah listen to Airfoilmod, he's cool and your procedure may kill you land straight ahead with only shallow turns to avoid obstacles,..as most flight handbooks advise

PA

SeanGG
17th Apr 2009, 22:34
Thanks PA, appreciate your explanation :)


In their own books, the FAA generally explains the hazards of attempting to turn back to the runway if you have an engine failure on take off. However, they also say this:

Quote FAA-H-8083-3A, Airplane Flying Handbook

Concerning the subject of turning back to the runway following an engine failure on takeoff, the pilot should determine the minimum altitude an attempt of such a maneuver should be made in a particular airplane.

As I said, it is all about knowing your airplane. Some will do it and some will not.

Pugilistic Animus
17th Apr 2009, 22:45
Concerning the subject of turning back to the runway

Meaning for a 360 power off pattern about 800-1000' for most;)

SeanGG
17th Apr 2009, 22:50
I'm not sure exactly what you meant by that, but here is the rest of the sentence you quoted:

Concerning the subject of turning back to the runway following an engine failure on takeoff

:ok:

Pugilistic Animus
17th Apr 2009, 23:35
SeanCG,...
no they definitely mean a 360 ---takeoff ends at 50' agl so the mean departure climb,...and many runways are off of virtual cliffs,..since the airplane flying handbook,..I have it [both of them:8],..borrows [steals] from many sources,...such as handling the big jets or aerodynamics for naval aviators,...sometimes the wording gets ambiguous,...but one of the best references available for non-engineer pilots:ok:


P.S. I only quoted the part of the sentence I needed

but an inquisitive nature such as yours is good in this business ---just be careful brother!!!

PA

sapperkenno
17th Apr 2009, 23:56
In airplanes that don't glide too well (like our school's piper arrow) there is no safe altitude.

Why is there no safe altitude? If you were doing your test pilot thing with the throttle at idle... then at best glide with the gear up, and the prop lever pulled back I'd imagine it doesn't do too bad?! :confused:

SeanGG
18th Apr 2009, 00:20
Pick up your AFH PA, and you will see that the context is definitely an engine failure shortly after take off on the departure leg. You will see it clearly, there are three big paragraphs concerning the turn back ! But oh well. I promise I will not kill myself doing these things :ok:

sapperkenno, I guess it's the weight and short stubby wings which makes it hard to turn back in that airplane.. I was at least unable to do it, it sinks way too fast. Perhaps it would be possible from like 800-1000 feet with a strong headwind on departure, but who knows. I would not risk turning back in that one, that is for sure!

Pugilistic Animus
18th Apr 2009, 02:45
Sean

Wilco!

PA

c100driver
18th Apr 2009, 03:55
Sean,

I hope like hell you are not teaching or thinking "a safe altitude to turn back in a C172 is xxxx feet".

If you are trying this out in flight then you are planning for it without including startle factor, reaction time etc so the testing you are doing to find out that altitude is not valid for a real world engine failure. Loss of about 200 feet prior to putting a plan into action is about what I see with my students when they are not expecting an EFATO.

There are far to many variables to make bold statements. What works at a sea level airfield will not work at a 3000 AMSL airfield or an airfield with 3000 feet PA or DA. A MAUW C172M would be lucky to do 300 fpm at a 3000 foot PA airport and that will put you a long way up wind before your magic altitude.

Trying to land back at a 2000 meter long will give you a false sense of confidence. What about landing back on a 400 meter airport?

What will the ground speed be on the attempt to return? What would be your limit? What radius of turn do you need to return to the runway? What is the aircrafts limit? How much energy will you have to dissapate before you go through an immovable object (runway end fence for example) and survive?

What about the aircraft taking off just behind you, how big is it and can it move quickly out of your way, how skilled is that pilot, and does he see what you are up to?

Is there a steep wind gradient on takeoff, or sink at the departure end?

A MTOW C172 will probably not make it to the airfield (nil wind) from the altitudes you are quoting. (If you insist on being a test pilot and to try it please do not load Pax to increase the weight).

Back to your question Vx or Vy.
Answer - It depends on the conditions on the day and the airport you are flying from.

When you look at all the variables the safe way is to land straight ahead into wind or there abouts, and hit the softest thing you can find (aircraft are easy to replace). Yes at some point a return to the runway may be possible but are you willing to BET YOUR LIFE and YOUR PASSENGERS LIFE that you have the skill and the luck to make it?

Finally thanks for bringing up the topic, great discussion so far.

SeanGG
18th Apr 2009, 04:42
Good post C100driver, thank you.

I agree mostly with everything you say. But do not get me wrong, if you re-read my posts in this thread you will see that I have never mentioned any specific altitude, and I have always said that it varies with atmospheric conditions etc. etc..

This is definitely a maneuver one must train for to be able to accomplish, and one must of course be aware of all the factors you mention to make the safe decision of turning back to the runway if that is possible. This is always also why I was taught to always do an emergency briefing prior to departure to go through all this before hand mentally and decide whether conditions would favor turning back or not etc. etc...In the end as I have mentioned countless times it's all about knowing what you and your airplane are capable of doing. If ever any doubt, landing straight ahead is the best option. However, as I once again already have said, if I know for sure that I can make it (partially because I have done it before), I won't hesitate.

Good training pays off, and one day it might save my life or save me from injury.


Back to your question Vx or Vy.
Answer - It depends on the conditions on the day and the airport you are flying from.

I am curious to know which conditions you think will favor Vx over Vy in this situation, if you do not mind sharing ?

c100driver
18th Apr 2009, 07:10
Three that I regularly operate from I use Vx unless Vy is the best choice for the conditions on the day. ie turbulence, windshear etc I don't use Vx in heavy 200 series cessna as they are not as forgiving as the 100 series when the engine stops. Piper Slab wings I always land ahead as the world can always do without one more Cheroclunk :rolleyes::rolleyes::rolleyes:

1 Takeoff from one airfield that departs over a nasty piece of open sea - making it back to land or very close to shore is the priority, returning to the strip is not possible however a clear area is along the coastline. Height v Distance

2 Takeoff uphill toward gently rising terrain. Ground rising under aircraft.

3 Short (300 meter) bush surrounded strip with a safe crash landing at the strip or in a river valley behind and to the side of the strip.

They are probably extreme cases but are examples were a different thought process than simple "must do this" rule apply.

One other that I can think of would be an extra long strip where a straight ahead landing is possible. (not the best one I could think of but another reason Vx could be better than Vy in that situation)

werbil
18th Apr 2009, 10:32
Landing straight ahead into any water is far better than stalling, crashing and burning trying to make it back to the airport.

Compare the outcome of the following two engine failures in PA-32 aircraft:

200204328 (http://www.atsb.gov.au/publications/investigation_reports/2002/AAIR/aair200204328.aspx)

vs

200802048 (http://www.atsb.gov.au/publications/investigation_reports/2008/AAIR/aair200802048.aspx)

In the first turnback attempted - literally crashed and burned and six people died.
In the second ditching accepted - five? people bobbed around in the ocean for a short period of time before being rescued.

Yes - turnbacks are possible in a high performance aircraft - it is a standard procedure for ASEPTA approved aircraft (IFR charter flights in single engine turbine aircraft) - and ASEPTA pilots are trained in the procedure.

Many people have died attempting turnbacks in piston singles - particularly when the aircraft is loaded - most people try it empty or with just an instructor on board. Whilst the glide angle doesn't change with extra load, the gradient achieved during climb certainly does. Add in high temperatures, high humidity (affects piston engine performance significantly) and high altitudes and the probability of getting back to the field reduces dramatically.

Also consider the energy equation with 15 knots headwind on takeoff and a touchdown speed of 45 knots:
Land straight ahead and the touchdown ground speed will be 30 knots.
Land in the opposite direction and the touchdown ground speed will be 60 knots.
Energy is proportional to the square of velocity - double the velocity equals four times the energy.
I don't know about you, but if the plan doesn't go perfectly I'd much rather have a quarter of the energy at the crash site.

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.

bookworm
18th Apr 2009, 10:48
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.

Spooky! I must be telepathic. ;)

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?

Let me add a slightly different explanation to those already offered. If you draw your standard flight mechanics four-force diagram and resolve along the flight path you get

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.

SeanGG
18th Apr 2009, 13:06
A lot of good points made! Thanks for explanations C100driver, werbil and bookworm.


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.

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.

airfoilmod
18th Apr 2009, 15:29
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

Silver Spur
18th Apr 2009, 17:48
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

SeanGG
18th Apr 2009, 19:40
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 really do appreciate your comments and I respect your thoughts, but let me explain myself.

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 don't neglect it. I told you earlier when you made your firsts posts in this thread to re-read my posts. I will say it again, because for some reason you are not paying attention to what I have been writing. Read over my posts and you will see that I specifically quoted you earlier (twice) and wrote paragraphs specifically addressed to that.

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


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


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 :ok:

V1... Ooops
19th Apr 2009, 02:49
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 (http://www.youtube.com/watch?v=9KhZwsYtNDE). 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

bodypilot
19th Apr 2009, 05:46
VX is my suggestion. If you practice the immediate forward stick reaction needed and are confident enough to turn steeply enough....

Aerobatics in California (http://www.aerobats.com/seminar_02-07.html)

A good video clip that is worth a full watch.

SeanGG
20th Apr 2009, 15:37
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/tfpflyingvideotipsweeklyn/035_The_Impossible_Turn_tfp_vt.m4v

His name is Jason Miller and has a bunch of instructional videos at Aviation Podcast - The Finer Points (http://www.thefinerpoints.net)

Enjoy!

V1... Ooops
20th Apr 2009, 19:04
...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.

I appreciate your confusion. The paradigm of 'save the equipment' versus 'save the people' is more easily observed in multi-engine operations. But, it certainly exists in single engine operations as well.

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

V1... Ooops
20th Apr 2009, 19:12
...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.

Sean, the whole "Vy versus Vx" question can be answered by simple physics, no analysis is needed. The math goes like this:

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

hawk37
20th Apr 2009, 20:18
I wouldn't be too quick to say V2 is effectively Vyse. It isn't. And V2 isn't Vxse either, although I'd guess that would be the closer of the 2.

Pugilistic Animus
20th Apr 2009, 21:37
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

Mark1234
21st Apr 2009, 03:37
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.

V1... Ooops
21st Apr 2009, 12:04
...I wouldn't be too quick to say V2 is effectively Vyse.

Obviously it's not. But if you look at the comment in the context of this whole discussion, which is a response to a question from a 19 year old student pilot, the generalization is appropriate.

SeanGG
21st Apr 2009, 18:47
Seeing a lot of good posts now :ok:

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.

Pugilistic Animus
21st Apr 2009, 19:13
double the height [ROC] and switch speeds

PA