Single engine normal climbout: Vx or Vy?
 

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!

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.

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.

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.

Assuming no obstacles generally I'd go with Vy for a number of reasons:

1. 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.
2. 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.
3. Engine cooling

Turnbacks 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.

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

Vx or Vy -
 

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

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?

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.

Question
 

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

I'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?

Sean
 

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

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.



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.


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

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.

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

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.

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?

Hello Sean:

Several posts up, you wrote
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

What
 

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

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.

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.

You are not paying attention
 

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

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?

Sean
 

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

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.

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:

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.

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!

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

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

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

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

I'm not sure exactly what you meant by that, but here is the rest of the sentence you quoted:

:ok:

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

Piper Arrow
 

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:

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!

Sean

Wilco!

PA

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.

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.


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

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)

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

vs

200802048

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.