EFATO interesting facts
Thread Starter
Join Date: May 2001
Location: 75N 16E
Age: 54
Posts: 4,729
Likes: 0
Received 0 Likes
on
0 Posts
EFATO interesting facts
Did anyone read the article in the AOPA mag this month, on whether or not you should turn back to the runway if you lose you engine on take off?
They did some experiments (at altitude) to determine how much height would be lost during a turn back to the runway, using different angles of bank. They simulated engine loss, and the pilot did nothing for 4 seconds before beginning the turn. The surprising thing was that using a 75° bank angle, the altitude loss was a lot less that a shallow turn, because the time of turn was a lot less.
In a 172, the altitude loss in a 180° turn was 380' in a shallow turn and only 210' in a 75° banked turn. Banking steeply at low altitude can lead to trouble though, the stall speed increases by 97% in a 75° banked turn, leaving little room for error. The conclusion to all of this is to use a 45° banked turn which gives the best results, a moderate turn rate and altitude loss and only a 19% increase in stall speed...Oh and turn into wind, so you don't stray any further than nescessary from the runway.
To determine an exact altitude at which you can attempt a return to the runway, they recommend taking the amount of altitude lost in a turn and add 50% (remember the 4 seconds of nothing). As runway length is a factor, a rule of thumb is that unless 2/3 of the turn around altitude is achieved before crossing the end of the runway then turn around should not be considered.
Pretty interesing stuff, worth going to altitude and experiementing with.
Cheers
EA
They did some experiments (at altitude) to determine how much height would be lost during a turn back to the runway, using different angles of bank. They simulated engine loss, and the pilot did nothing for 4 seconds before beginning the turn. The surprising thing was that using a 75° bank angle, the altitude loss was a lot less that a shallow turn, because the time of turn was a lot less.
In a 172, the altitude loss in a 180° turn was 380' in a shallow turn and only 210' in a 75° banked turn. Banking steeply at low altitude can lead to trouble though, the stall speed increases by 97% in a 75° banked turn, leaving little room for error. The conclusion to all of this is to use a 45° banked turn which gives the best results, a moderate turn rate and altitude loss and only a 19% increase in stall speed...Oh and turn into wind, so you don't stray any further than nescessary from the runway.
To determine an exact altitude at which you can attempt a return to the runway, they recommend taking the amount of altitude lost in a turn and add 50% (remember the 4 seconds of nothing). As runway length is a factor, a rule of thumb is that unless 2/3 of the turn around altitude is achieved before crossing the end of the runway then turn around should not be considered.
Pretty interesing stuff, worth going to altitude and experiementing with.
Cheers
EA
Join Date: Jun 2002
Location: New South Wales
Posts: 1,794
Likes: 0
Received 0 Likes
on
0 Posts
Ah, the good old turnback debate, hey? 
Saw the article. Scary stuff. On glide approaches the other day, the tendency to raise the nose to try and stretch the glide is very hard to resist, especially because you do get a transient increase in lift ('buoyancy' as Langewiesche would call it in Stick and Rudder) as you trade speed for attitude. You rationalise against it, but you feel yourself doing it even so and you understand why even highly experienced pilots stall / spin in.
You really do lose a lot of height in a turn and you have a lot to think about in such a critical turn as a turnback. In particular, if you don't keep the ball in the middle you risk a) Spinning in and b) losing even more height.
Experts only, in lots of practice. Not for your humble, low-time PPL scum like me.
QDM
Saw the article. Scary stuff. On glide approaches the other day, the tendency to raise the nose to try and stretch the glide is very hard to resist, especially because you do get a transient increase in lift ('buoyancy' as Langewiesche would call it in Stick and Rudder) as you trade speed for attitude. You rationalise against it, but you feel yourself doing it even so and you understand why even highly experienced pilots stall / spin in.
You really do lose a lot of height in a turn and you have a lot to think about in such a critical turn as a turnback. In particular, if you don't keep the ball in the middle you risk a) Spinning in and b) losing even more height.
Experts only, in lots of practice. Not for your humble, low-time PPL scum like me.
QDM
Join Date: Mar 2002
Location: on your left, a little low.....
Posts: 42
Likes: 0
Received 0 Likes
on
0 Posts
As runway length is a factor, a rule of thumb is that unless 2/3 of the turn around altitude is achieved before crossing the end of the runway then turn around should not be considered.
95 F with full tanks and a big lunch does not exactly inspire a 152 to soar like an eagle...
Sky
Thread Starter
Join Date: May 2001
Location: 75N 16E
Age: 54
Posts: 4,729
Likes: 0
Received 0 Likes
on
0 Posts
Ah, but the point is that you work all this sh*te out beforehand, so should you get caught by surprise you know that you can either turn back, or not turn back, no indecision.
Yea, know what you mean ! I watched a C152 use 4500' of runway to get airborne at Long Beach one day, watched as he flew out over the city, at about 200', not climbing, before doing a nice tear-drop turn and coming back to land on the reciprocal runway. I think I would have aborted take off myself! Scary thing was, the very next day the same aircraft was going for it again, would have thought they would have got the message
Cheers
EA
95 F with full tanks and a big lunch does not exactly inspire a 152 to soar like an eagle
Cheers
EA
Some more money for Capt PPRuNe
Join Date: Jan 2002
Location: Ici
Age: 56
Posts: 271
Likes: 0
Received 0 Likes
on
0 Posts
I have not seen the AOPA article however I believe there may be a further serious flaw here.
Assuming some headwind on T/O as would normally be the case you are going to experience an effect similar to that caused by windshear as your turn progresses. Lets suppose you are climbing out at 75kt IAS with a 15kt headwind (okay - a reasonable breeze but a very common situation). Hence your G/S is 60kt. However once turned through 180 deg your a/c needs to attain a G/S of 90kt (75 + 15)kt in order to still have an IAS of 75kt. Therefore additional height must be traded to get this - assuming perfect height to speed conversion efficiency the extra loss of height works out at about 200ft.
This is obviously very significant.
Worst still of course, is that if you intend to do a steep turn where as stated the stall speed has nearly doubled (75 deg, AOB)you then need to go from a G/S of (climbout speed - 15kt) up to say (100kt + 15kt) which will cost a much greater loss of height. (Admittedly you could convert the excess speed back to height after the turn assuming you haven't hit the ground by then). Even if you were already climbing at 100kt (which most singles don't) you would pay about 300ft due to the need to increase momentum to maintain IAS.
As the effect of wind speed is "differential" depending whether its a headwind or a tailwind then clearly the height loss due to what I've discussed is sensitive to the actual strength of the wind however it seems clear that for anything other than a gentle breeze that a turn back would cost considerable height.
Personally I think if I was at much less than about 700ft I would concentrate on landing the plane straight ahead. Least if you do bodge it you'll be travelling with a lower G/S & probably wings level. A bodged attempt at a turn back is unlikely to be so forgiving. As has also been pointed out there is the issue of the need to keep the a/c in balance through the turn whilst flying under much pressure.
Fujiflyer
Assuming some headwind on T/O as would normally be the case you are going to experience an effect similar to that caused by windshear as your turn progresses. Lets suppose you are climbing out at 75kt IAS with a 15kt headwind (okay - a reasonable breeze but a very common situation). Hence your G/S is 60kt. However once turned through 180 deg your a/c needs to attain a G/S of 90kt (75 + 15)kt in order to still have an IAS of 75kt. Therefore additional height must be traded to get this - assuming perfect height to speed conversion efficiency the extra loss of height works out at about 200ft.
This is obviously very significant.Worst still of course, is that if you intend to do a steep turn where as stated the stall speed has nearly doubled (75 deg, AOB)you then need to go from a G/S of (climbout speed - 15kt) up to say (100kt + 15kt) which will cost a much greater loss of height. (Admittedly you could convert the excess speed back to height after the turn assuming you haven't hit the ground by then). Even if you were already climbing at 100kt (which most singles don't) you would pay about 300ft due to the need to increase momentum to maintain IAS.
As the effect of wind speed is "differential" depending whether its a headwind or a tailwind then clearly the height loss due to what I've discussed is sensitive to the actual strength of the wind however it seems clear that for anything other than a gentle breeze that a turn back would cost considerable height.
Personally I think if I was at much less than about 700ft I would concentrate on landing the plane straight ahead. Least if you do bodge it you'll be travelling with a lower G/S & probably wings level. A bodged attempt at a turn back is unlikely to be so forgiving. As has also been pointed out there is the issue of the need to keep the a/c in balance through the turn whilst flying under much pressure.
Fujiflyer
FujiFlyer
I'm afraid that your argument is the classic downwind turn misconception, and neglects the fact that velocity, and therefore momentum, is a vector quantity.
Turning from a groundspeed of 75 knots (say) eastward to 105 knots westward requires no different aerodynamic forces from 90 knots westward to 90 knots eastward. In both cases the change in velocity is 180 knots to the west. There is no height loss associated with it, or at least no more in one case than the other.
A headwind may help or hinder depending whether you're in danger of landing short or overrunning once the turnaround is complete. I think it will usually help, though it does make the landing a downwind one, which may be difficult.
I'm afraid that your argument is the classic downwind turn misconception, and neglects the fact that velocity, and therefore momentum, is a vector quantity.
Turning from a groundspeed of 75 knots (say) eastward to 105 knots westward requires no different aerodynamic forces from 90 knots westward to 90 knots eastward. In both cases the change in velocity is 180 knots to the west. There is no height loss associated with it, or at least no more in one case than the other.
A headwind may help or hinder depending whether you're in danger of landing short or overrunning once the turnaround is complete. I think it will usually help, though it does make the landing a downwind one, which may be difficult.
Some more money for Capt PPRuNe
Join Date: Jan 2002
Location: Ici
Age: 56
Posts: 271
Likes: 0
Received 0 Likes
on
0 Posts
Agree as for as aerodynamic forces go but the point I was making was that to maintain a given IAS the a/c would have to increase its speed (as measured with respect to the Earth - ie ground speed) when turning downwind. Hence in the EFATO situation potential energy needs to be converted into kinetic in order to achieve this.
Put another way imagine a plane taking off into a very strong wind. It would do so easily - little effort would have to be expended by the engine prior to rotation. If you now had to land this plane downwind you would find that much energy had to be dissipated before it came to a halt. This energy has come from that associated with the huge increase in groundspeed which of course would have to be "found" during our EFATO turn.
Fujiflyer
Put another way imagine a plane taking off into a very strong wind. It would do so easily - little effort would have to be expended by the engine prior to rotation. If you now had to land this plane downwind you would find that much energy had to be dissipated before it came to a halt. This energy has come from that associated with the huge increase in groundspeed which of course would have to be "found" during our EFATO turn.
Fujiflyer
Avoid imitations
Join Date: Nov 2000
Location: Wandering the FIR and cyberspace often at highly unsociable times
Posts: 14,576
Received 425 Likes
on
224 Posts
I think it's worth saying again.
A turnback is a last-ditch manoeuvre and needs to be thought about before each takeoff.
RAF teaching is (or was in my day) that all options be considered as part of a pre-takeoff safety brief. Some days a turnback might be the best option, but another day, on the same runway, the conditions might favour not attempting this manoeuvre.
A turnback is a last-ditch manoeuvre and needs to be thought about before each takeoff.
RAF teaching is (or was in my day) that all options be considered as part of a pre-takeoff safety brief. Some days a turnback might be the best option, but another day, on the same runway, the conditions might favour not attempting this manoeuvre.
Grandpa Aerotart
To that I would add 'if you haven't been taught how and practiced it don't even think about it'.
FujiF
My memory of this area of aerodynamics is rusty but I don't think wind affects the aircraft as you say. There will be an optical illusion associated with turning downwind but in terms of aerodynamic effects on the aircraft?
The aircraft cares not for GS only IAS...if the body of air in which you are flying happens to be moving back towards the airfield then that is only a help...and believe me guys a downwind landing is not that big a deal.
What always leaves me wondering is why none of these articles talk about using flap to reduce stall speed...that's how I was taught to do it...and I've done it for real once.
The biggest danger of this manouvre is that it is not taught and practiced...except in gliders.
It is a 'no other options manouvre'...most of the time your best option is more or less straight ahead...it is NEVER a spur of the moment descision.
Chuck.
FujiF
My memory of this area of aerodynamics is rusty but I don't think wind affects the aircraft as you say. There will be an optical illusion associated with turning downwind but in terms of aerodynamic effects on the aircraft?
The aircraft cares not for GS only IAS...if the body of air in which you are flying happens to be moving back towards the airfield then that is only a help...and believe me guys a downwind landing is not that big a deal.
What always leaves me wondering is why none of these articles talk about using flap to reduce stall speed...that's how I was taught to do it...and I've done it for real once.
The biggest danger of this manouvre is that it is not taught and practiced...except in gliders.
It is a 'no other options manouvre'...most of the time your best option is more or less straight ahead...it is NEVER a spur of the moment descision.
Chuck.
Agree as for as aerodynamic forces go but the point I was making was that to maintain a given IAS the a/c would have to increase its speed (as measured with respect to the Earth - ie ground speed) when turning downwind. Hence in the EFATO situation potential energy needs to be converted into kinetic in order to achieve this.
Put another way imagine a plane taking off into a very strong wind. It would do so easily - little effort would have to be expended by the engine prior to rotation. If you now had to land this plane downwind you would find that much energy had to be dissipated before it came to a halt. This energy has come from that associated with the huge increase in groundspeed which of course would have to be "found" during our EFATO turn.
Do a search back about 4 months on Tech Log and you can see that we worked out you could do it in a B737 from 1,900ft....
I've been taught turnbacks, taught them, and once did one for real.
They have their place but only with experience, practice, pre-briefing and often there are better options.
WWW
I've been taught turnbacks, taught them, and once did one for real.
They have their place but only with experience, practice, pre-briefing and often there are better options.
WWW
Thread Starter
Join Date: May 2001
Location: 75N 16E
Age: 54
Posts: 4,729
Likes: 0
Received 0 Likes
on
0 Posts
Of course it depends on the other options. At somewhere like Bournemouth for example, you are surrounder by fields, and unless you really are certain you will make it back, then you best option is probably to opt for a field.
Having said that, take a typical airport in a city, where you are surrounded by built up areas. Your options are a lot more limited, you either land on the highway, or crash. So if there is a possibility of making back to the airport, even if you don't make the runway, but land on a taxy way, mid field, etc, then your survival chances are better.....crash rescue teams will be on scene faster as well.
One thing I neglected to mention was that in the AOPA article, they didn't recommend this precedure in a strong headwind (unless no other choice of course), and suggest that you may be better accepting a relatively slow crash landing.
Slightly off topic....there is a turn back procedure which can be used by the space shuttle if they have problems. It consists of getting rid of the SRBs, turning 180° and using the main engines to slow the shuttle down, then a glide back to the Cape. Never been tried of course, but in theory it should work
Cheers
EA
Having said that, take a typical airport in a city, where you are surrounded by built up areas. Your options are a lot more limited, you either land on the highway, or crash. So if there is a possibility of making back to the airport, even if you don't make the runway, but land on a taxy way, mid field, etc, then your survival chances are better.....crash rescue teams will be on scene faster as well.
One thing I neglected to mention was that in the AOPA article, they didn't recommend this precedure in a strong headwind (unless no other choice of course), and suggest that you may be better accepting a relatively slow crash landing.
Slightly off topic....there is a turn back procedure which can be used by the space shuttle if they have problems. It consists of getting rid of the SRBs, turning 180° and using the main engines to slow the shuttle down, then a glide back to the Cape. Never been tried of course, but in theory it should work
Cheers
EA
Some more money for Capt PPRuNe
Join Date: Jan 2002
Location: Ici
Age: 56
Posts: 271
Likes: 0
Received 0 Likes
on
0 Posts
Chimbu C
The aerodynamics only "care" for IAS but the point I am trying to make is that in the transient case of a sudden change of direction out of wind momentum must be gained to maintain IAS. Obviously in normal flight once this has been done then the a/c proceeds above the ground at a faster rate for a given IAS & therefore fuel consumption.
Bookworm, in the case of the balloon the energy comes from the air mass (ie it gives up a tiny proportion of its, to the balloon which sees viscous & frictional forces exerted on it until it has accelerated). However in the case of the sudden 180 deg turn our a/c needs to do, we are making a sudden change where surely we are not expecting to wait for these forces to accelerate us back up to the original IAS. (Guess the steep turn into wind would give us some of the required momentum though, but not all of it). I understand what you mean about the air mass's frame of reference and how it can do work but my problem is that when it attempts to do so by imparting momentum that initially the a/c will tend to "slip" within it (and therefore cannot quickly gain that required). If the air was a solid mass like a road surface, and moving then I would totally agree with what you've said.
FujiF
The aircraft cares not for GS only IAS...if the body of air in which you are flying happens to be moving back towards the airfield then that is only a help...
Bookworm, in the case of the balloon the energy comes from the air mass (ie it gives up a tiny proportion of its, to the balloon which sees viscous & frictional forces exerted on it until it has accelerated). However in the case of the sudden 180 deg turn our a/c needs to do, we are making a sudden change where surely we are not expecting to wait for these forces to accelerate us back up to the original IAS. (Guess the steep turn into wind would give us some of the required momentum though, but not all of it). I understand what you mean about the air mass's frame of reference and how it can do work but my problem is that when it attempts to do so by imparting momentum that initially the a/c will tend to "slip" within it (and therefore cannot quickly gain that required). If the air was a solid mass like a road surface, and moving then I would totally agree with what you've said.
FujiF
The aerodynamics only "care" for IAS but the point I am trying to make is that in the transient case of a sudden change of direction out of wind momentum must be gained to maintain IAS.
Thread Starter
Join Date: May 2001
Location: 75N 16E
Age: 54
Posts: 4,729
Likes: 0
Received 0 Likes
on
0 Posts
I remember my first (and only) radio controlled glider. Took bloody hours to build, and my first flight was going well, until I turned downwind. The thing just dropped out of the sky, and landed on the only rock in the huge field, nose first. Typical. Was a complete write off.
Think this was the point you were making wasn't it BW? In this case, height was traded for IAS, unsucessfully as it turned out
Cheers
EA
Think this was the point you were making wasn't it BW? In this case, height was traded for IAS, unsucessfully as it turned out
Cheers
EA
Join Date: Oct 1998
Posts: 10
Likes: 0
Received 0 Likes
on
0 Posts
Kinetic Energy
Kinetic energy and aircraft performance.
You are airborne in a B747 at 35,000 feet with a groundspeed of 500 kts. Inside the cabin is therefore an airmass travelling across the earth at 500 kts.
You tear a page from the in-flight magazine and fold it carefully to make a model aircraft. You stand up and throw it with a slight bank so that it flies in a circle. Its kinetic energy relative to the earth has absolutely no effect on its flightpath within its airmass.
A Cessna 172 in a 15 knot airmass behaves in exactly the same way.
What do you think Fujiflyer?
You are airborne in a B747 at 35,000 feet with a groundspeed of 500 kts. Inside the cabin is therefore an airmass travelling across the earth at 500 kts.
You tear a page from the in-flight magazine and fold it carefully to make a model aircraft. You stand up and throw it with a slight bank so that it flies in a circle. Its kinetic energy relative to the earth has absolutely no effect on its flightpath within its airmass.
A Cessna 172 in a 15 knot airmass behaves in exactly the same way.
What do you think Fujiflyer?
Some more money for Capt PPRuNe
Join Date: Jan 2002
Location: Ici
Age: 56
Posts: 271
Likes: 0
Received 0 Likes
on
0 Posts
What do you think Fujiflyer?
I think it looks like you're both right. I guess, as Bookworm says you need to consider momentum conservation rather than energy conservation as the moving air mass is able to give up a (small) amount of its energy to the aircraft in order to give it greater net energy with respect to the Earth.
Never the less I have noticed a tendency to sink sometimes when turning downwind in a strong wind. I suppose this is maybe due to not flying a perfectly balanced turn? (Englishal, perhaps this is what also happened to your model)
I have found this a very thought provoking discussion - my problem was that I failed to appreciate the forces which the a/c would experience when in the turn which would of course enable the direction of the momentum to be reversed whilst maintaining its magnitude wrt the airmass.
Bookworm - I bet you had no problem with Lorentz transformations and S.R.
Thanks for the discussion, great that we can have this sort of thing here,
Fujiflyer
:o