Double engine failure turnback
Had a bit of a play with the B737 in MS Flight Simulator 2002 earlier.
Who knows how acurate it simulates the performance of the real thing but this is what I found.
Also I only brought the thrust back to idle. I didn't fail them.
About the best performance I could get out of it was Flap Up, 210kts, 45 bank angle. From 10,000ft I did a 360 degree turn and lost 4000ft.
I tried various combinations of 25, 45, 60 degrees bank angle, 210 kts, 250 kts, 300 kts with Flaps UP, 180 kts with Flap 5, 150 kts with Flap 15 (yes the gear horn was blowing the whole time),
Any slower than about 190 kts with Flap up and 45 degrees I got the stick shaker. (Perhaps I should have tried Flap 1.)
So I figured for a cleaned up aircraft at 210 kts, you need at least 2500 feet for the turn plus at least 1000 ft for every 3 nm you are upwind of the runway.
I popped the gear down and selected Flap 1 at about 200 ft and landed with that.
The raduis of turn and angle from the runway centreline that I mentioned earlier seems to work out in the flight simulator.
Thankfully the Boeing family of planes (and Airbus too no doubt) glide much better that the lighties we all know. What a shame they must glide sooooo much faster.
Who knows how acurate it simulates the performance of the real thing but this is what I found.
Also I only brought the thrust back to idle. I didn't fail them.
About the best performance I could get out of it was Flap Up, 210kts, 45 bank angle. From 10,000ft I did a 360 degree turn and lost 4000ft.
I tried various combinations of 25, 45, 60 degrees bank angle, 210 kts, 250 kts, 300 kts with Flaps UP, 180 kts with Flap 5, 150 kts with Flap 15 (yes the gear horn was blowing the whole time),
Any slower than about 190 kts with Flap up and 45 degrees I got the stick shaker. (Perhaps I should have tried Flap 1.)
So I figured for a cleaned up aircraft at 210 kts, you need at least 2500 feet for the turn plus at least 1000 ft for every 3 nm you are upwind of the runway.
I popped the gear down and selected Flap 1 at about 200 ft and landed with that.
The raduis of turn and angle from the runway centreline that I mentioned earlier seems to work out in the flight simulator.
Thankfully the Boeing family of planes (and Airbus too no doubt) glide much better that the lighties we all know. What a shame they must glide sooooo much faster.
The "IMPOSSIBLE TURN" document that HugMonster quotes is hopelessly pessimistic in its assumptions. In particular the claim that a tighter turn offers no advantage is something that the original author clearly didn't bother to support with the nitty-gritty aerodynamics.
The optimum angle-turned/height-loss comes with 45 degrees of bank at maximum lift coefficient. That suggests that a practical application of the manoeuvre would have one operating as close to stall as possible, perhaps on the onset of the stick shaker. By holding the AOA precisely, the height loss for a 180 degree turn should theoretically be just hundreds of feet even for WWW's 737, though the height lost depends on v^2 for the speed corresponding to that max Cl.
I have no reason to doubt the accident stats quoted though -- clearly it usually is substantially safer to pick a reasonable landing spot straight ahead. I can think of a just few airports though (Antwerp, Tempelhof spring to mind) where trying a turnback from a few hundred feet in a light aircraft might just be preferable to a forced landing in the environs.
Dave Rogers article (cited by Code Blue) can be found here.
The optimum angle-turned/height-loss comes with 45 degrees of bank at maximum lift coefficient. That suggests that a practical application of the manoeuvre would have one operating as close to stall as possible, perhaps on the onset of the stick shaker. By holding the AOA precisely, the height loss for a 180 degree turn should theoretically be just hundreds of feet even for WWW's 737, though the height lost depends on v^2 for the speed corresponding to that max Cl.
I have no reason to doubt the accident stats quoted though -- clearly it usually is substantially safer to pick a reasonable landing spot straight ahead. I can think of a just few airports though (Antwerp, Tempelhof spring to mind) where trying a turnback from a few hundred feet in a light aircraft might just be preferable to a forced landing in the environs.
Dave Rogers article (cited by Code Blue) can be found here.
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The Rogers article is impressively analytical - but it assumes a constant rate of bank - a simplification which costs you in this special situation.
I experimented with this at some length in a single many years back and determined that (under the prevailing circumstances) one could gain considerably in performance by using an intentionally non-uniform bank/speed profile. To do so requires a prepared mind.
Pilots' information and analytical skills may be poor amid the confusing moments just after everything has clearly gone to heck. This is the strongest argument for accepting a forward + / - 90 degree target for an-off airport landing.
But if you're gonna turn around, this is what I figured out:
When the reverse course decision is made, job 1 is to reduce the vector velocity away from your intended landing spot. Turning is the only way to do this. The earlier and faster you turn, the greater the likelihood of reaching your goal.
By turning hard and early, you a) shorten the net distance, b) allow time to stabilize and assess the view, c) improve the odds for at least a successful off-airport landing nearer to those valuable emergency services on the field.
Slowing to anywhere near stall speed in a steep emergency turn is a bad practice in light aircraft and really bad in heavy ones.
The safer alternative is to crank in the 'maximum allowable' bank as soon as the decision is made, simultaneously pushing the nose down for acceleration. It is counterintuitive to dive when you only have x much precious altitude left, but doing so allows steepening the turn so that travel away from the airport can be stopped at the earliest possible time. If this is done in a smooth and 'aerodynamic' manner - flying through the turn rather than skidding - , then the total energy lost is not going to be vastly higher than optimum. (a la Bob Hoover) You will have traded some of the altitude for increased velocity, and the rest for the vector velocity cost of the turn.
Assuming your departure was straight out, the first 90 degrees of turn (into the crosswind) gets you to zero increase of distance from the airport. Ideally, this must be completed as soon as possible. The next 45 gets you onto a very nice converging downwind angle with your target, with time for shallow bank adjustments on the way in. When you are on the 45 and set up for max glide distance speed, you have a familiar, stable context and can then quickly intuit if it's going to work or if you need to find an alternative 'plan C'.
I experimented with this at some length in a single many years back and determined that (under the prevailing circumstances) one could gain considerably in performance by using an intentionally non-uniform bank/speed profile. To do so requires a prepared mind.
Pilots' information and analytical skills may be poor amid the confusing moments just after everything has clearly gone to heck. This is the strongest argument for accepting a forward + / - 90 degree target for an-off airport landing.
But if you're gonna turn around, this is what I figured out:
When the reverse course decision is made, job 1 is to reduce the vector velocity away from your intended landing spot. Turning is the only way to do this. The earlier and faster you turn, the greater the likelihood of reaching your goal.
By turning hard and early, you a) shorten the net distance, b) allow time to stabilize and assess the view, c) improve the odds for at least a successful off-airport landing nearer to those valuable emergency services on the field.
Slowing to anywhere near stall speed in a steep emergency turn is a bad practice in light aircraft and really bad in heavy ones.
The safer alternative is to crank in the 'maximum allowable' bank as soon as the decision is made, simultaneously pushing the nose down for acceleration. It is counterintuitive to dive when you only have x much precious altitude left, but doing so allows steepening the turn so that travel away from the airport can be stopped at the earliest possible time. If this is done in a smooth and 'aerodynamic' manner - flying through the turn rather than skidding - , then the total energy lost is not going to be vastly higher than optimum. (a la Bob Hoover) You will have traded some of the altitude for increased velocity, and the rest for the vector velocity cost of the turn.
Assuming your departure was straight out, the first 90 degrees of turn (into the crosswind) gets you to zero increase of distance from the airport. Ideally, this must be completed as soon as possible. The next 45 gets you onto a very nice converging downwind angle with your target, with time for shallow bank adjustments on the way in. When you are on the 45 and set up for max glide distance speed, you have a familiar, stable context and can then quickly intuit if it's going to work or if you need to find an alternative 'plan C'.
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Did it once in the A-320 Sim successfully. Can't remember the details but do remember clean wing, speed just above stall and a teardrop type approach. Gear down at 500 ft agl. & 0 flap landing.
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Just to be pragmatic, which I'm not normally known for; I’d use a speed slower than Vsuby in the turn and a Vsubx speed in the return. Questions, see the 757 post a couple units down, covers the same problem. Basically VsubY is based on the minimum power required to sustain flight speed, it is a speed higher then lowest point on the speed vs. power curve. Whereas the greatest distance per altitude lose is at around Vsubx, which is the nadir point on the drag curve. It's confusing to me, but so is most everything else.
I realise (sic) this is a predominantly British forum, please excuse my colonial spelling, courtesy of Noah Webster, if I find myself in possession of 150 quid, I will invest in the computer version of the OED.
[edited: italicized items are new because Tinstaafl pointed out my erroneous ways, the max endurance speed will be slower then the max range speed (I suppose that wasn’t clear in the above) keep reading it gets more clear as the posts progress – no really!]
I realise (sic) this is a predominantly British forum, please excuse my colonial spelling, courtesy of Noah Webster, if I find myself in possession of 150 quid, I will invest in the computer version of the OED.
[edited: italicized items are new because Tinstaafl pointed out my erroneous ways, the max endurance speed will be slower then the max range speed (I suppose that wasn’t clear in the above) keep reading it gets more clear as the posts progress – no really!]
Last edited by '%MAC'; 5th May 2002 at 23:51.
%MAC, unless I've misread your post I think you have it backwards.
Vg (range) usually corresponds with ~ Vy
Vg (min sink) with ~Vx.
That's my understanding. Of course I could always have misremembered something! :o
Vg (range) usually corresponds with ~ Vy
Vg (min sink) with ~Vx.
That's my understanding. Of course I could always have misremembered something! :o
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Tinny, Shame on you, You’ve dislodged me from my drunken stupor, American whiskey (Knob Creek) this time, Single malt, (Lagavulin) in Autumn and Winter. 
Not as I understand, here is my reasoning, correct me if I’m wrong.
The minimum sink rate in glide occurs at the minimum power speed, i.e. that speed in which the power which must be supplied by loss of potential energy is at a minimum, which is conveniently the lowest sink rate = a speed a bit lower than max climb rate for a jet Vy. (This offset occurs because the available engine power increases more quickly with speed at lower kinetic energy then the required power). Best endurance is the lowest point on the Power Vs. Speed Graph.
The minimum glide angle is that which minimum weight occurs in direction of motion, id est the minimum drag speed on the drag Vs. speed graph. This gives the greatest horizontal distance per vertical as the former gives the greatest loiter time. The drag graph corresponds to Vx. Id est weight just balancing drag.
One thing I can count on, you guys won’t let me get away with bull crap, so edify!!
Not as I understand, here is my reasoning, correct me if I’m wrong.
The minimum sink rate in glide occurs at the minimum power speed, i.e. that speed in which the power which must be supplied by loss of potential energy is at a minimum, which is conveniently the lowest sink rate = a speed a bit lower than max climb rate for a jet Vy. (This offset occurs because the available engine power increases more quickly with speed at lower kinetic energy then the required power). Best endurance is the lowest point on the Power Vs. Speed Graph.
The minimum glide angle is that which minimum weight occurs in direction of motion, id est the minimum drag speed on the drag Vs. speed graph. This gives the greatest horizontal distance per vertical as the former gives the greatest loiter time. The drag graph corresponds to Vx. Id est weight just balancing drag.
One thing I can count on, you guys won’t let me get away with bull crap, so edify!!
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Bookworm, the max coeficient of lift / rate of turn ratio is not a constant. It depends upon the design of the wing, the distance between the centre of lift and the centre of gravity, the airspeed and a great many other factors. As has also been stated, it is not appropriate to assume a constant angle of bank. The maximum roll rate of the aircraft is a major factor here as well.
What, as I read it, that article is highlighting is the inherent dangers of attempting to carry out such a maneouvre without having practiced it in your current type when other, far less dangerous options are usually open to you.
I have only once seen a pilot attempt to turn back to the runway after a power loss (it was not total) on the climb-out. He made it back to the runway (just), but the aircraft was a total loss. And this was an experienced pilot who (in my opinion) should have known better.
I know that the RAF certainly used to teach turn-back techniques (I don't know if they still do) but it is not something that should be attempted for real unless it has been practised.
What, as I read it, that article is highlighting is the inherent dangers of attempting to carry out such a maneouvre without having practiced it in your current type when other, far less dangerous options are usually open to you.
I have only once seen a pilot attempt to turn back to the runway after a power loss (it was not total) on the climb-out. He made it back to the runway (just), but the aircraft was a total loss. And this was an experienced pilot who (in my opinion) should have known better.
I know that the RAF certainly used to teach turn-back techniques (I don't know if they still do) but it is not something that should be attempted for real unless it has been practised.
Capt. Stable
You raise several interesting points.
I wasn't suggesting that max coefficient of lift / rate of turn ratio is a constant, merely that for a given aircraft in a given situation, minimum height loss per unit angle turned is achieved at max coefficient of lift.
I can well imagine that the optimum manoeuvre involves a changing angle of bank, but the point is that by rolling on 45 degrees of bank, a la Rogers, you achieve a result considerably better than the one given in the article that HugMonster cites. I can see that, particularly in larger aircraft, roll rate can be an issue. What's the maximum rate of roll to 45 degrees in WWW's 737?
I have no issue with the views that the turn-back manoeuvre is not usually worth the risk of getting it wrong and is also difficult to practise safely. But I do feel that the risk management should be based on proper physics rather than needlessly pessimistic data.
arcniz
The Rogers article indeed does assume a constant angle of bank, and it may be possible to do better. But I'm not convinced that your argument for increasing speed holds water. The rate of turn is very sensitive to speed, and I think Rogers shows in his paper that the trade-off you suggest is not a good one.
One further point: the state is not unaccelerated, and the assertion that maximum lift coefficient is optimal means flying an AOA rather than a speed. Thus you're absolutely right that the optimum is not going to be at constant airspeed.
Finally I don't doubt that given a few hundred feet more than the absolute minimum, your method may be a much safer and more effective option.
You raise several interesting points.
I wasn't suggesting that max coefficient of lift / rate of turn ratio is a constant, merely that for a given aircraft in a given situation, minimum height loss per unit angle turned is achieved at max coefficient of lift.
I can well imagine that the optimum manoeuvre involves a changing angle of bank, but the point is that by rolling on 45 degrees of bank, a la Rogers, you achieve a result considerably better than the one given in the article that HugMonster cites. I can see that, particularly in larger aircraft, roll rate can be an issue. What's the maximum rate of roll to 45 degrees in WWW's 737?
I have no issue with the views that the turn-back manoeuvre is not usually worth the risk of getting it wrong and is also difficult to practise safely. But I do feel that the risk management should be based on proper physics rather than needlessly pessimistic data.
arcniz
The Rogers article indeed does assume a constant angle of bank, and it may be possible to do better. But I'm not convinced that your argument for increasing speed holds water. The rate of turn is very sensitive to speed, and I think Rogers shows in his paper that the trade-off you suggest is not a good one.
One further point: the state is not unaccelerated, and the assertion that maximum lift coefficient is optimal means flying an AOA rather than a speed. Thus you're absolutely right that the optimum is not going to be at constant airspeed.
Finally I don't doubt that given a few hundred feet more than the absolute minimum, your method may be a much safer and more effective option.
Turnback in a Glider
Some decades ago, I witnessed a Grunau Baby glider (12:1 glide ratio?) release from an aerotow about 150 yards past the airfield boundary.
The pilot made it back to the field without difficulty, but the downwind approach resulted in a fast, heavy landing and minor damage. He would likely have done better landing straight ahead in the maize field, especially with the high wing. In an airliner, the extra 20 kt. is much less a big deal.
The Blanik with its 18:1 glide ratio similar to airliners would be a good machine to familiarise oneself with power-off approaches. And 45 degree bank angles are optimal.
It was suggested earlier to turn upwind immediately on an engine failure. Derek Pigott's advice for a midfield rope-break is to first turn downwind so that you can approach the runway with some headwind component. With an 18:1 glide ratio, you need some room as you are not coming straight down.
And yes, when making a landing approach in a glider, the practice is to accelerate to best glide speed from the minimum sink we were using until our lift/engine ran out and we had to head home.
Now for the big question: will there be enough hydraulics, electricity, air to operate the spoilers
The pilot made it back to the field without difficulty, but the downwind approach resulted in a fast, heavy landing and minor damage. He would likely have done better landing straight ahead in the maize field, especially with the high wing. In an airliner, the extra 20 kt. is much less a big deal.
The Blanik with its 18:1 glide ratio similar to airliners would be a good machine to familiarise oneself with power-off approaches. And 45 degree bank angles are optimal.
It was suggested earlier to turn upwind immediately on an engine failure. Derek Pigott's advice for a midfield rope-break is to first turn downwind so that you can approach the runway with some headwind component. With an 18:1 glide ratio, you need some room as you are not coming straight down.
And yes, when making a landing approach in a glider, the practice is to accelerate to best glide speed from the minimum sink we were using until our lift/engine ran out and we had to head home.
Now for the big question: will there be enough hydraulics, electricity, air to operate the spoilers
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departing aircraft?
i have thought of this many times, but they would rather us practice circle approaches rather than this in the sim.
then i always think of the aircraft that just took off after we did.
if we went straight ahead at least we could minimize the possibility of taking others with us into the hole in the ground.
i would think it very possible only with a lot of practice.
bob hoover could have done it, and maybe even roll it over on the way back.
then i always think of the aircraft that just took off after we did.
if we went straight ahead at least we could minimize the possibility of taking others with us into the hole in the ground.
i would think it very possible only with a lot of practice.
bob hoover could have done it, and maybe even roll it over on the way back.
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Had a long think about this over a couple bottles with a few mates last night and our conclusion is this.
IN reality not less than about 2200 AGL
Drop the RAT (apu?)
Drop your Guts
80/260 @ 45 degree AOB
If you were part of a stream departure off the same runway, tell everyone to clear off.
If @ F1 or F5 leave it if @ F15 consider how much headwind you have/had.
Gear as late as as you can
You should make it back to the hard surface (well the flyover at least).
Call for the tug...........
In reference to the NG and the guy that said he had a double separation then he would have had less drag & weight.
Best WX would be a LH X wind.
In the places we discussed straight ahead is usually not a great option, hills, Built up populus or water. The euros and seppos might have a better time where the terrain may be more forgiving.
IN reality not less than about 2200 AGL
Drop the RAT (apu?)
Drop your Guts
80/260 @ 45 degree AOB
If you were part of a stream departure off the same runway, tell everyone to clear off.
If @ F1 or F5 leave it if @ F15 consider how much headwind you have/had.
Gear as late as as you can
You should make it back to the hard surface (well the flyover at least).
Call for the tug...........
In reference to the NG and the guy that said he had a double separation then he would have had less drag & weight.
Best WX would be a LH X wind.
In the places we discussed straight ahead is usually not a great option, hills, Built up populus or water. The euros and seppos might have a better time where the terrain may be more forgiving.
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I hear what's been said about the unattractivess of a straight ahead, or approximately so, landing when the whole area is filled with offices space, hotels, suburbs or evil terrain. But I also hear what's being said about the precision with which the aircraft has to be flown, to have ANY chance of success.
I doubt that the average line crew trains for this, let alone the average single-pilot operation. And I feel sure the very rigorous and frequent training would be necessary. And, even then, how likely is it that the training would cover all possible scenarios that might lead to consideration of a turn around.
Many of the airstrips in my part of the world are equally unattractive for straight ahead landing. But, then, there is often not enough free airspace to permit any consideration of radius of turn, to return to the strip.
Over the years, I've happily settled for the rationalisation that the chances of loosing both engines is too remote to contemplate in my operational environment. The reason I've lurked on this thread, however, is that the unthinkable could happen. While it would certainly mean that I'd be having a VERY BAD day, its worthwhile to read all the comments here.
For the most part, we have SOPs that basically say its better to make a controlled crash at stall than to spear in, out of control in an unrecoverable stall/spin scenario. I'm not sure that I've yet heard anything here to change this philosophy but remain hopeful. I have to go back to the point that, unless the whole crew is trained and regularly refreshed on an emergency turn-back, the chances of success are very slight indeed.
I know that our SOPs won't work too well in many other parts of the world, so "horses for courses" is the phrase that comes to mind. I shall continue to lurk on this thread with interest.
I doubt that the average line crew trains for this, let alone the average single-pilot operation. And I feel sure the very rigorous and frequent training would be necessary. And, even then, how likely is it that the training would cover all possible scenarios that might lead to consideration of a turn around.
Many of the airstrips in my part of the world are equally unattractive for straight ahead landing. But, then, there is often not enough free airspace to permit any consideration of radius of turn, to return to the strip.
Over the years, I've happily settled for the rationalisation that the chances of loosing both engines is too remote to contemplate in my operational environment. The reason I've lurked on this thread, however, is that the unthinkable could happen. While it would certainly mean that I'd be having a VERY BAD day, its worthwhile to read all the comments here.
For the most part, we have SOPs that basically say its better to make a controlled crash at stall than to spear in, out of control in an unrecoverable stall/spin scenario. I'm not sure that I've yet heard anything here to change this philosophy but remain hopeful. I have to go back to the point that, unless the whole crew is trained and regularly refreshed on an emergency turn-back, the chances of success are very slight indeed.
I know that our SOPs won't work too well in many other parts of the world, so "horses for courses" is the phrase that comes to mind. I shall continue to lurk on this thread with interest.
%MAC, to be fair I was using piston engine curves for the Vx/Vy comparison with sink rate/glide range. I shouldn't have done that.
However, now that I have
, the engine's power & thrust curves are irrelevent because we're also referring to a no-engine scenario.
This means that we have to consider airframe drag/thrust/power requirement curves only and not the more usual 'greatest difference between available & required' ie maximum excess which is governed by the powerplant type.
We're talking about two different measurements - one involving angle of descent as a function, the other involving rate of descent. Rate includes a time factor.
The appropriate curves for each of these is the drag curve (for range) and the power required curve (for duration). Power is is appropriate for duration (min. sink rate) because power is a rate ie includes time as an element.
Best range (as far as the airframe is concerned) is achieved by flying at min drag and provides the best L/D ratio. I think of this as the least cost in D to achieve the lift, hence the range effect ie if drag was zero we'd be fly S&L indefinitely and if D=L then we'd be descending vertically.
This is also the same as flying at a tangent to the power required curve but by using this method we've effectively introduced a distance parameter into the situation (the tangent commences from the graph's origin). Handy if you know the headwind or tailwind component because you can adjust the tangent's commencing point to find the Best range speed for that wind component.
Best endurance (ie min sink) will be found by flying at the min. power required. This is slightly slower than L/D. This I think of as the least cost in energy and hence its effect on duration.
Bear in mind that this spiel is done entirely from memory and I could be wrong.
However, now that I have
, the engine's power & thrust curves are irrelevent because we're also referring to a no-engine scenario.This means that we have to consider airframe drag/thrust/power requirement curves only and not the more usual 'greatest difference between available & required' ie maximum excess which is governed by the powerplant type.
We're talking about two different measurements - one involving angle of descent as a function, the other involving rate of descent. Rate includes a time factor.
The appropriate curves for each of these is the drag curve (for range) and the power required curve (for duration). Power is is appropriate for duration (min. sink rate) because power is a rate ie includes time as an element.
Best range (as far as the airframe is concerned) is achieved by flying at min drag and provides the best L/D ratio. I think of this as the least cost in D to achieve the lift, hence the range effect ie if drag was zero we'd be fly S&L indefinitely and if D=L then we'd be descending vertically.
This is also the same as flying at a tangent to the power required curve but by using this method we've effectively introduced a distance parameter into the situation (the tangent commences from the graph's origin). Handy if you know the headwind or tailwind component because you can adjust the tangent's commencing point to find the Best range speed for that wind component.
Best endurance (ie min sink) will be found by flying at the min. power required. This is slightly slower than L/D. This I think of as the least cost in energy and hence its effect on duration.
Bear in mind that this spiel is done entirely from memory and I could be wrong.
Thread Starter
Thank you gentlemen. Would Boeing themselves have figures on this at all?
WWW
WWW
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I'm really not convinced by this don't turn back thing we're all taught. The Cessna twin (402 or 404) that crashed at Glasgow in Sep 1999 (G-ILGW) was less than 5 miles from the airport but it took 10 mins for the fire truck to arrive. Meanwhile flames had roasted most of the passengers and crew.
I can't see why if you have a bit of height, you shouldn't attempt to plonk the thing where everybody is ready for you and where kind people have created the biggest piece of open space for miles around. This is all the more so with jets where the direction you hit the ground relative to the direction of the wind is of less significance.
I can't see why if you have a bit of height, you shouldn't attempt to plonk the thing where everybody is ready for you and where kind people have created the biggest piece of open space for miles around. This is all the more so with jets where the direction you hit the ground relative to the direction of the wind is of less significance.
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Guten Tag Tinstaafl
Your post is right on, well written and informative. Whereas my posts were neither as eloquent nor as erudite, I am trying to say the same thing. Namely, these two different speeds are associated with different constraints. As you pointed out Best Range is a function of drag, whereas endurance is a function of power. Vx is a function of drag and Vy is a function of power. Though I realise that x and y speeds don’t appear on part 25 aircraft, it only confounded the issue. When I wrote that “lowest sink rate = a speed a bit lower than max climb rate for a jet Vy” I was being much too qualitative. And when I said I’d fly Vy in the turn I was just damn wrong. (It has since been edited for those that were going to try it). No, I would fly at max endurance in the turn and max range to get back to the aerodrome. To try to clarify for those I have unwittingly confused, mostly myself:
Max Range
Jet
Max angle of climb for a jet is derived where thrust subtract drag is the greatest, since thrust for a jet is relatively constant with speed, max T-D is at the lowest point on the drag curve vs. speed curve. The lowest drag gives the best range in glide: Vx = Best Range (jet)
Prop
Max angle of climb for a prop is derived in the same way except thrust falls off rapidly with speed so Vx in a prop is at a speed less than minimum drag speed: Vx < Best Range (prop)
Max Endurance
Jet
Vy speed in a jet is determined where the max excess power exists. In a jet the available engine power increases very quickly with speed (more so than the required power), so the greatest distance between the two curves is at a speed greater than minimum power speed: Vy >> Best Endurance (jet)
Prop
Vy speed in a prop is determined the same way, but in a prop the available engine power is relatively constant with speed so max excess power does occur at the lowest point on the power required curve: Vy = Best Endurance (prop)
Aha, and my math teacher said I couldn’t compare apples and oranges
Okay back to the original thread, let’s forget about Vx and Vy because they are only semi-relevant to the discussion of glide, we need to have a best glide endurance speed, and a best glide range speed available.
Your post is right on, well written and informative. Whereas my posts were neither as eloquent nor as erudite, I am trying to say the same thing. Namely, these two different speeds are associated with different constraints. As you pointed out Best Range is a function of drag, whereas endurance is a function of power. Vx is a function of drag and Vy is a function of power. Though I realise that x and y speeds don’t appear on part 25 aircraft, it only confounded the issue. When I wrote that “lowest sink rate = a speed a bit lower than max climb rate for a jet Vy” I was being much too qualitative. And when I said I’d fly Vy in the turn I was just damn wrong. (It has since been edited for those that were going to try it). No, I would fly at max endurance in the turn and max range to get back to the aerodrome. To try to clarify for those I have unwittingly confused, mostly myself:
Max Range
Jet
Max angle of climb for a jet is derived where thrust subtract drag is the greatest, since thrust for a jet is relatively constant with speed, max T-D is at the lowest point on the drag curve vs. speed curve. The lowest drag gives the best range in glide: Vx = Best Range (jet)
Prop
Max angle of climb for a prop is derived in the same way except thrust falls off rapidly with speed so Vx in a prop is at a speed less than minimum drag speed: Vx < Best Range (prop)
Max Endurance
Jet
Vy speed in a jet is determined where the max excess power exists. In a jet the available engine power increases very quickly with speed (more so than the required power), so the greatest distance between the two curves is at a speed greater than minimum power speed: Vy >> Best Endurance (jet)
Prop
Vy speed in a prop is determined the same way, but in a prop the available engine power is relatively constant with speed so max excess power does occur at the lowest point on the power required curve: Vy = Best Endurance (prop)
Aha, and my math teacher said I couldn’t compare apples and oranges
Okay back to the original thread, let’s forget about Vx and Vy because they are only semi-relevant to the discussion of glide, we need to have a best glide endurance speed, and a best glide range speed available.
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WWW Ive just been rostered for sim-duty tomorrow so Ill have the numbers for you late tomorrow or next day.
Ill also try to post pics of the sim read-outs in both dimensions of the successful profile.
Just to recap:
* flap 5
* APU off/no APU generater avbl
* engine and wing TAI valves closed
* max power TO in CAVOK conditions by day
* 9000ft EOL
* flat terrain
* wc +10
* GW 55T (if I have time Ill do one at 46T as you requested since a lighter weight would be more critical)
* MACTOW 22%, trim 4.2 (typical CG)
* ISA +10
* gear up at positive ROC
* Gear-lever left in UP position because the OFF selection is normaly done after flap retraction
* V2 to V2+5 (146 to 151 kts)
* no climb thrust reduction at normal 3rd seg altitude.
* sudden complete failure of both engines (the engine failures will be simulated by simpley pulling the start levers rather than lengthy engine-failure pre-programing).
* imediate initiatiation of loss of thrust on both engines recall items by PNF, followed by SYS A +B flight control sws to STBY RUD (which youd do in real life)
* PNF should then imediatley drops gear lever to OFF, then DN (in case pulling the handles is necessary), but the aim is to make the runway so gear will be select to OFF only, to protect what little hyd press you have left for primary flt controls. Belly land.
* All through this the PF turns to the left for return, and lands at Vref5 for 55T (168kt) and Id expect possible manual reversion.
This is gonna be bloodey interesting!
Ill also try to post pics of the sim read-outs in both dimensions of the successful profile.
Just to recap:
* flap 5
* APU off/no APU generater avbl
* engine and wing TAI valves closed
* max power TO in CAVOK conditions by day
* 9000ft EOL
* flat terrain
* wc +10
* GW 55T (if I have time Ill do one at 46T as you requested since a lighter weight would be more critical)
* MACTOW 22%, trim 4.2 (typical CG)
* ISA +10
* gear up at positive ROC
* Gear-lever left in UP position because the OFF selection is normaly done after flap retraction
* V2 to V2+5 (146 to 151 kts)
* no climb thrust reduction at normal 3rd seg altitude.
* sudden complete failure of both engines (the engine failures will be simulated by simpley pulling the start levers rather than lengthy engine-failure pre-programing).
* imediate initiatiation of loss of thrust on both engines recall items by PNF, followed by SYS A +B flight control sws to STBY RUD (which youd do in real life)
* PNF should then imediatley drops gear lever to OFF, then DN (in case pulling the handles is necessary), but the aim is to make the runway so gear will be select to OFF only, to protect what little hyd press you have left for primary flt controls. Belly land.
* All through this the PF turns to the left for return, and lands at Vref5 for 55T (168kt) and Id expect possible manual reversion.
This is gonna be bloodey interesting!
Last edited by Slasher; 7th May 2002 at 18:10.
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procedure
Hello all,
Actually tested in a 737-300 sim.
Wind 2 o'lock at 20 knots.
Min turn altitude: 1500 feet (2000 is much better)
flaps 1
apu operating
As soon as you notice turn into the wind bank 45 pitch +5 to the runway you just took off from.
With the loss of gen 1 and 2 only bat power is available.
Take apu on bus one to activate B hyd to extend the flaps to 5 (or 10 in case flaps 5 t/o).
As soon as this is done (you're already very low) disconnect bus one and connect to bus two to active A hyd and lower the gear.
In my opninion you have no chance taking off without APU since it takes to long to start it.
It's still a difficult manoever. The most difficult is that since you're coming at the runway from a 30 degree angle in heading you need to start the turn early or you'll overshoot.
But the most important is to level te wings otherwise you don't have the slightest chance to survive. Rather land within the airport perimeter but not on the runway, than crash into it.
Hope I could be helpfull,
regards. Tijmen
Actually tested in a 737-300 sim.
Wind 2 o'lock at 20 knots.
Min turn altitude: 1500 feet (2000 is much better)
flaps 1
apu operating
As soon as you notice turn into the wind bank 45 pitch +5 to the runway you just took off from.
With the loss of gen 1 and 2 only bat power is available.
Take apu on bus one to activate B hyd to extend the flaps to 5 (or 10 in case flaps 5 t/o).
As soon as this is done (you're already very low) disconnect bus one and connect to bus two to active A hyd and lower the gear.
In my opninion you have no chance taking off without APU since it takes to long to start it.
It's still a difficult manoever. The most difficult is that since you're coming at the runway from a 30 degree angle in heading you need to start the turn early or you'll overshoot.
But the most important is to level te wings otherwise you don't have the slightest chance to survive. Rather land within the airport perimeter but not on the runway, than crash into it.
Hope I could be helpfull,
regards. Tijmen
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Alright WWW with the parameters I stated above, the absolute minimum height is 1,350 ft AGL if your actions are immediate.
Im sorry Im not able to post the sim profile read-outs. Having trouble copying it clearley to the HD and photo-storage site.
PS and WWW fire away your questions and Ill do my best to answer them. Oh and just for info (if its useful to you) WWW, the exercise was conducted in a 1992 Hughes Rediffusion 6 DOF hydrostatic with Motorola computer under Full Flight Regime Simulation with Collins EFIS.
Im sorry Im not able to post the sim profile read-outs. Having trouble copying it clearley to the HD and photo-storage site.
PS and WWW fire away your questions and Ill do my best to answer them. Oh and just for info (if its useful to you) WWW, the exercise was conducted in a 1992 Hughes Rediffusion 6 DOF hydrostatic with Motorola computer under Full Flight Regime Simulation with Collins EFIS.
Last edited by Slasher; 9th May 2002 at 21:49.