Cessna 340 - lookin' for advice...
In a twin rotation speed should not be below Vmc
A large part of this discussion (which really ought to be centered on the 340, rather than aerodynamics or procedures) has been about the ability or efficacy of preventing a Vmc roll following engine failure while taking off at speeds less than the minimum single engine control speed.
Can you guys who assert this explain in terms of the aerodynamics why you believe a catastrophic engine failure at Vmc - 5 knots leads to more significant control problems in the air than on the ground, please?
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Can you guys who assert this explain in terms of the aerodynamics why you believe a catastrophic engine failure at Vmc - 5 knots leads to more significant control problems in the air than on the ground, please?
Even if throttles are closed, going off the end OR ending off to the side, is far better than finding oneself rolling inverted...with most times deadly results.
Because...while still on the ground (nosewheel especially), more directional control is most times obtained (due to said nosewheel)...
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I'm not sure that directional control is guaranteed.
Didn't say anything about 'guaranteed'.
And, I answered your question in Tech Log, with regard to 14CFR23 aeroplanes.
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Training
Nothing is life is guaranteed, but proper training and understanding of Vso, Vmc, Vyse, accelerate-stop charts and other asymmetric forces are very important to safely fly a multi-engine aircraft. The pilots whom have taken time and responded to these questions have succinctly stated that Vmc is a critical factor in flight safety considerations. I have no dog in this hunt. However the author of this rant suggested taking a course at Flight Safety, I think the Kansas location handles the 340 training and you could not ask for a better solution to this question. The instructors at Flight Safety are very professional and have the ability to demonstrate in a simulator various scenarios. I wish I could be there to observe what will happen if someone attempts rotation at 70 kts and with gear down and has an engine fail. If you do this, please send me an email and let me get some friends together with a cooler of Bud Light, I’ve got a friend at F/S and I think we could observe. I suspect it would take about 5 seconds until either a cartwheel occurs or the AI is brown over blue. I am sure the trainers will be amused; they have a passion to “educate” us. Simulator training is a wonderful way to envisage in a secure environment what realities could occur in real world situations. One of my personal favorites is losing an engine in hard IFR, 600 ft ceilings, 30,000 ft tops, no GNS530 or GPS on board, 30 nm from destination and then have your remaining alternator fail. If you’ve never sweated in a 65 degree cockpit you will in the Sims. If the author does follow through with the Flight Safety training he might consider doing a Youtube video to publish this takeoff scenario for others to benefit from.
The simplest and best answer is get proper training.
I'm out of here.
Life is Good
The simplest and best answer is get proper training.
I'm out of here.
Life is Good
Last edited by Lifeisgood; 12th May 2008 at 12:00.
Ahhh, bookworm, you might read again what I stated originally.
Didn't say anything about 'guaranteed'.
Didn't say anything about 'guaranteed'.
What I'm arguing is that, if that's true, there's no point in being precious about whether you rotate above or below Vmca. The decision is simple: if an engine failure occurs below Vmca, you close the throttles and do the best job you can, whether you're on the ground or in the air.
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Bookworm, you really confuse the issue by taking it between multiple threads or forums. For others following along, the reference question in Tech Log is http://www.pprune.org/forums/showthr...highlight=Vmcg
You also are asking about different subject. In the tech log question, you asked about Vmcg, which is not the same as Vmca. One is minimum ground control speed, one is minimum control speed in the air; each have different criteria and requirements.
When 411a says that a part 23 airplane doesn't have gauranteed performance after takeoff, he's correct. This isn't at all the same thing as a Part 25 airplane, which does have certain performance "gaurantees" based on the nature of certification. For example, a multi engine airplane certificated under Part 23 isn't required to maintain altitiude after an engine failure, by virtue of it's certification, nor is it required to be able to go around on one engine, fly a missed approach with an engine failure, etc. Part 25 certificated aircraft are required to meet specific climb gradients following loss of an engine on takeoff (which translates to a go-around or missed approach, too). The Part 25 airplane has certain performance "gaurantees," whereas the Part 23 airplane does not.
You're getting confused between topics, when asking about Vmcg and Vmca.
An engine failure on the ground which occurs below Vmcg means that unless corrective action is taken, directional control of the aircraft is not possible. Full aerodynamic application of rudder will not correct for the loss of directional control. The loss will occur as lateral deviation from the centerline, or in other words, the aircraft takes off in a different direction. Vmcg calculation does not take into account the effects of nosewheel steering or differential braking. Vmcg is less than Vmca, and if during a takeoff a failure occurs prior to Vmcg, clearly one's option is to reject the takeoff, because directional control is no longer possible.
Vmca is another matter. The airplane doesn't simply turn left or right. For reasons previously provided in this thread, a rolling motion is imparted, and for reasons already given in this thread that rolling motion may not be stoppable or preventable...even if the power is pulled back. Particularly in an airplane such as the 340 where the tip tanks tend to exacerbate the problem of stopping any rolling motion once it's started, and particularly at low airspeeds when control authority is less. Particularly at low airspeeds when control authority is less, when one has elected to take off at speeds less than the minimum control speed. I think you see where that's headed.
On the ground, you may end up in the weeds if you don't act properly. In flight, you may end up in the weeds, upside down, on fire. You see the difference, perhaps.
So, you ask, what's the big deal taking off below single engine minimum control speed if you might have directional control problems before or after taking off?
Consider the alterantive, when acting prudently. One takes off at an airspeed which permits safe control of the airplane in the event of an engine failure. One is above Vmc, and has the luxury still maintaining control with appliation of rudder, banking into the good engine retracting flaps and gear, and climbing (where possible) at Vyse. When losing an engine after takeoff when below Vmca, one is gambling, and has no chance of climbing out. If one is very close to the stall speed, which is very possible, one may experience a very rapid loss of control with no chance of stopping the event. Add to that the fact that your first inclination in the event of an engine failure is to push the power up...not pull it back. This only makes things worse.
By taking off at a speed which permits full control, you have options. You also have time to act and react, configure, prepare for either a forced landing or a climb out at Vxse or Vyse, and to handle the problem. In other words, you're prepared.
Sad experience over many decades of multi engine training, testing, and flying has taught the industry these things. The FAA, for example, stopped allowing even engine failures on practical tests at any more than 40% of the takeoff speed, due to the number of accidents during practical tests for pilot certification, when performing a high speed rejected takeoff. That's even before the aircraft gets off the ground, when a loss of directional control is far less critical. Loss of directional control in the air, especially on takeoff, is about as critical as you can get.
A light twin may or may not be able to climb out on one engine. Whether it can or not, even if it's just holding altitude or maintaining control, it's far better than actually intentionally planning for a takeoff when there's no such possibility whatsoever.
The 340, depending on weight and density altitude, is capable of climbing (at a very reduced rate) on one engine. If one has planned one's takeoff properly, having remained on the ground until above Vmcg and taking off above Vmca, the option and ability is then available to clean up and fly off under control.
For airplanes which will not maintain altitude on one engine, one still has directional control in one's favor if one has properly elected to fly above Vmca, and one has a significantly improved ability to put the airplane on the ground under control, at a controlled rate of descent...as opposed to the original poster's plan of simply intending to yank the power back on the good engine and accept whatever lies beyond.
I don't know if the original poster has had occasion to arrive at an altitude of 30' or so above the runway on takeoff and suddenly retard power on one engine, then the other, and attempt to reach the ground...he doesn't appear to have had the experience of a real engine failure at all. Certainly not with one engine having failed while below Vmc, then while starting to yaw and subsequently roll (again, for reasons already explained in this thread), attempt to pull back the other engine and then land the aircraft...but you may rest assured that he doesn't want that experience. Nobody does. Even without the loss of control, attempting to suddenly lose power and then get that airplane to the ground is not at all the same as losing one's only engine in a single, and gliding. In fact, he's got a high probability of stalling it in the process. As well as doing it while yawing and rolling.
Think about it.
You also are asking about different subject. In the tech log question, you asked about Vmcg, which is not the same as Vmca. One is minimum ground control speed, one is minimum control speed in the air; each have different criteria and requirements.
When 411a says that a part 23 airplane doesn't have gauranteed performance after takeoff, he's correct. This isn't at all the same thing as a Part 25 airplane, which does have certain performance "gaurantees" based on the nature of certification. For example, a multi engine airplane certificated under Part 23 isn't required to maintain altitiude after an engine failure, by virtue of it's certification, nor is it required to be able to go around on one engine, fly a missed approach with an engine failure, etc. Part 25 certificated aircraft are required to meet specific climb gradients following loss of an engine on takeoff (which translates to a go-around or missed approach, too). The Part 25 airplane has certain performance "gaurantees," whereas the Part 23 airplane does not.
You're getting confused between topics, when asking about Vmcg and Vmca.
An engine failure on the ground which occurs below Vmcg means that unless corrective action is taken, directional control of the aircraft is not possible. Full aerodynamic application of rudder will not correct for the loss of directional control. The loss will occur as lateral deviation from the centerline, or in other words, the aircraft takes off in a different direction. Vmcg calculation does not take into account the effects of nosewheel steering or differential braking. Vmcg is less than Vmca, and if during a takeoff a failure occurs prior to Vmcg, clearly one's option is to reject the takeoff, because directional control is no longer possible.
Vmca is another matter. The airplane doesn't simply turn left or right. For reasons previously provided in this thread, a rolling motion is imparted, and for reasons already given in this thread that rolling motion may not be stoppable or preventable...even if the power is pulled back. Particularly in an airplane such as the 340 where the tip tanks tend to exacerbate the problem of stopping any rolling motion once it's started, and particularly at low airspeeds when control authority is less. Particularly at low airspeeds when control authority is less, when one has elected to take off at speeds less than the minimum control speed. I think you see where that's headed.
On the ground, you may end up in the weeds if you don't act properly. In flight, you may end up in the weeds, upside down, on fire. You see the difference, perhaps.
So, you ask, what's the big deal taking off below single engine minimum control speed if you might have directional control problems before or after taking off?
Consider the alterantive, when acting prudently. One takes off at an airspeed which permits safe control of the airplane in the event of an engine failure. One is above Vmc, and has the luxury still maintaining control with appliation of rudder, banking into the good engine retracting flaps and gear, and climbing (where possible) at Vyse. When losing an engine after takeoff when below Vmca, one is gambling, and has no chance of climbing out. If one is very close to the stall speed, which is very possible, one may experience a very rapid loss of control with no chance of stopping the event. Add to that the fact that your first inclination in the event of an engine failure is to push the power up...not pull it back. This only makes things worse.
By taking off at a speed which permits full control, you have options. You also have time to act and react, configure, prepare for either a forced landing or a climb out at Vxse or Vyse, and to handle the problem. In other words, you're prepared.
Sad experience over many decades of multi engine training, testing, and flying has taught the industry these things. The FAA, for example, stopped allowing even engine failures on practical tests at any more than 40% of the takeoff speed, due to the number of accidents during practical tests for pilot certification, when performing a high speed rejected takeoff. That's even before the aircraft gets off the ground, when a loss of directional control is far less critical. Loss of directional control in the air, especially on takeoff, is about as critical as you can get.
A light twin may or may not be able to climb out on one engine. Whether it can or not, even if it's just holding altitude or maintaining control, it's far better than actually intentionally planning for a takeoff when there's no such possibility whatsoever.
The 340, depending on weight and density altitude, is capable of climbing (at a very reduced rate) on one engine. If one has planned one's takeoff properly, having remained on the ground until above Vmcg and taking off above Vmca, the option and ability is then available to clean up and fly off under control.
For airplanes which will not maintain altitude on one engine, one still has directional control in one's favor if one has properly elected to fly above Vmca, and one has a significantly improved ability to put the airplane on the ground under control, at a controlled rate of descent...as opposed to the original poster's plan of simply intending to yank the power back on the good engine and accept whatever lies beyond.
I don't know if the original poster has had occasion to arrive at an altitude of 30' or so above the runway on takeoff and suddenly retard power on one engine, then the other, and attempt to reach the ground...he doesn't appear to have had the experience of a real engine failure at all. Certainly not with one engine having failed while below Vmc, then while starting to yaw and subsequently roll (again, for reasons already explained in this thread), attempt to pull back the other engine and then land the aircraft...but you may rest assured that he doesn't want that experience. Nobody does. Even without the loss of control, attempting to suddenly lose power and then get that airplane to the ground is not at all the same as losing one's only engine in a single, and gliding. In fact, he's got a high probability of stalling it in the process. As well as doing it while yawing and rolling.
Think about it.
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At first I was worried that someone might actually be listening to what you are suggesting. Then I realized you are simply being argumentive, and that’s OK. I will also have faith that anyone that has a ME rating probably has a MEI and therefore has been trained by competent and knowledgeable CFI’s that teach solid aerodynamics principles (pardon the pun), safety practices and smart piloting techniques.
To that end I say, ask all the dim questions you want, assail us with foolish theories on rotation before Vmc, go ahead and run biofuel in you avgas engine.
In the words of Monty Python “I don't wanna talk to you no more, you empty headed animal food trough wiper! I fart in your general direction! You mother was a hamster and your father smelt of elderberries!”
To that end I say, ask all the dim questions you want, assail us with foolish theories on rotation before Vmc, go ahead and run biofuel in you avgas engine.
In the words of Monty Python “I don't wanna talk to you no more, you empty headed animal food trough wiper! I fart in your general direction! You mother was a hamster and your father smelt of elderberries!”
SNS3Guppy
In amongst what is undoubtedly good and thorough explanation, and also some rather patronising comments about what you think confuses me, is the central issue, which you put quite concisely.
The question, which I don't think you've answered yet, is why you think that on the ground you don't also end up "upside down and on fire". If the aerodynamic forces after an engine failure at that particular speed will roll the aircraft after its wheels have left the ground, why do you think that you will be spared if the wheels are still on the runway?
One possibility, put by 411A, is that the nosewheel offers a lateral force opposing the yaw and gives you a better chance of keeping the nose in front of the tail. But as I think we've now examined on Tech Log, no one seems to be able to come up with a certification requirement that suggests that the lateral force from the nosewheel will be available and sufficient to do so, even for a subpart 25 aircraft.
And that again, is pivotal. Once a subpart 25 aircraft has reached V1, which must be at least Vmca, there is that certification requirement that the aircraft can continue the takeoff. And because we rotate at or above V1, it's obvious that for such an aircraft we would never take it into the air below Vmca.
For a subpart 23 aircraft, the situation is different. Even after we take the aircraft into the air, we know that in the event of an engine failure we may simply have to do what we would do on the ground -- close both throttles and do the best job we can to keep it straight. If we fail to do that below Vmca, then of course we will "end up in the weeds, upside down, on fire". Even if we fail to do that above Vmca, there is a good chance we're still going to end up in the weeds and on fire because we don't have the performance to continue flight. Only when we reach a speed at which we know we can climb away on one engine (and I would choose Vyse) can we change the instinctive reaction to an engine failure and attempt to keep flying. Below that speed at which we would commit to flight, we close the throttles.
So for a subpart 23 aircraft, Vmca is not a useful speed at which to make that decision to commit to flight. It's usually way too low. Is it a useful speed to choose as a minimum for taking the aircraft into the air? Well the only reason it would be might be that there's a speed range below Vmca within which the aircraft is controllable on the ground but not in the air. And I'm waiting for you to explain why such a speed range should exist.
In amongst what is undoubtedly good and thorough explanation, and also some rather patronising comments about what you think confuses me, is the central issue, which you put quite concisely.
On the ground, you may end up in the weeds if you don't act properly. In flight, you may end up in the weeds, upside down, on fire. You see the difference, perhaps.
One possibility, put by 411A, is that the nosewheel offers a lateral force opposing the yaw and gives you a better chance of keeping the nose in front of the tail. But as I think we've now examined on Tech Log, no one seems to be able to come up with a certification requirement that suggests that the lateral force from the nosewheel will be available and sufficient to do so, even for a subpart 25 aircraft.
The Part 25 airplane has certain performance "guarantees," whereas the Part 23 airplane does not.
For a subpart 23 aircraft, the situation is different. Even after we take the aircraft into the air, we know that in the event of an engine failure we may simply have to do what we would do on the ground -- close both throttles and do the best job we can to keep it straight. If we fail to do that below Vmca, then of course we will "end up in the weeds, upside down, on fire". Even if we fail to do that above Vmca, there is a good chance we're still going to end up in the weeds and on fire because we don't have the performance to continue flight. Only when we reach a speed at which we know we can climb away on one engine (and I would choose Vyse) can we change the instinctive reaction to an engine failure and attempt to keep flying. Below that speed at which we would commit to flight, we close the throttles.
So for a subpart 23 aircraft, Vmca is not a useful speed at which to make that decision to commit to flight. It's usually way too low. Is it a useful speed to choose as a minimum for taking the aircraft into the air? Well the only reason it would be might be that there's a speed range below Vmca within which the aircraft is controllable on the ground but not in the air. And I'm waiting for you to explain why such a speed range should exist.
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The question, which I don't think you've answered yet, is why you think that on the ground you don't also end up "upside down and on fire".
An aircraft rolling along the ground doesn't mystically flip upside down, but an aircraft rolling out of control just after takeoff has no problem. You do see the difference, don't you?
If the aerodynamic forces after an engine failure at that particular speed will roll the aircraft after its wheels have left the ground, why do you think that you will be spared if the wheels are still on the runway?
One possibility, put by 411A, is that the nosewheel offers a lateral force opposing the yaw and gives you a better chance of keeping the nose in front of the tail. But as I think we've now examined on Tech Log, no one seems to be able to come up with a certification requirement that suggests that the lateral force from the nosewheel will be available and sufficient to do so, even for a subpart 25 aircraft.
Even if we fail to do that above Vmca, there is a good chance we're still going to end up in the weeds and on fire because we don't have the performance to continue flight.
Only when we reach a speed at which we know we can climb away on one engine (and I would choose Vyse) can we change the instinctive reaction to an engine failure and attempt to keep flying.
Below that speed at which we would commit to flight, we close the throttles.
You need to bear in mind that Vmcg is a technical number, as is Vmc. These are certification values. In a light normally aspirated piston twin, Vmc decreases with an increase in density altitude, and decreases in many cases with gear down, with the addition of flaps (though not necessarily), with a forward CG, etc. A published Vmc number does not necessarily represent the number at which directional control is no longer possible. The number may be less, and in some cases, it may also be more. It's a reference number. The same may be said of Vmcg.
Vmcg, for example, is one number; a certification number. The speed at which directional control may no longer be maintained does change; it can be increased at a rate roughly on a ratio of one to one with a crosswind, increasing one knot for each knot of crosswind on the side of the failed engine, and decreases at roughly the same amount for a crosswind from the other side. Other factors may also affect the minimum controllable speed, most notably among them the center of gravity.
And I'm waiting for you to explain why such a speed range should exist.
Vmcg occurs typically at a lesser speed than Vmc, but not always; the two may be coincident. Flight speeds are typically greater than ground speeds, as you can guess. The range does not exist between the two because it has a purpose; it does not. It exists because it exists. However, even though one has obtained Vmcg does not mean one is ready to fly, and accordingly one must be above Vmc prior to taking the airplane into the air.
Perhaps you meant something else.
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VMCA v VMCG
Bookworm, I've been following this thread since leaving these two people to their fun, cos I find the name-calling, patronising assumptions and so on to be a bit dull. I mean, I already went to high school, you know? But I thought their might some pearls of wisdom to be salvaged, or wheat amongst the chaff. (Choose your metaphor 
And there are.
To your specific question re VMCA vs VMCG: "If the aerodynamic forces after an engine failure at that particular speed will roll the aircraft after its wheels have left the ground, why do you think that you will be spared if the wheels are still on the runway? "...well, I wonder if there may be a pretty simple explanation.
It seems to me that you'd much less likely to roll if you're still on the ground, with a high speed engine failure that occurs before rotation, primarily because the "wheels on the runway" act as a stabilising factor against the development of a roll, or to be precise, the wheel that is under the failed engine, and therefore holding up that wing to some degree. Sure, you'll yaw, although nosewheel steering & differential braking may control that to some degree as you retard the working engine...but when on the ground, you have the the main gear to at least partially oppose a rolling motion, no? When practicing high speed engine failures, yes, with a very experienced instructor, I recall a startlingly fast yaw, until the good engine was retarded - but no hint of a roll. And even if a roll did occur and overpower the stability of having wheels on the ground, if you're still on the ground you have a wingtip to hit the ground first, which means that it could be ugly - but probably not as ugly as ending up completely inverted when airborne, where you'll presumably have a serious ROD, even from 20 feet or so, to compound the problem. So the most likely worst case, I would guess, would be departing from the runway - but right side up, and rapidly regaining yaw control as the power from the working engine winds down. Provided you cut power immediately, of course.
Once you're in the air, you've got no wheel on the ground under the failed engine to act as a stabilizing factor, and oppose the rolling motion, so a roll, it seems to me, would be far more likely to occur. And once the roll gets going, it could indeed, perhaps, be difficult to stop given the minimal effectiveness of controls at that speed.
Could it be that simple? The fact that the standard T/O technique is to holding a twin on the ground until VMC or faster would imply so, dontcha reckon?
And there are.To your specific question re VMCA vs VMCG: "If the aerodynamic forces after an engine failure at that particular speed will roll the aircraft after its wheels have left the ground, why do you think that you will be spared if the wheels are still on the runway? "...well, I wonder if there may be a pretty simple explanation.
It seems to me that you'd much less likely to roll if you're still on the ground, with a high speed engine failure that occurs before rotation, primarily because the "wheels on the runway" act as a stabilising factor against the development of a roll, or to be precise, the wheel that is under the failed engine, and therefore holding up that wing to some degree. Sure, you'll yaw, although nosewheel steering & differential braking may control that to some degree as you retard the working engine...but when on the ground, you have the the main gear to at least partially oppose a rolling motion, no? When practicing high speed engine failures, yes, with a very experienced instructor, I recall a startlingly fast yaw, until the good engine was retarded - but no hint of a roll. And even if a roll did occur and overpower the stability of having wheels on the ground, if you're still on the ground you have a wingtip to hit the ground first, which means that it could be ugly - but probably not as ugly as ending up completely inverted when airborne, where you'll presumably have a serious ROD, even from 20 feet or so, to compound the problem. So the most likely worst case, I would guess, would be departing from the runway - but right side up, and rapidly regaining yaw control as the power from the working engine winds down. Provided you cut power immediately, of course.
Once you're in the air, you've got no wheel on the ground under the failed engine to act as a stabilizing factor, and oppose the rolling motion, so a roll, it seems to me, would be far more likely to occur. And once the roll gets going, it could indeed, perhaps, be difficult to stop given the minimal effectiveness of controls at that speed.
Could it be that simple? The fact that the standard T/O technique is to holding a twin on the ground until VMC or faster would imply so, dontcha reckon?
Last edited by lostpianoplayer; 13th May 2008 at 09:20. Reason: spelling
It seems to me that you'd much less likely to roll if you're still on the ground, with a high speed engine failure that occurs before rotation, primarily because the "wheels on the runway" act as a stabilising factor against the development of a roll, or to be precise, the wheel that is under the failed engine, and therefore holding up that wing to some degree.
...Could it be that simple?
...Could it be that simple?
The fact that the standard T/O technique is to holding a twin on the ground until VMC or faster would imply so, dontcha reckon?
The aircraft I fly develops considerable lift in its recommended take-off configuration well below Vmca. At Vmca, if I hold it on, I'm holding it on the nosewheel, with no weight on the mains. An engine failure at that stage would be more catastrophic on the ground than in the air (where I could use some bank to assist control). The AFM simply says "keep it on or close to the ground until take-off safety speed".
If an aircraft can be kept on the runway producing little or no lift, and then rotated into a flying attitude, I can see an advantage in staying on the runway until Vmca. Perhaps that's the case for the 340. But I'm not convinced by the general case.
I think the VG equiped C340 is one of the safest piston twins when it comes to a takeoff engine failure emergency. That is because you can rotate at the 100 knot blueline VYSE speed. If the the oleos are properly inflated the airplane will sit level and therefore not want to fly untill it is positively rotated (this only applies with zero flap). Therefore if you select gear up immediately after rotation (as soon as you have positive rate of climb, of course) you will only have to feather the failed engine and the airplane will be at or above blue line and configured to climb away (i.e. flaps will allready be up and the gear will be retracting/retracted). Our SOP is to keep our right hand on the throttles untill selecting gear up and then move our hand to the prop levers. therefore if an engine failure happens with hands still on the throttles we would automatically retard both throttles and reject the takeoff. If the engine failure occures with our hand on the prop levers we would identify he failed engine (dead foot, dead engine) feather it and concentrate on keeping the airplane straight and set an initial 5 deg nose up attitude then adjust to maintain VYSE. We felt this procedure allowed us to come closest to a large aircraft SOP and therefore their levels of safety.
Last edited by Big Pistons Forever; 13th May 2008 at 18:14.
lostpianoplayer, after a digression into controllability, may I return to what I was going to say before SNS3Guppy and I locked horns (though how a fish and a worm lock horns is beyond me 
)?
The problem, in the context of operating off short fields that require lift off at low speed is this. In the ideal world, engine failures are infrequent and sudden. You recognise the failure, chop the throttles, go through the hedge at the end and accept that the insurance company owns the aircraft.
Real life is less straightforward. You accelerate beyond the speed and runway point at which a safe rejection is possible, but still below Vmca, and the engine coughs -- I could equally propose an oil pressure gauge in the red, or a strange noise from one engine. You now have a choice. You can leave the throttles where they are, continue to try to fly it, and risk a sub-Vmc roll. Or you can close the throttles, go through the hedge and accept the hull loss for sure. It was probably just a little cough, right? How lucky do you feel?
Coughing engines, sticky oil pressure gauages and unfamiliar noises are, fortunately or unfortunately, a lot more common than catastrophic and sudden engine failure. So unless you feel lucky on a regular basis, the price of operating from a short field is a much higher probability of a precautionary abort and consequential hull loss.
)?
I'm just researching the question, at this stage, and comparing viewpoints. Particularly on the issue of why you can't just cut power immediately to prevent a VMC roll on takeoff.
Real life is less straightforward. You accelerate beyond the speed and runway point at which a safe rejection is possible, but still below Vmca, and the engine coughs -- I could equally propose an oil pressure gauge in the red, or a strange noise from one engine. You now have a choice. You can leave the throttles where they are, continue to try to fly it, and risk a sub-Vmc roll. Or you can close the throttles, go through the hedge and accept the hull loss for sure. It was probably just a little cough, right? How lucky do you feel?
Coughing engines, sticky oil pressure gauages and unfamiliar noises are, fortunately or unfortunately, a lot more common than catastrophic and sudden engine failure. So unless you feel lucky on a regular basis, the price of operating from a short field is a much higher probability of a precautionary abort and consequential hull loss.
Or better still a Roberston STOL C206
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340A takeoff procedure
Here is how I takeoff in my 340A, in brief form and I welcome any comments or suggestions;
I believe this is the best method to pilot a 340A on takeoff. Advantages are;
- All pre-takeoff checklists performed.
- This includes accelerate stop distance, which is approximately 3,000 ft by the book; however I prefer a 4,000 ft minimum runway length.
- Obtain clearances as required.
- Lineup on runway, brakes on and increase power evenly to 30 inches MP for three seconds (recommended by Ram Aircraft) and then apply full power while releasing brakes.
- Check for engines gauges in the Green.
- Call our VMC speed, 74 kts.
- Call out Rotation Speed, 91 kts and Rotate, one may also rotate at Rotation minus five knots, but I prefer the higher speed. This is due to wanting to avoid as much as possible any Vmc issues.
- My right hand is on the throttles at max power.
- Depending on weight, CG and DA, actual rotation occurs in low 90’s
- Takeoff occurs and climbout to Vyse, 100 kts. This takes about three seconds from Rotation.
- If anything coughs, pukes, thumps or rattles during this phase of takeoff, I will immediately retard the throttles and land straight ahead.
- Now is decision time. By selecting gear up with my right hand, I am committing to continue the takeoff. I keep my right hand on the gear lever until I see three green lights and I do not put my right hand back on the throttles.
- Accelerate to Vy, 108kts and climbout straight ahead or as directed by ATC to 1000 ft AGL minimum at full power.
- During the initial climbout to 1.000 ft AGL I gradually nose over at the top of the climb profile to approximately 140 kts and reduce power to 32 in MP, 2500 RPM and 1500 EGT, a quick engine scan, and proceed with departure as planned.
I believe this is the best method to pilot a 340A on takeoff. Advantages are;
- You have adequate runway for a rejected takeoff.
- You accelerate through the Vmc speed before Rotation so that Vmc risk is minimized.
- You immediately accelerate to Vyse and then select “Gear Up” as THE decision making moment to commit to the climbout, regardless of engine failure, and treat an engine failure as an in flight emergency.
- At decision speed you are at Vyse 100 kts, and then accelerate to Vyse plus 8 kts. In case of engine failure and the ensuing long moments to identify, verify and feather, a small loss in speed will result in the target speed of Vyse.
- I rarely fly at MGTOW and find the SE climb performance to be 500 fpm or better at GTOW minus 400 lbs.
Last edited by Lifeisgood; 15th May 2008 at 00:12.