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Flaps 10 during inital emergency descent?
- Thread starter rumorhasit
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pilotyip
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Where?
"When performing a simulated glide approach Abeam the numbers for engine failure simulation go to best glide then flap 10 or leave them down?"
Other people said C-172, but the first post does not mention the airplane does it?
"When performing a simulated glide approach Abeam the numbers for engine failure simulation go to best glide then flap 10 or leave them down?"
pilotyip
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pilotyip
Well-known member
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That is the part just before the intermediate emergency descent that is followed by the final emergency descent.
I'm not sure there is proper terminology to define the parts of an emergency descent. Certainly if one is to specify the early part of the emergency descent, to describe it as the "initial emergency descent" is approprite communication. How one conducts the initial part of the descent is typically different than the way one conducts the majority of the descent. Depending on the aircraft and the operation, considerable activity may mark the initial part of the descent procedure, and can vary from simply establishing a glide speed to configuring an airplane, dealing with autopilots, making communication, maneuvering, donning oxygen, etc. I don't believe the original poster is out of line by specifying the initial emergency descent.
Where we can clarify the term is exactly what is the nature of the emergency; are we talking a true emergency descent in which an emergency precipitates the need to rapidly move to a lower altitude, or we talking an emergency in which we have no choice but to descent (such as an engine failure in the aforementioned Cessna 172)? Configuring the airplane with flaps is potentially appropriate in one situation, but not the other, and where and when one does configure is worthy of consideration.
If we're talking best glide, then most instructors know only one concept to get down, and teach one speed. In fact there are two which should be known, one of which is usually not published, but very pertinent to the descent. Best glide is often thought of strictly in terms of what speed gets us the farthest distance traveled...which is great if one has somewhere to go. However, one may be over the intended landing site, and going the farthest isn't necessarily a priority.
Minimum descent speed, however, is a priority, especially if one is make a power off descent at night or to a location where the specific ground elevation and obstacles can't readily be determined. Instructors often teach that any speed greater or lesser than "best glide speed" mean a higher rate of descent and a shorter distance travelled. This is partly true, because the gliding range is reduced when not at the proper airspeed/angle of attack for "best glide," but it's also untrue in that one can certainly achieve a lower rate of descent. This occurs at minimum sink airspeed.
With either best glide or minimum sink, aircraft configuration is just as important a consideration as airspeed. If one isn't on the proper speed, then one won't achieve the desired performance. Likewise, if one isn't configured properly, one won't achieve the proper performance. What does this imply? If one isn't on speed or properly configured, one wont' glide as far, or won't get the minimum descent rate that's possible for that aircraft. Applying flap early, for example, alters the performance expectation both in respect to gliding distance and glide time.
For the original poster, you'll find that in most light aircraft such as the 172, the best glide speed very closely approximates the sea level best rate of climb speed (Vy). The Minimum sink speed, not published in most cases, will closely approximate the sea level best angle of climb speed (Vx). (Vx and Vy converge as density altitude increases in a normally aspirated airplane as a function of engine power, but the sea level numbers are close enough to give you a good approximation to see the relationship between the two).
Given this, one needs to know what's intended. Are you attempting to reach a distant parking lot or field with an extended glide, or are you setting up for a landing on a meadow directly below and well within the gliding range of the aircraft? If you've just lost your engine and you've been maintaining good airmanship practices of always keeping a suitable forced landing site beneath you, then you may very well be setting up for something under you. This is usually best. With this in mind, you may not want to glide as far as you can...you may want to make your descent rate as low as possible to give yourself adequate time to run checklists, attempt engine re-starts, communicate your position or needs to ATC or other aircraft, or handle whatever needs to be accomplished before touchdown. Now you're looking at minimum sink speed offering you the best option.
Previously we alluded to the concept that one shouldn't invent procedures, and this is true. One should not. We're talking about a technique, however, and not a procedure You can see it for yourself, however, with a little experimentation. Go fly on a calm morning, and climb up to 4,000' or so. Reduce power to a predetermined setting (somewhere above idle, you can use 1500 RPM for example, as a arbitrary number), and establish a glide at 80 knots. Allow a thousand feet of descent, and make a note of the average descent rate. Climb back up to 4,000', then do it at 75 knots. Then again at 70, then at 65, then 60. Note your descent rate, and where the trend decreases, then increases again, and you're narrowing in on your minimum sink speed. You can then bracket or repeat the exercise, trimming the airplane to fly in 2 or 3 knot increments to see where exactly your airplane finds it's minimum sink.
As you've raised the question of flaps, repeat the same exercise using flap, and note the changes: see where you reach a point of the vertical speed decreasing, then increasing again (say, for example, as you approach a 60 knot glide you see your minimum sink, but at lower speeds it increases again...). Now compare what you've found, both the airspeed itself and the descent rate achieved at that gliding airspeed, with your numbers from power off descents. This will tell you what you want to know about configuring early, or in the initial parts of the descent, with flaps.
Now, if you're talking about an emergency descent with the intent of reaching the ground in the shortest time possible, or getting to a lower altitude in the shortest time possible, it's an entirely different matter. Depending on the aircraft in question, you may be better off configuring with flaps (and gear, spoilers, etc, as applicable to a particular airplane), and different techniques apply.
Where we can clarify the term is exactly what is the nature of the emergency; are we talking a true emergency descent in which an emergency precipitates the need to rapidly move to a lower altitude, or we talking an emergency in which we have no choice but to descent (such as an engine failure in the aforementioned Cessna 172)? Configuring the airplane with flaps is potentially appropriate in one situation, but not the other, and where and when one does configure is worthy of consideration.
If we're talking best glide, then most instructors know only one concept to get down, and teach one speed. In fact there are two which should be known, one of which is usually not published, but very pertinent to the descent. Best glide is often thought of strictly in terms of what speed gets us the farthest distance traveled...which is great if one has somewhere to go. However, one may be over the intended landing site, and going the farthest isn't necessarily a priority.
Minimum descent speed, however, is a priority, especially if one is make a power off descent at night or to a location where the specific ground elevation and obstacles can't readily be determined. Instructors often teach that any speed greater or lesser than "best glide speed" mean a higher rate of descent and a shorter distance travelled. This is partly true, because the gliding range is reduced when not at the proper airspeed/angle of attack for "best glide," but it's also untrue in that one can certainly achieve a lower rate of descent. This occurs at minimum sink airspeed.
With either best glide or minimum sink, aircraft configuration is just as important a consideration as airspeed. If one isn't on the proper speed, then one won't achieve the desired performance. Likewise, if one isn't configured properly, one won't achieve the proper performance. What does this imply? If one isn't on speed or properly configured, one wont' glide as far, or won't get the minimum descent rate that's possible for that aircraft. Applying flap early, for example, alters the performance expectation both in respect to gliding distance and glide time.
For the original poster, you'll find that in most light aircraft such as the 172, the best glide speed very closely approximates the sea level best rate of climb speed (Vy). The Minimum sink speed, not published in most cases, will closely approximate the sea level best angle of climb speed (Vx). (Vx and Vy converge as density altitude increases in a normally aspirated airplane as a function of engine power, but the sea level numbers are close enough to give you a good approximation to see the relationship between the two).
Given this, one needs to know what's intended. Are you attempting to reach a distant parking lot or field with an extended glide, or are you setting up for a landing on a meadow directly below and well within the gliding range of the aircraft? If you've just lost your engine and you've been maintaining good airmanship practices of always keeping a suitable forced landing site beneath you, then you may very well be setting up for something under you. This is usually best. With this in mind, you may not want to glide as far as you can...you may want to make your descent rate as low as possible to give yourself adequate time to run checklists, attempt engine re-starts, communicate your position or needs to ATC or other aircraft, or handle whatever needs to be accomplished before touchdown. Now you're looking at minimum sink speed offering you the best option.
Previously we alluded to the concept that one shouldn't invent procedures, and this is true. One should not. We're talking about a technique, however, and not a procedure You can see it for yourself, however, with a little experimentation. Go fly on a calm morning, and climb up to 4,000' or so. Reduce power to a predetermined setting (somewhere above idle, you can use 1500 RPM for example, as a arbitrary number), and establish a glide at 80 knots. Allow a thousand feet of descent, and make a note of the average descent rate. Climb back up to 4,000', then do it at 75 knots. Then again at 70, then at 65, then 60. Note your descent rate, and where the trend decreases, then increases again, and you're narrowing in on your minimum sink speed. You can then bracket or repeat the exercise, trimming the airplane to fly in 2 or 3 knot increments to see where exactly your airplane finds it's minimum sink.
As you've raised the question of flaps, repeat the same exercise using flap, and note the changes: see where you reach a point of the vertical speed decreasing, then increasing again (say, for example, as you approach a 60 knot glide you see your minimum sink, but at lower speeds it increases again...). Now compare what you've found, both the airspeed itself and the descent rate achieved at that gliding airspeed, with your numbers from power off descents. This will tell you what you want to know about configuring early, or in the initial parts of the descent, with flaps.
Now, if you're talking about an emergency descent with the intent of reaching the ground in the shortest time possible, or getting to a lower altitude in the shortest time possible, it's an entirely different matter. Depending on the aircraft in question, you may be better off configuring with flaps (and gear, spoilers, etc, as applicable to a particular airplane), and different techniques apply.
rumorhasit
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Cheese and beans guys, allow me to retort. okay for safety reasons I allow the students to descend to 1000agl for safety reasons. We recover and talk about the descent and climb back up to normal op alt. Then during our landings I pull the power to simulate engine failure using glide approach. My orginal question was during the inital pwr reduction is it better to add 10 degree of flaps after best glide or dump flaps on very short final? And yes as my second post indicated it is a cessna 172. Thanks
Why would you add flaps in the glide, if you're attempting to teach an emergency glide?
Again, are you trying to teach a realistic setup to an emergency approach to a landing?
The traditional flight instructor wave at teaching emergency engine-outs isn't sufficient, and instills a false education and a false sense of security.
The instructor repeatedly pulls the power to idle in the perfect position to land the airplane, abeam a hard surface runway, and the student subsequently lands the airplane.
In the real world, this doesn't happen, of course, and the student is left to experience his first forced landing alone, for the first time...because the instructor has never given him realistic training. Most often, the instructor wouldn't know what a real engine out feels like; he or she has never been shown, has never experienced one, and doesn't understand anything beyond what he or she was taught. Seldom is any forethought given to making the exercise realistic; just passing on what was given...to no avail.
What are you trying to teach the student in this scenario? Are you simply trying to show a glide? A glide to a spot landing? A glide to a spot landing under adverse circumstances? A glide to a spot landing under adverse circumstances, off field? Are you attemptin to reinforce a single-speed glide to a touchdown? If you're teaching best distance glide, then do you train at varying angles and distances and geographical locations from the runway to let the student see how he's able to work that glide? Do you do it over farm fields and roads, to teach the student how to reach a chosen landing site and set up to land there?
A good rule of thumb is never set up for emergency landing practice unless you're fully committed to making the landing with what you've got. If you've got a dead battery and a dead engine, you may not be able to move those flaps once they're down. Do you want to commit to dirtying up the airplane early in the glide, knowing that you're committed? Or do you want to wait until you're closer to the ground. You can always slip...but you can't get rid of the extra drag and performance loss created by the flaps.
By the same token, don't pull the power during emergency training without being fully prepared to execute the landing, too. Dont' assume you can put it back in, and don't let the student get in the habit of doing it either.
Again, are you trying to teach a realistic setup to an emergency approach to a landing?
The traditional flight instructor wave at teaching emergency engine-outs isn't sufficient, and instills a false education and a false sense of security.
The instructor repeatedly pulls the power to idle in the perfect position to land the airplane, abeam a hard surface runway, and the student subsequently lands the airplane.
In the real world, this doesn't happen, of course, and the student is left to experience his first forced landing alone, for the first time...because the instructor has never given him realistic training. Most often, the instructor wouldn't know what a real engine out feels like; he or she has never been shown, has never experienced one, and doesn't understand anything beyond what he or she was taught. Seldom is any forethought given to making the exercise realistic; just passing on what was given...to no avail.
What are you trying to teach the student in this scenario? Are you simply trying to show a glide? A glide to a spot landing? A glide to a spot landing under adverse circumstances? A glide to a spot landing under adverse circumstances, off field? Are you attemptin to reinforce a single-speed glide to a touchdown? If you're teaching best distance glide, then do you train at varying angles and distances and geographical locations from the runway to let the student see how he's able to work that glide? Do you do it over farm fields and roads, to teach the student how to reach a chosen landing site and set up to land there?
A good rule of thumb is never set up for emergency landing practice unless you're fully committed to making the landing with what you've got. If you've got a dead battery and a dead engine, you may not be able to move those flaps once they're down. Do you want to commit to dirtying up the airplane early in the glide, knowing that you're committed? Or do you want to wait until you're closer to the ground. You can always slip...but you can't get rid of the extra drag and performance loss created by the flaps.
By the same token, don't pull the power during emergency training without being fully prepared to execute the landing, too. Dont' assume you can put it back in, and don't let the student get in the habit of doing it either.
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