Glide descent leveling off technique
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Glide descent leveling off technique
An ex-airforce instructor tought this method of level off from glide descent - it seems this is the technique used in airforce PC7.
Assume glide descent speed is 70kts, cruise is 100kts.
- Initiate level off when 10% ROD of desired altitude.
- Simultaneously select full power and slightly higher than straight & level attitude.
- As airspeed increases, progressively lower the nose to straight & level attitude.
- 5kts before reaching cruise speed of 100kts, select cruise power.
- Hold straight & level attitude
- Trim
The main difference in this technique is that you select slightly higher than s&l attitude initially, then progressively lower to s&l attitude as airspeed reaches 100kts.
His reasoning is, as you are in a glide descent at 70kts, when leveling off if you select s&l (instead of slightly higher), you will still be descending due to the lower airspeed initially.
Any thoughts on this technique?
Assume glide descent speed is 70kts, cruise is 100kts.
- Initiate level off when 10% ROD of desired altitude.
- Simultaneously select full power and slightly higher than straight & level attitude.
- As airspeed increases, progressively lower the nose to straight & level attitude.
- 5kts before reaching cruise speed of 100kts, select cruise power.
- Hold straight & level attitude
- Trim
The main difference in this technique is that you select slightly higher than s&l attitude initially, then progressively lower to s&l attitude as airspeed reaches 100kts.
His reasoning is, as you are in a glide descent at 70kts, when leveling off if you select s&l (instead of slightly higher), you will still be descending due to the lower airspeed initially.
Any thoughts on this technique?
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All seems a bit complicated and jiggly to me. What with full power, attitude changes, cruise power etc. Perhaps it's type dependent, but in C150/152/172 and the PA28s I stick to the P-A-T model. As I'm approaching the level I want I add power to cruise, raise the nose, and trim.
Are there many instances when a full glide descent to a specified level is necessary? PFLs involve bursts of power for engine warming, and glide approach to either land or touch and go. Otherwise the P-A-T model should be ample unless type/POH requires another method.
Are there many instances when a full glide descent to a specified level is necessary? PFLs involve bursts of power for engine warming, and glide approach to either land or touch and go. Otherwise the P-A-T model should be ample unless type/POH requires another method.
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Yes, complicated... Perhaps advanced - turbine - aircraft respond well to this type of handling, but a light GA aircraft not so much. Obviously there are reasons for glide descents, though whoever pays for the engine cylinders will thank you for keeping such flying to a minimum. Shock cooling is not good for the cylinders. Easy on the power changes, particularly on cooler days....
Consider feeling what the airplane is trying to tell you more, and watching the airspeed less. When you are aware of what the plane is telling you, you're even more ready for other types. On the other hand if you are flying from a recipe of numbers and settings, you're going to miss some of the basics. If you have not done it yet in your flying, it should happen for you soon, that you fly entire circuits with some of the instruments (particularly the airspeed) obscured, just to make you feel rather than read your flying.
A gliding approach, when considering the care of engine, is excellent practice for forced approaches, and power off landings. Terminating a glide with full power is really ineffective energy management - Sort of like jack rabbit driving. I'm sure that sailplane pilots here would have lots to say about such techniques.
Fly as though you're trying to impress the owner of the aircraft with how in tune you are with it, and how gently and gracefully you'll treat it - Uncle Sam, on the other hand, is not so sensitive to this, so the Air Force probably has other techniques....
Consider feeling what the airplane is trying to tell you more, and watching the airspeed less. When you are aware of what the plane is telling you, you're even more ready for other types. On the other hand if you are flying from a recipe of numbers and settings, you're going to miss some of the basics. If you have not done it yet in your flying, it should happen for you soon, that you fly entire circuits with some of the instruments (particularly the airspeed) obscured, just to make you feel rather than read your flying.
A gliding approach, when considering the care of engine, is excellent practice for forced approaches, and power off landings. Terminating a glide with full power is really ineffective energy management - Sort of like jack rabbit driving. I'm sure that sailplane pilots here would have lots to say about such techniques.
Fly as though you're trying to impress the owner of the aircraft with how in tune you are with it, and how gently and gracefully you'll treat it - Uncle Sam, on the other hand, is not so sensitive to this, so the Air Force probably has other techniques....
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And I would suggest starting to re-trim the aircraft as soon as you've given full power. Coarse trimming! The plane can be a handful otherwise, especially for a new student trying to maintain a straight & level attitude. Then you can fine tune once the cruise power is set.
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Thanks for the info. I tend to disagree with the ex-airforce instructor. Can't use the "slightly above s&l attitude then progressively lower to s&l" in a C172, as from 70kts, when you apply full power, the response is real quick.
As for the full power from glide descent, well, of course it's done smoothly, not rammed.
The way we are thought about reducing & increasing airspeed is as follows:
When an airspeed change of more than 20kts is desired, use the full power / idle power initally , then select the proper RPM 5kts from desired airspeed.
eg. Aircraft at 70kts, you want to accel to 100kts. Select full power (eg. 2400RPM), as airspeed increases, at 95kts, decrease power to cruise at 100kts (eg. 2200RPM)
As for the full power from glide descent, well, of course it's done smoothly, not rammed.
The way we are thought about reducing & increasing airspeed is as follows:
When an airspeed change of more than 20kts is desired, use the full power / idle power initally , then select the proper RPM 5kts from desired airspeed.
eg. Aircraft at 70kts, you want to accel to 100kts. Select full power (eg. 2400RPM), as airspeed increases, at 95kts, decrease power to cruise at 100kts (eg. 2200RPM)
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Adding power in a piston aeroplane will always result in a quick response; this much fuel/air = this much rpm = this amount of pull. I've sat and watched many jets spool up to a higher power 10 seconds in anticipation. Piston props don't need it; I can't speak for turboprops but at a guess it'd be somewhere in between.
I'm not sure I understand the purpose of this method of changing speeds. You clearly know approximate power settings that achieve certain speeds. Therefore my method is exactly that. Select the power value I expect to maintain the desired speed, allow the ASI to settle, readjust the power as required for accuracy.
I'm also not sure of the situation you might do this. Acelerating and decelerating between 70kts and 100kts in a C172 is a challenge in itself whilst flying straight and level. My experiences of this are instructors assessing my ability to control the aeroplane whether visually or by instruments - control and scan exercises.
Now I am sure there cannot be many variants of the C172 that will maintain 100kts at 2200rpm
eg. Aircraft at 70kts, you want to accel to 100kts. Select full power (eg. 2400RPM), as airspeed increases, at 95kts, decrease power to cruise at 100kts (eg. 2200RPM)
I'm also not sure of the situation you might do this. Acelerating and decelerating between 70kts and 100kts in a C172 is a challenge in itself whilst flying straight and level. My experiences of this are instructors assessing my ability to control the aeroplane whether visually or by instruments - control and scan exercises.
Now I am sure there cannot be many variants of the C172 that will maintain 100kts at 2200rpm
Last edited by GeeWhizz; 19th Nov 2011 at 03:31.
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It's off topic, but in reply to the why change power from 70kts to 100kts from idle to full power:
An airspeed change of greater than 20kts technique:
Let's say you're at 1800RPM, 70kts s&l. To increase speed to 100kts in s&l you increase to full power, then anticipate 5kts before 100kts (at 95kts) select 2200rpm (which is supposed to give you 100kts s&l).
The reason of this extra burst of power before reducing it is to make the airspeed change faster.
An airspeed change of greater than 20kts technique:
Let's say you're at 1800RPM, 70kts s&l. To increase speed to 100kts in s&l you increase to full power, then anticipate 5kts before 100kts (at 95kts) select 2200rpm (which is supposed to give you 100kts s&l).
The reason of this extra burst of power before reducing it is to make the airspeed change faster.
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i dont believe this is an ex RAF method as its totally stupid! Why would you be descending at below cruise speed?
If anything you will be descending above cruise and watching the speed decay as you level and advance the Throttels back to cruise.
You have two sources of energy in the descent! The potential energy in your engine but more important in the descend you have the energy you are tapping into inherant in the airframe.
If you like you have surplus available in the descent hence the problem is one of going too fast not too slow.
Consider also its bad practice to descend a piston on a closed throttle and this theory makes no sense at all.
Consider also your PAX do they want big burts of power? No they want a smooth flight.
The only time you may want to come down slowly is more in IMC flight where you are entering heavy cloud or thunderstorm or in area of turbulence and are trying to protect the aircraft from structural damage but that is relevant to the cruise as well as descent.
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If anything you will be descending above cruise and watching the speed decay as you level and advance the Throttels back to cruise.
You have two sources of energy in the descent! The potential energy in your engine but more important in the descend you have the energy you are tapping into inherant in the airframe.
If you like you have surplus available in the descent hence the problem is one of going too fast not too slow.
Consider also its bad practice to descend a piston on a closed throttle and this theory makes no sense at all.
Consider also your PAX do they want big burts of power? No they want a smooth flight.
The only time you may want to come down slowly is more in IMC flight where you are entering heavy cloud or thunderstorm or in area of turbulence and are trying to protect the aircraft from structural damage but that is relevant to the cruise as well as descent.
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During a glide descent it is possible that the speed would be less that cruise. Glide performance for PFLs / approaches usually means about 20kts slower than the cruise, somewhere around powered approach speed.
Lastly, it may change the airspeed faster but at what cost? Control: many trim changes, pushing and pulling on the column. Uncomfortable for the pilot leaving out the passengers!
But If it works I guess
Lastly, it may change the airspeed faster but at what cost? Control: many trim changes, pushing and pulling on the column. Uncomfortable for the pilot leaving out the passengers!
But If it works I guess
Last edited by GeeWhizz; 19th Nov 2011 at 08:05.
Why full power? Why not select cruise power - ok fixed pitch propeller you'll have to set a tad more (50 rpm?) as the rpm will increase slightly as the speed increases.
Yes the initial attitude required will be that which is appropriate to fly at 70 kts - as the speed increases you will need to progressively lower the nose to maintain height (technically the student should know how to do this as he has already been taught straight and level flight at different airspeeds, hasn't he?).
Would teach a coarse trim initially and then fine trim as the speed stabilises.
shumway, agree but that assumes that you want to achieve target airspeed as quickly as possible - I believe CFS teach both techniques - ie slow/fast acceleration (and also slow/fast deceleration)
Yes the initial attitude required will be that which is appropriate to fly at 70 kts - as the speed increases you will need to progressively lower the nose to maintain height (technically the student should know how to do this as he has already been taught straight and level flight at different airspeeds, hasn't he?).
Would teach a coarse trim initially and then fine trim as the speed stabilises.
An airspeed change of greater than 20kts technique:
Let's say you're at 1800RPM, 70kts s&l. To increase speed to 100kts in s&l you increase to full power, then anticipate 5kts before 100kts (at 95kts) select 2200rpm (which is supposed to give you 100kts s&l).
The reason of this extra burst of power before reducing it is to make the airspeed change faster.
Let's say you're at 1800RPM, 70kts s&l. To increase speed to 100kts in s&l you increase to full power, then anticipate 5kts before 100kts (at 95kts) select 2200rpm (which is supposed to give you 100kts s&l).
The reason of this extra burst of power before reducing it is to make the airspeed change faster.
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Reselecting cruise power should make the aircraft level off. Nothing else should be needed.
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During a glide descent it is possible that the speed would be less that cruise. Glide performance for PFLs / approaches usually means about 20kts slower than the cruise, somewhere around powered approach speed
Read his opening piece! He is not talking about the final approach phase of the flight or a forced landing where he aint going to level for long anyway or have any power to do that leveling! but a typical descent and leveling at ones chosen altitude.
Obviously when you are landing you will come back to your reference speed with flap, gear etc where you do that is questionable?
I know pilots who will trundle in from 6 miles out causing a massive traffic jam while they stick to their 70kts blind to conditions or wind shear
I know others who will fly faster speed and reduce to their reference speed within the last 200 to 500 feet.
I was never a supporter of the closed throttle glide approach anyway and never understood the benefits of such an approach! Infact there are many inherant dangers in such approaches.
But he is talking about a normal descent and level to a chosen altitude!
Other than turbulent air there is no reason to be below CS.
Sometimes I wonder if we concentrate to much on bits in training rather than a much broader appreciation of energy and drag management?
Pace
Last edited by Pace; 19th Nov 2011 at 09:09.
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As for the full power from glide descent, well, of course it's done smoothly, not rammed
If a pilot has mismanaged their descent so much that glide descents are required, that's simply poor planning. Back in my turbo Aztec days, the requirement for descent power was to decrease by 1 inch of manifold pressure (which would roughly equate to 100 RPM - fixed pitch) per minute. A faster power change was considered potentially harmful to the cylinders, and an abnormal procedure.
Though turbine powered aircraft, which would include the military pilot's PC7 are capable of rapid power changes without harm, that does make it "good", smooth, or appropriate technique. Military aircraft and training are aimed at a very different role for the aircraft, and "smooth" and caring to the aircraft may not be elements of that training or technique.
IF, a power off glide is necessary because of botched planning, or some type of quasi emergency, then yes, flying the resulting glide at a slower airspeed is better for the engine, that rocketing down at idle power and cruise airspeed. Damage from shock cooling is very real, occurs in seconds, and is very expensive to repair. I once had to rapidly descent a Cessna turbo 207 because I had spotted a boat in distress on the lake. Though I closed the cowl flaps, and was still "gentle" with the power reduction to idle, and slowed the descent speed (reduces undesired cooling) I was stunned at the incredible rate of cylinder cooling indicated by the cylinder head temp indicator. I immediately though back to the 1 inch of MP per minute, and was reminded of the wisdom of that.
All that being said, as I read a lot of the foregoing, I see lots and lots of numbers, but little sense that the pilots are simply flying the plane. Is this a result of pilots spending hours in front of computer flight simulators before or in the midst of training? I opine that there is a shift in the emphasis away from to plane itself, and toward all of the information that today's indicators provide. Take yourself back to the Tiger Moth, the airspeed is indicated out on the wingstrut, and really is not that accurate anyway, and the tachometer really does not work that well either. I very much doubt that Tiger Moth instruction and operation was filled with all of these numbers!
Just feel the plane, listen to the engine and the airstream, and watch where you are going. During VFR, this should be all you need to fly very well! During my Caravan type training, I had a training pilot who was fixated on numbers. I got frustrated enough with this that I covered the airspeed indicator, and flew a very presentable (and totally safe) circuit. If you need to look at the airspeed this often, you need to improve your skills.
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All that being said, as I read a lot of the foregoing, I see lots and lots of numbers, but little sense that the pilots are simply flying the plane. Is this a result of pilots spending hours in front of computer flight simulators before or in the midst of training? I opine that there is a shift in the emphasis away from to plane itself, and toward all of the information that today's indicators provide. Take yourself back to the Tiger Moth, the airspeed is indicated out on the wingstrut, and really is not that accurate anyway, and the tachometer really does not work that well either. I very much doubt that Tiger Moth instruction and operation was filled with all of these numbers!
Just feel the plane, listen to the engine and the airstream, and watch where you are going. During VFR, this should be all you need to fly very well! During my Caravan type training, I had a training pilot who was fixated on numbers. I got frustrated enough with this that I covered the airspeed indicator, and flew a very presentable (and totally safe) circuit. If you need to look at the airspeed this often, you need to improve your skills.
Just feel the plane, listen to the engine and the airstream, and watch where you are going. During VFR, this should be all you need to fly very well! During my Caravan type training, I had a training pilot who was fixated on numbers. I got frustrated enough with this that I covered the airspeed indicator, and flew a very presentable (and totally safe) circuit. If you need to look at the airspeed this often, you need to improve your skills.
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Pace I think throughout this you more or less summed up everything previously. I was not disagreeing with you, merely answering your question...
Why would you be descending at below cruise speed?
Why would you be descending at below cruise speed?
By the way, the autopilot is u/s!
btw the way another occasion when you might need to do this in a higher performance aircraft is after an engine failure/shutdown enroute - in order to driftdown safely due to high msa (eg over the Alps) you descent with max continuous thrust on the operating engine at the driftdown speed (typically in the order of 230kt) - as you approach level off the nearest suitable airport for diversion is 250 nm away - having cleared the higher terrain you now want to accelerate to a more economical cruising speed (which is faster).
Farfetched? Academic? Whilst I agree we are not teaching all ab initio pilots to go on to greater things, it is fundamental that they should understand and be able to apply basic techniques.
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Academic nonsense really.
There is the method of recovering from a glide descent which is taught in the text books - which is fine for flying training to TEACH AIRCRAFT HANDLING AS AN EXERCISE - as GeeWhizz.
Then there is the 'real World' as IO540 suggests.
The analogy of driftdown in a jet on a Private Flying Forum
There is the method of recovering from a glide descent which is taught in the text books - which is fine for flying training to TEACH AIRCRAFT HANDLING AS AN EXERCISE - as GeeWhizz.
Then there is the 'real World' as IO540 suggests.
The analogy of driftdown in a jet on a Private Flying Forum
The analogy of driftdown in a jet on a Private Flying Forum
Also whenever I hear the term "real world" it means the world as you see it!
