Higher than POH speeds
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Higher than POH speeds
This question is with regards to C172 but I guess it can be used on any type of aircraft:
In my flying organization, the "SOP" for climb, glide (flaps up or down), final (flaps up or down) is all 70kts. Easy to remember right?
Now the question is - refering to the POH, glide & final speed with flaps up & down are 65 and 60kts respectively.
Looks like the organization is asking us to fly at a 5kt higher speed with flaps up and 10kts higher with flaps down (as compared to the POH).
The reasoning I can think of (since the instructors couldn't really tell me) is that so we can use the same point in the windshield as the aiming point (which in my case we take 3" above the glareshield), since we are flying at the same speed, irregardless of flaps setting. Flaps is used to steepen the approach, but whatever you see at about 3" above the glareshield will still your aiming point. Actually, in this case I would call it impact point.
Any comments on this (with regards to use of higher than POH airspeeds)?
In my flying organization, the "SOP" for climb, glide (flaps up or down), final (flaps up or down) is all 70kts. Easy to remember right?
Now the question is - refering to the POH, glide & final speed with flaps up & down are 65 and 60kts respectively.
Looks like the organization is asking us to fly at a 5kt higher speed with flaps up and 10kts higher with flaps down (as compared to the POH).
The reasoning I can think of (since the instructors couldn't really tell me) is that so we can use the same point in the windshield as the aiming point (which in my case we take 3" above the glareshield), since we are flying at the same speed, irregardless of flaps setting. Flaps is used to steepen the approach, but whatever you see at about 3" above the glareshield will still your aiming point. Actually, in this case I would call it impact point.
Any comments on this (with regards to use of higher than POH airspeeds)?
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The aircraft won't perform as well at the higher speeds and I suspect that the extra speed is to give a greater margin above the stall to allow for low time student errors.
The wisdom of this policy will no doubt come under scrutiny below.
The wisdom of this policy will no doubt come under scrutiny below.
I used to fly a C172P at flying club based on an airfield with an 800m runway, which was then extended to 1200m. Finals with 70 kts was what they demanded too, and the float on landing was not a problem with that runway length.
Then I changed to an operator based on an airfield with a 400 m runway, flying a C172N (where the flaps extend to 40°) and a C172P. Maintaining 70 kts on final right down to the flare will result in such a float that you won't make it down. 60 kts is what is taught here and it works a treat.
Some time ago I had a sort of refresher training with an experienced instructor in a C172, where we repeatedly took the aircraft to the very limits of the performance envelope. This included very, very slow flight in all configurations right up to and through the stall as well. Highly recommendable, particularly if you feel that 60 kts is too slow! You'd be surprised at which speeds a C172 still flies - and it was the first time that I had heard that the stall warning (at least in that aircraft) changes pitch the closer you get to the actual stall (all instructors I flown with previously only wanted to go to the first "beep" and then recover...).
Then I changed to an operator based on an airfield with a 400 m runway, flying a C172N (where the flaps extend to 40°) and a C172P. Maintaining 70 kts on final right down to the flare will result in such a float that you won't make it down. 60 kts is what is taught here and it works a treat.
Some time ago I had a sort of refresher training with an experienced instructor in a C172, where we repeatedly took the aircraft to the very limits of the performance envelope. This included very, very slow flight in all configurations right up to and through the stall as well. Highly recommendable, particularly if you feel that 60 kts is too slow! You'd be surprised at which speeds a C172 still flies - and it was the first time that I had heard that the stall warning (at least in that aircraft) changes pitch the closer you get to the actual stall (all instructors I flown with previously only wanted to go to the first "beep" and then recover...).
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If you want book performance, fly the book figures. Simple. But in initial training, particularly if runway length is not an issue, you see this "add five/ten knots for the folks back home" thing a lot. Because of the higher margins above the stall.
Not true. Deploying flaps has a number of effects:
- It increases the surface area of the wings, leading to greater lift (or equal lift at lower speeds)
- It changes the center of pressure, leading to an automatic pitch up or down
- It adds drag, leading to a reduction in speed
- It changes the average angle of incidence of the wing, initially leading to a pitch up, but eventually resulting in a lower fuselage angle of attack for the same wing angle of attack, and this results in a better view over the nose and a reduced risk of tailstrikes.
Which flap setting leads to which effect most prominently, depends to a large extent on the design but most of these factors will be present simultaneously somehow.
The last effect, the changed angle of incidence, will means that on flap deployment your "aiming point" will shift around the cockpit. They may have compensated for that by using an odd speed, but there is no guarantee whatsoever that this will work if the aircraft is loaded differently or if you start flying a different aircraft.
Working with an aiming point that's inside the cockpit in general doesn't work, since it changes with the speed, with the loading of the aircraft and is also dependent on head- and crosswind. To get a good descent you have to look at your "impact point" and the relative motion of the foreground/background vs. that point. If the sight picture around the impact point stays constant, and the background/foreground just gets bigger while you descend, you're going to end up at your "impact point". (And all you need to do further, is to prevent that impact.)
The reasoning I can think of (since the instructors couldn't really tell me) is that so we can use the same point in the windshield as the aiming point (which in my case we take 3" above the glareshield), since we are flying at the same speed, irregardless of flaps setting. Flaps is used to steepen the approach, but whatever you see at about 3" above the glareshield will still your aiming point. Actually, in this case I would call it impact point.
- It increases the surface area of the wings, leading to greater lift (or equal lift at lower speeds)
- It changes the center of pressure, leading to an automatic pitch up or down
- It adds drag, leading to a reduction in speed
- It changes the average angle of incidence of the wing, initially leading to a pitch up, but eventually resulting in a lower fuselage angle of attack for the same wing angle of attack, and this results in a better view over the nose and a reduced risk of tailstrikes.
Which flap setting leads to which effect most prominently, depends to a large extent on the design but most of these factors will be present simultaneously somehow.
The last effect, the changed angle of incidence, will means that on flap deployment your "aiming point" will shift around the cockpit. They may have compensated for that by using an odd speed, but there is no guarantee whatsoever that this will work if the aircraft is loaded differently or if you start flying a different aircraft.
Working with an aiming point that's inside the cockpit in general doesn't work, since it changes with the speed, with the loading of the aircraft and is also dependent on head- and crosswind. To get a good descent you have to look at your "impact point" and the relative motion of the foreground/background vs. that point. If the sight picture around the impact point stays constant, and the background/foreground just gets bigger while you descend, you're going to end up at your "impact point". (And all you need to do further, is to prevent that impact.)
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This sort of "SOP's" sounds a bit funny to me...
You have (hopefully) a POH and there the speeds are given by the manufacturer and thats the way the aircraft should be operated. The first approach to a very short runway but in the limits of the C172 will end with an overrun. Your described aiming point is NOT in the same spot at the same speed with flaps up or full down, as the attitude of the aircraft will be different.
Sounds maybe harsh, but your INSTRUCTORS will need training how to fly a C172 and then should train you properly. Instructing everbody to take 70kts as reference speed for all circumstances, they assume all the students/members of the club are to stupid to remember a few more digits and this is not a trustful manner towards the clientel.
Finally, this may end after an accident (which I hope will never happen) with a refusal to pay , when the insurance finds out, that the plane was not operated according POH.
You have (hopefully) a POH and there the speeds are given by the manufacturer and thats the way the aircraft should be operated. The first approach to a very short runway but in the limits of the C172 will end with an overrun. Your described aiming point is NOT in the same spot at the same speed with flaps up or full down, as the attitude of the aircraft will be different.
Sounds maybe harsh, but your INSTRUCTORS will need training how to fly a C172 and then should train you properly. Instructing everbody to take 70kts as reference speed for all circumstances, they assume all the students/members of the club are to stupid to remember a few more digits and this is not a trustful manner towards the clientel.
Finally, this may end after an accident (which I hope will never happen) with a refusal to pay , when the insurance finds out, that the plane was not operated according POH.
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Instructing everbody to take 70kts as reference speed for all circumstances, they assume all the students/members of the club are to stupid to remember a few more digits and this is not a trustful manner towards the clientel.
On asking about the speeds (one isn't going to read the POH on these trips, not with the family sitting around getting bored) being told "we do everything at 75mph in this aircraft" [except cruise of course] sounded like the right approach for me on that occasion
He/she will take care of all unplanned situations and basically he/she is PIC.
Until you need the manufacturers calculated glide performance, that's fine. When the engine quits, it doesn't know your on holiday! I guess that's what the instructor is there for.
Last edited by 500 above; 28th Jan 2013 at 08:56.
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No wonder there are so many instances of nose wheel collapse on C172 if this is being taught.
I don't subscribe to the theory that by using one number flying becomes easier. For heavens sake the speeds are placarded inside the aircraft.
If you come to visit my local field using that technique we will be pulling you out of weeds at the end of the runway.
D.O.
I don't subscribe to the theory that by using one number flying becomes easier. For heavens sake the speeds are placarded inside the aircraft.
If you come to visit my local field using that technique we will be pulling you out of weeds at the end of the runway.
D.O.
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Those here who tell you to fly it the way the Flight Manual says are right. SOP's are nice, when they reinforce, and supplement the FM, but not when they contradict it. The SOP does not say "Disregard the Flight Manual", so why would it pick and choose parts of the FM to disregard?
In view of the pilot is a required placard which reads:
"THIS AIRPLANE MUST BE OPERATED IN COMPLIANCE WITH THE OPERATING LIMITATIONS AS STATED IN THE FORM OF PLACARDS, MARKINGS, AND MANUALS"
(sorry for the bold, I just cut & paste from the TCDS)
Therefore, you, as the pilot are required by regulation to fly the aircraft in accordance with those speeds. If the operator of the aircraft feels so strongly that the FM speeds can be improved upon, they can go through the STC program, including flight testing (which is part of what I do for a living) to have a Flight Manual Supplement approved for the aircraft with different speeds.
I have included changed speeds for a Cessna (Caravan) as part of an approval. There are many factors which are used to arrive upon the book speeds, and I doubt that the SOP speed "guesser" has considered all of them. If this subject interests you, I highly recommend the book "Cessna Wings for the World" by Thompson. He is a former Cessna test pilot, and tells amazing stories about development of all of these aircraft. It is certain that if you have read this book, you'll know more about speeds in a 172 than the person who wrote the SOP ('cause they would not have changed speeds, if they knew what they were doing!).
A competent pilot can handle the plane at book speeds just fine. If there is a problem flying at book speeds, more training would be wise.
In view of the pilot is a required placard which reads:
"THIS AIRPLANE MUST BE OPERATED IN COMPLIANCE WITH THE OPERATING LIMITATIONS AS STATED IN THE FORM OF PLACARDS, MARKINGS, AND MANUALS"
(sorry for the bold, I just cut & paste from the TCDS)
Therefore, you, as the pilot are required by regulation to fly the aircraft in accordance with those speeds. If the operator of the aircraft feels so strongly that the FM speeds can be improved upon, they can go through the STC program, including flight testing (which is part of what I do for a living) to have a Flight Manual Supplement approved for the aircraft with different speeds.
I have included changed speeds for a Cessna (Caravan) as part of an approval. There are many factors which are used to arrive upon the book speeds, and I doubt that the SOP speed "guesser" has considered all of them. If this subject interests you, I highly recommend the book "Cessna Wings for the World" by Thompson. He is a former Cessna test pilot, and tells amazing stories about development of all of these aircraft. It is certain that if you have read this book, you'll know more about speeds in a 172 than the person who wrote the SOP ('cause they would not have changed speeds, if they knew what they were doing!).
A competent pilot can handle the plane at book speeds just fine. If there is a problem flying at book speeds, more training would be wise.
First off the POH figures are for Gross Weight, a normal landing in training happens with two people aboard and half tanks which will put the aircraft at least 300 lbs under gross. The "right" approach speed for any aircraft is the one which will allow a normal approach flight path culminating in a natural continuous pitch up to the landing attitude and a tail low touchdown after a short float; when the throttle is closed at the beginning of the flare.
The C 172 M and N model POH "speeds for normal operation" list the speed range for full flap as 55 Kt to 65 Kt and for zero flap as 60 kt to 70 kt. Trying to land this airplane lightly loaded and with full flap after a 70 kt approach is going to involve an extremely protracted float as the aircraft will have to loose 20 kts in order to touch down in the proper attitude. Excessive approach speeds do not help students, they hurt their ability to learn how to land properly.
I teach my students to calculate the GTOW and adjust the POH speeds accordingly. For very light weights the bottom of the range is used and for max weight the top. As it works out typical training weights are usually pretty constant so a mid range POH speed, 60 kts with flaps and 65 for zero flaps are the common speeds.
If the pilot is unable to memorize a few basic speeds and flying has to be dumbed down to a one size fits all speed how are these students going to cope with emergencies ?
Finally 70 kts is 10 kts higher than the flaps down POH Best glide speed. This will markedly reduce the glide performance. Teaching this IMO is unsafe
Last edited by Big Pistons Forever; 28th Jan 2013 at 12:54.
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Backpacker siad:
As a rule of thumb, (going back to Prandtl in the 1920s IIRC) deploying X degrees of flap without rotating the aircraft increases wing Angle of Attack by X/2 degrees. So if half the wing is flapped, and you add 30 degrees of flap, you should pitch 7.5 degrees down "theoretically" to maintain lift.* This pitch down is independent of whatever you need to do to the elevator to re-balance the pitching moments.
Of course with flaps down (and a lower stall speed) you can hold off at a high pitch and slow speed, and the nose wheel is no more vulnerable for having flaps down. Unless you are much too fast...
In any given configuration, extra speed in the hold off means lower pitch and a more exposed nose wheel. I learned to fly at a bumpy grass strip and the FIs would get quite grumpy about coming in too fast
*Conversely, the need to pitch up when you retract flaps makes this a very hazardous manoeuvre at low speed near the ground.
... Deploying flaps has a number of effects:
- ...
- It changes the average angle of incidence of the wing, initially leading to a pitch up, but eventually resulting in a lower fuselage angle of attack for the same wing angle of attack, and this results in a better view over the nose and a reduced risk of tailstrikes.
- ...
- It changes the average angle of incidence of the wing, initially leading to a pitch up, but eventually resulting in a lower fuselage angle of attack for the same wing angle of attack, and this results in a better view over the nose and a reduced risk of tailstrikes.
Of course with flaps down (and a lower stall speed) you can hold off at a high pitch and slow speed, and the nose wheel is no more vulnerable for having flaps down. Unless you are much too fast...
In any given configuration, extra speed in the hold off means lower pitch and a more exposed nose wheel. I learned to fly at a bumpy grass strip and the FIs would get quite grumpy about coming in too fast
*Conversely, the need to pitch up when you retract flaps makes this a very hazardous manoeuvre at low speed near the ground.
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When the engine quits, it doesn't know your on holiday! I guess that's what the instructor is there for.
Pilots Handbook
I have always considered the Cessna handbooks* to be entirely sensible and easy to understand, and if someone is flying a particular club aircraft on a regular basis then it makes sense to obtain one* as a reference.
Cessna make it easy to understand all aspects of the operation,and as they made the aircraft who should know better.
In the commercial world a Cessna pilot would have to show knowledge of the aircrafts operation/performance or at least know where to obtain it,and indeed would be asked questions relating to this on a check.It would therefore seem reasonable for anyone using a similar machine to adopt the same plan in order to keep themselves 'informed' of all aspects of the machines operation. This would have the added benefit of highlighting a machines T-Off performance in varying conditions which seems to get forgotten on a regular basis. It is surprising how many pilots think that because a machine has 4 seats it can carry four people.
I am looking at a 172L POH which states on the 'before landing check' Flaps down speed 65-75 Mph,and assumes you are at the correct height!
That speed takes into account that it may be gusty,and positive control has to be maintained. A 'fast' approach may lead to a longer landing run,but too slow and you can run into control problems just when you need it most. If when you 'do the numbers' at a particular airfield and it looks 'marginal' then remind youself that Cessna based them on a NEW aircraft with an engine developing full rated power,and a propellor that did not look like a hacksaw.Take a look at the machine your in,and if its not quite like that neither will be the performance.
Cessna make it easy to understand all aspects of the operation,and as they made the aircraft who should know better.
In the commercial world a Cessna pilot would have to show knowledge of the aircrafts operation/performance or at least know where to obtain it,and indeed would be asked questions relating to this on a check.It would therefore seem reasonable for anyone using a similar machine to adopt the same plan in order to keep themselves 'informed' of all aspects of the machines operation. This would have the added benefit of highlighting a machines T-Off performance in varying conditions which seems to get forgotten on a regular basis. It is surprising how many pilots think that because a machine has 4 seats it can carry four people.
I am looking at a 172L POH which states on the 'before landing check' Flaps down speed 65-75 Mph,and assumes you are at the correct height!
That speed takes into account that it may be gusty,and positive control has to be maintained. A 'fast' approach may lead to a longer landing run,but too slow and you can run into control problems just when you need it most. If when you 'do the numbers' at a particular airfield and it looks 'marginal' then remind youself that Cessna based them on a NEW aircraft with an engine developing full rated power,and a propellor that did not look like a hacksaw.Take a look at the machine your in,and if its not quite like that neither will be the performance.
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Its pretty standard with some places
Worse one I had was a 5 knt add on for mum. Then half the gusts which was another 7 knts which was then rounded up. Another 5 knts because it was more than 10 knts xwind.
And then you were made to fly a 3degree PAPI approach. And then given a bollocking if you didn't touch down next to the PAPI's which of course was impossible to do if you flared correctly you had to drive the thing onto the deck with only a couple of cm's between the nose gear and the mains touching. It was horrible but apparently I didn't know good airmanship and this was the industry standard way of flying.
Worse one I had was a 5 knt add on for mum. Then half the gusts which was another 7 knts which was then rounded up. Another 5 knts because it was more than 10 knts xwind.
And then you were made to fly a 3degree PAPI approach. And then given a bollocking if you didn't touch down next to the PAPI's which of course was impossible to do if you flared correctly you had to drive the thing onto the deck with only a couple of cm's between the nose gear and the mains touching. It was horrible but apparently I didn't know good airmanship and this was the industry standard way of flying.
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Originally Posted by Big Pistons Forever
If the pilot is unable to memorize a few basic speeds and flying has to be dumbed down to a one size fits all speed how are these students going to cope with emergencies ?
Finally 70 kts is 10 kts higher than the flaps down POH Best glide speed. This will markedly reduce the glide performance. Teaching this IMO is unsafe
Finally 70 kts is 10 kts higher than the flaps down POH Best glide speed. This will markedly reduce the glide performance. Teaching this IMO is unsafe
Originally Posted by mad_jock
Worse one I had was a 5 knt add on for mum. Then half the gusts which was another 7 knts which was then rounded up. Another 5 knts because it was more than 10 knts xwind.
And of course, this is 5-10 knots below cruise speed 
thats a good one good job we didn't do flapless that day.
I can think of many occasions whilst sitting at the holding point watching landing traffic pass in front of me. Probably 70% are going too fast and watching the ensuing landing speaks for itself. Very occasionally, you see a nicely controlled approach at the right speed followed by a near perfect landing.
The speeds in the FM are there for a purpose, it is our job as instructors to teach the student why they are there and how to use them.
The speeds in the FM are there for a purpose, it is our job as instructors to teach the student why they are there and how to use them.
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Wise words from Whopity
Thank you for that refreshing glimpse at the blindingly obvious !
It is clear that these strange SOP's are invented by someone, but why is what I am really interested in ? I can understand a Vat of say 69Kt getting adjusted to 70 Kt but some of the things I have seen are pure rubbish with the Vat being adjusted by all sorts of numbers for all sorts of reasons.
The fact that the POH numbers are quoted a MTOW would seem to indicate a safety factor for most flights but to keep adding speed is just going to use up runway during the landing ( may be the people think that they have paid for all the runway and are determined to use all of the runway!).
My own theory as to why this speed addition is happening is that it is invented by the type of young flying instructor who dreams of the day he will be flying a big jet and wants to turn flying into a black art to show how clever he is, get three or four of these guys in a crew room on a bad weather day and who knows what they will invent next.
It is clear that these strange SOP's are invented by someone, but why is what I am really interested in ? I can understand a Vat of say 69Kt getting adjusted to 70 Kt but some of the things I have seen are pure rubbish with the Vat being adjusted by all sorts of numbers for all sorts of reasons.
The fact that the POH numbers are quoted a MTOW would seem to indicate a safety factor for most flights but to keep adding speed is just going to use up runway during the landing ( may be the people think that they have paid for all the runway and are determined to use all of the runway!).
My own theory as to why this speed addition is happening is that it is invented by the type of young flying instructor who dreams of the day he will be flying a big jet and wants to turn flying into a black art to show how clever he is, get three or four of these guys in a crew room on a bad weather day and who knows what they will invent next.
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If someone who was instructed to fly a C172 with the "one speed for every occasion" wants to be checked out in a Mooney later on, the instructor will have a fair bit of work and the pilot will learn a few points.