Short Field Landing Airspeed Conundrum
Moderator
C172 N POH states stalling speed ...
.. except one doesn't do these sums with IAS .. speed calcs need to be in CAS with PEC corrections as/when appropriate to get to/from IAS.
IAS is a Mickey Mouse number ... very useful for reference as it is all we can see when pushing and pulling .. but it is still a Mickey Mouse number, not relevant for running sums.
More interestingly, once down towards stall, PECs can get a bit average .. run the sums in CAS and then see what the margins might be ...
.. except one doesn't do these sums with IAS .. speed calcs need to be in CAS with PEC corrections as/when appropriate to get to/from IAS.
IAS is a Mickey Mouse number ... very useful for reference as it is all we can see when pushing and pulling .. but it is still a Mickey Mouse number, not relevant for running sums.
More interestingly, once down towards stall, PECs can get a bit average .. run the sums in CAS and then see what the margins might be ...
Just fly it like the autopilot does, Leddie, and you won't go too far wrong
And which model of autopilot would that be, in which mode, in which aircraft.
Instead of the cryptic nonsense, explain what you mean (if, in fact, you understand yourself) what you actually mean in post #30.
Tootle pip!!
Leddie, I think you are trying to bait me into derailing the thread! Tut Tut. Suffice to say that the AFNA statement that ones uses power to control the approach path (p360-ish) is, in my view, Horsesh1t! 
Re the autopilot, it doesn't actually matter which type; I was referring to the autopilot's/autothrottle's technique for flying down final on the ILS.
Now, back to normal programming...
Re the autopilot, it doesn't actually matter which type; I was referring to the autopilot's/autothrottle's technique for flying down final on the ILS.Now, back to normal programming...
JT, thank yoU, one more thing I didn't know and nobody taught me. The margins are lower when calculated in KCAS. The 60 vref/44 vs goes to lowere to perhaps 1.3 in kcas. The "worst case" 55kias/44vs goes to about 1.13VS when calc'd in KCAS.
Leddie, I think you are trying to bait me into derailing the thread! Tut Tut. Suffice to say that the AFNA statement that ones uses power to control the approach path (p360-ish) is, in my view, Horsesh1t! Re the autopilot, it doesn't actually matter which type; I was referring to the autopilot's/autothrottle's technique for flying down final on the ILS.
Now, back to normal programming...
Re the autopilot, it doesn't actually matter which type; I was referring to the autopilot's/autothrottle's technique for flying down final on the ILS.Now, back to normal programming...
This fact provides a fundamental concept of flying technique: Angle of attack is the primary control of airspeed in steady flight. Of course, the control stick or control wheel allows the pilot to control angle of attack and, thus, control the airspeed in steady flight. In the same sense, the throttle controls the output of the powerplant and allows the pilot to control rate of climb and descent at various airspeeds.
The real believers of these concepts are professional instrument pilots....
The real believers of these concepts are professional instrument pilots....
Moderator
The margins are lower when calculated in KCAS.
Calculations based on IAS are a bit meaningless due to the system errors, especially down around the stall region..
With CAS you will get a reasonable idea of what the numbers are. The FT folk will be doing things to the best accuracy their kit permits and, with round off, etc., your calcs might be a little rough for small aircraft .. but, nonetheless, adequate for the task.
Calculations based on IAS are a bit meaningless due to the system errors, especially down around the stall region..
With CAS you will get a reasonable idea of what the numbers are. The FT folk will be doing things to the best accuracy their kit permits and, with round off, etc., your calcs might be a little rough for small aircraft .. but, nonetheless, adequate for the task.
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Pffft, too easy:
https://www.youtube.com/watch?v=SJ22dCkDr7Q
Into the flare, just retract the flaps and get it on the ground.
https://www.youtube.com/watch?v=SJ22dCkDr7Q
Into the flare, just retract the flaps and get it on the ground.
Pffft, too easy:
https://www.youtube.com/watch?v=SJ22dCkDr7Q
Into the flare, just retract the flaps and get it on the ground.
https://www.youtube.com/watch?v=SJ22dCkDr7Q
Into the flare, just retract the flaps and get it on the ground.
Reference light aircraft - Don't know why people 'stabilise' the min approach speed so far out thus exposing themselves to 'stall' incidents. IMHO, Yer only need that min speed seconds before touchdown.
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CASA's MOS for a tailwheel endorsement mandates that the trainee demonstrates that he/she do better than the unfactored distance in the manual - what a joke.
Thread Starter
Reference light aircraft - Don't know why people 'stabilise' the min approach speed so far out thus exposing themselves to 'stall' incidents. IMHO, Yer only need that min speed seconds before touchdown.
All getting a bit esoteric for my little peabrain. My ASI reads IAS and I tend not to fluff about with whizzwheels and what have you when trying to plant the wheels as close to the downwind end of the runway as possible. A reasonable margin above the number where she normally adopts a more downward trajectory generally suffices. As for the old chestnut about attitude for speed etc, I tend to come down on the side of the little Mexican lass; "why not both?" Most of us have mastered (I hope) secondary effects of controls and tend to apply that combination of inputs required to achieve the desired result. Teaching attitude for speed is all very well as a teaching device, but imo is not to be slavishly adhered to once one has a degree of familiarity with placing said aerial device back on terra firma.
Except in the case in which you have to do a real short field landing.
Agreed re the ASI, too. Folks who want to do real short field landings would give up an ASI for an AOA indicator, any day.
Moderator
Yep, but one must know the nominated standard.
Indeed, Dave .. which is why we often make reference to the TCDS in an endeavour to get folks to look these things up.
Overall, posts here have to be a bit truncated (otherwise we'd ramble on for pages and no-one would bother reading ..).
As a result, we don't cover all the ins and outs in great detail...
Indeed, Dave .. which is why we often make reference to the TCDS in an endeavour to get folks to look these things up.
Overall, posts here have to be a bit truncated (otherwise we'd ramble on for pages and no-one would bother reading ..).
As a result, we don't cover all the ins and outs in great detail...
Those who specialise in short field (carrier guys) are taught pitch controls AoA, and hence airspeed, power controls altitude (ROC/ROD). Though airspeed is mentioned, AoA is the prime instrument, located on the canopy bow so no need to go heads down. See at 4:50 for power variations (exhaust smoke) to maintain slope.
And just to reinforce another point about why AOA is so important (and such useful information if you can get it) when doing real short field landings: An aircraft stalls at the same angle of attack regardless of weight, dynamic pressure, bank angle, etc.
Those who specialise in short field (carrier guys)...
For us land lubbers it would be nice to be able to 'adjust' the runway so that all landings are into wind. Also nice to have a cast of thousands to assist with take-offs and landings - especially nice to have somebody accessing each landing and giving a wave-off if things don't look good. Allso good to have an arrester hook to hide any small landing errors... The other thing is normally over water the air is so clear of turbulence that even a plump turkey like julia gilLard could fly.
.
Last edited by Flying Binghi; 22nd Jul 2017 at 01:10.
Allso good to have an arrester hook to hide any small landing errors
normally over water the air is so clear of turbulence
Folks,
Now I will set the cat among the pigeons.
A teaching technique that applies to large aircraft (but Bloggsie wants to dance around the point) is to use "attitude controls climb and descent, power controls airspeed".
With some special variations not applicable here, and not applicable in RVSM airspace ever, this is exactly what modern (in fact almost all) autopilots do, and it applies equally well to a voice activated autopilot's hands and feet.
Indeed, many moons ago, when I had an ab nitio student who was having trouble with "attitude controls airspeed, power controls rate of climb or descent" I would dump the "approved" as preceding, and use as para1.
Indeed, I would go so far as to set a PA-28/C-172/whatever up on final, on speed and height/slope, and use a chinagraph pencil to arrange a "gunsight" cross on the windscreen and set on the aiming point on the runway.
Then: "Just keep the cross on the aiming point (usually the threshold marks on a sealed runway) and fly XX knots with the throttle". The transition to flying a stable approach, on speed, on slope,was rapid, and for students I can well remember, the boost to their confidence was (to them) remarkable, but to me, expected.
Indeed, one (then) young lady who had already done about 18 hours with another school, without looking like ever going solo, was off solo with us in a couple more hours. Said young lady suddenly really started to enjoy flying, to the degree that she decided to make it a career, went through to commercial with us. Last time I heard, she was an IRE/TRE flying seriously large machinery, a long way from the point where she was about to give up, until somebody suggested she change schools --- because "the other mob" did things differently" --- which we certainly did.
Going back to my "time warp" comments, "back in the day" in GA, all approaches were glide approaches, attitude certainly did control airspeed da-da da, and a burst of throttle or a side-slip, if/when necessary, to (in modern parlance) adjust the touchdown (another way of saying the aim) point, give or take for a flare and float.
That you can fly all aircraft the same way, (even a delta) regardless of size, seems to be lost on quite a few.
I most certainly agree about the primary importance of angle of attack, if you are on approach, on slope and on speed, you will have the desired angle of attack for that operation.
All the modern FAR 25 aircraft, of which I have a detailed knowledge, all have a series of inputs into an Air Data Computer, beyond just raw pitot and static pressure/temperature, and will include angle of attack and where available, inertial acceleration/deceleration, to compute and display IAS (effectively CAS), low speed limits and generate "stall" warnings, that are not "stall" warnings at all, but low speed warnings.
As some of you will be aware, "Vs" is no longer the basis for establishing various V reference speed for larger FAR 25 aircraft, such speeds are based on an increment above the Cl max. angle of attack CAS. For approach, that Vref is generally 1.2 Cl max CAS.
So, where does that get us, flying a light aircraft (FAR 23 or predecessor CAR) and being asked to demonstrate a "precautionary" or "short field" approach versus a "normal" approach.
There is a good argument to make, that there is no such distinction, what is being "demonstrated" is the ability to fly an approach at the "book Vref" IAS, instead of the generally quite excessive IAS speed all too often called "normal".
You should NOT be expecting/required to demonstrate a "different" approach when the landing field length is critical, if you fly the book figures for every approach (with a small allowance for gust), that becomes your "normal", and the day you fly into your mate's farm, or you have to land somewhere due, say, stress of weather, you will have no concern about you ability to fly the approach. You must have a "reasonable" margin over "the stall", the "Book" speed gives that, and it is always lower risk to roll off "the other end" at slow speed, than lose control on approach.
In the "Half MVsquared" world it is the Vsquared wot gets ya on a bad day.
Now I will set the cat among the pigeons.
A teaching technique that applies to large aircraft (but Bloggsie wants to dance around the point) is to use "attitude controls climb and descent, power controls airspeed".
With some special variations not applicable here, and not applicable in RVSM airspace ever, this is exactly what modern (in fact almost all) autopilots do, and it applies equally well to a voice activated autopilot's hands and feet.
Indeed, many moons ago, when I had an ab nitio student who was having trouble with "attitude controls airspeed, power controls rate of climb or descent" I would dump the "approved" as preceding, and use as para1.
Indeed, I would go so far as to set a PA-28/C-172/whatever up on final, on speed and height/slope, and use a chinagraph pencil to arrange a "gunsight" cross on the windscreen and set on the aiming point on the runway.
Then: "Just keep the cross on the aiming point (usually the threshold marks on a sealed runway) and fly XX knots with the throttle". The transition to flying a stable approach, on speed, on slope,was rapid, and for students I can well remember, the boost to their confidence was (to them) remarkable, but to me, expected.
Indeed, one (then) young lady who had already done about 18 hours with another school, without looking like ever going solo, was off solo with us in a couple more hours. Said young lady suddenly really started to enjoy flying, to the degree that she decided to make it a career, went through to commercial with us. Last time I heard, she was an IRE/TRE flying seriously large machinery, a long way from the point where she was about to give up, until somebody suggested she change schools --- because "the other mob" did things differently" --- which we certainly did.
Going back to my "time warp" comments, "back in the day" in GA, all approaches were glide approaches, attitude certainly did control airspeed da-da da, and a burst of throttle or a side-slip, if/when necessary, to (in modern parlance) adjust the touchdown (another way of saying the aim) point, give or take for a flare and float.
That you can fly all aircraft the same way, (even a delta) regardless of size, seems to be lost on quite a few.
I most certainly agree about the primary importance of angle of attack, if you are on approach, on slope and on speed, you will have the desired angle of attack for that operation.
All the modern FAR 25 aircraft, of which I have a detailed knowledge, all have a series of inputs into an Air Data Computer, beyond just raw pitot and static pressure/temperature, and will include angle of attack and where available, inertial acceleration/deceleration, to compute and display IAS (effectively CAS), low speed limits and generate "stall" warnings, that are not "stall" warnings at all, but low speed warnings.
As some of you will be aware, "Vs" is no longer the basis for establishing various V reference speed for larger FAR 25 aircraft, such speeds are based on an increment above the Cl max. angle of attack CAS. For approach, that Vref is generally 1.2 Cl max CAS.
So, where does that get us, flying a light aircraft (FAR 23 or predecessor CAR) and being asked to demonstrate a "precautionary" or "short field" approach versus a "normal" approach.
There is a good argument to make, that there is no such distinction, what is being "demonstrated" is the ability to fly an approach at the "book Vref" IAS, instead of the generally quite excessive IAS speed all too often called "normal".
You should NOT be expecting/required to demonstrate a "different" approach when the landing field length is critical, if you fly the book figures for every approach (with a small allowance for gust), that becomes your "normal", and the day you fly into your mate's farm, or you have to land somewhere due, say, stress of weather, you will have no concern about you ability to fly the approach. You must have a "reasonable" margin over "the stall", the "Book" speed gives that, and it is always lower risk to roll off "the other end" at slow speed, than lose control on approach.
In the "Half MVsquared" world it is the Vsquared wot gets ya on a bad day.
"Always remember and forever take heed: left hand for glidepath and right hand for speed!" (reverse for First Officers and those hanging on to the stick between their legs or with throttle centrally on the dash...).
Last edited by Capn Bloggs; 24th Jul 2017 at 05:48. Reason: added detail for leddie.