Aerodynamically the GS is irrelevant until touchdown, isn’t it?
Yes; correct.
Well, up to a point. If GS<AS you have a headwind which usually reduces as you near the ground, thereby reducing tendency to float during the flare. If GS>AS, the tailwind will reduce during the flare, so increasing the wing’s desire to keep flying.
But in answer to the OP, yes I make a habit of comparing the two after turning final, whether or not the landing site has some kind of windsock, or even someone giving me their estimate of wind strength and direction on the radio. This is chiefly because after touchdown, stopping distance varies as the square of GS, so it is somewhat relevant if the runway is not excessively long.
Some of us are (un)fortunate enough to undertake landing performance calculations that rely on wind velocity. :(
Well, there’s no point in us complaining about it, because the Regulator (peace and blessings upon him) insists that a commercial pilot “calculates” ground roll by:
(a) accepting as Правда some unverified wind(sock) and weather observations and forecasts for another place and time;
(b) interpolating from a lawyer-approved table based on some long-dead test pilot’s sorties in a different airplane on a different runway;
(c) applying all manner of additional Jesus factors for grass/long/short/sand/gravel/dirt/wet/dry/snow/slope/tarmac temperature/price of bananas etc. which might as well have been dreamt up by a Covent Garden greengrocer;
The unthinkable(?) alternative would be to cede control to these highly trained pilots who have executed (tens?) of thousands of landings and who know (not least because they’ve read the Highway Code), that braking distance varies as the square of ground speed.
Fortunately, none of this applies to us in the cheap (NCO) seats. We can trust our own windsock observation, verify with a quick glance or two at GPS and ASI and then trust our own judgement based on training and experience and (if in doubt) verify with a simple formula such as µ = (((v^2)/(2*g))-H)/L
Silvaire wrote:
Bear in mind while doing your approach, and before touchdown, that your glide angle at a given power setting is steeper with a strong headwind.
That’s true. My problem with that is mainly that one of my instructors says a steep approach is preferable for SEPs in VFR, while the other (who is a CPL/IR guy) prefers a shallow approach and would rather come from below the optimal glidepath than above. So how do I as a student pilot know which is better? Instinctively I prefer instructor No 1’s opinion (steep approach).
No GPS to check, but if the ground speed looks to be near the usual touch-down speed on final, (not over the threshold,) I’d increase speed. Otherwise I’d be heading for the “power behind drag curve” territory. See other thread.
Where the approach will take you to an uphill runway, in a strong wind there will be downdraft as well as windshear. And that can make a go-around impossible.
Landing distance depends on ground speed at touchdown.
Medewok: why not a stabilised approach ? Learning to maintain a constant glide path with speed and pitch management is vital. “Steep approach”, the way you describe it, sounds a bit like “let’s just see how it works”.
In my book in a SEP you should always be above the PAPIs in normal circumstances for the obvious reason that if the engine quits you will land short – why wouldnt you?
It simply a stabilised steep approach. Equally I definitely would not want to be under the PAPIs.
In a twin I am happy to go with the PAPIs.
BTW with a partially blocked pitot tube you may well be fast, possible very fast even if flying known power settings because when they dont “work” you will be tempted to use the throttle. In the same way you will seem slow on the take off roll.
EuroFlyer wrote:
why not a stabilised approach ? Learning to maintain a constant glide path with speed and pitch management is vital. “Steep approach”, the way you describe it, sounds a bit like “let’s just see how it works”.
Fuji_Abound wrote:
In my book in a SEP you should always be above the PAPIs in normal circumstances for the obvious reason that if the engine quits you will land short – why wouldnt you?
Doc, mine is another vote for the steep approach.
But you will need to practice both in due course. For now, contact flying, you fly steep and slow, adjusting pitch for speed and power for glide path. You can be pretty aggressive with the throttle, if need be, with eyes outside the cockpit.
When you start instrument approaches it will be all change. You will fly faster, on a shallower glide path, using small pitch changes to follow the glideslope needle and small power changes to maintain airspeed.
Nice summary Jacko. Steep and slow for VFR and shallow and faster for IFR.
