Headwind question

[Lump Jockey]

Two questions here really:
1) Is there a max headwind for landing, especially on airliners? (b), if there is, then what happens when the a/c is on the r/w and airspeed is quickly turned into g/s, due to the higher thrust you had on app? (Do you have higher thrust?:O )
2) Enroute headwind, is it a problem? Is there a figure that, say, would impede the progress of the flight due to added thrust, (and again, I'm not entirely sure you "accelerate" into the wind). Obviously airspeed would be greater but the distance over ground wouldn't be as long..... would it?
Thanks a lot!
LJ.

[Intruder]

1) Generally there is no max headwind for takeoff or landing. For small airplanes, a practical limit is when the wind is above the stall speed of the airplane.

Within normal wind ranges, more headwind means a shorter takeoff roll, shorter landing roll, and less rate of descent on the normal approach glidepath. Yes, slightly higher thrust is required during the approach.

2) Enroute headwind reduces ground speed, so a given trip takes more time and fuel. Maximum range airspeed is approximated by adding 40-50% of the headwind component to the normal cruise speed, up to that point where higher airspeed requires significantly more thrust (steep rise in the drag curve).

[chiglet]

L J When I woz in Borneo...etc..zzzzzz
I witnessed an aeroplane flying backwards
The "srface wind2 was 270/32kts the a/c was a "Twin Pioneer", stalling speed...30kts:D
Said "TwinPin" was about 50-70ft over my head:cool:
we aim to please, it keeps the cleaners happy

[Bullet Tooth Tony]

I'm not sure that strong headwinds effect the amount of thrust used. Aircraft tend to use standard power settings for climb/cruise/descent which translate to a given airspeed. When flying an airspeed the groundspeed to a certain extent is largely irrelevant. It obviously effects range, but generally aids the pilot during take off and landing.

[Miserlou]

Although there is no max headwind for take-off and landing, if the wind speed is greater than Vne, then you've got to go backwards just to have the aircraft outside.

Control of the aircraft on the ground (taxiing) wil be limiting before you get close to this.

Furthermore, and similarly limiting is the turbulence at lower levels which may result in wind shear.
The company will often cancel flights if the winds are getting extremely strong.

[OzExpat]

Range problems aside, I tend to think about very strong headwinds on descent as making a massive difference in the selection of my Descent Point. The other thought is that I'm likely to have a pretty significant crosswind as soon as I start to turn off the runway after landing. I realise that a really strong headwind during descent may not translate to such a strong wind at ground level but, in absence of an ATIS or even of ATC, I'll always think about the possibilities before landing.

Then again, the aeroplane I fly is a fairly light anyway.

The other thing I think about with string winds, in a general sense, is the potential for turbulence. Where I operate, there's a whole bunch of big hills around most every airport, so mechanical turbulence is often a worthy consideration. I've had some pretty interesting approaches, in strong turbulence, that usually aren't especially elegant.

[Bellerophon]

Just to re-state the point that Intruder has made about final approach, assuming you are flying on a defined glideslope at constant airspeed, an increasing headwind will require increasing thrust.

Groundspeed determines the rate of descent necessary to stay on a glideslope. Lower groundspeeds mean lower rates of descent.

At constant airspeed, as the headwind increases, the groundspeed decreases, the rate of descent required to stay on the glideslope decreases, and the thrust required to fly at the same airspeed, but at a reduced rate of descent, increases.

Regards

Bellerophon

[Tinstaafl]

We have a 50kt door opening limit, a crosswind component limit of 35kts and also some very restrictive individual airstrip limits.

One airstrip in particular has a SW, clockwise to NNW sector limit of only 15 kts and another 15kt limit for a 30deg arc from the E. Even that windspeed is...erm....challenging when the wind is from those sectors. The mechanical turbulance outclasses the a/c controllability above that speed.

[Lump Jockey]

Mechanical turbulance.....????:O

[Tinstaafl]

Orographic effects, if that's your terminology.

[redsnail]

Mechanical turbulence is the turbulence generated by wind blowing over (or through as the case may be) trees, buildings, hills close to the airfield.

[Bullet Tooth Tony]

Bellerophon

Fully agree with your point regarding thrust on approach. My point is the increase is largely irrelevant regarding the points made in the original question.

For every 50kts of extra headwind the rate of descent changes by only 250 fpm (at 100kts airspeed on a 3 deg GS). The amount of extra thrust required to maintain that ROD for the short amount of time that the aircraft is on the approach matters little in the big scheme of things.

Again, in answer to the original question relating to the differing thrust on touchdown, the extra thrust is more than compensated for by the reduced groundspeed and so even with the (small) increase in thrust your touchdown speed will generally be reduced.

I tend to agree with Oz. The biggest problems with strong winds occur whilst on the ground.

[Johnny F@rt Pants]

I operated into La Palma (Canary Islands) a couple of years ago and under certain conditions which I can't remember exactly but were pressure of below about 990Mb and the wind direction from around SW to NW then the limit for making an approach was 2 Kts!