I’ve just read (on a UK site) that somebody cancelled a flight because the runway was not long enough at the temperature and weight (fair enough) but he added there was no wind; only a crosswind. That is surely wrong… flying in a crosswind creates a headwind and the faster you go the more headwind it makes for you.
Isn’t it the opposite? When flying you want to maintain a track. The faster you go the less you need to compensate for drift, hence the less you need to turn into the wind, hence the less headwind component you will have?
If your concern is angle of climb, and you plan a turn into the wind, a crosswind may be beneficial.
In a sailboat, when your destination is into the wind you often want to point as far into the wind as possible, close hauled. Then the faster you go, the more the apparent wind will turn away, hence the further into the true wind you can sail (although your angle into apparent wind remains constant)
Airspeed is irrelevant to cross / headwind component – it is the directional difference to track that determines it. I suspect the OP means the crosswind was 90degrees across and hence no headwind component.
Peter wrote:
I’ve just read (on a UK site) that somebody cancelled a flight because the runway was not long enough at the temperature and weight (fair enough) but he added there was no wind; only a crosswind. That is surely wrong… flying in a crosswind creates a headwind and the faster you go the more headwind it makes for you.
For landing, yes there will be a headwind component as you crab down the extended CL….but for takeoff (usually more critical in terms of runway length required), since you are tracking straight down the runway, there is no headwind component…
Peter wrote:
I’ve just read (on a UK site) that somebody cancelled a flight because the runway was not long enough at the temperature and weight (fair enough) but he added there was no wind; only a crosswind. That is surely wrong… flying in a crosswind creates a headwind and the faster you go the more headwind it makes for you.
Assuming a 90degree crosswind, for runway performance that is the same as no wind ex some special crosswind takeoff limits. Do you mean apparent headwind when airborne and keeping a track with a 90 degree crosswind? But in that case, the faster you go the less the impact of a crosswind.
Peter wrote:
That is surely wrong
I would think so. It’s also a bit similar to dynamic soaring, like sea gulls and albatrosses excels at. Since you are not following the wind perpendicular on the ground, like you would when flying higher up and not compensating, you can take advantage of the sudden burst in headwind when turning into it immediately after the wheels are off the ground, for even added lift. I think…
Because of the veering of wind, a right hand crosswind in the northern hemisphere will quickly turn into a tailwind after liftoff, or during the ground run as gusts will also cause the wind to veer.
Obviously Maule, Super Cub folk etc can just take off across the runway 
AnthonyQ wrote:
For landing, yes there will be a headwind component as you crab down the extended CL….but for takeoff (usually more critical in terms of runway length required), since you are tracking straight down the runway, there is no headwind component…
In fact, because you will need to cross controls to keep straight down the runway when taking off, thus adding drag, a 90deg x-wind is actually worse than nil wind.so surely not wrong…
Taking off with a 90° crosswind might have a head or tailwind component gust. With a tailwheel you notice the poorer rudder control if a tailwind gust occurs, especially after lifting the tail.
Peter is right.
This has to do with relative wind. Think of riding a bicycle with no wind. The faster you ride the bike, the more wind you feel. This wind is called “relative wind” is no real wind as you on the bike are moving, not the wind. However, this behaves just like real wind. So, while speeding down the runway, with a crosswind from the left, this crosswind combines with the relative wind coming from the front.
This “relative wind” is in flight opposite the direction the aircraft is going and it is this “relative wind” that Is pushing against the wings at an angle to make it fly.
Of course, if there would be a headwind component already instead of only a wind from the side, he would need less runway for take-off and the real headwind component and the relative wind created by the forward movement of the aircraft on the runway during the takeoff run combine.
