My preference for (strong) crosswind direction is the one that subtracts from the propeller induced tendencies to yaw on the takeoff roll, which depends on which way the propeller rotates.
That’s another factor to consider Silvaire, although I’m not sure I’d prefer the tailwind over the p-factor unless I was well prepared.
The reason goes back to wind theory. When wind speed increases it rotates to a higher value (direction) due to centrifugal force iirc. So, If it originates from a 90 left crosswind, gusts will turn it into a headwind/crosswind. If it comes from the right you get an increase in tailwind as it picks up – not a desirable condition.
I would find that amazing, on such a small scale. The coriolis effect is very very small at those scales.
Not so much effect as in a gale but the effect is there. You don’t believe me, check the windsock next time. It’s the theory anyway..
In the case of the takeoff I still think the conditions may have been tailwind in combination with right crosswind and a veering wind during climb. Any thoughts on that?
Krister_L wrote:
You state the winds were 210/14 and that you were offered RWY 21 or 10 for takeoff.
That was almost two hours earlier. The tower reported the wind as being at 90° to the runway at the time of my departure. I know that a left crosswind is preferable to a right crosswind, but I haven’t thought it mattered much unless the wind was gusty. In gusty winds I would not have accepted runway 10 – but of course there can still be gusts even if they are below the limit for reporting. (10 knots above average wind IIRC.)
In this case I don’t think that any tailwind component would have made much difference given the length of the runway, but the change in wind direction with altitude could have mattered.
Krister_L wrote:
When wind speed increases it rotates to a higher value (direction) due to centrifugal force iirc.
Not quite. You typically find gusts in an unstable airmass. The reason being that vertical air movements bring down air from higher levels where the wind speed is higher, but also the wind direction has a higher value.
Since the airmass in my case was quite stable, any gusts would have been caused by thermals – this is what I believe happened in my case – and then the wind could turn in any direction depending on where you are in relation to the bubble.
My 2c:
First, if loaded to within a few percent of MTOW, I would have chosen the longer, hard rwy with the wind straight down. OK, it’s a longer taxi, but a PA28 is no rocket ship and I’d like to have that margin.
Second – why flaps? I have not flown a PA28 in years (but learned to fly on them) and IIRC flaps are only used for short-field t/o.
You don’t believe me, check the windsock next time. It’s the theory anyway..
What should I expect to see?
To be clear: I can believe the crosswind direction has an effect on takeoff (max power – due to prop torque) but not on landing (min or zero power).
Peter wrote:
What should I expect to see?
You should see the windsock turning clockwise (seen from above) in the gusts.
Second – why flaps? I have not flown a PA28 in years (but learned to fly on them) and IIRC flaps are only used for short-field t/o.
Normal take-off (the way we teach it here anyway) in a PA28 is first notch of flaps, 10 degrees. Short field is two notches, 25 degrees.
