Fernando wrote:
I got curious to hear what are your personal crosswind limits?
My crosswind limit is now 35, as I know from experience that rudder authority of my daily aircraft only lasts up to that – above only skidding landings are possible.
A DA 42 will land well in crosswinds well above 25knts using the crab technique. It’s not something I would recommend other than in real need as the insurers are not happy about anything above maximum demonstrated.
But it does depend very much on the aircraft, what crosswind I would accept in planning.
MichaLSA wrote:
My crosswind limit is now 35
Only in my dreams! 
Emir wrote:
25 kts but I’d analyze possible gusts and terrain.
Max demonstrated on a Cirrus is 20kt. I wonder how much it would take.
But what is your speed on final? Remember with a 40kt crosswind at 90° and a speed on final of 90 knts your maximum effective crosswind is around 27kts. Using good technique 40kts only becomes a problem with slower aircraft on final. With wing down/sideslip you more quickly run out of an effective counter to the wind and will drift off the centre line with no way of coming back onto it. There are many videos on YouTube of pilots using this technique giving up and going elsewhere having tried 2 or 3 times.
Demonstrated crosswind is only that " demonstrated". In other words it was the strongest crosswind the test pilot has during testing. The problem is that insurers tend to treat it as a limit.
gallois wrote:
Remember with a 40kt crosswind at 90° and a speed on final of 90 knts your maximum effective crosswind is around 27kts.
Sorry, can you explain? what is effective cross wind and how does it depend on speed?
I’ve not heard of it expressed as “effective crosswind” but the faster you’re going, the smaller the angle the aircraft crabs to counter a given crosswind component. Or the less you need to slip, depending on your preferred technique. This can be viewed equally as a vector sum or just that in the time available between two points on your track, the wind doesn’t have as much time blow you sideways when you’re going fast.
Silvaire basically summed it up there. It might be a French thing to talk about effective wind. One of the first things we learn for the PPL is what is called a Fb or facteur de base. That is 60/IAS or in certain cases TAS or even ground speed. So if your aircraft cruises at 120kts you have an Fb of 0.5. If the distance to your destination is 100nm it will take you 50mins (100×O.5) to fly there. The same is true for effective winds Ve your Fb is O.5 the maximum effect a 60kt crosswind will have is 30knts which you can narrow down further to say to easily calculate crab angles in your head.
Or effective wind on landing and take off.
It’s why for a crosswind take off you will need more into wind aileron at the beginning of the take off roll than when you get nearer to Vr. The same is needed in reverse on landing. Once you’ve taken off of course you level the wings and crab and on landing it’s the opposite.
You have to remember that most PPL and IR training in France is based on simple mental calculations. That’s not to say you can’t use a calculator or wizzy wheel or whatever if you need to. I have 2 wizzy wheels and a 2 calculators given as presents from Brit pilot friends. I have to say I have probably used them all together, less than the fingers on both hands. And even then probably to only see if I can use them and with instruction book.🙂
I have a hard time figuring out what you mean here. The angle, yes, it’s a function of airspeed. But the “effective crosswind” ? What exactly is that? The crosswind is the same no matter how fast you fly. Can you draw this on a diagram?
Besides, I almost never crab. I always slip into the wind where possible. Crabbing is for crabs
It is the effect the wind has on the aircraft.
The faster an aircraft flies the less effect the wind will have. I wont go into wind speeds and aircraft being measured in velocity x time and there is a mathematical proof of the point but I’ve forgotten what it is. But you can see it by drawing wind triangles.
As I mentioned you can see the difference it makes on the ground when you try to keep to the centre line in an strong crosswind particularly in a taildragger. An aircraft is designed like a wind vane in that it will always try to turn into the wind.To hold the centre line you make good use of the rudder and into wind aileron to stop the wind getting.under the wing and either pushing you off the runway or lifting the wing and flipping you over.
The faster the aircraft goes the less aileron is needed and also the less opposite rudder because with speed the wind has less of an effect on the aircraft.
Once In the air you can allow the aircraft to fly at is most efficient attitude in terms of lift and drag. Slipping wing down is not most efficient for either lift or drag. There are also limits where you have no aileron deflection left.
On final by crabbing the aircraft remains stable (doing what it was designed to do).
Slipping is not stable and the aileron limit may not be enough to cancel out the effective crosswind and the aircraft will be pushed off the centre line and it will be very difficult of not impossible to get back onto it.
Crabbing is much easier to get back onto the centre line and to keep the nose on it.
Of course you don’t want the wheels touching down in a crab position.. So during the flare you straighten with the pedals whilst applying a little into wind aileron. Then you increase the into wind aileron as you slow and remain on the centre line.
Although I was taught to make calculations mentally so it comes natural now, if you have a wizzy wheel or flight computer you can look at how much the effective wind changes at various wind angles and strengths on different aircraft ground speeds.
I apologise if this doesn’t make sense to you, in trying to answer I find it more difficult to explain on paper than to demonstrate.
So what you are saying is that the “effective” crosswind at a certain airspeed is the crosswind that would have the same effect as the actual crosswind IF you were flying at 60 kt?
It makes sense I guess, but I don’t see how it is useful in practise.
