On "maximum demonstrated crosswind capability"

[RFguy]

I am going to do a tailwheel endorsement in due course , has been suggested with Dan Compton at Dubbo.

[old man emu]

3 hours ago, RFguy said:

210-240 = 30, sine 30 = 0.5, so 30 kts at 210 or 270 will produce 15 kts Xwind on 240

Excellent simplification 

 

Here's a table of conversion factors that you can use to roughly calculate the crosswind component of a wind blowing from the side of a runway heading. The correction factor has, hopefully be reported in a way that overestimates the actual crosswind. It doesn't matter if the sum (Wind Direction - Runway Direction) gives a negative number, just use the absolute value of the number.

 

Now we can go into another factor of the effects of a crosswind on aircraft performance - how it reduces the headwind component.

 

In relation to runway heading, a wind blowing directly down the centreline is at an angle of Zero degrees to the aircraft. The headwind component is given by cosine(degrees) x wind speed. The crosswind component is given by sine(degrees) x wind speed.  The value of cosine(0) is 1, and sine(0) is 0. That means that when the wind blows down the centreline of the runway, all of the wind is headwind, with no crosswind. As the angle of the wind goes from 0 to 90 degrees, the value of cosine goes from 1 to 0, meaning there is less and less headwind component. 

 

That means that as the crosswind comes more and more from the side, the aircraft loses the headwind benefit of the wind. That's why you need to keep the Thrust up during a crosswind landing.

[RFguy]

Hi OME. I would not completely agree with the way you trying to convey an idea- the statement "That means that as the crosswind comes more and more from the side, the aircraft loses the headwind benefit of the wind. That's why you need to keep the Thrust up during a crosswind landing." 

I think that's simplistic. 🙂

I can see two reasons to keep thrust up- 1) you want to carry a little more speed so that the forward airspeed to crosswind airspeed ratio is a little higher , and b) you might want to go around, having some thrust already in the bank might make that easier.   Carrying more speed might not work if the thing doesnt want to settle on the deck. I have seen videos of taildragger pilots in a high crosswind smacking it down on the deck like an aircraft carrier- NO ROUNDOUT- flown onto the ground. and no bounce. obviously takes some skill.

Edited September 23, 2020 by RFguy

[RFguy]

Crosswind landing techniques are  a big  topic... I don't profess to know much at all -but there are some basic physics at work. 

[Mike Gearon]

On 9/22/2020 at 7:05 PM, Old Koreelah said:

Some of our farmer pilots might tell you the cost in (lost revenue) of leaving a strip of paddock uncultivated Is considerable. 

Who can afford a whole paddock?

Guess it depends if you farm grain or cattle. Cattle aren’t a problem for whole paddock landing and productivity. Except I guess keeping the runway short. Cattle also love new grass the best. Must be tastier when new shoots so they’ll intensively graze the mowed area anyway.

 

I guess what I’m saying is keep your main runway to prevailing wind direction mowed and otherwise just land in between the cattle on the less rough stuff. That’s my plan.

Edited September 23, 2020 by Mike Gearon

[old man emu]

4 hours ago, RFguy said:

I think that's simplistic.

It was meant to be simplistic.

 

I wanted to get people to think of the reasons of why you approach at a higher speed, which you do by using higher RPM than for a still wind landing. We  tend to concentrate on the ability of the plane to handle the crosswind component, but forget how the crosswind component erodes the headwind component, leading to an higher ground speed at touchdown.

[RFguy]

My wife wouldnt be too keen on cattle. But cropping would be fine.

What's the cost of 15m x 300m strip of happy Canola ?

7 hours ago, old man emu said:

I wanted to get people to think of the reasons of why you approach at a higher speed, which you do by using higher RPM than for a still wind landing. We  tend to concentrate on the ability of the plane to handle the crosswind component, but forget how the crosswind component erodes the headwind component, leading to an higher ground speed at touchdown.

OK understood. - which is why you were suggesting  the use of both cosine and sine, (or 90-theta)  so people can resolve both components, rather than just the X-wind component.  I look at it as a ratio of forward airspeed to cross airspeed. Tangent.

[old man emu]

KISS!

 

Since Tan ranges from a value of zero for a headwind to "infinity for a 90 degree cross wind, it is not a value that can be used as a correction factor when doing these calculations mentally.

 

Canola? Whatever happened to golden fields of wheat, barley or oats?

 

Has The Lord's Prayer been changed to "give us this day our daily, gluten-free bread"?

[RFguy]

OME. alright.. yes. different minds think different ways 🙂 

Remember I fly at Cowra, and it is Canola city.   When I am flying circuits in my head as an exercise, I have the yellow fields in my visions. 

[M61A1]

10 hours ago, old man emu said:

It was meant to be simplistic.

 

I wanted to get people to think of the reasons of why you approach at a higher speed, which you do by using higher RPM than for a still wind landing. We  tend to concentrate on the ability of the plane to handle the crosswind component, but forget how the crosswind component erodes the headwind component, leading to an higher ground speed at touchdown.

OMG!......How do gliders manage without an engine?

Higher speed for a crosswind landing than still wind because it erodes the (non existent) headwind component?

The only reason I add airspeed on an approach is to compensate for wind gradient and gusts.

[Mike Gearon]

I thought the higher speed was more related to extra command of the control surfaces. I guess the dipped wing and crab angle are bleeding speed. Also set up to float longer with the speed when you’d really like the ground and at least one wheel in contact with runway. Are any of us here good enough to run the plane down the runway on a single wheel? I’m not. That’d be a nice skill set for cross wind capability (IMO)

 

Giving up grain space for runway is relative to total planted. If it’s .001% and the farmer isn’t an x orchardist it’s probably ok.

[old man emu]

23 minutes ago, M61A1 said:

How do gliders manage without an engine?

Let a glider pilot tell us. Is their approach speed increased for crosswind landings?

 

24 minutes ago, M61A1 said:

Higher speed for a crosswind landing than still wind because it erodes the (non existent) headwind component?

Non-existent? You don't seem to understand vectors as they apply to a Force. Every Force can be represented by the sum of its vectors. 

 

 

The triangle of vectors for a landing is represented by this diagram

 

Where the line AC, is the runway heading and the line AB is the wind direction at an angle to runway of BAC. The line BC is the crosswind component.

The magnitude of the wind speed is "c" and the magnitude of the headwind is "b". The magnitude of the crosswind is "a"

 

If the the angle BAC is zero, then b = c and a=0. No crosswind, and headwind = wind speed.

 

As the angle BAC increases, and the value of "c" remains constant, the length of "a" (representing the strength of the crosswind component) increases, and the length of "b" (the headwind component) decreases. Try this by drawing a line "b" from Point A. Then draw lines of constant length "c" at various angles between 0 and 90 from Point A. Then draw lines at right angles to line "b" to meet the various end points of line "c". 

 

The diagram is a simplification. In the real world, the length of "b" would be (airspeed - headwind speed), which if represented to scale would be longer than length "c" representing wind speed. Consequently. the angle BCA would not be a right angle. The diagram would look like half a diamond, not half a square.

[RFguy]

the headwind component will be non existent for 100% crosswind.

I just dont think it is a good way to look at it ("eroded headwind component") 

Your airspeed is what it is.  The headwind was never "eroded". the headwind is what it is- the resolved vector- your headwind (COMPONENT) never went away to start with .  That would only be the case where someone told you the wind speed and didn't tell you the direction. 

[old man emu]

40 minutes ago, Mike Gearon said:

I thought the higher speed was more related to extra command of the control surfaces.

You are not wrong, but you are getting into a completely different area with that. 

 

Consider this. Let's say our aircraft stalls at 35 kts. In Nil Wind conditions, the ground speed at stall is 35 kts. If we have a 10 kt wind blowing directly down the centreline, the airspeed is still 35 kts, but the wind means that we only have to have enough power to get the airframe moving at a ground speed of (35 - 10 = 25) kts. If the wind is a crosswind, coming from an angle to the centreline, then that 10 kts is going to be reduced. Let' say that the the wind is coming from 30 degrees off the centreline. A 10 kt wind at 30 degrees will provide a headwind component of 5 kts. Ground speed will be (35 - 5 =30) kts, so you have to add power to get the airframe moving faster.

 

In relation to command of control surfaces, the instantaneous wind speed can vary greatly, so it is safest to approach the landing at a higher speed than for a still wind landing in order to have a margin of safety if the wind speed suddenly drops. By the same token, you have to be aware that the wind can also gust at an inappropriate moment.

[Student Pilot]

Lots of theory here folks. Ultimately it's how you handle what wind there is, I have seen the likes of 182's and 185's landed in winds way in excess of quoted crosswind.

Know your own and the aircraft capabilities.

[RFguy]

OK. OME now I know what your are getting it. 

The other thing is.... the aircraft VELOCITY - the aircraft will be carrying more stored energy at a higher speed. This is an interesting conundrum. If the headwind down the runway, (zero Xwind)  was blowing at your stall speed ,  and your IAS was == (fractionally above) stall speed, IE the aircraft is flying, but only just, it would be sitting there in mid air....

 

...then you would have zero velocity and zero kinetic energy (putting aside you have some potential energy because there is gravity and you have height) . If the wind suddenly died you would drop vertically  because you have no energy, no forward velocity. 

 

When headwind < IAS , in a steady state,  you have forward velocity and energy.  So if the wind suddenly disappears, and IAS = velocity  you have energy that keeps you going forward and maintains some lift until the energy runs out.

 

Conversely , if headwind > IAS , and IAS > stall speed, and you are steady state , you are going backwards. not sure where to go with that one. 

 

I have had a nice headwind on the nose in the roundout, 5 feet AGL,  and then got a big gust on the nose and gone 30 feet up in the air while at idle power. I triggered an immediate go around.  That was an eye opening. 

 

BTW how well do ASIs read with aircraft at high yaw to forward motion ?

-glen

 

 

 

Edited September 24, 2020 by RFguy

[M61A1]

11 minutes ago, old man emu said:

Let a glider pilot tell us. Is their approach speed increased for crosswind landings?

 

Non-existent? You don't seem to understand vectors as they apply to a Force. Every Force can be represented by the sum of its vectors. 

 

 

The triangle of vectors for a landing is represented by this diagram

 

Where the line AC, is the runway heading and the line AB is the wind direction at an angle to runway of BAC. The line BC is the crosswind component.

The magnitude of the wind speed is "c" and the magnitude of the headwind is "b". The magnitude of the crosswind is "a"

 

If the the angle BAC is zero, then b = c and a=0. No crosswind, and headwind = wind speed.

 

As the angle BAC increases, and the value of "c" remains constant, the length of "a" (representing the strength of the crosswind component) increases, and the length of "b" (the headwind component) decreases. Try this by drawing a line "b" from Point A. Then draw lines of constant length "c" at various angles between 0 and 90 from Point A. Then draw lines at right angles to line "b" to meet the various end points of line "c". 

 

The diagram is a simplification. In the real world, the length of "b" would be (airspeed - headwind speed), which if represented to scale would be longer than length "c" representing wind speed. Consequently. the angle BCA would not be a right angle. The diagram would look like half a diamond, not half a square.

I understand what's going on, I was just being a pedant ( a pedant on an internet forum.... Who would've thought?).

 While your track on the ground may be straight with a 90° crosswind, the act of crabbing into wind (whether it's wing down or with rudder) introduces a headwind component requiring you to either need more power or have a steeper approach angle than zero wind.

 

13 minutes ago, old man emu said:

Ground speed will be (35 - 5 =30) kts, so you have to add power to get the airframe moving faster.

The only thing that matter here is airspeed. If Landing, you will need to add power or begin your descent later to make the runway. You don't have to go faster.

[facthunter]

Your ability will vary also IF you've had a long day or it's 3 am you aren't going to be at your best. ADRENALIN does help (I know). Nev

[facthunter]

 When you are crabbing as with x country with a lot if drift, or during an approach to land you are flying in a moving airmass and THAT is all your aeroplane knows. It's when you wish to exit (or enter) that airmass that things happen. Touching down or lifting off. You will be tracking where your wheels are not pointing unless you are on one wheel or have just done a quick decrab (landing) Not that effective on a low wingload/inertia plane. Nev

[RFguy]

Aircraft that land with low airspeed and moderate headwind will have low kinetic energy . Does that in the real world play a part in the landing process? IE not carrying as much energy means your forward velocity  can drop more quickly, simplistically. and drawing on that, are more precarious  to land with some headwind ?

 

and while I am asking...

 

How to do you  land an aircraft with (pure) headwind > landing speed ? for this your airspeed is going to have to be > headwind to actually make it onto the runway.

 IE 45 kts headwind, 40 kts over the fence airspeed spec.  Fly it onto the ground at 80 kts ?  Hypothetical. I am not going to try it because of all the things that could go wrong. That's what reserve  fuel and alternative aerodromes are for......Assume steady wind, not gusting (unlikely !) . since if the wind dies you will fall out of the sky since your forward velocity is low and energy is low.  

 

[Old Koreelah]

15 hours ago, Mike Gearon said:

...Cattle also love new grass the best. Must be tastier when new shoots so they’ll intensively graze the mowed area anyway.

That’s a whole story in itself; plants communicate among themselves about the approach of grazing animals and release toxins into their leaves/blades of grass to encourage animals to bugger off in search of better-tasting fare.

 

Quote

 

I guess what I’m saying is keep your main runway to prevailing wind direction mowed and otherwise just land in between the cattle on the less rough stuff. That’s my plan.

Good luck with that, Mike. Cattle tend to wander in front cars and trucks, so why not your plane?

The other problem is after you’ve parked your precious aeroplane they are likely to gather around for an inspection, or to rub their itchy bits on its extremities.

[facthunter]

Flying a circuit without any heading change can be done if the wind is above the plane's stall speed. I don't fancy going backwards as I land. I doubt it's controllable. Once when a big blow came up and I was up in DH 82 I had to wait  for ground assistance  to come and I flew it on and held it with power tail up till two "substantial" people had the wingtips. and I could reduce the power. None of this is very safe and today you couldn't count on people knowing what was required.  That is the only  time I've ever used wingmen. Nev

[IBob]

Facthunter we can only hope that the increasing incidence of "substantial" people offsets the lamentable fall in people who actually know what they're doing, then?.............😬

[M61A1]

1 hour ago, RFguy said:

OK. OME now I know what your are getting it. 

The other thing is.... the aircraft VELOCITY - the aircraft will be carrying more stored energy at a higher speed. This is an interesting conundrum. If the headwind down the runway, (zero Xwind)  was blowing at your stall speed ,  and your IAS was == (fractionally above) stall speed, IE the aircraft is flying, but only just, it would be sitting there in mid air....

 

...then you would have zero velocity and zero kinetic energy (putting aside you have some potential energy because there is gravity and you have height) . If the wind suddenly died you would drop vertically  because you have no energy, no forward velocity. 

 

When headwind < IAS , in a steady state,  you have forward velocity and energy.  So if the wind suddenly disappears, and IAS = velocity  you have energy that keeps you going forward and maintains some lift until the energy runs out.

 

Conversely , if headwind > IAS , and IAS > stall speed, and you are steady state , you are going backwards. not sure where to go with that one. 

 

I have had a nice headwind on the nose in the roundout, 5 feet AGL,  and then got a big gust on the nose and gone 30 feet up in the air while at idle power. I triggered an immediate go around.  That was an eye opening. 

 

BTW how well do ASIs read with aircraft at high yaw to forward motion ?

-glen

 

 

 

 

[turboplanner]

19 hours ago, RFguy said:

Hi OME. I would not completely agree with the way you trying to convey an idea- the statement "That means that as the crosswind comes more and more from the side, the aircraft loses the headwind benefit of the wind. That's why you need to keep the Thrust up during a crosswind landing." 

I think that's simplistic. 🙂

I can see two reasons to keep thrust up- 1) you want to carry a little more speed so that the forward airspeed to crosswind airspeed ratio is a little higher , and b) you might want to go around, having some thrust already in the bank might make that easier.   Carrying more speed might not work if the thing doesnt want to settle on the deck. I have seen videos of taildragger pilots in a high crosswind smacking it down on the deck like an aircraft carrier- NO ROUNDOUT- flown onto the ground. and no bounce. obviously takes some skill.

Listen to him RF - he's just conveying a simple basic. Overthinking it with what someone might do introduces infinite variables. There's also a difference between using a crabbling method and crossed controls amd there also a big difference if you are hit by one or more quartering gusts, and apart from that the parasitic drag varies with the angles.

 

It's much safer to learn live from an instructor.