On "maximum demonstrated crosswind capability"

[RFguy]

Turbs, I do.

Amongst other methods I look forward to learning crossed controls method. That's certainly a high drag, high stakes scenario as you are really messing up the airplane....but I thought might be a bit better for a low inertia aircraft than crab-uncrab... as long as you have some engine power to counter the drag (or time it just right ) . DO users of crossed controls  come in  in a crab and then when established over the runway at a sensible height, go over to cross controls ? Seems a high risk manouver at low airspeed and 50-500 feet AGL...

Edited September 24, 2020 by RFguy

[andy310r]

1 hour ago, RFguy said:

Turbs, I do.

Amongst other methods I look forward to learning crossed controls method. That's certainly a high drag, high stakes scenario as you are really messing up the airplane....but I thought might be a bit better for a low inertia aircraft than crab-uncrab... as long as you have some engine power to counter the drag (or time it just right ) . DO users of crossed controls  come in  in a crab and then when established over the runway at a sensible height, go over to cross controls ? Seems a high risk manouver at low airspeed and 50-500 feet AGL...

I transition from crab to slip (cross-controls) during the round-out.

Some advocate for flying final in a slip. Each to their own but I find it not too comfortable especially for passengers, so I stay in the crab until I need to be slipping.

 

I really struggled with it initially. Finally something 'clicked' and my brain figured out that a) my feets' job was to keep track parallel to runway (alignment); and b) the job for my hands was to maintain runway centreline (stop drift). Then the slip becomes really natural, and landing on one main first just happens.

 

Of course as you slow down you need more control input (how much? Just enough!) and, once down, keep the upwind wing down with aileron. Do not let the wing lift. This is often forgotten. Some a/c forgive this to an extent but many don't.

 

Gusty is always more work than a steady crosswind, but I'll never forget when I finally "got it". That doesn't mean all my landings are great - they aren't - perfect landings only happen when no-one's watching :)

 

FWIW the rule-of-thumb I use for mentally calculating x-wind components is the clock model...

Wind 15 degrees off runway heading = quarter crosswind component (picture a minute-hand at 15 mins: quarter of an hour) (e.g. 12 knots, 15 degrees off = 3 knot component)

30 degrees off = half (e.g. 12 knots, 30 degrees off = 6 knot component)

45 degrees off = three quarters (e.g. 12 knots, 45 degrees off = 9 knot component)

60 degrees off = all of it (12 knots across).

 

Not exact but works for me.

 

 

 

[Bennyboy320]

40 minutes ago, andy310r said:

FWIW the rule-of-thumb I use for mentally calculating x-wind components is the clock model...

Wind 15 degrees off runway heading = quarter crosswind component (picture a minute-hand at 15 mins: quarter of an hour) (e.g. 12 knots, 15 degrees off = 3 knot component)

30 degrees off = half (e.g. 12 knots, 30 degrees off = 6 knot component)

45 degrees off = three quarters (e.g. 12 knots, 45 degrees off = 9 knot component)

Same rule we were taught in the RAAF on pilots course & I still use it to this day when flying the Foxbat 🦊 or the Bus. KISS.

[old man emu]

 

7 hours ago, andy310r said:

FWIW the rule-of-thumb I use for mentally calculating x-wind components is the clock model...

Wind 15 degrees off runway heading = quarter crosswind component (picture a minute-hand at 15 mins: quarter of an hour) (e.g. 12 knots, 15 degrees off = 3 knot component)

30 degrees off = half (e.g. 12 knots, 30 degrees off = 6 knot component)

45 degrees off = three quarters (e.g. 12 knots, 45 degrees off = 9 knot component)

60 degrees off = all of it (12 knots across).

Which is pretty much what I said earlier. I would not argue with that means of remembering things. The values in this table come from looking up the value of sine for the angles, and are more mathematically accurate, but the Rule of Thumb is acceptable.

 

People have been having difficulty in understanding what I mean by "eroding the headwind component"  Basically, if a wind of # kts is blowing straight down the runway, the headwind component is 100% of # kts. As the angle of the wind to the centreline of the runway increases, the headwind component reduces by a factor related to the cosine of the angle. 

 

I suggest an exercise with plotter, ruler, pencil and paper. Has anyone even tried to do that exercise. If you do, you will find that " eroding the headwind component" becomes crystal clear.

[RFguy]

What's the spread of pilots , lets call it the 'yield' that can cope with maximum crosswind for their aircraft under ideal (steady wind and minimal fatigue) condix ?

[M61A1]

1 hour ago, RFguy said:

What's the spread of pilots , lets call it the 'yield' that can cope with maximum crosswind for their aircraft under ideal (steady wind and minimal fatigue) condix ?

The strip I fly from is north/south our prevailing winds are easterly or westerly. It has necessitated learning to deal with crosswind if I want to fly.

It has taken some time and I have got reasonably proficient at it. There was a time when I wouldn't fly at all with wind over 5kts.

Now I choose not to if it's much over 20kts. The Drifter POH says 15kts, but 22kts is quite manageable, even when gusty. The 601 about the same, but I don't know what it's limits are supposed to be. The POH is made up by the builder, not the kit manufacturer.

Last weekend the sock was out straight and the ASI was reading a solid 20 gusting to 25 sitting on the ground.

[old man emu]

On 9/23/2020 at 7:55 PM, RFguy said:

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

Yes, it's a big topic. In this thread there have been posts relating to the sections: Why and How, and Who.

 

My contribution (?) was aimed at the Why, and the part that wind direction plays in the technique of landing (taking off, too). 

[facthunter]

The aspect out of the widow will tell you when you know the Plane. Watch this "crossed controls" thing. You need to be pretty close to the ground. Kick it straight with rudder and don't let the into wind wing rise and even lower it if the planes geometry allows it with the stronger X wind occasions.

  IF you stuff up a sideslip (as the majority I've found DO) it's just a rotten near wings laterally level SKID which as well as being uncomfortable just makes drag and predisposes you to drop a wing if you're slow. A SIDE slip has a large element of BANK held. Good airspeed control (by precise Pitch attitude) is ESSENTIAL OR you are dangerous.. Power is off as you're trying to steepen the approach angle without increasing AIRSPEED.. Be taught this by someone who KNOWS  and stay proficient or you'd be better off not doing it at all. Nev

[skippydiesel]

I find this conversation quite concerning - X wind landings are something best discussed and demonstrated by your instructor and as mentioned by others, often practised to stay proficient.

[facthunter]

What did my last line say? Nev

[skippydiesel]

Hi Nev - "and as mentioned by others" - that pretty well acknowledges all previous advice, dont you think?

[old man emu]

When I was learning, I couldn't get the gist of X-wind landings, so the CFI took me out in a C-150. 

 

His said to me, "Can you drive a car? Then use the rudder to keep the aircraft flying along the centreline, and steer the plane like you steer a car."  "Steering" is a method to keep the windward wing lower than the leeward wing. At flare, it's just a matter of centring the rudder while keeping the windward wing down with aileron. Land on the windward main wheel and slowly almost centre the ailerons as speed comes off so that the leeward main contacts the ground. When the leeward wheel touches, keep the aileron input going so that the windward wing doesn't produce as much lift as the leeward one. Then centre the elevators to drop the nose wheel. Using this technique, I nailed my X-winds after that.

 

Obviously the C-150 has a yoke aileron control which makes the mental and muscle memory knowledge transition from car to plane a lot easier than if the plane has a stick.

[Mike Gearon]

On 24/09/2020 at 9:22 AM, old man emu said:Ground speed will be (35 - 5 =30) kts, so you have to add power to get the airframe moving faster.

but....the airframe still has 35 knots of air moving over it and doesn’t care about the ground speed.  Compounding factor being the aircraft is moving down the runway wanting to slip into the windward side to maintain heading with roll countered by opposite rudder. This means extra power just to maintain airspeed because the pointy bit isn’t pointing the right way. 
 

Is this more related to the added power? 
 

 

 

[facthunter]

My General and consistent advice is especially at the earlier stages go with your instructor as he/she will have their way of presenting things. Keep confusion  at a minimum as you are taking it in fast. If you are having trouble like with some ailment get a second opinion. Flying is a bit the same. On the basics most instructors are on the same page or should be. 

 My only purpose in all of this is explain what's happening so understanding increases and we are MORE safe.. It's a pity when someone crashes and says I didn't know you could do THAT..Getting your Certificate doesn't mean you know everything. You have achieved a very basic level  and continue on from there as your experience grows.  (with a bit of luck).Nev

[Mike Gearon]

On 24/09/2020 at 10:15 AM, Old Koreelah said:

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.

 

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.

They ate my motorbike seat when I was 12 years old. Seems fitting we both work our way up to larger and more expensive items. Enjoying the discussion on crosswind. Not enjoying the idea of zero forward velocity/ kinetic energy and the wind just disappears as RF discussed. That dropping sensation would be annoying.

[old man emu]

The discussion has been plagued by ifs, buts and maybe's. Before getting into those dark and confusing areas, we must first understand things in very uncomplicated ways.

 

Therefore the parameters are:

1. The aircraft has a known airspeed at which the wing stalls.

2. Stall speed is a measure of the speed of the air relative to the surface of the wing.

3. The speed of the air, relative to the wing is obtained from three independent sources: engine thrust and wind speed, and gravity (which we will ignore)

4. The speed of the air, relative to the wing is the vector sum of the velocity of the wing, and the velocity of the air speed.

5. It is assumed for the discussion that direction of the vector of the velocity of the wing is parallel to the runway heading, therefore its magnitude is not reduced by sideways movement from the runway heading.

6. For the discussion, the velocity (speed and direction) of the wind remains constant - no gusting or direction change.

7. The vector of the wind speed is the vector sum of its headwind component and its crosswind component relative to the runway heading.

 

If these parameters are applied, then we find that:

a. The contribution of the wind speed to the speed of the air over the wing is reduced as the angle of the wind relative to the runway heading is increased.

b. In order to make up for the loss of that contribution to wind speed, Thrust must be increased to a level above that required to produce an airflow over the wings that is greater than the stalling airspeed.

c. The increase in Thrust may not register as an increase in Indicated airspeed

 

In relation to the influence of gravity - this is what gliders use in lieu of engine thrust, or what is used in dead-stick landings for powered aircraft.

 

 

[Thruster88]

3 is wrong. Airspeed is a function of pitch and power or pitch only in a glider. Wind does not have anything to do with airspeed.

[M61A1]

2 hours ago, Mike Gearon said:

Not enjoying the idea of zero forward velocity/ kinetic energy and the wind just disappears as RF discussed. That dropping sensation would be annoying.

Warwick airfield in SEQ has a notorious gradient if you have an easterly and are landing on 09. I have seen quite a few caught out by it. When I first found out about it I was carrying a little extra speed as it's quite a long runway.

The arxe really falls out the airspeed around 20 ft. If you aren't carrying the extra speed or do not add power immediately, pulling back still results in that "annoying" sensation, and for some, bent landing gear.

3 minutes ago, Thruster88 said:

3 is wrong. 

As are points 1 and 2....It's about AoA, not speed. The speed will vary depending on certain factors, the stall angle remains constant for configuration.

[facthunter]

A plane flies in a parcel of ait. To have airspeed you use potential energy (lose height in the parcel of air) OR have power from the engine  to provide the  force to equal the drag that exists because the wing is producing lift + parasite drag that doesn't produce lift..Stalling is an angle of attack thing not a speed thing. The usual "stalling speed" is only under precisely defined conditions.

  There was an old rule of thumb..... Use 1/2 the wind speed and ALL of the gust figure to add to your normal approach figure.. Nev

[old man emu]

1 hour ago, Thruster88 said:

3 is wrong. Airspeed is a function of pitch and power or pitch only in a glider. Wind does not have anything to do with airspeed.

Sit in your plane on the ground with it facing into wind and tell me that the ASI doesn't move. If I'm wrong, why do people use tie-downs?

 

1 hour ago, M61A1 said:

As are points 1 and 2....It's about AoA, not speed.

Point 1. So if I put a plane on trestles so that the wing is at an angle of, say 10 degrees to the horizontal, and there is no wind, then the plane will fly off the trestles?

Point 2. The speed of the air relative to the surface of the wing determines the amount of Lift produced. 

 

Pilot operating handbooks (POH) or generic flight manuals describe stalling in terms of airspeed. This is because all aircraft are equipped with an airspeed indicator, but fewer aircraft have an angle of attack indicator. An aircraft's stalling speed is published by the manufacturer, but the stalling angle of attack is not published. As speed reduces, angle of attack has to increase to keep lift constant until the critical angle is reached. The airspeed at which this angle is reached is the (1g, unaccelerated) stalling speed of the aircraft in that particular configuration

 

The problem we are having in this discussion is to do with semantics and relativity. Notice the highlighted words in this paragraph:

Stalls depend only on angle of attack, not airspeed. However, the slower an aircraft flies, the greater the angle of attack it needs to produce lift equal to the aircraft's weight. As the speed decreases further, at some point this angle will be equal to the critical (stall) angle of attack. This speed is called the "stall speed".

 

Now those words are what is causing the problem. Is the "slower" referring to speed relative to the ground it is flying over, or it is, as I have been saying, the speed of the air relative to the wing, as measured by an ASI?

[facthunter]

Your groundspeed has nothing to do with it. Your stall warning is not deriving info from the airspeed indicator. The little vane responds to angle of attack.. Icing will make the airspeed need to increase as the airfoil ls not efficient with ice on it.   Separation commences earlier.  Nev

[old man emu]

It got a tad breezy at Camden yesterday afternoon about 1600.

 

I wonder what the crosswind was on Runway 06 about 1615. NNW covers the bearings 320 to 330 degrees. The headwind component of that crosswind would have made stalling-on in most aircraft rather difficult. 

[RFguy]

drop a rope and get dragged in on a drum winch ?

[facthunter]

Since you are carrying large margins for the gusts, stalling it on is not an option. Leave those days for the BIG stuff with  very adequate spoilers, usually pre-armed that leave your hands free for other necessaries and make ballooning impossible.  Nev

[old man emu]

2 hours ago, RFguy said:

drop a rope and get dragged in on a drum winch ?

At that wind speed the rope would be standing out like a WWl fighter pilots silk scarf

 

Getting back to windsocks. If the sock is full, it means that the wind speed is equal to, or greater than 15 kts. From then on, it is only good for indicating wind direction. But I suppose commonsense (remember that?) would tell you to rely on drift as an indicator of windspeed. But who would like to go and play in a 15+kt crosswind?