Monday, March 13, 2017

I never said there wouldn't be math!

As I mentioned last week, I've been living vicariously through Aaron's posting of his adventures experienced while earning his private pilot's license.  Some of his more recent postings have dealt with learning to handle crosswinds.

(Hey! I'm on vacation and posting this through the magic of time travel, or something.  You might have to scroll through a few posts over there to find this one.  Aaron done writ good things, even if they're not always about flying...Read them!  Over.)

In ANY case, learning to fly a new aircraft in new and unusual circumstances like crosswinds can vex the best of pilots.

For example....



That airport is in Birmingham, England.  Remind me never, ever, never to book a flight there in the winter!

So, yeah, crosswind landings can be "sporty".  But did you know, our ancestors knew a way to make landing in one easier?

I suspect some folks might call it "magic", but the real answer is "math".

So, Sarge, yes, there will be math involved.  Specifically Geometry. Sines and Cosines to be precise.  (Sounds like a verse that could be sung to the Beverly Hillbillies, doesn't it?)

In any case, in almost all cases, wind is a good thing to a pilot.  Wind going over the wing is what gets them flying and then keeps them flying.  Once airborne, the direction of the wind isn't all that important, other than speeding up or slowing down your time enroute.  (If you want to see time stop, try flying in a northwesterly direction in the northern Pacific in the winter.)

Taking off in a crosswind can be a bit of fun, but if done properly, isn't usually too bad.  Previously viewed video notwithstanding.

Landing in a crosswind however.....Well the airplane will fly with it's nose pointed into the wind.  When landing, the pilot will align his flight path with the runway by pointing the nose into the wind according to a geometric formula which calculates the crosswind and headwind components of the actual wind direction and speed.

Which is all well an good while the airplane is in the air.  Once all the wheels hit the ground, the airplane is no longer flying and is now a ground vehicle.  Ground vehicles go the direction the wheels are pointed.  Unless the trucks (the landing gear assemblies) are steerable, that means the ground vehicle will go in the direction of the nose which is pointed towards the edge of the runway.

Great skill is involved in getting the nose pointed down the runway while keeping the upwind wing from beginning to fly again.  (As you move if forward to align the aircraft with the runway, it gains speed and may begin to fly again.)

Now, the Eagle was very aerodynamic which means if would fly without a lot of effort, so landing it in a crosswind was could involve all of your extremities.  Arms to control ailerons and throttles, legs to control rudder and brakes.  Sometimes swapping roles on an instant's notice.

When I first got to Kadena, many of the members of the squadron were involved in the aftermath of the KAL 007 episode.  My squadron had deployed to lovely Shemya AB in the Aleutians.  I was not in the squadron yet, so this story is at least second hand (and probably enhanced in the retelling by alcohol).

In any case, the squadron had deployed up there, being drug along by tankers, a flight of approximately 3000NM.  About 7 hours.  

Once in the vicinity, they got a weather report that put the weather very low, but within parameters although the wind was gusting outside crosswind limits.

Now, this was not normal times.  This was real.  The powers that be dictated that a squadron of Eagles deploy to Shemya and they would do so.  If the weather made landing impossible, the next stop was another 1500NM at Elemendorf.

The Squadron Commander decides to shoot the approach while the tankers and the rest of the squadron orbit at altitude.

He comes on down, enters the weather and is flying the ILS.  He's got the needles centered and as he breaks out of the clouds, he looks out the nose of the aircraft as he has several million times before.  

Nothing but water.  Out of the corner of his eye and outside the canopy bow (which is about 30o off the nose), he catches a glimpse of land.  Glancing that way, he sees the runway.  Holding his heading, he sideslips it in to land.

After getting it on the ground and after a few minutes to get his blood pressure somewhat under control, he keys the mike, draws a deep breath and in a voice that is only slightly quaking now says, "Okay, it can be done.  Here's how....."

All 12 managed to make it down with no incidents.

So, juvat, what is the secret solution that our ancestral pilots knew and we have forgotten?

Well, we now build runways parallel to each other and if we build a cross runway, we build it at 90o.

Our ancestors knew that the crosswind component is product of the sine of the angle between the wind direction and the runway direction times the wind velocity.  Which means that a 90o crosswind of 30K will be 30K of crosswind.  

They would build the runways like they were built at Pyote AAFB Texas in WWII.


Pyote AAFB is west of Big Spring (Webb AFB) and near Monahans. it was abandoned in the early 60's.

An Equilateral triangle has 3 angles of 60 degrees.  Once you get more than 30 degrees off one runway heading, you are less than 30 degrees to another. The sine of 30 degrees is 1/2.  1/2 of 30K is 15.  Well within the crosswind landing limits.  In fact, you'd have to have winds of 60K in order to be at the landing limit for all runways.
Been to or at least by most of these, some are still operational although without all three runways, usually.
Source

There were a boatload of airfields in Texas in WWII, almost all from the map above that I could find on Google Earth were in some form of an equilateral.  The picture of  Shemya above shows they also had that option.
Laughlin also had, emphasis on the past tense, that style runway.
And, because Math is hard when you're actually flying the airplane, the rule of thumb I used was to take the wind velocity and multiply it by 1/6th for each 10 degrees off the runway heading.  That should get you within a knot or two.

An airplane in the air is an airplane.  Fly it.  An airplane on the ground is a big car (requiring a little correction into the wind to keep the wing down), drive it.  The couple of seconds it takes to transition from one to the other can be very exciting, enjoy!














34 comments:

  1. Watching that video could make one swear off flying forever. I think I'll just never fly to Birmingham.

    I will remember KAL007 for as long as I live. My family and I rode that very same flight two years earlier. Well, our tickets said KAL007, don't know if it was the same airframe.

    I too like reading about A-Aron's flying lessons.

    Math, whoda thunk it? Word problems, they never explained those very well in school, but when you think about it, all of life consists of a series of word problems. Many requiring math. Life is hard, wear a helmet.

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    1. My IPs would say my head is hard enough to not need a helmet. Visited Castle Edinburgh today. Waaaay cool! Pictures & AAR to follow. you would still be up there Sarge. Connections to Waterloo and every other war you were in.
      Bags still AWOL.

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    2. Dang iPad....interested in! Although.......... come to think of it. ;-)

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    3. That's right Juvat, blame the iPad...

      :)

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    4. Thats my story and im sticking to it

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  2. I also know about AWOL bags. A most enlightening post juvat. Thank you.

    Paul L. Quandt

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  3. Landing in a crosswind may be a challenge but the taxi to a tiedown can be very sporting. One landed into a 40 knot breeze right down the runway (Roosevelt Field, Long Island, Cessna 170). Touched down with 1600 rpm and around 10 knots ground speed. Took nearly twenty minutes to get to the tiedown area.

    Have to believe something weighing more than 1200 lbs empty would be easier.

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    1. Yeah once you get down to taxi speed, every fighter i flew was pretty easy. It was that transition area that tended to be fun.

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  4. Ah, fun post Juvat.

    I don't think many folks remember or have even heard of KAL 007. And I'm not sure that many who do or have heard have ever taken the time to think about what it means when people make a conscious decision to shoot down a civilian airliner. I remember how the press couldn't do enough to give the corksachers a pass.

    Also worth thinking about people who would intentionally send a civilian airliner squawking F-14 transponder codes into a war at sea zone. The press really went all out to crucify the shooters in that one.

    Anyway, great post, and I'm looking forward to seeing some gopro video of that role swapping at an instant's notice. I'm really curious to see the legs on throttles and ailerons and hands on rudders and brakes. And they say navy pilots are the best because they land on carriers. SMH.

    Sorry! Sorry! You know I got that naval turrets syndrome thingy...

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    1. One of they advantages to a mobile runway is the ability to turn into the wind, thats for certain.

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  5. "An airplane in the air is an airplane. Fly it." Better advice than math.
    I remember looking at runway 01 (McCarren LAS) out of my retractable window in my swept-wing Boeing 727 (I know, I know). Full rudder at the end - I was afraid I was going to get a left wing tip. AH the heady days of Western Airlines, "the ONLY way to fly!"

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    1. Yep. Winds at Mccarren were sporty, but at least there was dust!

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  6. Yep... "Sporty" is a good family friendly word for it... LOL

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  7. Love looking into those old airfields. Found this site years ago that has a lot of info on them catalogued by state. http://www.airfields-freeman.com/

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    1. Looking forward to perusing that...when im not paying for wifi. :-)

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  8. Great article juvat. I've bookmarked it for future reference. I have my own crosswind story to tell. If I dust off my old logbook I note that my first solo was 2 1/2 hours. It was, as Lex would've said, "exciting"

    The instructor decided that with Crosswinds it 30 to 40 kits that would be a good time for my solo.

    Well let me just say by the end of that aloft time I learned that the rudderpedals were more than just foot rests.

    I have found interesting on the subject (since it almost killed me) is the different techniques one must use with different aircraft types.

    If you go on YouTube you can probably find this old video of a remote Brazilian airfield that Boeing aircraft used to use in certificating their airliners for maximum crosswind.

    I sat there looking at the video transfixed because they did not land those airliners the way I landed my piper. They would come in at some of seen angle of course and then hit the ground with the mains at that same angle. It was only once the mains head hit the ground would they use rudder to align the nose with the runway

    Some years ago the squadron commander at Beale Air Force Base invited our car club to watch the U2s.

    That is basically a jet powered glider. As the plane is crossing the numbers on the runway a fellow pilot in a Camaro or GTO on the tarmac guns it with a wide sweeping turn onto the runway following the aircraft.

    Other than removable running wheels on the wingtips the only wheels that that plane has are on the fuselage and the pilot in the car is calling out the distance from the ground to the rear main.

    FA 18, F-15s, F-16s… The toughest plane in the military to land I'm told is U2.

    Can you imagine trying to land that thing in any kind of a crosswind? You certainly couldn't slip it with that wingspan

    Hey slip, for those uninitiated, is where you're giving aileron into the wind and opposite rudder. The plane is using its lift to counteract the crosswind in the opposite writer is aligning it with the runway. I'm told you can't do that with airliners either because the engine overhangs are relatively close to the ground. Not to mention it would probably scare the blank out of the passengers.

    It's a good subject and when I've often thought of after my near mishap 30 some years ago.

    Oh one other thing. The B-52 has an unusual way with Crosswinds. With that massive wing of course you couldn't slip it so the main wheels actually can be turned in the direction of the runway while the plane is still crabbed at an angle.

    Good subject and I'll have to reread your post

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    1. "It was only once the mains head hit the ground would they use rudder to align the nose with the runway" YIKES! The main gear on the 727 were about as big around as a lamp post, but I wasn't taught to do that. I can remember a Captain I once or twice flew with landed said aircraft on the lip of the runway at Juneau. The aircraft shuddered not unlike taking ground fire in the Phantom. The head flight attendant (stewardess, in those days) came up and remarked that "that landing was so hard, my pantyhose fell down."

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    2. Looking forward to watching it when I get home to better wifi.

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    3. Dave,
      Ive bounced a Phantom on landing, but I don't think I've ever landed one as hard as you described. Poor girl!

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  9. Sorry for the miss spell's. I can't go back and correct what I've already published in with this iPhone I could not properly review it before I sent it. But hopefully I got the message across :-)

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    1. No worries. I'm world renowned for my love of apple spell check.

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    2. What I love - on my iPhone - is that I have it right and it changes it for me!

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  10. Shifting base of operations further north into the highlands. Fortunately, the Missing Baggage IFE has been resolved and blood pressures returned to normal. Edinburgh is high on our list of recommended places to visit

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  11. Here is that video of Boeing testing for maximum crosswind

    https://youtu.be/ljOxo0s33sI

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  12. Great story as always. Crosswinds certainly can complicate the learning and landing process. I'm getting decent at handling them at reasonable crosswind factors.

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    1. The laws of man can sometimes be ignored. The laws of physics however apply to all and are not to be violated. It's a terrible feeling when you've got all the controlls applied and realize that's not enough.

      Crosswind limits tend to be limits not guidelines.

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  13. I prefer a shorter and mobile runway that points itself into the wind.

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    1. We all have our crosses to bear.

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  14. There were dozens of triangular airfields in Canada, built for the BCATP (British Commonwealth Air Training Plan) in WWII. The purpose of the equilateral layout was to make sure training never stopped due to crosswinds. I'm told by my private pilot friends that landing a tail dragger, as almost all planes were at the time, is much more difficult than landing something with a nose wheel.

    Al_in_Ottawa

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    1. Multinational confirmation of theories is always appreciated. Ive never flown a tail dragger, but I've heard the same.

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Just be polite... that's all I ask. (For Buck)