The Flight Deck

Comment from MaxDamage
Time: March 30, 2010, 11:49 pm

Crosswind. Crosswinds are like gravity, you have to counter them at all times to remain standing but, unlike gravity which is constant and you’ve grown your entire life aware of and compensating for, crosswinds vary and you have to react to.

So, wind moves the plane a couple feet left, pilot adds in right rudder, you go right and he lets off, it drifts back left and he applies right rudder again, etc…

It’s also possible, on a multi-engine, to have this same sensation if one engine is not producing the same power as the other.

Your suspicion that moving ahead fast would make this less felt or noticed is easily put to rest. Let’s use gravity as an example. The falling rate is 9.8m/s^2, or about 32 feet per second squared. If you’re moving at 32 feet per second and gravity pulls you 32 feet down that’s pretty significant, a 45 degree descent. If you’re moving at mach 3 you’re still going to go down 32 feet per second, and you will feel it just the same even though your speed is higher and the relative change is less. In other words, you only feel the change in motion on the one axis, and you can have any speed on another axis but it doesn’t apply to what you feel in the seat of your pants. 1000mph going West feels the same as 10mph going East, but 10mph up or down is what you notice.

For those who have never driven a rear-wheel steering vehicle before, if you turn left it continues to turn left and will rapidly come to the point where the back end wants to swap places with the front end. In aircraft this is known as “rudder control,” given the rudder is at the back end of the aircraft. Try driving 40mph backwards in your car in a safe area to experience positive feedback in steering that a rudder provides.

So what you feel as side-to-side motion is the delay and correction the pilot applies to being off-track during the take-off run as he compensates for crosswinds or differential thrust.

Confession: I don’t know squat about this from experience, I’m giving you my best answer based on what I know of physics. So don’t, you know, risk your life on what I said above.

Lex? How’d I do on this quiz? Because my sister the new IFR-rated pilot asked a similar question last week, and I’d kind of like to know if what I told her is also wrong.

– Max

Comment from Larry Sheldon
Time: April 2, 2010, 9:38 am

I’m not an airline pilot.

But since this only happens during the ground run, I have to ask?

What is the effect of running a while down a row of lights?

What is the effect of ruts in the pavement?

What is the effect of the flying pilot (including the computer) sorting out the crosswind?

In a single seat or tandem two seat aircraft those effects would be less noticeable because:

You are the pilot.

The lever arm to the CG is a lot shorter.

Being launched from a trebuchet tends to focus your attention on other things.

Comment from Larry Sheldon
Time: April 3, 2010, 7:41 am

“What is the effect of running a while down a row of lights?”

That actually, at one point, said:

What is the effect of running a WHEEL down a row of lights?

Comment from MaxDamage
Time: April 19, 2010, 9:13 pm

Ummmm…. One point I didn’t make clearly, since the rudder is behind the tail surface wind pressure will cause it to return to a neutral position if the pilot lets go of the controls. While it does steer like driving a car in reverse, unlike your car it won’t take effort to get it going straight again.

My test in Thursday morning. My sister is flying up in a Cessna 150 and going to see how quickly I can figure out how to fly. I won’t technically solo, for insurance reasons, but it counts as a pass if I can take off, work a simulated pattern (the airfield we’ll be over is not controlled), navigate 50 miles and back, and land without asking any questions.

Wish me luck. If I do it in under 10 hours she buys me a steak dinner. If I don’t, the flight time is on me at $75/hr and she gets the hours in her logbook.

(sigh!) Time to put my money where my mouth is.

– Max

Comment from Michelle
Time: April 22, 2010, 4:56 pm

Too funny, Max.
So your test was today?!
Now that definitely deserves a Flight Deck post.
~Waiting impatiently ~

Comment from MaxDamage
Time: May 5, 2010, 11:47 pm

Alright, I’ll tell the sordid tale for you, Michelle. My sister (who is now rated commercial) and I rented the 150, and this being my first time at the controls since I was in grade school I thought it best to let her handle the take-off and landing part. Those being sort of, you know, critical. Since she was the PIC, me not being at all a pilot, I let her work the comms as well.

A slight southern drawl on a woman’s voice and I think ATC’s would hand over the airport if they thought they could get away with it.

So basically I took over from 500′ a little south of Sioux Falls, SD. We moseyed west of Sioux Falls airport, those four gerbils in their little wheels that power a C150 all running like heck, and headed north by northwest towards Madison about 50 miles away.

Which, flying alongside I-29 with it’s 75mph limit and finding we were only barely passing most of the traffic, and some passing us at our 90 knots indicated, pretty much convinced me this is not a hobby that will shorten my commute time.

We buzzed the farm, took pictures, buzzed a couple of neighbors just for the fun that’s in it, and headed west to Madison airport and its uncontrolled strip.

Once at Madison I practiced an approach a few times, little sis with her hands off the yoke until 250 feet and then being more prepared than anything. She read the checklist, I followed, we took it down to about 100′ then applied power and went around.

Once our fun at Madison was over, we headed back south to return the airplane. By this time I was fairly comfortable with the handling and decided I’d do the line-up but my sister would handle the actual landing. You know, for insurance reasons.

Returning to our point of origination, Sioux Falls ATC vectored us way to the west and I actually had kind of a tough time finding the airport. Once I spotted it we were at 2500′ and out came the checklist, I descended at a fair rate I thought, made my left turn on final, and was quite ready to go around because I was way too short and way too high to make this work nicely.

My sister took over and we dropped like a turd from a tall moose. Apparently one cannot actually over-speed the C150 in a dive because, well, it doesn’t have enough mass to actually push through the air under it’s own weight. Not with the flaps down, anyway.

I was actually the most nervous at that point. We’ve plenty of runway, airspeed about 120, and my kid sister is playing energy management as the motor idles. She did a very smooth landing, stomped brakes, and managed to catch our taxiway at 30mph without rolling the darned thing. I mostly managed to look calm.

Lessons learned?

1) Flying is easy. Take-offs, landings, comms, checklists, spin recovery, and otherwise getting yourself safely to your destination is hard.

2) Landmarks you’ve driven past every day for 10 years are suddenly unrecognizable from the air.

3) It’s *work*. If you get behind the airplane you can’t exactly stop at a rest area and think it through. If you get a muscle cramp or have to pee you’re pretty much stuck with it. And in a C150 you are *not* going to find room to stretch or anywhere you can walk it off.

4) I’m sloppy at control, rather than fight the lifts and drops and direction changes I just sort of hold the yoke in my fingertips and suggest the airplane might want to go somewhere. Which is fine and makes for a very smooth ride in a light little thing like the 150 at 2500 feet. At 100 feet on landing approach when you’re out of altitude and bleeding airspeed, smooth only makes you comfortable on the way to the crash site. I was informed that I need to, umm… assert myself.

So there went my first 2 1/2 hours out of 10. It was fun, of course, but I’ve not been bitten by the flying bug by any means. My choices now are to put in another 5 hours or so and see if I can hack it, for no real reward other than the bragging rights, or just admit this isn’t my passion and pay for my sister to get her multi-engine rating.

I’m thinking I’ll do the latter. I know a guy over near Pipestone, MN that has a Cessna 402 in pretty good condition, he’s a CFI, shouldn’t take her too long to get that rating. And the 402 has plenty of room for me to ride, stretch, and take pictures from.

Oh, I called the wife right before we took off and gave her our ETA. When buzzing the farm she and the 2 1/2 year-old were pointedly out in the garden as we roared by, waving for all they were worth. Priceless pictures.

As we were driving home my wife called. Apparently another aircraft had over-flown the farm and the Little Tricycle Motor immediately drew the conclusion that I was in that airplane as well. Shortly after supper LifeFlight roared on over. The look of confusion as her ears heard an aircraft and her eyes saw Daddy at the other end of the table was worth whatever this bet of mine costs me.

– Max

Comment from Curtis
Time: May 25, 2010, 4:39 pm

Rudder Authority!

Returned to the states through SFO, northerly approach on account of the sirocco. Rudder snapping us all over the bay after the Golden Gate.

I think it was the same type aircraft that the FAA had just condemned for it’s crash into Jamaica Bay for excessive rudder movement on the way out.

Comment from vikingTX
Time: June 11, 2010, 2:52 pm

The pilot is compensating for a slight or gusty crosswind. When the nosewheel is on the ground the effect of the rudder inputs by the pilot are much more noticeable because the “rubber on the road” is moving the nose. There is also a tendency to overcompensate because there is a slight lag between putting an input into the rudder steering system and when the (large) mass of the aircraft actually responds. You put an input in and nothing seems to be happening, so you put a little more input in and suddenly you have gone too far so you have to re-correct in the other direction. It is called PIO-pilot induced oscillation. The effect is more pronounced at lower speeds. As you accelerate the lag diminishes, and things are smoother. Also, once the nosewheel comes off the ground the only lateral directional control is through aerodynamic forces on the rudder which is smoother as well.

I don’t know of any autopilot takeoff systems in the commercial world. Many airliners can autoland, but takeoffs are flown by the pilots by hand.

The North flow into SFO is only used when there are strong winds out of the south. Think about the terrain from San Jose to Burlingame. Winds come over a flat area and then are lifted by the mountains north of SFO and again by the terrain at Sausalito. This causes the same eddies and whorls in the air that you see when a paddle is pulled through water. You feel it as turbulence in the aircraft. The stronger the winds, the stronger the terrain created turbulence. Auto pilot systems can handle most turbulence fairly easily, but the computers and servos are striving for a very precise flight path down glideslope and the ride can be harsh. Most pilots will hand-fly in gusty conditions because they give themselves a little more leeway on glideslope and can be smoother. Landings in gusty wind conditions generally safe, but it is very hard to be smooth.

Comment from Nose
Time: July 20, 2010, 9:20 pm

JR – Late to the party, sorry. Here’s the deal. With airliners, you can steer (on the ground) in three ways: First is with the tiller or wheel (depending on what kind of jet you are flying) which controls the nosewheel (usually hydraulically), second is also using the nosewheel steering mechanism, but this time controlled by the rudder pedals. Third is using the rudder aerodynamically. The tiller gives a very wide range of motion of the nosewheel, the rudder pedals give you significantly less.

On the jet I fly (the A320) we use the steering tiller for low speed taxi, like taxiing out to the runway. Once on the runway, during the takeoff roll, we use the rudder pedals. The tiller is much too sensitive to use at higher speeds. As the aircraft increases in speed, the jet uses NWS less and less and the rudder more and more.

So the side to side motion you feel is the pilot steering down the runway with the rudder pedals. Some pilots are better than others, and some jets are easier to control than others. As stated above, crosswinds also play a factor- the Airbus will fair into the wind so you have to apply some downwind rudder as the jet move faster and faster. Once airborne, the Stability Augmentation (which basically keeps the jet in balanced flight) takes over and you don’t have to control yaw with your feet any more, so you drop your feet off of the rudder pedals.

Nose