CFI myths..Special VFR day/night et al

[VNugget]

First one: no

second one: hmmmmm

 

[bigD]

The plane's weight will be the same - in this case 100,000lbs.

 

[Checks]

At low altitude you should be in the habit of turning into the wind. You will lose airspeed when turning downside, this is a FACT.
Try it sometime

 

[bigD]

Try it sometime

I have tried it. At altitude though (~6000 feet), in a 50 knot steady wind.

Bottom line, if the wind is steady, you'll never know it's there by looking at your airspeed alone. Now, at least around here, the wind never seems to ever be steady down low. But that's a different situation!

 

[Checks]

Maybe if you did a quarter standard rate turn then I might agree but if you did a standard rate turn from a 50kt headwind to a 50 kt tailwind and didnt initially see a drop in IAS as you turned downwind then your airspeed indicator must have bird crap in it.


Big D, when are you going to quit that real job and join us working poor?

 

[bigD]

No - I was doing real turns! Honest! The only change in airspeed was a small decrease because of my added AOA to maintain altitude - that decrease was noticed regardless of whether I was turning upwind or downwind. I dunno man, I just don't see physically why there's any difference between turning upwind or downwind. I'll have to try my experiment again sometime.

And as for my real job - I'm outta there as soon as I graduate! I can't wait to begin instructing. I can almost taste the Ramen now!

 

[VNugget]

At low altitude you should be in the habit of turning into the wind. You will lose airspeed when turning downside, this is a FACT.
Try it sometime

If you were originally following a straight groundtrack and applying crosswind correction, then yes.
Let's say you're tracking straight North, and there's a wind from the West, which you're crabbing toward. Well a turn to the East is actually bigger/longer (whatever word you use for angles) turn than one to the West! So if you try to finish it in the same amount of time, you'll have to bank higher and pull harder, and of course lose more airspeed.

Please don't take me wrong, I'm not trying to insult anyone here; I realize this is all ridiculously obvious to anyone, (especially you pilots with thousands of hours) but I had to lay it out in order to make the distinction from "just flying in the air" (sorry that sounds dumb, but sometimes I have trouble articulating my thoughts) and ignoring the ground.

if you did a standard rate turn from a 50kt headwind to a 50 kt tailwind and didnt initially see a drop in IAS as you turned downwind then your airspeed indicator must have bird crap in it.

Assuming a constant bank and altitude (i.e., "just flying in the air") ... why? Why does the ground have anything to do with what you're doing in the air?


One of us has to be missing something, and I hope it's me

 

[DrewBlows]

Here's another: Say your flying a freight plane full of 500 ducks. Total weight of the ducks (no cages just birds walking around) is 2500 lbs. Your airplane's takeoff weight is 100,000 lbs. Once you're in the air all of the ducks start flapping their wings and are flying around the cabin. Does your airplane now weigh 97,500 lbs. or does it still weigh 100,000 lbs?

I've pondered this one before. The airplane would weigh 100,000 lbs. Also, it shouldn't matter whether it is in the air or on the ground it should always weigh the same (fuel burn aside). The most logical explaination that I have reasoned is that since the birds are flying they are creating lift and therefore displacing air (which has weight) downwards. The displaced air would strike the floor of the airplane with the exact same force of the birds feet and the plane wouldn't know whether the birds were in the air or on the floor.

Does anyone else have a decent explanation for this? I am very interested to see someone else's analysis.

 

[SkyWestCRJPilot]

Correct,
You could replace all the ducks with helicopters or Harriers creating downwash that equals the force of their weight. (that would be pretty cool to see a Harrier hovering inside of another airplane.)

 

[100LL... Again!]

It is very interesting that aerodynamicists and physicists do not accept the 'downwind turn' concept. Only some pilots.

If you are flying into a wind equal to your airspeed, groundspeed equals zero. We all know this.

It can be proven easier with vector addition than words, but you can bank to turn downwind with no effect on airspeed than the normal loss due to banking while maintaining altitude.

The flaw in the reasoning is that the airplane can 'suddenly' turn around. This is impossible. The airplane must act against the atmosphere to begin the turn. As the turn begins the aircraft accelerates only relative to the ground. (Discounting the definition of turning as acceleration).

One must understand the concept (from physics) of an inertial frame of reference. Until this concept is understood, confusion will reign for some folks.

An understanding opf the laws of motion and how the acceleration works is also helpful.

Again, the fatal flaw in reasoning is that the airplane can accelerate independantly of the atmosphere.

Airspeed. Groundspeed. never the twain shall meet.

The exception is windshear, which we all know.

Windshear has much less effect on a light prop airplane than a heavy transport category aircraft due to the inertia of the larger aircraft.

The downwind turn can be mathematically disproven, at least for those who believe in science.

 

[Sctt@NJA]

Both sides are right on this.

1. The airplane doesn't care if it is in still air or moving (as long as its a steady-state wind)

2. Downwind turns ARE dangerous (but only when close to the ground)

Concerning point 1: The inertia type arguments don't pan out. Try doing a 180 in 100kt plus winds and you will see- the airplane doesn't care.

Concerning point 2: Its simply a matter of climb gradient. The RATE of climb will be the same with a headwind or tailwind. The ANGLE of climb relative to the ground will change. (clearly a poor ANGLE of climb is what is hazardous when you need to clear obstacles)

So low-level downwind turns are more dangerous than upwind turns due to the increased groundspeed which causes a decreased climb angle (remember angle of climb is the aircrafts ability to climb over distance relative to the ground) and thus reduced performance in regards to clearing obstacles.

Note: When I say "low-level" I mean low enough that nearby obstacles are a concern. 1000 feet over prairy land doesn't count. 10 feet with a tree line ahead does.

I would speculate that the other phenomina observed by some pilots (eg. incleased RATE of climb when turning upwind) are an illusion based on groundspeed and angle of climb.

The same maybe for those who say you lose airspeed... if you were doing a low level climbing turn to an increasing tailwind component the decreasing climb angle (due to increasing groundspeed) would cause the pilot to compensate and get their climb angle back by raising the nose, thus losing airspeed. The proximity of the ground is providing a reference of climb angle that doesn't exist higher up.

 

[bigD]

Does anyone else have a decent explanation for this? I am very interested to see someone else's analysis.

SkyWest's explanation about the downforce is right on. Just remember that air is a fluid in many of the same ways that water is. If you had a fishbowl full of water, and started adding fish to it, you'd kind of expect the weight of the bowl to increase as you add the fish, right? The weight doesn't just suddenly disappear because the fish are swimming around in the water. It's the same kind of thing when dealing with airplanes, birds, or whatever flying around in a closed vessel filled with air.

 

[100LL... Again!]

How 'bout we get together next time its blowing about 30-40 knots. I'll take off and do a rapid downwind turn while maintaining airspeed. If the downwind turn theorem is true, I would have to desend radically to maintain airspeed.

$100 bet. (I'll feel bad taking your money).

 

[bigD]

Wait, a $100 bet that you'll have to radically decend to maintain airspeed?

You're on!

 

[Sctt@NJA]

You wont have to descend to maintain airspeed. But if you need to clear obstacles you would be better off turning upwind.

See? The hazardous downwind turn "myth" is true. Its just the reason for it thats misunderstood.

Fact: For a given pitch and powersetting the airplane will maintain the same airspeed and rate of climb regardless of turning upwind or downwind.

Fact: That same airplane while turning downwind will have a greater groundspeed and lesser angle of climb, so its climb perfomance relative to the ground will be worse.

The people saying the downwind turn is a "myth" are correct in the sense that rate of climb and airspeed are not affected by a steady state wind. They are wrong however in thinking that a low-level downwind turn is not dangerous. Its all about ANGLE of climb. (How high you can climb for a given distance over the ground)