Another stall spin crash (usa)

[F10]

20 hours ago, Garfly said:

 

On this point we are all in furious agreement.

 

But given F10's savvy and experience he must have his reasons for complicating conventional wisdom with his practical observations.

Which is why I asked about the wind-shear 'exception'. I wondered if he meant that a quick 180 is a bit akin to rolling your own wind-shear.

Anyway, the theory around rapid turns within an air mass has long been debated.

Experts seem to disagree; that's nothing new in aeronautics. (Let's not get started on 'How does lift happen?"  ;- )

 

Yes you are quite right we "fly in a moving parcel of air" Wind drift on a navex is explained this way, which is fine. But it doesn't seem to quite fit when we are taking of in a "parcel of air" moving across the runway at 90 degrees...

 

Same thing here. If you turn rapidly (key word) downwind, your aircraft needs to be able to accelerate with that "parcel of air". Otherwise yes, very similar to windshear effect, turning rapidly downwind, you will see a drop on IAS in a light aircraft. you go rapidly from a headwind, to a downwind. We are talking a pretty fresh wind here, probably in the order of 15 kts. Remember you may be indicating 60 kts, but in a headwind, say after take off, your aircraft mass and therefore inertia, will only have your actual velocity to determine it, your GS in other words. (forget TAS for now, we are low). When you turn rapidly downwind, you have to accelerate your aircraft mass, to maintain speed, to a noticeably higher speed. It resists this due to inertia. Hope it makes sense? (-:

 

I was at a small country airshow, in South Africa, this guy in a microlight, similar to a thruster, but with a pusher engine/prop, flew down the runway and started doing steep turns in front of the crowd, (rapidly turning downwind). Unfortunately a strong surface wind of 15-20 knots. She staggered around in the first one and he kept turning...I turned back to a mate and said "this guys going to kill himself". As those last words were spoken, I heard the sickening metallic bang. I whipped around and there it was, tail straight up, nose first into the ground. Very not good.  

[facthunter]

Transitioning from a wheel directed path to one dependent on the air mass is often tricky BUT once airborne and at a reasonable height, the ground has no effect whatever on how the plane flys. It's likely the prang you witnessed is  because of the visual illusions of the pilot referencing the ground rather than flying with ball in centre and airspeed. A person unused to landing downwind will usually fly with too low an airspeed because it "feels" fast because the ground is close and the groundspeed is UP due the tailwind. Nev

[Garfly]

1 hour ago, F10 said:

Remember you may be indicating 60 kts, but in a headwind, say after take off, your aircraft mass and therefore inertia, will only have your actual velocity to determine it, your GS in other words. (forget TAS for now, we are low). When you turn rapidly downwind, you have to accelerate your aircraft mass, to maintain speed, to a noticeably higher speed. It resists this due to inertia. Hope it makes sense? (-:

I knew you'd have your reasons and your reasoning, F10.  I've followed this interesting debate among aeronauts for years.  But frankly, the 'parcel of air' conception still makes more sense to me, whether we're close to the ground or not.  As I understand that idea, the wing, along with its associated pitot/ASI, cares nought for the landlubbers' 'wind' nor the ground, for that matter. It cares only about the air molecules flowing by relative to itself. 

After all, when we take off in a stiff cross-wind, as soon as the wheels unload we're in no doubt that our aircraft has hopped aboard the air-mass train. We're instantly off in THAT direction unless and until we do something about it.

Yes, I suppose like the fly in the speeding train carriage we're slipping through the air but like the fly, surely we can never just "forget our TAS" (in favour of GS) while we're still flying.  Yes, it's the ground that may rise to smite us but only when the air decides to drop us. 

By the same token, then, I can't see a special need to "accelerate into our turn, downwind".   

 

But always happy to learn by being corrected.   ;- )

 

 

 

 

 

 

Edited May 26, 2022 by Garfly

[APenNameAndThatA]

Suppose you take off into the wind, have an engine failure and turn 180 degrees as you descend. In this case, your tail wind will decrease as you approach the ground, thereby actually increasing your performance!

 

The air moves slower closer to the ground. And Im not sating the effect is big. It’s like the Stinson crash, climbing with a tail wind, but different. 

 

F10 is incorrect (as we all are from time to time) but at least he’s polite about it! 

[Garfly]

 

For what it's worth, back in 2008, a couple of long running threads about this issue on Supercub.org involved some pretty sophisticated aeronautical theory, on both sides.  The arguments got pretty heated such that one contributor was prompted to write: 

 

"I think the single biggest problem with these type of discussions is that folks get so passionate about their stance that they begin to make blanket statements that are absolute and ambiguous at the same time."   

 

https://www.supercub.org/forum/showthread.php?33563-Downwind-Turns&s=4e085b14b628e1138e78f6dcfce72693

 

https://www.supercub.org/forum/archive/index.php/t-33563.html

 

And the beat goes on: an article in last month's Plane and Pilot 

 

The Downwind Turn: Hazard Or Fiction?

 

https://www.planeandpilotmag.com/article/downwind-turn/

 

 

Edited May 26, 2022 by Garfly

[kgwilson]

The difference between turning back and not turning back for most pilots and aircraft is you are more likely to have a controlled crash  or even a lucky out landing escape by not turning back.

[Garfly]

 

3 hours ago, kgwilson said:

The difference between turning back and not turning back for most pilots and aircraft is you are more likely to have a controlled crash  or even a lucky out landing escape by not turning back.

Actually, that was F10's main point.  It was the second part that stirred the possum.

On 24/05/2022 at 3:16 PM, F10 said:

Another thing I didn't see mentioned but may have missed it...I won't try a turnback under 500 ft in my Gazelle, regardless. Far less distractions and better options for a quick trouble shoot, by going straight ahead. But a major problem with turn backs is the wind. Taking off into a 10kt wind, of course means a 10Kt tailwind on landing. But even more critical, you will have to be able to accelerate in the turn to maintain a safe IAS, as you turn downwind. I am always amazed in a low inertia aircraft, how far down you need to stuff the nose, to maintain speed, turning rapidly downwind. I think there is a rule of thumb, but I would add at least 200Ft for every 10 kts of headwind.  

 

Edited May 27, 2022 by Garfly

[facthunter]

It's easy to check . Get up on a day with some steady wind and do a few medium  360 degree (or more) turns power on and level. IF you have an autopilot engage that. Once you're stabilised, you won't have to alter power.  Nev.

[Yenn]

The only reason to increase speed in a turn in any direction is to counter the effect of increased stall speed, caused by bank angle.

The biggest problem with flying close to the ground is that the pilot tends to think his observed ground speed is related to his air speed.

[facthunter]

That's why EVERYBODY should do low level training. Nev

[Garfly]

 

 

 

2 hours ago, facthunter said:

It's easy to check . Get up on a day with some steady wind and do a few medium  360 degree (or more) turns power on and level. IF you have an autopilot engage that. Once you're stabilised, you won't have to alter power.  Nev.

But F10's scenario involves "turning rapidly" so your leisurely 360 on AP is probably not going to test the theory.

 

On 26/05/2022 at 11:27 AM, F10 said:

Otherwise yes, very similar to windshear effect, turning rapidly downwind, you will see a drop on IAS in a light aircraft. you go rapidly from a headwind, to a downwind.

 

Anyway, I have my doubts about the phrase "you will see a drop in IAS in a light aircraft".  Really?  But how, in practice, can you see that?  Surely in any, quasi-emergency rapid 180, the ASI will be doing a merry jig (while we aim to tame the beast) so who's to say which jig, this way or that, indicates the "downwind turn effect" as opposed to, say, our ham-fisted stick work, that time?

Plus, I just can't conceive of an aerial reversal quick enough to approximate the 'shear' effect.  Soaring hawks don't turn on a dime and neither do Skyhawks.   

 

But who knows!?  If we could only see the damn air it'd be a lot easier to understand.

 

[Garfly]

52 minutes ago, Garfly said:

If we could only see the damn air it'd be a lot easier to understand.

 

Oh, wait ...

 

 

 

 

Nope, still hard to understand.   

 

Even on the basics, experts disagree:

 

 

YouTube Comment on "Airflow across a wing":
37rainman 

 

The "actual force upward" is caused by air molecules (mass) colliding with the wing and causing lift due to an equal and opposite reaction. Lift is not created by something happening somewhere "beyond the trailing edge". This does not in any way serve to deny that a part of the lift is attributable to the "shaped wing" concept, explainable by Bernoulli's principles.

 

 

 

 

 

 

 

Edited May 27, 2022 by Garfly

[facthunter]

Why would that statement be from an expert?? Nev

[Garfly]

He has the swagger of one.

 

But a better argument about experts disagreeing on basics is made in this Scientific American article from Feb. 2020

 

https://www.scientificamerican.com/article/no-one-can-explain-why-planes-stay-in-the-air/

 

 

No One Can Explain Why Planes Stay in the Air

Do recent explanations solve the mysteries of aerodynamic lift?

[excerpt]

In December 2003, to commemorate the 100th anniversary of the first flight of the Wright brothers, the New York Times ran a story entitled “Staying Aloft; What Does Keep Them Up There?” The point of the piece was a simple question: What keeps planes in the air? To answer it, the Times turned to John D. Anderson, Jr., curator of aerodynamics at the National Air and Space Museum and author of several textbooks in the field.

What Anderson said, however, is that there is actually no agreement on what generates the aerodynamic force known as lift. “There is no simple one-liner answer to this,” he told the Times. People give different answers to the question, some with “religious fervor.” More than 15 years after that pronouncement, there are still different accounts of what generates lift, each with its own substantial rank of zealous defenders. At this point in the history of flight, this situation is slightly puzzling. After all, the natural processes of evolution, working mindlessly, at random and without any understanding of physics, solved the mechanical problem of aerodynamic lift for soaring birds eons ago. Why should it be so hard for scientists to explain what keeps birds, and airliners, up in the air?

 

 

 

 

 

 

 

 

 

Edited May 27, 2022 by Garfly

[facthunter]

Lift is pure Newtonian physics. You have to apply them correctly though. Static plus dynamic pressures are a constant doesn't have much real meaning to most people but will pass the exam.   Wool tufts all over the wing show interesting effects, some air actually reversing direction  at high angles of attack.  Boundary layer control on the top surface etc. Nev

[Flightrite]

In over 42 years driving planes I no longer question what keeps us up, it just does, and that’s fine with me😂

[derekliston]

1 hour ago, Garfly said:

He has the swagger of one.

 

But a better argument about experts disagreeing on basics is made in this Scientific American article from Feb. 2020

 

https://www.scientificamerican.com/article/no-one-can-explain-why-planes-stay-in-the-air/

 

 

No One Can Explain Why Planes Stay in the Air

Do recent explanations solve the mysteries of aerodynamic lift?

[excerpt]

In December 2003, to commemorate the 100th anniversary of the first flight of the Wright brothers, the New York Times ran a story entitled “Staying Aloft; What Does Keep Them Up There?” The point of the piece was a simple question: What keeps planes in the air? To answer it, the Times turned to John D. Anderson, Jr., curator of aerodynamics at the National Air and Space Museum and author of several textbooks in the field.

What Anderson said, however, is that there is actually no agreement on what generates the aerodynamic force known as lift. “There is no simple one-liner answer to this,” he told the Times. People give different answers to the question, some with “religious fervor.” More than 15 years after that pronouncement, there are still different accounts of what generates lift, each with its own substantial rank of zealous defenders. At this point in the history of flight, this situation is slightly puzzling. After all, the natural processes of evolution, working mindlessly, at random and without any understanding of physics, solved the mechanical problem of aerodynamic lift for soaring birds eons ago. Why should it be so hard for scientists to explain what keeps birds, and airliners, up in the air?

 

 

 

 

 

 

 

 

 

Simple explanation, ignore the physics completely and call it what it is….Magic!!!

[rgmwa]

In summary, the air moving over the wing mostly holds it up, but sometimes it doesn't. 

 

[Garfly]

1 hour ago, derekliston said:

Simple explanation, ignore the physics completely and call it what it is….Magic!!!

 

Yeah, I'm also happy to put physics aside in favour of practical stick and rudder know-how.

My point (poorly communicated) was just to urge tolerance of alternate explanations when even the physicists can't agree.  

However, I should have taken my own counsel of a few posts back   "(Let's not get started on 'How does lift happen?"  ;- ) " 

 

Anyway, even if (as argued in the Plane and Pilot article, above) the hazard of the "downwind turn" is a myth

  "...  so long as pilots believe it, they're more likely to pay careful attention to their airspeed when they're close to the ground and especially on low altitude turns ... "

 

So all good.

 

 

 

Edited May 27, 2022 by Garfly

[kgwilson]

All the aerodynamic theories of Bernoulli, mathematicians, physicists, scientists, aeronautical engineers etc is BS.

 

I know what it is, IT IS MAGIC. Proof below.

 

[facthunter]

Showing pressure measurements around an airfoil section is useful in showing where lift is generated. Halve the airflow speed and you get 1/4 the lift. (It's V squared law). When an airflow is curved the low pressure is on the concave side of the flow lines. Has to be or it wouldn't change direction. Nev

[CT9000]

Could not help butting in on this one. It is not magic that makes planes fly it is money..... The bigger the faster the newer the heavier all need more money for each step up and lots of it.

[F10]

Well from practical experience, turning downwind during air shows and in other instances, I’ve had to roll off bank, to reduce my rate of turn, as I’ve noticed my airspeed wavering and dropping slightly as I turned. I put it down to the rate of turn, being too high so as to induce a tail wind component. This is not a large effect, I’m not saying you will wash of 20 knots turning downwind in a 20Kt wind, but I’ve seen the airspeed wavering and dropping slightly. When you are in a low energy aircraft, as I was in this case, we’ll that’s sure what it felt like to me. I still stand by my assertion that be very careful turning downwind with a high rate of turn, low speed, in a strong wind. Let’s say, a Tiger Moth was basically hovering in a 60 Kts wind. Th pilot rolls on 45 degrees of bank and turns through 180 degrees, I think he will notice a drop in airspeed, my experiences says so. Yes, doing leisurely turns on autopilot, isn’t going to show this up. I see one member is keen to paste warning signs on my posts, we’ll that’s fine, I still stand by what I’ve experienced. Won’t comment on this further, parcel of air theory is fine and I accept that in many scenarios, but I think there are some situations that it doesn’t quite cover.

[Garfly]

On 27/05/2022 at 7:33 PM, derekliston said:

ignore the physics completely and call it what it is….Magic!!!

That ain't magic ...      (THIS is magic ...  ;- )

 

 

 

and maybe this ...

 

 

 

Edited May 29, 2022 by Garfly

[kgwilson]

Nope, Bluetooth is complex but entirely explainable with zeros and ones, algorithms using packet data and spread spectrum technology over very short range in the 2.4ghz spectrum & so I imagine drones use similar technology but over a different radio spectrum and have physical interfaces via electric motors controlled by the software.