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The unstallable plane that stalled

fearoflanding.com

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Re: The unstallable plane that stalled

#161

Post by speedbird »

sumofproducts wrote: post #35
the__alchemist wrote: post #24

Soapbox: Stall speed is an approximation. It's baffling that GA aircraft don't have one of the most safety-critical measurements: AOA. Stall airspeed varies with a number of factors; this includes the mods described in the article, and weight change from burning fuel, passengers, payload etc. AOA is more invariant to that as a metric for choosing stall speed, speed down final etc.

I was very skeptical of this until I had the chance to fly one of those brand-new C172 models that come equipped with 'em. They're so convenient! Sure, ye olde haptic feedback + inner ear + stall horn/shaker combo has always worked for me—but if you are a new or overwhelmed or complacent or unlucky pilot, having a big angry indicator sitting atop the glare shield furiously (visually & audibly) informing you of the ap…

This +++. Most important parameter is AoA and we only have poor proxy for it in most GA. Nuts

Re: The unstallable plane that stalled

#162

Post by fransje26 »

WalterBright wrote: post #68
jcalvinowens wrote: post #17

It is not necessary to empirically determine a specific airplane's stall speed in order to operate it safely. It's not required in the US, we just use the number the manufacturer publishes. It's normal for airplanes of the same model to fly differently: I fly a little fleet of six Citabrias, and their stall characteristics are radically different. You'd expect more uniformity from a modern aluminum airplane, but stil…

> nobody should be flying an airplane like this so close to the edge the exact stall speed needs to be known numerically within one knot. An experienced pilot can feel the stall coming on with a bit of a "burble" in the stick. My dad (fighter pilot) told me that knowing exactly where the stall point is is life and death. When you're in a dogfight, the winner often is the one that can turn inside the other. Turning as…

> An experienced pilot can feel the stall coming on with a bit of a "burble" in the stick.

Without any disrespect to the flying abilities of your Dad, as an aerospace engineer, the short answer to that is "no".

You will have the luck to feel a "burble" if the airplane has been been built to be give you that warning. You have absolutely no guarantee that once the airplane has been modified beyond its original configuration, you will get any form of warning. This extreme behavior is actually partly present in the current case, with the stalling point jumping from the wing tip immediately to the wing root. That's no good.

It can be even worse if you're flying a plane that is licensed under the "experimental" category by the FAA. One of the preferred airfoil for some time was the NACA 5-series, as it can have very little lift-induced pitching moment. It has also criminal stalling characteristics with absolutely no warning. Something beautifully illustrated by the following lift polar:

https://media.cheggcdn.com/media/76b/76b33250-7f26-41f6-8f2c...

Re: The unstallable plane that stalled

#163

Post by fransje26 »

jcalvinowens wrote: post #17

It is not necessary to empirically determine a specific airplane's stall speed in order to operate it safely. It's not required in the US, we just use the number the manufacturer publishes. It's normal for airplanes of the same model to fly differently: I fly a little fleet of six Citabrias, and their stall characteristics are radically different. You'd expect more uniformity from a modern aluminum airplane, but stil…

> It is not necessary to empirically determine a specific airplane's stall speed in order to operate it safely. It's not required in the US, we just use the number the manufacturer publishes.

It is not necessary as in "there is no legal obligation", true.

But if you want to live, it is absolutely necessary. The numbers provided by the manufacturer will tell you absolutely nothing about the stalling characteristics of the airplane as soon as you start modifying it.

The non-linearity of the phenomena involved in stalling also mean that "intuition" and "small changes" will be of absolutely not help to determine by how much you changed the characteristics of your airplane.

Re: The unstallable plane that stalled

#164

Post by jnsaff2 »

ExoticPearTree wrote: post #158
the__alchemist wrote: post #24

Soapbox: Stall speed is an approximation. It's baffling that GA aircraft don't have one of the most safety-critical measurements: AOA. Stall airspeed varies with a number of factors; this includes the mods described in the article, and weight change from burning fuel, passengers, payload etc. AOA is more invariant to that as a metric for choosing stall speed, speed down final etc.

> Stall speed is an approximation. It's baffling that GA aircraft don't have one of the most safety-critical measurements: AOA. All aircraft equipped with a six pack, you have an artificial horizon indicator which can tell you what is your angle of attack. And Cessna's have them in all planes, even 50-60 years old ones.

The angle of attack is the angle between the chord line of the wing and the oncoming air (or relative wind). This is distinct from what the artificial horizon measures. The artificial horizon is concerned with the aircraft's orientation relative to the gravitational pull of the Earth, indicating whether the nose of the aircraft is above or below the horizon and how much the wings are tilted relative to the horizon.

Artificial horizon is not a reliable indicator of angle of attack.

Re: The unstallable plane that stalled

#165

Post by michaelt »

dramm wrote: post #119
avianlyric wrote: post #109

Earlier quoted context omitted.

As noted in the article, the plane had been modified with far more than just the STOL kit. > A further issue was that his Cessna 185 had been extensively modified. The addition of floats, cargo pack, short take-off and landing kit and a three-blade propeller had never had their combined effect documented. That’s a lot of things that modify the flight characteristics of a plane, all interacting together in what seems…

A three bladed prop modification along with floats is very common. Wipaire, the leading float manufacturer has its own STC for that. In combination with STOL kits is not uncommon either. I expect the Robinson STOL STC explicitly accommodates floats (Wipaire’ STOL STC sure do) but not sure since I don’t have the paperwork in front of me. You are over inflating issues here. Are you a pilot? The issue here is straight u…

I get what you're saying, and I agree this sounds like operator negligence to me.

But the article does say that investigators had to get another aircraft set up with the same modifications and fly it around with bits of wool all over it in order to understand the stall characteristics.

So I assume this plane setup isn't so widespread that its stall behaviour is common knowledge.

Re: The unstallable plane that stalled

#166

Post by psunavy03 »

datascienced wrote: post #153
JumpCrisscross wrote: post #147

Earlier quoted context omitted.

> An experienced pilot can feel the stall coming on with a bit of a "burble" in the stick Stall recovery has also been an essential part of my flight training.

Although can you recover at a height 15m above terrain?

. . . probably not, but does that mean you never practice? Most stall/spin incidents occur at low altitude, but not THAT low. It's often pilot inattention in the landing pattern.

Re: The unstallable plane that stalled

#167

Post by I_Am_Nous »

fransje26 wrote: post #162
WalterBright wrote: post #68

Earlier quoted context omitted.

> nobody should be flying an airplane like this so close to the edge the exact stall speed needs to be known numerically within one knot. An experienced pilot can feel the stall coming on with a bit of a "burble" in the stick. My dad (fighter pilot) told me that knowing exactly where the stall point is is life and death. When you're in a dogfight, the winner often is the one that can turn inside the other. Turning as…

> An experienced pilot can feel the stall coming on with a bit of a "burble" in the stick. Without any disrespect to the flying abilities of your Dad, as an aerospace engineer, the short answer to that is "no". You will have the luck to feel a "burble" if the airplane has been been built to be give you that warning. You have absolutely no guarantee that once the airplane has been modified beyond its original configur…

Is it possible there's a mechanical/design cutoff where most planes designed to be fully mechanical would feel the "burble" while a more modern plane would not, similar to ABS vs non-ABS brakes or powersteering vs none? Are there hydraulic assists for flight controls that might smooth out those mechanical tells?

Re: The unstallable plane that stalled

#168

Post by jcalvinowens »

fransje26 wrote: post #162
WalterBright wrote: post #68

Earlier quoted context omitted.

> nobody should be flying an airplane like this so close to the edge the exact stall speed needs to be known numerically within one knot. An experienced pilot can feel the stall coming on with a bit of a "burble" in the stick. My dad (fighter pilot) told me that knowing exactly where the stall point is is life and death. When you're in a dogfight, the winner often is the one that can turn inside the other. Turning as…

> An experienced pilot can feel the stall coming on with a bit of a "burble" in the stick. Without any disrespect to the flying abilities of your Dad, as an aerospace engineer, the short answer to that is "no". You will have the luck to feel a "burble" if the airplane has been been built to be give you that warning. You have absolutely no guarantee that once the airplane has been modified beyond its original configur…

> You will have the luck to feel a "burble" if the airplane has been been built to be give you that warning.

Airplanes which are designed to do this (most airplanes) do it very reliably, it's not luck. Several of the Citabrias I fly don't have stall horns, all I have is the buffet.

Complexity is always a tradeoff: it's harder to fuck up building and/or repairing a simpler airfoil.

Re: The unstallable plane that stalled

#169

Post by singleshot_ »

WalterBright wrote: post #68
jcalvinowens wrote: post #17

It is not necessary to empirically determine a specific airplane's stall speed in order to operate it safely. It's not required in the US, we just use the number the manufacturer publishes. It's normal for airplanes of the same model to fly differently: I fly a little fleet of six Citabrias, and their stall characteristics are radically different. You'd expect more uniformity from a modern aluminum airplane, but stil…

> nobody should be flying an airplane like this so close to the edge the exact stall speed needs to be known numerically within one knot. An experienced pilot can feel the stall coming on with a bit of a "burble" in the stick. My dad (fighter pilot) told me that knowing exactly where the stall point is is life and death. When you're in a dogfight, the winner often is the one that can turn inside the other. Turning as…

Not really, as to your final point; the race driver’s skill is not in avoiding the slide, but — with the mechanic’s help — finding it, and using it. Recall: loose is fast, and on the edge of out of control.

Re: The unstallable plane that stalled

#170

Post by Wistar »

schoen wrote: post #128
Wistar wrote: post #72

Earlier quoted context omitted.

I have been a passenger in a C-170 with a STOL kit that flew backwards over a beach on the Washington coast. We landed well behind where we took off. The takeoff and landing were both nearly vertical. Had a steady wind from the ocean.

Was that intentional or unintentional?

Intentional. The pilot was very good at it and his airplane, a highly-modified 170, had exceptional performance.
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