I can't make sense of this crash

[denverpilot]

It is not the spin itself, but the recovery that causes stress. As soon as you stop the rotation with opposite rudder, the aircraft is in a straight-down dive (actually slightly more than straight down), and will build up speed extremely quickly. That's the difference between a one-rotation spin and a five-rotation spin. Once autorotation has developed, it will take more time to stop the rotation, during which time the airplane will build up a high forward speed. A one-rotation spin can be stopped quickly, so less speed will be built during recovery. I agree that in any case the airplane should withstand 3.8G up to maneuvering speed, but that is for an airframe that has not been previously abused. I have yet to see a spin that did not cause a substantial g-force during recovery. I don't have numbers because I never flew with a g-meter. But if the wings or elevator were going to give out, that would be the time.

Speed doesn’t increase load very much.

Most trainers have seen much higher instantaneous loads in bad student landings and steep turns, than they’ll ever see in a lifetime of spin recoveries into dives.

*As long as the student doesn’t pull / the instructor blocks the yoke from aft travel.

If spin recoveries were pressing you into the seat harder than a 60 degree steep turn, they weren’t being done right, in something only rated for Utility Category. And we all go do steep turns all the time.

There’s no reason at all for a spin recovery to be a high G maneuver unless that’s the desired outcome.

Admittedly though it’s a pretty good way if you get the power back up to start a loop in the Citabria... Might as well use that nose down energy and add to it to get started.

Even that isn’t a high G maneuver though.

 

[Dan Thomas]

Once autorotation has developed, it will take more time to stop the rotation, during which time the airplane will build up a high forward speed. A one-rotation spin can be stopped quickly, so less speed will be built during recovery.

Hold on there. In the spin, the wings are stalled, which means huge drag, which means that huge speed cannot build. Only after rotation stops and the stall broken will the speed come up. Been there, done that as an instructor.

And the airplane isn't pointing straight down. It's still just a steep nose-down atttitude. It just SEEMS vertical. If it was pointing straight down, the wings wouldn't be stalled and we wouldn't be in a spin. It would be something else. A vertical attitude and vertical flight path means zero angle of attack, not stall AoA.

 

[Dan Thomas]

I don’t have a 172 POH infront of me, but spins with a rear pax seems like it wouldn’t be in utility catagory

You are right. They shouldn't have been spinning that thing at all.

 

[sarangan]

Hold on there. In the spin, the wings are stalled, which means huge drag, which means that huge speed cannot build. Only after rotation stops and the stall broken will the speed come up. Been there, done that as an instructor.

And the airplane isn't pointing straight down. It's still just a steep nose-down atttitude. It just SEEMS vertical. If it was pointing straight down, the wings wouldn't be stalled and we wouldn't be in a spin. It would be something else. A vertical attitude and vertical flight path means zero angle of attack, not stall AoA.

Rotation does not have to completely stop for the stall to break. As the rotation rate starts to slow, the plane will transition from autorotation to a spiraling dive. Even if I held the elevator full aft, it will still dive for a second or two before the nose comes up. How much speed it will build during this time depends on how slippery the airframe is, and power setting. When I used to do spins a lot, I got pretty good at minimizing this recovery time, but in most training environment there is no telling how much speed the airplane builds before they pull out of the dive.

Additionally, I believe it is at least theoretically possible to be pointing straight down in an autorotation. The stalled condition arises from the descending wing having a higher angle of attack than the rising wing, so that could happen at any pitch attitude.

 

[Juliet Hotel]

You guys know more about this stuff than I, but if both wings came off at the same time, couldn't that be sabotage?

Don't mean to get all spooky and Twilight Zone here, but I could understand if *one* wing came off, the plane gyrated wildly, and the other one came off shortly thereafter. But both at the same time? Or can eyewitnesses really tell on something like this?

Just curious.

This isn't my personal area of expertise but years back I had a conversation on this topic with a guy who was an accident investigator in the military. According to him when you stress the airframe enough to pull a wing off, both wings always fail, always one a fraction of a second behind the other. To the outside observer it looks like they both come off at the same time. He said that in low wing planes, the wings bend up and back into the airframe when they fail, often slicing the tail off the plane when they hit. He said you can tell which wing failed first in that scenerio because one wing will have leading edge damage (from going through the tail) and the other leading edge will be undamaged (because the tail was no longer there).

With a struted wing 172, it sounds like they just fold up and back and the tail stays with the airframe.

 

[Eric Gleason]

Two weeks ago on July 19, I was out doing stalls and spins in one of the Cubs.
Two other guys flew it in the intervening time after I did and didn't report any problems.
On Monday, July 30, I grabbed the left wing to give it a shake (to test the bungee cords on the landing gear) and the wing went "POP"!
Pure, unadulterated luck because I ALWAYS grab the right wing as I go past to put my gear inside.
It appears a bunch of wood parts in the left wing came unglued. It's 77 years old, so It shouldn't be a surprise.

Seems like you've had a string of luck this year finding potentially disastrous problems before going flying. How long ago was the gouge in the prop?

Glad to hear I'm not the only one who shakes wings. I learned it flying gliders, but I still do it with the powered planes too. Helps water shake out of wrinkles in the fuel tanks, finds loose parts/rivets/etc. I shake the tail, too. So far the worst thing I've found was a little water and a washer.

 

[Dan Thomas]

Additionally, I believe it is at least theoretically possible to be pointing straight down in an autorotation. The stalled condition arises from the descending wing having a higher angle of attack than the rising wing, so that could happen at any pitch attitude.

What you believe or do not believe does not change the facts. (A famous Boeing engineer said that.) An airplane pointing straight down and travelling straight down has an AoA of zero or close to it and cannot be stalled. Geometry and physics do not conform to wishful thinking or personal opinions.

The differential in AoA that causes the spin arises from the fact that the airplane is following a helical path. Can't do that by travelling straight down.

 

[Kenny Phillips]

pre-existing structural damage?

Many times, when a plane dismantles itself in the air, they find that the primary structural issue was the upward failure of the tail plane (typically pilot induced). After that, a high-speed dive is inevitable.

 

[Matthew]

I remember when this happened:

https://www.ntsb.gov/_layouts/ntsb.aviation/brief.aspx?ev_id=20060615X00738&key=1

In flight breakup of a Saratoga.

This is an example of Va.

He was descending into Kansas City International (MCI) and let his speed get to just below Vne. Maybe that was unintentional, maybe not.

Problem was, a 737 had passed that same spot about 600' above and 2 minutes earlier. The Piper hit the 737 wake and lost both sides of the stabilator and the left wing.

 

[sarangan]

What you believe or do not believe does not change the facts. (A famous Boeing engineer said that.) An airplane pointing straight down and travelling straight down has an AoA of zero or close to it and cannot be stalled. Geometry and physics do not conform to wishful thinking or personal opinions.

The differential in AoA that causes the spin arises from the fact that the airplane is following a helical path. Can't do that by travelling straight down.

Lets say, vertical speed = 3000 fpm (30 knots) 90-deg nose down. Airplane spinning axially at a rate of 0.5 rev/sec. Wing span = 25 ft. Lateral velocity of each wing tip will be +/- 22 knots. AOA of one wing will be +36 deg and other wing will be -36 deg. At middle of the wing, the AOA will be roughly half. So it is possible for one wing to be stalled and the other wing to be producing lift.

 

[3393RP]

Does this sound familiar?
http://www.aopa.org/asf//ntsb/narrative.cfm?ackey=1&evid=20030325X00386

I found this astounding statement in the NTSB report.

Examination of the crash site revealed the airplane collided with the ground.

 

[jaymark6655]

Lets say, vertical speed = 3000 fpm (30 knots) 90-deg nose down. Airplane spinning axially at a rate of 0.5 rev/sec. Wing span = 25 ft. Lateral velocity of each wing tip will be +/- 22 knots. AOA of one wing will be +36 deg and other wing will be -36 deg. At middle of the wing, the AOA will be roughly half. So it is possible for one wing to be stalled and the other wing to be producing lift.

0.5 rev/sec? I don't it would have any AOA because the wings would gone. Would't the wing tip be traveling at 46.5 kts lateral?

 

[Dan Thomas]

Lets say, vertical speed = 3000 fpm (30 knots) 90-deg nose down. Airplane spinning axially at a rate of 0.5 rev/sec. Wing span = 25 ft. Lateral velocity of each wing tip will be +/- 22 knots. AOA of one wing will be +36 deg and other wing will be -36 deg. At middle of the wing, the AOA will be roughly half. So it is possible for one wing to be stalled and the other wing to be producing lift.

Let me get this straight: You're saying that with the nose straight down, the descent rate is 3000 FPM, which is the same as 34 MPH. You'd better start studying real textbooks. No airplane is going to do only 34 MPH in a vertical dive, rotating or not.

 

[Matthew]

I found this astounding statement in the NTSB report.

Examination of the crash site revealed the airplane collided with the ground.

A guy I used to work with was big into skydiving. He was whatever the equivalent is of a Grandmaster Golden Seal CFI. I was talking to him at his desk one day and flipped through his skydiving magazine. The back pages had accident reports. They all ended with, "Cause of death: impact with the ground."

 

[Capt. Geoffrey Thorpe]

0.5 rev/sec? I don't it would have any AOA because the wings would gone. Would't the wing tip be traveling at 46.5 kts lateral?

2-3 seconds per turn is about right for a 150.

 

[sarangan]

Let me get this straight: You're saying that with the nose straight down, the descent rate is 3000 FPM, which is the same as 34 MPH. You'd better start studying real textbooks. No airplane is going to do only 34 MPH in a vertical dive, rotating or not.

The calculation is valid for whatever forward speed you pick - one wing will have a higher AOA than the other in a rotation. Its the magnitude of the AOA that changes. Pitch of the airplane does not enter into this analysis. I am sure it is not 100% accurate, nor am I an expert on aerodynamics of spins - this was just an opening for a fruitful discussion. However, so far you have not offered any quantitative analysis, insights or references, except criticisms and insults, so I'll stop this discussion here.

 

[jaymark6655]

I think this might go back to the whole "can a wing stall in a steep turn if the plane is descending", if its nose down does the AOA matter if the wings aren't being used to provide lift?

 

[denverpilot]

This thread needs a conveyor belt now.

 

[Dan Thomas]

The calculation is valid for whatever forward speed you pick - one wing will have a higher AOA than the other in a rotation. Its the magnitude of the AOA that changes. Pitch of the airplane does not enter into this analysis. I am sure it is not 100% accurate, nor am I an expert on aerodynamics of spins - this was just an opening for a fruitful discussion. However, so far you have not offered any quantitative analysis, insights or references, except criticisms and insults, so I'll stop this discussion here.

https://www.av8n.com/how/htm/spins.html

 

[Stephen Poole]

... when you stress the airframe enough to pull a wing off, both wings always fail, always one a fraction of a second behind the other. To the outside observer it looks like they both come off at the same time.

Ah. OK, thanks.

 

[Brad Smith]

I realize this is an old thread, but if we switch the subject aircraft from a 172 to a 150 Aerobat, are there a lot of inflight breakups of Aerobats on record? I used to do aerobatics (basic inside maneuvers) in those and it seems that it would be easy to let the speed get out of control on the down line resulting in a breakup. Any data on accidents regarding Aerobats performing aerobatics?

 

[Shepherd]

Having the letters "CFI" after a name does not always equate with wisdom, ability or good sense.
The 172 I flew for years was involved in a fatal accident with a CFI, a young female student and her father on board.
They were already in trouble (weight) before the plane took off. When they landed on a soggy grass strip 10 minutes later, they were only one bad decision away from death.
One bad decision later the CFI was dead, the young lady and her father were in critical condition.
No one saw the accident occur, and the two survivors had so much head trauma they don't remember what happened.

 

[flyingron]

I realize this is an old thread, but if we switch the subject aircraft from a 172 to a 150 Aerobat, are there a lot of inflight breakups of Aerobats on record? I used to do aerobatics (basic inside maneuvers) in those and it seems that it would be easy to let the speed get out of control on the down line resulting in a breakup. Any data on accidents regarding Aerobats performing aerobatics?

As I pointed out in another thread, there have been no in-flight breakups of A152s. In fact, there's only been 11 fatals total. Exceeding the structural limits contributed to none of them. There were three VFR-into-IMC, four stall-spins at low altitude, one failed loop (collide with terrain), and passenger who got hit by the prop while pulling the chock.

 

[Brad Smith]

Thanks. No worries about structural failures even when used for basic aerobatics. About as safe as you can get.

 

[flyingcheesehead]

Still no final report out on the original accident. I guess the NTSB can't make sense of it either...

 

[IK04]

Suicide?

 

[SToL]

Damping**** You didn't make the system moist.

How do you know?

 

[SToL]

It is not the spin itself, but the recovery that causes stress. As soon as you stop the rotation with opposite rudder, the aircraft is in a straight-down dive (actually slightly more than straight down)

WTF kind of spins are doing son?

 

[SToL]

Having the letters "CFI" after a name does not always equate with wisdom, ability or good sense.

Sadly this is too true. There's plenty of high time instructors out there who have very little real experience.

I like the way they do it in Europe. You spend a career flying, and then you retire and start instructing.

 

[midwestpa24]

WTF kind of spins are doing son?

 

[Capt. Geoffrey Thorpe]

https://www.kxly.com/news/moody-aviation-shares-names-of-victims-killed-in-plane-crash/769651663

https://app.ntsb.gov/pdfgenerator/R...tID=20180713X54012&AKey=1&RType=HTML&IType=FA

My friend's sister attended this school (not in the aviation program) and knew one of the victims. I'm having trouble understanding how a C172 had an in-flight breakup like this in visual conditions.

Not the first.
https://aviation-safety.net/wikibase/45309

 

[Snowmass]

Suicide?

Seems the most likely. Moody is a religious school which could provide a revenge or other motive by a fanatic. Both wings at the same time says a deliberate vertical dive and a last minute recovery attempt.

 

[Jaybird180]

I'm interested in the final report on this one.

 

[WDD]

Seems the most likely. Moody is a religious school which could provide a revenge or other motive by a fanatic. Both wings at the same time says a deliberate vertical dive and a last minute recovery attempt.

Yeah - because being Christian means more likely to be a fanatic suicide wack job. Indoctrination in the Gospel about loving each other, service to people, humility, etc. leads directly to killing yourself in a Cessna.

 

[Capt. Geoffrey Thorpe]

I'm interested in the final report on this one.

I got $10 that says the probable cause will be "The pilot's inflight loss of control and the pilot's failure to recover from the resultant dive for unknown reasons which resulted in flight beyond the design stress limits of the airplane and subsequent in flight airframe breakup." Just like before.

 

[midwestpa24]

I got $10 that says the probable cause will be "The pilot's inflight loss of control and the pilot's failure to recover from the resultant dive for unknown reasons which resulted in flight beyond the design stress limits of the airplane and subsequent in flight airframe breakup." Just like before.

Pretty much. Not much else to go on after the fact.

 

[Jaybird180]

I'm wondering if they can determine if the fore or aft wing attachment bolts came loose, resulting in a change of wing incidence inflight, making the airplane difficult to control in pitch.

 

[Dan Thomas]

I'm wondering if they can determine if the fore or aft wing attachment bolts came loose, resulting in a change of wing incidence inflight, making the airplane difficult to control in pitch.

Nope. If they come loose, which is really unlikely, the incidence would only change if the eccentrics were rotated, which is even less likely. They're difficult enough to rotate when adjusting the stuff. The adjustment is very, very small anyway, nowhere close enough to cause control difficulties. If the bolt and eccentrics came right out, the wing would tear off instantly. Those bolts are under shear load all the time and would be very difficult to remove in flight, too, even if the nuts weren't there.

 

[Shepherd]

Seems like you've had a string of luck this year finding potentially disastrous problems before going flying. How long ago was the gouge in the prop?

Glad to hear I'm not the only one who shakes wings. I learned it flying gliders, but I still do it with the powered planes too. Helps water shake out of wrinkles in the fuel tanks, finds loose parts/rivets/etc. I shake the tail, too. So far the worst thing I've found was a little water and a washer.

I didn't get as old as I am old by being sloppy. I check EVERYTHING before I get in the plane. Especially when I fly pre-war aircraft.

 

[Kenny Phillips]

Yeah - because being Christian means more likely to be a fanatic suicide wack job. Indoctrination in the Gospel about loving each other, service to people, humility, etc. leads directly to killing yourself in a Cessna.

You left out the bad stuff. And there's a lot of it.