Bonanza breakup video analysis, how does it affect Mooney?

[RescueMunchkin]

4 minutes ago, EricJ said:

Yes, it's trimmed for a much lower speed, so it tries to pitch up to reduce airspeed.   Pushing forward reduces the rate of pitch-up to reduce the g-load in the recovery.

 

18 minutes ago, Fly Boomer said:

That's what I was imagining.  As you approach VNE, if it's still trimmed for a lower speed, it will probably want to go straight up unless you push.

 

OK, but I'm also imagining that seat of the pants would allow the pilot/passengers to feel those kinds of g-forces pushing them down into their seat and a pilot who is aware of their sensations would want to pitch down to compensate for that anyways?

Edited June 12 by RescueMunchkin

[DXB]

On 6/8/2024 at 10:22 PM, Hank said:

Vne for my C is 200 mph = 175 knots.

Older models have lower Vne. 175 mph? 185 mph? I forget.

This is where units are important. 175 mph is indeed the top of the green / bottom of the yellow on my airspeed indicator. 

FWIW in 1969, Vno went from 150 to 175mph and Vne went from 189 to 200mph for the short bodies without any structural change to justify it.  

[Vance Harral]

37 minutes ago, RescueMunchkin said:

OK, but I'm also imagining that seat of the pants would allow the pilot/passengers to feel those kinds of g-forces pushing them down into their seat and a pilot who is aware of their sensations would want to pitch down to compensate for that anyways?

Your reasoning is logical, but that's not the way humans work.

I've given about 1000 hours of instruction.  That's not much compared to folks here with a lot more experience, but it's enough for me to have put a large number of pilots with varying experience in situations that make them slightly to largely uncomfortable, in a distracting environment.  The idea that pilots will make a rational response to specific problems based on logic like you're stating here, just ain't true.  I've seen pilots either lock up, or react "backwards" to all kinds of warning indicators: horns, buzzers, G-loads and so forth.  And these are smart people who can tell you all the right answers on the ground over coffee.  So I know based on what I've seen with my own eyes, that no one should take any comfort whatsoever from the idea they would "naturally" react properly to an unusual situation.

The best you can do is actually induce the situation, and train for the recovery, until it hopefully becomes instinctual to do the right thing.  Not instinctual because it's "logical", but just because it's what you did the last N times you actually experienced that situation, in training.  Deliberately putting yourself in such situations with an instructor is reasonable for a certain class of problem: stalls, spiral divergence, etc.  That's what Scott is doing in the video.  There's another class of problem where it's not reasonable to deliberately put yourself in the situation in anything other than a simulator, e.g. engine failure immediately after takeoff.  I try to get in the simulator to practice those sorts of things, but I don't do it as often as I should, and I don't suffer from any illusion that I'd be ice cool and always do the right thing in a pressure situation I've rarely or never experienced.  I try my best to convince other pilots the same.

[dkkim73]

1 hour ago, RescueMunchkin said:

Recovery is to roll back to wings level and push forward on the yoke, but why push forward?  Wouldn't pushing forward cause even more increase in speed?  Or is it that the trim of the aircraft is trying to cause too much pitch up and potentially overstresses the airframe if pitch is left unchecked?

Yeah, the intent is to avoid heavily loading the wing and, exactly as you say, the high speed in that nose-down orientation will naturally cause pitch up at that trim setting. It is trimmed for higher angle of attack (lower speed) but the plane is whipping along at a low angle of attack (high speed). 

Can be even more extreme with a lot of nose down and high bank. I think of it as "*unload the wing* (as needed, say if you've already inadvertantly started pulling), roll upright, then actively manage the recovery (which involves holding forward pressure to slow the pull-out and thus manage g-load)". 

HTH

[dkkim73]

On a positive note, I was impressed by the beefiness of the main (carry-through) spar on the wing. Here are a couple of photos I took of the last wing on the line when I was visiting Mooney in February (edit to add: it's not fully-built, but shows the center spar): 

[Fly Boomer]

4 hours ago, RescueMunchkin said:

 

 

OK, but I'm also imagining that seat of the pants would allow the pilot/passengers to feel those kinds of g-forces pushing them down into their seat and a pilot who is aware of their sensations would want to pitch down to compensate for that anyways?

I suppose, but I would probably forget the passengers, and focus on keeping the wings and tail attached.

[Ragsf15e]

6 hours ago, RescueMunchkin said:

I watched the youtube video posted above and am having trouble understanding why the recovery they stated is to push forward on the yoke.  Here's what's happening as I understand it:

After rolling to 45 and letting go, the plane gets faster and the bank angle wants to increase.  They recover at 60 degrees of bank or 140KIAS, whichever comes first

Recovery is to roll back to wings level and push forward on the yoke, but why push forward?  Wouldn't pushing forward cause even more increase in speed?  Or is it that the trim of the aircraft is trying to cause too much pitch up and potentially overstresses the airframe if pitch is left unchecked?

In addition to what others said about reducing the G in the pullup after rolling level, there are two other reasons to push forward and reduce the G load prior to rolling level.  First, the airplane (any airplane?) rolls much better with less G load, second, while not published, the rolling G structural limit is generally much less than the published “straight pull” limit.  Even in something tame like a Citabria or C-152, you can put a couple Gs on it and see the reduced roll capability.  Most aerobatic aircraft have a rolling G limit too.  None of this means you need to completely unload and throw everything off the floor, but a quick unload/power reduction, roll level, then feed the g back in gently to get the nose back up works best.

[kortopates]

FWIW in 1969, Vno went from 150 to 175mph and Vne went from 189 to 200mph for the short bodies without any structural change to justify it.  

I don’t really know for a fact but my understanding is that cowling improvements were made to allow the Vne increase.


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[philiplane]

On 6/8/2024 at 8:15 AM, 201er said:

If the wings remain attached, it still leaves some possibility of a late recovery 

Unfortunately the tail comes off first in most cases

[Pinecone]

On 6/12/2024 at 7:17 PM, Ragsf15e said:

In addition to what others said about reducing the G in the pullup after rolling level, there are two other reasons to push forward and reduce the G load prior to rolling level.  First, the airplane (any airplane?) rolls much better with less G load, second, while not published, the rolling G structural limit is generally much less than the published “straight pull” limit.  Even in something tame like a Citabria or C-152, you can put a couple Gs on it and see the reduced roll capability.  Most aerobatic aircraft have a rolling G limit too.  None of this means you need to completely unload and throw everything off the floor, but a quick unload/power reduction, roll level, then feed the g back in gently to get the nose back up works best.

For example, the F-15 has a 9G limit.  Rolling, the limit is 2.5G.

The faster the aircraft is capable of rolling, the lower the rolling G limit.  When rolling, on the upgoing wing,  you have both the symmetrical load and the load of the rolling.

And if you need to roll quickly, a hard push to 1G or less is a very good thing.  

[Jerry 5TJ]

On 6/9/2024 at 1:19 PM, Shadrach said:

The numbers to calculate for my bird would be as follows:

Vne = 175kias
Vs1 = 58kias 

Max G available = 9.103

He uses:

Vne = 175kias
Vs1 = 63kias 

Max G available = 8

The number’s he uses are not representative of any Mooney with which I am familiar.

The point of the simple equation 

     g max = (airspeed/stall speed)^2

is that the wing will generate a lot more lift than the 1 g weight of the aircraft and the max g load goes up as the square of the ratio of airspeed to stall speed.  

If the plane’s airspeed is 3x the stall speed in that configuration then the wing can theoretically generate 9 g before stalling.  In most GA airplanes the structure will fail before reaching that load.   

In a loss of control event a low drag plane (Mooney, Bonanza, Mirage, whatever) can easily reach 3 or even 4 times the stall speed and great care is required to keep the g load within limits during recovery.  
 
Even in a draggy 172 it’s possible to get to 3X stall speed and destroy the airframe unintentionally by over-vigorous control input.  I demonstrate this (in an AATD!) by failing the AI, rolling the plane inverted in (simulated) IMC and task the learner to recover.  It is common for the student to cause the AATD to “crash” after breaking apart mid-air— in software so only a restart is required.  But it is sobering   

The take-away is — don’t lose control.  

[Shadrach]

On 6/12/2024 at 1:58 PM, DXB said:

FWIW in 1969, Vno went from 150 to 175mph and Vne went from 189 to 200mph for the short bodies without any structural change to justify it.  

The "paper" changes to the limitations over the years are a bit odd.  The E as introduced in 1964 with 150 Vno and 189 Vne.  The F introduced in 1966 and G  introduced in 1968 both came with a Vno of 175 and Vne of 200mph.  I would like to know what was done to the J to increase Vne from 200mph to 225mph and Flap speed from 100mph to 127mph and gear extension from 120mph to 152mph and then finally 186mph... The numbers seem as though drawn from a hat rather than flight testing.

[201er]

2 hours ago, Shadrach said:

I would like to know what was done to the J to increase Vne from 200mph to 225mph

Changed the airspeed indicator from miles per hour to knots.

[201er]

Scott did a follow up demonstration video and briefly mentions Mooney again:

 

 

[Pinecone]

Ben is typically driven by flutter.  So changes in balancing or other moveable surface changes could change Vne

[RescueMunchkin]

It's just my guess based on my very limited flying experience that this Bonanza broke up mainly because of exceeding Vne instead of over-G. Reason for that is with a constant speed prop, it's very hard to tell when the plane is getting fast, but g forces can directly be felt by the pilot.

Edit....

Thinking about this a bit more, the spiral divergence recovery trim causing over-g can be very difficult to recognize during disorientation... But the V tail Bonanzas seem to easily damage their tails if exceeding Vne, so that's additional risk to consider.

Edited June 15 by RescueMunchkin

[Shadrach]

20 hours ago, RescueMunchkin said:

It's just my guess based on my very limited flying experience that this Bonanza broke up mainly because of exceeding Vne instead of over-G. Reason for that is with a constant speed prop, it's very hard to tell when the plane is getting fast, but g forces can directly be felt by the pilot.

Edit....

Thinking about this a bit more, the spiral divergence recovery trim causing over-g can be very difficult to recognize during disorientation... But the V tail Bonanzas seem to easily damage their tails if exceeding Vne, so that's additional risk to consider.

Have you looked at the flight data?  He banks right, accelerates and descends rapidly in a tightening turn.  Looks like spiral divergence to me. It’s my understanding that some V-tail failures appear to have been related to flutter but the vast majority are pilot induced, over control, scenarios where the “V” is bent flat causing the nose to pitch up abruptly, breaking the airframe. Most aircraft will easily tolerate excursions well over Vne provided the pilot doesn’t bend the plane by over controlling.

[RescueMunchkin]

2 hours ago, Shadrach said:

Have you looked at the flight data?  He banks right, accelerates and descends rapidly in a tightening turn.  Looks like spiral divergence to me. It’s my understanding that some V-tail failures appear to have been related to flutter but the fast majority are pilot induced over control scenarios where the “V” is bent flat causing the nose to pitch up abruptly breaking the airframe. Most aircraft will easily tolerate excursions well over Vne provided the pilot doesn’t bend the plane by over controlling.

The track shows a tightening turn implying overbank most likely due to disorientation, but I don't think it definitively proves the plane suffered over g. It only shows ground speed, and when a plane is diving into the ground at that rate of airspeed and angle relative to the ground, the ground speed would only be a fraction of its air speed. So a breakup due to tail flutter from overspeed is possible.

[Shadrach]

9 hours ago, RescueMunchkin said:

The track shows a tightening turn implying overbank most likely due to disorientation, but I don't think it definitively proves the plane suffered over g. It only shows ground speed, and when a plane is diving into the ground at that rate of airspeed and angle relative to the ground, the ground speed would only be a fraction of its air speed. So a breakup due to tail flutter from overspeed is possible.

Spatial disorientation is a given.  The NTSB will likely be able to determine if the structural failure was related to flutter or over control. I think the reason so many are leaning towards over control is the short time from which the aircraft left cruise altitude to breaking up. He was cruising at 9500 when the gentle turn started. As it tightened, his descent rate went from a few 1000fpm to over 12,000fpm in less than 30 seconds. By 3000’ below cruise altitude the rate of descent was in excess of 40,000fpm (likely in pieces). 

 

 

[DXB]

On 6/14/2024 at 1:24 PM, Shadrach said:

The "paper" changes to the limitations over the years are a bit odd.  The E as introduced in 1964 with 150 Vno and 189 Vne.  The F introduced in 1966 and G  introduced in 1968 both came with a Vno of 175 and Vne of 200mph.  I would like to know what was done to the J to increase Vne from 200mph to 225mph and Flap speed from 100mph to 127mph and gear extension from 120mph to 152mph and then finally 186mph... The numbers seem as though drawn from a hat rather than flight testing.

The midbody F and G airframes came with the taller rudder spanning full height of the empennage from the outset, and in '69, the short bodies adopted the same rudder along with the increase Vno and Vne to match those of the F and G.  I suspect the longer rudder had nothing to do with it, but I can't find any other significant structural change between 68 and 69 that might affect these speeds.

The reason for the flap speeds are also as clear as mud.  I think they all went up from 105 to 125mph for the C, E, and F (and new G) in '68.  This was a helpful improvement since 105mph is really very slow.  Then came  Mooney SB M20-21 in 1979 for inspection of the stub spar for in all the Mooneys with manual or hydraulic flaps (the last were made in '68).  That led to a doubler being installed in my plane and many others with rear spar cracks.

[RescueMunchkin]

3 hours ago, Shadrach said:

Spatial disorientation is a given.  The NTSB will likely be able to determine if the structural failure was related to flutter or over control. I think the reason so many are leaning towards over control is the short time from which the aircraft left cruise altitude to breaking up. He was cruising at 9500 when the gentle turn started. As it tightened, his descent rate went from a few 1000fpm to over 12,000fpm in less than 30 seconds. By 3000’ below cruise altitude the rate of descent was in excess of 40,000fpm (likely in pieces). 

 

 

Doing the math from ground speed and descent rate based on the data from the picture you posted, I'm calculating that between 17:01:58 and 17:02:01, the descent rate was 251.8 knots (1 fps = .5924 knots)  and with the ground speed of 162 knots, the speed of the plane relative to the ground was 299 knots.

If I use the average descent rate between 17:01:41 and 17:02:01 and the GS of 213 knots, the speed of the plane relative to the ground was 231 knots.

I agree we don't know what caused the break-up, but I also think that either scenario is plausible and can cause this outcome.

Before this thread, I wasn't aware that rolling wings level from an overbanking dive would tend cause a potential over-G condition because of trim, so all of this is great info.

[Shadrach]

1 hour ago, DXB said:

The reason for the flap speeds are also as clear as mud.  I think they all went up from 105 to 125mph for the C, E, and F (and new G) in '68.  This was a helpful improvement since 105mph is really very slow.  Then came  Mooney SB M20-21 in 1979 for inspection of the stub spar for in all the Mooneys with manual or hydraulic flaps (the last were made in '68).  That led to a doubler being installed in my plane and many others with rear spar cracks.

Yes. No difference in the flap system or structure from 67 to 68 but a 120MIAS increase in Vfe. I wonder if this change contributed to some of the stub spar crack issues and consequent SB? I have a 67 and have no visible cracks at the stub spar. I’m not saying the aircraft has never been above 105MIAS with the flaps deployed, but I would bet that the few times that it’s happened they have been in the take off position. Full flap deployments at 125MIAS would be more stressful on the system. 

[Jerry 5TJ]

2 minutes ago, RescueMunchkin said:

Before this thread, I wasn't aware that rolling wings level from an overbanking dive would tend cause a potential over-G condition because of trim, so all of this is great

At an airspeed much higher than the trimmed speed, yes, rolling level may demand significant FORWARD yoke pressure to avoid overloading the airframe.  

[Pinecone]

Inspection of the pieces should answer the question about how the breakup occurer.

Flutter would be alternately loading in both directions.  Over G would be only in one direction.

[Shadrach]

11 minutes ago, Pinecone said:

Inspection of the pieces should answer the question about how the breakup occurer.

Flutter would be alternately loading in both directions.  Over G would be only in one direction.

I’ve read that Vtail flutter sort of shreds the ruddervator at the attachment points.