Can anyone recreate this inverted flat spin behavior ?

[Shadow KT]

Can anyone recreate the flight departure described in this story ?
 

 

[Doc3908]

Just tried some flat spins. Works just fine - both upright and inverted. Not perfectly flat, but acceptable... I'll try again later to see if i can flatten it better.

 

 

[Shadow KT]

Getting any flat spin was not the what was asked for.

 

Getting in a flat spin following the moves mentioned in the video and experiencing the described phenomenom is what is looked for 

[bbrz]

Since this kind of problem was apparently rather uncommon and it isn't even mentioned in the manual, I doubt that this can be simulated at all, not even on the most expensive sims.

 

Interestingly the manual says that the minimum ejection altitude during an inverted spin is 15000ft and no rudder or aileron input is allowed.

[dolfo]

3 hours ago, bbrz said:

Since this kind of problem was apparently rather uncommon and it isn't even mentioned in the manual, I doubt that this can be simulated at all, not even on the most expensive sims.

 

Interestingly the manual says that the minimum ejection altitude during an inverted spin is 15000ft and no rudder or aileron input is allowed.

 

Curious which manual you are referring to? The -1 , Section VI, Inverted Flight Characteristics describes the Inverted Pitch Hangup in the first paragraph. It also elaborates that "

If recovery from the IPH is not accomplished, divergent roll oscillations or an inverted spiral may develop. " 

 

15000ft is minimum ejection alt for a dual F-5F. Solo F or E shows 10000.

 

As for being able to get an IPH in-game, I have tried a long time ago without success.

 

[bbrz]

I didn't read anything about an inverted flat spin which would directly develop from an IPH and again, no use of rudder is apparently considered essential to recover.

 

I have an F-5E -1 and the 15000ft apply to an ejection when inverted only. (Section 3)

[dolfo]

2 hours ago, bbrz said:

I didn't read anything about an inverted flat spin which would directly develop from an IPH and again, no use of rudder is apparently considered essential to recover.

 

I have an F-5E -1 and the 15000ft apply to an ejection when inverted only. (Section 3)

What I see is:

 

-1, Section III (3-19,3-20)

(...)

Flight experience has also shown that it is possible to enter an inverted flat spin mode.

(...)

If recovery does not occur and inverted spin entry is indicated, if a turn needle is available, determine the direction of spin rotation. Maintain stick position and: 

4. Rudder - Full Opposite Direction of Spin (turn needle).

(...)

If control is not regained from an erect or inverted spin by 10,000 feet AGL (F 10,000 feet AGL solo; 15,000 feet AGL dual) eject.

 

Section VI  (6-12)

(...)

If recovery from the IPH is not accomplished, divergent roll oscillations or an inverted spiral may develop. Ifthe inverted spiral is allowed to progress, an inverted PSG/spin results.

 

 

And no, I could not re-create the flight departure described in the video.

 

[Shadow KT]

Maybe we should ping a developer or mod to like the manual you are referencing 

[bbrz]

The difference between the manuals is interesting, because the problem obviously didn't occur (or wasn't reported  ) in the first few years, which means that Northrop didn't expect this to happen (as MCD thought that the F-15E wouldn't spin).

 

My F-5E -1 is from 1977 wih the last amendment from 1978 and USAF started operating the E in 74.

Edited December 25, 2020 by bbrz

[Shadow KT]

Well, the pilot in the video also mentions that the flat spin procedure did not work, so he had to somewhat improvize. Also the way he was informed about this and his reaction after his near miss tells me that maybe it really wasn't written in the manual, as well as pilots were keeping quiet about it for some time..

 

Just guessing tho, trying to connect the dots

Edited December 25, 2020 by Shadow KT

[Tiger-II]

It never ceases to amaze me how many people do not know how to correctly stall an aircraft.

 

The maneuver described is entry into a loop, but too slow over the top. The increase in alpha precipitates stall rocking and pitch down (relative to the aircraft axis) which results in the aircraft pitching up (relative to gravity) and losing even more speed. This pitch down over-powers the input for the loop, and the combination of low speed and negative g/and high negative AoA results in yaw (secondary effect of roll) and entry into an inverted flat spin.

 

At high angles of attack yaw rate induces roll rates to rival aileron input. Such is the strength of this, use of rudder at low speeds is PROHIBITED.

 

Secondary effect of roll is yaw.

 

Secondary effect of yaw is roll.

 

Earlier this year a T-38 was lost during a training flight because the pilot under instruction touched the rudders during landing to correct a small runway mis-alignment. They rolled over the top of the lead aircraft and crashed off the side of the runway, killing both crew.

 

A related topic: 

 

Coupling Dynamics in Aircraft: A Historical Perspective

 

https://www.nasa.gov/centers/dryden/pdf/88484main_H-2106.pdf

Edited December 30, 2020 by Tiger-II

[Shadow KT]

On 12/30/2020 at 4:14 AM, Tiger-II said:

It never ceases to amaze me how many people do not know how to correctly stall an aircraft.

 

The maneuver described is entry into a loop, but too slow over the top. The increase in alpha precipitates stall rocking and pitch down (relative to the aircraft axis) which results in the aircraft pitching up (relative to gravity) and losing even more speed. This pitch down over-powers the input for the loop, and the combination of low speed and negative g/and high negative AoA results in yaw (secondary effect of roll) and entry into an inverted flat spin.

 

At high angles of attack yaw rate induces roll rates to rival aileron input. Such is the strength of this, use of rudder at low speeds is PROHIBITED.

 

Secondary effect of roll is yaw.

 

Secondary effect of yaw is roll.

 

Earlier this year a T-38 was lost during a training flight because the pilot under instruction touched the rudders during landing to correct a small runway mis-alignment. They rolled over the top of the lead aircraft and crashed off the side of the runway, killing both crew.

 

A related topic: 

 

Coupling Dynamics in Aircraft: A Historical Perspective

 

https://www.nasa.gov/centers/dryden/pdf/88484main_H-2106.pdf

 

All fine and dandy, but I don't understand what was the point of this comment ?

Are you saying that it is in the sim and we just can't do a "proper" stall ? If so, please show us. 

[Doc3908]

Today I tried very hard to recreate exactly what the video describes - maybe a dozen times. I couldn't do it. Without using the rudder and opposite aileron, I cannot get her into a flat spin. Someone else may have better luck or perhaps the model doesn't allow this behavior. She feels very stable and reluctant to stall/spin.

[Deano87]

Is Inverted Pitch Hangup hangup modelled in the FM at the moment anyway? I haven't noticed it.

[bbrz]

On 12/30/2020 at 3:14 AM, Tiger-II said:

It never ceases to amaze me how many people do not know how to correctly stall an aircraft.

Out of curiosity, how do you 'correctly' stall an aircraft? 

Edited January 6, 2021 by bbrz

[Tiger-II]

.

Edited January 19, 2021 by Tiger-II

[Tiger-II]

On 1/4/2021 at 2:00 PM, Shadow KT said:

All fine and dandy, but I don't understand what was the point of this comment ?

Are you saying that it is in the sim and we just can't do a "proper" stall ? If so, please show us.

 

We can stall in the sim. All it means is the wing is no longer producing lift.

 

The video linked showed a stall with the aircraft climbing nearly vertically. The problem with this is it puts the gravity vector immediately behind the aircraft and will simply result in a tail slide/tumble.

 

What we're discuissing here is an accelerated stall during a looping maneuver, where there was insufficient airspeed at entry, and over the top the aircraft experienced an accelerated stall.

 

Due to the AoA effects of this particular aircraft, and the position of the gravity vector, it results in an increase in negative pitch attitude, negative AoA, which causes the aircraft to climb (fight gravity) and lose yet even more airspeed, and enter a phase of flight that results in inverted spin entry (remembering that at the onset of the "nose down" event the aircraft is inverted).

 

There are more details in the paper I linked.

 

Nice spin demos (left and right, upright, but different *entry* to what we are discussing here).

 

Edited January 19, 2021 by Tiger-II

[Shadow KT]

13 minutes ago, Tiger-II said:

 

We can stall in the sim. All it means is the wing is no longer producing lift.

 

The video linked showed a stall with the aircraft climbing nearly vertically. The problem with this is it puts the gravity vector immediately behind the aircraft and will simply result in a tail slide/tumble.

 

What we're discuissing here is an accelerated stall during a looping maneuver, where there was insufficient airspeed at entry, and over the top the aircraft experienced an accelerated stall.

 

Due to the AoA effects of this particular aircraft, and the position of the gravity vector, it results in an increase in negative pitch attitude, negative AoA, which causes the aircraft to climb (fight gravity) and lose yet even more airspeed, and enter a phase of flight that results in inverted spin entry (remembering that at the onset of the "nose down" event the aircraft is inverted).

 

There are more details in the paper I linked.

 

Can you simulate it in DCS ? Show us.

[Tiger-II]

1 minute ago, Shadow KT said:

Can you simulate it in DCS ? Show us.

Do you want a straight stall, or want me to try and replicate what we are discussing here?

 

What we are discussing here is inverted spin entry during a loop maneuver, but DCS doesn't simulate this specific phenomenon.

[Shadow KT]

1 hour ago, Tiger-II said:

Do you want a straight stall, or want me to try and replicate what we are discussing here?

 

What we are discussing here is inverted spin entry during a loop maneuver, but DCS doesn't simulate this specific phenomenon.

What were are discussing here... I mean, that is the whole point of this thread... is it possible in DCS. I tried to imitate the conditions described as close as I could and I did not experience the described behavior. 

That's why I found your comments confusing. You came in telling us how we can't stall an aircraft, which leaves the impression, that we just couldn't do it properly and that's why we did not experience the aforementioned behavior, but now you say yourself that it is not possible in DCS....

All this means that it is something that the real aircraft did and it is not simulated in DCS, which makes you question the flight model.

This needs to be looked at by the developers, maybe they just had a manual, from when the phenomenon was not described in it. 

Edited January 19, 2021 by Shadow KT

[Tiger-II]

22 minutes ago, Shadow KT said:

What were are discussing here... I mean, that is the whole point of this thread... is it possible in DCS. I tried to imitate the conditions described as close as I could and I did not experience the described behavior. 

 

I did both.

 

First, I attempt the inverted spin from a loop. I show the slats are deploying as a result of high AoA, then after the second attempt I unload and show the slats retracting in response to reduced AoA. The aircraft does not behave as described in the OP video.

 

Second, I show a +1 g stall, then attempt an upright spin (but it doesn't properly enter a spin state).

 

I did provide some commentary as I was flying but it got split out to a seperate track and isn't in the video uploaded to YouTube.

 

 

Edited January 19, 2021 by Tiger-II

[TOViper]

On 1/5/2021 at 11:10 PM, Doc3908 said:

Today I tried very hard to recreate exactly what the video describes - maybe a dozen times. I couldn't do it. Without using the rudder and opposite aileron, I cannot get her into a flat spin. Someone else may have better luck or perhaps the model doesn't allow this behavior. She feels very stable and reluctant to stall/spin.

Did some flights today trying with many variations.

With asymmetric thrust yes, but all other options: No.

Maybe asymmetric load-out might "help" ... 

 

Edited January 21, 2021 by TOViper