Rolling 'G'
 

For the aerodynamicists

I'm looking into UPRT training for large jet aircraft, specifically Boeing.

AFM limitations provide values for + and - G but no 'rolling G' (combined roll and pitch), and UPRT recovery generally separates manoeuvers by pitch and roll (not combined). During nose low recovery, the nose is often raised (unintentionally) by inexperienced trainees as the lift vector becomes more vertical, whilst they are rolling wings level, and thus inducing greater G.

Am I guessing correctly that the + and - G limits are fixed whether in a turn, rolling or wings level?

Thanks in advance..

It was my understanding that rolling G was limited to two thirds of the normal G limitation of the aircraft (so a 2.5G limit is reduced to 1.65 whilst rolling) - although I’m not 100% sure that applies to transport category aircraft, but it does apply to FAR 23 certified aircraft.

Certainly the G limit whilst rolling is NOT the same as the G limit in wings level flight.

In the UPRT simulator sessions that we do, there is a focus on rolling G and in fact the UPRT functions of the simulator give cautions to the instructor if the pilot conducts a recovery that triggers rolling G over a pre determined threshold.

Very much appreciate the insight Col. Klink...

Great gen...

Doesn't matter, people are gonna roll while pulling out no matter what. If that test pilot crew in the 717 video couldn't get it right when it counts, what hope is there for the average schmuck?

Another thread on the subject with test pilot comments

https://www.pprune.org/flight-testin...dangerous.html

Some flight manuals specifically state two thirds rolling 'g'.

§ 23.349 - Rolling conditions.
(b) (b) The loads resulting from the aileron deflections and speeds specified in § 23.455, in combination with an airplane load factor of at least two thirds of the positive maneuvering load factor used for design.

You can roll and pull. You just have a limit. T-38 max weight, straight pull - 6g, asymmetric pull - 4.4g.

Thank you all - greatly appreciated...

Sure, that's true. But what do you think is a pilot's capacity to respect this limit, when doing
- something extremely startling and disorienting
- for the first time in their life
- there is no instrument in the cockpit showing this information
- as the airspeed is rapidly shooting toward the limit, forcing you to pull high G to level off
- the airplane is trimmed for a big pull without the pilot doing anything
- and there is an overwhelming instinct to pull also
​​​​​​

Vessbot, jimtx, et al

You have to consider stick force per g in the human actions.
Commercial aircraft have much higher control forces than most military aircraft.
Then additively the ergonomics of the pitch combined with the rolling stick force

It's common to see a reduction in actual flyjng skill in test pilots.

On the other hand your poor average schmuck has been trained to roll and then pull. I think they'd do just fine.

Chesty, #10

Spherical Objects

also

Many accidents show that what we think will happen is not what happens in real, surprising conditions.

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Megan et al, the FAR reference # 5 was for a part 23 aircraft; the op question relates to 'large jet aircraft'.

However Part 25 is similar

§ 25.349 Rolling conditions.
The airplane must be designed for loads resulting from the rolling conditions specified in paragraphs (a) and (b) of this section. Unbalanced aerodynamic moments about the center of gravity must be reacted in a rational or conservative manner, considering the principal masses furnishing the reacting inertia forces.
(a) Maneuvering. The following conditions, speeds, and aileron deflections (except as the deflections may be limited by pilot effort) must be considered in combination with an airplane load factor of zero and of two-thirds of the positive maneuvering factor used in design. In determining the required aileron deflections, the torsional flexibility of the wing must be considered in accordance with § 25.301(b):

Question:- is the design maneuvering factor greater than the AFM limit?

3721
Not my words but the words of someone who, for the best part of the last 40 years, has been a military and civilian experimental and developmental test pilot and test pilot tutor/instructor who has flown more types than you or I ever will, probably combined,

Yes, by (unsurprisingly) fifty percent for the transport category.

I would have thought that the fifty percent is the difference between the design loads and the ultimate load ( unless it is stated that the particular load is actually the ultimate load).

Clandestino, zzuf, thanks,

Thus if the rolling 'g' limit is determined by the pilot's limiting stick force, or that the structure does not break (although it might twist) within the AFM 'g' limits, as determined by flight test, this implies that if you can do it (rolling g) then it's OK ?

From experience in a manual control commercial aircraft, the combined pitch and roll control forces at VMO / MM0 are very high, much higher than pilots might expect. Are simulators representative ?

For those who have been above VMO, the forces become extremely high which may require both pilots input for recovery.

This discussion should also raise the question of how such situations might be encountered, particularly if the aircraft started from a trimmed condition; and although some procedures (generically) require a check or reset of trim position to a normal range, trim should not be used to recover the aircraft because of the risk of exceeding the normal g limit.

Not my experience as a certification test pilot who flew with experimental TP's from: Aerospatiale, CASA, Boeing, Airbus, Dassault, GAF, Grumman, Hawkers, BAE, Shorts, RAAF, Cessna, Canadair, DHC, Swearingen, Beechcraft, Fokker, Scottish Aviation (as it was) probably a few other that I don't recall atm.
Generally, the majority of test points are easy to fly but some can be extremely demanding and require a work up and a few attempts to obtain acceptable data.

PEI3721
You are quoting a structural design standard, not a flight handling standard, and seem to be missing the intent of the standards, and probably misinterpreting what the requirements are.

zzuf, yes missing, misinterpreting - most probable.

The quest was for a practical answer - if rolling 'g' is not limited by the AFM, then do crew have to be concerned by a combined pull / roll during an upset recovery.

My conclusion is no, and that in some circumstances the control input is difficult.
Furthermore, with the surprise in such situations then the likelihood of the crew recalling an obscure limit, if it exists, is remote.

No the limit is shown by compliance with your quoted FAR ie 2/3 of the G loading used in structural design. The aileron angle will be maximum permitted or that limited by the pilot ability to apply the aileron eg pilot strength.
To find out what is required to be demonstrated in flight read the flight handling and performance parts of FAR 25. To get some idea of how to do, read the Advisory Circular - Flight Test Guide FAR25.
There are plenty of ways to break aircraft that are not covered by limitation in the AFM. What is the maximum rate of descent for landing, what is the maximum sideslip angle?
Also remember that once the aircraft is certificated there is no need to repeat any of the certification procedures.
A classic is training sections requiring a demonstration of VMC, in flight. That is a really good way to set up a loss of control situation.

zzuf,
It's along time ago, age, and feeble mind. (been there, done that, can't remember)
For simplicity, a practical situation, pilots perspective: aircraft 2.5'g' AFM limit, with roll and pitch upset.
What 'g' should the crew observe during a combined roll and pitch recovery; noting post # 2 Colonel Klink.