Rolling 'G'
Joined: Nov 2006
Posts: 416
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From: Down south
Roll and pitch combined upsets require special attention.
The loads to speeds graphs appearing in the aircraft flight envelope charts are for a single input deflection.
Engineers consider each axis separately in designing for the air loads accompanying a full control at any flight speed up to Maneuverin Speed (Va) in aircrafts flight envelopes.
Inputs on more than one axis simultaneously need to be taken into account separately.
Two factors need to be kept in mind during a banking pull:
The pull to counter the centrifugal forces and the increased apparent weight of the bank , are two forces adding to each other.
If the ball is kept in the middle, loads will be symmetrical both the wings and fuselage will feel the same acceleration levels.
The next factor to consider is when rudder is simultaneously applied to the pull wether in a bank or not this increases the load on the rudder’s side wing.
Inputs in more than one axis, like inside rudder while pulling then unloading (Aerobatics pilots know this maneuver as a "Flick" or "Snap Roll) will load inside wing approx 30% more than the G meter will display on fuselage panel G meter.
"Design loads" are another story they are structural "G" margins accounted for in certification as safety buffers expressed in percentage:
In "Normal" category, G loads are factored at 3,8G's + 50% margin; Structural failure should not occur before 3,8G's + 50% = (5,7 G)
In "Aerobatic" category positive G loads are min 6 G's + 100% = (12 G)
The loads to speeds graphs appearing in the aircraft flight envelope charts are for a single input deflection.
Engineers consider each axis separately in designing for the air loads accompanying a full control at any flight speed up to Maneuverin Speed (Va) in aircrafts flight envelopes.
Inputs on more than one axis simultaneously need to be taken into account separately.
Two factors need to be kept in mind during a banking pull:
The pull to counter the centrifugal forces and the increased apparent weight of the bank , are two forces adding to each other.
If the ball is kept in the middle, loads will be symmetrical both the wings and fuselage will feel the same acceleration levels.
The next factor to consider is when rudder is simultaneously applied to the pull wether in a bank or not this increases the load on the rudder’s side wing.
Inputs in more than one axis, like inside rudder while pulling then unloading (Aerobatics pilots know this maneuver as a "Flick" or "Snap Roll) will load inside wing approx 30% more than the G meter will display on fuselage panel G meter.
"Design loads" are another story they are structural "G" margins accounted for in certification as safety buffers expressed in percentage:
In "Normal" category, G loads are factored at 3,8G's + 50% margin; Structural failure should not occur before 3,8G's + 50% = (5,7 G)
In "Aerobatic" category positive G loads are min 6 G's + 100% = (12 G)
Last edited by markkal; 8th December 2024 at 18:06.
Joined: Jun 2000
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From: Australia
Rolling pull out can be dangerous. One example of this was at the Werribee (Victoria) bombing range in late 1950's. The aircraft was a RAAF Wirraway doing practice dive bombing. The briefed session was a 45 degrees angle of dive using partial power. Release the 25 lb bomb at 1000 ft followed by a straight ahead pull up to 1000 ft then join the circuit for another bomb run.
On this occasion the pilot decided he could bomb more accurately by steepening the dive to 60 degrees and with closed throttle to keep the speed in check. Witnesses saw the aircraft pull up at well below 1000 ft and immediately roll into steep climbing left turn to join the downwind leg of the circuit. One wing broke away and the aircraft crashed killing the pilot. The cause of the accident was found to be asymetric G forces on the wings.
The offcial accidenr report in part stated:
During a recovery from a dive bombing pass over the Werribee Air Weapons Range 1204hrs 01/04/58 the aircraft was overstressed resulting in the catastrophic failure of the port wing which then caused the aircraft to crash. Pilot was Warrant Officer E F Dillon was killed instantly. .
On this occasion the pilot decided he could bomb more accurately by steepening the dive to 60 degrees and with closed throttle to keep the speed in check. Witnesses saw the aircraft pull up at well below 1000 ft and immediately roll into steep climbing left turn to join the downwind leg of the circuit. One wing broke away and the aircraft crashed killing the pilot. The cause of the accident was found to be asymetric G forces on the wings.
The offcial accidenr report in part stated:
During a recovery from a dive bombing pass over the Werribee Air Weapons Range 1204hrs 01/04/58 the aircraft was overstressed resulting in the catastrophic failure of the port wing which then caused the aircraft to crash. Pilot was Warrant Officer E F Dillon was killed instantly. .
Last edited by Centaurus; 9th December 2024 at 07:07.
Joined: Jan 2019
Posts: 337
Likes: 82
From: Australia
Are you suggesting in the example of a 10 degree nose pitch down upset with significant bank on, that if I roll at the same as pulling up to wings level and an attitude of (around) 0 degrees, and as long as this is in balanced flight, that the G loading on both wings is symmetrical?
Because my understanding is that it is not - and if the upset happened to be a 45 degree bank to the right with significant nose pitch down, that rolling and pulling at the same time towards wings level would result in the right hand wing experiencing a far greater load factor than that of the left hand wing. Hence the need to roll to approximately wings level prior to applying any substantial G loading in the subsequent recovery.
Happy to be corrected though if I have any of that wrong!
Joined: Dec 1998
Posts: 163
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From: PENang, Malaysia
I think that the statement is essentially correct.
I flew the A4 Skyhawk and we did our share of ai to mus. The Squadron AEO became concerned at the number of worn rivets, predominantly on the RH wings. He had a long discussion with the Squadron Senior Pilot, who agreed that the pilots were pulling and rolling at 4+ g during the dive recovery.
The upshot was the Squadron AWI rebriefed us on dive bombing recovery: Straight pull at 4 g to 20 degrees nose up, release the g then roll to desired bank, then reapply the g. Voila the rivets miraculously stopped wearing out their rivet holes and brown streaks on the wing surface thinned out.
Much, much later, my airline began UPRT training on the guidance of senior Standards Captains. When I piped up and mentioned rolling g, I was laughed at, but I stuck to my guns and said that the limit is 2.5 *.66 or you will have airframe damage.the Standards Captains did at least go away and do their research. They changed their briefs to include mention of rolling g.
But the overstressed pilot staring at a window of brown and green is not going to think about rolling limits until much later.
I flew the A4 Skyhawk and we did our share of ai to mus. The Squadron AEO became concerned at the number of worn rivets, predominantly on the RH wings. He had a long discussion with the Squadron Senior Pilot, who agreed that the pilots were pulling and rolling at 4+ g during the dive recovery.
The upshot was the Squadron AWI rebriefed us on dive bombing recovery: Straight pull at 4 g to 20 degrees nose up, release the g then roll to desired bank, then reapply the g. Voila the rivets miraculously stopped wearing out their rivet holes and brown streaks on the wing surface thinned out.
Much, much later, my airline began UPRT training on the guidance of senior Standards Captains. When I piped up and mentioned rolling g, I was laughed at, but I stuck to my guns and said that the limit is 2.5 *.66 or you will have airframe damage.the Standards Captains did at least go away and do their research. They changed their briefs to include mention of rolling g.
But the overstressed pilot staring at a window of brown and green is not going to think about rolling limits until much later.
Joined: Sep 2010
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From: by the seaside
Interesting the right wings damage; my first paraglider turned right continuously - thought it was me being cack handed - the lines showed no differences so it was a deformed canopy. Discussed it with my VC10 instructor who after retiring worked with the paragliding world champion who stated it was over stressing pulling out of a spiral decent; surprisingly occurred with right handed but also left handed pilots with all wings turning right after being over stressed.
Joined: Nov 2006
Posts: 416
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From: Down south
Thank you for your remark,
I can relate my observation to stalling which is function of G load. Ther may be other factors
In a stall while establishing an angle of bank first, then pulling to the break, if ball is in the midle the aircraft will mush
in case the ball is not in the middle one wing will fall and it's the one where rudder is applied. if rudder is not countered it will start to roll.
This if pilot first puts aircraft in a bank, neutralses the bank and then pulls,
Need to check for behavior if one continues to bank while pulling.
We have aerobatic aircraft with recording G meter, and can give it a try will be happy to come back with my findings.
If there is a test pilot somewhere who can help, will be highly appreciated,
The spiral descent as its referred to here is a killer as speed goes up exponentially (Conratry to a spin when its low and stable) and stall speed increases, This leads to an accelerated stall where stall speed is function of the square root of the G load
I can relate my observation to stalling which is function of G load. Ther may be other factors
In a stall while establishing an angle of bank first, then pulling to the break, if ball is in the midle the aircraft will mush
in case the ball is not in the middle one wing will fall and it's the one where rudder is applied. if rudder is not countered it will start to roll.
This if pilot first puts aircraft in a bank, neutralses the bank and then pulls,
Need to check for behavior if one continues to bank while pulling.
We have aerobatic aircraft with recording G meter, and can give it a try will be happy to come back with my findings.
If there is a test pilot somewhere who can help, will be highly appreciated,
The spiral descent as its referred to here is a killer as speed goes up exponentially (Conratry to a spin when its low and stable) and stall speed increases, This leads to an accelerated stall where stall speed is function of the square root of the G load
Joined: Sep 2018
Posts: 199
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From: Laredo, TX
I think that the statement is essentially correct.
I flew the A4 Skyhawk and we did our share of ai to mus. The Squadron AEO became concerned at the number of worn rivets, predominantly on the RH wings. He had a long discussion with the Squadron Senior Pilot, who agreed that the pilots were pulling and rolling at 4+ g during the dive recovery.
The upshot was the Squadron AWI rebriefed us on dive bombing recovery: Straight pull at 4 g to 20 degrees nose up, release the g then roll to desired bank, then reapply the g. Voila the rivets miraculously stopped wearing out their rivet holes and brown streaks on the wing surface thinned out.
Much, much later, my airline began UPRT training on the guidance of senior Standards Captains. When I piped up and mentioned rolling g, I was laughed at, but I stuck to my guns and said that the limit is 2.5 *.66 or you will have airframe damage.the Standards Captains did at least go away and do their research. They changed their briefs to include mention of rolling g.
But the overstressed pilot staring at a window of brown and green is not going to think about rolling limits until much later.
I flew the A4 Skyhawk and we did our share of ai to mus. The Squadron AEO became concerned at the number of worn rivets, predominantly on the RH wings. He had a long discussion with the Squadron Senior Pilot, who agreed that the pilots were pulling and rolling at 4+ g during the dive recovery.
The upshot was the Squadron AWI rebriefed us on dive bombing recovery: Straight pull at 4 g to 20 degrees nose up, release the g then roll to desired bank, then reapply the g. Voila the rivets miraculously stopped wearing out their rivet holes and brown streaks on the wing surface thinned out.
Much, much later, my airline began UPRT training on the guidance of senior Standards Captains. When I piped up and mentioned rolling g, I was laughed at, but I stuck to my guns and said that the limit is 2.5 *.66 or you will have airframe damage.the Standards Captains did at least go away and do their research. They changed their briefs to include mention of rolling g.
But the overstressed pilot staring at a window of brown and green is not going to think about rolling limits until much later.
Fleet Manager
Joined: Apr 2001
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From: various places .....
A very useful and valuable discussion for those who might read it. As a now pilot theory instructor, I try to push the takeaway to be along the lines of "if you are pulling hard while rolling, pull a bit more gently". Most pilots have no objective way to measure what loads they might be applying, so a generic approach might be the next best way to reduce the chance of their killing themselves ?
Joined: Oct 2004
Posts: 255
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From: australia
A very useful and valuable discussion for those who might read it. As a now pilot theory instructor, I try to push the takeaway to be along the lines of "if you are pulling hard while rolling, pull a bit more gently". Most pilots have no objective way to measure what loads they might be applying, so a generic approach might be the next best way to reduce the chance of their killing themselves ?
It should not be lost on people that for the majority of the airborne time, a jet transport does not have the manoeuvre margin to get even close to the 2/3 limit load.
Also, the design limit rolling input could be seen as fairly aggressive: at Va - full roll control, at Vc - the same roll rate at achieved at Va, at Vd - one third the roll rate achieved at Va.
Interestingly, during maximum rate turn manoeuvres fighter pilots, to avoid reducing the G loading, change bank angle to correct pitch attitude and airspeed speed error. The roll inputs, in these cases are relatively small.
Joined: Feb 2005
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From: Correr es mi destino por no llevar papel
While I have the feeling you're on the right way, I'm not sure I follow you completely here so let me try to clarify: to get certified, transport category aeroplanes have to withstand 3.75G positive without structural damage. Some terms & conditions also apply, the ımportant for us it is straight pull, no rolling. What you and Megan have posted is the requirement there would be no naughty surprises if the roll is ıntroduced at two third of that, which is (not at all coincidentally) 2.5G, the AFM limit. So while you are right that properly designed aeroplane should withstand roll abuse at its positive G limit, making advantage of it makes no sense operationally as one has no idea how much G one is pulling without G-meter and it can get you quickly into the uncharted envelope territories, not to mention it's harder to maintain spatial orientation while fighting the aeroplane in two axes simultaneously. Thence the folks who believe that 0.666 factor applies to the AFM limit are actually advocating the right stuff for the wrong reason.
Joined: Oct 2004
Posts: 255
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From: australia
While I have the feeling you're on the right way, I'm not sure I follow you completely here so let me try to clarify: to get certified, transport category aeroplanes have to withstand 3.75G positive without structural damage. Some terms & conditions also apply, the ımportant for us it is straight pull, no rolling. What you and Megan have posted is the requirement there would be no naughty surprises if the roll is ıntroduced at two third of that, which is (not at all coincidentally) 2.5G, the AFM limit. So while you are right that properly designed aeroplane should withstand roll abuse at its positive G limit, making advantage of it makes no sense operationally as one has no idea how much G one is pulling without G-meter and it can get you quickly into the uncharted envelope territories, not to mention it's harder to maintain spatial orientation while fighting the aeroplane in two axes simultaneously. Thence the folks who believe that 0.666 factor applies to the AFM limit are actually advocating the right stuff for the wrong reason.
FAR 25.349 is clear that the 2/3 factor is applied to the design manoeuvre load.
Attempts, by pilots, to develop aircraft handling procedures by reference structural design standards can be fraught, particularly if you don't understand the intent of the of the standard and the history of its development.
As I wrote before I would encourage study of AC25-7D, especially
CHAPTER 5. FLIGHT: CONTROLLABILITY AND MANEUVERABILITY
Joined: Nov 2006
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From: Down south
In my extensive collection of books I have got one, "Stalls Spins and Safety" by Sammy Mason, which adresses this issue in one of its paragrahs.
Now I have moved abroad for pension and have most of my stuff in boxes due to lack of space. Just in case somebody has the book i'd appreciate to let us know.
When I have a moment I will go in my garage and see if I can find it.
It adresses both climbing turns and descending turns if my memory is correct.
One point though, during my flying career (As a hobby, it was not my profession) I have owned many aircrafts, all aerobatic, and I have tried to correlate aerodynamics effects experienced in flight with the fundamental of physics being fond of the subject.
Subject that even with the correlation between theory and practice can still leave many questions unanswered to me. That is why also above I mentionned if there would be a test pilot somewhere who reads this, to get involved. Cheers to everybody, am happy to find out there are many passionate and knowledgeable pilots !!!!
Now I have moved abroad for pension and have most of my stuff in boxes due to lack of space. Just in case somebody has the book i'd appreciate to let us know.
When I have a moment I will go in my garage and see if I can find it.
It adresses both climbing turns and descending turns if my memory is correct.
One point though, during my flying career (As a hobby, it was not my profession) I have owned many aircrafts, all aerobatic, and I have tried to correlate aerodynamics effects experienced in flight with the fundamental of physics being fond of the subject.
Subject that even with the correlation between theory and practice can still leave many questions unanswered to me. That is why also above I mentionned if there would be a test pilot somewhere who reads this, to get involved. Cheers to everybody, am happy to find out there are many passionate and knowledgeable pilots !!!!
Joined: Aug 2012
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From: Lincolnshire
Joined: Mar 2006
Posts: 1,115
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From: England
JT, zzuf, Clan, et al, interesting views.
zzuf, 'Limit is shown by …'; actually its demonstrated for certification (playing with words - the manufacturer shows that the requirement is met).
However, the lowly flight-crew have no indication, no show and tell, no instrument or tech description; thus take it easy as JT #29.
zzuf, Back to #20, or without load indication, not knowing doesn't matter because you can't get there #30 ?
Clandestino, we are facing the same direction.
However, is your application the 0.666 factor to the AFM 'normal g' limit a precaution because the pilot has no indication (good practical advice), or a real limit to be respected ?
Three Wire, re A4; as I recall a high 'g' pull up with asymmetric slats (one hangs up - not enough grease) resulted in significant rolling 'g'. There was a video of a TA4J shedding a large drop tank.
zzuf, 'Limit is shown by …'; actually its demonstrated for certification (playing with words - the manufacturer shows that the requirement is met).
However, the lowly flight-crew have no indication, no show and tell, no instrument or tech description; thus take it easy as JT #29.
zzuf, Back to #20, or without load indication, not knowing doesn't matter because you can't get there #30 ?
Clandestino, we are facing the same direction.
However, is your application the 0.666 factor to the AFM 'normal g' limit a precaution because the pilot has no indication (good practical advice), or a real limit to be respected ?
Three Wire, re A4; as I recall a high 'g' pull up with asymmetric slats (one hangs up - not enough grease) resulted in significant rolling 'g'. There was a video of a TA4J shedding a large drop tank.
Joined: Dec 2006
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From: The No Transgression Zone
It's imperative that one must roll the wings level then pull out of the dive...
below may help a little. Just change Va to Vp it's confusing but where I got Vp from is Aerodynamics for Naval Aviators and he calls Vp maneuver speed...I keep forgetting to write the correction so I'll do it now.
Minimum radius of turn?
below may help a little. Just change Va to Vp it's confusing but where I got Vp from is Aerodynamics for Naval Aviators and he calls Vp maneuver speed...I keep forgetting to write the correction so I'll do it now.
Minimum radius of turn?
Joined: Oct 2004
Posts: 255
Likes: 15
From: australia
JT, zzuf, Clan, et al, interesting views.
zzuf, 'Limit is shown by …'; actually its demonstrated for certification (playing with words - the manufacturer shows that the requirement is met).
However, the lowly flight-crew have no indication, no show and tell, no instrument or tech description; thus take it easy as JT #29.
zzuf, Back to #20, or without load indication, not knowing doesn't matter because you can't get there #30 ?
Clandestino, we are facing the same direction.
However, is your application the 0.666 factor to the AFM 'normal g' limit a precaution because the pilot has no indication (good practical advice), or a real limit to be respected ?
Three Wire, re A4; as I recall a high 'g' pull up with asymmetric slats (one hangs up - not enough grease) resulted in significant rolling 'g'. There was a video of a TA4J shedding a large drop tank.
zzuf, 'Limit is shown by …'; actually its demonstrated for certification (playing with words - the manufacturer shows that the requirement is met).
However, the lowly flight-crew have no indication, no show and tell, no instrument or tech description; thus take it easy as JT #29.
zzuf, Back to #20, or without load indication, not knowing doesn't matter because you can't get there #30 ?
Clandestino, we are facing the same direction.
However, is your application the 0.666 factor to the AFM 'normal g' limit a precaution because the pilot has no indication (good practical advice), or a real limit to be respected ?
Three Wire, re A4; as I recall a high 'g' pull up with asymmetric slats (one hangs up - not enough grease) resulted in significant rolling 'g'. There was a video of a TA4J shedding a large drop tank.
25.1 Applicability.
(a) This part prescribes airworthiness standards for the issue of type certificates, and changes to those certificates, for transport category airplanes.(b) Each person who applies under Part 21 for such a certificate or change must show compliance with the applicable requirements in this part.
There are plenty of times where "acceptable means of compliance" can mean other than demonstration.
Your comment on "not knowing because you can't get there" was done to death before any certification authority accepted the manoeuvre limiting features of most FBW aircraft. I suggest some research into the development of the current FBW standards.
Your suggestion that 2/3 factor could even be considered to be due to what instrumentation is fitted does not stand much scrutiny for what is a structural design standard.
Strictly speaking, there is no limit in the AFM this is a structural design standard for which compliance has been SHOWN during certifcation. There are plenty of structural design standards not mentioned in the AFM.
The suggestion that transport aircraft should be fitted with accelerometers has been discussed many times as are "alpha" indicators. Demonstrably, the certification authorities have not been convinced.
Last edited by zzuf; 11th December 2024 at 07:02.
Joined: Dec 1998
Posts: 163
Likes: 2
From: PENang, Malaysia
PEI ,You are correct, but we learnt to sense and give a little rudder input to force the slat to release.
The problem for us in academic bombing was that the circuit was right handed, hence the brown lines from fuel seeping from worn rivets. There was an approved fix; a "rubber bomb" introduced to the wing via inspection panels that reinforced the tank lining.
The problem for us in academic bombing was that the circuit was right handed, hence the brown lines from fuel seeping from worn rivets. There was an approved fix; a "rubber bomb" introduced to the wing via inspection panels that reinforced the tank lining.
Fleet Manager
Joined: Apr 2001
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From: various places .....
where I got Vp from is Aerodynamics for Naval Aviators and he calls Vp maneuver speed
An old, but good, book referring to old references. What is Va was Vp in CAR3 at p3.184. If you can't be fussed digging CAR3 out, I put a bit of a story on Bob Tait's website at Bob Tait's Aviation Theory School - Maneuvering Speed with weight - Bob Tait's Aviation Theory School Forums Hopefully I didn't waffle on too much into nonsense stuff in the thread
An old, but good, book referring to old references. What is Va was Vp in CAR3 at p3.184. If you can't be fussed digging CAR3 out, I put a bit of a story on Bob Tait's website at Bob Tait's Aviation Theory School - Maneuvering Speed with weight - Bob Tait's Aviation Theory School Forums Hopefully I didn't waffle on too much into nonsense stuff in the thread
