Jet Transport Barrel Rolls
Alternative is to go below 1g while inverted but this causes other problems like fuel feed.
You can perform a constant positive G barrel roll from level flight, but it involes more than one G on the pitch up, less than 1 G (but more than Zero) over the top, and more than 1 G on the recovery.
And Bloggs- agree and disagree- started from nose high, an Aileron Roll is very simple (as in- apply Aileron!!). This is different from a slow roll.
What is different is that a in well flown barrel-roll the aircraft remains in balance, and so all stresses on it are on the nomal axis.
In either an Aileron or slow roll there will but tortional stresses that are unlikely to be accounted for in the design of the average people-mover.
Last edited by Wizofoz; 7th Jun 2012 at 09:04.
Yes between 0 and 1g there is still a good chance of continuous fuel feed but the reliability will be reducing with the g load. Reason being that the inertial mass of the liquid remains the same while at the same time the force pulling the fuel down (into the outlet) reduces. Therefore disturbances will cause increasing levels of swirling in the tanks. Therefore with low fuel levels in the tanks keeping the sustained g > +0,5 in a non-aerobatic aircraft might not be a bad idea even though levels below should not immediately lead to disaster. It's just not extremely prudent.
The allowed stress level of an airframe will indeed only be the limiting factor for the altitude you need for the recovery.
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Zero-g vomit comet
Alert: Thread creep!
I am curious about transport aircraft (KC-135, 727...) used for astronaut training, thrill rides, etc. Seems to me that the issues of fuel feed and lube/bearing system integrity are a real factor when flying repeated zero-g parabolas - how is this addressed technically?
I am curious about transport aircraft (KC-135, 727...) used for astronaut training, thrill rides, etc. Seems to me that the issues of fuel feed and lube/bearing system integrity are a real factor when flying repeated zero-g parabolas - how is this addressed technically?
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You can perform a constant positive G barrel roll from level flight, but it involes more than one G on the pitch up, less than 1 G (but more than Zero) over the top, and more than 1 G on the recovery.
Again, differences in airplane performance may dictate deviations from the traditional "true" barrel roll, which is a roll in 3 dimensions about a point on the horizon 45 deg off base heading. While some may go below 1 G across the top, they should ALWAYS have positive backstick displacement referenced from the trimmed pitch position at entry speed.
To keep it in the context of transport category airplanes, it is more likely a 30 deg reference point would be used, keeping max pitch to +/- 30 deg instead of 45 deg. A faster roll rate would be required, but less pitch authority, initial airspeed, and G.
Dog Tired
I have never read such rubbish.
A barrel roll has four distinct features:
* The wings are vertical at the horizon in the first quarter
* horizontal (inverted) at the top (well above the horizon)
* vertical at the third quarter (on the horizon)
* recover to the horizon, wings level, at the end.
All positive G.
QED
A barrel roll has four distinct features:
* The wings are vertical at the horizon in the first quarter
* horizontal (inverted) at the top (well above the horizon)
* vertical at the third quarter (on the horizon)
* recover to the horizon, wings level, at the end.
All positive G.
QED
I have never read such rubbish.
A barrel roll has four distinct features:
* The wings are vertical at the horizon in the first quarter
* horizontal (inverted) at the top (well above the horizon)
* vertical at the third quarter (on the horizon)
* recover to the horizon, wings level, at the end.
All positive G.
QED
A barrel roll has four distinct features:
* The wings are vertical at the horizon in the first quarter
* horizontal (inverted) at the top (well above the horizon)
* vertical at the third quarter (on the horizon)
* recover to the horizon, wings level, at the end.
All positive G.
QED
Yes, all positive G, but positive G at values that can be both greater and less than 1 (you can do the entire maneauver at greater than 1 g, but the G will still vary throughout).
Last edited by Wizofoz; 8th Jun 2012 at 07:02.
The way a barrel roll was originally explained to me is to think of a loop (as in looping the loop) as a coil of wire. Hold the two ends of the wire and pull them apart and hey presto you have a barrel roll.
So you can have a small barrel or a large barrel (or anywhere in between).
Whilst a good barrel roll involves only modest amounts of "G" there is, in fact, more looping involved than rolling.
The hazards of rolling an aircraft which is not cleared for such maneuvers is that if you mess it up you might end up pulling lots of G and/or exceed limiting speeds.
Recall the story of Neil Williams (who was probably the best aerobatic pilot around at the time) who when he was a demonstration pilot on the Jetstream performed a barrel roll in cloud whilst the sales people were in the back with potential military buyers sipping their gin and tonics. Allegedly nobody even noticed that he had done so!
So you can have a small barrel or a large barrel (or anywhere in between).
Whilst a good barrel roll involves only modest amounts of "G" there is, in fact, more looping involved than rolling.
The hazards of rolling an aircraft which is not cleared for such maneuvers is that if you mess it up you might end up pulling lots of G and/or exceed limiting speeds.
Recall the story of Neil Williams (who was probably the best aerobatic pilot around at the time) who when he was a demonstration pilot on the Jetstream performed a barrel roll in cloud whilst the sales people were in the back with potential military buyers sipping their gin and tonics. Allegedly nobody even noticed that he had done so!
Anyone have an iPhone app that can record video and its accelerometer readings at the same time?
Some measurements will go a long way towards answering what goes on during various rolls.
Some measurements will go a long way towards answering what goes on during various rolls.
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Barrel rolls by big aircraft and large formations
Have a look at this earlier pprune series ....
http://www.pprune.org/military-aircr...nk-please.html
A barrel roll to the left usually starts from initial level flight with a gentle descending turn to the right to pick up speed. At about 30 deg right bank the roll starts to reverse to the left, 'g' increases, and the nose is pulled up to start a flight path which describes the perimeter of a barrel.
Slight positive g is maintained at the apex of the 'barrel' albeit pulling the aircraft downwards as the aircraft (one or a formation) are nose high upside down at this cardinal point. The roll continues to the left, the nose slowly drops towards the horizon at the 270 degree point, the roll continues to a slightly nose low finish which becomes level flight once more as the aircraft (or formation) completes the full 360 degree rotation.
A barrel roll by say a B-707 or an aerobatic team will describe similar flight paths. The 707 has lowish structural limits and a formation team needs to keep the 'g' lowish to enable safe close formation flying, particularly by the outer and inner wing men in large formations.
http://www.pprune.org/military-aircr...nk-please.html
A barrel roll to the left usually starts from initial level flight with a gentle descending turn to the right to pick up speed. At about 30 deg right bank the roll starts to reverse to the left, 'g' increases, and the nose is pulled up to start a flight path which describes the perimeter of a barrel.
Slight positive g is maintained at the apex of the 'barrel' albeit pulling the aircraft downwards as the aircraft (one or a formation) are nose high upside down at this cardinal point. The roll continues to the left, the nose slowly drops towards the horizon at the 270 degree point, the roll continues to a slightly nose low finish which becomes level flight once more as the aircraft (or formation) completes the full 360 degree rotation.
A barrel roll by say a B-707 or an aerobatic team will describe similar flight paths. The 707 has lowish structural limits and a formation team needs to keep the 'g' lowish to enable safe close formation flying, particularly by the outer and inner wing men in large formations.
Anyone have an iPhone app that can record video and its accelerometer readings at the same time?
Some measurements will go a long way towards answering what goes on during various rolls.
Some measurements will go a long way towards answering what goes on during various rolls.
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Hogwash
Sorry, late to the discussion.
DKM needs to get out more. In fairness the Nimrod the crashed at Toronto into Lake Ontario was NOT doing any sort of roll. I was there.
It was a very sad day.
DKM needs to get out more. In fairness the Nimrod the crashed at Toronto into Lake Ontario was NOT doing any sort of roll. I was there.
It was a very sad day.
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Further to post #35 about 'barrel rolls' in large jets or formations ...
I have found an early 1960s video of 9 Lightning F1s rolling in formation at the RAF Coltishall 1962 Battle of Britain Display (great days sadly now disappearing).
In this video East Anglian Film Archive: Spitfire To Lightning, 1962 towards the end at 13 mins 25 secs 74(F) Sqn does a 9 aircraft formation barrel roll.
One can imagine a B-707 with a smaller wingspan than a 'diamond nine' of Lightnings flying a similar trajectory.
With the B-707 the wings are of course all one fixed structure: thus on entry to a roll to the left the aircraft first descends nose low to the right, thus the right wing tip is descending and the left wing tip is rising. The same happens in the 'diamond nine' formation (Lightnings or Red Arrows) with the outside aircraft on the right initially descending and the outermost left aircraft initially ascending. Line astern is a little easier with aircraft stepped down to avoid jetwash. But they are still offset slightly (downwards) from the formation leader's flight path throughout the roll manoeuvre.
I have found an early 1960s video of 9 Lightning F1s rolling in formation at the RAF Coltishall 1962 Battle of Britain Display (great days sadly now disappearing).
In this video East Anglian Film Archive: Spitfire To Lightning, 1962 towards the end at 13 mins 25 secs 74(F) Sqn does a 9 aircraft formation barrel roll.
One can imagine a B-707 with a smaller wingspan than a 'diamond nine' of Lightnings flying a similar trajectory.
With the B-707 the wings are of course all one fixed structure: thus on entry to a roll to the left the aircraft first descends nose low to the right, thus the right wing tip is descending and the left wing tip is rising. The same happens in the 'diamond nine' formation (Lightnings or Red Arrows) with the outside aircraft on the right initially descending and the outermost left aircraft initially ascending. Line astern is a little easier with aircraft stepped down to avoid jetwash. But they are still offset slightly (downwards) from the formation leader's flight path throughout the roll manoeuvre.
