Agree with you up to this point- any positive G should not result in fuel feed problems, and Airliners sre stressed to (IIRC) +2.2 -1 G with flaps up.

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.

Re Fuel feed:
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.

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?

A true barrel roll should not go below 1 G. Even "over the top" (which is really more like "across" the top at [30 to] 45 deg nose high and [30 to] 45 deg heading from base course), approx 1 G is maintained to pull the nose across, continuing to [60 to] 90 deg from base course when inverted and at the horizon. Barrel rolls can be done in formation without the wingman ever having to go below 1 G.

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.

Tex J was happy enough to call it a barrel roll...he also did a couple of 'Barrel Rolls' in B47's.

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

Did anyone say any different?

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).

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!

I get these headaches...

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.

Barrel rolls by big aircraft and large formations
 

No, but I have extensive expeience in Aircraft with actual G meters- what would you like to know?

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. :sad:
It was a very sad day.