Jet Transport Barrel Rolls
 

Impossible to maintain a 1g barrel roll? Bob Hoover and I will have a jolly good laugh about that.:p

Loose rivets

I think you may have meant +g rather than 1g?

You will need more than 1g to keep the pitch going - how much will depend on the pilot and the aeroplane.

The video just shows that Bob was able to maintain the g-forces in z-direction of the airplane. It does not show or demonstrate the absolute value of the g-forces. If you look close enough, you will see that he began the rolls while in climb.

EDIT: The latter serves as proof enough that a barrel roll is NOT a 1-g-throughout manoeuvre. (You cannot initiate a climb from level flight without pulling more than one g.) Since Tex stated such in his interview, most pilots believe the one-g-barrel-roll must be true. Well, physics is optional for a pilot...

All you need do is make the normal force of your butt in your seat be +1, which is completely doable with the right helical trajectory.

You'd better not try it any other way...

G forces in a roll
 

Think about it. When the aircraft is inverted, to maintain a perceived +1G in your seat, the aircraft has to be accelerating toward earth at the equivalent of 2G, which is the acceleration of gravity plus the perceived 1G on your butt. That's the equivalent of 64.4 ft / sec^2, or a descent that increases by almost 4,000 ft/min for each second the aircraft is fully inverted.

If you fly a helix that starts in level flight and sees a perceived constant +1G in your seat, you will end up in a steep dive that will require much more than 1G to recover from. Both Hoover and Johnston executed their rolls by first pulling up into a climb (>+1G) to reduce the altitude loss when making the maneuver, but both saw greater than 1G at the beginning of the loop, and likely at the end. It's simple physics.

Well, sorta. I'd put a +/- 0.5g tolerance band on that 1g - and absolve Capt. Johnston of all sin. ;)

Not exactly a barrel roll, but it proves the point that in maintaining positive g, you end up going downhill.

Well I did think about it, and you need a centripetal acceleration at the top of the loop of 2G, which tells you the radius and roll rate (smaller radius = bigger roll rate) at the top, where it is maxed out - the rest amounts to literal "seat of pants" flying to adjust the roll rate sinusoidally until wings level + 360.

-drl

Arr, yes, the standard barrel roll since time began.

Back on thread, you lot!

http://www.runemasterstudios.com/gra...ges/hijack.gif

They performed a modified aileron roll, not a barrel roll. A barrel roll is something entirely different:

Barrel roll - Wikipedia, the free encyclopedia
Aileron roll - Wikipedia, the free encyclopedia

Since you are worried about thread drift, I'll leave it to you to sort out the difference.

... and following through, tell us what radius you would need to maintain 1G as you level out at the bottom of the loop. (Infinite is not an acceptable answer.)

1g barrel roll
 

So you start at 1g, level flight. You want to roll while maintaining +1g. This goes great until you roll wings level with the nose pointed at the earth. If you can get back to level flight without pulling more than 1g then I'll eat my G meter. Of course you could start with the nose well above the horizon, at 1g. Again, you would have to somehow get that nose up there...

Ex CEO and ex owner of CimberAir J.Nielsen might know some details...

ATR may have been damaged in 'barrel roll'

Hogwash. DKM needs to take a few aeros lessons. :O

Oh, and the video ain't there.

Dunno what the "hogwash" is about...

While you might get pendantic about his use of the word "axes" in context, a proper barrel roll is done in 3 dimensions. The visual reference is a point/object at or slightly above the horizon approximately 45 deg left or right of the nose. The object is to keep that point stationary on the canopy/windscreen as you "roll around" it. Acceleration felt in the airplane should never exceed 2 Gs, which is within the limits of transport category airplanes.

OTOH, it is easy for a novice to mess it up and "bury" the nose when inverted, get scared/anxious, and pull excess G to recover.

The first usable description of a true barrel roll. And now the 1g barrel roll people please explain, how you are going to do that with a constant 1 g. :ugh:

Dont ask, i know how barrel rolls are flown, not in transport aircraft but in jets. I can count at least one thousand of them and either did all of them wrong as not a single one was a contant 1 g roll:) or it´s just my old memory which plays tricks on me:\

Watch my smilies, its a funny discussion.

franzl

I should have expanded... My "hogwash" comment was directed at the claim by DKM in the Flight article that a barrel roll is more complex than an aileron roll; IMO an aileron roll is far more likely to overstress an airframe than a properly flown barrel roll.

A barrel roll IS more complex than an aileron roll! It is more difficult to learn, and more difficult to perform correctly.

If performed unloaded (0 to +0.5G) and started with sufficient nose-up attitude appropriate to the airplane's roll rate, an aileron roll is VERY unlikely to result in any overstress.

Either maneuver, done improperly, can result in excess nose-down attitude. In either maneuver, this is the most likely time the inexperienced pilot will panic and overstress the airplane. As OK465 indicated, it is MUCH more likely with a poorly executed barrel roll than with an aileron roll, since the barrel roll will normally result in a momentary 30-45 deg nose down when done properly. An aileron roll should not result in more than 5-20 deg nose down, again depending on the roll capability of the specific airplane.

Exactly !
You can't do a 1g barrell roll without finalling crashing into the ground.
And the reason is simple:
God's own G.
Meaning if you want to keep 1g on the airframe even while inverted, you will be accellerating towards mother earth with 9,81 m/s * (1-cos Alpha). alpha being the angle of bank.
The longer you are inverted, the more vertical descent rate you build up.
If not exceeding 1g you will not be able to arrest this descent.

Therefore the slow roll rates of an airliner make this maneuver so much more problematic than in an aerobatic aircraft. Not only will the latter be able to take more g, it will even require less due to the shorter time in inverted position and thus lower descent rate.

Alternative is to go below 1g while inverted but this causes other problems like fuel feed.

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.