Jet Transport Barrel Rolls

[Loose rivets]

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

Bob Hoover Airplane Roll - YouTube

[John Farley]

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.

[TripleBravo]

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...

[deSitter]

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.

[stepwilk]

If you look close enough, you will see that he began the rolls while in climb.

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

[ST27]

G forces in a roll

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.

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.

[barit1]

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...

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

[barit1]

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

Howard DGA 15 Barrell Roll - YouTube

[deSitter]

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.

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

[Capn Bloggs]

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.

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

Back on thread, you lot!

[ST27]

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

Back on thread, you lot!

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.

[ST27]

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.

... 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.)

[Lumps]

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...

[no-hoper]

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

ATR may have been damaged in 'barrel roll'

[Capn Bloggs]

Originally Posted by David KM

The climb is indicative of a "barrel" roll, a manoeuvre more complex than a basic aileron roll because it requires constant changes, in all three axes, to the aircraft's direction of travel.

Hogwash. DKM needs to take a few aeros lessons.

Oh, and the video ain't there.

[Intruder]

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.

[RetiredF4]

Intruder
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"

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.

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 itīs just my old memory which plays tricks on me

Watch my smilies, its a funny discussion.

franzl

[Capn Bloggs]

Hogwash. DKM needs to take a few aeros lessons.

Dunno what the "hogwash" is about...

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.

[Intruder]

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.

[henra]

Originally Posted by RetiredF4

And now the 1g barrel roll people please explain, how you are going to do that with a constant 1 g.

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.