Barrel Roll - How much G?

[fireflybob]

As you guys in the military do more aerobatics than us civvies I thought you might take a look at this thread:-

Barrel Roll (http://www.pprune.org/forums/showthread.php?t=326695)

Just how much G do you pull in a well executed barrel roll?

Thanks for any help

[soddim]

Allright, I'll bite.

How long is a piece of string? A barrel roll can be as tight or loose and lazy as you like and the G varies accordingly. As the manoeuvre is simply an elongated loop (imagine a crooked loop around the inside of a cylinder) that involves rolling and pulling the size will determine the amount of G needed for any given entry and exit speed.

At, say, 400kts entry speed, a typical airshow barrel roll will be around 4G max.

No doubt there will be as many different answers as there are barrel rollers in military jets!

[VinRouge]

The key to keeping the G+T in the glass is maintaining positive G all the way round. to this end, its NOT a 1g roll. as you bottom out you will always be pulling more than 1g to bring the nose up to the horizon.

If you dont pull enough at the top the G+T will end up in your lap!

[Bob Viking]

Not that I profess to be any kind of authority on the subject of aeros, but I know we're not all experts!
A girl on my Linton Course (no names, no pack drill!) managed to overstress the Tucano in NEGATIVE G (can't remember the limits) during a barrel roll!
I seem to recall the 'book' described the barrel roll as a gentle rolling/looping manouevre involving moderate positive G!
How we laughed.
Before we realised aeros are really only for losers with nothing better to do!
BV:E;)

[Roland Pulfrew]

The key to keeping the G+T in the glass is maintaining positive G all the way round

As ably demonstrated by the legendary Bob Hoover.....!

http://uk.youtube.com/watch?v=Xp2Uc9XvmjY

[bayete]

VB,
It is possible to go the other way, I am sure many a QFI has had a go in the Tutor (+6 to -3g limits). With varying amounts of success.;)
Outside loop starting at the top is scary:\

[soddim]

There is a popular misconception that the barrel roll is one of the least risky airshow manoeuvres. In fact, many pilots have crashed during low level barrel rolls because they have allowed the pitch attitude to get too much nose down during their rolling pull. Sadly, many do not realise that they need to roll wings level and recover, opting instead to continue the rolling pull.

Ground kills are invariably 100%.

[Occasional Aviator]

There's also a misconception about the stress this puts on aircraft. Just as the G will vary as you are pulling with or against gravity, it also varies across the aircraft - ie the g at the inner wingtip is less than the g at the outer (I think I got that right) placing a lteral stress on the airframe.

[soddim]

Agreed, stress is an issue that is addressed in military aircraft limits - rolling G limits are invariably lower than the limits for a symmetrical pull.

Glider pilots should be particularly aware of rolling limits.