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Old October 5th 14, 04:20 AM posted to rec.aviation.piloting
Orval Fairbairn
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Default Unbelievable Airbus A380 vertical Take-off + Amazing Air Show ( HD ) Paris Air show 2013

In article ,
Dudley Henriques wrote:

On Saturday, October 4, 2014 1:35:03 PM UTC-4, Orval Fairbairn wrote:
In article ,

Dudley Henriques wrote:

On Friday, October 3, 2014 5:28:05 PM UTC-4, Robert Moore wrote:

Orval Fairbairn wrote

Any airplane that can take 3G can be aileron rolled successfully. It

would be like watching an elephant dance.

Why 3Gs? I don't recall any specific elevator input when doing

aileron rolls back in my Navy aerobatic training nor more

recently while flying a YAK-52. You aren't one of those people

who confuse aileron rolls with barrel rolls are you?

Bob Moore

I'm fairly sure Orval means that the airplane should be capable of at

3g's coming off the backside of the roll, especially for a non-aerobatic

airplane. In an aileron roll in these airplanes you will be above 1g

temporarily as you pull the nose up to a set point to initiate the roll.

the roll begins you can of course unload the wing or go over the top at
1g as

desired. But the back side recovery will be a rolling pullout with

asymmetrical g loading on the wings. It's here you have to be careful in

aerobatic aircraft. The ability to handle at least 3g's would be a


Dudley Henriques

Another factor, not usually talked about is the lateral centrifugal

accelerations imposed on the engine pods -- both lateral from the

rolling and the coupled inertial forces between the rotating masses and

the airframe attitude changes.

An old co-worker described an autopilot test in the Convair 880:

He was applying a preplanned set of gains to the autopilot and reading

the aircraft responses when another told him to look outside at the

engines. He said that one of the engines was moving in a figure-eight

motion -- they immediately suspended the tests.

When you have such large, flexible structures flying in unusual motions,

you may see some unusual (and not always pleasant) sights.

Orval, I take it you are referring here to Johnston's prototype roll over the
Seattle yacht races?

No -- that was a previous poster.

The story I told was the experience of a former co-worker who was
working on the autopilot gains on the Convair 880 or 990. He was
plugging in a gain schedule and pulsing the autopilot and noting the

The pod dynamics are yet another issue rarely discussed outside
technical circles, but they can have major consequences.

If so, absolutely right on lateral g effect on the pods.
Word had it after the incident that Johnston studied what he wanted to do
before the flight and decided the answer to all the issues combined was in
getting the nose attitude high enough before he initiated the roll that
once initiated, diagonal yoke pressure would produce a 3 dimensional roll
path with inside (bottom) rudder being released through the top to minimize
the back side dish out.
In other words what he actually did was a loaded 3 dimensional roll using
minimum g but held positive throughout the roll. By keeping it ball centered
throughout the roll he kept the plane of symmetry in line with the velocity
vector thus minimizing the lateral g.
The word was his biggest concern was keeping the scavenger pumps working.
It was a gutsy stunt for sure and Allen gave him holy hell :-) To keep
everything going in the right direction (forward with no yaw) he was
completely committed to the back side recovery arc with whatever the dish out
would be coming over the top.
It sold one hell of a lot of airplanes for Boeing !
Dudley Henriques

I am not sure that Tex Johnson considered the pod issues when he did the
(in)famous roll over the Gold Cup races, but I agree that it sold a lot
of Boeings.

I briefly knew Harold "Trimotor" Johnson, back in the early 1960s. He
was reputed to have looped and rolled B-24s.