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Old October 4th 14, 11:54 PM posted to rec.aviation.piloting
Dudley Henriques[_3_]
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Default Unbelievable Airbus A380 vertical Take-off + Amazing Air Show (HD ) Paris Air show 2013

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 least


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.. Once


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 non


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


number.


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?
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
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