60 years ago: The famous Boeing 707 prototype barrel roll over Lake Washington

originally posted by: buddah6

originally posted by: F4guy

originally posted by: verschickterack to level with the result that the aircraft
So what is it now, aileron or barrel-roll? Tex himself called it a "short barrel roll".
Where does one start to differ between those two? I know how they are described both.
If you reduce it to that, an aileron roll would be a tiny barrel roll also, because you end up in pitch movements unvoluntary/have to pull up nose to not loose altitude

It depends a little on whose doing the defining. When I first began international precision aerobatic competitions the barrell roll was a compulsory figure in the known program. The criterion was that it was a constant angular momentum pitch change of 360 degrees (a loop) integrated with constantly increasing bank to 180 degrees and then constantly decreasing bank back to level with the result that the aircraft finished the figure or manuever 90 degrees off heading to the entry heading. There was no figure delineated as an aileron roll, but the closest thing was a "slow" roll which is a full 360 degree roll with constant roll rate and constant flight track. What the nose does during this roll depends on airfoil section (symetrical v. high cambered) and angle of incidence of the wing. The g loading for this roll starts at +1, goes to 0 (actually +1 laterally) at 90 degrees bank, to -1 at inverted(where it gets really quiet because unless you have fuel injection or a pressure carb and a header tank system the engine quits) and back to +1 at the end. And then you have the "snap" roll, which is an accelerated stall autorotation on a constant heading and constant altitude, unless you are doing the snap on a vertical up or down line. In the Sukhoi I would routinely see +9 gs on mutiple inside snaps and -9 on outside snaps

I think where we disagree is that you are flying an airplane with neutral dynamic stability and I flew an airplane with positive dynamic stability. You have to force your plane through maneuvers and my bird wants to correct itself without inputs from me. Your plane stays where you point it and that's why you pull negative Gs at the top of your roll. Just a guess.

No, dynamic stability will have no effect on g loading at the inverted point of a correctly performed slow roll. It may affect the amount of control input necessary to maintain the correct attitude and flight path. For example, a Bellanca 8KCAB is a very dynamically stable aircraft. If you do a perfect roll, you will see -1g at the inverted point. You have to. G loading is physics, not aerodynamics.Because even though it has a semi symetrical airfoi with some camber on the bottoml, it still takes a negative angle of attack to maintain altitude in inverted flight. You are upside down and you are not helping gravity by descending, so you have 1 negative g. Now, because it is a stable airplane and it wants to split s back to upright, compounded by the large angle of incidence, further compounded by the pig-like roll rate,it takes both arms and hands shoving forward on the stick to maintain altitude in level inverted flight. In fact, with some female students it took jamming the trim tab full nose down (which is up if you are inverted) and grabbing the diagonal cross-member above the glareshield for leverage. With the Sukhoi with neutral stability, 0 incidence, fully symetrical wing and a roll rate of 540 degrees per second, You still see -1g at inverted but the control pressure is negligible. A rule of thumb is that the more dynamic stability a plane has, the more control pressure it takes. A Stearman or Waco or DC3 will wear you out in pitch. The Dc3 will also strain you in roll forces if it's heavy. The Pitts (S-1 models), Extras, Caps, T-38s, Learjets, and G150s are fingertip airplanes. But you will see -1G at the inverted point in every one of them

a reply to: F4guy

I think, you are describing my point. A PDS airplane flies differently than a NDS airplane. I believe that a fighter is built with NDS to make it more maneuverable. If I understand NDS, it means that if you roll to 60 degrees and remove your hands from the controls the plane will remain at 60* until more input from you. A plane with PDS, when you remove your hands, the plane will recover to a level condition. Is this correct?

BTW, I owned a 7KCAB for about 5 years.

originally posted by: buddah6
a reply to: F4guy

I think, you are describing my point. A PDS airplane flies differently than a NDS airplane. I believe that a fighter is built with NDS to make it more maneuverable. If I understand NDS, it means that if you roll to 60 degrees and remove your hands from the controls the plane will remain at 60* until more input from you. A plane with PDS, when you remove your hands, the plane will recover to a level condition. Is this correct?

BTW, I owned a 7KCAB for about 5 years.

You've got the general idea right but stability round the roll access is more a function of wing dihedral. With a lot of positive dihedral the center of gravity is below the center of mean aerodynamic lift so they want to align on the vertical axis and the way to do that is to level the wings. The Sukhoi was so neutral it didn't even have a elevator trim tab. That's why it tumbles so well.

a reply to: F4guy
Could we both be correct on the barrel roll? On your F-4, you may need to push negative at the top of the roll because of it's NDS. On my airplane with PDS doing a barrel roll I wouldn't necessarily need to push negative because of the inherent tendency to right itself. I could release the controls at the top of a roll and wings would right themselves and after a phugoid or two would level out. You couldn't do that in a F-4 could you?

originally posted by: buddah6
a reply to: F4guy
Could we both be correct on the barrel roll? On your F-4, you may need to push negative at the top of the roll because of it's NDS. On my airplane with PDS doing a barrel roll I wouldn't necessarily need to push negative because of the inherent tendency to right itself. I could release the controls at the top of a roll and wings would right themselves and after a phugoid or two would level out. You couldn't do that in a F-4 could you?

I was talking about the slow roll. With a true barrel roll, you have positive g all the way around but it has bothing to do with stability, dynamic or otherwise. It is because of the helical flight path. There is angular momentum throughout the manuever and that is an acceleration vector that produces a positive g. That helical flight path doesn't occur with a slow roll, where, for a time, the aircraft maintains a level flight path while upside down. That results in -1g at that point. And you talk about a phugoid oscillation leading to wing levelling. Phugoids only relate to pitch and not roll. It is a trade-off of kinetic energy and potential energy leading to equilibrium. Your Citabria will eventually roll back to upright because of the 2 degree wing dihedral.

a reply to: F4guy

I know that dihedral causes the wings to level and phugoid is in pitch. Maybe I need to be more clear in what I write. As far as the Citabria dihedral of 2 degrees...I'm not sure but 7* comes to mind.

I taught unusual attitudes to my two oldest children and a handful of CAP cadets in the Citabria. We put about 300 hours on it in five years. Then I moved on to a Grumman AA-5B Tiger. As fate would have it, the Tiger was destroyed in a tornado that tore up several planes and two hangars in 1986.

a reply to: buddah6

F4guy, I was racking my heavily medicated brain about why you needed to go negative on the top of a barrel roll. I looked at the dynamics and you said "NO" to that. I know that I never had to go negative while doing a barrel roll in any of the aircraft that I've flown. I was under the impression that we were discussing the maneuver performed by Tex Hill in the B-707. Now, you state that you were referring to another type of roll other than the barrel roll being discussed. I was having a difficult time putting my head around what you were saying...I never considered that you were jerking my chain.

a reply to: buddah6

You can push negative at the top of a barrel roll by releasing back pressure past neutral to create a 2point barrel roll. In air combat manuevering it would be a half displacement roll, followed by a slicing roll to lag pursuit.Also, to the extent that a rolling turn involves a somewhat helical flight path(barreling) in practice, negative gs occur at the inverted point of every roll, or at the upright point of every roll if the rolls are opposite to the direction of turn.

a reply to: F4guy
a reply to: buddah6

I really enjoyed reading your discussion
The +1G / -1G, is it in perspective to ground or to the pilot? Strange question maybe.

What I mean, if you are upside down and push the stick forward doing an outside loop, at the top point where you are leveled and heads up, is it designated negative or positive G? I suppose it´s negative?

But when you do a -lets say- nose dive, you are accelerating towards earth, law of inertia makes your body want to stay where it is while accelerating faster then 9.81m/s² so you get pressed in your seat. Is this also considered negative?
They only would get positive when decelerating towards earh and your momentum of inertia now points downwards?

Could you say:
Downwards (towards earth) momentum -> +
Upwards (away from earth) momentum -> -

Or is it relative to your craft?
Upwards (away from seat/craft) -> -
Downwards (into seat/craft) -> +
regardless of the planes relative position towards earth

I learned all these things in physics but not in this millenium and I never needed them again so bear with me please.

a reply to: verschickter

To keep it simple, a positive g is one that pushes you down in the seat. Negative pushes you up out of the seat. On an outside loop from the bottom like you described, at the top where you are momeushing and pulling them.ntarily upright, there is still a slight bit of negative g. An analogy would be swing a can of paint in the vertical plane in a perfect circle. You still feel your arm pulled up at the top, although not as much. Of course, talking about gs is not as much fun as pulling and pushing them