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I have heard that the F4 Phantom pilots can make barrel rolls at lower speed /higher AOA. They use only rudder deflection and keep the stick column centered (left /right wise)-only pull onto the belly to have the G's- to prevent adverse yaw effects. Does the spoiler on top of the wing move during the maneuver if the aileron stay neutral? The way it works for level rolls is : one side aileron deflected down but the other one is not (there is some slat(spoiler) on the other wing to assist the aileron down deflection. Is there a built in type of assistant like ailerons - rudder interconnection to help maneuvering? Or do the wings remain clean with no deflection of the control surface?

enter image description here

of course it depends upon the situation and the specific fighter. when maneuvering at high angles of attack and high G, I always used solely aft stick and rudder, never any aileron or spoilers input. Sometimes I would use full rudder, all the way to the stops. Other times, not so much.

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    $\begingroup$ "When the F4 Phantom pilots makes barrel rolls at higher AOA, they use only rudder and keep the stick column centered." Where does that come from ? It seems highly confusing to me, are you sure you didn't mix things up ? $\endgroup$
    – MaximEck
    Oct 4 '20 at 9:55
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    $\begingroup$ The second option you're describing is not a barrel roll but a snap roll which is actually a spin carrying a lot of forward speed. $\endgroup$
    – MaximEck
    Oct 4 '20 at 14:52
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    $\begingroup$ I don't think he's describing a snap roll. A swept wing with dihedral tips will certainly exhibit aerodynamic coupling between yaw (or more properly sideslip) and roll, and this effect will be most pronounced at high angles-of-attack. Needs to be developed into a proper answer, but I'd have to find appropriate sources as I'm no expert on the F-4. $\endgroup$ Oct 5 '20 at 17:10
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    $\begingroup$ where does that image come from? and that citation? $\endgroup$
    – Federico
    Oct 7 '20 at 11:10
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    $\begingroup$ The first thing you need to fix, which may get some of the DV's removed, is the idea that the slat is a surface on top of the wing. That's not what a slat is. The deflected surface shown in your photo is a spoiler or spoileron. I don't know whether the F-4 used differential spoiler deflection (i.e. spoillerons) as part of the roll control system. Your basic question seems to be, in part, whether surfaces on the wings automatically deflected whenever the rudder was deflected; the answer is almost certainly "no" $\endgroup$ Oct 7 '20 at 18:09
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A Barrel Roll is a maneuver where the aircraft flight path follows what would be the surface of a huge horizontal barrel in the sky. To do this you of course need to roll the aircraft. To roll the Phantom, no matter what maneuver you are attempting, requires that you create differential lift on the wings. (more lift on the up-moving wing than on the down-moving wing). At low angle of Attack (AOA), in any model of F-4, you use the ailerons/spoilers to do this. At higher AOA, the ailerons would induce adverse yaw, and therefore you need to create this differential lift by yawing the aircraft with the rudder (since it's a swept wing aircraft). As AOA increases above 10-12 units, the pilot needs to blend in more and more rudder, and less aileron, until at high AOA (19 units in early non-slatted aircraft like F-4B/C/D), he is using rudder exclusively. In later slatted aircraft (USAF F-4Es, F-4Js, USN F-4J/S, etc.) this effect was somewhat mitigated by the slats (they energized the airflow over the top of the wing), and the pilot could use some aileron throughout the AOA range, (but still less and less as AOA increased), all the way to 25 units AOA.

As to your other question about slat deployment, this happened automagically, based on AOA, at about 12-14 units AOA as I recall. And then would retract when AOA fell below 10-12 units... No pilot input was necessary.

So, in the execution of a Barrel Roll in the F-4, starting at 450 KIAS and low AOA at the entry point, the aircraft would climb and descend 4-5000 feet, and slow to somewhere between 200-250 KIAS and higher AOA at the high point, and then accelerate back to 450 KIAS and low AOA at the completion of the maneuver. As a result, the need for aileron and rudder to effect the roll continuously and gradually changed throughout the maneuver.

NOTE. (to address comment made in the question relating to photograph). The F-4's ailerons did move up slightly when the stick was deflected towards that wing, but at high AOA, the aerodynamic effect was negligible due to the wing blanking the airflow back there. SO the F-4 also had spoilers on the top of the wing that would deflect upwards as well, both to decrease the lift on the wing and cause a roll in that direction, and to add drag on that wing to balance the drag from the down aileron on the opposite wing. The control surface deflected on the upper wing in the photo is the spoiler, caused by the pilot pushing the stick to the left.

The following is from the USAF F-4E flight Manual: enter image description here enter image description here

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  • $\begingroup$ Pretend that not everyone here is a pilot. What is a "unit" of AoA? Is it a degree, some percentage of max elevator deflection, something else entirely? $\endgroup$
    – FreeMan
    Oct 5 '20 at 14:41
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    $\begingroup$ In the F-4 AOA was displayed and referenced in all manuals and documents in arbitrary "unit"s, which represented the actual AOA angle. The relationship between AOA units and AOA degrees, or radians, or Milliradians was not specified. We were only taught the relationship between the units and the aerodynamic properties that the aircraft at various AOA values, Un-loaded (very low AOA) was 3-5 units, L/Dmax occurred at 10-12 units, Cl max (Max performance or approach AOA) occurred at 19.2 units (non-Slatted) and at 25 units (slatted). Stall (loss of directional control) occurred at 23/29 units. $\endgroup$ Oct 5 '20 at 15:31
  • $\begingroup$ ... and my apologies for not "pretending"... I've never been good at that... otherwise I might "pretend" that not everyone here was polite.... oh wait, they're not... $\endgroup$ Oct 5 '20 at 15:35
  • $\begingroup$ Thanks for the info. That strikes me as odd that they would use "units" and not something that people would come in with a basic understanding of. Most people can reasonably guestimate 15° or 30°, but 25 "units" has no built in human intuition point. OTOH, maybe that's why they went with it... $\endgroup$
    – FreeMan
    Oct 5 '20 at 15:42
  • $\begingroup$ no worries, I added the explanation from the USAF F-4E flight Manual. It appears that the units, from 0 to 30 "units" represent angular rotation of the AOA probe from -10 to + 40 angular degrees. How that aligns with actual AOA is of course ALSO arbitrary, as it is a measurement taken from the arbitrary line of the mean aerodynamic chord (MAC) of the main wing. $\endgroup$ Oct 5 '20 at 15:47
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They are 3 different ways to roll an airplane:

First the barrel roll during which the airplane is flying normally, you are keeping positive g rate and using ailerons to induce the roll. The trajectory is making a wide spiral and you use rudder input to keep the symmetry of the flight.

Second the aileron roll, where the aircraft continues in a straight line and your airplane is almost rolling on itself, the roll rate is dependent on your ailerons input and you use rudder to displace the nose of the aircraft around the central axis by mostly crating lift when your roll position is equal to 90 or 270°.

Barrel roll vs aileron roll

Finally and that is what you are describing is the snap roll or flick roll. Which is basically a horizontal spin. flying low you simultaneously apply full rudder deflection and pull the yoke. This means you have high AOA and non symmetrical flow inducing a spin by stalling one of the wing. But you have enough forward momentum to continue in a straight line, thus making it looks like a roll. Once the snap roll initiated, some aileron might be needed to either keep or stop the rotation but as for a normal spin this might change from one aircraft to another.

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  • $\begingroup$ True, but I asked about the F4 only-there's something ( a system maybe that couples the rudder with slats)? That's all? $\endgroup$
    – George Geo
    Oct 4 '20 at 15:40
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    $\begingroup$ A mechanical link between rudder and any control surface on the wing doesn't make sens as they are supposed to work around two different axis. What exist are yaw damper that replace rudder input in coordinated turn and electronics. New military aircraft have combined control surface deflection to increase maneuverability and the flight performances of the aircraft. But that's the onboard computer doing it and I don't think this apply to the F4 $\endgroup$
    – MaximEck
    Oct 4 '20 at 15:48
  • $\begingroup$ I asked because in some simulator the opposite slat lifted a bit(3degrees) and along with the aileron if rudder deflection to cancel any little disturbance from the level flight. $\endgroup$
    – George Geo
    Oct 4 '20 at 16:50
  • $\begingroup$ I think the categorization of rolls into 3 types is somewhat arbitrary. For what you are calling the "aileron roll", you are saying that the rudder is used to create sideways lift at 90 degrees and 270 degrees. Does it not also follow that forward stick should be used to create negative (skyward) lift at 180 degrees? But the diagram you posted doesn't show the aircraft in a nose-high attitude when inverted, nor does it show it in a nose-high attitude at 270 degrees. (The attitude at 90 degees isn't illustrated.) (ctd) $\endgroup$ Oct 5 '20 at 17:00
  • $\begingroup$ (....ctd) I think most pilots would consider an aileron-roll to be a positively-loaded maneuver, just with a higher roll rate, less time to complete, and less variation in G-load and aircraft attitude and trajectory than a "barrel roll". Meanwhile your description of an "aileron roll" really sounds more like a "slow roll"-- which in theory could be completed at any roll rate, slow or fast, but the key point being that the aerodynamic force vector / G-loading continually points in the skyward/ earthward direction, rather than "upward"/ downward in the pilot's reference frame. $\endgroup$ Oct 5 '20 at 17:03

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