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Champs, F-4s, Adverse Yaw

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  • Champs, F-4s, Adverse Yaw

    Thought this discussion should be on a new thread. FYI I learned to fly in a J-3 Cub, flew a Cessna 140 and one of the very early Citabrias that still had oleo gear. Later, when I was in the USAF I flew newer Citabrias and owned a homebuilt flat wing Pitts with a 135hp engine and later was partners in an S-2A. Wish I could afford to do that kind of flying again. When I went to jet upset school 2 yrs ago I realized that was the first time I had been upside down or pulled more than 1.35 gs since I was involved with the Bud Light BD-5J 20 yrs ago.

    I flew the champ between those two events with Roscoe Morton (chief announcer at OSH and LAL, captain of the US aerobatic team when Charlie Hillard won the world championship, Roscoe hired me on the airline and later was a roomate for a while which explains how I got on the OSH announcer's stand) at Walt Ruckel's grass strip in Niceville FL probably about the middle 1980s, and I just couldn't keep the thing coordinated even in a gentle turn to save my life. Both my landings surprised me, maybe I was lucky but they were both greasers, and I'm usally only about a 30% "shooter" on landings. Even on the DC-10, the easiest airplane to land in my almost 40 years of flying, I only "shoot" about 40% (maybe because they are all 9 hour legs when you're up all night crossing the Atlantic, dreaming about air racing). (We're parking the DC-10s, absolutely a joy to fly but a huge fuel hog. I'll miss her.)

    I flew the "hard wing" F-4s, had about 3 rides in C models and the rest of my 2 years in "double ugly" were split between Ds and Es. At Korat we had very unique airplanes (we were the ones with the shark teeth on the nose) in that we had the "new" cockpit (hands on throttle weapons select, front seat auto-aquisition, better lighting, etc.) but the old hard wing.

    Many folks don't realize that the ailerons on the F-4 only deflect down, they don't go up. The spoiler on the down going wing goes up. The problem seems to me, and I'm no aerodynamic expert, that the aileron was twice the size of the spoiler and maybe it should have been the other way around.

    Due to the wing sweep, at high G rudder gave you a very good roll rate. If you noticed the F-18 demo at Reno, on each flight he did a high G/high AOA rudder roll to the right heading away from the crowd while in burner.

    At low AOA you can use aileron just fine in the F-4 and when dirty there is an aileron/rudder interconnect that coordinates the turns in the traffic pattern (like the T-34 and Convair 580, the only other airplanes I've flown with that, there's probably more out there.) As AOA increases the adverse yaw increases to the point that the airplane will depart controlled flight. They added an aural tone that worked in a series of "beeps" and varied pitch, starting out at low pitch and low repetiton, speeding up to a high pitch then at C/L max AOA would be a steady tone (there was also the visual aoa guage that corresponded to the tone), and as I recall this was at 21.2 units AOA which was an arbitrary scale. Above 21.2 you starting getting a higher pitch beeping that would increase in frequency until the airplane departed, at which point you had a lot more on your mind than a tone in the headset. So any time you heard a beep, which started at 15 units AOA, you quit useing aileron. Obviously you could use less and less aileron up to a point as AOA increased but there was no way to guage it so we just used the rule of thumb any time you hear the tone neutralize the ailerons and use rudder.

    What I never understood is that the T-38 did a real pretty 1G rudder roll, whereas the F-4 at 1G the rudder would give you mostly yaw, but at 21.2 units AOA, which at 480KIAS (corner velocity for the hard wing airplane) and 8.5 g, rudder only would give about 200 degrees per second roll rate, which was pretty adequate.

    You may be interested to know that these airplanes don't really "stall" the way the Champ does. In the T-38 (which actually buffets at 2 gs in the pitch out in the traffic pattern) as AOA passes C/L max you start getting wing rock of about 45 degrees either way and a huge sink rate. In the F-4, the Dash One (flight manual) defines the stall as "directional stability deteriorating and going negative as angle of attack is increased". In other words, the tail tries to go in front of the nose. The recovery is "stick forward, ailerons and rudder neutral, if not recovered maintain full forward stick and deploy drag chute" (these memory items were reviewed at every briefing and I remember them after 35 years). It is possible to spin both the T-38 and F-4, in the T-38 the spin is un-recoverable because both engines will flame out and not windmill enough to provide hydraulic pressure for the flight controls, but it's very difficult to force the airplane to spin. Likewise, the F-4 has to be forced to spin. What is interesting about the F-4 is that a "normal" departure is a very violent manuever, whereas the spin is a very comfortable ride (so I'm told). Since the airplane can roll right while yawing left (yes, I've seen the video) the best way to find you're in a spin is that it is a smooth ride with forces pushing you forward in the seat (due to gyro forces since the CG is behind you) and the turn needle will be pegged in the direction of the spin. The procedure for that is "stick, maintain full forward... aileron full WITH spin, aircraft recoverd, ailerons neutral" (this assumes you already have the chute out.) The interesting thing here is that aileron is applied full WITH the spin to use adverse yaw to recover. Opposite rudder is never applied, don't ask me why. Rudder stays neutral.

    In a "normal" departure you're pulling more than you should, the AOA tone is high and fast, and all of a sudden you feel a big uncommanded yaw and before you can unload your'e gyrating and being thrown all over the cockpit. You hold the stick full forward and after a few gyrations the airplane instantly unloads and you fly up against the canopy, the airplane does a couple uncommanded aileron rolls, and you're back flying, minus about 300 knots of airspeed. Never did have to deploy the chute, but I always had a bunch of altitude.

    In the USAF we were never supposed to get to the point of departure although I did twice, both times with an IP in the back seat and I'm pretty sure the guys talked me in to departing on purpose. We were not to get below 200 knots but I saw zero airspeed on my own several times, no problem. The Navy and Marines, which do not have controls in the back seat like the USAF, and therefore didn't have IPs in the back, TOLD their students to do both zero airspeed and intentionally depart the airplane. Kind of like the debate over spin training in GA today.

    The modern airplanes use computers (the F-4 did have pitch, roll, and yaw dampers although the roll damper was supposed to be off for heavy manuevering, and having lost the yaw damper gets a little goofy on landing but no big deal) and fly by wire to allow the pilot to use controls in a conventional manner. If the pilot wants to bank right he puts in right stick, the computer decides which controls to move, it may be only the rudder(s) move and the ailerons don't. So the newer planes are easier to fly. But they have so much more capability, like sustained G, but mainly the amount of information bombarding the crew, plus many fighters only are single seat, that they are much harder to "fight" than the older airplanes. A lot easier for the brain to go in to "hydraulic lock" trying to digest all the data, so I think it's probably harder to be a fighter pilot today than "way back when", even though the airplanes are easier to fly (had an ex-Thunderbird tell me what a scam the inverted pass is, all they do is put the flight path marker from the HUD on the horizon and you have a perfect pass, and I do NOT mean this a knock against the T-birds!)

    Hope this wasn't too boring, I got a little long winded but that's why I put it on a separate thread.

    Ron Henning
    Ron Henning

  • #2
    Re: Champs, F-4s, Adverse Yaw

    Ron, Let's go have a few beers together -- I want to hear more! Sky Galley Restaurant @ KLUK! Or meet you half way at Lexington, Blue Grass.

    This just increases my respect for the test pilot community! How much of the F-4's "departure" characteristics -- and recovery procedures -- were predicted, and how much was seat-of-the-pants learning? The multi-variate recovery options boggle the mind, much less when trying one more option, or hitting the silk!

    I'd almost rather be a Saab driver! Thus the Karmic proverb, "'Reborn' from jets." Peas
    Last edited by Peashooter; 09-21-2006, 06:55 PM.
    Rutan Long EZ, N-LONG
    World Speed Record Holder

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    • #3
      Re: Champs, F-4s, Adverse Yaw

      Thanks Ron!

      Comment


      • #4
        Re: Champs, F-4s, Adverse Yaw

        Originally posted by Ron101502
        The modern airplanes use computers (the F-4 did have pitch, roll, and yaw dampers although the roll damper was supposed to be off for heavy manuevering, and having lost the yaw damper gets a little goofy on landing but no big deal) and fly by wire to allow the pilot to use controls in a conventional manner. If the pilot wants to bank right he puts in right stick, the computer decides which controls to move, it may be only the rudder(s) move and the ailerons don't.
        That's only sort of true. For fully fly-by-wire aircraft like the F-16 and F-117, this is true (I assume it's probably true for the Raptor and F-35). For jets like the Hornet and Eagle, it still works a lot less high-tech than you might think.

        In the F-15E (which the ex-Rhino pilots call the 'Phantom III' because of the many system and handling similarities to the F-4) the fly-by-wire system ONLY controls the rudders and differential stabs. Even then, the surfaces move exactly the way that they're commanded by the stick in the cockpit. The only difference is that the Eagle, like the Phantom, has the aileron-rudder interconnect at all times (except after touchdown). Side note: this creates very sloppy habit patterns for guys like me who also want to fly piston aircraft -- especially tail draggers -- because we essentially fly around with our feet on the floor unless we're dogfighting!

        Now, the flight control computer does make changes to the control surfaces, but the vast majority of it has to do with rates of control surface movment at different AOA (not with which direction the surfaces point). What this applies mostly to is the ailerons, which are still commanded directly my a hydro-mechanical link to the stick. At high AOA, the FCC reduces the amount of aileron deflection to reduce the potential for a departure induced by adverse yaw.

        In the twin-tailed jet, we HAVE to use rudder at high AOA to make the nose move because of the washed-out ailerons. The differential stab deflection that lateral stick movement at high AOA gives does roll the jet, but because the stabs are all ready nearly fully deflected at high AOA, they don't deflect to command the roll as far as they could at lower AOA. This means that the two rudders are significantly more effective at pointing the nose than the stabs are.

        The jet is also spin resistant, but there are plenty of ways to depart the jet while being a buffoon with the stick. The famous way to do that in an Eagle is to go from a high-AOA, aft-stick position and push the stick forward while simultaneously moving the stick laterally a bit. That roll input inertially couples to give the jet basically an outside snap roll (but slower and less violent). It's a very effective gun jink, by the way, but prohibited in the Dash 1!

        Originally posted by Ron101502
        I think it's probably harder to be a fighter pilot today than "way back when", even though the airplanes are easier to fly
        I think that's the idea behind making the airplane easier to handle from a stick and rudder aspect....to free up brain cells to work the avionics. I think the Eagle is an easier airplane to fly than the T-38: the E-M diagram of the Eagle is so much more forgiving and allows essentially the same rate/radius turn to be commanded over a 100-know window. The T-38 has about a 20-knot window.

        Sure would have loved to get some time in the F-4 though. That's an airplane that wins on style points, hands down. Like a big '57 Chevy Belair.

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        • #5
          Re: Champs, F-4s, Adverse Yaw

          Randy,
          Not trying to hi-jack the thread, but Hey it's good to hear your input on these supercharged blow-torch characteristics. Hope you guys are doing fine.
          John Slack

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          • #6
            Re: Champs, F-4s, Adverse Yaw

            Coolest... thread... ever!
            _________
            -Matt
            Red Bull has no earthly idea what "air racing" is.

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            • #7
              Re: Champs, F-4s, Adverse Yaw

              Originally posted by Ron101502
              In a "normal" departure you're pulling more than you should, the AOA tone is high and fast, and all of a sudden you feel a big uncommanded yaw and before you can unload your'e gyrating and being thrown all over the cockpit. You hold the stick full forward and after a few gyrations the airplane instantly unloads and you fly up against the canopy, the airplane does a couple uncommanded aileron rolls, and you're back flying, minus about 300 knots of airspeed. Never did have to deploy the chute, but I always had a bunch of altitude.
              Ron Henning
              Reminds me of two things: 1)SI's Rick Reilly recounting his Blue Angles ride: "I egressed the box of Milk Duds I had in 6th grade"; and 2) my ride when my dad was checking out in a Bonanza when I was 12 -- they did successive accellerated stalls, which for me brought on the quickest onset of "mal-de-air" I ever had! "Hey, what's the ground doing up there!?! -- whoof!
              Rutan Long EZ, N-LONG
              World Speed Record Holder

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              • #8
                Re: Champs, F-4s, Adverse Yaw

                I've watched and called out the rudder "kick" and return to neutral during flight control checks on hundreds of F-4 launches (I was a D-model crew chief)...........and I've never heard the reasoning behind it explained as well as this thread has done!

                THANKS!

                Roger

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                • #9
                  Re: Champs, F-4s, Adverse Yaw

                  As I remember the rudder would kick back to neutral when we pulled the "paddle switch" on the stick that disabled what passed for computers in those days so the rudder would go back to neutral as the ARI was disconnected. Someday a poor Airbus A318/319/310/321/350/380 pilot will wish they had a paddle switch.

                  Ron
                  Former A319/320 F-4 pilot
                  Ron Henning

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