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Official Freewing 90mm F-4 Phantom II Thread

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  • Grabbed a quick flight this evening and practised long smooth banked turns .......went fine for the first, say half circuit, then the nose started to drop needing a wee bit rudder to lift it. Happened three time, carbon copies...screws up the smooth turn a bit. I'm already 15mm behind stock CG and don't want a repeat of the vertical lift off I had when the battery was further back although I know it would help keep the nose up. The plane will obviously lose some airspeed in a turn but it is still travelling at a fair lick ........... Is a rudder/ail mix the only answer?

    Comment


    • Originally posted by locharrow View Post
      Grabbed a quick flight this evening and practised long smooth banked turns .......went fine for the first, say half circuit, then the nose started to drop needing a wee bit rudder to lift it. Happened three time, carbon copies...screws up the smooth turn a bit. I'm already 15mm behind stock CG and don't want a repeat of the vertical lift off I had when the battery was further back although I know it would help keep the nose up. The plane will obviously lose some airspeed in a turn but it is still travelling at a fair lick ........... Is a rudder/ail mix the only answer?
      Edit: Definition: Adverse yaw means the nose goes left when the aileron is commanding a right roll. And vice versa.

      Well…..I shall give my perspective from flying planes with shorter wing spans and my 80+ ft long wing ASH-25E sailplane which has tremendous adverse yaw. Also, knowledge from several instructors and text books. Take it for what it is worth. Apply it as you will.

      First the aerodynamics and physics. When wings are level, the lift vector is straight up. This vector counters the weight vector. In a bank, assume no pitch change, the lift vector now points sideways at an angle. Since the lift vector hasn’t changed in magnitude, if you resolve the vector into a right triangle, you will see the vertical component is less. Therefore, the aircraft will descend in a turn. This has nothing to do with CG. It has everything to do with vectors. To offset the loss of effective lift and to counter the weight vector so you do not descend, the pilot must apply up elevator when banked.

      Now for the rudder. The ONLY purpose of the rudder (outside of aerobatics) is to counter the adverse yaw generated by the ailerons. So, a proper/coordinated turn will require application of the rudder while the ailerons are deflected at the start of the roll/bank. Once the bank is established, the rudder is moved to the center because the ailerons are no longer deflected. To keep the “ball” centered or the yaw string centered, rolling to the right one MUST apply right rudder…and rolling left, one must apply left rudder. All the while applying an amount of up elevator. Coordinated turns look good, and feel good if you are in the plane.

      In the ASH-25E sailplane, a nearly full rudder is required to keep the yaw string centered while rolling into the bank. The rudder is re-centered once the bank is established. And, a small amount of up elevator is required. The ailerons are WAY OUT THERE, so they generate a huge amount of adverse yaw.

      Now let’s move to short wing aircraft (say a Cessna) or RC planes. The ailerons are so close to the fuselage, very little adverse yaw is generated when the ailerons are deflected. Not much rudder is needed when a roll is initiated. Technically speaking, the yaw moment of ailerons close to the fuselage is minimal.

      Some long wing RC planes AND lllooonnnggg wing RC sailplanes benefit from the application of rudder in the turn (or maybe they don’t even have ailerons) to counter adverse yaw. For RC planes without aileron, the skidding by the rudder application causes a differential lift vector on each wing, and the plane banks. For these planes, the rudder banks them. You can do this in full size planes, too….but your passengers will throw up. It feels terribly uncoordinated because it is.

      For the F-4 or MiG-29, or P-38 or AL37, I never touch the rudder unless I am on the ground, or doing some aggressive aerobatics. The ailerons are so close in and/or tiny that their adverse yaw is negligible. For my LONG wing RC sailplane, I apply enough rudder to make it look coordinated. Right bank = right rudder at the start of the bank and vice versa.

      However, when I bank….up elevator is applied to counter the effective loss of the vertical lift vector. The AL37 needs a lot of up elevator in a bank.

      If rudder is used to raise the nose, you are no longer in a coordinated turn, but instead slipping sideways.

      Bottom line, in short wing RC aircraft, using rudder in a turn is a waste of effort. Use it if you want to, but it isn’t needed. And using it to raise the nose in a bank will mean you are in an uncoordinated slip.

      And my full scale fighter jet pilot friends tell me they leave their feet on the floor most of the time (figuratively speaking). Why? The ailerons of these jets (or tailerons) produce very little adverse yaw. The rudder isn’t needed when turning. In my long wing sailplane, by golly, a lot of rudder is needed…but needed to keep the turn coordinated…not to raise the nose.

      -GG

      PS Answer this question on any FAA exam other than “to counter adverse yaw” about the purpose of the rudder, and you will miss that question. Why? There are many dead pilots who attempted to turn their aircraft from base to final using rudder….skidding as it were. This set-up can induce a stall of the wing on the inside of the turn (among other things the pilot may do), and the plane fatally spins in.

      Comment


      • Would what you saying be the same as doing a knife edge? I ask because if you are doing a knife edge and the nose starts to drop, don't you apply rudder to keep the nose up?

        Comment


        • Originally posted by Coconut View Post
          Would what you saying be the same as doing a knife edge? I ask because if you are doing a knife edge and the nose starts to drop, don't you apply rudder to keep the nose up?
          Of course….and that is why I stated that I don’t touch the rudder unless I am doing aggressive acrobatics.

          My main point was….rudders are not needed once the coordinated turn is established. AND in a coordinated turn, up elevator is required to increase the vertical lift vector to avoid descending in the turn. AND with small span RC planes, there is not enough adverse yaw as you deflect the ailerons to begin the roll to need rudder anyway. Once established in the bank, rudder is neutral and ailerons are neutral (or slightly held opposite the bank to avoid increased bank angle).

          Using rudder to raise the nose means you are slipping. Slipping means increased drag and this exacerbates the slowing in the turn.

          A knife edge is an aggressive slip maneuver….totally not coordinated. When I do this in an aerobatic full scale plane, the ball or yaw string (in a sailplane) is NOT centered.

          In a knife edge, the vertical component of lift from a wing at 90 degrees bank is zero (do the trigonometry). So only side-load lift off the fuselage (for lack of a better term) that resolves into a vertical component of lift AND the thrust vector from the prop or jet engine with the nose raised by the rudder resolve into a vertical component both additive and sufficient to counter the weight vector.

          -GG

          Comment


          • GG, thanks a lot for your write-up, that was very good information. I find that I do need to use rudder on all of my longer-wing planes, like my B24. I find that its really useful to mix the rudder in with the aileron on the radio. That way the rudder is used with the aileron, as you suggested. I don't usually do aerobatics with the B24, but I have a switch to turn off the mix if I want to. I agree, using rudder in the turns isn't needed on short-wing planes.

            Interestingly, I found that mixing rudder in with the aileron is very useful with the F104 Starfighter. Just a bit. I find that when you apply aileron the nose tends to want to go in the opposite direction. The F104 has stubby wings, so its not adverse yaw from the ailerons - from what little I understand, it has to do with the fact that the F104's tail fin has almost as much area as one wing panel.
            Marc flies FW & FL: AL37, MiG-29, T45,F4, A4, A10, F104 70 and 90, P38, Dauntless SBD, Corsair, B17, B24, B26 & P61, Lipp.P19, ME262, Komets, Vampire, SeaVixen, FMS Tigercat, FOX Glider & Radian XL.

            Rabid Models foamies, including my 8' B17 & 9' B36... and my Mud Ducks! www.rabidmodels.com

            Comment


            • Thanks!!

              However, key point. Your statement below “IS the classic definition of adverse yaw”. What the rudder overcomes. Thus, at the initiation of a right turn, right rudder is needed to keep the nose from going left.

              “I find that when you apply aileron the nose tends to want to go in the opposite direction.”

              Comment


              • Originally posted by GliderGuy View Post
                GG PS Answer this question on any FAA exam other than “to counter adverse yaw” about the purpose of the rudder, and you will miss that question. Why? There are many dead pilots who attempted to turn their aircraft from base to final using rudder….skidding as it were. This set-up can induce a stall of the wing on the inside of the turn (among other things the pilot may do), and the plane fatally spins in.
                GG, It is possible to rudder stall an 1:1 F-4D and induce an inverted spin. That is all that needs to said about that. Best, LB
                Captain: Got any ideas?
                F/O: Actually not.
                — Captain Chesley B 'Sully' Sullenberger III and F/O Jeff Skiles—

                You'll never be good at something unless you're willing to suck at it first.
                ~Anonymous~

                AMA#116446

                Comment


                • Dumbfounded on thus one. I recently upgraded my Phantom for the 8S setup due to struggle of taking off on a grass strip. I have a set of Gooniac's fireybooties installed. I also switched out my AR636 for a AR637T. After I got everything installed, checked the AB lights using a servo tester and the flight pack, and everything worked as should be. Then Y'd them to the throttle channel of the 637T and voila, smoked one of the leads to the ESC controlling the AB lights. No throttle applied. Disconnected the burnt ESC and re-tested the ESC and BEC for the motor, and all sames to work fine. I'm at a loss on what could've caused this. Did not have the red wire connected, just the signal and negative.
                  Attached Files

                  Comment


                  • I have a question. I'm not arguing. Just trying to learn something. If I'm in a left aileron bank and notice that I'm losing altitude(the nose is dropping), can I use right rudder to keep altitude(keep the nose from dropping)?

                    Comment


                    • Some additional info about Adverse Yaw, if I may beg your patience.

                      What causes adverse yaw? And a BIG thanks to the Wright brothers for inventing the rudder allowing them to achieve CONTROLLED flight by man - a true first.

                      Important fact/law: If lift increases, drag also increases.

                      Situation: Controls are moved to initiate a roll to the right.

                      Results of this control stick movement: Right wing’s aileron moves up, and the left wing’s aileron moves down. This is like lowering a “flap” further out on the left wing and having an upward reflexed flap further out on the right wing.

                      Therefore, the lift increases on the LEFT wing (down aileron) and the lift decreases on the RIGHT wing (up aileron).

                      More lift = more drag! So, the LEFT wing experiences MORE drag. The left wing is pulled back WHILE the wing rolls to the right. Hence, adverse (or opposite) drag. Rolling right while yawing left.

                      In the early experiments with manned flight, adverse yaw killed pilots by throwing the plane out of control.

                      The Wright bros came up with the brilliant and simple rudder to overcome the differential drag caused by controls moving such as to roll the wing right and left (at first wing warping….the aileron came later).

                      -GG

                      Aside: Through experiments with a large scale RC flying model of a Pteranodon, it was determined that this giant flying dinosaur twisted its head to obtain yaw control. On some video, I recall seeing a pelican go out of control and crash into the water when it got too sideways and the head locked into a sideways twisted ugly yaw lock due to air loads.

                      PS Yes...I know that the change in lift is due to the change in camber that is introduced by the deflection of the ailerons (and/or flaps). But, I was trying to keep the concept more easily understood.

                      Comment


                      • Originally posted by Coconut View Post
                        I have a question. I'm not arguing. Just trying to learn something. If I'm in a left aileron bank and notice that I'm losing altitude(the nose is dropping), can I use right rudder to keep altitude(keep the nose from dropping)?
                        Outside of intentional aerobatics….

                        But why would you intentionally do something that will introduce a case of uncoordinated flight? Pitch control belongs to the elevator.

                        Application of the right rudder to raise the nose “may” work, but you are making the plane enter into a side slip (uncoordinated flight). Application of the elevator does NOT cause the plane to enter into a side slip.

                        Note: Some planes, if the airspeed is slow, may violently and suddenly snap roll to the right when the top/right rudder is applied. An “over the top” uncontrolled roll can happen. Same if banking left with top rudder.

                        Applying elevator to raise the nose is far less likely to introduce such a reaction.

                        The short answer is….coordinated flying is MUCH better. Defining coordinated flight as: the ball will be centered or the yaw string will be centered (read…no yaw).

                        -GG

                        Aside: When flying the V-tailed Sisu sailplane (photo) in a steep thermalling bank, I discovered fine adjustments in airspeed/pitch were more easily accomplished with the rudder. I reasoned, with some thought, that (while in a steep bank) the more horizontal of the “V” tail parts would (because of the V-tail mixer mechanism) be acting like a more horizontal (parallel to the horizon) elevator. So, to slow a few knots, I would apply top rudder a little. Only a slight displacement of the yaw string would result and the nose would nicely come up a degree or two.

                        Click image for larger version  Name:	82E0D8B6-A64C-416B-B382-B234FD1DAA21.jpeg Views:	0 Size:	86.1 KB ID:	315209

                        Also, anyone who knows about the deadly spiral dive and pilot killer knows that in very steep turns, the application of up elevator only tightens the turn and increases G loads….eventually causing structural failure. My little discovery about the V tail was related to behavior in very steep banks. But….I don’t think that many of us are flying RC planes that have V tail mixer mechanisms. (Not the same thing as the inverted V of the F-4 tail). If you have a V-tail sailplane with a transmitter mixer setup, you can try my technique for pitch control in steep thermalling turns. It might work well.

                        By the way, to get out of a deadly spiral dive….roll wings level. Then slowly bring the nose up with the elevator. Vertigo in clouds may prevent non-instrument rated pilots from being able to find a wings level flight attitude.

                        Comment


                        • One more tip for pitch control in a bank…..

                          This may seem to fly in the face of what I present above, but TRY IT….you’ll LIKE IT!

                          Mind blowing time / here goes - For slight pitch adjustments in a bank it works nicely to change the amount of the bank angle AND NOT ADJUST THE ELEVATOR AT ALL.

                          To wit - Decrease the bank to raise the nose and conversly, Increase the bank to lower the nose.

                          This technique relies on what the bank angle is doing to the vertical component of the lift vector.

                          I primarily do this for fine tuning pitch changes vs using the elevator.

                          But the most fun application is with the MiG-29 or F-4. Be on base leg a bit high and roll into a steep bank to line up for a high speed pass. As you roll in, the nose will drop and by playing the bank angle vs lining up vs altitude, you may never need to adjust the elevator until it is time to get parallel to the ground.

                          The most practical use is if I see that I am beginning to change altitude in a wide sweeping turn, a slight bank angle adjustment stops the altitude change in an instant and with a seemingly finer response than with application of elevator.

                          Note: Using this technique does not, for short wing aircraft, introduce uncoordinated (yawing) flight. Whereas, application of the rudder to control pitch DOES produce uncoordinated slipping or skidding flight which may have bad consequences as discussed above.

                          -GG

                          Comment


                          • Originally posted by rlcamden View Post
                            Dumbfounded on thus one. I recently upgraded my Phantom for the 8S setup due to struggle of taking off on a grass strip. I have a set of Gooniac's fireybooties installed. I also switched out my AR636 for a AR637T. After I got everything installed, checked the AB lights using a servo tester and the flight pack, and everything worked as should be. Then Y'd them to the throttle channel of the 637T and voila, smoked one of the leads to the ESC controlling the AB lights. No throttle applied. Disconnected the burnt ESC and re-tested the ESC and BEC for the motor, and all sames to work fine. I'm at a loss on what could've caused this. Did not have the red wire connected, just the signal and negative.
                            Quick update...I replaced the burnt esc and re-installed my AR636 rx back into the Phantom. Hooked everything up, and no smoke.

                            Comment


                            • Safety update. After smoking my ESC for my AB lights on my F-4, if you run the 8S setup and a Spektrum AR637T, you will smoke the negative side of the throttle lead. I replaced the 1st ESC with another one of the same style and received the same results when I powered the AB lights. When I only hooked up a 6S battery, everything work without any issues. The minute I plugged in the 8S, smoke. Just thought I would share this so others would know.
                              Attached Files

                              Comment


                              • Originally posted by rlcamden View Post
                                Safety update. After smoking my ESC for my AB lights on my F-4, if you run the 8S setup and a Spektrum AR637T, you will smoke the negative side of the throttle lead. I replaced the 1st ESC with another one of the same style and received the same results when I powered the AB lights. When I only hooked up a 6S battery, everything work without any issues. The minute I plugged in the 8S, smoke. Just thought I would share this so others would know.
                                What AB are you using? I use the RC Geek burners. I've got 11 of them but I power them off of a 2S 250-450 mah Lipo. I don't believe the AB's are set up to run off of the power from the RX, 6S or 8S. IMO, a much better set up is a small 2S Lipo solely for the burners.
                                Hugh "Wildman" Wiedman
                                Hangar: FL/FW: Mig 29 "Cobra", A-10 Arctic, F18 Canadian & Tiger Meet, F16 Wild Weasel, F4 Phantom & Blue Angel, 1600 Corsair & Spitfire, Olive B-24, Stinger 90, Red Avanti. Extreme Flight-FW-190 Red Tulip, Slick 60, 60" Extra 300 V2, 62" MXS Heavy Metal, MXS Green, & Demonstrator. FMS-1700mm P-51, Red Bull Corsair. E-Flite-70mm twin SU-30, Beast Bi-Plane 60", P2 Bi-Plane, P-51.

                                Comment


                                • Click image for larger version  Name:	1A66D96D-07EB-4049-980D-010718E1DF3F.jpeg Views:	4 Size:	75.7 KB ID:	315352
                                  Can’t have too much (or too many) of a good thing.

                                  8s JetFan powered Brigadier General Richard Stephen "Steve" Ritchie F-4 on the left. Ready for maiden.
                                  6s JetFan powered Colonel Robin Olds F-4 on the right. About 25 awesome flights to date.

                                  Comment


                                  • Flyinhigh ...Do you think you could breed young 'uns off that pair??

                                    GG....thank you for the dissertations on the nose drop in a "smoooooth" banking turn. Out yesterday again with 1/4" back on battery but still only get + - half circle before I have to give up. How about this I found on'tinternet ???

                                    In a conventional aircraft you don't use the rudder to control the nose up or down in a coordinated turn, you use the elevator. The rudder is used to keep the turn coordinated.(Overcome the yaw created by difference in lift between left and right wing.)

                                    As you enter the turn (starts to bank) the correct deflections are:
                                    1. Apply aileron in the direction of the turn.
                                    2. Almost at the same time as you apply the aileron you start to give some rudder in the same direction.
                                    3. As the aircraft starts to bank smoothly increase elevator to keep the nose at the same attitude. (Or slightly higher.)
                                    4. When you have the desired bank angle, ease off on the aileron deflection, at the same time as you decrease rudder deflection. In order to maintain the same bankangle you gonna end up with having to actually put in some aileron in the OPPOSITE direction as you are turning in.

                                    This mean that established in a turn the controls should be: Back pressure on the elevator, rudder in the direction of the turn and aileron in opposite direction of the turn.

                                    This is true for real conventional aircraft, and as I understand it should also be true for model aircraft as well.


                                    Where the guy says opposite aileron is much the same as you say, ease off the bank.............that will be my next step. If successful I will toast you with a glass of wine, if not I will drown my sorrows in two glasses!!

                                    Comment


                                    • What he should have typed is…..

                                      This mean that established in a turn the controls should be: Back pressure on the elevator, rudder IS Decreased to NEUTRAL and aileron in opposite direction of the turn.

                                      Why no rudder needed in the established bank? Once the bank is established, the aileron deflection goes away. This means adverse yaw is GONE. Therefore, NO rudder is needed any more.

                                      A slight opposite aileron may be needed to keep the bank from getting steeper.

                                      The key is that most short wing RC planes have VERY little adverse yaw. You don’t need rudder! If you use rudder when there is no adverse yaw, you WILL BE skidding or slipping and flying uncoordinated.

                                      Save your rudder for doing aggressive aerobatics.


                                      -GG

                                      Comment


                                      • Couple of flights today...did one trial long banked circuit entering with 3/4 throttle and increasing to full about 1/3 way round Seemed to hold things together a lot better with little or no nose down tendency. Couldn't guarantee it is a solution because it was just a single run. (Still looked and sounded awesome) Weather permitting more tomorrow hopefully !

                                        Comment


                                        • Originally posted by locharrow View Post
                                          Couple of flights today...did one trial long banked circuit entering with 3/4 throttle and increasing to full about 1/3 way round Seemed to hold things together a lot better with little or no nose down tendency. Couldn't guarantee it is a solution because it was just a single run. (Still looked and sounded awesome) Weather permitting more tomorrow hopefully !
                                          Good show!

                                          A short analysis (I promise), The reduced vertical lift component caused by the bank is being countered by #1 increased thrust vector and/or #2 increased speed = increased lift or both.

                                          So, you can do the same thing by applying back stick. In a steep bank with a full size plane, the throttle is advanced (and the rudder is centered once the bank is established).

                                          -GG

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