Ailerons, Rudder & Adverse Yaw RC Model Airplanes

[@robertgordon5562]

Excellent video. Could we get a video of you flying your sporty yellow airplane?

[@TimMcKay56]

Sure, it is the Radian UMX. Tim kzbin.info/www/bejne/npXWoaGFZ8mmaZY

[@tauncfester3022]

Tim, I believe the model robertgordon5562 is referring to, is the one in the jump cut starting @6:48 in this video. I'd like to see it fly also.

[@robertgordon5562]

@@tauncfester3022Yes that is the one.

[@johncarroll993]

Excellent, so many questions answered in a very uncomplicated way. I built a foam board profile 4 channel electric model so I could practice this without fear of disaster or expense. Now, I have a much better understanding of what I set out to learn. Thank you 👍

[@TimMcKay56]

Glad things worked out!

[@craighermle7727]

The more I fly FPV drones, the more respect I gain for "you" rc guys

[@TimMcKay56]

😊👍🏻 Tim

[@Hneely]

I only had to look one place to answer a question that I’ve needed an answer to. Thanks Tim👍

[@TimMcKay56]

Thanks for checking in! Tim

[@mikenadler7118]

Very good video. I taught basic aeronautics to 2nd, 3rd, and 4th graders on a very limited basis after I retired. More discussion on "coordinated turns" would have been helpful. Thank you for another great video.

[@TimMcKay56]

Mike: Many thanks! Tim

[@echassin]

In the case of rudder-only, dihedral is important to start and end the turn simply because the skid/yaw caused by the rudder forces the large surface of the opposite wing directly "sideways" into the air flow. With just-right-perfect dihedral, a rudder-only plane can easily do rolls, even snap rolls. For aileron-only planes, there are ways to prevent adverse yaw if it's even an issue: first, avoid any bit of aft CG (which is all too common and often overlooked when diagnosing an odd-flying model). A slightly forward CG will keep the nose down in a bank and give the model the appearance of carving out a nice path even though there's no rudder. If that's not enough, another way to eliminate adverse yaw is with aileron differential throws, either achieved mechanically at the servo horn and/or control surface horns, or with the transmitter using dual aileron servos. The up-going aileron travels farther than the down-going aileron and eliminates the excess drag on the opposite wing. One can even go as far as not having any downward aileron travel but I've never seen that. These techniques can be useful because for a beginner or intermediate flyer, coordinated turns with rudder and aileron together is easy to suggest but that can be an insurmountable challenge.

[@TimMcKay56]

Great points, thanks! Tim

[@vincentfittante5979]

Great job professor!

[@TimMcKay56]

Thanks! Tim

[@Coops777]

Great video Tim. I'm currently studying my recreational instructors certificate and, when seeing "adverse yaw" in your title, couldn't resist watching! (My CFI got me to perform a classroom brief and then we flew "Effects of controls" with him as my pretend student). We are using a Legend AL3 cub (J3 clone). It is a great design and only has mild adverse yaw (but still requires rudder to co-ordinate the turn)

[@TimMcKay56]

Thanks for the info, and best of luck with your training! Tim

[@txkflier]

Adverse yaw is generally only a problem on planes that have a flat-bottomed wing such as a trainer. If the ailerons deflect up and down equally, the down-going aileron will cause much more drag than the up-going aileron due to the air pressure difference above and below the wing. I eliminate the adverse yaw by making the up-going aileron deflect further than the down-going aileron. Some people mix aileron into the rudder channel. That's just hiding the problem and could cause other issues. Other people use the differential function in their transmitter. However, that requires the use of two channels and decreases the throw of the down-going aileron by decreasing the servo travel in that direction. Whenever you decrease the travel in your transmitter and servos, you decrease the resolution of your radio. And when the linkage doesn't move as far, any slack becomes a greater percentage of the travel which decreases the positioning accuracy of the control surface. If the linkages are below the wing, I create differential throw by taking the servo arms off the aileron servos and putting them back on with a one tooth offset toward the leading edge of the wing. If for some reason, you can't offset the servo arms, you can achieve the same result by moving the control horns back from the hinge line of the ailerons a little bit. In either case, you'll have to lengthen the pushrods so that the ailerons are centered at neutral. In my experience, the up-going aileron needs 1-1/2 to twice as much throw as the down-going aileron.

[@TimMcKay56]

Excellent inputs from an experienced plane builder! Tim

[@tauncfester3022]

So I can add an observation from one of the Edwardian oddities that I scratchbuilt. I made an Avro model F, the 1911 or maybe '12 enclosed cabin fuselage monoplane with mid depth mounted, undercambered wings with a not a lot of dihedral. It was 29" WS and very light at 7 oz.. I initially made it with wing warping, which was not easy to do with wings covered with Doculam. At any rate first flight was over our back yard, and the undercambered wings immediately stopped flying on the outside wing and it would plummet out of the air when you added warping/aileron input. It could be ameliorated by giving a bit of down when turning to keep the outside wing flying but there wasn't much forgiveness in that thin wing's lift, when it was warped just a few degrees up it wasn't flying anymore. I eventually removed the warping and the servo and it flew much better on RET. This is something to consider when building a pre WWI and (or) WWI wing warping aircraft, especially if retaining the undercambered airfoil. at these Reynolds numbers I think they rapidly go from flying to becoming parachutes with very little increase in angle of attack

[@TimMcKay56]

@@tauncfester3022 Excellent points! Tim

[@peterboy209]

Maybe it'll be beneficial to only actuate the inner aileron to counter the adverse yaw problem.

[@TimMcKay56]

Peter: Excellent observation! Many aircraft, to include the F-4 and some airliners use just a spoiler (control surface going up) on the lower wing to bank. Tim

[@txkflier]

@@TimMcKay56 Spoilers only work when the wing is producing lift. See the B-52 crash at Fairchild Air Force Base in 1994..

[@txkflier]

On the subject of rudder only or RET, the wing must have a sufficient amount of dihedral so that when the plane yaws, the relative wind hits the bottom of the wing on the outside of the turn and perhaps the top of the inside wing. I don't see the speed change of the two wingtips creating much difference in lift. There's not that much speed difference due to the yaw. A low-wing plane will need more dihedral than a high-wing plane. On a high-wing plane, I think the relative wind from yawing hits the side of the fuselage and increases the air pressure under that side of the wing. On a low-wing plane, it would tend to increase the pressure above the wing, preventing it from banking into the turn. And, the fuselage would tend to block the relative wind from hitting the top of the wing on the inside of the turn. I've had shoulder-wing planes that would just yaw without rolling and low-wing planes that when yawed would roll in the opposite direction. You can also see these tendencies when trying to perform a knife-edge pass with top-rudder. High-wing planes tend to roll back upright, shoulder-wing planes with no dihedral tend to stay in knife-edge, and low-wing planes with the right amount of dihedral will stay where you put them.

[@TimMcKay56]

Thanks for this update! Tim

[@emersonb5764]

Yes. I built one once, rudder only, with very little dihedral. It took a ridiculous amount of space to complete a turn. Even with a rudder nearly doubled in size. Later I cut the rudder back down and added polyhedral to the outboard 1/4 or so of the wing and it turns like an sob now. It banks like it had ailerons.

[@TimMcKay56]

@@emersonb5764 Great idea! Tim

[@CrashKizzmo]

Tim (gr8 name, btw!), Love yr videos - u break the science down so even a newbie like me can understand! Just bought the FMS F-35 v2, and am blown away by no rudders on the twin tails! Want to add them myself - but do you th8nk they are needed on this bird? Or just bank&yank?

[@TimMcKay56]

CK: Zero need for rudders on your F-35, enjoy! Tim

[@spartan3299]

Ah great video. I know several pilots who never use their rudders. I almost always do, but on some planes I've noticed that I use an opposite rudder input, left aileron turn and a bit of right rudder to keep the dose up, something like Knife edge and a bit of up elevator? Maybe because I'm using more aileron than the standard bank angle requires. I'd sure like to see so kind of coordination indicator, except I don't want to look down at it while flying LOS. I guess on one of my 4 channel FPV planes one could be incorporated into the OSD. I may be over thinking this.

[@TimMcKay56]

No, you are thinking the problem through. Different airplanes can have very different responses to aileron inputs. All good! Tim

[@egtreadway4232]

Very helpful vedio thanks, so on my strix stratosurfer I'm going to mix in rudder with elevons but wondering what would be good percentage of rudder to start with? Thanks again

[@TimMcKay56]

Not sure exactly. But experiment with a smaller amount, see how it works, add more throw as needed. Good luck!

[@egtreadway4232]

Will do thanks

[@collinmccallum]

thumbs up!

[@TimMcKay56]

Thank you! Cheers!

[@craighermle7727]

A little back pressure helps as you steepen the bank

[@TimMcKay56]

Roger that! Tim

[@craighermle7727]

@@TimMcKay56 I used to fly sailplanes. Let me tell ya about adverse yaw

[@tauncfester3022]

I just wanted to add some interesting exceptions. Back in 2003, Hobby Lobby International was selling a Cz. made, EPP foamy 3D trainer with a brushless motor and 4 channels, called the Pigi-3D. It had a huge, slab sided fuselage and it would psuedo yaw-roll rudder turn like a high winged, significant dihedral 3 channel RET model. In ways it would do this both upright and inverted. I believe it did this because of the fuselage was airflow blanking the inside wing in the turn. Edited to add: The DH82 Tiger Moth: Did you know the Tiggy had just ailerons on the lower wing, and they had significant differential where the up aileron angle was nearly 3 times the down angle, to keep the amount of aileron coupled adverse yaw to a minimum. Something to consider if I ever make a DH82 with ailerons in the future. I've also built and scratched a number of balsa/film WWI planes and the RAF SE5a and in particular the plans built Air-Trails freeflight rubber powered SE5 from the late 1930's, when scaled up to 27 inches rudder turned like it had ailerons, if you kept the plans dihedral, and tail surface dimensions. I believe that this was an Earl Stahl design. Peter Rake's AVRO 511 Arrowscout would rudder turn with alacrity with only 3 degrees of dihedral and 20 some odd degrees of wing sweep back, I assume the full flying comma rudder had a bit of help in setting up conditions for this. Your videos are interesting, thanks for taking the time to make them.

[@TimMcKay56]

Great inputs and observations!! Tim

[@robertgordon5562]

I still fly my Pigi-3D occasionally. It was my first foamy.

[@chriskeithb]

Tim I've been told to add elevator in an aeliron turn to help control the loss of altitude the side slip produces. Would I be better to use rudder instead? This is on a PT20.

[@TimMcKay56]

Chris: You are 100% correct. For turns add a bit of up elevator to compensate for the loss of lift with the banked wing. Rudder as needed for a coordinated turn (ball in center of turn indicator). More bank = more back pressure (up elevator). Tim

[@my_dear_friend_]

I thought that in a case of rudder-only turning, the plane banks and turns because the angle of attack of the forward rotating wing is increased (in relation to the air flow) and therefore the lift of that wing is increased? In particular (or only?) when the plane has positive dihedral. The increased airflow over the wing theory appears to me would only apply for the short time one wing is actually moving forward fast than the other and the airspeed difference isn't that great anyway.

[@TimMcKay56]

That is part of it. But I have found the drag from the ailerons has the larger effect on adverse yaw. Especially with the older, WW1 era biplanes with slow flight and a lot of aileron surface. Tim

[@garygullikson6349]

Some low-wing warbird models may not have rudder controls, having only aileron, elevator and throttle controls. They must have some dihedral, and be flown with "yank and bank" style control inputs. i.e. bank model with ailerons, pull up-elevator to make the turn, level wings with ailerons and use elevator and throttle to regain lost altitude. Models flown by "yank and bank" do not fly gracefully. Models without rudders are difficult to taxi and take off, having no tail wheel or rudder for steering to control tendency to yaw left. Rudder control is also necessary during takeoffs and landings to control ground looping tendencies. Well controlled and safe flying of models, or full scale aircraft, actually requires proper coordination of ailerons, rudder, elevator and throttle inputs learned in "ground school" from an instructor and by considerable in-flight practice.

[@TimMcKay56]

Smaller models fly well on three channels of control. You really do not use the rudder that much in flight. You are correct, the fourth channel is needed for steering on the ground and takeoff. Where you really need rudder is with older, slower flying models such as WW1 fighters, where adverse yaw is a real issue.

[@dieterweik6858]

You said that the elevator isn't involved in turning the aircraft. So... using the ailerons to roll the aircraft then pulling up elevator and using the rudder to counter the adverse yaw if it occurs - I've heard this referred to as "banking and yanking" - Is that wrong? Is there another way to make a really tight turn without using the elevator?

[@TimMcKay56]

Well, to be fully accurate with light aircraft you need to use a bit of up elevator prior to any turn, as the banked wing produces less downward lift vector. The up elevator has the wing at a bit of a higher angle of attack thus more lift. As you slightly raise the nose bank is applied and rudder as needed for a coordinated turn (ball in the center of the turn indicator). There is more up elevator when doing steep turns (a training exercise), usually at 45 degrees of bank. Tim

[@dradden1556]

I have an nx8 and just set up a 1.2 ,Eflite Corsair with some as3x, safe etc. Well while doing a control surface test I noticed, when i move the elevator , the ailerons are moving slightly,as it's on my bench. I'm afraid to fly it cause I can't figure it out why it's doing that. I've checked everything appears to be set up as instructed by spektrum. Do you have any ideas why it would be doing that?

[@TimMcKay56]

Not sure as I never have flown with SAFE on. Is there a way to turn SAFE off and fly just with AS3X? Tim

[@dradden1556]

@@TimMcKay56 yeah I can try that . Thank you.