Bill Rusk
BENEFACTOR
Sandpoint, Idaho
Folks
This discussion came up recently and I thought I would share a concept that developed while I was doing a lot of tailwheel instruction.
I would like to propose that most ground loops are not the result of the
rudder but the result of elevator. Allow me to explain. The center of mass is behind the main gear and we know how that affects stability and that the airplane would really rather go tail first, thus the ground loop. But the
center of mass location also affects the stability relative to the elevator.
When the mains contact the ground first with any downward vector (or sink rate) the mass behind the main gear keeps going down and that slaps the tail down. When the tail goes down in a tail dragger that increases the AOA. More AOA equals more lift and thus the airplane balloons back into the air. In a tricycle gear airplane as the mass (in front of the mains) goes down it slaps the nose wheel down but this effectively lowers the AOA so there is less lift and the airplane stays on the ground, assuming we do not bounce it too hard. Furthermore any drift or crab will be corrected for by the dynamics of the tricycle gear configuration.
But lets go back to that groundloop....
You do not get all the speed out of the airplane before it touches down and it has a little sink. The mains hit and it slaps the tail down, increasing AOA and thus lift. You bounce into the air. But you know that a stall is bad so you push the nose over. When you do you lower the AOA, loose lift, the airplane sinks, AND, with the push over it hits on the mains, slapping the tail down, increasing AOA and you are airborne again. I guarantee that in this flail you will take the crosswind controls out. Also you may have added a little power in the bounce sequence and thus just prolonged this series of pilot induced oscillations. So now we have no X/W correction, the plane is crabbing into the wind and drifting sideways, and at touchdown the airplane ground loops. Then you blame the whole scenario on rudder control.
Wrong.
You didn't know what do with the elevator and THAT is what set up the groundloop. So what is the solution you ask.
Simple.
Get the stick back and weld it to the stop with all your might. If you bounce KEEP the stick all the way back during the bounce. The second touchdown will probably be firm and tail first but that’s OK. When the tail hits first it LOWERS the AOA as the mains come down thus giving you less lift so the plane stays on the ground. In a three point landing you want to get the stick all the way back to the stop BEFORE any part of the airplane touches the ground. Then KEEP the STICK anchored to the stop. Do NOT let it flop forward on touchdown or during the bounce. This is a little unnatural. It is easy to let the stick come forward in a firm landing. At the very least this will cause the tail to come up and then slam back down thus beating up the back end of the plane. Keep the stick back. In a nut shell the stick is basically all the way back and welded to the stop in a three point type landing or in a wheel landing the stick goes forward to pin the mains down. But one of the main points of this thread is that the stick does not just wander fore and aft willy nilly during a landing. It is either hard aft or forward but it is not going forward and aft all over the place on landing. One or the other. Get control of what you are doing with the elevator.
Now for all the disclaimers. If you bounce REALLY bad you will need to push the nose over, add power and go around, but in a little bounce just keep that stick all the way back and the plane will sit down. It may not be pretty but it will be safe.
Folks there are all sorts of what if scenarios and "you didn't say this or that". This is a grossly simplified discussion, but the point I am trying to
make is .....Don't let that elevator flop around during landing.
What are you doing with the elevator on landing?
Hope this helps
Bill
This discussion came up recently and I thought I would share a concept that developed while I was doing a lot of tailwheel instruction.
I would like to propose that most ground loops are not the result of the
rudder but the result of elevator. Allow me to explain. The center of mass is behind the main gear and we know how that affects stability and that the airplane would really rather go tail first, thus the ground loop. But the
center of mass location also affects the stability relative to the elevator.
When the mains contact the ground first with any downward vector (or sink rate) the mass behind the main gear keeps going down and that slaps the tail down. When the tail goes down in a tail dragger that increases the AOA. More AOA equals more lift and thus the airplane balloons back into the air. In a tricycle gear airplane as the mass (in front of the mains) goes down it slaps the nose wheel down but this effectively lowers the AOA so there is less lift and the airplane stays on the ground, assuming we do not bounce it too hard. Furthermore any drift or crab will be corrected for by the dynamics of the tricycle gear configuration.
But lets go back to that groundloop....
You do not get all the speed out of the airplane before it touches down and it has a little sink. The mains hit and it slaps the tail down, increasing AOA and thus lift. You bounce into the air. But you know that a stall is bad so you push the nose over. When you do you lower the AOA, loose lift, the airplane sinks, AND, with the push over it hits on the mains, slapping the tail down, increasing AOA and you are airborne again. I guarantee that in this flail you will take the crosswind controls out. Also you may have added a little power in the bounce sequence and thus just prolonged this series of pilot induced oscillations. So now we have no X/W correction, the plane is crabbing into the wind and drifting sideways, and at touchdown the airplane ground loops. Then you blame the whole scenario on rudder control.
Wrong.
You didn't know what do with the elevator and THAT is what set up the groundloop. So what is the solution you ask.
Simple.
Get the stick back and weld it to the stop with all your might. If you bounce KEEP the stick all the way back during the bounce. The second touchdown will probably be firm and tail first but that’s OK. When the tail hits first it LOWERS the AOA as the mains come down thus giving you less lift so the plane stays on the ground. In a three point landing you want to get the stick all the way back to the stop BEFORE any part of the airplane touches the ground. Then KEEP the STICK anchored to the stop. Do NOT let it flop forward on touchdown or during the bounce. This is a little unnatural. It is easy to let the stick come forward in a firm landing. At the very least this will cause the tail to come up and then slam back down thus beating up the back end of the plane. Keep the stick back. In a nut shell the stick is basically all the way back and welded to the stop in a three point type landing or in a wheel landing the stick goes forward to pin the mains down. But one of the main points of this thread is that the stick does not just wander fore and aft willy nilly during a landing. It is either hard aft or forward but it is not going forward and aft all over the place on landing. One or the other. Get control of what you are doing with the elevator.
Now for all the disclaimers. If you bounce REALLY bad you will need to push the nose over, add power and go around, but in a little bounce just keep that stick all the way back and the plane will sit down. It may not be pretty but it will be safe.
Folks there are all sorts of what if scenarios and "you didn't say this or that". This is a grossly simplified discussion, but the point I am trying to
make is .....Don't let that elevator flop around during landing.
What are you doing with the elevator on landing?
Hope this helps
Bill