• If You Are Having Trouble Logging In with Your Old Username and Password, Please use this Forgot Your Password link to get re-established.
  • Hey! Be sure to login or register!

How to set up a groundloop

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
 
Darn good advice. A must read. If you bounce ("boing") up a bit high just give a little burp of power to ease the ineveitable descent while keeping that stick welded all the way back.
 
I also found, in my airplane anyway, that when you think you have the stick to the stops.....you actually have another inch or so.....
 
I know that what Bill says to be the awful truth. My 170 with the early springy gear was terribly unforgiving of any less-than-greasy touchdown, and if not that, then the classic tail slapdown effect produced the exact above described scenaro. Crosswind controls? Those were long forgotten in the midst of that bounce. :) Many runway lights have found need to purchase new pants thanks to me.

Z
 
Thanks for the info Mr. Rusk. I am a rookie pilot and I am terrified of ground loops.
 
Good logic, Bill....... also, a firm tail down will cause surface drag which will have a stabilizing effect (pulling on the CG from the rear) as the aircraft decelerates on the rollout.

Controllability is also affected by the main gears ability to slide when not tracking straight. Under or low inflated tires are not good on hard surface runways..... they will eventually aggravate the ground loop as it develops, whereas on grass the side load will often be lessened by the tires sliding on the grass/dirt. When training tailwheel on hard surface, I most often insist that the main tires be inflated to max rated pressure.... more bouncing... but they also will slide better too.

As for the rudder.... it is still the best control when it comes to directional control. When training in high performance bi-planes, I always pounded home the montra.... the rudder keeps the aircraft straight and the ailerons keep the wings level. The eyes must be directly connected to the feet and hands. If the brain gets in the middle, it's usually too late. This must be instinctive and pro-active. Re-active use of controls does not often work, especially during a strong cross-wind landing or a near out-of-control pitch induced porpoise.
.
 
By and large, I agree--a groundloop is not an out-of-the-blue event, but something you can usually see coming for a while. When I'm in the front seat of the J3 I can usually tell on short final if it's a good possibility. By the time the student starts to round out I'm waiting within quick reach of the controls. I won't jump on until the student is sideways and not moving to correct.

I have had many where the landing itself was beautiful but the crosswind correction was lacking and the airplane just drifted off. Then they will fight with just the rudder but by then the airplane is too slow and needs opposite brake too. It's fun to take them out on a nice gusty 10-15 kt 90-degree crosswind day to bring all the little mistakes they didn't know they were making out into clear view.

Fundamentally a ground loop is still caused by misuse of the rudder but the trail of mistakes goes back much further than that--messy approach into a sloppy roundout and flare right up to the actual event. Porpoising is probably the first mistake that has to be trained out of a student, and once you get them to understand when to land and when to cut their losses and go around, then it's time to start tossing in the crosswinds :angel:

Thanks for explanation--I think it does a good job of drawing attention to what it takes to set up a groundloop rather than just focusing on what happens right before you're looking at runway lights 8)
 
A groundloop is caused by incorrect directional control, how you get there has nothing to do with it. I agree with, and teach full, firm back stick when the plane is on the ground though.
 
Bill, excellent post, as usual. You articulated what I've "mostly" tried to do, but hadn't quite put my finger/wrist/feet on.

Whilst sitting on the "Liars Bench", I've gotten in the habit of watching the elvevator/pitch control. Smooth and appropriate=good landing, mostly.
Get out the Landing Scoring Paddles...

Thanks. cubscout
 
Good advice Bill. While reading your post, I kept thinking to myself, pilots who are having this trouble should get some time on skis with someone, sure is a good description how to land on skis in rough snow after a bounce. Even relates to floats if the bounce isn't to high.
Personally, I feel setting up for 3 point landings is the start of the ground loop. But that's just me.

Brad
 
Brad, would you take a minute and discribe the type of landing you do, maybe starting from right over the numbers. I watch my spray pilot here, He has a Air Tractor and a Super Cub and somewhere in that 10-12000 hour range of time with no incidents and ive never seen him do a three point landing. This is my own thinking but i often wonder if he can do one, does all wheel landings, and it dosent matter how hard or what direction the wind is from they always look so smooth. But then everything is from our paved strip. No bush stuff. I remember one time you told me the only trick to flying a tailwheel is just KEEP THE TAIL BEHIND YOU. It awes me how much power the rudder has even on the ground down to the point of speed where not much damage will happen if one would loose control. I will probably do one now today but i still think your advise is the whole trick in not doing one, is to just keep the tail where it belongs. Those pedals and your feet are there for a purpose. And like citibricker says, no matter what kind of an approach you do. my.02cents. doug
 
The two highest time tailwheel pilots I know prefer the 3 point landing and keeping that stick all the way back from just before touchdown and the majority of the time when on the ground (expcept taxiing slowly downwind in a good breeze). Their thinking is that the three point is a bit slower landing and with all three solidly planted and the airplane done flying you've got plenty of control to keep things straight.

There is, of course, an opposite view out there that has no doubt been articulated on this site a few times. :p
 
jrussell said:
The two highest time tailwheel pilots I know prefer the 3 point landing and keeping that stick all the way back from just before touchdown and the majority of the time when on the ground (expcept taxiing slowly downwind in a good breeze). Their thinking is that the three point is a bit slower landing and with all three solidly planted and the airplane done flying you've got plenty of control to keep things straight.

There is, of course, an opposite view out there that has no doubt been articulated on this site a few times. :p

I tend to agree with them.

Having said that, I have NEVER made a 3-point landing in a DC-3 or a Twin Beech D-18...... and NEVER a wheel landing in a Pitts or Christen Eagle.

As for Cubs, Champs, Citabrias, C-180s, and such, I've made a lot of both but definitely prefer the tail first landing profile.

Save me some popcorn, Mike.....
.
 
I had a groundloop last spring and I did everything wrong! Starting with the decision on which runway to land on. There was someone mowing the infield so I decided to land to the north with a slight tailwind. Mistake number one. I use to carry to much airspeed on final WAY TOO MUCH. Mistake number two. With all the airspeed I never really had full stall landings, so the stick was never fully “welded” to the stops. Mistake number three. Once on the ground I was paying more attention to the guy on the lawnmower than flying my cub. Mistake number four. The tailwind helped out with a nice 180 degree turn. When it started going around I had full right rudder and brakes and there was no saving it. Luckily there was not damage. I think I learned more from that one landing than I have learned in the three years I have owned the J3. Shortly after that experience I flew with JRussell and he took me out to a couple of local strips and worked on landing on hills and off cambered grass strips, that along with flying with a couple different CFI’s I am a lot better pilot today. Thanks Jeff…

Larry :oops:
 
Landing

Bill is one of my Instructors and is a great guy to learn from. Another instructor friend is also the King of the tail wheel lander's in the area.
I bought the C.D. tail wheel 101 and just about wore it out learning from it. What I found out is that sometimes when you bounce in on a three point landing, if its not too bad of a bounce just push the stick ahead and make nice two point out of it. So almost all of my landings are two point landings, I just feel its easier on the tail of the plane as well.
Guess every landing has its place due to wind ect. I still have the ability to stop at a airport once and land three times :-? So come on back Bill Rusk, I need more training.

Bill
 
Bill,

Be REALLY careful converting a three point to a wheel landing. You're right--it CAN be done. It can also result in the prop stuffed in the dirt.

MTV
 
mvivion said:
Bill,

Be REALLY careful converting a three point to a wheel landing. You're right--it CAN be done. It can also result in the prop stuffed in the dirt.

MTV

+1 Always have a plan as far as wheel or 3 point and stick to it.

That being said...

It seems to me that most accidents/incidents are results of several mistakes piled on top of another.
 
"Once on the ground I was paying more attention to the guy on the lawnmower than flying my cub. Mistake number four."

Just a notion but I think inattentiveness is a principal cause of groundloops. Or overconfidence; both same thing, I guess.

Landing requires all of our senses and judgement---and a little bit more.

My instructor, who flew in combat in the First World War and was acclaimed as one of the best light aircraft pilots in Canada, was all-business landing a J3 on wheels or floats. Fifty-seven years later, so am I.

As for the groundloop itself, Stick and Rudder made it clear that you're just along for the ride; there's not much you can do about it.
 
Rudder

Well, now that we have introduced the concept of the center of mass and its affect on the elevator, lets talk about the rudder.
As was properly pointed out in this thread, the elevator may set things in motion for the ground loop but it is the rudder that will prevent it. You were told back in pilot training to always use smooth control inputs and to use smooth pressure on the controls. Well, that's true most of the time BUT when on the ground in a tail dragger you want to punch, jab, or tap the rudder. No smooth pressure here. Quick jabs. When on the ground the tail wants to swing around and go first right? Right. Remember the taildragger is statically unstable on the vertical axis when on the ground. Once you start a motion it wants to keep going. It's that same mass that slaps the tail down when you have a little sink rate and hit on the mains first. When you make a rudder input, that swing will continue unless you stop it. So to move the nose you tap the rudder to get the nose moving, then it will take another quick tap to stop this motion. Now if the nose is not where you want it, or it moves due to wind, terrain, etc., you will tap it to get it going in a direction then tap it again to stop that motion. So the rudder is constantly being tapped. If you try to use smooth control pressures you will get behind the airplane to the point that you loose control. PIO city here we come.
Imagine a upside down bowl and a steel ball bearing. You put the ball on the bowl and it will roll right off. You the pilot have two little popsickle sticks (rudder) to bat that ball back and forth to keep it on the bowl. The closer it is to the center/top of the bowl the easier it is to keep it there, but the further that ball gets from the center of the bowl the faster it rolls and after a point you can't keep it on the bowl no matter what you do. Different airplanes have different shaped bowls. A J-3 is shaped like your dogs water bowl. It is pretty flat. Not too hard to keep the ball in play. A Pitts looks more like a upside down V and you are trying to keep that ball on the top of a pin. Every airplane has a different shape bowl. Some are pretty flat but there is a sharp break at the edge where that ball just goes straight down. If the ball gets there you are in a ground loop and you are along for the ride. There is a point of no return for every airplane. Your job is to keep the ball from getting there.
You can look at the shape of an airplane and get a pretty good idea of the shape of its bowl. A short fuselage usually means a heavily curved bowl. Think Pitts, Thorp T-18, Formula 1 etc. Look at the rudder. How big is it, and is it going to be blanked by the fuselage and wing in the three point attitude? Is the main gear close together or spread wide. The Stearman has a long fuselage but the narrow stance of the main gear and lots of weight up high give it a big curve on that bowl. Taylorcrafts, Cubs, Champs all have pretty flat bowls.
Someone talked about doing wheel landings in Ag planes. Most Ag planes have a pretty long fuselage, and very powerful tail surfaces so it is REALLY easy to get the tail down WAY first and drop the mains down hard, so wheel landings are often preferred to avoid this. Otherwise they must be landed like a high performance taildragger, by setting the landing attitude and controlling the flare with throttle, but that is another whole discussion we will save until later. We'll call it "attitude" landing when the time comes. Think of how long the fuselage is on a DC-3. If you incorrectly three pointed that baby you could land tail first with the mains about 20 in the air. That would get exciting really fast. Most warbirds are wheel landed. Fuselage length, visibility over the nose, rudder authority, prop clearance, etc all play a part in the best way to land each individual airplane.
But, a point to consider, if you will. In a low performance tail dragger, i.e. Cubs, Tcarts, Champs, etc. IF you get the tail down first, the AOA will go down when the mains come down, and you will have extracted all the energy from the airplane before it touches, i.e. full stall, and it will sit down (assuming you don't drop it in from several feet) on landing. This will allow you to avoid all that bouncing we talked about earlier, and you can concentrate on the rudder. This is how I approach an unfamiliar airplane on the first couple of landings. It may not always be the most picture perfect landing but it is the safest landing until I become more familiar with it. Never flown a Funk before. No problem. Look at the airplane and predict its handling. Then try to do a couple of tail first landings to see how it handles. Then start to play with it.

Now a concept that will get folks thinking or maybe all fired up. In a high performance taildragger, (think lots of curve on the bowl), or a really nasty, gusty, windy day, some folks will tap the rudder on touchdown even if the airplane is going straight. What this does is allow you to get ahead of the airplane. You now KNOW which way things are going to go. If you land and wait to see which way the nose is going, then try to correct you are automatically in the reactive mode, behind the airplane and trying to catch up. Just a quick tap at the outset sets the ball in play except, you know which way it is going. Better to be the server than the receiver in tennis. Offense Vs defense. I am not suggesting that you do this only that it is a concept to think about. You may find that you are already subconsciously doing it.

Hope this helps

Bill
 
Is this not the best flying forum on the planet, or what!? Bill, you are a master. :wink:
 
Bill,

There are two kinds of tailwheel pilots:

Those who CONSTANTLY joggle the rudder back and forth

And, those who react to what the airplane is doing when its on the ground.

Either way works fine, depending on the pilot.

I happen to be of the second persuasion, and I find that MOST STUDENTS in tailwheel airplanes who THINK they have the "joggle the rudder" thing down pat are actually disturbing the airplane, then fixing the disturbance, then disturbing it again, etc. Ad infinitum.

I prefer to land the airplane STRAIGHT in the first place, then react to what the airplane does. I see no point in upsetting the stability of the airplane merely to have to react to that upset.

Now, there are airplanes that are "quicker" than some others, but if a pilot can't react successfully to whatever a CUB throws at him, he really needs a bit more dual.

One other thing to consider: Some airplanes do not have steerable tailwheels. In at least some of those, it makes little sense to put the tail down and blanket the tail feathers with the fuselage and flaps before the plane is done flying. Keeping that rudder up in clean air makes all the difference in some of those airplanes.

In ANY tailwheel airplane, the rudder is NOT your only steering tool. And, the ailerons are NOT just for roll control. Due to adverse yaw, the ailerons provide a good bit of yaw control as well as keeping the proper wing down. If you start to drift, put the stick the direction you're drifting. The old timers from C-46 and C-47 times called it "Driving it into the ditch". The adverse yaw created by the down aileron will tend to yaw the nose of the airplane AWAY from the direction you're headed.

Had a kid out this morning, doing one wheel landings on his third flight in the Cub. Land on one, roll it down the runway for a couple thousand feet on one, then lift off on one.

He's now got a total of a little over three hours in the Cub, and he's doing really well. A lot of fun to fly with someone who figures it out that fast.

Looking for something to surprise him with, but he's a quick learner.

MTV
 
Mike

Thank you for your input. I don't profess to know it all by any means and am glad to have other ideas presented, cussed and discussed, so that we may all learn.

Hydrocub

Well said and thank you as well.

Brad

Excellent input re skis. Looking forward to a little practice myself soon.


Bill
 
Training

Hope this thread keeps going. Great help coming out of this.
Sometimes just the little details can mean so much to us learning.

Thanks guys.


Bill Ingerson
 
Ground loops can happen at any time during your flying career. A month ago I had to pull off a landing with the left brake on my Maule totally locked. I'm glad that I am very familiar with the use of differential braking to forgive my sins. I realise that from the instuctors stand point teaching max brake control is difficult since it is an input you cannot remove if a student does it wrong. However, differential use of the brake is the best tool for saving you when you start going around and there will be a time when the rudder will not help you.

Jerry
 
I've found that most pilots never have a chance to learn flying on the ground. That 5-15 secs T/O or landing roll just ain't enough. A lot of pilots are driving their airplanes while on the ground and don't start flying until they're in the air, or stop flying the moment the wheels touch down. Wouldn't it be nice to give every student a 12,000' long 400' wide wet grass runway to get to know his airplane? Better yet, a 10-mile frozen lake to practice X-wind flying (and control) on the ground.
 
Aviator said:
I've found that most pilots never have a chance to learn flying on the ground. That 5-15 secs T/O or landing roll just ain't enough. A lot of pilots are driving their airplanes while on the ground and don't start flying until they're in the air, or stop flying the moment the wheels touch down. Wouldn't it be nice to give every student a 12,000' long 400' wide wet grass runway to get to know his airplane? Better yet, a 10-mile frozen lake to practice X-wind flying (and control) on the ground.

My tailwheel instuctor had me repeatedly (I thought we were gonna wear the tires out) taxi up and down the runway on the mains and on three in all kinds of wind conditions before we even got to the part where we get in the air. Correct stick placement, etc. when taxiing was insisted upon (I can hear "stick all the way back please" in my sleep). :-?

I think there is a lot to be said for learning to fly on the ground through these exercises as your actions become automatic and you're much better prepared for learning takeoffs and landings. Especially when you toss in one wheel and two wheel (tailwheel and upwind main) practice, too. Making the basic mistakes and learning from them in this environment is a lot less expensive..... :oops:

Any decent grass strip or paved runway (start them there as it is more challenging) will do. And if you have a 10,000 foot grass strip like they do in the Carolinas, have at it! :eek:
 
"Especially when you toss in one wheel and two wheel (tailwheel and upwind main) practice, too. Making the basic mistakes and learning from them in this environment is a lot less expensive..."

During my TW training, I had two instructors (first one got called up to a regional airline). #1 said that I was ready to go, #2 said that we needed to do some more ground work. OK, says I, I've got my books, my E6B, everything, let's sit down at the desk.

Oh no, says she, I mean flying on the ground. 1 wheel, 2 wheel, 1 wheel, different 2 wheel. Hated it, felt uncomfortable, etc. ....but didn't get wigged out that first X-wind landing either.

Lots to be said for relatively high speed practice on the ground.
 
Back
Top