Video - How to have a ground loop

1200AGL said:
What did the pilot do wrong to cause that?
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Watch the flight controls as the tail comes down. The elevator remains deflected down the entire time - that's why the tailwheel starts bouncing and skidding. There was no weight on it.
 
What do you say when the student says "Gee, when my nose-wheel starts to shimmy like that they tell me there's too much weight on it and I need to lighten the controls."
Fearless Tower said:
Watch the flight controls as the tail comes down. The elevator remains deflected down the entire time - that's why the tailwheel starts bouncing and skidding. There was no weight on it.
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wabower said:
What do you say when the student says "Gee, when my nose-wheel starts to shimmy like that they tell me there's too much weight on it and I need to lighten the controls."
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Shimmy in a nose-wheel OR tailwheel for that matter is indicative of a mechanical issue. Weight may or may not exacerbate the symptoms, but it is not the source of the problem.

But, to perhaps better answer your question, I would tell them to relax some pressure (but not all)......and have an A&P check out the tailwheel or nose gear.

I'm actually dealing with that right now in the 170. If I do a 3 pointer and have the yoke all the way back after touchdown, I get a shimmy. Relaxing some (but not that much) back pressure makes the shimmy go away. At least for now. I don't expect to have that problem anymore after the main leaf spring is changed out today.
 
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Very fundamental mistake. Always bring the stick all the way to your belly button when the tailwheel is down.

OK I will edit, always bring the stick or yoke all the way back when the plane is done flying, if wheel landing you should be holding the tail off until it doesn't want to fly anymore, then bring it all the way back.
 
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It's always NDH until someone makes a log entry.......or a video shows up on YouTube.....
 
right, NDH means there is either No Damage or No History :D
 
Yeah, he didn't pull the stick back when the tailwheel touched, but that shouldn't cause shimmy in most TW airplanes (don't know anything about the AT-301). Looks to have a locking, non-steerable tailwheel. Looked like it may have been unlocked? Again, don't know about this plane, but most locking tailwheels will not shimmy on landing if left unlocked. Of course, you better be ready to use the brakes for directional control. Seems this pilot made no effort to use power (or brake?) to control it or go around. In most tailwheel planes, you can easily recover a developing swerve if you don't get the stick back right away. But of course, if you have enough basic skill and experience to recover, you probably wouldn't have left the elevator down in the first place. ;) This seems an odd result and course of (non) action, considering anyone flying equipment like this would likely be a working pro.

dell30rb said:
http://www.youtube.com/watch?v=Qa12veWQEgU&feature=endscreen&NR=1

Or you could just miss the runway altogether and stall/drop it real hard from 10 feet off the ground.
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Damn those things are strong!
 
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i'm guessing that last guy was really starting to doubt the value of a silly insignificant STOL contest about 10 microseconds after he slid to a stop.
 
tonycondon said:
i'm guessing that last guy was really starting to doubt the value of a silly insignificant STOL contest about 10 microseconds after he slid to a stop.
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I am sure you are correct... I just wish I would have heard what he said in the cockpit.
 
He came screaming in, relatively speaking. He knew he wasn't coming close to winning with that landing, so I think he was trying to avoid a ribbing about landing longer than the C-150 in a Super Cub. He succeeded.
 
whifferdill said:
Yeah, he didn't pull the stick back when the tailwheel touched, but that shouldn't cause shimmy in most TW airplanes (don't know anything about the AT-301).
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Shimmy isn't caused by the stick action - it is a symptom of either looseness in installation or more commonly improper tailwheel geometry (ie the leaf spring is out of alignment).

When I first watched the video, I thought there was something wrong with the tailwheel because while he was working the rudder, the wheel seemed to be skipping/skidding along the runway sideways. Then I looked at it again and noticed the elevator down deflection and it made more sense - the wheel was skidding because he still had a decent amount of speed and there was no weight on the tail and the pilot never made the effort to get the stick back. In fact at that speed, the deflection downward would have made the tail actually pretty light.
 
Fearless Tower said:
Watch the flight controls as the tail comes down. The elevator remains deflected down the entire time - that's why the tailwheel starts bouncing and skidding. There was no weight on it.
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That was a normal wheel landing. The tailwheel needed work, probably because the pivot axis was out of whack, and the serious shimmy contributed to a loss of control. The pilot should have been able to control it with brake.

Dan
 
There may be more to the problem than just the spring. Prior to my purchase, somebody incorrectly assembled the entire mechanism on my prior 180.

Fearless Tower said:
Shimmy in a nose-wheel OR tailwheel for that matter is indicative of a mechanical issue. Weight may or may not exacerbate the symptoms, but it is not the source of the problem.

But, to perhaps better answer your question, I would tell them to relax some pressure (but not all)......and have an A&P check out the tailwheel or nose gear.

I'm actually dealing with that right now in the 170. If I do a 3 pointer and have the yoke all the way back after touchdown, I get a shimmy. Relaxing some (but not that much) back pressure makes the shimmy go away. At least for now. I don't expect to have that problem anymore after the main leaf spring is changed out today.
Click to expand...
 
Fearless Tower said:
Shimmy isn't caused by the stick action - it is a symptom of either looseness in installation or more commonly improper tailwheel geometry (ie the leaf spring is out of alignment).
Click to expand...

True in general, which is why I said the shimmy shouldn't have been caused by leaving the elevator down. Although in the Pitts, depending on the tailwheel type, shimmy can be caused by pulling the stick fully aft on touchdown. Since the Pitts has a heavy tail, lots of elevator authority, and lots of speed on touchdown, full aft stick can compress even a good spring enough to cause the kingpost to trail at enough of an angle to produce shimmy. This is prevented by holding the stick in the position you touched down 3-pt, and slowly pulling it fully aft as speed decreases.
 
The pilot did not lock the tailwheel. I landed the N3N with the tailwheel unlocked once and almost went for a ride like that. Caught the lock lever with my sleeve reaching for something and didn't check tailwheel locked on landing. Haven't done that again in years. Don
 
Fearless Tower said:
I'm actually dealing with that right now in the 170. If I do a 3 pointer and have the yoke all the way back after touchdown, I get a shimmy. Relaxing some (but not that much) back pressure makes the shimmy go away. At least for now. I don't expect to have that problem anymore after the main leaf spring is changed out today.
Click to expand...

When your 170 has a shimmy your plane of rotation of the tailwheel is forward edge down, not good, have your main leaf spring rebent, to support the tail wheel in a leading edge up and it will quit shimmying.
 
Fearless Tower said:
Or you could try this....he put plenty of weight on the nose wheel.....

http://www.youtube.com/watch?v=NMmHYWjEmkY&feature=related
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:eek:

OK, so maybe you don't necessarily have to go around after one bounce (and porpoise)... but eight? Eight!? And each one more violent than the one before? :rolleyes2:

As for the first video: looks familiar- did the same thing, in the Champ shown in my avatar pic... only in that case, it was a busted spring (which I probably broke on the previous landing, lol). Darn thing just said "Screw your rudder inputs- I'm going over here!"
And yes, it was after a wheel landing (my first really smooth one), but I had the stick all the way back after the wheel touched down.
 
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rottydaddy said:
As for the first video: looks familiar- did the same thing, in the Champ shown in my avatar pic... only in that case, it was a busted spring (which I probably broke on the previous landing, lol). Darn thing just said "Screw your rudder inputs- I'm going over here!"
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Actually the spring may have been just worn out. It is recommended that you change out the main leaf every 4-500 hrs (at least for the Scott 3200). Otherwise the result is exactly what you describe....or worse - the tailwheel just drags along held on only by the rudder chains and beats the hell out of your rudder.
 
Tom-D said:
When your 170 has a shimmy your plane of rotation of the tailwheel is forward edge down, not good, have your main leaf spring rebent, to support the tail wheel in a leading edge up and it will quit shimmying.
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Srping was replaced today - the geometry was definitely out of alignment. Funny thing was that when I bought the plane, I asked the previous owner when they had last changed the spring out. He told me within the last couple years and less than 100 hrs......so, the other day I am going through the log books and found the entry.....sure they replaced less than a hundred hours ago......the entry stated "replaced with serviceable USED one" No clue how many hours that thing had on it.
 
wabower said:
There may be more to the problem than just the spring. Prior to my purchase, somebody incorrectly assembled the entire mechanism on my prior 180.
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Ouch....what did they screw up? Does the 180 use a 3200?
 
Without looking I think it's a 3400. We took it apart to check for broken parts, and during the disaasembly noticed that the guy had put the washer in the wrong place. That in turn constricted the mechanism when the bolt was tightened and caused the steering/centering gismo to hang up, always in left-turn mode. The problems were most noticeable during landing roll after the plane had slowed. At first I thought cross-winds through the hangars were messing with me, until one day the cross-wind was from the right. I was ready for the right turn when it went hard left again, and it was off the plane and on the bench before sundown.

Fearless Tower said:
Ouch....what did they screw up? Does the 180 use a 3200?
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Fearless Tower said:
Actually the spring may have been just worn out. It is recommended that you change out the main leaf every 4-500 hrs (at least for the Scott 3200). Otherwise the result is exactly what you describe....or worse - the tailwheel just drags along held on only by the rudder chains and beats the hell out of your rudder.
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The 170s have a soft spot in as much as the main leaf of the tail wheel stack has a history of cracking which allows the stack to flex too much which causes the front of the plane of rotation to be to low. That causes the tail wheel to ride forward of the axel, and it will shimmy ever time.
 
Fearless Tower said:
Shimmy in a nose-wheel OR tailwheel for that matter is indicative of a mechanical issue. Weight may or may not exacerbate the symptoms, but it is not the source of the problem.

But, to perhaps better answer your question, I would tell them to relax some pressure (but not all)......and have an A&P check out the tailwheel or nose gear.

I'm actually dealing with that right now in the 170. If I do a 3 pointer and have the yoke all the way back after touchdown, I get a shimmy. Relaxing some (but not that much) back pressure makes the shimmy go away. At least for now. I don't expect to have that problem anymore after the main leaf spring is changed out today.
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First thing I check is tire pressure. Normally it is low. Tire shimmy alone should not cause loss of failure to maintain centerline. Something else is going on. He was drifting to the right side of the runway on landing. It looks like he over corrected trying to correct back and keep it on the runway.
 
Nope, the spring had either busted at one end or departed altogether, i dont recall which.
Fearless Tower said:
Actually the spring may have been just worn out. It is recommended that you change out the main leaf every 4-500 hrs (at least for the Scott 3200). Otherwise the result is exactly what you describe....or worse - the tailwheel just drags along held on only by the rudder chains and beats the hell out of your rudder.
Click to expand...
 
rottydaddy said:
Nope, the spring had either busted at one end or departed altogether, i dont recall which.
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That's what I meant about being worn out....the springs don't have an indefinite life and if they wear out they will break.
 
Fearless Tower said:
That's what I meant about being worn out....the springs don't have an indefinite life and if they wear out they will break.
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Actually the tailwheel spring for the 170 is 5/16" thick by nearly 2" wide, it will last forever when the 170 is flown as it should be. it will crack and fail when you do those panic stops that raise the tail and allow it to slam back down.

When I do an annual on a 170 for the first time I remove the spring and dye check it, and I have found several cracked and still functioning properly.

When they sag the attachment hardware is usually the problem.
 
Tom-D said:
When I do an annual on a 170 for the first time I remove the spring and dye check it, and I have found several cracked and still functioning properly.
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Yeah, but when they go, they REALLY go from some of the stories I've heard on the 170 board.

With mine, I just didn't want to take a chance particularly since I had no clue how long that 'serviceable used' one had been in service.
 
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