Another tailwheel discussion

[t j]

Just what is the mysterious force that allows the tailwheel to unlock in flight then swings the tailwheel 90 degrees forward into the slipstream, and how does this mysterious force prevent the tailwheel from going into trail and centering at the moment of touchdown?


Just curious.

John

Forward slip with rudder pedal to the stop could unlock it if not rigged correctly. Not sure what happens in the air but on the ground I have to use opposite brake and swing the tail to lock it back up.

[av8rps]

Matco's recommendation on tailwheel release. On and off the ground.
(videos)

Unfortunately, the video doesn't show how the swivel reacts to just moving the rudder pedals alone. But then again, I can't imagine why any manufacturer would want a tailwheel to unlock in flight.

I agree that it seems somewhat mysterious that a tailwheel will cant to one side or another, rather than following the airflow. But it will. I'm guessing that sometimes it will follow the airflow, so nothing is noticed out of the ordinary. But when it doesn't follow properly and ends up canted in one direction or the other, you'll know it as soon as the tailwheel hits the ground. I'm thinking when the tailwheel does flop over one way or another, it might just be moving because the airplane is tipped /banked one way or another, causing the weight of the tailwheel to flop over in that direction. But that's just my idea of what might be happening.

I have noticed the tailwheels that are operated unchained by back country pilots typically have a lot of resistance, which I think keeps them from flopping over in flight. Or it might just be that they can get away with what the normal guy can't because they land so much slower, and almost exclusively use wheel landings in an effort to protect the weakest part of their planes (the tail).

In consideration of all this tailwheel discussion, here are two videos that challenge the typical tailwheel ideology;



http://www.youtube.com/watch?v=ucdb0TKu3rk

[t j]

I did the sawhorse tail wheel breakaway test today. I am one of those that has had no problems with my maule tail wheel breaking loose except when I want it to. To break it loose I need to be moving slowly and push the rudder pedal all the way and "Stab" that brake when the pedal hits the stop.

Doing the sawhorse test the tail wheel does not break loose in either direction when the pedal is pushed to the stop.

Then I pushed the rudder with one hand while pushing hard sideways on the wheel with the other hand. It broke loose in both directions when the rudder horn was about 1/16" from the stop.

I looked back through my builders manual and notes. The manual says to file the rudder stops to get 30 degrees deflection in each direction. At about 25 degrees the cable on the opposite side would hit the stop so I called the factory. He said 25 degrees would be fine. I filed the front of each rudder stop to clear the cables and left it at 25 degrees.

Tail wheel breaks free with side pressure here
Rudder Stop.jpg

Front of rudder stop filed down to clear cable on opposite side
Rudder stop filed to clear cable.jpg

[tomec]

CAM03398.jpg no more trouble

[cap01]

what is it ? did it have a fairing at one time , is that what the holes in the yoke are for ?

[tomec]

locking tailwheel, I do have fairing for it but not going to use it:, land like a trigear

[cgruby]

I just can't stand it any longer. Although I don't consider myself the Bevo Howard of tail wheel airplanes, a few thing I have observed in the 60 years I've been flying. Tail-wheel airplanes that are "squirely" on landing can usually be attributed to:
1) a very aft cg
2) misaligned landing gear (personally I like the wheels adjusted straight ahead)
3) crappy brakes , such as my KF.

I have never flown an airplane with a properly position main gear that ever exhibited uncontrollable characteristics. I've flown full swivel tail wheels which required brakes for steering, with no big problems.

If you want squirelyness, try an N3N Stearman with a misaligned gear and a non-lockable tail-wheel. You had better have good brakes and you really need to use 'em sparingly.

I don't know the answer to all the points brought out here, but I'm inclined to question gear alignment and lackluster brakes as ranking pretty high on the list.

I'm relatively new to the Kit Fox and am still trying to find the sweet spot in all my landings. I have made some real zingers, but have never felt the airplane was going to ground loop. You can't be afraid to get on the brakes if you run out of rudder control, but use 'em sparingly. Anything is permissible to maintain control.

Just my $0.02 worth.
Cheers,

[jrevens]

I sure do agree with you, Chuck. I've only been flying taildraggers for 40 years, and the one time a crappy tailwheel got me was because I screwed up and didn't use the brakes quick enough.

Wheel alignment is a huge factor. When I test flew my Thorp T-18 24 years ago, I wasn't sure I was man enough to fly the thing again. It was a beast! I rechecked the wheel alignment and corrected it to straight - no toe in or out. I knew better but somehow screwed up when I set it the first time. The difference was amazing - made a *****cat out of it. In general, everything happens a lot slower in a Kitfox, & I'll make sure the wheels are straight on mine!

Yep, CG makes a big difference too. Good points!

[av8rps]

TJ,

Thank you for taking the time to do a test on one that doesn't have an issue. Your results are what I would have expected. But I also find your comments and photos about rudder throw very interesting, as it further reinforces what I have suspected all along...

While the NTSB was investigating the crash of that Avid Flyer I previously referred to, even though they initially claimed it was just pilot error (always the default I think), collectively everyone agreed if there was a mechanical issue with the airplane the crash was "probably" caused by too much rudder throw, which may have caused the tailwheel to unlock before touchdown.

So after the NTSB left we tested things further and verified that if the rudder throw was reduced the tailwheel would not unlock (originally it had more than 30 degrees of throw). The builder insisted that Avid didn't specify the travel amount, so he felt that more rudder throw was better.

But knowing what I know today, more rudder throw is not better. It's most likely worse. And your explanation about how your Kitfox was set up makes that much clearer, knowing that they only wanted 25 degrees rather than 30. Maybe that is another reason why some of our planes are ok with the Maule, and some aren't?

But the other thing I've always wondered about that Avid crash is if the tailwheel springs weren't too tight? That Avid tracked on the ground really nice and positive, much tighter feeling than most taildraggers. Understanding more about how these tailwheels need to be set up, I'm now suspect it was a bit too positive (tight).

So maybe the combination of too much rudder throw coupled with springs that were too tight was the problem with that airplane. Unfortunately, at that time none of us were sure about any of this, so the airplane was taken away for rebuilding before we could completely get to the bottom of the problem.


Paul

I did the sawhorse tail wheel breakaway test today. I am one of those that has had no problems with my maule tail wheel breaking loose except when I want it to. To break it loose I need to be moving slowly and push the rudder pedal all the way and "Stab" that brake when the pedal hits the stop.

Doing the sawhorse test the tail wheel does not break loose in either direction when the pedal is pushed to the stop.

Then I pushed the rudder with one hand while pushing hard sideways on the wheel with the other hand. It broke loose in both directions when the rudder horn was about 1/16" from the stop.

I looked back through my builders manual and notes. The manual says to file the rudder stops to get 30 degrees deflection in each direction. At about 25 degrees the cable on the opposite side would hit the stop so I called the factory. He said 25 degrees would be fine. I filed the front of each rudder stop to clear the cables and left it at 25 degrees.

Tail wheel breaks free with side pressure here
Rudder Stop.jpg

Front of rudder stop filed down to clear cable on opposite side
Rudder stop filed to clear cable.jpg

[n85ae]

Tailwheel Caster Angle:

Even if the tailwheel is unlocked, if the caster angle of the pivot is correct,
THEN the airplane will will land perfectly normally ... Since the correct
caster angle will make the tailwheel straighten right out.

It would only ever have a tendency to make the airplane turn, if the
caster angle is incorrect.

So I would assert that if an unlocked tailwheel is causing the plane to
go off course, then the caster angle of the tailwheel is incorrect.

The exception to this is if you are countering a strong crosswind on the
ground with the tailwheel, then it unlocks and rudder alone cannot keep
it straight.

Jeff