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09-12-2016, 08:15 PM
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Join Date: Jul 2007
Location: Madison, Wisconsin
Posts: 778
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Quote:
Originally Posted by scsmith
With the tail wheel on the ground, it should be much more willing to go straight. Had I sucked the stick back hard, maybe the added downforce would have helped the tail wheel track the airplane straight....unless the swivel unlocked.
I think the tail wheel swivel unlocked. I think at that instant, I was doomed.
thoughts?
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Steve,
Congratulations on not damaging the airplane or yourself; quite an accomplishment I'd say!
If the rudder was really deflected enough during the rollout to break the tailwheel loose then the tire must have been skidding big time? Seems like you might have felt this happening?
More likely perhaps that the tail wheel broke loose at a lesser angle, due to burrs either on the latching pin or on the inside radius of the control arm? I wrestled with my tailwheel not locking for some time before I realized the problem was not the pin but the control arm. Filed off some burrs near the corners of the notch that takes the pin and everything was good.
__________________
Alan Carroll
RV-8 N12AC
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09-12-2016, 08:43 PM
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Join Date: Feb 2016
Location: Boynton Beach, Florida
Posts: 62
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Whewwwww......bet the heart got going.
My initial thinking is that the ability of the rudder was simply exceeded. All airplanes want to weathervane. Once it starts followed by braking, the mass of the tail wins over braking and contributes to the groundloop.
Remember, you're already slightly cocked , the tail weighs more than the area between it and the pivot point, gear/engine, and a 'jackknife' begins.
As many groundloops I have experience or listened too, I can't recall any that were stopped once 'all **** broke lose'.
Humble pie.....is a scary aviation moment without scratching your plane.
I don't order it.....but eating it over my 47 years of flying everything made me a better pilot. Have thanked the lord a few times my 747 is a tricycle.
You did just fine....
Tip....if things get bad with choices nil...consider a judgement call , see if the tower will allow landing across the runway rolling out onto the taxiway. You pretty much have experience the aircraft limit. Anything more and the risk of damage increases rapidly.
H Retting
Old and no longer bold
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09-12-2016, 09:06 PM
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Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,035
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I don't know if it was a factor or not, but from your description it sounds like it could be.....
I have been cautioning builders for many years (ever since there was a rocket link on the RV-7 prototype) that they need to confirm that when the rudder is hard over at the left and right stop, that it isn't rotating the arm on the tail wheel beyond the disengage point.
I believe a lot of the ground loops that have occurred over the years were caused by this. Chains and springs have enough slack that this isn't a problem.
This is one of the reasons I don't like the rocket style links, and why the RV-7 prototype was switched back to springs.
It is also possible for the tail wheel to break out under load if the arm and/or lock pin has gotten worn.
Glad to hear it turned out to be nothing more than a learning experience.
__________________
Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.
Scott McDaniels
Van's Aircraft Engineering Prototype Shop Manager
Hubbard, Oregon
RV-6A (aka "Junkyard Special ")
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09-12-2016, 09:10 PM
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Join Date: Dec 2009
Location: Boulder, CO
Posts: 4,435
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I watched a groundloop in a non-RV where the pilot kept the tail up and with brakes and power, attempted to control the direction. It was well off the runway and trying to go sideways when one wingtip touched and then it went over on its back.
Simultaneous brake and power did it for him.
I'm glad you're both ok and upright.
Dave
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09-12-2016, 09:19 PM
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Join Date: Jul 2009
Location: Longmont, CO
Posts: 236
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Quote:
Originally Posted by rvbuilder2002
I don't know if it was a factor or not, but from your description it sounds like it could be.....
--snip--
It is also possible for the tail wheel to break out under load if the arm and/or lock pin has gotten worn.
Glad to hear it turned out to be nothing more than a learning experience.
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Fearing this, I case hardened both the notch area and pin using Cherry Red hardening compound. I inspect both regularly and in over 200 hours of use I cannot yet detect any wear. And I am flying a Rocket which puts more stress on both pieces.
YMMV, but I believe this does indeed help.
__________________
Mark Olson
RV-7A First flight 2005 Sold 2019
F1-EVO Rocket First flight 2010
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09-12-2016, 09:33 PM
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Join Date: Mar 2008
Location: Seattle
Posts: 1,412
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Yes, I experienced tail wheel break out on landing, and the subsequent ground loop in my T-18. I simply got too close to the left edge of the runway and gave a big quick jab of right rudder, more than I'd ever given with this tail wheel, but just a brief moment. It went around just as you described. It was the first flight after I had disassembled, cleaned and greased the tail wheel post & lock pin assembly. This is a Van's style rod spring with a popular aftermarket tailwheel system. The chains are 'kinda tight'.
"Last thing worked on, First thing to break"
I got away with that back when I had the Maule tail wheel assembly and leaf spring on it. Go figure.
I'm wanting to mill the cam slot a bit wider to delay the release to full swivel, on recommendation of one of the Thorp gurus.
I did manage some pretty gruesome April cross wind landings in the RV-8, one @ Sedona pushed me over to the leeward side of the runway, but it stayed in control. Returning home, a gas stop @ Red Bluff had something like 19-Gust 24 70-80 degrees and I stayed in the center, but as we slowed to under 20 mph, the tail wanted to weather vane bad, trying to push us to the up wind side. Taxiing to the pump was difficult with the wind at our back. The RV-8 chains are "kinda loose"
I feel your pain. We don't get much cross wind experience in the Pacific Northwet, so trips to California, Arizona, Texas etc give me the Willies.
Aerobatics for me, are great. I just don't like strong crosswind landings. It's something for me to work on, like my 'off heading' slow rolls.
__________________
Scott Emery
http://gallery.eaa326.org/v/members/semery/
EAA 668340, chapter 326 & IAC chapter 67
RV-8 N89SE first flight 12/26/2013
Yak55M, and the wife has an RV-4
There is nothing-absolute nothing-half so much worth doing as simply messing around with Aeroplanes
(with apologies to Ratty)
2019
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09-12-2016, 09:54 PM
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Join Date: Sep 2007
Location: pittsburgh pa
Posts: 533
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I have a different theory on this I would like to throw out for discussion.....
In a xwind, as the the aircraft slows, forward stick used to hold the tail up. As speed further decreases, more rudder will be required to hold alinement. Now when the tail finally drops, the rudder and more importantly, tail wheel (still locked) will be very displaced. When it touches down, it will swerve the aircraft until it unlocks.
This is somewhat opposite to what I think Steve is saying. To avoid this, one of two techniques could be used:
1) get the tail wheel on the deck sooner, rather than holding it off, while the rudder has more authority and therefore it and the tai wheel would be straighter.
2) If holding the tai wheel off as long as possible, neutralize the rudder just as the tail wheel touches down, so that the tail wheel is straight when it touches. Once on the deck, a straight tail wheel will hold the aircraft straight more effectively.
Is this (a severely cocked tail wheel at touchdown) a more likely explanation of what happened here and in other ground loops.
Isn't a less cocked tail wheel at higher rudder deflections what is going on in a "loose chains" rigged airplane??
__________________
Gary Reed
RV-6 IO-360
WW 200 RV now an Al Hartzell for improved CG
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09-13-2016, 12:26 AM
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Join Date: Aug 2009
Location: Southern California
Posts: 882
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Throttle
Quote:
Originally Posted by scsmith
thoughts?
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In my -8 I've learned to be ready on the throttle during roll-out. If a sudden gust hits and you suddenly find yourself out of rudder and opposite brake, a quick stab of throttle will give you a lot of rudder authority and straighten things right out. The one time I really needed this, it worked like a charm (in 580 RV-8 hours).
Skylor
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09-13-2016, 06:19 AM
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Join Date: Apr 2005
Location: White Salmon, Wa
Posts: 71
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I think Gary's thought is correct.
I have the link on my Rocket rather than the chains because I like the look. The problem with it is that you can't put the tail down with any rudder deflection or it can skid the tailwheel. The more rudder, the worse it is. I tend to center the rudder for an instant as the tailwheel comes down.
My link broke last year so I flew without any tailwheel steering for a couple of weeks. Really liked how that felt so I'm guessing that is how a set of loose chains feel. They allow the tailwheel to be straight with a large rudder input.
Russ
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09-13-2016, 06:33 AM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Quote:
Originally Posted by rvbuilder2002
....confirm that when the rudder is hard over at the left and right stop, that it isn't rotating the arm on the tail wheel beyond the disengage point.
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+1 for sure. My original tailwheel setup (with cables and springs, not a single-sided link) had the pin very near disengagement at full rudder deflection, and in fact it did go full swivel unexpectedly while landing in a good crosswind at OSH.
Today, a close look will find that the tailwheel steering attach points on the rudder horn have been moved inboard about 1/2" on each side. It allows full rudder deflection with less tailwheel deflection.
Side note; the ball bearing JD Air tailwheel I'm flying now seems to have a very firm lock pin. Can't say that about all tailwheels.
__________________
Dan Horton
RV-8 SS
Barrett IO-390
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