Replies to This Discussion

Permalink Reply by Brian A Manlove on December 3, 2013 at 11:09am

All valid points John - and I totally agree that the design of *any* nose wheel strut should include the ability to fail "gracefully" - and my mod should not change that at all.  The split bearing block is pinched together by two AN342A bolts.  My mod maintains that "separation of states" of the plastic block.  The same "separate-ability-ness" exists, I'm using the spec'd AN342A bolts provided by ZAC.  If the impact is backward or forward, those bolts should fail, and then the block will "fail" by the 2 halves coming apart, and then the strut will collapse either forward or backward as the case may dictate.  

The purpose of my mod is to there to only do three things:

1. Allow use of AN Nyloc nuts that do not require safety wire, and to secure the block in a more positive fashion for what I see will be constant up/down,  turning torque, and direct impact actions (banging on the plastic from the steering pins as the bungee does what it is supposed to do.)    
2. More stringently guarantee that because of normal wear and tear, I will never have to even think about the possibility of a piece of threaded plastic losing it's positive clamp.  I can see more potential for unintended or unwanted "breakability" by threading into plastic, than I can see with a more positive mount.
3. It will make me feel better about my airplane and it's ability to "forgive" me when I make a less than perfect landing.  I am personally willing and ready to accept any potential risk this mod may add.

I don't really care that much if anyone else has NOT had a problem with their installation.  In aviation there are numerous examples of stuff going south with no previous visual indication of impending failure, and/or no history of a specific part "consistently failing." (ZAC knows all about this, I guarantee you.)  I wonder how many nose wheel collapses from hard landings have occurred where the collapse itself damaged the airplane much, much worse than might have occurred. Would you point at the plastic block and say "this damage occurred because that block failed?" or would you much more likely say, "this damage occurred because I landed too hard?"    

A great example is the Remos GX - a great little LSA. Hundreds of happy customers, thousands and thousands of hours of faithful service.  But, when put into service as a primary trainer, they started experiencing repeated failure of the nose wheel strut due to collapsing.  Further investigation showed that the structural attachment of the strut was "too weak."  Remos redesigned their front strut mechanical mounting and came out with a retrofit upgrade for existing planes.   This was only discovered *after* the airplanes were put into more severe service, going through many more "rough" landings over a shorter period of time.  The air frame itself was more than capable of handling the additional "stress" of a stronger design.  It was actually just a couple of brackets, nuts, and bolts.  

   

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Permalink Reply by John Austin on December 3, 2013 at 11:44am

And your points are all good points, too!   ;>)  But actually, your Remos example makes my initial argument ... most if not all the models of the Zenith series use this bearing design and they do have a considerable service history including landing on surfaces no one would think of taking a Remos into (unimproved turf, sand, gravel bars, etc) - and apparently no problems with the bearing block!

However, I do concede my concerns are more theoretical than practical ... any event that generates enough force to tear out the bearing block is probably going to do a lot of damage even if the bearing block is still bolted to the mount!

 

Innovations and improvements such as yours keep us thinking outside the box!

 

Thanks,

John

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Permalink Reply by Brian A Manlove on December 3, 2013 at 2:24pm

I still think the Remos example is applicable.  The ZAC's landing on river beds are (mostly) 701's and later, 750's, with much better downward visibility.  Any pilot who is doing that is extremely skilled and capable and probably keeps his nose off the ground as long as possible (as with grass...) also.  I have never heard of a 601/650 put in service as a daily trainer, with inexperienced pilots just beginning to learn how to do short/soft field ops, or just plain landing the airplane.  I know I had many landings in the Remos that were pretty darn hard, not by intent... :>O  The plane flew many hours almost every single day, so the total hours and constant work occurred much faster than a pleasure bird.  

 Plus - you never know.  Look for collapsed nose wheel strut, not the bearing block... I'll bet you find some action.

A few hits:

http://www.aaib.gov.uk/cms_resources.cfm?file=/Zenair%20CH250%20Zen...

http://www.zenith.aero/forum/topics/750-front-gear-tubing

http://forums.matronics.com/viewtopic.php?p=237160

http://copilotco.com/mail-archives/matronics.2004/msg29552.html

http://airsafety.info/wp-content/uploads/xas111201.pdf

Talks about his "modified landing gear" : http://www.stol-adventures.com/bluff-landing.html

Just a few hits... again, it's totally realistic to say MY nose gear would collapse in any of these scenarios, if they were indeed beyond the structural capacity of the air frame.  Also - I have nothing but the highest regard for Chris Heinz' design.  He purposely kept many facets as simple as possible, keeping in mind amateur builders, simple tools, etc.  Maybe if you asked him to design a 650 TRAINER his nose gear would be beefed up a little bit... ya never know.

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Permalink Reply by John Austin on December 3, 2013 at 4:00pm

Those are mostly good examples of nose gear collapse, but none of them address the bearing block as having anything to do with their problem. Here's a more relevant comment (Mike had a STOL 750):

Comment by Mike Schlichtman on May 20, 2011 at 3:04pmDelete Comment

Paul,  The only thing that had any damage was the gear.  The cowl had a little damage when the nose dropped to the ground, but I am going to go ahead and replace it with new due to the fact that I did a lot of experimentation with ducts and airflow until I got the cooling figured out.  The fuselage, firewall and everything else held solid.  I did replace the lower bearing due to when the nose gear over twisted, it cut into the nylon just a little.  In reality, I could have reused it, but decided to replace it with new.  So to answer your question, even though the tube failed, everything else pretty much held its integrity.

John

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Permalink Reply by Brian A Manlove on December 3, 2013 at 11:37am

P.S. - I discovered this perceived weakness due to my own stupidity... I had my front strut completely installed, with bungee, steering rods, etc. I had everything done except for the 4 bolts going into the bottom of the plastic block. I had both AN342A bolts torqued.  Without the bungee, it was totally smooth and turned almost effortlessly, and slid up and down with no binding.  

After I got the bungee installed, in my impatient haste to play pilot and experience my rudder pedals for the first time, I got into the cockpit and was stepping right and left.  The last time I stepped, the entire bottom third of the strut support channel separated from the firewall, popping the heads right off the A4 rivets.  It was then that I realized that the only thing countering that from happening was the 4 bolts, going into a plastic block.  It was after that realization, and re-riveting the channel with A5's,  that I decided to use a more positive method of fastening that block.    

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Permalink Reply by John Austin on December 3, 2013 at 11:49am

NOW, I understand your concern! Lol!

 

I hope you at least got to make some airplane noises in the cockpit before the channel popped!

 

Just Kidding!!!

John

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Permalink Reply by Brian A Manlove on December 3, 2013 at 4:22pm

My guess is that if more builders did what I did and saw the immediate result... they'd think the exact same thing I did. It wasn't done out of guessing or speculation... seeing is believing, as they say.

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Permalink Reply by Don Morrisey on January 16, 2018 at 5:44pm

Brian, you inspired me to do this mod on my Cruzer.  It was fairly straightforward...I used a 5/8" Forstener bit to drill the holes in the bearing block, Inserted the AN4 bolts, filled with JB Weld per your instruction and also added side brackets and also (probably total overkill) a bracket on the front of the block (the rivets on the front corner brackets are countersunk so the bracket sits flat and tight against the front of the bearing block).  Solid as the proverbial brick outhouse and negligible weight gain.  Thanks for the inspiration...

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Permalink Reply by Samuel McNair on January 7, 2020 at 7:58pm

You mentioned that some builders have added spring loaded steering rods to their planes. I have an 801 and the solid steering rods are a real pain. Does anyone have a spring loaded rod design that they are happy with?  How did you handle maintaining rudder cable tension with that mod?

Thanks

Sam

N733YD (a.k.a. Rollerskate)

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