Spring gear problems

Legeorgen · Post by **Legeorgen** » Fri Feb 17, 2012 10:13 pm

Hi everyone,

I'm sorry to hear about your mishap with the spring gear Al. You must be totally bummed.

Has anyone heard of Dennis Finley with CNC Machines? He is supposed to be a guy who makes an after market spring gear reinforcing mod. He claims the gear is a problem that the factory may not be acknowledging it has with the spring gear. I got his email address from a friend and hope to get a response from him soon, that I will share with the list.

I am a little concerned after hearing about Al's accident. I have purchased and applied the latest 2 inch angle aluminum spring gear mod MAM has provided and now ships with all new kits. I wonder if this is enough. I intend on using my Rebel on unimproved strips and not just on paved airstrips as the factory planes do. MAM claims hundreds of hours on their planes without a problem but I figure they only operate out of paved airstrips.

I didn't give the gear much thought when I bought the half finished kit but now after learning more on this list I think I would have opted for Wayne's strut gear or even the bungee. My Kitfox has a one piece Grove spring gear that works great on some pretty rugged terrain.

Bruce G 357R

Walter Klatt · Post by **Walter Klatt** » Fri Feb 17, 2012 10:13 pm

Yes, I know Dennis very well. He recently bought an almost completed Elite kit, and I helped him pick it up and transport it home. He is local to my area, and it was seeing my Rebel on amphibs that convinced him that he had to have one.

I didn't have the spring gear on mine, but heard about all the problems/fixes with it on this list and from others, and advised him to be sure that his was up to date. After talking to lots of people, including MAM, he decided he wanted to strengthen his further and came up with another mod. He reviewed this with MAM, who thought it was overkill, but did say that it would definitely make it really strong. It is a triangular brace fitting that bolts to the front of the upright cage piece (don't have the part number handy) and the front carrythrough. Then he has the solid piece that goes inside the carry through that also had to be machined to fit properly.

Since he did his, a lot of other spring gear owners, that he had been in contact with, have asked for a set as well. I think he made up about 6 sets so far and all have been taken. He would have to do another run on his CNC machine, but would probably do it, if enough people wanted it.

I will copy him on this email, so you can contact him directly for a proper description of the fix, and if he would manufacture any more.

-----Original Message-----
From: murphy-rebel@dcsol.com [mailto:murphy-rebel@dcsol.com]On Behalf Of Legeorgen@cs.com
Sent: Saturday, May 25, 2002 9:59 PM
To: murphy-rebel@dcsol.com
Subject: Re: Spring gear problems

Legeorgen · Post by **Legeorgen** » Fri Feb 17, 2012 10:13 pm

Thanks Walter,

I just finished painting my Rebel this weekend and what a job! It took twice as long as I had anticipated. It looks great though. I really don't want to take the thing a part to apply another fix again now. I want to but it back together and fly it!

I will talk to MAM and Dennis to get more info before I do anything. It will be no more work now to apply Dennis's fix later if I decide I need it. I'm to close to the coral, if you know what I mean. I think I'll stick with what I got and get the thing in the air.

Bruce G 357R

Legeorgen · Post by **Legeorgen** » Fri Feb 17, 2012 10:13 pm

Al,
I sounds like from your description you had a bolt failure or maybe a torqueing thing. Did the bolt appear to shear or did it tear out the carry thru tube first? MAM stresses re-torqueing the bolts after the first run.

My spring gear is one of the first they shipped in 94 and the saddle bolts and inner bolt are AN6's not the AN-5's MAM ships with the gear now. I don't know when they made the change or if it even makes a difference. I believe it was to make a better fit with the carry thru tubes.

It will be interesting to see what Daryl and Brian have to say after viewing your plane.

Bruce G 357R

Wayne G. O'Shea · Post by **Wayne G. O'Shea** » Fri Feb 17, 2012 10:13 pm

Bruce, FYI the SR has an entirely different set up for the spring gear compared to the Rebel/Elite. The Rebel was an "after thought" bolting on below the carrythrough, while the SR was a "preplanned" assembly with an internal "gear box" similar to the Cessna series, but instead of castings machined/bolt together parts for simplicity.

The problems I have seen with the Rebel spring gear have all been related to the saddle bolts pulling into (or right through) the hollow carrythrough tubes and once that starts to happen the main 3/8" bolt gets twisted off (don't think the 5/16" vs 3/8" saddle bolts changes anything here!). The other bolt failure of a main gear bolt was from hard landings stretching the main bolt, as it is in tension on the Rebel, and just tightening it back up only to break completely a few more high G landings later.

With the SR, the saddle "block" is fairly substantial, with 12 x 5/16" bolts (in shear) holding it to the two carrythrough bulkheads. The gear leg sits up against this block and then a saddle (pretty much identical to the Rebels lower one) holds it in place with two 5/16 bolts in tension. The main gear bolt is 1/2" (7/16 on the 2500) and holds the gear legs top end <down> onto a machined fitting that is bolted to the carrythrough bulkheads with 6 x 3/8" bolts. This means that this main gear bolt area fitting is taking the normal landing load and the bolt is not in tension, but simply holding the leg in place on the fitting (unlike the Rebel where the landing load is trying to pull the nut off the 3/8" main bolt on every landing). Might be a little shear load on the bolt due to the angle the fitting is on, but definitely no tension load on it (in a normal landing).

Now if we get the airplane going sideways (which adds some inward loads) and hit the brake to straighten out (which adds some twisting loads), we now have the forward 5/16 saddle bolt taking the twisting load trying to stretch it or pop the nut off and of course the 1/2" bolt is trying to have the head twisted off at the same time in addition to a shear load from the inward push of the leg (and possibly some tension load as the leg is trying to bend the other way if the tire digs in). Compared to a Cessna, the 5/16 saddle bolts MAY be the weak link here, as a Cessna has a solid casing (that are prone to cracking) that holds the leg from twisting. The main gear bolt is retained in a similar fashion on both and is only susceptible to being sheared off if you get her going sideways with enough inward force to shear the 1/2" bolt. In defense of Murphy, if you get her this far around you're in trouble on any aircraft. Even one of the UTVA's, that the group of us brought into Canada, had the gear cleaned off one side. You can land these things in a full stall landing from 10 feet up, as that is what they are designed to do, but if you want to slide them sideways the (Beaver style nutcracker/rubber block) gear is going to fold up underneath (as only 2 x 3/8" check bolts keep the gear from going the wrong way).

I don't want to put any more "speculation" into what happened to Al's new SR. I know his gut wrenching feelings all too well, as he sits quietly waiting for Darryl and Brian to arrive tomorrow (nice that they are close enough to do so in such an expedient manner!!). Let's allow them to evaluate the <ENTIRE> situation to it's fullest and wait to see what the analysis reveals. We don't need to add any unnecessary "fear" to all the SR builders minds at this point in time, as there are others flying very successfully without this failure (some on very large tires which multiply some of these loads!) wondering what they have gotten into. The dust will clear, the answers will come out, and we can all carry on with our projects. Unfortunately for Al he has some rework to do, after the analysis, but the good thing is that Al's still around to do it!

Regards,
Wayne G. O'Shea
www.irishfield.on.ca

----- Original Message -----

Legeorgen · Post by **Legeorgen** » Fri Feb 17, 2012 10:13 pm

Wayne,

Thanks for clarifying the Rebel and SR gear situation. Having never seen a SR gear, It was a little difficult following your description of the SR gear completely but I think I got the picture. I was under the mistaken impression Al was flying a Rebel or Elite. Well, I guess it doesn't make any difference to Al anyway. He still has a plane to fix. And the rest of you will, for sure, be very interested in MAM's assessment.

Bruce G 357R

Brian Cross · Post by **Brian Cross** » Fri Feb 17, 2012 10:13 pm

Hi Bruce

I don't understand your comment "I was under the mistaken impression Al was flying a Rebel or Elite."

Was he not flying a Rebel or Elite? I thought he was the bolts holding the saddle clamp in place failed.

Appreciate some clarification.

Thanks

Brian #328R

At 09:09 PM 5/26/02 -0400, you wrote:

Wayne G. O'Shea · Post by **Wayne G. O'Shea** » Fri Feb 17, 2012 10:13 pm

Brian,

Al was flying his new tail dragging SR and had a gear leg attachment failure. Darryl Murphy and Brian Godden were to be in Seattle today to investigate and to see if indeed it was the saddle bolt or main gear bolt that failed first.

Cheers,
Wayne

Brian Cross · Post by **Brian Cross** » Fri Feb 17, 2012 10:13 pm

Hi Wayne

Thanks very much for the update. I am way behind in reading my email. I did not pick up the thread properly i.e. storyline to this failure.

Do you have any upgrades or fixes to the standard Rebel re: making it stronger etc.? It has always been a source of concern to me.

Regards

Brian #328R

At 11:13 PM 5/27/02 -0400, you wrote:

Wayne G. O'Shea · Post by **Wayne G. O'Shea** » Fri Feb 17, 2012 10:13 pm

Brian, I have tackled reinforcing Rebels, with the spring gear installation, in a couple different ways as previously discussed here. If you don't want to tear anything apart to reinforce her, at least do the "fix" that MAM has posted on their site showing the addition of an angle to the forward carrythrough tube. This adds significantly to the pull through strength of the forward bolt, in case you stick the tire in a chuck hole, snow bank, etc.

Regards,
Wayne G. O'Shea
www.irishfield.on.ca

Legeorgen · Post by **Legeorgen** » Fri Feb 17, 2012 10:13 pm

Hi Brian,

When I responded to Al's email over his gear failure I thought he was flying a Rebel or Elite. His Gear accident was in a SR. That's all.

Blue skies and tailwinds,

Bruce G 357R

Legeorgen · Post by **Legeorgen** » Fri Feb 17, 2012 10:13 pm

Brian,

MAM came out with a spring gear reinforcement a few months ago. It is on their web sight with a picture. It's pieces of 2" aluminum angle riveted to the each carry thru from inside the cabin. All new kits are shipped with it.

Bruce G 357R