Pietenpol-List: Re: Bungee gear versus springs

matronics · Post by **matronics** » Wed Jan 11, 2012 10:22 am

Original Posted By: "Dick N"
Subject: Pietenpol-List: Re: Bungee gear versus springsMark, my plans included BHP's cub-style split axle gear, which use bungees in tension for shock absorption. The shock struts attach at the apex of the gear "V" down by the wheel, and go diagonally up to the opposite landing gear/flying strut fitting on the fuselage. If you look at the Cub and other later airplanes with this type gear, they have a solid "V" between the gear, and the shock struts attached to the apex of that fixed "V" Go look at any J-3 Cub to see what I mean. My point on this is that the angle between the gear "V" and the shock strut is pretty small on BHP's design. If the cables limiting the travel of the shock strut are a bit too long, the gear can go 'over center' with a hard landing, or in my case, a tight turn on the ground heavily loaded. If that happens, the gear collapses. I have a nice CloudCars wood prop, with 40 hours on it, and 4 inches off the tips to show the result. So, if you do the bungee shocks, look at adding in that center "V" on the shock strut system. Go look at a Cub and you'll be pretty close to what you need for the Piet.I fixed my bungee struts with a shortened limit cable, and by doubling up the bungee wraps. In 60 hours since the problem, they've worked fine, but I worry a bit when I have a passenger and a full load of gas. The other option is to go with the die spring struts, which provide shock absorption in compression rather than tension. There are drawings on the list-serve for this design. Replacing my bungee struts with the spring struts is my winter-time project. Matt PaxtonNX629ML________________________________________________________________________________

matronics · Post by **matronics** » Wed Jan 11, 2012 11:47 am

Original Posted By: John Hofmann
I changed my bungees to springs. One of the bungees failed after several landingsfollowing the 2010 Brodhead landing debacle. The safety cable prevented majordamage and we did a field expedient repair to get home. The spring design allows you to rely on steel instead of rubber. I used Hans vander Voort's design. It took me a weekend to make the change.--------Kevin "Axel" PurteeNX899KPAustin/Georgetown, TXRead this topic online here:http://forums.matronics.com/viewtopic.p ... __________

matronics · Post by **matronics** » Wed Jan 11, 2012 12:05 pm

Original Posted By: "Bill Church"
Kevin,Do you find the landing gear more "bouncy" since the change to springs or do you notice any difference at all?-john-John HofmannVice-President, Information TechnologyThe Rees Group, Inc.2424 American LaneMadison, WI 53704Phone: 608.443.2468 ext 150Fax: 608.443.2474Email: jhofmann(at)reesgroupinc.comOn Jan 11, 2012, at 11:47 AM, kevinpurtee wrote:> > I changed my bungees to springs. One of the bungees failed after several landings following the 2010 Brodhead landing debacle. The safety cable prevented major damage and we did a field expedient repair to get home. > > The spring design allows you to rely on steel instead of rubber. I used Hans van der Voort's design. It took me a weekend to make the change.> > --------> Kevin "Axel" Purtee> NX899KP> Austin/Georgetown, TX> > > > > Read this topic online here:> > http://forums.matronics.com/viewtopic.p ... 082#363082> > > > > > > > > > ________________________________________________________________________________Subject: Pietenpol-List: Re: Bungee gear versus springs

matronics · Post by **matronics** » Wed Jan 11, 2012 1:12 pm

Original Posted By: "kevinpurtee"
Several years ago, Hans posted a copy of his LG spring plans at mykitplane.com,here:http://www.mykitplane.com/Planes/filesL ... mID=75Bill C.Read this topic online here:http://forums.matronics.com/viewtopic.p ... ___Subject: Pietenpol-List: Re: Bungee gear versus springs