Pietenpol-List: Re: Bungee gear versus springs
Posted: 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________________________________________________________________________________
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________________________________________________________________________________