Pietenpol-List: Re: how did you fall in love Jack ?
Posted: Tue Feb 16, 2010 9:41 am
Original Posted By: "K5YAC"
A long time ago I needed to ascertain the desired tension on something which was directly comparable to this. Turns out that optimum is no initial tension but zero slack, too. Some tension is better than some slack, so if you must, make the error that direction.The main purpose for initial tension is to overcome the effects of expansion or contraction. With metal airplanes that's usually due to temperature. With wood airplanes it might be a combination of temperature and humidity. I have no guidance for that, sorry.If it were my plane, I'd follow those rules of thumb that hurt - uh, that provide a moderate amount of initial tension, certainly not much. I have seen an old wood and wire fuselage that has damage due to excessive initial tension. Two main bulkheads have buckled.David Paule>> I think I caused more confusion than necessary with my "why use them at > all" comment. I was being a little sarcastic.>> I understand the purpose and the need for the cables. I'm not really too > hung up on the whole thing, I just haven't been able to find any definite > answer on how tight these things should be. Yes, I have read all the > replies here, and I do appreciate all the input. I've also read several > other threads that have basically ended in the same conclusion, which > is... there are several different techniques and a wide range of tensions > that will obviously work. I also spoke to several experienced > builders/technical advisors last night at our EAA meeting. None of them > seemed to think that what I had done was necessarily wrong, or dangerous. > The consensus was that I should have all the cables taut while maintaining > the squareness of the wing. How taut? Again, that was up for debate... > no one knew for sure.>> Given all of the input here, and from my discussions last night, I think > I'll back my turnbuckles off a bit. I agree that there is no reason to > apply excessive tension on the cables, this is just where I ended up using > the "twang" method. I fully agree that some amount of tension (it will be > my secret) is adequate for these cables to do their job and keep "drag" > and "anit-drag" from distorting my airfoil. Agreed?>> Thanks again for all the input. On to the next piece of the puzzle.
>> --------> Mark - working on wings>>> Read this topic online here:>> http://forums.matronics.com/viewtopic.p ... 636#286636>>> ________________________________________________________________________________Subject: Pietenpol-List: Re: how did you fall in love Jack ?
A long time ago I needed to ascertain the desired tension on something which was directly comparable to this. Turns out that optimum is no initial tension but zero slack, too. Some tension is better than some slack, so if you must, make the error that direction.The main purpose for initial tension is to overcome the effects of expansion or contraction. With metal airplanes that's usually due to temperature. With wood airplanes it might be a combination of temperature and humidity. I have no guidance for that, sorry.If it were my plane, I'd follow those rules of thumb that hurt - uh, that provide a moderate amount of initial tension, certainly not much. I have seen an old wood and wire fuselage that has damage due to excessive initial tension. Two main bulkheads have buckled.David Paule>> I think I caused more confusion than necessary with my "why use them at > all" comment. I was being a little sarcastic.>> I understand the purpose and the need for the cables. I'm not really too > hung up on the whole thing, I just haven't been able to find any definite > answer on how tight these things should be. Yes, I have read all the > replies here, and I do appreciate all the input. I've also read several > other threads that have basically ended in the same conclusion, which > is... there are several different techniques and a wide range of tensions > that will obviously work. I also spoke to several experienced > builders/technical advisors last night at our EAA meeting. None of them > seemed to think that what I had done was necessarily wrong, or dangerous. > The consensus was that I should have all the cables taut while maintaining > the squareness of the wing. How taut? Again, that was up for debate... > no one knew for sure.>> Given all of the input here, and from my discussions last night, I think > I'll back my turnbuckles off a bit. I agree that there is no reason to > apply excessive tension on the cables, this is just where I ended up using > the "twang" method. I fully agree that some amount of tension (it will be > my secret) is adequate for these cables to do their job and keep "drag" > and "anit-drag" from distorting my airfoil. Agreed?>> Thanks again for all the input. On to the next piece of the puzzle.
>> --------> Mark - working on wings>>> Read this topic online here:>> http://forums.matronics.com/viewtopic.p ... 636#286636>>> ________________________________________________________________________________Subject: Pietenpol-List: Re: how did you fall in love Jack ?