This is a request for an engineering opinion on a general principle of aircraft design. For the purposes of this post, it's not specific to any one design.
Suppose we have a generic Cub-ish high wing UL/LSA tube and fabric aircraft design. 4130 traditional steel tubes for the fuselage and wing struts. And let's further suppose that the same basic design was offered with two separate wing strut sizes. The early version of this little hypothetical aircraft used V-shaped main wing lift struts that were made out of 3/4" OD steel tubes with fittings welded to the ends. Later on, another version came out that used 1" OD 4130 steel tube wing struts. But you can't just buy the upgraded struts from the manufacturer any more.
Let's suppose that (Assuming the same gross weight, and the rest of the structure is the same on both versions) the big difference is that - with the smaller diameter wing struts the airplane was good for 6G positive and just under 2G negative, and with the larger diameter struts the airplane was good for the (likely more than) 6G positive but it went up to 3G negative. And let's assume that this increase in negative G loads (or hard landing loads) was because of a larger diameter tube's obiously greater resistance to buckling (Euler and all of that)
So let's say that a fairly conservative, safety-conscious person, who was stuck with one of the airplanes with the smaller struts really wanted to use the larger struts. NOT because of any intent to fly aerobatics, but because this pilot just wanted to have an airplane that was safer in turbulence, gusts, or accidentally blundering into a wave rotor.
And let's also say that the guy was trying to not have to fabricate entirely new struts. So he came up with an idea: Cut the existing small struts apart, and weld the end fittings into a piece of larger strut tube. This would yield a strut where the majority of it was the large diameter. The central main portion of the strut that he assumed was most likely to see the compression/buckling problem would be larger and more buckle resistant. The only small diameter parts would be at the very ends.
So here's the educated engineering opinion I'm looking for... If the majority of the strut was increased in diameter, except for short sections at the end, which is necessary to weld and sleeve the small tubes up to the large tube... would this be likely to increase the negative G buckling tolerance of the strut up to the level of the larger struts, OR would the presence of even a short section of tube be the "weak link" and result in no significant improvement in the negative G / landing load condition? In other words, exactly how much better off would this guy be if he fabricated new struts without re-using the existing end fittings ??
Suppose we have a generic Cub-ish high wing UL/LSA tube and fabric aircraft design. 4130 traditional steel tubes for the fuselage and wing struts. And let's further suppose that the same basic design was offered with two separate wing strut sizes. The early version of this little hypothetical aircraft used V-shaped main wing lift struts that were made out of 3/4" OD steel tubes with fittings welded to the ends. Later on, another version came out that used 1" OD 4130 steel tube wing struts. But you can't just buy the upgraded struts from the manufacturer any more.
Let's suppose that (Assuming the same gross weight, and the rest of the structure is the same on both versions) the big difference is that - with the smaller diameter wing struts the airplane was good for 6G positive and just under 2G negative, and with the larger diameter struts the airplane was good for the (likely more than) 6G positive but it went up to 3G negative. And let's assume that this increase in negative G loads (or hard landing loads) was because of a larger diameter tube's obiously greater resistance to buckling (Euler and all of that)
So let's say that a fairly conservative, safety-conscious person, who was stuck with one of the airplanes with the smaller struts really wanted to use the larger struts. NOT because of any intent to fly aerobatics, but because this pilot just wanted to have an airplane that was safer in turbulence, gusts, or accidentally blundering into a wave rotor.
And let's also say that the guy was trying to not have to fabricate entirely new struts. So he came up with an idea: Cut the existing small struts apart, and weld the end fittings into a piece of larger strut tube. This would yield a strut where the majority of it was the large diameter. The central main portion of the strut that he assumed was most likely to see the compression/buckling problem would be larger and more buckle resistant. The only small diameter parts would be at the very ends.
So here's the educated engineering opinion I'm looking for... If the majority of the strut was increased in diameter, except for short sections at the end, which is necessary to weld and sleeve the small tubes up to the large tube... would this be likely to increase the negative G buckling tolerance of the strut up to the level of the larger struts, OR would the presence of even a short section of tube be the "weak link" and result in no significant improvement in the negative G / landing load condition? In other words, exactly how much better off would this guy be if he fabricated new struts without re-using the existing end fittings ??
