Expert: Marc Ebelini - 5/18/2009

Question
Hi Mark
Could you tell me when the wing struts on a Cessna-152 are unbolted, how
are the wings kept in place until the strut is fixed back in? Maybe the wings
do support themselves without the strut, but I do not know this.
If so what exactly is the function of the wing strut?
Also it would be great if you know what force of impact is required for a nose
gear to collapse and rotate rearwards.  

Answer
Let's answer the last question first. I have never seen a specification on the force required to push a nose gear backward on the Cessna. This is usual found in military specification requirements. The force is normally expressed by stating the speed and size of the rise. The only one I remember was the Beech bonanza that had a limit of of not to exceed 15 MPH when contacting a 4" rise.
This was why Navions were used by the army instead of the Beech. Having a larger nose wheel allowed it to contact the rise at a higher speed. Except for the Cessna 210 all the others requires a lift strut for support. Removing the strut without supporting the wing tip can cause damage to the wing root attach point. The forgings in the 210 also used hardened pins to attach the wings. The carry through spar on strutless aircraft must be of greater strength to support the tension, shear and compression.  The carry through spar on strut aircraft only requires compression strength. The strut does all the work on a strut aircraft. Visualize a strut supported wing as a triangle. The wing root could require only one bolt to support the wing at the root. Attaching a strutless wing requires two. One at the lower end of the spar and one on the top. + G's put the upper bolt in compression and the lower one tension -G reverses the forces and in each case great shear forces are applied to the bolts or pins. Another way to understand wing support Remember the old aircraft with wires supporting the wing. The lower wire held the wing front going up and the wire to the king post about the wing held from falling down. But using a stiff member instead of a wire on the bottom that would not bend if the upper wire was removed is the beginning of the use of struts instead of wires. With wires the upper one could be removed in level flight, however once the + G s were removed when landing the wing would fall down.