Comment

Comment by Normand Lambert on July 27, 2016 at 11:11am

Hi Steven and Bob,

You are both right. Never do anything without involving some aeronautical knowledgeable person when changing something. Steven, When I decided to use square 4130, I already knew the thinkness would have to be increased using table especially designed to provide comparative measures. Also, my CH701 does NOT use TEFLON to route cables; pullyes are used throughout unless the cable goes STRAIGHT... That will be replicated in my CH750.

For the wing, my doubler was already longer than the one in the plans. Never liked oil canning on ANY SURFACE especially not the wing. For Z strip on the CH701, I sure do remember since I did this modification BEFORE it flew...

Thanks for the comments; they keep me in check but don't worry, I ALWAYS check first and do it later.

Regards,

Norm

Comment by STEVEN and TARA SMITH on July 27, 2016 at 2:13am

I agree with Bob Pustell. Always seek our Aeronautical professional advisers advice. Also remember to use your Nations publications of standards. I have a vast background in sheet metal and structures. Remember it is important to know the difference between primary and secondary structures. wing and flying surfaces are primary. You would be best not to modify the structure of the wings without serious considerations.  fuselage secondary. You will always have a safe airplane if you follow the plans. Having said that, with exception of the square feed thru tube, you will find all of the other mods you have posted - already have a proven history of safety. reference the modification strings on this website. Remember - square tube is not as strong as round and should usually be used in tension. Remember the famous "z" strip on the 701"s. needed beefed up due to its compression loads. Three areas I would personally recommend upgrading are as follow. use pulleys for all of your cables as opposed to Teflon glides. Cable glides are normally used when the cables path is straight. In the ch 750 - all of the cable have a directional change threw the Teflon and is too abrupt, and tends to saw the Teflon. Many are referring to it as the "rope effect" and is difficult to get a cooperative finely tuned centered ball. This is not an aircraft standard. Second -  Extend the aft spare rear channel doubler as it is parallel with the aft wing strut attach point.  Any video of the aircraft flying (when viewed from above) will tell you that the wing is oil-canning as a result of a bending moment of wing lift. keep in mind that NO  ch750 has folded a wing in this area. But remember - oil-canning on an aircraft is a sign that something is wrong. third - add a thicker spacer and longer bolt on the flap / aileron bell crank rod ends (inboard rods). This problem becomes evident when the flaps are lowered. You will notice binding in the ailerons while the flaps are down. essentially the bell-crank is trying to pop the ball out of the rod end. Adding a thicker spacer will take the load off of the rod end and your roll control will be smooth again (be sure to use proper "AN" hardware).

cheers for now. Steven Smith

Comment by Bob Pustell on July 23, 2016 at 6:35pm

I will be the wet blanket that urges caution. Unless you have a lot of aeronautical structures and engineering expertise it is easy to modify yourself into an overweight airplane at best and a dangerous one at worst. In aircraft structures everything effects everything else, sometimes in very subtle ways. Some years ago I read of a builder that decided to use thicker skins on the wings of his project. He ended up with spar damage after a period of flying the plane. It turned out the thicker skins changed the way loads were distributed around in the wing structure and forces that had not converged on the main spar now did -- if the failing spar had not been detected during an inspection it would have eventually failed in flight. I may have the exact details of the story right, I read this many years ago, but it was a story about seemingly harmless "improvements" that caused dangerous structural problems. Airplane structures are very carefully designed by very smart people and I am nervous to do too much in the way of "improving" them because I don't have the depth of knowlege needed to be sure an improvement is really an improvement. Ya'll be careful out there.

Comment by STEVEN and TARA SMITH on July 17, 2016 at 6:29pm

Hi Norm. Just some thoughts. when I started my project - there was no such thing as a ch750. I was re-building / re-storing my ch701 I had recently purchaced. soon after I bought the 701 - Zenith came out with the 750. I was very disappointed with the 701 size at that point. So when I started my project, I went well off the reservation. I used square tubing for my frame as well. I double the thickness from the plans and have been very happy with the results. I also went 10 inches wider than the plans. My airplane is 50" wide at the hips before the bubble doors. my cabin is not only wider but is also taller and deeper. I eventually bought a set of ch750 plans and have been building from the 750 plans using all of the favorable ideas from all three airplanes 801,750,701. My airplane sits 6 inches taller to accommodate a 78" prop for my o-320. Every modification I have made has had an equal amount or more modifications requirement to make the original modification work. ie. wider body needs a modified "collective flap torque bar modification. oddly enough - by the time the ch750 version 3 came out - I had met or exceeded every Zenith item version 3 had incorporated. I did not use square tubing on the spare carry through, just the door frames etc... I have been very happy with the modifications I have made. they all make sense to me. please keep us all posted - I just love watching your progress. Steven Smith.