Building a CH750 and making modifications along the way !!!

January 12th,2017

Hi again,

Time to report back on my CH750 build. What has been done so far :

1) CH750 : stabilitor is finished but not closed. It is full symmetrical to match the symmetrical elevator.

2) CH750 : wing are done - not closed and inspecting them right now...

3) CH750 : ordered some control parts (aileron mixer) to finish the setup. Got the rudder pedals and brakes/reservoirs

4) CH750 : aileron + flap skeltons are being assembled and checked against the wing brackets

5) CH750 : rudder is done - not closed for inspection

The CH750 won't have Slats; the brackets were not even installed. Instead VGs will be used on the main wing.

The cockpit cabane (4130) will be made of SQUARE tubing for welding ease. Thickness will be increased.

Also, the Beanie mod and corner reinforcement (instead of tube across cabine) will be used for more headroom.

Still debating the twin stick option versus the center stick. My CH701sp has the twins and center engine management controls and I like it...

Regards,

Norm

CH701sp C-GFEU

CH750

CH701SP

Sept. 28th 2016.

Hi Again,

The CH750 elevator is finished for now. Let's work on the stab. Some changes :

1) Tip ribs will be constructed from 2 parts - rear rib and nose rib riveted together.

2) Front spar thickness went from 0.0250 to 0.032 for increased durability.

3) Rib design changed to full symmetrical profile keeping all height the same as the original ribs.

Changing the rib design to symmetrical also means only one set of form blocks; shape being the

same upside down.

Regards,

Norm

--------------------------------------------------------------------------------------------------------

July 20th,2016

Hi all,

I've constructed most of the elevator skeleton and made some changes. They are :

1) tip ribs are made of 0.025 (instead of 0.016) for added strength

2) Tip ribs will be constructed from 2 parts - rear rib and nose rib riveted together.

3) In the plans, the rear elevator skins are made of 1 part that wraps around the trailing edge. This is too complicated

    and time consuming. I will split that part in 3 module : Top skin (0.020), bottom skin (0.020) and trailing edge

    (0.032). This will add rigidity to the trailing edge that very often gets dinged....

4) nose rib design changed to full symmetrical.

So much fun, so little time !

Till next time.

------------------------------------------------------------------------------------------------------------

Hi all,

My CH701sp is flying and well at that but as I was reviewing its flight characteristics, I realized that a longer wing would be a nice improvement. I looked up the blogs and checked out the plans for the CH750 and found that the 750 wing could be mated to the 701 and it would make an even STOLer aircraft.

Now, my girlfrined and I went for a couple flights and she told me that the 701 was a little cramped for the both of us; she hates confined space and was used to the Cherokee... Hum, time to look up for a 750 wing or a CH750 all together ???


So, here goes nothing !

The CH750 plans are here and building has started. I intend to make quite a few modifications from my CH701sp building experience.

They are :

1) NO Slats   : these parts DELETED from my CH750 and replaced with Vertical Generators on main wing;

2) Stab Ribs   : replace upside-down ribs with FULL SYMMETRICAL ribs for both STAB and Elevator;

3) Beanie Mod  : replace Flat top over cockpit with curved section;

4) Replace 4130 : wing carry thru over cockpit made of square 4130 tube instead of round

Other changes may come to mind and will be added as I dig in.

Let's see how this goes. I'll keep you posted.

Regards,

NormTheStorm

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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.

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