Online Community of Zenith Builders and Flyers
(Last Revision May 20, 2012)
The added roof space on the new CH 750 at SNF 2012 attracted great attention.
What about CH 701 community?
There are at least two members of this group that have built/modified their CH 701 with added head room, as well as a smoother air flow over the roof at high angle of attack. Both members I know have already enjoyed flying their planes. Mine is unfinished, untested and untried. I am showing old photos together with newer ones. With wing folding kit installed, showing the horizontal yellow tube, I could not just follow the Beanie Mod of Joe Spencer, and so... I did it my way. Comments are welcome.
Of course, to do this mod., the wing roots need to be rebuilt with new Rear Root Ribs and new Wing Root Top Skins (that you make them yourself. I live too faraway from most of you to offer a kit. Freight charge can be uncomfortable. I can advise one on one if needed). You will need a 3' x 4' sheet (1.5' by 4' for each wing) of wing skin, and 3' by 4' sheet of wing rib material (1.5' by 4' per wing, with excess material) at the start. Kansas Airparts, for one, can cut 3 ft. length off their rolled aluminum sheets for you.
Roof modification without welding
Living and flying with the long aluminum diagonal on roof is an easy choice for most. No need to take the cabin tube frame off the fuselage for cutting and welding, or risk the trouble of welding it in position. WIth wings off or firmly supported, cutting the aluminum tube at 120 mm from each corner starts the transformation. More on this tube later.
Forget the acrylic bubble windshield. A 1/8" thick one-piece windshield and roof polycarbonate sheet doesn't crack as easily, while not as expensive. It won't restrict the roof curve as does the bubble windshield. The new windshield now continues to go over the roof in a very smooth curve up to 90 mm above the original roof. An inverted L angle of 20mm X 20mm at 7 millimeters above the front cabin tube helps the windshield to sit snugly in its place on the first try.
I did not quite place the Left Roof Side Rib on the exact center of the left roof side tube, and had to relocate the rivets.
The rough sketch below explains how I shaped the Roof Side Rib. The inverted L angle cut short 3" at each end helps the windshield to curve easily to its left and right edges without heat forming required. My coordinates for the curve over roof side tubes that you may use to start your cardboard templates are:
0-0, 100-57, 200-85, 300-90, 400-78, 500-55, 600-32, 700-6, 720-0
You may adjust the first and the last points as you see fit.
Note 1. If the inverted L sits too low for the rivet length, you will not be able to install the rivet properly.
Note 2. If you want to use the bubble windshield since you have invested big money, you can lower the height of the curved up roof to keep a smooth curve from the middle of the bubble windshield to the roof, or you can still keep the 90 mm high curved roof for a higher efficiency and live with a small rolling at the joint of windshield and roof.
The Wing Root Ribs have to match the curved up roof, but just a little bigger to allow Wing Root Top Skins to overlap the roof sides. Picture below shows the left wing root with wet wing tank unfinished. The hole in Rear Rib 1 is for fuel sender off a pick up truck. You can guess it right that making wet wing slows me down.
Back to the cut-off tube on the middle of the roof.
Press the middle of the cut-off tube against a narrow work bench or the corner of a low table, then hand bend it so that the middle gets 70mm off a straight line. I did mine at 45mm since I planned to have a narrow rib on top of this tube at the highest point. 100mm length of curved steel tubes are inserted at both ends. The curved steel tubes mentioned are steel conduit that are a little bigger than the aluminum diagonal cross tube. I flattened them a little to fit the aluminum tube inside for riveting 6 of A-4 on top and bottom while filling the void between the tubes with epoxy steel filler the best I could for a firmed joint.
Roof support along the diagonal cross tube. The curved steel connector 100mm long (a comfortable length for my hand) at the cockpit front left corner will be used as the pilot's handhold. Same length of connector is used at the rear right end.
Showing two roof supports, with the twisted Z angle in the middle.
With polycarbonate roof installed. Looking from left to right.
Close-up of the twisted Z angle of .025" 6061T6 joining the diagonal cross tube and the middle roof thin rib, looking from left to right.
From right to left. Another leg of X on this 2mm roof is not necessary unless flight testing proofs otherwise. The curved roof feels firm to the touch as is.
My inverted L angle over the cabin front tube. AN-3 bolt in the middle holds the wing-fold cross tube (painted yellow in picture).
On Acrylic and Polycarbonate
Acrylic has been flying fast and high with jet planes for so long but I prefer polycarbonate to acrylic sheet for my small plane. Properties of polycarbonate can be found on the internet for those interested.
Roof modification with welding
I take off the three aluminum tubes on roof frame, then weld in the steel side tubes and short diagonals at the two front corners. After seeing it done at CH 750 Forum (similar to CanZac made cabin tube frame for CH 750), later I will add a lower cross tube at the 'lower edge' of instrument panel, and another one joining the rear ends of roof side tubes, with a short diagonal, between the side tube and rear tube, at each end.
This won't be too much for scratch builders. Hopefully, this mod will give enough elevator control on power off approach from flare to touch down.