(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.

Here are the pictures on the curved up diagonal cross tube and its related members.

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.

My diagonals needed to be cut and extended a little. Continuous welding (became too hot and) caused a pull inwards of the side tube rear ends.

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.


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Comment by Ron D Leclerc on August 12, 2012 at 3:01pm

Hey Champ


I guess having the mods for the 701 done as per Sabastians post was just wishful thinking and will not happen.  I don't like people that make those kind of comments and then they quickly forget about it.  To be honest I did not put to much into his comments... I could tell that he just said it to get us off of his back!  When you steal intellectual information and claim it as your own... tells us what kind of people we are dealing with... it's not what is good for the customer - but it's what is good for them(kind of selfish)!!!!!!! 


Comment by Ron D Leclerc on August 12, 2012 at 2:52pm

What's happening Champ?  It has been kind of quit here.  Have not been doing much on the 701.  Spending some more time on my engine.  Got my parts for the redrive, they look pretty good better then expected... just need the Thrust Plate and Spacers.  See photos in my album!   Will need a 4" prop extension yet.  Balanced my Rods and 96mm Pistons to within 0.1 grams.  Painted my 96mm jugs with flat black paint cut with 50% gas and they are ready for the oven(baking at 170 degrees for 3 hours)... will do the same to the case.  I have to have  2 plug holes on the engine drilled and tapped for  3/8 NPT plugs and also will have the case cleaned up internally... it's not bad but I want to make sure it's ok!  My 2L crank will be sent out to have the journals polished.   Otherwise the engine is now ready to be put together.  I still have to get a Rotex TBI-40 mechanical fuel injection unit.   Not decided on what igintion to use... I may use a Pertronic billet distributor with the Flame Thrower II iginitor...


Other then that it's time to get going agin...


Comment by Chumphol Sirinavin on August 12, 2012 at 11:51am

Well, Ron,

There is a long list of wishful mod. that needs to be cut short, or I may get too old to fly upon finishing the long list. ;^)


Comment by Chumphol Sirinavin on May 29, 2012 at 12:04pm

My welded cabin tube frame may end up with left-right cross tubes at front and rear, with an X on roof. Attaching the rear end of roof side tubes to rear wing attachments with AN bolts is being considered. 

Comment by Chumphol Sirinavin on May 12, 2012 at 12:14am

The welded roof frame is made from that off an old CH 701. It will be on my second CH 701. My first remains happy with the bent up diagonal aluminum tube under the cockpit roof.

To do the roof frame similar to that of a Savannah had been considered and dropped. It was too complicated and would spoil the Beauty of Simplicity of CH 701 design.

Comment by Chumphol Sirinavin on April 29, 2012 at 9:42pm

Want more head room?

Within prudential structural and weight limitations, you can try a " bubble canopy".

For less drag? You can make the square top into a gentle inverted U, or V, with added storage. I really admire John Gilpin, seeing him put his folding bike on the back of his Savannah under a roof, at:  http://www.stolspeed.com/bike-on-board

All ...within prudential structural and weight limitations...

Comment by Chumphol Sirinavin on April 28, 2012 at 10:17pm

The butt joint with hot glue seemed to work.

But when I added more weight this morning, the joint with hot glue failed. It needs to be reinforced with 40-45mm aluminum strip epoxied over the joint. Three rows of alternating rivets with top row on the front edge of roof, middle row on the (inverted L angle over) the front tube and bottom row on the top windshield edge will be sure to work. Again, you don't need this butt joint if you can do it in one piece. 


Comment by Ron D Leclerc on April 28, 2012 at 9:57am

Hey Champ


Here is drawing of a Beany Mod that would be a starting point. The windshield and roof are one piece 1/8(3mm)  PC with a smooth transition.  Not to much forming here can be doen with a heat gun.  It looks like you will need a min. of 130 degrees C with complete workability of 170 to 180 degrees.  I don't know if heat would be required a the is no extreme bending needed here! 


Comment by Paul Saccani on April 28, 2012 at 9:29am

Re the butt joints on polycarbonate - I've recentlyh done some testing with a variety of solvents, including methyle chloride.

In theory, these solvent welds should be just as strong as the base material.  In practice, I was not able to achieve satisfactory strength, even with lap joints.  So whilst I'm still sure it can be done, I reckon it will be tricky.


Given the scope of home building, it would be seem to be likely to be a frustrating exercise to go down this route.


Cheers, Paul.

Comment by Chumphol Sirinavin on April 28, 2012 at 12:12am

G'Day Ron,

If it's good for CH 750,1/8" should be good for windshield and roof of CH 701. For your extra wide cockpit, butt joint wIth 40-45mm aluminum strip over the joint, three rows of alternating rivets with top row on the front edge of roof, middle row on the front tube and bottom row on the top windshield edge will be sure to work. I just hate to think of the roof piece departing airplane while slow and low with high angle of attack. 

Thais are funny people. We are supposed to use all metric system. In a beauty contest, they measure  her height in meter and her weight in kilogram, but chest, waist and hip of the girl in inches. A ruler will have one edge in inch, another in centimeter. This goes well with CH 701 plans where measurements shown in both metric mm. and fraction of an inch.

I haven't tested the outcome of glueing test for butt joints yet. 


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