CORKY'S CHRISTAVIA MK 4 WEBPAGE

This page will be continually updated as work progresses
Here is the Christavia Mk 4 in a photo supplied by Ron Mason, the designer. This is the prototype and is no longer in Ron's hands, he was made an offer for it which he could not refuse. You'll have to picture this with a V-6 up front rather than the Lycoming and having a cooling system scoop underneath the prop similar to the F-86. The plan is to have all cooling systems in the nose, if weight and balance allow.

This is a shot of me sitting in the cockpit of what will be the Christavia Mk4. Things to observe: if you can see it with the resolution of the JPEG, the door opening is square tubing rather than round. You can also see that the forward section has not been created yet. That's next. Also, the board across the front is only there temporarily, it's just clamped their so I can clamp the rotisserie base to it to enable me to rotate the fuselage. In practice this isn't working as well as I'd liked and for the moment I'm using the metal stand I made as one end of the rotisserie to hold the tail up. I let the front sit either on the floor or on concrete blocks. This allows me to rotate the fuselage to four different positions for welding.


This is a close up of what the floor of the cockpit area looks like. The cross pieces are 1 inch outside diameter tubes. The ones that will be supporting the landing gear are .055" wall thickness. Also, it's a little easier to see the square tubing used for the door opening in this shot.

Another shot, this time showing the rear of the fuselage


A new picture of the now completed firewall area.
This is a shot of the horizontal stabilizer leading edge "hold down", for lack of a better term. The leading edge fits inside the tube you see and is anchored by a 3/16" bolt through the holder and the leading edge. The two bolts set in standoffs at both ends allow washers to be fitted underneath them to adjust for the horizontal stabilizer angle of incidence. This may seem a flimsy manner of locating the horizontal stabilizer but it makes more sense when you know that the horizontal stabilizer is held in place with two wires from the vertical stabilizer and two more from below and attached to the fuselage. So the wires actually provide the strength of the tail group, the tubes merely locate/attach it. It's actually pretty robust as is common with everything that goes into the Christavia. It's a 1" .049 tube sleeved on the outside sections with a larger 1 1/8" .049 tube. I did not actually have a 1 1/8" tube around so rather than buying one, I took a larger 1 1/4" tube, which I have plenty of, and sliced it down the middle, then ground off enough so that I could wrap it around the 1" tube and weld it in place.


The above picture was of the leading edge holder, this is the trailing edge holder. The leading edge fits *inside* it's holder, the trailing edge fits *outside* it's holder. Like the leading edge holder, this is reinforced; it's a 3/4" tube inside a 7/8" tube and spot welded around the edges to hold it together. The way the horizontal stabilizer is set up, the leading edge is 7/8" .035 tubing. The trailing edge is 1" .049 tubing. This means that there is a slight wedge effect from leading edge to trailing edge. From the leading edge of the elevator to it's trailing edge, the change is far more pronounced as the trailing edge of the elevator is constructed from 3/8" tubing. This will be one area where I will completely ignor the designer's plans. Let me explain. Since the horizontal stabilizer leading edge differs from the trailing edge by 1/8", you can't match up a tube to the two edges. So you're supposed to bend up a rib using .035" sheet metal such that one end has a cross section of 7/8" and the other is 1". The same would hold for the elevator and rudder but in those cases the rib goes from 1" to 3/8". Instead, I will make a streamline form and bend 3/8 square tubing around it and weld them to the leading and trailing edges. This will allow the fabric to take on a streamline shape, rather than the wedge shape of the plans. I will of course weld in vertical trusses to strengthen the ribs. This is common practice for construction. It will entail more welding than the plans ribs would but the results should make for cleaner aerodynamics and less drag.

By the way, in the background on the bench you can see the center control stick. I bought two bronze bushings out of the MSC catalog to use for each end. I now have to fabricate the collars that will bolt around them and weld the collars to the cockpit floor.


Here's a closeup of the one of the corners that the engine mount will bolt to. This was built to Piper specifications. By that I mean the measurements for the bolt holes are 30 inches across and 20 inches down. I built a jig to make sure the bolt holes were absolutely accurate. I used a plywood base and once the measurements were made, drilled the four holes through the plywood the same size as the bushings that would be welded into the rectangle, then fit scrap tubing into the holes to use as guides around which to fabricate the firewall tubing. Then I cut the tubing on a 45 degree angle and fit it around the guide tubes. Once everything was ready, I carefully and quickly tacked the four pieces in place, removed the frame and thoroughly welded the four corners. Next I cut out four short pieces of tubes and 45'd the ends and welded them into the corners. Finally I cut out eight triangular pieces of 4130 sheet steel .072" and center punched each one where the hole should be for the bushing. Each triangular piece was drilled out on the drill press. Then each pair was fitted over the corner with the bushing loosely in place and adjusted so that the bushing was nestled into the corner snugly and the bushing was at a 90 degree angle to the frame. The welding went nicely which is what I'm hoping the picture will show. I had to be careful welding the bushings in place so that I didn't melt into the machined ends. On the inside, or other side of this picture, I welded in some flat stock such that once the bolt is pushed through from back to front, it nestles inside the flatstock which prevents it from turning. This is a good idea because eventually there will be a firewall mounted over this part of the fuselage and access to the bolts from inside the cockpit will be problematic. Just one of those little things you need to do to make life easier for you once everything is covered. Thanks to Bruce Frank for that advice.







This shows the fuselage in a line drawing. The drawing does not reflect accurately the way the fuselage is supposed to look when you study the plans. This is one of several areas in which the plans are a little wonky. But what you're seeing isn't supposed to be used for construction it's just something included in the plans so you can have a general look at the way the fuselage is supposed to be. The actual plans, which are much larger than the 8X11 drawing, show additional tubes mounted in various locations. If you study carefully you'll see the additional tubes in the photo's. For the record, I'm having a REALLY fun time welding the fuselage up and can't wait to get in to the shop each night to work on it.