A couple of weeks has passed since my last blog post. Christmas is a very busy time for everyone and I'm no different. Two back to back work road trips right before the holidays, but any chance to be in the shop that came up I went.
With the left (pilot) cabin side fit up, time to replicate the right (passenger) side to match.
Used the same method for the matching the cabin longerons, placing them back to back, prior to back drilling them to the skins.
Before heading home one evening, I decided to see what the cabin width would look like. Very rough estimate, but liking what I see - lots of room for two people sitting side by side!
Next time in the shop, I decided to compare the cabin sides and they are perfectly matched - everything will be straight and equal once I create the cabin floor and attach it to the rear fuselage.
Both cabin sides, initial fit-up complete:
A somewhat more accurate placement on the bench using the landing gear channel as a guide. This picture shows the rear cabin longerons as they bend inwards to match the tapering fuselage in the baggage area:
Upsizing the cabin side longerons, doublers and uprights to A4 in preparation for debur, prime and assembly.
Further investigation was required regarding the forward edge of the lower cabin doubler. Shown at bottom right in this photo, it needed to be trimmed back.... but....
The plans show two different things. Circled in red below the plans show the doubler extending forward to the front edge of the cabin skin. However the view from the bottom on the same plan drawing (circled in green) shows that the corner has a relief cut.
The cabin skin plan drawing shows the relief notch at the corner. That seems to match the green circle above. Time to email Zenith.
While waiting for Zenith to respond to my query, I continued to drill out the cabin parts to the correct size (A4)
I heard back fairly quickly from Zenith and it turns out the drawing in the plans is wrong. The doubler only extends forward as far as the front most upright angles. That leaves the notch free to allow the boot cowl skin to form around that corner later. So with that questioned answered, time to pull everything apart for deburring and prime:
With all holes deburred I put the door sill longerons/angles back in place briefly in order to final sand the cabin skins to match them. I also stripped the protective plastic of the the outside of the skin along the rivet lines so I can prime the rivet lines ahead of placing rivets:
Added the last two cabin side rivet holes, but only up to A3. These will be the pilot holes for joining the cabin sides to the rear fuselage. Still need to bend the rear edge inwards to match too:
Debur, scuff with Scotchbright and clean prior to priming:
Decided to change track a bit while I had room to work on the bench and got started on laying out the cabin floor. The camera distortion doesn't show it well, but the cabin floor is a tapering rectangle, narrow end (furthest from camera) being the front end towards the firewall:
Laid out the location of the rudder pedal bearing channel and started to secure it with A3 clecoes:
Next headscratcher.... I see in my plans that there is a gap above the floor skin between the heel support channel (on the left in pic) and the pedal bearing channel (on the right):
Is there any reason this gap needs to be there? I don't see anything in the plans that says that the gap needs to be there for other stuff and to my way of thinking it will just be a place to gather dirt, dropped pens, travel snacks debris on long trips etc.
What I was thinking of doing is widening the heel support channel to overlap the rear flange of the pedal support bearing with his eliminate the gap, then riveting both flanges together (green stars):
I asked in the forums and in an email to Zenith and there is no reason not to widen the heel support. Turns out the gap is a carry over from the 701 design where every chance to save weight was made. The 750 Super Duty model has already covered this gap in the same way I am suggesting, so no issue to proceed, so I will.
Next up is the lower cabin floor corner longerons. Cut them to match (one for each side) and mounted them. This support the cabin sides, so I'll wait to drill them together when fitting the floor into the cabin:
Also on the bottom of the cabin floor is the centre stiffener whih runs from the firewall back to the gear channel. Additional lateral stiffeners will be added later:
Seat support channel is added on the top side of the cabin skin:
Lots left to do on the cabin floor, but off to a good start, next will be the heel support once I fabricate the new wider one:
Back to the cabin sides. Primed and ready for assembly.
Priming of outside of cabin skins:
Final assembly in progress after priming. I'm waiting to add the long forward and long rear longerons until I confirm where they meet the firewall and cabin:
All of the cabin side A4 rivets are driven with the air hammer, similar to the wing spar caps. Fortunately, some of these A4 hard rivets are also close enough to the edges of the cabin skin that I can use the rivet squeezer to complete the assembly:
Forward upright now fully installed:
The others I could reach witht e squeezer are the tops of the rear uprights, the doubler L's and the door sill angle.
I set aside the cabin sides for now to work on the fuselage bottom assembly. First thing was to cleco forward corner doublers to the bottom skin and the fuselage longerons. Next I clecoed all the diagonals and lateral stiffeners to the fuselage skin:
Installed the riv-nuts that will be the mounting points for the stainless screws to hold the hell-hole access cover in place:
All riv-nuts secure and tested with the screws that will eventually be in place - very happy with how these turned out.
Worked the air rivet gun back and forth equally across the diagonals and lateral stiffeners, leaving the ends free to tuck in the side fuselage skins:
Incredible how rigid the lower fuselage skin is now with the rivets lines across the middle of each bay:
I started to work on the end plate gussets and cross angle, but soon realized the plans don't define at what measured location this gets installed. Spoke with another builder and he noticed the same thing with his kit and we agreed this needs to wait until the controls they support in the hell hole are installed ensuring correct alignment.
Next up, the front and rear horizontal tail frames. I'd previously fitted these to the bottom fuselage, now it is time to start building up the box that becomes the tail support area.
Kit builders have this step much easier. The rear side skins and longerons are drilled already, whereas a scratchbuilder like me needs to think a bit how to place them in the right location relative to the rest of the fuselage.
To that end, it is time to start fitting up the side fuselage skin to the bottom skin.
I decided on starting with the right side, mostly because was closest to the edge of the bench!
I added a couple of upright boards which are screwed to the bench, then lightly clamped the skin one of them through the cabin window. The it was just a matter of sliding the skin fore and aft a bit until the front lower corner matched the front right corner of the bottom skin. With the rear side skin clecoed together, I know the distances are correct (and I confirmed this as well).
I drilled the side skin to the lower longeron along several places. As mentioned before, the fuselage has a gentle curve towards to the tail on all four corners. By matching the side skin taper to the longeron and securing it as I went, the fit up was relatively easy to accomplish. I still need to remove each of the diagonals and uprights on the side skin for priming, I just clecoed them in place for now give the side skin some rigidity for this task:
Here is the left side with the rear side skin temporarily clamped in place. I also clecoed on the the top coner longeron to further stiffen up the side skin for back drilling the rear tail frames:
Front and rear tail frames fit up and drilled to A3, eventually these wil be brought up to A5:
A bit hard to see among all the clecoes, but I added the rear frame diagonal as well, these too will be brought up to A5. I've got a clamp holding the ear corner of the skin to the lower longeron and will drill them later once the left side fuselage skin is in place and I confirm everything is square.
Very pleased so far. All the work to get the fuselage skins laid out, cut and replicated side to side is working very well. I'm also pleased that all the fore-thought on order of operations (what to drill now, what to wait for later) is paying off now in the assembly stage.
Thanks for following along, more to come soon!
Another productive weekend at the shop. Work continues on the cabin sides which are being built ahead of time. Once complete, they will be temporarily stored until the rear fuselage is put together.
With the radii complete in the cabin side skin blanks, I realized I needed to duplicate the holes where the longerons and other cabin wall supports would be installed. Once trimmed to final size the pilot holes around the perimeter would no longer be available.
With new duplicate rivet lines established, I started to cut away the door sill on the master cabin side (left/pilot side). I started with rough cuts between the radii circles:
This allowed me access to completely trim away the door sills. I used a scoring tool to ensure perfectly straight lines between the radii, then snapped off the remaining trim away scrap. Same with the bottom edge where it will fold inwards to form up part of the cabin floor.
Also trimmed away the last part of the forward cabin edge where it will join the boot cowl (area between instrument panel and engine cowl:
In order to preserve my ability to stack left and right cabin skins until absolutely ready to bend them, I left a pilot hole dog ear at each top corner. These will be trimmed off later.
Fiipped the left cabin side over and stacked it on the right side cabin skin. Radius holes match the door sill radii which confirms both will be equal once cut out:
Trace the left onto the right:
Follwed the same method to remove the trimmed scrap from the right skin, restacked to confirm and now I have a cabin skin blank for both sides:
Now to start laying out the longerons and supports on the left cabin skin, looking towards duplicating them on the right skin. Until I install the 040 doubler along the folded lower section, I left the longerons and supports a bit long. I can trim them later to fit.
The forward longeron which connects the cabin to the boot cowl and firewall is the only piece of this assembly that crosses completely from corner to corner, so I started with it. Plans call for 3/4x3/4 inch 093 thick angle, but I'm upsizing this to 0.125 thick. The extra strength will be worth the very small weight penalty, giving the cabin that much more rigidity when the aircraft gets put on floats later on:
The lateral leg of the longeron extrusion forms part of the door sill, so it abuts to cutout in the cabin skin:
Next I started fitting the uprights and once positioned correctly, laid out the rivet lines on the extrusions and drilled them on the drill press to A3 hole size. This is kind of like a jigsaw puzzle figuring out what piece to do next to best suit the trimming order required. Again, I intentionally left the uprights and diagonals long until I bend the lower section inward ( on the line just above the red material stamping) and fit the 040 doubler angle (more on this later):
Working at the edge of the bench allowed me to clamp the upright to the edge of the bench and back drill two cleco holes through the extrusion into the skin.
Next up was the forward lower extrusion which makes up part of the cross bracing. An adjustable angle tool was handy here for determining the trimmed edge where it meets the forward longeron:
This piece was left long for later trimming:
Temporary placement of rear upper cabin longeron so I can determine trim angle of the top end of the rear cabin upright extrusion:
Any part that will interface at the inside corner of the side skin and cabin floor is left long for later trimming to match:
The rear cabin longeron runs from the centre of the cabin skin at the forward longeron back through the rear cabin and into the baggage area. In order to fit, the longeron needs to be bent inwards to match the taper of the baggage area at the rear of the cabin side skin. A taper of 11 degrees inwards. Another thing done by the factory for kit builders to overcome. I also had to make sure the radius of the bend was in proper location at the back edge of the cabin skin.
I figured someone else MUST have done this before in scratchbuilding, and a quick search revealed others have used several methods including hydraulic press bending, hammer forming on a jig, etc. The method described by one builder seemed simplest - build a bendging block on the bench edge and use a length of pipe over the extended edge to bend the extrusion being carefull to avoid any twisting.
To that end here is what I came up with and it worked very well. Start with a stout block (left) and a small support block adjacent to it:
The support block is rounded on the end to spread the bend over a radius and the upper inside edge is sanded round to match the inside curvature of the extrusion:
The extrusion is held tightly against the the support block by another board screwed to the table and the whole thing is clamped down tight via a bridge of blocking screwed to the outer blocks. To approximate the 11 degree bend, I stuck a piece of card stock underneath. Not perfect, but close enough for this purpose. I also chose a bend location that left me enough room to trim the angle at the X and long enough to meet the rear of the baggage area as per the plans (total length 1440mm):
Bent it past 11 degrees to account for springback and nailed it pretty much the first go. This worked amazingly well. I would have liked the radius tighter, but this is acceptable and I didn't want to risk cracking the aluminum. There was a bit of twist that I expected, but I was able to flatten the twist out with some gentle persuasion using the vice and deadblow hammer:
Placed the bend at the rear edge, then trimmed away the "X" edge. Transferred the rivet line to the extrusion, drilled the A3 holes out on the drill press and fitted the extrusion to the skin:
With the location of both forward and rear longerons now confirmed, fabricated the extrusion for the bottom of the door sill.
Careful trips to the bench grinder to taper each end until the match the longerons and the door sill:
Used a couple of blocks to hold the bottom door sill extrusion in place then back drilled through the skin. Then I added the vertical L doublers that are at the edge of the cabin skin doubler:
Remove everything except the rear and forward uprights.
Slide the cabin skin doubler blank under the cabin skin, secure using clecos in back drilled holes through the skin into the blank once the radius holes in the blank match the radii on the skin:
The doubler width is from the rear doubler L to the front doubler L. Trace the edge of the cabin skin onto the doubler blank, then cut the same as the edges on the skin.
So everything is ready on the left cabin skin assembly that I can bend the lower portion inward at this point. However, in order to duplicate the extrusions to the right side, I need to mirror them for drilling. I started with the rear upright, clamping the now drilled left one to a blank and undrilled one for the right, after matching the angled end on the new one:
Back drill though the left one, making a perfectly matched hole on the right one:
Did the same for all the other extrusions, with the exception of the long rear longeron, which I sill need to bend and fir correctly to the right side skin:
Now I have perfectly hole matched extrusions for both cabin sides. The lengths are approximate, still waiting on final fit-up once the lower cabin skin corner is bent:
Repeated the process for matching up the doubler blank to the right cabin skin:
For curiosity, I stacked both the now trimmed left side doubler onto the right side doubler and then onto the right side skin. The door sills match perfectly!
I've been very consciously aware that the bottom bend of the side cabin skin is important do do accurately in order to ensure both left and right cabin sides are symmetrical. A test piece of 032 cut to replicate what the bend will look like when complete serves the purpose.
With that in mind, I proceeded to bend the left cabin skin:
I couldn't be more happy how this bend finished out. Dimensionally perfect, now I just have to replicate the same process on the right side skin.
On the inside of the cabin skin bend is a 040 doubler angle. 30 pitch rivet line laid out:
The green tape helped protect the cabin skin while I drilled in the tight corner. The doubler will be trimmed back to match the front and rear edges once final hole sizes are complete.
Prior to drilling the corner inside rivet line in the doubler, I added the cabin skin doubler and clecoed it in place:
Then I trimmed the uprights, the L's and the longerons to properly match the new corner doubler:
Pilot side cabin skin fabrication complete, awaiting final hole size drilling and solid rivets. This picture really shows the rear longeron taper:
Outside facing cabin on the pilot side. It doesn't look like much, but this is where the door will be and the seats of the cockpit! I'm slowly getting closer to sitting in my creation and making airplane noises!!
Next up, the rest of the right (co-pilot) side skin fabrication. Thanks for following along!
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Husband, father and 911 dispatcher. Long time pilot with a licence that burns a hole in my pocket where my student loan money used to be. First time aircraft builder. Looking to fly my own airplane.