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J-4 project-3.14159265359

That is a worthy goal, I had hoped to get a plane back together before my dads passing 12 years ago, personally you got to make a try. Even if you do not fully achieve the goal you have a more comfortable life than the hollow feeling of not trying. My personal thoughts anyway. One for me was to see if I could have gotten my dad back up in a B-25 one more time. The one semi local B-25 to me was out west through all the years and my Dad had 99 missions in Air Recon way back in time so I was hoping for a 100th flight. Never happened but was well beyond my resources to have made it happen.
 
This part to me is a very thought provoking part. First image is a screenshot of the tube cluster where the lift strut and composite leaf spring mount. Nothing complex but as I machine the actual parts that once ready will be welded into these sub-assemblies.
Even though the brackets have a 10:1 overbuild my mind keeps going, "all the lift loads are through here". It is kind of interesting how many stressed parts I have made in my life but for now these have my attention.

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A little bit more done to the lift strut carrythrough but not ready for welding yet. Here is the bracket now with lugs to support the tubes.
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And same part with the doublers added, the aft tube is perpendicular so it got welded into place, the small tube passing through the doubler is where the aileron cable passes through and into the lift strut. The front doubler needs to be clocked which I am not ready to do, more parts to make such as the firewall structure to guarantee proper alignment.
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And the carrythrough roughed together, a bit more tube fitting before this is ready to weld.
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Here is the firewall structure going together on it's jig.
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And a few of the parts shown previously as they came off the welding bench.

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The past month has been hectic for me. I had decided to shorten the height of the firewall a few inches since there was not the need for the height and the change will allow for better visibility over the nose.

Part of the lead-up to that change to the previously welded structure is that I have been spending time back in the drawings. Most recently has been making sure I have the rudder pedals optimized for my needs. This image of the drawing from the underside of the plane shows how many parts are involved and the complexity in building the adjustable pedals in the plane.
Damn it makes me want to use fixed position pedals. Not all the brackets are drawn in yet so there is more to do before all the parts are made.

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The past month has been hectic for me. I had decided to shorten the height of the firewall a few inches since there was not the need for the height and the change will allow for better visibility over the nose.

Part of the lead-up to that change to the previously welded structure is that I have been spending time back in the drawings. Most recently has been making sure I have the rudder pedals optimized for my needs. This image of the drawing from the underside of the plane shows how many parts are involved and the complexity in building the adjustable pedals in the plane.
Damn it makes me want to use fixed position pedals. Not all the brackets are drawn in yet so there is more to do before all the parts are made.

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Wouldn't it be easier and LIGHTER to make an adjustable seat back cushion?

Glenn
 
Wouldn't it be easier and LIGHTER to make an adjustable seat back cushion?

Glenn

Right now the section of the fuselage I have built is sitting on the living room floor with the seat set in place. So yes the option is open to make the seat move some. The seat is adjustable vertically by using foam shims, not a method suitable for inflight adjustments. The seatbacks are separate on each side and will be adjustable for lean angle as well.

Luckily any brackets for the pedals can not be installed till the fuselage will no longer need to go on the build table so I do have plenty of time to decide and by then more options for making the seat movable. This option will become more attractive if I do not go with a bench style seat bottom.

For one thing the controls in this plane are all using REP bearings for all movable joints at the cables and pushrods, as in about $1500 of them. This adjustable pedal setup has 14 bearing type rod ends in it. But I already have most of them in stock.
 
Keep in mind this plane will be considerably different than a true J4 in it's wing design as well as having more than 200HP.
Many aspects of this build are lighter than a Piper design while other aspects are heavier.

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The slats are hinged, composite. The mounts for them are at this time intended to fit into slots in the leading edge so they are removable/ replaceable since I doubt I will get the hinge position in the right place the first time. I expect the slats will be built in 48" segments but I have not run numbers on them yet. At this time I do not intend to build full span slats in that I am more interested in a balance between low speed performance as well as the safety enhancement they offer.
 
Introducing a J-4 project

Charlie,

I really like your design... not only does this look like a very capable aircraft but also looks really nice...

Question on gear... your earlier rendering had what looks like oleo type gear and this latest one is spring gear... change of mind going on there..?? And what is with the tuning behind the spring gear..??

Brian


Sent from my iPhone using Tapatalk
 
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Thank you Brian,

The oleo gear was getting difficult, my growing issues with it was drag and complexity. I was going to use motorcycle fork tubes mounted in custom framework. This would allow me the gross weight increase with good damping properties but was going to have secondary development issues that I do not want to deal with once the plane is to fly.
So as the plane developed I started looking at a spring gear, originally utilizing a Cessna spring but soon decided I would layup a one piece composite leaf. The composite offers great weight and good damping.
The weight savings in the main gear alone allows for some weight creep in other areas as we see developing.

Had the design stayed based on an O-200 then the oleo might have stayed. Lord knows since my medical certificate has not arrived yet this may all change.
 
Fresh off the printer, the control stick tops. I am going with round tops on my control sticks and I want the trim switch and PTT built in not to mention I need them to be handed since this is a side by side seater. It became clear that 3D printing the parts might just be the best way to get what I need.
My first parts are a good proof of concept but I recognize that if I choose to use any form of soft grip on the stick then the ball needs to be larger in diameter. If this is to be a bare ally tube then this ball is not bad for a fingertip size grip.

Shown here is the first ball top with switch holders and then the ball which I roughly trimmed and then fitted the switches into.
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Decisions, decisions.
With the project back down in the shop for a few days I am building out the aft 145" of lower longerons.
As I am preparing the cross tubes to weld in I keep questioning the diagonal bracing that will be used. Most recently the floor structure up front, as in seat area and first few feet of baggage area will be a composite structure bonded to the tubing. With this cored composite there is no need for diagonal tubing in these bays. Now as I am building back from there, the next two bays which are 5' in length were to be conventional tube structure with fabric cover over the tubes providing for generous floor space for lighter weigh bulky baggage.
Now I am questioning if I should just do away with the cross tubes and go with a bonded in hard floor. Humm, granted this is not exactly conventional construction for Cub guys but it is a convention in sports racing cars where the active loads are considerably higher than in this fuselage.
 
Interesting thought Charlie.
What would the weight difference be between the two methods? Will the bonded floor in one bay be lighter than the one cross tube and whatever you have in mind above it?

Can you be 100% certain that the tubing under the bonded floor structure will be corrosion/rust proof?
 
I think in this aft 5', the Oratex and .028 wall cross tubes will be lighter. The braces here are intended to be a full X where FEA states just a cross tube is enough. I personally do not trust real long unsupported tubes in compression.

That aft section if I go hard floor will be Innegra skins with ¼ balsa core. I will do a full wrap around the tubes so they will be encapsulated.
Now, 30 years later, will that bond not have failed, hard to say. So I do not have a true feel of the lifespan before repairs.

I do know judging from other mixed structures I have built 15 years should be no issue without degradation.
 
I admire your ability to accomplish this project using CAD and FEA. That was my desire and purpose of buying my first computer 25+ years ago. Never could get my head wrapped around it. I find the process fascinating.

Could you reduce the size of the cross tube enough to compensate for the added weight of the X configuration? I understand your apprehension of the long tube in compression. How much compression possibility is there in this particular location?
 
Ah, 25 years ago you would have been on Autocad 12 or 13 using Algor for the Fea. Autocad was just transitioning to a Windows platform but for the most part the Dos programs worked much better. I did find surfacing better in 13 Win. Algor was still Dos then. Pro-E was a sweet high end system as well but not nearly as easy to learn.

The compression loads in the lower rear fuselage are from twisting the tail feathers and side loads of the tailwheel.
Twist one way and the diagonal would be in tension, other way will compress.
Both wall thickness and diameter can be reduced with an X structure. I do not build to the minimums as to what an FEA program says I can since the program has no clue what an O360 Lycoming can do to light structures not to mention the miss belief that you have the loads of a groundloop on rough ground calculated. Over the decades I have stopped trying to get every ounce out of a structure. I build light by design but I build structurally strong as well. I add doublers in areas they may never be needed, till one groundloops or truly slams a landing. Will all these doublers and added braces add weight, up, 3 to 5 pounds in a 1100# plane.
 
Definitely a good idea for extra strength in this area with an 0-360 up front. This is particularly important if the engine is ever operated with magnetos instead of a variable timing electronic ignition.
 
Definitely a good idea for extra strength in this area with an 0-360 up front. This is particularly important if the engine is ever operated with magnetos instead of a variable timing electronic ignition.

I hear you there, I have no desire to invest in magnetos, technology has come a loooong way since they were called good.
 
A further thought. If you were to replace a diagonal with a composite filling in the rectangle, that could have a considerable effect on the natural frequency of the entire fuselage. Reducing flexibility in just one bay could cause a drastic effect for better or worse. Does your FEA have the capability to analyze this? I have witnessed how much the installation of an oxygen bottle in a Twin Comanche effected it's natural frequency. It was enough for a requirement to reduce the VNE in order to prevent tail failures. A couple of days spent participating at Piper's flight test center was very illuminating.
 
It will make a change and I do not know how to honestly check it. The composite structure I choose to use has allot of inherent damping where as the tubes alone are fairly lively. The tubes wrapped with fabric are damped so the structure is rather interesting to really test. I can only get numbers on the tubes without consideration of vibration or damping of them. So in this case I need to rely on past experience and make sure I do not put what one might call "a hinge" part way back in the structure.
Right now I have been redrawing the control systems. Once I actually had steel welded up I could see a way to simplify the elevator controls which eliminates a 61" pushrod and a bellcrank. The aft bellcrank required a fair bit of structure to support it. This will add up to fewer hours as well as a few pounds eliminated.

I will soon have a decent CNC mill available which will entice me to upgrade the drawings for all the bellcranks and a number of the flap system parts rather than making these on my Bridgeport. This will be a nice upgrade in the finished parts yielding a more complex part that is both lighter and easier to make.
I might 3D print the parts to prototype them before committing to metal. This allows me to confirm motion ratios and clearances before making the real parts.
 
I have decided that I will use tubing diagonals supporting the lower longerons. I weighed and evaluated many options here and then just said to myself, I can do the tubing in the one bay that is really wobbly today rather than waiting a few years till I will be doing the composite work. So once I made the decision, ½hr later two tubes were fitted and partially welded in. The structure was then stable enough to carry up stairs back into the living room.

Looks like I have not posted any updates here in the month. Back in early December I installed the mounts for the brake master cylinders as well as the lower doublers for the structure going up to the front spar. I had also more recently built the longerons back another bay to where the rear float mounts should the plane be setup for seaplane use.

Here is a general shot of the forward lower fuselage prior to the most recent work session,
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followed with a master cylinder hung in place as well as showing the lower engine mount pivot.
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This shot is where the vertical tube in front of the doors will eventually go.
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The non pivoting engine mounting points utilize a 3/8 bolt through a sleeve, the sleeve is located to the fuselage over the mount points.
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Hard to get a good shot of small tubing with this cluttered background. At this time the lower longerons are in 3 subsections that have slip joints allowing the moving and jigging on the weld table.
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The aft section has most of it's brace tubes in place.
Off to the starboard side of the rear section is the cabin top structure as well as automotive wire harnesses that get used in the custom driveline swaps I do.
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The front section of this structure is where the 3 sections separate such that I can not install diagonal bracing yet.
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A little frustration at the end of today's work session. I decided I would form the upper longerons and get as far as welding in the cross tubes. All was progressing well with a little difficulty making sure the assembly was symmetrical. All was looking good although I had to put a little tension to insure the laser hit it's marks.
Then when I unclamped the assembly from the table and turned it over to weld the bottom side, the laser did not hit it's marks, damn. Turns out on the very front cross tube which in this case is just temporary to allow jigging followed by fitment once the upper cabin structure is ready, well I had that C/L way off, like ½" off. I work with multiple tape rules and the one I used when marking that tube is both metric and imperial markings such that when you reverse the tape, well you can make an error.

It does not look like I need to cut any tackwelds out. With diagonal tension in one bay the properly marked centerlines line up well. Still frustrating. I decided it was time to walk away and pour a Bourbon and sit for awhile.
 
I decided it was time to walk away and pour a Bourbon and sit for awhile.

That's a good move.

Boatbuilders have their "moaning chair." Mine is just folding wooden chair in the corner. But I saw one that had a nice little cubby for the bourbon and shot glasses--and aspirin.

BTW, my metric-imperial measurement devices are relegated to the garden shed tool box. I fall for that problem all the time.
 
Yesterday I fitted the front door posts, hard to get decent shots of the dark tubes.
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The Formed tubes laying on the lower rails are the diagonals from the base of the firewall up to the outer ends of the spar carry through.
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It was a last minute decision to make these in one piece and add the kickout to provide an added inch on each side for the pedals. That lower bend will get a doubler but I feel this change to be worthwhile since not one's feet will be straight out in front as well as a bit more room for stick travel. After I made that bend last night I then undertook about 5 more hours making little but valuable changes in the CAD drawings. one of these was simplifying some aspects of the pedal system which greatly reduced the needed support structure in the fuselage. :lol:

Tomorrow some consumables will arrive and I can get back to fitting tubes again. Thought I had enough cutters in stock, Oh well.
 

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Our furry black barrel :smile:. When She is not being my heated pillow she is my chief inspector.
Then there is the golden boy on the foot stool under the TV, that one, well I still do not know about him. He adapted us back in the spring of 2015, only reason we kept him is he survived that bitterly cold winter of 2014. He has not been well received by our other cats which he caused the passing of two of our favorites.
 
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