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Building a Javron Cub

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This is the lower cowl brace rod where it attaches to the nose bowl.


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Take the time to get your nose bowl positioned where you want it. If you put it a little low (note that the prop flange is not centered in the hole in the nose bowl) it will help your over the nose visibility and also give you a little room for the engine to sag over the years. Just a technique. Make it look good to your eye. In general there should be a nice smooth descending line from the instrument panel to the top of the nose bowl. Clamp it down good so it does not move while you are building the cowling.

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Side view of the cowl brace rods.

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Cowl door coming together. Note the descending line under the long ruler. I lowered the engine 2 inches to get the built in Thrustline mod "kink" out. Jay built my engine mount this way and he is jigged so he can build others this way as well.

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I pretty much used the plans from Christian Sturms site for all of this. I just print the drawing I need on an 81/2x11 sheet of paper and take it to the hangar. Follow the drawings with some allowances for differences. For example the nosebowl for the 180 Hp 0-360 is a little larger than the 0-320 nose so the dimensions may need a little tweaking to make it all work out. Just keep it all square and watch out for parallelograms.

Hope this helps

Bill
 
Take out the windshield strip, the ruler will lay perfect,it looks real nice. That will be sharp looking when done. Does Your mount moves the engine a full 2 inches down and did you move it back any? Bill is jay putting out his wing kits yet? Very nice.
 
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Bill, How did your bootcowl skins fit on the fluted firewall? I did not like the gaps around the flutes and opted to cut the lip off and bought a PA18 firewall flange from Clyde Smith and riveted in with some PRC to seal it. Don't want oil and stuff seeping in.

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Steve

I like your idea better. I managed to make it work but it was a pain. I used Flamemaster CS1900 sealant between the firewall and the top piece.

Bill
 
Bill, It all looks great. Keep posting, it is really helping me with my project. Appreciate all the post from all of you great builders out there. Greg
 
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Bill, here is sortve a neat baffling plenum idea. No air leaks and no seals.
 

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If doing a plenum, make sure it installs and removes easily.

The early Cessna 170 models had a plenum and it was fastened with Dzus 1/4 turn fastener's for easy access to stuff.(spark plugs and leads, in our case here, oil pressure relief)

A great way to save weight would be to substitute carbon fiber for aluminum in this application.....save half the weight of the metal!

Plenum or not, make sure to pay attention to EVERY gap on the low side of the "pressure area", i.e., around the alternator brace and belt, around the junction of aft baffling/crankcase, intercylinder baffles, front and rear lower baffle/cylinder junction, rear baffle to accessory case.

The losses of seal and resulting "easy" airpaths have overheated more than one hotrod engine in a Cub. Wayne Mackey has done aLOT to optimize this point!
 
I have found that at Super Cub speeds, the openings in the front of the lower cowl matter very little. I have very tight baffle seals and very leaky front lower cowl openings. Doesn't seem to matter how much I open up or seal the front of the bottom cowl, the engine runs fine with good cooling. Though what I do get is a puffing up of the top sheet of the top cowl at cruise -- makes me wish I had wider cheek openings at the back of the side doors to let the air out or a lip at the back of the lower cowl. But why bother when the temps are 350F CHT and 1350 EGT.
 
Tempdoug - Lowered 2 inches and built in Thrustline mod, but I did not try to move it back any. I felt it would make maint harder and might also eliminate the use of some exhaust systems. With all the lightweight engine accessories and props I am not really worried about my CG at this point.

Darrel - I agree that cooling is generally not a problem with "normal" engines but if these guys are going to use a "hotrodded" engine it can be a problem. They have had to work pretty hard to get the temps under control on the CC with the 0-340, and on other airplanes with the 0-375's etc. Sounds like your numbers are spot on. I had some problems with my last hotrodded 0-320 but this time my 0-360 is pretty close to stock so I don't anticipate needing a plenum. I also agree that the rear edge of the top cowl needs a couple of fasteners and I will put those in. My cheeks were a little undersized and tight on the last one so I will make them a little larger on this one per your input above.

Wings - I had asked Jay to look into drilling out the wing spars to save weight. This is pretty popular with the Portland crowd and they have not had any wing failures, nor do I know of any in the CC fleet so it obviously works. I believe the savings to be around 2.5 pounds. I have also spoken to a couple of folks who expressed their opinion that a drilled spar wing may not hold up as well under non flight related stress. Alder tree impact, mild groundloops, hangar rash etc. Things that would not normally do much damage to a stock wing, supposedly crumpled a drilled wing pretty good. I do not have any hard data to support any of this at this time.
However, the new ribs, spar drilling, and a couple of other things, have delayed the Javron wing. Jay has been trying to accommodate my requests in this area and so, a big part of the holdup, has been my fault. Sorry folks. Jay has decided to move forward with the wing using a standard undrilled spar at this time so I expect the wings to come together pretty soon. I know the ribs are finalized and being produced now. I believe Jay has one more wing test to run and once satisfied with that things should go pretty quick. As soon as I have data I'll post it here. I believe the wings will be excellent - strong, true, and quite a bit lighter than the other wing options (excluding the CC wing) available at this time. It is my understanding that Jay intends to offer the wings in either kit form and/or fully assembled when it is all said and done. This might be a great option for the guys scratch building.

Hope this helps

Bill
 
Bill,
I agree with Darrel. The cheek openings on mine are 2-5/8". I can feel the heat by placing my hand on the inside of the fabric next to the door (no interior). I also left out the baffle which seals between the air filter and air box, just to see what happens. Do not need it. My temperatures are perfect in the middle 300s. I do not have the same problem with the top leading edge puffing up, but I do have looseness in the aft end of the top cowl. I did manage to reduce this by doubling up on anti chafe materiel. I guess that I did not hold down the aft end tight enough when I was drilling holes. Letting the hot air out is as important as getting the cold air in.
 
I also left off the little nuisance plate around the carburetor. I noticed one year at Oshkosh that Cubcrafters didn't bother to close off that area either.
 
Do you mean the vertival plate behind the filter? Wouldn't that pressurise the low pressure side? Or is there a horizontal plate around the carburettor that I don't know about?
 
On my last cub I tried a before and after test of blocking the filter/carb area. Yes, theoretically, leaving it open should pressurize the low pressure side, but I could not see any change in engine parameters with or without blocking off this area.

Bill
 
Do you mean the vertival plate behind the filter? Wouldn't that pressurise the low pressure side? Or is there a horizontal plate around the carburettor that I don't know about?

Yes, that is the plate. It doesn't seem to do any harm by leaving it out. It may even help cool the oil a bit.
 
Man that plate is a pain. I finally worked out how to work around the filter. I have a sutton exhaust and to get the lower cowl over the exhaust and threaded onto the filter spigot was imposible. So I cut the spigot off and made it removable by welding a nut on the end and a bolt on the air box. Works a treat. now I have been able to seal the back of the filter to my liking.
 
That all does not make sense to me. We go to great lengths to get air out of that area! Maybe it works as some sort of venturi?
 
CubCrafters Top Cub at Oshkosh in 2006 -- no plate around the carb air box.
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Here is another Top Cub
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Our Super Cub, N18SY, during rebuild. I like the big hole for the ring gear/starter -- makes it easier to time the mags. The air box where the oil cooler used to be provides fresh air to my feet through the "rear seat" heater ducting in the summer with some ducting rerouting -- lots of leakage around the black air box too. The plate around the carburetor intake is not installed.
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Working down the "do list" prior to covering the fuselage.


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Be sure to rig and check your elevator cables. Mine were not the correct length. I did a lot of head scratching, figured out I could fix the problem by using different turnbuckle parts. THEN after much grief (and a few words I should not be using) I discovered I had the cables hooked up backwards. I never cease to amaze myself. :oops: So.....the cables are fine. Jay does good work. But I did note the elevator was hitting the bracket a little prematurely and thus I was not getting full up elevator. You can see that the attach tab extends well aft of the control horn. No problem. I reshaped it so it looks like this ..........

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Whaaala.......full up elevator now.

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The rudder cables will fit through the furles from back to front only. You will want to install these prior to cover, otherwise you will have to cut out your access covers before you want to.

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You may have to clean up the powder coating a little to get the cable guides in.

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Post clean up. Don't forget to primer and paint the inside of this guide before the plastic insert is put in, otherwise it will rust. A quick thought on primer. Most primers are porous and as such the metal will rust right through the primer. It will slow it down a little but primer alone is not a rust preventative. Variprime is an excellent product but it is very porous. You must paint over it to get true rust prevention. I like and use an epoxy primer PPG DP40. This is MUCH less porous than Variprime and though you should probably topcoat it you can definitely get away with it alone as the porosity of this product is extremely low. It comes in several colors. I recommend the white color. Topcoats better.

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I found a little welding slag in this guide so used the Dremel tool with a grinding bit to clean it up. Another thought if I may. Folks, do not expect the kit you purchase to be perfect, regardless of where, or from whom, you get it. You are building an airplane not assembling a Lego
toy. Every kit will have some issues. That is part of the building. Javron is awesome and his attention to detail is great but this is a BIG project and I sometimes hear stories from guys that think it should just assemble with everything perfect the first time. Maybe, if a manufacturer put out a 100,000 kits and all were exactly alike (no customization at all) they could get it down better, but the reality is each kit is different due to the customization and thus it may not be perfect. I am extremely pleased with my kit but I don't want folks to get unrealistic expectations that this is going to be an easy weekend project. It is quite doable for the average person, just go slow and take it one step at a time.

As my neighbor says......I liked his saying and I adopted it.....

Its just a series of problems to be solved

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I would prefer to use a reamer to clean out the holes but sometimes you just can't get one in there.........
Sometimes you have to remind yourself you are not building a space shuttle.......like a lot of builders I tend to be pretty picky and try to do my best, thus I get stressed when I feel like I am not doing it PERFECTLY, thus I sometimes have to remind myself.....
its not a space ship.......

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I do recommend you use a reamer whenever you can......its just better......

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The rudder horn is on the stop but there is a lot more possible travel before it interferes with the elevator, so........

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Whip out the die grinder with a cut off wheel and get as much rudder travel as possible. You only need about an inch of clearance between the rudder and elevator. It slips much better with lots of rudder travel. If you get a little too happy and overshoot and cut too much of the stop tube off, you can tap the inside of the tube and insert a bolt or screw to increase the length back out.

Hope this helps

Bill
 
Great posts Bill along with pictures showing exactly what you're referring to. Almost like a Builders Manual.

I like the end of this last post where you are shortening the rudder horn stops. More travel is better. I did that on my EX too. But the flip side of this is that with some kits you don't want to shorten the stops so much that the rudder pedal hits the inside of the firewall at full travel. That was a possibility with mine.

So you must be back home now from God's Country?
 
Bill when changing the control stops for additional clearance from the original specs could you be introducing the potential to induce a stalling of the control by exceeding it's critical angle of attack? I don't know if my question is relevant here as you may just be adjusting the stop to meet specs but you did say "as much rudder travel as possible" and I wonder if the original designers had them limited on purpose?
 
I also left off the little nuisance plate around the carburetor. I noticed one year at Oshkosh that Cubcrafters didn't bother to close off that area either.

I retained the rear plate and added an extra hinge so it was easier to remove the lower cowling with the Sutton exhaust.

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Be sure to rig and check your elevator cables. Mine were not the correct length. I did a lot of head scratching, figured out I could fix the problem by using different turnbuckle parts. THEN after much grief (and a few words I should not be using) I discovered I had the cables hooked up backwards. I never cease to amaze myself. :oops: So.....the cables are fine. Jay does good work. But I did note the elevator was hitting the bracket a little prematurely and thus I was not getting full up elevator. You can see that the attach tab extends well aft of the control horn. No problem. I reshaped it so it looks like this ..........

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Whaaala.......full up elevator now.

Bill, That tab acts as your elevator stop. It is flat like that so the whole thing contacts the tab in the fuselage and doesn't wear down over the years with use.
 
qsmx440 - I have not found any problems increasing the elevator or rudder travel so far. It is an experiment so to speak, but also the certified airplanes can be pretty conservative sometimes. I did the same on my last cub and had no adverse handling issues at all. (excluding water entry)

Steve - very nice carb air box idea. Slick. Thanks for the input on the elevator horn. Mine is now shaped so that all three parts, 2x horns and 1 bracket all hit the backstop together. I think it will be good. It gives me 28 degrees up travel Vs the book value of 25 degrees. Folks - just because I am doing things a certain way does not necessarily make it right. I appreciate the inputs to let others know there are other ways to do things and the logic behind those ideas. Sometimes I don't always give enough info when I deviate from the tried and true methods.

Spinner2 - I'll be back ASAP :lol:

Bill
 
Some of us like so much rudder and elevator travel that we make them bigger than the stock ones. :)

Bill, the white primer in the DP series is not as good for rust preventative as the others in that series. It is lacking some of the good stuff that the green, red, and "yellow" DP primers have. Sorry to tell you this.

Also, the so called "Boeing Primer" such as "Crown Metro" or "Axxon" or "Super Koropon" are much, much less porous than the DP series and I would not consider using the DP stuff for its' "epoxy primer" qualities unless it is topcoated.........the "Boeing Primer"-types are excellent without a topcoat.............. FYI. :)
 
Bill when changing the control stops for additional clearance from the original specs could you be introducing the potential to induce a stalling of the control by exceeding it's critical angle of attack? I don't know if my question is relevant here as you may just be adjusting the stop to meet specs but you did say "as much rudder travel as possible" and I wonder if the original designers had them limited on purpose?

There is a test for "rudder lock" which is done on multi engine airplanes. It is an asymmetrical thrust situation and not something that is likely to be found on single engine planes. The test looks for air pressure reversal which pushes the rudder against the stop, thus holding it against the stop. This is not allowed under modern regulations.

I do believe that the primary reason for the rudder stops is to keep the rudder from hitting the elevators.
 
Dave - I was surprised to hear that the other colors of the DP series of primers are better than the white as rust preventatives. I called the tech rep at PPG this morning and asked that very question. He assured me that the ONLY difference between the primers is the tint. They have exactly the same chemicals, in the same proportions, one to another except the tint/color. Your experience may prove otherwise but that is what the manufacturer says.

I am very interested in the other primers you spoke of and will be doing my homework on those. Always looking for better products. Thanks for the info. Lets see what the RV forums say. They call them the "primer wars" over there as there are so many threads and "discussions" on this topic in that community. Hehehe - this could get interesting.....


Bill
 
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