Building a 4 Seat (4S) Javron Cub

[wireweinie]

I'd like to add a couple of things about the magnetometer wiring. If you are running LED nav/strobe lights, those lights PROBABLY will not draw enough to effect the readings from the magnetometer. But, if you run pitot heat and/or landing lights (especially incandescant lamps), there is a good chance the current draw from these will change the magnetometer readings. To prevent this from happening, keep the magnetometer wires separate from all other wiring. As Bill pointed out, there are places like the windshield post where the wiring simply cannot be spaced apart. So keep the wiring separated when you can and in the tight spaces just don't tie the the mag wires into the bundle with other wiring. Also, I've had good luck just 'gluing' the wires into place on the spar using RTV. Tape wires into place and add dabs of RTV. Pull the tape once the RTV sets up. Still allows you to pull the wires out if needed, in the future.

Nothing wrong with the mounting bracket in the pics, but I agree with Bill, I don't like extra holes in the spar. I prefer using a bracket between the ribs. Which ever way you decide, make sure you use the correct hardware! It should not need to be said but DO NOT use ferrous hardware. Garmin instructions even say to not use magnetic screwdrivers or electric drill motors when installing or maintaining these items. While Garmin says stainless screws are ok, I still use brass screws nuts and washers.

Web

 

[Bill Rusk]

12) Install aileron balance cable
The aileron cable that goes through the tank bay and through the pulleys in the wing needs to be threaded in before you cover. A couple of feet will hang out of the root area, and the other end needs to be tied off in the wing. This cable end will be fished out via a wing inspection hole and will come out the bottom fabric and will connect to the bottom side of the aileron horn. (the other cable runs up the strut, through the wing, and comes out on top and connects to the top side of the horn.)



View attachment 62526
I just taped it off to the drag/anti drag wire. After cover and paint it can be fished out and pulled through the fabric and then the end turnbuckle swaged on to fit.


13) Install the pocket pieces
Jay has created these little metal pieces that help build a pocket for the strut ends to go up into. When you install the struts on a covered wing the end of the strut will protrude up into the fabric. It can be a messy install. Jay has made these little fairing brackets that create a pocket for that strut end to go into.



View attachment 62527
This goes on the front strut. It is just laying in place. Tuck the ends under the LE and put a rivet in each end before cover.




View attachment 62528
This piece goes on the rear strut attach point. It will be installed after cover and then reinforced and cleaned up with tapes and or doilies.




View attachment 62529
An over view showing both pieces laying in place to give you location reference. These pockets need to be pretty deep. Otherwise you are pressing hard into the fabric and forcing it to give. You may end up having to split the fabric if you do not create these pockets. Then you have a substandard ugly install.


Last Pre-Cover checklist

1) Check every Ince for sharp edges
2) Use an air nozzle to clean out all drill chips and other debries
3) Clean any and all ink off - it WILL bleed through
4) Safety wire the tank bay rib
5) Don't drill the landing light trim piece until after cover and paint


That should be most everything (I hope ) that needs to be done to the wings before covering.

Hope this helps

Bill

 

[Bill Rusk]

I don't know why it is giving me the "attachment" issue on photos. I will try to get that fixed.

Lets talk about the fuselage.

I spent a couple of days in Jays shop going over the fuselage and making changes. I'm sure some of these will be incorporated into future kits and others will remain as possible options, depending on how you want the fuselage configured to suit your particular "Build for 90% of your flying" axiom.



I did have Jay weld in the mounts for lead to adjust the CG



After talking with the structural engineer we determined we could adjust the dogleg and increase the size of the baggage door. It will go from about 24 x 25 to 27x27.




The prototype fuselage had rudder pedals and toe brakes suspended from the upper longerons. It does make for a clean floor. Our objective was to make this as much like a Superb as possible so this assembly will be put under the floor and the rudder pedals will look like a stock cub and it will have heal brakes.



These top two tubes will be relocated under the floor to create something more akin to a stock superb. We will also run the rudder cables under the floor so they will have a straighter run and also that will get them completely out of the baggage area.

 

[Mudofficer]

Hi Bill, Thanks for starting this thread. I have been on the list with Jay since the spring for one of these 4S kits. Looking forward to seeing the next round of progress and refinements you make.

 

[thaefeli]

Just got back from a week at Javron. It is an amazing experience!
Jay and I spent a good amount of that time building control cables. One of the things not finalized for the kit yet. He now has them mapped for the center stick, hanging pedal setup. Brad's mods will require different cables.
Other items not finalized are the engine mount, Boot cowl, engine cowling and fuel system.
Over the five days: mounted empennage, electric trim, hanging rudder pedals, wings and controls. Built the cables. Rigged everything (dihedral, washout, control throws, etc.). 95% of the kit hardware is mounted where it belongs. Disassembled and loaded in trailer.
I did bring my project back home.
First thing for me is designing and installing a fuel system. What I have in mind won't work with dual sticks.
Next will be the boot cowl.
Jay was very generous in cutting a practice instrument panel and firewall. He also cut a final instrument panel. Titanium firewall still in the works, he ran out of sheet Ti.
Re above posts: both wings now come with the landing light cutouts already in place. Complete with holes for rivets and nut plates. Jay figures a 5 hour savings per side.
Their new laser cutter is amazing and allows for very rapid prototyping. Mike spent about 10 minutes on the CAD program, and the cutter took almost 30 seconds to cut the practice firewall blank.
They are working on Brads fuselage to accommodate the changes Bill mentioned.
I stayed in an apartment I found on the AirBnb website. Called the Studio on 6th street, it is right in the middle of Brainerd. Same price as the cheapest hotel I could find in Baxter, but it is three miles closer to Javron. Also within walking distance to restaurants in downtown Brainerd. It has stove, microwave, fridge, etc. I saved a fair amount of money by visiting the grocery store and eating some meals there.
All in all, it was a blur. Jay has great people working for him and an incredibly capable shop.
Now if all you guys with kits would quit calling him for a few months so he has some time to work on finishing the 4S kit...........
Tom

 

[rc dude]

...
Now if all you guys with kits would quit calling him for a few months so he has some time to work on finishing the 4S kit...........

If you pesky guys with your fancy four seat cubs would leave Jay alone, my kit would ship out sooner! :lol::lol:

Just kidding, I'm following along with your build eagerly as I wait for my kit.

 

[Bill Rusk]

Folks

Been quite a while since I posted. I do apologize. The transition to retirement has been a little different than I anticipated. Hopefully I will be able to focus on this project a little more.

Back to changes Brad and I requested to the fuselage to meet our goals. Its all about the mission and then the "Build for 90% rule"



This is not really a change, but just a FYI. The Javron 4S Cub will have the overhead flap mechanism.





Because of the controls, wider fuselage, cable runs, seats, etc it would be very challenging to locate it anywhere else


Rear seats

This was a big change. And not everyone may agree with my logic, but here we go. The stock 4S cub comes with folding rear seats. After the cushions are removed, they fold up against the sidewalls, and/or can be removed altogether if desired. It is my OPINION that this is a feature that would be seldom used. Let me explain. When I flew for the Part-135 operation in Alaska a couple of summers back, it was not uncommon to take seats in and out (or fold them up in the C-180) and switch from cargo to passengers. We would often take the seats out and lay them in the back of the 206, or fold them up in the 180. We would then load a bunch of cargo, boxes, and mail, and fly to McCarthy. Unload, reposition seats so we could haul passengers back to Gulkana. On any given day we would move the seats several times. This Cub will not (and can not) be used for commercial ops. So I don't think the seats will go in and out very often. It will be a 2 seat airplane until the grandkids come to town. The back seats will go in to give rides for a day or two, then they will come out for 3 to 6 months or more. I doubt folks are going to load this cub with cargo, fly to their cabin, fly passengers, then swap and load cargo, fly, swap back to passengers several times a day. So......I wanted removable (Vs folding) seats. The difference is what sticks out when the folding seats are not in the airplane. The sidewalls will have 2...... 4 inch fingers that stick out from the sidewalls and would rip into tents, sleeping bags, or whatever you load. The seat posts would stick up out of the floor so your cooler will not sit flat on the floor. We redesigned the whole rear seat(s) assembly so that when the rear seats are not in the airplane the entire cargo area is flat with no protrusions. When I had my C-170B I just took the rear seat out most of the time and it sat in the hangar, until the 2 or 3 times a hear when I needed the back seat. Remember to build for what YOU will do 90% of the time. If you have 2 kids and the whole family goes flying all the time, perhaps folding seats are best. If you think it is you and a friend 90% of the time, the "removable" seats will clean up the cargo area.
You will be able to order your kit (I think, I am not Javron) with either style seats. Your choice.




This is the folding rear seat assembly (welding rod just holding it in place)



These are the mount tabs for the folding rear seats that will be sticking up out of the floor when the seats are not in the airplane



These arms will stick out from the sidewalls when the seats are not in the airplane.


By making the seats "removable" Vs "folding" we are able to get rid of all the protrusions sticking into the cargo area when the seats are not in the airplane. The folding seats are pretty cool and they are wildly popular in C-180/185 aircraft, especially when used in commercial operations. You pick what you think will work for you.



The seat belts will have these flush mounts in the floor......common to Cessna 206 and others....They pop up and.........



The seat belt will have a clip (upper left of the photo) to clip in when needed. Otherwise the seat belt can be removed and the floor is once again flat with no protrusions.


More tomorrow.

Bill

 

[Bill Rusk]

FRONT SEATS




This is the normal SC front seat. We will not be using this. We will be putting in rails and using a Cessna style seat. This allows more seat for/aft travel and also allows for much quicker removal. This will allow the side doors to be used to more easily load cargo if necessary. Will also make maintenance easier.



I anticipate the airplane will be used on floats and the manual pump system (could also be used for retract skis) will be mounted on the floor between the seats allowing either front seat to pump (15 strokes) the gear up and down.




The yellow tape is showing a cargo tie down anchor. There will be 6 on the floor and 4 in the ceiling. This will be critical so I will say this in bold print. The cargo area is huge. You can not allow cargo to shift. It could easily result in an aft CG and unsafe situation.

THE CARGO MUST BE SECURED FROM MOVEMENT DURING FLIGHT


​Bill

 

[Bill Rusk]

The arrows point to the rudder cable runs. This was going to be in the cargo area and would need to be covered to protect a primary flight control from being impacted from cargo. This would create a barrier to loading and unloading cargo. We completely rerouted the rudder cables under the fuselage so they are completely out of the cargo area. In a nutshell we completely opened the cargo area so it is smooth with nothing in it at all. (remember we put the rudder pedals on the floor rather than hanging down). I will show more pictures when we get the fuselage. It will be easier to understand.




This picture sucks but the idea is...... we welded channel on the lower door frame so we could put plexiglass on the lower door half. Adds weight, I know but that is what the owner wanted. I'm just helping.




We will weld a tab where the arrow is to put in a panel brace. The panel is wide enough that we will need a brace. Especially since that is where the throttle quadrant will be. Dual sticks means the throttle will be in the center.

Bill

 

[thaefeli]

All good ideas for sure. As far as the rear seat mounts, I see opportunity. My plan is to fab up an aux fuel tank, 35-40 gallon, that utilizes the tabs and side arms. Quick release pins and it'll pop right out.
I've looked very hard at it and it will be very hard to mount some sort of belly pod for fuel.
Tom

 

[Bill Rusk]

Tom - Get idea. Yeah, it might a while before anyone has a pod for the 4 seat cubs.

Another thing we did, no picture. There will be tabs welded on so we have a metal belly under the seat area. Not a metal belly all the way, just under the seats. It is such a PAIN to take the floorboards out of a stock cub, to clean the belly, I wanted a belly panel. This is something Jay is doing on the 2 seat cubs (if you ask for it) and it is something I REALLY wish I had on mine.

We also welded a tab in for the water rudder retract cable handle.

More to follow. Thanks for following

Bill

 

[akavidflyer]

I dig the fold up seats. I have been wanting to do something like this in my pacer. I am constantly taking the seat in and out for cargo runs.

 

[wireweinie]

You can weld a nut to the tab if you want to make it easier to remove floor board hardware.

Web

 

[skywagon8a]

All good ideas for sure. As far as the rear seat mounts, I see opportunity. My plan is to fab up an aux fuel tank, 35-40 gallon, that utilizes the tabs and side arms. Quick release pins and it'll pop right out.
I've looked very hard at it and it will be very hard to mount some sort of belly pod for fuel.
Tom

Tom - Get idea. Yeah, it might a while before anyone has a pod for the 4 seat cubs.
Bill

Make your own belly pod. With a wide fuselage it wouldn't need to be very deep to have a good capacity. 5052 aluminum makes a nice belly pod.

If you put one inside the cabin, be certain to vent it outside.

I even have a few left over new Facet fuel pumps from a belly tank project.

 

[cubdriver2]

Make your own belly pod. With a wide fuselage it wouldn't need to be very deep to have a good capacity. 5052 aluminum makes a nice belly pod.

If you put one inside the cabin, be certain to vent it outside.

I even have a few left over new Facet fuel pumps from a belly tank project.

Ive talked to Jay about making a predrilled belly pod kit for a Cub. Could be UPS in a flat box and built at home. 4 place sides would be same as tandem cub. He's your chance Jay, 2 birds with one stone

Glenn

 

[Bill Rusk]

Folks

ATR composite listed in post #35 for floor board material is no longer an option.

Bankruptcy and reorganization. Maybe in the future but not now.

Bill

 

[Mudofficer]

Would this work instead? (not cheap, but has a quote builder and live pricing tool for the fiberglass composition) https://www.professionalplastics.com/Showa-Aircraft

 

[skywagon8a]

Would this work instead? (not cheap, but has a quote builder and live pricing tool for the fiberglass composition) https://www.professionalplastics.com/Showa-Aircraft

This is an excellent type of material for floorboards. 60+ years ago when I worked for Sikorsky this type of material was being used for the floorboards of the helicopters which were being built for the military. You know it was subject to abuse. As I recall the honeycomb portion was aluminum foil with aluminum deck material.

 

[hotrod180]

..... The stock 4S cub comes with folding rear seats. After the cushions are removed, they fold up against the sidewalls, and/or can be removed altogether if desired. It is my OPINION that this is a feature that would be seldom used. Let me explain. When I flew for the Part-135 operation in Alaska a couple of summers back, it was not uncommon to take seats in and out (or fold them up in the C-180) and switch from cargo to passengers. We would often take the seats out and lay them in the back of the 206, or fold them up in the 180. We would then load a bunch of cargo, boxes, and mail, and fly to McCarthy. Unload, reposition seats so we could haul passengers back to Gulkana. On any given day we would move the seats several times. This Cub will not (and can not) be used for commercial ops. So I don't think the seats will go in and out very often. It will be a 2 seat airplane until the grandkids come to town. The back seats will go in to give rides for a day or two, then they will come out for 3 to 6 months or more. ...

I have the BAS seats in my C180.
(I think you are familiar with the plane, I bought it from a friend of yours)
They are generally kept in the stowed position, folded up against the sidewalls.
On more than one occasion, I have been tasked with giving a ride home to people whose airplane (or pilot) was disabled.
Often this came up when I was already out away from home,
so if the seats were out of the airplane I would have had to fly home, re-install the seats, then fly the mission.
Without upholstery, they are still plenty comfortable for short flights,
and take up very little room when stowed.
I consider them a very handy feature.

 

[Bill Rusk]

Folks

The fuselage is in the hangar and we have started to look at it.


This is what the floor mounted style rudder pedals look like. We will have brakes on the left side only.




What it looks like with two adults in the rear seats



Front seat and rear seat occupied.



We will be using Cessna seat rails and a Cessna type seat (Javron is making the seats). This will allow greater fore/aft movement and also quick and easy removal and installation.


The Paint booth is pretty much done. This turned into a MAJOR effort in both time and money.


This is the back wall which goes to the garage door. I can open this door and park my car in the booth when it is not in use.



But I did not want to paint the garage door so I used a couple of doors, that are hinged to create a back wall just inside the garage door. The large gap in the lower left is for the exhaust fan outlet.



This is the other wall with double doors to get large stuff in and out of the booth. If it is to large for this door we can use the garage door.



This is what the fan box looks like. The plug in and outlet has been moved outside the booth. The fans will have filters over them.



This is the double door at the other end and wall of inlet filters. Also you can see the man door on the left.



This is the fan box with the filters in place. The box has enough depth so that the main garage door comes down on top and creates the seal. You can see the right door open here. It is pretty complex and certainly not normal but we had to work with the hangar configuration that I have. It was the best place for exhaust air but I still wanted to be able to use my car parking spot when not using the booth. When the fan box is not in use it can be moved around to include being out of the booth all together.

 

[Bill Rusk]

This is a general look at the what the removable rear seats look like. When they are not in place the rear cargo area is completely flat with no cables and no protrusions. 85" long and 44 inches wide - tapering to 35 inches at the rear. It is HUGE. We have 6 tie down locations in the floor and 4 in the top for cargo straps or nets.



Trial fit of the tail feathers. All control surfaces are oversized.



We are using the Air Tech fabric system. First parts in the booth and in primer.


More to follow and thanks for following.

Bill

 

[Bill Rusk]

ENGINES

After much consideration we ended up going with a Penn Yan rebuilt 0-360. Penn Yan has a long history and an excellent reputation and it was a pleasure dealing with the owner Bill Middlebrook. Bill is a long time cub owner and is VERY familiar with Cub mods and engine requirements. He was able to give us an excellent price, and delivery time, both of which are greatly appreciated. This will be a stock engine. Not an 0-370, 0-375, 0-390 etc. Just a well built stock 180 to 190 hp engine. It will have conical mounts, dual Emags, Carb, Magnesium flywheel and sump, B&C 20 amp alternator on the rear case, and lightweight starter. We elected a rebuilt engine to save weight. The new engines have put on several pounds.
I anticipate we will be using the Sutton exhaust and possibly the Sensenich ground adjustable prop.
We seriously considered Aero Sport Power for the engine, and several others. My understanding right now is Titan may be the best price but their lead time is 12 to 14 months.

We will weigh the engine when it comes in and post the engine weights that we know at that time

Hope this helps

Bill

 

[Mudofficer]

Thanks for the update @billrusk ! This seat configuration makes for a very versatile and large space. Will it be sleepable? Now that you have sorted out the revisions, do you think that they will also be adopted by Jay? Also, will your build be using a performance STOL type flap from Keller & Javron?

 

[Olibuilt]

Very nice build. You realize it is a big airplane when you see 2 grown men in the back seats!!

I would have looked for a stronger engine to haul all that weight?


Can't wait to see more progress. Thanks for sharing!

 

[Bushmaster1]

Is there any good reason not to use a UE520T other than cost and new to market?. Would make a huge difference on a float plane on on higher elevation lakes. 60hp more at 5000 feet would be a game changer for short lakes and strips.

 

[skywagon8a]

Is there any good reason not to use a UE520T other than cost and new to market?. Would make a huge difference on a float plane on on higher elevation lakes. 60hp more at 5000 feet would be a game changer for short lakes and strips.

This one? https://ulpower.com/en/engines/ul520/ul520t#3-dimensions

Other than the higher maintenance for the turbo system, look where the turbo is mounted. To complete the installation connections to the turbo will be aft between the turbo and the firewall. This will require pushing the engine forward creating a forward CG situation. Particularly with the extra 64 pounds for the turbo components.

 

[dirthog4]

High pressure fuel injection more you know about it in a airplane less you want to. Need small diameter usually 3 blade controllable propeller inefficient rpm range.

 

[Bushmaster1]

Yup that’s the motor.269 lbs which incudes alt and baffling and starter it looks like.Needs a intercooler which I will make up weight of of 15 lbs almost which is about the same weight as a o-360 carb engine.There will be some added weight for fuel pumps and return fuel lines.should be far less weight than a angle valve engine which I would think many people would consider on a 4 place. Not sure what problems you are referring to on high pressure fuel injection I’ve only heard of good I guess I few guys around here running it.Tuneable injectors,no carb heat,no primer,no mixture,better fuel consumption and starts better.It has a list of props that are compatible which includes catto and MT.Maybe something like a Catto 86/43 should push a four place bushed out cub at 105+ mph and super short take off.The only real big negative I see is it’s not a time tested and short tbo of 1200 hours

 

[Bill Rusk]

Bushmaster

Why not the UL520?......and the answer is......never heard of it before. Interesting. It seems to have potential. 1500 TBO is a little low. For simplicity I am not sure I would want the turbo, but obviously that has advantages as well. Sure more power is always good. After all we could go to an 0-470 or 0-520 or even a 0-550.
But here are my thoughts on why not a bigger engine.

1) Weight...... bigger engine means bigger and heavier prop. I will need more fuel = more weight. I will need to add more structure to handle the loads and weight = more weight. It is a massive snowball and pretty soon we have Mike Patey with Draco and Scrappy.

2) This is somewhat subjective but try not to focus so much on the 4 seat concept, but look at the gross weight and empty weight. We can use "useful load" to carry people, fuel and/or cargo. We are hoping for an empty weight of less that 1200 pounds and a gross of 2400 pounds, thus a useful load of 1200 pounds. My current cub performs VERY well at 2300 pounds with an 0-360. This 4S cub should perform the same. Same engine, same airfoil, same incidence, etc. and roughly the same weight. On floats, at max gross, I am off in 18 to 20 seconds. On wheels at max gross I am off in 175'. How much more do you want and at what price? So with 1200 pounds of useful we can haul 48 gallons of gas = 288 pounds, 4 x 200 pounders and 112 pounds of baggage. Ok....so maybe not enough useful load to haul 4 full size adults, all their gear (400 pounds) and we want to haul out the 3 moose they just shot? Now we are in a totally different aircraft category. What we will have is a 2 place side by side aircraft that will carry full fuel, 2 adults and have 512 pounds of cargo capacity. Or 2 place plus room for the grandkids. Or 4 adults around the local area. Or 4 smaller adults, say.... 2 guys at 200 and 2 wives at 150 gives 212 pounds for baggage or camping gear which should work pretty well.

For comparison the Bearhawk model 5 uses the 540-580 engines (6 cylinder engines) with an empty weight of about 1500 and a gross of 3000 for a 1500 pound useful load. Cruises faster but I guarantee it will not get in and out as short as a Cub. It all depends on your mission. One of the builder/owners in our project is a serious sheep hunter and so his mission includes some pretty short and rough strips in the mountains of Alaska. Most hunter outfitters in Alaska are using Cubs because they can go where 185's 206's etc just can't go. So they ferry in hunters one at a time. Still tough to beat a Cub.

Probably a little late for this build as we have Penn Yan building the engine now. I am very pleased with all the communication we have had from Penn Yan. The owner/CEO is a cub guy and has been great. I anticipate we will get the engine in the next couple of weeks.

Thanks for the input on this engine. It looks like it is certainly something to be considered and perhaps it will work out for someone who has not already committed to an engine.

Mudofficer
Yes....in the 2 seat configuration it will sleep 2 people. 85" long and 42 inches wide tapering back at the feet. It would be a little cozy for two but huge for one person.
Jay is adopting most of our changes unless you want something different. I believe he will still be offering it as a single stick,or two stick, toe brakes or heel brakes.
We are going to start with stock flaps but may certainly opt for Pstol/Keller flaps in the future. Starting on Goodyear 26" tires because of airport and local area, but it will likely end up on 31's or probably 35's in the near future.



Paint scheme to be gun metal gray with yellow stripes



Brad in the paint booth spraying Airtec primer.


Hope this helps

Bill

 

[Bushmaster1]

As you might guess I’m Bushmaster type guy. I agree keeping it light is very important because once one thing is heavier you got to make everything heavier like wings,gear legs,struts,and structure.This is going to be a fantastic build to watch and a hard one to beat. My mission is pretty much the same as the sheep hunter fly 600 miles North with 2 guys and hunting gear for two weeks on floats or wheels and use super cub strips or lakes and ferry flight to longer surfaces and fly home. Pretty hard to put that much stuff in a cub even with a pod.It just looked interesting similar weight engine with 60hp more. I think on floats it could be beneficial like 2000’ lake at 5500’ and a couple stone sheep on board. Thanks for documenting all the cub builds many of us reference back to it when doing our own stuff extremely helpful. What is the wing and struts good for. 2400lbs?