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Building a 4 Seat (4S) Javron Cub

Bill Rusk

Sandpoint, Idaho

Here we go again. Another marathon, mega thread. I will be helping and mentoring Brad as we (he) builds the prototype 4 seat Javron Cub.
I will try to post helpful info and make this a manual for the 4 seat cub (4S), as much as possible.

The following are our goals:

1) Keep it as close to a Cub as possible
2) Shooting for an empty weight of 1150 (I will be happy under 1200) with a gross of 2400
3) Have the plane at Oshkosh 2023

We will be using an 0-360, carbureted for simplicity and weight. Trying for 260 pounds or less with all accessories, except exhaust. Looking at magnesium sump, lightened cylinders, 9 to 1 comp ratio, Pmags, Skydynamics flywheel, B&C Alternator on the back, EarthX battery, Conical mount, no swing, built in thrust line. I am currently getting bids on the engine.

What I think I know so far.

The Javron fuselage is 44" wide and is a clean sheet design by a well known cub engineer. 19" longer overall. I believe it weighs, with powder coating, 138 pounds, but that will change as we are still working on finalizing the configuration. All other parts, other than the fuselage, will be standard Cub parts. All the angles will be standard Cub to keep the flight characteristics as close to a "Cub" as possible.
The other 4 seat fuselage is available from Airframes Alaska. It is 40" wide, and weighs in at 155 without powder coating. Further options are the PA14, and Bushmaster versions of the Pacer/Tri-Pacer, which are much narrower (about 36"), and probably smaller in length and corresponding cargo area.

The cargo area of the Javron 4S (I will here after refer to this plane as the 4S) is huge. Unlike the Airframes fuselage it does not have the dogleg, or shelf tubes. From the rear of the front seat, (rear seats will be fold up similar to a Cessna 180, and easily removable altogether), to the back of the cargo area is 7'. It is huge. Right now the door is 23" x 24" and does not have a lip. So you will be able to slide things in and out. It might be possible to increase the door size but my understanding is that to do so, and maintain structural integrity, would require a truss under the door and thus a 4 to 6" lip. So the door would be bigger but stuff would have to be lifted over the lip as opposed to sliding stuff. The right front seat will be easily removable to allow loading cargo through that larger door. Everything is a compromise. Lack of the shelf tubes could be looked upon as a negative as it does not allow an upper and a lower baggage.

Due to goal #1 it will have dual cub clamshell type doors. My understanding is this may actually make getting in and out easier than with the seaplane doors, but I do not know that for a fact yet. Remember.....this is the prototype. In the future I am sure you could get Javron to make seaplane doors if that is your preference. One of the great strengths of Javron is the flexibility Jay offers to customize a kit to your specific mission, and desires.

Float fittings
Electric trim
Structure for bolt in lead to adjust CG
Lots of cargo net attach hooks (very necessary with such a large cargo area)
Baggage floor will be on longerons
Easily removable right seat to allow loading cargo through that larger door
Metal belly under front floorboard to facilitate cleaning

We are still working on the stick, rudder, and brake configurations. My preference is in goal #1..... thus dual stick, floor mounted rudder pedals, and heel brakes. But sometimes the monkey motion required for this may not make it the best option. We will see. Brad would like full dual controls and I agree with that.

No pictures yet.

So the first thing we need to do is acquire tools. I will post a list as soon as I can.

Next we need to build a paint booth.


Having been down this road a few times in the past here are some of my thoughts. I do not particularly like plastic (visqueen) booths for the following reasons. I was painting the rocker boards on a VW many years ago so was kneeling down on my ankles. When I stood up I lost my balance a little and put my hand out to steady myself and pulled the entire flimsy booth down on the wet paint car. Fixing that was a LONG process and made a more rigid booth a top priority. Plastic gets static electricity and attracts dust which then falls off when the plastic flexes which it will do every time you turn on the fans or turn them off. It might be fine if just using the booth one or two times but when building a Cub there are a TON of times you will be in the booth. 40 or 50 would be my guess. Way too much for a flimsy plastic booth. I know many have used plastic and gotten a perfectly good job. I'm not that good. I have to use every trick in the book, the very best gun, compressor, filters etc just to get an average job. I know, and envy, the folks that can get a 39 dollar gun from Harbor Freight, paint outside, and the darn thing looks like a Lexis finish. I can't do that. So......I will be building a 12x24x8 paint booth that will be fairly permanent so to speak. I will post that as I go.

After a little internet searching I found this....

*You need full air exchange twice per minute
*Calculate your area LxWxH (24x12x 8' ) = 2304 .....x2 = 4600cfm needed to attain that
*A one hp motor can usually move about 1800cfm which means I need about a 2.5hp motor (or a couple of lower Hp units)
*For the intake filter area you need 1500 sq in per 1000cfm, so I will need 6900 sq in or.........12 24"x24" filters
*For exit filters you can use 1000sq in per 1000 CFM so I need 8 24"x24" filters or use fiberglass rolls
*Positive pressure is best thus would also need an intake fan......best number positive pressure is .3 wc
*3/8" couplers flow twice as much air as 1/4" couplers
*Lots and lots of light. Can't have too much light.

Not sure I really need to hit all that but it is certainly a goal and will be much better than my last booth.

Let the games begin........

Hope this helps

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Great. Keep the post coming. My 4s is on order. I own a body shop so on the paint booth I am ahead of the game . Everything else I have to learn
Sounds like a great project! I made a few slight modifications to the door on Janes new cub to make entry and exit a bit easier.

Picture on left blue tape is normal lower door size. Pic on right is slightly modified seaplane opening. Not only is back seat easy to enter but I should be able to swing my leg past right side of front seat. Truss on bottom for support. I screwed up on rear door upright going to move tubes to get rear straight instead of current slight indent with tubes. I have lowered rear stick so flat cover will make for large extended baggage when in cargo mode. That horizontal tube in door will go away.


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This assumes you have the basic screw drivers, wrenches, tape measures, etc.
If you guys see an obvious omission please add it in.

Drill - I like a smaller size electric battery powered, I really don't use an air powered one much. (Unless you are building a non-quick build RV kit)
Drill bit set with numbered and lettered drills
#30 and #40 drill bits to include 3 each long (12") or so drill bits
Step drill bit (I use this a lot)
Left and right tin snips
Straight snips
8"x 24" belt disc sander (I use this ALL the time)
Dremel tool with attachments
Straight edge meter stick (ie metal yard stick but I like the extra few inches of the 1 meter size)
12" and 6" rulers in at least 32nd incriments
grinder with scotch brite wheels
Snipix smooth jaw pliers
Die Grinder with a cut off wheel
Angle drill attachment and bits
Spring punch
Set of reamers (from 1/16 to 1/2" in 1/16 increments)
Cleco pliers and 40 each of #30 (copper color) and #40 (silver color)
Rivet squeezer with die set (#40, #30, dimple #30 and #40, flat set for flush rivets
Digital level
1/4" socket set (I rarely use 3/8 stuff on airplanes)
Dial caliper
Magnifying glass
Rivet spacing tool
Pop rivet set (I like Marson)
Torque wrench 20-200 inch pounds
Tap and Die set (use it a lot, worth it)
Ball end hex key set (allen wrenches)
Mirror and a magnet on an extension
single edge razor blades (buy a box of 100)
16,8,and 4 oz Ball Peen hammers
Deburing tool
Microstop Counter sink tool
Countersinks #30 and #40
X-Acto set
Flaring tool
Tubing cutter (small and large)
Volt Ohm meter
heat gun
Organizer 30 drawer cabinets (I use a different color for non aviation hardware, ie acft cabinets are gray, home stuff cabinet is red trim)
Shelves (I like to keep all parts together, you will be amazed how a part can hide)
A couple of good scales (we are going to weight everything. one small up to about 5 pounds in grams and/or1/10th of an oz, and one to about 100 pounds in oz)

Big stuff
Compressor (Buy a good one and have it for life)
Drill Press
Band Saw (variable speed)

Borrow Stuff (join local EAA chapter, they often have this)Finger Brake
Foot Shear


Need a bench or two. I have two 2'x6' benches and if I need more I just throw a 4x8 sheet of plywood on a couple of saw horses
Will need a few saw horses
Trash can and LOTS of bags
Lots of no color bounty paper towels

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I don't suppose the magnesium sump or lightened cylinders would be legal on a certified cub or would they? I don't think the Pmags are or the Skydynamics flywheel would be legal. Just trying to make my certified cub as light as I can.
I took this picture a while back for reference. This is a cubcrafters 360 with CF plenum, FI, starter, no flywheel, no alternator, preservative oil only. 267 lbs



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Denny - love that door. Thanks for the pictures
Dave - I think all are experimental. Sorry.
Aflyer - good info. It is amazing how little emphasis has been put on engine weight. Many rebuilders have no idea what their engines weigh.
KCJ - This build will be in Sandpoint Idaho

Bill-are you still commuting? Last time I saw you was in the crew lounge in DEN.
If you are going to change the wing incidence (Jay has spar attachments to do is so stock fuselage is fine) now is also the time to adjust the tail angle to match any wing change. DENNY
It may not have been this forum, but I read about a guy converting an enclosed trailer into a mobile paint booth. Had great LED lighting and he ran the fans off a trailer generator. When he finished his project he was renting it out. Sounded like a great business plan.

Anyone have the stats on cylinder weights vs longevity?

Its heavier than standard, but has there been any reviews on skydynamics valve cover gusset plates?

Hi Bill! Good to see you’ve launched this, been anticipating it.
Tools….Dittos on the small battery drill, and I’d add several other battery items. I like the Milwaukee M12 stuff because it is small/light and tough. Their 90* drill is handy, Santa wife brought me a 20,000 rpm cutoff tool that’s as handy as a pocket T shirt, and the 1/4” drive ratchet is also. On the air side, if that die grinder you have listed isn’t a 90* one, you owe it to yourself to pick one up. Can be had at Harbor Freight for $10, quality isn’t too bad. At $10 you can buy several and give ‘em the heave ho if they get balky. I like having (have) 5 or six with a different burr or scotch brite or cutoff in each one. Save an unbelievable amount of time changing that stuff around. My straight die grinder became an almost an unused relic when the 90*s showed up about 30 years ago.
That’s it for now, need pics of that fuselage now!
Hammer down!

Whitney punches.

The punch has a point in the center that easily slips into a center punch prick. Fast and accurate and in thin material the hole stays round.



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I can't wait to see how this goes. I am in line for 4S airframe #2 (if you count the prototype as #1)
My build will be quite a bit different: center stick, set up to fly from left seat ie flaps, throttle, switches.
This airframe already has the hanging rudder pedals, I'll play with that.
Bill, I have really taken to heart your "build for 90% of your flying". Gonna by a very simple panel. No EFIS.
Jay is building up the engine. Mag sump. machined fins & acc case, skeletonized flywheel. P mags. ported and polished. SD8 pad alternator
Sensinitch prop, firewall battery.
Everything going towards the lightest airframe possible.
Thanks for the input gents.

KCJ - yeah, about 19 commutes to go. Not that I'm counting.
Denny - excellent point but we are not planning to change the incidence.
Chet - interesting idea. Hmmmmm
Oz - Thanks for the input. Brad.....you paying attention?
Dan - I don't have one of those. Will check it out.
Tom - I saw your frame in the shop. I'm sure we will be in touch, sharing ideas. Yes, prototype #1 which is good for you. There is an old saying in the aviation community (which I will be violating) "Never fly the A model of anything" LOL Sounds like you have the idea on weight. Keep it simple and light.


Some tool sources. The "main Squeeze is reported as being the absolute BEST hand squeezer out there.

There are several tool sources

Obviously Home Depot will have some items, and Harbor Freight.

Others online





Here are a few items that would be good from Cleveland. You will probably spend about 3K on tools.This is close to 1K but is a lot of the more expensive stuff. Under tool bundles get the ......

"Main Squeeze Kit"
Angle Drill Attachment Kit
Threaded Micro Stop Countersink Cage
SKU: CT196Cleko Pliers


If you can find them get the Wedge Loc Clecos

Hi everyone,

I'm the lucky guy who gets to build alongside Bill on this new project! I am brand new to this world so thought I'd mention a little about myself.

First, I am a student pilot. Just passed the written and now get to focus on the flying. I live in Sandpoint Idaho and have wonderful flight instructions in Annie, KT, and Ken at Pilot Training Northwest. Winter is a slow time of year up here, but hope to gain experience quickly as the weather improves!

Second, I am an absolute beginner as far as building is concerned. In fact, if I didn't have the good fortune to have Bill in my community, I'm not sure I'd have the confidence to start such a project. But, he has encouraged me to follow this new dream so I am all in! I guess what I will try to add to this thread is my perspective as a newbie in building and aviation in general. I will have more questions than answers (we'll leave the answers to Bill) but am so excited to join this group. I, like so many others, have read through many past threads and love the community.

Oz- thanks for the advice on the 90* die grinder. I literally just got back from Home Depot and bought that very item wondering if it might be useful. Question answered!

I will spend the next couple weeks getting my shop (3 car garage) ready for the fuselage and wings, which will hopefully arrive in Sandpoint late March. Bill is going to give me a crash course in fabric covering, etc so I will be somewhat ready to hit the ground running. I am so grateful to Jay at Javron for allowing Bill and I to build up this prototype! He has already been amazingly responsive and willing to help me.

I humbly welcome any and all advice. So far, from my time with Bill and my flight instructors, I have 2 things solidly running through my mind- "keep it light" (Bill) and "more right rudder" (my patient flight instructors).

We're off!


I will try to post our orders from various suppliers as we go. This might help someone who is starting out.

Got the landing light kits from Javron. This includes the lenses, and z bend parts to fabricate the landing/taxi light bays. We have not selected the actual lights yet.

Ordered fabric, tapes, rib lace, and glue from Airtech

We ordered the Aveo Ultra Daylight wingtip lights. These are position, strobe and Nav lights. Lowest weight and least expensive of the full service lights.
Positive strobe daylight for the tail. Highly recommended to keep from getting run over from behind.

50' of 4 colors of 20 gauge wire for the tip lights. 50' of 4 colors of 18 gauge for the landing lights. Unshielded.

A couple of organizer hardware cabinets......be SURE to get cabinets that have dividers in the drawers. You don't need a full drawer for 10 nut plates. They used to make a cabinet with 3 dividers per drawer but I can't find those anywhere now. I guess they quit making them. Best I could find was drawers with one divider.

Then hardware you will probably need......

Soft rivets.....3-3, 3-4, 3-5 and 3-10 both flush and round head. I get a small number of long 3-10 rivets and cut them down for the rare occasion when you need a longer rivet. No sense having a bunch of long rivets you will almost never need.
Soft rivets......4-3,4-4,4-5 and 4-10 flush and round
Hard rivets ......same as above

This will take up 16 compartments or 8 drawers

Screws.....for starters......

SS MACHINE SCREW AN526C- philips head Get 25 each of 6/32 x 3/8, 1/2, 5/8, and 3/4 same 4 lengths of 8/32 and 10/32
MS21047L06K ANCHOR NUTS Get 25 or so 6/32, 8/32, 10/32 (maybe only get 10 of 10/32) also get miniature of these
"U" TYPE TINNERMAN A1785-6Z-1D and A1784-6Z1D get at least 25 of each then get the type B screws, Stainless, philips, in the 4 lengths above

Although Javron includes a lot of the hardware with the kit, you will have lots of needs and getting it together before you start will speed your progress if you do not have to stop and order screws you did not have. I have found most of the "assortment" packages from Spruce includes a lot of stuff you will never use. I will continue to post these as we go and hopefully it will help.

Our current plan is to get the wings, flaps, ailerons, and tail feathers covered and painted this summer. So much of what you see above is prep to get the wings covered.

More to follow

50' of 4 colors of 20 gauge wire for the tip lights. 50' of 4 colors of 18 gauge for the landing lights. Unshielded.


Use 20 gauge, three conductor, shielded wire for at least the nav/strobe combos. Easier to install, each conductor already marked, and you can use the shield as the ground wire, to get the light assembly ground out of the wing and into the fuselage. Put a four pin, Molex style connector, at each light, each wing root, and at the rudder to make removal easier.

Agree with Web. The shield also makes the wire tougher. I even use 1 conductor shielded wire if it has much of a run just because of this. Also, the new solid state strobes do still generate some noise.

Brad, welcome to the site! More knowledge here than you can imagine. I’m glad you grabbed a 90*. You won’t be sorry.
You are fortunate indeed to be building with Bill, he is a treasure trove of knowledge and great ideas. I’m still in a build of my own and his first Javron build thread plus his friendship has been a great asset to me. He’s just a great guy to have for a friend anyway.
I’ll be following along as this unfolds, stay flexible and have fun, I’m sure you will. Btw, love Sandpoint, have several other friends there.

Cheers, Oz
I have not heard of interference or noise from the Aveo lights, and I have not had any noise on mine. I am not planning on the synchronized strobes (I can't find any data that indicates they provide better visibility) so we will only be running three wires. EVERYTHING will be grounded to a ground buss. Nothing will be grounded to the airframe. The shielded does not offer value (to me) for the increased weight. However, I have a great deal of respect for Webb, so I will make sure we can replace the wires with shielded if necessary. And I do like the quick disconnect idea. Thank you Webb and Oz.

This will be an interesting and exciting thread to watch!

On the comparison(s) mentioned in your initial post Bill, the 2+2 plans call out 39" and the Busmaster/Producer widths should be right at 40" as well. The pa-22 drawings I have note the cabin width at 40" at the widest part, right at the front of the cabin. That drawing doesn't show the doors though, so it the actual "space" in the cabin might of course differ. So if I might ask, where did you get the widths you mentioned in the initial post? I ask this question because I am very much interested in building a 2+2 from plans, and putting some "stock" wings on the thing...although I'd like to get to at least 2200 pounds gross weight. So for the 2+2 then, that would likely mean widening the fuselage a bit, and I've been researching that very thing here in the forums for more than a week now. I've seen several owners/pilots of the 2+2 recommend widening it, but only one or two who've apparently done it: One builder made theirs 1" wider, and another finished aircraft reported at 45" of width. No details were specified though, so the search for information continues.

Very cool though that Jay's 4-place SC fuselage is 44", and I wondered about the wide of the Airframes Alaska product. I didn't know that was only 40", so thanks for providing that number as well. That's about the width of a C-172, near as I can tell (from available online references), and a C-182 appears to be a bit wider at around 42" or so.

Thanks for starting the thread--I'll definitely be following along!

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