Building a 4 Seat (4S) Javron Cub

[hunt/trapak88]

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.


View attachment 64696
Paint scheme to be gun metal gray with yellow stripes


View attachment 64697
Brad in the paint booth spraying Airtec primer.


Hope this helps

Bill

I’m following this closely as I too have money to Jay for his kit. Had a 1150lb 0-360 cub with a long dong very well performing propeller, Keller’s etc. Cub flew and performed well. I’ve always wondered how this 4S will do loaded with a 360 based engine.

Am I reading this right Bill? Your 0-360 “standard” Javron cub is/would defy gravity in 175’ at a gross of 2300lbs in a no wind configuration!!?? 175’!!?? If so, I have second thoughts on my cub. Which I thought was a performer….

 

[Bill Rusk]

Folks

A little update. Going slower than hoped for but that is pretty much always the case. It seems this spring Brad and I have both been gone a lot. tough to build an airplane when you are not there.



Carbon Fiber floor board material came in. 2 ply on top and one ply on the bottom, comes in at .565 pounds per sq ft.



We got our alternator(generator) from Monkworkz. This is a relatively new unit designed by an electrical engineer. Primarily used in the RV community as a back up power source. I am very impressed by the construction and customer service. I think this will be a winner. It weighs, with the regulator 2.6 pounds. That is 3.5 pounds lighter than the B&C direct drive units. Produces 15 amps at 1000 rpm and 30 amps at 1800 rpm.




Just for a size comparison. That is a standard can, like a can of corn, soup etc. So it is much smaller than the B&C , and cost the same as well.




The engine came in from Penn Yan and looks great. This is without a starter and generator so add abut 9 pounds and we are at 257 with carb, mags, plugs, wires, starter, generator, and oil filter. It came in at 196hp, and plus 35 pounds torque. 9/1 pistons. I am VERY pleased. We did get some damage on the flywheel so ordered a new one. Checked to make sure that was all that was hit.




Bill Middlebrook at Penn-Yann was, and is, awesome to deal with. Great guy and a cub guy as well.


Engine and prop test mount. We will be doing some prelim testing of W&B to adjust motor mount if necessary.


Hope this helps some

Bill

 

[Buschpilot]

Looking great Bill! I hope to get out your way for a visit sometime before you guys finish her up. Our kit is due to arrive in August or September, and I would love the chance to soak up a few good ideas before we start building!

 

[Bill Rusk]

Buschpilot - Happy to have a visit anytime.

Bill

 

[Bill Rusk]

We will be doing some early, best guess, W&B/CG calculations in order to make sure we have the right length motor mount.






Bill

 

[Mudofficer]

Any progress reports on this project? What changes and configuration lessons learned? Curious how you are going to lay out the panel, pedals and stick(s)? Any cowl considerations being made at this point?

 

[Brandonc]

Any progress reports on this project? What changes and configuration lessons learned? Curious how you are going to lay out the panel, pedals and stick(s)? Any cowl considerations being made at this point?

I am feeling the silence on this thread. I am ready to get started on my build

 

[Bill Rusk]

Folks

Long time since I have posted. My sincere apologies to those following.

It was a busy summer. Almost 2 months in Alaska in the Cub on floats and 6 visitors. Two long motorcycle trips, and a pretty extensive missionary trip kept me occupied. Plus the other two guys who are really building this thing (I'm just mentoring) were busy as well. But progress was made.



Jay DeRosier came up to Alaska again this year. This is his 8th time. He is getting to know the SE part of Alaska pretty well. Great guy to fly with. He gets about 1 week off a year. But this year I managed to drag him out of the shop twice. This is at the Red Bay Lake Cabin on Prince of Wales Island.



Jay and I took a pretty epic 3000 mile motorcycle trip up through Canada and into Alaska. This is outside Skagway Alaska. Boring video of the trip here

Yours truly near Hyder Alaska. Not much there, but the Canadian sister city of Stewart was pretty cool.


But you guys don't really care about that.........




Brad is learning to paint.




At this point the wings, flaps and ailerons are covered and painted. The horizontal tail surfaces are also covered and painted. Paint scheme is as depicted in a previous post. All gray with yellow trim.



We did a preliminary weight and balance.


We assembled everything we had........





And then we placed weights based on our best guess as to where the additional weight would go. ie 30 pounds for the instrument panel. 50 pounds for the muffler and cowling etc. No consideration was given to the total, but coincidentally it came in about where I expected and/or hoped for. At 1175 pounds. Using the prop as a datum, and a range of 70.5 - 79 inches, the CG fell at 76". NOT GOOD. I ran some numbers and we extended the motor mount 2" further forward. This should help get the empty CG closer to the forward limit. Remember this is the prototype. We are learning as we go.

 

[Bill Rusk]

So here is where things get tricky.......


I had the opportunity to fly a very very similar aircraft (a one off, not Javron, but VERY similar) that was recently completed. Workmanship is fantastic. Flight performance is generally excellent, although the empty weight came in at 1400. Angle valve, dynafocal, fuel injected, CS prop, etc. It all adds up. We are hoping for 1150 and will be happy under 1200 pounds.

The builder of the Cub is a VERY experienced Cub pilot. He and I both flew the Cub and felt it was weak in stability on the vertical axis. It was especially noticeable on short final with crosswinds. So I got into all my aero books and boned up on stability issues and aircraft design. You will find Thurston "Design for Flying" and Dan Raymer "Aircraft Design, a Conceptual Approach" to be good sources. I added to that a couple of textbooks from some coursework I did at the Univ of So Cal back in my Air Force days and came up with the following.

I will abbreviate vertical stabilizer to VT (vertical tail)


After doing some research it would appear that the Super Cub VT and rudder may be on the small size to start with. Several books on areodynamics all seem to agree that the Coefficient for a VT (Cvt) should be in the vicinity of .04 for most GA aircraft.
After a little homework it looks like the tail was designed originally around the J-3. The value of the Cvt is typically smaller for sailplanes and lower powered aircraft, in the range of .02. Thus the Cvt is pretty much spot on for a 65hp J-3. When the Supercub was designed, the rudder was changed to a balanced control surface and increased slightly in size, but was still designed around the lower hp C-90 engine. Typically as engines get bigger more rudder is required and thus the Cvt increases. Here we are many years later with a rudder that was designed for 90hp and we are running 180hp. The lack of rudder shows up more definitively when on floats, often necessitating the need for some type of ventral fin.

Using the formula...Cvt = Svt x Lvt/ Sw x b

Cvt = Coefficient vertical tail
Svt = Surface area vertical tail
Lvt = length between the Aerodynamic center of the wing to the aerodynamic center of the horizontal tail (roughly 1/3 of the wing to 1/3 of the tail)
Sw = wing area (178.5 round tip wing. Sq tip wing will increase the demoninator and lower the Cvt)
b = wing span (again the Sq tip wing will increase the demoninator and lower the Cvt to .022)


What we currently have on a Supercub..... Cvt = (1686 x 156) / (25704 x 423) = gives a Cvt of .024. Quite a bit smaller than the .04 value desired (Svt used here includes the oversized rudder from Javron. Using the stock SC rudder results in a Cvt of .022)

What we have now is....... Cvt = (1686 x 175) / (25704 x 423) we get a Cvt of .027 (oversize rudder and 19" longer fuselage)


I proposed, and we built and installed a new larger vertical stab and rudder using the following calculations.
Cvt = (2048 x 175) / ( 25704 x 423) = Cvt = .033 (less than .04 but I was reluctant to make too large a jump. This was a 22% increase in tail surface area.

The vert stab obviously directly affects the stability on the vertical axis. But when combined with dihedral it also affects both lateral and spiral stability. Given the relatively low amount of dihedral, and generally weak longitudinal stability inherent in Cubs, I had some concerns about spiral stability, but felt it would be manageable.

The builder and I both flew the Cub with the larger tail and came to similar conclusions once again. Most aspects of the flight envelope were much improved; however, we lost some performance in the forward slip arena. Turning slips were fine, and ground handling, crosswind performance, etc was all much improved. Spiral stability was decreased but still completely manageable with little effort. It would probably not be noticeable to the average pilot.

As you know stability and maneuverability are pretty much diametrically opposed. We increased the stability, and of course, lost some maneuverability. For the mission of this type aircraft, maneuverability (and especially a good forward slip) is a desirable, and necessary, characteristic.
At this point I have once again redesigned the vertical tail, and rudder, to be roughly 1/2 the increased tail discussed above. This is the new tail that Jay will be using on the Javron 4S kits in the future, and retrofitting to the few kits currently in the field. (I think there are 4 kits currently in customers hands). We basically split the difference between the original Cvt of .027 and the redesigned tail Cvt of .033, thus the new tail will have a Cvt of .030. We have not flown the new tail, but I am quite confident it will be perfectly suited to this new 4S fuselage.


If you have managed to wade through all this, my hat is off to you. I have no doubt it is far more than you wanted to know. I have spent a considerable amount of time in this endeavor. But it is my sincere belief, having flown a very similar aircraft, both in its original configuration, and in the oversized VT configuration, that this is going to be a great performing Cub, that will accomplish its mission with aplomb.



I don't think this is the final version, but it is close. Stein did the initial work but Pacific Avionics is doing the final version and it should be finished in the next couple of weeks. After the holidays we will be full steam ahead on the fuselage and making regular updates to this thread.


Hope this helps

Bill

 

[BC12D-4-85]

Have you explored the addition of a forward fillet to the VT above the fuselage? Sized via performance testing?

Gary

 

[fishhook]

The mackey sq12s and the such have the front of the vertical extended forward quite a bit and even more oversized rudders. I would say moving the vertical more forward would be the ticket but then you have to redesign the jackscrew or get rid of it all together and go with the linear actuators that everyones doing.

 

[skywagon8a]

So here is where things get tricky.......

After doing some research it would appear that the Super Cub VT and rudder may be on the small size to start with. ....... The lack of rudder shows up more definitively when on floats, often necessitating the need for some type of ventral fin.

I proposed, and we built and installed a new larger vertical stab and rudder ......

The vert stab obviously directly affects the stability on the vertical axis.

Good for you in wading through all the numbers. As you have learned Piper always did as little as possible when changing models in order to keep costs as low as possible. You will notice when looking at the type certificate 1A2 Note 110. The large round air filter is not approved on floats. The addition of this little bit of extra vertical area well forward of the CG is just enough to exceed the existing size requirements of Piper's VT. Since Piper didn't want to change the tail, it was easier to just not approve the round filter on floats. This marginal sized same tail was previously noted on the PA-12 when it was put on floats. The tail wasn't large enough so a ventral fin is required.

 

[thaefeli]

I talked to Jay last week. He said his shop is starting two 4S airframes this week. He also told me the windshield mold is finally in progress.
As for me, the boot cowl is done. I made it 4 piece with removable side panels.
I have the new extended engine mount and engine, and everything on the firewall is located. I started on the cowl yesterday. It will be a standard Cub type.
Going with a pretty basic panel, shouldn't take too long.
Once the new fin and rudder arrive, I should be ready to cover.

 

[Brandonc]

Thanks for the update. I am excited to get going on my build. Have you test fit the panel? I wanted to verify the fit before moving forward with the cad drawing. I really appreciate all your work on redesigning the tail. These airplanes have went through lots of changes over the years and there has been little improvement in that area If your adding slats to the wing would it change your calculations?

 

[DENNY]

I would consider putting the switches and fuzes on drop out panels, simple to do and makes working on them easy down the road.
DENNY

 

[Bill Rusk]

Brandoc

Here are some photos. I feel the panel is accurate. You could tighten it up a bit, but I suspect you would not be able to get it in and out if you did. It is great to make everything super tight and a perfect fit but I can't tell you how many times that did not work for me. Then you discover it won't go around the corner and fit into place.

Bottom line, I think it is good.












Hope this helps

Bill

 

[Brandonc]

Do you have a picture of the rear of the panel installed in the airplane

 

[Supercubrancher]

Hey Bill, what is the dimensions of your paint booth?

thanks Brian

 

[tempdoug]

Hey Bill, what is the dimensions of your paint booth?

thanks Brian

not to butt in here, but im going to own one of these by spring, guy in a neighboring town has one and said it works great, they come with fans and filters.https://www.homedepot.com/s/inflatable%20paint%20booth?NCNI-5 want to add its just for the one project im doing

 

[Bill Rusk]

Brandoc - No, I can take one but there is not much to show. Unless you are just looking at where the tubes are that you have to avoid. Happy to take a couple of shots if you want.

Brian - It was supposed to be 12 x 24 but when all was done it is closer to 12 x 22.5. You really can't get much smaller and get around both ends of the wing.

The concern I have with inflatable booths is keeping the paint from flaking off the sidewalls. When it is deflated it will loosen anything clinging to the sides, roof etc. When re-inflated that stuff seems like it would create a lot of dirt that will end up in your paint job. I might be wrong. Never used one, just seems like that would be an issue. Painting a cub project is unlike painting a car and many other projects. You will be in and out of the booth 40 or 50 times in the course of the build. A car is mostly painted all at once as are many airplanes. But a cub is painted a few pieces at a time, often over an extended period of time.

Just my opinion etc

Bill

 

[Mr. Ed]

A friend bought an inflatable booth to paint his plane. He said what Bill speculated. Every time you set it up you have to clean all the interior to keep what stuck painting the last part from falling into the paint job in progress. They are also not light and easy to move around when deflated.

 

[Dave Barras]

What Bill said. I have painted in visqueen paint booth with great success but it is
a one time use and then change out the visqueen for the next application.
As mentioned above, great for cars not so much for the cub.

 

[Formandfunction]

You can't really clean the plastic booth without loosening particulates and it ending up in your paint. Same goes for hard booths. Best paint jobs come from undisturbed dirty dungeon booths.

 

[skywagon8a]

Just wet down the hangar/shop floor with water to hold the dust...leave the doors open. If a bug lands on the wet paint...pick it off...the paint will flow out. Cover or remove the stuff you don't want paint dust on.

 

[supercrow]

I have had good luck with an inflatable paint booth by using a broom and a powerful leaf blower. With the exhaust fan on high one guy gently brooms the interior surfaces of the booth while the other guy blows the leaf blower. It’s amazing how clean you can get it floor and all.

 

[Mudofficer]

But you guys don't really care about that.........


.

Well, That's a nice tease for motivation... I don't mind seeing the fruits of your labors as I wait for this prototype to come together!

 

[Mudofficer]

Any progress on this project? Looking forward to the next update...

 

[Bill Rusk]

Folks

This is a difficult entry to make.

After many life challenges (sometimes "life" gets in the way of our hobbies) the builder has decided to discontinue building this Cub. I am not the builder, owner, or financier of this project. I was just the mentor. So this post will effectively close this thread out.

It is my understanding that the owner has decided to keep all the parts, ( except the fuselage itself,) to be used on another 2 seat cub project. Thus the fuselage will be up for sale. It will need work, to include some welding, to complete. If you are interested please send me a PM and I will put you in contact with the owner.

I still believe this project and the Javron 4 seat cub has a great deal of potential and has a LOT of great qualities. I have my hands full with other projects, to include going back to Alaska in a few days and I will be up there until September so I don't have the time to pursue this project myself. Thank you for following this thread up to this point and I am sorry not to be able to offer more help via this thread to those following.

Bill

 

[Scott A]

Understand life challenges. Thanks for all the good information you have passed along.

Enjoy the AK trip - but you can't keep Jay there that long (wink)

 

[Mudofficer]

Oh sad, not the update I was hoping to see... Any further details about the hurdles that will be required to make this 4S fly? I have been patiently waiting in the queue with a deposit for this kit to complete and deliver via Javron assuming the/this prototype flew. Is there another aircraft out there under construction that somebody would be willing to update the thread with? My understanding was that there were 3-4 kits made so far, and I was in the +5 slot, but not in a rush as early tweaks were incorporated.