Folks
This thread will be about my build up of a Supercub Kit produced by Jay DeRosier of Javron, thus a Javron Cub. http://javroninc.com/
We will start with a stock Piper PA-18 fuselage produced from Piper drawings. From that base I will be asking Jay to make the following modifications....
( I included some notes on the mods for the folks here that may not be familiar with all this stuff )
1. Reverse dog leg - makes it easier to get stuff in the extended baggage area - weight penalty zero
2. Metal Belly Tabs - tabs on last 4 feet of fuselage to attach a metal belly pan - access improved and easier to wash out fuselage - weight penalty will be tabs, hardware, and .020 AL pan itself
3. Removable rear crossbar - makes loading larger items in baggage easier - weight penalty will be a small section of tubing (2" or so) and hardware
4. Tie Downs in Cargo area - to keep loads from shifting - weight would be the tabs
5. Bushing the tailwheel attach tube - keeps the tubing from collapsing - weight penalty will depend on tubing size increase and bushing.
6. Extended cargo area - room to carry more stuff - weight penalty will depend on several factors. I plan to use the lower longerons rather than build the shelf. This will necessitate running the elevator cables under the fuselage.
7. Float fittings (FWD)
8. Float fittings (AFT) - rather than weld on the external fittings I used a flush set up on my last build that I think worked well and added little if any weight. Here is a link to some photos and a description. http://www.supercub.org/forum/showth...ing+smith+bill (you will have to scroll past the electric trim section).
9. Lift rings for floats - these can be welded in or they could be left out and the brackets bolted to the spars as necessary. There are advantages to each. The spar brackets would only be added if someone went to floats so perhaps a few ounces lighter for someone who is not planning on floats but that then requires cutting into the wing fairing and they are not easy to take on and off so they tend to be left on year round. With the weld in ones the holes in the skylight can be plugged easily and the eyebolts are easy to remove or install when going to or from floats.
10. Extra tail lift handle - Easy to weigh a piece of tubing to get the weight. The handle needs to be a little larger than factory so you can get a gloved hand in there and the extra handle is useful for ski flying where it is necessary to manually move the tail around. If there is only one handle there is a tendency to push on the side of the fuselage, often using the shoulder, which then bends the upper turtle deck stringers. Thus with the extra handle you can pull on the fuselage rather than push.
11. Tabs for Amphib float set up. - I don't know much about this in terms of where they should best be located.
12. Firewall Brace tubes - the extra tubing effectively makes an X brace on both sides of the fuselage at the firewall. Cubs are known to collapse the engine in a hard landing/crash often crushing the pilots ankles and possibly trapping them in the wreckage. The extra tube is easily weighed so we could determine the weight penalty here. I have seen this mod without tying the tubes together. That would significantly reduce the effectiveness of this mod. Much better to weld the tubes together at the X even though it would require a small (1/2") interconnecting brace of some type. This mod does interfere with the map pocket.
13. Overhead X brace - Pretty standard now. Keeps the wing attach area from caving in during a crash causing head injuries. The original tubing was a 3' beam. By welding in the X the beam is now only about 18" now so we might be able to reduce the tubing size, or thickness, or both to save weight. Also makes it easy to put in the cross tube for the shoulder harness.
14. Extended gear - most common is 3" which is what I will get. Some are also going to 3X3 gear which is 3 inch extended and the axle is moved forward 3 inches as well. This makes the tail heavier (bad for ski flying) but it allows more aggressive braking without standing the plane on its nose.
15. Seat belt attach welded in to the floor tubes rather than being attached to the seat.
16. Shoulder harness attach fittings welded in.
17 Flap handle moved outboard - I like to take credit for this one but the reality is someone else probably thought of this before I did. I think all the experimental airframes are pretty much doing this now. No weight penalty and helps with the knee interference issue in a crosswind.
18. Bushing the landing gear for the long step
19. No tabs for the BLR fins. (Some folks are using the BLR set of Vortex Generators. These require tabs for the metal fin attached just forward of the horizontal stabilizers. The BLR system and the Micro VG's seem to be about equal in effectiveness with the edge going to the Micros. The downside to the BLR system is that big metal fins on the side of the fuselage. It REALLY gets in the way when moving the airplane around by the tail lifting handles when on skis, thus I am not a big BLR fan. I think the only ones using this system are Cub Crafters).
20. Longer seat attach fittings for rear legs of front seat. This will get the bolt up high enough so it does not conflict with the floorboard making it hard to get the front seat out.
21. ELT antennae mount
22. Tail "X" brace or "H" brace. Strengthens tail area for ski and off road work.
23. Third seat/baggage area reinforcement. I think some of the reinforcement tubes may be overkill in terms of size and thickness so I will work with Jay to see if we can go smaller and still retain the strength.
24. Reinforce/brace outside rib of Horiz stabs to keep the fabric from warping it. Also move it 1/2" closer to fuselage to gap seal this area.
25. Extend the arm on the bottom of the stick by 1" where the aileron cables attach. Gives more aileron throw to the stick.
26. Make the front seat back folding and set the angle at 80 degrees Vs the factory 90 degree seat. No one sits bolt upright. Makes the seat much more comfortable but you have to be more careful with rear stick interference.
27. Control lock brackets welded to front seat, and on front stick base. (This is the "V" shaped lock that hooks into a bushing on the front stick)
28. Tail stinger light mount on rudder.
29. Remove the false cowls (behind the boot cowl). Weld the ginger bread accordingly. Thus fabric will go all the way to the boot cowl.
30. Upper and lower baggage doors.
31. No brackets for the manual trim system except for the electric motor under the jackscrew.
32. Bungee gear set up. Saves 3 pounds over the die spring set up.
I have probably neglected a few things. I am open to inputs. What am I not thinking of?
( and so it begins)
Bill
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Originally Posted by Bill Rusk
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