Javron Cub Building for Dummies

Bill Rusk said:

Vented to inside and based on my GPS airspeed is within 1 MPH. Keep it simple. You are not building a rocket ship to go to Mars, just a 100 mph Cub. Just my opinion and all that rot.

Bill

Click to expand...

He already has it in Bill and one nylon 1/4" tube only weighs a couple ounces so why not use it. The Aussie Cub I built had it vented to the cabin and the ASI and Altimeter were always a little twitchy. When I rebuilt it after the wreck I put one of these pitot's in it and it is now rock steady. Talked to Jay a few times in the last few weeks and he said you guys had another epic Alaska adventure.

The Clipper had the static ports open behind the panel as did the early Pacer. The Tri-Pacer started off with the static on the pitot and then Piper found that they worked better if installed on the belly in the aft fuselage. Before we rebuilt my Dad's Clipper (basic same fuselage as a Pacer/Tri-Pacer) he always complained about the inaccuracy of the airspeed indicator. At rebuild we installed the staitc ports per the Tri-Pacer drawing and his AS is accurate and doesn't vary in winter, summer, window open, closed, vents open closed etc.

First thing I noticed when I flew the first CC18 Top Cub, the airspeed was accurate, Cub Crafters figured out where to put the static port.

Mark Erickson was certifying the Super 18 and discovered the inaccuracies of the AS indicator with flaps down. Where was the pitot/static tube? Right in front of the flaps where it got disturbed air when the flaps were deployed. Moved it outboard and it worked fine.

Most people in tune to their aircraft don't need airspeed. People ask me all the time what speed I land at, I have no idea, it is by feel and I am not looking at the AS. I do use it compared to GPS ground speed when looking at an off airport spot to help judge if I have a tailwind or not. An accurate airspeed indicator is not a necessity but it is nice if it works accurately in my book.

pittsdriver said:

He already has it in Bill and one nylon 1/4" tube only weighs a couple ounces so why not use it. The Aussie Cub I built had it vented to the cabin and the ASI and Altimeter were always a little twitchy. When I rebuilt it after the wreck I put one of these pitot's in it and it is now rock steady. Talked to Jay a few times in the last few weeks and he said you guys had another epic Alaska adventure.

Click to expand...

A 1/8" tube weighs even less. The tube only transfers pressure, free flow doesn't need a consideration.

skywagon8a said:

A 1/8" tube weighs even less. The tube only transfers pressure, free flow doesn't need a consideration.

Click to expand...

Most are set up for 1/4" tubing so Trying to mix and match fittings becomes a pain. I'm with Steve KIS. I've flow several airplanes with and without static ports and it seems like with things are more accurate. I also agree airspeed indication isn't really important but it is nice especially for training.

pittsdriver said:

Most are set up for 1/4" tubing so Trying to mix and match fittings becomes a pain. I'm with Steve KIS. I've flow several airplanes with and without static ports and it seems like with things are more accurate. I also agree airspeed indication isn't really important but it is nice especially for training.

Click to expand...

Don't disagree, only pointing out it is a pressure sensor not a flow. I'll not enter the training discussion.

Pittsdriver

Yes, I agree, already in, and certainly not a bad thing, I was just pointing out (for someone else that might read the thread) that you could get away without it. And, as you pointed out, it can be added after the fact if it does not work the way you hoped.
Yes, Jay and I had a pretty epic adventure coming back from Alaska. Good fun. I haven’t posted anything about this summer yet, but I will. Trying to figure out how to do a video. Hopefully I’ll have something in a few days.


Hope you’re doing well


Bill

Thank you all for the comments…especially the differences of opinion. I think it adds to the discussion.

I should have added that another factor in my decision to redo it was that it was a little work now. But if I kept my original plan, it would be much more difficult to change it later. Some time in the (very far, it seems) future when I’m flying, I can play around with this status set up and straight cabin static to see what, if any, the impact is.

Thanks again,
Sam

Covering update

I got a couple of nice notes from folks who follow my progress, and I realized I owe an update. Since I finished prepping the wings, I have turned to covering. I did have an EAA tech rep come look at things before covering but there is not too much to see at this point. But what there is to see, will soon be hidden.

Covering notes:
I chose to do the Stewarts Systems covering process – mostly because turquoise-colored glue matches most of my clothes. So far, no complaints about the process. A year or so ago, I did attend a weekend seminar at Marty’s (Marty57). This was VERY helpful. He encouraged us to make lots of mistakes (or rather not worry about mistakes) and then see which ones affected the outcome and which ones didn’t. Like the builder assist time in Brainerd, this was a great way to break the ice and gain some confidence with the process.

One thing we discussed was the order of covering. Most control surfaces have a top (visible side) and bottom (mostly hidden side). So you do these first and when it comes time to do the rudder (with both side visible), you have gotten better at the process. One thing I noticed in looking at the Piper drawings, the rudder drawing has more detail on how the finish tape is arranged than the elevators. I ended up guessing about right on how it should be done. However, it would have helped me a lot if I looked at the rudder drawing first!



My recent head scratcher was trying to figure out how to cover the ends of the flaps/ailerons. After talking with Robbie from AirTech at Oshkosh and looking at his plane, I decided to: 1) cap the ends with a piece of fabric, 2) overlap the main sheet onto the ends, 3) re-cap the end. I like how this turned out so far.



Misc: There are lots of Piper drawings showing covering. In addition, Steve Pierce has posted stitching diagrams I believe he got from Clyde Smith showing more current rib stitching for tail feathers (more stitches, as engines got more powerful). These have both been helpful.

Alaska Trip

One distraction from the project earlier this summer was a trip I made with my daughter to Talkeetna in June to get a seaplane rating at Alaska Floats and Skis. I feel like I know understand the draw of both flying on floats and flying in Alaska! As an aside, I can’t recommend Alaska Floats and Skis enough. It was a terrific experience all around.

I have done 7 complete cover jobs 5 Supercubs, 1 Javron PA-12 and a Kitfox. Did one Supercub in Stitts and I'll never use it again, I did the 12 in Superflite and the rest Airtech. I liked the Superflite and the green color made it easy to get the right amount of glue on everything. It didn't stick quite as well as Airtech and I hated the primer. I talked to Robbie about coloring the Airtech and he would like to do it but it would cost thousands of dollars to re certify it. I'm going to try some Rit Dye the next Airtech job I do. I've also done some Stuart and Ceconite and dope over the years. Airtech is by far the best system.

Thanks Sam! Never too many pictures of builds in progress (hint, wink).

Congrats on the seaplane rating! Used to take students on x-country flights to Talkeetna from Merrill Field, a lifetime ago. If you have not done skis yet you need to add that to the list also.

Wing cover prep - screw heads

I'm in the final throes of prepping the wings for cover. One small item I spent too much time on is covering the many screw heads prior to cover. Hopefully this will help someone else out (or at least provide some schadenfreude).

On the wing, there are a bunch of spots where screws are used (leading edge, false spar, reinforcing box, etc). There seem to be just as many different ways to cover these screws before or during the cover process (cover the leading edge in felt, extend rib tapes over the front/rear of wing to cover the screws, double cover or overlap the fabric over the screws). However, I found a number of screws that I wanted to cover without a long run of tape.

For the ribs and other protrusions, I'm using Howie's Hockey Stick tape. Its worked well so far. But knowing that there were a number of screws I wanted to cover, I thought there must be some sort of fabric tape circles I could buy online and save some time...no such luck. I did end up finding these masking tape circles that I thought would do the trick.



However, given that the masking tape does not stretch, it was near impossible to get it lay down smoothly. However, I wasn't quite sure if this was really going to be an issue after cover and paint. To check, I mocked up a piece of aluminum with some screws and covered and painted it. Sure enough, it doesn't look very good.



So, Plan B was next -- trying to cut circles into the fabric tape. I unrolled the tape onto some wax paper (or so I thought, apparently it was parchment paper...only the finest in our house apparently) and laid out circles with a quarter. Cutting was pretty easy with the scissors (better to try to make one long cut on each side for a smooth arc). Here's the layout and a comparison between the two. I've got a few circles to cut out now...

I do the double cover then you don't need all those tapes.

Wing bottom covering: Aileron pulley cove and aileron cable exits

I chose to cover the bottom of the wing first in order to be able to lay out the inspection rings and get the cable exits right before the wing is enclosed. I’ve been following a checklist based on Steve Pierce’s wing covering checklist and some other sources I’ve found. I’ll attach my final version once I’m done – it’s currently a work in progress.

Javron has a set of pieces available to handle the covering around the lift strut attach points. I ordered these and installed them as shown



Right before covering, I did some pre-work with fabric in this area to cover some of the gaps. I also added a small extension to the cove piece to fill the gap between it and the leading edge. Finally, I pre-covered the area before putting on the wing fabric.



Finally, here is a picture after the wing has been covered. I’ve still got a little clean-up to do, but I’m happy with how it turned out. I may put one overall reinforcing path here – but if I do, I’ll wait until after rib stitching because I believe that tapes will terminate at this point.



I also decided to locate the holes for the aileron cable exits after the first shrink. I think the experienced folks wait until everything is done to do this task but I wanted to make sure it all worked now. I also figured this wasn’t too much of an issue because this is how it works in the Stewart’s video.

Way back when I had put the wings on the plane and rigged the controls, one thing I did was to try to take good notes of where the cable exits were. I compared them to the Piper drawing and they were right on with one exception which I believe is due to the Javron design.



I located where the holes should be and made small holes in the fabric. I then temporarily hung the aileron and used string to check my work (I figured the string is narrower than the cable and I could open the hole for the cable and correct placement issues at the same time).



Once I was comfortable that the holes were in the right location, I routed both cables to the ailerons and created a little more clearance for the cables. I was trying to decide between the traditional leather patches to cover the cable exits and forming tunnels (as is shown in the Stewarts video) and ultimately decided on the traditional patches. The last thing I did was to reinforce the fabric around the holes to lock everything in place for the final shrinking.



I think I can leave the aileron cable tied up to the N-brace from here on in. Once everything is complete, I can fish it through the hole with help from the aileron pulley inspection plate.

So how long does it take to build one of these planes?

How many have you built before?

Here's an interesting data point. I began prepping the left wing for cover on 10/5/22. I finished covering that wing on 1/23/23. I began the right wing shortly thereafter and finished up yesterday (2/16/23). So, my first wing took me almost four months. The second wing took four weeks. The "work" hours are probably pretty similar between the two (aside from some testing I did the first time). Really the difference is time spent figuring things out. That time also came in smaller increments -- and lots of going away and coming back.

I've got room for the fuselage cover now...

Takes me about 800-1000hrs to build a Cub but I'm on #6 right now. It helps a lot if you have a wing and fuselage rotisserie. Just a lot of little and big jobs and then it is done.