My J-1T Build

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Aerowerx

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No pictures, just a quick update on my progress.

I have the cracked longeron repaired. At first I tried sloping some epoxy into the crack But I did not like the way it looked, and it did not lay flat on the table causing a kink in the side. Then I tried scarfing in a length of longeron stock, but didn't like that either. Besides, I was concerned about the left side (the damaged one) bending the same as the right side. So I ended up just ripping the whole longeron off and replacing the entire thing. Fortunately, I had cut an extra piece of longeron stock, so I didn't have to go through the entire process of power planing and ripping more.

So now I am back to where I was almost 2 weeks ago. Both sides are sitting upside down on the table, with temporary bulkheads in place. Looks nice. I'll try to get some pictures tomorrow, for all you build log addicts.

I have also come up with an easy to build, bolt together nose gear assembly. In order to get the correct amount of trail (steerable nose gear), I have to tilt it back about 15 degrees. Coincidentally, the bottom of the fuselage where the gear will be mounted is at a 15 degree angle to the horizontal. That will make things easier. When I beef up the floor in that area, the hole I have to drill for the gear will be at 90 degrees to the floor:)!

I also sat in the thing again, just to get an idea of the relative position of the engine controls, rudder pedals. etc. It looks like the pedals will be in about the same place as the nose gear bracing, which will make a good attachment point for the pedals---another happy face:)!
 

Aerowerx

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After a severe bout of Real Life the last couple of weeks, I was finally able to spend a bit of time in the Flugzeugfabrik.

Really didn't get much accomplished, though. Spent most of the time figuring out what to do next, and just looking things over. One thing I have been puzzling over is how to clamp the front end (with the inside skin) to remove the bow in the skin and the twist in the lower longeron.

I did, however, get the longeron patched:
001.jpg002.jpg
The picture on the left is the area that was scorched by the heat lamp. As stated previously, it will have plywood on 3 sides.

On the right is a divot caused by the router bit wandering out of the collet, as I was trimming the plywood. I had the guide roller running on the longeron, and as the bit worked its way out of the collet it went off the edge of the longeron. It is not as bad as it looks, however. Only 1/8 inch, or 3/16th at the most. This area will have plywood on 2 sides, plus it is right at the rear bulkhead so it will have plenty of bracing.

So what is that brown gunk, you are wondering? Instead of trying to cut and fit a plug I ground up some scrap Douglas Fir on the disc sander, and then mixed it with T-88 until it was like gooey peanut butter.
 

Aerowerx

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I was going to post this last night, but Time Warner had a major internet outage in this area.

In spite of not feeling too good yesterday, I did get a bit of time in.

Some of you may have seen the thread in the Composites forum on how to remove rubber thingys from fiberglass. A lot of good ideas, so I decided to try the simple ones first.

Using a razor saw would work, but would take a long time.

Next I tried this:
001.jpg
I trimmed off the rubber around the edges with a razor saw, and then used a harp chisel and mallet to remove the pad itself. Working carefully it only took about 10 minutes to remove the pad.
002.jpg
This method removed about 99% of the pad. The rest of it will require a bit more persuasion. Maybe some abrasion or grinding. The problem is that the rubber is, well, rubbery. Instead of grinding it flexes, although putting it in the freezer, if it fits, should help.

I am going to eventually need some rubber pads when I mount the gear. There are 3 more of these, so with practice I may be able to reuse them. I'll have to see.
 

Aerowerx

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The patched longeron, all cleaned up and ready to go:
001.jpg002.jpg
The excess epoxy was removed with the little handplane you can see in the background of the left picture.

Then, for practice, I removed this rubber pad from my landing gear spring:
003.jpg
All in one piece! But then I notice that split down the side. From the forensic evidence (how dirty the split is), my guess is that it was already there. After all, it is 30 years old with 62000 miles on it, and probably sitting in a scrap yard for 20 of those years.

When getting that pad off, I nicked the fiberglass:
004.jpg
I am holding one splinter with my thumb. This is actually not a problem, since I plan on cutting the thing off just to the left of this location. (One spring is too short, and two are too long.) I will just have to be careful when I do the other spring.

In the previous post I mentioned trying to reuse the rubber pads. I don't think the intact one, in the picture above, will be too useful, but these will be:
005.jpg
So I tried working around the edge of it with the chisel. It was hard to see what I was doing, so maybe I will have to trim the edges with the razor saw like I did previously, and then find another source for rubber pads. After all, I would rather destroy the rubber than the fiberglass!
 

Aerowerx

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I did some work on the temporary bulkheads.

006.jpg007.jpg008.jpg
I made a change to the ones in the empenage area, in the 2nd and 3rd picture. There are notches cut into the corners, so the longerons are supported in two directions.

I still have to do some trimming and alignment.

And these will all get covered with my anti-sticky tape, as I am going to leave them in until I get the real bulkheads in place and the outer skin on. They are made of MDF, so they will be easy to knock apart.

I still have some concern for the cockpit area, regarding how to eliminate the bow in the ply skin.

Remember these gussets?
009.jpg
I'm going to be removing them, as the temporary bulkheads do a much better job of keeping everything in place.

It also looks like it is time to do a general cleaning. Things are looking messy and there is a nice layer of sawdust on the floor. Maybe I should open a western style saloon?:)
 

Aerowerx

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I really haven't felt like doing much the last week or so. Better Half has been in the hospital with a bowel obstruction, complicated by pneumonia. Better now, by the way, and they have moved her to a rehab facility.

Anyway, last night, to give myself something else to think about, I tackled my "twisted longeron problem" with an idea that had popped into my head.

001.jpg002.jpg
What I did was remove the left side from the jig, lay it flat, and add those stiffener ribs.

They are epoxied only to the plywood. There is no epoxy between the stiffeners and the longerons. My reasoning is that I wanted the longerons to be able to bend as required while keeping the plywood straight.

95% success! Those light/dark areas in the right-hand picture are because of ripples in the plywood. The light areas correspond to the stiffener locations (IIRC without running out and looking again).

I am still going to add foam between the inner and outer ply, and think that should eliminate the ripple. Anything left I think I can live with.

I also would like to soak the sides to reduce the built-in stress, if I can come up with something big enough. I may just wrap them in a wet blanket and plastic sheet, and let it set for several days.
 

Aerowerx

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Haven't felt much like doing anything on the project, due to Real Life getting in the way. So I have to make myself do something, even if it is minor. This actually makes me feel a bit better about the world!:grin:

001.jpg
What is that mess, you asked? Well, I had put the plywood stiffening ribs on the second side. Then wrap them in a couple of blankets, poured a couple of buckets of water on them, and then wrapped everything in a sheet of plastic.

What a mess! I spent several minutes running around stopping the leaks from the edges of the plastic. Maybe I needed a bigger sheet of plastic, but building a plywood "bathtub" lined with plastic would have been better.

Anyway, I went ahead with this idea to see how well it worked.

To keep the water warm I used an old aquarium heater I had:
002.jpg
It is an under-gravel type heater with a heating cord about 15 feet long, and I ran it back and forth inside the wet blankets. It was able to keep the temperature at about 85 F degrees.
003.jpg

After a good 24 hours I took the contraption apart, getting water everywhere, including some on my good plywood (stored under the build table):mad2:!

This shows it back in the jig>
005.jpg006.jpg
I don't know yet if it made any difference, but it seemed to me that it went into the jig a lot easier than when it was dry. My idea is that the wood will take a set as it dries, thereby removing (or lessening anyway) the pent up stresses.

I then added these:
007.jpg
One problem I was having when it was dry was that the longeron with the compound curve was twisting itself, trying to relieve the stresses. Without actually measuring it, it looked better, but I added these clamps and paint cans anyway. This is the area where the twist was the worst. My idea is that, as the wood drys, these clamps will provide a counter-twist and the longerons will end up straight. Or straighter anyway. If there is any twist left I will have to straighten them out with a hand plane. The longerons are Douglas Fir, and I kept the original dimensions so it is essentially over built strength-wise. This gives me a bit of extra that can be planed off without affecting the strength significantly.
 

Aerowerx

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I thought I would give you a preview of upcoming events.

I have decided to scrap what I have done so far and start over, having learned a bit about making wood do what you want it to do. The results so far are not satisfactory.

What I am going to do is make some new temporary bulkheads, and also some new longerons. The longerons will be steam bent, which will hopefully prevent the twisting. They will be clamped to the temporary bulkheads until dry. The truss-type bulkheads in the rear fuselage will be installed along with the nose piece. I may also put in the main gear box---haven't decided yet.

Then the bottom outer skin will be installed. My idea would be to next remove the assembly from the jig, with the temporary bulkheads staying in the fuselage, and then installing the outer plywood skins. The reason for this is that I am concerned about keeping the epoxy in place on a vertical surface. By removing the fuselage from the jig I can lay it on its side.

All of this will help minimize the built in stress. The longerons will be steam bent, and there will be almost no stress in the plywood skins. The inside skin will be installed later.

The first step is to build a steam bending device, shown here under construction:
001.jpg
That is a total of 10 feet of 4 inch PVC pipe. The T in the middle is where the steam will be injected.

This is a steel bucket I picked up at a farm supply store for about $15. The fittings are just resting on the top in this picture, to get an idea of how it will go together.
002.jpg
It should be able to supply several hours of steam.

And the heat will be supplied by this:
003.jpg

I will have to build a stand to hold the PVC pipe along its entire length. After I had bought the pipe I was reading that I can expect it to soften at steam temperature, and I want to keep it from sagging.
 

Aerowerx

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Thought I would finish this off, in case anyone wonders what the status is.

Since I was having trouble getting the compound curve in the longerons, I decided to start over. And this time I decided to build a ragwing.

So this thread is closed for now, and I will be starting a new thread.
 

Aerowerx

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Suprize everyone! I'm back. Back on my J-1T project, that is.

I've been doing some soul-searching, and my decision to abandon the project was made during a fit of despair and discouragement. Never a good time to make a decision.

So I have started it up again. I have also done some thinking as to what I was doing wrong.

Today I made a fuselage jig:
044.jpg

The fuselage shape is defined by 4 points.

The nose...
045.jpg

The two main bulkheads...
046.jpg

And the tail...
047.jpg

Theoretically it should be necessary to clamp the longerons at only the nose and tail, and they would then form a "natural" curve.

Here I am trying length of douglas fir just to see how it looks. This is not a real longeron, but something I had cut for the RW-4 project.
048.jpg

The nest task is to finish the steam box, as described two posts ago.
 

Aerowerx

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Here is my steam bender sub-project. Almost done! Just checking to see if I got the stand at the right height to match the bucket on the grill. Looks good:)

001.jpg002.jpg

I still need to drill some drain holes on the bottom, to drain off the condensation. Also there is supposed to be some carriage bolts horizontally through the pipe, to support the longerons.

Can't remember where I stashed the hardware for safe keeping! I'll have to look for it.

The open end will be stuffed with rags when in operation. This is only about 10 feet long, but only the front half of the longerons need to be bent, so it will be OK. About 1/3rd will be sticking out.

And, yes, when I "fire it up" it will be farther away from the garage and vehicle. Perhaps even out on the grass.
 

Aerowerx

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Today was a "live fire" excercise---of my steam bender. Found a number of things that need improvement.

First, I dry fit of a length of Douglas Fir.
001.jpg

It is barely noticeable in this picture, but there is a twist of about 4 degrees.
002.jpg
This is not a real longeron, but a piece I had cut for the Ragwing. It is not square like the longerons, which may affect the amount of twist.

I put a couple of gallons of water in the bucket. Turns out that the bucket leaks. The label does say "dry food storage", so I guess it was my fault for not paying attention. So I soft soldered the seams with some lead-free solder using a propane torch.
003.jpg
Galvanized sheet steel takes solder quite well, by the way, even though the steel itself will not. I also used the lead-free solder because it has a higher melting point than tin-lead solder, and I was concerned that it would melt when in use (turns out it was OK).

Please ignore the scorch marks on the build table.:ermm:

Ok, I'll confess. I had the bucket sitting on the edge of the table and was concentrating on getting a good flow of the solder as I turned the bucket. Turns out that the bucket was sliding inward as I turned it. Well, you can see what happened.

If you are going to solder galvanized, do it in a well ventilated area. As I understand it, the galvanizing can give off some nasty fumes when heated.

And here it is, in action
004.jpg005.jpg
Sorry for the fuzziness. I guess my smartphone doesn't like taking pictures in bright sunlight. Or maybe some setting is wrong (still haven't figured the thing out completely).

Here is one of the problems
006.jpg
A leak at the flange junction.

One of the problems is that I think the pipe is too long, and maybe too small. I can eliminate the leak by putting a 2 inch PVC pipe directly up to the galvanized L at the top of the bucket. I also need to find some way to insulate the bucket, and the whole assembly for that matter.

Another thing is that it took 2 hours to get hot enough to boil. Next time I think I will start out with hot water.

After it started boiling, it took an hour before the heat became significant in the steam bender itself, by measuring the surface temperature with an IR thermometer. At the center junction it was about 150 degrees, about 110 at the closed end and 95 degrees at the open end (stuffed with rags.

Either I need to run it for most of the day, or make it more efficient.

I took the wood out and shut the system down after boiling for about 1.5 hours. That was all the time I had for the day, as I had promised Better Half that we would go out to eat. The wood was wet, but not steamed. I put it in the jig anyway.

I was beginning to think that maybe steam bending wasn't needed as the test piece, but then when we got home I went out too look at things, and noticed something didn't look right...
007.jpg
The nose looked way to pointy, so I checked it against the plans. It turns out that the bottom longeron does not form a "natural curve" between the front bulkhead and the nose, but instead curves more sharply near the nose, with the maximum cockpit depth being about 10 inches in front of the bulkhead. That means the curve is defined at more than the 4 points I mentioned in a previous post.

I will have to make 1 or 2 more jig blocks, and steaming will certainly be needed.
 

Aerowerx

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I added 3 more jig blocks to the fuselage jig.

They are #2, 3, and 4 in this picture.
001.jpg

I think this will be sufficient, but that decision will have to wait until I secure the blocks to the table. When I try to clamp and bend the test longeron the blocks move out of position. Then I can measure everything and see how it matches with the plans.

I will also have to redo #4, as it got messed up. Even though it wasn't very hot here today, it was a typical Ohio August day----very high humidity. Someone forgot to tell the weather that it ain't August! I was getting hot and couldn't think anymore. Time to stop before I really screw things up.

It does appear that steam bending is going to be needed.

[Edit] do to my fuzzy thinking at this time, somehow this extra picture got attached>>>>
 

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Aerowerx

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Update
It cooled off as the sun went down, but still quite sticky. 90% humidity.

I replaced jig block #4. Every thing looks good except I found that jig block #5 is too short. I goofed I guess.

I don't think I have another piece of MDF that is big enough, but I can put some shims under it to bring it up to the correct height.

It takes quite a bit of force to bend the first 200 mm of the longeron, and the test piece I am using is undersized so the full 20x20mm will be even worse.

Steam bending will definitely be needed.

Next step is to make some improvements to the steam bender.
 

Aerowerx

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I didn't get a picture of it, but today I put a shim under jig block #5, so it is now the proper height. This is where the main bulkhead will be, which is also the front spar carry-through.

I then put some nails in to keep the jig blocks from moving....
003.jpg
They go through the MDF and into a 2x4 block on the other side.

Things are now looking pretty good.
001.jpg004.jpg

Except right at the nose, everything fits smoothly into the notches in the jig blocks. Maximum twist is about 6 degrees, in the center of the picture on the right.

Right at the nose, it takes quite a bit of force to get it to fit.

Tomorrow is my last day of vacation, and I will be heading back to work Tuesday. So I will not have as much time to put into the project. Because of this I was thinking of just soaking the longerons instead of steam bending. This would certainly save on propane, and I could leave it set and not have to keep an eye on it. It may take a couple of weeks of soaking, though. I am going to do a bit of research to see what the difference between cold soak and steam bending would be.
 

Aerowerx

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A quick update from my research...

The critical area is on the inside (compression) of the bend.

Steam bending is the preferred method. This has the lowest failure rate and least damage to the wood. The wood has to be completely soaked and at a preferred temperature of about 200 degrees Fahrenheit. For best results it should be a "wet" steam, essentially a 212 degree fog. Dry steam is not as good. One way to do this is to have some distance between the steam generator and the steam box, to allow the steam to condense slightly. Once the steam is being generated, it shouldn't take even an hour to get the wood soft enough.

Cold soaking will work but not as well.

It is possible to bend wood using just heat. This is what a lot of luthiers use, but they mainly bend thin pieces, like the sides of a guitar.

Another possibility is cold soaking followed by the use of a heat gun as the wood is being bent.
 
Last edited:

Aerowerx

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I had forgot that there are some half-length longerons on the bottom of the cockpit area, so I took the jig apart and cut these notches
010.jpg

That is the "test longeron", to see how everything fits. I don't know if you can see it in the picture, but there is something going on with jig block #5. The slots don't appear to be lined up properly, which causes the longeron to swerve. I will have to check that out. Right now I am too tired to think about it.

I had left the test longeron clamped in the corners of the jig blocks, for almost weeks now. When I removed it, I noticed it had (somewhat) conformed to the desired curve...
009.jpg
...in both directions!

So it is not going to take much steam bending to get it right.
 

Aerowerx

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After taking a bunch of measurements on the jig blocks, I found the problem:
003.jpg
This is jig block #5, where I thought the problem was. The smaller darker mark is my orginal witness mark for the center line. The longer mark is where I measured it again. There is a 5 mm difference. The error probably came when I measured the width, and then divided by 2 in my head. I find this disturbing. 40 years ago I used to add a column of 4 digit numbers in my head. Not any more! I think this comes from my brain rotting at my present place of employment.

Here is a before and after picture:
002.jpg004.jpg
"before" is on the left, and "after" on the right.
 

Aerowerx

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Today I did some improvements to my wood steamer.


001.jpg002.jpg
This is a manifold made from 3/4 inch schedule 40 PVC. There are 1/4 inch holes drilled every 8 inches. The idea is that it will distribute the steam more evenly.

I had bought this 45 degree elbow, thinking that the manifold would rest on the bottom of large tube.
003.jpg

Turns out the geometry was wrong and it would not fit. I had modified that 3/4 threaded to 2 inch adapter to allow a 3/4 inch pipe to be glued into the "back side", which was then supposed to go into the elbow.
004.jpg

Fortunately, I had a bunch of PVC fittings left over from my "tropical fish tank fiasco", and was able to kluge up a "plumbers nightmare". I didn't get a picture of it, but everything fits together now.
005.jpg


The manifold rests inside the 4 inch pipe like this, just below the bolts
006.jpg

I was afraid that the manifold would block the holes for the bolts that support the wood. It turns out that there is enough flex in the 3/4 inch that this is not a problem.
 

Aerowerx

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I have a long weekend because of the Columbus Day holiday, so today I set up for cutting some longeron stock:
013.jpg014.jpg015.jpg
The yellow thing is a plastic finger board. It is supposed to keep the wood down tight against the saw table, and also prevent kickback, although I have never had a problem with that (except when working with small pieces).

Everything lookede good, except the first piece I cut looked too wide. I measured it at about 25 mm. Hmmm, must of goofed. I thought I measured everything correctly. Put it aside and trim it down later.

So set the rip fence up again. The second piece:
016.jpg
OOPS! What's going on here? That is not a camera illusion. The longeron is getting wider. Now I am really concerned, as I figured I had just enough to get what I needed (I do have another board I can mill down if needed, but I was saving it for the wings and tail).

Then I realized the problem. The finger board was causing more problems than it was fixing. Because of the tension of the finger board, I had to put enough force on the wood to feed it, that it was pushing the rip fence out of place!

So off with the finger board! Reset the rip fence.

After recutting the crooked pieces I had just enough to get the 5 longerons I need. One of them will be cut in two to get the two half-length longerons for the cockpit bottom.
017.jpg

And here I am checking the fit of one of the top longerons.
018.jpg019.jpg
The fuselage jig is upside down at this stage of construction, so the top longeron is against the table
 
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