Friday, May 25, 2012

Trojan T28 Rebuild

This is the account of my reconstruction of my crashed Airfield (FMS) Trojan T28.  I hope you have time, because, although the damage was not that great, this was big task as there was a lot to do.

Surprisingly the motor and mount are just fine.  With the impact and shattering of the prop hub, I thought sure that something here would have been severely damaged.

Humpty Dumpty of propellers
This is what I have to start with for the propeller and hub.  I was just going to order another hub, but it was hard to find one that I could get for a reasonable price from a place that had one on hand.  Nitro planes has them for only about $5, but they never seem to have any in stock.  Other sources have them, but they are twice the price and then shipping doubles this cost again.
All fit back together
So, I decided to try to repair mine.  I saw a post from another pilot who had the same issue and he mearly used Goop glue to put his back together and replace small pieces.  I thought if he could do this and be successful, I could do it too.  My prop blades are in great shape with no chips or gouges, so no issues there, just the hub.  I started the repair process by dry fitting all the pieces together to see
Other side
how they would fit together.  Once I was happy with how they fit together, I CA glued them to hold all of the pieces together.  I did this for each half.  I also test fit the two halves together to make sure that they would still mate up.

Epoxied together
Once I was happy with the two halves, I fill the void spaces with 5 minute epoxy.  I used a narow wooden stick to made sure that the epoxy got down into these voids and filled them to the top.

When the epoxy was almost dry, I used the tip of a small flat blade screw driver to scrape off any overage and trim everything down.

Now I was ready to fit the blades back into the repaired hub.  Although the hub was still a bit distorted, it fit back together better that it did originally.

This is what it looked like when I finally got it all back together.  I was a little worried about tightening down the screws as I thought it might break everything apart again, bit this was not to be the case.

Now on to the cowling.  There was only one broke off part but everything else had to be formed back together before this part would fit properly.  So, I fit the parts together as best as I could and CA glued them in place.  Then I secured everything with epoxy.  The tape in the photos served two purposes.  One was to hold things together and the other, to act as a glue dam.  I glued this from the inside so that it would not show on the outside.
Once the cracks were glued up and everything was close to aligned, I was able to glue back on the air scoop piece that was broken off.

Now it's all ready to go back on.

Before the cowling can go back on the mounts need to be repaired.  The cowling almost pulled out all three of its plastic mounting points.  The picture shows the worst one.  It will take some effort to repair to get these repaired.  I started with the top center mount and used a pair of needle nose pliers to jockey it around until it looked good with the cowling.  Then I used CA glue to hold it in place.  Then I did the same with the other two taking care to stuff any loose foam bits back in.  Once all three looked good and were secured with CA, I used hot glue to fill in the gaps and secure them even more.

Next, on to the tail sections.  Both the rudder and elevator movable surfaces were broken off and so they needed to be put back on.  Fortunately, there was no serious damage and the hinges were the only thing affected.  The rudder was easy and only needed the plastic spike hinges glued back in as they pulled straight out.  I used Goop as it gave me time to work and would not cause any serious issues if it got on the hinges.
 For the elevator surfaces I used these really cool paper hinges that I thought I would never use.  But, they were what I had and so decided to try them out.  They worked great and now I love them.  Check out my video and just see how easy they were to install.  All that is needed is a hobby knife, the hinges, and CA glue.

In this video I show the basic installation steps for these hinges.  I started with the movable surfaces. Since these used molded foam hinges, I had to start by trimming away all of the old hinge material.  This actually helped me in locating the hinge line and made for a good guide to follow.
This video shows more detail in how the hinges go together and how they are glued up.  The hinge material is made of a fiberus material that will wik the CA glue into the slot and make for a good bond.

You can see at the end of this video that even with the glue in the hinge material, they still move quite well.  I will be using these when ever I need a hinge where tape will not suffice.

Here is a photo of the ailerons fixed back up with the same paper hinges.  At first glance the wings looked fine but on closer inspection the aileron hinges on both sides were found to be badly cracked.  I just cut them the rest of the way off, trimmed the excess material, and repaired them just like the elevator.

Clevis repair
One of several repaired clevis
I had several clevises that broke.  At first I was going to just replace them but I had problems finding the right ones.  My LHS did not have a decent selection of them and online it was hard to tell for sure what size they had and if they would replace what I needed.  So, I decided to just repair what I had.  I started by trimming off the remains of the pin. Then I used a small drill bit to make a hole where the pin was.  Now all I had to do was to bend a trim a piece of paper clip to fit.  A small piece of fuel line is all that is needed to keep everything secure.  I have since found out that this is a common way of doing clevises.

Decal distorted by a fracture
Fracture can be seen here
 On to more fuselage damage.  This was not obvious for while, but there was a fracture across the fuselage above the back edge of the wing.  I noticed this because of the decal distortion (stretching).  Looking further revealed the fracture.  Since it wasn't that deep I repaired this by opening it up enough to squirt CA glue in and then close it down.  This seems to have done the job and it is holding well.

Front corner landing gear box damage
Another view of the damage
Doors and linkage broken free
What turned out to be the worst damage was the front landing gear.  The gear was broken, just flopping around, both doors were broken off, linkage was broken, and finally the landing gear box was cracked in the front and pushed back.

I started by removing all the broken parts and landing gear.
Fixing the box required using a needle nose pliers to pry on the bent surfaces until they fit back together.  I did this by inserting one jaw of the pliers down in between the plastic box and the foam.  The other side jaw was then inside the box.  I pushed them down until the tip was right at the bend.  I then pried back on the plastic until the pieces were back in alignment.  Then I used glue to hold everything in place.

Landing gear removed
Opened up showing
broken trungeon
 Now I needed to repair the broken landing gear.  This required the removal of the four small screws holding it all together.  This revealed the motor, electronics, and moving parts.  This gear works by moving a bar back and forth on a screw shaft rotating the gear itself.  The pawls on this pivoting part (trungeon?) were broken off.  Fortunately I had another one from the defective landing gear it originally came with.  I pulled this one apart and removed what I needed.
Part replaced and
ready to go back in
There was one issue with this and that was that the replacement piece was not intended for steering gear but for the shaft to be held in tight.  To resolve this I needed to drill out the strut hole so that it would pivot for steering.  This was easily done with my drill press and I carefully drilled out the plastic and brass to enlarge the hole.  Now I only needed to put all the pieces back together being careful to get all the pieces lined up and keep from pinching the wires.
Making sure the wires aren't pinched

You can see from these photos that it all went back together and now I have a functioning front steerable landing gear again.

Going back together
All back together
OK, the following video is a little lame, but what ever.  I was holding the camera and doing the servo tester at the same time.  Yeah, I could have used a tripod (I do have one), but I was in a hurry.  Any way, it still shows that the landing
gear works!

Pin replacements

Closer view
Next, on to the doors.  The obvious damage to both was that the servo horns were both broken off.  Fortunately one was still hanging on and I found the other.  These were glued back in place with a little CA glue.

Less obvious was the loss of the hinge pins on one end of each.  At first I did not know what to do.  I thought I was going to have to purchase new ones.  Then I got the idea, why don't is just make new ones?  I shaved the ends off flat and then drilled a hole where they used to be.  Then I carved down a piece of bamboo skewer and press fit them in.  These came out so nice I did not need to use any glue.

Covers installed
Now all was repaired and ready to go back together.  It took a little doing, but I got everything back in place.  Not easy to do with my fat fingers (not as dexterous as I used to be).

Ready for assembly
Everything is all fixed now and ready to be re-assembled.  The picture at the right shows all the repaired parts.
Please ignore all of the other stuff on the table

OK, was that enough for everybody?  I know it was for me!

Now I'm at that usual point of waiting for the right day and weather to go out and fly again.

Thanks for stopping by my blog.  Please feel free to post comments, good or bad, and be sure to come back and check for future posts.

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