Tuesday, September 16, 2014

Trojan T28 Repair, Flap Servo

So, what do you do when you have a flap servo go out in your Airfield/FMS T28?  This is not a regular servo but the slow rate servo.

Well, if you're a normal person, you find a source for this special servo and order/buy another one.  But, if you're a cheap Dutchman like me, you fix it!

This video shows the failed servo.  When I first tried to move it, it was locked completely and did not move.  By the time I made this video, it freed up and appeared to be working OK, but I think you can see (even with the bad focus) that was not working smooth and was catching.

One good thing this video shows, is that the servo circuitry should still be fine.  It just needs new gears.

Here is the server just after popping it loose from the wing.

Here is  the servo with most of the glue removed and sitting next to the tiny Phillips screw driver tip that was needed for the tiny screws (better get your glasses prescription up to date).

You may be asking by now "How are you going to fix this broken servo?"  Well, it just so happens that I have the burned up servo from my front gear door repair, and this servo looks exactly the same (see the photo below).  If you read my blog post on this, you know that the a jamb caused the burned up the motor and/or circuitry.  Now this "donor" servo does not have the slow circuitry, but that's not what I need.  I just need the gears, and they should still be fine.  The broken flap servo should only need a gear or two replaced, as the circuitry is fine.

This below, photo shows the start of the tear down of both servos.

This photo shows the broken gears removed and set aside (on the right in the middle) and the gears from the donor servo (left) already removed and installed in their place.

There was one difference between the two and that was that the case screws from the original were slightly shorter that the donor screws.  The donor screws also had longer threads for a more secure bite.

Since a test fit showed that the longer screws worked just fine, I decided to use them in the repaired servo.

Below is a video of the assembled servo showing that it is now working just fine.  There's that focus problem again!

In this case, this repair saved me about $15 and shipping for a replacement servo.  Some times it pays to be a cheap Dutchman keep all of your old broken crap that most people would just through away.

Ya, another one down.  Still more to go.

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Tuesday, September 9, 2014

Trojan T28 Repair, Nose Gear Repair

From my last post you know that I have several repairs to complete on my Airfield/FMS Trojan T-28.  In this post I'll update you on how I repaired the nose gear strut.

The strut had a compound bend mostly back and to the side.  I have no idea how it bent this much without any damage to the plastic parts or the servo.

Any way, this is how it looked:

A big concern of mine was "how am I going to bend this back without breaking the thing?"  It really looks like any pressure on this thing is going to shatter any and all of that plastic.

My first thought was to use a bench vise and smash the thing straight again.  The big problem with that is that this method does not always come out completely straight and, worst of all, it most likely would leave lots of marks that would prevent free movement.

What else to do?  I thought about using a large pair of pliers or vice grips, but they tend to become unwieldy and would also most likely leave marks as well.

Needing some help, I browsed some forums for advice.  I did find one post that reported the same repair to their T-28 gear and they did use a vise, but only as a support to pry against.  They also mentioned that you could put a considerable amount of force on the plastic covered part without it breaking.  This sounded pretty good, but my vice isn't mounted down well enough to pry against (just sits on my bench).  So what next?

I was at work and thinking about where I might find something that I could insert the gear into that was sturdy and I could pry against.  This wasn't exactly what I was thinking of, but it's what I found.
I used my Excelite driver handle.  It worked great!  What I did was to hold the gear in my left hand and the Excelite screw driver handle in my right hand.  Then I used by thumbs to lever against the bent section.  Sorry but I did not get any photos or video of the process.  It did take some time as I took it slow, not wanting to over bend it or put too much force on the plastic.  I started with correcting one direction and got that straight and then worked on the other direction until it looked straight from both sides.

Soon, I had something that looked like this:

This was enough and it slipped right back into the trunnion of the gear servo without any issues.

After this I realized that I could have used any sort of pipe or tubing that was sturdy and long enough.  This sure seemed a lot better than using a couple of pliers.

So, with this resolved, I just had to take the landing gear servo apart and put it all back together with the strut back in place.

One down and how many to go?

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Trojan T28 Repair, Again

Well, the last time I took out my wonderful Airfield/FMS Trojan T-28, I was experimenting with the flaps and coming in for slow passes.  I was having a log of fun with this.  Until I came in low and hit that point where it tip stalled and did the left roll thing down into the ground.  Everything after that was pretty much a blur.  The air frame survived without much more than scratches, but a lot of little things suffered.  Needless to say I now have a bunch of repairs to do.

So now here is my list of my needed repairs:
The nose gear strut has a nasty compound bend.
  It's not real clear from this photo but the bend is mostly back and also to the side.

The nose gear door broke the horn.
I've tried gluing this part several times and with different glues and have yet to find a good solution.  I've tried super glue, epoxy, and model glue.  Nothing holds very well and eventually breaks loose.

The right wing gear came loose.
It was only loose, but I decided to take it out completely to make sure it gets secured in good.

The left wing flap servo is jammed.
This is a view of the servo after being removed.

This video shows how the servo is sort of functioning, but you can hear is clicking as the gears skip.  Sorry for the blurry image.  If it was clear you could see the current and voltage readings on the meters.

The motor mount/firewall is loose.
You can see from this video that something is loose and in multiple directions.

There are also several misc repairs such as a loose cowl exhaust flap.
The flap here isn't broken, but it is loose and a little floppy.

Well now you know what I'll be doing for the next few (or many) blog post.

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.