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Those trees are closer than they look!
By Michael Payette
3/5/2006 3:28:01 PM
Three Mustang PTSs went out that day… Only two came back.
If you’ve been to the Renegade field you might have overlooked the average, inconspicuous trees lining the North end of the field – Some say guarding the North end of the field.
You see, legend has it that when the wind is from the South these trees stand poised, ready to ensnare unsuspecting pilots who venture too close during final approach. Their movements seem natural enough with their branches swaying in the wind, but if you look closely, something’s just not right about the way they move… Ever wonder why the shortest tree is conveniently positioned for perfect line-up and approach to the runway? Almost an invitation to thread the needle between its two neighbors…
Well, this is a story about one P-51 PTS that flew too close.
What follows is not for the weak. In addition to the PTS carnage there are pictures of a newbie doing his first plane repair.
The damage was minor, considering what happened. The plane managed to pull free from the tree’s clutches but was swatted to the pavement during escape. Thanks to Foofinator for helping me pick up the pieces. Unfortunately, I don’t have a picture of the wreckage on the ground. Another newbie mistake.
 Post Mortem:
1. Firewall pulled loose, spinner bent, prop broken.
2. Wing torn off, shearing the nylon bolts and breaking the wooden frame they attach to. Wing was mostly undamaged. Both droops broken, which probably saved the wing.
3. Fuse support structure cracked and broken in several places.
4. Servo tray broken loose.
5. Ultra-cote torn on both sides of the fuse.
6. Wing dowel broken (not the main spar, just the dowel that holds the wing to the fuse).
7. Exhaust pipes pulled loose.
8. Miscellaneous abrasions here and there – all minor.
  (Left)The middle of the plane was broken when the wing was torn off.
(Right)More of the internal damage.
Firewall pulled out and spinner bent. Better view of the debris (Pictured to the right).
 I could just buy a new fuse for under $100, pay someone to repair it (probably more than $100) or try to learn to repair it myself. This is a skill I will need to develop so why not start here…
I began by removing the broken or loose wood pieces from inside the fuse. Like G-Pete and Foofinator told me – It’s just like putting pieces of a puzzle together.
Below is a pic with most of the damaged parts removed. Ever wonder what it looks like deep inside the fuse of the PTS?
 Most pieces were in reasonable shape, some needed a little repair. The broken pieces need to be fixed before trying to put them back in the plane. To do this, test fit them back together to ensure a good fit. Next use thick CA and hold the parts together until the CA cures (10-20 seconds). You can use thin CA but it isn’t very forgiving if you don’t fit the pieces together perfectly in a couple of seconds.
Once the puzzle pieces are usable again, it’s time to begin the repair on the fuse itself.
Make repairs from the inside out. In other words, don’t glue something together if it covers up a broken area that still needs to be repaired. Not only will it be harder to repair the underlying damage, it may also keep you from moving the parts around to make them fit back together. When a plane crashes, it is bent and twisted out of shape. You may have to bend and twist the parts a little to make them pop back into place.
 I had to peel back the coating over the damaged area of the fuse. I hoped this wouldn’t be necessary but it seemed that the tension of the coating was keeping the wood from lining back up and popping into place. After removing the coating the fuse pieces fit together nicely.
Next, I began to repair the support structure. CA and Popsicle sticks go a long way…
   
 The shell of the plane was shaping up nicely. Time to start putting the removed pieces back in. Once again, thick and thin CA was used to attach and strengthen the wooden parts.
 The firewall was next. It popped back into place with a little help. This was secured with a little CA. I used CA along the entire perimeter of the firewall both inside and out. The thin CA seems to penetrate the wood better, working it’s way between parts to be repaired and making the wood stronger as it goes. The thick CA was good for further strengthening and gap filling. Next, I used a tip from G-Pete, which he shared with me at the Lone Star RC plane repair clinic. By drilling small (1/16th, or so) holes around the perimeter of the firewall, going through the fuse and into the firewall about ½ inch, you can CA in toothpicks for added firewall strength. Cut the toothpicks off flush with the fuse. The cowl will cover this area.
Firewall repair ala G-Pete:
 While we’re looking at the firewall, here’s a lesson I learned about fuel proofing. The PTS comes with the firewall still needing to be fuel proofed. When I first got the plane I removed the cowl and brushed polyurethane on the exposed portions of the firewall. As it turns out, this isn’t enough. In this pic you will see signs of damage to the firewall in the area that was covered by the engine mount. It’s still pretty minor but would have gotten worse over time. While the engine mount was off I finished fuel proofing this area. You have to remove the engine mount to fuel proof this plane’s firewall… (another newbie lesson learned).
 Well, the plane is nearly finished. It’s time to do the coating. I dreaded this part. All the work I’ve done so far will be hidden away inside the plane. The coating has to look good…
 First, I sanded any rough edges where the exterior of the plane was repaired. Use a sanding block. CA-repaired wood is harder than wood without CA on it. Plywood is harder than balsa. Without a sanding block, you will wear away at the softer wood making the repairs stick out even more.
Next, Gulp, the Ultra-cote… I picked up an iron and boot at Plano RC and was ready to do battle.
Lou, G-Pete, Hector, and others gave me lots of advice here. I can’t put it off any longer.
 I decided to patch the old coating instead of re-coating the entire side of the plane (both sides, actually). I pulled the coating back into place and began to “iron” it down, moving from where the coating was still attached down over the damaged area. Watch out for wrinkles here. Keep the coating tight in all directions and work your way down to the edge of the coating. In my case, it was the original tear across the side of the fuse.
I was surprised how easily this stuff went back on. If I wrinkled it too much, I could just pull the wrinkle out and continue on. Within a minute or two the first part of the repair was done. Now on to the other side of the tear.
 When the two sides of the torn area were ironed back into place, I used a strip of Ultra-cote to cover the tear itself. Actually, I used the strips of coating that came with the PTS.
When this was done I used a heat gun to shrink the coating a little and it was done. Ultra-cote is great! Here’s a before/after shot of one side.
  The other side came out a little better.
Last repair to make was the wing dowel. A little 5/16th wooden dowel and 5-minute epoxy worked just fine.
After that, it was just a matter of re-mounting the engine, cowl, prop, and spinner.
That’s about it for the repair.
 Oh yea… Root cause of the crash turned out to be pilot error. As shipped, the PTS has NO PILOT in the cockpit! While the canopy was off I corrected this. I re-attached the canopy with J&Z Super Z RC-56 glue. It dries clear and flexible (and seems a lot like what was there from the factory).
Here are some pics of the final result. A few hours (maybe 15) and about $10-$15 for supplies (prop and spinner the biggest expense) and she’s ready to fly. Many thanks to Scott R. for taking her up for me after the repair. I was a little gun shy not knowing how stable it would be after I did so much to it. It also was the fist flight without the droops. Scott was flying his own plane that day, it was getting late, and he took time away from his plane to help me out. It is greatly appreciated.
   
That’s how a newbie repairs a plane. I’m sure lots of mistakes were made, but that’s the best way to learn. I suspect I’ll have more chance to practice soon :-)
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Last Updated by: Michael Payette
3/6/2006 12:40:51 AM
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