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Old 09-01-2019, 10:21 AM
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Pulse 125 - Crash rebuild, and upgrades

Howdy folks, and welcome to this repair thread. Within I'll show the recent crash damage to old faithful, my Hangar 9 Pulse 125. This airplane is (over)powered by an RCGF 32.

I last flew it in July. After several circuits I did a low and slow pass and when I added power at the end to pull up, then engine bogged and would not throttle up. Without the altitude or airspeed to get back to the runway I set it down in the tall grass 100m or so from the end of the field. It must have hit something solid because...





I was thinking this was going to be a winter project but I started fiddling with the airframe soon after.

This thread will cover:
  • airframe repair
  • firewall replacement
  • cowl lengthening
  • battery upgrade
  • gas tank upgrade
  • new power switch and fuel dot
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Old 09-01-2019, 10:31 AM
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The first job was to get everything apart. Here's a lot of it on the bench.






Next was to look at the broken pieces to see how they fit back together.




Fuselage glued back together...








Broken sections were reinforced above and below.

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Old 09-01-2019, 11:16 AM
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A little history on the airplane, especially the firewall. This was my first gas airplane and my first ARF (I learned on an RTF glow trainer). I had some failed attempts at mounting the first engine, a DLE 20. So I plugged the holes with dowels until I got it right.




I upgraded to the RCGF 32 after a year for some extra power. It's a longer engine, however, and to fit it into the cowl required a large hole in the firewall for the carb and the lines.



After the crash it was pretty clear that the firewall needed replacement.




How to remove it? A razor blade and tack hammer ought to do the job, right?




Well, three or four razor blades. But eventually it was off.



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Old 09-01-2019, 01:25 PM
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Hangar 9 has the new Tiger 30cc coming out pretty soon. Perfect for your 32cc. Playing devil's advocate here. Actually I'm glad to see a new build/repair thread from you
Mr. Grosbeak. This looks like a much easier fix than a plane that broke just about the same place on me last spring. The plywood just shattered and there isn't much left to piece back together. Good luck.
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Old 09-01-2019, 08:34 PM
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The old firewall served as a good template for the new one, cut from good quality plywood.






Now for the dilemma - use the same standoffs and cut the firewall, or adapt the airframe to fit with longer standoffs?




In the end I chose to lengthen the cowl. A little over an inch was needed for the engine to fit properly. I was going to extend it with balsa but I found something better at my LHS... 1/64" plywood.

After cutting a strip a little water and a clamp helped put a bend in it.




I attached the strip to the inside of the cowl with clothes pins and dribbled thin CA to wick between them.




The next step was an outer strip, attached to the inner one aft of the cowl.

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Old 09-01-2019, 08:37 PM
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Quote:
Originally Posted by Texastbird View Post
Hangar 9 has the new Tiger 30cc coming out pretty soon. Perfect for your 32cc. Playing devil's advocate here. Actually I'm glad to see a new build/repair thread from you
Mr. Grosbeak. This looks like a much easier fix than a plane that broke just about the same place on me last spring. The plywood just shattered and there isn't much left to piece back together. Good luck.

Good to hear from you, and thanks for the suggestion.


I was lucky with this repair in that the fuel tubing and wiring kept the pieces together.
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Old 09-01-2019, 08:48 PM
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Next, fiberglass for the inside to tie it all together and give it strength.






After a test fit it got a coating of epoxy on the outside of the wood.






The epoxy was sanded back to give the covering something to grip.



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Old 09-01-2019, 09:01 PM
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Back to the firewall... I usually eyeball the location of the holes for the fuel line and the throttle linkage; this time I created pins to mark more accurately.

In the foreground by the red arrow is the fuel line marker. The throttle marker is in the background, out of focus.




Marking the fuel line...




And the throttle.




A larger hole was needed for the spark plug wire. The hall sensor wire and carb equalization line will pass through here also. Once all the holes were drilled it was time to fuelproof the firewall - I like to use Helmsman Spar Urethane.




The fuselage sides contain blind nuts for attaching the cowl. Some pointed bolts and recessed holes in the side of the firewall made a good way to mount the firewall temporarily as needed.





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Old 09-01-2019, 09:19 PM
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I think he's a little concerned. Everyone's a critic...




Onwards...

Not a lot of pictures of the new battery and fuel tank setups... for the battery I replaced the aging NiMHs for the receiver and the ignition with a single A123 and a Tech-Aero Ultra IBEC.

For the fuel tank I tossed the stock unit with bent brass tubing and soldered barbs and used my favourite combination of a Fiji water bottle (330 mL in this case) with a 3-line setup, like this:




The original switch and fuel dot combination broke in the crash. Since I only needed one switch (one battery) I went with this one:




A backing plate was needed. I keep disassembled orange crates for just such occasions.




Here's the fuel dot, also with a backing plate:





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Old 09-01-2019, 09:41 PM
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Space is at a premium in the front of the fuselage so it was helpful to have the firewall out of the way. When the time came for attachment I applied some of my favourite PVA glue and clamped it to cure.




Next step was to pin the firewall. Because it's fairly thin I used bamboo skewers, and this is my favourite method...

Drill the hole



Fill with PVA glue



Insert skewer



Trim the skewer



Tap the skewer in with a small hammer; it will peen a bit



When the skewer bottoms out, the end will bend over and split



Clip off the excess



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Old 09-01-2019, 09:44 PM
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After setting the CG, the last step was to repair the covering. It's getting pretty tired but it's 50/50 perfect - 50 feet away going 50 mph. :P

And we're done!








re-maiden coming soon.
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Old 09-02-2019, 04:08 PM
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Looks great from here!
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Old 09-04-2019, 03:13 PM
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Quote:
Originally Posted by Texastbird View Post
Looks great from here!

Thanks man!
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