broken F1A tailboom

[OLIVER CAI]

Hello,

I just broke an F1A tailboom on a M&K model for the first time today during practice. The boom is broken at one place a couple inches behind the pod/boom joint so I am looking towards replacing the entire boom and keeping the pod. I am trying to salvage as many parts as possible. Does anyone have any advice on replacing the entire boom section?

Thanks in advance,

Oliver

[gos]

Do you really need to replace it?
How about soft balsa jammed into it over a few inches and cyano it all together, making sure it was all lined up. Just a thought, as I did that years ago on a ‘glass boom on a PINK ELEPHANT that’s still here.

[OLIVER CAI]

Thanks for your suggestion. However, I don’t think balsa will be strong enough to handle the hard launches of a bunting F1A. The M&K booms are wrapped alum-carbon-alum. The broken joint is only several inches behind the kevlar wrap of the pod/boom joint so it is a very critical area for withstanding launch forces. Several lines also run inside the boom so it must be hollow inside throughout. I was thinking of taking a slightly larger diameter carbon tube and wrapping it around the broken portion, put some hot stuff or epoxy, then wrapping it with kevlar but from what I have seen these fixes don’t last very long.

I am wondering if it is possible to soften the epoxy via heat at the pod/boom joint to remove the boom section. Then purchase a new boom and attach to the old pod.

[Anonymous]

Yes, I believe you should be able to heat the epoxy and work the old boom off. But first, re-align, as best as possible your broken pieces back together and take as many measurements as possible……rudder/fin position, stab mount, overall length….you get the picture. And if the heat doesn’t do the trick, you’re going to have to sand it off. It’s a dirty job, but will ultimately give you what you need. Good luck and many thermals to you. insptrjf

[nffs-admin]

Oliver,
sorry to hear you broke the tail boom. The answer is yes on getting the epoxy to soften up. While I have not replaced the F1A tailbooms I have done far too many F1B tailbooms. Try using a soldering iron/pen. take your time and move it slowly. It will heat up the epoxy enough to remove everything.

While Kyle has broken several F1A tailbooms, they were always the mechanical ones. I am ashamed to say I never took the time to learn how to repair with the amount of lines and tension that is required on these models. The electronic models I understand are much easier to repair since there was only 2 lines. I believe Jim Parker wrote in the SCAT or maybe even in this forum how to do it.

Good luck.

[OLIVER CAI]

Thanks insptrjf and Charlie! Hopefully I can get this done soon. Unfortunately I won’t be able to make it to Patterson this year due to SAT studies but school is always important.

[Anonymous]

Sorry I’ve not checked in for awhile- here’s the instructions I provided to Oliver to replace F1A tail booms. JIM

Best to replace a gold boom with a gold boom and a silver with a silver boom.

Different size boom can be used, it is more work. A gold boom is slightly smaller than the older silver boom. Replacing a gold (small) to an old silver (larger) is difficult . This requires reducing the Fuselage stub size by slicing and heating, reforming and over wrap– I’ve done it once but now I keep spare silver booms– available from Vasily via Don Zink. Replacing a silver large boom to a new gold smaller boom is easiler but you need to wrap the fuselage stub with epoxy wetted fiberglass to fill the gap– this makes alignment more difficult.

Dremal cutoff wheel just aft of the fuselage stub, cut off any kevlar wrap– then strips of the boom will peel off. Measure and note your rudder to stab mount and stab mount to bunt roller distances. You can use heat to soften the epoxy but I find once the boom is cut off near these pieces, the boom will peel away. Sand- knife the epoxy from the pieces.

Clean the old epoxy from the fuselage stub, you can sand a small amount of the fuselage but not much– this is a critical area and sanding at the transition area between the fuselage outside shape and the stub will weakien it– I’ve seen several broken fuselages because of this. You can sand the fuselage stub outer fiberglass layer but do not go much into the CF. I also sand the inside end of the fuselage stub to a thin-sharp edge, This reduces the stress concentration at the transition and also helps later when stringing the lines.

Start with fittingg the Stab mount first. The stab mount can be ground out some if needed to slide more to the wide end. Measure the fuselage diameter, add 2x the boom thickness. Set your caliper to that dimension. Slide cliper on the boom to see were the fuselage to boom diameters are equal. You need to work the the fits between the stab fit and the boom- fuselage. If your are fiting an M&K Gold boom with a new gold boom, the fit of the this pieces will be easy–the stab piece will natural fit to the correct spot. Use a diffent size boom will require a lot of fit adjustments to get the boom fuse – stab mount – bunt ftgs to fit properly. DO NOT force the boom onto the fuselage stub– it is easy to split the boom.

When you think you have the lengths figured out, cut the boom with a dremal cut-odd wheel– leave an extra 1 inch on the first cut– check fit, cut off in 1/4 section– can’t make the boom longer!. As mentioned above, a gap between the boom and fuselage can be filled with wet fiberglass wrap during the bonding process so its better to be a bit larger than smaller. Also be sure to roughen up the inside of the alum tube (make a 1’2 dowel sanding tool- 220 grit). Also measure and note the length of the fuselage “stub” . Use a good epoxy– not 5 minute– #3M DP is best– Hobby Poxy long cure will work if you can not get the 3M DP. I’ve tried alignement fitures but find my eye ball works just as well– get the boom straight and set in a place to cure. After the fuselage to tube joint is cured and cleaned up, wrap the end of the boom at the fuselage two places, one at the very end of the boom and the second at the end of the fuselage stub. Use kevlar tow .2 inch wide (not tread or towline), let me know if you need some. Use a dab od CA to secure the ends but use thin epoxy rubbed into the kevar and then wrap with plastic to get nice finish.

I’m re-doing a fuslage for a friend that had already had one boom replacement (ie “non-factorty repair”) and noted that fuselage to boom
had a large (.030-.050 inch) gap which had large voids in the epoxy bond (ie no figerglass wrap/filler), the inside of the boom was not roughen and only one the end of the boom kevlar wrap was use (did not have the second at the end of the fuselage stub. If these small details had been done, the boom may not have broken.

Now bond the stab mount in place checking for proper tilt (zero to slight amount of right side high). Now epoxy the bunt roller making sure the distance between the stab mount hingle line and the drum axis is to “factory spec” per the measurement you made before ripping the old boom apart.

Restring your lines and go fly again.

JIM

[Jim Farmer]

Hi Oliver,

I’ll add just a couple of things from a rookie perspective having recently replaced a boom for the first time with help from Jim Parker along with Lee Hines, and Don Zink. To repeat and emphasize what Jim said, measure everything before any disassembly! If you can tape the boom back together in its original position and your lines are all still strung and operational, here’s some additional measurement suggestions. Measure the rudder position and note the position of the rudder cable hole in the boom. If you don’t have them already, measure and note stab and rudder deflections for at least one flight point, like glide or straight tow. Slight mounting position errors will have a big effect on control surface deflections. You can correct for errors with the cables but only if you know what the angles are supposed to be. Another thing I did and found helpful was to take before photos. Good luck!

[Author]

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