Wingtip Bow Repair/Replacement advice sought

[Glenn Farrant]

Hi Everyone,

I've been getting N43887 ready for its annual, which is only 10 days away. I'm really looking forward to flying it.

Unfortunately, yesterday, my hangarmate closed the hangar door and impacted the left wingtip bow. It's fairly bent and I would like to get your opinions on how to fix it.

Description of the Damage

As far as I can tell, without removing the fabric, the damage is limited to the bow itself. The leading edge/front spar seems unaffected, although the impact was between the front spar and the light. The rear spar and tail of the rib are OK. The impact was slow (an electric hangar door closing).

In the following photos, you can see me pushing on the fabric to locate the inner part of the dent between the front spar and the light. It is pushed in approximately 1".



In these photos you can see that the bow has been tilted up too.



Repair Thoughts?

What would you suggest for a repair?

Do you think the bow could be straightened? Or am I likely to need a replacement?

What other damage should I be on the lookout for?

I'm new to fabric work. Should it be possible to cut away the fabric in the area and then replace it with a large patch that envelopes the bow?

Thanks for your thoughts on this.

Cheers

Glenn

[Glenn Farrant]

I'm aware of these photos on the web of the structure. Ideally I'd like to avoid pulling the outer leading edge pieces off, but I'm not sure that will be possible.

[Hank Jarrett]

Fixing the bow isn't what worries me, it is the potential for HIDDEN damage! We had a split in the root of the aft spar from a wing tip impact that didn't even break the glass lens on the Grimes light! You are talking about a 16' lever arm and the force can cause real damage at the root. I hate to say it but I would take the wing off for a careful inspection of the root for damage. As you can see from the photos you posted the tip repair is pretty easy, but will probably require removal of the fabric from the tip at least one rib in. My plane had been repaired that way and the fabric had been removed from the tip to just past the formed leading edge at the end. I would imagine they had to tap out some dents (since there were still some after they were done). Smooth out that tip leading edge carefully, damage WILL show through the fabric. Looks like a great chance to learn some fabric techniques. Try to see it as an opportunity.

Hank

[Glenn Farrant]

Thanks Hank,

Yes, I'm looking at it as an opportunity to learn. I am bummed about it as it will delay my plans, but I also want to fix it properly and an opportunity to learn is always appreciated.

Thanks for the guidance on where to cut the fabric. I had been wondering about that.

The leading edge is smooth and appears undamaged.

It's a good point about the 16' lever arm. I'm assuming from your comment that the only way to check the root is to remove the wing?

Cheers

Glenn

[Hank Jarrett]

You can take the wing band off and get in with a mirror to see if it is REALLY bad, but I doubt I would feel secure in that to see if there was NO damage. An early look could confirm you need a new spar or wing. Sometimes it takes a long time to get new spars. Looking while attached won't tell you it ISN'T damaged, only if it IS for sure. Get at least two EXTRA people when you take he wing off and support the other wing! Thee seems to ALWAYS be something that requires people to stand holding the wing for longer than they can. PLAN for it. Also get a bunch of Phillips screw drivers to slide in as you pull each bolt. You don't want to end up holding everything up in he air because the LAST STINKING BOLT is stuck! Get a REALLY LONG rod or screw driver for the wing to fuselage bolts. They are deep in the gap and hard to reach (and easy to get your hand crushed if you aren't careful!)
Next make sure the turnbuckles will go through the guides in the fuselage. Mine wouldn't! We spent a LOT of time holding that #%(&_#@&* wing up because we FORGOT to feed the cables and turnbuckles through. Hint, the pressed paper guides in the steel tube stubs can be removes to give more diameter! Unfortunately my 41 had replacement turnbuckles that were larger than stock. By this time the guys holding he wings up were screaming! My arms STILL hurt! Why someone didn't think of the screw drivers is beyond me, but getting the bolts back in was impossible with all the shaking going on. We cut the cables. Oh well, new aileron cables isn't a bad idea.
Learn from my mistakes!!! It is why we are all on this group, and I have made LOTS of mistakes!

Hank

[Glenn Farrant]

Thanks Hank. That's hard-won advice right there. Glad I don't have to re-discover it. I'm sure there are plenty of mistakes awaiting me.

[Hank Jarrett]

I am betting you can't find a mistake I haven't at least almost made. I have made a lot, but I am super conservative about safety.

[Glenn Farrant]

Yeah, in this case I think I need to be conservative. The description of the incident was that it was a slow speed rubbing of the hangar door on the wing tip, but because I wasn't there, I can't sense what forces were involved.

[N96337]

Glenn, what's the covering system? That will dictate quite a bit of the process. As far as the rest, I'd wait to get too carried away before I looked in the tip with no fabric. I'm all about being safe, but I'd want more details before I remove wings.
John

[Glenn Farrant]

Thanks John,

It's ceconite with butyrate dope.

Cheers
Glenn

[Robert Lees]

Are the hangar doors operated horizontally, or are they bi-fold? In other words, what was the orientation of the impact?

Rob

[Glenn Farrant]

Hi Rob,

The hangar doors are bifold. According to the guy who did it, the aircraft was on the outside of the hangar and the wing was near the door when the door was opened and as the bifold section moved outward, it rubbed, pushed and bent the wingtip. So the majority of the force seems to have been upward and inward. It doesn't seem that there was fore-aft force that would be pushing the wingtip backwards or forwards.

I'll be back out at the hangar in daylight today and will look for evidence of the impact (paint) on the door. I'll also pull the fabric and share the photos of the wingtip.

Cheers

Glenn

[Robert Lees]

OK, thanks Glenn. (I assume the appropriate insurance companies have been notified, because this could be a big bill for someone).

The reason for my question was that had it been a horizontally-moving electric door, with the wingtip in line with the hangar door axis, then any spar "load" would have been along the span-wise direction of the wing, which would have been of a lesser concern.

But any fore-and-aft movement (in a chord-wise sense) would be of concern to me (also consider an up-and-down movement on the tip, but this might mean damage to struts & the associated weldments & fittings, particularly the spar at the strut-to-wing fitting).

I certainly think you and your hangar mate should be chatting with your respective insurers. The wing-tip fabric repair is a minor inconvenience (I've done it but for different reasons) but the risk of spar damage may be there.

Let us know what you see during the hangar inspection. Take photos / simulate where the aircraft was during the mishap.

Rob

[Glenn Farrant]

I'm out at the hangar now. Fabric is off. Pictures follow.

Looks like force was "span-wise" rather than "chord-wise" to use your vernacular. There is no damage to the outer end of the spars.

[Hank Jarrett]

You might just have dodged a bullet! I would STILL pull the wing, but like I said, I am a bit conservative where safety is concerned, plus it is easier to work on the wing cover with the wing on supports instead of on the fuselage. Painting the underside of a wing in place isn't fun.

By the way, SECURE that wing tip Grimes lens! If it falls off it will break and they are REALLY expensive!!!