Flap handle wear

[Battson]

We discovered that the flap handle is wearing at the lower bolted connection. The bolt and the hole were both in bad shaped, after 1,000 flight hours. The hole is supposed to be 3/16".

In terms of repair options, there are a couple:

1. Weld up the hole with filler rod and re-drill. Bob said that weldment will be harder and less consistent (heat affected zone) than the 0.100" substrate 4130N steel. He said welding on a reinforcing washer was also possible, and wear would still occur. There's not room for a washer if the normal cable shackles supplied with the Bearhawk are to fit over the welded assembly (tto wide), I am not sure if wider shackles are available. This would be easy enough to do, but may only last so long - after a few sequential repairs it might be more weldment than substrate, and that could lead to embrittlement / cracking in the worst case.

2. Drill it up a size and fit a sacrificial bushing. This requires at least 1/8" of edge distance from the bushing to the edge of the 0.100" substrate 4130N steel. I have room to drill a nice 1/4" hole, however if we'd picked this up sooner there may have been room to drill to 5/16" hole. The advantage being it would allow for an easier job finding / making a bushing. As long as you have that edge difference. Personally I prefer a press-fit bushing, to ensure any wear happens to the bushing, instead of the bushing wearing on the substrate.

Personally I prefer the sounds of the second option. In theory the bushing can be changed every 5 to 10 years as required, and no further work is needed (re-welding etc).

IMG_20221128_185719.jpg

[Battson]

jaredyates Perhaps I should have put this under maintenance... feel welcome to move it, if it bothers you

[jaredyates]

Doesn't bother me in any case, thank you for posting it!

[alaskabearhawk]

Personally, I wish I had this problem.

[Sir Newton]

Me to!
Lol

[Mark Goldberg]

If you welded on a reinforcing washer you can just pry open a bit the cable shackle so it would still fit. Mark

[Sir Newton]

I 2nd Mark's motion.
& for peace of mind, would assign homework. Research into the terms normalized, annealing, stress reliefing.

[Steve W]

You could bend up two tangs of a similar thickness and weld to either side of the arm with clearance for the shackle to fit between the assembly, like a hinge. Center drill the holes. Would give you three points of contact on the arm instead of one.

[geraldmorrissey]

The first one lasted a thousand hours. Build another handle, there's another thousand hours. Put some into your spare parts bin for the next owner. Think of it as a non-rotable subassembly.

[kestrel]

geraldmorrissey, wouldn't it be less work to make 10 bushings and install the first one. ...then you'd be all set for 10,000 hrs.

[geraldmorrissey]

Agreed, but this is definitely a Bob issue. I would not effect a repair or modification to the flaps, no matter how insignificant, without his blessing. A replacement handle to the print is a lightweight, simple, reliable solution until Bob has examined the issue.

[Battson]

Bob has approved either of the approaches I listed above, builder's option.

[svyolo]

We discovered that the flap handle is wearing at the lower bolted connection. The bolt and the hole were both in bad shaped, after 1,000 flight hours. The hole is supposed to be 3/16".

In terms of repair options, there are a couple:

1. Weld up the hole with filler rod and re-drill. Bob said that weldment will be harder and less consistent (heat affected zone) than the 0.100" substrate 4130N steel. He said welding on a reinforcing washer was also possible, and wear would still occur. There's not room for a washer if the normal cable shackles supplied with the Bearhawk are to fit over the welded assembly (tto wide), I am not sure if wider shackles are available. This would be easy enough to do, but may only last so long - after a few sequential repairs it might be more weldment than substrate, and that could lead to embrittlement / cracking in the worst case.

2. Drill it up a size and fit a sacrificial bushing. This requires at least 1/8" of edge distance from the bushing to the edge of the 0.100" substrate 4130N steel. I have room to drill a nice 1/4" hole, however if we'd picked this up sooner there may have been room to drill to 5/16" hole. The advantage being it would allow for an easier job finding / making a bushing. As long as you have that edge difference. Personally I prefer a press-fit bushing, to ensure any wear happens to the bushing, instead of the bushing wearing on the substrate.

Personally I prefer the sounds of the second option. In theory the bushing can be changed every 5 to 10 years as required, and no further work is needed (re-welding etc).

IMG_20221128_185719.jpg

I just did a repair on a clutch pedal last year similar to your #2. It was a standard repair rtecommended for the worn out hole. Weld it closed, redrill larger if you have the edge distance. You can then weld on something, tube, or thick washer on each side. Press fit a bronze bushing. The thick washers can also compensate for not enough edge distance. Works great, not hard or time consuming to do.

[sherrre]

I know you are making individual threads as you find things during your 1,000 hour inspection but could you also write a summary thread when you return the airplane to flight? Perhaps a Bear Tracks article? I’d hate to miss one of your findings. I think this information is especially useful for us new and potential builders as we can make a small change now based on what you learn.

[Battson]

To be honest, the aircraft "flew" through the inspection. There were very few issues to report! I think I made this post, and one other about dirt building up in the belly area. Otherwise we are now aiming for 1,100 hours Of course there are always very minor things, like slight surface corrosion on various parts - this is all within normal expectations.

[sherrre]

Even better news, thanks Battson!

[kestrel]

How many Bearhawks have crossed the 1,000 hr mark? Mine did this summer, but I don't fly often enough to to have thought that was unusual. A few on the US southwest must be well past the 1,000 hr mark?

[Battson]

I reckon Mark Goldberg's plane (now Jared's) and Pat Fagan's must have done some of the highest hours. I bet there are dozens of aircraft with a lot more time on them.

Are you seeing any of these same issues? Very interested to hear!

[kestrel]

This fall I found minor cracks starting to form at the upper ends of the horizontal stab struts. A couple years ago I broke a gear leg, but I believe that was due to a combination of factors that are not design related. My exhaust tunnel burned/rusted through about a year ago. I blame that on a poor choice of material. I don't know that mine has been gone through as thoroughly as yours, but I've found it to be a solid airplane that gets not so gentle use, even if not as much use as I wish.

[geraldmorrissey]

Any info on the maintenance history of that system? Could a lack of lubrication be a contributing factor? Were the detail parts dry when you disassembled them? Good job identifying this.

[whee]

Good find Jono. A press fit bushing would be my solution. I may incorporate one if I ever remove my handle to extend it.

I can’t recall how many hours Mike C had on his plane, 1200ish? I don’t think he had this issue come up.

I wonder if the longer flap handle has anything to do with it? Not that your exceeding flaps speeds but you use them a lot, can deploy them with authority and have them rigged for maximum deflection.

[Battson]

Hard to say definitively, however I do observe flaps speeds religiously.

[Battson]

Any info on the maintenance history of that system? Could a lack of lubrication be a contributing factor? Were the detail parts dry when you disassembled them? Good job identifying this.

Parts were clean and dry when assembled and have remained so. The bolted connection was not lubricated to my knowledge. This was an oversight, with the benefit of hindsight, although I doubt it makes much difference.

The bolt also got worn down, it looks like galling - indicating the bolt may also be rotating in the hole under tension, which was Bob's view as well. So lubrication may assist with preventing that failure mode, but given the pressure on that bolt - I doubt it - the lubrication will not stay in there. I think it really wants a bearing of some kind, if we wanted to prevent wear and tear entirely.

Not only was the hole enlarged and elongated, but also the metal was splayed out to the sides where most pressure was occurring - plastic deformation - indicating that other failure modes may be occurring at the same time. To my knowledge galling does not cause metal to change shape like that. I figured that low temperature creep could be part of the cause (the only other way I could explain it, would be stress exceeding the yield strength of 4130N - but that seems very unlikely / impossible!). If anyone else has some ideas, please share!

[AZBearhawk272]

Left field possibility’s……

1. Clevis and bolt vibrating extensive while flaps retracted and unloaded? Forcing function exhaust acoustic or engine vibe?

2. Flap cable vibrating at natural freq?

3. Bad material or post weld properties of arm.

Kevin D
272

KCHD

[Battson]

Have a look at the direction of the wear into the substrate. Based on the direction of the wear, and the plastic deformation (not pictured clearly) it appears that the wear is occurring when the flaps are deployed and the metal is under quite a lot of strain.

[geraldmorrissey]

Could you include a picture of the bolt. Could the fitting have been built from "A" material? It seems unlikely that an average 200lb pilot could impart enough stress into the handle with one arm to deform a steel fitting. Somthing else is at work here. The Patrol has a .080 arm plus a .062 reinforcement washer welded to it. I do not know how the handle is built on you plane but on the Patrol, one could easily grind the weld down and remove the affected fitting and weld in a new one with any upgrades. Have you checked to see if the assembly complies with the latest dwg?
Gerry
Patrol #30

[Battson]

Simple answer. It's factory.