Need Help with Flap Stop in 4-place

[jonmiller0]

Good afternoon Bearhawkers,

Pardon my ignorance, being a non-builder who participates in the forum. My friend Daryn and I have been flying a Bearhawk 4 place now for about 4 years. We are the third owners. Never once have we had an issue with the flaps until today when suddenly the 3rd notch of flaps (40) got stuck. Up until now I haven't paid much attention to the intricate details of the four place design. I've simply enjoyed being the caretaker for the original builder, and a local proponent of this sweet aircraft design! But with today's hiccup started digging in and realized what a help it would be if I knew more about the design and initial plans.

So next Daryn and I grabbed our A&P and we started looking closely at the flap stop/notch device (I don't even know if I'm calling it correctly). We noticed the curve of the design isn't perfectly round but rather appears logarithmic. I've never had the pleasure of flying anyone else's Bearhawk, let alone look inside another one except many many years ago at Oshkosh, which is why I'm asking you all for advice. Is this what yours looks like too? Is this a standard part of the QB kit, or does every builder design and manufacture their own? It appears to me (a non-engineer, non-A&P, pilot only) that based on the photos with the clearance at flaps 10 vs flaps 40 that the curve of this flap stop was never correct to begin with...but then again, it has flown without any hiccups or issues or friction etc until today's fateful flight.

I still don't understand how 700 hours of flight and there have been no issues, and yet today I gets jammed (jam is free but obviously can't use that third notch, or fourth for the matter, until it gets figured out). Any ideas why something like this could have changed so suddenly without forewarning?

Any advice is appreciated. I think Daryn is going to try to call Mark G to get some advice, as well but this forum has always been a great wealth of information. I imagine somewhere, someone has a plan or schematic of this part and I can get a local A&P friend with CNC machine to make it and I can swap it out. But if the attachment points aren't in the right place to begin with then perhaps we'll have to get my first taste of building. Long overdue.

Thanks,

Jon M
KMAN



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[Bcone1381]

As you know the flap lever has a slot. The slot captures the "Flap Stop Notch" part. It is designed to be round with a radius that evenly places it equal distance from the flap arm axle bolt.

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I took a screen shot of your photos and annotated them each with a single red arrow.

I suspect that your "Flap Stop Notch" mechanism was overstressed on a previous flight. It appears to be cracked at the last notch. That "Flap Stop Notch" part is not a big deal to fabricate. The Patrol design, which I show, looks similar and is made from commonly available 2024-T3 aluminum that is .125" thick. I would be very surprised if The Four Place design is identical. I show it to help you see how your works.

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[ThreeD]

Great analysis Brooks

[jaredyates]

Do you have a set of plans? The piece that is badly bent on your plane is depicted there and you could make a new one. A drill, a woodworking bandsaw, a belt sander, and a file could get it all done. I worry though about what else might have been damaged in the system by the apparent overspeed/over-stress situation. A careful inspection of the whole system is in order for sure.

[jaredyates]

Look here for how it is supposed to be:

http://bearhawksafety.com/4-place/changejan06.html

[Nev]

Interesting reading the engineering change. Mine is very difficult to pull the fourth notch if the passenger seat is anywhere other than full aft. It's possible, but the issue is that the seat blocks your hand.

[Nev]

What the others said above is all sound advice.

Several times I've had passengers come very close to bending that piece on mine accidentally with a foot while climbing into the aircraft. Being made from aluminium makes it rather easy to bend, and if it had happened and was then straightened may well lead to the fatigue crack shown in the photos.

I'll consider replacing mine in the not too distant future. It should be a fairly straight forward project using the original as a template. As Brooks already mentioned the top part should form a round curve. Incidentally, I'll probably omit the "flap one" notch and also widen the lower portion to prevent the handle dropping to the floor in the "flaps up" position.

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[Battson]

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This photo clearly shows "necking" of the aluminium quadrant. Meaning the quadrant has stretched (elongated) under tension.

Seeing necking like this means the part has almost certainly been overstressed, i.e. something has pulled (or pushed) down on the quadrant with a huge amount of force. This would have required an enormous amount of force, I am amazed to see it.

It makes me wonder if the builder has used the wrong grade of aluminium for the quadrant, that is the only logical explanation I can come up with.

Edit to add, that situation could have been aggravated by someone stepping on the quadrant, or trying to force the handle down with a lot of weight. But that alone wouldn't really explain the stretched and squashed shape of the damaged quadrant, it definitely looks like the metal has been overstressed in the direction the flap level applies force.

I notice the slowest speed on your Vf sticker is 75 MPH, whereas the "full flap" speed for the Bearhawk 4-place is about 65 mph, depending on how far your flaps extend. I don't have all the details we need to make an informed comment, but that may also be worth investigating.

I would also say the notches in the flap quadrant are deeper than necessary, and that will have weakened the part considerably.

[Nev]

Looks like the fourth "notch" may be drawn in place with a marker pen, but not cut out, therefore limiting the flaps extension to the third notch.
I wonder if the flap handle internal mechanism is shaving (wearing) the aluminium each time it is used.

[AZBearhawk272]

Trying to be helpful and tactful here.
Everyone's observations and comments are spot on.
I have a little history with this plane.
Maybe 6 years ago a previous owner solicited my assistance with rigging and handling issues on this aircraft.
One of the areas that needed a bit of love was flap actuation.
It required super gorilla strength to activate the flaps.
The flap handle was bent at the slot and the mechanism was generating a fair amount of shavings.
The notches in the arc sector were not implemented per Bob's plans and would frequently release to Zero flap in flight.
Got the handle corrected, doublers installed, sector cleaned up a bit and slots adjusted, there were only 3 notches if I remember correctly. And think that the sector was .093. not .125.

Subsequent flight testing displayed still, a need for gorilla strength while operating the flaps.
Additional investigation revealed that the length from handle pivot point to cable attach was longer than current plans, seemed to be modified to get the cable to clear the gear truss.
And if I remember correctly the actuating arms to the flap torque tube in the wing roots were also shorter than current plans. Hence a lack of mechanical advantage.
I do know that at the time the sector did not have ramps.
Not sure if the sector was ever addressed by subsequent owners.

So the takeaway here is. Stay with the plans. Pay close attention to the details, they matter.

Kevin D
#272

KCHD

[Nev]

Very interesting Kev. So if I understand correctly, the added leverage would cause the flaps themselves to generate significantly more force back at the handle, and each "notch" has to hold that increased force on a "sector" made from thinner material, even when flying to the correct flap limit speeds.

[AZBearhawk272]

Yes.
This plane was a very early plans built and there was some learning here that ultimately made a path into plans revision and kits.

Kevin D

[AK2ID]

Thanks for all the info AZBearhawk272. We ordered one of the factory kits from Mark last week to replace the guide and flap handle. Hoping this will correct our problem and get us back in full flap function.