Mistake in Flap Hinge Mounting Dimensions on Plans

[spinningwrench]

Today I went to attach my flap push rod to the flap hinges and discovered that the rod end bearing as called out in the Bearhawk Patrol plans will not fit between the hinges. The print calls for a .29" gap between the hinge faces but the rod end bearing is .434" wide. I wished I would have caught this before I mounted my flap hinges. Now I will have to do a kludge to make it work. In my view this should be an engineering change notice.

[jaredyates]

Does the hole need to be big enough to clear the rod end bearing, or can it be installed after you pass the rod through the hole? Keep in mind I haven't built a Patrol so I might be totally off track.

[spinningwrench]

I sent a drawing and response to email@jaredyates.com

[jaredyates]

I see, that is not what I was thinking about.

[svyolo]

A couple of folks, including me, have asked the same question. Mark G responsed to put a joggle in the hinges to make them wide enough. My initial response was to try to find a different rod end bearing, unsuccessfully. So I tried putting a joggle into a piece of 4130. It wasn't that hard to do, and worked perfectly. I put the hinge in a bench vice, and put a drill bit where I wanted the bends, and bent by hand/piece of wood. Pretty easy.

[spinningwrench]

Yes I understand. I just think it’s a known problem that should be addressed with an engineering revision so the next guys don’t make the same mistake.

[jaredyates]

I've forwarded your drawing to Bob, thank you for pointing it out. It's up to him about how to proceed but if I hear back I'll let you know.

[Ski]

When I was making my hinge mounts I ordered my bearing from McMaster Carr. McMaster Part# 63195K61. I'm not 100% sure they are correct but dimensionally they are correct. If I headed down the wrong rabbit hole I can throw them away but they sure seemed like they would work to me.

[spinningwrench]

Ski that is the correct bearing for the hinges but I am talking about the large rod end bearing called out to mount on the push rod for the flaps. The bearing is wider than the .29” gap in the hinges. One would have to go to a much smaller rod end to make it work. The gap in the hinges needs to be increased to accommodate the larger rod end. Joggling the hinge brackets is a kludge that works but the design needs to be updated to avoid that fix.

[svyolo]

My initial response was the same as yours, but I could not find a suitable rod end bearing. I was surprised how easy the joggle was to do.

[Ski]

Ah I see. Sorry, That's why I usually just read and not respond. I usually don't know what I'm talking about !!! I'm getting ready to bend my hinges in the next few days. Should I put the joggle in them now or just mount them further apart when I drill the spars?

[Mark Goldberg]

I suggest you mount the hinges as shown on the drawing. And just joggle the "arms" that the pushrods attach to. That is what Bob intended. Mark

[spinningwrench]

If you mount them with a wider gap there will be no need to joggle. You only need to do this for the one hinge where the flap pushrod hooks up. Measure the width of your pushrod rod end bearing. Mine was .434”. You will require some spacers or just washers at the actual hinge bearing to fill the gap.

[jaredyates]

Here is Bob's reply:
The flap hinge shows a width of .29. But can be reformed to fit a wider bearing at the push rod attach point.
Bob

[svyolo]

I am sort of the middle of this discussion. My initial thought was to buy a solution. I tried with some scrap 4130 to joggle and it was so easy to do that I just joggled it. I put the hinge plates in a vise, put a drill bit where I wanted a joggle, and bent it by hand with a piece of a 2X4 and my own arm strength. Not hard at all and not a big job. But mounting them a bit wider, and using washers to fill in the gap for the hinge bearing, I am sure also works. Your choice.

[Bcone1381]

There is a space limitation inside the hinge cavity. If the hinge is centered in its cavity the AN3 bolt is too long to insert it into the hinge angle. If the hinge angles are spaced out wider I suppose it could exasperate this issue.

[Ski]

Thanks all. I'll probably just space out the hinges to fit the rod end bearing. That seems easier since it really requires no extra work at this point. I have almost all my steel parts done for the wings and onto the spars next. I've read everything I can here about that but I'm sure may still have some questions.

[Bcone1381]

Reference post 11.1. Make sure you have space to insert the hinge bolt. This view from the Patrol Plans, flap spar drawing. It shows that the hinges are not centered in their respective hinge cavity. The bolt will get inserted into its hinge from the side with more space.

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[spinningwrench]

After assembling all my hinges on my Quickbuild flap today I realized that the final location of the center hinge is not offset in the pocket nearly as much as the plans call for even though I was religious about making the two end hinges offset per the drawings. Measuring the flap I see it is different enough from the print that getting a bolt in with more widely spaced hinges would be a problem so I see that using the joggle technique to give your self a bit more room at the hinge bearing location to get the hinge bolt in is a good idea. As it is you may still have to splay out the arms at the rod end location to get a AN3-10 bolt in but that is doable.

[svyolo]

I will check again tomorrow as I just did one side a couple weeks ago, but if I remember the two aileron pockets had the same offset, but the flaps pockets did not.

[spinningwrench]

Exactly. The flap pockets should in theory all have the same 1-3/8” offset but mine do not. They pushrod hinges ended up centered in their pocket.

[svyolo]

My inboard hinge is centered, but I can get the bolt in. Just lucky.