Author Topic: Bellcrank Question (Read 1571 times)

Dennis Saydak · « **on:** December 02, 2019, 01:04:25 PM »

Guys, I have a brand new 2-line D-speed bell crank that I want to use in a new construction project. I suspect there is a problem with it because the bell crank is virtually frozen onto the center brass bushing. Is this normal with a button crank or is mine defective? I've never used one before.

bob whitney · « **Reply #1 on:** December 02, 2019, 02:41:35 PM »

yes the bell crank should be free moving on the brass bushing..soak the bell crank in some type of solvent( carb cleaner ) let it sit for a while .tap the bushing out .take 400 sand paper and sand bushing and bell crank till clean and a slide fit ,a little oil and u should be good to go

Dennis Saydak · « **Reply #2 on:** December 02, 2019, 04:44:14 PM »

Thanks Bob. The busing has a flange on both sides so I'd have to drill it out to remove it. It doesn't look to me like a regular bell crank bushing that is installed from one side. I wanted to build a Kansas Twister (have the kit) last winter but postponed the project because I didn't have a suitable bell crank. I don't really want to order another bell crank as the US$ exchange rate plus shipping etc. really adds up quickly.

bob whitney · « **Reply #3 on:** December 02, 2019, 07:56:05 PM »

don't give up on it. it looks like a really good bell crank .u should be able to soak it as I said ,grab the bushing with a big pair of plyers and try moving the bell crank if u get it loose flush more until it feels free and oil.if u like ,send it to me and I will get it freed up for u, no charge

bob whitney · « **Reply #4 on:** December 03, 2019, 08:28:12 AM »

Dennis, I take it u are not in the USA

Dennis Saydak · « **Reply #5 on:** December 03, 2019, 09:32:00 AM »

I'm in Canada. Yes, it's steel, not aluminum. It was made by one of the speed product suppliers. Other than the frozen bushing it is beautifully made.

Bob Heywood · « **Reply #6 on:** December 03, 2019, 01:22:42 PM »

Dennis,

The bushing is a press fit in the bellcrank by design. It is intended to pivot on a steel pin that is secured in your airplane. If you try to remove the bushing you will destroy the part. Remember, there ain't any more to be had!

You will need to trap the pin with the wing on one side and a piece of wood or metal on the opposite side of the bellcrank. The screw you show WILL NOT work.

And yes Walt, it will do just fine in a "D". Marty Higgs made these things to take the load, especially considering the cough syrup we have to run for fuel...

Dennis Saydak · « **Reply #7 on:** December 03, 2019, 02:03:51 PM »

Many thanks Bob. What you say makes perfect sense to me. My picture shows the crank sitting on a small test piece of wood I made just to see how much wood needs to be relieved for attaching the lines. I can now go ahead and build my K.T.

Bob Heywood · « **Reply #8 on:** December 03, 2019, 02:34:17 PM »

Dennis,

With that motori you're gonna have a really neat speedster!

Dennis Saydak · « **Reply #9 on:** December 03, 2019, 02:55:55 PM »

Bell crank Update.
Prior to Bob's first reply I followed the previous advice to tap out the bushing. I carefully placed the crank on a socket and gave it a few light taps with a brass drift punch. Nothing budged at that point so I left it alone. Today I handled the crank and the brass washer fell of by itself. The bushing does not protrude above the surface of the crank. It is flush. The washer was basically glued onto the steel surface (JB Weld?) or some sort of locking agent. It cleaned off nicely with thinner and a little elbow grease. I will have to reattach the washer somehow. The inside diameter of the bushing is .145" and I don't have any M.W. of that size. I'll probably use the drill bit shown for a pin unless advised otherwise.

bob whitney · « **Reply #10 on:** December 03, 2019, 11:21:34 PM »

from the looks of it that other bushing should be loose also so hat when u tighten it down the bell crank should spin freely..probly a 6/32 bolt to hold it all together

Bob Heywood · « **Reply #11 on:** December 04, 2019, 05:51:57 AM »

I figure the bellcrank is intended to be installed the way Bill Wisniewski did his Pink Lady F-40. The load bearing pin is supported in double shear, secured in such a way that it can't move up or down and is in enough meat to take the pull test / flight loads. I would put a flat washer on both sides of the bellcrank bushing, with just enough clearance to pivot freely and allow for the push-pull rod.

Dennis Saydak · « **Reply #12 on:** December 04, 2019, 09:27:38 AM »

Thanks to everyone for all the input. I've learned a lot from you. I am surprised to see that some bell cranks are made so that they don't spin freely on the bushing. That's a first for me.

bob whitney · « **Reply #13 on:** December 04, 2019, 10:13:31 AM »

I still think that other bushing should come out .dose it come up enough to have a bit sticking up

Dennis Saydak · « **Reply #14 on:** December 04, 2019, 11:38:52 AM »

The bushing does not stick up at all. It is flush with the bell crank surface. So the bell crank cannot be mounted with a nut & bolt tightened up on it. It wouldn't turn at all.

bob whitney · « **Reply #15 on:** December 04, 2019, 11:46:37 AM »

just heard from Bob Heywood ,.he says that it is a Marty Higgs bell crank and the bushing is solid with the B/C and a pin is used to mount it ,not a bolt Bob

Dennis Saydak · « **Reply #16 on:** December 04, 2019, 12:53:05 PM »

Thanks again for all the help guys. If the pin was included in the package with the bell crank I probably wouldn't have even questioned it.
I won't start on the K. Twister until after Christmas. When I do I'll post a few pictures of the installation.

C.T. Schaefer · « **Reply #17 on:** December 05, 2019, 05:19:03 AM »

Interesting. We have a D pan and a Dooling 61

Dennis Saydak · « **Reply #18 on:** December 05, 2019, 12:26:21 PM »

Quote from: C.T. Schaefer on December 05, 2019, 05:19:03 AM

Interesting. We have a D pan and a Dooling 61

You mean like mine?

Dennis Saydak · « **Reply #19 on:** December 05, 2019, 06:10:59 PM »

Continuing this discussion:
I've been working on how to install the button crank in my Kansas Twister wing. This is definitely NOT an easy task especially considering that the kit wing is only 1/4” thick. Making it out of 3/16” basswood is a possibility but that would certainly increase the weight by approximately 50%.

Anyway, the hard part is placing the bell crank so that the button line grooves are in the centre of the wing. Here is a first cut mock up showing the top view and inside the fuselage view. The bell crank pin will be supported by double maple shear plates, which should more than withstand any pull test.

The only way I can line up the button grooves properly is to have the buttons facing upwards. This means that the lines will have to be permanently attached to the buttons first. Then the bell crank placed onto the pivot pin. Finally, the inside fuselage shear plate will be attached inside the fuselage locking the entire bell crank into place “permanently".

The wing of Wizniewskies F 40 speedster is 3/8 of an inch thick and would make mounting the bell crank so much easier. But I don't have that luxury with this design.

Your thoughts & observations are appreciated. Please be kind.

Dave Hull · « **Reply #20 on:** December 06, 2019, 01:58:58 AM »

Dennis,

Cool project. Some random thoughts:

On a good airplane design, there is usually a type of hardware and installation that was intended to go into it. The trick is to see how the original was done, or a successful copy was done, and get your hands on that stuff.... I assume from your pictures that the buttons are fixed, not free to rotate. True? If so, then you need to use double loops on your lines.

If I planned to eventually fly the beast, I can't say I'd be happy about building the lines into the plane permanently--or even semi-permanently. There has got to be a way to get at it. If the wing sits above the pan, then the buttons would best face down.

What are you going to close out the grooves in the wing with? If you used 1/64" or even 1/32" plywood strips you could have the buttons pretty close to the bottom of the wing. Again, this works best if the buttons face down. So in your mockup, it would seem that you could get it centered ok, and the only issue would be whether you are going to be happy with the thickness of the upper and especially the lower bellcrank support.

A hole size of .135" seems a bit odd to me. Who has got rod stock that size laying around? It's not even a close fit for 9/64", which would be .140. It doesn't look metric, either. But what it is, is a tight fit for a 6-32. So what did the maker have in mind?

The washer that came off of your assembly must have just been a shaft spacer. For sure it wasn't going to help distribute the line loads into the shaft. If the button slots are offset from the center of the bellcrank plate (they always are) then there is a twisting moment on the crank. The joint needs to handle this twist without wearing out real fast and certainly without binding up. The thicker the actual bushing, the less of a problem this is. I'm kind of with the Motorman here. I wun'ta done it that way, notwithstanding that Bob H. sez these are pretty good unobtainiums.

Stuffing a crank into a thin wing happens on racing planes too, and can be a pain. I've seen plenty of planes that had the bellcrank arms bent down (or up, depending on which side you mount from) slightly to get the lines to line up vertically with the slot in the wing. The issue there is that this increases the offset, and therefore the twisting load against the bearing.

Hope you find a clean way to do this,

Dave

C.T. Schaefer · « **Reply #21 on:** December 06, 2019, 06:02:16 AM »

Our Dooling is glow.. You may have to do some modifying there. Thicker wing? Plane was designed around a monoline unit. 3/8 would make your life easier.

Dennis Saydak · « **Reply #22 on:** December 06, 2019, 09:09:29 AM »

Guys I flew a lot of speed back in the mid to late 60s (monoline & 2-line models). My mono line handles are long gone and I gave away my spare Stanzel control units to other builders like Kirk in Florida for his projects. I absolutely don't want to revisit monoline for only one model and I'd like to build my K.Twister to be air worthy. That's why I hunted up a button bell crank for this project.

I have two H&R torque units (see picture below) but given their age I wouldn't trust them due to possible internal corrosion. There aren't many choices for a two line control system for speed models other than having external lead outs.

The buttons do rotate freely on the bell crank. I'm not worried about the offset wear factor on the shaft. This isn't a stunt model and the slight control movement is really for trim purposes primarily on landing & takeoffs. These models just hang in a groove once airborne.

The shaft size .145 is definitely odd but probably there is a good reason for it. I will use a drill bit for the shaft since I don't want the bushing to wear on the threads of a 6-32 bolts.

I'll try another mock up to see if I can provide access to the buttons. But it's starting to look like I may have to go with a thicker wing. I'd close off the line grooves with thin plywood. I have both 1/32” & 1/64th on hand.

Dennis Saydak · « **Reply #23 on:** December 06, 2019, 10:03:14 AM »

Mockup #2:
It looks like going with a thicker wing is the only logical answer to my dilemma. I can center the button grooves on the bottom of the 1/4" thick wing and add a second 1'8" wood layer on the bottom of the wing for thickness. As long as I leave the bottom of the wing basically flat along the airfoil high point I should be good to go.

bob whitney · « **Reply #24 on:** December 06, 2019, 01:09:16 PM »

the problem is that Wisniewski's F40 was inverted so he could get to his bell crank from the top... here is 2 more ways to go .I would press the bushing out and make one that would let the bell crank pivot and use a 6/32 flat head bolt to keep things flush .then u could feed the lines into the wing ,pull them out far enough to attach to the buttons and slide everything back into the fuse and tighten everything up

or u could do like the TR guys and make short leadouts that come about 2 in from the fuse .make ovule cut outs in the under side of the wing and attach lines there.

once u have the lines in do like the FAI guys and leave them attached to the plane