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[Motorman]

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[Brent Williams]

No bearing info, but here is some info regarding phenolic material. 

Crist Rigotti has some good tutorials on using 1/8" phenolic for bellcranks.  Here's one of his (several) awesome build threads: https://stunthanger.com/smf/gettin-all-amp'ed-up!/2013-electric-stunter-a-build-log/

I use 1/8 phenolic for my bell cranks.  I triple it up by the post using epoxy.  This keeps the bell crank from tipping and give a larger "bearing" surface.

The bell crank uses 1/8 music wire post, 2 4-40 fender washers, and 2 1/8 line eyelets.  I use solder the secure the whole assembly.  The ball link sits on a spacer and uses a 4-40 screw with a washer under the head.

[Randy Cuberly]

Anyone ever put a ball bearing in a bellcrank? Wondering if you thought it was worth it.

I'm looking for the right material to cut out a bellcrank and I came across  phenolic resin Garolite LE sheets. Anyone have experience cutting this stuff?

https://www.mcmaster.com/#phenolic-sheets/=1afjnve

Thanks,
Motorman

Functionally an oscillating motion isn't the best application for a ball bearing especially small ones.  In the constant stopping and reversing motion, such as an oscillating motion creates, the balls tend to skid as they change motion and that increases the wear factor by a very large margin.

However in our applications the actual bearing speeds would be very low so the increased wear factor might not be that much. 

In short, they might work but probably not any better than a good lubricated plain bearing and they require more maintenance and lubrication etc. They would also be heavier, and would require protection from dirt etc.  Sealed bearing would solve that problem but the seals increase friction so I'm not sure there would be any plusses for our bellcrank application!   

Randy Cuberly

[Tony Drago]

This is what you would need. Flanged bearings I used these for years. Use a bearing on top and bottom. Center hole around 3/32 to 1/4th in. Center holes for mounting will vary. Rated at (67,000) rpms. https://i.ebayimg.com/thumbs/images/g/Hv0AAOSwiQ9ZTNMK/s-l200.jpg
 Item number on   362165988262
Slot Car Axle Flanged Ball Bearings, size is 1/8" x 1/4", shielded bearings, Bearings are packed 10 bearings in one plastic tube, bearings are made from Chrome Steel and can rotate up to 67000 rpm, each bearing has 2 metal shields to protect the bearing from dust or any possible contamination, also bearings are pre-lubricated with grease.

[tom hampshire]

Here's a slightly more precise anti tip/wobble bellcrank.  Make it so the tubing fills the space between the spars, less the anti slide washers or clamps...  Make the bottom gussets like the top....

[TDM]

They sell bronze bushings at McMaster Carr 1/8ID x.25ODx3/8Long. Press them in the Garolite and you are good to go. By the looks of it you are using the 1/8in (3mm) Garolite which is fine.
https://www.mcmaster.com/#2868t33/=1afqvoo

[peabody]

I believe that Bill Byles built amazing bellcranks that had bearings in them....very hi-tech and truly art.
Not sure if he offers them any more

[Trostle]

I have not used a bellcrank with a ball bearing.  I have heard from several people over the years that tried them and they found the ball bearings to not wear very well because of their environment of loads and vibration.

Same problem with using ball bearings for pushrod connections to flap and elevator horns on our stunt ships.

Keith

[Garf]

I built a large profile model long ago using a homemade bellcrank made from 1/4" thick aluminum. I installed a ball bearing removed from an aircraft instrument. It worked well till I crashed it.

[Paul Bray]

Total Noob so I probably don't have much of value but so far I have 'done' 3 C/L models and was worried about the play in the bellcrank and in the bearing surface so I printed some plastic inserts on my 3D printer to spread the load and the plastic which I used to print is a bit 'soapy' (sure that you know what I mean).

Seems to work a treat but I can't get pictures onto my PC or onto here at the moment.

Paul

[Paul Bray]

Found a really poor picture but you will get the idea.....


Paul

[Peter Nevai]

Anyone ever put a ball bearing in a bellcrank? Wondering if you thought it was worth it.

I'm looking for the right material to cut out a bellcrank and I came across  phenolic resin Garolite LE sheets. Anyone have experience cutting this stuff?

https://www.mcmaster.com/#phenolic-sheets/=1afjnve

Thanks,
Motorman

See the first thread, I did this on my Vector 40 kit as well. Controls extremely responsive, absolutely no detectable friction at the lead outs. Not necessarily recommended for novice pilots as the slightest touch of the control illicit's a response from the model (No Damping at all). But I do believe that it provides greater control when the model gets lighter on the lines as there is virtually no friction to overcome.

https://stunthanger.com/smf/building-techniques/construction-of-the-pathfinder-le-kit-by-rsm/msg213749/#msg213749

[Tim Wescott]

Phenolic works great.  If you haven't bought any yet, it's way cheaper at Aircraft Spruce (which I found out after I got mine at McMaster).  I machine aluminum journals for my bellcranks, but seeing the pic of the one with the phenolic triplers all I could say to myself was "d'oh".

This isn't the best picture, but should get the idea across.  Aluminum riding on steel probably isn't the best bearing material, but it's worked well for me (although phenolic may be in my future -- phenolic makes a good bearing material).  The one in my overdue-to-be-replaced Twister is still going strong after over 500 flights.  I just assembled it with some Phil Woods' bicycle grease, and it's been fine ever since.

[RandySmith]

Anyone ever put a ball bearing in a bellcrank? Wondering if you thought it was worth it.

I'm looking for the right material to cut out a bellcrank and I came across  phenolic resin Garolite LE sheets. Anyone have experience cutting this stuff?

https://www.mcmaster.com/#phenolic-sheets/=1afjnve

Thanks,
Motorman

YES  I have done that, twice,  BAD idea  it does not  hold up to the vibration, and the metal hold bar and steel balls  beat each other from the vibration, it would work if you could spin it and have some motion to create a film of lubricant
If you want a bearing that works  use  Needle bearings  or  sleeve  bearings

Randy

[frank williams]

Last year there was discussion about ball bearings and I heard that they wouldn't last due to motor vibration.  Well I had to try it.

Earlier I had begun to worry about the wobble of the bellcrank due to the loads from the standoffs of the ball links, and wanted a thicker bearing surface at the center.  I decided to go ahead and try a pivot utilizing ball bearings.  Actually two ball bearings top and bottom to add to the height to take wobble out and a 1/4inch titanium tube for the center shaft to help also.  Very smooth motion. 

After a year of flying I have noticed no degradation of the bearing's feel.

[Howard Rush]

BAD idea  it does not  hold up to the vibration, and the metal hold bar and steel balls  beat each other from the vibration...

Randy, the engines you are using must have too much vibration.  Perhaps you should use whatever brand Frank uses.   

[Jim Hoffman]

I’m not sure what Motorman was trying to accomplish in his original post.  I suspect either reduce friction or eliminate bellcrank rock, (aka wobble).

I feel that bellcrank rock is a WAY more important issue.  A stock Sig bellcrank bushing is pretty low friction, but it’s susceptible to a lot of wobble.

Bellcrank rock results in control slop at the flaps that is most undesirable

To eliminate bellcrank rock, the BC bushing needs a high Length/Diameter (L/D) ratio.  There are four examples of Axle configurations with this feature.

   Brent William reply #1 – his BC has an increased L/D.  Better than most

   Tom Hampshire reply #4 – his BC has a high L/D and should be free of any rock

   Tim Wescott reply #12 shows a journal w/ a hi L/D

   Frank Williams reply #14 has a dual ball bearing configuration that will also eliminate BC rock


I think a bushing has a weight advantage too.  Hard to imagine a ball or needle bearing configuration lighter than an 1/8” ID copper tube bushing riding on 1/8” dia music wire.

[John Rist]

Just let Tom Morris build you a bell crank.  Works great and last a long time.  For that matter Tom can provide the whole control system. 

[RandySmith]

Randy, the engines you are using must have too much vibration.  Perhaps you should use whatever brand Frank uses.

These were in  ST 46 powered  planes,  and  I used  1  ball bearing,  a  Bearing  EXPERT  told me that they would  NOT get lubed just  flying with vibration, and  turning back n forth  10 to 25 degrees ?  ya  pay your money and take  what ya get, 

Randy

[Randy Powell]

I've tried it with sealed roller bearings. Seems fine after 200 flights, but I guess we'll see.

[Keith Renecle]

For years I've been using a simple bellcrank made from 6 mm polyethylene which I'm told makes a nice bearing material. I stick a piano wire shaft through it. I saw a rather neat idea that Brian Eather uses on his Firecracker models. He uses a threaded rod, or bolt on a steel bellcrank with a nut soldered on each side. Just recently I took one of my polyethylene bellcranks and tapped a thread in the shaft hole and use a M4 threaded rod and it works well. You don't need any spacers either. At first I thought that the up and down movement could be a problem, but in practice the bellcrank only rotates over a small angle.

For connecting the lead-outs I use 1.5 mm galvanized household wire from any hardware store as you can see in the photos. For my take-apart models I use the Sullivan type of line connectors, and for the other models I loop the lead-out cable through the hole and crimp/bind it together.

Keith R

[Tim Wescott]

What Jim said about wobble -- that's exactly why my journal bearing has some height to it.

I suspect that if ball bearings made any difference either way, it'd be something on the order of a top-5 pilot at the Nats getting an average of 1/2 a point better, or less, and all of us lesser beings (even those who have a shot at top 20) wouldn't see any difference at all.

And from what I know about ball bearings, I'm not sure if that's be 1/2 point better, or 1/2 point worse.

I would take the effort involved in making a ball-bearing bellcrank and put it into making the rest of the control system as free as it can be where it should be free, and as rigid as it can be where it should be rigid.

[Dennis Toth]

I know this is an old thread but found some material that I was wondering if it was worth using from McMaster -  Garolite G-10 is also called epoxy-grade industrial laminate and phenolic (https://www.mcmaster.com/phenolic-sheets/thickness~1-8/width~2/). I know there is a linen based phenolic that has been used but this stuff is much stronger, twice the price is it over kill for bellcrank material?

Best,          DennisT

[Jim Svitko]

I am making bell cranks from the Garolite.  I use the 3/8 thick sheet and slot the ends for a teardrop fitting that holds the leadout cable.  The McMaster-Carr part number for the Garolite is 8474K161.  I think this is a resin-linen material.  It is easy to cut and shape and strong enough.  It has withstood my proof loads without any problem so I trust it.

There might be other suitable materials, and some Garolite versions that are stronger, but I see no reason to change what is working for me.

[John Carrodus]

 Being a retired 'Chalky' and really enjoying the pictures to illustrate the building of good CL hearts. As I get more seasoned, I often get befuddled trying to see between my ears what the writer is trying to get across. More photos, drawings etc please.

By the way. why are some bellcranks banana shaped? It's also interesting seeing how many bellcranks get drilled full of holes - no not the 4 we need, the big buggers for weight reduction. ( I often fill my models with holes wherever excess weight can be shed and cop flak for it! Ha!)

We are in the middle of the Covid wave going ballistic here in NZ so I'm staying at home doing lots of 'roundtoit' stuff and enjoying reading Stunthanger as often as my warrant officer will let me. Cheers form downunder.

[Lauri Malila]

You can buy Tufnol sheet (150X200mm, the Phenolic/Cotton type) cheap from toni-clark.com.
when properly drilled and oil-impregnated, it does not need any other bearing elements. L

[Motorman]

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[Dave Hull]

I know this is an old thread but found some material that I was wondering if it was worth using from McMaster -  Garolite G-10 is also called epoxy-grade industrial laminate and phenolic (https://www.mcmaster.com/phenolic-sheets/thickness~1-8/width~2/). I know there is a linen based phenolic that has been used but this stuff is much stronger, twice the price is it over kill for bellcrank material?


Dennis,

It really depends on what you are trying to do with it. How heavy a plane are we talking about? Assuming that you want it to survive the 10G pull test for stunt (and sport) models, I would add a factor of safety of at least 1.5. That is in the spirit of "let the lines break and not important stuff deep inside the plane."  If the 'crank was only around 1/2" wide at the base, and neglecting the output arm load sharing, the linen-based material isn't going to cut it for a 60 oz. airplane. Increasing the area moment (ie. "triangularizing" the shape of the crank, as opposed to a Brodak BB-389 kind of shape) is the quickest way to reduce the stresses. Or, if you didn't want to do that or had some kind of interference issue inside the wing, you could move up to the FRP (fiberglass reinforced plastic).

There are a lot of other factors such as the machinability. The circuit board material (epoxy-glass laminate; G-10 FRP) chews up bandsaw blades and anything else. If you are only making a couple, you may not care. The linen phenolic is much easier on tools but smells like a burning chicken house when you cut it. Again, cutting out one 'crank may not bother you. If you were making a handful while you had the tools out, then....

While most would say that the linen-phenolic materials make a decent bearing and can be lubricated without delaminating (the linen acting also as an oil reservoir), I'd have some reservations about the FRP. It is really abrasive. And while a bellcrank bearing is not a particularly difficult application to my thinking, it might start chewing on a steel post a bit. Probably not a worry unless you expect thousands of flights?

If you have a BC design you plan on making, toss us a sketch and the key dimensions and maybe we can get some real stress numbers for you.

Dave

[Dennis Toth]

The bellcrank I am planning on is for a 40 size ship <38 oz., it will be double ended 4" with 1/2"- 5/8" arms, this allows the flap horn and tail horn to be on the bottom (two pushrods, one to each side) of a profile ship. I think the 1/8" linin resin phenolic will be strong enough and reasonable to make with simple tools.

Best,     DennisT

[Motorman]

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[Ken Culbertson]

The bellcrank I am planning on is for a 40 size ship <38 oz., it will be double ended 4" with 1/2"- 5/8" arms, this allows the flap horn and tail horn to be on the bottom (two pushrods, one to each side) of a profile ship.

What does the plane look like.  I am having a hard time visualizing a pushrod exiting the bottom of the wing going directly to the elevator.  F-5 maybe?  What is gained by doing it this way?

Ken

[Dave Hull]

Here are some numbers for a 4" span BC made from 1/8" thick CE Phenolic. I assumed it was 1/2" wide in the middle and the pivot hole was 1/8".

The stresses are derived using your assumption of a 38 oz. airplane and the load case is the 10g pull test. The shear loads from this case are minimal, so I didn't bother with the von Mises stresses; thus, this is based entirely on the bending stresses. This small difference should be covered by the FOS.

The factor of safety was assumed to be 1.25. No material knockdown factor was used. The resulting margin of safety is 4%. Personally, I would design to a FOS of 1.5, minimum. In that case, your MOS is actually negative, which is bad.

There are other load cases and failure modes, but this is the one that most guys "intuit," using ROT (rule-of-thumb) methods.

It is also important to note that using McMasters material data is simplistic, at best. For example, they show no difference in the minimum tensile properties between the LE (linen) and the CE (canvas) grades. For comparison, one material manufacturer lists these two at 8,750 and 7,500 respectively. Using these values, and a FOS of 1.5 you end up with a positive MOS. This is exactly why the military and the FAA require formal material qualification testing and inclusion of that data in the approved database before the analysis is accepted. For most metallic materials this not a big deal since most of them are already in it. You simply must purchase the material with the requirement that it comply with such and such spec. For composites it is much, much harder. You have to qualify the producer, their process, and it is only for that manufacturing site. Just one reason that composite airplanes (and we're not talking about experimental homebuilts, here) are much more expensive to design and qualify.

Dave

[John Park]

Anyone have experience cutting this stuff?

Electric fretsaw with a very fine-toothed jeweller's piercing saw blade works for me.  I love that smell!

[Dennis Toth]

Ken,
The purpose for the double ended bellcrank is to be able to have the pushrods and horns on the bottom of a profile ship, simply for looks. They function the same and I like the clean look without the flap horn and pushrod over the top viewing area, just a personnel choice.

Dave,
Great spreadsheet, could you give the definitions for the acronyms. It's been a long time since I did any stress analysis and just would like to understand the terminology. From what I can tell the McMaster 1/8" Garolite LE phenolic resin material should be just fine for most bellcrank applications.

Best,    DennisT

[Ken Culbertson]

Ken,
The purpose for the double ended bellcrank is to be able to have the pushrods and horns on the bottom of a profile ship, simply for looks. They function the same and I like the clean look without the flap horn and pushrod over the top viewing area, just a personnel choice.

My question is with the routing of a pushrod exiting the bottom of a wing to an elevator above the wing without going through a flap horn.  That could only work on a plane that is inline.  I have no problem exiting the bottom.  The plane I am building right now goes out the bottom but for other reasons.

Ken

[Dennis Toth]

Ken,
The ship is going to be a Flat Winger - NAVY Avenger profile similar to the Aussie "Yardstick". With the controls on the bottom, it has a clean look to the top, yes, the elevator pushrod is next to the fuse and will need clearance around the flap but that is the same as if it were on top. The ship is in the layout stage will post pic's once I get going on the build.

Best,   DennisT

[Ken Culbertson]

Ken,
The ship is going to be a Flat Winger - NAVY Avenger profile similar to the Aussie "Yardstick". With the controls on the bottom, it has a clean look to the top, yes, the elevator pushrod is next to the fuse and will need clearance around the flap but that is the same as if it were on top. The ship is in the layout stage will post pic's once I get going on the build.

Best,   DennisT

Will your elevator pushrod be bent?  Last I checked the Avenger stab was well above the wing.  I am simply not getting the mental picture.   I will wait for the pictures.  I am sure you know what you are doing!

Ken

[Motorman]

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[Dennis Toth]

Ken,
If this were a scale ship it would be an issue, for semi-scale we can take some liberties with the layout. Although the stab is slightly high, I can drop it to the normal position on the top of the fuse so the pushrod will be in a normal angle. Also, because it is a Flat Winger (wing is 1/4" thick) the rods don't need to be bent but it is a good point, and I will look at it as the build beings.

MM,
I ordered the McMaster material today. Really nice BC I like the idea to use the two reinforcement of the bolt area and keeping the 1/4" radius of material around the holes, what did you use to cut it out?

Best,    DennisT

[Dave Hull]

BC--Bellcrank

Material Allowables--The published minimum properties of the material that are traceable to standard testing. This is easy with metals, which are generally isotropic. Much different with reinforced composites. Most of this test data is generated by a significant number of repeated tests (test coupons) allowing a statistically significant result.

Comp Strength--Compression Strength. You generally don't differentiate this from tensile strength for metals, but for composites it is a big deal. Note in the table that the difference between the two for Phenolic is a factor of 4. (The table is simplified. You actually need to know more things, but I didn't think it important to clutter things up.)

"Knockdown Factor"--a term used to include many things, such as the reduction of strength of plastic as used in a propeller due to significant temperature increases around the hub from engine heating. Also applies to fighter jet wings and structure due to friction heating (stagnation temperature). The knockdown factor will be unique to the load case and is based on materials test data.

FOS--Factor of Safety. This is a historically interesting factor that has always been applied to aircraft (and most everything else) to take into account the fact that analysis can't take everything into account. Strange combinations of loads, manufacturing variations, simplifications of the environment, etc.  It is a pretty interesting story to understand how the usual FOS for aircraft design became 1.15 many, many decades ago, and despite all the analysis tools we have benefit of today, it still remains 1.15, minimum.

MOS--Margin of safety. This term misleads people when they hear it, and perhaps try to apply a layman's interpretation. It is completely different than FOS; in fact, the MOS is derived using the FOS. Simply put, it is the "excess" structural capacity above the calculated stress.

Elastic Modulus or Young's Modulus--A measure of the stiffness inherent in the material

Perhaps another comment:  from your description, I assumed a BC shaped in planform like the Brodak BH-389. The geometry for that is nowhere near as robust as the skeletonized triangle that MM shows in his post. Another way of saying this is that the area moment of the triangular shape is huge compared to the simple bar-shaped BC, which is why it is popular. Less material, but better distributed, lower weight, higher strength and stiffness. He also benefits to some degree in that the extra thickness at the pivot which helps stabilize the BC from tipping moments caused by the now-ubiquitous ball or rod-end connection for the pushrod, also carries bending loads at the very center, which is the highest stress area. That's a two-fer in terms of weight.

[Tim Wescott]

Garolite G-10 is also called epoxy-grade industrial laminate

I am making bell cranks from the Garolite.

Gotta be careful with brand names.  G-10 is an epoxy-glass laminate.  Fiberglass is pretty abrasive; I wouldn't use it as a bearing unless someone has done fairly extensive testing and shown it doesn't wear the shaft.

The part number that Jim quotes is for phenolic-cotton -- phenolic-cotton and phenolic-linen laminates are known to be really good bearing materials (and plenty strong for a bellcrank).

If you were going to make the bellcrank itself out of G-10 -- sure, great stuff.  But marry that to some other material (phenolic-linen, aluminum or brass) for the actual bearing.

[Istvan Travnik]

Dear Jim Svitko,
My bet is on your solution! No need for added bushing/bearing, and this joint of leadout line is safe, elegant,and correct in the aspect of perfect, minimal friction-free requirements.
If you want to improve anything, you can change the good phenolic-linen material to ZX-100. (Less friction, no need for impregnating with oil/grease, and  absolute abrading-free. Maybe better vibrations damping. )
See:
https://www.zedex.de/en/brands/zx-100

And:
https://www.flickr.com/photos/171504164@N04/48094490337/

Istvan

[Jim Svitko]

Maybe a separate bearing is not needed, but I use a piece of brass tubing for bearing material.  The pivot shaft hole and the pushrod hole will get the brass tubing.  The teardrop fitting is nylon but I still use the brass tube here as well.

When drilling these materials, it is not like drilling metals.  Getting a precise hole is difficult.  Especially with the nylon, I found that you have to go slightly oversize but how much?  So, I will drill a nominal size hole and press the tubing in place, a slight interference fit.  The ID of the tubing matches common music wire diameters.  A drop or two of oil for lube.

[Motorman]

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