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Author Topic: Bellcrank Inspection Panel  (Read 1779 times)

Offline Alex Shongut

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Bellcrank Inspection Panel
« on: February 01, 2021, 06:18:30 AM »
I'm working on scratch building a basic trainer from outerzone plans with a built up wing. I was going to sheet the entire wing and then fiberglass. However, I realize it will be difficult to inspect the bellcrank once the wing is fully fiber glassed and sheeted. Have other modelers been known to cut an inspection panel in the wing just large enough to inspect the bell crank?

https://outerzone.co.uk/plan_details.asp?ID=8692

Offline Dave Rigotti

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Re: Bellcrank Inspection Panel
« Reply #1 on: February 01, 2021, 07:14:17 AM »
Care to share how you make yours 100% dependable?  Seem we have a newbie asking here and I'll bet they would like to know.....
Dave Rigotti
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Offline Dan McEntee

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Re: Bellcrank Inspection Panel
« Reply #2 on: February 01, 2021, 07:19:27 AM »
    Not generally. You do fine removable covers on some ARF models, and that will let you inspect the bell crank if you desire to. But for the most part, most people just use good materials and construction methods, and once the bell crank is installed and wing completed, you can have the confidence that the controls will out live the rest of the airplane and no need to inspect it. The basic rules of thumb are:
   
      1) Don't use a metal bell crank and cable lead outs, or the bell crank will saw through the cable. This can happen in an amazingly short number of flights. The answer is to bush the bell crank with brass bushings at the cable attachment point. This can also be done by slipping a length of brass or copper tubing over the cable, then bending that assembly into a tear drop shape, running that through the bell crank.

    2) Use solid wire lead outs with metal bell cranks. On most models, .030" music wire is plenty big for lead outs. The main caution here is to avoid sharp bends that may fracture and break from vibration and stress. Always have some kind of radius at any bend and this is accomplished with round nose pliers.  Some of us don't like solid lead outs because the exposed ends at the wing tips tend to catch on things when handling the model and you get lots of "twanging" with that.

   3) If using a plastic bell crank and cable lead outs, it still pays to bush the bell crank. My son Sean lost a model at the NATS one year that didn't have a lot of time on it, because the up lead out broke at the bell crank. In retrospective thinking about it, I think he may have just cinched the cable too tight at the bell crank when terminating the lead outs. I didn't get the chance to check them out before he sheeted the wing, but after looking at them after the crash, I'm pretty sure that may have been the cause. If too tight, you can still get a lot of stress on the cable as the bell crank moves and saw the bale through.

   Search out bell crank on the forum here and you will find all sorts of different methods of building bell cranks and there operations. In the upper levels of the event with more powerful models and power plants, you need more strength. One thing that applies to all is that you want them as free and smooth as possible or it really shows during the pattern and can cause fatal results during flight. But once you learn what works and is known to be bullet proof, you won't need to have any method of inspection. A more desirable option would be the ability to adjust the push rods and maybe even the rod position on the horn.

  Type at you later,
    Dan McEntee
AMA 28784
EAA  1038824
AMA 480405 (American Motorcyclist Association)

Offline Alex Shongut

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Re: Bellcrank Inspection Panel
« Reply #3 on: February 01, 2021, 07:33:51 AM »
    Not generally. You do fine removable covers on some ARF models, and that will let you inspect the bell crank if you desire to. But for the most part, most people just use good materials and construction methods, and once the bell crank is installed and wing completed, you can have the confidence that the controls will out live the rest of the airplane and no need to inspect it. The basic rules of thumb are:
   
      1) Don't use a metal bell crank and cable lead outs, or the bell crank will saw through the cable. This can happen in an amazingly short number of flights. The answer is to bush the bell crank with brass bushings at the cable attachment point. This can also be done by slipping a length of brass or copper tubing over the cable, then bending that assembly into a tear drop shape, running that through the bell crank.

    2) Use solid wire lead outs with metal bell cranks. On most models, .030" music wire is plenty big for lead outs. The main caution here is to avoid sharp bends that may fracture and break from vibration and stress. Always have some kind of radius at any bend and this is accomplished with round nose pliers.  Some of us don't like solid lead outs because the exposed ends at the wing tips tend to catch on things when handling the model and you get lots of "twanging" with that.

   3) If using a plastic bell crank and cable lead outs, it still pays to bush the bell crank. My son Sean lost a model at the NATS one year that didn't have a lot of time on it, because the up lead out broke at the bell crank. In retrospective thinking about it, I think he may have just cinched the cable too tight at the bell crank when terminating the lead outs. I didn't get the chance to check them out before he sheeted the wing, but after looking at them after the crash, I'm pretty sure that may have been the cause. If too tight, you can still get a lot of stress on the cable as the bell crank moves and saw the bale through.

   Search out bell crank on the forum here and you will find all sorts of different methods of building bell cranks and there operations. In the upper levels of the event with more powerful models and power plants, you need more strength. One thing that applies to all is that you want them as free and smooth as possible or it really shows during the pattern and can cause fatal results during flight. But once you learn what works and is known to be bullet proof, you won't need to have any method of inspection. A more desirable option would be the ability to adjust the push rods and maybe even the rod position on the horn.

  Type at you later,
    Dan McEntee

Thanks for your comment. I have some aluminum tubing and aluminum eyelets. Would that be ok to bush the bell crank instead of using brass? I'm using this for a .15 - .19 size plane.

Online Ken Culbertson

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Re: Bellcrank Inspection Panel
« Reply #4 on: February 01, 2021, 09:24:02 AM »
My first reaction was to disagree and argue that an inspection panel is a plus especially if you use ball links at the bellcrank.  I have also toyed with adjustable settings to get different flap ratio's.  I think that is a mistake now and making the flap horn accessible and adjustable eliminates any need to ever see the bellcrank again if you do it right in the first place.  One thing I would add to all that has been said here is to wrap the leads at the bellcrank instead of crimping.  I have never had a wrapped one fail but I have had several crimped ones either fail or get snagged on something.

Ken
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If it is not broke you are not trying hard enough.
USAF 1968-1974 TAC

Offline Alex Shongut

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Re: Bellcrank Inspection Panel
« Reply #5 on: February 01, 2021, 10:19:22 AM »
The airplane you linked has a solid wing with the bellcrank on the bottom.

I'm building the built up wing version

Offline Howard Rush

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Re: Bellcrank Inspection Panel
« Reply #6 on: February 04, 2021, 01:42:54 PM »
Alex makes an interesting point and has us thinking about something we may not have thought about.  Inspection panels are common in other areas of human endeavor.  I don't think I ever considered one for a combat plane, because every four flights or so I was able to inspect the bellcrank when I transferred it to a new plane.  Stunt planes last a lot longer and are worth more, so an inspection panel may be prudent.  The picture below shows what happened when a stunt plane leadout wire bumped a rib just a little at full control deflection.  Here is a story about a consequence of inadequate control system access: https://stunthanger.com/smf/open-forum/abusing-medical-technology-to-oil-soak-the-inside-of-my-airplane/msg535214/#msg535214 .  My new stunt plane comes all apart, so its mechanisms are all controllable and observable, so to speak. 

Alex asks about aluminum bushings.   I've noticed that cable leadouts saw through aluminum bellcranks and aluminum leadout guides, so I would be shy about having anything rubbing on aluminum. 
The Jive Combat Team
Making combat and stunt great again

Online Ken Culbertson

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Re: Bellcrank Inspection Panel
« Reply #7 on: February 04, 2021, 03:07:14 PM »
Alex makes an interesting point and has us thinking about something we may not have thought about.  Inspection panels are common in other areas of human endeavor.  I don't think I ever considered one for a combat plane, because every four flights or so I was able to inspect the bellcrank when I transferred it to a new plane.  Stunt planes last a lot longer and are worth more, so an inspection panel may be prudent.  The picture below shows what happened when a stunt plane leadout wire bumped a rib just a little at full control deflection.  Here is a story about a consequence of inadequate control system access: https://stunthanger.com/smf/open-forum/abusing-medical-technology-to-oil-soak-the-inside-of-my-airplane/msg535214/#msg535214 .  My new stunt plane comes all apart, so its mechanisms are all controllable and observable, so to speak. 

Alex asks about aluminum bushings.   I've noticed that cable leadouts saw through aluminum bellcranks and aluminum leadout guides, so I would be shy about having anything rubbing on aluminum.
That is why God invented heat shrink.  y1
Ken
AMA 15382
If it is not broke you are not trying hard enough.
USAF 1968-1974 TAC

Offline Dave Hull

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Re: Bellcrank Inspection Panel
« Reply #8 on: February 05, 2021, 05:29:50 PM »
Howard,

Care to explain how "The picture below shows what happened when a stunt plane leadout wire bumped a rib just a little at full control deflection."  What the picture seems to show is a stress concentration failure at the leadout termination. Sooooo.....?

Dave 

Offline Howard Rush

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Re: Bellcrank Inspection Panel
« Reply #9 on: February 06, 2021, 04:26:04 PM »
Howard,

Care to explain how "The picture below shows what happened when a stunt plane leadout wire bumped a rib just a little at full control deflection."  What the picture seems to show is a stress concentration failure at the leadout termination. Sooooo.....?

Dave 

Each time the wire bumped the rib it put the leadout in some bending at that termination.  I presume it fatigued. 

Stunt advice from the Jive Combat Team: if you are flying a stunt plane and a line goes sproing, you probably hit an insect, but if there's a shift in neutral, you should look in your bellcrank inspection panel. 
The Jive Combat Team
Making combat and stunt great again

Offline Shorts,David

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Re: Bellcrank Inspection Panel
« Reply #10 on: February 07, 2021, 12:01:09 AM »
I don't have any pictures I can upload, but my newest stunt plane, still uncovered, has two inspection panels made from lexan and painted with a transparent red which I hope will blend with the paint job.
Why?
Cause.
Why two inspection panels?
So you'll know it wasn't a mistake.
Of course, that's not the only unusual idea about my new plane...i.e. formula for disaster...or just maybe--mediocrity.

Offline kevin king

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Re: Bellcrank Inspection Panel
« Reply #11 on: February 16, 2021, 02:02:05 PM »
I don't think I would sheet and fibre glass the entire wing. Seems a bit much to me.


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