Bellcrank options

[Matt Brown]

I have these options to put in my new Brodak Legacy kit. On the left is the stock crank that came with the kit. In the middle is an Sig biased crank and on the right I think is a Tom Morris. I picked it up a couple years ago and don’t remember who I got it from. The Brodak and Morris are conventional cranks, only the material is different. I’d like to try to Sig since it’s different. I’ve been trying to think through what effect the bias will have but my brain isn’t working so great tonight!

Thanks, Matt

[Motorman]

I would shy away from the Brodak or the Sig on a full size stunter. I have used the Brodak on a Twister sized plane but the black polymite plastic version not the nylon unit. Also the offset in the Sig would feel less responsive and have less travel although I've never used one. Both of those are bolt on units.

The Tom Morris unit is basically bullet proof on a pull test. You'll have to determine where to drill the hole for the push rod. Tom Morris makes two size systems. If you use the smaller control horns I would drill 11/16" center to center from the pivot. If you use Toms longer control horns I would go 13/16" or maybe 7/8". I would draw it out on paper to make sure you have enough travel. Either way I think you'll find that particular bellcrank of Toms is very big but won't hurt anything. Make sure the lead outs move freely in the holes.

Hope that helps,
MM

[Dave_Trible]

Not thinking so much about materials or construction but rather configuration,  the bias crank I think I'd avoid.  Though I've never tried one I think the idea is for the crank to self-center in hopes of making level flight easier.  In fact I think it might fight you.  If it isn't exactly 'centered' at the same position the control surfaces are 'centered' they would be in a tension with each other meaning you would feel a need to apply a degree of up or down to hold the airplane in level flight.  Then you would expect the opposite to happen inverted.  Depending on any play in the controls or minor trim adjustment it might be fine one way and fight you the other.    To me this isn't worth taking a chance on.

Dave

[Matt Brown]

I was a little bit concerned about the leadout connections on the Tom Morris as they appear to be a crimped deal of some kind versus a typical wire wrapped termination. If I use it, I’ll do a good pull test on the terminations before it goes into the plane.

Matt

[Dave_Trible]

Now that you mention that there has been a lot of discussion about that lately after a couple high-end contest ships were lost due to crimped connections.   You are better off to cut those off and wrap your own with fine soft wire.....

Dave

[Matt Brown]

Not thinking so much about materials or construction but rather configuration,  the bias crank I think I'd avoid.  Though I've never tried one I think the idea is for the crank to self-center in hopes of making level flight easier.  In fact I think it might fight you.  If it isn't exactly 'centered' at the same position the control surfaces are 'centered' they would be in a tension with each other meaning you would feel a need to apply a degree of up or down to hold the airplane in level flight.  Then you would expect the opposite to happen inverted.  Depending on any play in the controls or minor trim adjustment it might be fine one way and fight you the other.    To me this isn't worth taking a chance on.

Dave

I was thinking that it would have the effect of helping with level flight which is something I’ve been needing. I’ve been flying SV11 ARFs the last several years and if I get them balanced to where they turn well, I can’t fly a decent level lap to save my soul. I got used to flying them nose heavy and not turning well so that I could fly a few level laps. I’ve been wanting to try more handle overhang to help but haven’t had weather or a handle with decent overhang yet.

Matt

[Howard Rush]

I don’t think the bellcrank will fix the level-flight problem.

I did an analysis of the “self-centering” bellcrank and posted it here somewhere.

[Matt Brown]

I don’t think the bellcrank will fix the level-flight problem.

I did an analysis of the “self-centering” bellcrank and posted it here somewhere.

I’ll go look for it. Maybe I’ll learn something!

Thanks, Matt

[John Rist]

deleted

[Dan McEntee]

I was thinking that it would have the effect of helping with level flight which is something I’ve been needing. I’ve been flying SV11 ARFs the last several years and if I get them balanced to where they turn well, I can’t fly a decent level lap to save my soul. I got used to flying them nose heavy and not turning well so that I could fly a few level laps. I’ve been wanting to try more handle overhang to help but haven’t had weather or a handle with decent overhang yet.

Matt

     You might try wider spacing instead of more over hang. If you have a 4" bell crank you want at least that much or more of handle spacing. I have been building and setting things up with the Bob Whitley method of bench trimming for years. Even models I rescue and previous owners plane get the treatment if I can. Basically that's 1 degree down thrust and 1 degree right thrust on the engine, and one degree or so positive incidence on the horizontal stab.  I can't remember that last model that I had a hunt problem after doing this.
  Type at you later,
    Dan McEntee

[Neil Rogers]

I have used all three of those bellcranks without issue.  I didn't notice anything different about using the Sig bellcrank other than it puts the up line at the front instead of the traditional back position.  My choice of the three would the the Tom Morris bellcrank.  They're well made and I've used them in a number of PA models.  The ends are wire wrapped with heat shrink tubing over the wrap.

[Dave_Trible]

I was thinking that it would have the effect of helping with level flight which is something I’ve been needing. I’ve been flying SV11 ARFs the last several years and if I get them balanced to where they turn well, I can’t fly a decent level lap to save my soul. I got used to flying them nose heavy and not turning well so that I could fly a few level laps. I’ve been wanting to try more handle overhang to help but haven’t had weather or a handle with decent overhang yet.

Matt

This sounds to me more a problem of the airplane being mis-aligned or the flaps and elevator not in sync or the controls too tight.  You may need to work on those things.  The bell crank wouldn't solve those problems.   

Dave

[doug coursey]

I was a little bit concerned about the leadout connections on the Tom Morris as they appear to be a crimped deal of some kind versus a typical wire wrapped termination. If I use it, I’ll do a good pull test on the terminations before it goes into the plane.

Matt

THEY ARE NOT KRIMPED THEY ARE SWEDGED WHICH IS DIFFENT AND DOESNT KINK THE CONNECTION

[Ken Culbertson]

I’ve been wanting to try more handle overhang to help but haven’t had weather or a handle with decent overhang yet.
Matt

Matt - Give some overhang a try.  I have tried to use the hardpoint type handle of my youth and found that I was just trading one form of hunting for another.  Overhang on a cable type handle has helped me overcome most of those issues.  It doesn't take much.  My handles are adjustable over about a 1" range and I have settled on about 1/2" from the knuckles on the up line and 5/8" on the down.  Flying nose heavy really helps smooth things out but I have never liked having to horse my plane through a maneuver just so I could fly a level lap.

On my latest, I have a canard up front and that alone let me move the CG 1/2" forward and still maintain the corner.  Still, I think most hunting issues are the plane not being in trim.  Moving the CG forward only masks the cause.

Another thing that I have tried that really works is TE fences on the stab.  I will leave it to the aerodynamics experts to explain why but they really smooth out level flight and the effectiveness of the elevator.

Ken 

[Matt Brown]

This sounds to me more a problem of the airplane being mis-aligned or the flaps and elevator not in sync or the controls too tight.  You may need to work on those things.  The bell crank wouldn't solve those problems.   

Dave

It is possible that the wing/tail/ engine isn’t in ideal alignment as Dan described. I pretty much assembled them as they fit together. I didn’t use an incidence meter on them and if I had, I’d have set them all at 0/0/0 not knowing any better. The controls are very free and flaps and elevators all line up as straight as I can see. As I have had several of these ARFs, I have noticed that the glow powered versions are easier to fly level and the electrics seem to have a touch of stiction when trying make tiny adjustments in level flight. I think the glow version don’t do this because the much greater vibration keeps the stiction out of system. All horns are brass bushed and Dubro ball links are on every connection.

Matt

[Dave Harmon]

All horns are brass bushed and Dubro ball links are on every connection.

Matt

Hi Matt....
I did the same on my first ROJETT 67 powered SV11 ARF but I still had a hunting problem.
I stupidly did not epoxy the flap and elevator couplers into the lucky boxes.
The hunting got worse and worse until it couldn't be ignored.
When I glued them in, magically it stopped hunting.
Not noticing this problem was I think, caused by having the c/g too far fwd....to me it felt like leading a dog on a leash with that fwd c/g.
When I moved the c/g aft is when the sloppy lucky box fit really showed up.

[Speed Demon]

Matt if you decide you don't have what you are needing or wanting, I can cut you carbon fiber one in any size or geometry to want.

[Matt Brown]

Hi Matt....
I did the same on my first ROJETT 67 powered SV11 ARF but I still had a hunting problem.
I stupidly did not epoxy the flap and elevator couplers into the lucky boxes.
The hunting got worse and worse until it couldn't be ignored.
When I glued them in, magically it stopped hunting.
Not noticing this problem was I think, caused by having the c/g too far fwd....to me it felt like leading a dog on a leash with that fwd c/g.
When I moved the c/g aft is when the sloppy lucky box fit really showed up.

Flap and elevator horns have all been epoxied from the beginning. All of the SV11s I’ve put together have also had ball links on all connections. Virtually zero slop on any of the planes. I’m getting things together to change over my current electric SV from 4S lipo to 6S 18650 system. This will definitely move the CG back, maybe too far! I just need to finish assembling batteries and swap out the motor for a lower KV unit. I’m also going to modify my handle for another 1/2” of overhang. Probably not all at once though. Just have to wait for tolerable weather to do any flight testing.  Nothing in the forecast for the next several weeks.

Matt

[Paul Van Dort]

I was thinking that it would have the effect of helping with level flight which is something I’ve been needing. I’ve been flying SV11 ARFs the last several years and if I get them balanced to where they turn well, I can’t fly a decent level lap to save my soul. I got used to flying them nose heavy and not turning well so that I could fly a few level laps. I’ve been wanting to try more handle overhang to help but haven’t had weather or a handle with decent overhang yet.

Matt

Hi Matt, make sure that the natural neutral of the handle aligns with the neutral of your hand. If those diverge, it becomes difficult to fly level. extra overhang makes the problem worse.  E.g. a symmetrical handle should not be flown with down or up biased in. It should be flown with the cable exits perpendicular to the lines. If that does not work for you, you need to make an assymetrical handle or purchase a fully adjustable one (3 parameters: Overhang per side. linelength and line distance)

[Dave Harmon]

Also....in my experience, hunting can be caused by the prop....especially Zinger props.
Not had any problems with APC.

[Dave_Trible]

Also....in my experience, hunting can be caused by the prop....especially Zinger props.
Not had any problems with APC.

But Dave,  they make great stir sticks for the dope......  Just FYI.

Dave

[Brett Buck]

   Hunting is almost always caused by control friction/binding somewhere and adding noseweight only slows it down, not fix it.

     There may be other problems, too, that are obscuring the binding. There is nothing about an SV-11 design-wise that requires you to pile on noseweight to the point you have trouble maneuvering and the CG position should be very tolerant. I would strongly suggest that you measure everything for straightness and alignment, return to a baseline "bench trim" and then start over. But *for sure*  check very carefully for any sort of binding, even the slightest rub anywhere will cause it.

     Brett

[fred cesquim]

i have used the SIG on quite a few planes, and the result is awesome, have no complaints at all, just make sure it´s centered perfectly and you have a smoother response than with the regular types

[Dan McEntee]

Hi Matt....
I did the same on my first ROJETT 67 powered SV11 ARF but I still had a hunting problem.
I stupidly did not epoxy the flap and elevator couplers into the lucky boxes.
The hunting got worse and worse until it couldn't be ignored.
When I glued them in, magically it stopped hunting.
Not noticing this problem was I think, caused by having the c/g too far fwd....to me it felt like leading a dog on a leash with that fwd c/g.
When I moved the c/g aft is when the sloppy lucky box fit really showed up.

   The purpose of a "Lucky Box" is to allow for some lateral movement of the horn due to misalignment. You should NOT epoxy a elevator/flap horn in a Lucky Box. If for whatever reason you have some misalignment, either accidental or on purpose because of a forward sweep in the hinge line or accidental misalignment, if you epoxy the horns in, they will never hold neutral and will pop over center, so to speak and if one does this, that means they both will and you have a hint, probably a pretty severe one.
  Type at you later,
  Dan McEntee

[Dan McEntee]

But Dave,  they make great stir sticks for the dope......  Just FYI.

Dave

     Or as a blank for carving something that might just work!!

   Type at you later,
   Dan McEntee

[Howard Rush]

E.g. a symmetrical handle should not be flown with down or up biased in. It should be flown with the cable exits perpendicular to the lines. If that does not work for you, you need to make an assymetrical handle or purchase a fully adjustable one (3 parameters: Overhang per side. linelength and line distance)

Or set the symmetrical handle so neutral is with the handle vertical and get used to flying it that way.

[Howard Rush]

Also....in my experience, hunting can be caused by the prop....especially Zinger props.
Not had any problems with APC.

Then you really wouldn't like the Igor hollow prop.  See Brett's note about friction.