Bellcrank stops.

[Curare]

Hey guys, I'm just about to glue a bellcrank, when suddenly I was struck by the fear of god.

I've got the bellcrank flap assembly moving smoothly, and not catching on anything, but the way it's all worked, I have about 75˚ of movement from centre. They're not even either. Should I be worried at this time? I'm assuming that the control surfaces will ultimately determine travel, but I'm just concerned that I should be throwing some stops in there to halt it going to far.

Am I right or wrong.

While we're on the subject, even if I have even travel in both directions, will I ever get there? Will the Netzeband wall stop me far before that?

Once again (for the fifty millionth time it seems) I apologise for clogging the forum with what must seem like stupid questions.

Thanks

Greg

[Perry Rose]

I try to get the bell crank away from any kind of interference. Then adjust the geometry to get equal up and down on the surfaces.

[EddyR]

Miss understood question.
Ed

[john e. holliday]

I have had bell cranks that would move well past what some would call normal movement.  Even my first Ringmaster years ago with about 80 degree elevator movement was fun and easy to fly.  But, I noticed in all circumstances that I could never move my wrist/arm far enough to get to those movements.   The one I had the most trouble with was a Ruffy I built for VSC and never got to fly there had about 20 degree flap with 25 degree elevator and a bell crank that moved very little to get there.  The plane was very quick on turns and I never could get a smooth pattern out of it.   My ISW, a Red Rheinhardt design has lots of bell crank movement with the pushrod as close to the pivot point as I could get it.  Had to drill new hole in bell crank to get it to match the plans.   Now before you put stops in,  hook your handle to the leadouts and see if you can move it far enough to lock up before continuing.

[Juan Valentin]

 Hello Greg
                       I placed stops at 45 degrees on the bellcrank of my scratchbuilt P-51B profile and didn`t notice any ill effects. The plane was a great flier but I crashed due to a mental lapse. I dont think that I was hitting the stops in flight and the plane would turn equally both ways. What I liked was that I was able to set my flight controls for equal travel without guessing I used a gauge a friend loaned me to make sure I had 45 degrees of travel both in the flaps and elevator. I will be building another one and will place the stops on the bellcrank again. I`m building a Jetco Dolphin and didn`t put any stops on the bell crank and I also have more travel one way than the other I left a hole on the center sheeting to see bellcrank centered position  to make sure I have the same amount of travel at 45 degrees of bellcrank travel..Here are some pics.

[Brett Buck]

Hey guys, I'm just about to glue a bellcrank, when suddenly I was struck by the fear of god.

I've got the bellcrank flap assembly moving smoothly, and not catching on anything, but the way it's all worked, I have about 75˚ of movement from centre. They're not even either. Should I be worried at this time? I'm assuming that the control surfaces will ultimately determine travel, but I'm just concerned that I should be throwing some stops in there to halt it going to far.

Am I right or wrong.

While we're on the subject, even if I have even travel in both directions, will I ever get there? Will the Netzeband wall stop me far before that?

Once again (for the fifty millionth time it seems) I apologise for clogging the forum with what must seem like stupid questions.

    There's no reason to have stops that I can think of.

    Brett

[bob whitney]

just a reminder ,if u use stops ,,everytime u hit a stop, the complete weight of the plane is in one line, so instead of two .015 =.030 or two .018=.036  evrything is on one .015 or .018

[Larry Fernandez]

Hello Greg
                       I placed stops at 45 degrees on the bellcrank of my scratchbuilt P-51B profile and didn`t notice any ill effects.


Juan. if you relocate  the push-rod to the inner hole of the bell crank, you would not need the stops.

Larry, Buttafucco Stunt Team

[Mike Lauerman]

I'm gonna go with Bob here, 'cuz it reminds me of Hollywood Squares.

...and 'cuz it makes the most sense!

[Juan Valentin]

Hello Larry
                      If I would have moved The bellcrank hole in I wouldn`t be able to achieve the deflection of 45 degrees at the elevator and flaps without moving the pushrod on the flap to a lower hole. I ended reducing the travel on both by going to the top hole in my flap horn and moving the lines in on my handle. I flew the plane many times without any of the lines going slack But I have to say that what Bob Whitney says makes sense.
                                                                                                    Juan

[Steve Helmick]

    There's no reason to have stops that I can think of.

    Brett

I recall an instance where Mr. Fancher had a line break on pulltest, possibly at a WC or TT. The pull went directly to one line, pushed or pulled the pushrod far past normal, and screwed up the flap horn support bearing in some way. Some sort of limit stops would have prevented this. I have not figured out a wonderful way to put stops in, but some sort of shock absorbing material would seem best. Hard rubber, etc. I did decide that it would be best to have the stop coincide with the end of the BC arms on each side.

As for actual flight, there is no need, because you can't possibly use more than 15*-20* (each direction). But if one line does break, then having more control would be good, because it will slow the plane and (in theory) reduce the effort it expends on bending Mother Earth.   Steve

[Brian Hampton]

I use bellcrank stops (as for instance in my SV-11) set at 45 degrees bellcrank travel mainly so that it's not the control system itself taking maximum deflection loads. I then arrange control horn lengths to give a maximum deflection of 25 degrees for the flaps and 35 for elevators which generally is more movement than you use in flight with normal hand movement.

[Curare]

Thanks for all the input guys, I'll run without any on this one. As I said I've got about 75° from centre up and down before I hit the main spar. If it ever gets to that point I'm pretty sure I'll have a bigger problem than an over worked bellcrank!

[bob whitney]

i have been thinking about the problem when one line breaks on pull test more than one plane has been busted up  what would happen if u hooked both lines together for the pull test  .i dont even know if it is legal , just a thought

[Trostle]

i have been thinking about the problem when one line breaks on pull test more than one plane has been busted up  what would happen if u hooked both lines together for the pull test  .i dont even know if it is legal , just a thought

The pull test is intended to put a load on the entire control system, including the handle, lines, leadouts, line clips, leadout attachment to the bellcrank and the bellcrank mount.  An Event Director who allows only a pull test on the lines is not doing his job.  And actually, the thong is also to be pull tested.

regarding some other comments on this thread about stops for limiting the bellcrank deflection --  I see no need to design or build an airplane to withstand a pull test failure.  Just like, there is no need to design and build a CLPA airplane to withstand a crash.  To do so means that something is added to the structure that does nothing other than add weight which only impairs the model performance.

Like Brett said, there is no reason to add stops to limit the bellcrank movement.

Keith