Circular Bellcranks

[Bill Gruby]

  OK we are back to 101 again;

       I am working on something "BIG"----It is a profile----Big Block Fox .78.  I do not want to hear can that engine, it stays. The subject is "Bellcranks, Circular to be exact. I have never used one, I need input from those that have. This ship is in the 70-75 oz. range. 68" Span. OK let's hear from you. Good or Bad?

         "Billy G"   

[Randy Powell]

G-Man,

I've used them. They work, but in some ways overcomplicate the issue. Can be tough to make accurately and there is always the possibility of the cable skipping out of the groove. Somewhat different feel from a standard bellcrank.

[Willis Swindell]

Ditto on what Randy said that is the same feeling I got when I used them. I have made some fancy ones even with a top and bottom receiver so the cable couldn’t jump out.
Willis 

[Shultzie]

I have an old "KIDNEY shaped bellcrank that I salvaged from an old Kenhi Panther that I flew for a short time after I dorked my infamous old Blue Nobler that I won the Canadian Internats with in 1967. The controls were really sloppy and badly worn on tht old Kenhi Kitty so  can't give much of a review.
  I flew that old Panther for about a month with that half round bellcrank and what I remember most was the how that old model seemed to grooooooove so nicely and how how much "feel" that model seem to telegraph back to my handle. I could feel the smallest engine change vibration, and even the feeling of the smallest flutter of the flaps n' elavators.

After that old Kitty came apart IN THE AIR....(THE ENTIRE NOSE FELL AWAY DURING THE SQUARE 8's) That front end almost hit a car waaaaay over on the other side of the parking lot...and toasted that old McCoy Red head with a shaft run from hell after it hit the tarmac.

TALK ABOUT A STRANG FEELING..when trying to land a stunt model...SO DARNED TAIL HEAVY.....WITHOUT A FRONT END!!!

I couldn't  believe how ovaled out both the elevator and flap horns appeared. Amazing that model could fly at all....except I think it was Joe Dill who told me that some pretty successful stunt flyers...actually BUILD IN EXTRA SLOPPINESS into the elevator horn with an over sized dia. hole drilled so that the pushrod allows for extra....elevator slop.
(The weird idea that the elevator in flight will actually seek its netural setting)....so that if their was bellcrank..pushrod alignment was off a tad....this would actually prevent the "hunting" in level flight that some flapped stunters AND especially stunters with short distances from the flap hinge line to the elevator hinge line moment arms.

IS THIS AN OLD STUNT-GRUNT HUSBANDS TALE OR WHUT? 
Bottom Line:
I think the round or half round kidney shaped bellcranks were designed to induce a smoother and considerably more even rate of movement from full up to full down...without that uneven "Swing" feeling that a smaller sized normal T bellcrank telegraphs to the flyer?
ALL THIS IS PURE DRIVIL ANYHOO...except to say that I hope that someone who has worked with these interesting well thought out and designed bellcranks can JUMP IN HERE AND SET THE RECORD STRAIGHT...about their true benefits?

[Gary Anderson]

Hi, doesn't Mr. Ted Fancher use these type bellcranks? Gid used one in his Lazer and it flew very well. Never used one myself, heard stories about leadout lines coming off of the bellcrank. So I've stay away from them. I believe there is a lot of positive about them, Gary

[Randy Powell]

More accurate to say that Ted has used them. I think he came up with pretty much the same conclusion I did. They work fine but are a lot of extra work and you don't get a significant benefit.

[dennis lipsett]

Dynamic Models [Hi Johnson] used to sell circular bellcranks. I never used them but i do have a few NIP.
dennis

[Bill Gruby]

Dynamic Models [Hi Johnson] used to sell circular bellcranks. I never used them but i do have a few NIP.
dennis

   Dennis;

     Does this mean that one might be availlable? If so how big are they, I have a large one from "Golden State Models" in Kingsburg, Ca. I don't believe they are in business anymore. I tried to "google" them today -- nothing? I don't even remember how I got this one, I think it was in a package deal?

         "Billy G"

[Richard Grogan]

   Dennis;

     Does this mean that one might be availlable? If so how big are they, I have a large one from "Golden State Models" in Kingsburg, Ca. I don't believe they are in business anymore. I tried to "google" them today -- nothing? I don't even remember how I got this one, I think it was in a package deal?         "Billy G"

Probably came with a Big Block Fox .78 on e-bay.....  

[Greg L Bahrman]

More accurate to say that Ted has used them. I think he came up with pretty much the same conclusion I did. They work fine but are a lot of extra work and you don't get a significant benefit.

It's obvious that Randy has had some bad experience with this bellcrank which left a negative impression on him. I actually used it in one of my favorite planes for 8 years and found it to be a joy. Can't say it was really better than anything else, I guess that's a matter of opinion, but it did work really good. It installs just the same as any bellcrank with a shaft thru the center and captured at the top and the bottom. Check out the winning smile. I don't have a clue what Randy is talking about when he refers to all the extra work. Randy is the kind of guy that is always creating extra work for himself, he loves it. OK Randy, Your turn, but be nice or I will sick Bill on you.....Grins

[dennis lipsett]

   Dennis;

     Does this mean that one might be availlable? If so how big are they, I have a large one from "Golden State Models" in Kingsburg, Ca. I don't believe they are in business anymore. I tried to "google" them today -- nothing? I don't even remember how I got this one, I think it was in a package deal?

         "Billy G"
[/quote

Bill,
Found them and your probably not interested in them. I have 4 of them, all of them are 2 inch  for Rat/team race. They do however have all the hardware even a hex wrench . Don't know if I'd like a pulley type control system, perhaps I'll try one on something, sometime,someday. If you want one let me know, ok.
Dennis

[minnesotamodeler]

[
I couldn't  believe how ovaled out both the elevator and flap horns appeared. Amazing that model could fly at all....except I think it was Joe Dill who told me that some pretty successful stunt flyers...actually BUILD IN EXTRA SLOPPINESS into the elevator horn with an over sized dia. hole drilled so that the pushrod allows for extra....elevator slop.
(The weird idea that the elevator in flight will actually seek its netural setting)....so that if their was bellcrank..pushrod alignment was off a tad....this would actually prevent the "hunting" in level flight that some flapped stunters AND especially stunters with short distances from the flap hinge line to the elevator hinge line moment arms.

IS THIS AN OLD STUNT-GRUNT HUSBANDS TALE OR WHUT? 
eZ@@ZZZ

[/quote]

Dunno who else uses it, but it's an old Rat Racer trick from the 60s.  If your model had a hunting problem and balanced OK, the next step was to wallow out the hole in the elevator horn.  It always worked.  Only problem was, it would wear bigger quickly, to the point of wearing completely through, so you had to keep an eye on it.  I always figured it was from the elevator vibrating in flight or something.  Put on a new horn without wallowing out the hole and your hunting problem would reappear.  Weird.  I wish someone would explain the aerodynamics of that.

--Ray

[Bill Gruby]

  Ray;

    You are a "Glutton for Punishment". Didn't you get enough on the "Missing Formula" thread.      Explain the aerodynamics ot that indeed.

    To all of you thank-you. Jim Snelson at CL Central has agreed to build us a light weight, bullet proof control system for this project. A wonderful man to deal with.


   "G-Man"   

[dennis lipsett]

[
I couldn't  believe how ovaled out both the elevator and flap horns appeared. Amazing that model could fly at all....except I think it was Joe Dill who told me that some pretty successful stunt flyers...actually BUILD IN EXTRA SLOPPINESS into the elevator horn with an over sized dia. hole drilled so that the pushrod allows for extra....elevator slop.
(The weird idea that the elevator in flight will actually seek its netural setting)....so that if their was bellcrank..pushrod alignment was off a tad....this would actually prevent the "hunting" in level flight that some flapped stunters AND especially stunters with short distances from the flap hinge line to the elevator hinge line moment arms.

IS THIS AN OLD STUNT-GRUNT HUSBANDS TALE OR WHUT? 
eZ@@ZZZ



Dunno who else uses it, but it's an old Rat Racer trick from the 60s.  If your model had a hunting problem and balanced OK, the next step was to wallow out the hole in the elevator horn.  It always worked.  Only problem was, it would wear bigger quickly, to the point of wearing completely through, so you had to keep an eye on it.  I always figured it was from the elevator vibrating in flight or something.  Put on a new horn without wallowing out the hole and your hunting problem would reappear.  Weird.  I wish someone would explain the aerodynamics of that.

--Ray

Hi Ray, I flew Rat in the 60's up to 72. I don't remember seeing this trick used and I didn't use a loose control system. actually the faster it went the plane had a tendency to groove. Shame getting old I probably couldn't hold on to one for a complete tank anymore.
Dennis

[Scott Jenkins]

(The weird idea that the elevator in flight will actually seek its netural setting)....

Not really that wierd the faster you go the more instability is induced into the flight controls by the wind and lines being hit by the wind and even a hickup by the pilot therefore a little slop is a good thing. Most of those who race quickie rat and the faster events Goodyear and F2C actually do build a little slop into the controls to gain better control at high speed. Plus properply shaped and mounted control surfaces will not start to flutter until you get above 135 to 140 mph not something your average stunt plane has to worry about.

Scott

[Andrew Borgogna]

Will someone explain what the stated avantage of a circular bellcrank is over the traditional bellcrank.  The extra work must have yielded some benifit that nobody has yet mentioned or if they did it went over my head.  Second regarding "slop" in the elevator control horn Windy U. recommends it in his video CDs.  I forget the exact reason but it had to do with making trimming easier. 
Andy

[Randy Powell]

Greg,

No, no bad experience. As I say, they work fine. They give a bit smoother feel at the handle and you avoid the negative exponential progression that comes with a regular bellcrank, I suppose. I just didn't see any practical advantage to using one. If I had both, it might be worth using one for whatever advantage, real or preceived. But I just thought they were a lot of extra work for little real benefit.

[James Lee]

I've used round (circular) bell cranks in several planes....   Biggest practical problem I had was they tended to be a bit heavier...  And they take up a bit more room....   One benefit I found was on my Spirit of ST Louis OTS plane I was able to bring the leadouts out the side of the fuse through eyelets without cutting a big slot in the side to let the leadouts move fore and aft at the bellcrank....   FWIW...
thanks
Jim

[Shultzie]

Greg,

No, no bad experience. As I say, they work fine. They give a bit smoother feel at the handle and you avoid the negative exponential progression that comes with a regular bellcrank, I suppose. I just didn't see any practical advantage to using one. If I had both, it might be worth using one for whatever advantage, real or preceived. But I just thought they were a lot of extra work for little real benefit.

EXPOOOONENTIAL PROGRESSSSSSION DEEELEEEASH-US!
Thanks Randy I just learned a new word today!!! I couldn't put a name to that feeling I was gettin at the handle? 

[Steve Kientz]

 Since we're discussing circle bellcranks,I have a question. Has anyone tried to figure out a pull-pull system for control line?

Steve

[minnesotamodeler]

Been done, many times I think.  Don't know any more about it than that.

--Ray

[minnesotamodeler]

  Ray;

    You are a "Glutton for Punishment". Didn't you get enough on the "Missing Formula" thread.      Explain the aerodynamics ot that indeed.

   "G-Man"   

There is no end to my masochism...I never miss a chance to flaunt my ignorance.  I notice no-one's tackling the explanation.

Dennis, the "hunting" Rats were the exception, not the rule; they generally grooved well--just glorified, overpowered trainers, after all.  But for the occasional stubborn hunting problem, wallowing out the horn was a quick, sure fix.  Nothing worse than a Rat that won't sit where you put it, especially in a crowded circle.  Ever fly five up in contest conditions?

--Ray

[Bill Gruby]

   Steve and Ray;

          I just know I'm puttin my foot in it again, but would you PLEASE explain push pull method for me? Ignorance is not just your trait to flaunt Ray, I have a little myself, and for some reason never fail to let it hang right out there.



                    "Billy G"   

[rob biddle]

  I suppose if you built an oval shaped bellcrank you could have true exponential control, something I've been thinking about for a while but never had the patience to cut out the bits for a slotted bellcrank.

 Rob.

[minnesotamodeler]

   Steve and Ray;

          I just know I'm puttin my foot in it again, but would you PLEASE explain push pull method for me? Ignorance is not just your trait to flaunt Ray, I have a little myself, and for some reason never fail to let it hang right out there.



                    "Billy G"   

Bill, the common system we use is "push-pull", that's the action of the pushrod as the bellcrank moves.  A double system (pull-pull or push-push) uses a bellcrank with two pushrod arms, one outboard and one inboard, kinda like a cross or "x".  Then a double elevator horn, one above and one beneath.  2 pushrods (push-push) or two cables (pull-pull), one from each bellcrank arm to each horn.  Makes a very positive system with absolutely no slack or flex. Also very heavy, complex and hard to set up in that each pushrod or cable must be EXACTLY the same length.  And can you imagine the nightmare of trying to adjust elevator neutral with pushrod length?? (Lengthen one, must shorten the other)

Another kind of pull-pull system runs the flying lines directly to the double horns via pulleys or curved tubing, no bellcrank at all.  I made one like that once just to see if it would work, using curved tubing.  It did, sort of...if you don't count the problem of friction inside the tubing (squirt WD-40 down them before each flight) and the super-sensitive 1/1 control movement, hand to elevator.  Those 2 characteristics together made for a wild ride. You'd need about 2" tall horns to calm it down.  Fun to experiment with, though.

--Ray

[dennis lipsett]

There is no end to my masochism...I never miss a chance to flaunt my ignorance.  I notice no-one's tackling the explanation.

Dennis, the "hunting" Rats were the exception, not the rule; they generally grooved well--just glorified, overpowered trainers, after all.  But for the occasional stubborn hunting problem, wallowing out the horn was a quick, sure fix.  Nothing worse than a Rat that won't sit where you put it, especially in a crowded circle.  Ever fly five up in contest conditions?

--Ray

No 4 was my limit. it is crowded enough with that many up. Flying a fast rat was work but it was supposed to be fun too. Too many planes was to me an accident waiting to happen

[Mark Scarborough]

With regards to the pull pull system, I actually have talked to Randy about this one, I think he is out of town for the week so probably wont respond for a while, anyway, He has done a cable pull  pull system. RC guys do it on some larger scale ships too. In practice, this means there are two bellcranks, one at the control surface, and in the RC case on on the servol there is a cable attached to each end of the bellcrank so that a cable pulls the surface up, and a different cable on the other end pulls the cable down. adjusting can be lots of fun!!!One supposed benefit is that they system is in tension at all times with any direction of movement and makes more linear "feel " at the controls. I think Randy decided that like the circ bellcrank any percieved gains were mitigated by the intense amount of labor. With regards to the non-linearity natuer of a bellcrank system . I recieved a real eye opener about how much or how little movement is really needed to fly our planes. My Q ship in its short life, was ultra sensitive to control input, controls were set up per the instructions, I ended up with the handle spacing at slightly less than three inchs and it flew great, instant response, enough control to make hard corners. after I got it where It was good, I looked, from neutral to full up that I could put in at the handle, MAYBE about 15 degrees!!! I was shocked at how little movement was needed. Ant believe me, this was no featherweight airplane flitting about, she was a clydsdale, or as Randy put it, an offensivve tight end, not a wide reciever! Now mind you that was full deflection of the controls and I cant say I was using all of that in flight even on my squares! That said, I really think that the minor change in linearity of the conventional bellcrank is probably a mute point for most of us mortals anyway. I would put it in the realm of using 4-40 washers for adjusting tip weight, can YOU feel the difference? HOWEVER, I do know, the percieved difference, the cool factor, the comfort factor is something that cant be overlooked, I know I always feel more "in tune" with a plane I a plane I am flying that looks good, as opposed to one of my war weary oft repaired beasts. Honestly its more phsycological than we may want to admit, at least thats what my therapist says,,, hehehehehe,,,,

[minnesotamodeler]

No 4 was my limit. it is crowded enough with that many up. Flying a fast rat was work but it was supposed to be fun too. Too many planes was to me an accident waiting to happen

Yup, too crowded.  Even just 3 sometimes could get a little hairy.  So many things can happen in a Rat Race: Run out of fuel just as you pass someone, and have to "float" till they get out from under (shutoffs solved that); or get caught behind a slow plane with another over you, and have to pass under and run out around him, ducking under his lines, and trying to keep your feet, and trying to keep up with your plane all at once;  or deal with some idiot doing a VTO and catching EVERYBODY'S lines...planes that take off or land right through your (active) pit...I still have scars from that.

What a load of fun!!!

--RAy