Two inch bellcrank in CG Cosmic Wind?

[Joe Ed Pederson]

I'm restoring a 1960s Carl Goldberg Cosmic Wind built by a friend.  I was surprised to discover it had a 2" bellcrank.  Did Carl Goldberg put 2" bellcranks in the kit or did my friend change it to a 2" bellcrank?   This sure helps to explain why the plane was so twitchy.

I'm going to replace the 2" bellcrank with 3 1/2" bellcrank.

Would it be a good idea to blunt the leading edge before recovering the wing?

Joe Ed Pederson
Cuba, MO

[Dave_Trible]

Jo Ed that is a great flying little airplane as is kit form.  There would be nothing to gain by altering the standard leading edge.  As far as the crank goes- I don’t remember but the hole spacing in the ribs for the lead outs should tell you.  No harm in going to a larger bellcrank.  I enjoyed many evenings in a pasture with the one I had (Fox .35).

Dave

[Will Hinton]

In the late 60's early 70's our club had an "official" combat event that went all summer and the rules were simple and made everyone equal except for the flying abilities.  The plane had to be a CG model with Fox 35 and 5% fuel and same props.  What a blast that was.  They were/are great airplanes.

[Dave_Trible]

I found my Cosmic Wind plans.  They plainly say to purchase and install a good quality 3" bellcrank.

Dave

[Joe Ed Pederson]

Dave,

Thanks for your responses.  I'll leave the leading edge alone and install a 3 12" bellcrank from Tom Morris.

In my late teens I built a Goldberg Shoestring.  I covered the wings with transparent orange Monokote.   It was neat seeing inside the wing.    I might still have that plane, but it was my first experience with Monokote and didn't know how to seal the monokote so oil wouldn't get under it. 

Now that I'm 65, I would rather use Polyspan and dope despite how time consuming a dope finish is.

Thanks again for responding,
Joe Ed

[Dan McEntee]

   Hi Joe;
  A 2" bell crank ain't the best control option, but they can be dealt with. Sterling put out Ringmaster kits at some time along it's history that came with solid rubber wheels that looked like they came off a toy truck and a two inch bell crank. I have a Craig's List rescue Ringmaster that was built from one of those kits. It was still in pretty good shape and an examination showed that it was quite sound and ready to fly. I didn't see any sense in cutting things open to change the bell crank, so I just lengthened the control horn to almost 1 1/4" or more and narrowed the handle line spacing to almost two inches to slow the controls down. It's very flyable and good enough for a loaner, balloon bust, that sort of thing. It flies the OTS pattern quite well and has a venerable Fox.35 in the nose. I recently acquired another one, but this one may get the 3" crank treatment, as it's not in as nice shape. I wouldn't install a 2" bell crank on purpose unless  there wasn't room for anything else or it is a speed model, but in a case like the one I explained, it can be made to function. A stock Ringmaster with 2" bell crank and a Hot Rock or 5" EZ Just handle and that short elevator horn is just about un-flyable! No wonder so many people had problems back in the day!  A Shoestring or other Goldberg model would pretty much be the same.
  Type at you later,
   Dan McEntee

[Howard Rush]

3 1/2” sounds good.

[L0U CRANE]

Personally, I see no reason to use less than a 3" bellcrank in ANYTHING we wish to stunt - including 1/2A models!

Consider: most of us started with something simple (think Ringmaster and Fox 35, or the more recent more or less equivalents.)

The handle motions and the travels of the control surface horn(s) were proportioned to be comfortable for flying. The line separation at the handle fitted outside our fingers, and the range of 'wrist' angle required also fitted comfortably.

THOSE relationships do not depend on wingspan! So many small models have been declared touchy, nearly uncontrollable, because the relationships of hand size, angle range, line separation and horn radii were shrunk too far.

Larger 'span' bellcranks are longer levers to operate controls as needed for heavier models, and the greater 'mechanical advantage' is useful to make the needed surface motions.

If it takes somewhat more 'wrist' to input for a square turn, we can do that. We gain a wider "dead zone" around neutral for level flight and straight sides to square and triangular segments...

Weight is not a consideration! Yes, it could be measured in grams, but not that many of them - in view of the comfort gain.

Thoughts, just IM(notso)HO.

[Joe Ed Pederson]

Personally, I see no reason to use less than a 3" bellcrank in ANYTHING we wish to stunt - including 1/2A models!

When I was a kid, we were more than happy if we could get the motor started and fly the plane until the fuel ran out.  I had no idea of all the ins and outs of control line.  Probably still wouldn't if it weren't for Stunthanger and PAMPA's magazine.  I wouldn't know about Stunthanger if it weren't for Dan McEntee who clued me in a while back. Thanks, Dan.

And a big thank you to Mr. Stunthanger, RC Storick, for creating and maintaining this wonderful site.  And if you see this RC, please demote me to "Beginner."  I'm still a beginner no matter how many times I've posted.  When it comes to knowledge, skill, flying ability, etc. I'm no commander of CL.

I'm going to switch my two sheet balsa wing 1/2As, a Sig 1/A Skyray and a Rick Sarpolus Beech Bonanza to 3" bellcranks.  Fortunately, Sig still makes a nylon 1/2A three inch bellcrank.  Of course, one could always make a 3" bellcrank out of plywood like all the 1960's Carl Goldberg 1/2A kits made 2" bellcranks out of plywood.  (I don't think there's a single CG 1/2A kit I didn't build as a kid.)    There isn't enough room in the Baby Barnstormer I'm building to install a 3" bellcrank, so I'm stuck there.

Gratefully,
Joe Ed Pederson
Cuba, MO

[Ken Culbertson]

THOSE relationships do not depend on wingspan! So many small models have been declared touchy, nearly uncontrollable, because the relationships of hand size, angle range, line separation and horn radii were shrunk too far.

Larger 'span' bellcranks are longer levers to operate controls as needed for heavier models, and the greater 'mechanical advantage' is useful to make the needed surface motions.

Thoughts, just IM(notso)HO.

Lou:

Everything you say is true and I certainly prefer a 4" if it will fit, however, the mechanical advantage comes from the length of the horns and the length of the connection arm.  The force to drive it comes from the length of the bellcrank arms coupled to the line spacing.  Equal force can be applied to the flap horn with any size bellcrank(within reason).  To me the only reason to use a larger bellcrank is that you have a wider line spacing at the handle which takes some pressure off of your wrist.

I was out of the hobby for about 30 years and when I returned "everything" had changed.  Few models used 4" when I left, in fact I don't think anybody manufactured them (I could be wrong since I wasn't looking for them).  PA type planes were lighter, most around 40oz.  Line pull was something we begged for.  When I came back I quickly built two ships.  One was a .35/40oz size since (I had an engine) with a 3" crank and the other was a .46/50oz with a 4" crank.  Once trimmed, there is no real difference in response.  Line spacing is quite different.

Personally I don't like my planes to require massive differences in control input to fly the pattern.  The first thing I noticed when I flew the 4" was that I needed a whole lot more wrist to turn a tight corner.  Since I am a "finger" type this was uncomfortable so I moved the line spacing out till it turned quick enough for me.  Surprisingly, there was not enough difference in the pressure on my wrist to be noticeable. 

This is NOT an argument against 4" cranks, quite the opposite, it is just that they don't make the plane fly any different.  What they do is make it easier for us to make them fly the same which, in many ways was your point.

I don't see how this argument would be any different going from a 2" to a 3" on a 1/2a.  I doubt seriously that any of us complain about line pull on a plane that small and the line spacing and horn height can easily be adjusted to give it proper response but like many things, my opinions are based on years of personal experience and are 100% open to being changed by a superior argument.

Ken

[L0U CRANE]

Joe Ed and Ken, thanks for your adding thoughts of value to this...

Couple more ideas that may "amuse." Fitting an "oversize" bellcrank into a small wing? Think - the bellcrank pivot location is NOT critical! What IS critical is the location of the leadout guides with regard to the CG.

As long as you  can set a definite neutral, and the leadouts won't chafe, bind  or saw through the guides, it can be anywhere (within reason.)
 
Of course, the forces depend on the relative lever lengths, and the loads they have to meet. If that is "scaled" up or down at the same proportions, at least the control surface response angles will be much the same. We know pretty well how to refine that to our preferences..

[Joe Ed Pederson]

Lou,

Thanks for the info on bellcrank pivot location.  I had assumed it was dangerous to move the pivot point from the location shown on the plans.   I also thought the pivot point was placed as near the spars as possible to keep from pulling the bellcrank out of the model during pull tests.

Joe Ed

[Ken Culbertson]

Lou,

Thanks for the info on bellcrank pivot location.  I had assumed it was dangerous to move the pivot point from the location shown on the plans.   I also thought the pivot point was placed as near the spars as possible to keep from pulling the bellcrank out of the model during pull tests.

Joe Ed

You are correct in your second assumption.  Where it is doesn't affect how it performs but mounting it where it gains the most strength from the surrounding structure is important.  Let that guide you.

Ken