Classic Designs > Classic Planes

4" Bellcranks, are they necessary in Classics??

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Jim Pollock:
Guys,

I have used and others have used 4" Bellcranks in .35 sized airplanes that were originally flown with
3" Bellcranks.  I have even made a 3.5" Bellcrank and used it in a Classic airplane.  I think that 3.5" is
really as large of a bellcrank that is needed for a 50-56" span classic.  I think the more important value
in a bellcrank is that amount of control throw built into it.  Example, a slow enough control system can be
built with a 3.5" bellcrank and a 9/16 throw.  What do y'all think, anway........

 

Bill Little:
Hi Jim,

For some reason, I like Tom's 3 1/2" bellcranks in the "standard Fox .35 size" Classic plane.

I found it interesting when a couple weeks ago, Kent Tysor flew my "restored" Charles Parrott P-47.  A pretty good sized "35 Classic".  I built it in '94, flew it in Classic for a year or so with a Fox 35.  Not enough engine, so I left it alone until a little over a year ago.  When I built it, I used a 3" Sig nylon BC, and some Top Flite horns I had.  It is now about 4 oz. lighter, and has a T&L McCoy 40 in it. 

Anyway, after Kent flew it, he remarked that he just couldn't fly it himself on a regular basis.  The controls were just too fast!  I was used to it, so it didn't bother me.............. but everything I have built of a serious nature in the past 10 years has had at least a 3 1/2" BC and "modern horns".

Dennis Adamisin:
Jim:
A lot of the classic plans show very short horns, sometimes on inner holes of bellcrank... mechanically they are a disaster!  Thus I think one of the best things you can do for most classic designs is to give them a modern control system.  For me that includes using the 4" cranks with the 15/16" (outermost) throw to a 15/16" elevator horn, flaps usually slower.  If the classic bird did not have room for a 4" crank then..... I guess I would readjust everything so the outputs came out the same.

Dennis Adamisin:
Jim P:
Thanks.  I believe in the early 1960's you will also find the name of a Mr. Gerry Cipra, who I believe earned the trophy as a JUNIOR.  And yes, he WAS that good!

I won Junior in 1969 with my Hawker Typhoon, in 1972 I flew my Fouga Magister in Senior & the Walker Cup.  Al was then, and still is the leading proponent of semi scale CLPA, we spent a lot of time chewing over this and that.  I still think the Sea Fury was the single most impressive CLPA model ever, but his new Bearcat looks pretty good too!

My tag line just lets me trash talk a little..!  8)

OK back on topic & CASE IN POINT: I am looking over Sheeks Swinger plan and the one thing I MUST change will be the controls.  The plans show the Pushrod going from #2 hole in the bellcrank to the middle hole of the flap.  Weak mechanically but not unheard of.  The killer is that it shows the elevator driven off the innermost hole off the flap, to the middle hole of the elevator; meaning the elevator travel will be 1/2 the flap travel - don't think Jack built his that way, and I for sure will not!  I will stuff a 4" bellcrank into it, reversed so front line is up (per Al!), and run a rod from the outer hole of the crank to the outer hole of the elevator.  I will then run a second rod from #2 hole in the crank to the outermost hole in the flap.  This should result in a 2:3 flap to elevator, and some pretty light bearing loads at all points.  However, I will also probably have to put a "hump" on the top of the fuselage to cover the longer horn!

Tom Niebuhr:
There is no doubt that the larger horns and Bellcranks, are much better because they have a better mechanical advantage. just remember that that the actual movement of the surfaces are due to the relative distance between the holes.

The only restricting factor, in some cases, is the available space.

Dennis,
Can't to wait to see your progress on the "Swinger"
I talked to your dad.. sound like you and Archie are both back! Boy, is that great!

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