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Author Topic: 4" Bellcranks, are they necessary in Classics??  (Read 6904 times)

Offline Jim Pollock

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4" Bellcranks, are they necessary in Classics??
« on: June 23, 2007, 09:24:15 PM »
Guys,

I have used  4" Bellcranks in .35 sized airplanes that were originally flown with
3" Bellcranks.   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.


 
« Last Edit: September 21, 2023, 12:04:04 AM by Ty Marcucci »

Offline Dennis Adamisin

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Re: 4" Bellcranks, are they necessary in Classics??
« Reply #1 on: June 24, 2007, 07:35:07 AM »
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.

Denny Adamisin
Fort Wayne, IN

As I've grown older, I've learned that pleasing everyone is impossible, but pissing everyone off is a piece of cake!

Offline Dennis Adamisin

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Re: 4" Bellcranks, are they necessary in Classics??
« Reply #2 on: June 24, 2007, 10:03:37 PM »
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!
Denny Adamisin
Fort Wayne, IN

As I've grown older, I've learned that pleasing everyone is impossible, but pissing everyone off is a piece of cake!

Offline Dennis Adamisin

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Re: 4" Bellcranks, are they necessary in Classics??
« Reply #3 on: June 25, 2007, 05:04:17 PM »
John & Tom:
You are right, I can get the correct ratios, but to do so inside the low Swinger fuselage means using a 1/2" horn on the flaps, with corresponding short output off the bellcrank.  However, I get real anal about maximizing the mechanical advantage and reducing bushing loads.  Thus I intend to use the 3/4" output from the bellcrank to a 1" flap horn.  Unfortunately that is about 1/4" ABOVE the top of the fuselage, thus the "radome" bump, which should look right at home on the jet anyway.  You know the Type 13 radar used on the second production batch of the F111b... - HONEST!!!  n~
Denny Adamisin
Fort Wayne, IN

As I've grown older, I've learned that pleasing everyone is impossible, but pissing everyone off is a piece of cake!

Offline Dennis Adamisin

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Re: 4" Bellcranks, are they necessary in Classics??
« Reply #4 on: June 25, 2007, 08:45:44 PM »
BTW, just checked out the plans for Sheeks Ryan SC and Bob Millers "extended Gee Bee"  Both show the elevator pushrod set up to give LESS elevator than flap throw.  This cannot be right (can it???)

Denny Adamisin
Fort Wayne, IN

As I've grown older, I've learned that pleasing everyone is impossible, but pissing everyone off is a piece of cake!

Online John Miller

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Re: 4" Bellcranks, are they necessary in Classics??
« Reply #5 on: June 25, 2007, 09:16:07 PM »
Ya know, Dennis, in the old days, we simply used 1 to 1 ratio for the flaps and elevators. Nowadays, with planes with a reasonable wing loading, we've found that we don't need as much flap as we used to use.

I was speaking with Gordan Delaney about this very subject, the other day. He and I both agree that most of our planes have about a 6 or 7 degree difference, at full throw. The degree readouts on my most recent plane is about 24 degrees flaps, and about 32 degrees for the elevator. It's a very good idea to use an adjustable elevator horn. Too much flap can make "swoopy" turns, as I'm sure you already know..

John
Getting a line on life. AMA 1601

Offline Dennis Adamisin

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Re: 4" Bellcranks, are they necessary in Classics??
« Reply #6 on: June 26, 2007, 07:17:59 PM »
Yup.  Kinda hard to explain it was a model of a French trainer in Belgian Airshow Team colors.  However, one guy called it a Nobler....

Denny Adamisin
Fort Wayne, IN

As I've grown older, I've learned that pleasing everyone is impossible, but pissing everyone off is a piece of cake!

Offline tom hampshire

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Re: 4" Bellcranks, are they necessary in Classics??
« Reply #7 on: August 13, 2007, 07:27:49 AM »
The above posts are all correct.  BUT... It is humbly submitted that the missing part of the analysis so far is the ergonomics, meaning the hand movement necessary to generate a given control deflection.  Clearly, a 3 incher will give more angular bellcrank deflection for a given hand movement than a four incher.  This excess bellcrank rotation generates two undesirable effects, the first being that over rotation.  Once the bellcrank is past 20 or 30 degrees,  the effective moment arm of the bellcrank gets noticeably shorter.  The shorter the arm, the more force is required, and the less tolerant the whole system is to minor corrections.  Which leads to the major difficulty with 3 inchers, the controls are too quick.  Think of it in terms of control deflection per length of leadout travel, not per the angular rotation of the bellcrank.  Most of us have experience with some plane which had ultra quick controls.  Try one again sometime, and see how difficult it is to fly accurately with quick controls.  The slower controls make the whole setup easier to fly accurately.  So most of the poster so far haven't thought of it in terms of flyability, e.g. the comfort of the pilot.

Offline tom hampshire

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Re: 4" Bellcranks, are they necessary in Classics??
« Reply #8 on: August 20, 2007, 06:39:22 PM »
Hi Alan & Bill - I don't know why a narrow handle spacing doesn't feel right to me... only that it doesn't.  If you want to slow down a set of to fast controls, usually you wind up with a front slider bar handle.  Funny thing, I wandered into the team trials about 15 years ago and got drafted by Mr. Tiahrt to be pit boss.  I learned that none of the entrants at that level used a handle with a slider bar.  All of the handles had the control hardpoints as close to the knuckles as could be.  My guess is that the excess overhang (Having the handle arms too far from your knuckles) gives excessive sensitivity around neutral.  Other opinions welcome.  Tom H.

Offline Dennis Adamisin

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Re: 4" Bellcranks, are they necessary in Classics??
« Reply #9 on: August 20, 2007, 08:04:34 PM »
I think Lou's comment on long horns and lower pushrod loads really nailed the issue.  H^^  Lower bearing loads = long lifed control systems.

Whether you use a 1" or 5" bellcrank, it is POSSIBLE to get the correct ergo relationship between hand movement and control surface movement, but you mght have to take some extreme measures.  I just find that with my fixed spacing handle, a 4" crank works pretty darned good - so I will continue to use those cranks and the longest feasible control horns I can.

BTW I use a DIFFERENT (smaller) handle for a bird with a 3" crank and just got another handle ready for a bird wih a 2" crank.  Then there's the Goldberg handles for the 1/2A's!

Denny Adamisin
Fort Wayne, IN

As I've grown older, I've learned that pleasing everyone is impossible, but pissing everyone off is a piece of cake!

Offline Ron King

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Re: 4" Bellcranks, are they necessary in Classics??
« Reply #10 on: October 10, 2007, 05:44:06 AM »
When I built my first Oriental, after returning to the hobby, I calculated the angular deflection of the 3 inch bellcrank versus the 4 inch bellcrank. I determined where I needed to drill the push rod hole based on these calculations to make the control systems equal and built the plane with a modified 3 inch bellcrank.

To this day, I cannot tell the difference at the handle when I'm flying. The controls in my classic Oriental move the same as the controls in my big ship. I want and need this similarity because I don't want to waste time getting reacquainted with each plane.

My .02,

Ron
Ron King
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Wannabe Stunt Pilot since 1963
 Amateurs practice until they get it right; Pros practice until they cannot get it wrong.

Offline phil c

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Re: 4" Bellcranks, are they necessary in Classics??
« Reply #11 on: October 10, 2007, 02:06:13 PM »
the biggest thing I see is that using a larger bellcrank gives you the OPTION of slowing down the controls and, even bigger, reducing the pushrod and bearing loads.  If you use the exact same geometry on a 3 in. bellcrank setup and a 4 in. bellcrank setup the 4 incher puts a lot less load on the pushrods.  Also, as Tom points out, the smaller bellcrank reacts faster to a standard 4 in. handle and going to an adjustable handle with the lines attached outside your knuckles makes the control forces you feel go way up.  The overhang between the handgrip and the lines is just another lever- the longer it is, the harder it is to move the controls.  The old EZ Just got it almost exactly right for most people with only an inch or so of overhang.
phil Cartier

Offline Leo Mehl

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Re: 4" Bellcranks, are they necessary in Classics??
« Reply #12 on: October 18, 2007, 10:36:05 PM »
In the 60's we used very fast controls which meant that we had to stay at a constant attention during maneuvers. The total leadout pull from neutral was about one inch or less. I have built two classic planes lately and I went from an inch to about 2". What a difference this made as far as flying a classic plane. I have seen some of the Orientals that Don McClave has built and he still makes his controls fast. In any case the classic plane flys better with slow controls. Also most classic planes have shorter tail moments. y1 y1 y1 y1 y1

Online doug coursey

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Re: 4" Bellcranks, are they necessary in Classics??
« Reply #13 on: December 13, 2021, 07:50:06 PM »
don still used 2 3/4 inch bellcranks in his stuka stunt with 45 degrees of flap and elevator....i know its old but i had to post this because im building a stuka stunt and going with an Okie 3 1/2 inch bellcrank. the wing is on the small side 47" wing span. 
« Last Edit: December 14, 2021, 06:24:10 AM by doug coursey »
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