Large bellcranks

[Paul Van Dort]

Hi all, I always have been wondering why we are not using larger bellcranks, in combination with larger handles. E.g. the maximum size bellcrank that can fit into the wing. With a larger bellcrank you can create more force on the pushrod for a given linetension.
Larger bellcranks will postpone hitting the Netzeband wall and you will be able to steer better with reduced linetension (like overhead eigths in windy weather)
My bellcranks are 5 inch, but i don't see larger (+ 4 inch)  bellcranks used commonly. The extra friction at the leadouts can be neglected in my opinion.
Any thoughts?

[Brett Buck]

My bellcranks are 5 inch, but i don't see larger (+ 4 inch)  bellcranks used commonly. The extra friction at the leadouts can be neglected in my opinion.
Any thoughts?

   Yes - I am not sure what you are seeing, but 4" is common to the point of ubiquitous, the only reason I don't go to 4.5 is that with my current wing templates, theres not enough room without building enough structure to move the pivot back.

   I haven't heard of anyone using a 3" bellcrank on a regular stunt plane for decades. They are OK for smaller airplanes like the Flite Streak and Skyray 35, the control loads on those are  extremely low anyway.

   Brett

[Paul Van Dort]

   Yes - I am not sure what you are seeing, but 4" is common to the point of ubiquitous, the only reason I don't go to 4.5 is that with my current wing templates, theres not enough room without building enough structure to move the pivot back.

   I haven't heard of anyone using a 3" bellcrank on a regular stunt plane for decades. They are OK for smaller airplanes like the Flite Streak and Skyray 35, the control loads on those are  extremely low anyway.

   Brett

I meant plus 4 inches. Larger than 4 inches are quite uncommon, while there are mechanical advantages to larger bellcranks in my opinion. Indeed that would require moving the pivot back, away from main spars etc... But not impossible.

[Motorman]

It's leverage Vs travel. If you make the bell crank longer with the same push rod arm then it has to rotate farther, then you loose the leverage gain due to the Akerman effect.

4" is just convenient for average hand size and linkage attachments. You can make it 5" or 6" you're just adding weight. Also you don't want a system that needs allot of travel on the handle because you won't be able to correct fast enough.

If you make the bellcrank bigger with the same push rod arm ratio and corrispondingly bigger handle spacing then there's no increase in leverage, you're just adding weight.

The thing to explore imho is to minimise the elevator travel while making the plane as tail heavy as possible to make it turn. I think modern designs have it pretty well sorted out.

Motorman

[Paul Van Dort]

It's leverage Vs travel. If you make the bell crank longer with the same push rod arm then it has to rotate farther then you loose the leverage gain due to the Akerman effect. 4" is just convienient for average hand size and linkage attachments. You can make it 5" or 6" you're just adding weight.

Motorman

Indeed leverage  vs travel. . If you keep all equal wrt the bellcrank (same angular movement, same pushrod hole distance), except the span (let's say increase from 4 to 5 inches) and you increase your spacing at the handle accordingly. You will be able to have about 20% more steering power for a given line tension. The akerman effect I need to reserch on.

[Motorman]

Ackerman effect: if you are pulling on a 5" bellcrank when you start the maneuver you'll be pulling on a 1" bellcrank at full deflection. The more the bellcrank turns the less leverage you have. If you do one thing you loose another. Draw it out on paper.

[Dan McEntee]

Ackerman effect: if you are pulling on a 5" bellcrank when you start the maneuver you'll be pulling on a 1" bellcrank at full deflection. The more the bellcrank turns the less leverage you have. If you do one thing you loose another. Draw it out on paper.

      When are you ever at full deflection in a maneuver, unless you just screwed the pooch and are in a panic situation? Beyond the bell crank, you have two control horns and then line spacing adjustments to get what you want and need.
     The oldest reference and drawing of a 4" bell crank I have ever seen is on an old Fox kit called the Stunt Runt. Probably mid 1950's.
  Type at you later,
   Dan McEntee

[Paul Van Dort]

Ackerman effect: if you are pulling on a 5" bellcrank when you start the maneuver you'll be pulling on a 1" bellcrank at full deflection. The more the bellcrank turns the less leverage you have. If you do one thing you loose another. Draw it out on paper.

That's why I mentioned "If you keep all equal wrt the bellcrank (same angular movement, same pushrod hole distance),"

[Brett Buck]

I meant plus 4 inches. Larger than 4 inches are quite uncommon, while there are mechanical advantages to larger bellcranks in my opinion. Indeed that would require moving the pivot back, away from main spars etc... But not impossible.

    Of course - I was one of the people trying to convince everyone that we ought to go from 3 to 4 in the first place!  Once you have everything set up for 4, you can't easily drop in 5+.

    Brett

[Motorman]

That's why I mentioned "If you keep all equal wrt the bellcrank (same angular movement, same pushrod hole distance),"

You don't understand what I'm trying to tell you. OK you don't go to full deflection but you still lose leverage the more the bell crank turns from neutral. That's why some tried circular bellcranks.

If you just make everything bigger by the same percentage, how are you changing anything?

[Paul Van Dort]

You don't understand what I'm trying to tell you. OK you don't go to full deflection but you still lose leverage the more the bell crank turns from neutral. That's why some tried circular bellcranks.

If you just make everything bigger by the same percentage, how are you changing anything?

You always lose leverage the more the bellcrank turns from neutral. for any size of bellcrank. My bell crank only has a bigger distance between the leadouts (5" instad of 4") . The rest remains the same as the 4 inch version. So the extra distance gives more leverage. 20% more.

[Brett Buck]

You don't understand what I'm trying to tell you. OK you don't go to full deflection but you still lose leverage the more the bell crank turns from neutral. That's why some tried circular bellcranks.

If you just make everything bigger by the same percentage, how are you changing anything?

  Because you get more torque capability  for a given amount of line tension. That's what it is about, that is the advantage of larger bellcranks.

   I also note that while you get the same torque capability at any deflection with a circular bellcrank, when used with a conventional handle, the rate of change of the bellcrank angle to the handle angle slows down as you get more deflection, sort of a reverse-exponential action. Conventional bellcranks can have exactly linear, faster at the ends, or slower at the ends, depending on the relative sizes VS the handle spacing VS, the lever arms of the internal parts.

    Brett

[Howard Rush]

Paul is basically correct. 

Another factor is how far the bellcrank rotates.  You can move a 6" bellcrank a little or a 4" bellcrank a lot and get the same leverage over control surface hinge moment.  Pick the combination that best fits in your wing.  My 4" bellcrank moves +/- almost 90 degrees, giving a handle spacing of about 5.6".  Control response between leadout travel and elevator deflection is pretty much a straight line.  I don't know from Ackerman, but he or she may have been concerned with amplification of slop in the linkage, rather than overall control response. 

[Howard Rush]

Here's a plot of my old dog's controls. Bellcrank movement is only 83 degrees one way and 69 degrees the other.   I had Excel put a linear trendline on elevator response. 

I'll send a copy of the program to calculate this stuff to anybody who wants it.

[Howard Rush]

Ackerman effect: if you are pulling on a 5" bellcrank when you start the maneuver you'll be pulling on a 1" bellcrank at full deflection. The more the bellcrank turns the less leverage you have. If you do one thing you loose another. Draw it out on paper.

But the bellcrank output arm gains the leverage that the input arm loses.  The flap linkage thickens the plot.  Drawing it on paper won't help: it's a three-dimensional problem. 

[Air Ministry .]

One thing from  ' line seperation ' , The 60 Oz Whirlwind Twin first flight in hard buffety air - was bouncing / porposing generally . Pulling like blazes ( I think on 65 of .015 solids )

First thought was I was overcontroling corrections & it needed CLOSER handle spacing ( 3.3 inch dubro bellcrank incidently )

Second Thought was the already closeish handle spacing was letting the rubber line effect take predominance .
INCREASING the handle spacing out past 4 inch , and a light fingetipish grip - It Flew intself straight fine .


SO , the moral of the story  =  SEPERATION gets increased control through lesser percentage of line length varieation due to strong Nor Easters ( and Others )

No Doubt a one foot line seperation might be taking it a bit far . But the New de H 88 2 metre span runs a FIVE INCH bellcrank - has yet to be flown .

If anyone doubts line stretch - put two stout nails in a stout fence 4 in. apart . Lean Back like the pull in a howling gale - at the handle .
With the nails closer the handle can jiggle jelo like if you try jiggling it while your heaving back . representing varying tension line to line .
AS IT IS HEAVING IT INTO A MANOEUVRE !

Essentially , the further apart they are ( for a given line ) the greater is the stability of the variation of stretch ( line to line )
 So , the ship will run truer ( assuming matchiing handle to surface ratio ) with better seperation / spacing . Like They run wider bars dirt track than tarmac .

[Howard Rush]

One thing from  ' line seperation ' , The 60 Oz Whirlwind Twin first flight in hard buffety air - was bouncing / porposing generally . Pulling like blazes ( I think on 65 of .015 solids )

First thought was I was overcontroling corrections & it needed CLOSER handle spacing ( 3.3 inch dubro bellcrank incidently )

Second Thought was the already closeish handle spacing was letting the rubber line effect take predominance .
INCREASING the handle spacing out past 4 inch , and a light fingetipish grip - It Flew intself straight fine .


SO , the moral of the story  =  SEPERATION gets increased control through lesser percentage of line length varieation due to strong Nor Easters ( and Others )

No Doubt a one foot line seperation might be taking it a bit far . But the New de H 88 2 metre span runs a FIVE INCH bellcrank - has yet to be flown .

If anyone doubts line stretch - put two stout nails in a stout fence 4 in. apart . Lean Back like the pull in a howling gale - at the handle .
With the nails closer the handle can jiggle jelo like if you try jiggling it while your heaving back . representing varying tension line to line .
AS IT IS HEAVING IT INTO A MANOEUVRE !

Essentially , the further apart they are ( for a given line ) the greater is the stability of the variation of stretch ( line to line )
 So , the ship will run truer ( assuming matchiing handle to surface ratio ) with better seperation / spacing . Like They run wider bars dirt track than tarmac .

Line stretch effect is determined by mechanical advantage over control surface hinge moment at the airplane (and line tension on the nonlinear bowing of lines in the wind).  Line spacing at the handle won’t change that. Line spacing at the handle is a dependent variable. A big mechanical advantage will result in big line spacing at the handle.

[Air Ministry .]

Harumph .



These Suckers ( in the Twin ) or 4 / 4 1/4 inch copies , in 2 kilo / 71 Ounce Things , when it gets over around 18 knots  ( or whatever it is ) BREEZE -

3    8-12    7-10    Gentle Breeze    Large wavelets. Crests begin to break. Foam of glassy appearance. Perhaps scattered white horses.
Leaves and small twigs in constant motion; wind extends light flag.
4    13-18    11-16    Moderate Breeze    Small waves, becoming larger; fairly frequent white horses.
Raises dust and loose paper; small branches are moved.
5    19-24    17-21    Fresh Breeze    Moderate waves, taking a more pronounced long form; many white horses are formed.
Small trees in leaf begin to sway; crested wavelets form on inland waters.
6    25-31    22-27    Strong Breeze    Large waves begin to form; the white foam crests are more extensive everywhere.
Large branches in motion; whistling heard in telegraph wires; umbrellas used with difficulty.

One Gets 18 thou. Steel seven strand laystrate TWANGING on ONE LINE in the lower squares , where presumeably the highest wind effect is , at times .

As when controls cranked on , ( with the reversed bellcrank ! ) - one arm is sffectively LONGER ! so ' one ' can anchor on the other as ' the force ' of the corner
is primarilly ? on the line youve hauled in ! so varying the less loaded side gets ' fine tuning ' of the rounds in the windy conditions . 

The elevator ears are balance tabs - so reduce control loads - the cornerings thus more even & easyier to fine tune so the rounds dont EGG .



I used the later type - on the plank wing sucker wot gotta lotta flying inna da wind . Normally lightish line tension . Tryed more tip Wt & it was Steadier .
Till it fell off halfway through .  ( We wont mention the 4 ounce ' misslayed ' noseweight impossable to remove with the engine in , in the hurricane .
there seemed to be no holes in the walls of any adjacet houses  . 

Thus ; the more heavilly loaded line - reaches the elastic stretch sooner !

The elastic limit depends markedly on the type of solid considered; for example, a steel bar or wire can be extended elastically only about 1 percent of its original length, while for strips of certain rubberlike materials, elastic extensions of up to 1,000 percent can be achieved.

Dual Lines in bouncey atmosphere are irregularly & unevenly loaded . if ( 16 thou. solids ) theyre being operated at the initial stretch load , the irregular loading can produce mild ( 6 - 12 in pitch ) porpoise .

SEPERATING the lines further at the handle ,, for the next flight  - the sucker flew straight & smooth , with manouvres thrown in . Was stomping along at around 80 mph , Fox 19s on 8 x 6's . !

[Air Ministry .]

JUST
to illustrate um .

The Mosquito with more side area Fwd , is yaw prone in gusts and recovering from inverted on the outer upward ( DONT ) its chewed its own lines up twice trying that trick .

The Westland whirlwind ( The subject of the remarks ) is steadier . they all ave the Brodack Crank ! and not overlong horns . Pushrod to flaps THEN another aft to elev . Braced .

Those  two are around 60 ounce .  ( original 1974 W Wind was 35 , 262 38 Oz. OS Max 20 on plain fuel ( nitro free )  262 would wingover repeat & lower rounds in calm on 70 ft 3 strand . 012 ! ! ) ! !
+ 3 for MUFFLERS ( Paternal enquirey . Do thosen engines have mufflers . Ans. Yes . Paternal Advice = YOU WILL FIT THE MUFFLERS )

The Dunger 262 THERE is 70 / 72 Oz. 25s init . 70 ft. .018 7 strand laystrate steel . All the side area , V steady on lines - even pull - pilot leans aft a little .

262 v stable and Accurate . ( lotta side area - flying wing fence )
W Wind . Steady & accurate . Lighter in all respects . ( deeper fuse & rounder nacelle noses than Mosquito )
de H Mosq. Lively & accurate - light on lines - ( Flatish parrallelish nacelle fronts 7 YOU can see the toothpickish fuselage . )
 better suited to COMBAT ( uvers're to predictable ) gotta lead at the andle inna da vind , or itlle getch ya - maybe inna da TEEFF , TICLY ON LAUNCH .

But Shela Backpackers do fine lanches . On Instruction . UNLIKE stroppy young gits- who run along . hop , run , stop , look at pilot , stop , let go . Which results in 2 1/2 barrel rolls on the mosquito
before it bores in aft of the pilot . If He's ran . Or itll getcher inna da teef at the 2 roll mark , if ya dont drop flat . DESPITE BEING ENSTRUCTED ENTIRELY TO THE CONTRARY .
( We wont mention OS 35s in it on 10 x 6's . However it hits earlier . ) also had the 5 ft sq 5/8 glass booby trapped to snap the outer wing once . and it still lives ! tho has had one or two repairs .

RIGHT . the .016 SOLIDS in gusty variable punchy good clean healthy solid country air down through off the far hills and not mentioning a large ocean , depressions , etc , discernably unevenly STRETCHES
one or'tother of the .016 solids .
Winds 15 to 22 steady gusting .

 

[John Carrodus]

Mr Airminister
Love your wing of twins. The 262 looks very similar to a stunt 262 I designed and built about 6 years ago...you didn't fly at Bruce McLaren Intermediate School in Auckland about then did you. Gerald tells me you're a Kiwi in a Wallabies jersey?

[phil c]

That's why I mentioned "If you keep all equal wrt the bellcrank (same angular movement, same pushrod hole distance),"

using a 5in bellcrank with just up-scaled dimensions and a 5in. handle with, again, proportional changes should work well.  You may have to build a new plane, I'd suggest a profile with a styrofoam sheet or the zig-zag flat formers for stiffness.

Good Luck.  You've got plenty of time to throw together a test plane before it snows,

Phil Cartier

[Steve Helmick]

"First thought was I was overcontroling corrections & it needed CLOSER handle spacing ( 3.3 inch dubro bellcrank incidently )"

DuBro has never made any CL bellcranks. The one Air Miseries pictured is a Brodak product.  Steve 

[Motorman]

That's why I mentioned "If you keep all equal wrt the bellcrank (same angular movement, same pushrod hole distance),"

My bell crank only has a bigger distance between the leadouts (5" instad of 4") . The rest remains the same as the 4 inch version.

So which is it? You contradicted yourself.

[Paul Van Dort]

So which is it? You contradicted yourself.

Quote from: Paul Van Dort on August 26, 2022, 07:49:04 AM
That's why I mentioned "If you keep all equal wrt the bellcrank (same angular movement, same pushrod hole distance),"

Quote from: Paul Van Dort on August 26, 2022, 01:47:21 PM
My bell crank only has a bigger distance between the leadouts (5" instad of 4") . The rest remains the same as the 4 inch version.

I don't see the contradiction. I went up from 4inch line distance  to 5inch. The other parameters remained the same as the 4 inch version. same angular movement and pushrod hole distance. So for a given linetension I can apply more force on the pushrod because I can apply more leverage.