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Author Topic: Lateral Bellcrank Location .  (Read 122094 times)

Offline Air Ministry .

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Lateral Bellcrank Location .
« on: August 16, 2015, 08:15:27 PM »
Any Yaw / Roll effects putting the bellcrank at the inner or outer boom .  :-\





I sort of visualise the plane turning about the bellcrank , when you least expect it . This isnt a good question to ask yourself at bedtime .  S?P a veritable pandoras box . There has to be a simple
definition of the force vector diagram ! .  :( :) .

Anyone used the bellcrank at the Boom on a Team Racer . Accelerative / decellerative turning troubles ,  :-\

Thanks .  H^^

Offline frank mccune

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Re: Lateral Bellcrank Location .
« Reply #1 on: August 16, 2015, 09:00:23 PM »
      Hello Matt:

      Are you in he above picture? If so, which one is you?

                                                                                       Frank McCune

Offline Tim Wescott

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Re: Lateral Bellcrank Location .
« Reply #2 on: August 16, 2015, 11:28:59 PM »
Matt: no.

Well, only insofar as it affects the balance, and you were going to correct for that with tip weight anyway.

The leadout guide position affects how the lines affect pitch, roll & yaw, not the bellcrank position.
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Air Ministry .

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Re: Lateral Bellcrank Location .
« Reply #3 on: August 17, 2015, 03:41:51 AM »
Naye , Frank . Though envisageing a push pull plane , somewhat like that . Even Got Two OS 25 LAs for it , but they might be pirated for a 67 in Comet De H 88 .
Been Fumeing Ive only got two 3/4 x 1/8 spruce for spars for over a year , hunting more close grain straight spruce . Got out the drg, and found I only NEED TWO .
 :P

The bellcrank thing , visualising say - a 12 knot 15 mph STEADY wind - from afar, minimum  . So theres a steady constant drag the pilot etc Downwind .

So say we're in the horizontal eight - heres a bit of line tension . ( theres a marlin on the line  :##) LATERAL LOAD  restrained at SAY outer placed bellcrank .
NOW , say THAT load is equivalent to the LIFT load ; about the same amount , call em equal .

Being pushed and pulled sideways away thru ( American spelling ! ) the DOWNHILL Curve , where I find theres a few forces operating .
( degressing , in 20 Kt - the lower Sq. Eight & Sq. loop corners give a bigger Jolt down the wires than the Hourglass / Triangle corner,
I figure this is the Duration of the Corner is Shorter , thus a  ' thump ' rather than say a ' heave ' in the later .)

Thus our plane is sequered at say 2/3 span ( if the booms are @ 1/3 out ). Yet the LIFT is ( say ) equal A L O N G the span .
so the LIFT is 2/3 inboard of the point of lateral restraint .
If we're pulling rather a lot of lift , to stop the sidedraft dragging the ship into the deck - more top control required in the lower quarter of the loops ,

IS the sideforce on the wires sufficient to steady the tip from lowering or raising .

following this train of though ; If the mounts at the Inner Boom ( say 1/3 out ) is the 2/3 lift OUTSIDE the ' secureing point '
going to lift the outer wing against the Half the  ( tip guide ) restraint , as the tip is half the distance of the Outer Placed crank .

Ive Found a bit of Diheadral sort of centers the lift . upright the ' sink ' effect concentrates with outward flow ??
and inverted the main support  ( turning inside ) is concentrated toward the center with inward flow effect .Perhaps .
At least they seem a sight steadier in gusty turbulent air , that'll pull a flat wing about , over about 18 knots ,
discernible from about 15 with heavyish aeroplanes , maybe 12 with lightly loaded ones .

The MB3 at about 18 lb per Sq Ft was marvellously steady in the wind , visually .small overpowered plane on 18 thou. 7 strand steel .
the 016 solids would discernably stretch or give a bit of a twang , wind over 18 Kts on this and the 63 in Spitfire , once Id Diheadraled that .
A disturbing  LL~ thump at the handle in the bottom corners of the squares , as the winds hard and steadier at ground level .
After Id epoxied the under C.S. sheet join on the MB3 , I did a session of mainly squares in the wind . The thumps opened the crack thru
the lower wing sheet join again . This was done to Al Rabes Mustang 5 Formular / Airfoils , bar scale flying surfaces plan ,
Tho his TailPlane Ratio Formlar verified it ( the Tailplane ) was adequate . A hoot to fly , but ' relaxing ' wasn't the operative word .

So what im getting at is , say a light ( 11 Oz Sq Ft ) twin boom sucker going to start getting awkward if theres enough air around to fly a kite way up or get a yacht moving ,
if the bellcranks NOT in the Center Section . Id stuck it there in the 78 in. P-38 , with attendant serpentine control layout ,
pushrod split to left & right inner Flap - Horn at outer edge of inner flaps , to pushrods down BOTH booms ( technically you need lighter pushrods - I used 3 / 32 ) to elevator horns in Ea Boom .
No the lowest component count , with this set up . And a ' flying ' pushrod back from the center nacelle isn't going to work on a Push Pull plane . Hence the Picture .

Theres also the ' lines've gone slack ' trip . What will happen when the thing hits back out on them .
The MB# without a ' anti ' P ' rudder could ' cut out ' if you wertnt carefull at the Top Hourglass Corner or going into the Cloverleaf . This required running like snot . ( never hit the deck ) BUT ,
if it disappeared over your right shoulder to say ' 10 O'clock , with deadupwind being 12 , downwind 6 . say . BUT itd been going to bore in halfway out so youd lept severally that far over across
4 or 5 O'clock way , AS they snapped tight on Full Down with it at 5 Ft Inverted  INTO the wind , It'd Do Another ' P ' effect Turn Nose Up Across the Top Again , but in a Straight Line rather than out on the wires .
This'd have you leaping Full Bore up 2' O'clock way . Rather Quickly .
This was all rather good fun . But definitely not relaxing .
As I said it never cracked up , unlike the straight wing suckers the wind would carry more  .

So Im Wondering if that belcrank position out on a boom is going to work trying stupid stunts like this . They tell me its safer than motorcycling .
Was definitely considering a Crash Helmet with the MB3 as  650 plus Ounces pulled by a G 51 would've hurt if you ended up wearing it , which couldn't be discounted tripping over or something .

We're trying to figure a realistic MB 3 fuse , too .

Offline Paul Smith

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Re: Lateral Bellcrank Location .
« Reply #4 on: August 17, 2015, 07:34:06 AM »
That will be a tricky plane to hook up.  If you mount the bellcrank in either boom, the flap forces will be transmitted a long way to one of the tips.

I would put the BC in the middle and drive the elevator through BOTH booms.
« Last Edit: August 17, 2015, 08:45:04 PM by Paul Smith »
Paul Smith

Offline Tim Wescott

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Re: Lateral Bellcrank Location .
« Reply #5 on: August 17, 2015, 10:18:34 AM »
Matt, you are simultaneously over- and under-thinking this.  You're tossing so much detail at yourself that you're covering up the fact that you're not paying attention to ALL the detail.

If you want to take all the forces into account and ponder on what it does to each bit of the airframe, then you need account for the fact that (a) there's tension on the lines and (b) the lines bend when they go through the leadouts, which leads to (c) the lines exert force on the leadout guides as well as the bellcrank.  When you do that, you can then go do an astonishing amount of math on the affect of the bellcrank position on the airplane dynamics, and in the end you'll find out that what matters is the position of the leadout guides.

The only time that this won't be 100% true is if you have really stiff solid leadouts, in which case it'll act like your leadout guide position is somewhere between the actual position and the ends of the leadouts.

And, this is ignoring friction (the more your leadouts bend going through the guides the more friction) and structural integrity (the bellcrank is still absorbing all of the pull on the lines).
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Trostle

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Re: Lateral Bellcrank Location .
« Reply #6 on: August 17, 2015, 02:13:07 PM »
As has been explained many times on this and other forums, the bellcrank can go anywhere.  What is important is where the leadouts are relative to the CG.  Makes no difference if the aircraft configuration has twin booms or not.  Now, it makes sense to place the bellcrank where it would be structurally practical to do so and to minimize the bending of the leadouts as they pass through the leadout guides.

Now, regarding the twin boom layout - Unless the elevators are driven by the pushrod at the centerline of the elevators (like with an exposed pushrod), use transfer cranks so that there is a pushrod to each side of the elevator.  Unless the elevators or super stiff (heavy) they will twist, making final trim of the model difficult.  Also unless the flaps are driven by a single pushrod at the center section, again, use transfer cranks to have pushrods driving the flaps so that there will be consistent forces driving the flaps on both sides of the wing.  Otherwise, unless the flaps are super stiff and the transfer horn between the flap segments are really stiff (as in really heavy) it will be difficult if not impossible to trim the airplane for top performance.  This is because the flaps will twist unequally and the transfer horns though the booms will also twist unevenly because of the unequal loads between the inboard and outboard flaps.  One solution to this problem would be to only move the center section flaps and do not use flaps on the wing sections outboard of the booms.  But, if you are not looking for top performance, then do whatever suits your fancy.  However, you will be disappointed in the way the airplane will yaw and roll through different maneuvers and wind conditions.

By the way, that twin is being held by Bob Whitely.  The photograph was taken sometime in the last 5 or more years and looks like it was taken at Whittier Narrows.  The model is called the Too Much, designed by Rich Loomis who won Senior with the design at the 67 Nats.  Somebody can fill in some details, here but I think Rich built this model and was flown at VSC several years ago.  Whitely worked with Rich and others to get the model trimmed and flying.

Keith

Offline Howard Rush

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Re: Lateral Bellcrank Location .
« Reply #7 on: August 17, 2015, 03:10:05 PM »
Put the bellcrank on the inside boom and use carbon torque tubes with +/- 45-degree plies.  It's light and easy.  I think I'd use a spar running to the LE root as well as the usual spar.  You might add a little carbon or Kevlar on those spars to take the extra tension, but I haven't done the ciphering.   
The Jive Combat Team
Making combat and stunt great again

Offline Air Ministry .

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Re: Lateral Bellcrank Location .
« Reply #8 on: August 20, 2015, 07:00:35 PM »
Hypothetical at this stage , Ive got Tupkers D23 on paper . He used the outer boom location . & ive a set of preliminary drawings for one of these nasty things .



amougst others . If there were ten of me , Id getim all built , and have a spare me to do a few other things .



got this drawn up , long and thin , @ 57 in, for a 40 FSR S too . Need a extension / bearing set up with
Engine about where youd normally have it . Test a few feories on nose lengths . Figureing a light ( timber ) prop'd help .

I still consider Aerodynamic forces considerably greater than inirtial , if the wind gets up . So as they overpower them .
Not quite the DC3 in the Monsoon Clouds , but you get my drift . Not that I will fly'em in monsoon Clouds .

Offline Air Ministry .

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Re: Lateral Bellcrank Location .
« Reply #9 on: August 20, 2015, 07:16:33 PM »


this is the sort of ( propportionally  relative ) conditions that cause concern , or envisageing - theoretically .

Lokks like the undercarrage designer at 9 minutes got it right . Thanks for the tips , Howard .
Saw a bellcrank go down the inner wing of a nice F2B ship with lots of ribs , in the N.Z. nats around 74 .
Was a few Team Racers hanging on the prop on lift of , slight gust and theyed tourque roll  hard left
across the circle . Amazing theyd give the pilots a shock , and hit ' lines tight' on the other side ,
swing left & away . The 60 mph odd transfering to 60 mph forward lines tight .

There was the sound of a 'B' cruising at 100 + and instant silence . The up line broke . Grass Circles tho
and not sun baked ground . One or Two Neg. ' G 's tho in decelleration when they do that .

Thanks.

Offline Brett Buck

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Re: Lateral Bellcrank Location .
« Reply #10 on: August 21, 2015, 08:40:35 AM »
Put the bellcrank on the inside boom and use carbon torque tubes with +/- 45-degree plies.  It's light and easy.  I think I'd use a spar running to the LE root as well as the usual spar.  You might add a little carbon or Kevlar on those spars to take the extra tension, but I haven't done the ciphering.   

   This is the perfect application for my multiple-point drive idea, although in this case, it would only be two points (both ends of the elevator).

    Brett

Offline Howard Rush

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Re: Lateral Bellcrank Location .
« Reply #11 on: August 21, 2015, 11:11:27 AM »
   This is the perfect application for my multiple-point drive idea, although in this case, it would only be two points (both ends of the elevator).

This is a perfect application for some actual analysis. 
The Jive Combat Team
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Offline Brett Buck

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Re: Lateral Bellcrank Location .
« Reply #12 on: August 21, 2015, 04:39:07 PM »
This is a perfect application for some actual analysis. 

My analysis is that until you make a torque tube that is infinitely stiff, you are better off not driving it from one end.

    Brett

Offline Tim Wescott

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Re: Lateral Bellcrank Location .
« Reply #13 on: August 21, 2015, 05:11:56 PM »
My analysis is that until you make a torque tube that is infinitely stiff, you are better off not driving it from one end.

That's the mathematician's answer.  The engineer's answer is "That's OK, I'll get close enough!"

(Subject, of course, to enough analysis.)
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Howard Rush

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Re: Lateral Bellcrank Location .
« Reply #14 on: August 22, 2015, 12:28:26 AM »
Yup.  Other things are in play here, such as how much things bend under load and the hinge moment distribution along the control surface.  I suspect that the two outer flap ends on regular stunters deflect different amounts, and the difference is a function of airspeed. This may be beneficial, hence stiff flaps are bad, or stiff (but not infinitely stiff) flaps should be driven from someplace off center.  Beats me.  Eric Viglione was speculating on this awhile back after taking the picture below of an airplane in a maneuver.  An analysis of all this stuff plus some flight data might give some interesting insight. 

If you decide that the asymmetric flex of the pretty-stiff torque tube is objectionable, two much lighter ways of canceling it would be a balance tab at the far end or a concentric inner torque tube that connects to the outer torque tube (the one connected to the flaps) at the spanwise aerodynamic center of the flaps.




The Jive Combat Team
Making combat and stunt great again

Offline Brett Buck

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Re: Lateral Bellcrank Location .
« Reply #15 on: August 23, 2015, 07:30:12 PM »
That's the mathematician's answer.  The engineer's answer is "That's OK, I'll get close enough!"

(Subject, of course, to enough analysis.)

  Again, thanks. As an artist/dreamer type, I don't have the logical mind or experience necessary to develop anything practical.

   Brett

Offline Tim Wescott

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Re: Lateral Bellcrank Location .
« Reply #16 on: August 23, 2015, 10:31:00 PM »
  Again, thanks. As an artist/dreamer type, I don't have the logical mind or experience necessary to develop anything practical.

Geeze Brett, lighten up.  Just assume a damned faggoty smiley face* as appropriate on my posts.

* Thank you, Dirty Dan.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.


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