Pulley cable angles

Rowdyflyer1903!

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Please forgive me if this is opening up a new thread on a much discussed topic.

A sentence used in describing the proper installation of AN210-3 anti friction control pulleys has sent me hitting the books trying to define what they mean. I have struck out.

The first being AN2103B and others pulleys shall not be installed on frequently used aircraft controls to bend cable more than 15° from a straight line.

Another says when used frequently in aircraft controls when the cable wrap angle should not be more than 15° from a straight line.

Research has gleaned that any fair lead should not deflect the cable angle more than 3 degrees.

Does this mean that the cable travel from the rudder level to where,
for example, a Dominator airframe rises to the level of the pilot, that a pulley cannot be used to make that 45 degree turn (X2)?

This recommendation seems very conservative and if this is the case then are bell-cranks used? I do not seem to remember any other type system being used in a stepped type airframe used to position thrust lines to CGs.

Bill
 

Brian Jackson

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Thanks for asking the question, Bill. This is a new topic for me too and interested to read the replies & learn something. Is this item-specific information for a given diameter pulley? I would think the angle deflection is proportional to the pulley diameter, since a larger pulley puts less 'bend' in the cable for a given deflection. In other words, that same 15 degree jog would be spread out over a larger arc length. Just guessing here though.
 

Rowdyflyer1903!

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One of the pulley listed on page 137 of the current catalogue is AN210-3. This is a 2” pulley with a .250“or AN4 ID bolt size.
 

Doug Riley

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It's common for control cables to turn 90 deg. in FW planes (think about getting a cable from the fuselage out to the ailerons on, say, a Cub. The prohibition against large angles on the MS 20220 pulleys refers, I think, only to the small-diameter -1 units. The larger ones can accommodate larger angles without overstressing the cable. Dominators employ pulleys to route the cables through quite large angles up from the low tail tube to the high keel tube.

That said, some of us have used nylon rollers sold in hardware stores for sliding glass doors, with no ill effects -- but for small angles only. Airplane control cables are loaded at a certain tension to help prevent control-surface flutter. A gyro rudder is a less sensitive item, and only a light pre-load is necessary, in my opinion. A counterweight should serve to prevent flutter.

Be very certain to make and install one or two cable keepers at each pulley, to keep the wire from jumping off the pulley.

Run the cable through a cloth-covered hand now and then to check for broken strands a/k/a meathooks.
 

Rowdyflyer1903!

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of course I have seen control cable pulleys enabling redirections exceeding what was written nevertheless it was confusing and certainly lacked clarity. Riggers handbooks speak of forces being multiplied with angles. My initial reaction was the forces could exceed that of the .250” AN4 bolt. This too seems fanciful.
 

Doug Riley

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The radial force on the pulley comes from the sum of any pre-tension plus the pressure from the depressed pedal. An AN-4 has a shear strength of about two tons. 1/8" cable has a tensile strength of a bit over one ton.

At the gym, I hit the calf-and-ankle-extension machine now and then, but I don't believe I'm pressing 2 tons with both feet, never mind one foot. The real issue here is the fatiguing of the strands of the cable on the outside of the turn.

Bear in mind that Bensen called out 1/16" dia. cables, with a breaking strength of about 550 lb. He used wood-lined, graphite-lubed homemade fairleads of 1" diameter, not pulleys, to make the cables change direction. The sharpest change of direction on a Bensen was about 30 deg. Many builders traded up to 3/32" or 1/8" cable, I think more for wear resistance than any strength issue.

IIR, the FAA wants "primary" controls to use at least 1/8" cable. Is the rudder on a gyro "primary?" Certainly it is if you think about what happens if one cable jams or fails. You will get very dizzy on the way down.
 

Rowdyflyer1903!

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Bill’s build ongoing saga.

Oh how wonderful it would to have a kit or at a minimum a set of plans where one could follow the toils of another on your personal path to the freedom of flight ( sans ads-b out) Actually that is not me at all. The challenge of this journey is, I find, quite stimulating if one can keep the depression at bay from the lack of MONEY!

This is the one problems with organically building something which has a lot of systems which have to work harmoniously together. Issues and challenges can compound themselves when you have taken on the work of others. Fox example, is it more cost effective and less labor intensive to build a new house or remodel one? Open for debate.

We stand upon the shoulders of giants and it would be foolish, in my opinion and manner of thinking, if building an almost scratch machine as not to include the design lessons given to us from the pioneers of our past. Also driving me is the overwhelming thought that this is my machine and I will configure it to my satisfaction.

So with that in mind, I truncated the fuselage, fashioned the gussets and raised the CG to more or less in alignment with the thrust line of the power plant.

Smiling at my self, I then went to work hooking up the maze of of fuel lines connecting the tanks added because the 11 gallon seat tank would not allow me to wander far from the confines of the place which I left. What fun is that if you cannot explore the world via an open cockpit flying machine.

11 gallons many would say is quite enough and indeed it would be for some buzzing popular and expensive modern engines far from the monetary reach of this poor candidate of the air. So a semi run-out Lycoming with a guttural sound and a slow moving propeller is what will be pushing me through the air.

Yes very old school full of massive cubic inches and the requirement of adequate venting of the fuel tanks least they be sucked thin from the demands of such a beast. At best 7 gallons per hour and at worst 12 gallons per hour of a minimum of 92 octane free of the gasket stupefying alcohol our government has made so common.

The wood which it spins is 68x46. Calculations predict a maximum speed of 88 mph if the old girl can spin at 2700 rpm. Throttled back to an rpm which doesn’t require the application of carburetor heat of 2100 rpm,I have hopes of seeing my airspeed needle shake at 65-70 mph. This, which is a comfortable speed facing the brutality of the wind. We will see, for the many flat sided and what is worse, round structures protruding into the viscosity of the air makes even that modest goal doubtful.

I seem to remember, in ancient times when I trained on a Parsons and hearing the faint scoffs of those who knew or thought they knew, that the machine was a 55. It left the runway at 55, it cruised at 55 and it landed at 55. Kind of sad but I know what is coming. Parasitic drag can be improved and no doubt this will be a area for improvement once the FAA gives me the nod. 55 was indeed the final approach speed.

An engine of that pedigree requires that you be the engine control unit (ECU). The amount of monitoring Instruments and controls is daunting to oversee the health of that old engine.

I was thrilled that in my organic style of building and in my myopic world, I had stumbled upon a place to mount my fuel lines and electrical connections on an open frame machine and ( and this is a very very big and) to keep the source of spark away from the thing that burns. Granted, just how far can that be on a thing which is built from 1x2” aloooominum tubing. Well, it’s not far but each will have its little area enclosed to keep their mutual bad influences away from each other.

So happy I was till I returned my thoughts to the blessed rudder cables. Now they can saw through fuel lines and electrical bus’s. Mother of Pearl! What to do what to do? I can dip the little buggers below the arc of the propeller, skimming across the top of the rock guard and go under the non suspended and stiff Bensen style axle, flying under the gusset to climb ever so lofty to the altitude of the cockpit. Sounds great but do I really want those cables exposed as the lowest protrusion of the airframe? Drat!

Ok then, what about routing over the top of the gussets but then this gets in the mix of limited real estate in the area of the control yoke. Not good. What about marine push- pull cables? Talk about a love hate relationship on this forum. The options are varied and wide.

I expect something hybrid is or will be the answer. Push pull cables could be used with only the sheath being used to guide the cables though the danger zone so to speak and the rest be naked to the world for inspection otherwise.

In a not so normal nut-shell for me, I am looking for other methods than pulleys and fair leads to route the cables, which has to have a minimum of friction. There is that too.
 

Brian Jackson

Platinum Member
Joined
Jul 17, 2004
Messages
3,351
Location
Hamburg, New Jersey USA
Aircraft
GyroBee Variant - Under Construction
Bill’s build ongoing saga.

Oh how wonderful it would to have a kit or at a minimum a set of plans where one could follow the toils of another on your personal path to the freedom of flight ( sans ads-b out) Actually that is not me at all. The challenge of this journey is, I find, quite stimulating if one can keep the depression at bay from the lack of MONEY!

This is the one problems with organically building something which has a lot of systems which have to work harmoniously together. Issues and challenges can compound themselves when you have taken on the work of others. Fox example, is it more cost effective and less labor intensive to build a new house or remodel one? Open for debate.

We stand upon the shoulders of giants and it would be foolish, in my opinion and manner of thinking, if building an almost scratch machine as not to include the design lessons given to us from the pioneers of our past. Also driving me is the overwhelming thought that this is my machine and I will configure it to my satisfaction.

So with that in mind, I truncated the fuselage, fashioned the gussets and raised the CG to more or less in alignment with the thrust line of the power plant.

Smiling at my self, I then went to work hooking up the maze of of fuel lines connecting the tanks added because the 11 gallon seat tank would not allow me to wander far from the confines of the place which I left. What fun is that if you cannot explore the world via an open cockpit flying machine.

11 gallons many would say is quite enough and indeed it would be for some buzzing popular and expensive modern engines far from the monetary reach of this poor candidate of the air. So a semi run-out Lycoming with a guttural sound and a slow moving propeller is what will be pushing me through the air.

Yes very old school full of massive cubic inches and the requirement of adequate venting of the fuel tanks least they be sucked thin from the demands of such a beast. At best 7 gallons per hour and at worst 12 gallons per hour of a minimum of 92 octane free of the gasket stupefying alcohol our government has made so common.

The wood which it spins is 68x46. Calculations predict a maximum speed of 88 mph if the old girl can spin at 2700 rpm. Throttled back to an rpm which doesn’t require the application of carburetor heat of 2100 rpm,I have hopes of seeing my airspeed needle shake at 65-70 mph. This, which is a comfortable speed facing the brutality of the wind. We will see, for the many flat sided and what is worse, round structures protruding into the viscosity of the air makes even that modest goal doubtful.

I seem to remember, in ancient times when I trained on a Parsons and hearing the faint scoffs of those who knew or thought they knew, that the machine was a 55. It left the runway at 55, it cruised at 55 and it landed at 55. Kind of sad but I know what is coming. Parasitic drag can be improved and no doubt this will be a area for improvement once the FAA gives me the nod. 55 was indeed the final approach speed.

An engine of that pedigree requires that you be the engine control unit (ECU). The amount of monitoring Instruments and controls is daunting to oversee the health of that old engine.

I was thrilled that in my organic style of building and in my myopic world, I had stumbled upon a place to mount my fuel lines and electrical connections on an open frame machine and ( and this is a very very big and) to keep the source of spark away from the thing that burns. Granted, just how far can that be on a thing which is built from 1x2” aloooominum tubing. Well, it’s not far but each will have its little area enclosed to keep their mutual bad influences away from each other.

So happy I was till I returned my thoughts to the blessed rudder cables. Now they can saw through fuel lines and electrical bus’s. Mother of Pearl! What to do what to do? I can dip the little buggers below the arc of the propeller, skimming across the top of the rock guard and go under the non suspended and stiff Bensen style axle, flying under the gusset to climb ever so lofty to the altitude of the cockpit. Sounds great but do I really want those cables exposed as the lowest protrusion of the airframe? Drat!

Ok then, what about routing over the top of the gussets but then this gets in the mix of limited real estate in the area of the control yoke. Not good. What about marine push- pull cables? Talk about a love hate relationship on this forum. The options are varied and wide.

I expect something hybrid is or will be the answer. Push pull cables could be used with only the sheath being used to guide the cables though the danger zone so to speak and the rest be naked to the world for inspection otherwise.

In a not so normal nut-shell for me, I am looking for other methods than pulleys and fair leads to route the cables, which has to have a minimum of friction. There is that too.
I feel both your pain and enthusiasm at the same time. Yes, a kit would have been so much easier but the cost goes way up unless you factor in your time savings. Scratch building does teach us a lot of new skills though. We also get the benefit of education because we are forced to consult with people more knowledgeable than ourselves in this field to get answers to questions. Yes, it is indeed a journey. Sometimes the destination just seems so far away.

Share some pics when you get a chance. Love looking at build work. I've learned much from others' build threads and everyone gets to put a critical eye on things. Cheers.
 

Rowdyflyer1903!

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Messages
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Location
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Cessna 140, Stinson 108-1, Culver V, Parsons Trainer
Total Flight Time
1000 hours
I am so thinned skinned that I hesitate. But here are two.
 

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Doug Riley

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Messages
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Cheapskate me would run ordinary 3/32" or 1/8" cables over a pulley mounted on the mast-keel cluster plates, down the diagonal axle-keel strut, then over another pulley over the axle and aft beside the tail tube. Make and install wood, nylon or phenolic cable guides as needed to keep the cables away from the frame, prop, etc.

If worried about chafe of the cables on other exposed bits (gascolator, etc.), run the cable through some (oversized I.D.) clear-plastic hose, secured to the frame, in the area of concern.
 

Martin W.

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Winnipeg
.

Smallest radius I have seen is on the Bell 47 helicopter tail ..... cables run from the pedals back to the boom and have several wraps around the aprox 1.5 inch actuator (picture) and then back to the pedals.

Not heavily loaded ... it rotates an acme thread which changes the tail rotor blade pitch ... easy to check every preflight

.
BELL 47 tail rotor cable wrap.JPG
 
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