Pulley Size

The designer of the Acey Deucy specified a pulley size of 1-3/4" diameter for the aileron pulleys. These pulleys handle a 90 degree change in direction of the 1/8" control cable. From what I've read of Tony Bingelis, this is too small. On page 126 of his Sportplane Builder text, Tony mentions that a convention of 20 times the control cable diameter is a minimum. Based on that convention, the minimum pulley diameter would be 2.5". What's more, Tony errs on the side of smooth control movement. He suggests a 3" pulley would be better.

I would appreciate learning the knowledge of others on this matter.

Plan ref: http://zoemertech.com/ad/760-aileron...ruts_small.jpg

Image ref from my Solidworks model: http://zoemertech.com/ad/aileron_pul...e_question.png

Thank you.

Every airplane design, and I mean every design, is a set of compromises. The compromises may be in regard to ease of building, holding cost in check, available components, or bias toward a particular corner of the performance envelope.

A motto to keep in mind......Perfection is the Enemy of Completion. I suspect most Acey Deucys have been built per the plans, but as the builder you are free to deviate as you please. But ask yourself if you really want to redesign this aircraft.......or fly it. :)

If you do make design changes, don't be surprised when the Law of Unintended Consequences raises its gnarly head.....

Having said all that, I don't know what dictated pulley size on your plans. Perhaps this is what was commonly available back in the day, or maybe there is enough leverage in the control circuit to make larger pulleys unnecessary. 7x19 cable is more flexible than 7x7 cable, I don't know which is specified on the plans.

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Originally Posted by Sam Buchanan

... If you do make design changes, don't be surprised when the Law of Unintended Consequences raises its gnarly head ....

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Your caution regarding unintended consequences is certainly considered and is appreciated. The power of having modeling tools like Solidworks is in being able to depict in three dimensions the impact of updates to the design (as well as detect discrepancies in the plans, of which I've found a handful so far). An hour spent at the computer can prevent the wasting of precious days in the workshop and many dollars in wasted material. Right now, I am determining where to place fittings on the spars. More importantly, I am making note of when to drill holes. The locations of some holes is rock solid (wing butt attachment fitting and wing strut fitting for example). On the other hand, I won't place and drill the holes for the aileron pulley bracket until I finalize the pulley diameter.

I am very glad you mentioned the cable types. The plans make no mention of it.

Thank you again, Sam.

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Originally Posted by conodeuce

The designer of the Acey Deucy specified a pulley size of 1-3/4" diameter for the aileron pulleys. These pulleys handle a 90 degree change in direction of the 1/8" control cable. From what I've read of Tony Bingelis, this is too small. On page 126 of his Sportplane Builder text, Tony mentions that a convention of 20 times the control cable diameter is a minimum. Based on that convention, the minimum pulley diameter would be 2.5". What's more, Tony errs on the side of smooth control movement. He suggests a 3" pulley would be better.

I would appreciate learning the knowledge of others on this matter.

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I think what Tony B quoted is standard practice. A lot of manufacturers compromise on that guidance. I know of one model in particular that has ~90 degree change in direction around small pulleys in the rudder cable run and the cables do wear out in that spot first due to excessive bending/flexing. So they they just get changed more often, that's all.

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Originally Posted by conodeuce

....I won't place and drill the holes for the aileron pulley bracket until I finalize the pulley diameter......

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I suggest you don't drill any pulley attach holes in the spar until you are ready to install the aileron controls.

Discrepancies in plans for many (most) of the older, traditional designs is due to the designer, or builder, of the prototype (many of these old planes were not 'designed', they are based on established designs) expecting the builder to "build-to-fit". Instead of having ultra-precise dimensions for the wing attach points on the fuse, the builder is most likely expected to build wings, then build the fuselage to fit the wings. This process is repeated multiple times during the course of the project....this is why we often refer to our crafts as "custom-built". ;)

My point is that there are very few dimensions on a simple aircraft that require more precision than a yardstick and a chalk line. When the plans call for 1/8", that is not 0.125", it is instead referring to the small marks on the yardstick. Many of these simple planes are built from lines drawn on the shop floor. If you wish to spend time with CAD, so be it, but this is sorta like building a vintage Harley with robots. ;)

Best wishes for an enjoyable journey regardless of which road you take!

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Originally Posted by Sam Buchanan

...this is why we often refer to our crafts as "custom-built". ;) ...

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That's very apparent. :-) Commander John Powell, designer of the 'Deuce, built a Baby Ace, then he built this plane. It's not like the plans have gone through any cycles of revision -- at least not in the last four decades. I knowingly tackled a virtual orphan of an airplane project; so, I have no complaints. But, I certainly will use every tool available to ensure a successful result.

Conodeuce,
Check your mil spec for minimum radius turn for the cable you are going to use. My Fokker D VII plans called for a 1.75" pulley but when I cross check the mil. spec of the cable I was going to use the minimum was 3.5" I doubled the size of all the brackets for the pulleys and the pulleys. What will happen is if you force a cable into too tight of a radius it will eventually cut through itself.
Fokker Builder

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Originally Posted by Fokker Builder

Conodeuce,
Check your mil spec for minimum radius turn for the cable you are going to use. My Fokker D VII plans called for a 1.75" pulley but when I cross check the mil. spec of the cable I was going to use the minimum was 3.5" I doubled the size of all the brackets for the pulleys and the pulleys. What will happen is if you force a cable into too tight of a radius it will eventually cut through itself.
Fokker Builder

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Yes, I agree. It's clear that the original pulley size is simply too small. Up-sizing it won't be a problem.

Thank you.