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Author Topic: Centrak retract unit  (Read 3165 times)

Offline Ian Busch

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Centrak retract unit
« on: March 28, 2025, 01:12:14 AM »
Does anyone out there have a  Centrak retract unit or know of someone who does that would be able to post some close up photos of the unit here. It was designed by Norm Bracken and marketed by well known Bill Johnson of control line carrier fame in the late 60s I think. The unit quite cleverly used the centrifugal force of the model to retract the undercarriage. I would be most grateful if someone could help. An article: Wheels Up, originally from an unnamed magazine, was posted about the unit in RCgroups control line section. I did have a go at making one but was not happy with its operation due mainly to my lack of  finesse and inability to make binding free connections. Thanks Ian
« Last Edit: April 12, 2025, 05:20:40 PM by Ian Busch »
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Offline Trostle

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Re: Centrak retract unit
« Reply #1 on: April 26, 2025, 01:40:01 AM »
Quote from: Ian Busch on March 28, 2025, 01:12:14 AM
Does anyone out there have a  Centrak retract unit or know of someone who does that would be able to post some close up photos of the unit here. It was designed by Norm Bracken and marketed by well known Bill Johnson of control line carrier fame in the late 60s I think. The unit quite cleverly used the centrifugal force of the model to retract the undercarriage. I would be most grateful if someone could help. An article: Wheels Up, originally from an unnamed magazine, was posted about the unit in RCgroups control line section. I did have a go at making one but was not happy with its operation due mainly to my lack of  finesse and inability to make binding free connections. Thanks Ian

I have a "Centrak" unit made by Bill Johnson.  I met him at his house in the early 70's.  It is unused.  I have not figured out how to post a photo on this Stunt Hangar website.  Maybe I could send some photos over the phone.  No, I do not want to sell it.  No, I am not willing to let you "borrow" it.

I also have instruction sheets prepared by Bill Johnson.  These show a good drawing with the unit installed in a wing and the linkages to the LG struts and where the spring goes.  It also has drawings of how the LG wire is formed.

Keith




Keith
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Offline Dan McEntee

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Re: Centrak retract unit
« Reply #2 on: April 26, 2025, 09:48:11 AM »
Quote from: Trostle on April 26, 2025, 01:40:01 AM
I have a "Centrak" unit made by Bill Johnson.  I met him at his house in the early 70's.  It is unused.  I have not figured out how to post a photo on this Stunt Hangar website.  Maybe I could send some photos over the phone.  No, I do not want to sell it.  No, I am not willing to let you "borrow" it.

I also have instruction sheets prepared by Bill Johnson.  These show a good drawing with the unit installed in a wing and the linkages to the LG struts and where the spring goes.  It also has drawings of how the LG wire is formed.

Keith



    I got to know Bill Johnson later in his life, when he used to come into the hobby shop in the evenings when I worked there. Bill was quite the character!! He explained his retract system to me at the time but I don't remember anything about it. I think he said that it was detailed in Aeromodeller magazine back then, might not have been in any of the US magazines I have a pretty fair collection of Aeromodeller and if we can determine what issue the article was in, I may have it. I am not sure where to start looking myself. Perhaps Charlie Reeves might know and can shed some light on the subject if it possible to contact him still. I don't think Bill Johnson is still among us.
  Type at you later,
   Dan McEntee
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Offline Paul Smith

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Re: Centrak retract unit
« Reply #3 on: April 26, 2025, 09:52:02 AM »
All of that mechanical finesse and skill of the past is why they made retracts DOUBLE bonus item.
That's history.  Now you can buy a variety of electric retract with the motor included and just put the device onto your receiver.
We need to reduce retracts to a single 10-point bonus to be fair.
Plus, in the pre-2.4 days engineering a reliable method of operating the retracts was a hurdle that is now gone.
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Paul Smith

Offline Trostle

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Re: Centrak retract unit
« Reply #4 on: April 26, 2025, 10:04:50 AM »
Quote from: Dan McEntee on April 26, 2025, 09:48:11 AM

    I think he said that it was detailed in Aeromodeller magazine back then, might not have been in any of the US magazines I have a pretty fair collection of Aeromodeller and if we can determine what issue the article was in, I may have it. I am not sure where to start looking myself.
 
   Dan McEntee

Hi Dan,

I can remember my visit with Bill Johnson at his home.  The time frame would be no later than 1973 and no earlier than 1971, maybe late in 1970.  (I made a number of trips to the St. Louis area during that time and I am sure of the time frame.)  I do not have many Aeromodeller magazines and very few from that time, and do not remember any article on the Centrak system.  You might check what you have.  I doubt that there would be any more information there than what Johnson had and showed in his instruction sheets.

Keith
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Offline Ian Busch

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Re: Centrak retract unit
« Reply #5 on: May 30, 2025, 04:37:32 PM »
Hello Keith, thanks for replying. It great to know someone has a Centrak unit. I'm not sure I can help with the photo upload. I did upload photos and drawings I produced of my rendition of the unit in RCgroups control line section years ago but like I said previously was unhappy with the movement of the unit. I need to refine the connections so it works smoothly . I made my unit based on the magazine article posted in RCgroups but the article photos were low quality so it was difficult to see the connections in the unit I would be most grateful if you could advise me of the materials used on the unit especially the moving connections. I have attached a couple of photos of my unit rater crudely held together with bolts which needs improvement.
Many thanks Ian
« Last Edit: May 31, 2025, 04:51:14 AM by Ian Busch »
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