News:


  • March 29, 2024, 05:05:03 AM

Login with username, password and session length

Author Topic: A three line bellcrank?  (Read 882 times)

Offline Mark Mc

  • 24 supporter
  • Trade Count: (0)
  • Captain
  • *
  • Posts: 718
A three line bellcrank?
« on: June 22, 2021, 10:16:31 PM »
I'm hankering to build a throttled engine plane.  I have two of the old Cox Synchro Pilot handles, but not one of the three line bellcranks.  I know that I've seen three line bellcranks that people have made up for 1/2A, but I can't seem to find them now.  I did a search on the Carrier forum, but didn't see anything.  Can anyone point me to a set of plans for a 1/2A size carrier bellcrank?

Mark

Offline Dave Hull

  • 24 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 1902
Re: A three line bellcrank?
« Reply #1 on: June 22, 2021, 10:59:47 PM »
You could look at the Sept. 1995 issue of Model Aviation. Had an article on just such a thing. Just tweak it to your needs.

Dave


Offline Mark Mc

  • 24 supporter
  • Trade Count: (0)
  • Captain
  • *
  • Posts: 718
Re: A three line bellcrank?
« Reply #2 on: June 23, 2021, 02:48:53 AM »
Thanks, Dave.  I just looked that issue up on the AMA website and copied the article.  Up to this point, the bellcrank pictures I'd seen were confusing and I didn't quite understand how it all worked together.  Looking at the drawing in the article cleared it up and it makes perfect sense now.

Mark

Offline Paul Smith

  • 24 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 5793
Re: A three line bellcrank?
« Reply #3 on: June 23, 2021, 07:12:43 AM »
On a 1/2A you can get by with a stacked bellcrank made with a metal bellcrank on the bottom and light plastic on top.

The wire loop on the top figure is a stress relief device that keeps the updown bellcrank from being pulled too far inboard at high speed.

As you can deduce, the throttle bellcrank bears ALL the stress and thus needs
 to be made stout.

The throttle bellcrank needs to be sized as such.  The throw as determined by the leadout end which needs to match the throw of the handle.   The distance from the pivot to the updown bellcrank needs to be HALF the length of the leadout arm.  If this is done, line pull will equalized between the three lines.
Paul Smith

Offline 944_Jim

  • 24 supporter
  • Trade Count: (0)
  • Captain
  • *
  • Posts: 840
Re: A three line bellcrank?
« Reply #4 on: June 23, 2021, 08:24:56 AM »
Mark,
I have info for you related to this. I did the same lookup several years ago, and also have the Cox Synchro-handle...and the accompanying 3-line bellcrank.

What I have will be filler for what is already here.

If you PM your email address, I can send several articles. Select the "email user" link so your request comes to my inbox.

The "sharing" Jim

Offline Trostle

  • 22 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 3338
Re: A three line bellcrank?
« Reply #5 on: June 23, 2021, 08:30:48 AM »
Why not just use the small Roberts type 3-line system that is available from Brodak?

Offline Mark Mc

  • 24 supporter
  • Trade Count: (0)
  • Captain
  • *
  • Posts: 718
Re: A three line bellcrank?
« Reply #6 on: June 23, 2021, 10:15:51 PM »
Mark,

If you PM your email address, I can send several articles. Select the "email user" link so your request comes to my inbox.

The "sharing" Jim

Jim, mailed you my email address.  The address I sent you is the mail account I check daily, not the email account of record here on Stunthangar.  Than you very much.

Mark

Offline Mark Mc

  • 24 supporter
  • Trade Count: (0)
  • Captain
  • *
  • Posts: 718
Re: A three line bellcrank?
« Reply #7 on: June 23, 2021, 10:18:19 PM »
Why not just use the small Roberts type 3-line system that is available from Brodak?

I looked at them.  They seemed heavy, complicated, and expensive for a model that I anticipate will be in the 6 ounce range.  I would rather build my own, even if I mess up a couple of times in the beginning.  The "stacked" method seems pretty bullet proof.  I also can't wait to see what Jim sends me.

Mark

Offline john e. holliday

  • 24 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 22752
Re: A three line bellcrank?
« Reply #8 on: June 24, 2021, 10:44:58 AM »
The stacked bell crank works great on small or super light planes.   Mine folded at the NATs that I used it in.  Don't remember how many flights I had on it with no problems using my pull scale. D>K
John E. "DOC" Holliday
10421 West 56th Terrace
Shawnee, KANSAS  66203
AMA 23530  Have fun as I have and I am still breaking a record.

Offline 944_Jim

  • 24 supporter
  • Trade Count: (0)
  • Captain
  • *
  • Posts: 840
Re: A three line bellcrank?
« Reply #9 on: June 24, 2021, 03:30:11 PM »
I'm out of town until tomorrow evening. I'll try to remember to post pics of the Roberts rig side-by-side with the Cox Synchro-whatever...Synchro-Pilot sounds familiar. I'll also weigh them on my digital scale.
« Last Edit: June 24, 2021, 05:31:41 PM by 944_Jim »

Offline Paul Smith

  • 24 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 5793
Re: A three line bellcrank?
« Reply #10 on: June 25, 2021, 05:45:01 AM »
From what I see on Brodak, he's making the old GS / Sturi-Built products designed for Class I/II Carrier.  They're intended to survive a 100-pound pull test.  I guess a 1/2A would fly with one, if you don't mind a bellcrank that weighs as much as the airframe.  Plus it will set you back at least $30 with tax and shipping.

Assuming you have some old parts about, this won't cost you anything and it works.

This was NOT an entry in a beauty contest, but rather a successful effort to convert a Slow Combat plane to Carrier without a trip to the shop.


Paul Smith

Offline 944_Jim

  • 24 supporter
  • Trade Count: (0)
  • Captain
  • *
  • Posts: 840
Re: A three line bellcrank?
« Reply #11 on: June 25, 2021, 07:21:10 AM »
Mr. Paul,

I know Mark is itching to do this. Doing 3-line control in 1/2A has been on my wishlist for the last few years too.

Thanks for showing your setup. I'll be certain to add the pictures and text to my folder of 3-line notes. It will be studied closely!
« Last Edit: June 25, 2021, 09:47:02 AM by 944_Jim »


Advertise Here
Tags:
 


Advertise Here