News:


  • June 17, 2024, 07:24:48 AM

Login with username, password and session length

« previous next »
Pages: [1]   Go Down

Author Topic: Comments on Split Bellcrank design please  (Read 2526 times)

Offline Kevin Wright

  • Trade Count: (0)
  • Ensign
  • **
  • Posts: 42
Comments on Split Bellcrank design please
« on: October 26, 2010, 05:12:21 AM »
I've noted comments in previous posts on bellcrank positioning that
the usual bellcrank location will cause differential flap operation due to the slope
of the pushrod from bellcrank plane to flap horn.

I've come up with a design using a bellcrank on a post passing through the wing
with a horn fitted to the top of the post. Please see the attached image of the (incomplete)
installation.

I'd appreciate any comments on the design.
Logged

Offline Allan Perret

  • 2017
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 1892
  • Proverbs
Re: Comments on Split Bellcrank design please
« Reply #1 on: October 26, 2010, 06:05:54 AM »
I have seen pictures of this arrangement before, and like the idea.  But am concerned about how to lock the crank and output arm to the shaft.  How do you plan to do that ?  
Looks like you have metal to metal at the line connection.  Not good, need some kind of bushing there.  What do you plan to use for bearings on the crank shaft ?

The differential you refer to can easily be taken care of by standard bellcrank and custom flap horns which keep pushrods at 90° to the horn arms.
Logged
Allan Perret
AMA 302406
Slidell, Louisiana

Offline Kevin Wright

  • Trade Count: (0)
  • Ensign
  • **
  • Posts: 42
Re: Comments on Split Bellcrank design please
« Reply #2 on: October 26, 2010, 03:52:32 PM »
Allen,
The crank and the output arm are soldered to the central post - fluxless aluminum solder which is stronger than the base material.
The bushing for the leadouts is also aluminum tube in place of the usual copper or brass to avoid electrolytic corrosion.
I plan to machine bearings from Delrin.
Rgds, Kevin
Logged

Offline Randy Powell

  • 21 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 10478
  • TreeTop Flyer
Re: Comments on Split Bellcrank design please
« Reply #3 on: October 26, 2010, 05:01:51 PM »
Seems a different solution to a previously solved problem. Cool.
Logged
Member in good standing of P.I.S.T
(Politically Incorrect Stunt Team)
AMA 67711
 Randy Powell

Offline Allan Perret

  • 2017
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 1892
  • Proverbs
Re: Comments on Split Bellcrank design please
« Reply #4 on: October 26, 2010, 05:34:04 PM »
Quote from: Kevin Wright on October 26, 2010, 03:52:32 PM
Allen,
The crank and the output arm are soldered to the central post - fluxless aluminum solder which is stronger than the base material.
The bushing for the leadouts is also aluminum tube in place of the usual copper or brass to avoid electrolytic corrosion.
I plan to machine bearings from Delrin.
Rgds, Kevin
Not familiar with "fluxless aluminum solder".  If it is stronger than the base material, that would be sufficient.  But I am a skeptic, can you provide some reference ?   If this is truly a soldering operation,  I dont see how it can be as strong as the base.   I would think more heat than what you can get with soldering would be needed. 

The bellcrank is aluminum right, so you have aluminum bushings in an aluminum crank at the leadout connections ??

Delrin bushings for the bellcrank shaft.  You gonna split the one to get it around the shaft between shaft and output arm ??
 
Logged
Allan Perret
AMA 302406
Slidell, Louisiana

Offline Kevin Wright

  • Trade Count: (0)
  • Ensign
  • **
  • Posts: 42
Re: Comments on Split Bellcrank design please
« Reply #5 on: October 26, 2010, 05:53:42 PM »
Allan,
The solder is made by Durafix. Here's a link to their website - http://www.durafix.com/
I've pulled a joint apart with pliers and was amazed to find lumps of aluminum pulled out by the solder.
Its strong.

Aluminum soldering can be difficult. The key (as recommended by Durafix) is to clean the oxide off the aluminum only with
a stainless steel wire brush. I'm using a dremel drill with a small SS brush to do the job.
Clean with nothing else or there will be contamination making soldering difficult.
See the Durafix FAQ for more details on soldering aluminum.

Next step is to 'tin' the parts to be soldered at the proposed joints then sweat the parts together adding additional
solder.

Yes, aluminum bushings in an aluminum crank, and yes thanks for the suggestion! split delrin shaft bearings.
Rgds,
Kevin



Logged

Offline Wynn Robins

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 1684
Re: Comments on Split Bellcrank design please
« Reply #6 on: October 26, 2010, 08:27:00 PM »
seems like a lot of work and additional complexity/weight to solved an already solved issue......but at least you are trying something different ....kudos
Logged
In the battle of airplane versus ground, the ground is yet to lose

Offline BillLee

  • AMA Member
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 1299
Re: Comments on Split Bellcrank design please
« Reply #7 on: October 27, 2010, 05:51:21 AM »
This design is used on a great many CL Racing models where the wing is too thin to get a pushrod connected to the belcrank. It works well but with all of the caveats about attaching the pushrod arm securely to the belcrank.

OTOH, it seems to be a bit of overkill for a model with a thick wing and very little space constraints.

Regards,

Bill Lee
Logged
Bill Lee
AMA 20018

Offline phil c

  • 21 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2480
Re: Comments on Split Bellcrank design please
« Reply #8 on: October 30, 2010, 10:30:28 PM »
Brian Hampton(Australia) showed a similar bellcrank system he uses.  He put the elevator and flap on opposite sides of the shaft, with sliders so he could adjust  thr elevator travel and the flaps to zero travel.  He's had good success with it.  Couldn't find the pictures anywhere though.  I believe he ended up with 5 deg. of flap movement, ~ 20 deg. of elevator.
Logged
phil Cartier

Offline Steve Helmick

  • AMA Member and supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 9956
Re: Comments on Split Bellcrank design please
« Reply #9 on: October 31, 2010, 06:16:58 PM »
I had thought about this setup for a biplane with flaps on both wings. But I decided that with the handicap of two wings (mostly engine-out glide and windy weather, IMO), a biplane wasn't a solution to any problems I had. Not needed on a typical monoplane layout, with doglegged-type control horns, either.  D>K Steve
Logged
"The United States has become a place where professional athletes and entertainers are mistaken for people of importance." - Robert Heinlein

In 1944 18-20 year old's stormed beaches, and parachuted behind enemy lines to almost certain death.  In 2015 18-20 year old's need safe zones so people don't hurt their feelings.

Offline Chris Wilson

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 1710
Re: Comments on Split Bellcrank design please
« Reply #10 on: November 02, 2010, 06:43:13 PM »
Quote from: phil c on October 30, 2010, 10:30:28 PM
Brian Hampton(Australia) showed a similar bellcrank system he uses.  He put the elevator and flap on opposite sides of the shaft, with sliders so he could adjust  thr elevator travel and the flaps to zero travel.  He's had good success with it.  Couldn't find the pictures anywhere though.  I believe he ended up with 5 deg. of flap movement, ~ 20 deg. of elevator.

Try this link and see post 15 -

http://stunthanger.com/smf/index.php?topic=17589.msg%msg_id%
Logged
MAAA AUS 73427

You have enemies? Good. That means you've stood up for something, sometime in your life.
 Nothing in life is so exhilarating as to be shot at without result.  It's not enough that we do our best; sometimes we have to do what's required

Offline phil c

  • 21 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2480
Re: Comments on Split Bellcrank design please
« Reply #11 on: November 09, 2010, 05:54:26 PM »
Thank you Chris,  I couldn't find the right search terms.
Logged
phil Cartier

Offline Brian Hampton

  • Trade Count: (0)
  • Captain
  • *****
  • Posts: 580
Re: Comments on Split Bellcrank design please
« Reply #12 on: November 09, 2010, 08:49:16 PM »
I missed seeing a follow up question from Allan Perret in that link above so I'll answer it here. I used 5/32" wire for the shaft to keep any bending to a minimum and supported it top and bottom in brass bushes inset into 1/2" square bearer wood shaped and glued to the main spars. The external bellcrank is locked to the shaft with a setscrew (or as we call it here in Australia, a grub screw) seating in a flat in the shaft. I made a "skeletonised" internal bellcrank from 1/8" brass so it could be silver soldered to the shaft. In future though I'm considering using a main rotor drive shaft from one of the electric helicopters because it's the right diameter, has a flat already milled for a set screw and comes with ball races. And they're cheap :).
Logged

Offline Chris Wilson

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 1710
Re: Comments on Split Bellcrank design please
« Reply #13 on: November 09, 2010, 09:07:29 PM »
That set up has to be the best solution that I have ever seen and the Heli shaft is another winner also!

Fantastic!
Logged
MAAA AUS 73427

You have enemies? Good. That means you've stood up for something, sometime in your life.
 Nothing in life is so exhilarating as to be shot at without result.  It's not enough that we do our best; sometimes we have to do what's required

Offline Allan Perret

  • 2017
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 1892
  • Proverbs
Re: Comments on Split Bellcrank design please
« Reply #14 on: November 10, 2010, 07:16:00 AM »
Quote from: Brian Hampton on November 09, 2010, 08:49:16 PM
I missed seeing a follow up question from Allan Perret in that link above so I'll answer it here. I used 5/32" wire for the shaft to keep any bending to a minimum and supported it top and bottom in brass bushes inset into 1/2" square bearer wood shaped and glued to the main spars. The external bellcrank is locked to the shaft with a setscrew (or as we call it here in Australia, a grub screw) seating in a flat in the shaft. I made a "skeletonised" internal bellcrank from 1/8" brass so it could be silver soldered to the shaft. In future though I'm considering using a main rotor drive shaft from one of the electric helicopters because it's the right diameter, has a flat already milled for a set screw and comes with ball races. And they're cheap :).

Hey Brian:  Thanks for reply,  I am interested in trying this setup.  Do you have any additional info on the heli rotor that might work for this application.  Manufacturer and part number.
Would this set up use a set screw for the internal crank also,  and do you think that would be a secure connection ?
Logged
Allan Perret
AMA 302406
Slidell, Louisiana

Offline Brian Hampton

  • Trade Count: (0)
  • Captain
  • *****
  • Posts: 580
Re: Comments on Split Bellcrank design please
« Reply #15 on: November 10, 2010, 09:34:56 PM »
Hi Allan
The only electric helis I've had are 2 of the Walkeras and even those use two different methods to lock the main drive gear to the shaft. The small one (2.7mm drive shaft) uses a grub screw but IMO would only be suitable for small and light models. The larger heli has a 4mm shaft but the drive gear is locked with a pin so would need a flat machined for a grub screw or a roll pin could be used. I've never checked other brands to find something suitable with a reasonably large shaft but most LHS now have a fairly wide selection of leccy helis so it's just a matter of checking the spare parts bin. Personally I wouldn't use a grub screw for the internal crank because it's obviously inaccessible. I do check the grub screw for tightness on the external crank occasionally for my own peace of mind.
Logged

Offline Allan Perret

  • 2017
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 1892
  • Proverbs
Re: Comments on Split Bellcrank design please
« Reply #16 on: November 11, 2010, 07:12:49 AM »
I just realized that you have the 2 output arms on the bottom of the fuse. 
No issue for the pushrod to the flaps, but doesnt that throw off the geometry for the elevator pushrod ? 
With the typical stunt layout (elevator ~.75" above wing) do you still have a straight shot for the elevator pushrod ? 
Logged
Allan Perret
AMA 302406
Slidell, Louisiana

Offline Brian Hampton

  • Trade Count: (0)
  • Captain
  • *****
  • Posts: 580
Re: Comments on Split Bellcrank design please
« Reply #17 on: November 11, 2010, 09:11:30 AM »
Quote from: Allan Perret on November 11, 2010, 07:12:49 AM
With the typical stunt layout (elevator ~.75" above wing) do you still have a straight shot for the elevator pushrod ? 
It isn't dead straight but because the elevator pushrod (aluminium cored CF) goes from basically the high point of the wing at the root it's quite long so there's very little angular change. Even less in my model because I had the elevator at the same level as the wing.
Logged

Advertise Here
Pages: [1]   Go Up
« previous next »
Tags:
 


Advertise Here