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Very Hot Topic (More than 25 Replies) Bristol Beaufighter (Read 1746 times)
alfakilo
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Re: Bristol Beaufighter
Reply #31 - Jan 24th, 2022 at 12:50pm
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staubkorb wrote on Jan 24th, 2022 at 12:35pm:
OK...
I went thru the whole schmear (construction diagrams and article) and "discovered" that the wing center section is removable - hence, the knitting needle (old time bone) is actually the wing mounting system!† NOT a bad idea, tho a more modern, aluminium needle would be as stiff and lighter.


Ah, of course! I read that too but didn't make the connection(no pun intended)!! Smiley

I love these old methods! I'm still looking at the fuselage motor mount and trying to see how the rubber was attached to it.

As for stretch winding the motors...maybe he removed the nacelle cowling, disengaged the rubber from the drive shaft, and then wound the motor??
  
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staubkorb
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Re: Bristol Beaufighter
Reply #30 - Jan 24th, 2022 at 12:35pm
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OK...
I went thru the whole schmear (construction diagrams and article) and "discovered" that the wing center section is removable - hence, the knitting needle (old time bone) is actually the wing mounting system!  NOT a bad idea, tho a more modern, aluminium needle would be as stiff and lighter.
  

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alfakilo
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Re: Bristol Beaufighter
Reply #29 - Jan 24th, 2022 at 12:05pm
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staubkorb wrote on Jan 24th, 2022 at 11:55am:
My thought is that it is simply a fixture for alignment purpose during construction and was just left in place for "whatever".† Unless it was actually glued to the motor peg bits, it seems to serve no real purpose.


That was my thought too. The plan article doesn't explain the purpose of the needle other than some info about using it as a drive shaft which made no sense to me.
  
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staubkorb
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Re: Bristol Beaufighter
Reply #28 - Jan 24th, 2022 at 11:55am
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alfakilo wrote on Jan 24th, 2022 at 11:34am:
Many thanks staubkorb!

Makes a little sense now, here's a pic of the spring. Still not sure about the knitting needle. Another poster suggested that it was a brace for the motor mount, something similar to a motor stick. Seems a little elaborate for that.


My thought is that it is simply a fixture for alignment purpose during construction and was just left in place for "whatever".  Unless it was actually glued to the motor peg bits, it seems to serve no real purpose.
  

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alfakilo
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Re: Bristol Beaufighter
Reply #27 - Jan 24th, 2022 at 11:34am
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Many thanks staubkorb!

Makes a little sense now, here's a pic of the spring. Still not sure about the knitting needle. Another poster suggested that it was a brace for the motor mount, something similar to a motor stick. Seems a little elaborate for that.
  

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Re: Bristol Beaufighter
Reply #26 - Jan 24th, 2022 at 11:05am
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alfakilo wrote on Jan 24th, 2022 at 9:23am:
I ran across this plan and am amazed at its apparent complexity!!

Does anyone know what a "spring curtain rod skew drive" is??!! And what is the purpose of that knitting rod in the fuselage??!!

https://outerzone.co.uk/plan_details.asp?ID=11936

That "skew drive" works on the same principle as the old speedometer cables - essentially a tightly wound spring - which allows quite tight radius snaking while still allowing it to spin.† Finding something like that and adding the hook at one end and the shaft at the other might also be a problem.  Model boaters use this type of "universal joint" between the motor and shaft.

I can't see any way to stretch wind the motors as stated on the plan.† I think the method to best get some decent length would be as in your third drawing - with a short removable (for scale judging) "cheat stick" added.

A very nice effort!
  

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alfakilo
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Re: Bristol Beaufighter
Reply #25 - Jan 24th, 2022 at 9:23am
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I ran across this plan and am amazed at its apparent complexity!!

Does anyone know what a "spring curtain rod skew drive" is??!! And what is the purpose of that knitting rod in the fuselage??!!

https://outerzone.co.uk/plan_details.asp?ID=11936
  
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alfakilo
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Re: Bristol Beaufighter
Reply #24 - Jan 24th, 2022 at 8:11am
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Thanks bjrn and welcome to the forum!

Good points and here's a couple of things I'm considering. First, this plan is semi-scale in that Towner doesn't seem to have a particular mark in mind, it's just a generic Beaufighter. I haven't found a publication date for the plan but given Towner's early 1940s activity, it may have been before the redesign that produced the new tail.

As you no doubt are aware, many of our plans have the horizontal and/or vertical stabilizer size increased to improve stability. In this Peanut plan, Towner made the horizontal stab a good 20% larger than real life. My guess is that he did that to improve model aerodynamics more than any attempt to replicate real life factors.

Lastly, there is the matter of the reported instability of the earlier marks. From what I can see, the issue here was lateral control in the event of an engine failure. There seems to have been a concern that there wasn't "enough tail" to deal with the asymmetric thrust effects of single engine operation at high power settings. The added dihedral increased the effective yaw control to correct this deficiency.

Will this be an issue on a model of this size? I doubt it! There are so many other things that the builder might get wrong that might affect stability to a greater degree.
  
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Re: Bristol Beaufighter
Reply #23 - Jan 24th, 2022 at 1:37am
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Nice looking work. One thing that struck me is that the model has horizontal tail planes. That is true to the plan, but only the Beaufighter prototype and very early models were configured like that. The prototype had poor longitudinal stability and the final solution was to increase the area of the tailplanes by 20% and give the 12 degrees of dihedral. I donít know whether the same instability would carry through to a peanut sized model, but a modification now might save trimming problems later.
  
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Re: Bristol Beaufighter
Reply #22 - Jan 20th, 2022 at 3:46pm
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I was re-reading some of the old FAC Newsletters and Wally Farrell has an article on his trimming procedures.† He mentions that for short motors he uses a 1.5 times hook to anchor length and tightly braids the rubber to take up as much slack as possible.† This might help in your straight back to the trailing edge hook arrangement.† I used a similar setup on my Connie.†

As for the holes through the ribs is there anyway to make a short plastic or heavy paper tube to keep the rubber from banging around against all the edges of the ribs etc.?† Just a thought.† The "Fort" looks good!

OOPS... I just reviewed your post and looks like you've already done the tube thing.   Embarrassed Lips Sealed Cry
  

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alfakilo
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Re: Bristol Beaufighter
Reply #21 - Jan 20th, 2022 at 12:52pm
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Good news, a test run functioned. Bad news, not very well!

The rubber path from the prop shaft hook to the rear mount is pretty cramped for space, especially at the rear where the rubber goes thru the root rib/fuselage joint. In the plan, you can see where Towner made the rear end of the root rib larger to allow a bigger hole for the rubber but in this scale, even that is marginal at best. In the pic, the circular plan motor hole (red) is barely big enough to allow a loop of 1/16" rubber to pass thru. I increased that hole to about 1/4" (blue)

I hand cranked in about 50 turns and let 'er rip. The rig spun merrily away albeit with a bit of clattering!!

Edit: Attaching the rubber to a trailing edge hook would be much easier. I figure it would shorten the motor length by about 1/2", not sure that it significant. And we could always extend the motor to the rear using a motor stick. See side and bottom views for the general idea.
  

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alfakilo
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Re: Bristol Beaufighter
Reply #20 - Jan 20th, 2022 at 10:32am
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Thanks, Mike. The motor set-up is definitely affected by the small size of the model...just not a lot of space there to allow things to sort themselves out.

I'm going with a single loop of 1/16" rubber to begin with just to see if I can get the prop to spin!! I ended up not using the soda straw "blast tube" idea, no room. Maybe in a dimer size model.
  

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Re: Bristol Beaufighter
Reply #19 - Jan 20th, 2022 at 10:25am
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Looks great. I love watching people do something new (old) and different. A twin in that scale is really unique. Can't wait to see the props in motion, even if it doesn't take to the air.
ian
  
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Re: Bristol Beaufighter
Reply #18 - Jan 20th, 2022 at 9:31am
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That's great AK.  I'm very curious how the angled motor setup and motor tubes work out - please post updates once you've had a chance to try it out.

Mike
  
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alfakilo
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Re: Bristol Beaufighter
Reply #17 - Jan 20th, 2022 at 8:56am
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Mostly done, down to installing the motors. There's a hatch below the motor peg. I'm going to try to make 4" counter-rotating props from 1/32" ply using the can method.
  

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