Control Lines For all you fly-by-wire fanatics!

J Roberts Cobra

Reply
Old 03-07-2011, 09:16 AM
  #1
4u2nv-RCU
Thread Starter
 
Join Date: Apr 2003
Location: Spring, TX
Posts: 365
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default J Roberts Cobra

I just picked up an interesting plane. It is a J Roberts Cobra. Looks like A P-39/63 but the fellow that built this one decided German markings were in order. Trike gear and a 38 in wing. It is fitted with the 3 line belcrank and the plane has never flown. It came with Plans/instructions(not really plans) and the most notable thing I can see is there is no center sheeting. Anyone who can she dsome light as to how old this plane might be or any info really will be greatly appreciated.

4u2nv-RCU is offline  
Reply With Quote
Old 03-08-2011, 04:29 PM
  #2
xby-1
 
Join Date: May 2010
Location: , MD
Posts: 53
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: J Roberts Cobra

There is a discussion of the kit on the stunthanger.com site, carrier board. Those guys can probably answer your question If you aren't a member you may have to register.
xby-1 is offline  
Reply With Quote
Old 03-09-2011, 03:59 AM
  #3
perttime
 
perttime's Avatar
 
Join Date: Dec 2005
Location: Tampere, FINLAND
Posts: 1,630
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: J Roberts Cobra

On Stunthanger, john e. holliday has a recent thread on J.Roberts Sabre and Cobra. He has the kits and has been tracing the parts on paper.
http://stunthanger.com/smf/index.php?topic=20212.0

Looks like J.Roberts stuff is pretty well known to the "old" guys...

I think you need to register to view that part of the forums. Which is not a bad idea anyway if you are into C/L.

I think this thread on Stuka Stunt might have something interesting:
http://www.clstunt.com/htdocs/dc/dcb...ng_type=search
perttime is offline  
Reply With Quote
Old 03-09-2011, 10:58 PM
  #4
Dave Harmon
 
Join Date: Jul 2002
Location: Sperry, OK
Posts: 651
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: J Roberts Cobra

All the J Roberts stuff was from the mid 50's.
I still have a U-Reely from back then.
Their 3 line system worked really well but if the plane was marginal on power or had a tendancy to be a light pull on the lines.....the 3 lines could cause problems.
Generally though....it was ok.
Dave Harmon is offline  
Reply With Quote
Old 03-10-2011, 08:59 AM
  #5
4u2nv-RCU
Thread Starter
 
Join Date: Apr 2003
Location: Spring, TX
Posts: 365
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: J Roberts Cobra

Now I understand why such a large engine for the plane that size. I had a Sterling F-51 profile that was about the same dims and it flew great with a Veco 19. This was drilled for an OS 30. ( I have an OS 29 with a carb I will be using) The lack of center sheeting worried me until I looked at the instructions and it appears there is a couple of substantial hardwood pieces joining the wing halves. Should I even be flying a 50 year old plane?(60?)
4u2nv-RCU is offline  
Reply With Quote
Old 03-10-2011, 10:08 AM
  #6
Dave Harmon
 
Join Date: Jul 2002
Location: Sperry, OK
Posts: 651
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: J Roberts Cobra

It really depends on the condition of the plane.
Also.....J Roberts equipped models almost always had a tremendous amount of side thrust and sometimes had linkage to a moveable rudder to make sure it stayed tight on the lines at low speed.
There could be problems especially at low airspeed when the throttle was advanced quickly.
This would make the rudder move toward center and cause a lot of torque tending to roll the model to the left.
This along with the weight of the third line made J Roberts owners plan ahead to avoid problems.
Dave Harmon is offline  
Reply With Quote
Old 03-15-2011, 01:12 PM
  #7
50+AirYears
 
Join Date: Jul 2004
Location: Irmo, SC OH
Posts: 1,628
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: J Roberts Cobra

the J. Roberts 3 line system was a great inovation for CL scale and Navy Carrier flyers. I've had a couple planes fitted with it, and while it does work quite well, it is quite critical that all 3 lines be the same length, and that the lead-outs be made up with the correct stagger. Thought you might be interested in this little clipping. You might want to check the measurements on the plane and handle, I've heard that the newer Brodak system might be slightly different.
Attached Thumbnails
Click image for larger version

Name:	Ca81956.jpg
Views:	12
Size:	408.7 KB
ID:	1579226   Click image for larger version

Name:	Ig11112.jpg
Views:	11
Size:	369.0 KB
ID:	1579227  
50+AirYears is offline  
Reply With Quote
Old 05-23-2011, 07:05 PM
  #8
chenpangpang
 
Join Date: May 2011
Location: , BC, CHINA
Posts: 3
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: J Roberts Cobra

Mix Your Own Fuel....It's Easy!


Microsoft Office 2010
Microsoft Office 2007
chenpangpang is offline  
Reply With Quote
Reply


Thread Tools
Search this Thread
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



All times are GMT -8. The time now is 11:17 PM.