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CMPro Piper J-3 Cub 120 91"

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CMPro Piper J-3 Cub 120 91"

Old 08-19-2013, 11:14 AM
  #176  
BadAzzMaxx
 
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Thanks for the reply,
I am installing a 30cc engine and going to install two servos in the tail for the elevator and maybe I can get it right without adding any weight to the tail.

Milton
Old 08-23-2013, 06:39 AM
  #177  
redball8
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Default Wing Tubes for CMPro Piper J-3 Cub 120 91"

Pranged my Cub while doing touch-n-go's, and she's now in the shop getting the roof repaired. Found a source of cheap wing tubes - Tent Pole Technologies http://tentpoletechnologies.com/?page_id=17. They make tent poles (duh) and masts for RC sailboats. I bought two 26" 19mm (0.742") tubes and one 26" 11mm (0.433") tube from them for less than $25 shipped - enough for two wing tube sets. They're very light, and made of the stronger 7075 alloy (vs 6061). The main tube is a hair smaller than 19 mm (18.9mm), but fits just fine.
Old 08-23-2013, 07:33 PM
  #178  
bikerbc
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cowboy1969 I tried the O Rings and found they worked okay but still deteriorited fairly quickly so I started using 1/8" shock cord (bungie cord) the same stuff found insided tent poles... It works great.. Lasts forever ..You can buy it up here in Canadian tire stores..You cut about 21" length and tie the ends together and CA the knot then wrap it where the O rings were , You sort of adjust till you get the tension rite..You will never look back..
Old 07-20-2014, 06:19 AM
  #179  
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Hi all, I know, this thread is old but I want to ask you, how do you solve question of fuel tank mount? I don´t like the solution which you can find in istruction manul.
I have H.K. Piper L-4 Grass hopper, but it is the same ARF kit as CMPro Piper J-3 91".
Old 06-20-2022, 01:02 PM
  #180  
rjpmodel
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Originally Posted by Prekin View Post
Hi all, I know, this thread is old but I want to ask you, how do you solve question of fuel tank mount? I don´t like the solution which you can find in istruction manul.
I have H.K. Piper L-4 Grass hopper, but it is the same ARF kit as CMPro Piper J-3 91".

This thread is Very Old but I have just received a CMP 91” J3 cub and am totally confused about the CG. The cg has been described several times on this thread as 100mm(3.94”) and on the spar. The front of my spar is at 109.2mm(4.3”) and the center of my spar is at 119.2mm(4.7”) ???????
Old 06-20-2022, 04:56 PM
  #181  
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Default J3 cg

The c.g. on most straight wing planes is in the 25-30% of the wing cord measured from the leading edge. You will find the main spar within that range.
it is advisable to have the fuel tank at c.g. or forward
good luck
Old 06-20-2022, 05:51 PM
  #182  
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Originally Posted by rafeeki View Post
The c.g. on most straight wing planes is in the 25-30% of the wing cord measured from the leading edge. You will find the main spar within that range.
it is advisable to have the fuel tank at c.g. or forward
good luck
Thanks for the reply. The center of the spar is at 35% and the front edge of the spar is at 32%. There has been some comments on another thread that the cg should be 97-104 mm. 100mm would be at 29.4% but they also stated that this would be at the spar and my spar is at 119mm(35%). This is why I am confused. I hope that someone that has successfully flown this plane would state where the cg was set.
Old 06-20-2022, 07:20 PM
  #183  
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Default Cg

You should try balancing the plane with the fuel tank empty.
The 25-30% figures I gave u are a good starting point... Don't get hung up on the slight differences u mention.
just have an experienced flyer try it out for the maiden flight , less disappointment.

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