Go Back  RCU Forums > RC Airplanes > Golden Age, Vintage & Antique RC
Reload this Page >

Question about CG for vintage planes.

Notices
Golden Age, Vintage & Antique RC Want to discuss some of those from the golden age, vintage rc planes or even an old classic antique vintage rc planes, radios, engines, etc? This is the place for you. Enjoy!

Question about CG for vintage planes.

Old 04-25-2021, 01:21 PM
  #1  
Hortco
Thread Starter
 
Hortco's Avatar
 
Join Date: Feb 2015
Location: Greenfield IN
Posts: 134
Likes: 0
Received 4 Likes on 4 Posts
Default Question about CG for vintage planes.

Iím getting my Cloud Clipper ready to fly but I need help with the CG.
The book shows the CG behind the main spar.
Do old time RC airplanes with short noses balance differently from normal modern day RC planes?

The main spar is in Red. The plan show the CG far behind the main spar. This is a vintage style Cloud Clipper by Value Planes. The manual says NOTHING about balancing this plane. The plans DID NOT show any CG- I had to email the company to get the picture above. I donít know if I should trust the CG that they show.

Old 04-25-2021, 02:03 PM
  #2  
speedracerntrixie
My Feedback: (29)
 
speedracerntrixie's Avatar
 
Join Date: Jun 2010
Location: Happy Valley, Oregon
Posts: 8,174
Received 71 Likes on 68 Posts
Default

I would balance between what is shown on the plans and the spar. My bigger concern is the fuel tank being located do far away from the engine ( assuming you are running glow ).
Old 04-26-2021, 12:42 AM
  #3  
UStik
 
Join Date: Oct 2006
Location: Augsburg, GERMANY
Posts: 991
Likes: 0
Received 2 Likes on 2 Posts
Default

Originally Posted by Hortco View Post
Do old time RC airplanes with short noses balance differently from normal modern day RC planes?
The other way around: this kind of airplane is short-nosed because they balance quite aft. Their wing airfoil is cambered and hence they need some decalage. Apart from that, the pictures of this airplane in the Web show a far forward main wing spar. I would definitely trust the C/G shown in the picture.
Old 04-26-2021, 04:53 PM
  #4  
Hortco
Thread Starter
 
Hortco's Avatar
 
Join Date: Feb 2015
Location: Greenfield IN
Posts: 134
Likes: 0
Received 4 Likes on 4 Posts
Default

Thanks guys.
BTW- I mounted my tank right behind the firewall like it should be.
Old 04-28-2021, 11:56 AM
  #5  
Truckracer
My Feedback: (19)
 
Join Date: Apr 2004
Location: Des Moines, IA
Posts: 5,142
Likes: 0
Received 25 Likes on 25 Posts
Default

These older almost glider like designs do balance with a CG well behind what is common for a typical airframe. I'd have no problem balancing the plane as shown on the plans. If you don't trust that CG, add some additional removable nose weight for the first few flights then remove the weight as you feel comfortable.
Old 05-21-2021, 05:06 AM
  #6  
378
My Feedback: (4)
 
378's Avatar
 
Join Date: Jan 2004
Location: Lebanon, TN
Posts: 2,858
Likes: 0
Received 2 Likes on 2 Posts
Default

It might also have a lifting tail. My old VK Cherokee 60 has a fully aerfoiled horizontal stabilizer and a correspondingly aft CG.
Old 05-21-2021, 02:37 PM
  #7  
GREG DOE
 
Join Date: Jul 2005
Location: , TN
Posts: 747
Likes: 0
Received 4 Likes on 4 Posts
Default

"It might also have a lifting tail. My old VK Cherokee 60 has a fully airfoiled horizontal stabilizer and a correspondingly aft CG" .BINGO
Old 05-23-2021, 07:05 PM
  #8  
otrcman
 
Join Date: Oct 2004
Location: Arroyo Grande, CA
Posts: 727
Likes: 0
Received 2 Likes on 2 Posts
Default

Originally Posted by UStik View Post
The other way around: this kind of airplane is short-nosed because they balance quite aft. Their wing airfoil is cambered and hence they need some decalage. Apart from that, the pictures of this airplane in the Web show a far forward main wing spar. I would definitely trust the C/G shown in the picture.
UStik has it right. This may be a little confusing, but I'll try to explain it a little more thoroughly.

The 1930's models were flown free-flight. They were designed to be light, and to glide as efficiently as possible. To that end, most were designed not as monoplanes, but as tandem wing biplanes. That is to say, both the wing and the "tail" flew at a quite high, positive angle of attack, both contributing to lift. Because of the high trimmed angle of attack and the rather large horizontal stabilizer (without an elevator), the model was plenty stable in pitch.

A critical element in what the 1930's modelers called the "Force Arrangement" is that the highly cambered wing airfoil had a large nose-down change in pitching moment as the angle of attack approached zero. That meant that the model flew OK at a high angle of attack, but it had to remain at that high AOA for safety.

The upshot of all this is that, when we add radio control to our old time models, it is possible to get into a "death dive" from which there is no recovery. The safest way to prevent the death dive is to keep the elevator fairly small and/or limit the travel of the elevator. Or, you can move the CG forward a bit to alter the "force arrangement" to a more modern setup.

As a side note, having the main spar well forward is more of a structural consideration than aerodynamic. Typically, the spar is placed at the point where the airfoil is thickest. Deeper spars are stronger spars. And coincidentally, the highly cambered airfoils have their maximum thickness point fairly far forward.

As a comment on the Cloud Clipper, that model doesn't appear to conform to the 1930's force arrangement that we're talking about. The horizontal stabilizer is on the small side for a 30's free flight, and the distance from wing to tail is a bit short. If you notice, the airfoil is not of the thin, highly cambered type that we see on a Playboy, Zipper, Ramrod, etc. So one wouldn't expect to see the CC with a super far aft CG like a Zipper or a Playboy. The CC looks more like a conventional monoplane to me. The area of the horizontal is generous, so you will probably do fine with the CG as shown on the plan. If it were me, I might put a little extra nose weight in for the first flight just for added insurance, but would expect to find that it wan't needed.


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


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright © 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.