Notices
RC Warbirds and Warplanes Discuss rc warbirds and warplanes in this forum.

effect of CG

Old 10-11-2005, 01:24 PM
  #1  
daw
Senior Member
Thread Starter
My Feedback: (6)
 
daw's Avatar
 
Join Date: Jun 2002
Location: Kouts, IN
Posts: 173
Likes: 0
Received 0 Likes on 0 Posts
Default effect of CG

I've been experimenting a bit with the CG on a few of my warbirds. It appears that as the CG moves toward the tail the landing of the craft becomes more difficult. I haven't moved the CG drastically and notice very little difference in flight but have noticed a bit more trouble getting the smooth two point roll outs. Anyone else with more knowledge have an explanation? I started this exercise in an attempt to lighten up a bird not just for jollies. One would think that as the CG moved back the plane would have less tendency to nose over. Not the case, even have played with this on the flight sim with same results.
Old 10-11-2005, 02:48 PM
  #2  
SpitfireMKI
Senior Member
My Feedback: (2)
 
SpitfireMKI's Avatar
 
Join Date: Jul 2002
Location: RAF Turnhouse 603 Squadron, MD
Posts: 1,463
Likes: 0
Received 0 Likes on 0 Posts
Default RE: effect of CG

Aerodynamic CG is different from your gear placement. Yes, moving it back will make the plane tip over less to a point, but it will make your plane more pitch sensitive in the air.

Warbirds always fair better a little nose heavy (IMO) too nose heavy leads to bounces and higher landing speeds, too tail heavy and you got a roller coaster of a tip stall machine.

My T-bolt is tough to taxi with the short coupling of the mains to the tailwheel and the long nose out front. However, she's grease to land and as no tendency to tip until back down to taxi speed.

S1
Old 10-11-2005, 06:34 PM
  #3  
Beechbum
My Feedback: (11)
 
Join Date: Mar 2004
Location: some where, CA
Posts: 274
Likes: 0
Received 0 Likes on 0 Posts
Default RE: effect of CG

Well,

CG is usually in front of the center of lift ( cl). The function of the horizontal stab is to exert a down force on the tail of the aircraft. This is so it can balance the tendancy of the aircraft to rotate forward about the center of gravity as the wing makes lift. At a constant airspeed, power setting, and in trim the forces are balanced. The the distance ( moment) between the cg, cl and the cl off the stab are designed to give a desired level of stability. If you move the cg aft towards the cl, the moment on the stab changes. It obviously gets shorter. Because less down force is needed than what the stab is providing, pitch will become more sensitive. When landing a normal pitch control input may be too much, which leads to a correction, which is usually hasty. An occillation is not far away. After landing the cg being farther aft makes the tail swaping tendancy of tail wheel aircraft worse. It has a longer lever with which to act around the main gear. Hope this helps. Don't know why it wants to nose over more. More bouncing?



Regards, 'Bum
Old 10-11-2005, 06:46 PM
  #4  
the-plumber
Senior Member
 
Join Date: Aug 2004
Location: East Cobb County, GA
Posts: 1,390
Likes: 0
Received 0 Likes on 0 Posts
Default RE: effect of CG


ORIGINAL: daw
One would think that as the CG moved back the plane would have less tendency to nose over. Not the case, even have played with this on the flight sim with same results.
Um . . . no.

As was pointed out, the relationship between CL and CG controls how the model handles in the air.

The relationship between CG and the LG is how the model handles on the ground.

Set the LG for best ground handling, and set the CG within the limits defined by the designer.

Lastly, do recall that nose-heavy models usually fly poorly, tail-heavy models usually fly once.
Old 10-11-2005, 08:03 PM
  #5  
Beechbum
My Feedback: (11)
 
Join Date: Mar 2004
Location: some where, CA
Posts: 274
Likes: 0
Received 0 Likes on 0 Posts
Default RE: effect of CG

Ha!, Yes indeed. Usually you only get one take off on an aft CG. The landing most often is vertical nav to a spot landing...er splat landing.

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 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.