HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Nov 09, 2014, 08:58 PM
Registered User
United States, WA, Seattle
Joined Aug 2014
20 Posts
Discussion
variable cg?

Forgive the naive question...I'm new.

I was reading this by G_T:
"The desired CG location is not a constant. As turbulence levels change, the optimal airspeeds change (the more turbulence, the faster, even with no camber changes and even with no ballast added). The optimal CG position changes as well."

...and it made me wonder: Has anybody played with trim ballast under servo control?

What possibilities would it open up in a top-level ship if you could move a couple of grams fore/aft from the CG? Wouldn't it allow for attitude trimming without deflecting any control surfaces?

bd
seattle
barry d is online now Find More Posts by barry d
Reply With Quote
Sign up now
to remove ads between posts
Old Nov 09, 2014, 09:40 PM
Registered User
Thermaln2's Avatar
Reno Nevada
Joined Oct 2007
2,648 Posts
Barry,

Yes, variable CG has been done in F3B over 15 years ago, by Rolf Decker in Germany, I believe. The weight of and additional servo and the idea to move weights really did not provide an advantage. Decker also experimented with variable aspect ratios during flight and that too dis not give the advantages in flight one might expect.

In general, DLGers have found that if they did not add ballast in the wind that often just adding a penny to the nose helped immensely. Since this is a relatively quick change you could do it, if you desired, between launches.

It is better to know you plane as conditions change and rarely should you be second guessing yourself during a flight window.

Chris
Thermaln2 is online now Find More Posts by Thermaln2
Reply With Quote
Old Nov 10, 2014, 05:09 AM
Jens Hoffmann
jensdk's Avatar
Denmark, Region Zealand, Herlufmagle
Joined Jul 2006
437 Posts
Quote:
Originally Posted by barry d View Post
Forgive the naive question...I'm new.

I was reading this by G_T:
"The desired CG location is not a constant. As turbulence levels change, the optimal airspeeds change (the more turbulence, the faster, even with no camber changes and even with no ballast added). The optimal CG position changes as well."

...and it made me wonder: Has anybody played with trim ballast under servo control?

What possibilities would it open up in a top-level ship if you could move a couple of grams fore/aft from the CG? Wouldn't it allow for attitude trimming without deflecting any control surfaces?

bd
seattle
Oh Yeah !!!
even tested compressed helium in a steelbowel.
but it seems moving the bowl around did change CG to much

Often, only a tat (1-2g) of lead is enough, to change Cg.
But changing inflight, maybe is a bit too complicated and you'll end up with,bad settings for every kind of wind.
jensdk is offline Find More Posts by jensdk
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion Variable-planform, variable-incidence wings robert_houdin Modeling Science 14 May 03, 2013 09:08 PM
Discussion variable pitch vs variable rpm vs both? jy0933 Multirotor Talk 13 Dec 14, 2012 04:25 AM
Idea Variable CG FrogChief Sailplane Talk 20 Mar 05, 2012 08:16 AM
Discussion Determining CG...with variables involved. golem Electric Plane Talk 3 Jun 21, 2009 12:26 PM
Would an inflight variable CG help in DLG? MattyB Hand Launch 6 Aug 24, 2005 01:57 PM