Center of gravity and hovering
 

Hi to everyone
It’s my first post to your great forum, so I’d introduce myself. I’m Vladimir from Russia, not new to aero modeling but I’m new to 3d. I am trying to learn hovering and my question is: Would back center of gravity help to do this maneuver? I use to have 28% cg on my plane. Today I also tried to move cg further buck till 34% of chord. I try to hover relatively low so I can’t “catch” falling to spin plane with back cg.
Thanks in advance
Vlad

http://markov.baikal.ru/temp/acrobat_web.jpg

RE: Center of gravity and hovering
 

Vladimir, an aft CG will help with hovering, but you don't want it so far back that the plane becomes unstable. Probably the most important thing in learning how to hover is burning gallons of fuel practicing the maneuver.

RE: Center of gravity and hovering
 

i can move the battery from the fuel tank to right behind the wing of my Cougar, and the only difference i notice is the loops screw out, prophang, no difference. tho i leave it back incase it helps with TR and helps me learn it.

RE: Center of gravity and hovering
 

Just as impoertant if not more impoertant is the exsact side and down thrust, and looking at your model it doesn't look like youv'e got any side thrust. I use some petrol pipe hose of a car to make washers behind mount. cut them different thicknesses to guess the right amount req'd then simply tighten up any bolts a tad req'd at the field to get it spot on. No need to dismantle bolts etc, + prat about with washers, it quietens down the noise + vibration also.

RE: Center of gravity and hovering
 

I agree with all that has been said above and would like to add one more tip.

Try to prop your engine with a longer propeller with a flat pitch you want it to pull and not for speed.

RE: Center of gravity and hovering
 

See this site also:





http://www.gsal.org/articles/flying/torque_roll.htm

RE: Center of gravity and hovering
 

It is an inverted pendulum. In the 40's scientists had problems with their rockets flying strait. They flew straiter when they were able to have the center of mass closer to the bottom.

In my opinion some planes fly better tail heavy. They are less stable when you fly them, but harriers, hovers and flatspins are better. I learned to fly tail heavy.

RE: Center of gravity and hovering
 

Contrary to popular belief, an aft CG doesn't make hovering much easier. During flight an aft CG will make the plane more pitch sensitive as the CG moves back toward the center of lift. In a hover that effect disappears. Additionally,the difference between 25% to 35% CG does not increase the "pendulum effect" very much.

I have a very nose heavy trainer that hovers fine :)

It's all in the thumbs.

RE: Center of gravity and hovering
 

Sure its all in the thumbs but I have an GP Extra 300 that torque rolled on its own when the battery pack came loose during flight and got near the stab of the plane. It was already tail heavy but became really tail heavy. So tail heavy that I had to maintain down elevator for landing.

I think it depends of the plane.

RE: Center of gravity and hovering
 

GEOHARRY, your not the first and wont be the last person to state c+g doesn't effect hovering performance because you have gone PAST the stall !. Quite right but you all forget what about getting into the hover, getting out of the hover and combing manourvers before and after the hover ???? All of which would be very difficult with a forward c+g and blooming dangerous with too far an aft c+g. Needless to say the c+g is critical for whatever you want to do - for 3D it wants to be aft but not so the plane becomes a real handfull in normal flight - PERIOD.

RE: Center of gravity and hovering
 

Vladimir,

Trim the plane to fly neutral, ie very little down elevator to maintain level inverted flight, putting the CG any farther back won't help you hover.

RE: Center of gravity and hovering
 

You havn't read, dont comprihend, or just dont want to accept my point !

Aft CG for torque roll / hover
 

As a mental exercise, imagine a bowling ball on a broom handle.

Would you rather try to balance the ball stick combo with the ball at the top of the stick or bottom?

It's not an absolute correlation, but it seems to work the same for airplanes also. If your wing isn't working anymore, who cares how aft the CG is as long as you still have control.

I find I can TR MUCH easier with planes that have the CG so far aft that they're either climbing or diving with very little elevator imput during "normal" flight. No fun to fly around this way, but noticeably easier to horse around once the wing isn't working anymore.

RE: Aft CG for torque roll / hover
 

Wind Junkie , I cant resist being a smart ass. Try that with the bowling ball and broom stick. It's a lot easier with the ball on top.
I agree with your point though. The CG being towards the aft seams to help.
Later David

heavy objects on sticks
 

Hey, DOH! (Sounds of heavy objects falling and glancing off toes).

Bad analogy. Not sure what I was thinking. The thrust is applied from the wrong end also.