C of G balancer recommendations

[Tim Donald]

Can anybody recommend a decent C of G balance that doesn't cost the earth?  Needs to work with a wide variety of models from 70" IC acro planes to EDF's and gliders (and be more accurate then my current finger and thumb 'that'll do' system 😂)

 

 

[Graff]

Sounds like you need a Vanessa rig.

Easy to build and use.

[Tim Donald]

Just googled that - great idea, thanks !

 

[Cuban8]

You could use the calculation method of finding weight and balance that the full size aviation world uses. Plenty of info on microlight flying web sites. An interesting process even if you use a physical balance etc.

[Tim Donald]

Thanks,  might be a bit overkill for my needs but interesting none the less.

[Andy J]

Tim, this is what I built for my 1/4 scale size models. Width of the two balance arms is variable and the degree of tilt is limited by end stops. Worked a treat on a large Sparrowhawk.

[Tim Donald]

Thanks Andy,  very nice - I might have to make something similar.  

[KenC]

Has anyone mentioned fuel tank position and measurements of C of G  when empty and full at takeoff ?

[kc]

It is normal to have fuel tank empty when adjusting CG.  When flying & almost out of fuel CG will still be on the safe side.

[KenC]

What I was suggesting is, the position of the fuel tank ( unless sited under the COG ) is important.  What about slightly nose heavy for takeoff when full of fuel and even allowing small amount of tail down as it lands to increase the ease of a flared landing.  Everything I have seen with the rigs suggests that there is an empirical balance point for bubble level and plumbline certification.  Perhaps this is why the real things pump the wet stuff round to alter the balance.

Edited March 18, 2023 by KenC

[Frank Day]

Had a cheap ply jobby  that was terrible but now us this one: Multiplex Centre of Gravity Gauge 693054

[Don Fry]

On 18/03/2023 at 14:29, KenC said:

What I was suggesting is, the position of the fuel tank ( unless sited under the COG ) is important.  What about slightly nose heavy for takeoff when full of fuel and even allowing small amount of tail down as it lands to increase the ease of a flared landing.  Everything I have seen with the rigs suggests that there is an empirical balance point for bubble level and plumbline certification.  Perhaps this is why the real things pump the wet stuff round to alter the balance.

Standard practice, get the COG empty. Fill it with fuel, fly, land.

If it lands early, not a problem, a bit dead on the elevator. Wring every last second out of the flight, run out of fuel, need to get it right, then you have not got to cope with a bucking bronco on the elevator. Simples.

 

PS, keep the tank near the motor. If you don’t the motor gets an uneven fuel delivery, centripetal forces (centrifugal forces in some vocabularies). And then it stops.

Edited March 20, 2023 by Don Fry

[KenC]

Luckily Don my tank is against the firewall to avoid long runs and issues. Interested in your bucking bronco analogy.  I think mine would fly nose heavy on the takeoff and  about trim for the home run.