Aft C of G issue

[380busdriver]

Hi All

My complete but unpainted RV6A weighed in yesterday at 975lbs, which is not too shabby but the problem is the ARM is 72.21 inches aft of datum. In order to be able to satisfy my requirements I need to move this forward 1.5 inches to 70.71 or so. Can anyone give some guidance and or suggestions on how to achieve this.

Many thanks

Dave

[jpowell13]

Several posters have suggested putting an old fashioned Lycoming starter on the engine. They Weigh about 16 lbs. john

[Mel]

If the battery is in the original position, you might try moving it to the firewall if there's room. A heavy crush plate will also help.

Also keep in mind that when you paint, the C/G will move further aft.

[M McGraw]

I have a Landroll balancer I do not plan to use. I bought it for $500 on this site. I do think you could accomplish a lot with the heavier starter recommended earlier.

[jpowell13]

Don't know what prop you are using. Sounds like it's wood or something very light based on your total weight. My 6a has an aluminum Sensenich FP which puts plenty of weight right on the nose. John

[380busdriver]

Thanks for the responses gents. The prop is a sensenich ground adjustable. very light! i also have the light weight starter and pmags, all nice to have but don't help the c of g issue. The battery is already on the fire wall.

Does anyone know if there is a formula for how much extra weight and how far forward I need to place it in order to get the 1.5 inches forward. I would be happy to carry a little dead weight if it would help.

Marvin what is a "Landroll balancer"?

[alpinelakespilot2000]

Originally Posted by 380busdriver

Does anyone know if there is a formula for how much extra weight and how far forward I need to place it in order to get the 1.5 inches forward. I would be happy to carry a little dead weight if it would help.

Marvin what is a "Landroll balancer"?

If you computed the weight and balance you already have the formula. If you put your W&B on a spreadsheet it should be pretty easy to experiment with different configurations.

Saber makes a ~20# steel crush plate. I would guess this would go a long ways toward improving your c.g. envelope. The good thing about using a crush plate is that that is the farthest forward from your current datum and therefore requires the least amount of weight to move the c.g. fwd.

[Mel]

Originally Posted by alpinelakespilot2000

However, the arm would be a negative number instead of a positive number since it is forward of the datum point.

Probably not! It all depends on where the datum is. The datum is only a reference point and can be anywhere. However, since he is talking in the 70" range, I assume that his datum in forward of the prop. Therefore all numbers will be positive.

[alpinelakespilot2000]

Originally Posted by Mel

Probably not! It all depends on where the datum is. The datum is only a reference point and can be anywhere. However, since he is talking in the 70" range, I assume that his datum in forward of the prop. Therefore all numbers will be positive.

You beat me to my change, Mel. I realized my mistake and changed my previous post just after submitting.

[M McGraw]

A Landroll Balancer bolts to your prop flange to add weight at a forward CG. If it were me and the light weight propeller were new and returnable, I would consider a heavier prop, a crushplate, heavy starter, or Landroll. They all solve your problem.

Weight x arm = moment

Since you have already done a weight and balance just measure the distance to your prop flange or starter (arm). Increase the weight of the prop or starter until you get the CG you want, that will tell you how much weight you need at the prop flange or starter location. Another route is to move something aft to a more forward location with the same formula.

Good luck,
Marvin