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Centre of Gravity

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sjjonesnz

Well Known Member
Well, an exciting day is coming to a close...we weighed the beast (which means we're real close to inspection time) and got the following numbers.....

Left: 531.31lb @ 69.25" aft of datum (datum is 70" forward of leading edge)
Right: 534.62lb @ 69.3125" aft of datum
Tail: 79.37lb @ 249.625" aft of datum

Soooo, we have an empty weight of 1145lb @ 81.78" aft of datum which seems to be fine for cruising and solo aerobatics (I'm ~175lb), however as soon as I want to go upside down with a likely suspect of adult size I've got a CoG which exceeds the aft aerobatic CoG limit published by Vans (84.5" aft of datum) and only doing aeros on my own has absolutely zero appeal. :(

I have an RV7 with Aerosport O320 with sensenich FP prop so I s'pose I could consider a CS prop (more $$ :eek:) - for those that have made this change how did it affect things??

Also have dual LSE Plasma II+ ignition, dual PC680 batteries and SkyTec 149NL starter.

Any other ideas??
 
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What starter do you have? The old prestolites add 8-10 lbs pretty far forward compared to the current generation of lightweight starters.
 
I am not very experienced with W&B in the RV, but that said you seem to be in a box. Meaning that adding weight to the nose (takes a lot to make significant CG change) by changing out equipment will diminish your useful load which now is two 170 lb. persons and about 18 gal. of fuel (aerobatic gross). Either way you end up with a lighter passenger.

If there was any way to lighten or move something from the tail forward of the CG, antennae, lighter tail wheel, elt, anything that can be lightened or moved forward.

Just my thoughts.
 
49clipper

If you have a -6 with the small lycoming and light fp prop, then from I see. you will have an aft cg, period. I have been dealing with that for the last year. I have nothing that can be moved forward. I hate to add a 20# spacer to the prop, and on paper, that does not do much anyway. Its easy to figure by writing it up on excel and placing weights here and there.
 
49clipper said:
If you have a -6 with the small lycoming and light fp prop, then from I see. you will have an aft cg, period. I have been dealing with that for the last year. I have nothing that can be moved forward. I hate to add a 20# spacer to the prop, and on paper, that does not do much anyway. Its easy to figure by writing it up on excel and placing weights here and there.
Click to expand...

Not true in my case. I have a wood prop and an 0-320. On trips to Oshkosh, I plan for about 75 pounds of baggage with ~375 lbs of people on board and plan to land with 10 gallons or more remaining in the tanks. This keeps my airplane within the aft limit. If the situation arises where I have to land with less fuel, I'll have the passenger grab a small bag out of the passenger compartment and place under his/her knees right in front of the spar. That'll move the CG a tenth or two of an inch.

One thing I did when I built my airplane was plan for the light engine/prop combo. I retained the Prestolite starter and mounted the ELT, strobe power supply, etc. as far forward as possible.
 
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