REFLECTOR: Re: Weight & Balance

[Dave Black <asterisk@erols.com>]

Eung Tai Kim,


> >Your fuel tanks do not run all the way aft to the spar, do they?
> 
> ............ What does the above sentence mean?
>              I made the fuel tank exactly by the manual.

Then you're OK. Some builders have increased their fuel capacity by allowing
the main spar to serve double-duty as the aft fuel bulkhead. While this
provides a major increase in fuel quantity, it also shifts the CG dangerously aft.

> ....... I thought the Velocity Co. recommented MT C/S prop for the
> perfomance improvement.

I'm just restating what Duane told me several years ago. They do recommend the
MT Prop on the XL, but it's my understanding the XL was designed with the
extra weight and CG of the MT Prop in mind. 

The MT is an excellent prop, so I believe you made a fine choice of brands. I
wish I had one for my plane. But I would definitely expect to move the battery
or add ballast in order to keep the plane balanced. 

> ......... With one pilot of 150 lb and no passenger, the CG locates 125"
> after Datum which is more than 4" after the aft limit.With four men each on
> board, the CG locates 120.5" after Datum which is close to the aft limit.
> I surely seem to have a problem.

4" certainly sounds like way more than I'd expect from the MT Prop alone. From
your description, it sounds as though you'll need something close to 50 pounds
all the way up in the nose to balance the plane. That's a huge amount of
ballast. How heavy is your battery? If I needed to add weight to the nose, I'd
consider a larger battery, and I'd move the battery as far forward as
physically possible. As long as you're going to carry extra weight, it might
as well be "useful" weight.