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joen6171b
10-07-2018, 12:38 PM
Hi folks. A friend of mine just complete a 10 year build on his Skyraider Ultralight. Yeah I know, he took his time..Im going to do the Initial flight because of my Ultralight experience.

We calculated the CG today. Empty CG was 8 inches aft of the datum (leading edge). With me in the seat it was calculated at 12 inches aft of the datum.


Sky Raider CG work sheet says 12-15 inches aft of the datum. It seems to me that the more important calculation would have the pilot in the seat?

The Empty weight CG appears to be too far forward, mostly due to the half VW engine.

The CG with me in the seat cancels that out because of my 220lb weight.

Fly it as is? Or add weight to the tail?
DaleB
10-07-2018, 01:59 PM
I'd check with the designer or manufacturer, but...

Specifying the CG of an empty airplane doesn't seem to make a lot of sense, does it?

But I'd make absolutely bloody sure of it before becoming a test pilot. That's no time to be making even an educated guess.
joen6171b
10-07-2018, 07:44 PM
From the CG worksheet
cub builder
10-07-2018, 08:51 PM
The empty CG is only done as a starting point worksheet to make your loaded CG calculations easier.

You really don't care about the empty CG unless you plan to fly the plane empty (no pilot or fuel). The only CG that counts is where it's at while you are flying, so make sure you include fuel loads in your calculations, both full and nearly empty, as well as the pilot and gear as loaded.

-Cub Builder
Sam Buchanan
10-08-2018, 07:33 AM
If this plane is supposed to be an ultralight I see a major problem on the worksheet........
joen6171b
10-09-2018, 06:21 AM
If this plane is supposed to be an ultralight I see a major problem on the worksheet........

Going to have to make it an ELSA. :thumbsup:
DaleB
10-09-2018, 06:46 AM
Going to have to make it an ELSA. :thumbsup:

It would have to be E-AB that just happens to fall within Light Sport parameters. E-LSA has to be an exact copy of an S-LSA.
1600vw
10-09-2018, 04:26 PM
If this plane is supposed to be an ultralight I see a major problem on the worksheet........

Unless he lives in Canada.
joen6171b
10-09-2018, 08:44 PM
It would have to be E-AB that just happens to fall within Light Sport parameters. E-LSA has to be an exact copy of an S-LSA.

You are correct, E-AB
Stolch
10-11-2018, 05:15 PM
As you research another consideration is does CG move fore or aft as you burn fuel in this aircraft?
gyrojohn
10-11-2018, 05:21 PM
You are correct, E-AB

The loaded
CG should be around 25% of the wing cord. The datum is just a convenient place to take measurements.