[grosbeak]

After I put my Pulse 125 together I did a preliminary CG check - it's definitely tail-heavy. I found an old thread about calculating counterbalance weight and I figure I can apply it here. So:



I'll check CG again and note the weight where the top of the vertical stab touches. I'll measure the distance from the CG to the stab contact point and the distance from CG to spinner and I should be able to calculate how much weight I would need. Before I add any weight, however, I'll moved what I can forward and check it again.

[grosbeak]

I was able to move the ignition and its battery forward an inch or two, which lightened x to 1.87 oz. After a lot of feedback (not here, as you can see!) I abandoned the spinner in favour of the firewall as a place to add balancing weight. That shortened b to 10-3/4" inches which resulted in a new y value of 6.32 oz.

On a parallel topic, the stock configuration of the main landing gear on the Pulse 125 is not ideal. Apparently the gear is very flexible which can result in prop strikes on less-than-greased landings. And it's prone to tipping when taxiing on less-than-perfect fields. To kill two birds with one stone I rotated the gear 180 degrees - and she balanced.



I'm in the process of swapping the wheel pants over now - all that's required is to relocate one of the blind nuts in each unit.

[Flypaper]

Don't know how accurate the drawing is but it looks like the cg is measured from the front of the spinner whereas it should be measured from the front of the wing. This would move the cg furthur back on the wing where you may not need the added weight. Of course this method gets you safely in the air where you can set the cg to suit yourself.
I screwed up myself. I should have shown in front of the wing instead of the spinner, so I fixed that. Sorry.

[grosbeak]

The CG is 3-11/16" back from the LE of the wing - the drawing doesn't show that very well because the vertical reference line is missing.

[Guest]

Putting the "wheel pants" on the right way will help, marginally!

[grosbeak]

Scratch the last mod - I certainly didn't visualize it very well, but moving the wheel forward amounts to less ground clearance.

I've also read that the change can cause a lot on instability on takeoff and landing - so it's back to the drawing board. Slightly updated drawing, though:



So it's back to putting ~6 oz on the back of the firewall... unless I learn of another solution.

[Flypaper]

Don't know if it helps but rule of thumb is to have the wheel axles in line with the leading edge of the wing. for good ground handling and not tipping over on throttle up. You can get more ground clearance by bending the gear inwards a bit. Used to have the Pulse 40. Nice flying plane.

[Thunder Chicken]

Here's a formula that should tell you how much weight to move how far to move your CG
(and explains it better than I can.)
Used for full scale, but will work for our applications as well.

http://ma3naido.blogspot.com/2008/09...-equation.html