Wing loading is the amount of weight being supported by each square foot of wing area. The higher the wing loading the faster the plane has to fly in order to generate enough lift to stay in the air.
The Salto specs are:
Wing Span: 2.45 m (96.5")
Wing Area: 30 dm2 (465 sq. in.)
Wing Airfoil: HN 805
Wing Loading: 46 g/dm2 (15 oz/sq. ft.)
Flying Weight: 1.4 kg (50 oz
http://www.nitroplanes.com/sah12racosa.html
So, take 465 sq inches and divide by 144sq inches per sq foot. = 3.23 sq ft of wing area
Divide 50 oz/3.23 sq ft and that gives you 15.48 oz/sq ft.
My Ava has a wing loading of about 5.2 oz. Floats like a feather.
My Supra has a wing loading of about 8.8 oz. Has to fly faster than the AVA to stay in the air.
Your Salto has a wing loading of 15.48 oz so it has to fly roughly twice as fast as my Supra or about 3 times as fast as my AVA just to stay in the air. I am sure some engineer will point out that the air foil is a factor and drag and other stuff, but you get the general idea.
The wing loading is not provided for your Sonic, but I am going to guess it is around 10 oz/sq ft. So, if you fly the Salto like the sonic, the Salto will stall and fall out of the sky. That is what I think you have been doing.