Is this glider stable?
Typical Designs
You're starting out from a fairly mistaken idea of how things normally work. In particular, you're showing the horizontal stabilizer lifting upwards.
At least in most normal designs, the horizontal stabilizer does not lift upward at all. In fact, it's normally flying at a negative angle of attack, so its &quot;lift&quot; is actually pushing downward on the tail.
We normally start by looking at the center of lift (CP) of the wing by itself. That'll typically be somewhere around 40-45% of mean aerodynamic chord (MAC).
The CG is at least somewhat forward of that (25% of MAC is a pretty common starting point).
Then you trim the downward lift from the horizontal stabilizer to maintain level flight. The CP acts as basically the fulcrum point. We put the horizontal stabilizer at the end of a long tail to give it a lot of &quot;leverage&quot;, so it doesn't have to generate much downward pressure to maintain level flight.
This is what gives static stability. If you stall the wing, it will lose lift. As the wing loses lift, the CG being so far forward will cause the aircraft to pitch nose down. That, in turn, will (at least normally) reduce the wing's angle of attack, so it will recover from the stall.
If the CG were arranged where you've shown it, behind the CP, you wouldn't get that automatic stall recovery--if the wing or (especially) the horizontal stabilizer stalled, the CG would be far enough back that the aircraft would tend to pitch nose up, increasing the angle of attack, stalling the airfoil even more deeply (a &quot;deep stall&quot;, which is usually unrecoverable).
Alternative Designs
Although it's fairly unusual, you could do a design where you kept the CG somewhat behind the CP, but loaded the wing more heavily than the horizontal stabilizer. In this case, both the wing and the stabilizer would be lifting upwards, but since the wing is more heavily loaded, at higher angles of attack, the wing would stall before the stabilizer, and when that happened, the nose would drop.
To achieve the front wing being more heavily loaded than the rear, you typically end up having to shrink the front wing, and (to maintain overall lift) expand the rear wing. And that gives a canard design, such as the Rutan Vari-EZ and Long-EZ, and the Quickie Q2. Thanks to their use of canards, the Rutan designs are extremely stall resistant. The Quickie claimed to be completely stall proof (and as far as I know, that was accurate).