Hi, from a newbie in duct fan.
With standard prop planes, i usually power/prop them to have more thrust visit weight.
Exemple: 5lbs racer plane, with ±7lbs thrust and prop pitch of 8 or 9 = ±140 mph and more.

With ducted fan Im lost?

Here my setup:

Neu motor 1521 (780kv)
Castle creation HV 110A
2x 35C 6S 4000mAh (45volts)
4” (101mm) modified Haoye fan (intake lip, balance rotor, motor mount reinforcement)
I push this setup easily over 3000 watts, and with fresh lipo it stand between at 3600, 4000 watts. No overheating at all (ok, zippy lipo start to puff a little! need to change them for 35 or 40C)

I put an intake lip and a 85% fsa thrust tube (6" long), it give me 9lbs of thrust full throttle.
Without the thrust tube, I get 11.5lbs of thrust.

The airframe is big and massive but clean (I will post pictures soon), its a 70 inch upper wing configuration , no retracts.

9lbs of thrust visit 9lbs ready to fly weight, what should I expect from?

It's not really how much static thrust you make - but how much E-flux you put out.

With that fan - you should get pretty decent preformance. Of course it also depends on your airframe, intake, exhaust, etc....there are many varibles that will determin your final preformance.

I agree with Skyhawknut.

With a 1:1 thrust to weight ratio, you should get good performance. Assuming you have a reasonable air flow with your 85% FSA, you can also use the watts per pound rule. Use a setup with at least 200 watts per pound for good performance. A setup with closer to 300 watts per pound (or higher) will provide great performance.

Good luck!

The back in the day approach will yield about a 1.62 X static thrust = AUW
of a scale jet capable of being flown in a prototypical manner.

200 to 250 watts per pound equates to the same thing. Remember flying is
not taking off and going straight up or having a two position switch on the
left stick.

I'm running a 1512/2y on 10s 5000 zippy, tj100 fan. 3200 watts static. Makes my Spark do around 150mph level flight.

Without the thrust tube you said your thrust was higher without a thrust tube and 2:1 inlet lip than with
a thrust tube with an outlet diameter equaling 85% of FSA. OK, what was the result at 100% and 110%
of FSA?