How to calculate minimum takeoff speed due to distributed propulsion?
Is there a quick way or rule of thumb way to calculate effects of distributed propulsion?
I understand NASA is doing research in this area and is determined to prove an increase in efficiency of 500% in real world tests, although this may include the benefits of electric distributed propulsion.
I understand they swapped the wings out on their Dornier, from 17psf to a 45psf wing loading. That's an increase of almost 300% in just the aerodynamics!!
I understand the bigger the prop disc, the more efficient the prop.
if I have a small ultralight with 25 hp, and now use two 12.5 hp motors instead with newly optimized props....
What is the approximate % increase in efficiency/thrust as the prop disc is now twice as big? ( assume only a small weight increase)
Now let's say I have a 10' span, with 2 motors with 6' props. The entire wing and tail is in the prop wash.
What is the formula for propeller exit speed(v2)?
Is this my new indicated airspeed(v+v2)?
In other words, if my stall speed is 40mph and my prop exit speed is 20 mph at zero ground speed distributed over the entire wing, can I take off at a 20mph ground speed? i.e IAS= 20mph ground speed + 20 mph prop exit speed= 40mph need for takeoff.
Is this correct, at least conceptually, after all, it's just like a headwind, no?