Looking at Flow Blockage in EDF ducting.

L Edge

Master member
In working with foam, structure is important part of building. Add EDF's (compared to motors) you still need to re- enforce across the wing so I always use carbon rods hot glued imbedded in the foam. So what do you do for blockage? I have used pitot tubes examining the exit(vertical and horizontal) to see what the flow pattern looks like. Essentially, the longer the ducting, the better the flow downstream. Yes, velocity was reduced. But not great. How much?

Point, I am bring up you can argue from the reference material or gut feeling, but hey, JUST DO IT.

My three areas of interest are hovering, high angles of attack, STOL'S and VTOL.
Torque is a big factor when trying to hover an EDF, (the Thrust Vectoring Nozzles handle pitch and yaw) but not rolling. So, I invented the THRUSTERS 13 years ago. So to counteract the torque, why not pick off the dynamic airflow (Static doesn't work) right behind the blades and have it flow to the end of the wing and exhaust perpendicular to counteract torque. Hey, why not also re-enforce the wing by a carbon rod going thru the duct. In my case the exhaust tube was 10" long.

Here's a demo of torque when hovering (0:42)
By the way, like the way he traps the inlet air at high angles of attack.

My design of thrusters:

Have a real cheap 64MM EDF with 5 blades


Lots of leakage out the front when spinning.

This is the setup I ended up with.


Outside wing to counteract the torque. Notice 90 bend to exit flow perpendicular to wing.


In the duct, the solid rod in the back is design to strengthen the wing by hot glue.

Up in the front are 2 tubes that were about 1/4" behind the blades to pick up the dynamic flow and transport the airflow backward and turn 90 degrees outward to the end of the wigs which had 90 degree turns so it acted like a thruster(a valve controlled by a servo) to provide enough torque to prevent the torque and it would hover. Just like Apollo, to control direction or stop it. I wanted to

Now, that is adding a lot of garbage to the airflow, so, "just do it" and it worked, but it was weak.

Here's the video:
Points are 30sec., from 1:40 to over 2 min( run at .25 speed to better see it.)
It actually slowed down rotation compared to just trying hover without thrusters. As you can see, it did not generate enough airflow to increase pressure to have it quit rotation.

By the way, my main objective was to eliminate aileron structure(structural lighter), but to use a round open tubing with a thin slot all the way across the aileron and flap area that rotates. providing exit airflow that blows the air up or down to act as an aileron or flaps. Could you imagine it to be a blown flap kind of thing or a new type of aileron if I had enough pressure?

When I designed and flew my SR-71, the outer wing is outside each of the EDF ducts. Just ran a small carbon rod thru the 64 mm EDF ducting and on to wing to strengthen and prevent flutter.
EDF blockage, don't worry!!!!

To observe it in hovering(took some good practice using an EDF since response is a lot slower than prop), from about 1:40 to over 2:00 run it at .25 speed.
I walked away from this project very happy.

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