Do EDF/BDF cause torque roll and how to negate them

JetCrafts

Active member
so i want to make a small single BDF (blade ducted fan) trainer. so I was wondering do they cause torque roll of any sort or something like that and how to neagte it
 

quorneng

Master member
"EDFs/BDFs do not cause torque roll."
I have to disagree.
A single EDF/BDF will certainly create a torque roll effect. Not as much a prop but the motor torque has to be resisted somehow unless there are sufficient 'vanes' in the duct aft of the fan set to completely counter the torque. For most EDFs the exhaust duct is kept as obstruction free as possible.
An example of EDF motor torque at slow speed.
Once sufficient airspeed is obtained the normal controls have no trouble countering the motor torque.

The biggest EDF/BDF effect is the lack of 'prop wash' over the tail surfaces that provide a significant degree of control at low or even zero forward speed like in prop hanging.
 

L Edge

Master member
The only way to stop it is a multi approach, so if you are designing, you use a CW/CCW EDF.

Agree , here is 2 samples of showing what Quorneng is saying.

After it got spinning, I just went the other way to show I was not causing it.


Here is a launch showing the torque effects before airflow.

 

MrKilometer

Member
I stand corrected - thanks for the great videos demonstrating that there's still torque roll! I have not encountered enough in my limited experience with EDFs to notice it, so I assumed there was none (should've realized... there's still a rotating fan in the edf, so there must be torque).
 

JetCrafts

Active member
but is their any method of negating them before reaching airspeed cause I'm trying to build a glider trainer .
maybe like putting a straw at the end of the EDF/BDF and rerouting it to the tip of the wing. FYI THE EDF/BDF is 5.5 inchs in diameter
 

dap35

Elite member
but is their any method of negating them before reaching airspeed cause I'm trying to build a glider trainer .
maybe like putting a straw at the end of the EDF/BDF and rerouting it to the tip of the wing. FYI THE EDF/BDF is 5.5 inchs in diameter
Any tendancy for torque roll on an EDF is an order of magnitude lower than a prop. I have several, including the FT Viggen and Grunjuet where I installed a 64mm fan instead of the 50mm and it had zero torque roll. I don't know the size of your planned glider, but I would expect a larger wingspan than my EDF's which would furthern dampen any issue.

I would build it without additional features and see how it goes. The biggest risk is not that there is some torque, but a rapid change on take off. So tossing the plan and immediately slamming the throttle to max on any plane is going to increase any problem you have with torque.
 

L Edge

Master member
but is their any method of negating them before reaching airspeed cause I'm trying to build a glider trainer .
maybe like putting a straw at the end of the EDF/BDF and rerouting it to the tip of the wing. FYI THE EDF/BDF is 5.5 inchs in diameter

Won't work. I really wouldn't worry about it launching for a glider. About 13 years ago, my goal was to see if I could take a single EDF, stop the torque and get it to hover without rotation. I did it collecting the dynamic airflow behind the blades and routing it to the ends and exiting 90 degrees of wing. It did work(see video at ), but not strong enough. I called it "thrusters".

I also explored blockage as well using a pitot tube and U-tube at an angle. Like Dap35 said, don't worry about it. Address it if it happens.


https://forum.flitetest.com/index.php?threads/looking-at-flow-blockage-in-edf-ducting.72821/


I
 

quorneng

Master member
JetCrafts
If your EDF glider has typical glider wings their inertia will slow down the torque effect and the aileron a long way out will be much more effective than the typical EDF jet wing layout. Even at hand launch speeds EDF torque will not be a problem after all powered gliders have props and big ones at that but manage ok.
I think you are worrying about a problem that really isn't there.