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Oct 23, 2017, 01:55 AM
Registered User
Discussion

Tricopter with EDF


Hello everyone,

I am thinking of making a VTOL flying wing with Tricopter setup. Two EDF in the front of wing and one propeller with servo in the back.
Please check the below image.
Front two EDFs are inter connected and swivel by a servo motor.
A rear propeller rotates longitudinally to counter yaw.
When transitioned to flying mode, the rear propeller stops and only EDF make thrusts.

I know how to setup tricopter with normal propellers however have not experience with EDFs.
Normally two front propellers rotate in the opposite direction but in case of EDF, should they also rotate the same way?
To my understanding about the nature of EDF, its torque is much smaller than propeller due to its low inertia. Am I right?
Otherwise I have to find suitable CCW EDF. How do you think about this idea?
Thanks,

Kyu
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Oct 23, 2017, 02:11 AM
Registered User
RCvertt's Avatar
EDF's that spin the same direction should be fine for the reason you mentioned. Worst cast, you'll angle them a little to compensate. The problem with EDF is that you will get much shorter flight times than you would using props.

Your CG will be close to where you have the two front EDF units so they will do most of the lifting. Other than that it should work.
Last edited by RCvertt; Oct 29, 2017 at 11:14 PM.
Oct 23, 2017, 05:12 AM
Registered User
@RCvertt Thank you for your comments. I should keep in mind about the point of pivot.
Good to know I can order same EDF.
Oct 23, 2017, 01:34 PM
Registered User
Ran D. St. Clair's Avatar
Quote:
Originally Posted by kyuhyong
@RCvertt Thank you for your comments. I should keep in mind about the point of pivot.
Good to know I can order same EDF.
RCVert is correct. EDF's are generally best for high speed, not high thrust. which is what you need for a VTOL. Other than that, your idea will work.
Oct 23, 2017, 05:52 PM
Nicholas Jacobs
njacobs's Avatar
Quote:
Originally Posted by kyuhyong
Hello everyone,

I am thinking of making a VTOL flying wing with Tricopter setup. Two EDF in the front of wing and one propeller with servo in the back.
Please check the below image.
Front two EDFs are inter connected and swivel by a servo motor.
A rear propeller rotates longitudinally to counter yaw.
When transitioned to flying mode, the rear propeller stops and only EDF make thrusts.

I know how to setup tricopter with normal propellers however have not experience with EDFs.
Normally two front propellers rotate in the opposite direction but in case of EDF, should they also rotate the same way?
To my understanding about the nature of EDF, its torque is much smaller than propeller due to its low inertia. Am I right?
Otherwise I have to find suitable CCW EDF. How do you think about this idea?
Thanks,

Kyu
That is so weird. Yesterday I was thinking of tri-copter edf myself. Only using 3 EDFs all rotating. Glad you posted because its clear now from the responses, that due to the nature of EDFs, the rear one would have to tilt left-right for yaw and not front back or tilt both ways - unless they all rotate front-back and operate independently, where the front two can use thrust direction differential to control yaw...

As an FYI, on my tri-copter I tried having counter-rotating props on the front and same direction rotating ones too. They both worked. The only difference
was that with both rotating the same way, the copter did not quite fly level.

I have more ideas than time to build em! But don't we all ?

Cheers
Nicholas
Oct 24, 2017, 07:06 AM
Registered User
Quote:
Originally Posted by njacobs
That is so weird. Yesterday I was thinking of tri-copter edf myself. Only using 3 EDFs all rotating. Glad you posted because its clear now from the responses, that due to the nature of EDFs, the rear one would have to tilt left-right for yaw and not front back or tilt both ways - unless they all rotate front-back and operate independently, where the front two can use thrust direction differential to control yaw...

As an FYI, on my tri-copter I tried having counter-rotating props on the front and same direction rotating ones too. They both worked. The only difference
was that with both rotating the same way, the copter did not quite fly level.

I have more ideas than time to build em! But don't we all ?

Cheers
Nicholas
Oh did you? Yeah I was concerned about putting counter rotating EDF on one of two fronts. Previously I have made with props with CW and CCW but It is hard to find suitable and affordable EDF with such combination.
I choose to use following parts for my project.
Phantom FPV Flying Wing EPO Airplane 1550mm V2 (KIT)

https://hobbyking.com/en_us/phantom-...mm-v2-kit.html

2x Blade High Performance 70mm 12-Blade EDF Unit

https://hobbyking.com/en_us/blade-hi...-fan-unit.html

Haven't decided what motors to use yet. Hope this setup works well.
Oct 27, 2017, 01:44 PM
mr1
mr1
Registered User
Hi I also wanted to test some EDF for my VTOL or buildung an EDF quad. After I looked at the thrust-efficiency tabels of some ducted fan - motor combinations, I decided not to use ducted fans. The reason is that they are 5 to 10 times less efficient than propeller-motor combination that with same weight (depending on ducted fan, motor and throttle). All that at high current, even at 6S and more expensive. My batteries could not handle that high current.

Did you also do that to find out which components you would need?
Oct 28, 2017, 11:55 AM
Nicholas Jacobs
njacobs's Avatar
Quote:
Originally Posted by mr1
Hi I also wanted to test some EDF for my VTOL or buildung an EDF quad. After I looked at the thrust-efficiency tabels of some ducted fan - motor combinations, I decided not to use ducted fans. The reason is that they are 5 to 10 times less efficient than propeller-motor combination that with same weight (depending on ducted fan, motor and throttle). All that at high current, even at 6S and more expensive. My batteries could not handle that high current.

Did you also do that to find out which components you would need?
mr1 - I would not be so concerned about the 5 - 10% loss of efficiency, so long as you have enough thrust to easily lift (and propel) the aircraft.

You need a minimum of 250W/kg to lift an aircraft off the ground.

So if you know the trust of a motor in grams or the power draw in Watts (hook the motor, esc, battery up and use a watts-up meter) then you can calculate what you need.

For example, I have a Dr. Mad Max 50cm EDF, 3300 kv. When I hook it up to a 40A plush ESC with a Turnigy 4s1600 mAh battery, my watts-up meter shows it draws 425 W at around 25 A at max power, with a full battery. So theoretically it could lift 1.7kg aircraft. Given that 250W/kg is minimum and that the power available will deminish as battery gets used, I'd probably assume it could like 1kg for the whole flight and be pretty safe. So for a tri-copter with 3 of these EDF's would need to weigh a max of 3kg.

The 50cm EDF weighs 90g (aluminum casing), 4s1600 mAh battery is 220g, ESC is 40g. Assuming 3 x all that for power alone is 350g x 3 = 1050g. (one larger 4s 3300 mAh or 5000 mAh battery perhaps). So the rest of the aircraft could be up to 2kg and still lift.

Anyway, that's an example of how I'd do it, given the EDF that I have.

There's an example of a really nice 3 EDF VTOL in the top thread here
https://www.rcgroups.com/forums/show...&postcount=333

Hope that helps.

Cheers
Nicholas

(example above - weights stated are approximate, from memory, but should be fairly close)
Last edited by njacobs; Oct 28, 2017 at 10:10 PM.
Oct 29, 2017, 03:12 PM
mr1
mr1
Registered User
Quote:
Originally Posted by njacobs
You need a minimum of 250W/kg to lift an aircraft off the ground.
So if you know the trust of a motor in grams or the power draw in Watts (hook the motor, esc, battery up and use a watts-up meter) then you can calculate what you need.
For example, I have a Dr. Mad Max 50cm EDF, 3300 kv. When I hook it up to a 40A plush ESC with a Turnigy 4s1600 mAh battery, my watts-up meter shows it draws 425 W at around 25 A at max power, with a full battery. So theoretically it could lift 1.7kg aircraft. Given that 250W/kg is minimum and that the power available will deminish as battery gets used, I'd probably assume it could like 1kg for the whole flight and be pretty safe. So for a tri-copter with 3 of these EDF's would need to weigh a max of 3kg.
The 50cm EDF weighs 90g (aluminum casing), 4s1600 mAh battery is 220g, ESC is 40g. Assuming 3 x all that for power alone is 350g x 3 = 1050g. (one larger 4s 3300 mAh or 5000 mAh battery perhaps). So the rest of the aircraft could be up to 2kg and still lift.
Anyway, that's an example of how I'd do it, given the EDF that I have.
There's an example of a really nice 3 EDF VTOL in the top thread here
https://www.rcgroups.com/forums/show...&postcount=333
Hope that helps.
Cheers
Nicholas
(example above - weights stated are approximate, from memory, but should be fairly close)
Where do you have that 250W/kg from? I calculated for my copters howering power from 160-200W/kg. But you also need acceleration, so 250W/kg seems realistic. But that is for propellers and not EDF. I will explain it.

Lets take your 425W. How much thrust does it produce? Hobbyking says at 14.8V and 27A it produces 650g Thrust. 14.8V*27A=400W., which are almost your 425W. So lats say (optimistic) it produces 700g thrust at 425W, which are 1.65g/W.

With 700g thrust, you can only lift 700g vertically and not 1.7kg! Otherwise your airplane would look like this when "flying": https://en.wikipedia.org/wiki/Avro_Canada_VZ-9_Avrocar

I looked at one of my propeller-measurements, and with 420W I can produce 1600g of thrust with 9x5" prop. This are 3.8g/W. 3.8/1.65=2.3. That means that an EDF is 2.3 times less effecient than a propeller at the same power and you need 2.3 more power for hovering or you get 43% less flight time. Not 5-10%. At half throttle (for hovering) the difference should be higher but I can't find any talbes to EDFs at low throttle at the moment. I rembember 5 times but cant find the table at the moment.

I want to say that an EDF VTOL is be much more inefficient than a propellered VTOL. With an VTOL you want to combine the benefits of an efficient airplane with a multicopter but with EDF you would destroy the benefits because of its inefficiency compared to propellers. That why I decided not to use EDFs. The only benifit is the higher pitch speed, which could allow higher top speed with an airplane with very low drag. And the better look, of course!
Last edited by mr1; Oct 29, 2017 at 03:28 PM.
Oct 29, 2017, 08:14 PM
Registered User
Quote:
Originally Posted by mr1
Where do you have that 250W/kg from? I calculated for my copters howering power from 160-200W/kg. But you also need acceleration, so 250W/kg seems realistic. But that is for propellers and not EDF. I will explain it.

Lets take your 425W. How much thrust does it produce? Hobbyking says at 14.8V and 27A it produces 650g Thrust. 14.8V*27A=400W., which are almost your 425W. So lats say (optimistic) it produces 700g thrust at 425W, which are 1.65g/W.

With 700g thrust, you can only lift 700g vertically and not 1.7kg! Otherwise your airplane would look like this when "flying": https://en.wikipedia.org/wiki/Avro_Canada_VZ-9_Avrocar

I looked at one of my propeller-measurements, and with 420W I can produce 1600g of thrust with 9x5" prop. This are 3.8g/W. 3.8/1.65=2.3. That means that an EDF is 2.3 times less effecient than a propeller at the same power and you need 2.3 more power for hovering or you get 43% less flight time. Not 5-10%. At half throttle (for hovering) the difference should be higher but I can't find any talbes to EDFs at low throttle at the moment. I rembember 5 times but cant find the table at the moment.

I want to say that an EDF VTOL is be much more inefficient than a propellered VTOL. With an VTOL you want to combine the benefits of an efficient airplane with a multicopter but with EDF you would destroy the benefits because of its inefficiency compared to propellers. That why I decided not to use EDFs. The only benifit is the higher pitch speed, which could allow higher top speed with an airplane with very low drag. And the better look, of course!
You already know the reason why I choose EDF for VTOL.
Prop driven VTOL looks ugly especially when in flying mode.
Look V-22 when flying in the air. It looks as if the prop is chosen by a child. BIG wing and BIG prop
Also it fly faster with ducted fan.
Oct 30, 2017, 04:18 PM
mr1
mr1
Registered User
Okay do it with EDF!
About the top speed, tell me if it is really higher. Drag increases to the power of two at higher speed.
Oct 30, 2017, 09:44 PM
Nicholas Jacobs
njacobs's Avatar
Quote:
Originally Posted by mr1
Okay do it with EDF!
About the top speed, tell me if it is really higher. Drag increases to the power of two at higher speed.
Ok, I stand corrected on the 250 w/kg for hover for EDFs. As you have quite correctly shown me that the EDF is indeed less efficient and therefore cannot yield the same thrust for given power.

Now lets turn the discussion to thrust tubes. You "should" be using thrust tubes on your EDF's to get some back pressure and to increase the speed/thrust by focusing the turbulent air down a tube. Ideally, I'm reading, it should be 3 x the dia of the EDF fan shroud. Some say 4x.

Ok, having said all that, this month a lovely 3 EDF VTOL shows it done without thrust tubes!!! Must be enough to do the job and just not worry about efficiency for hovering, after all , we're not staying there too long anyway.

Its all about having fun, and learning. Thanks Mr1 for correcting my poor assumption.

Cheers
Nicholas
Nov 02, 2017, 02:40 AM
Registered User

Tilt mechanism


A proof of concept tilt mechanism for the front EDF is 3d printed and tested.
This is one of major milestone to actually design and build EDF VTOL Tilt-rotor.

Tilt Mechanism For EDF VTOL (0 min 13 sec)


Still need to adjust the linkage and servo horn for the best angle.
Nov 02, 2017, 08:04 PM
Nicholas Jacobs
njacobs's Avatar
Quote:
Originally Posted by kyuhyong
A proof of concept tilt mechanism for the front EDF is 3d printed and tested.
This is one of major milestone to actually design and build EDF VTOL Tilt-rotor.

https://youtu.be/ejuhay0tQEY

Still need to adjust the linkage and servo horn for the best angle.
Very nice. Smooth. Did you print the servo arm, pipe clamp and base with bearings too ? You are using ball-bearings ?

Another option is to put a gear on the pipe and a gear on the servo for a direct drive. Then you can change the gear ratio to get more/less tilt. Also you will not get any tangential force differences and won't need the extra linkage stuff. This would be like Tom Stanton's tilt mechanism in reverse: https://www.rcgroups.com/forums/show...4&postcount=28

Just a thought.

Cheers
Nicholas
Nov 03, 2017, 02:17 AM
Registered Hack
HACK's Avatar
Are you ok with 3-4 minute flight times?

HACK


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