• This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn more.

B-2 Stealth Bomber - 70mm EDF

Zephyr1

Well-known member
#1
This is an incredibly difficult design to make into an RC version. As such, I made a 50mm EDF version first. To test weight and balance and stability. I then moved on and built a 70mm EDF version to make it full scale. Testing the 70mm version didn't go so incredibly well. As such I will be needing to rebuild it and make a better 70mm version.

B-2 Pic.jpg


1571762928867.png
This was the 70mm Version. It had a wingspan of 84 inches, or 7 feet. I did create split rudders for this version as an attempt to create drag and stabilize the model.

1571762981484.png
This is the 50mm version. It had a wingspan of 60in or 5 feet. It did not have split rudders. The control surface was attached to the outer elevon.



So flying the B-2. I found that when I went full power on the 50mm version, it would have a tendency to loose lateral stability and yaw over, uncontrollably. I think this was the problem with the 70mm version. To climb out I was using full power and that lost my yaw stability. I was able to achieve good flights with the 50mm version because I wasn't going full power. But I did have a similar issue. I don't fully understand this issue, and if any of you have any suggestions I would love to here it.


Here's the flight video for the 50mm version. I go into more depth about the project in the video and I'm really quite proud of the flight.
 
#2
I've made a couple of these (pusher props) and I found that the stability increased with speed. If you are getting yaw at full power, I would look at an asymmetry in thrust or a thrustline issue.

Good luck!
 

Piotrsko

Well-known member
#3
Yaw probably caused by motor torque particularly if it's fore or aft center of drag. The real deal flies with the split rudders open a smidge on top & bottom both sides, based on what I saw during testing @KEDW. They are throwing a bit of drag way past the center of drag. Perhaps a click or two of up on the outboard surfaces both sides, then no up on the in board surfaces. No demo how you rigged those surfaces. Aha, shows in your picture of the real one too.

Nice looking plane.
 

Zephyr1

Well-known member
#7
I've made a couple of these (pusher props) and I found that the stability increased with speed. If you are getting yaw at full power, I would look at an asymmetry in thrust or a thrustline issue.

Good luck!
That's a pretty good idea. I'm kinda currently thinking it could be caused by unbalanced edfs. I noticed they shake somewhat when they go up to full power. But I (kinda) eyeballed the thrust line so that could very well be the issue.
 

Zephyr1

Well-known member
#8
Yaw probably caused by motor torque particularly if it's fore or aft center of drag. The real deal flies with the split rudders open a smidge on top & bottom both sides, based on what I saw during testing @KEDW. They are throwing a bit of drag way past the center of drag. Perhaps a click or two of up on the outboard surfaces both sides, then no up on the in board surfaces. No demo how you rigged those surfaces. Aha, shows in your picture of the real one too.

Nice looking plane.
I did leave the split rudders open a little bit, but not much. I think you're right and leaving them open even more would definitely increase the stability of the B-2.
 

FoamyDM

Building Fool-Flying Noob
#9
So... Has ANYONE developed a decent EDF Power Pod? because I want to put my 55mm edfs in this model, the L-39, the reduced sized Hydra wing this... and many others.
 

L Edge

Well-known member
#10
You have taken on a very tough problem and made good progress. If you use drag brakes, you also incorporate a pitch problem as well. Ask me how I know. I designed my X-47B and used only 2 servos and my thrust vectoring 64 mm nozzle to solve my yaw problems. No gyro was used. Took me almost 6 months of crashes to get it going.

Here is the maiden flight in 2015.


First thing, can you research to see if you can get cw, ccw 70 mm EDF's?
Did you know that the gear landing doors(when down) help the yaw stability factor!!
 

FoamyDM

Building Fool-Flying Noob
#11
I don't think cw ccw edfs are a thing. As the post-fan vanes correct for the torque.
I'm sure they can be done though.
The landing doors makes sense.
 

L Edge

Well-known member
#12
I don't think cw ccw edfs are a thing. As the post-fan vanes correct for the torque.
I'm sure they can be done though.
The landing doors makes sense.
I bought a model from Seb-Art that has cw ccw so it can hover. Have a spare set.

P1010033.JPG

This is my "sled" trying to get plane to fly without rudders. Tried both 70's cw and ccw with same bad luck.
 

L Edge

Well-known member
#13
Have you ever thought about using a gyro for assistance? For differential thrust, did you use mixes and what radio?
Was it sensitive enough?

Point- when you launch your plane, it needs to be horizontal. Crunched 2 planes due to positive angle of attack where it lifted nose high and then the stall took over. Lok at my video.
 
Last edited:

Zephyr1

Well-known member
#14
I don't think cw ccw edfs are a thing. As the post-fan vanes correct for the torque.
I'm sure they can be done though.
The landing doors makes sense.
They're a thing if you use BDFs, which i've been toying with...

So... Has ANYONE developed a decent EDF Power Pod? because I want to put my 55mm edfs in this model, the L-39, the reduced sized Hydra wing this... and many others.
Hydra wing! Hydra wing! Hydra wing!

I'm waiting on some monster foam to redo it... But it will return
 

Zephyr1

Well-known member
#15
Have you ever thought about using a gyro for assistance? For differential thrust, did you use mixes and what radio?
Was it sensitive enough?

Point- when you launch your plane, it needs to be horizontal. Crunched 2 planes due to positive angle of attack where it lifted nose high and then the stall took over. Lok at my video.
It's been suggested that I use a gyro, I haven't put enough research into one yet. If you know of any good ones, I'd love to hear. I did use mixes for the differential thrust on my Spektrum Dx6, and yes, it was sensitive enough. I'm well aware of the horizontal need, the first launch of the 50mm B-2 flipped end over end because it wasn't horizontal rip.

Additionally, that XB-47 is extremely impressive. I've given thought to thrust vectoring before but I thought I would test it out on say my F-15 first. I hadn't considered putting it on an already unstable airframe, but that could be what I need.

And yes, I did know the doors helped with stability. I printed out a bomb bay for the B-2, and the plan was to install it after some successful flights. With the doors down acting as landing door stability.

Ultimately, I believe the issue with the 70mm version was that it wasn't powerful enough and that the edfs were unbalanced. This meant that at full power the edfs caused a vibrational dissonance that yawed the plane over and caused a crash. It wouldn't have been an issue if I hadn't been going full power. To fix this, I am going to up the voltage and get new edfs that are well balanced and will not vibrate. Additionally, I will leave the split rudders open to create drag rudders, adding stability. And I might attempt to glue some foam to the bottom to simulate the landing gear doors.
 

L Edge

Well-known member
#16
It's been suggested that I use a gyro, I haven't put enough research into one yet. If you know of any good ones, I'd love to hear. I did use mixes for the differential thrust on my Spektrum Dx6, and yes, it was sensitive enough. I'm well aware of the horizontal need, the first launch of the 50mm B-2 flipped end over end because it wasn't horizontal rip.

Additionally, that XB-47 is extremely impressive. I've given thought to thrust vectoring before but I thought I would test it out on say my F-15 first. I hadn't considered putting it on an already unstable airframe, but that could be what I need.

And yes, I did know the doors helped with stability. I printed out a bomb bay for the B-2, and the plan was to install it after some successful flights. With the doors down acting as landing door stability.

Ultimately, I believe the issue with the 70mm version was that it wasn't powerful enough and that the edfs were unbalanced. This meant that at full power the edfs caused a vibrational dissonance that yawed the plane over and caused a crash. It wouldn't have been an issue if I hadn't been going full power. To fix this, I am going to up the voltage and get new edfs that are well balanced and will not vibrate. Additionally, I will leave the split rudders open to create drag rudders, adding stability. And I might attempt to glue some foam to the bottom to simulate the landing gear doors.
Did the rollover's and crashes happen in the same direction or random? Are your split rudders design to be very precise. I had poor luck with my setup.

 

Hondo76251

Well-known member
#17
Have you ever thought about using a gyro for assistance? For differential thrust, did you use mixes and what radio?
Was it sensitive enough?

Point- when you launch your plane, it needs to be horizontal. Crunched 2 planes due to positive angle of attack where it lifted nose high and then the stall took over. Lok at my video.
I'm with you on this one. The real bird flies with a lot of fly by wire help, I'd build it with a gyro reciever that controlled differential thrust for yaw... I've had good luck with the spektrum ones...
 
Last edited: