design and build log of Northrop x-47b

[akimbo]

I came across this flying wing and decided needed to make an rc version. To figure out the cg, I built a small glider which is far from the final design, but it gave me a good idea of how it would need to be. For now, I am planning to make this a pusher prop but let me know if you guys would like it to be an edf. I decided not to go with an edf because I would have to alter the look of the flat exhaust . If a Northrop style exhaust is possible with an edf, let me know what would be the best way to implement it.

 

[quorneng]

akimbo
You worry about a flat exhaust (it also has a crescent inlet!) but you also have a big non scale fin.
If you go to an EDF you will have to have an idea of the likely weight to determine how big a diameter the EDF will need to be. It would quite likely need bigger non scale ducts anyway.
You may have to choose between a 'scale look' and it actually being able to fly.

 

[akimbo]

I have been struggling to make a 2d plan for some of the more complex shapes so I am just going to make the basic wing shape and put a small box for the fuselage so I can test out different fins and airfoils. Also, if anyone knows how I can prevent the plane from furiously spinning due to prop torque, that would be helpful. I had that issue with my mirage plans, the plane would not stop spinning until I cut the throttle.

 

[akimbo]

 

[akimbo]

it did not work, too much prop torque. Maybe a larger wingspan will fix it but i might have to use an edf

 

[akimbo]

akimbo
You worry about a flat exhaust (it also has a crescent inlet!) but you also have a big non scale fin.
If you go to an EDF you will have to have an idea of the likely weight to determine how big a diameter the EDF will need to be. It would quite likely need bigger non scale ducts anyway.
You may have to choose between a 'scale look' and it actually being able to fly.

that's the issue with this aircraft. it is a complex shape and it has no large vertical stabilizers.

 

[quorneng]

It is unwise to assume an EDF doesn't produce a torque. It does! Yes less than a prop using the same power but then EDFs do need a lot of power to start with.
A bigger light airframe with low a power prop installation is likely the best course.
Note that airframe in full size uses some very sophisticated aerodynamics to give adequate control. It is almost impossible to replicate it at small sizes. The viscosity of air is a constant so its effect on aerodynamics is very different as small sizes.
A bit of an exaggeration but to a small plane air is like flying through treacle!

 

[akimbo]

It is unwise to assume an EDF doesn't produce a torque. It does! Yes less than a prop using the same power but then EDFs do need a lot of power to start with.
A bigger light airframe with low a power prop installation is likely the best course.
Note that airframe in full size uses some very sophisticated aerodynamics to give adequate control. It is almost impossible to replicate it at small sizes. The viscosity of air is a constant so its effect on aerodynamics is very different as small sizes.
A bit of an exaggeration but to a small plane air is like flying through treacle!

Thank you, I will keep this in mind for the next prototype. Also, where would be the best place to put small fins? I was thinking either a f-117 style tail, or two fins in between the small part of the wing and the large part.

 

[quorneng]

Basically any fins want to be as far aft of the CofG as possible where they will have the biggest influence.
You can see why the Panavia Tornado was nicknamed "the flying tail fin"

.

 

[L Edge]

The flying wing that doesn't have any vertical components or tail, always presents a roll/yaw problem. The way I solved it is to use a 64mm EDF with a thrust vectoring nozzle hooked to only 2 servos with the right length of servo arm (took a number throws to get it right.

Also learned that when you launch, you release horizontal or you in trouble.

My X-47B. The two servos contain 2 wires, one goes to the elevons and the other travels down the fuse and hooks to the thrust vectoring nozzle. If your interested in seeing the video, let me know.

 

[Mr NCT]

The flying wing that doesn't have any vertical components or tail, always presents a roll/yaw problem. The way I solved it is to use a 64mm EDF with a thrust vectoring nozzle hooked to only 2 servos with the right length of servo arm (took a number throws to get it right.

Also learned that when you launch, you release horizontal or you in trouble.

My X-47B. The two servos contain 2 wires, one goes to the elevons and the other travels down the fuse and hooks to the thrust vectoring nozzle. If your interested in seeing the video, let me know.

View attachment 239420

You bet! I'd love to see the video.

 

[L Edge]

Still fly it occasionally(8 years old) at AMA airshows. This is the type of stuff that keeps me going.

 

[quorneng]

That is impressive level of control to what is basically an unstable design.

 

[akimbo]

I was planning to continue the design with an edf but mine just decided to not work anymore. It will probably be more of a pusher prop flying wing now.