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Foam Board SR-71 Twin 50mm EDF(?)

Mid7night

Jetman
Mentor
#22
Ok, this is my new favorite thread. A foamboard Blackbird, AND personal stories of dads who were trained by Yeager and people who met him?!? I’ve got my eye on you. 😜

For the prop situation, please feel free to scale the duct to fit 2” props, as they’re far more available. I went with 1.9” because they were on sale (major discount), but in hindsight I probably should’ve gone with 2”. 😆

If you aren’t comfortable tweaking the duct, I’ll see what I can do about uploading one that works with 2” props this week. 😉

Keep up the great work, this is awesome!! I’m so proud that my crazy BUFF project prompted you to try one of your own! Can’t wait to see it fly!

~ Ben
 

PsyBorg

Wake up! Time to fly!
Mentor
#23
Maybe mechanics like this would work? Simple, single servo in the fuse operates both. Would need thick wire like the large landing gear wire.

Should even be able to offset throw by the angle of the wire by going off parallel like in my crude drawing.

Would require something stronger then foam in the pylon to keep that C bend wire in place where it all pivots though.

sr71 stabs.jpg
 
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#24
Ok, this is my new favorite thread. A foamboard Blackbird, AND personal stories of dads who were trained by Yeager and people who met him?!? I’ve got my eye on you. 😜

For the prop situation, please feel free to scale the duct to fit 2” props, as they’re far more available. I went with 1.9” because they were on sale (major discount), but in hindsight I probably should’ve gone with 2”. 😆

If you aren’t comfortable tweaking the duct, I’ll see what I can do about uploading one that works with 2” props this week. 😉

Keep up the great work, this is awesome!! I’m so proud that my crazy BUFF project prompted you to try one of your own! Can’t wait to see it fly!

~ Ben
I was really excited when I saw you were doing an "EDF" B-52. I thought the idea of building an edf using a standard quad motor was great. Even though it has less thrust than a standard EDF, it also needs 1/4 of the battery. If I was to use true 50mm EDF's on this plane would need two 3s 2200mah instead of a single 3s or 4s 850mah. That would truly make it a flying brick.

I hadn't even considered scaling up to 2". I could scale it up in the slicing software easily, but the bolt holes would be a little off (not enough to really matter). I do all of my 3D modeling in AutoCAD, and it can export .STL files, but not import them. If you are going to do an updated file for 2" that would be awesome, otherwise if you have the base file available I could tweak it easily myself.

Maybe mechanics like this would work? Simple, single servo in the fuse operates both. Would need thick wire like the large landing gear wire.

Should even be able to offset throw by the angle of the wire by going off parallel like in my crude drawing.

Would require something stronger then foam in the pylon to keep that C bend wire in place where it all pivots though.

View attachment 118914
This is how I had initially envision the rudders working, and may give it a try. I had initially dismissed this option because I had convinced myself it would ruin the look of the plane. But I may rig this up at some point to see how it looks. If every thing is painted black it may not be that noticeable. A bonus to this setup is that it would allow the plane to stay on a 6 channel receiver.
 

PoorManRC

Well-known member
#25
I LOVE THIS GROUP!!!
Seemingly insurmountable issues, seem to have a solution from Someone. Truly an eclectic Group of Minds!!
I'm glad you're thinking about scaling it up. That should give more needed room for "creative engineering"! :eek::geek:
 

kilroy07

Well-known member
#26
I had initially dismissed this option because I had convinced myself it would ruin the look of the plane.
+1

A bonus to this setup is that it would allow the plane to stay on a 6 channel receiver.
6?... I see elevons, rudder, throttle, gear.
Are you thinking differential thrust?

Maybe we should either all get together and work this out or have a "contest"...
It might be REALLY awesome to see a flight of blackbirds at FF 2019!!
 

PoorManRC

Well-known member
#28
+1
?... I see elevons, rudder, throttle, gear.
Are you thinking differential thrust?

Maybe we should either all get together and work this out or have a "contest"...
It might be REALLY awesome to see a flight of blackbirds at FF 2019!!
OMFG!!!!
A recreation of the 9th SRW!! Be still my Heart. I would stowaway on a Bus to see that!!! :p
 
#29
see elevons, rudder, throttle, gear.
Are you thinking differential thrust?
+1


6?... I see elevons, rudder, throttle, gear.
Are you thinking differential thrust?

Maybe we should either all get together and work this out or have a "contest"...
It might be REALLY awesome to see a flight of blackbirds at FF 2019!!
I had intended to run each control surface on of it's own channel, but after you said this I was looking at the plane and realized if I were to spin the inboard servos 180 degrees I would be able to Y the left 2 servos and right 2 together. Good thing to note for when I update the plans and build version 2. I will probably set up differential thrust on the plane since I have the extra channel for it.

Yeah, I’ll break out the laptop this week and make a 2” version, maintaining the same mount holes.
That would be awesome, I appreciate it. I got the motors and ESC's in the mail yesterday. When I was assembling things last night I realized that even thought the props I ordered said 1.9" and are labeled so on the bag, in reality they are 2". So I had to sand them down to fit in the mount. Balancing a 5 blade prop is much harder than a 2 blade.

20181120_233028.jpg
 

Zephyr1

Active member
#34
Holy crap this is amazing. You're going to need to remove those inlet cones for flight though.
My MiG-21 wouldn't work with it on...

Truly impressive build, way to go man
 

Chuppster

Well-known member
#36
This is awesome! I'm bummed I just discovered it now...

Have you considered just doing twin pushrods for the rudders? A single servo in the fuselage with two thin pushrods guided by zip ties, one to each rudder? It'd be simple and lightweight. It would be asymmetrical, one pushrod would go to the outside of one rudder while the other would go to the inside of the other.
 
#37
UPDATED! I just uploaded an update to the 3D printed EDF duct: https://forum.flitetest.com/index.php?resources/3d-printed-edf-duct-1106-gremlin-motor.46/

Now sized to work with 2" props, and maintains the same motor mount holes.
This is great. I'm going to get some of these printed off so I can use them in the Version 2.

This is awesome! I'm bummed I just discovered it now...

Have you considered just doing twin pushrods for the rudders? A single servo in the fuselage with two thin pushrods guided by zip ties, one to each rudder? It'd be simple and lightweight. It would be asymmetrical, one pushrod would go to the outside of one rudder while the other would go to the inside of the other.
I had thought of something similar to this, but think it may ruin the look of the plane. I will probably try it at some point.


I had the plane all together and ready to do a test flight this past weekend, however I ran into a problem. When I plugged the battery in to test the electronics (I had done everything independently with a servo tester prior to this) one of the ESC's cough fire, and the motor it was connected too has melted some so it no longer spins.
20181128_080706.jpg

20181122_211833.jpg

When connecting the 2 ESC's to the receiver I made sure to pull one of the red wires to not have doubled up BEC's. I'm not sure what happened, but I have ordered another Motor and ESC. Hopefully they come soon and I can get Version 2 built and test flown in the next 2-3 weeks.
 

Chuppster

Well-known member
#39
This is great. I'm going to get some of these printed off so I can use them in the Version 2.



I had thought of something similar to this, but think it may ruin the look of the plane. I will probably try it at some point.


I had the plane all together and ready to do a test flight this past weekend, however I ran into a problem. When I plugged the battery in to test the electronics (I had done everything independently with a servo tester prior to this) one of the ESC's cough fire, and the motor it was connected too has melted some so it no longer spins.
View attachment 119349

View attachment 119350

When connecting the 2 ESC's to the receiver I made sure to pull one of the red wires to not have doubled up BEC's. I'm not sure what happened, but I have ordered another Motor and ESC. Hopefully they come soon and I can get Version 2 built and test flown in the next 2-3 weeks.
That's a bummer. Cooking electronics is such a bad feeling...
 
#40
I wonder if a screw was too long and shorted the coil in the motor.... (I "have a friend" who might have ruined a motor or two by doing that...) :rolleyes:
I also have a "friend" who may have done this in the past. However I made sure that was not the case on this motor. The screws for the motor to the motor mount were plenty short. The screws for the props to the motor I shorten a bit because even though the didnt seem to be hitting anything, they just looked too long.