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Blackbird fly... blackbird fly, Into the light of the dark black night. Twin 69mm EDF SR-71 Build/Project

kilroy07

Well-known member
#46
Hello again true believers...

I am WAY over due for an update.... and for that I apologize!

As some of you know here in the US Flite Fest will kick off this Thursday and I have been frantically working on a couple of projects...
(Note to self... Make a FEW REALISTIC goals for FF next year!!....) :rolleyes:

Before we get started, I will NEVER AGAIN think to myself while looking/following one of these builds on the forums "Gee, why haven't they finished it yet?!!"... I have a new found healthy bit of respect now for ANYONE who tackles a build from scratch!

So here's a quick stitched together vid to keep you occupied while I type the rest of this update... (Warning, little to no editing...)

Things learned;

1. battery tray worked like a charm...
You strap in the batteries, plenty of room to shift CG;
IMG_9089.JPG
The fuselage side has a slot to slide it in;
IMG_9090.JPG
The batteries plug into sockets on each side, each driving a separate EDF;
IMG_9091.JPG
The nose piece slides down the arrow shaft and has a cavity to hold the battery leads.
IMG_9092.JPG

2. Poster Board SUCKS!!
She looked pretty before I started the poster board (to be fair, this is my first time trying to do poster board from scratch...
I honestly think it weights as much as foamboard... so I may address this in the beta build...

3. If you are going to 3D print a bunch of cool parts for your project... You "MIGHT" want to consider where you are going to route wires...

4. Turns out PLA gets all soft and mushy when you pile a bunch of hot glue on it (say when the &^$%@#^ Poster board won't cooperate...)

5. Even when your "crush zones" work perfectly... it still sucks that your plane got crushed!

6. using duct tape for field repairs on poster board is NOT smart!! (It'll rip that stuff right off the plane!)

So, project status....

One more Alpha build, hopefully this one will fly (even better if it flies at FF!)

I am cutting everything out again and doing a few quick redesigns (cough firewall routing holes cough) and my plan now is to work on her there at flite fest... Maybe with some great guys like Ben (@Mid7night) looking over my shoulder we can really turn this girl around!
;)
 

kilroy07

Well-known member
#49
No real way to verify thrust at the moment, I have all the makings for a thrust stand... I'll start it after FF...

I have the makings for a bungee... and making a ramp outta PVC ties into an update for the chickens... (so that'll make the misses happy... and after she sees to CC bill from Flite Fest, I'll need all the help I can get!!) :LOL:... :(

I've got an idea for making it without the posterboard... (probably draw up plans and cut tomorrow) have to wait for the build though 'cause I really want to start on Casper... heck, who needs sleep, right... It's not like I have a 10-11 hr drive coming up soon or anything?! :LOL:
 

bracesport

Well-known member
#50
I love the challenges you face with this awesome plane - I suspect you are closer to realisation than the video suggests - I can only offer encouragement on this one! o_O
 

Horseman3381

Well-known member
#51
When watching the Alpha maiden video I was having flashbacks to when I was trying to get my smaller one to fly.On mine it "Tail Stalls" when it was going too slow. This made it seem like the plane was tail heavy, so I kept moving the battery forward. Then after I moved it forward too far I didn't have the elevator authority to pull up. I fixed the problem by upgrading to a 2.5-1 thrust to weight ratio, which is probably not an easy option on yours.

A simple foamboard cart to launch it on should help it get up to speed. From what I saw if you simply got a little more speed at launch yours will fly.

Looking forward to seeing it/you at FF.
 

Zephyr1

Well-known member
#52
I agree with Caroline that you should try without the inlet cones. There's simply no way my MiG-21 can fly with the nose cone. Additionally, I would attempt flight once more on a single battery, grab a y harness and see if your weight really is the issue that way.
Still, it looks amazing, keep up the good work!
 

tamuct01

Active member
#53
What if you made the inlet cones out of a wire or plastic mesh painted black? It would probably be a compromise in airflow between the solid ones and not having them at all, but provide a better look (at a distance).
 

Vimana89

Well-known member
#56
Pretty close! At this point it is probably as simple as not having enough static thrust. Once she flies, do you plan on maybe adding some thrust differential? The engines are far enough apart on the Blackbird to where it would probably work well.
 

kilroy07

Well-known member
#57
Thanks everyone for the words of encouragement and suggestions/wisdom!

Hot off the press....
IMG_9105[1].JPG
IMG_9104[1].JPG
I dearly love the look of the cone, I made it the diameter of the spindle at the opening, but maybe that was not enough...
And I figured while I was at it, I would make them appear a tad more "scale"...

On the exit side, I understand you should have the exit at 80-85% of the fan area. I believe (I'll have to check the cad file to make sure) I have it right at 83%

After ff I'll work on getting my thrust stand put together and we will get some real numbers and try to sort this out!
I'm not giving up on cones, but I do want to see her take flight!

Thanks again everyone!!
 

Vimana89

Well-known member
#58
Thanks everyone for the words of encouragement and suggestions/wisdom!

Hot off the press....
View attachment 135699
View attachment 135700
I dearly love the look of the cone, I made it the diameter of the spindle at the opening, but maybe that was not enough...
And I figured while I was at it, I would make them appear a tad more "scale"...

On the exit side, I understand you should have the exit at 80-85% of the fan area. I believe (I'll have to check the cad file to make sure) I have it right at 83%

After ff I'll work on getting my thrust stand put together and we will get some real numbers and try to sort this out!
I'm not giving up on cones, but I do want to see her take flight!

Thanks again everyone!!
the tapering down from 5-15% is based on preference and individual project. I bet if you were to have a less drastic slim down to your exits, like 90-95% instead of 83, you would see a big increase in static thrust, which would help at launch! I have not yet built an EDF jet but I've done research and watched a lot of such projects get done here.