Broken (Mini) Arrow

[Robert S]

So last month, I tore apart my arrow in order to retrieve the parts to put into a new arrow that would be built around the very streamlined and elegant design found here: https://www.thingiverse.com/thing:3033273 .

I was eventually successful in printing the plane. But I crashed it the first day. I was successful in fixing it but after a half dozen more flights, it was obvious that it was about to tear apart again at the middle (there is only so much hot glue can do). The design was good but I'm a bit rough with my toys and this design required a finesse that I apparently was not ready for. When it did fly, it was very nice. I saved all of the printed body parts, I have another speed build kit that was just delivered and I will do this again but, for the moment I've put this aside.


So after I ordered a new Mini-Arrow Speed build kit, I was pursuing Thingiverse and stumbled upon this: https://www.thingiverse.com/thing:4017750 . I realized that I had a set of broken Arrow wings and could make it... so I did.


Because its so much heavier than a regular arrow, I decided that I needed to move up from the 2205 2300kV / 20A ESC that comes with the F Pack. I figured that it now was moving into the same size and weight category as a Spear so I and ordered a 2218/1180kV w/ 35A ESC (same as the C pack). That arrived today and as you can see by the picture, it has been installed. That being said, 10 x 4.5 prop that normal comes with the C pack is not going to work. I think its a hair too big so I'm going to try and find something in the 8 to 9 inch range. minus the prop, it weighs 757g fully armed.

But while I was waiting for the new motor, I got bored. I started thinking to my self, "Hey, this thing is a broken Arrow. Broken Arrow is the code word for when a term for a nuclear bomb is lost. Wasn't there a movie called "Broken Arrow that involved a B-2 Bomber that lost a bomb?" " A B-2 is a wing, isn't that a funny coincidence." "Hey I wonder if I can make this thing drop bombs too?" Then things quickly got out of control from there. I build one at full size but the 5g servo I had was too small to fit so, I did some math and printed one at 85%. Those of us with prior military aviation experience should appreciate the significance of the fake bomb being painted in blue. (Blue Death)
" Weapons are part of my religion," The Mandalorian

Now as soon as I find a Prop and put on the top cover, it will be all set for flying. Not quite sure how landing is going to work with the bomb drop on the bottom but one way or the other I guess I'm going to find out.

 

[Robert S]

Went with a 9x6 prop. Regardless of what other issues I might have, I don't think "not having enough thrust" will be one of them.

https://youtube.com/shorts/2M36Fp_8nYU?feature=share
(3S 30C Battery)

 

[Robert S]

Ok, so... broken arrow didn't go so well. I think the wings that I tried to reuse had some un-detected damage at about where the servo was and, when I landed nose down hard (due to it being to nose heavy to begin with), it basically just sheared from back to front along where the servo and the wing storage area are. Its a shame because it flew well up until then. I thought I had pictures bit I can't seem to find them. Right after I had a business trip and then spent a couple weeks of my free time doing "Honey Dos" for the wife. I honestly just needed some time away from building.

So now, this week, I tried it again. I built brand new wings and used the full chord, 3D printed a whole new body, changed out the wood dowels called for in the original plan for carbon fiber (cheap arrow shafts from Walmart), got rid of the FPV (for now), and heavily reinforced every joint and part of the build I could think of.

The results have been positive.


(A big thanks to my wife for coming out to the park and taking the video)

 

[Robert S]

Next I'll...:
- see if I can design a better nose (one with a hole for my camera)
- figure out a better way to hold all of the panels on top with something other than rubber bands, and, still allow me to rewove them for access to the inside if I need it
- integrate FPV back into the design
- add the bomb drop again but, make it as far back as I can so as not to screw with CG like the first version did. Also make it so I can fully remove it if I want with as little effort as possible
- I might fiberglass this thing

 

[JasonK]

- add the bomb drop again but, make it as far back as I can so as not to screw with CG like the first version did.

best would be to have the bomb drop be right at the CG, then holding the bomb by its CG, that way there is no shift (except up/down) in your CG.

you might need a touch of up elevator as the bomb would be adding drag below your CG, which would pitch the craft down.

 

[Robert S]

you might need a touch of up elevator as the bomb would be adding drag below your CG, which would pitch the craft down.

I'll probably just move my flight mode button over to a three way switch and make a new " Ground Attack" flight mode that gives me a little more elevator and and emphasizes straight and level stability with the gyro.

Then once I release I can flip over to one of my other modes. It's going to be fun to dial this in.

 

[JasonK]

I'll probably just move my flight mode button over to a three way switch and make a new " Ground Attack" flight mode that gives me a little more elevator and and emphasizes straight and level stability with the gyro.

Then once I release I can flip over to one of my other modes. It's going to be fun to dial this in.

if you have a flight controller, it will automatically add that elevator need via the I term, so you most likely don't need to mix anything in for that.

 

[Robert S]

if you have a flight controller, it will automatically add that elevator need via the I term, so you most likely don't need to mix anything in for that.

I think your right but I've been finding out, via trial and error, that the more I'm able to dial things in to fly without the gyro on, the better it flys with it.

In one of the videos above, durring one of the full throttle runs,you can hear the servos moving like hell to keep it flying straight. I want to make it so the plane Flys well with or with out the gyro.

Although, that also might be because the little servos I had couldn't deal with the pressure generated by all of the air moving over the surfaces at high speed.

 

[JasonK]

I think your right but I've been finding out, via trial and error, that the more I'm able to dial things in to fly without the gyro on, the better it flys with it.

In one of the videos above, durring one of the full throttle runs,you can hear the servos moving like hell to keep it flying straight. I want to make it so the plane Flys well with or with out the gyro.

Although, that also might be because the little servos I had couldn't deal with the pressure generated by all of the air moving over the surfaces at high speed.

for fixed wing, there is also the trim speed and a scaling factor to reduce the throws as the speed/throttle goes over that trimed speed, as the faster the craft goes, the more effective the control surfaces get, so you could have got into P term oscillation at the higher speeds.

 

[L Edge]

I think your right but I've been finding out, via trial and error, that the more I'm able to dial things in to fly without the gyro on, the better it flys with it.

In one of the videos above, during one of the full throttle runs, you can hear the servos moving like hell to keep it flying straight. I want to make it so the plane Flys well with or with out the gyro.

Although, that also might be because the little servos I had couldn't deal with the pressure generated by all of the air moving over the surfaces at high speed.

Looking at your bomb drop mechanism for landing, the front black holder will be left vertical due to servo position( suspect it will hit and drag in the grass/dirt) and the rear holder( will be tipped down at some angle flopping and probably catch in the grass/soil) doing major damage.

If you have a leaf blower or large fast lowing fan, get a distance from it to see (20-30mph) wind to see what happens after release of the bomb. Flopping it in for landing won't work.

 

[Robert S]

If you have a leaf blower or large fast lowing fan, get a distance from it to see (20-30mph) wind to see what happens after release of the bomb. Flopping it in for landing won't work.

Like I mentioned, the broken arrow did fly and successfully drop a bomb twice before it broke. When I finally landed it the last time, I was planning on coming back with my wife to take video. Sadly, that landing was her last.

That being said, you are correct. Landing was not pretty and I figured even in tall soft grass, that mechanism was going to be damaged.

I'm thinking a ski type landing system that both sits down low enough to protect the bomb drop and comes out forward far enough to both prevent roll over and to protect my nose might be something to work on. Kinda like the love child of the B-2 and Santa's Sliegh.

 

[Robert S]

Update:

Broken Arrow 2 now has FPV and her bomb release programed and all set up. I took it for her first FPV Maiden today. I didn't go under the hood due to me being alone but, I did record video from the receiver.

The bomb release is removable so for the first Maiden with FPV, I removed it. The CG was close. I did have to dial in some trim to keep the nose up at slow speed but at higher speed it was close but I ran the trim on the controller all the way out and it still would not stay perfectly nose up. I'll give it another 2 or 3 degrees via the linkage and I think it will be GTG. Oddly enough, this time I have the bomb release so far back that with the bomb on it, the CG might be better.

This weekend I'll grab my daughter and we'll go to the park early in the morning before anyone gets there to try out the bomb release. I think I'll point the camera down (I can depress it about 45 degrees) and have her put the goggles on and be the bombardier while I fly LOS.




Please excuse the quality. I forgot to turn the video TX power up from the lowest setting. Also, the sound was horrible so I changed it out with some music.