Candy Bomber v.2

This is Version 2 of the "Candy Bomber" which was built specifically to drop candy and beverages from the sky.  Version 1 was built before I found FliteTest and used heavy, Elmer's foamboard.  This version is Dollar Tree foamboard and has improvements over version one.

Credit to Experimental Airlines for some of the ideas and definitely inspiration.  It's completely my own design, but I borrowed elements heavily from the C-23 Sherpa and CJ-27 Trojan.

I incorporated a host of features in this version to improve flight performance, versatility and ruggedness.

Here are some key features:

Leading Edge Extensions

I built leading edge extensions to help low speed performance, improve stability and allow for high angle of attack flight with no bad tendencies.  I was pleasantly surprised how effective this feature worked.  Even holding full up elevator the plane would not drop a wingtip. Using throttle management I could achieve a near vertical landing with about a 15 degree nose up angle.  It also allowed for very steep turns at low speeds.  Here is a photo cross section showing the leading edge droop.

Here's a cross section of the wing extension.  You can see it is a typical flite test wing, with a cuff added on that drops the leading edge.  The step at the top of the cuff (where it attaches to the wing) also acts as a vortex generator, helping keep the airflow attached at high angles of attack.

Wing Tip Droop

I put a foam piece on the wingtips to act as an end cap and drooped wing tip.  In theory this should help reduce wing tip vortices and help aileron control at low speeds.  Can't say for sure, but seemed to work well.

A shot of the wing tip droop or cap.  Cleaned up the end of the wing and helped low-speed handling.

Castering Nose Wheel

Since I used differential thrust, I opted for a free castering nose wheel.  This greatly simplified the landing gear.  I put a paint stirrer in the nose across the inside of the bottom panel.  I then screwd a .90 sized tail wheel bracket into a sheet of plywood, thru the foam and into the stirrer.  This created a rigged area to spread the load. It proved very durable.  I bent the landing strut back a little to help it track. I also placed the mains close to the center of gravity, so I was able to land nose high and keep the nose wheel up for part of the landing roll.  The only disadvantage is the road I land on is sloped, and with this setup I only have positive steering when applying power (can't steer while coasting), but I didn't find it too much of a problem.

This is a Sullivan (I think) .90 tail wheel bracket with a 2" foam wheel for a free-castering nose wheel.

Cargo Box

The first version had a more traditional bomb bay with doors and the payload was released vertically.  This version has an 18"x6"x5" cargo bay.  I built a foam board box that fit inside the bay with a parachute attachment point.  To hold the cargo in, I utilized magnets embedded in the cargo bay floor and used washers glued into the floor of the box to align with the magnets.  It provided enough hold for maneuvering, but once the parachute deployed, it pulled the box free.  For candy drops the box had flaps that would open downward and release the candy once free of the plane.  For dropping beverages, the box was taped shut.

I don't have a great shot of the cargo area.  This shows a general view of the fuse construction.  There was a deck about 1" down from the top for the electronics and wires to keep the cargo area clean.  The floor was two layers of foam sandwhiching a few paint stirrers laid across the fuse.  The main gear screwed into the stirrers.  I also glued stirrers along the wing saddle to reinforce the dowels that the wing rubber bands attached to.  Hatch was taped at front, used a magnet to hold it down.  Battery was on platform in this nose section.

Two parachute system

For more precise cargo delivery, I used two chutes.  The first was a mesh chute about 12" in diameter on a 48" length of paracord.  The paracord had a small loop that fit into a release built into the ceiling of the cargo bay, with another 36" of cord attached to the peak of the main chute.  The main chute was a 60" nylon umbrella ($5 at DG).  The small chute was closed in the cargo door.  When the door opened, the chute would fall free and drag behind the plane.  When I popped the release, it would quickly pull out the main chute which would in turn inflate and pull out the cargo.  This system worked extremely well and allowed me to set up the drops with great accuracy.  See the video.  The release was 3D printed.

This is the 3d printed release used to tow the Flag and release the drogue shoot to engage the primary.  A small piece of piano wire goes into the slot on the far right of the bottom photo.  The pin slides thru a metal ring attached to the chute or flag.  When the servo retracts, the ring is released.  Worked very well.  Glued to the inner deck just above the main cargo door which was servo operated.

3D printed Motor Mounts

The mounts worked really well, attaching the Emax 2220/07 motors and allowing for the speed control to be mounted just below in prime airflow.

This is the 3d printed mount (sorry it's upside down in the top pic).  The motor attaches with screws, the esc is zip tied in place.  It looks kind of like a turbo prop setup with a scoop just below the motor.  Kept the esc very cool and then I just glued the mount into a foam housing.  You can see the foam still trying to hang on.

How did it die?

I was stupid, that's how. One of the things I never got around to doing was disabling the low-voltage cutoff.  On the last flight, I pushed my time and the LVC cut the right engine.  Of course this means all power went to the left and it started to roll.  Unfortunately in this situation you can't really use rudder, because the differential thrust just wants to put more power to the engine that is dead, and cuts throttle to the "good" engine.  the result is it rolled over.  I was too close to the trees and it ended about 50' up in a maple where it stayed for about 4 days.  In the rain.  It came down, but was beyond repair.  :(

What I will do different in Version 3

1) Disable LVC !

2) Make the nose wheel steerable

3) Use waterproof foamboard.

Specs and Equipment/

Wingspan - 60"

Length - 45"

Power:  2 Emax 2220/07 1200KV with 3 blade 9x6 master airscrew props

ESC: 30 amp Hobbyking ae-30 x2 plus dedicated UBEC

Battery:  5200 mah Multi-star 3s for longer flights, 3000 mah Zippy 4S for heavy cargo, towing

Radio: Taranis 9x, 8 channel X8R

Cargo Capacity: 18x5"x6" - easily a bottle of favorite beverage or 2lbs candy

Servos: 9 gram for flaps, aileron, elevator.  5g for rudders.  Standard servo for cargo door

REFERENCE PHOTOS

PHOTOS AT THIS LINK:  CANDY BOMBER V2