Saturday, January 01, 2011

Mega-Review: Art Applewhite Helix Monocopters (13mm, 18mm and 24mm)

The Helix is an extremely simple monocopter design that uses a section of  tubing as the central hub. If you have built one Helix, you have built them all. I know that sounds corny, but they all have the same basic components and construction techniques. As a result, some of the material from my original reviews have been pared out. If you've read my review of the 29mm version, you might just want to place your order and start building.


13mm


Construction:

The parts list:
* 1/16" Basswood sheet
* 24mm tube
* BT-5 motor mount
* ¼" dowel
* ¼" launch lug

This kit requires Elmer's Glue All, and an X-Acto knife with a new #11 blade. It's almost so easy that it could be considered ARF (almost ready to fly). You start by cutting the pre-marked holes from the 24mm tube. The patterns are polygons so this involves multiple straight cuts. These are best accomplished by starting inserting the tip of the blade at one vertex with the cutting surface directed along the line. If you carefully insert the blade the rest of the way, the cut will be made. The tube is flexible so be careful that you don't crimp it or cut yourself.

The parts are all inserted and fillets are applied inside and out. Because the holes are supposed to be snug, I found it helped to insert a motor in the motor mount when it is inserted.

I'd recommend waiting until these fillets to at least partially set before proceeding...but I didn't. The wing fits in the end of the tube and needs to be trimmed slightly. The fit should remain snug and internal fillets are again applied. I checked several times as the glue set to ensure the wing was aligned properly and was straight.

Finishing:
Art says to apply two light coats of enamel to protect the kit from moisture. I used Helmsman Spar Urethane as a clearcoat.

Flight/Recovery:
You form a thrust ring with masking tape and friction fit the motor so it won't fall out. The motor is oriented with its nozzle down. If you put it in backwards you will win closest to the pad (don't ask). You need a sturdy pad with a short ¼" rod (1" or so). Art provides plans for a suitable monocopter pad in the instructions.

I flew this kit on both an A3-4T and an A10-3T. The A3-4T flight was longer and higher so I recommend this motor. Both flights ejected near the ground so care should be taken if people are around or if there is a fire danger. After burn out the model quickly slows and tumbles to the ground.

18mm

The parts list:
* 3/16" Basswood sheet
* 29mm tube
* BT-20 motor mount
* ¼" dowel
* ¼" launch lug


Flight/Recovery:


You form a thrust ring with masking tape and friction fit the motor so it won't fall out. The motor is oriented with its nozzle down. If you put it in backwards, you will win closest to the pad (don't ask). You need a sturdy pad with a short ¼" rod (1" or so). Art provides plans for a suitable monocopter pad in the instructions.

A C6-3 gave this little monocopter a nice ride. After burn out the model quickly slows and tumbles to the ground.

24mm

Parts list:
* 1/8" Basswood sheet
* 38mm tube
* BT-50 motor mount
* 3/8" dowel
* ¼" launch lug



Flight/Recovery:
You form a thrust ring with masking tape and friction fit the motor so it won't fall out. The motor is oriented with its nozzle down. You need a sturdy pad with a short ¼" rod (1" or so). Art provides plans for a suitable monocopter pad in the instructions.

Art Applewhite 24mm Helix I flew mine on an E9-4. It flew great and the ejection charge fired close to apogee.  After burn out this 24mm model tumbled for a short period before beginning to autorotate.