Descon Dust Devil

Scratch - Dust Devil {Scratch}

Contributed by Dick Stafford

Manufacturer: Scratch
(Contributed - by Dick Stafford)

I had originally decided to build a monocopter exclusively for the Estes E9 motor. However, my concept soon changed, and I decided to use a 29mm motor tube. The larger tube would let my fly on either an E9 (with an adapter) or a 29mm motor. Please read on to see how this project continued to evolve...

Click for Large imageConstruction Notes

I got several ideas from the Mountainside Hobbies site, but mine differs significantly. The wing is made from a 24" x 3" piece of 3/16" balsa, airfoiled, with a couple of strips of 1/64" Birch to stiffen it. It is glassed with 2 oz cloth and has 1/64" G10 plates laminated on the inner 6 inches. First, here's a drawing of the wing:

These are photos of the partially completed wing:

And, two photos of the completed but unfinished wing. When the glass was setting, I blocked up the tip so the wing has a slight upward twist. The second photo illustrates this twist; the trailing edge is flush with the counter.

The hub started as two strips of 3" x 12" x 1/8" plywood, which will overlap the last three inches of the wing. I left these strips the full 12" long until I could get a better feel of where the lateral CG was, both with live motors and spent casings. I temporarily attached these plates to the wing and started balancing motors and components on them. I found the hub might have to be quite a bit longer than I had anticipated, and was glad I had left them long to start. I also began to worry about whether an E9 would be enough to lift this thing. Should I use an Econojet G35? F23? Should I spring for a 32mm RC casing and go for a G12? Finally, I decided I would have multiple mounts. I'd have a 32mm tube to allow the use of the RC motors, or with an adapter made from LOC tubing, a 29mm motor. I'd also add two 24mm tubes to allow TWO E9's to be clustered. Yeah, that's it! The following is an early photo of the motor mount assembly. It is glassed and has a makeshift plastic ' cone' installed. If the monocopter works, I may re-think the cone later, or maybe add some LEDs in the clear cone for night flights. I have yet to acquire/make 24mm cones.

With the motor mount and various motors, I decided the plates should be about 8 1/2" inches long. This should allow me to position the launch lug at a position between the CG before and after launch. It's a lot longer than most monocopter hubs, but that isn't necessarily a problem - I hope. I used a piece of 3" x 1" x 1/4" ply to support the plates at one end, and would angle the wing between them at the other. I used another piece of 1" tall ply as a spacer while I first glued the end plate on, and later when I installed the wing. When I recomputed the wing's angle, I decided the 1" spacing between the plates would result in too great an angle, so I added two strips of 1/8" ply to the inside of the hub, reducing the spacing spanned by the wing from 1" to 3/4". This resulted in an angle of about 11 degrees (remember the tip is also swept up a bit). After the wing was epoxied in, I used 3/16" balsa to fill the gap between the wing and the opposite plate, forming a solid side panel. These are two photos of the roughed-out hub.

Next, I epoxied on the motor pod, aligning the joint of the two 24mm mounts with the corners of the hub's end piece. This provides a 20 degree angle. I added a 1/8" plywood support on the top front and a strip of heavy fiberglass around the rear of the motor mount and overlapping the hub. I then re-verified the lateral CD with both live motors and spent casings, and installed the launch lug (1/4" brass tubing) in between. It just missed the end of the wing within the hub. I cut two pieces of plywood to fit inside the hub, and drilled holes to fit the fiberglass balance beam. These were trimmed so they abutted the wing, and the beam just missed the launch lug. I once thought the balance beam should be centered on the launch lug, but this isn't the case. Having a continuous beam run throught the hub is a lot easier to mount and should be stronger. I attached the beam supports with carpenter's glue. I used JB Weld to hold the beam in place, and used the extra to create fillets on the support members. The beam itself is 18.5" x 3/8" piece of hollow fiberglass pole from a collapsable tent, with 7.25" extending out of the hub on either side. The final issue were cones for the 24mm motor tubes. I visited several local hobby shops and couldn't find any so I decided to make them. I made them out of papier mache using a plastic cone as a mold. This is not a refined technique, so I won't bore you with the details. The results aren't bad, but if the 'copter flies I may get some from BMS, along with a matching cone for the larger tube. The following photos show various views of the completed item, with a few coats of white primer.

The following is the launch lug for my monocopter. It consists of an old, dull 7/32 drill bit, a piece of 1/4" brass tubing, and a washer. The bit is epoxied into a piece of tubing so only the top 3/4" of the shaft is exposed. A washer is slid down to the tubing and is tacked in place. This will clamp nicely into the pad that I use for my launch rail.

Flight #1

I flew the Dust Devil on 10-19-2002 at the Higgs' Farm in Price, MD. The winds were blowing hard (our American flags were outstretched) and the ground was moist (so there wasn't any dust for the Dust Devil to kick up). I used two E9's that I had plugged with epoxy. The Dust Devil rose nicely, but at burnout it turned with the wind until it was perpendicular to the ground. It reached an altitude of maybe 15 - 20 feet. It flopped to the ground and the wing broke off. The following sequence show the start of the flight, the monocopter on the way up, and the smoke trail blowing away. You really can't see the 'copter, but the smoke trail shows where it is/was.

Rocket Pic

Current Status

I repaired the Dust Devil, added a bit of weight to the balance beams, and was hoping to fly it again on two E9s. With the added weight, the flight will have less altitude, but it would convince me to try it on a G. I have little doubt that it will fly nicely, assuming the winds are reasonable, but still want to try it on the E9s. Unfortunately, it appears all my MDRA launch opprtunities have 'dried up', I have no 'solo' fields, and since I modified the E9's, a NAR launch opportunity is out. At the risk of being highly criticized on entering a design with a less than perfect record, I decided to enter the Descon anyway - hey the boost phase was good. With monocopter and tri-copter entries already there, I just couldn't resist! If I happen to get a chance to fly it, I'll update this page.

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