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Old Apr 26, 2005, 08:06 PM
iPhly R/C with iPhone
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Slow-G manual beta thread

I'm putting together a manual for the Slow-G autogyro conversion kit. "Slow-G" is the provisional marketing name for my twin-rotor model that is covered in this thread. The kit converts a GWS Slow Stick airplane into an autogyro.

I'll be posting construction photos and explanations here as I develop them. You are welcome to post questions and suggestions for clarifications.

Although I retain copyright over my photos and text,
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.2
or any later version published by the Free Software Foundation
Full text of GNU FDL is available at http://www.gnu.org/copyleft/fdl.html

This premission extends to any medium whatsoever. For example, if you want to take these notes and make a kit based on them, you are welcome to, as long as the design itself remains free, i.e. anybody is free to reproduce your reproduction of my design under conditinos no less limiting than these.

If you'd like to buy a pre-production kit, check this thread in the for-sale forum.

Ari.
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Last edited by iter; Apr 28, 2005 at 06:39 PM. Reason: FDL clarification
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Old Apr 26, 2005, 09:41 PM
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Rotor assmebly

Here's what a finished starboard rotor should look like, top and bottom views mounted on its wing pylon:
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Old Apr 26, 2005, 11:51 PM
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Laser-cut parts

A photo and a drawing of the laser-cut parts with part names. Note the arrows on base plates and wedges. These will need to match when the head is assembled.
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Old Apr 27, 2005, 12:10 AM
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When separating the parts, I found it helps to cut off pieces around the 3/8" wedges first to avoid damaging the wedges.

It's important to cut the bottom of these wedges smooth where break tabs used to be. If you don't, the wedges will not sit flat on rotor base-plates and there will be variations between angles of attack on different blades. You don't want that! It's better to have a little notch where the tab used to be than to have remains of the tab protrude.
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Old Apr 27, 2005, 12:44 AM
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Glue the 3/8" spacer to its marked location in the center of base plate. Glue 1/32" ply cap on top of it, making sure their holes match. The spacer's function is to maintain proper distance between wedges and to provide spacing between nuts on the shaft, so that the rotor is less likely to wobble.

Right and left versions of the spacer and cap are identical except for markings, but gluing right on right and left on left will help you keep track of which finished rotor spins in which direction. This will be especially helpful when you glue blades in the next step.

Important: Blades must be set at a negative angle of attack to autorotate. To help you put the wedges on the right way, they have been marked with arrows that correspond to arrows on the base plate. There are 4 wedges with arrows that go one way and 4 with arrows that go the other. Make sure you glue the right wedges to the right base plate, and make sure they slope in the right directions.

Last photo shows the finished subassembly. These parts show more burnt wood than most laser-cut kits I've seen :=)
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Old Apr 27, 2005, 01:38 AM
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Mounting blades

Every blade in the kit is individually marked with its weight in 1/100th of a gram to make static balancing easier. Which end of a blade is marked is random (well, depends on the batch). You want to sort the blades by weight and divide them into two groups (four for each rotor). Assign the heavier blades to one rotor and the lighter to the other. A difference of half a gram between rotors will not be noticeable, but a difference between blades of a rotor will make it hard to balance. In this example, the weights are

2.10, 2.11, 2.12, 2.12 (assign to the right rotor)
2.15, 2.15, 2.16, 2.17 (assign to the left rotor)

Within each group, arrange blades so that blades opposite each other have similar weights; this will further make balancing easier. For the right rotor in this example, 2.12g blades should be opposite each other and 2.10g opposite 2.11g.

Important: Blades must be set at a negative angle of attack to autorotate. If this is your first autogyro and you've built airplanes before, this will go against everything you are familiar with and you'll want to glue your blades to look like a propeller or a fixed-pitch helicopter's rotor. Resist that temptation! Leading edges must be lower than trailing edges for this model to work. Leading edges go closer to the rotor's axis and trailing edges protrude further back (the axis passes through the blades' extended 1/4 chord line)

Make sure that blades are parallel (or at 90 degrees) to each other and the hub. The easiest way to ensure that is to use a cutting mat or a piece of graph paper. It is also important that the blades all be in one plane. You can use a piece of scrap 1/16" wood (or 1/16" parts from the kit) to shim the free end of a blade while gluing it.

Last photo shows finished rotor. Note that there is only one way to put a blade on a given rotor, so you are stuck with marks on the root side of some blades and tip sides of the others - there is nothing you can do about that. If you try to match marks to all be "inside" or "outside", you'll end up with some blades that are on backwards.
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Old Apr 27, 2005, 02:29 AM
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Pylon assembly

This model uses GWS LPS (Light Power System) gearboxes as pylons for it rotors. Credit is due to Mickey Nowell for this idea. These gearboxes are inexpensive and readily available. They provide a simple an effective bearing block with dual ball bearings per rotor. Note that you need to mount the shafts in reverse of how they are mounted on the original. Make sure you have all parts for two pylons. Here, one set is shown in its packaging while the other is laid out on the bench.

Press the bearings in their slots, then push the shaft though until it catches on what will be the top bearing. Its other end will protrude about 3/16". Put the small washer ("thrust washer") on this protruding end. Then press the E-clip (thanks Mickey) onto the shaft so it slides into a notch at the shaft's end. The e-clip prevents the shaft from lifting out of the whole assembly. Putting it on is a little tricky; don't let it jump out of your hands and roll into the far corner :=)
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Last edited by iter; Apr 27, 2005 at 12:02 PM. Reason: terminology clarification
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Old Apr 27, 2005, 02:34 AM
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Wing assembly

The Slow-G wing is designed to hold rotor pylons on its tips, and to fit into Slow Stick wing mounts without modification or adjustment. The longitudinal member's length is identical to stock wing's chord and it attaches to stock wing mounts.

Measure 3 1/2 inches from the front of the 3/16x2 plank. Glue the triangular wing supports to it so that their fronts are 3 1/2 inches from the front of the plank, and the supports themselves form a dihedral saddle.

One side of each wing panel comes angled at 12.5 degrees so as to fit the saddle. Note that you have one left and one right wing and there is only one correct way to put them together. (In kits shipped prior to 4/30, wing panels did not have the angle cuts and the modeler must sand the appropriate angle in. If you have one of these early kits and want a set of angled panels, PM me) Dry-fit the panels to make sure they fit together with no gaps over the saddle and glue them in.

After the glue dries, turn the assembly over and mark the middle of the plank; glue the 1/8x3/32 spruce stick along this line. This stick will ensure the wing doesn't move and stays centered in its mount.

You can strangthen the wing with a piece of strapping tape across the top of the now-joined wing panels.
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Old Apr 27, 2005, 02:57 AM
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Wing/pylon assembly

Note: this step may be eliminated from production kits which may come with pre-drilled wings.

Test-fit 1/16" ply pylon reinforcements (the last remaining laser-cut parts) to wing tips and mark the locations of all 5 holes on the wing. With a sharp needle, mark 4 pilot holes for the #0 screws that will hold pylons to the wing. Using a 1/4" bit, drill a hole about 3/16 deep. This hole is needed to accommodate the protruding lower end of the rotor shaft. There is some up-down play in the shaft. The hole you drill must be deep enough to accommodate the shaft in its full-down position (its position at rest). The shaft must spin freely even when it's fully recessed into the pylon, or friction will make it difficult for the rotors to spin up.

Glue the 1/16" reinforcement on the wing.

Using #0 screws, fasten the gearbox housing (pylon) to the wing.
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Old Apr 27, 2005, 03:12 AM
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Mount rotor on shaft using the remaining nuts and washers. The order is as follows: nut, washer, rotor, washer, nut. Position the lower nut such that with all of these parts assembled, about 1/16" of the shaft protrudes above the top nut. Tighten the top nut with a wrench, pliers or simply a spare GWS prop.
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Old Apr 27, 2005, 03:22 AM
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Rotor balancing

It is important to balance the rotors because disbalance will cause vibration when the rotors spin. This vibration can be strong enough bend the shaft, which will in turn increase vibration.

Sorting blades as described under "Mounting Blades" helps the balance. However, even small variations between blades and the amount of glue used to mount them may affect balance. If you have a prop balancer, use it. If not, hold the wing in your hand such that the shaft is horizontal and spin the rotor. Mark the lighter blade (the one that consistently ends up pointing up) and add a piece of tape to its tip, or smear some glue on it. Repeat until the rotor stops with random blades pointing up.
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Old Apr 27, 2005, 03:27 AM
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(Photos or diagrams of complete model with CG marked will go here)

Mount the finished wing on your Slow Stick, check the CG and radio range and your Slow-G is ready for a test flght!
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Old Apr 27, 2005, 05:11 AM
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WOW, when do you sleep.
It's called an "E" clip.
mickey
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Old Apr 27, 2005, 05:24 AM
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Ari,
How about a link to the conversion kit??
Thanks!
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Old Apr 27, 2005, 11:56 AM
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Don, I posted in the For-Sale forum. At this point, I have 17 pre-production kits; if these sell, I'll go to full production and will make a "proper" website for it.

Mickey, don't ask :=) Thanks for the term.

Ari.
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