Micro-Bipe (oz7574)

About this Plan

Micro-Bipe. Radio control model for micro electric RC. Wing area is 198 sq in, AUW 83g.

The original Micro Bipe used a Wes-Technik DC5-2.4 motor, geared 5:1 with a K&P 6in prop, a Skyhooks micro Rx, two 2.4g Wes-Technik servos and a JMP type 9 ESC. Batteries were 2 x 430 mAh lithium rechargeable Tadiran.

Quote: "Hi Steve, Attached is the Micro-Bipe plan which was a free download with RC MicroFlight magazine [now defunct] of April 2000. Regards, DeeBee1."

Direct submission to Outerzone.

Update 20/4/2022: Added article, thanks to Pilgrim.

Quote: "While looking for a model to test some new micro RC equipment, including receivers, motors, props, batteries, etc, I thought that a low aspect ratio biplane would be ideal. Such configurations can be built to be sturdy, yet are lightweight. With lots of wing area in a small package, the wing loading can be kept low enough to allow slow flight and good maneuverability - just right for flying over restricted soccer and Little League fields.

Several scale subjects (such as the great Farman sport biplane) are suitable, but I was in a hurry and wanted a simple, quick-to-build model that could use a range of new RC equipment. A few lines on some graph paper, and the Micro-Bipe appeared! I built it very quickly and tried a variety of micro RC items. The little bipe seemed to enjoy all of the equipment I tried in it.

At about 3 ounces all-up weight, the model proved to have a wide dynamic flight envelope, i.e., it can fly slowly and well on minimum power and can also handle enough added power to really gun around the sky. It is stable, handles nicely - even in a little breeze - and is kind of cute cruising around up there. ROGs and touch-and-go's are a real treat.

I'll indicate the various components I tried and which of them seemed to suit the Micro-Bipe particularly well. Because the model is a conventional stick-andtissue design, I will comment only briefly on its construction. The key is to keep it light: don't reinforce or beef up the little guy. When it comes to micro RC models, remember: the heavier they are, the worse they fly - and the harder they hit!

EQUIPMENT OPTIONS: I used several of the popular micro (less than 5g) FM receivers, including those by Garrett, CETO (Potensky) and Sky Hooks & Rigging. For electronic speed controls (ESCs), I used the JMP 7 as well as the FMA 05, which has no low-voltage cutoff and was useful for lower voltage battery testing. Servos used for all flying were 2.4g Wes-Technik. For most of the flying, I used a Wes-Technik DC5-2.4 geared 5:1 (which is a smaller gear ratio than is usually used on the DC5-2.4). I found that the K&P 6-inch prop matched the system very nicely (and it's a neat looking, scale-like prop, too!). Batteries used included two and three non-rechargeable CR2 lithium cells; six and seven of the tiny new NiMH Double Time cells from Cloud 9; and two 430mAh Tadiran rechargeable lithium cells.

I now fly the Micro-Bipe strictly for fun with the following gear: Sky Hooks receiver, JMP ESC, the 5:1 DC5-2.4 with the K&P 6-inch prop and two 430mAh Tadiran cells, with which I get more than 30 minutes of flying time on a full charge (!). These cells are relatively expensive and require a special charger - plus, recharge time is quite lengthy - but there is a less expensive, simpler and very effective alternative: six, or preferably seven, Double Time NiMH cells. These little cells are only the size of 50mAh Ni-Cd cells and have about 120mAh capacity! They behave and are charged like Ni-Cds, too. You can expect to get about 10 minutes of flight time with the Double Time cells. As for other motors I've tried in the Micro-Bipe, the DC5-2.4 with 5:1 gearing (using a 30-tooth spur gear and a 6-tooth pinion) and K&P 6-inch prop proved to be a highly efficient, almost perfect fit.

BUILDING: The fuselage framework is constructed of firm 1/16 balsa. Note that the cabane struts are made of 1/16 x 1/8 and are built as part of the sides to ensure alignment. The front former F-1 has a cutout to hold the DC5-2.4 motor, which is lightly glued into place with 'airplane' glue such as Ambroid - not CA. An alternate and neater mounting method would be to make a small 1/32 ply scab that's screwed to the front of the motor with two M1.6 capscrews. Glue this mounting scab to former F-1. Anything RC sells ready-made, laser-cut 1/32 ply mounting plates, including the M1.6 screws, for the DC5-2.4.

To simulate metal cowl pieces, I used bond paper sprayed with aluminum paint to cover the forward part of the fuselage. A few louvers, rivets and panel lines drawn onto these parts add a little scale flavor.

I made the Micro-Bipe's first set of lightweight wheels out of two laminations of 1/16 balsa circles. I covered both sides with paper discs onto which I had drawn fake spokes and tires. A 1/32-i.d. aluminum tube bearing completed the wheels. They worked great but soon were dented and banged up by the rough asphalt surface of my parking-lot airport. I made a second set, but this time, I added a suitably sized O-ring tire to the balsa discs. These wheels have held up very well, and they are silent - even on the rough asphalt!

Install the radio, including servos and pushrods, before you cover the fuselage. For pushrods on these small models, I use a length of firm 1/16-square balsa, with short lengths of .015- to .020-inch-diameter piano wire glued to both ends. I use a Z-bend on the servo end, and on the control horn, I use a 90-degree bend retained by a glued washer.

The geared DC5-2.4 motor has a 2mm carbon output shaft for the prop. Propellers with 2mm shaft holes can be press-fit onto the shaft, but this makes it very difficult to replace or change props on a model such as the Micro-Bipe. Also, unless the prop hole is quite exact, the prop can't be pressed on, and it may slip. To hold the prop securely and make it very easy to change props, I attached two 00-90 brass machine screws to the spur gear to 'capture' the prop when it's on the shaft. A loose slip-fit of the prop on the shaft allows easy prop replacement, and a small piece of silicone fuel tubing holds the prop on the shaft. If you drill the holes in the spur gear and secure the screws before you assemble the DC5-2.4 gearbox, the 00-90 screws are easy to fix into place.

Cover the model with light Japanese tissue or a light film such as Litespan or Airspan. If you use tissue, shrink it very lightly with alcohol to prevent warping; dope with a non-shrinking dope such as Sig Litecoat or clear Krylon spray.

After assembling the model, use light Dacron thread or synthetic fishline, e.g., Spiderwire, to rig the wings. If you have already drilled holes at the indicated places on each interplane strut, this is a snap. The rigging is not only for looks; it adds tremendous strength and anti-warping insurance to the wings - worthwhile!

TRIMMING AND FLYING: The usual preflight checks are in order. Make sure that there aren't any warps, the CG is in the right place, control surface movement is the correct amount and in the right direction and, last, that the radio works with and without the motor running. OK? OK! With a fresh charge on the battery, choose a relatively calm day and try the first flights on a reasonably large field. Tight, confined spaces are better postponed till you have the Micro-Bipe tuned up, and you have a few confidence-building flights under your belt.

Launch into the wind at about 1/2 power, and after getting the model straight and level, add power, climb to a comfortable altitude and get the feel of the little bipe. Flies nicely, eh? Now land, recharge and try some ROGs, a few aerobatics, and maybe a touch-and-go if you have a hard surface area on your micro airdrome. Those really close-in flybys and the silent maneuvers - in the air and on the ground - make it all worthwhile, don't they?"

Update 14/4/2023: Added article, thanks to theshadow.

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