Installing an electric motor (FES – Front Electric Sustainer)

For many glider purists, installing an electric motor or Front Electric Sustainer (FES) is a sin. I agree that a glider without FES certainly looks better without FES. But I’m also a very practical person. I like to go flying very often and without FES the occasions on which I would be able to fly on my club’s airfield would be very limited. But also on the slope I’ve lived through many occasions where the FES saved the life of my glider (and me from major moments of stress). Most of all, I’ve found that the presence of a FES allows me to take more risks than flying without one and I end up finding a thermal where without FES I would have aborted my flight. So even though I regularly fly a couple of gliders without motor, and really enjoy doing so, most of my gliders have FES installed.

Installing FES is not that hard. What’s important is that you install the motor at a 2.5 to 3.5 degree downward angle to ensure that it goes up in a nice straight line without having to give much down elevator. I once almost lost a plane because after a hand-launching the glider went into a steep climb and stalled before I had the chance to give down elevator. But if you don’t succeed in getting the downward angle right, don’t panic. Most transmitters allow you to mix a bit of down elevator with the throttle, allowing you to automatically compensate for the motor angle and get the glider into a healthy upward trajectory.

Important is that the spinner is a nice fit for the fuselage. This requires a nice spinner and a fuselage that’s round. What’s a nice spinner is mostly a matter of taste and budget. I almost always use Freudenthaler (RFM) spinners.They have a huge range, including a number of special “scale” spinners, but they’re not cheap. I buy mine through Leomotion or with my planes (Chocofly also uses Freudenthaler). Both also offers a few custom-made RFM spinners that you can only get through them.

To install the motor, a club colleague who does a lot of building for Chocofly showed me how to build this nifty little tool. It does two things: 1) it allows you to measure the downward angle of the motor pretty well; and 2) it allows you to “force” the fuselage into a round(ish) shape.

The tool is easy to build yourself. It consists of a 6mm  threaded wire with an attachment for the bulkhead and an aluminium profile to pull the bulkhead into the fuselage. To help measure the angle of the bulkhead in relation to the wing I use these cheap “incline meters” that you can buy through the internet.

How to use it? I first drill a 6mm hole through the front of the fuselage. Then I install the rod without the aluminium profile through the hole in the fuselage, positioning the bulkhead in the fuselage. Using the incline meter I position the rod (and thus the bulkhead) at a downward angle of approximately 3.5 degrees (I use a ruler on the wing rib to define the angle). I roll up sheet of paper with the diameter of the spinner and place this over the front of the glider. Making sure that the 6mm treaded wire is in the middle I roughy draw out how much of the nose of the glider needs to be cut off, and where.

I then remove the bulkhead and rod again and using a dremel with cutting disc cut off the nose of the glider, taking care that I cut off a bit (2-3mm) less than where I placed the markings on the fuselage earlier. Using rotary file on my dremel I sand down the inside of the fuselage where the bulkhead will be installed. Note that if you have a nose that’s not round, or part of the nose has more layers of glass, you may want to sand down a bit more so that it becomes a bit flexible and you can push it into a round shape with a bit of force.

Now place the bulkhead on the carbon rod again and place it into the fuselage and check the downward angle and center position. Pull the bulkhead into the fuselage by carefully tightening the aluminium profile (see picture below), while making sure that you keep the required downward angle. You can place a wire between the nose and top or tail of the plane to ensure that it’s centered.

Once you’ve got the bulkhead in the right position you can fix it with a couple of dots of 5 minute epoxy resin. Wait for it to harden out and remove the tool, taking care to leave the bulkhead in the correct position in the nose of the plane. Carefully mount the motor on the bulkhead and the spinner to check if everything is ok. If so, permanently fix the bulkhead using epoxy resin and on or two strands of carbon roving.

Once the resin has hardened out you can now sand back the nose so that the spinner fits perfectly. To do so I use a thick piece of wood in which I drill a hole with the diameter of the motor axle and to which I attached a piece of sandpaper (see picture below).

You can place this piece of wood over the axle of the motor and then rotate it to sand down the nose of the aircraft to get the perfect fit for your spinner. Done.