From downsized Steve Schumate plans and inspired by Sal C's project, here's my first crack at an EDF powered model. I did own a Kamdax Mig-15 with a glow powered ducted fan, but it was a dog at this elevation (about 5000', but someone at the field called the airport on that hot summer day and the barometric altitude was about 7600' at the time).
 

 It's powered by a Hyperion Y12L-5800kV brushless inrunner, that produced 74 watts when I tested it a few days ago. Everything in the second picture weighs 3.5oz, and totalled 6oz even when I put an 850mAh 11.1v lipo on the scale. So I'll be somewhere between 185 and 200 watts/lb when the remaining foam parts are added. To avoid adding much weight coloring it, I'm going to use markers and draw on the F-15 Active color scheme (without the canards, though).

When Sal C did his, he thickened the entire fuselage to accommodate the fan. I forgot about that while I was cutting the pieces and ended up improvising. I placed the front lip of the fan right at the TE of the wing assembly, which also happens to be the root of the vert stabilizers. So the fan sticks up 6 or 8mm above the plane of the wing, and the top rear panel of the fuselage will go on over the fan, making the fuselage thicker only between the stabs. I also cut a small section of the main wing away to make a cheater hole; the regular intakes are about 118% of the FSA, but my experience with the Mig is making me paranoid. I'm also running the wiring from the esc and elevator servo over the top of the wing and inside the turtledeck to keep the interior of the plane from the intakes to the fan clean of wiring for smoother flow.

 All that remains is attaching the elevators and the top rear fuselage, and making the canopy and nose cone. With any luck, I'll get those done after the Colts win today and test it out this evening.


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It came out very nose heavy, and I had to cut a hole in the back wall of the battery compartment to slide the battery backward even more. The CG was still about 1/4" too far forward after moving the battery back and adding gobs of hot glue to any cavities I could find near the tail. AUW was 6.25 oz with the 850mAh battery.

With the CG off and a stiff breeze blowing, I decided to fly it anyway. I threw it into the wind at least 10 times, and each time it would climb out decently, but turning downwind, it didn't have enough thrust and there wasn't enough air blowing over the ailerons for them to be effective. About 4 of the 'flights' required going back inside for touch ups with the hot glue gun, which sat warm and waiting through the whole ordeal. Very displeased, I gave up for the night, half tempted to list the motor/fan/esc assembly in the classifieds.

I woke up before the alarm went off this morning, so I decided to give it another try. It was cool, calm, and overcast outside when I gave full throttle and threw the F-15 skyward. With the cooler (denser) air and the absence of wind, I could actually keep it up in the air flying circles for a minute at a time. In the nose-heavy condition, about 6 clicks of up elevator trim were needed to maintain level flight.

After a few good looking low passes this morning, I've decided to give ducted fans one more shot. I'm going to trash this airframe and build a new one with a few things in mind: use a slightly smaller battery (<2oz, probably TP 480 ProLite's), provide larger ailerons for low speed handling, and use the adhesives as sparingly as possible.

* * *

I finished and flew the second model yesterday. AUW was 5.7 oz. It did have enough thrust this time to fly adequately. I'd guess the quicker passes were in the 35 - 40mph range, which is pretty quick for the plane's size. The entire flight was a real exercise in energy management, but maybe that's what jet flying is mostly about. It does have a tendency to want to snap to the right at times, but I have yet to diagnose what the cause is.

I did do a couple things differently this time, as I mentioned before. I use some 20C-30C 540mAh lipos this time, instead of the 850mAh lipos I tried the first time. The ailerons are slightly larger, and I think I need dual rates to tone down the response at higher speeds--rolls were just a little too quick, even at half-stick. I thickened the entire fuselage to accommodate the fan. It's really not even as noticeable as I thought it would be. The thicker fuselage allowed for a conical thrust tube, as opposed the the last one that changed cross section from circular right at the rear of the fan shroud to semi-rectangular as it exited the fuselage. I think the conical thrust tube is what's helping the most.

I'm going to give it another try tonight and see if I can find out what's causing the sudden snaps. If it just happened at lower speeds, I'd assume it was a stall, but it happened at a variety of speeds. The other possibility is a radio glitch, I guess. The range check was fine, but maybe it's an issue of the plane's orientation or something,\. (When the plane is flying straight away, the antenna is pointed straight back at me, and the fan and esc would be right between the rx and tx. But I don't recall if it always happened during a single orientation or not.)

I'll also need a canopy eventually, but that'll wait until I find a method I like. The only part of the Schumate plans I don't really like is the laminated canopy and nose cone.

I'd like to get some video, but my wife is terrible at tracking planes. This one's small enough and quick enough that I don't expect big things from her.

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 I just had a thought as to why the plane occaisionally rolls quickly to the right. Notice that the spar I put in the wing extends outward only halfway from the outside of the fuselage to the wingtip. I picked the plane up once by the wingtips, and there was a considerable amount of wing flex. The ailerons would also flex with the wing.
I'm thinking that the wing constantly has some flex during flight, and the hingeline geometry is such that the ailerons do not wish to deflect at all. When the servo finally pushes or pulls hard enough to overcome the hinge's resistance, the ailerons snap into a greatly deflected position.
I have some flat carbon strips I'll epoxy to both sides of each wingtip later today, inline with and slightly overlapping the spar.

* * *

I stepped out for a spur of the moment flight on Tuesday the 2nd. I only flew 2 circuits before it rolled over and nosed into the ground.  The damage is pretty severe, and I won't try to repair it or rebuild. I guess I should have attempted to stiffen the wingtips before I tried it again.
Oh well, now the motor and esc will go to my son for an upgrade on his GWS Pico Stick.