F18 Hornet scratch built from RCM Plans

This is one of the few scratch building project I've undertaken. I wanted a jet, but my wallet and our field are not conducive to ducted fans, so I went with this. I considered the Combat Models F16, but I'm a Navy person and this model was bigger and more impressive. Also it was ideal for me to scratch build as it had only 4 plywood parts to cut out, the firewall and the three retract mounts (I don't own a scroll saw).

I modified the plane fairly significantly from the plans. I used stabilators instead of the separate stabilizer/elevator shown on the plans, I added working rudders, I'm using separate servos for the ailerons so I can do flapperons, I added a retracting tail hook that performs the function of the fixed tail skid shown on the plans, and I made a few modifications to the airframe to make the shape more scale. These included modifying the intakes so they are round and separated from the wing like the full size, the leading edge extensions are separated from the fuselage with a slot in between, and it has removable drop fuel tanks.

The finish is going to be fiberglass and paint with the paint scheme of Hornet One, the original prototype. Power is a pumped OS .61 FS, so the fuel tank can go on the center of gravity, and it uses Springair retracts.

These are photos from when the structure was completed. Its in the finishing stages now and I hope to have it flying by the Spring of 1998.

UPDATE December 8th, 1997:

I've completed the fiberglassing, painting, and trimming. I painted it with Pactra Jet White gloss paint after wet sanding and priming with Plasticote automotive sanding primer. When I attempted to mask off the areas to begin painting the trim, I discovered that, even after a week of curing, any masking tape I used pulled the base paint off. In desperation, not wanting to have to repaint the whole thing, I tried using Monokote trim sheets for the blue and gold trim work. I applied it using the Windex method, and it worked like a charm! The gold trim is chrome gold, so its a bit shiner than scale, but the crisp lines and the fact that I had all the trim applied in a week more than made up for it.

I've begun the "systems integration" part of the work now. That includes permanently installing the control surfaces, (re)installing the retracts and radio gear, installing the engine and fuel system, etc. One problem I discovered was that when I permanently installed the stabilator control mechanism with the servo in the nose (48" away), there was way too much play in the servo/control rod setup. I've been worried about flutter in the stabilator all along, so I statically balanced them before I glassed and painted them, but with that amount of play in the control mechanism, I was asking for trouble. To solve this problem, I'm going to mount the elevator servo in the tail, under the tail hook hatch, with a 6 " wire pushrod to the stabilator control horn. This should give me a much tighter control setup and only cost me 2 oz or so more in the nose to counter balance the weight.

The Hornet has been completed and was displayed at the January club meeting. Pictures will be displayed here soon.

UPDATE January 30, 1998:

I have made two attempts to fly the F18 on two successive weekends. On the first weekend, we had a major problem with the prop hitting the ground when the airplane went over the smallest bump. I shortened the nose gear at the field enough that we could make one real attempt at a takeoff. During that attempt, the plane left the ground, but began a series of short, "hops" that increased in height and force of impact with the ground. Our first thoughts were PIOs caused by excessive throw in the stabilator, but post-crash review of the video tape and a more through examination of the airframe setup has revealed that it was probably porpoising caused by the interaction of a slight nose-down trim condition with too positive an incidence in the aircraft attitude while sitting on the gear.

In examining the post-crash video, the aircraft can be seen to leave the ground briefly and what appears to be insufficient flying speed. It flys for a moment and then settles back to the ground at which point the nose gear hits first. This impact sends the plane back into the air at an increased nose-up condition. It settles back down nose-first again, but this time at a greater rate, causing another bounce into the air, more nose-up. Finally, after the third bounce, the impact with the ground is enough to cause the aircraft to rotate to a point where the prop impacts the ground, breaking it and stopping the engine. This leaves the plane at approximately 15' of altitude with zero airspeed, and a 45 degree nose-up attitude. At this point, it assumes the ballistic trajectory of a "lawn dart."

Design changes before the next attempt included fabricating and installing a new set of main landing gear that are 1 and 1/4" longer then the previous set (which were in fact 3/4" shorter than they should be - we're not too sure how that happened), installing a new prop, and decreasing the stabilator throw electronically and moving the CG ahead by 1/4", just in case.

On the second weekend, I made two serious attempts at a takeoff, and in both cases, it took almost the entire field before I could get it to lift off the ground. Once it did lift off, it took almost full up to keep the nose from dropping and I could not seem to get it to climb. Both attempts resulted in it landing in the high grass at the end of the runway. On the second attempt, I increased the stabilator throw to the maximum I could get, and added a significant amount of up trim, and it handled better, but I still don't believe that it would have climbed above the trees at the end.

I have a few more modifications in mind to help fix this problem. First, I'm going to move the CG back to the point shown on the plans (its about 3/4" further forward now). Second, I'm going to increase the length of the nose gear by 1/4" to get more positive incidence on the ground. Third, I'm going to increase the throw in the stabilator mechanically and then cut it down with the radio so I can easily increase it more if I need to. Third, I'm going to check the thrust angle of the engine to be sure there is no down thrust.

UPDATE October 18th, 1998:

After moving to Richmond, starting a new job, building a new house, and moving into it, I finally got a chance to make the above modifications. I took the F18 out to the RARC field on Sunday the 18th, and I decided that it was going to fly, or come home in a box, because it takes up too much room in my workshop to be a hanger queen and still keep around. I had a few problems keeping the engine going, but a new glow plug fixed that. The field at RARC is only about 350' long, so I anticipated some problems getting it off the ground. I started the first takeoff run at the extreme end of the field and by the time it got to the 3/4 point, it finally lifted off. It reached an altitude of about 2' and then slowly nosed over and began to decend. By this point, I was past the end of the runway and I decided that I had to go for it, so I pulled back on the stick and it began to climb. It flys!

As it picked up speed, less back pressure was needed to keep the nose up, but I discovered that I needed all of the up trim I had, plus more, to keep it from decending from level flight. That made the first flight and landing somewhat interesting. I left the gear down and had to make 3 passes before I could get it low and slow enough to touch down, and even then, it ran off the end of the runway, but it still flew successfully and was in one piece!

I made some trim changes, fixed the bent nose gear, and went for a second flight. This time it was in better trim, so I tried retracting the gear. The result was an immediate pitch up in trim and a major jump in the flying speed. Man this thing is fast! At least compared to what I'm used to. I tried a dive to a high speed pass and that's when someone watching heard and saw the rudders flutter. I decided to land it, but the gear wouldn't come down. I resorted to belly landing it, and the damage was very minor. So, for next time, I had to fix the rudder flutter and do something about the engine noise. With a Slimline muffler and turning an APC 11X7 pusher prop at 14,000 RPM on the ground, the sound is extemely loud.

UPDATE October 25th, 1998:

I hastily built an after-muffler out of a chrome plated drain pipe (suprisingly light) and some JB Weld, and tightened up on the rudder linkage to combat the flutter. I also sealed the rudder hinge gaps and "preloaded" the rudder surfaces by adjusting the linkage so that they are both canted outwards a few degrees when the plane is at rest. The 3rd 4th, and 5th flights went much better - no rudder flutter and the gear went up and down correctly. This thing is really fast! Full power dives to a fast low pass, followed by a high G pull out at the end result in a 300' altitude gain before it starts to run out of speed. Its fun! I have a few more adjustments to make before its really ready to go, and I had some problems with my home-made after-muffler that I have to work out. I haven't tried flying it with the fuel tanks yet, and I'm afraid that I wouldn't be able to get it off the ground with them on, but after I get comfortable with it, we'll see...

I'll try and get a few pictures in the completed form the next time I take it to the field.

UPDATE November 3rd, 1999:

I had to build a stonger muffler that was not actually attached to the engine as the other after-muffer I built eventually fell apart from the vibration. I also had to buy a foot of Tygon (sp?) tubing ($25/foot from Small Parts, Inc.) to connect it to the engine as the high temperature silicon tubing kept splitting. The muffler works well now, but the engine is still too loud. Not much I can do now as its mostly prop noise. I finally took some color pictures and here they are: