Back “in the day” of my modeling mayhem I built a Byron’s F-20 Tigershark which appears in many of the banners on this website. This plane was large with a fuselage length close to 8 feet. Recently I was perusing the internet searching for “electric jets” and happened across the Electric Jet Factory.
There I ran across the HET F-20 which oddly enough had an almost identical color scheme to my old Byron’s bird. Although already waist deep in a F-18 scratch built project guess that nostalgia took over and I “had” to have it.
I want to thank Robert of EJF.com for being very helpful in answering some of my questions and helping me choose a power system for this project as well. Shopping at the electric jet factory was an enjoyable experience.
May 25, 2007
My 2nd package arrived. The fan (WeMoTec mini fan 480), motor (Typhoon EDF 2W-20) and ESC (Tsunami 72 amp) arrived the day before. When Robert from EJF told me I’d be receiving 2 boxes 1 small and one large he wasn’t kidding about the LARGE box. I opened it expecting to find a smaller box inside but this was not the case. This huge box contained the pieces of the kit all well packaged with individual components wrapped in plastic to prevent damage in shipping. It also made the 15 dollar & change shipping fee for the 2 packages understandable.
I did go ahead and un-package the kit to test fit a few of the pieces and take some photos but it will probably be a week or two before beginning actual construction since I want to get the F-18 out of the way 1st and wait for the mini retracts I’d ordered (before ever seeing this kit) to come off back order so I can see if it’s feasible to use them with this model.
May 27, 2007
Just couldn’t stand it any longer and started construction after reviewing the construction CD a couple of times. I didn’t really agree with the construction sequence shown and routed the main power supply wires 1st. Then attached the ailerons to the wings before mounting the wings to the fuselage. I also went ahead and cleaned out the servo wire exits since it just seemed to make sense to do it before attaching the wings.
Here is a place where I hope others can benefit from my mistake. (and/or error in the CD instructions) I followed the instructions almost exactly for mounting the wings except for making myself a .9 mm shim and taped it to the bottom of wing trailing edge. (with tape a 1 mm shim) Then a straight edge was used across the bottom of the fuselage and wing positioned so the shim touched the straight edge. After the epoxy cured the second wing was attached in the same manner so that the trailing edges were at 1 mm from fuselage bottom and the leading edges at 10 mm just as the instructions called for. Both wings fit nicely against the fuselage sides with no gaps evident on either one. After the epoxy on the second wing cured I set the fuselage down on my work table and the 1st thing noticed was that the left wing had a bit of dihedral in it while the right wing was just about flat. Too late for me, but would suggest to others that after installing the 1st wing to set the model down on a flat surface and check the distance from wing tip to the surface. Make a small block that fits under the wing tip. After installing the second wing and pinning in place but before the epoxy sets again place the model flat on the work surface and use the block to insure both wings have the same dihedral angle. I’m going to finish construction and it should still fly but won’t fly as well as it could with everything in proper alignment.
While I was at it, also attached the nosecone since I’ll be using my Spektrum radio & receiver and didn’t have to worry about routing a long antenna wire. Considering the amount of work that has to be done with the model upside down decided not to install the vertical fin yet although it is the next step in the CD manual.
May 31, 2007
The making of the thrust tube. I was unable to find any “duralar” in a 5 mil thickness but the office supply store I visited (they did have 3 mil) carried something they called a desk protector in the same basket where the 3 mil duralar was located. This looked close enough to me and is probably closer to a 10 mil thickness. The 25” x 40” sheet was only $5.00 and has enough material to construct 8 tubes the size the F20 calls for.
Again I deviated from the listed construction methods and opted for something I thought easier. After making the initial 12”x10” cut wrapped the tubing around the front side of the fan unit so I could get at least a half inch overlap on the fan unit. Next I slid the tail cone over the other end of the tube until about 1/4” protruded through it. Then taped the front in place and another piece at the tail cone (see photos). Using a felt tip pen drew a line down the tube at the seam, then removed the tube opened it back up and finished drawing the line the whole length of the tube. Afterwards cut away the excess allowing about 3/8” of material to remain outside the line. I then lightly sanded the area between the line and the edge of the material as well as the opposite side where it will join. Now tape the tube back together over the fan unit and inside the tail cone. Several pieces of tape can be used for now just to keep the surfaces mated properly. Once satisfied with the fit, remove the tail cone and using thin ca drip it inside the tube so it runs about half way down and wicks into the sanded area. Remove the fan unit and repeat from that end. Set aside and allow the ca to cure. Once cured you can remove the tape strips from the outside of the tube and replace them with the packaging tape as recommended on the CD.
Slide the fan unit into the fuselage and slide the tube in from the rear. Mark the top locations of the mounts for a reference and pull the tube back out Cut the 3/8” notches to clear the mounts and reinstall to check fit. Slide the tail cone on and mark the exit for cutting. Remove the cone and tube then trim the exit along the line. This portion is now done.
June 3, 2007
It was just a little too windy to go flying this weekend and got bored enough that I decided to attach the stabilizer. This was done according to the CD manual with the exception of attaching the elevators before gluing the assembly to the fuselage. (To me it was just easier that way). I went ahead and removed the top hole of the linkage before installing the stab too. From here I was sort of at a standstill until I get my battery and rig the fan and ESC and get them mounted permanently in the fuselage. I don’t think there will be room to get the fan in or out once the elevator servo is in place.
June 4, 2007
If nothing else decided to make the battery tray this evening. Again I varied from the plan just a bit and took the hints offered by the CD. I built mine up to even with the bungee hook block with balsa and arranged the strips so I didn’t have to carve out the clearance for the Velcro straps. (again see photos). The battery should arrive tomorrow so I can set up the ESC and get the fan mounted before moving on to the next step.
June 5, 2007
The battery arrived and after about an hour of fighting with the ESC finally got it programmed. (Damn I miss jumpers & switches for setting up electronics). With that done I finished up the battery tray (had to stop at the local sewing store for some Velcro) and test ran the motor for a few minutes just to cycle the pack down a bit and get an idea of run time. Three minutes of half throttle with several full throttle bursts of 15 seconds duration dropped the pack from 4.2 to 3.8 volts per cell on the 3200 ma 4S pack. I was really impressed with the amount of thrust even at half throttle. And, this was running without the thrust tube or even the fan access plate installed.
June 6, 2007
Elevator servo installation went smoothly enough and the CD manual had it down just right. Once all linkage was installed and tested, reinstalled the thrust tube and taped it to the fan unit. The same thin gauge wire used for pulling the aileron servos is also very handy for routing the elevator servo lead underneath the thrust tube to the receiver location on the other side of the fuselage.
June 7, 2007
I got aggravated with trying to run the thin wire for pulling the aileron servo leads last night. They kept wanting to go all the way to the opposite side of the fuselage instead of coming out where they were supposed to. I found a roll of solder to be most useful for getting them through today. It was flexible enough to get between the elevator servo and the bulkhead but still strong enough to form a hook to fish the wires through into the fan compartment.
This would actually be a good step to do right after the wings are attached. That way nothing is in the way of getting them routed where you want them. Just make them extra long and tie the ends together to keep them from falling out during the other steps. Aside from being 1 pushrod short and having no control horns, (minor stuff available from my “collection” of parts) aileron connection & setup went according the CD manual.
June 8, 2007
With pretty much everything else done finally attached the vertical fin this evening. (by the manual) and started attaching the cockpit/canopy. Although the CD details construction of a scale cockpit closely, it doesn’t say anything about what to do with the light ply base that comes with the kit. The rear support wasn’t attached in mine although it did look as if it might have been at one time. I laid a piece of wax paper between the fuselage and base, set up the back support and ca’ed it back into place. There was a small piece 1/8” dowel in with the other hardware so drilled a hole in the center of the forward brace and through into the fuselage. After checking for fit glued the dowel into the cockpit base and allowed it to set. (see photos)
I was really guessing when I took the two small ply strips and glued them to the underside of the fuselage where the rear of the canopy base sits, but it seems to have worked out well enough. Some scrap light ply was used to make a strip for the magnets to attach to the canopy base. (again see photos)
After getting the canopy cut to fit the base it was attached.
June 9, 2007
The construction was completed today! The only thing lacking was applying paint to the canopy and installing the launch hook. I could have even taken it with me for a test flight but wanted to test the bungee on my home made (cheap) F-18 foamy before trying it on the somewhat expensive and good looking F-20. With the F-18 the launcher, and my two prop job (warm up planes) in the Explorer there just wasn’t enough room.
June 24, 2007
Holy crap! This thing is ungodly fast! The day of the 1st test filght finally arrived and want to give a special thanks to John Walton for performing the piloting chores and to Steve Bevington for manning my second camera. Between the two of us we managed to catch almost all of the 5 minute+ (real time) flight without too much open sky. Not an easy task when this little bullet is at full throttle. Most estimates were in the 140-150 mph bracket. It would have been interesting to have a radar gun and find out for sure.
With a finished weight of 32 oz (w/o battery pack) and flying weight of 42 oz. with a 3200mah 4S 20c lipo pack this one has a really good thrust to weight ratio. The Tsunami 72 ESC and Typhoon 2W-20 motor really cranks some wind through the 480 mini fan. Not enough to do a vertical hand launch like you can with a 3-D model but enough to go vertical out of sight with a running go. And, enough power to allow the use of "throttle management" and stretch out flight times. The test flights were done with control throws set at the CD-Rom manual suggestions. Elevator set for 10mm up and 5mm down. Ailerons at 12mm up and down. The CG was located at 66mm back from the wing leading edge where it joins the fuselage.
From what I could see (I still haven't flown it yet and won't until I get in a little more stick time) it will still fly with authority at about half throttle and John had it down to about 1/4 throttle with nose high before it would finally stall. I noticed it did fall to the same side every time he tried it and will blame that on the uneven wing dihedral. I still haven't decided if I should be pissed at the guy who did the construction manual for leading me to believe that the wing angle fit was built in that close, the manufacturer for the kit not being built as precise as the manual would lead you to believe, or myself for not thinking "old school" and checking the angle before the epoxy cured.
Regardless, it's a bullet for those with a need (or desire) for speed. Properly built it should be a precise flyer as well. Hopefully you will have picked up a couple of tips from here if you decide to build your own.