Tim I’ve been watching your laser projects for a while now. I’ve been saving to maybe join the club one day. Well the time has come, but unfortunately I wasn’t able to overcome a ventilation solution without a lot of rework in the basement.
Enter my new 3D printer. They’ve come a long way over the last year. Most notable is the ability to print carbon fiber infused nylon. I’m a total neophyte, but so far I’ve managed to print a lifetime supply of fuel clips, and some small tool holders. Below a pic of a small vase being printed. Just 6hrs to print
Same as usual, first thing was to cut the opening for the engine (pre marked) and holes in the front and back of the wing saddle area, then generally clean up the inside with sandpaper.
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Last edited by KRProton on Sat Feb 27, 2021 6:18 pm, edited 1 time in total.
My new Small Wonder came with this beautiful firewall with carbon fiber laminated on the face, but sometimes I like to make my own firewall because...I can, and it's easier to make the hole for the fuel cutoff with the firewall out of the fuselage, so I asked for it without the firewall installed. After about six or seven attempts with my CAD and laser cutter, I came up with the correct firewall outline with cardstock. I then moved onto a prototype firewall cut from 1/4" plywood, but this time with the engine mount and fuel cut tube holes added. This took about three or four attempts before I got all the holes in just the right place.
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Last edited by KRProton on Sat Feb 27, 2021 6:19 pm, edited 1 time in total.
Now that I have the firewall drawn, I can make the real firewall. Think I'll use three layers of 1/8" aircraft ply (6-ply I got from Sig Aircraft). This stuff cuts a mess on my laser cutter because it's so hard you have to use a lot of power at slow speed to cut it - must be a lot of glue resin in there too because of all the layers. But I made it oversize so I can sand to the correct shape with a slight bevel after gluing, so it'll clean up nicely.
Finishing resin on all mating surfaces and 1/8" dowels to hold alignment, then clamps and wait overnight.
I sanded the edges of the firewall to a slight bevel on my Harbor Freight belt sander and it cleaned up nicely, so I then I got stupid with my laser cutter.
I test-fitted the engine mount and mount ring to the firewall, then took it apart and test-fitted the assembly into the fuselage; a wire through the throttle cut tube partially aligns the ring and a little finagling got the ring aligned up with one of the mounting bolts and the other two went right in.
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Last edited by KRProton on Sun Feb 28, 2021 6:08 pm, edited 1 time in total.
I mounted the engine with a 1/32" plywood disc behind the spinner to set the spacing and aid with alignment. Once the firewall was in perfect position as determined by the alignment of the back plate of the spinner to the fuselage, I then drilled holes through the fuselage sides into the edge of the firewall. (Actually, the hole locations in only the fuselage had been pre-determined and drilled when I had the engine and firewall installed earlier).
After drilling each hole I temporarily pressed in a carbon fiber rod to key the firewall into position. "Pinning" the firewall allows for gluing in the firewall next without having to have the engine and engine mount installed. This way I can do a clean install without making a damn mess and for a tidy glue fillet necessary in this fuselage because there is little room around the engine mount and engine mount ring.
Once the firewall is set, I disassemble everything, mix up my Loctite 9462 (this time I added a little Don Stegall white micro fibers), and apply to the firewall and inside the fuselage. I put in the firewall and temporarily realigned it with T-pins, then traded the T-pins for the carbon fiber pins.
Neaten the fillets and remove excess glue with wood coffee stirrers, then clean up the rest with small paper towel squares and denatured alcohol.
Normally I would reinstall the engine and double-check alignment, but I don't want to smear any glue if the engine mount or engine mount ring come into contact with it, so I'll live dangerously and leave it set overnight. Any imperfection in the alignment should be able to be corrected when potting the engine mount later.
I lied in the last post. I went ahead and temporarily mounted the engine to make certain the firewall was set. With the engine and spinner in place I could see that it needed the slightest nudge for perfect alignment. NOW I'll let it sit overnight, then I'll pot the mount later.
Same as I did on my first Small Wonder, I cut the holes in the fuselage sides for the elevator joiner, then drilled and countersunk the elevators for the joiner screws. I also mounted the battery to the back the engine mount ring (same as before also). You can find this if you look back in the thread.
I temporarily mounted the engine mount with the ring and battery, then slipped in the fuel cut tube just to see how it fits. With the battery velcroed to the engine mount ring, it was a LOT easier to install and position the ring to align the screw holes with the engine mount screws - the battery made it a shorter reach and was kind of a "handle" for positioning the ring. This will be good to know when I glue on the engine mount and the engine mount ring soon.
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Last edited by KRProton on Wed Mar 03, 2021 6:41 pm, edited 1 time in total.
On my first Small Wonder I had taken an educated guess on where to position the servo tray for C.G. It ended up requiring like .35 oz. of ballast on the tail to balance, so I could have mounted the servo tray slightly farther aft. On this one, I want to use the elevator pushrod from the first one since it was fine, but this means I can't relocate the servo tray farter aft. But this is okay because I plan to paint the fuselage, so the tail on this one will probably be a little heavier, so I won't worry about changing the servo tray location or making a new elevator pushrod.
That said, I decided to change up the way I do the servo tray. Instead of positioning the servo tray cradles on top of the servo tray, I'll position them on the bottom of the servo tray. This will make it easier to align them for gluing in and besides, all the force pushes the servo tray down, so it makes more sense to have the cradles under the tray!
I laser-cut new cradles, positioned the servo tray, then tack-glued the cradles to the fuse sides with thin CA using care not to inadvertently glue the tray into place yet.
I removed the servo tray, securely glued the cradles to the fuse side with more thin CA, then glued the servo tray to the fuse sides and cradles with epoxy mixed with filler.
Quick comment regarding charge jacks in general. The norm for several years has been to secure the connector to the tray and drill a couple holes in the side of the fuse aligned with the pins on the charge connector. This is great and nice and clean. However, carbon is conductive and if the pins on your charge cord make contact with carbon, it will short out, damaging the battery (FIRE), or damaging your charger. If your servo tray has provisions for this like the picture shown, it is best to either put the entire connector through the side of the fuselage or find a different location for your charge jack. Been there done that, have the burnt up fuselage to show for it.
Public service announcement complete. Back to your normally scheduled program.
kane wrote: ↑Tue Mar 09, 2021 8:11 am
Quick comment regarding charge jacks in general. The norm for several years has been to secure the connector to the tray and drill a couple holes in the side of the fuse aligned with the pins on the charge connector. This is great and nice and clean. However, carbon is conductive and if the pins on your charge cord make contact with carbon, it will short out, damaging the battery (FIRE), or damaging your charger. If your servo tray has provisions for this like the picture shown, it is best to either put the entire connector through the side of the fuselage or find a different location for your charge jack. Been there done that, have the burnt up fuselage to show for it.
Public service announcement complete. Back to your normally scheduled program.
DK
Awesome Dan! Gee, thanks for that tip. Actually, I think someone told me that somewhere before, but I guess I forgot about it. Thanks for participating and for great advice!
