Firewall Soundproofing

Time: 2 hrs

Things done today:

  • Installed soundproofing on interior side of firewall
  • Working on trying to fix lumps in rear fuselage skin near parachute box opening
  • Made extra spacer for luggage door area

I didn’t have much luck with fixing the little bit of lumpiness on the top of the rear fuselage near the parachute box. I drilled out a few of the rivets and trying to rework the area. It’s minimally better, but not much of an improvement. The good news is that once the skin that covers the hole for the parachute goes on you’ll never see it. So while I know it’s there at least cosmetically it will look OK.

A suggestion from Jean (Torrance TAF) was to install soundproofing on the interior side of the firewall. He had mentioned that he did this on the prototype and was very happy with the way it reduced the amount of engine noise in the cockpit. He wasn’t really concerned about heat he said that the firewall really doesn’t get very hot.

The job went much easier then expected since I had already installed a few items on the firewall I thought it would be much more difficult. I did one full sheet of material on the top part above the bracing and then I separated the bottom section into to pieces. On the bottom section I started by sticking the long edge of the material under the brace and then worked my way down by peeling the backing off the material. I used new, sharp exact blade to cut around the heater box and the console sides. The grommet holes were made form the other side of the firewall with a long razor blade. They came out OK, not as perfectly round as I’d like, but still not too bad.


I made an extra spacer for the short section on the right side of the luggage door. The spacer installs between the skin and a channel piece that fits above the luggage door. I had noticed that the skin was getting pulled in a bit too much on those two rivets that hold in this section. The gap between the skin and the channel piece is about 1/8″ and the spacer provided is only about 1/16″. I had some scrap material that got me pretty close to 1/8″.


Search for things to do

Time: 2 hr

Did some random stuff on the plane in an attempt to keep busy while I wait for my parts.

Things done today:

  • Ran wiring for AP servos
  • Drilled out two holes for battery reinforcing bracket
  • Notched top of battery reinforcing bracket
  • Riveted battery reinforcing bracket to firewall
  • Installed a few rivnuts in firewall
  • Riveted top front rib
  • Put a few rivets in the seat rails
  • Installed M3 screws into throttle assembly
  • Installed edge grommet on rear bottom seat section


I did a rough run  of the wires to the roll and pitch servos (which I don’t have yet… Hey Christmas is coming so I can hope). I will daisy chain the power, ground, AP disconnect, and CAN bus from the roll servo over to the pitch servo. The roll servo also gets an extra 22-2 for RS-232 to the GMA307 AP Controller. The pitch servo will eventually have an additional (2) 22-2 runs for the pitch trim motor. The pitch servo is also the end of the CAN bus so will have to jumper some pins on the connector when I wire that up. I also need to install some adel clamps or the like to keep the cables in place.


I figured it was safe to install the battery reinforcing bracket. There were two holes that got covered by the top firewall reinforcing channel so I needed to drill those out. Also the bracket overlap the top bracket (grey bracket in photo) so I made a small notch in the battery bracket so it sits flat on the firewall.

I also received the M3 socket cap screws from BoltDepot today so I loosely installed those for the throttle stops in where I think they need to go. I added some heat shrink on the screws just so the throttle lever wasn’t hitting the threads of the screw. It took some experimenting, but what I ended up doing was to cut a piece of heat shrink and put it on the smooth end of a 7/64″ drill bit then heated it to lately shrink to that size. I then removed the heat shrink from the bit and slid it over the screw threads when installing the screw. I probably could have just shrank it right on the screw after it was inserted, but I was worried that for one the heat gun would bubble the primer and two the heat shrink would stick to the screw making it very difficult to remove the screw if I needed.


Installed some edge grommet to the seat belt holes in the rear seat bottom section. The paint came out pretty good too… not too bad for a table in the back yard with a can of rustoleum from HD.

Firewall and control sticks

Time: 4 hrs

Things done today:

  • Fit firewall blanket
  • Cut out holes for a few parts in firewall blanket. I don’t have the firewall forward kit so I’m not really sure what needs to go where or how big to cut out the spaces.
  • Riveted bracing channels (FF-CHL-001 Left & Right) to firewall
  • Riveted bottom angel to firewall
  • Loosely mounted engine mount to firewall
  • Installed rudder boots to firewall
  • Installed control stick brackets. Which needed to be primed again.

Some photos of the firewall and heat blanket. The engine mount was a real pain to mount… I really don’t want to have to take it off. I didn’t tighten up any of the bolts just incase I do though. I also tried to mark out holes that I think I need (from looking at other builders logs) just to try to understand where things go. The heat blanket material isn’t very easy to work with. There is a mylar layer that its somewhat tough to cut and they it can tear easy. The adhesive is pretty sticky, but seems to not stick to the foam when you peel off the backing. Maybe mine is just old or got hot too many times sitting in the warehouse. The large portion of the heat blanket isn’t instal yet. I have quite a few more things that need to be cut out and I don’t have the parts yet so I’ll have to wait to finish that you before sticking onto the firewall.

Photos of the rudder boots. I used a little glue to stick it to the bracket so it would stay. You can arrange it so that the flanges on the leather boot fit on the bracket so that the space between them doesn’t interfere with the rivet holes, though you still may need to ream it out just to clean out any leather in the way. I also trimmed back the leather so it didn’t go past the edge of the bracket just to make it look nicer. I riveted from the other side of the firewall so that the heat blanket sits flat.


Just found this while looking through the Sling 2 Build Manual. So it looks like I need to remove a few washers and change one set to thin washers plus I need to put the bolts inside and nuts on the engine mount side (EDIT: bolts alway point down or aft so the head should stay on the engine side of the firewall) . So glad I found this… I was close, but good to know this is the correct way to put it together.


Engine Mount with Parachute (PDF)

Also found where these other firewall pieces go (the cowling mounting strips). They need to go on prior to putting on the front fuselage skin.

firewall-mounting-stripsFirewall Mounting Strips (PDF)


Miscellaneous work

Time: 4 hrs

Things done today:

  • Prepped more of the front fuselage inside skins
  • Prepped some of the firewall parts I have
  • Reamed the holes on the “Upright Joining Channel (CHL-008 Left & Right) from 4mm to 4.8mm to match the holes on the “Front Seat Belt Bracket” (BKT-019 Left & Right)
  • Worked on fixing the tight fitting control stick tubes



I had tried a few things to make the control stick tubes move a little more freely. I tried to bend the bracket that mounts them to the main spar to be more in line with the way the tube sites (there’s a slight angle to it). I had already made sure that the brackets weren’t gripping the vesconite bushings too tight on the tube. Also tried to file the parts on the control tube itself that touch the vesconite bushings. The only thing I found that really helped was to elongate the holes in the brackets that the 4 M4 screws mount to. They are already belonged to be adjustable, so I just added about 1/8-3/16″ to them. The control sticks are still a little tight but getting better. I’ll work on it more tomorrow.



Rear fuselage and firewall

Time: 3.75 hrs

Things done today:

  • Test fit rear side skins to tail cone
  • Reamed out a few holes from 3.2mm to 4mm on SKN-005 right
  • Prepped more rear fuselage skins
  • Fit AN5 bolts to firewall
  • Riveted the “Firewall Mounting Channel” (CHL-021) to the firewall



These are the “Rear Side Skins” (RF-SKN-005 Left & Right). You can see some of the holes on the right skin are a bit different then the left. The ones on the right skin are 3.2mm while the ones on the left skin are 4mm. Also the holes on both the left and right of the flanges on rib8 needed to be ream to 4mm as well. After a bit of pulling and stretching the skins fit OK. All the holes seems dot line up, just these few holes needed to be reamed to 4mm.


Loosely fit the AN5 bolts through the firewall. The manual doesn’t say what bolts to use exactly. It looks like the 5AN-10A on the right and 5AN-7A seem to work for the upper mount point. I used the longer bolt on the right because there’s still the engine mount and reinforcing bracket it needs to go through.


Front side of the same bolts. Any yes I realized that I was missing a part here. The “Firewall Forward Plate” (FF-PLT-001) needs to be riveted where those 6 rivets around the  right bolt is. I later removed those rivets and added in the plate. I’ll upload a new photo soon.


Here’s the bottom bolt. This is a 5AN-6A.


All bolts view. The engine amount is not attached it would mount to the bits in the channel.