Step 1: Preparing and fitting the top cowl
The top half of the cowl gets fitted first. The first thing to do is hot-glue a couple of 3/16" spacers to the front of the cowl. These will position the cowl the appropriate distance back from the spinner. (SJ instructions say 1/4". 3/16" puts you closer but also gives you some wiggle room when fitting.)
Next you need draw a line on the forward top skin of the fuse. The line should be 3" back from the front edge. This line is a reference and will aid you in marking the trim line on the cowl. (SJ instructions have you making a little tool to do this.)
You will need some way to support the front of the cowl to hold it at the correct height. SJ instructions indicate to glue a couple strips of aluminum to top of cowl. I just used a small block of wood taped to the top of the prop extension that the cowl rested on. Either method works.
Position the cowl over the engine. Adjust the cowl at the front to get the approprirate fore/aft position using the spacers glued to face of cowl. Also position it left/right so it is centered with the spinner bulkhead. Finally position it vertically. If you have the bare spinner back plate, keep in mind that thickness of the actual spinner.
With the cowl now positioned, use the reference line to measure forward 3" and make a mark on the cowl. Do this every 3 to 4 inches. When done, connect the lines. This line will serve as your trim line. (Alternately, you can put a bright light under the cowl which will easily illuminate the edge of the skin.) Be careful when making the lines to not shift the cowl. You should either clamp it along the sides or drill a couple holes through the cowl and use cleco's to hold it in place.
(My time: 1.5 hours)
Remove the top cowl from the fuse and using a cut-off wheel, cut the excess off the aft edge of the cowl. Say 1/16"-1/8" from the line. After cutting the excess, use a long straight sanding block to sand up to the line.
You'll need to install the hinge material along the top edge of the firewall to support the cowl. You can do this permanently if your top skin is already riveted on or temporarily with cleco's. If you're installing permenantly, use some Proseal or some sort of fire retardent goop between the skin and firewall flange to prevent any nasties from entering the cockpit. You may need to include a shim between the hinge and the firewall to get the thickness to match that of the cowl.
Using Van's plans, a short piece of hinge goes on the right side of the upper firewall, then a 3 1/8" space, then a longer piece running the rest of the way across the top and down the left side. The gap allows you to put in/pull out the hinge pins. The gap is on the right side near the oil door for easier access. The hinge material along the top is the 20257-4. (You might also want to cleco a couple of short pieces of aluminum along the vertical sides of the firewall near the top to help hold the sides of the top cowl out.)
Update: The Van's design for the hinge setup makes it a bit of a challenge to get the hinge pins in and out. A new builder trick is to put two pieces of hinge along the firewall with a small 2-3" gap in the top center. A small cutout in the cowl and a plastic block mounted to capture the hinge pins makes it MUCH easier to insert the pins from the outside of the cowl instead of through the oil door. If I can find a picture, I'll post one but seriously consider this option.
With the hinge in place, position the cowl back on the fuse. Continue to make adjustments to the fit by sanding the aft edge until you get a uniform edge. Remember to leave _at least_ a 1/32" space between cowl and skin for a paint gap, otherwise your cowl will rub and crack the paint.
(My time: 2.5 hours)
Next you need draw a line on the forward top skin of the fuse. The line should be 3" back from the front edge. This line is a reference and will aid you in marking the trim line on the cowl. (SJ instructions have you making a little tool to do this.)
You will need some way to support the front of the cowl to hold it at the correct height. SJ instructions indicate to glue a couple strips of aluminum to top of cowl. I just used a small block of wood taped to the top of the prop extension that the cowl rested on. Either method works.
Position the cowl over the engine. Adjust the cowl at the front to get the approprirate fore/aft position using the spacers glued to face of cowl. Also position it left/right so it is centered with the spinner bulkhead. Finally position it vertically. If you have the bare spinner back plate, keep in mind that thickness of the actual spinner.
With the cowl now positioned, use the reference line to measure forward 3" and make a mark on the cowl. Do this every 3 to 4 inches. When done, connect the lines. This line will serve as your trim line. (Alternately, you can put a bright light under the cowl which will easily illuminate the edge of the skin.) Be careful when making the lines to not shift the cowl. You should either clamp it along the sides or drill a couple holes through the cowl and use cleco's to hold it in place.
(My time: 1.5 hours)
Remove the top cowl from the fuse and using a cut-off wheel, cut the excess off the aft edge of the cowl. Say 1/16"-1/8" from the line. After cutting the excess, use a long straight sanding block to sand up to the line.
You'll need to install the hinge material along the top edge of the firewall to support the cowl. You can do this permanently if your top skin is already riveted on or temporarily with cleco's. If you're installing permenantly, use some Proseal or some sort of fire retardent goop between the skin and firewall flange to prevent any nasties from entering the cockpit. You may need to include a shim between the hinge and the firewall to get the thickness to match that of the cowl.
Using Van's plans, a short piece of hinge goes on the right side of the upper firewall, then a 3 1/8" space, then a longer piece running the rest of the way across the top and down the left side. The gap allows you to put in/pull out the hinge pins. The gap is on the right side near the oil door for easier access. The hinge material along the top is the 20257-4. (You might also want to cleco a couple of short pieces of aluminum along the vertical sides of the firewall near the top to help hold the sides of the top cowl out.)
Update: The Van's design for the hinge setup makes it a bit of a challenge to get the hinge pins in and out. A new builder trick is to put two pieces of hinge along the firewall with a small 2-3" gap in the top center. A small cutout in the cowl and a plastic block mounted to capture the hinge pins makes it MUCH easier to insert the pins from the outside of the cowl instead of through the oil door. If I can find a picture, I'll post one but seriously consider this option.
With the hinge in place, position the cowl back on the fuse. Continue to make adjustments to the fit by sanding the aft edge until you get a uniform edge. Remember to leave _at least_ a 1/32" space between cowl and skin for a paint gap, otherwise your cowl will rub and crack the paint.
(My time: 2.5 hours)
posted by Matthew
2 Comments:
I'm stealing your idea that you used to position your front bulkhead. I.e the 3/4 in pvc tubes.
I don't have my prop extension and am hoping to avoid it if I can. I have a C/S prop so its only 2" I have to shorten it by. Any I bought two 1/2" by 5.5 long bolts to postion the spinner on 3/4" tube cut to length on the table saw using the James dimensioned drawing...The other 4 bolts are simply 6" long 1/4" carriage bolts. I hope to compare the clearance around the engine both with and without the 2" extension. The only gotcha I see is I will have to cut a deeper slot for the nose gear, but that is easy to patch if I end up going with the prop extension. I think the intake air trumpet (FF sump) can be shortened with a small design change.
By
Frank, at November 14, 2005 6:00 PM
Hmm...after playing with it last night looks like the standard induction tube set up will not work no way without lopping off about 3"...which won't work. The only alternative is to use a different intake system which Might work...But that is $650. Certainly the prop extension is cheaper and will work for sure.
By
Frank, at November 15, 2005 3:39 PM
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