Making the scoop-to-FAB 'plug'

LettersFromFlyoverCountry · #1 07-26-2011, 05:45 PM

Does anyone know of any Web site or well-written narrative that describes the process of using the foam block to make the "plug" that mates the front air scoop to the filtered air box (FAB) on a vertical induction engine (in this case an IO-360)?

The instructions to me -- as well as the drawings -- in the FAB kit are gibberish:

The cowl air scoop intake lip must be filed or sanded down to avoid decreasing the intake area when the fiberglass is laid. Taper the amount of material removed, very little at the front of the lip and most of the fiberglass at the rear. Shape the foam block (VA-130-1) to wedge tightly into the cowling behind the air scoop....etc. etc. etc.

Huh? Then it goes into taping (or some other adhesive) the foam block in place, cutting it somehow, even blowing up a flippin' balloon. Help!

If you know of any site, images, narrative etc., please post a link or two here.

thinkn9a · #2 07-26-2011, 07:07 PM

Bob,

I do not recollect all the details, and certainly don't have pictures. But thought I would try and walk through what I did.

To start with,... you are trying to get a "tube" from the front edge of the cowl,.... to CLOSE but not AT the FAB. While you are getting the tube, you don't want to lose any of that good RAM air that RVs are known for,.. so you don't want to restrict the "tube".

My approach was to:
- first take "initial alignment" from the front of the cowl opening to the FAB,... in my case it was a little off centerline and I had to make a little drift, rather than run straight back. All this really was a look in the front and visualize where the FAB sits in relation to the cowl. Don't sweat being absolutely perfect,.. unless you are absolutely a perfectionist.... for me it was a very short run,.. so I couldn't screw it up too much.
- second jam the foam block on the cowl snorkle to "cut an imprint" of the cowl opening in the foam,..... so then you know the MINIMUM size of the opening you must make,... really need to make it larger,. but this will get you started,.... so .. you can start hollowing out the block. (out in your hands,.. prior to getting it "installed" and it is harder to work and visualize) think little drills, big drills, chisels,.. etc..Remember this is the mold that will define the inside (and outside) of your inlet tube,.. so you don't want lumps and bumps (you may want to mark the back side of the block with the FAB opening... so you know what you are transitioning to.)
- set the block in place - easier said than done,... recommend look for helpful notes from others, I ended up using some epoxy to hold the block in place. good news.. I could move the cowl around and work on the block (file and sand) without a problem bad news... I have some "extra epoxy" inside,.. not visible until cowl removed...
- finish sizing the block - and make sure it does not "narrow down" the "tube from outside to FAB",.. meanwhile providing a "smooth transition" from the snorkle to the tube that will be created...... that is,.. open the block a little more... to allow a few plies of fiberglass to build up inside the foam block,.. when you create the tube. I used a rat-tail file working from the front of the cowl and filing the inside of the block.
- set the fiberglass - I'd recommend some "bi-ax",.. it shapes much easier than plain weave. I stood the cowling on firewall end so the work was "down-hand" and the "tube" was hanging down,... thinking that the tube would have less tendency to collapse than if it was sitting horizontal. Don't sweat the length,... just make sure you have enough "good length" of good glass.... so you can trim back as necessary for the standoff between the "tube" and the "fab". some of the big tongue depressors work well for reaching in and working
- knock off the block,.. and "clean up the tube" inside with final sand/file/filler coat,.. trim,..

good luck,... I had some problems sorting through it... but once I got started in fell in ok,...

p.s. thought you had exceeded the standard time for a good answer on the forum,... so felt I needed to at least give you something,....

flion · #3 07-26-2011, 07:24 PM

My pictures are horrible (http://www.mykitlog.com/users/displa...g=87678&row=15) but it was really easy. The first couple of sentences are referring to preparing the scoop opening for putting in your fiberglass. If you just lay glass in there, you will reduce the size of the opening. Sand/file the opening so the glass tapers to thin at the back of the opening. This way, your layups will build it back to the original size of the opening. Don't remove much at the front of the scoop opening.

I mixed up some epoxy and lots of microballons to make a light paste and used 3 dabs of it to glue the foam block behind the cowl scoop opening. Then I fit the cowling to the fuselage (it took a bit of trimming to fit the block to the FAB (a slight gap is Ok). Then I used a 1" bit to drill a hole through the into the FAB (don't have the filter in for this). Next I used a rasp and a round file to cut the foam away, enlarging the hole so it matched the scoop at the front and the FAB at the back. You won't overdo it, the FAB and scoop limit you and are harder than the foam. Also, by the way, it's a good idea to plug the intake while you are doing this.

Once you've got the foam pretty well shaped, remove the cowl. You don't need to worry too much about the smoothness of the foam unless you are finishing the inside of your cowl. With the cowl off, lay up a couple of BID inside the hole you just carved, smoothing it around the scoop opening. After they initial cure, lay up a final layer with peel ply to give you a good finish inside the opening. I had about 3 inches excess aft of the foam block that took no particular shape. I also let the front extend over the front of the scoop and then back on the outside about an inch, it being easier to smooth the transition on the outside of the scoop rather than inside the opening.

Once the peel layer had cured, I cut the layup off even with the foam block and then removed the foam and as much of the dabs of micro paste as I could. Then I put the cowling back (you may need to trim the layup a bit more to avoid interference with the FAB) and marked forward from the FAB where I needed to trim the layup. Don't make it too close or you won't be able to work the baffle material when trying to install the cowl. Remove the cowl, trim the layup, install the baffle material on the FAB, and test fit the cowl, trimming more if necessary.

Steve · #4 07-26-2011, 07:40 PM

1. The whole point is to build an extension tunnel from the back edge of the scoop to within approx 3/8" of the front opening of the FAB.
2. Install the lower cowl. Measure the distance from the scoop rear edge to the FAB fron edge. It should be greater (3/8-1/2") than the thickness of the styrofoam brick.
3. Remove lower cowl. Shape the outside periphery of the brick so it slides against the back edge of the cowl scoop. I buttered the outside of the brick with bondo and reinstalled it into the cowl.
4. After the bondo dries, reinstall the lower cowl. I used a vacuum cleaner with it's metal extension wand to scrape and "liposuction" a tunnel thru the brick to the FAB. Use coarse emery wrapped around your finger for final shaping. Note, the FAB is offset to one side and lower than the scoop. Your's may be different.
5. Now for the balloon. Remove the cowl. The plan is to layup a few layers of cloth inside the foam tunnel and hold them in place with the inflated balloon while the West System epoxy cures. I used wetted strips of cloth approx 4-6" long x 2-3" wide. This will get messy. The wet sticky balloon will want to squeege thru the tunnel. The strips of cloth will move the other way. Work slowly and carefully. Test the balloon beforehand. "Long" balloons work better than spherical ones.
6. Remove the balloon after the epoxy cures. Trim off all the excess cloth. Chip out the remains of the foam brick. Sand and fill and sand and fill and sand to make a smooth inlet. I also wrapped a layer of cloth around the outside of the butt joint after I removed the last of the foam brick.

Ref Van's drawings for actual distances mentioned above. Your local craft store has replacement foam blocks in the dried flowers aisle.

LettersFromFlyoverCountry · #5 07-26-2011, 08:25 PM

Oh man, these are so helpful. thanks, guys. I'm measuring about a 2 1/2" distance between the front of the scoop and the FAB to about 2 5/8"... so I'm a little off center.

N15JB · #6 07-26-2011, 08:35 PM

All of the above are good suggestions, but as with Van's instructions, they have you carving a hole through the center of the foam, trying to get it contoured and allow for the thickness of your layup. I found it much easier to reverse the process. I started with a cylinder of foam a little larger than the air intake, which I jammed into the intake from the rear. Shape one end to match the contour of the intake, and the other end to match the fab contour. It is easier to smooth the cylinder than a hole. Do your layup on the exterior of the cylinder, and you are done.

Jim Berry
RV-10

Zero4Zulu · #7 07-26-2011, 08:42 PM

This is how I did mine. This was a repair/rebuild but it has the same result you need, Bob. I made a foam plug that fit through the opening of the snorkel. I first made a little cardboard template to transfer the shape of the opening to the end of a piece of foam about 5" long. (I had to laminate two pieces of foam together to make it thick enough to make the shaped plug). It was long enough to protrude out the front and back as far as needed. I band sawed the shape oversize then used another chunk of foam like a sanding block to shape the plug to size. Just rub the plug with another piece of foam to wear it down to the final shape and size. Then wrapped a layer of clear packaging tape around the foam plug and shoved it in the snorkel opening. Line it up straight and secure it with tape on the front outside of the cowl. Then I used about five layers of fiberglass cloth to build the tunnel. I used shorts pieces about two to three inches wide and tucked them around the plug. shorter pieces overlapping where easier to handle because it is kind of a reach getting in there. I used a paint stick to tamp and poke things around. Once it harden overnight, I carved the inside of the plug out to remove it and was very surprised how well it worked. I added some resin and flox to the inside fillet to strengthen it some and a little micro on the outside to patch it up a bit. I was quite pleased with the result...

I hope this is clearly written.

Steve

OneCharlieKilo · #8 07-27-2011, 12:00 AM

Bob,
Lots of good descriptions in the replies so I won't add more to that but pictures of what I did are at:

http://rv6aproject.ckhand.com/Firewa...airbox_pg3.htm

Before putting wetted cloth in place:

Balloon holding curing fiberglass in place:

LettersFromFlyoverCountry · #9 07-27-2011, 06:27 AM

Awesome pictures, Chris. The instructions talk about sanding the cowl inlet and tapering it. I don't see any mention in these about doing that. Can someone explain what, if anything, I should be doing to the inlet itself in this process?

flion · #10 07-27-2011, 07:29 AM

Bob, reread my description and you'll see that I talk about it. You want to sand the inlet to prepare it for the layup. As you do, take more material from the back of the inlet than the front, so that the fiberglass thickness tapers and you don't decrease the size of the opening with your layups.

Also, I didn't need to use the balloon; like someone else mentioned, I set the cowling on it's firewall end and used short pieces of glass so it stayed put as it set up. I'm not a big fan of the male plug idea because you have to make sure the aft end lines up with the FAB somehow, but if it works for you then fine. Also, it is normal and correct for the FAB to be offset a bit; if you followed the instructions you will have 'clocked' the FAB to line up roughly with the opening and the purpose of this layup is to match any remaining offset.