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-   -   RV-3B Dave's in Colorado (https://vansairforce.net/community/showthread.php?t=85658)

David Paule 01-11-2023 06:56 PM

The seat cushions arrived, un-upholstered, from Oregon Aero for a test fitting. They need a fair bit of rework, so it was good to have them to assess what’s next. They are now back at Oregon Aero. If you’re considering custom seats, consider adding two or three iterations of shipping to the estimate.

Continued tweaking the cowl, and like many of you, it’s a frustrating experience for me.

Then I had a bit of inspiration - since I was taking the cowl on and off so much anyway, why not use those cycles to trim the baffles? Turns out that although the baffles are a welcome change from the fiberglass, they are mutually incompatible. - if the baffles don’t fit the cowl won’t, and then there’s no cowl work to be done. I started by omitting the forward half of the baffles because they won’t go on without trimming. The back ones will since they only contact the upper cowl.



After some trimming (and over-trimming the RH aft piece, replacement part on order) I was ready to try the paperclip trick. Here are some paperclips after a couple of cycles of measuring and adjusting. I learned some things about this.

1. I didn’t know if a standard paperclip would work so I got large. This proved a reasonable idea.

2. As you can see, I am doing this with the blue vinyl on. This gives a somewhat slipper surface for the paperclips to grab, and I had to slightly bend each paperclip to increase the grabbing force. Paperclips might work better on bare aluminum.

3. The paperclips tend to bend over sideways. Measure from the apparent surface of the cowl to the baffle. Instead of measuring in a vertical direction, the measurement is perpendicular to the baffle contour line.

Since I was afraid of over-trimming other pieces, I took it slowly. Slowly, in this context means lots more reps of measuring, trimming, reinstalling paperclips, fitting the top cowl, repeat.



For me, trimming was either with snips or the bandsaw. For most cuts, the bandsaw was much easier. For short fairly straight cuts, and there weren’t many of those, snips worked perfectly fine. If your snips cut .032 aluminum like paper, hey, go for it. For mine, .032 is close to the limit.

So far, I haven't the slightest idea where I'm going to mount my non-standard oil cooler, except that I'm hoping to put it forward of the firewall.

Dave

David Paule 01-20-2023 01:33 PM

I somewhat over-trimmed the aft right baffle and had to order a new one. It came with none of the blue vinyl, just bare aluminum. I trimmed that one and finished trimming the sides. Still havenít started the front pieces. Heres the bare naked replacement baffle in place.



In the middle of the trimming. Still using the paperclips.



Since this is an RV-3B and has the cowling cheeks, the side baffles get narrower than for the side by side models. The side baffles have a joggle at the top where the aft side nestles into the front side. In my case, I trimmed them off, and then used some magnets to hold the front and back sides together. The orange magnets are merely tooling here.



My Vetterman exhaust system uses a horizontal cross bar to stabilize the four pipes. I have it in place here, temporarily. The fixtures to something above that keep the assembly from falling down are not yet installed.



These are here to align the exhaust so that I can build the glass fairings on the bottom of the cowl for them.

While I was doing all that, I was thinking about how Iíd actually make the fiberglass fairing where the exhaust protrudes through the back end of the cowl, one of the many things I needed to figure out for this airplane. I looked through my handy collection of photos and saw numerous shape variations, and my mentor recommended the absence of a fairing - which has itís attractions. Ultimately I cut some pink foam into strips as a starting point. Here are the foam strips.



Dave

scsmith 01-20-2023 06:35 PM

Quote:

Originally Posted by David Paule (Post 1659440)

So far, I haven't the slightest idea where I'm going to mount my non-standard oil cooler, except that I'm hoping to put it forward of the firewall.

Dave

Now that right there is funny enough that I just sprayed wine all over my monitor!

My recommendation is to mount the cooler perpendicular to the firewall somewhere, and make a fiberglass transition piece that turns the flow 90į and transitions from 3" SCAT in your case to the cooler.

Other than for access to other stuff, you don't need hardly any additional room from the back of the engine to the cooler, it could squeeze in just about anywhere.

scsmith 01-20-2023 06:40 PM

Quote:

Originally Posted by David Paule (Post 1661471)

While I was doing all that, I was thinking about how Iíd actually make the fiberglass fairing where the exhaust protrudes through the back end of the cowl, one of the many things I needed to figure out for this airplane. I looked through my handy collection of photos and saw numerous shape variations, and my mentor recommended the absence of a fairing - which has itís attractions. Ultimately I cut some pink foam into strips as a starting point. Here are the foam strips.



Dave

Start out by cutting clearance slots about 3/4" or 1" in your lower cowl around your pipes, so they can exit where you want them. Then, wrap your pipes with 1/2"--5/8" of stuff, (foam, cardboard, whatever will wrap around it and give you a surface. Then, cover that wrapping with packing tape and lay up a couple of plies of glass cloth on that. This will give you the foundation to build more plies of glass and including nice radii in the intersection between the normal cowl contour and the pipe wrap areas.

We use a higher temperature epoxy for the cowl areas like that which live close to the pipes. We use PTM&W 2080. I can probably send you a pint or so. It needs a post-cure up to 150F to get the higher T_g and good toughness, so you need some way to get it warm after you do the layups and initial cure.

David Paule 01-20-2023 08:11 PM

Steve, thanks for the comments. I'll certainly remember what you suggested for the oil cooler.

The cowl was already cut out to allow for the pipes - had to do that to get the lower cowl on with them in place. I've started gluing the foam strips on; once I've shaped them and laid up some glass, they'll get removed and the glass glued on. I'll have some photos in my next post. The only 5 minute epoxy I had handy was from the local hardware store, it worked and that's about all I'll say for it; I won't buy that product again. Except for the hassle of removing it later, it's adequate.

Thanks for the epoxy offer - I don't actually need much of the stuff very often. This was the first time I've even used 5-minute epoxy in ages. I had some that was only 30 or 40 years old, stored in the basement, and gave that a try. You can guess how well it cured. It's now gone.

Dave

David Paule 01-23-2023 01:05 PM

I used 5-minute epoxy to glue those foam strips over the exhaust pipes on the lower cowling. The glue was foam to cowl, not to the exhaust, of course.



With the lower cowl off, it was time to play with the #1 cylinder forward baffle. This is the one with the oil line to the governor. The constant speed prop I intend to get for this airplane is causing a lot of hassle, sure would have been simpler to plan on fixed pitch. Wirejock sent me a photo of the slot in his to allow for the oil line and I decided to do something roughly similar. His slot was from the aft side to the access hole. Mine was from the inboard edge to the access hole. You can see the support bracket almost hidden underneath.



In place without that bracket. Eventually I'll use #6 screws there, same screws as for the seat pan.



Not shown, I need to make a removable cover to block the slot I just made after installation. Wirejock avoided that; his is a more straightforward approach. Mine is easier to install.

Oregon Aero sent the seat cushions back to me for another trial fit. Looks like one more round. This is very much an iterative process, at least for this seat. Granted, my seat isn’t quite stock:

a. The seat bottom is flat instead of recessed.

b. The bottom of the seat back is slightly forward of the stock position since I have short legs and like to slouch.

c. And finally, this airplane has a decidedly non-typical crotch strap mount.

Since the plane has a manual flap handle on the left, the seat cushion has to allow for that. I’m not going to include photos showing the current mis-fit situation since I don’t want to give you the wrong impression. It’s fairly close, all but a few details.

With the seat temporarily in place, I needed to check the head to canopy clearance, so I brought the canopy home from the hangar. Here's what it looks like right now. Sure would be good to have enough more space to put the tail on. And the wings, too, as long as I'm dreaming.



Dave

rockitdoc 01-25-2023 03:36 PM

One Wing at a Time?
 
Maybe one at a time?

David Paule 01-25-2023 05:01 PM

Can't line them up for sweep that way.

Dave

rockitdoc 01-25-2023 05:03 PM

Quote:

Originally Posted by David Paule (Post 1662695)
Can't line them up for sweep that way.

Dave

My issue, also.

David Paule 02-13-2023 05:23 PM

After sanding down the exhaust fairing foam, I taped it using packing tape so the fairing itself would release. The tape was placed in a way that bridged some of the poorly-sanded areas.



Then I laid up the three layers of glass and, just to make sure they wouldnít fall off since I was working upside down, taped them in place. Duct tape releases too, on both sticky and smooth sides.



Here they are on the cowl, with the cowl on the bench, before trimming.



This shows the contour from the aft side. The cowl has not been trimmed yet.



I replaced the cowl on the plane and held the fairings in place. Turns out that there is insufficient gap between the fairings and the exhaust. Okay. That was all a good exercise and demonstrated a satisfactory approach to making the fairings. Now to go add some clearance and re-do them.

Dave


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