Show me your baffles

Could folks post a few pictures of how you positioned the baffle material around the nose inlets? Should it be tucked up under the (topside) the inlet or is it intended to go below the inlet (which would seem to disrupt the airflow)?

crickets....

Mine sits on top of the inlet ramps.

Some baffle material is under/inside the fiberglass and lays on top of the Al ramps. Remainder of baffle material (prop side and cylinder head side) is riveted to the Al and lays up against the top cowl fiberglass. Sorry, I don't have photos. The key thing is to think about how the air would flow, and position the baffle material so that it channels airflow over the cylinders.

greg

Hi Bob,

here you have some pics:
http://websites.expercraft.com/PHVII/index.php?q=log_entry&log_id=16390
and
http://websites.expercraft.com/PHVII/index.php?q=log_entry&log_id=10496

We mounted a piece of baffle on the cowling which lays on top of the inlet decks.

all the best,

Clarification. I'm talking about how the baffle material interacts with the fiberglass inlets, not the AL inlet decks

Under the lower cowl nose inlets. Held in place by a few rivets (per plans) or screws & nuts (per my modification) through the cowl, through the baffle material, and through a piece of aluminum keeper.

greg

Bob,

Hopefully, you have a baffle kit manufactured within the past four years, There were major improvements to the material and drawings. Yet there are some places where improvement is required - like around the inlets.

The left and right ramps are depicted way too close to the lower cowl fiberglass inlets. First caution: the cross-ramp bend. It has a radical affect on where the front edge lies with respect to the fiberglass, so proceed carefully. That said, first problem. There is a cross-section view showing the seal strip clamped to the underside (and up the sides) of the lower inlet by a strip of aluminum. In this view the ramp top surface is shown in alignment with the bottom surface of the fiberglass inlet and line-to-line edge clearance - effectively scissoring the seal strip that bridges the gap. Installing the bottom cowl would be impossible. The cure is cutting back the forward edge of the ramp to clear the aft edge of the inlet 1/2 inch. This much clearance is also appropriate on the side baffle pieces and forward bulkhead (behind the spinner). Not to worry. The seal strips will not blow through this much gap.

Second problem: The elephant ears are curved on the sides, but too much so. You may need to heat and flatten them, then lay up additional glass, then trim the ears around the bulkhead to provide a better transition for the seal strips. The extent of this effort depends on where you installed the ears. These bulkhead seal strips are the most difficult of the seal strips to get right; patience my son.

John Siebold
Boise, ID

Finished installing yesterday with the exception of the nose inlet ramps. I fit them but have not riveted them yet. I'm going to attach them directly to the AL ramps rather than to the cowl, on the advice of a DAR. I think it will enhance the ability to get the bottom cowl on.



It's a tight fit in the front, but I'm also planning for an engine sag, which should make everything fine.

Next steps: Oil cooler door, fab P-lead and figure out a route, penetrate firewall for Lightspeed wires, figure out how to wire up the GRT EIS4000, final alternator wiring, prop install, spinner, engine start.

If anyone is in the South St. Paul, Minn., area and has experience, stop by on a Saturday morning and pick up a tool.

Bob, fixing them to the ramps instead of the inlets means that incoming air, slowing and gaining pressure, will try to force the rubber away from the bottom of the fiberglass inlets, creating a big leak. Conversely, if the rubber is attached per plans, the inrushing air tends to flatten the rubber against the aluminum ramps, the opposite effect. Something to thing about.

I didn't install

the lower ramp seals because it looked like cowl R&R would be a PITA. The inlet to ramp gap on my 9A measures between 1/4" and 3/8" and the aluminum ramp edge is just below the 'glass inlet.
No problems with oil and cyl head temps.

Lars said:

Bob, fixing them to the ramps instead of the inlets means that incoming air, slowing and gaining pressure, will try to force the rubber away from the bottom of the fiberglass inlets, creating a big leak.

Click to expand...

because of the rivet heads?

No.....

Installed as per plans, the incoming air presses the baffle seal against the ramp making a good seal.

Installed as your DAR has suggested means the incoming air can push the seal away from the underside of the fibreglass inlet, hence leaving a gap.

Steve

I wonder if anyone has ever tested this. On my installation, and with the planned attach method, there's an extremely tight pinch between the ramp and the fiberglass of the nose cowl to hold the rubber down. If the attach point is, say 1/2" aft of the edge of the aluminum ramp, I would think it almost impossible for the rubber to radius that sharply to create a gap. Maybe, though.

Here's a sketch of how I did mine. Pretty much per plans, with the rubber attached to the bottom of the cowl, sandwiched with a thin strip of aluminum. I used #6 countersunk screws to attach it. The top surface of the aluminum baffle ramp is flush (to the extent I could get it) with the bottom surface of the cowl inlet where the rubber attaches. Getting the cowl on with the 1/4" gap is a bit tight, but not enough to make me curse like a sailor, let alone throw things. I was pleasantly surprised at how well the rubber laid down on the baffle inlet when I was done.

How did you get the fit right? You can't hold the rubber/clamping strip in place while it's fitted, and then drilled.

Bob Collins said:

How did you get the fit right? You can't hold the rubber/clamping strip in place while it's fitted, and then drilled.

Click to expand...

Lars drawing is just about the ideal from my experience Bob, and while my fit isn't quite that good, it looks roughly the same. The thing is that you keep bending the baffles until they line up just slightly below the lower lip of the inlet, then just take the cowling off and rivet on the baffle seal.

I am somewhat paranoid about really good baffle seals all around - that is the only way we used to be able to keep the engine temps under control in the old Grumman single world. back then, we found that even minor leaks had a measurable affect on CHT and Oil temps.

The Valkyrie has pretty good seals, an no temperature issues. Mikey, Louise's RV-6, has NO seals in the front inlets, and we frequently have to pull back and/or push over due to high CHT's. Why don't we fix it? Because it is a pain to do the modification and we'd have to ground the airplane for a few days to get it done. Which means, if you want to do it right, do it NOW, before you start flying....you'll never find time to stop to fix "annoyances" once you're flying....

Paul

Why do it today? when you can always put it off until tomorrow!

Bob Collins said:

How did you get the fit right? You can't hold the rubber/clamping strip in place while it's fitted, and then drilled.

Click to expand...

I did pretty much what Paul described- I got the fit between the cowl and baffle ramp where I wanted it first. What follows might be called historical fiction I don't remember the precise details of how I did things, but this is pretty close.

The seal material is around 1/16" thick (don't quote me on that). I found a rectangular piece of aluminum about the same thickness in my (very large) scrap pile- I'd guess around 1" wide by, oh, 4" long. Laid that on the baffle ramp with cowl in place and attempted to slide it forward under the cowl lip. Continued messing with the baffle till the test strip just slid under the cowl everywhere I planned to have rubber.

With the cowl off, I cut the rubber to length, then made the aluminum reinforcement strip, then marked on the cowl where I wanted the holes. I have enough Pony spring clamps left from my Sikaflex canopy project to supply every hardware store in the area, so I used a few small ones to hold everything on while I drilled the holes. Knowing me I probably used a #40 drill at first, in case I needed to move a hole a teeny bit (unlikely here, but you never know). What I do remember clearly is that when I opened the holes up to fit the screws, I made the holes in the rubber substantially oversize so I could pull and tug on the rubber to get it "just right" before final tightening.

As for Paul's mention of potential heating issues due to leaks, that was my motivation for trying to get this right. I've read enough about heating issues that I figured I'd get my baffles well-sealed up front. Summer temps here routinely top 100? F, so I don't want to give away any performance.

Just another chime in on this - I did basically what Lars did (nice drawings, by the way!) and bent a piece of scrap aluminum around the bottom half of the cowl inlet. I also have a similar 1/4-inch gap and a tight fit, but find that when installing the cowl, I just fold the baffle material back over the inlet (over the top of the screw heads in the diagram) and that allows it to slide up past the ramp. Let go of the baffle material and it sits right down on the ramp.

cheers,
greg

OK, I ended up doing it your way.



By the way, all the drawings seem to show a 1" strip of .063 for a clamping strip. But the Van's kit provides only a 1/2" strip. Fortunately, I had plenty of .063 hanging around.

BTW, it took me 10 years and 2,502 hours to conclude that the worst -- the absolute worst, foulest smelling part of building an RV-7A is Pliobond.