Trim inlet ducts or baffle sides?

[alpinelakespilot2000]

I'm trying to figure out how/where to locate my inlet ducts on my top cowl. (Baffles are all trimmed down except for the front side corners.)

1. Do I just locate the untrimmed inlet ducts fore/aft and side-side where they seem to best fit the contour of the top cowl?

2. Do I trim the inlet ducts to fit the front side baffles or do I trim the front side baffle to fit the inlet ducts? Or does it not matter?

Any help would be much appreciated. Thanks.

[Brantel]

Here is what I did:

1. Locate them where they fit the nicest....

2. Trim the baffle sides to fit the inlet ramps.....

It is an on off on off on off on off deal but take a little at a time and eventually you will get them carved down.

[alpinelakespilot2000]

Thanks Brian. I did as you suggested and it's looking pretty good. It's just hard to visualize all this until you do it. I think I'm seeing that the baffle fabric will cover a large number of sins, which is a good thing!

[Noah]

Anybody else got an opinion on this?

Seems like trimming down the baffle sidewalls (and baffle bulkhead aft of the prop) to fit the fiberglass inlet ducts might make life more difficult? The baffle seal fabric would need to transition from sealing against the top of the cowl to sealing against the ramp - and the transition wouldn't be smooth. I would think this would be harder to get to seal well, and the fabric shape might be more complicated than if you trimmed the fiberglass to be well clear of the baffles?

Anybody got some pix of this?

[Rick6a]

Originally Posted by Noah

Anybody else got an opinion on this?

Seems like trimming down the baffle sidewalls (and baffle bulkhead aft of the prop) to fit the fiberglass inlet ducts might make life more difficult? The baffle seal fabric would need to transition from sealing against the top of the cowl to sealing against the ramp - and the transition wouldn't be smooth. I would think this would be harder to get to seal well, and the fabric shape might be more complicated than if you trimmed the fiberglass to be well clear of the baffles?

Anybody got some pix of this?

Noah,

Having done it BOTH ways, my thoughts are these. A good seal is possible no matter how you do it. In fact, my -6A (on the left) with it's (one piece) rubber seal tends to run cool. This suggests to me that sealing is not much of a problem. Certainly, faced with a choice during construction, it is a bit easier to install the baffle seal by trimming the forward baffle with a distinctive swoop as illustrated on the right. In my case, that rubber seal had to be installed in sections to achieve a good tight seal. All in all, I personally think the untrimmed baffle just plain looks better. I'm sure others may feel quite differently. Do it the way you want. This construction detail is just one more in the long line of decisions we make as builders.

[Steve]

I maintained the approx 7/16 (or finger width) distance between the top edge of the baffles and the inside of the cowl and ramps all the way around the engine.

[Noah]

Originally Posted by Rick6a

Noah,

Having done it BOTH ways, my thoughts are these. A good seal is possible no matter how you do it. In fact, my -6A (on the left) with it's (one piece) rubber seal tends to run cool. This suggests to me that sealing is not much of a problem. Certainly, faced with a choice during construction, it is a bit easier to install the baffle seal by trimming the forward baffle with a distinctive swoop as illustrated on the right. In my case, that rubber seal had to be installed in sections to achieve a good tight seal. All in all, I personally think the untrimmed baffle just plain looks better. I'm sure others may feel quite differently. Do it the way you want. This construction detail is just one more in the long line of decisions we make as builders.

Rick, you are the voice of experience! It is great to find somebody who has done something both ways, who can give the honest pros and cons for each option.

I am still a little confused. In the left photo, are you saying that the seal material is sealing against the inlet duct (ramp) surface, rather than the cowl? What is the clearance athwartship (lateral) between the baffle side and the inlet duct (ramp)? Originally I thought that if you trimmed the glass instead of the baffle (as shown in the left photo), you would have a slit in the baffle seal where the upper duct (ramp) is bonded to the cowl - and that the seal material would go UNDERNEATH the duct (ramp) and still seal on the cowl, not the duct (ramp). This does not seem to be what is happening in this photo. It seems like maybe what is happening is that the seal material goes straight up, hits the cowl, and turns 180 and comes straight down. As such, you would need a generous gap between the baffle sidewall and the ramp, no?

Question 2. If you seal the fabric against the ramp as shown in the right photo, what prevents air from circulating in an outboard direction between the upper cowl and the inlet duct? Wouldn't air that entered from the inboard side of the duct under the inlet duct just spill over the side of the baffle into the lower cowl? Does option B require that the glass inlet ducts be modified to add sidewalls or internal foam/filler so that air cannot travel between the duct and the upper cowl? I am having trouble visualizing how this could work without an additional mod like this.

Any pix of the seal detail in this area with the top cowl in place??

[Rick6a]

Noah,

The top picture taken with the upper cowl installed cannot show much detail. The lower picture more clearly shows how the baffle seal located outboard of the ramps makes contact with the cowl.

[Noah]

Thanks again for the photos Rick - very helpful. Looks like there is quite a bit of lateral clearance between the baffle sidewall and the inlet duct, so no slitting of the baffle seal is required. Makes perfect sense, a picture's worth a thousand words.

Brantel, Steve, or Alpinelakespilot- How did you prevent air from spilling underneath the inlet duct and over the baffle sidewall? Did you just glass in walls on the edge of the ducts (ramps)?

[N941WR]

Noah,

To keep the air from crossing under the ramps I filled them with Great Stuff foam. Next time I might get the fiberglass out but the blue Great Stuff worked good enough.

As for trimming the baffles to fit your cowling, the paperclip trick worked for me:

(More details here.)