Air box bypass

[Mike Coady]

Can anyone tell me if they chose NOT to install the air box bypass assembly? I'm using an O-360 with carb heat and wondered if anyone thought it is a necessary add on or not. I just don't like the idea of when you open the bypass, it has to be manually closed upon landing. Advise here please. Is it a must or not? Thanks!
Mike

 

[plehrke]

Is it a must or not?

Depends on the risk you want.
Two most likely scenarios are flying in snow or ice and filter gets plugged or taking a bird strike that gets guts in the filter. Both of those scenarios I would think you would want to keep the bypass open until on the ground.
I put in the original magnet bypass but since have removed it. I have no bypass right now but do have inlet heat valve (not technically carb heat since I am fuel injected) with assumption I can melt the snow/ice if I encounter it but do not fly if any chance of snow or ice. I have no protection if I am unlucky enough to experience bird guts but contemplating adding back in a manual bypass.

 

[DanBaier]

I've held off not being quite comfortable with the notion of hardware being drawn into the engine.

Search the site - there is one person that came up with a solution where a piece of aluminum simply slides open / closed and when the weather gets a little better, that that's the one I'll probably go with.

Dan

 

[Ron RV8]

On the off chance I ever need it...

To avoid the problem of things coming apart, I glassed an aluminum ring to the bottom of the air box, then riveted on the ring for the bypass. I also glassed in a piece of aluminum for the Adel clamp...

I re-designed the Bowden cable attach using a pushrod clevis from a large R/C model and a hand made swivel. If you play with the geometry before attaching the ring you can get it to open and close.

I also glassed in a piece of 1/4" aluminum tubing so I could attach a hose to drain water / fuel outside the cowling...

Not purdy but it works...

 

[crabandy]

I glassed over a piece of .063 and then cut it out for rails and use a countersunk screw through the .063 plate to attatch a Bowden cable. Easily opens and closes at full power, never tried to block the filter and operate the door.

 

[GLPalinkas]

I've held off not being quite comfortable with the notion of hardware being drawn into the engine..........

Dan

+1 I think it more likely that bolts/nuts etc. enter the carb intake than a bird. Just my opinion .... YMMV

 

[Buggsy2]

I just went through this decision with a wise, experienced helper:

• Leave the bypass off, for VFR pilots it would rarely/never be needed.
• Build it per Vans, you have to release it on the ground.
• Build an alternative that can be set/released from the cockpit.

In the end we choose the 3rd alternative, mainly because a local builder had already done it and sent a good description and lots of pictures. It's the back-and-forth sliding plate version. We added a small patch of screen to prevent totally unfiltered air from entering, reasoning that snow/ice blocking the front opening wouldn't be so likely to block the cowled, warmer underside, and the screen prevents big chunks of whatever entering the engine.

My helper, BTW, left the bypass off his RV-6A and never had a need for it in 1500 hours of VFR flight.

 

[Captain Avgas]

My helper, BTW, left the bypass off his RV-6A and never had a need for it in 1500 hours of VFR flight.

I know lots of guys who have hull insurance, and fire extinguishers, but have never had a need for them. Does that mean they're a bad investment ? Some things we purchase in the hope that we will never need them.

It's hard to speculate as to what might block a filter. Birds and snow are obvious ones but there are other common hazards. With no alternate air, a plastic bag floating around could ruin your day very quickly.

 

[Mike Coady]

Thank you all for the suggestions. I think I'm going to hold off on the bypass until I decide on a good mod for an on/off version. I am worried also about ingesting something, bugs, anything and I like the idea of a fine mesh screen or something there. I'll leave it off as I finish my build . And , will explore the mod as I approach the IFR portion of my flying. Thanks again for all the photos and suggestions, you're all super builders I can tell. Maybe see you at OSH. I'll be N771MK.

 

[N941WR]

I did not install the bypass on either of my engines.

Ice is probably the biggest concern and to handle that I used a different / better carb heat muff than the juce can Van's sends with the kit.

As for the bird in the intake scenario, you have a greater chance of taking one through the canopy (it's a bigger target), so what precautions are you going to take there? (There's an entire thread dedicated to that topic.)

 

[bruceh]

sliding alt air door

Here is my solution to the problem of the Van's hinged alt air door. I spent a few days on this and it turned out great. You can open/close it easily. Nothing can become injested in the engine intake.

Closed position:

Open position:

Installed:

Lots more photos and commentary on the FAB alt air modification on my web site.

 

[NeilMcLeod]

Nicely done, I've been contemplating adding one to my airbox and this is the best solution I've seen. Thanks for posting it. I installed Van's original magnetic door but after it disintegrated I glassed it over and have been running without since then.