Alternate air source??

[Zuldarin]

Originally Posted by N941WR

No need for one.

Almost 1,000 hours and no bird, leafs, or plastic bags have tried to commit suicide by jumping into the intake.

The thought of something happening on take off, the pilot realizing the intake is blocked, and opening the alt air before a forced landing is probably a stretch.

I wouldn't bother adding the complexity. I suspect there has been more problems caused by engines ingesting parts of the alt air contraptions than caused by the lack of alt air.

Hence the ?no pilot action required? option I used. You only need it when you need it. Not before. It?s purely a risk tolerance issue. Many don?t feel the need because of their experience, others do... personal decision and only one person can make that call.

[9GT]

Originally Posted by maniago

Hmmm. To me that seems like something thats outside of the DARs purview to decide.....where exactly is the line between a DARs responsibility and a design decision?

Its what he wanted to see, so that's what I made sure was there. Its HIS decision on weather or not to sign the AW certificate.

[N941WR]

Originally Posted by 9GT

Its what he wanted to see, so that's what I made sure was there. Its HIS decision on weather or not to sign the AW certificate.

And it is your decision to use him or not.

[BMC_Dave]

Huh, so DARs can demand designs that adversely affect safety of flight. That's unfortunate...

[N941WR]

Originally Posted by Zuldarin

Hence the ?no pilot action required? option I used. You only need it when you need it. Not before. It?s purely a risk tolerance issue. Many don?t feel the need because of their experience, others do... personal decision and only one person can make that call.

And many of those have come apart with rivets, bolts, etc. getting sucked up into the engine.

No thanks, I'll take my chances with a plastic bag.

[chris mitchell]

Well, it's interesting to see the range of responses. I absolutely see the " its only essential if you need it" view. I thought maybe I should have said mandatory - but even that seems to be contentious.

I guess on balance I will feel a bit uncomfortable about not having one. I'll see if I can engineer the space I need to get a side arm on the length of tubing between filter and adapter. Maybe shorten the nose cone a little, use a shorter filter. THe two things that are fixed and cannot be re-engineered are the location of the adapter on the front of the fuel servo and the location of the intake on the front of the cowling - the former can't move back and the latter can't move forward.

I'll see where I get to and post some photos.

Many thanks for all the comments.

Chris

[brad walton]

IIRC, an RV 7 went down in a snow storm attempting to cross the Sierra mountains when it is believed to have ingested enough snow to clog the air filter. Two died. Perhaps other can fill in the details.

[Bicyclops]

Originally Posted by chris mitchell

Well, it's interesting to see the range of responses. I absolutely see the " its only essential if you need it" view. I thought maybe I should have said mandatory - but even that seems to be contentious.

I guess on balance I will feel a bit uncomfortable about not having one. I'll see if I can engineer the space I need to get a side arm on the length of tubing between filter and adapter. Maybe shorten the nose cone a little, use a shorter filter. THe two things that are fixed and cannot be re-engineered are the location of the adapter on the front of the fuel servo and the location of the intake on the front of the cowling - the former can't move back and the latter can't move forward.

I'll see where I get to and post some photos.

Many thanks for all the comments.

Chris

Howdy Chris,
This is how I did it:







I made an airbox out of fiberglass. I believe the filter is a 0995. The alt air door hinge/gasket is sheet silicone rubber stock. It is manually actuated. I had to put a spring steel strap with a ramped block on it to make it seal properly.

Ed Holyoke