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dave.saylor.aircrafters(a
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 Posted: Thu Dec 30, 2010 8:21 pm Post subject: Alternate Air intake |
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The way the valve is designed uses a small channel to locate the gate
in place. If you saw it, it would make perfect sense, and I wish I
had a picture--the plans on Tim's site are a different (older?) style
than I have. On mine, there's no mechanism to guide the gate back
into the closed position once it's been opened. Someone could design
a heavier and more complicated mechanism to be closed from the cabin.
I've never opened mine in flight. I drilled a small hole through the
knob and tied it down with break-away wire so I have to give it a
pretty good tug to open it. I sealed the valve with a thin layer of
silicone to keep unfiltered air out of the intake. I test it once a
year before I remove the FAB at annual time.
The rubber part of my filter wore through the floor of the FAB after
about two years. I ended up basically rebuilding the bottom of the
FAB in aluminum, including the alternate air valve.
Ice, birds, a big leaf, or a plastic bag are all things I've thought
about fouling the intake. The ground-resettable valve is a pretty
good compromise.
Dave Saylor
AirCrafters
140 Aviation Way
Watsonville, CA 95076
831-722-9141 Shop
831-750-0284 Cell
On Thu, Dec 30, 2010 at 7:06 PM, Linn Walters <pitts_pilot(at)bellsouth.net> wrote:
| Quote: | I'm with Roger ..... and since I'm not to that point, please tell me what
prevents installation of a 'reversible' bypass control???
Linn
On 12/30/2010 9:31 PM, Roger Standley wrote:
I don't usually get worked up over threads like this but I have a problem
with any control in the cabin that is not reversible. Under what conditions
(scenario) would you pull such a control, realizing that once you did, you
can't reverse it? I am not trying to be ornery here, just trying to learn
something so please educate me.
Roger
-----
Original Message -----
From: Jesse Saint
To: rv10-list(at)matronics.com
Sent: Thursday, December 30, 2010 5:41 PM
Subject: Re: Alternate Air intake
There have already been a lot of replies, but IIRC, the plans call the trap
door in the front of the FAB the "alternate air" and the one on the bottom
the "air filter bypass". Â I think the air filter bypass is definitely
needed, but not the alternate air, which really, as Tim mentioned, just acts
as a carb heat. Â I have personally never had to use either. Â In the case of
icing conditions, I can see how the alternate air could possibly be a help
that could avoid needing to bypass the filter, but beyond that one scenario,
the alternate air seems to add no service. Â I always install the bypass door
so it an be closed by pushing the knob, but I realize that if it has to be
used, it will likely not need to be closed again in flight, so that's
probably not very important.
Jesse Saint
Saint Aviation, Inc.
jesse(at)saintaviation.com
C: 352-427-0285
F: 815-377-3694
On Dec 30, 2010, at 11:57 AM, Phillip Perry wrote:
Yeah I'm not asking about the static, that's pretty easy and I have it
installed.  I'm more concerned with a blocked filter scenario.
Does anyone have photos of their installation? Cowling mods, etc? I'm
trying to get my mind around the plumbing, etc.
Thanks for the help,
Phil
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rv10rob(at)gmail.com
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| Posted: Thu Dec 30, 2010 9:01 pm Post subject: Alternate Air intake |
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I put epoxy/flox between the FAB and aluminum plate. I was then paranoid about the rivets and/or the extra epoxy/flox getting loose and sucked up into the engine, so I put tank sealant over everything. Now if the tank sealant gets loose....
On Thu, Dec 30, 2010 at 6:35 PM, John Gonzalez <indigoonlatigo(at)msn.com (indigoonlatigo(at)msn.com)> wrote:
| Quote: | How about using fuel tank sealant on the airfilter bypass door in addition to the rivets??
As for also installing the carburator heat door, seems to me that activating this door once the realization of icing or hail would be prudent and may allow one to not have to activate the "air filter bypass door". Seeing that the later cannot be closed in flight, the carb heat door would be the first line of defense.
Shut down proceedures might also be to close the Carb heat door to keep snow, nesting birds, other critters or insects out.
Just thinking out loud.
getting close to paint
John G
From: jesse(at)saintaviation.com (jesse(at)saintaviation.com)
Subject: Re: Alternate Air intake
Date: Thu, 30 Dec 2010 20:41:52 -0500
To: rv10-list(at)matronics.com (rv10-list(at)matronics.com)
There have already been a lot of replies, but IIRC, the plans call the trap door in the front of the FAB the "alternate air" and the one on the bottom the "air filter bypass". I think the air filter bypass is definitely needed, but not the alternate air, which really, as Tim mentioned, just acts as a carb heat. I have personally never had to use either. In the case of icing conditions, I can see how the alternate air could possibly be a help that could avoid needing to bypass the filter, but beyond that one scenario, the alternate air seems to add no service. I always install the bypass door so it an be closed by pushing the knob, but I realize that if it has to be used, it will likely not need to be closed again in flight, so that's probably not very important.
Jesse Saint
Saint Aviation, Inc.
jesse(at)saintaviation.com (jesse(at)saintaviation.com)
C: 352-427-0285
F: 815-377-3694
On Dec 30, 2010, at 11:57 AM, Phillip Perry wrote:
| Quote: | Yeah I'm not asking about the static, that's pretty easy and I have it installed. I'm more concerned with a blocked filter scenario.
Does anyone have photos of their installation? Cowling mods, etc? I'm trying to get my mind around the plumbing, etc.
Thanks for the help,
Phil
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http://kochman.net/N819K
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scottmschmidt(at)yahoo.co
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| Posted: Fri Dec 31, 2010 4:24 am Post subject: Alternate Air intake |
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Yes and think of the engine quitting.
The alt air is an emergency system. I don't think I would pull it unless MP became so low that airspeed or altitude could not be maintained.
I read a report a few years back of a Pitts that sucked a bird in the inlet hole that caused the engine to quit. The pilot made an emergency landing and I believe damaged the airplane doing so. After he was upset at himself for not going through his emergency checklist. Pulling the alt air would have made this a non-event.
If you pull it you will be landing at the next airport to check what happened and reset.
On Dec 30, 2010, at 9:02 PM, "Roger Standley" <taildragon(at)msn.com (taildragon(at)msn.com)> wrote:
[quote] <?xml:namespace prefix="v" /><?xml:namespace prefix="o" /><![endif]--> OK, agreed. But let's follow this icing scenario. I am flying along and notice a drop in MP as the filter and maybe a drop in AS as the pitot ices up. I add throttle and get little response, maybe a drop in EGT. So I suspect icing? I pull Alt Air (it's reversible). MP gradually increases. AS continues to drop. I look at the GPS ground speed and see no change. I am thinking, the pitot is icing over, the engine filter was icing over but the Alt Air is working and keeping the engine going near normal. I descent looking for warmer air.
Is this the right way to work through this?
Roger
[quote] ---
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Tim Olson
Joined: 25 Jan 2007
Posts: 2881
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| Posted: Fri Dec 31, 2010 9:32 am Post subject: Alternate Air intake |
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You may notice a gradual drop in MP as the filter ices
up, but you said "I pull Alt Air (it's reversible). MP
gradually increases." You have to get out of the mindset
of carbureted engines. If you pull the alternate air,
your engine will now have a free and open path to
air. It won't be gradual, if indeed your filter is
icing up. It will be instantaneous.
Also remember that our IO-540's, if you're fuel injected,
don't have carburetor venturis to ice up. Carbs ice
up because of the pressure changes happening due to
the venturi. We just have a big gaping hole. IO's
don't have to worry about icing in a carb. So, for
us, having an alternate air door should be plenty.
If you pull it, it's open. It will stay open the
whole flight, and honestly, there is NOTHING wrong
with that unless you're flying in dusty/dirty
conditions. We really wouldn't even NEED an intake
filter if we didn't care about it being clean. So
it really isn't a big deal. If you pull the Alt
Air accidentally, just close it when on the ground, but
it's not something that means you have to land immediately.
If you pull it on purpose, then you were probably in
conditions you don't want to continue on in anyway,
so land, close it, and go stay in a hotel.
The pitot icing over is completely a separate thing,
and of course, any time you're operating below freezing
you can just turn on the pitot heat and you likely
won't have an issue. If you test the pitot heat
before any flight where you COULD have an issue
(IFR in the clouds or such), then you won't likely
have a problem there. The biggest problem is probably
forgetting to turn it on in the first place.
The alternate static is something that if you're flying
IFR you should really have. It's dead simple to
come up with at least some method of opening the
static line inside the cockpit. There are all sorts of
cool valves and such that you can use. Mine is a
simple lever-lift toggle valve, next to my Left knee
on the sidewall up high, just below the panel.
At any rate, I see no real need for an alternate air
pathway on the intake...could be more trouble, actually,
than it would be worth. The alternate air on the bottom
of the air box though, is one you should definitely
install....although in nearing 700 hours, I've never
had to pull it for any reason in flight....accidental
or on purpose. If I ever did, it wouldn't be a major
deal for me...it just means I was flying in heavy snow
or supercooled clouds and I iced up stuff....and I didn't
belong there in the first place. I have flown before
though in visibility of just over a mile forward,
but 4 or 5 miles out the side windows (surprising
how much worse forward viz can be), in fairly heavy
snow that WASN'T an icing worry. I don't think it's
all that easy to plug these filters up...they can
handle quite a bit.
Tim Olson - RV-10 N104CD
On 12/30/2010 10:02 PM, Roger Standley wrote:
[quote] OK, agreed. But let's follow this icing scenario. I am flying along and
notice a drop in MP as the filter and maybe a drop in AS as the pitot
ices up. I add throttle and get little response, maybe a drop in EGT. So
I suspect icing? I pull Alt Air (it's reversible). MP gradually
increases. AS continues to drop. I look at the GPS ground speed and see
no change. I am thinking, the pitot is icing over, the engine filter was
icing over but the Alt Air is working and keeping the engine going near
normal. I descent looking for warmer air.
Is this the right way to work through this?
Roger
---
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Bob Turner
Joined: 03 Jan 2009
Posts: 885
Location: Castro Valley, CA
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| Posted: Fri Dec 31, 2010 1:06 pm Post subject: Re: Alternate Air intake |
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small correction: in carbureted engines, most of the cooling is due to the evaporation of the fuel, not the slight pressure drop.
I see the biggest problem is forgetting you even have the alternate air control when you need it, since it is never used. Same as the story of the 182 guy with snow impacting and closing his air filter - carb heat (which is also alternate air in carbed planes) should have fixed the problem.
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Bob Turner
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