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alternate air?

larrys

Well Known Member
Building a 14 with a Thunderbolt motor. I am doing the snorkel now and it says to do an alternate air plate. I am inclined not to do it. But what are the pros and cons? I do not understand why it is provided and a couple of plan pages are dedicated to it?
Hope you guys can fill me in.
Thanks, Larry
 
I found it not difficult to install and you would really not what to be in the, I should have done that group.
It is a lot easier to now then retrofitting later.
 
Why wouldn't you want to install the alternate air door? Having one can be a real lifesaver and it's easy to do, especially during the initial build.
 
Why wouldn't you want to install the alternate air door? Having one can be a real lifesaver and it's easy to do, especially during the initial build.

Because many of them have shed parts which have been sucked into the engine.

For those who say it will save their life on takeoff, should they ingest a plastic grocery bag on takeoff, I say they won't have time to diagnose and resolve the problem before the crash.

925 hours without one and counting.
 
The design of this one reduces the possibility of parts injection greatly. All moving parts are outside the air box unlike the old doors on previous models.
 
Because many of them have shed parts which have been sucked into the engine.

For those who say it will save their life on takeoff, should they ingest a plastic grocery bag on takeoff, I say they won't have time to diagnose and resolve the problem before the crash.

925 hours without one and counting.

Just like a fire extinguisher. I am sure some choose not to carry one because they have never had a fire in 925 hours. We are fortunate in this hobby that each individual can set their own risk tolerance and equip accordingly. Op should set his own risk criteria. It can be dangerous looking for consensus on these types of decisions.

Frankly, I am more concerned with water saturation and ice than garbage bags. But hey, if you never plan on flying in ice or rain, it shouldn't be a problem:rolleyes: Not sure how the K&N will tolerate it, but I have had a auto engine stop running due to a water logged paper air filter.

IMO there is no benefit to not installing this beyond the 45 minutes saved. On the flip side, it could save your life, regardless of how remote the probability is. If you fly IFR, this is as essential as pitot heat IMO. Though you will find plenty of folks that say they are not necessary because they never experienced an iced over pitot.

Risk of ingesting parts of the assembly can easily be addressed by using thin aluminum sheet under the shop head of the rivets.

Larry
 
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It's too easy to do NOT to do it. The design limits risk of FOD ingestion and it's only going to happen if you need to open the door anyway. And if you need it FOD is the least of your concerns.

A no-brainer IMHO.
 
The comment above answered my question. It will be installed

Frankly, I am more concerned with water saturation and ice than garbage bags. But hey, if you never plan on flying in ice or rain, it shouldn't be a problem Not sure how the K&N will tolerate it, but I have had a auto engine stop running due to a water logged paper air filter.

IMO there is no benefit to not installing this beyond the 45 minutes saved. On the flip side, it could save your life, regardless of how remote the probability is. If you fly IFR, this is as essential as pitot heat IMO. Though you will find plenty of folks that say they are not necessary because they never experienced an iced over pitot.

The comment above answered my question. It will be installed
Thanks! Larry
 
Just like a fire extinguisher. I am sure some choose not to carry one because they have never had a fire in 925 hours. We are fortunate in this hobby that each individual can set their own risk tolerance and equip accordingly. Op should set his own risk criteria. It can be dangerous looking for consensus on these types of decisions.

Frankly, I am more concerned with water saturation and ice than garbage bags. But hey, if you never plan on flying in ice or rain, it shouldn't be a problem:rolleyes: Not sure how the K&N will tolerate it, but I have had a auto engine stop running due to a water logged paper air filter.

IMO there is no benefit to not installing this beyond the 45 minutes saved. On the flip side, it could save your life, regardless of how remote the probability is. If you fly IFR, this is as essential as pitot heat IMO. Though you will find plenty of folks that say they are not necessary because they never experienced an iced over pitot.

Risk of ingesting parts of the assembly can easily be addressed by using thin aluminum sheet under the shop head of the rivets.

Larry

Bingo!!!! Well said!^^^^^ I have seen the "garbage bag" analogy pop up several times. If you fly IFR long enough, eventually you will get into to an icing situation that could require an alternate air source. At that point garbage bags will be the least of your problems.
 
Sorry, every time i read the alternate air discussion I can?t help myself. I agree with the need for an ifr pilot,most of us are not. For the pilots that support alternate air how about another separate source for venting your fuel? Mud dauber ARE common.
 
It's possible to design an alternate air door offering zero chance of parts ingestion. It's also possible to eliminate the need for pilot decision and/or action after power loss due to filter blocking, be it ice or plastic bags or whatever.

This one opens at a deltaP of ~3" H2O, by test. As installed, it has a microswitch on the external arm to illuminate a panel LED if it opens. It never has....so far.

Posts 15 and 19:

http://www.vansairforce.com/community/showthread.php?t=44856&page=2
 
Has alternate air ever been needed?
R

I guess not.
R

Lack of a reply here in this forum would hopefully never be considered a definitive answer to a question such as this......

In the earlier years of RV kits, since they were marketed as primarily sport flying airplanes, there was no alternate air system engineered for the engine induction air system (in fact the very early RV-3 & 4 systems didn't even have an air filter).

Builders continued to expand the mission profile of the airplanes, even to night IFR operations.
It was a double fatality during IFR flight into (forecast) icing conditions that instigated the development of an alternate induction air system for all of the airplane models.
 
Sorry, every time i read the alternate air discussion I can’t help myself. I agree with the need for an ifr pilot,most of us are not. For the pilots that support alternate air how about another separate source for venting your fuel? Mud dauber ARE common.

This is also a big issue for me. I used a tee with a one way check valve (.5 psi rating) in my left fuel tank vent. This way, if the vent line opening becomes covered with ice, my left tank will be able to still flow fuel. Small protrusions from the aircraft surface skins are the first to become coated with ice, so this should be dealt with in any IFR ship IMO.

I still believe that alt air is important for VFR ships as well. I believe that water saturation of the filter from rain is still a threat, though it may be a small risk.

I also use the paper clip trick to help unwanted visitors from building a home in my vent line. Daubers are a real threat and have sent more than a handfull of pilots on glider landings. Though they are not as prevalent in northern climates.

Larry
 
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you don't need to be in clouds to get carb ice. ;)
get a fire extinguisher too, ask me how i know. :eek:
IMG-2453.jpg
 
I am using Van's horizontal induction snorkel and the supplied alternate air door. I was able to make some modifications includung adding spring washers, that allow the door to be opened AND closed using a ratcheting Bowden cable. 300+ hrs. and no issues.
 
The design of this one reduces the possibility of parts injection greatly. All moving parts are outside the air box unlike the old doors on previous models.
I'm not familiar with the RV-14 Alt Air Door design on a snorkel - it's different than the design used on previous models? How about a photo of the hardware or the plans?
 
you don't need to be in clouds to get carb ice. ;)

Just so no one gets confused.....
The alternate induction air systems provided in RV kits being discussed here have nothing to do with carb ice, and they will not prevent nor mitigate it if it has developed.

They are for use when the induction system is plugged with ice because of airframe ice accumulation that is also effecting the induction air filter.

Carb heat for use to prevent or mitigate carb ice, is a totally different system.
 
Just so no one gets confused.....
The alternate induction air systems provided in RV kits being discussed here have nothing to do with carb ice, and they will not prevent nor mitigate it if it has developed.

They are for use when the induction system is plugged with ice because of airframe ice accumulation that is also effecting the induction air filter.

Carb heat for use to prevent or mitigate carb ice, is a totally different system.

Thanks for your clarification. The 14 is injected and that is why I started the tread. It was not heated air so what was the point. But on the issue of Ice as in icy rain. That makes sense.
Thanks, Larry
 
Lack of a reply here in this forum would hopefully never be considered a definitive answer to a question such as this......

In the earlier years of RV kits, since they were marketed as primarily sport flying airplanes, there was no alternate air system engineered for the engine induction air system (in fact the very early RV-3 & 4 systems didn't even have an air filter).

Builders continued to expand the mission profile of the airplanes, even to night IFR operations.
It was a double fatality during IFR flight into (forecast) icing conditions that instigated the development of an alternate induction air system for all of the airplane models.

Thank you for the background info. leading to the alt.air design change. I tend to be curious how aircrafts evolve. Misfortune in this case improved safety, as is often the case.
R
 
In response to an earlier comment, here's a bit of trivia I just googled because I had heard it before:

From this article just picking the first source on the list:
https://www.flyingmag.com/pilot-technique/instrument-flight-rules/getting-instrument-rating/

"More than half the pilots eventually get an instrument rating but only a small percentage of those maintain instrument currency. One association president said a while back that only 15 percent of its instrument-rated members were instrument current."

So when someone says "Most are not", that's not really accurate. Most eventually will be, may be closer to the truth.

Either way, I feel an instrument rating is worth it for any pilot.
 
I am using Van's horizontal induction snorkel and the supplied alternate air door. I was able to make some modifications includung adding spring washers, that allow the door to be opened AND closed using a ratcheting Bowden cable. 300+ hrs. and no issues.

Jake send me some pics of your mod if you can.

Thx
 
@TimO I agree completely. I would also think that there is a larger percentage of -10 and -14 owners with a IFR as the mission of the planes tends to be primarily focused to xcountry compared to the prior models.

What I tell every VFR pilot when they ask me if they should get their IFR - It will make you a MUCH better and more confident VFR pilot.
 
What I tell every VFR pilot when they ask me if they should get their IFR - It will make you a MUCH better and more confident VFR pilot.

Absolutely. I also advocate for a good 10-hour basic aerobatic course, a tailwheel endorsement, and a commercial rating for the same reason. Glider flying, too.

Really, anything one can do to acquire (and encourage others to do so) varied additional aviation experience will be to the good.

The aerobatic course, especially, will make for a better and more confident VFR pilot - what with the elimination of unusual attitudes and the experience of utilizing full control deflections as/when necessary.
 
Danger of snow

Lack of a reply here in this forum would hopefully never be considered a definitive answer to a question such as this......

In the earlier years of RV kits, since they were marketed as primarily sport flying airplanes, there was no alternate air system engineered for the engine induction air system (in fact the very early RV-3 & 4 systems didn't even have an air filter).

Builders continued to expand the mission profile of the airplanes, even to night IFR operations.
It was a double fatality during IFR flight into (forecast) icing conditions that instigated the development of an alternate induction air system for all of the airplane models.

I am very familiar with both that fatal accident in California and another non-fatal in Illinois where an RV-10 made an off airport landing due to engine failure. In both cases the cause was snow buildup which blocked the air filter. My -14A has the alternate air system installed per the plans and although I have never had to use it, the system is there if needed.
 
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