[Ironflight]

Now this is getting down to details....

We were having a small debate in the hangar last night over the need for a Whistle Slot in the crankcase breather. As we have all been taught, a hole should be placed in the breather tube up above the end, preferably inside the cowling, so that if the end freezes over, we don't overpressurize the crankcase. Good idea!

But what if the end of the breather tube is ALREADY inside the cowling, and moreover, poised just above the exhasut pipe (as many folks have done in an attempt to burn the oil, rather then streak the belly...)? It is highly unlikely that the breather tube could freeze over! Is the hole still necessary, or is it just traditional? And should it be a true "Whistle slot" (A slit across the tube, with one side pushed in), or is a simple drilled hole sufficient?

Inquiring minds want to know! (See what happens when you bring out the beer at sunset?)

Paul Dye
Not responsible for the question, but interested in the answer....

 

[Bob Axsom]

No hole or slot on mine

I have the end of the breather tube barely below the fuselage directly over the left exhaust pipe with no freeze relief hole or slot in the serpentine routing of the breather tube. The end of the tube is cut in a way that conforms to the outline of the exhaust pipe with about 3/16" spacing above and behind with respect to the direction of flight. I can't imagine any freeze problem but adding side vent back from the end will not hurt anything except a little oil coating of the area adjacent to the hole - almost a non-issue. I have been flying my RV-6A for a year and a half with the first few months in Southern California (based at Chino) but the rest operating out of Drake Field in Northwest Arkansas (Fayetteville). I have experienced no problems.

Bob Axsom

 

[Mel]

Is the slot really necessary under these circumstances? Probably not. But why not? Another small plus for the slot is that air going into the slot (a true whistle slot) produces a small siphon effect thereby helping to evacuate the breather.
Mel...DAR

 

[sf3543]

I agree with MEL. On my -6, I had the tube coming down to the exhaust as well, with 4 small holes (#40, I think) drilled around the diameter of the tube a couple inches up from the end. However, I wanted to try the whistle slot on the tube so I cut the slot and bent in the wall, as in production applications and guess what...it did start siphoning and I actually started throwing out more oil. So, I went back to the original set up and no more oil out the tube. I guess if you played around with it and identified a better location for the slot it would be ok.
At any rate, I never had any problems with out the slot, but then again, I live in San Antonio and it doesn't get very cold down here.

 

[gmcjetpilot]

True whistle?

Is the slot really necessary under these circumstances? Probably not. But why not? Another small plus for the slot is that air going into the slot (a true whistle slot) produces a small siphon effect thereby helping to evacuate the breather.
Mel...DAR

Mel: True whistle slot, how do you make it to create a siphon effect. Can you describe or have a picture. I agree why not have it since it is a back-up or safety, especially if it costs and weighs nothing. I was always thinking of a short cut in the rubber using an exacto knife/razor and that was that. Not real sophisticated. I can't see a siphon. Thanks George

 

[RickWoodall]

Whistle slot?

Was just doing some research and wondered if there is anything new on this? Do you just drill a hole and bend the bit over to give the whistle effect? Will I use up more oil? Would three or four #40 holes be better?

Just havent seen this discussed for awhile and wasnt sure what the brain trust suggests now.

 

[Mel]

Mel: True whistle slot, how do you make it to create a siphon effect. Can you describe or have a picture. I agree why not have it since it is a back-up or safety, especially if it costs and weighs nothing. I was always thinking of a short cut in the rubber using an exacto knife/razor and that was that. Not real sophisticated. I can't see a siphon. Thanks George

Typically I just drill the hole then stick a punch in the hole and bend it up thereby "denting" the top of the hole in.

 

[RickWoodall]

Thanks for the quick reply Mel.

I have seen several builders put it in different positions. Some right up tight to the air box, others only a few inches from the end. Also, some have it on the outboard side (possibly done after install) others turn it in so I suppose it would get more heat ...is that just fluff...doesnt really matter stuff?

Funny all the dorky questions that come up when building. Thanks.

 

[SteinAir]

Mel: True whistle slot, how do you make it to create a siphon effect. Can you describe or have a picture. I agree why not have it since it is a back-up or safety, especially if it costs and weighs nothing. I was always thinking of a short cut in the rubber using an exacto knife/razor and that was that. Not real sophisticated. I can't see a siphon. Thanks George

I don't have anything to add other than where the heck have you been George !?!?! It gets awfully quiet sometimes....

Cheers,
Stein

 

[Jamie]

I don't have anything to add other than where the heck have you been George !?!?! It gets awfully quiet sometimes....

I had the same thought but after a second look I realized that this is an old thread from 2005 and likewise George's post was from 2005. I miss George's posts.

 

[L.Adamson]

I had the same thought but after a second look I realized that this is an old thread from 2005 and likewise George's post was from 2005. I miss George's posts.

And I couldn't figure out how Bob Axsom's plane was only flying a year and a half. Thought I was delusional.

L.Adamson --- RV6A

 

[mattsmith]

Since the thread is alive again Ill ask the question, why cant the breather tub be ran into the air filter box and any oil would be sent back into the engine and burned, I know it cant be done just curious to why it cant.

 

[SteinAir]

Jeez...you're right. Shows how much attention I paid - I was just so surprised to see a post from George that I didn't even look! I guess Larry was right, the dead giveaway should have been Bob's plane. Heck, he's been through about 118 airframe modifications/revisions since then!

As to running it into the airbox, I can think of a number of reasons I wouldn't want to do that....basically it'd make a mess. I don't know if it'd affect the venturi in a carb, but the impact tubes/diaphragms in an injector servo certainly wouldn't like it.

Cheers,
Stein

 

[Mel]

Since the thread is alive again Ill ask the question, why cant the breather tub be ran into the air filter box and any oil would be sent back into the engine and burned, I know it cant be done just curious to why it cant.

What you're thinking about is "positive crankcase ventilation" or PCV. It works fine on cars. BUT, it has to be designed in.
Simply sticking the vent line back into the carb intake doesn't work.
And like Stein says, It would make quite a mess.

 

[scard]

Don't anybody look, but this is one of the signs of a nearly mature network or community, when a thread (,concept, idea, interaction, useful nugget) from four years ago can come back to life as if it never died. Ok, I used to be an AI junkie... This is a great thing as far as I can tell. The database is critical. I know Doug is aware since HE owns it! Long live Doug (and Audrey?) and his allowing us to use HIS database freely.

 

[noelf]

OK, my 2 cents on feeding the vent to the air box...

...don't do it. The air box "sees" a positive pressure due to the ram effect of the cowling design. This positive pressure is good from a performance / hp point of view, but is not desirable from a crankcase pressure point of view.

The crankcase needs a slight "negative" pressure that vents the crankcase "vapors" overboard, and this negative pressure is not always available from the airbox.

 

[andrew phillips]

not airplane related

No hijack intended! The breather froze up on my generator engine while being run in the winter. The pressure blew out the dip sick and eventually all the oil. My first clue, inside the house, was when the power went out due to the connecting rod seizing to the crankshaft. Luckily the rod is aluminum and the crank steel. Clean up the crank, new rod and back in business.

Made me appreciate the value of the extra hole in the airplane breather tube!

 

[Craig23]

Cut mine today

I was up at the hangar today and cut the whistle slot using a dremel. I used a small flat head screwdriver to try and bend the top side of the slot in, but now the opening looks kind of wide. I put the slot up fairly high on the breather tube. Should I be worried about venting oil inside my cowling?

 

[IowaRV9Dreamer]

why the whistile shape?

What is the theory behind the whistile shape? Woudn't a simple hole or slot work just as well?

 

[strahler13]

Might be needed

A friend of mine co-owned a Cherokee-6 in MN a number of years back. His partner took off one day and had oil on the windscreen. He found his dip stick had popped out. He re-inserted and flew again with the same results. He then wired the dip stick tightly in place and left on a trip. The front seal failed and an off airport landing resulted with damage. Of course it was a frozen crankcase vent tube.

BTY, what happened to George? Will he ever be back? Is he banned? He certainly livened up the forums.

Mark

 

[Mel]

What is the theory behind the whistle shape? Wouldn't a simple hole or slot work just as well?

The idea is to entice warm air down into the tube.
A simple hole or slot would be fine as a pressure relief but probably not as efficient.

 

[Ironflight]

BTY, what happened to George? Will he ever be back? Is he banned? He certainly livened up the forums.

Not banned as far as I know....he used to post on a lot of different forums around the net, and seemed to disappear from all of them about the same time. He had a lot of good stuff to say.

Paul

 

[Captain Avgas]

Not banned as far as I know....he used to post on a lot of different forums around the net, and seemed to disappear from all of them about the same time. He had a lot of good stuff to say.

Paul

Paul,

It might well be that George simply got sick of all the inane political correctness and subsequent over zealous censoring, particularly on VansAirforce.

George liked to dish it out and he was totally intolerant of fools so he could be quite curt at times....but in his defence he was also prepared to cop it on the chin as well. He just seemed to revel in the argy bargy.

Aaaah history has a way of redefining itself. One year you're a troublemaker and social misfit.......the next year you're a sorely missed font of greater knowledge.

 

[RickWoodall]

George

I for one learned a ton from George. He was one who would spend 1/2hr typing a reply with clips to articles and research all the time. He didnt know me from Adam, and donated his free time to helping me and countless others here....yes even when I asked really stupid questions.

I did read under his handle here awhile back that he was BANNED. That is unfortunate, I know this is a business and has rules...but he was a great character.

Wish he was still here, hope he is well and enjoying life. I respect those that just put it all out there and dont worry about treading carefully and playing by the rules everyday. Thats just kind of cool.

 

[odlee]

I just hope

his absence is by choice and not some misfortune such as health or accident. His dissertations often were very informative and interesting, maybe even acidic!

Happy New Year to George and all the other RVer's.

David

 

[Sam Buchanan]

I for one learned a ton from George. He was one who would spend 1/2hr typing a reply with clips to articles and research all the time. He didnt know me from Adam, and donated his free time to helping me and countless others here....yes even when I asked really stupid questions.

I did read under his handle here awhile back that he was BANNED. That is unfortunate, I know this is a business and has rules...but he was a great character.

Wish he was still here, hope he is well and enjoying life. I respect those that just put it all out there and dont worry about treading carefully and playing by the rules everyday. Thats just kind of cool.

George has not been banned from VAF, he posted as recently as last September. His account is still active.

 

[lostpilot28]

Thread creep

I for one learned a ton from George. He was one who would spend 1/2hr typing a reply with clips to articles and research all the time. He didnt know me from Adam, and donated his free time to helping me and countless others here....yes even when I asked really stupid questions.

I agree with this...that guy was worth his weight in gold.

I think it's refreshing to see different personalities come out in these forums. If we over-do the political-correctness, then I think we start losing site of what identifies us as individuals. There's a lot more that could be said about this topic, but I'm already guilty of drifting away from the "whistle slot" topic!

Speaking of which, I just drilled a single #30 hole about 5 inches from the bottom and called it good. I do notice oil on the end of the tube quite often and wonder if that's normal.

 

[L.Adamson]

I do notice oil on the end of the tube quite often and wonder if that's normal.

That can depend on how much oil you put in. Although my Lyc can hold 8 quarts, it likes to blow some out, if it's over 6. Many others do the same.

L.Adamson --- RV6A

 

[lostpilot28]

That can depend on how much oil you put in. Although my Lyc can hold 8 quarts, it likes to blow some out, if it's over 6. Many others do the same.

L.Adamson --- RV6A

Thanks for the fast reply, Larry...I only put in 6 at oil changes. I learned my lesson early on!

 

[rvbuilder2002]

Why no wistle hole on an RV?

A little late to this discussion but maybe some in-site will still be helpful.

Years ago their was AD's issued on some aircraft that didn't have them. If I remember correctly, every one of these had crank case vent tubes that penetrated the cowl with the end of the tube out in the (cold) airstream.

As we now know this is a bad thing...moisture in the vented gases condenses in the cold (out in the air stream) end of the tube and freezes blocking the tube. End result could be a blown out crankshaft seal and loss of engine oil.

Correct me if I am wrong but I am pretty sure their are type certificated airplanes flying around right now (legally) that have no whistle hole. Because their vent tube outlet is not in the cold airstream.


Most RV's ever built have had the vent tube exit point within the area of the cowling airflow and as a result do not have a whistle hole.

 

[Norman CYYJ]

In Canada it is mandatory to have a whistle slot.

 

[RV6_flyer]

--- snip ---

Most RV's ever built have had the vent tube exit point within the area of the cowling airflow and as a result do not have a whistle hole.

After 12+ year and 2,338 hours flyng my RV-6, there is NO whistle slot but NONE of the breather hoses are clamped. The breather hose is a very loose fit on my oil separator and should fall off it there were any pressure in the breather hoses. It may make a mess under the cowl but should not blow the crankcase seal out.

 

[IowaRV9Dreamer]

whistle slot

The idea is to entice warm air down into the tube.
A simple hole or slot would be fine as a pressure relief but probably not as efficient.

Thanks Mel - that makes sense to me. I looked at my Beech Skipper yesterday. It has a 3/4" OD tube that stickes out about 3" below the cowl. There is a slot in it (no whistle that I could see) several inches above the cowl line. I get a lot of old out the tube (old engine) but the slot was dry.

BTW - gmcjetpilot is still out there... read this weeks aero-electric list for a very typical example (of both good and bad)...