Power loss. Off field landing...

[gregpro50 64]

They have the springs on each side.  The design is a little different.

My carb vents were into the filter on top of the carb throat.  Any fuel leakage would have been sucked right back into the carb throat.

[Bandit 286]

I know you want answers but lets slow down a bit here. Speculation is less than worthless.

1.) "I don't think the filters were over oiled but before they were not oiled at all."

The filters were purchased, received and installed several years ago. Bought off eBay or Amazon, I can't remember anymore but you may have the receipt. As I did not have proper filter oil on hand and the sale did not mention a supply of oil, I contacted the vendor who indicated they were sold lightly pre-oiled without additional reserve oil. To be honest, my initial impression upon receipt was uncertainty whether they had been pre-oiled or not. They were very clearly not soaked (been there, done that, like Mark had to fix that). But then, they did not look or feel totally dry to me either. I have used and oiled KnN filters in the past so not totally ignorant but I ended up convincing myself they may have had a very light oiling at best. There were other more pressing items on the To Do List and I never had the opportunity to either clean or oil them after install.

2.) "I just really question whether a combination of that and the vent line route could have really brought forth a mixture problem due to the atmospheric pressure differentials inside and outside the carb.  In my head I wouldn't think so but when the throttle is opened up all the way those filters are really sucking in a lot of air."

Terminating the vent lines into either an airbox or air filter (doesn't matter to my thinking) results in a more equal atmospheric pressure differential, IMHO. If the Rotax requirement is to be as equal as possible to the air entering the intake throat (not entering the airbox or filter), how could it not be preferable to hanging in the breeze under cowl somewhere? Even if proper length vent lines are terminated at the carb and secured by the float bowl bail (which is the Rotax configuration when not using the optional airbox and most likely meets Rotax's ram-air and vacuum free zone requirement for the majority of installations), stands to reason when referring to a KF installation they are subject to significantly more buffeting and other forces that impact and increase atmospheric pressure differential under cowl. I don't think throttle position matters at all if the lines terminate within the airbox or filter, carb pressure is still always going to be closer to the air pressure at the intake than if outside the airbox or filter. I also think if there were any suction risk under normal operating conditions at all, Rotax would not route carb vent lines directly into the airbox.

3.) "There certainly does seem to be quite a bit of evidence of prior instances from other aircraft where vent line routing caused power loss.  Just Google Rotax 912 vent line power loss and there is all kinds of issues with it."

I used your search parameters exactly and concluded the following: every single loss of engine power that may have had carb vent lines in the equation appeared due to improper length of vent line, improperly terminating in a ram-air or vacuum zone and a possible blocked vent line. All of which have -zero- to do with routing the vent lines into an airbox or filter. I went through several pages of search results but if I've missed something, please do help me out. When I researched the topic years ago I never found one single instance where venting the Bing 64 carbs into a 912ul airbox or filter of any kind caused so much as rough running, let alone was blamed or linked to a fire or a loss of RPM due to fuel dump caused by faulty or failed carb float(s). Doesn't mean it couldn't or didn't happen here, there is always a first time, but I sure would be interested in any FACTS or empirical data that confirms it actually happened before.

I agree the issue of carb venting must be taken very seriously, it has been demonstrated many times just how sensitive and important the Rotax venting requirements are. The first flight of your plane is perfect example of why proper vent line length when terminated to atmosphere under cowl is critical. That entry sure got my attention! I don't think removal of the carb heat airbox is a factor, guessing the majority of 912 installs in KF airframes omit it due to cowl and carb location. However, that is completely different scenario and question than routing vent lines to an airbox or airfilter. These engines are installed in so many different airframe/cowl/pusher/tractor configurations Rotax necessarily leaves it up to the plane manufacturer to meet their requirements (ram-air and vacuum free zone) in whatever way they so choose. Rotax specifically recommends and provides provision to vent carbs directly into their airbox. My Aeropro has carb vent lines into the airbox, as do many other SLSA's. 

If Rotax finds routing vent lines to an airbox a preferred method, is routing to a filter appreciably different or problematic? Nowhere in any Rotax BRP-Powertrain install, operation or maintenance manual does it prohibit or direct against venting carb lines into a round or conical filter which, of course, are Rotax approved air filter configurations that Rotax also provides. The way Rotax ALWAYS errs on the side of caution, it they believed that somehow it was ok to vent lines into their airbox but for whatever reason venting into a non-oem airbox or particular or different style filter was a liability waiting to happen, you would think there would be an big fat Notice or Warning box in the manual(s) somewhere.

Well, after some further thought and with benefit of now owning a plane with an airbox, I think maybe there is a caution to note. Here's why: not sure precisely how the Rotax airbox works but on my Aeropro airbox, the vent line nipples enter thru the side of airbox to the outside the filter media. Therefore, anything coming though the vent line has to make it's way past the filter to enter the intake throat. If you route a vent line into the backside of a round or conical KnN filter, you enter to the inside of the filter media. Therefore, an unrestricted path to enter the intake throat. Obviously two different installs that -may- react differently to a possible fuel dump caused by a bad float. Not trying to argue anything, but is a vent line even large enough to deliver a sudden fuel dump into either airbox or filter in an amount sufficient to cause an immediate and large loss of RPM? Let's say fuel makes it's way into the KnN filter via the vent line which enters in the lower portion of the filter below the intake throat. At the time it enter the filter I presume it is a solid stream, rather than atomized. So does gravity cause it to fall and pool or be absorbed by the filter media, or does it get sucked upwards into the intake throat? Is that even possible? I have no clue how much suction force that would take, other than I would guess a lot more for a free flowing filter and less for an obstructed filter. Does anyone know for sure?

I also found some interesting info on the float failures. A soggy float, at least as far as I've read, doesn't generally manifest itself in the form of a catastrophic failure, suddenly and completely all at once without some foreshadowing 'tells'. Most posts I found discussing failed floats included comments suggesting they were alerted by odor or rough running, as opposed to total or significant loss of RPM. Heck, some with intermittent symptoms even continued to fly before completing their diagnosis, yikes. So, no prior fuel odor on the ground or in flight? No prior evidence of fuel saturation on the filter element? No prior unusual or erratic engine RPMs? No prior engine miss at all, at any RPM? No prior evidence of fluid, fuel or condensation, noted in the clear vent lines during pre-flights? That would seem unusual to me, but I'm no expert even with 20/20 hindsight and just thinking out loud. You may never know with certainty exactly what happened, can't let it eat you up.

Remember this winter I had a fuel logged float in my front carb. My plugs kept flooding and it was hard to start. I did fly it even with the bad float. After a few times of cranking my ass off I checked the floats and found the sunk float. After a new float and new plugs the problem was solved. In Preflight I do not take the cowlings off and check to see if the vent lines are dripping or the filters are fuel soaked. Although after a few times of trying to start it without even so much as a cough I did notice a strong fuel smell. Of coarse that is when I started to did into my problem.

[Av8r3400 1179]

From memory of a discussion on this topic during my IRMT (Rotax 912) training:

SInce these carb vents do burp fuel on occasion, this fuel coming out the vent and soaking the filter media will wash off the oil, and if enough, will saturate the media making one backfire in to a major fire.  This burping fuel into the filters can and does enrichen the mixture uncontrollably and unevenly side to side, which can and does cause rough running.  Running the vents into a intake air box will not have these same effects.

Dave, the builder of Sputzee, routed his vents to the filters.  The filters even had what appeared to be attachment points for these vents.  The fuel going through them eventually damaged the filter media causing it to become crumbly.  He replaced the filters and put the proper short vents to the float bails.

I do not believe that terminating the vent lines in the filters caused or even contributed to this incident.  I do believe it is not good practice to terminate them there.

 

Direct experience of syphoning:  A friend and hangar-mate with a Rans S6 and a 912UL installed, routed his extended vent lines out the bottom of the cowl.  This was sufficient to syphon the fuel out of the bowls causing a full loss of power just after rotation.  He landed on the runway and jumped out of the plane due to heavy fuel smell.  Fuel was found on the belly of the plane after the vent line termination.  He then made a funnel type of syphon-stop mounted to the fire wall.  This did not stop the problem.  Replacing the vent lines with the proper 4" lines terminating in the bowl bails solved the problem.

[dholly 718]

Larry - good info. Did the iRMT class ever give any indication what the 'normal' amount of fuel one could expect to be expelled thru the vent lines under normal operations was?

[Av8r3400 1179]

I have seen directly (yesterday for example) on bumpy thermally days when the plane is getting bounced about, the fuel sloshing about in the bowls will drip overboard from these vents.  I've also noticed after long power off or steep decents, the engine will "load up" and run rough until cleared.  This rough running, especially on a IV, with the reversed intakes will produce fuel at the vents.  

It's not a lot, maybe spoonfuls, but it does happen, more often than you'd think.  

[BryceKat 125]

Greg,

How much did your Kitfox weigh and where was the cg? Thanks

[gregpro50 64]

Greg,

How much did your Kitfox weigh and where was the cg? Thanks

I don't have the papers handy but it was about 630 or so with the grove gear.  I can't remember the cg number off the top of my head.

[herman pahls 9]

My 2 cents worth.

I am taking special interest in this discussion since i am about to order a HACman fuel mixture controller for my 912 ULS.

I had also installed a HACman on my 582 powered Kitfox which I found to be a great asset.

As I recall, one side of the mixture control was plumbed to both the vent tubes on both  the Bing carbs and the other side was plumbed to the joint  KN air filter.

If you happened to land with the HACman valve in the leaned position it would not start.

Based on how the HACman leans the Bing carbs, there could be an issue when the vent tubes are vented into the filter, because that is what I believe the HACman does.

My 912 has approx. 4" individual vent tubes tucked under the float bowl bail.

 

Fuel flow and adequate fuel pressure could also be an issue.

I fly with a fuel pressure gauge, a back up electric fuel pump and a warning light that comes on when the fuel pressure is below 3 pounds.

At idle and low power setting the pressure is around 5 PSI.

Sometimes at full power take off the pressure drops slightly below 3 psi in the 2.8 range.

I have heard it  said that Kitfoxs will run on gravity only from the wings but not at full power.

 

My 582 was set up to start cold with a primer.

Give it a 1/2 primer stroke too much and it would flood the engine.

I would suspect that if both vent lines were pouring fuel into the carbs, the results could be significant loss of power.

I am please to hear you are well.

Herman

 

 

 

 

 

Edited 18 Apr 2016 by herman pahls

[Av8r3400 1179]

I understand the benefits of the Hacman system on a Bing 54, but don't really follow the need for it on the constant velocity Bing 64.  The 64 already compensates for air pressure, moving the main jet needle in and out as required. 

I've personally had my 80 hp 912UL above 10k and the EGTs were fine, the engine was making good power and sustaining more than 500 fpm climb. 

[gregpro50 64]

Still digging up info...

Denney Aerocraft for Kifox issued service bulletin #11A recommending to leave carb vent lines as they come from the factory due to numerous instances of engines that have run excessively lean.

SkyStar for Kitfox issued service bulletin #11C states that the correct way to vent the carbs is a short length of carb vent line routed just below the carb and tucked into the carb bowl spring.

Also interesting info is found from the original build log for this plane.  The builder experienced what is worded in the log as "engine cut-out" on the first two flights.  Further information shows that they contacted Rotax and were told to route the carb vents to the recommended installation.  After which the log is noted as saying that the engine ran perfectly since then.

Just before I started flying the plane the original carb heat box was removed and the air filters installed with the carb vents running into them which was a change to the installation of the carb vents the builder had trouble with.  The first flight went alright but thinking back there were symptoms of an issue.  After the initial climb on the first flight there was a fuel smell in the cockpit after the throttle was reduced for cruise.  It was strong enough that we discussed returning to the airport to check it out but then seemed to go away.  Everything seemed to work fine during cruise throttle settings.  Then during landing the throttle was reduced and after landing the engine ran very rough and almost quit on the runway but then seemed to clear out when we gave it a little throttle and ran fine again.

In the back of my head I remember reading this info before and looking at the carb vent setup.  I just though the way the vents were ran into the filter seemed like a much better idea than them hanging out in the open so I never thought twice about it.  I'm just having trouble believing that the vents are that sensitive to the installation.

Edited 18 Apr 2016 by gregpro50

[Av8r3400 1179]

Greg, if you look back a few posts, I agree the vent lines are most likely not a factor in your incident.  It is, however, a common thing that's done incorrectly (per Rotax) that can have some ill effects. 

[gregpro50 64]

I'm thinking a perfect storm of a bad float and the vent routing.  What do you think?  The float bowls had fuel in them so it couldn't have been starvation.  It wasn't an ignition problem.  So what does that leave?  The valves seem clear and operate as they should.   I just really want to understand it before I strap my ass behind a rotax again.  The fuel pump is new as per the rotax AD.  I'm a pretty smart guy when it comes to this stuff.  Its women I have trouble with.  I've built all kinds of racing engines for cars and boats and these Bing carbs are identical to motorcycle carbs I've worked on in the past.

[gregpro50 64]

I met with insurance this morning.  They just want to total it out.  They would like me to buy it back from them and told me to give them a number.  Does anyone know what the salvage value for something like this might be?  I'd like to get it back for repair if reasonable.

[1avidflyer 1983]

Just a wild guess, but if the adjuster can get a problem to go away fairly easy, I think they will do it.  I know of  a plane that was 1/2 a mile back in a bad swamp.  They told the adjuster they would get it out for the salvage rights.  Otherwise the insurance com pany  would have needed to hire someone to do it for them and they would have been way behind when all was said and done.  The adjuster was in florida, the plane was in Mn.   The adjuster went along with it, and myself and 4 friends with 4 wheelers had it out in about  4 hours.  I would angle for $5000 and see where it goes.  Get them to offer a figure first if you can.   After they take a plane, they have to store it and put it up for bids.  That all costs them $.  I'm sure Rotax says a prop strike is a prop strike and needs a tear down = less value for salvage.  Weather you do it or not is up to you, but it's another bargaining point.  Might want to put a dial indicator on the prop shaft for sure to make sure it's still in spec.  How were the FAA guys to deal with if you don't mind saying?  Jim Chuk

[akflyer 1427]

Normal insurance buy back here is around 10%

 

[Av8r3400 1179]

10% of insured value?

We'll talk later about 912 engine and prop strikes and mandatory tears downs.  

Edited 19 Apr 2016 by Av8r3400

[Av8r3400 1179]

Suggest not talking too much on an open forum on this topic. 

[dholly 718]

Hmm 10%, eh?
I'll buy it but you gotta include the seats.

[gregpro50 64]

.  How were the FAA guys to deal with if you don't mind saying?  Jim Chuk

The FAA guy I met with was a manager who happened to be in the area.  He took photos of it and was going to turn it over to an investigator underneath him to see if it even warranted a visit.  It seems they aren't really in a hurry to look into something if no one was hurt.  He said they want to make a determination as to whether it is going to be an "incident" or an "accident".  If an accident the NTSB may get involved.  He said he was leaning towards an incident since it was basically gear collapse damage with no injuries.  He was really a super nice guy to talk to.  He tells us these things happen all the time and commended us for even reporting it.  There were some that suggested not reporting it after it happened but I was always trained to do things by the book and this guy made me feel better about it.  He said they aren't interested at all in placing blame or punishment but that they just want to understand what happened.  He told us of some horror stories he's had to deal with in the past.  Just an interesting guy to talk to.  I just want to know whether they are going to continue investigating or whether I can have my plane back.  I haven't really touched it until they say I can.

As far as the engine goes since it did break the tip of the blade off I need to understand the protocol for getting it checked out.  From what I've read they can do a runout test on it without even removing the engine but I need to confirm.

[gregpro50 64]

Hmm 10%, eh?
I'll buy it but you gotta include the seats.

I'll give you a killer deal and sell the seats for only 5% of the total insured value.

[dholly 718]

Crank run out test is pretty simple, refer to Heavy Maintenance Manual. Here's a quick video.

I remember reading a comment on the Rotax-owner.com forums suggesting an error in the Heavy Maintenance Manual... found it  > http://www.rotax-owner.com/en/rotax-forum/3-4-stroke-technical-questions/4381-912ul-912uls-gearbox-inspection

[gregpro50 64]

Its my understanding that checking for the runout on the crank is only part of it.  The crank shaft is pressed together with pins and not one solid unit.  So upon a sudden stop the crankshaft could twist on the pins.

I've got to check around and see if there is a Rotax tech that can perform this test for me.  The gearbox can be sent out to get checked.

[1avidflyer 1983]

Was the engine actually running when the prop hit?  If it wasn't, not likely that the crank twisted but prop shaft could still be bent from sideways pressure.   Pretty easy to put a dial indicator on the edge of the  prop shaft and check for runout.  YMMV  Jim Chuk

[gregpro50 64]

The prop was spinning but likely just wind-milling.  The throttle was pulled back before the prop hit and it was only the tip of one blade that broke.  I'd be pretty confident in saying that there is no damage to the gearbox or crank but I just want to make sure the required tests are done and documented.

[gregpro50 64]

Insurance is settled.  Whoever said 10% on the buyback was dead on.  So far I've made out pretty well since I insured the aircraft for more than I had into it and my insurance had no deductible.  It's put the money back in my pocket and I get to keep a repairable aircraft.  The insurance company has been excellent to work with.   It was Hallmark Insurance company that I found using the EAA online quote.  I was contemplating having liability only but I'm really glad I went for the full coverage.

Now I need to get the engine checked out.  Any recommendations as to where to send the gearbox and what the cost might be? 

I'm also contemplating selling this engine as is and upgrading to the 100hp 912 but I have no idea what this engine would be worth on the market.