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Engine failure on take-off.

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Jim Feldmann

Joined: 01 Sep 2008
Posts: 54
Location: Burbank, CA

Posted: Sat Mar 28, 2009 6:41 pm Post subject: Engine failure on take-off.

I had an engine failure on takeoff today. Fortunately it was a long runway and it happened at 10 feet altitude. No injuries, no damage, and no idea why it happened. 



Actually, the engine (Rotax 912 ULS) did not stop. It was running smoothly during taxi and warm up. Mag check was fine. I held short for 5 minutes or so for incoming traffic, running the engine from 2500 to 4000 for short periods. No problems. On takeoff, the engine pulled cleanly to 5000+ for the 5 or 6 seconds it took to break ground, then suddenly started running very rough and dropped to 2500 rpm or so. I immediately pulled the throttle to idle and landed. 



While taxiing back to the hanger it ran fine, I tried full throttle again a couple of times and it ran perfectly. So what I have is an intermittent or one time problem that could be deadly. 



I don't think it was ignition related, because if it was a failure of one "mag" it would have run much better than it did, and if both failed, it wouldn't have run at all. That leaves fuel or mechanical. 



The carbs have recently been rebuilt. After I calmed down, I checked the float bowls, they are clean, the gascolator is clean and the fuel pump is putting out 4.5 psi., right on spec. Fuel is flowing freely through all of the inline filters and the header tank is full. I did recently drain all of the fuel out of the airplane to fix a leak in the header tank. Then I simply refilled the tanks from the top. Could there have been air in the fuel line between the header tank and the gascolater? The engine had been run for half an hour or so since then, but mostly at low throttle. 



I have checked the throttle linkages also. No problem there. The plugs look good too, but my runups on taxi back would have obscured the evidence anyway. 



My A&E suggested that it could be sticky valve. 



Has anyone experienced a similar problem? Any thoughts on what to look for? I'm very hesitant to fly it again until I know what caused the problem

_________________
Jim Feldmann
Kitfox IV Speedster / 912 lost to prop failure
Building a Kitfox 5 Voyager

thilo.kind(at)gmx.net
Guest

Posted: Sun Mar 29, 2009 2:03 am Post subject: Engine failure on take-off.

Hi Jim,



I had a similar experience a while ago, although the RPM only dropped to

4,000 or so and engine was running very rough. Turned out, that the choke

was not completely closed (the spring didn't pull the choke all the way to

close).



Thilo 



--

karoliina.t.salminen(at)g
Guest

Posted: Sun Mar 29, 2009 3:42 am Post subject: Engine failure on take-off.

Hi,



 	  Quote: 	
		   Actually, the engine (Rotax 912 ULS) did not stop. It was running smoothly during taxi and warm up. Mag check was fine. I held short for 5 minutes or so for incoming traffic, running the engine from 2500 to 4000 for short periods. No problems. On takeoff, the engine pulled cleanly to 5000+ for the 5 or 6 seconds it took to break ground, then suddenly started running very rough and dropped to 2500 rpm or so. I immediately pulled the throttle to idle and landed.


	


I know of one case of Rotax running rough at one point and it was

noticed that it does not quit unless you get the carburetors flooded

because of vibration. Good idea is to reduce power (not apply full

power because it could aggravate carburetor flooding) and land as soon

as possible.



There were three causes in this case:

- one spark plug cable was faulty and sometimes disconnecting

- fuel lines had been replaced and some pieces of the rubber pipes had

contaminated

the fuel lines by mistake, very tiny pieces were enough to cause

problems and even if the tubes

had been inspected for dirt, some pieces still got in the system

- choke cable was jamming and was not completely closed (caused

vibration and significant reduction of power)



The choke cable caused general roughness and lack of power while the

spark plug cable

problem finally identified itself in magneto test. It was very hard to

reproduce the problem on the

ground.



Mechanically the engine

was in fact in excellent condition. Maybe you should check these

things first before suspecting

a mechanical problem. I have never heard of anybody having a

mechanical (valve/cylinder) problem in a

Rotax 912 and the engines have constantly reached their TBO hours in

our flying clubs without a single mechanical

failure that I would have heard of.



In your case, the rpm dropping to 2500 sounds like it the carburetors

were already flooding. It is not the issue itself,

but the consequence of it. If full power is continued when the carbs

are flooding, the engine will quit.



Best Regards,

Karoliina

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Sun Mar 29, 2009 3:43 am Post subject: Re: Engine failure on take-off.

jim,



I do not believe a single sticky valve would cause a 50% drop in rpm at full throttle.  You don't mention how large is your header tank. If it is small enough for it to be nearly exhausted during your long wait for traffic with periodic throttle advancements to 4000 rpm then your fuel flow to the header could have been interrupted and the header emptied. Assuming your tanks are above the header tank I would run a gravity only fuel flow test from each tank to header tank in normal take-off attitude (tail down). Each tank should flow a minimum of 150% of full throttle fuel requirement by gravity alone. If this does not reveal a problem then I would suggest you tie down the airplane securely for extended static run-up and see if you can repeat this. If you can not repeat this I would dismantle and inspect each segment of the fuel system one at a time checking for anything that could cause a one time or intermittent blockage.



This is a good bit of work but should take a lot less time than recovery in the hospital and rebuilding your airplane.  The timing of the power loss could have been a lot worse and could be next time it happens if you don't find the cause.

_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

daveaustin2(at)primus.ca
Guest

Posted: Sun Mar 29, 2009 3:51 am Post subject: Engine failure on take-off.

Have you checked the tank venting?

Dave Austin  601HDS - 912

airgriff(at)surferz.net
Guest

Posted: Sun Mar 29, 2009 4:39 am Post subject: Engine failure on take-off.

Hi Jim, glad all went well. I’m not a mechanic but my initial thoughts were that the engine ran fine during start up, taxi, run up, and faltered when it was looking for a full volume of gas. Very likely something restricted the flow when a large amount of fuel was needed. You could have carb bowls full during low rpm, normal pressures, and still not have full flow at full rpm.  I would check for debris, main tank filter, off-on valve, pinched or crimped lines, etc., something that may have restricted the flow?  

Fly Safe  

Bob Griffin  

       [quote][b]

Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Sun Mar 29, 2009 5:23 am Post subject: Re: Engine failure on take-off.

Hi Jim,



I'm with Thom on this. It is most likely a fuel issue and especially since you just worked on the fuel system. Do as Thom suggest and check the fuel system, do a flow test and tie it down and do an extended max rpm run test. Something may be floating in the system and doesn't go to a small clog point until you demand high fuel flow then it trys to flow down stream and gets hung up.

At some point you may have to pull the carbs, but do the other inspections and test first. When draining fuel use a white strainer of some sort or some container that is very clean to look for debris in the fuel.

_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Sun Mar 29, 2009 5:56 am Post subject: Engine failure on take-off.

This is just a rough guess... emphasis on the word rough.



Your engine picked up something, probably water when the throttle was opened

and the fuel flow through the carbs was faster.  I'd suspect condensation in

the carb bowls.  At lower throttle settings the water wasn't being picked up

but once you oened the throttle...  I'd try tying the tail down and doing a

couple of full throttle runs of maybe 30 sec to a minute each.



Do you have a gascolator?



Noel



--

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

lucien

Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM

Posted: Sun Mar 29, 2009 6:35 am Post subject: Re: Engine failure on take-off.

 	  Roger Lee wrote: 	
		  Hi Jim,



I'm with Thom on this. It is most likely a fuel issue and especially since you just worked on the fuel system. 	




I had a similar experience with my 912uls right after I'd done a fuel line/filter change. The motor ran fine during warmup and during the mag check, but on the takeoff run as I approached full throttle basically one side of the engine shut down. Shook the entire plane and of course I got right off it.



Turned out to be some debris having gotten into one of the carbs. A small piece of rubber or something came out when I pulled the main jet and sucked through it.



If you do anything with the fuel system you have to exercise absolutely operating room cleanliness and diligence. I.e. when you change the lines, make sure you debur and cleanup any sharp edges on any "T"'s or other fittings you may use. These edges can slice into the line and send the little bits downstream into the carbs.



What I do when I make the new fuel line assemblies is I flush them very thoroughly with clean gas and then cap the ends with (clean) rubber stoppers from the autoparts place. This way there's no possibility of any junk getting in the lines as I thread them through to their final positions. Only after that do I uncap and then push them onto the fittings at the fuel pump and carbs. I also cap those fittings while I'm off making the fuel line assemblies.



There's no amount of attention to cleanliness and anality that's sufficient when working with the fuel system and lines. My case where my engine got crap in the carburettor was inattention to this detail when I redid the lines. I was lucky in that it happened on the ground and not in the air....



LS

_________________
LS
Titan II SS

Tom Jones

Joined: 12 Mar 2006
Posts: 752
Location: Ellensburg, WA

Posted: Sun Mar 29, 2009 6:40 am Post subject: Re: Engine failure on take-off.

 	  Quote: 	
		  When draining fuel use a white strainer of some sort or some container that is very clean to look for debris in the fuel. 	




Paint strainers, easy to find and inexpensive.

_________________
Tom Jones
Classic IV
503 Rotax, 72 inch Two blade Warp
Ellensburg, WA

rampil

Joined: 04 May 2007
Posts: 870

Posted: Sun Mar 29, 2009 7:21 am Post subject: Re: Engine failure on take-off.

At the beginning of my flight testing I had a very similar event

which repeated several times.



Look for soot around your float bowls.  It turned out that at high

throttle, my #3 exhaust to muffler pipe would jiggle loose and

shoot a jet of hot gas at my carb bowl, boiling the fuel and stopping

one side of the engine!



Do you have carb heat shields?

_________________
Ira N224XS

Jim Feldmann

Joined: 01 Sep 2008
Posts: 54
Location: Burbank, CA

Posted: Sun Mar 29, 2009 8:15 am Post subject: Re: Engine failure on take-off.

Thank you all for your replies and suggestions.  I will definitely follow up on all of them.



I am particularly intrigued by Rampil's response, because I just noticed a smudge above the right EGT probe, which is below the right carb.  That will be the first thing I take care of.



If anyone has any other thoughts, please add them to the list.

_________________
Jim Feldmann
Kitfox IV Speedster / 912 lost to prop failure
Building a Kitfox 5 Voyager

gfmjr_20(at)hotmail.com
Guest

Posted: Sun Mar 29, 2009 10:23 am Post subject: Engine failure on take-off.

Jim--

  Had a similar issue and it turned out to be debris C however C it was not obvious on warm up C taki or extended full throttle attemps. It finally was found when we tied the plane down in a climb attitude-about 15 degree slope. We found a grassy slope on the airfield  C tied it down and cranked full power. It still took a couple of minute C but eventually the engine began to loose power. One carb had run dry due to debris in the fuel line that would float back and forth C but clog things up at attitude and fulll power.



Good luck

George



[quote] Subject: RotaxEngines-List: Re: Engine failure on take-off.

 From: feldesign(at)earthlink.net

 Date: Sun C 29 Mar 2009 09:15:58 -0700

 To: rotaxengines-list(at)matronics.com

 

 --> RotaxEngines-List message posted by: "Jim Feldmann" <feldesign(at)earthlink.net>

 

 Thank you all for your replies and suggestions.  I will definitely follow up on all of them.

 

 I am particularly intrigued by Rampil's response C because I just noticed a smudge above the right EGT probe C which is below the right carb.  That will be the first thing I take care of.

 

 If anyone has any other thoughts C please add them to the list.

 

 --------

 Jim Feldmann C 3rd owner

 1994 Kitfox IV Speedster / 912

 Working on my Sport Pilot Certificate

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=236666#236666

 

========================Quick access to Windows Live and your favorite MSN content with Internet Explorer 8.   	  Quote: 	
		  [b]

b.carl@sympatico.ca

Joined: 20 May 2008
Posts: 77

Posted: Sun Mar 29, 2009 2:58 pm Post subject: Engine failure on take-off.

Hi Jim,

Lots of good advice from the list.

Let me add the possibility of vapour lock after the long ground run.

Also recommend you add a fuel press gauge and warning light. They help to 

diagnose problems as well as ident them before they lead to and engine 

failure.

Carl

---

Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Sun Mar 29, 2009 6:17 pm Post subject: Re: Engine failure on take-off.

Hi Guys,



While on the subject of vapor lock I would recommend that all have a recirculation line in the fuel system if you don't as this will help reduce a chance of vapor lock. The is Rotax recommended.

_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056

321PT

Joined: 23 May 2006
Posts: 40
Location: Texas

Posted: Mon Mar 30, 2009 5:52 am Post subject: Engine failure on take-off.

Had it happen once to me... has never happened again (200 hours now).  I was actually taxing out to take off.  Mine was in Florida, early AM, high humidity.  Probably carb ice.  [quote][b]

ralston

Joined: 14 Jun 2009
Posts: 2

Posted: Sun Jun 14, 2009 5:21 pm Post subject: Re: Engine failure on take-off.

Have you determined the reason for your low RPM on take off as of yet?



ra

Jim Feldmann

Joined: 01 Sep 2008
Posts: 54
Location: Burbank, CA

Posted: Mon Jun 15, 2009 8:14 am Post subject: Re: Engine failure on take-off.

Well, we think so.  Sorry for not getting back to the list.  And thank you all for your suggestions.  We checked them all.  



The airplane is flying again and has never had a recurrence.  I found a very small exhaust leak around the right EGT probe which was directing hot exhaust toward the bottom of the right float bowl.  That combined with the long wait to take off and the auto gas I was using probably caused the fuel in the right carb to boil.  We have decided that it was vapor lock in one carb.



I fixed the exhaust leak and switched to 50% avgas, and we have been unable to duplicate the problem.

_________________
Jim Feldmann
Kitfox IV Speedster / 912 lost to prop failure
Building a Kitfox 5 Voyager

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