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Rejected Take Off

B

bryanhorgan

Member
I had my first ever rejected take off today.

While taxiing, I had what I thought was some light vapor lock.
Fuel pump on, increase RPMs, problem seemed to be solved.

Normal run-up. Go to take off. I'm full fuel, close to gross weight. Full power, adjusted mixture. Plane struggles a bit to take off (this is the point I SHOULD have rejected). I push on, thinking I'll gain speed and be fine.

Then I get a "ENGINE TEMPERATURE" warning. CHTs are 426. Not good.
I'm off the runway, in ground effect. I decide I have to land immediately.
Pull power to idle, fight ground effect, slam on brakes, stop 50ft short of the runway end.

I wanted to remind everyone to pay attention to your ground roll. If it seems slower, or longer than it should, REJECT the takeoff there.

Also, anyone have any ideas on what would cause high CHTs so quickly? Fuel pressure was 6 psi (normal). I found an oil leak coming from between the engine case and the oil sump. Mid time Slick mags. 0-360 RV7A.
 
Good job getting back on the ground safely. My first guess would be clogged injector causing a lean mixture on that cylinder.


bryanhorgan said:
I had my first ever rejected take off today.

While taxiing, I had what I thought was some light vapor lock.
Fuel pump on, increase RPMs, problem seemed to be solved.

Normal run-up. Go to take off. I'm full fuel, close to gross weight. Full power, adjusted mixture. Plane struggles a bit to take off (this is the point I SHOULD have rejected). I push on, thinking I'll gain speed and be fine.

Then I get a "ENGINE TEMPERATURE" warning. CHTs are 426. Not good.
I'm off the runway, in ground effect. I decide I have to land immediately.
Pull power to idle, fight ground effect, slam on brakes, stop 50ft short of the runway end.

I wanted to remind everyone to pay attention to your ground roll. If it seems slower, or longer than it should, REJECT the takeoff there.

Also, anyone have any ideas on what would cause high CHTs so quickly? Fuel pressure was 6 psi (normal). I found an oil leak coming from between the engine case and the oil sump. Mid time Slick mags. 0-360 RV7A.
Click to expand...
 
"Mid time Slick mags. 0-360 RV7A."

2 thoughts:
-As mag points wear out, ign timing advances, but this would be a gradual change.
-Carb for some reason is leaning out. I had a carb do this once, the lean mixture valve hsg that should have been solidly crimped in the bottom of the fuel bowl started rotating - gradually leaning & starving the metered fuel flow.
There was a SB out on MA4 carbs a long time ago for this, but the knockoff (new) Avstar carb I had didn't.
 
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Bryan, any data you can download to pinpoint the cylinder/timing of the event etc.?

Since you said you found an oil leak I'm assuming you've had the cowl off looking for squirrel nests and such? Did you take a good look at intake tubes and fittings for obvious failure that could cause a super lean condition? Loose mag?

SO many questions! Well done getting it back and solid lesson learned.

Cheers
 
Itll take me a day or 2 to post data. Plane's in tip top shape. Hangared. No nests, cooling, baffle issues. The intake tubes are a great suggestion, I'll have to check them.
 
Ralph Inkster said:
"Mid time Slick mags. 0-360 RV7A."

2 thoughts:
-As mag points wear out, ign timing advances, but this would be a gradual change.
-Carb for some reason is leaning out. I had a carb do this once, the lean mixture valve hsg that should have been solidly crimped in the bottom of the fuel bowl started rotating - gradually leaning & starving the metered fuel flow.
There was a SB out on MA4 carbs a long time ago for this, but the knockoff (new) Avstar carb I had didn't.
Click to expand...

We did retard the ignition about 150 hours ago from 25 to 23 degrees as we previously had high CHTs on climbout. It stopped the issue then. Do you think 2 degrees advancing in 150 hours is probable?

Carb is an AVSTAR LVC-5-5BPA. Sounds like I may have avoided that SB.
 
Carb

The carb issue also has been an issue on MS carbs. This is a rich condition that should not cause high CHT. High CHT is timing or lean condition.
CHT red line is 500 degrees. 425plus is not a cause for concern except for break in of new engine. I believe Mahlon Russell has stated that he has never seen any evidence that 425 CHT causes any engine damage.
I would suggest that there are probably thousands of older airplanes with NO CHT INSTRUMENTATION that have operated for perhaps millions of hours with CHT well above 400.
If you had valid reason to believe the engine was not producing normal power that is an entirely different situation.
 
Runway lenght ?

Bryan, glad you made it safely back on ground.
When the engine is just "slightly" below par, that's arguably a difficult decision to make at one of the worst time in a take-off.

Out of curiosity, what would you say is the lenght of your take-off run/land and brake distance ?
I notice you have an "A" model, making it somewhat easier to brake harder once on ground.
Good luck in correcting the problem.
 
The runway I was on is 4000 ft. I had juuust enough room to take off in ground effect, decide continuing was worse than stopping, come down, burn off some energy and stop.

I'm betting my takeoff distance was around 1200ft. I struggle to call it takeoff because I really hadn't.
 
jrs14855 said:
The carb issue also has been an issue on MS carbs. This is a rich condition that should not cause high CHT. High CHT is timing or lean condition.
CHT red line is 500 degrees. 425plus is not a cause for concern except for break in of new engine. I believe Mahlon Russell has stated that he has never seen any evidence that 425 CHT causes any engine damage.
I would suggest that there are probably thousands of older airplanes with NO CHT INSTRUMENTATION that have operated for perhaps millions of hours with CHT well above 400.
If you had valid reason to believe the engine was not producing normal power that is an entirely different situation.
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While I mostly agree, the rate of CHT increase was the problem. At takeoff start it was around 350. it increased 75 degrees in about 1200 feet. My engine monitor has a warning at 410. The increase happened so quickly, by the time I heard the aural warning and looked at the temp it was at 426. Had I continued I have no doubt I would have hit 500 degrees where I also have no doubt the cylinder heads would have departed the aircraft.
 
bryanhorgan said:
We did retard the ignition about 150 hours ago from 25 to 23 degrees as we previously had high CHTs on climbout. It stopped the issue then. Do you think 2 degrees advancing in 150 hours is probable?

Carb is an AVSTAR LVC-5-5BPA. Sounds like I may have avoided that SB.
Click to expand...

That SB you found doesn't describe what was happening with my Avstar carb.
In my case the vertical lean mixture rod thru the carb fits into a half moon valve sleeve at the bottom of the float bowl. According to the Marvel Schrader MA4 SB, some of these half moon sleeve valves were not secure & should have been shot peened around them to prevent rotation (& therefore causing mixture or shutoff issues). As the Avstar carb is a copy of the MA4, they should have secured this valve similarly, but didn't.
So when your carb is being serviced for the SB you found, have them also make sure that bottom valve can't move.
 
Ralph Inkster said:
That SB you found doesn't describe what was happening with my Avstar carb.
In my case the vertical lean mixture rod thru the carb fits into a half moon valve sleeve at the bottom of the float bowl. According to the Marvel Schrader MA4 SB, some of these half moon sleeve valves were not secure & should have been shot peened around them to prevent rotation (& therefore causing mixture or shutoff issues). As the Avstar carb is a copy of the MA4, they should have secured this valve similarly, but didn't.
So when your carb is being serviced for the SB you found, have them also make sure that bottom valve can't move.
Click to expand...

Thanks for the heads up. Ill make sure to mention this.
 
CHT

The engine is not going to come apart at 500 degrees CHT. Instead of enhancing safety an improperly set engine alarm decreases safety.
I have over 2500 hours Pitts time. 1000 plus with 0 360 parallel valve, fixed pitch. I don't think I have ever flown a Pitts with CHT gage. There is absolutely no doubt in my mind that when flown hard the Pitts is routinely at 500 degrees CHT and probably over 500. Lycoming in the past has told me the engine will run to TBO with the temperatures at red line. I don't know if that is their current position.
In your case 350 at start of takeoff is not normal in my opinion. My 0 320 powered Tailwind has a much tighter cowl than typical RV. I was very concerned departing Oshkosh but when I started the takeoff the CHT was below 350 and stayed below 400. Cowl flap and custom plenum.
 
What the guys are saying about the CHT may very well be true, but something is different. Something has changed with your aircraft, and your engine may be talking to you. If you can pull up the data, did all of the CHTs go high, or just one cylinder? What were the EGTs doing across the cylinders?

It's been hella hot lately; was the engine already pretty toasty by the time you applied WOT for takeoff, or did the CHT "run away" quickly? If it's the latter, it could possibly be a detonation or preignition issue. Mike Busch talks about a Cirrus that had a CHT run crazy high and the piston destroyed itself within minutes. The pilot didn't see his EFIS alert until it was too late. I don't want to steal his thunder, but he conducted an EAA webinar (it's on YouTube) where he talks about that. I think it was titled something like How Hot is Too Hot? Even if that's not what happened in your case, it's an informative webinar.
 
Yet another reminder to never do an intersection takeoff and give up runway behind you. Thanks for the story.
 
I was going to respond to your comment about the “cylinder departing the airplane” but jrs14855 beat me to it. Pay attention to his comments. They are true. Lycoming has a 500 deg max limit but that in no way suggests your engine will immediately come apart if you reach that temp. Lycoming also states their engine can run at 450 deg. So, if you believe Lycoming then my suggestion is to reset your CHT warning to 450 and trust they no what they are talking about.

As for your situation, perhaps something could be awry or perhaps not. If you are concerned about whether you did some kind of damage perhaps you should take a look and see. Borescope the cylinders with a knowledgeable person and see what it looks like in your cylinders.
 
bryanhorgan said:
I had my first ever rejected take off today.

….

I wanted to remind everyone to pay attention to your ground roll. If it seems slower, or longer than it should, REJECT the takeoff there…..
Click to expand...

This is a good comment. I always look for 2/3 flying speed no later than 1/2 the runway length. That is used frequently by backcountry pilots.
 
Related comment - Do you taxi with the engine *leaned aggressively**? You don't get lead scavenging at lower temps and plugs load up with carbon/lead deposits. High power burns it off. LEAN aggressively on the ground, what I do. My plug fouling wows went away long ago.

"*leaned aggressively*" - My definition, lean to rough, loss of RPM, starting to cut-out; then enrich for smooth operation (on the ground but that works in the air as well below 75% power). No engine gauge required. Before we had flight test instrumentation (CHT, EGT every jug, FF) it was done by feel, sound. When leaning you don't yank it out fast and kill engine, but once you know your plane you know where "ground lean" mixture position is.

I remember renting a planes late 80's and flight instructing in the 90's, besides the engine instruments required by the FAR's (OP, FP, RPM, MAP), if the plane I was flying had a single CHT gauge it was deluxe ha ha. Hey I am a nerd, love data, but may be TMI. In this case, sure if not normal still on ground reject. However if a short runway, and stopping would mean going off the end, go fly. In summer you may hit 430 CHT. It may only require leveling off, reducing power, enriching if applicable. Like cars, check engine/master warning light sometimes means nothing. :D Don't make a warning into an emergency is my point.
 
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bryanhorgan said:
it increased 75 degrees in about 1200 feet.
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I took off with the cowl plugs in once. I didn't get to 400 until pattern altitude; that is full power and zero cooling air flow. In my mind about the only thing that can raise CHTs 75 degrees in 2 or 3 seconds is detonation or pre-ignition. If it were my engine I would be borescoping the cylinders and looking for a serious issue in the ignition causing extreme advance; Talking 10 or 20 degrees, not a few. Lean conditions can also cause detonation at full power, though not as common as excessive advance.
 
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We had an RV-6 that always had hot CHTs on climb out and our climb was done with respect to the CHT gauge rather than IAS.

We talked to the head engineer at Lycoming on the phone and he told us a Lycoming will go to TBO up to but not over at 500 degrees with a handful of temp excursions above 10 degrees or so not making a big difference.. The lower limits set by airframe manufacturers is their way of eliminating off-tolerance gauges and provides a buffer with respect to liability. He says that's the call of the airframe manufacturers but causes him phone calls like ours all the time.
 
lr172 said:
I took off with the cowl plugs in once. I didn't get to 400 until pattern altitude; that is full power and zero cooling air flow. In my mind about the only thing that can raise CHTs 75 degrees in 2 or 3 seconds is detonation or pre-ignition. If it were my engine I would be borescoping the cylinders and looking for a serious issue in the ignition causing extreme advance; Talking 10 or 20 degrees, not a few. Lean conditions can also cause detonation at full power, though not as common as excessive advance.
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You left cowl plugs in. Wow. CHT's did not get hot? Great. Detonation is not noticeable to pilot, can happen quickly, and high(er) CHT (than nominal) is not necessarily the hall mark of detonation, at least to where pilot can react. Detonation happens fast and can be catastrophic. I appreciate your caution but engine damage is unlikely here (at least because of lean condition). It's just slightly high CHT well below Red Line CHT. Carbs have one advantage over FI, no blocked injector issue. Carbs have their own issues, but in general fuel distribution in a carb does not radically cut one jug out like a blocked injector.

If CHT is high Pull power back, reduce climb, increase air speed. You can not get detonation below 75% power. RV's climb well at 75% power.

Lycoming CHT RED LINE 500F!!! Now you'd be kind of nuts to fly around w/ CHT near Red Line CHT. 430F is not an emergency. Lycoming recommends much lower CHT for long engine life.

My goal is keep CHT below 400F. My CHT "Red Line" is 420-430F.
 
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What JUG? 1, 2, 3, 4? Hours and Maintenance history of engine? Did you check your baffling. I have seen this happen where a baffle to cowl seal blows out or inner cylinder baffle went away.

Cheers.

NICE scope pics. Yep may be time to pull the jug. The score I don't know. How is the leak down? A carbon chunk on valve seat can cause issues. The beauty of Lycs is you can pull jugs with engine installed fairly easily. I have done it, and the tools are not expensive. I had A&P help me, but I could do it myself again. I did the Oshkosh Lycoming Tear Down and Assembly course at Air venture this year. No hands on just observe and Q&A. I recommend it. I got 4 hrs credit towards A&P certificate. Now building an EAB kitplane log that can be towards an A&P.
 
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gmcjetpilot said:
What JUG? 1, 2, 3, 4? Hours and Maintenance history of engine? Did you check your baffling. I have seen this happen where a baffle to cowl seal blows out or inner cylinder baffle went away.

Cheers.

NICE scope pics. Yep may be time to pull the jug. The score I don't know. How is the leak down? A carbon chunk on valve seat can cause issues. The beauty of Lycs is you can pull jugs with engine installed fairly easily. I have done it, and the tools are not expensive. I had A&P help me, but I could do it myself again. I did the Oshkosh Lycoming Tear Down and Assembly course at Air venture this year. No hands on just observe and Q&A. I recommend it. I got 4 hrs credit towards A&P certificate. Now building an EAB kitplane log that can be towards an A&P.
Click to expand...


1100 Hour Engine. No previous issues. Oil changes and Camguard every 50-75 hours. Plane is flown at least every 2 weeks. Goes through a quart every 6 hours, probably 70% of that is an oil leak (another issue I'm tracking down).

Our Baffling is like a 9/10. There's only a couple areas that *may* leak. I'm gonna sew a couple sections together to get it to a 10/10.

Cyl 2 is the one with the scoring. It's also the one with the lowest indicated CHT. So maybe no correlation to my issue? I still need to do a leak down test. After everything I've read though, I'm not sure they're the best indicator of a problem.
 
bryanhorgan said:
Yes. Fuel Pressure was normal. around 6 psi.
Click to expand...

My thoughts would still be focusing on either a fuel issue or a bad bearing. A clogged main jet or enrichment circuit would cause an overly lean condition, which could lead to detonation and a very quick temp rise. It would also limit power and cause the drop in max rpm.

You might start by disconnecting the fuel line at the inlet to the mechanical pump and seeing how many gallons per minute your flowing from the tank. This would rule out a clogged pickup tube, tank selector, air leak before the electric pump, or restriction in the electric pump.

Then possibly pull the carb bowl and inlet screen and check the main jet and float. A clogged main jet is self explanatory. A stuck float could cause a low level in the bowl and cause a lean condition as well.

What did your plugs look like when you pulled them for the boroscope pic? Where they still tan/black or did they have an ash/white color on them?

I only mention a bad bearing as a remote possibilty, but a bearing that is starting to seize will have extra drag (limiting max rpm) and will create extra heat. Pull a set of plugs and rotate the engine by hand. You should be able to feel a bearing this bad when you pull the engine through.
 
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