RVG8tor

RVG8tor

Well Known Member
Okay I am going to get the knuckle head award on this one. I was on my third flight of the day, ( good weather in the NW so I wanted to get as much testing done as possible), The is hour 20 on the engine.

At the end of the flight I decide to do a few touch an go. After the first one on downwind I want to bring the prop back a bit for noise reduction but I am still climbing so I don't touch the throttle which is WOT. I pull but don't hear the usual sound so instinctively I pull more then engine gets rough and backfires.

I pull the throttle back and in doing so I see that instead of the prop I was pulling the mixture back. I shove it to full rich and every thing seems normal. I fly one more pattern and land and no abnormal indications from my engine.

I downloaded my data from the EFIS and the event was just under 30 seconds. My CHT never changed but the EGT went from 1350 to 1495 on the hottest (#1 it reads hotter than the others) The other cylinder EGT maxed out in the 1440-1460 range.

So if I understand things correctly I more than likely had a detonation event, so what do I look for to make sure the engine is okay. Post flight inspection shows nothing abnormal. It is good weather again here today and I want to fly again but I feel like I need to do something more to make sure I did not damage anything. At a minimum I want to look in the spark plug holes, I don't have a bore scope but I have a snake camera. I figure I can see damage to the top of the piston and anything abnormal on the bit of the piston walls that I can see.

So any advice from someone experienced with engines or any recommendations on how to proceed. Any prompt replies are appreciated. Since it would be good to get some hours in on the good weather day we will have today.

I did learn the deluxe throttle quad and flying with gloves on requires a bit more attention to detail when adjusting levers!
 
I don't read anything in your description that says anything to me other than normal leaning (with too much % power) which puts you in the "red box". This doesn't automatically mean detonation, just that you are in the danger zone. Detonation is characterized by a runaway CHT which you didn't see.

Even a full-on detonation event is not going to trash an engine in a few seconds.
 
detonation

You most likely have nothing wrong in your engine. But, if you really need to look, detonation is usually shown around the top edges of the piston. But, it takes a while for that to show. It would look like corossion or eating away at the edge of the piston. For a brief moment of this, you will not see any damage. I see it when I rebuild engines, but they have hundreds of hours on them. These engines can run in light (underline light) detonation for hundreds of hours before anything bad usually happens. it can lead to preignition which of course is detrimental to the engine in mere seconds.
Jim
 
Thank goodness

As usual I am making this out to be more than it needs to be. I will take a look inside and then go fly again. Looking at the data the throttle was back to a normal position with in about 10 seconds but it took 30 seconds for the EGT to peak and come back down.

This is a relief, i was reading about detonation and had convinced myself I must have done this.

Cheers
 
As has been stated, you made an error that briefly leaned the engine into an area of POTENTIAL DANGER but not necessarily ACTUAL DAMAGE.

Just to clarify a point. One key to understanding the difference: you stated in your description that your CHT's "never changed". Detonation is a cylinder heat issue (CHT) NOT an exhaust gas heat issue (EGT). Watching your EGT's rise drastically for a few seconds then pushing the mixture knob rich when discovered did nothing to your engine of any consequence. When leaning your engine you want to observe the EGT temps while making the big mixture pull (BMP) because of the extremely fast reactionary time of that EGT reading. This allows you to be in control of the event before something gets out of hand. However, if detonation were to occur, it will be the CHT readings that will give it away. Paying attention to the CHT readings is the important observation point for maintaining control over whether you are dancing with disaster with detonation or not.

Live Long and Prosper!
Steve
 
Another good example of why Lycoming should publish the FAR-required detonation survey results. In the vacuum, we get the Red Box.

Mike, you'll find some of the detonation survey data for the angle valve IO-360 here:

http://www.vansairforce.com/community/showpost.php?p=566697&postcount=81

Specific to your question, the first chart indicates zero detonation at WOT and 2700 RPM. Two caveats; data was taken with timing at 20 BTDC, and the parallel valve combustion chamber may net a different result.

Obviously I prefer data, but my belief here is like the others....a non-event.
 
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Very useful build blog

Hi Mike,

Totally unrelated to this thread, but I just wanted to send you a short "thanks" for your blog - lots of very useful information on there!

Regards,
Mickey
 
I sat with a major fuel component supplier and key sponsor to the often cited and highly regarded engine operation guru's (names omitted on purpose) at Osh a few years ago. He said it was highly unlikely that you could cause detonation on the four cylinder lycomings or clones even if you tried. (Normal configuration properly timed).
I will throw out my challenge again to anyone who can find an example of a detonation event occurring as a result of pilot error. Thus far, none have come forward.
I am not saying we should not be mindful of how we operate our engines or be careless but accidental mixture pulls happen all the time and nobody has hurt anything that I have been aware of. Not saying it has not happened but....
 
The thing I always think of during events like this is how many thousands of times this must have happened in trainer aircraft. Have never seen or heard of a 150/152/172 engine being damaged by detonation....I would say that if it were that easy to do, we would see it all over the place.
 
Brantel said:
The thing I always think of during events like this is how many thousands of times this must have happened in trainer aircraft. Have never seen or heard of a 150/152/172 engine being damaged by detonation....I would say that if it were that easy to do, we would see it all over the place.
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Bingo - these are pretty rugged power plants (the four-bangers, non-turboed, not souped up for racing Lycs...), and people have been ham-handing them for years. We never used to have any significant instrumentation, and as long as they were maintained, they lasted just fine.

It's not NICE to mistreat them, but they will take quite a bit of abuse before showing signs of distress.
 
JonJay said:
I will throw out my challenge again to anyone who can find an example of a detonation event occurring as a result of pilot error. Thus far, none have come forward.
Click to expand...

Which is not to say you can't make one detonate, because you can.
 
DanH said:
Which is not to say you can't make one detonate, because you can.
Click to expand...

I trust you Dan. But you just quoted a snip it of my comments. According to my source, you couldn't if you tried without messing with timing, etc...
So, how can you make a normal four banger denote? I really want to know as while I understand theoretically it should be possible, what conditions would you say it would take?
 
JonJay said:
I trust you Dan. But you just quoted a snip it of my comments. According to my source, you couldn't if you tried without messing with timing, etc...
So, how can you make a normal four banger denote? I really want to know as while I understand theoretically it should be possible, what conditions would you say it would take?
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Pull the prop knob while maintaining high manifold pressure, then lean to ~50F of peak on the rich side.

This example is with very conservative timing (20 BTDC), although CHT, oil temp, and induction air temp are all at max per certification standards:

dexxf7.jpg


Timing at 25 should increase detonation frequency or require reduced temperatures.
 
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DanH said:
Pull the prop knob while maintaining high manifold pressure, then lean to within 100F of peak on the rich side.

This example is with very conservative timing (20 BTDC), although CHT, oil temp, and induction air temp are all at max per certifications standards:

2n5edv.jpg


Timing at 25 should increase detonation frequency or require reduced temperatures.
Click to expand...
And if you have no PROP KNOB (i.e. fixed pitch) and you lean. . . to 100F of peak on the rich side. . . will you get the same effect?

It seems to me one would have to be able to manipulate the Mixture, the MAP and the RPM in order to make this happen.
 
Every fixed pitch plane takes off at full manifold pressure and low RPM.
The static RPM is typically 2200 @ full throttle, which would be outside the safe zone on the graph. All thru the take off and climb out, the same. RPM increases to 2400 or so, but still over square.
We have a manifold pressure gauge with fixed pitch prop. It seems to be over square all the time until stable cruise speed.this is the un monitored reality of most certified fixed pitch planes. So how does this fit in?
 
RVbySDI said:
And if you have no PROP KNOB (i.e. fixed pitch) and you lean. . . to 100F of peak on the rich side. . . will you get the same effect?
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Steve, I posted the wrong graphic (limiting manifold pressure) and have since replaced it with the correct one....the dyno chart from a detonation survey. Sorry, my bad.

To answer your question, no, not if your engine is the one in the dyno chart. It didn't detonate until leaned past 75 ROP, with a detonation range of 75 ROP to 50 LOP.

SHIPCHIEF said:
Every fixed pitch plane takes off at full manifold pressure and low RPM.
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And, in general, at full rich. Not that it matters if you're careful. Take a good look at the pro-detonation settings above. You could easily lean to 150 ROP, pick up some power, and still be outside the detonation zone.
 
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Detonation will knock down the boundary layer of air molecules that insulate the combustion chamber parts , the flame front heat will then transfer to the piston and head, increased CHT and you will actually see lower EGT
 
Dan - am I understanding the chart that even at these extremes of CHT, OT, and Induction air temps detonation occurred less than 15% of the time in this survey?
If so it would seem to support what I was told: you can't cause detonation even if you tried.... Or maybe better put, you would have to try and try hard.
I apologize if I am not reading the graph correctly.
Really interesting stuff regardless.
 
JonJay said:
Dan - am I understanding the chart that even at these extremes of CHT, OT, and Induction air temps detonation occurred less than 15% of the time in this survey?
Click to expand...

As I understand the chart, 15% of firing events.

If so it would seem to support what I was told: you can't cause detonation even if you tried.... Or maybe better put, you would have to try and try hard.
Click to expand...

Clearly you can, but true, not under typical conditions, the key difference being temperatures. Certification requires oil and induction air temperature at maximum, one CHT at maximum, and all other CHT's within 50F of maximum.

Again, please note....the detonation survey charts posted here are for an angle valve cylinder head run at 20 BTDC. They're a pretty good guide for my IO390 (same compression, combustion chamber, and timing), but perhaps not representative of your engine.
 
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Education Never ends!

Thanks everyone for the information, my bone head mistake has caused some good discussion. Thanks Dan for the link to the previous thread, it helps me understand things more.

The real lesson I learned is noise be damned when in the pattern off a touch and go leave the prop forward and just wait for the throttle to come back once on downwind.

Weatherman really missed the mark today, it snowed with not even rain was in the forecast last night, go figure. Tomorrow shows promise, only 18.2 more hours of testing which will be filled with some aerobatic maneuvers!
 
Not necessarily

SHIPCHIEF said:
Every fixed pitch plane takes off at full manifold pressure and low RPM.
The static RPM is typically 2200 @ full throttle, which would be outside the safe zone on the graph. All thru the take off and climb out, the same. RPM increases to 2400 or so, but still over square.
We have a manifold pressure gauge with fixed pitch prop. It seems to be over square all the time until stable cruise speed.this is the un monitored reality of most certified fixed pitch planes. So how does this fit in?
Click to expand...

RVG8tor said:
Thanks everyone for the information, my bone head mistake has caused some good discussion. Thanks Dan for the link to the previous thread, it helps me understand things more.

The real lesson I learned is noise be damned when in the pattern off a touch and go leave the prop forward and just wait for the throttle to come back once on downwind.

Weatherman really missed the mark today, it snowed with not even rain was in the forecast last night, go figure. Tomorrow shows promise, only 18.2 more hours of testing which will be filled with some aerobatic maneuvers!
Click to expand...

Hey Nemo:

Congrats on getting your machine in the air. Good on ya!

I would suggest that you should set RPM during pattern work, else you will get used to a differt drag profile. It's OK to set 2400 as your max RPM and work from there - in fact, you don't need FT at all in our planes. This might make the equation easier.

I doubt you upset your engine - as noted previously, detonation registers as a CHT event, and you saw nothing.

BTW practice finals with the prop lever all the way back, just to get a picture of what is possible in terms of glide ratio...

Carry on!
Mark
 
Mike - one suggestion being new to your airplane that might help. Sit in your airplane and walk yourself through all of the controls, switches, etc... Then close your eyes and walk through them again until you can find everything without looking. The mixture knob and the prop knob actually feel differently. It's subtle but if you practice blind the difference will jump out at you.
 
Gloves

JonJay said:
Mike - one suggestion being new to your airplane that might help. Sit in your airplane and walk yourself through all of the controls, switches, etc... Then close your eyes and walk through them again until you can find everything without looking. The mixture knob and the prop knob actually feel differently. It's subtle but if you practice blind the difference will jump out at you.
Click to expand...

This is very good advice and it is something I did as advised by my Flight Adviser before the first flight, mostly in case of emergency, on this particular flight I happen to ware gloves for the first time so the tactile feel of the knobs was different. I was also doing touch and gos which I had not done up to this point. This all proves once more that new airplane and new flight regimes present potential for lapse in performance.

Cheers
 
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