Has anyone been unable to richen the mixture to the 75 degree rich of peak level. I have a Cirrus SR20 and get a peak EGT of 1410 degrees. At times/altitudes I can not get below 1350 degrees unless I turn on the electric fuel pump.
Any help would be appreciated. … Personal replies welcome
w8nn@chartermi.net Thanks
In reply to:
I have a Cirrus SR20 and get a peak EGT of 1410 degrees. At times/altitudes I can not get below 1350 degrees unless I turn on the electric fuel pump.
Bill,
Not at all unusual for a '20… because of the automatic altitude compensation built into the mixture system. 1350 is 60 ROP… close enough, probably.
The bigger issue, one you should bear in mind, is that 1410 was your peak at a certain altitude, temperature, power setting, etc… it’s not a constant… and unless you have an engine monitor, it’s the peak for just one cylinder. If you DON’T have engine monitoring, well, personally I’d just leave the mixture control firewalled forward for most operations. (The exception would be where I needed performance for high density altitude takeoffs, something to be very careful of in a '20 anyway).
Hope this helps…
Mike.
Bill,
I fully agree to what Mike said. I live in an area where we mostly see standard temperatures - no leaning necessary for the SR20 below 7000 ft is my experience. The automatic compensation works great.
Timm Preusser N747TG
That puzzles me. Is everybody agreeing here? On our '20, there is always some leaning necessary in cruise flight to achieve 75°ROP, even when cruising at 1000 feet in winter. That’s also consistent with the fuel flows. If I set the MP for 75% and don’t lean, fuel flow is usually in the 12-13 gal range, then another 1-2 gals are “leaned off”. Anyone?
BTW, peak EGT occurs usually at around 1440 on the steam gauge. No engine monitoring, though.
Phil
I see the same as you. With the mixture full rich and full power, the EGT needle doesn’t budge off the stop, at any altitude, at least any that I’ve paid attention to. In cruise at any altitude with power pulled back to 75%, the mixture knob needs to come back a fair way to get 75ROP. Peak is usually in the range 1425 to 1450.
My experience is similar to Phil and Clyde’s - I have to lean about an inch or so back from “full rich” to get to 75 ROP.
In addition, for ground operations, I have to lean WAY back (to within about a 1/2 inch from idle cut-off) to prevent plug fouling. Do you guys that need to leave the mixture firewalled see this behavior on the ground?
Steve
In reply to:
In addition, for ground operations, I have to lean WAY back (to within about a 1/2 inch from idle cut-off) to prevent plug fouling. Do you guys that need to leave the mixture firewalled see this behavior on the ground?
I need some help here. When/why would I need to do this? I haven’t yet so far. What am I missing? I have a 20.
In reply to:
I need some help here. When/why would I need to do this? I haven’t yet so far. What am I missing? I have a 20.
You may not have to do it – in fact, it may be MY plane which is weird, which is why I was asking the question. I also have a -20.
But I’ve noticed that I get plug fouling (i.e. rough running enigne and large RPM drop during single-mag portion of the run-up) if I taxi around a lot with the mixture full rich. So, just like in the “old days” (i.e. Cessna flying), I have now started to pull the mixture to be almost fully lean when on the ground, and seem to have had fewer problems with plug fouling.
So, if you don’t ever have this engine roughness when doing the run-up, you’re probably fine. If you DO start getting this roughness, then maybe start leaving the mixture leaned while on the ground, and it’ll help.
(And when you actually notice the plugs fouled, you can usually clear them with a relatively high-power [say 2000 RPM], 30-60 second runup, on both mags, with the mixture leaned as far back as it will go without killing the engine. Then re-try the normal mag check and it will likely be better. Just like on a Cessna or Piper.)
Steve
P.S. (added later) – I should add that if you’re going to do this, make sure to check and double check mixture rich before takeoff. What I normally do is taxi around with mixture leaned, but right before the run up, I go to mixture rich.
In reply to:
But I’ve noticed that I get plug fouling (i.e. rough running enigne and large RPM drop during single-mag portion of the run-up) if I taxi around a lot with the mixture full rich. So, just like in the “old days” (i.e. Cessna flying), I have now started to pull the mixture to be almost fully lean when on the ground, and seem to have had fewer problems with plug fouling.
For whatever reason, this has not happened to me. I do have “Mixture Lean” on my post-startup checklist, but I don’t do it except after starting a hot engine. If the engine was cold, my engine wants to die if I lean more than just a tiny amount. Yet, in almost 700 Hobbs hours (or 550 ETH - Equivalent Tach Hours), I’ve experienced plug fouling on the ground only once.
In reply to:
And when you actually notice the plugs fouled, you can usually clear them with a relatively high-power [say 2000 RPM], 30-60 second runup, on both mags, with the mixture leaned as far back as it will go without killing the engine. Then re-try the normal mag check and it will likely be better. Just like on a Cessna or Piper.
Just what I used to have to do regularly on N7995G – my trusty old C172 with its 180 HP Lycoming. However, I was somewhat taken aback to read the following in the TIPS ON ENGINE CARE book that came with my airplane (Page 12, Rules of Ground Run-Up):
11. Never but never attempt to “burn out” a magneto drop with ground run-up. This “time honored” procedure succeeds only at the expense of the engine’s mechanical health.
Having said that, all I can say is that I’m glad I’ve only ever experienced fouled plugs once. After all, what choice is there? Cancel the flight, taxi to a shop, remove the cowl, pull the plugs, clean them, reassemble… etc? I suppose it could be done, but wow! Certainly makes leaning the mixture to avoid having it happen in the first place, an important and good decision.
This is similar to the admonishment in the Hartzell book to NEVER pull or push the airplane by the propeller. I know I do it - again, what choice is there? At least with this one, there is a preferred way to do it IF YOU MUST.
In reply to:
I should add that if you’re going to do this, make sure to check and double check mixture rich before takeoff.
I have a near-foolproof mechanism for this: When I lean on the ground, I lean SO much that the engine simply won’t run if I open the throttle any. Deakin has written quite a bit about this - you won’t hurt the engine a bit, no matter how lean you make it, because you’re not developing any significant power. This way, when you start the run-up, there’s a good reminder in the form of the coughing and sputtering of the engine if you forget to enrichen the mixture (I’ve done that). I have another rule, too: No more leaning after the runup. If there’s going to be a long enough delay to cause me to want to lean, then I’ll do another runup, too.
FWIW…
Mike.
Thanks Steve - I understand now. I’ve not had the fouling issue.
Mike,
Thanks for the note about the TCM manual. I guess I will think twice before trying to clear the plugs that way - luckily now that I lean on the ground, I never seem to have that problem any more.
I’m a little bit confused though since, as you correctly point out, leaning to ANY point when operating below 65% power should be fine for the engine.
And in the run-up issues I’ve mentioned, it runs rough on one mag but runs fine on “both” - and when I do the higher-power lean runup to clear the plugs, I’m running on both.
So, all I am really doing is leaning the mixture at approx 2000 RPM (still well below 65% power) and leaving it there for 30 seconds or so. I don’t quite understand how this could be harmful…
But, hopefully I won’t have to worry about it - as I said, I haven’t had to do this in a long time now that I lean on the ground…
Steve
Mike, like you, I’ve only experienced a fouled plug once on the SR20, however the Grumman Tigers I used to fly did foul plugs quite often. I used to clear them with a medium power, leaned run, but an instructor for whom I have great respect told me not to bother with that, just run the power to full, with mixture full rich, for 30 seconds - he said that would clear a plug just as well as anything else. And it worked. Basically all you are trying to do is get the plug hot enough to burn off the lead deposits that are shorting out the plug element. I did the same thing with complete success when the SR20 had a fouled plug.
And I can’t imagine any reason (except for picking up stones) that the engine manufacturer could complain about a short full power ground run with mixture full rich - otherwise how would we ever take off? So in fact the only reason (but a damnned good one!) for clearing the plug before takeoff is to make sure that it is in fact just a fouled plug.
Regards, Clyde
In reply to:
I’m a little bit confused though since, as you correctly point out, leaning to ANY point when operating below 65% power should be fine for the engine.
And in the run-up issues I’ve mentioned, it runs rough on one mag but runs fine on “both” - and when I do the higher-power lean runup to clear the plugs, I’m running on both.
Steve,
I’m confused, too, but I always think that it’s just ME!
Actually, this is just one of a long list of contradictory things I hear about my airplane. The engine itself includes lots – just think about all of the ongoing controversy about LOP operations in terms of disagreement between TCM and Deakin, or even between different things written or approved entirely by TCM.
It doesn’t stop there.
– Turn the prop forwards or backwards to reposition it? Depends whom you ask – my A&P says BACKWARDS to minimize the chances of inadvertent firing of a magneto; I believe (and read) FORWARDS to minimize damage to the vacuum pump.
– Use reflective sunshields in winter? Window manufacturer says NO WAY – too much heat buildup in the gap between the shield and the window. Avionics manufacturers INSIST on it. Cirrus has said both things – depends where you look. And you can find the same inconsistency of advice on the use of an external cover…
I’m sure I could come up with more examples - not even controversial stuff like “What constitutes Known Ice?”!
Mike.
“So, all I am really doing is leaning the mixture at approx 2000 RPM (still well below 65% power) and leaving it there for 30 seconds or so. I don’t quite understand how this could be harmful…”
FWIW I remember being told it was not good to hold the revs @ 2000 rpm+ on your car while in P or N. Believe it had to do with the lack of “load” on the engine. Might be the same rationale. Just my TCW. Richard
You do the Mag check at 1700 with no load, so what’s the difference at 300 RPM higher?
Walt
I don’t know. As I said I am not an engineer. It was something I had been warned about too many years ago. Maybe there is no connection.
Richard
In reply to:
And I can’t imagine any reason (except for picking up stones) that the engine manufacturer could complain about a short full power ground run with mixture full rich - otherwise how would we ever take off? So in fact the only reason (but a damnned good one!) for clearing the plug before takeoff is to make sure that it is in fact just a fouled plug.
Clyde,
Agreed, especially with your (wry) observation that we couldn’t take off if we follow their admonishment.
The section of the book that I quoted from is titled Ground Run-Up, and it’s entirely devoted to the subject. The gist of their message seems to have mostly to do with cooling – the fact that a modern engine is very INadequately cooled at high RPM when the airplane isn’t moving (although they contradict even this statement at one point in the article).
Don’t have time right now to type out the relevant passages – if you have the book, you’ll find the chapter on page ten. But here is a summary of their 12 rules:
**
- Always face into wind for run-up.
- Avoid prolonged/unnecessary run-up.
- Avoid high power run-up except when aboslutely necessary, and then only as long as necessary.
- When high power run-ups are necessary, idle at 600-800 RPM for a few minutes prior to shutdown, for cooling.
5, 6 - More “don’ts” for turbocharged engines… - Don’t run-up with Alt. Air on (dust)
- Don’t run up with prop in “steep pitch” except for the momentary propeller pitch check.
- Don’t start or run-up with prop feathered.
- Always open cowl flaps during run-up.
- Never but never… burn off a plug… previously quoted.
- Don’t run-up with high power with cowling off.**
Just the facts, ma’am… not saying that they’re right, not saying that they’re wrong… just saying that they said it.
Mike.
Clyde, I was told by an A&P to use the following procedure to clean the frequently fouled plugs on my 172:
Prior to shut down -
Run up to 2,000 RPM
Lean aggressively
Run for 30 seconds
Pull mixture all the way back (to lean/shut-off) to shut off.
This worked every time, was quick and easy, and was also usable if the pre take-off runup showed fouled plugs (roughness in the mag check). Of course, if you’re using it prior to take-off, don’t kill the engine with the mixture at the end.[;)] This technique also worked at a much lower power setting than full power.
Regardless of how aggressively I leaned on the ground, I always seemed to experience some fouling in the 172. One interesting side affect is that actually experiencing roughness during the mag check and being able to fix it seemed to instill great confidence in passengers.
I’ve never experienced any fouling in the SR22.
Marty
Seems like overkill to me. The amount of time the engine is in high RPM for a runup is so short that I cannot imagine ANY significant risk of overheating.