M20C optimal idle speed

[DXB]

Basic question- sorry if it has been covered here ad nauseam- search function was no help.  Neither was searching the lycoming O-360 operator's manual.

What is the optimal idle speed setting on my carb for my O-360-A1D?  

On the ground at full rich, mine idles at around 800, goes down to 700 with the carb heat on, and runs pretty smooth at either speed.

I ask because lately I seem to be getting long floats even when I nail my speeds, and I wonder if I'm making too much power at idle.  I'm not in the habit of checking my gauges when I'm over the numbers, but I did on Saturday- my rpm read 850 after pulling the throttle to idle. I typically turn off carb heat on short final in preparation for possible go around.  That float seemed endless though my airspeed was 70-75 as I started the flare. Could have just been the variable and gusting winds, or my being a crappy 250hr pilot...

[Jim Peace]

3 minutes ago, DXB said:

That float seemed endless though my airspeed was 70-75 as I started the flare. Could have just been the variable and gusting winds, or my being a crappy 250hr pilot...

Happens to me as well and I have a lot more time than you.  Were you empty? Min fuel with no pax?  a few extra knots and a short runway can make it seem like forever....

Every landing is different......

 

 

[cctsurf]

I hear AOA could help with that...  I've been trying to use the stall warning as my aoa.  If it just squawks as I flare, I know I'm at the right speed.  When I get it right, I do not float at all.  I need WAY more practice on that.  I've been spending all my airplane time and money on repairs, rather than flying recently.

 

 

[cctsurf]

Yes, his idle setting sounds fine.  Depending on his loading, it would seem that he is carrying too much speed over the fence.  I struggled heavily with this in my initial transition training.

I consider every landing a performance landing.  Carrying some speed on a gusty day is good practice, obviously.  OTOH, I don't have 5,000', loosing 1,500' would put me into the runway overrun.

I'm in favor of self-criticism.  Because I don't regularly see, let alone fly with, other pilots, it's the only type of criticism I get.  I'm always trying to become a better, safer pilot.

 

[DXB]

23 hours ago, Jim Peace said:

 

20 hours ago, cctsurf said:

Yes, his idle setting sounds fine.  Depending on his loading, it would seem that he is carrying too much speed over the fence.  I struggled heavily with this in my initial transition training.

 

Happens to me as well and I have a lot more time than you.  Were you empty? Min fuel with no pax?  a few extra knots and a short runway can make it seem like forever....

 

 

21 hours ago, daver328 said:

You're normal. RPM sounds normal.

Thanks all-  light bulb just went on- I'll quit perseverating on the idle speed.  Yes in fact I was alone in an empty plane with <20 gal on board - about as light as I've ever flown it. Come to think of it, my other recent unexpected long floats have come at the end of long legs, alone in my plane, light on fuel.  Makes sense now.  

I had actually planned to try landing at Aeroflex Andover for the first time that day (1891x50) -  http://www.andoverflight.com/information_about.html  It would have been my first real world "short field."  Looks pretty, but I saw gusty conditions and thought the better of it.  

Instead I went to my usual cheap fuel stop Sky Manor (2900ft).  I finally touched down around the midpoint of that runway with sweat on my brow after struggling to keep it lined up while floating in the gusting crosswind for what felt like an eternity.

[carusoam]

Which document is it that has the official rpm setting for idle speed?  (Your mechanic will know)

If it is 700rpm, an extra 100rpm will add some float in ground effect.

Lacking 100 rpm, the engine may stop running after landing.  (It is that sensitive)

On short final, my last throttle activity is making sure it is full out.  My throttle has a twist, literally, when it hits the throttle stop, it won't twist either.

A little added throttle can make a really soft smooth landing on a nice day.  

Cutting the throttle can give a solid landing on a windy day.

Both are nice to have available to the pilot.

Best regards,

-a-

[jetdriven]

I lowered my idle and it definitely improved the landing distance. I set mine where it is slow enough to just start stumbling when the throttle is pulled firmly to idle. Around 650 RPM. 

[Piloto]

One way to eliminate the floating flare is by raising the flaps just before touch down (5ft AGL). As the flaps raise the nose pitch up slightly assuring a mains first touch down. I use this techniques on crosswinds, gusty conditions, short runways and ice on the runway. At touch down it gives you a firm grip with the runway and better controllability.

Too low idle speed can cause the engine to quit after touchdown or when taxing. It can get embarrassing trying to re-start on the taxiway with a hot engine.

José

Edited April 25, 2016 by Piloto

[Guest]

850 is way too fast.  I have set the idle speed on all of my planes at about 500, or minimum smooth idle speed. I can put my IO-720 powered brand P into 1000' regularly.

Clarence

[DXB]

24 minutes ago, M20Doc said:

850 is way too fast.  I have set the idle speed on all of my planes at about 500, or minimum smooth idle speed. I can put my IO-720 powered brand P into 1000' regularly.

Clarence

Ok senior A&P opinion wins.  I'm guessing adjustment to 500 with the carb heat on in my case is optimal, so I don't kill it when I turn it on? Also I'm guessing you need to reset the idle mixture once the idle speed is messed with?  Just curious- I have zero intention of messing with this myself.

[Guest]

19 minutes ago, DXB said:

Ok senior A&P opinion wins.  I'm guessing adjustment to 500 with the carb heat on in my case is optimal, so I don't kill it when I turn it on? Also I'm guessing you need to reset the idle mixture once the idle speed is messed with?  Just curious- I have zero intention of messing with this myself.

I would set the idle RPM to the minimum smooth speed in the configuration you land the plane.  Remember that in the flare the engine will be at a higher speed than minimum idle speed you set static on the ground.

Idle mixture should be set to a very slight RPM rise when the mixture control is pulled smoothly to cut off.  Carburetor heat will richen the mixture and cause even lower idle speed and may cause the engine to quit.

Clarence

[Shadrach]

Set Idle to 500rpm, but don't use that as idle speed. Shoot for at least 900RPM during ground ops.

[DXB]

On 4/25/2016 at 8:23 PM, M20Doc said:

I would set the idle RPM to the minimum smooth speed in the configuration you land the plane.  Remember that in the flare the engine will be at a higher speed than minimum idle speed you set static on the ground.

Idle mixture should be set to a very slight RPM rise when the mixture control is pulled smoothly to cut off.  Carburetor heat will richen the mixture and cause even lower idle speed and may cause the engine to quit.

Clarence

Ok time to revive this thread, after expending some failed effort trying to get this right with an A&P who knows the carb'd Mooneys well.  We spent several iterations adjusting idle speed and idle mixture settings.  First we flew it. Then on the ground with it warmed up, we got it so that it idles just under 600, which was as slow as we could set it with carb heat on without it quitting.  Idle mixture was set correctly for about a 50 rpm rise when mixture is pulled to cut off.  Then we went an flew it in the pattern again. In the flare with the throttle at idle, it runs at >1000 rpm.  And floats and floats and floats.   

I guess it should idle a bit faster in the flare than on the ground, but I don't get the huge disparity.  Any ideas, anyone?

[Hank]

Mine idles on the ground closer to 800. Can't tell you what is in the flare, I don't have time to look over that way, I'm eyes outside. But it makes sense that descending at idle, the prop drives the engine and RPMs are higher than idle.

Full flap landings will float longer. Higher speed landings float longer. I come in with Takeoff flaps, and with 2 people and almost full tanks shoot for airspeed in the low-70-mph range; this generally has me touching down around the third stripe, plenty of room at the 3000' field I was based at for 6 years, and plenty at the 3200' field I'm at now. The flaps are just another flight control, I put them wherever needed to land where I want--if I'm high or the wind is calm, I'll add a little more, if it's really strong or gusty I may raise them a bit.

The stall horn usually sounds just before or as the mains touch. Search vimeo for "mooney landing KHTW" for an old video shot with my wife's point-and-shoot camera. 

But a lot of it is being at the correct speed. I shoot for 85 mph on final, slowing down to (75 - 5 mph for every 300 lbs below gross) on short final, and being mid-60s by the numbers.

[orionflt]

Dev,

Before we go too crazy we need to get the throttle cable readjusted so we are hitting the stops of the carb instead of the end of the cable. that is part of the low idle fluctuation we were seeing, once we do that we can get the idle to stay where it should be consistently at a lower RPM. once that is all adjusted correctly I am hoping that will bring the RPM down on final with the power pulled back but I doubt it. you were having the same issue before the throttle cable was changed so there is something else going on. 

I will sit down this week and see what I can find, the fact that we can not get the RPM's down below 1000 in flight is the issue. I am missing something obvious and as soon as the light comes on I will let you know. i'm sure Doc will have a few ideas that will be helpful.

Brian 

[DXB]

1 hour ago, orionflt said:

Dev,

Before we go too crazy we need to get the throttle cable readjusted so we are hitting the stops of the carb instead of the end of the cable. that is part of the low idle fluctuation we were seeing, once we do that we can get the idle to stay where it should be consistently at a lower RPM. once that is all adjusted correctly I am hoping that will bring the RPM down on final with the power pulled back but I doubt it. you were having the same issue before the throttle cable was changed so there is something else going on. 

I will sit down this week and see what I can find, the fact that we can not get the RPM's down below 1000 in flight is the issue. I am missing something obvious and as soon as the light comes on I will let you know. i'm sure Doc will have a few ideas that will be helpful.

Brian 

Brian- makes sense to make sure the throttle cable is pulling the lever all the way back to the stop- hadn't noticed this was an issue prior to today.   I'm really not sure if idle was an issue before the cable was changed - I was pretty green in the plane back then.  

But today was actually the first time I've ever looked at my rpm in the flare (my first time watching from the right seat of my own plane). So I went back and looked at my old JPI data - all of which is after the new cable.  Rpm is typically 1000-1050rpm when I go to idle on short final - similar to what we saw today. Rpm on the ground when I intentionally go to idle with carb heat on after runup  (to make sure it doesn't quit) is recorded at around 600.  Basically no different than what we saw today.

 I'm wondering what rpm other folks see at idle in the flare - particularly those with access to engine monitor data from carb'd planes.

[carusoam]

Dev, I like your questions.  Deep and full of detail that you know...

Brian, I like your depth and honesty.  And ability to reach out to others...

 

Getting idle speed set properly seems to be a continuous challenge.  Every few years I seem to need an adjustment.

- too little, the engine croaks before you want it to.  Usually on roll-out... (Something about the engine driving the prop again/more)

- too fast, the plane never lands.

- I believe my target rpm with throttle pulled out is 700rpm.  I check on the ground while taxiing.  Any too fast, the taxi speed gets outrageous... The alternator discharge warning light comes on with the rpm dialed out...

- Unable to check during the landing.  My throttle does get checked to be fully out. Commit to landing, throttle out...  Fast and high, check the throttle adjust the attitude. Mine is an untwist type of device.  It comes to a hard stop.

O360 doesn't seem much different than an IO550.  Other than the carb heat part...(warm air enriching the fuel mixture).

Best regards,

-a-

[Guest]

Generally a 50 RPM rise is too rich.

Clarence

[cnoe]

16 hours ago, DXB said:

 I'm wondering what rpm other folks see at idle in the flare - particularly those with access to engine monitor data from carb'd planes.

Just another data point for you...

In my IO360 the JPI data shows an in-the-flare idle speed of around 850-900 rpm and a static idle of 700-750 rpm. All seem normal to me.

[DXB]

Dork that I am, I kinda enjoyed this basic video on idle speed and mixture adjustment for the Marvel Schebler carb on the O-360.   Pretty simple stuff, very approachable.

http://bcove.me/cwz0zl0w

 

[aeromancfi]

Check your tachometer with a strobe and find out what the real RPM is, and go from there with all these recommendations. My tach reads low by 50 rpm, so 650 rpm at idle is actually 700 rpm and works fine for smooth operation. Aeroman.