best idle speed

prkaye · #1 07-15-2010, 06:24 AM

When I did my first few short engine runs, I found the idle speed was set way to slow (the engine sputtered at idle, which was only maybe 200 - 300 RPM). I've increased it (by the adjustment screw on the carb) to between 650 and 700 RPM now. My only concern is that if I set it too high I will have trouble getting it to land on my first flight. I have 4000 ft of runway to work with, but I've been told teh -9A will float a lot, and that even a little bit too much idle power will exacerbate this.
Is between 650 and 700 RPM a suitable idle speed?

Geico266 · #2 07-15-2010, 06:32 AM

I think 600-700 RPM is fine.

The 9 will float (as will any plane) if you carry too much speed in. If it looks like you are not going to set it down do a go around, but IMHO you should figure out where your stall is on the 1st flight. You might not need to do a hard stall on the first flight, but slow flight to the edge of stall would be my recommendation.

4,000' runway is plenty!

yakdriver · #3 07-15-2010, 06:44 AM

I like the idle speed about 500 rpm. You will adjust the idle mixture to get it running smooth at idle. As far as landing use the old 1.3vso over the fence and it works very well. I can use the 800' first turn off at my airport without trying very hard and not using brakes in my 7. I use 70mph over the fence solo and 75 with a passenger. The 9 is the only RV I haven't flown but I know will stall slower than my 7. Don

apkp777 · #4 07-15-2010, 07:11 AM

"negative ghostrider, the pattern is full", 700rpm and you'll do lot's of flybys. My idle RPM is about 600. With a Catto prop, I really can't go much lower than that, but I wouldn't want any higher. You really just don't want the engine to die when doing your idle power check.

Dmadd · #5 07-15-2010, 08:47 AM

The 9 will flatten out as soon as it hits ground effect. (more so than the other RV's) So if your fast, it just slides along just above the runway.
It's exactly the same profile of an older Mooney, in case you have access to one of those to see what the approach will look like... (or can get a ride in one)

videobobk · #6 07-15-2010, 09:47 AM

I have a 320 with a Catto three blade. I idle at 450 and find it slows much more than at 700 (I can try that be adding just a bit of throttle. You won't notice any roughness down final (at least I never have) as the engine will be turning 700 or above due to airflow over the prop. If it is a bit rough on the ground, just add a touch of throttle there. Mine is smooth at 450, so I rarely add throttle except to taxi.

Bob Kelly

apkp777 · #7 07-15-2010, 10:51 AM

I rechecked my idle RPM today, it's about 550 ish. It runs kindof smooth, I could probably dial it back a bit.

JonJay · #8 07-15-2010, 11:32 AM

Per lycoming to avoid deposits that lead to spark plug fouling and potential valve sticking. Engine should be operated between 1000-1100 rpm during warm up periods, holding, and for long taxi.
So, setting your idle and idle mixture accurately before your first flight might be a bit tricky as your engine needs to be at operating temperature to do this properly. Not wise to do too many ground runs, so your in a bit of a pickle.
4000' is a lot of runway for an RV. I would error on the high side of idle rather than the low side on a first flight. My engine came from Aeropsort set for 750rpm on the stand.

Daver · #9 07-15-2010, 11:52 AM

Help me out here. I'm kinda new at this flyin' thang, but....

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"negative ghostrider, the pattern is full"

You're not suggesting that ATC would NOT let a pilot go around IF, the pilot as PIC, thinks he may not have enough runway to land safetly and needs to go around, are you? The reply "UNABLE" comes to mind....

Although I've received some not-so-great instructions from ATC, they seem to bend over backwards to help you out.

I think I may just avoid controlled airspace

At my first engine start last Sunday, my idle was less than 500. I think I'll leave it alone for awhile and see what further testing reveals.

Dave
-9A getting close

RVbySDI · #10 07-15-2010, 11:53 AM

I am wrestling with this right now on my brand new ECI IO-340 engine with ECI fuel injection system. ECI states this engine idle should be set at 750-800 RPM. That is a far cry higher than you guys are showing at 400 - 500 RPM. In fact, with my 3 blade catto prop I am not sure this engine would continue running at that low RPM.

As far as the 9A floating issue on landing, I had a first flight last Tuesday that I landed on a 3000' grass runway (yes, it was indeed a grass strip with a nose gear airplane!) I had the RPM somewhere above 1000 and it came down and landed just fine. I know I landed long and it did indeed float but I was down within the first 1/4 of the runway regardless. As long as you have plenty of runway a pilot can get the plane down so I would be inclined to not try to get the idle down to something ridiculously low until I had time on the engine and airplane to make sure everything is functioning as it should.