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Idle RPM recomendations

bret

Well Known Member
From what I have read here, Idle RPM is important as far as slowing these things down on decent and final, my set up is purring at 500 RPM, where is yours set at and what are your experiences with different settings?
 
slowing down

That's a good ?
Also Lycoming says something about piston slapping below 1500 rpm with C/S driving the prop I would like others thoughts too.
Bob
 
500 is great! You probably have a metal prop. The inertial really helps here. I've typically run wood or light composite (wood core) props and can't get quite that low. Ultimately, you want it as low as it can go without quitting when you tug back on the throttle with a couple pounds force.

HINT: It really helps to set the idle mixture right first. Otherwise, you'll set your idle adjust too high because it will load up after 10 seconds. You know mixture is set right when after 30 seconds of idle RPM stays put and you can goose the throttle and it just slightly hesitates, but doesn't cough.

I don't know anything about slapping pistons.
 
You shouldn't have any issues slowing down with the CS prop. I have a Catto and EFII ignition and have my idle set at 480-500 any lower and it starts to get rough. The lower idle is noticeable mostly in the pattern given steeper descent rates and less landing distance than 625 RPM.
 
500 is great! You probably have a metal prop. The inertial really helps here. I've typically run wood or light composite (wood core) props and can't get quite that low. Ultimately, you want it as low as it can go without quitting when you tug back on the throttle with a couple pounds force.

HINT: It really helps to set the idle mixture right first. Otherwise, you'll set your idle adjust too high because it will load up after 10 seconds. You know mixture is set right when after 30 seconds of idle RPM stays put and you can goose the throttle and it just slightly hesitates, but doesn't cough.

I don't know anything about slapping pistons.

I have the EFII full system and this fuel ration gauge http://www.plxdevices.com/ProductDetails.asp?ProductCode=897346002719
have not seen any loading up issues so far.
 
Mine with a CS prop will probably quite at 750 or 700 but I recall either hearing or reading that Lycoming recommends 1000 or above for idle speed.
 
500-550 with my IO 360 and Hartzell BA. I have set it as high as 750 and that was ok, but I have had no loading or other issues at the lower rpm.
 
My O-320 powered 9A is set at 650rpm (FP metal prop), which works well and doesn't float excessively - the 7A would float even less I imagine.

Lycoming recommends minimizing time at idle RPMs to reduce cam lobe stress, and I believe that is where the 1000rpm guideline comes from - it is not the proper true idle speed though - I'm not sure the 9A wing would even land at 1000rpm!

Chris
 
Unless you want to set a land speed record or burn up your brakes, 1000 rpm is way too high when taxiing. I set my RV7A/CS idle speed such that it lopes at full retarded throttle when sitting still. When moving, such as on final, there's no noticeable roughness and landing float is definitely minimized. Set idle speed too low and you'll have a stopped engine on your rollout, not desirable :)
 
My recollection is the 1000 to 1200 rpm recommendation relates to temperature at which lead scavenging will occur. 650 rpm's is good on mine for a minimum
 
Depends on engine temp. My IO-360-B2B engine idles at 800-900 cold but 600-700 hot. I had a lower cold idle rpm but had the engine die when landing on roll out.

I lean aggressively during all ground engine running.
 
My O-320 powered 9A is set at 650rpm (FP metal prop), which works well and doesn't float excessively - the 7A would float even less I imagine.

Lycoming recommends minimizing time at idle RPMs to reduce cam lobe stress, and I believe that is where the 1000rpm guideline comes from - it is not the proper true idle speed though - I'm not sure the 9A wing would even land at 1000rpm!

Chris
It's almost that extreme in a -4. With a fixed pitch prop, a thousand feet of float wouldn't be surprising at that rpm.

Set it as low as it will idle reliably, and be happy if you can get down to 500 rpm safely.

Charlie
 
Wow...1000-1500. Looks like everybody's doing it wrong. ;)

If you try a 1500 rpm idle with a pitched up FP metal prop (let's say a Sensi at 87" or above), many RV's will fly along nicely at that RPM and will be really tough to land....

C/S is a different story, but that's still a bit (ok a lot) extreme in my experience. After doing FP metal, FP wood, C/S metal, C/S composite using a landoll ring/not, etc.. (across RV-4/6/7/8/9) we usually try to set the idle RPM as low as is comfortable for the engine. No reason to use a low cruise speed as an idle speed if the engine will handle much lower. I've seen some C/S lycos idle beautifully at 450, whilst a wood FP often needs 800+/- to keep 'er alive and not shake like a wet dog. Do be careful with the FP though, high pitch numbers and high idle on many RV's makes for a very long landing....

Just sayin! :)

Cheers,
Stein
 
Mine with a CS prop will probably quite at 750 or 700 but I recall either hearing or reading that Lycoming recommends 1000 or above for idle speed.

IMHO, what Lycoming is recommending is that you open the throttle and set approx. 1000 RPM for extended idle operation, say waiting for takeoff, etc.

They are NOT recommending that you set the minimum idle at 1000!

Especially on a FP prop, the idle should be set as low as you can possibly stand it, even if it lopes, or runs rough. On the ground, you can always open the throttle a bit to allow smooth running. In the air, the engine idle speed will be fine, because the airflow at 70 knots is plenty to keep it turning over smoothly.

A low ground idle will allow you to land shorter, and may save brakes.
 
Idle speed

When my engine was new and had two mags, 800 rpm was the lowest I could idle with Catto prop. I now have 400 hours and 1 Electroair, and have the stop set at 650.

I have also heard Lycomings should be warmed up at +1000 rpm to provide better camshaft lubrication, and use this higher rpm on my way to run-up area. After flying, I use 650 rpm to save the brakes.

I lean aggressively for taxi to help keep plugs clean, which may affect idle performance.

Jay
 
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