Should I land at idle?

[Ed Cesnalis]

The 912 responds from idle really fast to where you can go from 'about to stall with my wheels 5' above the runway' to full power in the blink of an eye. How reliable is the 912 at responding at idle? Is there a better RPM and what is it?

 

I know someone that was giving a demo, approaching at idle and lost his engine in a CTSW, he had to use the starter after he demo'd a dead stick.

[CT4ME]

There have been rare instances of this happening when idle was set too low. There is a thread here somewhere with a discussion of idle speed. The argument centered on just this issue, the fact that at really low idle speeds, the engine could quit on approach. (I guess because of the high compression ratio).

tim

[sandpiper]

Yes, you can have it set too low. Mine is set such that at a 55K approach idle power gives me 1900-2000 RPM.

 

Anyhow, CT, your post will probably be good for about 2 pages of controversy!:blink:

[Jim]

What is your idle speed set at? Mine is at 1800, a tad higher than my preference. I'd like something closer to 1600. My airplane was delivered with the idle at 1400 and that's too slow. At 1400, pulling the throttle to idle and yanking the nose up would kill the engine.

[Ed Cesnalis]

I idle at 1,700RPM. The question at hand isn't what our idle RPM should be but:

 

"When doing a power off approach is idle ok in terms of fast and reliable response time to the throttle or is there a higher 'best response time' setting recommended for the 912?"

[Jim Meade]

The CTSW POH recommends a little power to address this very issue. Having said that, I frequently do most of the approach at idle. However, I have always flown a pretty high, tight approach and could virtually always make the field if my engine quit at any time. How that would affect a go around is another story. I have restarted with the starter at 50' AGL with no issues on one occasion. I have never had an engine quit or even stumble at idle in the pattern. I'd have to give some thought to how much drag the prop is causing at idle that might make it shut itself down. It doesn't seem right at first impression.

 

Some older airplanes like the Cessnas recommended a short burst of throttle occasionally to "clear" the engine in the pattern but I doubt if that is the issue with a Rotax.

 

Adding even a little power adds a lot of distance to the approach, in my subjective observation. It feels to me like you are dragging it in.

 

Flying a radial engine such as was in the T-6, pilots were told to advance the throttle in no less than 2 seconds because if you jammed it ahead it would flood. Accidents have happened because someone got excited and rammed the throttle forward. I don't have any experience with that happening in any airplane I've flown, but I've never flown a radial. With turbofan engines you have to give is tome time to spool up but that is a different affair.

 

It would seem to me that if one was confident one had the field made and if one was confident a go around was not a required option, then idle is OK. If one is worried about either of the above, I suppose one might carry a hint of power.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[Jim]

I idle at 1,700RPM. The question at hand isn't what our idle RPM should be but:

 

"When doing a power off approach is idle ok in terms of fast and reliable response time to the throttle or is there a higher 'best response time' setting recommended for the 912?"

 

That's what I was getting at. If your idle is at 1700, I think you're ok. If it's at 1400, I'd worry that it might stumble.

[sandpiper]

I try to make throttle closed approaches all the time unless it's really cold then I like the idea of keeping the engine warm. If I have to add power (in the summer) to make the runway, then I am too low. Sometimes I will add a couple hundred RPM as I flare if runway lenght is not a problem. Never had a problem with the Rotax not responding. I'm more likely to bump in a couple hundred RPM with flaps 30 or 40, probably to make up for my lack of precision. These methods work for me. Others, I'm sure, prefer other methods.

[207WF]

I always use idle unless the airport is very hot and high. At my sea level drome I still have to reduce power midfield and fly a slightly extended final, compared to the Cessnas. The rpms tend to stay up until you get pretty slow anyway. (My idle is 1800). WF

[Roger Lee]

CharlieTango said:

 

I idle at 1,700RPM. The question at hand isn't what our idle RPM should be but:

 

"When doing a power off approach is idle ok in terms of fast and reliable response time to the throttle or is there a higher 'best response time' setting recommended for the 912?"

 

Hi Ed,

 

Two things here. If you have a WOT setting that only gets you 5200 flat and level verses another guy that gets 5700 WOT flat and level the spin up time for the flatter pitch is a little faster and you already have a slightly better climb setting to help save you. The second thing here is , if I need a minimum of 4000+ rpm to save my butt in an emergency which will get me there faster? A prop at idle let's say 1700 rpm or a prop turning 2800 rpm? This one should be an easy answer. If your one of these people that have a 1500 rpm at idle it may leave you a little short in an emergency. I believe in hedging my bets and chances for survival and plane salvation and the extra rpm is my ace in the hole. Been there done that twice.

 

So the bottom line is if the prop is set to get 5600+ rpm WOT flat and level and you have 2800 rpm of power in during landing then the answer is yes it would be able to get to a saving and safe rpm quicker. The two times I have needed this over the last 6 years all I did is lower the nose, slap the throttle to wide open and off I went without sinking to the runway and that was allot heavier than 1320.