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Rotax idle rpm

edward7048

Well Known Member
What idle rpm are RV-12 users using. Van's maintenance manual
calls for 1650 after the engine is warm but my rotax maintenance
tech tell me that it should not be below 1800.
 
With my short time behind the throttle I like the 1800 rpm idle or a little higher as the engine warms up. It is suppose to be better on the gearbox too to have the rpms up. I can slow the engine to the 1650 rpm at the stops but I do not keep the rpms there for any length of time.
 
There is a difference between what RPM the engine is adjusted to for minimum ground idle, and what RPM the pilot idles the engine at when operating on the ground.

The green arc on the tach starts at 1800 and that is what should be used as a ref. by the pilot.


If you set the actual idle stops higher than 1650, you will be making looong landings.
In flight, gliding with the engine at idle, it will be higher than 1650 because of the slip stream driving the prop.
 
There is a difference between what RPM the engine is adjusted to for minimum ground idle, and what RPM the pilot idles the engine at when operating on the ground.

The green arc on the tach starts at 1800 and that is what should be used as a ref. by the pilot.


If you set the actual idle stops higher than 1650, you will be making looong landings.
In flight, gliding with the engine at idle, it will be higher than 1650 because of the slip stream driving the prop.

Ditto and well put, you beat me to the response
 
Idle rpm, a personal preference

Idle rpm can have a range and a user preference. 1700-1800 is usually a good place to be for the 912ULS. On first start of the day to warm up anywhere from 2100-2400 is a good place to be. There isn't any real load on the engine and it keeps the engine smooth until all metals and the oil warm to operational temp. Even after warm up running the ULS down below 1700 for any time isn't great for the engine with a 10.8:1 compression ratio. Your better off while on the ground at or above 1800. If you do have the idle set down at 1650 then use the throttle to keep it higher during time on the ground. Here's the thing with your rpm, unless artificially high it really shouldn't increase the glide when landing. You control your speed with the stick. So if you have a little extra rpm on landing and many do leave a little power in on landing then just pull the stick back a little more to keep your speed down or bleed it off. Your throttle controls altitude and the stick controls speed and at those low rpms it's easy to bleed speed and loose that last foot or two. Even with throttle in pulling the stick back will decrease the speed and you'll settle to the runway. I can land in 1000' with 1700 rpm or 2700 rpm. Won that one on a bet. I just have more aft stick with the higher rpm to reduce speed.

So in reality having the idle set at 1650 or 1750 which isn't enough to worry about anyway won't make you land any longer unless you fail to correct your control input.
 
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Here's the thing with your rpm, unless artificially high it really shouldn't increase the glide when landing. You control your speed with the stick. So if you have a little extra rpm on landing and many do leave a little power in on landing then just pull the stick back a little more to keep your speed down or bleed it off. Your throttle controls altitude and the stick controls speed and at those low rpms it's easy to bleed speed and loose that last foot or two. Even with throttle in pulling the stick back will decrease the speed and you'll settle to the runway. I can land in 1000' with 1700 rpm or 2700 rpm. I just have more aft stick with the higher rpm to reduce speed.

So in reality having the idle set at 1650 or 1750 which isn't enough to worry about anyway won't make you land any longer unless you fail to correct your control input.

Roger, with an RV-12 this is total incorrect (And I would love to see you land an RV-12 at 2700 RPM... It can't be done without a 10000 ft runway).

Idle RPM is very much a factor.
Maybe it is not an issue in higher drag airplanes that use the 912, that you have experience with, but it is for the RV-12.
A big part of the reason for that is airplanes using the 912, that only cruise at 90 - 100 kts, are using a much lower pitch on the prop. An RV-12 at close to 120 Kts cruise, has a prop pitch that produces a lot of residual thrust even at idle. In fact, this is a problem with all RV models using a fixed pitch prop (search the forum here, there is a lot of information and personal experience).
 
What I have - -

I have mine set at 1400 - 1500. On landing, pull back to idle. It will be much above the desired low of 1800. When you touch down, it will finally drop below 1800. Pick up the throttle as needed to be at 1800 or above. I do pull it back for 3 seconds before shut-down. It does not turn long for sure.
 
Hi Rvbuilder2002,

Our friends in the UK challenged that too. We took 3 guys and went and marked the runway at 300m or 1000'. Did it ten out of ten times and didn't need that much runway. I would bet most could do it with just a little practice and a slight alteration with their technique. Go to some altitude of your choice and set the throttle to 2700 rpm and set up your approach and pull the stick back. What happens is the speed bleeds and will continue to reduce until you hit stall and you will be loosing altitude before that happens. Same in ground effect on the runway in landing. You just need to pull the stick back far enough , not approach too high or too fast. If planned right and the control input is good the plane will slow and settle. You just have to be willing to pull the stick back farther than you normally do. We do the same basic thing when we practice stalls and many times the power on stall rpm is much higher than 2700 rpm. If you pull that stick back far enough the plane has to loose altitude and reduce speed to and through a stall. When I transition pilots I teach them both ways (idle and power on landings) and that includes everything from no flaps to full flaps. Even with extra rpm you should be able to set down in less than a1000' any day unless you have a high object to clear on close approach then that would be a good technique to choose.
Can you float with extra rpm, certainly, but that can be corrected for wit technique.

Our discussion here is mainly about the difference of 100 rpm (1650-1750) and not a1000 rpm and this should be pretty trivial for most to deal with.

I'm sitting here with another LSA slippery plane flier :) and posed the same scenario to him. He said the same thing change your landing technique and it shouldn't be any big deal. Here is the scenario. You have a 1000' runway. No approach or take off obstacles. You have 100' target to land in if I land at 1700 rpm touch I have 900' to brake. If I come in and land (what would you do different?) in that same 100' you still have 900' to brake. All I did was change my approach (flatter) and stick position to further back and a little more nose high than the first landing and touched my wheels within the same 100'.
 
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Roger,

What approach speed are you using? It sounds like you are significantly slower than the 55KTS recommended.

Rich
 
Hi Rvbuilder2002,

Our friends in the UK challenged that too. We took 3 guys and went and marked the runway at 300m or 1000'. Did it ten out of ten times and didn't need that much runway. I would bet most could do it with just a little practice and a slight alteration with their technique. Go to some altitude of your choice and set the throttle to 2700 rpm and set up your approach and pull the stick back. What happens is the speed bleeds and will continue to reduce until you hit stall and you will be loosing altitude before that happens. Same in ground effect on the runway in landing. You just need to pull the stick back far enough , not approach too high or too fast. If planned right and the control input is good the plane will slow and settle. You just have to be willing to pull the stick back farther than you normally do. We do the same basic thing when we practice stalls and many times the power on stall rpm is much higher than 2700 rpm. If you pull that stick back far enough the plane has to loose altitude and reduce speed to and through a stall. When I transition pilots I teach them both ways (idle and power on landings) and that includes everything from no flaps to full flaps. Even with extra rpm you should be able to set down in less than a1000' any day unless you have a high object to clear on close approach then that would be a good technique to choose.
Can you float with extra rpm, certainly, but that can be corrected for wit technique.

Our discussion here is mainly about the difference of 100 rpm (1650-1750) and not a1000 rpm and this should be pretty trivial for most to deal with.

I'm sitting here with another LSA slippery plane flier :) and posed the same scenario to him. He said the same thing change your landing technique and it shouldn't be any big deal. Here is the scenario. You have a 1000' runway. No approach or take off obstacles. You have 100' target to land in if I land at 1700 rpm touch I have 900' to brake. If I come in and land (what would you do different?) in that same 100' you still have 900' to brake. All I did was change my approach (flatter) and stick position to further back and a little more nose high than the first landing and touched my wheels within the same 100'.



Not saying that an RV-12 can't be landed fine with an idle of 1700 RPM (You originally said between 1700 and 1800... there is even a noticeable difference between those values).

I will guaranty it couldn't be landed within the distance specified in the POH unless you do a slow dragging approach flying behind the power curve.
This would require you to fly dangerously close to a stall (an RV-12 normal power off approach speed is about 50 Kts). Not a good practice unless absolutely necessary.

Come on up to Oregon and fly the RV-12 demonstrator, and I will show you the difference.
 
Oregon

RVbuilder,

I'm I close to guessing you live in or close to Independence, OR and do you know John Horn?


p.s.
You can do it with a 60 knot approach. Just flatten your approach and touch within your first 100'-200'. This is nothing more than target acquisition and landing on your marks and not leaving any runway behind you and I never said you had to round out over the numbers. A nice flat approach makes this landing easy. Remember no obstacles on either end. Everyone here would agree once on the ground you can brake in the last 800'. So once you learn to land in the first 100'-200' the rest is easy.

It's more or less spot landings for accuracy 101 and never leave usable runway behind you when you need it.
 
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\
RVbuilder,

I'm I close to guessing you live in or close to Independence, OR and do you know John Horn?


p.s.
You can do it with a 60 knot approach. Just flatten your approach and touch within your first 100'-200'. This is nothing more than target acquisition and landing on your marks and not leaving any runway behind you and I never said you had to round out over the numbers. A nice flat approach makes this landing easy. Remember no obstacles on either end. Everyone here would agree once on the ground you can brake in the last 800'. So once you learn to land in the first 100'-200' the rest is easy.

As I said before, come on up to Van's and try out the RV-12 demonstrator.

It's more or less spot landings for accuracy 101 and never leave usable runway behind you when you need it.

I know of John, but don't know him personally.


I guess i will just have to suggest that until you have tried what your talking about, with an RV-12, I guess you wont know, what you don't know.

I regularly land, stop, and make the first turn-off at our airport (about 300 ft) with RV-12's (but I assure you I don't do it with an approach speed of 60 kts), so I do know about landing accuracy.
 
Hi Scott,
You could do it at an approach of 60 if you round out 30-40 yards before the runway edge and level at 4'-6'. Then when you get to the runway you will be down at your regular speed and you'll land just like normal, but within the first 100'-200' of the 1000' runway. So you'll have lots of runway left. Your thinking inside the normal landing box. This is where you cross the numbers already slow and slightly high to make sure you make the runway. I never said you should make a normal landing, but adapt your landing technique, speed and control input to match your landing scenario. I try to teach landing techniques that are routine and then landing and thinking outside the box. When things go bad thinking and landing in your comfort zone and routine box usually doesn't happen.

We had a major thread drift here. The original post was more or less would or should landing be any tougher at 1700-1750 verse 1650? The original poster wanted to know if it was a problem. I get to fly a number of LSA aircraft and I haven't found that rpm difference any big deal in any of them even with 14:1 glide ratios.
 
Hi Scott,
You could do it at an approach of 60 if you round out 30-40 yards before the runway edge and level at 4'-6'. Then when you get to the runway you will be down at your regular speed and you'll land just like normal, but within the first 100'-200' of the 1000' runway. So you'll have lots of runway left. Your thinking inside the normal landing box. This is where you cross the numbers already slow and slightly high to make sure you make the runway. I never said you should make a normal landing, but adapt your landing technique, speed and control input to match your landing scenario. I try to teach landing techniques that are routine and then landing and thinking outside the box. When things go bad thinking and landing in your comfort zone and routine box usually doesn't happen.

Roger,
What you can do, to justify having a faster idle speed, and what you should do, are two totally different things.
I think it is very bad advise to suggest that someone new to the RV-12 should just plan on rounding out at low level, 90 to 120 ft before the edge of the runway, so that they can land near the beginning of the runway.
We all know that lots of runways do have obstacles. Your technique would not always be possible.

We had a major thread drift here. The original post was more or less would or should landing be any tougher at 1700-1750 verse 1650? The original poster wanted to know if it was a problem. I get to fly a number of LSA aircraft and I haven't found that rpm difference any big deal in any of them even with 14:1 glide ratios.

Actually the original question was whether there was a difference between 1650 and 1800 RPM. There is. Does it make the airplane unlandable? Of course not. But it does effect the landing performance. Particularly for less experienced pilots new to the RV-12. Some of the pilots reading this are low experience and new to the RV-12.

I feel your advice is very ill advised, and hopefully RV-12 builders/owners will trust the recommendations of the kit manufacturer (based on a combined total flight time experience with the RV-12 approaching 2000 hrs), rather than yours.

Bottom line...
There is absolutely no benefit to an idle RPM set higher than 1650 RPM, but there is numerous negative aspects.

Over, and out.
 
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I would like to ask - -

for those that feel a higher idle is good, what 'fault' do you see with a lower idle speed ? When the engine is cool, or cold, you have to adjust the idle anyway to stay at 1800 or higher, so what difference does it make ? ROTAX wants to limit gear 'rattling' as much as possible. ( below 1800 RPM ). Slowing it down for 2 - 3 seconds, to below 1800, then turning off mags, reduces the "rattle-time" to my way of thinking. I had mine too high early on, and after changing it to the RPM idle called for, I fell it lands much easier.
 
I use 1750 which gives me smooth ground operation. As long as I slow down early my landing distance has been comparable to my Cherokee, but if the speed gets away from me on short final there is no quick way to lose it and I'm gonna float! Transitioning from the Cherokee I was surprised that full flaps on the RV-12 don't act like an air brake. Full flaps on the Cherokee gives me immediate deceleration.
 
You don't want the idle so low that the engine might stop as you slow down on the runway. I would have to go check but mine is some where around 1650. That allows for about 1950 on a 55K throttle closed final.

That results in RPM falling into the yellow as I slow down on the runway - if I let it which I rarely do. On the ground I keep it at 1900-2000. In my opinion, you don't want to be running it in the yellow any more than you can help. But, that is only my opinion.

At one time I tried an 1800 idle but did not like having 2200 plus on final with a closed throttle. That is my preference as I like steeper approaches and not carrying power.
 
Hi Scott,

I'm not advising landing any special way or rpm. I simply stated that it was a personal preference and that you can land with higher rpms and if you can't then change your technique and 100 rpm from 1650 to 1750 shouldn't be an issue.
If we are following ill advised then 1650 is below the Rotax engine MFG recommendation and class teachings and can cause unwanted vibration stress on the gearbox and crank if used too much and long term on the ground.

The point as I see it is to advise people that a bottom line of 1650 is okay so long as you tell them in the same sentence you should not run there on the ground and should keep it around 1800+/- depending on the circumstances top of the yellow arc) when just sitting idling and higher during warm up.

My rpm point was when you said you CAN'T land at higher rpms and I just pointed out it was all technique not an aircraft issue. The RV12 is a good aircraft and it's performance can depend more on the pilot rather than its design.
 
It's like Groundhog Day all over again

Okay, I am going to jump in where I don?t belong and see if we can?t clear away some of this smoke. While I have zero experience with the RV-12, I do have about 30 years of maintenance experience on F-15?s and F-22?s and about 10 years of that were at Edwards AFB doing flight test maintenance on those airframes. One thing that I noticed during those years is that pilots, maintainers, and engineers have differing vocabularies. They use the same words, but each has a slightly different meaning attached to many of those words. This being the case they often talk past each other using the same words loaded with differing meaning and wonder why the others don't understand their meaning. My Pilot-ese to Engineer-ese to Maintanier-ese phrase book still seems to be functioning. Here is what I am hearing.

1) On final approach with a closed throttle the propeller is going to be spinning at about 150-200 RPM faster than Warm Ground Idle. It is kind of like shifting down to third going down a steep hill.
2) If Warm Ground Idle is set to 1800 RPM you will be in the 1950-2000 RPM range during final. If Idle is set to 1650 you will be in the 1800 RPM range.
3) Engine speed is going to have a significant impact on the landing technique. Air Force pilots become proficient in No-Flap landings and in fact I have seen F-15?s touch down at well over 200Kts and I was even involved in testing the F-22's Arresting Gear (Tail-Hook). That test involved landing at a specified speed, catching the cable, lather, rinse, repeat with + 5 knots until they ripped the arresting gear off the aircraft. (After that the pilots' call sign was changed from Dragon to Draggin?) The moral is that while ?Stuff? happens, the landing profile in the POH is preferred. The other profiles, while sometime necessary, are additional tools in the bag to be used when appropriate. In the case of the the tail-hook test the obstacle at the approach end of the runway was 25 miles of Rogers Dry Lake.
4) If I were a Rotax operator/maintainer (which I hope to be in the not too distant future) I would set the Warm Ground Idle to 1650 RPM. As the engine warms up after a cold start I would advance the throttle to maintain no less than 1800 RPM during ground operations. It would appear that in-flight RPM?s would be no lower than about 1800. After landing operate the power plant at or above 1800 until shutdown.

Seems pretty simple to me. The original question was "I am getting conflicting information, which should I use?" The answer appears to be both. Set the Warm Ground idle to 1650RPM, operate the power plant no lower than 1800RPM. Okay guys, I am sure that I have erred technically somehow or at the very least I have conjugated a verb badly or left a dangling participle (or is it a dangling modifier now), so bring it on.
 
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I agree Tom - -

What I said ( or tried to anyway ). Here is another point. I fly my -12 as though it was more like 'most' GA planes land. I keep speeds around 70 knots right to the beginning of the strip. On short fields, that will not work of course. My thinking is, at much slower speeds, you do not blend into most GA traffic landing speeds as well. I go to many Fly-in breakfast, and most planes are landing at higher speeds than an RV-12 requires. If you keep the speeds up, I feel you fit in better.
 
+10 for Tom! And, yes you could "land" an RV12 at substantially higher rpm, only limited by insane angles of attack and maybe dragging the tailhook (a.k.a. tie down ring) upon touchdown - a nosedragger "three point landing..." Actually I would love to see Roger build or buy an RV12 (sure not volunteering mine!) and video a test series showing landing at progressively higher rpms until landing cannot be achieved.

And while the flaps could be more effective on the 12, it slips BEAUTIFULLY.
 
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4) If I were a Rotax operator/maintainer (which I hope to be in the not too distant future) I would set the Warm Ground Idle to 1650 RPM. As the engine warms up after a cold start I would advance the throttle to maintain no less than 1800 RPM during ground operations. It would appear that in-flight RPM?s would be no lower than about 1800. After landing operate the power plant at or above 1800 until shutdown.

Seems pretty simple to me. The original question was "I am getting conflicting information, which should I use?" The answer appears to be both. Set the Warm Ground idle to 1650RPM, operate the power plant no lower than 1800RPM. Okay guys, I am sure that I have erred technically somehow or at the very least I have conjugated a verb badly or left a dangling participle (or is it a dangling modifier now), so bring it on.

You actually have it exactly correct (and it is what some of us have been saying in this thread all along)
 
Exactly,

"4) If I were a Rotax operator/maintainer (which I hope to be in the not too distant future) I would set the Warm Ground Idle to 1650 RPM. As the engine warms up after a cold start I would advance the throttle to maintain no less than 1800 RPM during ground operations. It would appear that in-flight RPM’s would be no lower than about 1800. After landing operate the power plant at or above 1800 until shutdown.

Seems pretty simple to me. The original question was "I am getting conflicting information, which should I use?" The answer appears to be both. Set the Warm Ground idle to 1650RPM, operate the power plant no lower than 1800RPM. Okay guys, I am sure that I have erred technically somehow or at the very least I have conjugated a verb badly or left a dangling participle (or is it a dangling modifier now), so bring it on."
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I just took it a step further to show it can be done and without any problems and that worrying over and being ridged over 100 rpm shouldn't be an issue for a skilled pilot.

What's nice about my job is I get to fly all kinds of LSA and get to teach others what to do when everything isn't normal like when you have unexpected problems, weather, engine issues or field changes from what you are used to. Anyone can fly their plane when every thing is normal, but that's usually not what causes crashes. Not too long ago I had to cross the numbers at 100+ mph and yes I had a nice long runway, but the landing was still normal just not the approach.

Train for the worst be happy with the mundane and routine. If your mind is ridged so is your technique in emergencies and problem solving becomes narrow in the thought process. I have been flying light aircraft since 1980 (about 6K hrs) along with gyros and helicopters and I have been a Rotax IRC for years and just finished 912is training.


Hi Bill,
Landing with additional rpm can be a good technique under certain conditions, but I'll be the first to say there is a point of diminishing returns. It's up to each pilot to educate themselves on where that is for each plane since they can be different. Each landing out of your norm carries different trains of thought and possibly a different skill set from the norm. I have flown RV12, Gobosh, Allegro, Remos, Flight Design, Sport Cruiser, Highlander, Rans, Kolb's, Zenith, Kitfox, Skyboy and others over the years. Nothing magical about any of them.

p.s.
You won't have to worry about volunteering your plane to build I have had enough years ago and know I don't want to do that any more. I'm happier buying already assembled or SLSA.


I like JBpilots inference. The approach can be anything it's what you do with it at the end and what the conditions and techniques that were used for that particular landing that separates the good from the bad.
 
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Tom,

In my Rotax experience, limited to the engine in my CT, a warm ground idle of 1800 gives me around 2200 on final and a warm ground idle of 1650 gives me 1950 or so on final. Just the opposite of what you said in #2.
 
I defer

We'll then John, I defer to your experience. From the numbers you gave me it looks like the same principle holds, just at a factor of two. Instead of a 150-200 RPM increase in the pattern you are seeing about a 300-400 RPM difference.

Tom
 
In our CT, I used to set for about 1700 idle and on the ground kept the speed up at 1800 or more, mostly by feel actually - you can really hear and feel the gear lash at the lower RPM, and just add throttle to stay above that. This allows you to keep the idle thrust down on approach.

You can always slip the airplane too. The CT could slip at pretty extreme angles and still be well in control; not sure about the -12.

TODR
 
OK, Today's experience

Since building 143WM (120241) I've had the minimum idle speed (warm) set at about1450. That said. I NEVER idle there-- 1900-2500 until warm. Per training, on final RPM at 2500 until I'm positive the runway is made, airspeed 50-55 kts (weight dependent), and then power full off giving a windmill idle of around 1900 RPM. With 5-10 mph headwind I can make the first turnoff (700 feet) without heavy braking.

Just finished the 200-hour inspection with a Rotax-trained A&P to take the carbs apart. He insisted on a warm idle if 1900 RPM. Flew her today and it was VERY hard to slow below 60 kts; windmill idle was 2500-2650 RPM. When I finally did get the speed on final down to 55 knots (higher AOA) I was able to flare at the desired spot but power all the way off gave me windmill idle if 2600 slowing to 2215-2200 and we used a LOT of runway before slowing down-- easily twice as much as I'm used to. With 50 kts, full flaps, and 2300-2500 rpm I think I could fly the length of the runway in ground effect.

Monday ground idle gets set to 1450 RPM!!!!

Wayne 120241
 
MUCH better!!!

Reset the idle MINIMUM RPM to 1550 today. Test flight gets me back to where I was-- power off idle at 55 kts. about 3000-2100, during flare it continued to drop, and with 8 mph headwind (two aboard) I had to add power during taxi to make the first turnoff at about 900 feet. Yesterday I had to use brakes to make the second one at 2300 feet-- prop just kept pulling her along.

Wayne 120241 143WM
 
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