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Rotax idle high RPM issue

cactusman

cactusman

Well Known Member
I have had a successful 1st engine run, and successful taxi tests and was down to a carb balance which I attempted today after watching the video and getting a briefing from a RV-12 owner with several hundred hours.

I did a mechanical sync prior to first start and then went to a full taxi, run-up and a AHRS mag setup on a compass rose. All went fine. Last start was friday. Today (monday) went to sync and 1st warmed up engine and noticed the engine would start at low RPMs and then magically jump to 2000 RPM and that was the lowest idle.

After several starts and shutdowns with the carb balancing (dial type from Lockwood) hooked up, I frequently gave up on the balance and went back to the idle - finally ended up backing the idle screws all the way out and went to a fresh mech sync. That worked for a start. I got 1650 RPM at idle - warm engine. Everything green.

OK - started to sync again - idle first. Then I noticed the engine would start at 1200 RPM for a few seconds and immediately jump to 2800 RPM. Whoa.

Throttle cable at idle. Friction set. Everything looks fine. Choke secure - not the problem.

Called Van's and they think it might be the soft start modules. Checked all the plugs and wires and I didn't see anything screaming at me.

I think I will start from scratch tomorrow - do another mech sync, unhook the pneu sync equipment and see if I can get the idle set again. If not, I guess I am calling Lockwood in the morning.

If anyone has any suggestions - please by all means....right now I have an idle of 2800.....no cable issues that I can tell - all original Rotax springs and original throttle cable.

Many thanks
 
What you are probably seeing is what happens when the soft start system switches between start mode and run mode.
While the timing is retarded right after start, it will run slower at any given throttle setting, then speed up when soft start returns timing to normal.
Your idle is fast because you haven't properly completed the carb synch / adjustment procedure.

When it is properly set up, the initial RPM right after start, if teh throttle is near idle, will only be 1200 - 1300 RPM
 
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I agree with everything that Scott said. It is normal for the engine to start at slow RPM, then speed up after a few seconds when the ignition changes timing. The idle speed after engine start is controlled by the carburetor. No ignition problem whatsoever can make the engine run faster than allowed by the carburetor. It is physically impossible for the engine to run faster than what is allowed by the fuel flow. So the high RPM of 2800 is due to either the throttle cable or choke cable or other carburetor problems, NOT due to ignition. Read this THREAD Especially Posts 1, 8, and 12
Although the engine should never idle below 1400 RPM, the idle speed should be capable of idling at a lower RPM so that the plane will not float down the runway when landing. The airspeed on final will keep the engine running faster than the idle set point. Even though the idle speed is capable of being operated below 1400, I am not saying to operate below that speed. After landing, push the throttle in slightly to keep the RPM above 1400. An analogy is a car that is capable of going 100 MPH. Just because it is capable of that speed doesn't mean that one should drive that speed.
Joe Gores
 
Mich48041 said:
I agree with everything that Scott said. It is normal for the engine to start at slow RPM, then speed up after a few seconds when the ignition changes timing. The idle speed after engine start is controlled by the carburetor. No ignition problem whatsoever can make the engine run faster than allowed by the carburetor. It is physically impossible for the engine to run faster than what is allowed by the fuel flow. So the high RPM of 2800 is due to either the throttle cable or choke cable or other carburetor problems, NOT due to ignition. Read this THREAD Especially Posts 1, 8, and 12
Although the engine should never idle below 1400 RPM, the idle speed should be capable of idling at a lower RPM so that the plane will not float down the runway when landing. The airspeed on final will keep the engine running faster than the idle set point. Even though the idle speed is capable of being operated below 1400, I am not saying to operate below that speed. After landing, push the throttle in slightly to keep the RPM above 1400. An analogy is a car that is capable of going 100 MPH. Just because it is capable of that speed doesn't mean that one should drive that speed.
Joe Gores
Click to expand...

And I agree with almost all of what Joe said...

Rotax recommends that the minimum idle speed setting be 1400.

During ground operations you should always operate the engine within the green range on the tach (which starts at 1800 RPM) to minimize wear to the gear box.
Otherwise I agree with Joe... set the idle at 1400 - 1450 and then manually operate it at 1800 or above for ground ops. This will give you an low idle that will help with landings. Note: idle speed will increase slightly as the engine warms up to normal operating temp, which is hard to obtain during ground runs, so I set the idle at about 1375 or so, and it usually results in a full temp idle of about 1450. You have to eyeball an average RPM when it is this slow because it does not idle smooth and the numbers jump around.
 
John,

When you say you adjusted the idle screws, do you mean the stops for the throttle arms? When I was at the ROTAX course the instructor said the mixture adjustment screws were sometimes adjusted by owners from the factory settings and that caused idling problems. He recommended that owners don't mess with the mixture adjustment.

Rich
 
Another 2 cents worth - -

I went thru my carbs for the five year thing. I had never adjusted the idle mixture jets, but thought I would check them. They were set at 1 1/2 turns out from light seating. Seemed to make sense to me. I set HOT idle at about 1400, and set the cable stops about 10 - 20 thousands away from the cable housing. If you pull hard on the throttle cable, the stops keep you from possibly over-torqueing the throttle arms. Runs perfect, and works well for landing and shut down as has been mentioned above. If you have messed with the idle mixture adjustment, I'd suggest setting to 1 1/2 turns out, and set and balance the carbs from there. Should give you excellent performance.
 
1.5 turns out is the book standard for the mixture screw and is what all ULS and UL's should be set at. I personally don't set idles too low (and is advised against in schools) just so it doesn't lead to an engine out issue at the wrong moment or cause hammering on the gearbox due to the 11:1 compression ratio. Yes you can keep throttle in to keep the idle up, but I keep seeing the majority that don't. If your speed or rpm is a little high on landing it isn't usually a poor idle setting, just pull the stick back farther. The prop will load up and the plane will descend with a slightly nose up attitude. Throttle controls altitude and the stick controls the speed when properly executing a landing.
You can land in 1000' all day long with 2700 rpm on landing. You only need some flaps and pull the stick back farther. I did this test because of a fun challenge with our UK friends because they typically use shorter fields than we do.
 
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roger lee said:
You can land in 1000' all day long with 2700 rpm on landing. You only need some flaps and pull the stick back farther. I did this test because of a fun challenge with our UK friends because they typically use shorter fields than we do.
Click to expand...

Roger,
Please don't start this whole debate again.
This is very bad advice and I hope all RV-12 owners ignore it.
Maybe with proper technique at that idle setting you could land in 1000', but with a proper idle speed you can land in 400'
 
OK guys - thanks for the advice.

No I did not touch the idle mixture screw on the bottom of the carbs - I assume it is still set per the factory to the 1.5 turns. The MM says to assume it is set properly on new engines.

I'll reset the idle after warm up to the 1400-1450 min advised.

Then I'll try the balance procedure in the MM again.
 
It's only to demonstrate that a superficially low idle settings doesn't fix speed and landing spot issues.


Hi Cactuspilot,

While using the manuals for Rotax remember they are written for 3 different engines. Unfortunately in some instances like the low 1400 rpm listed in the book it has the UL in mind with the much lower compression ratio and not appropriate for the ULS. We try to remind people in schools to watch out for these types of things and advise them that higher rpm's should be used for the ULS idle settings.
 
From most recent rev Operators Manual

Effectivity: 912 S/ULS
BRP-Powertrain
page 2-5
OM Edition 3 / Rev. 0 September 01/2012
d05666.fm

2.2) Operating limits (912 S/ULS)

Idle Speed / Minimum 1400 RPM
 
Actually Scott and I agree on all points. I said to keep the RPM above 1400 and 1800 is above 1400. :D
Joe Gores
 
Hi Scott,

Except the 1400 wasn't meant for the ULS. It is Rotax's poor segregation of the three engines in the manual. It is unfortunate because most people that have never taken all the Rotax classes know when or how to separate the info about the 3 engines in the manual unless it is very specific like it is in some sections. No school I have ever been to in the last 12 years advocates 1400 for an idle rpm for the ULS.

This poor wording is nothing different from the misprint that was in the manuals about which way to turn the idle stop screw which was wrong and all the other misprints from poor interpretation to English.
 
Seems like Rotax could issue a simple Service Instruction about this topic since there is about 400 RV12 ELSA with 912ULS on them not to mention other plane manufactures with the 912uls on them to. Roger is there a tech rep you could talk to about this subject?;)
 
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Well long story short - fixed.

Reset the 3/8 throttle cable nuts (lower Torque in MM) - that may have been distorting the cable somewhat as it was not rotating freely when you pushed the throttle cable in/out....started with a clean, by the book mech sync....

Also redid Lockwood's carb sync device per the following pics - that helped (credit goes to Denny M in Deer Valley for the inspiration)

- then I synched the right carb (it had the higher reading in Hg) per the MM at 2500/3000/3500 RPM and it remained synced during following up testing through all throttle ranges (pretty close anyways)...note 2 flats adjustment of the forward nut = approx .5 in HG for others

Idle (when I pull - hopefully not too hard to distort the idle stop) I get 1550 RPM.....but it seems to naturally idle around 1700-1800 now....I may have to back off the idle screws a 1/2 turn but now that everything is working fine I don't want to screw with it.

Thanks all for everyone's help....on to other issues.

2h80qvq.jpg


n6yy3o.jpg
 
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Mans got to know his own strength.

Idle (when I pull - hopefully not too hard to distort the idle stop) I get 1550 RPM.....but it seems to naturally idle around 1700-1800 now....I may have to back off the idle screws a 1/2 turn but now that everything is working fine I don't want to screw with it.
Click to expand...

Think Floater.:eek: Just kidding, don't want in the middle of the, "Idle wars" :D By the way Roger what was that Rotax recommended idle speed for the 912ULS? Anyways it takes a long time to break in a Rotax, maybe Roger would talk to this, so after you put a few hours on the engine it will be easier to adjust the idle lower. When you are ready just turn the both idle screws out a 1/4 turn not a half each, no rebalancing of the carbs required. Just don't forget to move the cable stop to.:) Sounds like you are getting closer to the end of 90% done and 90% to go.:p
 
Floaters

Yep and I have Engine No 678xxxx so it looks like I am "floater" check every 25 hrs/60 days affected....just printed out the blog, the SB and put my request in for the special syringe kit from Lockwood.

Yea. Joy. Bliss.
 
Here is a good way to make sure that you can't over stress the idle stop screw plate. Install this cable stop. Without this owners who have a Vernier throttle setup usually don't have stops on how far you can pull back the throttle and with a little extra pull you bend the idle stop screw set plates. I bet I have seen at least 50-60% of the owners do this without some sort of stop in place.


see the 5th post post picture.
http://www.rotax-owner.com/rotax-forum/3-4-stroke-technical-questions/4733-carb-sync-for-beginners

If you adjust the idle stop screws you should always have gauges inline for a sync because turning one 1/4 turn is not usually equal to 1/4 turn on the other in regards to rpm change. One carb usually is affecting the rpm a tad more than another. If this wasn't true then after a mechanical setup with the feeler gauge it would make these dead equal.

The carb sync should be done when new and every 100 hrs. or the annual. Things like cables relaxing and stretching, pulleys wear, moving parts in the carb settle in, ect..
Once you learn how and understand what's going on it really only takes 5-20 minutes.

Idle setup in school is taught around 1800 rpm for the ULS. That said it can be set lower so long as the owner knows not to just sit there and let it rumble away at 1600 or something low like that. The ULS is 11:1 compression and will cause extra wear long term to the gearbox dogs. I have seen beaten low rpm gearboxes at the inspection times. There is a real difference. The UL only has a 9:1 compression so it doesn't hammer like the higher compression ULS. Running the idle a little higher in rpm while on the ground keeps the impulses to the gearbox smoother. Setting the idle lower than 1800 can help some land, but you can control that with the stick too. I teach almost all my people that get transitioned to use some power right to touch. Always thinking every engine must be at absolute idle on landing is a hold over from the old days that some CFI's can't seem to get away from. Pull the stick back at even 2700 rpm and you will land because your will control the speed with the stick. Many I have transitioned here find landing much easier with 2500 rpm left in to touch. (we are talking normal landings on a normal airstrips, not short field or emergency landings where short stops are a must) There are many ways to land and I don't believe in learning just one way.

The 912 series engine technically doesn't need a break in like the two strokes. Just go fly and vary the throttle on the first few flights, but for the most part it's ready to go. The parts won't really get all settled in for a while, but that just comes with time. At the 25 hr. inspection and oil change I usually double check it because cables settle and stretch.


Wish Vans would allow pictures here. It would make things easier on its members.
 
Official (long) Rotax response to proper idle speed RPM

I say long, because for our RV-12 owners/builders benefit, I am posting an entire e-mail exchange between myself and Dean Vogel at Lockwood Aviation in Sebring FL...

I have a good working relationship with Dean. Lockwood Aviation works with a lot of RV-12 builders and owners, and is a Factory Authorized Service Center for S-LSA RV-12's. Dean knows he has an open line to me anytime they have a question or feedback, and I have the same with him.

Good morning Dean,
I have a couple questions for you if you have a moment...

In general, a question regarding when a mechanic is referencing the
documentation to make engine adjustments such as in the Line Maint.
Manual Chapter 12-20-00 / 10.3.1, to do an Idle Speed Check/Adjustment. It describes the process to use, but gives no detail regarding the specific
specification for the idle speed. Where is the proper/official place to
look up this specification? The operators manual? What is the correct
idle speed to set for a ULS engine? Is there a difference in the spec.
between a low compression version (80 HP) and the higher compression
version (S, 100 HP)?
The questions are based on a perpetual debate in the RV-12 on-line forum.

Thanks in advance

Hi Scott,

That would be why I avoid ? assiduously ? the online forums.* It?s like wrestling with a pig.* You both get dirty and the pig loves it.

There is no difference between the low compression and the high compression engines.

The only specification given is to not set the idle below 1400 rpm.

There is a sweet spot ? as it were ? at 1800 rpm.* If you go above that, you start to disable the starting carburetor.* If you go below that, you introduce more wear and tear on the gearbox.

On many airplanes, it is advisable to set the idle lower than 1800 rpm because at that speed, there is still a goodly amount of residual thrust. *Small, light, slick aircraft can be difficult to land with this setup (we set the CTs at 1550).* If a lower speed is used, the operators should be instructed to not leave it there when sitting still on the ground ? again, because of the gearbox wear. *If they are sitting in the chocks, or awaiting their turn for the runway, they should bump the throttle up to 1800-2000 rpm.* If they want to pull it back from there ? while taxiing ? to avoid brake pad wear, that?s fine.

Also note that the idle speed changes with engine temperature.* If the oil temperature is 140?F while you are doing the carb sync and idle adjustment, you can count on the idle being about 100 rpm higher when the engine is at normal operating temperature.

Bottom line is that Rotax does not specify an idle speed ? the OEM gets to do that.* So you can give them a number and say ?Because I said so.?** J

Does all that help?

Dean

*

Yes, that helps a lot.
What we do (and recommend) is no less than 1400, but shoot for 1400-
1500 at normal operating temp (I am aware of the ~100 RPM change) to help with landing, just as you describe. But then stress that for all
operations (idling on the ground, taxi, etc.) the operator should manually
keep the RPM within the green range (1800 RPM or higher). So it sounds
like we are doing it correctly. Do you mind if I quote you?

I don't mind at all.
D.

Headed for the showers now....... ;)
 
Getting opinions from different instructors is like pig wrestling too. It isn't unnique to forum members.

This might actually be fun. I know about 6 instructors it wiould be interesting to pose the same question as you wrote it to each and I know 3 master distributors.
I'lol copy your letter when I get home from the airport and send it out to the others without Dean's comments.

His own words below 1800.
"If you go below that it introduces more wear and tear on the gearbox." How in one sentence can you say it's okay to be at 1400-1500 and then say at anything below 1800 is okay,but wears on the gearbox. That's just saying go ahead and beat on the gearbox .
His other statement is also my point that Rotax doesn't specify a difference in the manual for all three engines, but in class we do. In writing it looks technically right, but Even accoording to Dean that causes extra wear on the gearbox.
 
Dean actually said what many have been saying. The sweet spot is 1800 and when run lower it wears on the gearbox. Here is the kicker for me. You could set the idle down at let's say 1500 so long as you always knew never to idle there on the ground and only use it when pulling back idle in the air on approach. The issue I have had with the majority is they don't know that or follow that rule. They idle too low on the ground. It also causes some to have a tad more starting issues in cold weather. If all owners were all at the same skill level and education then doing some things wouldn't be an issue, but things at times need to take inconsideration all levels of education and skill levels and not just the top people.

Here is a simple fun little experiment. Instead of landing at absolute idle leave 2200-2400 rpm right to touch. The only thing different is to pull the stick back farther than you would at idle to keep the exact same speed you had at 1600 rpm. Pulling the stick back reduces speed and the plane can not fly at 2400 rpm. Will you glide an extra 75', sure, but does it REALLY make any difference on a normal paved runway and not trying to land in the shortest distance possible? Most have found that this technique gives them the smoothest landings out of 100.

Give it a try and see what you think. If you don't like it then no harm no foul and you'll see rpm isn't the big deciding factor on a good landing. The stick will keep your speed as it always is.

Never hurts to try something new.


p.s.
I talk to his mechanics occasionally and they don't all set idles down at the 1500 area, most are higher. Right from their lips.

Pig wrestling seems to be rampant than any of us knew and more wide spread than the WWF. LOL
 
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The tach on the RV-12 has a yellow range from 1400 to 1800. The green range starts at 1800 RPM on up to 5500.

A licensed pilot has a certain level of responsibility when operating an airplane.
That is the primary reason that one thing not on the panel is a placard that say "Do Not Crash"
 
Jetguy said:
Seems like Rotax could issue a simple Service Instruction about this topic since there is about 400 RV12 ELSA with 912ULS on them not to mention other plane manufactures with the 912uls on them to. Roger is there a tech rep you could talk to about this subject?;)
Click to expand...

For once, the 'rest of the world' beats the USA in numbers.

;)Beyond the 400 or so RV-12s there have been over 50,000 91x engines produced...

PS I'd wager that our runway at <800m (2600 ft) with an approach over trees would disappear quite quickly at an 2400rpm idle.
 
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It seems that everyone agrees that there is less wear on the gearbox if the engine is operated at 1800 RPM or above. The disagreement is over what RPM the idle stops should be set at. Roger is the engine expert and prefers 1800 to prevent gearbox wear. Scott is the airplane expert and prefers 1400 for shorter landings, but keeps the RPM above 1800 with the throttle. Roger is concerned that some pilots might not pay attention and let the RPM get too low. I am one of those pilots who does not always pay attention to the RPM and my engine idle is set somewhere around 1400. I always look at the tach after engine startup and keep it in the green; but I never watch the RPM during the flare and landing. And so I analyzed my Dynon data from a recent Young Eagle's event where I made 10 or so full stop landings. On final approach with the throttle closed, the RPM is somewhere between 1800 to 2000. As the wings stall, the RPM is about 1700 and drops to 1500 as the plane slows down. The RPM did drop to almost 1400 on a couple of landings when I was slow to add power after landing. The time during which the engine RPM was between 1400 and 1500 varied between 0 - 8 seconds per landing. I am concerned? No. I routinely operate from a short grass strip. It will cost a lot less money to repair worn gears than to repair a damaged plane if it runs off the end of the runway. The RV-12 will float if RPM and airspeed are not controlled.
Joe Gores
 
I usually set rpms at 1700 and make sure the owner understands not to just sit there or warm up there. I does happen and it happens a lot. By not setting it artificially low for most users you help keep them out of the gray area.


I have no issue with lower rpm settings for the engine IF the user understands the issues involved with sitting at low rpm on the ground. It will never get that low in the air.

The other issue for me is that thinking a lower set rpm controls the speed of the plane and its touch down point. Once down at those rpms (i.e. 1600-1800) the speed at which you approach or actually touch should be the same. The only thing that should change is how far the stick is back to maintain that preferred speed. 1400 up to 1600 is just not needed. Pull the stick back at 1500 or 2700 and the speed will drop and you will stall at the same speed. The only difference landing at an idle of 1500 (which won't be that anyway as air passes through the prop) and 2700 rpm is you'll just have the stick back farther to keep the exact same speed at both throttle settings. I demonstrate this to all the high time pilots transitioning from a heavier aircraft to LSA. The higher the rpm usually the higher the nose just before touch which helps keep the nose off and touch mains first and allowing the nose to settle, but even more importantly for me and especially in bad cross winds it allows better control and air flow over the tail and elevator. When you get too slow and loose that air flow then these inputs are sluggish and sometimes needs big inputs. With a tad rpm on landing you have great rudder and elevator control which comes at the same speed as the guy with the low rpm landing.
I would guess about 70% of the people I work with keep this technique. They not only more smooth and consistent landings, but all of them can land in pretty severe cross winds because you maintain better directional control and not soft inputs.

There are many ways to land and I think everyone should learn them all as they all have a time and place for use. Learning them all keeps panic and stress out of the cockpit during more complicated landings and maneuvers and gives the pilot a much larger mental toolbox to draw from.


Several of these things like idle landings verses some throttle at landing and less rpm settings verses lower are all Personal preference items and there isn't any issues unless the end user fails to understand that there may be consequence for things theyy don't fully understand at this particular point in time.

This is exactly why we talk about these and we all learn from each others class teachings and actual experience with our individual aircraft and engines.


As my professor used to say: The mind's a terrible thing to waste and when you think you know all of it then just open the next door and there will always be more.

The Rotax instructors that teach the instructors still keep learning according to them.
 
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Roger,
I hope you will take what you wrote at the end of your post to heart, because you obviously don't have all the answers regarding the influence of engine thrust on a landing airplane.

What you keep writing is probably spot on for a high drag aircraft like the wire braced ultralights you may have experience with in the past, but it is totally bogus in a light wing loading, low drag airframe.
Heck, even the people that fly the other model RV's with fixed pitch props know this. There is tons of discussions about it here in the forums.
If that is the stand you want to take, there hundreds of RV-owners that already know you are totally wrong.

At this point all I can do is hope that people that don't already know it, don't listen to a single word you say on the subject.
 
roger lee said:
His own words below 1800.
"If you go below that it introduces more wear and tear on the gearbox."
Click to expand...
So, I know this is likely to be impossible to quantify, but in general, how much more wear and tear? It's like I tell my doctor when he goes on about my triglyceride levels: "Doc, if not eating bacon means the difference between only reaching age 83 instead of 85, that's a trade I'm willing to make on quality of life grounds, although I reserve the right to change my mind when I'm 82."

In your experience, how damaging is it to use a non-optimal idle speed? I'm running 100LL exclusively (with Decalin), so I'm already looking at some earlier-than-nominal gearbox issues, but for various reasons that is a trade I willingly make. Is this idle thing in the same neighborhood of increased wear and tear, or is it horrendously bad?
 
Hi Dave,

It isn't horrendously bad at all. Admittedly from all instructors it just cause wear and possible extra maint. to a gearbox during its life. It may cause some extra cost during a gearbox inspection.

All this is predicated on how long and often the engine is allowed to run at those rpms. Every single individual is different and there is now way to accurately predict an outcome.

It's a lot like smoking for people. Some show signs of the affects of cigarette smoking early on and some don't. Some people may develop cancer or COPD and some may not. You just don't know and no way to accurately predict the individual's symptom outcome

It's a **** shoot and you just never know so we try to error on the what we call the "Best Practice" scenario and stay away from things that may lead to a problem later. This is one reason in Dean's own words and most all other instructors that 1800 was a sweet spot and lower rpms could have extra wear on the gearbox. Keep in mind we are addressing the ULS and not the UL. Having the rpm set lower isn't bad in itself if used properly and not allowed to actually run down there for any length of time. Pulling back at landing won't allow it to get there because of air passing through the prop. Using it just at the moment for engine shut down to slow the prop is good. Idling sitting on the ground in low rpm not so good.
 
aerofurb said:
PS I'd wager that our runway at <800m (2600 ft) with an approach over trees would disappear quite quickly at an 2400rpm idle.
Click to expand...

This is so true. Right now, my idle has crept up a little high and is around 2,000 RPM when hot. I kept it there because I like to warm it up at this speed and it taxis nice. However, I've been having a little difficulty getting the -12 to come down over the trees to our 2100' runway. Then duh, the light bulb went on, and I realized the high idle speed is making a high approach impossible. Pulling the cowl now to re-adjust.

It is true that the -12 does not want to come down and will float quite a bit with just a little extra speed. I think it's harder to slow down than my fixed pitch RV-6.
 
Dean Vogel is quoted as saying,
"Bottom line is that Rotax does not specify an idle speed – the OEM gets to do that."
Click to expand...
And the OEM (Van's Aircraft) specifies on page 12-14 of the "RV-12 MAINTENANCE MANUAL" dated 08/12/13:
VERIFY THE IDLE SPEED AND ADJUST AS NECESSARY TO ACHIEVE 1600-1650 RPM AND SMOOTH ENGINE OPERATION
Click to expand...
Even so, I will leave the idle set point at 1400, but maintain the RPM above 1800 with the throttle. I want to land as short as possible on my grass strip.
Also on page 12-14 the RV-12 maintenance manual says,
OPERATING AT IDLE SPEEDS WHERE THE ENGINE IS MAKING A KNOCKING / RATTLE TYPE NOISE WILL CAUSE GEARBOX DAMAGE
Click to expand...
I have noticed a knocking / rattle type noise while parked in a cross wind, even though the RPM is in the green. Does that noise mean that the gearbox is experiencing excessive wear?
Joe Gores
PS: I determined the firewall was making the noise. Installed Van's firewall reinforcement kit.
 
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Lost in translation....

I wrote that I adjust the idle speed to 1400 - 1450, but that was in the context of a value to use when making the adjustments during maint. ground runs.
As already mentioned, the idle speed is faster once the engine is at full operating temp., compared to what it is at the 130F or so oil temp that we typically have when doing the adjustment.
This will typically bring the full temp. idle up to around 1600 or so.

I say or so, because in the 1400 - 1450 range, the engine is not running very smoothly and the tach reading will be jumping around... I go by the lowest numbers I am seeing.
 
Mich48041 said:
I have noticed a knocking / rattle type noise while parked in a cross wind, even though the RPM is in the green. Does that noise mean that the gearbox is experiencing excessive wear?
Joe Gores
Click to expand...

Possibly, but not necessarily.
There could be other sources of the noise...
The relatively high blade pitch that we use causes a strange noise sometimes when the wind is blowing through the prop arc at just the right angle from the side. The next time it happens, try letting the airplane creep fwd and turn slightly, and see if the sound goes away.
 
Does it sound more like rpm and harmonics or a definite metallic rattle?


If the rpm is too low the 30 degree play in the dog gear can move back and forth slightly and may not be fully engaged leading to this sound. This comes from the exhaust pulses due to the higher compression. If this is low rpm caused increasing the rpm should make it go away.
Wind hitting the prop from the side or back can give it an odd harmonics and rpm change that the human ear can pick up. This is usually more rpm and harmonic and usually isn't a metallic rattle. When I carb sync I always turn into the wind. That 30 degree play (which is only 15 degrees in older engines) is the one you feel when you put the crankcase locking pin in place and move the prop the 30 degrees through its arc doing the gearbox friction torque check during an inspection. As you can see this junction is not a solid hook up and can have movement back and forth.

Here is a picture:

https://plus.google.com/photos/115442716220402518613/albums?banner=pwa


I hope this link works.
 
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Roger,
It has been a while since I last heard the noise and can not remember exactly what it sounded like. If I hear it again, I will try changing the RPM or turn more into the wind. Thanks for replying.
Joe Gores
 
Think of it this way. The picture has to be addressable on the Internet somewhere for you to post it here in the forums. It can't be on your hard drive, phone, etc. That means you can either find the picture somewhere ( like an online catalog or similar) or you have to save it on the Internet. You can use photo hosting services, your own web server if you have one, or other. I'm not sure if there are restrictions from using something like Facebook, but it would not surprise me if there are.

Once you find the photo, right click on it and click properties, and copy the net address. Click on the photo icon in the posting top tool bar and insert the web address in the little window that opens.

It's actually harder to write this all down than to actually do.
 
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Sort of worked for me

roger lee said:
I usually set rpms at 1700 and make sure the owner understands not to just sit there or warm up there. I does happen and it happens a lot. By not setting it artificially low for most users you help keep them out of the gray area.


I have no issue with lower rpm settings for the engine IF the user understands the issues involved with sitting at low rpm on the ground. It will never get that low in the air.

The other issue for me is that thinking a lower set rpm controls the speed of the plane and its touch down point. Once down at those rpms (i.e. 1600-1800) the speed at which you approach or actually touch should be the same. The only thing that should change is how far the stick is back to maintain that preferred speed. 1400 up to 1600 is just not needed. Pull the stick back at 1500 or 2700 and the speed will drop and you will stall at the same speed. The only difference landing at an idle of 1500 (which won't be that anyway as air passes through the prop) and 2700 rpm is you'll just have the stick back farther to keep the exact same speed at both throttle settings. I demonstrate this to all the high time pilots transitioning from a heavier aircraft to LSA. The higher the rpm usually the higher the nose just before touch which helps keep the nose off and touch mains first and allowing the nose to settle, but even more importantly for me and especially in bad cross winds it allows better control and air flow over the tail and elevator. When you get too slow and loose that air flow then these inputs are sluggish and sometimes needs big inputs. With a tad rpm on landing you have great rudder and elevator control which comes at the same speed as the guy with the low rpm landing.
I would guess about 70% of the people I work with keep this technique. They not only more smooth and consistent landings, but all of them can land in pretty severe cross winds because you maintain better directional control and not soft inputs.

There are many ways to land and I think everyone should learn them all as they all have a time and place for use. Learning them all keeps panic and stress out of the cockpit during more complicated landings and maneuvers and gives the pilot a much larger mental toolbox to draw from.


Several of these things like idle landings verses some throttle at landing and less rpm settings verses lower are all Personal preference items and there isn't any issues unless the end user fails to understand that there may be consequence for things theyy don't fully understand at this particular point in time.

This is exactly why we talk about these and we all learn from each others class teachings and actual experience with our individual aircraft and engines.


As my professor used to say: The mind's a terrible thing to waste and when you think you know all of it then just open the next door and there will always be more.

The Rotax instructors that teach the instructors still keep learning according to them.
Click to expand...

Thought I'd give Rogers theory a test this afternoon. Nice calm day here at Barton, UK , with a quiet circuit on 09R 522m of grass.

I normally approach at 50kts, a little slower than the handbook but still around 1.3 our 39kt approach configuration stall speed.

First tried 2500rpm then 2700rpm. The approaches worked fine and I wasn't overshooting. I managed to keep the power on almost to touchdown using 2500rpm but I had to cut power just after the airfield boundary in order to land using 2700rpm or I'd have overshot the runway.

I'm sure that Rogers ideas would work using a longer runway. Here at Barton I'm sure the ideas would work flying a CTSW with its more powerful draggy flaps. But I'll need a lot more practice to succeed using our RV-12 with its less draggy flapperons. Also couldn't have done this prior to fitting the vernier throttle as the old throttle wouldn't hold a setting.

Not saying a more competent pilot can't do it, and I totally agree with Roger in building up a larger mental toolbox.


John.

PS Roger. I find you Rotax posts really interesting and useful. Keep up the good work!
 
F1,

You must be a computer geek! Us lesser beings just want to know what button to push to make the white man's Magic happen?:D

Rich
 
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