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TAXI the RV-12iS - Do you need lots of power and dragging brakes? Do RV-12iS naturally have turning tendancy.

J

jackking123

Well Known Member
Patron
So I have RV-12iS experience. However I have more time in right seat as a CFI than actual stick time doing checkouts, flight reviews, instrument practice. I fly with many people and different planes. I am stumped here... is this normal?

Observing the pilot/owner taxi. his RPM is is way high and I feel he's dragging brakes. I suggest he let go of brakes, use rudder (to the floor and if needed) reduce power. Well a few things happened. We start going left. He also pulled power back and PROP almost stopped (more on that below ***).

My questions
1) can you taxi an RV-12iS without higher power over 1800 RPM and dragging brakes?
(I get with a cross wind that would be needed but it was just past sunset dead calm. I've flown free castor planes, RV's, Grumman, understand differential braking, even a Metroliner turboprop, nose gear steering was turned off on takeoff and landing.)

2) What would cause a RV-12iS to have turning tendency landing or taxi (which is not left turning tendency from prop or x-wind)?
(Plane does seem to pull in one direction unlike RV-A models,. Gear tracking issue? One tires has a flat spot after 100 hrs. Locked it up once or twice?)

3) If an RV-12iS likes to go left or right, can you adjust that out?
(I haven't built an RV-12iS (built RV-4/-7), no toe/camber adjustment once gear installed.)

*** PROP STOP/Engine stall not focus of post, but feel free to comment. I read recommended Rotax 912iS min idle at 1650 to 1800 rpm. When cold pilots should set 2200 rpm after start, when engine is cold, for smoother ops and gearbox happiness. Not my plane but really would like to know for my own CFI knowledge. I read idle stop screws on the throttle bodies adjust idle. Factory setting may be too low. Recommended for smooth 1650–1800+ RPM to avoid excessive gearbox vibration. I can say this RV-12iS the prop stops on the ground at full idle.
 
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Minimum idle of 1800 rpm would be way too high. Makes (properly) slowing down for landing more difficult.

Taxi with no wind should be possible with no brakes and 1800-2000 RPM with good steering response from just rudder, to stay centered on taxi way.
I agree with your idea that pilot should first use all of the rudder available and then add brake if that doesn't give the required result.
A quick blast of power with rudder input can even allow for tight maneuvering without the need for brakes.

If an RV-12 wont taxi straight on a level surface with no wind, there is probably a problem with landing gear alignment (something that needs to be measured and adjusted during initial gear assembly). An improperly adjusted/maintained nose gear assembly can also make what is an easy to taxi airplane (once you have learned), into one that can be very frustrating.
 
When you say the prop stops at full idle, are you saying the engine dies? If the idle is between 1650- 1800RPM it shouldn’t die. If it is dying, the idle is set to low. The breakout for the nose wheel should be around 20lbs, which helps. The RV 12 is a lot lighter that the other RV’s and the other airplanes that you mentioned, so it’s P factor whe n taxing is going to pull it a lot more. Does take a little getting used to so your not riding the right brake all the time. At real slow speeds with not much air getting moved by the rudder it not real effective and you can chase it instead of being ahead of it. Kind of little like staying ahead of a tail dragger.
 
Regardless of the idle RPM, there is no need to drag the brakes while taxiing unless there is a strong crosswind.
My idle RPM is set lower as Scott recommends. However, I routinely taxi at 2000 RPM or higher without using the brakes.
 
Lots of confusion regarding RPM settings with Rotax. Here are some notes based on Operators Manual
Immediately after start run up to 2500 rpm to facilitate generator switching. 5-10 seconds.
Throttle back to 2000 rpm for first 2-3 minutes to warm oil, after 2-3 minutes. If oil temp not up to operating temperature of 122 F or 50 C, then can increase to 2500 rpm to continue warm up.
After warm-up, check full throttle response and throttle to 4000 rpm to do lane ignition checks. Throttle back to 2000 rpm and perform fuel pump check.
Taxi around 2000 rpm and perform full throttle run up before take off.
Throttle at idle should be 1600 to 1800 rpm. 30 degree gearbox is not happy at low rpm (and 1800 is low for a Rotax 912is ) and will chatter noticeably at 1600 rpm.

Learn to taxi at 2000 rpm and manage energy in glide slope and landing and gearbox will last a long time.
 
Mich48041 said:
Regardless of the idle RPM, there is no need to drag the brakes while taxiing unless there is a strong crosswind.
My idle RPM is set lower as Scott recommends. However, I routinely taxi at 2000 RPM or higher without using the brakes.
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Yes. The adjusted idle speed, and the RPM used during ground operations are two totally different things..
Just because the idle is set at 1600 to 1650 RPM doesn’t mean you have to operate the engine there.
That is only so that the engine is idling slow enough that with the throttle closed on approach, you have good speed control.
In flight with the prop being driven by the relative wind, it is not detrimental to the gearbox to be operating below 2000 RPM.
 
docjjrmd said:
Lots of confusion regarding RPM settings with Rotax. Here are some notes based on Operators Manual
Immediately after start run up to 2500 rpm to facilitate generator switching. 5-10 seconds.
Throttle back to 2000 rpm for first 2-3 minutes to warm oil, after 2-3 minutes. If oil temp not up to operating temperature of 122 F or 50 C, then can increase to 2500 rpm to continue warm up.
After warm-up, check full throttle response and throttle to 4000 rpm to do lane ignition checks. Throttle back to 2000 rpm and perform fuel pump check.
Taxi around 2000 rpm and perform full throttle run up before take off.
Throttle at idle should be 1600 to 1800 rpm. 30 degree gearbox is not happy at low rpm (and 1800 is low for a Rotax 912is ) and will chatter noticeably at 1600 rpm.

Learn to taxi at 2000 rpm and manage energy in glide slope and landing and gearbox will last a long time.
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See my previous post
An idle set as specified in the KAI does not negatively influence the gearbox when the airplane is in flight
Another thing to keep in mind in the RV 12 forum is that there is a whole bunch of RV – 12s that have the ULS engine installed, which makes some of the operation recommendations slightly different but everything you mentioned would work with that engine as well.
 
rvbuilder2002 said:
An idle set as specified in the KAI does not negatively influence the gearbox when the airplane is in flight
Another thing to keep in mind in the RV 12 forum is that there is a whole bunch of RV – 12s that have the ULS engine installed, which makes some of the operation recommendations slightly different but everything you mentioned would work with that engine as well.
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I agree, in flight is not an issue, but on ground or taxi at idle is not good on gearbox. Every one needs to look at manuals for their particular engine, thus I try to put my reference in comments which I missed this time around. Ref Operator's Manual 912is Sport 2nd ed.
 
whity1231$ said:
When you say the prop stops at full idle, are you saying the engine dies? If the idle is between 1650- 1800RPM it shouldn’t die. If it is dying, the idle is set to low. The breakout for the nose wheel should be around 20lbs, which helps. The RV 12 is a lot lighter that the other RV’s and the other airplanes that you mentioned, so it’s P factor whe n taxing is going to pull it a lot more. Does take a little getting used to so your not riding the right brake all the time. At real slow speeds with not much air getting moved by the rudder it not real effective and you can chase it instead of being ahead of it. Kind of little like staying ahead of a tail dragger.
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First landing at unpowered airport I asked him after landing to go to idle so we could make a taxiway and not have to use as much brakes. He had a habit of keeping the RPM up at 2000 or higher with the throttle. He did as I asked, went to full idle, PROP STOPPED. Using energy we had rolled just off the runway onto taxway. He had to power everything down and back on. It started right away,

Second time landing at towered airport, his base airport, taxing back to ramp, he was using normal technique, high power (guessing 2200-2500) dragging brakes differential to go straight. I asked if he could pull the power back, let go of brakes and steer just with rudder peddles. Full right rudder it started veering Left definitively. using all rudder no brakes... Also the engine started to stall, and it was caught with throttle before prop stopped.

Appreciate you comments. Just FYI tail dragger, way easier to taxi. Tail wheel is steerable. No brakes normally needed. Lycoming /w Constant Speed prop idles well and thrust at idle is not too bad. Most times taxi on flat ground, no tail wind, no brakes required to taxi, unless you want to make a sharp turn. My tail wheel is locked with rudder, until I jab one brake with rudder. Than the side load breaks the tail wheel detent loose, so it castors, You can turn on a dime. Looks cool at the fuel pumps or pulling up to hanger I am a tail wheel fanboy. .

Min Ground Idle from reading, van's says 1600-1650 rpm I recall. Rotax factory out the box may be 1450 rpm AI/Google says some people find 1800 rpm a min idle to keep gear box vibrations down. All I know this RV-12iS the prop stops on the ground at idle. :oops:

Steering difficulty, it may be normal needing power and dragging brakes all the time as required. However also apparently airplane related issues may contribute:
  • main gear alignment
  • nose gear breakout force (18-20 lbs but AI/Google says some use 26 lbs).
  • tire pressure

Going to help him check gear alignment, tire pressure and nose gear breakout. On other RV's to measure alignment of mains, I dropped plumb bobs from plane centerline, popped chalk line on hanger floor, use long straight edges, measured if lines ere converging or diverging and were they even from L to R. Than I will try to taxi it to see what is up. If it has a LEFT turning tendency one brake, right, dragging a little and enough power to move the plane should be all you need.
 
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Google and AI searches will only give you a cross-section of all of the information on the Internet. A lot of which is wrong.
Rotax specifies the minimum idle speed to be 1400 RPM. That doesn’t necessarily mean that that is a good RPM to adjust to and most people agree it is not.
If by factory recommended RPM, you meant Vans Aircraft, they specify 1600 to 1650, and that is where all of the factory production aircraft are adjusted to when they are delivered.

It sounds to me like the airplane you are flying should have some maintenance and inspections done to it before it is flown again.

The kit assembly instructions have a very detailed process of how to check the landing gear and Axel alignment, and properly adjust it while the airplane is being built.
 
I'm a little bit surprised you flew the second flight without resolving the unreliable engine. I would recommend starting there before you worry about the steering. I also recommend that Van's PAP idle range of 1550-1650 as opposed to the factory 1400. Also verify that it's the idle stop on the engine that governs this, not the stop on the throttle lever.

As for the steering, you have listed everything but the checking the brakes. Put the plane on sawhorses and check the free spin of the main gear. With the operations that you describe it's possible that an o-ring is compromised and the caliper is not fully releasing one or both sides, leading to a draggy brake.
 
It takes a bit of technique and practice to turn that thing (or stop a turn) just the right amount. The slightly sticky castering nosewheel takes getting used to and requires tapping/jabbing the brake just right. Dragging tends to stop the plane rather than turn it, especially if the nosewheel breakout is too tight. That leads to higher taxi RPMs (and hot brakes) to compensate. Once your foot is calibrated 😆 you'll be able to straighten out and then taxi straight with only the rudder (assuming no wind). The 1600 RPM idle stop is a target for a mechanic tuning (on the ground) to facilitate easier/safer landings. After that, stay above 1800 with wheels are on the ground. A ULS will benefit from a bit higher RPM for smoothness and reduced plug fouling. Unless your mains are misaligned, taxiing down wind at "walking speed" while maintaining 1800 RPM is not possible without brakes, and x-wind just plain sucks. Having replaced my own brake pads, they're so damn cheap & easy there is no reason to sweat any of this, and--yes--the right brake has 2x the wear. Prop wash 101.
 
N8DAV8R said:
I'm a little bit surprised you flew the second flight without resolving the unreliable engine. I would recommend starting there before you worry about the steering. I also recommend that Van's PAP idle range of 1550-1650 as opposed to the factory 1400. Also verify that it's the idle stop on the engine that governs this, not the stop on the throttle lever.

As for the steering, you have listed everything but the checking the brakes. Put the plane on sawhorses and check the free spin of the main gear. With the operations that you describe it's possible that an o-ring is compromised and the caliper is not fully releasing one or both sides, leading to a draggy brake.
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Don't be surprised. In flight idle was fine. It was evaluated it on the ground before departure. PIC decision deemed it safe. What to do? Fly back to base and yes it has not been flown since, going in for the condition inspection. Idle will be increased.

As far as steering I am told the main gear has shims or shims can be used if alignment is not correct. Builder swears he did it perfect. We (I) will check the alignment. Stay tuned. I have enough time in RV A's, Grumman Tigers and Yankees to know this is not tracking, at least as well as it could be..
 
rvbuilder2002 said:
Google and AI searches will only give you a cross-section of all of the information on the Internet. A lot of which is wrong.
Rotax specifies the minimum idle speed to be 1400 RPM. That doesn’t necessarily mean that that is a good RPM to adjust to and most people agree it is not.
If by factory recommended RPM, you meant Vans Aircraft, they specify 1600 to 1650, and that is where all of the factory production aircraft are adjusted to when they are delivered.

It sounds to me like the airplane you are flying should have some maintenance and inspections done to it before it is flown again.

The kit assembly instructions have a very detailed process of how to check the landing gear and Axel alignment, and properly adjust it while the airplane is being built.
Click to expand...
Roger that, it is not flying until going into condition inspection... except may be for some ground taxi test for steering and ground idle, all best to check before tearing it apart. There is a list of items I wrote up in the 1 hr flight.... FUN TIMES!

Van's (Gary) said the RV-12iS mains have the ability to be shimmed? Not sure... Having built two RV's (RV-4 and -7 with totally different gears than a -12). I know how to drop a line and do alignment check. Not that hard. It can eliminate this being a cause. The builder swears he did everything right per plans. We have not been able to get together and do some taxi test. I am going to taxi it and see how much is the pilot and how much is the plane.
 
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jackking123 said:
Roger that, it is not flying until going into condition inspection... except may be for some ground taxi test for steering and ground idle, all best to check before tearing it apart. There is a list of items I wrote up in the 1 hr flight.... FUN TIMES!

Van's (Gary) said the RV-12iS mains have the ability to be shimmed? Not sure... Having built two RV's (RV-4 and -7 with totally different gears than a -12). I know how to drop a line and do alignment check. Not that hard. It can eliminate this being a cause. The builder swears he did everything right per plans. We have not been able to get together and do some taxi test. I am going to taxi it and see how much is the pilot and how much is the plane.
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You don’t even need to try and figure it out. The KAI for building the airplane details the entire process, including shimming to get the alignment within the stated tolerance.

I think there has been a couple of instances where nose gear legs were a bit out of spec, such that the pivot point where the front fork attaches was not vertical
This will make the caster function of the nose wheel Fork always wanting to induce a turn. This would be another thing to check as well.
 
rvbuilder2002 said:
I think there has been a couple of instances where nose gear legs were a bit out of spec, such that the pivot point where the front fork attaches was not vertical
This will make the caster function of the nose wheel Fork always wanting to induce a turn. This would be another thing to check as well.
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This was more common than you think. It was the first batch of nose gear legs for the SB 19-08-26. My first and second replacements were canted forward beyond spec and did cause a bit of wandering. I helped a friend with his SB and checked his 1st replacement which was also out of spec. I think many actually got mounted without being checked.
 
GOOD NEWS!!! Thanks everyone for input. Went out to airport with owner and did the following. After some checks and service it taxis like a dream!!! The three things we did:

  • Checked Main Gear Toe and Camber... Relative to L & R - They were close to even, considering crude measuring technique & tools (no lasers).
  • Tire Air Pressure, were all Low especially the Nose Tire...Corrected and all brought up to max recommended pressure.
  • Nose Gear Pivot Pre-Load was way too high and not smooth. Fixed as below, Temp fix but improved with lower pivot force and smoothness.

Tire pressure is no doubt important and I am sure proper pressures helped. However the Nose Gear Pivot Torque way too high and somewhat rough. Removed cotter pin, castellated nut, two cone washers. Cleaned it all off and re-greased washers only. Did not remove wheel fork. There was a lot of grit inbetween the cone washers. Cleaned the threads, nut, and cone washers. Re-installed with Aeroshell #6 (only thing I had). Put it all back together. When tightening the castellated nut position, where nose gear fork rotated with some drag seemed ideal. One additional slot in nut to align cotter pin, fork drag seemed too tight. Again using feel no gauge.

TAXI TEST.... Very easy to taxi straight at slower speeds with about 2000-2200 RPM rudder only. Taxi faster still easy no brakes needed, unless making a turn. It was responsive to rudder only input for small corrections. ​

I did not take fork off completely out on ramp. One reason, did not have grease. AeroShell Grease 22 is recommended as I read. Builder did not know what grease he used. Said he did what the instructions stated was needed. Mixing grease is a no no.

Second reason, I was there to troubleshoot the taxi issue. It will need to be fully taken apart, cleaned and re-greased at condition inspection in a month or two. The results of this service (you can do on ramp in 20 min or less, dramatically improved taxi quality. The service I did resulted in a smooth nose gear pivot with some resistance grabbing the wheel at the aft edge. The intent was isolate the taxi issue. I understand the ideal value is about 18-20lbs side force at the axial. Again no scale with me, so I estimate it was less than 18-20 lbs. However going one more notch on nut seemed to be too much. The point was to improve and do taxi test. It worked.

This will need future attention, but TAXI control is a pleasure now. Not sure what part tire pressure had and nose gear preload made, and which made the most difference. Doing the two services make a World of difference, more than I could have imagined. I love it when things work like that.

Take Away:
Builder may have had too much pre-load from get go, not sure, However plane sits on ramp, no gear pants. When I removed the nut and cone washers water came out. :oops: There was a lot of grit and dirt between cone washers, which may have increased pivot forces. I do not think he serviced the nose gear at last condition inspection. If you park outside, get WHEEL COVER for nose gear to keep dirt and water out of the pivot. The main gear wheels are somewhat protected by the wing, but would benefit from covers as well.

Do not skip removing the nose gear assembly and greasing it with the proper grease often, at least annually. DO NOT mix greases and get the PROPER GREASE not whatever you have. Keep it well greased including the cone washers. DURING PREFLIGHT (every other, 3rd, 4th) find a tail tie down on ramp or get helper to push down on tail, so you can check nose gear pivot for smoothness and pivot force.

I am not sure about service bulletins, e.g., SB 16-05-23, redesigned, thicker nose fork (WD-1230-1) to handle the stresses and prevent cracking. This is a late model kit circa 2020-2023 I think. Likely has late model gear. I am no expert on RV-12iS, never built or owned one, but learning. Thanks everyone for the help! (y)
 
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Paul A said:
If I taxi at 2000 RPM with very little wind, I can stay on centerline with full right rudder and no brakes.
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Now that the RV-12iS's nose gear pivot and tire pressure are all sorted out, I agree 2000 is a good RPM. Long wide taxiway, can pick up a little speed with higher RPM.
 
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