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Nose wheel stiffness

V

volucre

I'm New Here
Glad to report that our RV12 ZU-XII has flown 41.1 hours so far and is going strong! :D

Having just enjoyed my 1st hour of training towards my NPL (SPL in the States) my instructor asked a question that I hope you learned fellows on VAF can help me with. :rolleyes:

According to him the nose wheel is too "stiff". XII does not straighten out after a bit of brake is applied to the one side or the other but instead keeps on turning. Because of that a lot of differential braking is required.

When we lifted the nose in the air and pushed the wheel from side to side it certainly does not swivel around like a shopping trolley (not sure that i should! :eek: ) but requires around 1kg (maybe 2lb) of pressure.

I am hoping that you guys can let me know if ours are too stiff???

Any feedback would be appreciated!

G
 
The other nosegear airplanes recommend 10 Kg

Our -6A had over 10Kg breakout force. We used a scale, attached to the axle area to set it according to Van's.

Later, we used an extension from a ratchet and pushed against it with a bathroom scale. Check the plans for details.....too loose and it might shimmy.

Best,
 
G,

My nose wheel swivel was way too tight after setting it per the plans. Had exact same problem as you are experiencing. I jacked up the nose and removed the cotter and large nut, and slid off the whole nose wheel asembly. Cleaned and greased the fitting. Then reinstalled and set the tension so I could comfortably move the wheel back and forth by hand. Then test taxied and checked for binding or shimmy. I did several iterations of this while I kept tightening one flat of the nut each time. Its a trial and error process but I ended up with a nosewheel that steers easily and shows no inclination to shimmy.

It seems, that in at least my case, the specified torque in the plans was way too high.

John
 
Check the Other Nose Wheel RVs and Nose Wheel Shimmy as a result of not setting the nose wheel break out force correct...do a search and you'll see...I would keep the break out force at 26LBs as per the plans = 11.7 KG
 
PCHunt said:
Is the RV-12 nose gear the same as -6a, -7a etc?l Original post is re: RV-12.:confused:
Click to expand...

Nope. RV-12 has stiffer nose gear and larger nose wheel than -7 or -9. Not sure about the -6 and others. I got this info from phone conversation with tech person at Vans.
 
diamond said:
Nope. RV-12 has stiffer nose gear and larger nose wheel than -7 or -9. Not sure about the -6 and others. I got this info from phone conversation with tech person at Vans.
Click to expand...

Size doesn't really matter here between RV models it is the principle that is the same. To loose a front nose wheel leads to shimmy, read more about it here...

http://www.vansairforce.com/community/showthread.php?t=32610&highlight=shimmy

Bob Axsom said:
I have experienced the shimmy, that is actually an understatement. it shakes so bad I thought I had blown the nose tire the first time it happened. Then I thought I had let the nose down too soon and on my next landing I rolled the mains on with nary a squeek and held the nose off until it couldn't be held off any more - bang-bang-bang-bang-bang all the way until the plane stopped moving. Then it taxied like a pussy cat. I had torqued the nose gear and set the breakout force as described in section 10 to 23 lbs (the book actually says 22 lbs) and I have no holes in the nose fairing for an easy way to check the breakout force so checking it is not high on my things I like to do list. Off came the fairing and sure enough the the breakout force was way down (I don't remember the number if it even registered on my coarse fish scale). I retorqued and tested until I had it up to 24 lbs. and the problem went away completely! Several months later after I had retired and moved to Arkansas it happened again. There was no hesitation this time I removed the fairing retorqued the nut and kept testing until the breakout force was back up to 24 lbs and there has been no recurrence so far. The manual gives a detailed procedure that allows you to get rid of some of the "give" in the system but with wear and "settling" it probably will recur less and less frequently as the system ages. If it happens check and reset it immediatly (or as soon as you get home) and check it annually during the condition inspection is my humble recommendation. It is a heck of an airplane and nosewheel shimmy is NOT something that you "just have to live with." All of the reasons for the emergence of tricycle landing gear as the landing gear configuration of choice for production airplanes are just as valid for the RV series. The tricycle landing gear configuration is harder to build on the RV-6 and I assume the RV-7 is the same; the extra big wheeled prong probably makes it a little slower; if you lose brakes you also lose taxi steering; etc. etc. I went with the tricycle gear strictly because my wife insisted on it and during the build process I cussed the unnecessary complications I had to deal with because of that choice. Now that I am done with it, having spent 50 years in aerospace, I wonder at the wisdom of this little lady who knew the right choice for us and her elevation above my petty belly aching about it. You will not be disapointed if you prefer tricycle gear and build one. Don't let the shimmy shake your resolve.

Bob Axsom
Click to expand...
 
Been reading with interest the posts above about nose wheel castoring tension and shimmy. One thing I am wondering is how transferrable the experiences of other RV models is to the '12, regarding shimmy problems.

What I do know is that with the tension set to the 26 ft/lbs of breakaway force, my '12 was very difficult to taxi. I had to get up some speed and "stab" the brakes hard to make it alter course. The change in track at that point would be only appproximate and I would have to "stab" again. Making a turn from a stopped position was impossible, so manuevering in tight quarters was nerve wracking at best.

After my experiments with different tension settings, as described in my earlier post, my ability to taxi where I want is just about perfect. Smooth and accurate. During the process of adjusting the tension I did some high speed taxi tests with some very loose settings. Even then, I noted no tendency to shimmy.

So in my case at least, I have the tension set somewhere less than specs (don't have a number, too hard to determine with the pants on) and it seems perfectly OK.

As to the advice to not mess with the original recommended torque - well, I think this is why they call these airplane "Experimental" - one gets to experiment and try to attain optimum performance based on one's personal preferences and abilities. Obvoiusly any changes from the plans should be approached very cautiously and with careful step-by-step testing.

Just My Humble Opinion!:D
 
When it does happen.

As Bob pointed out....it's EXPLOSIVE when it happens and you'll be surprised that the motor mount is still attached to the airplane! Been there, done that and so ours stayed torqued to Van's specs.

Best,
 
Pierre, Just curious, with your nosewheel torqued to specs, how hard was it to steer? That's my main issue - it's just too darn hard to steer the airplane on the ground with that 26 ft/lbs.

John
 
It takes a while.

It doesn't take long to realize that you just have to 'stab' at the brakes and it becomes second nature shortly.

Best,
 
Agree with John

I too originally had mine set exactly to spec. It was difficult to steer, did not want to taxi straight, and my EAA tech counselor who runs an RV Builder's Assistance center and has built and flown multiple RV's concurred that it was much too stiff. I also found tremendous variability in the breakaway force between tries- might be 23 pounds on one try and then 28 on another, particularly if it had been sitting for a bit. So like John and a few others, I just loosened it a bit. It is far from being "loose" and still sits around 20 pounds (as I recall). However, steering is much improved and I have never had a problem with nosewheel shimmy. Not sure that the scales typically used to measure these are all that accurate either. Hence, I think a bit of fine tuning is not unreasonable.

Jeff
 
Control Group

Just as an input from a neutral party, I have mine set per Van's instructions. I do not find it hard to steer. With that said, it is very different to steer than an airplane with a sterrable nose wheel or tail wheel, particularly in a cross wind. I typically try to touch down as clost to the turn off nearest my hangar as I can to reduce taxi time.

I have no difficulty taxiing in tight quarters, but since where I am based there is always a crosswind it is difficult to keep straight without riding a brake. I swerve down the taxi way a little, but I tell people I'm doing S-turns for visibility.
 
This is too stiff!

It's annual inspection time, and I had made a note to myself to slacken the nosewheel steering, as mine was rather difficult. Indeed on grass I could not turn right, the brake locked and the wheel would just skid.

Well, before adjusting it I re-measured the side force required. Yup around 26. 26 kilos that is!!!

I'm really looking forward to trying with just 26 pounds;-)

You live and learn...Keith
 
Nose gear adjustment after insp

Just finished my 2nd annual inspection. I removed the nose gear assy, inspected all the bits and pieces, re-assembled per the book.
Now....as I tighten the nut....heading for my 26lb number, the force for sideways movement of the nosewheel increases slightly (as you'd expect) then the nut bottoms out and the forcegoes way up.....like 40-50 lbs, way more than the 26lb.

Has anybody experienced this, and what is the cause?
Is seems kinda bizzare, but I'lll ask it; do the "bellville" washers lose their "spring" and thus render the intent of the design ineffective?

Total time = 200 hrs, no problems with this up to now.

Thx much
 
parts installation

Yes, the washers are installed as () and the installation is "dry", except for the mating of the bushing against the spindle, which is greased.
 
As Pierre said, if you set the tension too loose on the nosegear, when it does start a shimmy on landing you will get a real attitude adjustment about proper torque. I had this happen and when it shimmied on landing I thought I had a flat tire. It was violent. I retorqued the setting to a little over 26 lbs and have no problems steering or with shimmy. Personally I would rather have it too tight than too loose. (RV6A)
 
Grease and balance

Those with shimmy - did you balance / not balance your nose wheel? For smooth breakaway re the Bellville washers () seems that you should grease the washers and set to factory specs. Setting up mine now - your experience?
 
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