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My first video, or "Nose Wheel, the Movie"

kentb

kentb

Well Known Member
OK, I have everything rigged up for movie making and tested out my camera mount (Oregon Scientific camera). I want to know what is going on with my nose wheel during takeoff and landing (who would care about it in flight). My fairing are now off for painting prep (my wrist is sore from sanding). :eek:

The first video is of taxi, takeoff and landing at Lenhardt airpark (7S9).

http://www.youtube.com/watch?v=YYCerJM_Qww

The next two are takeoff and landing on pavement one from 7S9 to UAO.

http://www.youtube.com/watch?v=VdOL44YGMX0

and then the return trip from UAO to 7S9.

http://www.youtube.com/watch?v=gY_XTSLBggM

I need to figure out how to turn off the sound because it doesn't help that much. I have edit the last two to reduce the length. The first one I chopped off the front and ends some, but should have edited down the middle to make it shorter. So while you are playing that one just skip over the downwind part of the pattern. I needed to do a 360 for spacing.

All takeoff and landings were done with the stick full aft. Taxi was done at a fast walk. I looks to me as though the most gear movement occurs while doing the taxi. I am not to concerned about my nose wheel on grass strips, but will add some extra support in the nose wheel fairing to disallow the nut to dig in.

Let me know if I didn't explain something in the video and any suggestions on how to improve the quality. It looks like youtube downsamples the videos. I noticed it was hard to see (too dark) sometimes. Next time I think that the camera will be pointing forward.

Kent
 
Good question Steve

I don't have the answer here at work.
I'll get back to you tomorrow.
For now pilot 230 lbs. Fuel about 120 lbs.

Kent
 
Tight nose wheel axles...

kentb said:
....
All takeoff and landings were done with the stick full aft. Taxi was done at a fast walk. I looks to me as though the most gear movement occurs while doing the taxi. I am not to concerned about my nose wheel on grass strips, but will add some extra support in the nose wheel fairing to disallow the nut to dig in.
......
Kent
Click to expand...
A friend visiting some time back with a RV-6A had a bad fore-aft vibration on his nose gear. It was very visible from outside during a slow taxi on smooth asphalt... but he could not feel it inside (note fore-aft, not a side-to-side shimmy).

We looked at his nose wheel, and his axle was too tight. I adjusted it to the "Grumman Standard" of drag of about one revolution when pushed by hand. This fixed the problem.

Apparently the breakout force for the tight bearings was setting up an oscillation... even though it was very visible, I was surprised he couldn't feel it.

Another item to check for on the nose gear....

Kent ... can you check how many revolutions your nose wheel has for a good push by hand when it's off the ground?

gil in Tucson
 
Gil, I'll check it tonight.

I forgot to mention that during the conditional inspection I made sure that all tires are at 35 lb and the front wheel breakout force is at 22 lbs.

Kent
 
kentb said:
I forgot to mention that during the conditional inspection I made sure that all tires are at 35 lb and the front wheel breakout force is at 22 lbs.

Kent
Click to expand...
As long as you brought it up again (nice video); may as well include all of the data:
- Old/New Fork : looks like old
- Gear leg vintage: ?
- Nose gear breakout: 22 lbs
- Tire Pressure: 35 psi
- Axel type (old/new): ?
- Bearing preload: 1 revolution spin?
- nose wheel static weight:
- What else??
 
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Here is more data.

GrayHawk said:
As long as you brought it up again (nice video); may as well include all of the data:
- Old/New Fork : looks like old
- Gear leg vintage: ?
- Nose gear breakout: 22 lbs
- Tire Pressure: 35 psi
- Axel type (old/new): ?
- Bearing preload: 1 revolution spin?
- nose wheel static weight:
- What else??
Click to expand...

- Old/New Fork : it is old
- Gear leg vintage: Vans late 2004
- Nose gear breakout: 22 lbs
- Tire Pressure: 35 psi
- Axel type (old/new): Vans late 2004
- Bearing preload on the mains: Tightend nut until I could do one rev and then backed off to the last hole (1/6 turn - max 60 degrees). I repacked the bearings with #5 grease.
- Bearing preload on front: Torqued as specfied in the plans, but I can't remember what that was. I will look it up tonight.
- nose wheel static weight: I need to figure this out.

Kent
 
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Smoke

Bill,

I don't think that's smoke. Looks to me like a timed reflection of some sort. It also looks as if the wheel has some sort of binding issue. The pulsing sure looks as if it has a pattern.?. IMHO
 
LifeofReiley said:
Bill,

I don't think that's smoke. Looks to me like a timed reflection of some sort. It also looks as if the wheel has some sort of binding issue. The pulsing sure looks as if it has a pattern.?. IMHO
Click to expand...
OK, not smoke. Don't want to jump to conclusions! Thanks Darrell.
 
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Thank you for your time and effort in giving us all this look at a nose wheel in action being properly handled. Looks like it reacted as I expected. Reinforces my feelings about the integrity of the nosegear. Nice flying. That grass runway did not look billiard table like and you did your plane (and me) proud.

Roberta
 
az_gila said:
That's just like the oscillations I saw in my friend's RV-6A (see earlier post)... went away when the axle nuts were loosened...

gil in Tucson
Click to expand...
Thank Gil. It could very well be the same plane as the video link tracks to AZ. Also good information as to the cause.

Do you know which type axel he had/has?
 
Different from video

GrayHawk said:
Thank Gil. It could very well be the same plane as the video link tracks to AZ. Also good information as to the cause.

Do you know which type axel he had/has?
Click to expand...

No different plane from the video... old nose fork, and I presume old axle.... about a 1998 SB kit, made in S. California... before I moved to AZ... :)

gil in Tucson
 
Here is the answers to yesterdays questions.

The front bearing axle is torqued to 85 inch lbs. The manual says to use 7 to 10 ft lb, so this is at the 7 ft lb value. With the front wheel in the air there is no spin of the wheel after giving it a flip. It just stops now. I used my digital fish scale and measured the force to start spin by taping the hook to the outside (tread) of the tire. I measured 2 lb 11 oz of force to start movement.

I am not sure how to compute my videos static weight of the nose wheel.
Here are the numbers: empty weights are:
front 283 @ 34.50
mains 841 @ 91.88
total 1124 @ 77.43

The flight weights are:
1474 @ 79.76

Sense I had the wheel and gear fairings off about 10 lbs should be removed in both cases.

I have been thinking about adding the set screw to pin the front fork to the axle assembly as Roberta and some others have done.

Roberta, if I do this what do you torque the axle bolt to?

Kent
 
THANKS!

Kent,

Thanks for taking the time to make the video and for gathering the extra data. Also as Roberta said, your grass field takeoffs & landings show good technique; and give hope to those of us who hope to also fly into & out of grass and/or soft strips. I feel the nose weight of the plane is important as when you slow down on the roll out & the elevators lose authority; the nose weight will approach the stopped nose weight.

I've been working on some thoughts, a summary, and an article that could be titled "Care & Feedng of the RV Nose Gear" but won't post it here as I feel people are fed up with the topic. Maybe later in another location.
 
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please post

GrayHawk said:
I've been working on some thoughts, a summary, and an article that could be titled "Care & Feedng of the RV Nose Gear" but won't post it here as I feel people are fed up with the topic. Maybe later in another location.
Click to expand...
Hi - Please post it here.... there are those of us who are very interested and not fed up. I feel that with the NTSB report and the videos, we are making excellent progress understanding this issue.

If you don't post it here, can you post a link to the other location?

Thanks!
 
Nose wheel axle torque...

kentb said:
The front bearing axle is torqued to 85 inch lbs. The manual says to use 7 to 10 ft lb, so this is at the 7 ft lb value. With the front wheel in the air there is no spin of the wheel after giving it a flip. It just stops now. I used my digital fish scale and measured the force to start spin by taping the hook to the outside (tread) of the tire. I measured 2 lb 11 oz of force to start movement.

......

Roberta, if I do this what do you torque the axle bolt to?

Kent
Click to expand...

Kent... I just checked the exact wording in the Grumman Maintenance manual, since the Tiger nose gear is essentially the same as the RVs (didn't Van own a Cheetah once?... :) ...)

They say to tighten the axle nuts until a "very slight drag is evident when the wheel is rotated". Your almost 3 lbs of force sounds too high by this description..

Perhaps you can run the next video series with your axle nuts loosened to the above spec?? It made a big difference to my friend's RV-6A...

gil in Tucson
 
az_gila said:
Kent... I just checked the exact wording in the Grumman Maintenance manual, since the Tiger nose gear is essentially the same as the RVs (didn't Van own a Cheetah once?... :) ...)

They say to tighten the axle nuts until a "very slight drag is evident when the wheel is rotated". Your almost 3 lbs of force sounds too high by this description..

Perhaps you can run the next video series with your axle nuts loosened to the above spec?? It made a big difference to my friend's RV-6A...

gil in Tucson
Click to expand...
Aahhh! That would be nice. A way to set the peload on the nose wheel bearings other than by feel.

Just to be sure about the axel type we are talking about (Vans versus Grumman); which of these is the axel type?

normal_66AP_front_wheel_bearing.jpg


OR

normal_180_8077%2520%28Small%29.jpg
 
Hi Kent,

I don't measure the torque when I set the front axle bearing preload. I just tighten until I have removed any bearing slop and side play. There will always be some drag on the wheel as the rubber seal on the bearings adds fricton. I do recommend the staking of the mushrooms.

Roberta
 
nice videos

Regarding the old video - the "whateveritis" appears to be in front of or at the front of the tire. In much of the video, it appears to be timed with the prop shadow. Not sure if we have strobing playing a factor with the frequency of the prop shadow. I think strobing is a factor later when prop shadow goes backwards and the "whateveritis" frequency increases. I would guess dust kicking up from the passing prop.

The other videos show to me that the wheel is moving predominately forward from static and the strut is moving upward from static. There are a couple of places where the wheel moves slightly aft. Just as you would expect from rolling across small bumps. Try laying a straig edge along the strut and see which way it goes. Also lay a vertical straight edge at the aft end of the wheel. You can see the wheel move forward most often as a factor of deflection the strut upward. In a few cases, the wheel moves somewhat aft, about 1/2 or less of the wheel flange.
 
Nose Gear Video

The gear leg does not hinge at the engine mount. It bends in a curve, with exaggerated motion at the tip, something like a fishing rod. Since the gear leg starts out angled down about 45 degrees, upward motion of the wheel actually tips the nose wheel nut upwards. On the other hand, dropping the undamped wheel into a depression at just the right speed, followed by hitting a bump at just the right distance on the other side (before the wheel has a chance to snap back) could ruin your day. The motion of the wheel is a bit more complicated than described above, but I think this covers the basics. If you drop the airplane in hard on soft ground and with low tire pressure, it may not be the initial impact that trips you. It may instead be what happens as and after the nose gear snaps back down into full rebound.
 
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Nosewheel Video

I watched the first video and went back a few times to the point where the nose wheel lifts off. It stops like right now. The front axle bolt is way too tight.
I have assisted on many annuals on our club aircraft and the A&P says between one and two spins by hand is about right.

I would be concerned about seizing up the bearing by leaving them that tight. That smells of noseover in the future.

Dave Nellis
 
tapered roller bearings

reiquire .002 preload and will last almost forever.you cant feel this by hand but your spin plus one turn sounds like a good preload. im not sure what good staking the mushrooms does but as long as it helps then go for it. in the unlikely event the bearings seized i would like for the mushromms to be free to spin. mine dont have rubber seals they are felt. this is what came with the kit ..its 2 years old. when in doubt tighten the nut just untill all play is gone then just a touch more( the weight of the wrench with one light tap on it.). lasts for 50,000 miles on cars and 1" trailer bearings. new tapered bearings run 20-25 inch lbs of drag torque and used bearings go arouns 0-10 inch lbs of drag torque. so what you adjust to new will be more than following adjustments.
 
Bearing Preload

I think Van actually did his homework with the bearing manufacturer in determining his torque spec for the front axle, and I believe he does point out that things will spin more freely as the seals bed in. "Old and traditional" isn't necessarily the same as correct. These tiny, light weight tire and wheel assemblies have almost no inertia compared to old-fashioned automotive counterparts, yet the bearing sizes are not that different. If you ignore Van's spec in order to get a free spinning wheel, you will almost certainly need to stake the mushrooms to keep them from spinning and quickly wearing. Excessive preload will certainly shorten the life of a bearing. Proper preload should actually reduce cyclic fatigue loading of the bearing components by spreading the load over several rollers. A nice loose bearing is basically running on one roller at a time. For those worried about nose overs, a loose bearing will have some effect on the frequency of the nose gear assembly, but I'm not sure I want to touch that subject.
 
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Not "free spinning"...

chunt0 said:
I think Van actually did his homework with the bearing manufacturer in determining his torque spec for the front axle, and I believe he does point out that things will spin more freely as the seals bed in. "Old and traditional" isn't necessarily the same as correct. These tiny, light weight tire and wheel assemblies have almost no inertia compared to old-fashioned automotive counterparts, yet the bearing sizes are not that different. If you ignore Van's spec in order to get a free spinning wheel, you will almost certainly need to stake the mushrooms to keep them from spinning and quickly wearing. Excessive preload will certainly shorten the life of a bearing. Proper preload should actually reduce cyclic fatigue loading of the bearing components by spreading the load over several rollers. A nice loose bearing is basically running on one roller at a time. For those worried about nose overs, a loose bearing will have some effect on the frequency of the nose gear assembly, but I'm not sure I want to touch that subject.
Click to expand...
Charlie,
The goal I mentioned earlier (from a FAA Approved Maintenance Manual for a similar, but larger, 5 x 5 wheel) is not for a "free spinning wheel", but for a wheel that will spin only 1 or possibly 2 revolutions when pushed by hand.
My friend's RV-6A certainly determined that this axle nut torque has an effect on the fore and aft oscillation at a slow taxi speed. It was the only variable we changed.

gil A
 
Bearing Preload

Gil,

Since reducing the axle nut torque on your friends airplane stopped the fore-aft oscillation, I agree there was something wrong with bearing drag. My gear is not on the airplane yet, but it is fully assembled. What I see on a new assembly using Van's torque range (with well lubed rubber seals) is 3-5 lbs of very smooth consistent drag. With my new seals, even at zero torque, there is no way I could get a full 360 degree spin. A consistent drag should, in theory, actually provide some damping to the gear. Cyclic drag, caused by a damaged bearing or a spot of contamination in the grease, would obviously tend to excite the gear in a fore and aft direction. There is some possibility that loosening the axle nut might have relieved the symptom without fixing the real problem.

Obviously, I believe in a bit more pre-load than many. I won't be trying to get a full spin out of my nose wheel. With that said, my personal comfort zone probably ends near the bottom of Van's spec, and I will be monitoring nose wheel drag and mushroom rotation closely for the first few hours. The way this experimental stuff works is that we are Van's ultimate development team, and the more ideas and information we share the better. The two videos provided so far are priceless! Everybody keep up the good work.
 
Good point

chunt0 said:
Gil,
.....
Cyclic drag, caused by a damaged bearing or a spot of contamination in the grease, would obviously tend to excite the gear in a fore and aft direction. There is some possibility that loosening the axle nut might have relieved the symptom without fixing the real problem.
....
Click to expand...
Charlie.... good point, I'll call him... for the price of two new bearings, it probably would be just as easy to replace them... :)

gil A
 
RE: other nosewheel video

hey thats my video, taken in 2002. this is a highly compressed video file and I think what looks like smoke is just a compression artifact. I need to find the original one day and run it again to a new wmv file with less compression. I bonded an oak stiffener on and flew it trouble free except for the fore aft motion that started around 28mph. March 2008, a brand new gearleg and fork were installed (new design). Ninety percent of the motion is gone. I only notice a little and mostly if I am braking to make a turnoff. Over 550 hours so far and looking forward to thousands more.

Dave Biddle
RV-6A
Phoenix, AZ
 
dbiddle said:
hey thats my video, taken in 2002. this is a highly compressed video file and I think what looks like smoke is just a compression artifact. I need to find the original one day and run it again to a new wmv file with less compression. I bonded an oak stiffener on and flew it trouble free except for the fore aft motion that started around 28mph. March 2008, a brand new gearleg and fork were installed (new design). Ninety percent of the motion is gone. I only notice a little and mostly if I am braking to make a turnoff. Over 550 hours so far and looking forward to thousands more.

Dave Biddle
RV-6A
Phoenix, AZ
Click to expand...
Dave,
Which type bearing with old nose gear and fore & aft motion? Which type bearings with new nose gear and no fore and aft motion?
Any mods (staking of 'pucks', spacers)?
 
Stiffeners

GrayHawk said:
Dave,
Which type bearing with old nose gear and fore & aft motion? Which type bearings with new nose gear and no fore and aft motion?
Any mods (staking of 'pucks', spacers)?
Click to expand...

Dave... did you add an oak stiffener to the new gear leg? gil A
 
Thanks Kent

Kent, I have to compliment you on the size of your boys there. After problems with the nose wheel on a few RV-A's it seems rather brave of you to go off through the weeds just to let us all have a look see at your nose wheel in action. As I was watching your videos I found myself holding my breath a few times. Nice job and thanks for the info.
 
Jim, thanks for the kind words.

Rivethead said:
Kent, I have to compliment you on the size of your boys there. After problems with the nose wheel on a few RV-A's it seems rather brave of you to go off through the weeds just to let us all have a look see at your nose wheel in action. As I was watching your videos I found myself holding my breath a few times. Nice job and thanks for the info.
Click to expand...

Ever sense I was little, I wanted to be either an astronaut or a test pilot. I didn't realize how easy it was to become the latter.;)

At the time I was pretty confident that all the problem were made by the other pilots.

I should try loosing the torque a little and see if that make a difference in the gear leg motion, but have been busy with other things.

Kent
 
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