RV-9A front gear folds

[Jamie]

I hope in that video the landing was for the purposes of the video because it certainly isn't the correct way to land an -A model RV.

His nose is on the ground less than a second after the mains. What's up with that? Keep the nose off when you land...you get aerodynamic braking that saves your brakes and you put less wear and tear on the nosewheel. You don't have a steerable nosewheel so it's going to do nothing for you on the ground.

Sorry, I don't mean to sound like I'm coming down hard on Kent, but I see these 'flat' landings all the time in tri-gear RVs.

You should easily be able to do touch-n-goes in your RV with the nosewheel never touching the ground.

 

[GrayHawk]

As the gear flexes aft, doesn't it get closer to the CG? And if that's true, doesn't the weight on it increase? How much does it need to flex before that weight exceeds the Van's limit?

Also when flexed aft, the ground clearance of the leading edges of yoke, nut, leg would be less.

 

[jrs14855]

landing gear

Steve Wittman invented and patented the flat spring gear in the early 30's and the round gear I think in the late 40's. The round gear was first ussed on the prototype Wittman Tailwind, first flight in Jan. 1953. A copy of the flat gear patent application is on display in the Wittman hangar at Oshkosh. Wittman built a tri gear Tailwind in 1957 with a Cessna 180 tailwheel for the nose wheel. The airplane was flown several hundred hours in this configuration and then converted to tailwheel. The original RV3 and RV4 gears are basically Wittman Tailwind gears with some minor changes. The Wittman spec is SAE 6150 steel and from memory I believe the heat treat spec is 42-44 rockwell C hardness. I will try to verify this later. There are some additional specs for the heat treating but the rockwell hardness is the important issue. The later Vans gears have increased in both length and diameter. The gear in the non heat treated condition will support an assembled Wittman Tailwind, weight in the 800# range. Several W10 Tailwinds are flying with a tri gear very similar to the RV6A. One is based on a grass strip. One has had an excursion off the end of the runway after and engine failure. There have been zero problems with the nose gear on the Tailwind. The typical empty weight of these aircraft is in the 900# range. I do not have info on typical weight on nose, but it is substantially less than RV's. Harmon Lange built round gears for the Tailwind long before the RV's. Harmon produces a quality product and does not take short cuts. As far as I know Harmon sends out all his heat treating to a heat treating specialist. In recent years I have heard that 6150 was no longer available. So it MAY be possible that a different alloy steel is being used. There have definitely been some sporadic heat treat issues with the gears in recent years. Many years ago I had a VERY hard landing in my W8 Tailwind following a elevator control system failure on short final. The impact caused the gear to bend so that the lower cowling touched the ground. The gear sprung back to almost normal with just a slight bow. Wittman called the round gear the "safety gear". He stated that the round gear would absorb a hard landing to the point that the bottom of the aircraft touched the ground, while absorbing a tremendous amount of energy. In the early days the gears were only available in the straight configuration and not heat treated. I have formed the lower bend in several sets and even with the gear heated to cherry red, considerable force is required to form the bend. I believe that the nose gear in the San Diego incident was either improperly heat treated or not heat treated at all. The failed gear should also be tested to verify the proper grade steel. For those that wish to test the hardness of their undamaged gear, it should be possible to test the end of the axle and/or the upper face of the gear without compromising the integrity of the gear.

 

[GrayHawk]

Related Video

www.eaa538.org/azwing/pictures/nosegear.wmv

 

[kentb]

Stick full back.

I hope in that video the landing was for the purposes of the video because it certainly isn't the correct way to land an -A model RV.

His nose is on the ground less than a second after the mains. What's up with that? Keep the nose off when you land...you get aerodynamic braking that saves your brakes and you put less wear and tear on the nosewheel. You don't have a steerable nose-wheel so it's going to do nothing for you on the ground.

Sorry, I don't mean to sound like I'm coming down hard on Kent, but I see these 'flat' landings all the time in tri-gear RVs.

You should easily be able to do touch-n-goes in your RV with the nosewheel never touching the ground.

Jamie, I have no problem with your comments.
I did these videos more than a year ago after there was another nose wheel incident and people were asking questions. I also wanted answers and so thought that this was a good excuses to buy a small video camera.

I landed the 9A as slow as possible and with the stick back. This provides the littlest amount of energy to be put on the nose wheel. At this speed the 4 to 6 seconds of "hang time" is all that can be expected.

At the time I had about 40 hours in my RV9A and 500+ in Cessna's.

By keeping the speed up you will be able to hold the wheel up longer, but you will still need to let it down at the same point as I did. I also don't wait until the last minute (second) before I let it down so that I don't drop it.

I maybe that the quality of the video gives the wrong impression, but these were not flat landing and I was trying to demonstrate the gear under best landing practices.

Kent

 

[jtrusso]

I agree, crucial piece of information

We are still missing a very valuable data point here: What was the height of the 'bump' at the intersecting runways?

I agree that this is a key piece of information. Here is my theory, and I don't believe whether or not the gear leg is properly tempered makes a difference in the outcome if my theory is correct.

If the height of the ledge is greater than the clearance between the wheel bracket and the ground, then the force imparted to the gear leg during that impact should have been large enough to bend the gear leg back. In this design there is no other mechanism to absorb that force other than deformation of the gear leg.

If the bracket where to catch at a high speed then a very large force would have been generated. The energy goes with the square of the velocity, so even at 20mph that is 70 KJ (70,000 Joules or 52,000 ft*lbs) of energy still left to dissipate.

I'm trying to figure out how to calculate the force that would be imparted to the grear leg, but I'm making so many assumptions as to make the results meaningless. Any advice from the engineers on the board on how to calculate this force?

 

[MrNomad]

It's time to solve the problem and quit waiting for someone else to do it for us

Testing steel for hardness is routine stuff. There are two primary tests: the Rockwell test is used for a quick and dirty figure of merit, the Brinell test is better but a bit more involved. Both are affordable as far as I know. The test would want to be done to several sections of the gear leg to check for non-uniform heat treatment. To the degree possible, unbent sections should be selected to avoid the strain hardening that occurred. Important: tests should be performed on the center of the leg as well as the surface to determine what degree they are surface hardened vs. through hardened.

There may be testing services closer to AZ than So Cal, but I didn't find it.
http://www.thermal-vac.com/services/index.html

There is perhaps a better way to skin this cat, however. I seem to remember direct testing of shaft strength by suspending each end of the leg on vee blocks, and then applying calibrated force via hydraulic ram to the center of the shaft. Both spring rate and ultimate yield could be determined directly. Those are the numbers you really want. Of course, the leg would have to be straightened first.

I would be surprised if certified aircraft vendors don't do something like this.

Best,
T.J.

Ted, You've actually segued into a subject more likely to lead to some fruitful end. Let's close some doors and see where the future leads us.

For example, my good buddy who is one of the most successful trial lawyers in the USA says that a legal challenge to Vans would be expensive and probably not productive. Let's assume that door is closed.

Based on the reply I got when I spoke to Vans which went something like: "We've never bent a gear in 4000 hours", it's apparent the vendor has no plans to address this further. That saddens me but, apparently, that door appears closed.

Improved piloting skills are always a positive so that door needs to remain open and further explored. As the expression goes: "A good pilot is always learning". Is there one person amongst us all who can video landings and document the way to avoid this? I'll bet there is some adventuresome soul out there who's willing to provide footage. Yes, I had transition training and got my BFR during that training, but would I watch a video on this subject?

You bet.

Would others who are building A's watch this video?

You'd have to be nuts not to.

An improved front gear is also an idea. Given the incredible talent that has entered into this discussion time and time again, it is apparent that this door is wide open too.

BOTTOM LINE: When all else fails, creative people solve their own problem. Surely we have the ability to produce video that demonstrates the problem/solution and suggests the best approach speeds to avoid oscillation.

Surely, we have the ability to consolidate nose gear improvement ideas onto one website to teach others how to beef up the front gear.

Surely, we also have the ability to identify a better gear, get it built, and find someone in our midst who will test it. I've only been flying for 4 years, but some of the threads I read suggest that our talent pool is extraordinary.

What I'm proposing that instead of bashing Vans, hiring lawyers, or converting A's to tail draggers, we create a national RV committee which will address this issue. Each "nose dragger" should seed the committee with $100 so there are funds to work with, and solve the **** problem.

Surely there is a CPA amongst us where we can send the CONTRIBUTIONS and form a committee that decides how to spend it.

Trust me, I don't wanna go thru this again and I don't want anyone else to go thru it either. I should be out there making holes in the blue Tucson sky, instead I'm removing what was a perfectly good Sensenich prop and warming up my credit card.

My gear will be available for testing soon. If we can organize and identify areas of responsibility, let's just solve the problem and quit waiting for someone else to do it for us.

Barry
Tucson
520-797-0265

 

[ArVeeNiner]

Airport's liability?

So, if you're landing an FAA certified airplane, including homebuilts, on an official runway and some defect in that runway contributes to damage to your airplane, wouldn't the airport be at least partially liable?

Kelly Johnson

 

[Mark Burns]

Lets do it!

<clip>
Surely, we also have the ability to identify a better gear, get it built, and find someone in our midst who will test it. I've only been flying for 4 years, but some of the threads I read suggest that our talent pool is extraordinary.

What I'm proposing that instead of bashing Vans, hiring lawyers, or converting A's to tail draggers, we create a national RV committee which will address this issue. Each "nose dragger" should seed the committee with $100 so there are funds to work with, and solve the **** problem.

Surely there is a CPA amongst us where we can send the CONTRIBUTIONS and form a committee that decides how to spend it.

Trust me, I don't wanna go thru this again and I don't want anyone else to go thru it either. I should be out there making holes in the blue Tucson sky, instead I'm removing what was a perfectly good Sensenich prop and warming up my credit card.

My gear will be available for testing soon. If we can organize and identify areas of responsibility, let's just solve the problem and quit waiting for someone else to do it for us.

Barry
Tucson
520-797-0265

Barry,
I agree with you that this is our best bet. My $100 is waiting for an address!

Thanks!
Mark

 

[GrayHawk]

xxxx snip xxxx

BOTTOM LINE: When all else fails, creative people solve their own problem. Surely we have the ability to produce video that demonstrates the problem/solution and suggests the best approach speeds to avoid oscillation.

Surely, we have the ability to consolidate nose gear improvement ideas onto one website to teach others how to beef up the front gear.

xxxx snip xxxx

Barry
Tucson
520-797-0265

Was thinking similar thoughts about an hour ago as I was looking through my nosegear file of videos, photos of the jockstrap, etc. Maybe add as many specific incident reports as can be collected, make the data visible in different ways, hints, tips, etc. all concentrated in one place.

 

[Mike S]

Something to think about

Guys, I have made this suggestion a couple of times in the past, never heard anybody banter it around.

Vans changed the entire nose gear system on the 10. It is a pretty much rigid leg, which pivots at the lower firewall, spring action comes from a stack of rubber donuts that are compressed by the leg motion.

The prior thread about Tailwinds and weight got me thinking yet again about why Vans made the change.

Lets see, the 10 is the heaviest of the RV's.

Most nose wheeled single digit RV's way less than a Tailwind.

Steve Whitman designed the gear for use on RV's--------not.

I am not attempting to criticize Vans here, I am just "thinking aloud".

I am not an engineer, but I used to be one------fire engineer that is, so I am not qualified to make determinations as to the suitability of the gear, but I do see enough of a logic thread in what is going on here to follow it down this path.

When a mechanical design gets close to reaching the limits of its capabilities, failures start to show up sporadicly-----and if this design is pushing the envelop, it is reasonable to see sporadic failures just due to the fact they are all individually built, and not a production line assembly.

So, after all my rambling, what I am pondering is this; would a -10 style nose gear be a reasonable thing to explore as a retrofit for the "A" designs???

Has any one ever figured out the percentage of "A" models that have had a problem?????

There are thousands flying, which bodes well for a "Proof of the pudding" argument that the design is sound, but ..............................

Whew, my poor fingers are running out of breath.

Comments??????????

 

[szicree]

For example, my good buddy who is one of the most successful trial lawyers in the USA says that a legal challenge to Vans would be expensive and probably not productive. Let's assume that door is closed.

Based on the reply I got when I spoke to Vans which went something like: "We've never bent a gear in 4000 hours", it's apparent the vendor has no plans to address this further. That saddens me but, apparently, that door appears closed.

It hadn't even occurred to me that a lawsuit against Van's was being considered. Regarding their reply, I think you have to appreciate just how many calls and emails they field and what percentage of them turn out to be some builder basically ignoring the plans. Have they seen the photos and heard of how you straightened it with a wrench and cheater? I am absolutely certain that Van's would be VERY interested if you could show that your gear was of a substandard material (which I personally feel it was). Don't get me wrong, I really feel your pain, but I would hate to see the lawyers get involved.

Also, I noted in one of your previous posts that you do not intend a tear down unless the crank flange is out of spec. Isn't this in direct contradiction to the engine manufacturer's recommendation on any prop strike? It is my understanding that prop strikes have produced cracked shafts that checked ok at the front flange. To my mind, a crank of uncertain quality is a whole lot bigger deal than a noodly nose gear.

 

[rv6ejguy]

Vans has always stepped up to the plate when safety is an issue. I think they would be interested if substandard legs are making it into kits and will want to make it right for those affected. I'd be PO'd too if this happened to me but please, let's not talk of lawyers getting involved.

Get the leg tested independently and see if heat treatment was an issue first. Anything else is jumping the gun. This is only a theory at this point.

As parts are scaled up like RV10 nose legs, tubular sections make a lot more sense from a weight and cost standpoint. I see the RV10 design as the best engineering/ cost compromise rather than a fix for something wrong with the solid section RVXA design. It is very well proven when given proper heat treatment.

 

[adburhoe]

I regularly send materials out to be heat treated. I can probably get my vendor to check the hardness of this leg. My guess is that if he doesn?t do it for free, it?ll be around 20 bucks. The hitch is that you?ll have to send it to me in Northern California. Give me a ring if you'd like to coordinate.



Aaron Burhoe
Burhoe Machine Works
209-533-1231
www.burhoemolds.com

 

[rv9aviator]

I build tooling for a living a do most of my own heat treating. I would be glad to check the hardness of the leg at no charge, but there are other factors in the heat treatment that only a metalurgy testing lab can do. The hardness is only one factor, and there are several other qualities of the treated piece of material that would tell if it is correct for the application. Testing is not that expensive. I'm sure there is one in Arizona but if not I can help find a source.

 

[osxuser]

I think that this thread should be moved out of the classified.

To Safety or General Giscussion.

Kent

2nd that.

Also considering that we are once again on this topic, is it too tactless to say I told you so?

I've probably offended more people in the RV community when it comes to this discussion than any other including alternative engines, but there is just no excuse for the way the nosegear is put together on these things. I came up with a preliminary drawing to try to figure out how to remedy the design problem, but I'm not an engineer, so I'm faced with the shotgun type approach. Beef the heck out of it, and hope it works. The plan includes a RV-10 nosegear leg, the use of the 5.00x5 tire, and modifying the current engine mount.

I thought about making it a kit, but the problem of a million different engine configurations makes that really hard.

 

[Ted Johns]

Barry,

"My gear will be available for testing soon. If we can organize and identify areas of responsibility, let's just solve the problem and quit waiting for someone else to do it for us."

Excellent attitude, Sir. Kudos to you!

rv6ejguy,

"Get the leg tested independently and see if heat treatment was an issue first. Anything else is jumping the gun. This is only a theory at this point."

Exactly right. However, in addition to knowing if the gear leg met spec, it would be nice to know what margin the design has. Isn't this done on certificated aircraft with a drop test? Has Van done this sort of testing? Is it a destructive test?

When I get my 7A flying, I won't be flying without a reinforced nose pant. That blunt piece of metal scares the **** out of me.

Best,
T.J.

 

[6 Gun]

sending off crank

i would not send the crank to a company with R,s in there name as they will


grind it to under size with only 64 hr on it they told me they grind them all if they need it or not

 

[az_gila]

Revised numbers....

Barry, I hate that this happened and can't even begin to imagine how you and your wife must feel. I lost a cylinder on a 172 and made a "precautionary" landing at Birmingham many years ago, and I can still remember the emotions I felt after getting out of that airplane. Sounds like your mental state is starting to mend. Glad to hear you're not going to sell after all.

Not sure if this is to Barry or to Gil, but based on the previous post by Gil, I'm interested in what your "Weight on Nose Wheel vs. Gross Weight and CG location" were at the time of the incident. In other words, can you reconstruct these data and place them on Van's chart for the 9A? I understand you might have to estimate, but it would be helpful to know where your data point falls on the chart provided by Van. This goes a little farther than what Gil posted previously.

Hope you get it back in the air soon,

Don

Don... I got refined numbers from Barry. He had stopped for fuel before reaching San Diego, which knocked my estimate off.

His static nose gear weight was close to 300 # and a CG at 20% chord. Still easily within Vans RV-9A numbers.

gil A

 

[Pmerems]

I believe I can help Barry

Barry,

Gil called me tonight and asked if I had heard about " Barry's RV-9". I have been very busy at work and I haven't read many new posts on the forum. My heart sank thinking the worst. Then he told me that the gear folded and that you and your wife were OK and the plane was back in Tucson.

I too am concerned about whether the gear leg was heat treated properly and I believe I can help get it hardness tested for free.

Here are some options.

1. Pima Community College (Aviation programs) has a heat treat oven. If they have a heat treat oven they most likely have a hardness tester.

2. University of Arizona college of Engineering Materials Science Department-No question they have the equipment and I can work my contacts if you wish to have them test it.

3. I can most likely have it tested at work by the best materials engineers money can buy. But I would have to check with the Materials and Process department manager first (shouldn't be a problem).

In addition, I don't mind packing a lunch driving across town and helping on a Saturday or Sunday to get you flying again. Anytime (except the week of Oshkosh). I have been known to shoot a good rivet or to.

Let me know what I can do.

 

[Bob Brown]

Besides heat treating, could there also be an issue with the composition of the steel? Variation in the stock that the gear legs are cut from? It's too bad this stuff isn't tracked by lot or batch...or maybe it is. There's lots of variables in play that's for sure...

 

[N916K]

I've been looking into this for quite a while and there is one area that many people seem to be missing. I believe the nose wheel itself is a major player in this problem. The wheel bearings are not being tensioned correctly. There is no spacer between the bearings so you have to use bolt torque, this is not how those bearings are to be used. Along with the poor way the bearings are tensioned they use a seal that is very tight and tell you it will break in. So, when the wheel has a lot of friction it causes the nose gear to tuck in when it touches the ground. The nose gear begins to move fore/aft and the draggy nose wheel makes the problem worse and worse. I installed a spacer on mine so I could torque the axle down properly. I also cut the original spacers down so the seal wasn't so tight. I ended up with a nose wheel that would spin freely.

 

[rv6ejguy]

I've been looking into this for quite a while and there is one area that many people seem to be missing. I believe the nose wheel itself is a major player in this problem. The wheel bearings are not being tensioned correctly. There is no spacer between the bearings so you have to use bolt torque, this is not how those bearings are to be used. Along with the poor way the bearings are tensioned they use a seal that is very tight and tell you it will break in. So, when the wheel has a lot of friction it causes the nose gear to tuck in when it touches the ground. The nose gear begins to move fore/aft and the draggy nose wheel makes the problem worse and worse. I installed a spacer on mine so I could torque the axle down properly. I also cut the original spacers down so the seal wasn't so tight. I ended up with a nose wheel that would spin freely.

This is another topic but I agree, the RV front bearing setups are poor- sorry Vans guys but rubber against aluminum side spacers and no center spacer just isn't right. It kinda works but I can't say I like the design.

 

[tomcostanza]

Barry,
I agree with you that this is our best bet. My $100 is waiting for an address!

Count me in.

please, let's not talk of lawyers getting involved.

Ditto.

An improved front gear is also an idea. Given the incredible talent that has entered into this discussion time and time again, it is apparent that this door is wide open too.

This seems to be the best idea, but...who among us is going to be the guinea pig and risk a $100k+ bird for testing. Then again, if not us, who? It's clear that unless and until a Van's owned plane has a collapse, Van isn't going to do anything. And from his perspective, that may be OK. But wringing our collective hands won't solve the problem. I wish I could do more, but I don't have the necessary skills. Seems like taking Aaron or Jim or Paul up on their offers to get the gear tested is a logical first step. Then reevaluate based on what is found.

Let me know if I can do any needed grunt work.

Regards,

 

[Rick6a]

....... I believe the nose wheel itself is a major player in this problem. The wheel bearings are not being tensioned correctly......

Excellent tip Cam, and one that I am going to follow up on! After complying with the recent nose fork SB I am not pleased with what has occasionally followed. I routinely land holding the nose gear off the pavement until full back pressure and elevator authority finally yield to gravity and the nose wheel settles onto the pavement. Occasionally there is a certain relatively high transitional speed in which a strong shaking of the nosewheel assembly and/or leg develops. Left unchecked, it shakes the instrument panel something awful. If and when that happens, I've learned to firmly apply the brakes for a moment to quickly slow down past that excitation speed and the shaking quickly stops. The shaking only occurs at a relatively high taxi speed. I was going to experiment with altering the tire pressure, break out force, axle torque, or even install a wooden gear leg stiffener if I have to. A spacer between the bearings as you outlined makes a lot of sense and I'll try that fix first because as it is now, that nosewheel does not spin freely as some friction exists due to bolt/axle torque. Thanks for the helpful heads-up.

For the purposes of this discussion in which any number of factors may come into play including wheel bearing friction, I think it important that whether one elects to land a nose wheel RV in the "correct" way or not as some would insist, the pilot should not have to worry about a nose gear assembly that should be reasonably forgiving of all but the most egregious of pilot error.

 

[AlexPeterson]

I've been looking into this for quite a while and there is one area that many people seem to be missing. I believe the nose wheel itself is a major player in this problem. The wheel bearings are not being tensioned correctly. There is no spacer between the bearings so you have to use bolt torque, this is not how those bearings are to be used. Along with the poor way the bearings are tensioned they use a seal that is very tight and tell you it will break in. So, when the wheel has a lot of friction it causes the nose gear to tuck in when it touches the ground. The nose gear begins to move fore/aft and the draggy nose wheel makes the problem worse and worse. I installed a spacer on mine so I could torque the axle down properly. I also cut the original spacers down so the seal wasn't so tight. I ended up with a nose wheel that would spin freely.

I agree totally. Please see these for quite a bit more information:

http://www.vansairforce.com/community/showthread.php?t=23475
http://www.vansairforce.com/community/showthread.php?t=19069
http://www.vansairforce.com/community/showthread.php?t=18885

I believe we need to go back to the original 6A design, which includes a fork to fork spacer. Somewhere in the above threads I posted pictures of this.

 

[cytoxin]

The wheel bearings are not being tensioned correctly. There is no spacer between the bearings so you have to use bolt torque, this is not how those bearings are to be used. Along with the poor way the bearings are tensioned they use a seal that is very tight and tell you it will break in. I ended up with a nose wheel that would spin freely.

Tapper roller bearings have been used in this manner for longer than most of us have been around. All rear wheel drive cars are set up exactly this way and see service of 100,000 miles or more. most all front wheel drive cars have the spacers you mention. but these are select fit shims and are to be re-select fitted with each bearing replacement, if the bearing is serviceable, most are not. I have reused the original spacer many times with no ill effects. But that is attributed to using good bearings made to exacting tolerances such as Timken) perhaps a crush collar could be used between the bearings to achieve the proper preload. or a solid spacer to fill the gap then reduce overall length by .002 for preload.

All that said there are millions, if not billions of bearings set up this way going up and down the highway right now. Spacer or not you still need the same amount of preload on the bearing. Tighten the bearing down to 25 ft. lbs then loosen the nut re tighten to 15-20 inch pounds. New bearings run 20-24 in lbs of drag torque, used go about 1-10 NOT INCLUDING SEAL DRAG
I would shoot for around 10 in lbs (new) due to the small size of these bearings. Tapper roller bearings do run just fine a little loose but then that may induce or allow the propagation of shimmy. So we have concerns on both ends of this issue.
YMMV

 

[AlexPeterson]

Tapper roller bearings have been used in this manner for longer than most of us have been around. All rear wheel drive cars are set up exactly this way and see service of 100,000 miles or more. most all front wheel drive cars have the spacers you mention. but these are select fit shims and are to be re-select fitted with each bearing replacement, if the bearing is serviceable, most are not. I have reused the original spacer many times with no ill effects. But that is attributed to using good bearings made to exacting tolerances such as Timken) perhaps a crush collar could be used between the bearings to achieve the proper preload. or a solid spacer to fill the gap then reduce overall length by .002 for preload.

All that said there are millions, if not billions of bearings set up this way going up and down the highway right now. Spacer or not you still need the same amount of preload on the bearing. Tighten the bearing down to 25 ft. lbs then loosen the nut re tighten to 15-20 inch pounds. New bearings run 20-24 in lbs of drag torque, used go about 1-10 NOT INCLUDING SEAL DRAG
I would shoot for around 10 in lbs (new) due to the small size of these bearings. Tapper roller bearings do run just fine a little loose but then that may induce or allow the propagation of shimmy. So we have concerns on both ends of this issue.
YMMV

How many cars use a 3/8" bolt? The issue is flexibility - the spindles on cars are much larger (yes, the loads are also larger). The stiffness goes up by 16 fold each time you double the diameter. What is of great concern is not the bearing drag when the nose wheel is hanging in free space. How much drag does it has when the wheel hits a transient load, and that little 3/8" "axle" flexes. What is the equivalent pre-load then?

Something needs to explain why the incidence of this problem is almost non-existent in the much larger 6A population than in the newer trike designs. One difference is the higher main gear, but another is the change in axle/bearing design which occurred somewhere near the end of the 6A run.

Read all of the three aforementioned threads - good stuff there.

 

[Steve Brown]

Test along the whole length

.......To the degree possible, unbent sections should be selected to avoid the strain hardening that occurred. ......

Agree with everything Ted says except this. All sections should be tested. The bent sections will have some strain hardening, but they may be bent because they are the softest if the heat treat was not uniform (verses not done at all)

This thread makes me want to get mine hardness tested. I agree there is no way that thing should have bent. It is supposed to be a spring.

 

[MrNomad]

Offer from the latest victim follows.

My thanks to the many people who have offered me their condolences, money for a special purpose fund, and ideas how to resolve this nose gear dilemma for my 9A and other RVs. One would hope that Vans would take the lead on this issue (given that they are far better equipped than this old man), but until that occurs we'll have to organize ourselves.

Here's my offer. "I'm gonna make you an offer you cannot refuse". I believe it's time to create a website page that offers tips on remedy and prevention. I volunteer to create such a separate page on my website for those front gear ideas and suggestions people send in.

If you have ideas & suggestions concerning actual procedures you've implemented to remedy/prevent the folding of front gear on an RV, please send them in the form of a WORD document or plain text.

Send the pictures as attachments with as much detail as possible so people can read and view what you've done. I have serious carpal tunnel so make it easy for me to post your ideas.

Please add your name, phone number, and email address so interested people can call you directly, not me. I am not an expert in engines, html, piloting, or the building of airplanes. However, I have a fervent interest in preventing this from happening again to me and everyone else.

Ideally, we should be able to avoiding having to convert A's into tail draggers.

If you have video of actual landings which captured the dreaded oscillation, that would be great. The goal is to prevent mishap, not just remedy. I'm not sure how to post avi files to a website, but I'll figure it out.

I am in the process of checking my 64 hour Superior O-360 with a dial indicator. I will then disassemble the engine, have the appropriate checks performed (not sure what they all are), and will document that too. I assume there is an expert out there who has already walked this path so please feel free to send your pics and comments. According to every document I've read, the only safe solution is disassembly, checkout, replacement as required, reassembly. Bite the bullet, and just do it.

Please limit the scope of the conversation to RV airplanes. As I have already admitted, I am not an expert at HTML and cannot do fancy gizmos and whatnot. If there is an expert html person out there, please volunteer and I will focus on organizing other efforts with the same goals, remedy and prevention.

If you want to call, please do so after 8am MST. The wife has seen the estimates for repair and has resumed talking to me again, anyway.

Barry @ arizonaairparks.com
520-797-0265

PS: Tom Constanza just suggested Doug Reeves as the host for this effort. I will happily make a contribution to make it profitable for Doug. Without this website, few of us would ever complete these planes in a timely basis.

 

[rtry9a]

RV10 gear

Can someone post a picture and/or a drawing of the RV-10 strut arrangement with the rubber donuts mentioned earlier?

 

[Sam Buchanan]

PS: Tom Constanza just suggested Doug Reeves as the host for this effort. I will happily make a contribution to make it profitable for Doug. Without this website, few of us would ever complete these planes in a timely basis.

If Doug is inclined to pursue this effort, he can create a new sub-forum here in just a few moments, no need for anyone to worry about creating web pages.

However......I suspect that if anyone has valid suggestions in regards to gear failures they are already in the archives of this forum.

 

[JHines]

photos

Can someone post a picture and/or a drawing of the RV-10 strut arrangement with the rubber donuts mentioned earlier?

The top row of photos on this builder's page shows the mechanism pretty clearly.

http://www.myrv10.com/N104CD/engine/20050827/index.html

 

[whirlpool]

$100.00

I'll throw 100.00 in to hear the test results/new ideas. I would like to know if we could test other failed gear legs. Let's find several and test a few of them!! Heck, how much is a new one from vans, lets test one of them. I for one am sick of worrying about this problem and would love to get a solid "fix".
Ed Edwards 479 629 1986

 

[rv6ejguy]

The posts about the RV bearing setup being the same as automotive are incorrect. No car has the rubber bearing seals in contact with the tightening device. Always metal to metal on tapered roller bearings.

The RV10 setup is also poor even with the spacer. I modified mine so it works correctly.

 

[osxuser]

The posts about the RV bearing setup being the same as automotive are incorrect. No car has the rubber bearing seals in contact with the tightening device. Always metal to metal on tapered roller bearings.

I must add here than many Bonanza's, and others have this setup, it's the "old" way of doing things though, and I don't know why Van's would go that route.

The two things that discouraged me from working further on the -10 STYLE nosegear for the little guys were:

The 5.00x5 nosewheel that everyone will undoubtedly bitch about weighing too much also doesn't give any better ground clearance angle than the new fork on the -A's. This is in spite of the fact that Van's knew there was an issue AND they have a bigger tire to work with... Duh!

I don't have a -A model (nor to I ever intend to), and I hesitate to borrow someone else's airplane to do testing on.

 

[rv7boy]

More Data

Don... I got refined numbers from Barry. He had stopped for fuel before reaching San Diego, which knocked my estimate off.

His static nose gear weight was close to 300 # and a CG at 20% chord. Still easily within Vans RV-9A numbers.

gil A

Gil,
You got two out of three. We can't verify the data on the chart without the GROSS WEIGHT at the time of the incident. Was it greater than 1550 lbs?

Don

 

[az_gila]

Weights and charts

Gil,
You got two out of three. We can't verify the data on the chart without the GROSS WEIGHT at the time of the incident. Was it greater than 1550 lbs?

Don

<chart removed - see above>

About 1630 #

However, the angled lines on the chart are for Vans specific aircraft only, and are not applicable to other aircraft (diifferring empty weights and empty CGs)

You can't place a dot on Vans chart CG chord % lines for other aircraft...

The nose gear weight was done as an extra calculation on the W&B spreadsheet from Barry's specific numbers.

I don't have a -9A worksheet on my web site, but the -7A one is here, and includes the nose gear weight calculations.

http://home.earthlink.net/~gilalex/RV/wb-RV-7A.xls

gil A

 

[kentb]

Me too Cam...

I've been looking into this for quite a while and there is one area that many people seem to be missing. I believe the nose wheel itself is a major player in this problem. The wheel bearings are not being tensioned correctly. There is no spacer between the bearings so you have to use bolt torque, this is not how those bearings are to be used. Along with the poor way the bearings are tensioned they use a seal that is very tight and tell you it will break in. So, when the wheel has a lot of friction it causes the nose gear to tuck in when it touches the ground. The nose gear begins to move fore/aft and the draggy nose wheel makes the problem worse and worse. I installed a spacer on mine so I could torque the axle down properly. I also cut the original spacers down so the seal wasn't so tight. I ended up with a nose wheel that would spin freely.

One of my kids is a Machinist and so I drew up plans for a pair of spacers. Unfortunately I got the dimensions off and they don't fit. I hate to ask him to make more (besides I would have to admit that I screwed up the measurement).

Do you have drawings for you spacers? Or have more that I could buy?

Kent

 

[David-aviator]

I think we should wait to redesign the nose gear assembly until we find out what caused this latest event. The strut needs to be tested and runway intersection needs to be photographed and the mis aligned pavement depth measured in that area.

A problem has not been identified beyond the report by the guy at the NTSB and most of us have complied with the recommendations although not everyone agrees with the fix. Stuff happens in aviation and will continue to do so.

The only fact we know for sure about this event is it happened.

 

[John Clark]

Thanks Captain!

I think we should wait to redesign the nose gear assembly until we find out what caused this latest event. The strut needs to be tested and runway intersection needs to be photographed and the mis aligned pavement depth measured in that area.

A problem has not been identified beyond the report by the guy at the NTSB and most of us have complied with the recommendations although not everyone agrees with the fix. Stuff happens in aviation and will continue to do so.

The only fact we know for sure about this event is it happened.

Ah, a voice of reason. I was just about to stop following this thread, too many speculations and unproven "cures." A careful inspection of the runway surface is critical.

John Clark
RV8 N18U "Sunshine"
KSBA

 

[vlittle]

(

As I recall, Van's information stated:

-Implement the nose gear SB
-keep the tire well inflated
-always install the nose wheel pants
-load the a/c in the recommended envelope
-don't use the nose wheel as a landing gear (!)

In this situation, it may be that more than one factor contributed, including the possibility of faulty heat treatment of the nose gear leg.

Perhaps the NLG can be sent to Van's. The NTSB has a file on this issue, and I'm sure that if there is any evidence of improper manufacturing, everyone wants to find it... or rule it out.

BTW, I still have a residual skid plate in my nose cone (e-glass flox-- very tough stuff).

Vern

 

[Rivethead]

I'm in

I've seen several offers to help offset the cost of analysis of the steel nose wheel strut. I would also like to also offer to donate to a fund to have this done. However, I will only add my bucks if a thorough analysis is done. Not only would I want hardness checked but I'd also want the grain structure of the steel and any alloy content checked. I'm building a 7-A and have been wondering if I just plain made a mistake. It would also be nice to perhaps send some of the other struts that have failed along for comparative analyses if they could be obtained. Request for my cash payment can be sent to my email address and I will happily pay my part.

 

[jtrusso]

Don't jump the gun

Ah, a voice of reason. I was just about to stop following this thread, too many speculations and unproven "cures." A careful inspection of the runway surface is critical.

I agree that all this talk of redesigning the gear is premature until there is a solid understanding of why the gear legs are failing. There is a lot of speculation but none of the theories have been tested. How can you design out the flaw if you don't know what the flaw is? Sure you can go by trial and error, but a thorough analysis of the failures and the commonalities between them will lead you to the solution much quicker with a lot less headaches.

I really think a key factor in this failure is the height of the ledge at the intersection of the runways.

If the height of the ledge is greater than the clearance between the wheel bracket and the ground, then the force imparted to the gear leg during that impact should have been large enough to bend the gear leg back. In this design there is no other mechanism to absorb that force other than deformation of the gear leg.

Regarding testing of the gear leg - testing of sections that have been bent and straightened again will not tell you the condition of the material when it was installed. For hardness testing you will want to test a "virgin" section, which will give you an idea of the heat treat the material received. However there is more than just the heat treating that determines the strength of the material. Things like the chemical composition should be examined as well as the homogeneity of the material. A better test would be to section the gear leg and to look at the grain structure of the material. I would look into having this tested at a true materials laboratory if you really want to know the condition of the material. Also, don't do anything else to it - the more it is bent the less you're going to know about what caused the failure.

Just my 2 cents.

 

[kentb]

John and John

I agree that we would like to get to the bottom of what happened. I would like to see more information on the runway intersection also.

But the failure of the A gear legs has been going on for sometime now.
I believe that some of these failures were the cause of pilot error or unfortunate circumstances.

But there has been enough of a risk in the design that Vans has redesigned the gear. I, like Vern have gone to reinforcing my nose pants and would also like to relieve the friction on the nose wheel bearing. The design of the RV10 nose wheel already does this. Also in talking to a number of people more knowledgeable than I about the simple RV9A design, they found that the rolling resistance of the wheel was not necessary or desirable.

I know that a number of A flyer's have solved this problem by backing off on the torque and using a set screw to keep the parts from spinning.

I am very careful with my plane, but do need to taxi across grass to get to the runway. I have cracked the nose wheel pant twice.

Kent

 

[rv7boy]

I agree that we would like to get to the bottom of what happened. I would like to see more information on the runway intersection also. <SNIP>


Kent

I'm wondering if anyone with a wing mounted camera would be willing to re-create the landing on the runway where Barry landed. Wow, that's asking a lot isn't it? Of course, the first video would not have to be an RV-XA, just an airplane with the camera viewing the nosegear movement at that intersection.

The previous mention of actually measuring the pavement discontinuity is of interest, too.

It does sound like, from Gil's post above, the nose gear weight was close to Van's upper limit, so even though it was probably in the "white area" of allowable nose gear weight, the pavement condition is certainly a contributing factor, if not the cause, of the accident.

I need to go back through the thread to know, but can anyone tell me if Barry did or did not have the nose gear wheelpant in place?

This isn't meant to be funny, but these A-model nose gear prangs are reminiscent of what happens to a pole-vaulter's pole. It's really just a big spring and when the nosegear bends back and under, there must be a tremendous amount of energy stored in the leg. Imagine a side view of the nose gear fork tucked under and you'll see the resulting "springback" tends to rotate the airplane away from the ground further and in the direction of landing on its back. The addition of e-glass flock or whatever to reinforce the bottom of the pant resulting in a skid pad looks like a good mod to me. If the nose gear fork hits something solid, it needs to slide over it instead of digging in. So what we may find out is incorrect heat treatment may have actually prevented further damage to Barry's RV! If the leg hadn't bent, it might have gone through the "bend-a-spring, release-a-spring" cycle and flipped his RV on its back. We already know RV-XA's can end up on their backs, so it is a possibility.

Barry, I really hope you get your bird fixed and back in the air soon.

Don

 

[David-aviator]

.....I'm building a 7-A and have been wondering if I just plain made a mistake. ....

I think not. It has been a good airplane for me and mine is nose heavy as is.

Keep the stick full aft all the time on the ground while taxiing, always try to make nose high full stall landings, suck the stick aft after touch down - so far, so good. Ten degrees of flaps works best for me approaching at 70 knots.

I also keep tire pressure at 45 psi across the board. With new stop leak tubes from Desser, they actually hold pressure for six months.

Trike pilots do not get the medal of honor like TD guys but we are fearless in that we do not ever fear a cross wind.

 

[GrayHawk]

Modified List of Data Needed

Here is the data I'd like to see collected for each one of these incidents. I think the NTSB/FAA study contained some of this data for some of the incidents; but not all. If a large enough sample could be collected then some common threads might become visible:

GENERAL:
Model: 6A,7A,8A,9A
Engine:
Prop:

WEIGHT & BALANCE (at time of incident):
Nose:
Left:
Right:
Location on the Van's W&B charts:

NOSE GEAR:
Leg: (believe there have been 3 versions)
Leg Metalurgy Testing:
Yoke: (believe there have been 2 versions)
Bearings: (believe there have been 2 versions)
Biscuits staked:
Tire pressures:
Bearing Preload:
Pull out:
Pants Installed:
If installed, ground clearance, tire clearance:

GROUND SURFACE:
Operational Phase: landing, taxi, etc
Ground Speed:
Density Altitude:
Wind Conditions:
Material: sod, gravel, dirt, asphault, etc
Hardness:
Smoothness:
Topology at start of or just before the catch or skid: Dead rabbit, pot hole, ledge, etc.

 

[MrNomad]

The latest victim offers more information

Paul Merems agreed to handle the strength/heat testing of the front gear with the local college. He will have the parts from me by Tues and expects a week turnaround.

I'm not sure what the cost will be, but assume it's nominal. The goal I had for a common fund is to be able to hire/compensate the appropriate people to conduct the appropriate tests.

Admittedly, a gear that has been bent like a pretzel will have different properties than a new one.

FYI: I have no clue what those tests are. I leave it to experts like Gil and a few others to figure that out. It would also be nice to have some video of actual oscillation and the $$ fund could be used to buy the pilot's gas.

I will happily post the results. If I know Gil, he'll post the results too and his analysis will be much more thorough than mine.

To those of you who have sent private emails, thanks a lot. I have received more than a hundred so it's obvious this issue concerns many people. I'd say the "senders" were equally split amongst people who are building and have little to no experience, and others. Know that I had 64 hours in 7BD, did hundreds of landings, but will visit Dan Anderson in Payson to become more proficient. If Chet comes along, he can watch me and Dan and take moving pictures. This "ain't" gonna happen again.

AIRCRAFT ENGINE SPECIALISTS (Chandler, AZ) will go thru the engine at $75 per hour (zyglow, magnaflux, and more). I will disassemble the O-360 and given the fact that the case was not painted, all of the analysis should be less than 5 hours.

Assuming they find nothing wrong (remember, I was at idle and have all ten fingers crossed), it's gaskets, rod bolts and more.

Prop should be < $700.

My expert A & P to reassemble... full tank of gas and dinner for him and his wife.

VANS: Mount, gear, and fork: $1,400. (Gee, just what I wanted to spend my first SS check on).

Then there is the improvements. Like so many others, during the first 64 hours of utter bliss in the air we thought of many mods we'd make, given the opportunity.

The opportunity is here.

WHEEL PANTS: I was waiting for one more piece from Fairings Etc, so, NO, the pants were not on.

Back to the shop now for more disassembly.

Barry
Tucson

 

[rv6ejguy]

Not much use testing a new leg from Van's as this could be just fine from a metallurgy and hardness standpoint and proves little other than having a benchmark. We should be testing several failed legs first. If these are dead soft, they are not right and we have a problem. Most spring steel will test around 43-47 Rockwell C If I remember right.

Most legs are probably fine, we need to find out if some bad ones are slipping through QC. Van's most likely has these made by subcontractors.

If you really don't like the design, you can build your own but you are going to be slicing and dicing the engine mount and spending a lot of time to do this. This is not rocket science. The -10 leg is way overkill for smaller RVs and would take extensive mods to fit on one.

Finally, I've said it before, the new fork design will not save all fold up incidents from happening. It is only of use where the terrain variations exceed the height of the original fork design. Anything higher and it will probably fold still. Know your turf runway condition or just say no to grass. I go over big pavement transitions at a good angle as well.

For those with heavy engine/ prop combos, be aware that margins on the nose gear are reduced by your FF choices.