Year long discussion of "Another nosegear failure" -09/19/2010

[az_gila]

The original -6A

...
I think that it would even be better to have the leg designed so that in the event of failure it would fail completely, i.e. fold under the airplane and thus prevent pivoting on it. ......

...had a failure point at the entry point into the motor mount tube, IIRC - one of the reasons the later, fatter leg was produced.

I also think, looking at 2-3 inches of paint removed from my old style gear leg, that there was a Vans notice about checking for machining marks at this location.

 

[RVWanabe]

I went to a flyin this past saturday. It was held at a grass strip.There were 4 or 5 "A" models there. I tried to watch their takeoffs & landings. Those gears sure jiggle a lot fore & aft. Also, I noticed the fusilages seems to be nose down on level ground. Would it not help if the nose gear was a little taller?
I spoke to a 7A pilot & he said his stick was in his gut the whole time. His nose gear jiggled fore & aft the whole time his plane was moving.
It made me nervous to watch.

 

[Ron Lee]

I was thinking while cutting grass. Come up with a "Rough field" landing gear (nose) mod (which is optional). That way if it requires a new engine mount and 20 pounds more worth of stuff up front, I won't be forced to install it should insurance concerns drive me in that direction.

 

[David-aviator]

......My impression, partly given by Van's video, is that grass strips are perfectly OK. I've been kicking around the idea of building my own strip at some point but after reading this and other related threads I'm a bit wary of the idea of landing anywhere but on pavement.

Nonsense.

Many RV-xA's are flown of off grass. I've done it for 5 years, so have others.

This is what's wrong with this thread, it is spreading information not based on fact.

 

[GrayHawk]

I went to a flyin this past saturday. It was held at a grass strip.There were 4 or 5 "A" models there. I tried to watch their takeoffs & landings. Those gears sure jiggle a lot fore & aft. Also, I noticed the fusilages seems to be nose down on level ground. Would it not help if the nose gear was a little taller?
I spoke to a 7A pilot & he said his stick was in his gut the whole time. His nose gear jiggled fore & aft the whole time his plane was moving.
It made me nervous to watch.

They must have been 7A,8A,9A models which have a longer main gear. The 6A has shorter main gear which makes them sit lower to the ground. I've always felt the lower CG of the 6A makes them less susceptable to tip overs.

 

[tonyjohnson]

which A models

Is there a source of reliable information on which of the A models are most affected by this problem? I don't specifically recall hearing of an 8A pitchpoling.

 

[RV7AV8R]

Is there a source of reliable information on which of the A models are most affected by this problem? I don't specifically recall hearing of an 8A pitchpoling.

This thread has the data you are looking for. http://www.vansairforce.com/community/showthread.php?t=61178

 

[kymjon]

Reading the latest flight safety magazine (January 2011) for Australia there were two reported RVxA nose gear failures in October 2010 in Australia.

An RV7A nose gear entered a depression on landing roll out and flipped onto it's back and an RV6A on landing had the nose gear fail and the aircraft stopped abruptly and then fell back on the mains. The descriptions in the magazine are brief but probably describe the usual issues with the A.

Makes one wonder how many of these happen but are not generally heard about through the VAF forums

 

[F1R]

My 2 cents

I started out with the same number of tailwheel hours that anybody ever does. ZERO. Now passed 2000. For anybody starting out or considering a new build, there is nothing to fear about a tailwheel RV. When I took my pilot girlfriend flying in my rocket she asked me what rotation speed was. My response was "I don't drop my eyes on take off or landing, somebody once told me, the only place for your eyes on take off or landing is straight down the runway." I never look, never have and never will. In a C-310 or heavier, it's a different set of rules. In any twin you need blue line and rotation speed. But RV's and similar just fly when they are ready and there is nothing you can do to prevent it.

Tail wheel flying is one of the more enjoyable parts of life. If anybody tells you it's difficult, hire a better instructor.

 

[Mike S]

Little food for thought.

Glad to see this thread re-surface.

I have been saying for years that the RV 10 style of nose gear would seem to be a solution to the flexi rod setup.

Finally someone posted a photo of the RV 10 nose gear that really shows the way it is setup, so I "borrowed" the photo from another thread----Thanks Mike A.

Yes, it is heaver. Yes, it is going to take a mod to the motor mount. Yes, it is going to cost $$$

But....... if it keeps an "A" model on its wheels---->priceless?

 

[Andy Hill]

While you've got that picture there Mike, an article in our latest LAA magazine refers to cracks found in the RV-10 engine / nosegear mount on a 150hr example.

It says "Vans are working on a small design change here to prevent further cracking" so Vans seem in the loop on it - whether they've passed it on I do not know?

The aircraft can continue flying for now, monitoring, but when the repair is done, engine / mount will need to come off. The crack, I think, is at the top of that bunch of black rubber spaces, between the struts / at the base of the larger circular assembly.

Andy

 

[rleffler]

While you've got that picture there Mike, an article in our latest LAA magazine refers to cracks found in the RV-10 engine / nosegear mount on a 150hr example.

It says "Vans are working on a small design change here to prevent further cracking" so Vans seem in the loop on it - whether they've passed it on I do not know?

Andy,

Please post a link to the article. As a RV-10 builder you just got my attention, since I've not heard of this issue previously.

thanks,

bob

 

[Bob Ellis]

Hi Bob

I have scanned the article - sorry about the blurred left edge but you get the gist.

Bob
www.rv-8.co.uk

 

[Andy Hill]

Andy,

Please post a link to the article

I was going to say the LAA is stuck in the paper age, but see that is slightly unfair...

It will appear in the Jan 11 'Safety Spot' here LAA Link "soon"...

When they publish it there, hopefully Bob can delete his post before they lock him up for breach of copyright

Andy

 

[Av8torTom]

Agree with Mike

I think a RV-10 style nose gear would be a big improvement.
Is it my imagination or does this nose gear failure seem to be less frequent in the RV9A? If true, do you think this is due to slower landing speed? Maybe there are just a lot more 7s out there and it's a statistical thing.

T.

 

[Captain Avgas]

RV take-off and landing video

I have argued for many years that the Vans two-place nose gear design is deficient in that it is best suited for lighter loads and is struggling to cope with the loads now associated with increased gross weights, bigger engines, and heavier constant speed props.

However I also recognise that many RV pilots have take-off and landing techniques that are not suitable for a nose gear RV. Many pilots simply do not keep the nose gear off the ground for as long as possible during take-off and landing. They are asking for trouble.

This is a URL to a 5 minute HD video of RVs taking off and landing shot by Doug Reeves (a very good video).

http://www.youtube.com/watch?v=kWYxU83KmZo

There is only one nose gear RV in this video (an RV8A). I would ask you to go to the 1.05 minute mark on the video to see it take-off. And then go to the 2.25 minute mark to see it land.

This is the type of flying technique that puts very large stresses on the nose gear and greatly increases the probability of nose gear failure. People can learn something from this video.

 

[LifeofReiley]

Bob,

You would be correct in that the nose wheel is a TAXI wheel, and in NO way a MAJOR load bearing wheel or any part of the TRUE LANDING gear.

I have argued for many years that the Vans two-place nose gear design is deficient in that it is best suited for lighter loads and is struggling to cope with the loads now associated with increased gross weights, bigger engines, and heavier constant speed props.

However I also recognise that many RV pilots have take-off and landing techniques that are not suitable for a nose gear RV. Many pilots simply do not keep the nose gear off the ground for as long as possible during take-off and landing. They are asking for trouble.

This is a URL to a 5 minute HD video of RVs taking off and landing shot by Doug Reeves (a very good video).

http://www.youtube.com/watch?v=kWYxU83KmZo

There is only one nose gear RV in this video (an RV8A). I would ask you to go to the 1.05 minute mark on the video to see it take-off. And then go to the 2.25 minute mark to see it land.

This is the type of flying technique that puts very large stresses on the nose gear and greatly increases the probability of nose gear failure. People can learn something from this video.

 

[DeltaRomeo]

snip...And then go to the 2.25 minute mark to see it land.
This is the type of flying technique that puts very large stresses on the nose gear and greatly increases the probability of nose gear failure. People can learn something from this video.

I respectfully disagree.

I think if you go back and look at the landing again you'll see that there is daylight between the nose wheel and the ground for almost all of the high speed part of the rollout. The nosewheel may have momentarily scuffed a high spot in the pavement, but only hard enough to gently start the wheel spinning. I have a unique perspective for this particular 8A's landings, as I keep my RV hangared right off the bravo turnoff (midpoint) on this runway. I have seen it land dozens of times, always with the nosewheel held an inch or so off the pavement. Kay is very good at landing, as he is retired and flies it nearly every day.

In this particular landing Kay was carrying a little more speed because there were other aircraft from the formation flight landing just behind him. This resulted in a slightly faster rollout, so the wheel was probably only 1 inch or less above the surface. And since it was around 1,500 feet away from me, the lens doesn't pick up this level of detail.

Kindest,

Doug Reeves
(the guy who shot the video - and playing the video back on a large screen TV absolutely shows daylight between the nosewheel and the pavement - but only about an inch)

 

[Ron Lee]

My view is that many of these incidents involve hitting a pothole, landing in turf and sinking into the ground etc.

 

[Captain Avgas]

I respectfully disagree.

I think if you go back and look at the landing again you'll see that there is daylight between the nose wheel and the ground for almost all of the high speed part of the rollout. The nosewheel may have momentarily scuffed a high spot in the pavement, but only hard enough to gently start the wheel spinning. I have a unique perspective for this particular 8A's landings, as I keep my RV hangared right off the bravo turnoff (midpoint) on this runway. I have seen it land dozens of times, always with the nosewheel held an inch or so off the pavement. Kay is very good at landing, as he is retired and flies it nearly every day.

In this particular landing Kay was carrying a little more speed because there were other aircraft from the formation flight landing just behind him. This resulted in a slightly faster rollout, so the wheel was probably only 1 inch or less above the surface. And since it was around 1,500 feet away from me, the lens doesn't pick up this level of detail.

Kindest,

Doug Reeves
(the guy who shot the video - and playing the video back on a large screen TV absolutely shows daylight between the nosewheel and the pavement - but only about an inch)

Doug, you must have much better eyes and equipment than me. And I admire your willingness to defend a friend.

However what I see is the aircraft accelerate on take-off and the nose gear is firmly planted until rotation (typical spam can take-off).

On landing I see the nose gear positively contact the runway less than 1 second after the mains which indicates a very flat landing (typical spam can landing).

I'll have to take your word for it that there may be some sliver of daylight under the tire for some period after the first nose wheel contact but I'd be quite comfortable in saying that Mike Seager would not regard this take-off or landing as an illustration of best RV(A) practice in virtually nil wind conditions. Others may form their own opinion.

 

[Jack Tyler]

Bob, what you see and describe is what I see - and especially the landing. The 'bounce back' of the nose gear after initial runway contact seems to me to be quite evident. And that uphill grade at the roll-out, mid-field point doesn't help, either. This reminded me of landings I've made, in a free-castering nose wheel AA-5, about which I was not very proud.

Jack

 

[Fred.Stucklen]

Nose Gear Techniques

Doug, you must have much better eyes and equipment than me. And I admire your willingness to defend a friend.

However what I see is the aircraft accelerate on take-off and the nose gear is firmly planted until rotation (typical spam can take-off).

On landing I see the nose gear positively contact the runway less than 1 second after the mains which indicates a very flat landing (typical spam can landing).

I'll have to take your word for it that there may be some sliver of daylight under the tire for some period after the first nose wheel contact but I'd be quite comfortable in saying that Mike Seager would not regard this take-off or landing as an illustration of best RV(A) practice in virtually nil wind conditions. Others may form their own opinion.

I've provided a fair amount of transition training to guys getting ready to fly their own creations. All have been done it in RV-XA models. The one thing I stress is that the top of the cowl should be parallel with the runway on take-off AND landing.
On take-off hold aft elevator until the the nose raises, and stop the rising movement at the point the cowl is parallel with the runway. The rest of the takeoff roll is like any other aircraft.
On landing, the approach speed is set such that the cowl top is level (slight up nose attitude) and held there until touchdown (using the throttle to adjust rate of descent, especially near the ground just before touch-down). The constant pitch attitude sets the approach speed. The pitch is the landing attitude. The pitch is maintained on the ground until the elevator runs ut of authority.
I've got 3383 Hrs in RV-XA aircraft. I did break a nose gear once due to a defect in the shaft near the motor mount (where it broke - old style landing gear), but, IMHO, due to proper technique, I haven't bent a nose gear under. I do not land on grass strips unless I am VERY familar with the condition of the field. If it's at all questionable, I won't land there.
The nose gear leg is KNOWN to be the weakest link in the landing gear. Respect it and it will serve you well. Abuse it, and it's not a matter of IF, but WHEN it will fail....

 

[Andy Hill]

See RVator p3 for what Vans considers the (nosedragger) "landing attitude"

Read on a bit

LANDING/TOUCHDOWN
I find it difficult to imagine how anyone can consistently land safely without a mastery of low speed control. While this point may be argued, the traditional landing objective is that of contacting the ground at or near minimum air speed. (A survey in the October 2010 issue of Sport Aviation showed a 52/48 percent preference for wheel landings over three-point landing. This would contradict my above statement of the ?accepted? preferred landing technique. It could mean that while the textbook dictate is the 3-point landing, user preference is a higher touch down speed ?wheel? landing. If so, one explanation could be that most pilots prefer the wheel landing because it is smoother for them, or it could mean that they lack the skills or confidence to do 3-point landings. I?ll discuss this in a future article.

and oh dear, he's going to have a go at the following RV-8 in the video as well for doing a wheeler

I make no comment

Andy

 

[Captain Avgas]

I've provided a fair amount of transition training to guys getting ready to fly their own creations. All have been done it in RV-XA models. The one thing I stress is that the top of the cowl should be parallel with the runway on take-off AND landing.
The nose gear leg is KNOWN to be the weakest link in the landing gear. Respect it and it will serve you well. Abuse it, and it's not a matter of IF, but WHEN it will fail....

When I learnt to fly decades ago in a Cessna 172 my instructor spoke of the importance of keeping the weight off the nosegear on landing (as do probably all instructors) but in keeping with the generous safety factor on Cessna nosewheels he was not dictatorial on the matter. As long as it wasn't a flat landing and the nose gear touched down some appreciable time after the mains he was basically happy. On take-off it was just blast down the runway and pull back on the yoke when you wanted to leave the ground.

So I merrily flew over the ensuing years without mishap on take-off and landing convinced that I had quite good technique.

Flash forward many years and I'm building an RV7A and I decide to get some transition training from Mike Seager in Oregon.......BIG awakening!!!

Of the 8 hours I did with Mike at least 5 hours were just repetitive touch-and-goes. Learning to fly a nose gear RV with Mike is predominantly all about learning to keep as much weight as possible off the nose gear at all times....during taxi, during take-off and during landing. Mike's mantra is that you take the nose gear off the ground (right off the ground) on take-off as soon as you have enough elevator authority to do so (which is almost immediately in a typical RV) and let the plane eventually fly itself off the ground....there is NO rotation. On landing the nosegear remains off the ground until all elevator authority is FULLY exhausted. With time you learn to finesse the nose wheel onto the ground smoothly just as the last of your authority runs out.

What I learnt from flying with Mike is that my previous technique was grossly inadequate for a nose gear RV....and that I had no real concept of how bad my previous technique really was. I learnt that I had to re-learn my whole approach to take-offs and landings.

When I mention my learning experience under Mike Seager and the importance of keeping loads off the nosegear to other RV(A) pilots they invariably say: "That's exactly what I do". But strangely enough when I fly with these people I generally find that many of them have no real concept of keeping the nosegear off the ground to the full extent of elevator authority.

In other words many RV(A) pilots have terrible take-off and landing techniques...but they just don't know it. That is why video of good and bad RV landing techniques is so important to highlight the difference between the two. It's just something that cannot adequately be explained in words.

 

[rubber314chicken]

RocketBob, Doug, others:

While I am not an engineer, the gist of many of the comments I've read seem to agree that if the gear leg nut was higher off the ground, the incidence of rollover would decrease.

Others have suggested a larger front wheel & increased tire pressure (amongst other ideas) will get the nut further from the ground and reduce incidents. To a retired software guy like me, that seems logical.

Please take a look at the following two photos. Using Photoshop, I altered the angle of the fork. Said change will raise the nut further from the ground. I suspect it also alters the load on the gear leg and maybe even the cg a bit but I am not qualified to validate such claims.

Photo of the original fork....

Photo-shopped altered fork....

My thoughts as an engineering student is this is probably the best solution we can work out. I think that modifying the fork to fit a larger tire should also be done. The problems are though is if the fork is extended too much the gear leg will have to reinforced to handle the extra torque the same force on the wheel will apply to the leg. While this doesn't sound like a bad thing, the less that leg flexes (within design specs) the more of that shock is transferred to the airframe and the pilot. This could mean it starts cracking some other portion of the airframe from the forces on that gear leg.

As far as movement in the gear leg itself, the choices are basically to leave the leg as is, or redesign the motor mount to have a design like the -10. The current design appears as though it shouldn't be TOO difficult to redesign, but like anything, that is still a lot of work.

 

[Sig600]

When you compare these photos of planes with a similar nose gear but two without the problem there are other differences as well. Gruman and DA40 have wider lower stances. Just looking at these photos, which looks more unstable?

As someone who has substantial time in both the AA-5 and AG-5B I can tell you that the Tigers are VERY prone to prop strikes and nose gear collapse. It's a different structure as well. IIRC the tube runs back the length of the fuselage.

Had a buddy of mine get sued by the school he worked for when his student banged the prop on what was NOT a very hard landing. Shadey outfit, details outside the scope of this conversation.

Can't speak to the DA40.

I've got a lot of time flying a 6A off of very short grass, and never thought twice about the integrity of the nose gear. You have to fly the thing correctly, regardless of who built it, to it's limitations.

 

[diamond]

Very nice video Doug
Do you recall what the crosswinds were at the time of shooting?

 

[PCHunt]

DA-40

I've seen two DA-40's that had a prop strike. One on landing, and the other one was merely doing a 180 on the taxiway in front of my hangar, at slow speed, and in a SLIGHT dip, the prop hit.

Bad design, IMHO. Or else something was wrong with the nose gear. The nose tire was slightly low.

 

[Snowflake]

As someone who has substantial time in both the AA-5 and AG-5B I can tell you that the Tigers are VERY prone to prop strikes and nose gear collapse. It's a different structure as well. IIRC the tube runs back the length of the fuselage.

Elsewhere in this thread (or maybe it's the "let's redesign the nosegear" thread), there are photos of the Grumman setup. The nosegear pivots around a horizontal tube that runs between the lower corners of the firewall. The tube is essentially the full width of the firewall. It's more like the RV-10 gear, IIRC.

I think the solution that people should be looking for is to make the same change you'd need to turn an original Van's non-swivel tailwheel into a Doug Bell tailwheel fork. Remove the almost horizontal sheet-metal swivelling portion, and replace it with a steeply angled, forged fork. That would raise the bottom of that pivot almost three inches, and remove most if not all opportunity for it to contact the ground. It would require serious redesign of the nosewheel pant, or perhaps switching to a simple spat trailing the wheel. Not the prettiest solution, I know. But it would probably take one heck of a beating before it failed.

 

[vgb]

Nose gear

It would be great if you always landed on a smooth paved runway but we have a runway in northern Calif that is paved and would be very apprehensive about landing there.
How about off field landings in a emergency.
When I'm flying and always keeping a eye out for landing spot I just figure I'll flip if I land in a alfalfa field' but what better place to put her down If I had to.
The gear should handle that.
I don't comment very often but the nose gear bugs me and sometimes wish I had built a taildragger.
Wait until the insurance companys figure out this nose gear problem and we will be paying more for a nose dragger instead of a tail dragger

 

[Captain Avgas]

Very nice video Doug
Do you recall what the crosswinds were at the time of shooting?

Check out the video. You can clearly see the windsock. It's almost limp.

 

[Ifly12]

nosewheel failure

Well,

You guys have talked me right out of buying a 6a. So, a 6 it is!

Regards,

John

 

[cbo111]

Much ado about nothing

Ok, this thread has gone on for 230+ responses, and we are no closer to defining a problem with the nosewheel RV than at the start. On behalf of the multiple-thousand nosedragger pilots who have had zero problems, do not fear the nosewheel. Learn to land with the nose off the ground until gravity brings it down and you will do just fine with an A-model. There are a few nervous nellies out there, many of whom don?t even fly A-models. Please don?t let that influence your decision. If there was an increased danger with the A-model, you can bet the insurance companies would be factoring it into their rates.
cbo

Well,

You guys have talked me right out of buying a 6a. So, a 6 it is!

Regards,

John

 

[Bill Palmer]

A Professional's Point of View

From ?Spitfire: A Test Pilot?s Story? by Jeffrey Quill, end of Chapter 9.

Quill was the principal Spitfire test pilot and one of the most accomplished, professional test pilots of all time.

See http://www.bbm.org.uk/Quill.htm

?Late in 1937 David Hollis-Williams, the Chief Designer of General Aircraft Ltd at Hanworth, was experimenting with a tricycle undercarriage ? a concept that was then entirely new in Britain. He had modified a twin-engined Monospar aircraft and invited me over to Hanworth to fly it. I went on 6 December 1937 and there was the machine standing on a fixed undercarriage with a rather spindly nosewheel leg. I did several takeoffs and landings with Hollis-Williams and was at once converted to the concept. Taxying was easy and foolproof; the tricycle arrangement was inherently stable directionally on the ground and eliminated any risk of ?ground looping? after landing. All one had to do after touchdown was to let the aeroplane pitch onto its nosewheel and it would run straight, even in a stiff crosswind. The configuration also permitted the use of much more powerful wheelbrakes, and rendered the sometimes demanding ?three-point? landing a thing of the past. All in all, the tricycle undercarriage seemed to me a fundamental step forward of immense importance. Hollis-Williams said he was looking for a high-performance aeroplane on which to experiment ? what about the Vickers Venom? I said I had to admit there did not seem to be much future for it as a fighter, but it would not be a huge engineering problem to move the main gear aft and fit a nosewheel. He said it could be done at least for experimental purposes. I reported this to Mutt Summers and to Sir Robert McLean, neither of whom seemed at all interested ? still less were they interested in my enthusiastic advocacy of the principle. Ten years were to elapse before the first Vickers aircraft was to fly with a tricycle undercarriage (the Viscount in 1948) which was curious for a company that had a thriving business designing and manufacturing undercarriage legs!?

 

[L.Adamson]

From ?Spitfire: A Test Pilot?s Story? by Jeffrey Quill, end of Chapter 9.

Quill was the principal Spitfire test pilot and one of the most accomplished, professional test pilots of all time.

It was my uncle, who spent a piloting career with the USAF shortly after WWII,.... that convinced me to go with the nose wheel. The Air Force knew about all the tail wheel problems & remedies too.

L.Adamson --- RV6A

 

[bignose]

It would be great if you always landed on a smooth paved runway but we have a runway in northern Calif that is paved and would be very apprehensive about landing there.
How about off field landings in a emergency.
When I'm flying and always keeping a eye out for landing spot I just figure I'll flip if I land in a alfalfa field' but what better place to put her down If I had to.
The gear should handle that.
I don't comment very often but the nose gear bugs me and sometimes wish I had built a taildragger.
Wait until the insurance companys figure out this nose gear problem and we will be paying more for a nose dragger instead of a tail dragger

Much more taildraggers in the world, like Cubs, Maules, 180 and 185 have flipt over in aviation history than all Vans A models together, that's for sure... All you need is break a little bit harder when the tail is up, or hit a bump or pot hole, and you are on your back. I allways heard that taildraggers were much more prone for flipping over than nose gear... And now people are wishing taildraggers again. For "Real" Pilots maybe...

 

[don.olandese]

we debated about choice of nosegear or tailwheel too...

...and this is why our plane may ultimately be named "Conventional Wisdom."

 

[Snowflake]

From ?Spitfire: A Test Pilot?s Story? by Jeffrey Quill, end of Chapter 9.

... All one had to do after touchdown was to let the aeroplane pitch onto its nosewheel and it would run straight, even in a stiff crosswind. The configuration also permitted the use of much more powerful wheelbrakes ...

Ironically, letting the nose pitch onto its nosewheel after landing, and braking heavily, are the two things that exacerbate the problem with -A models going over on their nose.

Flying is a challenge. If I wanted it to be easy, I would have bought a Cessna.

 

[jws_39]

Technique is the key

Here is a couple of video clips I took just a couple of months ago. I put together a short movie of takeoff and landings. I have about 185hrs in the RV7a and have felt pretty good about my technique of keeping the pressure off of the front nose. The only thing I have noticed is in doing so the front wheel does shimmy a lot until I do allow all of the weight to settle on it. You will see the shimmy on takeoffs because I am keeping the pressure on the stick during the roll out.

http://www.youtube.com/watch?v=2m5nd7qmQXw

I can live with the little bit of shimmy instead of flipping it over.

 

[60Bubba]

So here's my uneducated observation:

All along when I heard people talking about wheel shimmy, I was assuming we were talking about a lateral shimmy, like a grocery cart castering wheel that was messed up. Maybe this is an issue in some cases. Looking at this video, especially the landings, it certainly seems to my untrained eye that what I am seeing is a fore/aft vibration. That's not at all what I was expecting, but to me it seems to show how one of these things could vibrate/flex enough to fold under.

As the previous post mentioned, there was little weight on the nose gear, so if it is still bucking fore and aft, wouldn't that point to a resistance of the front wheel to turning? The old objects at rest tend to remain at rest/ inertia bit? Is this the kind of issue that has prompted the discussions over the front axle design and bearing preload for these nose gear?

 

[gasman]

So here's my uneducated observation:

Is this the kind of issue that has prompted the discussions over the front axle design and bearing preload for these nose gear?

Yes, it is. You can find it in a search.

 

[MTBengel]

Timid question

I'm a newbee (have my RV7A tail and was told yesterday that my QB fuselage is in and ready to ship!). I haven't had a opportunity to much spend time under an RVxA cowl so at the risk of showing my ignorance, is there not room to engineer a front strut arrangement similar to the new SR22 nose gear?

http://cirrusengineering.blogspot.com/2010/06/new-nose-landing-gear.html

With the tiny oleo to absorb and dissipate shock one could do away with the problematic spring gear and use a more robust leg. I would also love to see a slightly larger tire and fork with a recessed nut.

I understand the need for proper landing technique, but let's face it, we are all going to suffer a less than perfect landing at one time or another. Having such an unforgiving weak link does not instill confidence in what is otherwise such a fine airplane.

 

[plehrke]

So here's my uneducated observation:

All along when I heard people talking about wheel shimmy, I was assuming we were talking about a lateral shimmy, like a grocery cart castering wheel that was messed up. Maybe this is an issue in some cases. Looking at this video, especially the landings, it certainly seems to my untrained eye that what I am seeing is a fore/aft vibration.

Not all fore/aft motion is shimmy. What you are calling fore/aft shimmy in the video can be up and down motion of the gear as it rolls over bumps in the runway. The shock absorption for the gear has the spring action pivot up near the engine mount. When the gear compresses (goes up) it also moves forward slightly and when it extends (goes down) it moves aft when viewed from a camera attached to the plane.

The only thing I have noticed is in doing so the front wheel does shimmy a lot until I do allow all of the weight to settle on it. You will see the shimmy on takeoffs because I am keeping the pressure on the stick during the roll out.

http://www.youtube.com/watch?v=2m5nd7qmQXw

My nose gear has what feels like a fore/aft shimmy when the gear is loaded and moving about 30 kts. If I have full aft stick, then no shimmy. If I am going faster then 30 kts or slower then 30 kts, then no shimmy.

 

[PCHunt]

My nose gear has what feels like a fore/aft shimmy when the gear is loaded and moving about 30 kts. If I have full aft stick, then no shimmy. If I am going faster then 30 kts or slower then 30 kts, then no shimmy.

Umm........, easy answer: Keep FULL back stick whenever you are on the ground and in motion (however slight.) And avoid 30 knots except when passing through. You wouldn't taxi that fast anyway (I hope), so as you takeoff, hold FULL back stick until the nose wheel lifts off, and when you land, hold "almost" FULL back stick until the nose wheel touches down. Control the nose gear touchdown, don't let it "slam" down. Then use brakes to slow below 30 knots as quickly as is feasible. Spend as little time at 30 knots as you possibly can.

PS: Fly all tri-gear airplanes, not just RV's, this way, and you will be happy.

YMMV, JOMO. My $.02 (USD). FWIW. etc.

 

[pierre smith]

http://cirrusengineering.blogspot.com/2010/06/new-nose-landing-gear.html

...........With the tiny oleo to absorb and dissipate shock one could do away with the problematic spring gear and use a more robust leg. I would also love to see a slightly larger tire and fork with a recessed nut.

.

Mark, the RV-10 has a nose gear very similar to the Cirrus.....hinged at the firewall and dampened by rubber doughnuts, with little flexing of the rather stiff gear leg.

The problem of adapting something similar to the two-seaters is that you'd essentially have to either build a new motor mount since the gear leg socket is an integral part of it, or cut up an existing mount, add a pivot point and shock absorbers of some sort. Then the problem of finding/manufacturing a gear leg......not insurmountable problems but it seems difficult to justify since the vast majority of nosegears haven't folded.
Best,

 

[Ron Lee]

My nose gear has what feels like a fore/aft shimmy when the gear is loaded and moving about 30 kts. If I have full aft stick, then no shimmy. If I am going faster then 30 kts or slower then 30 kts, then no shimmy.

Unless you have someone competent look at the nosewheel, you have no idea what is going on. Odds are that your nosewheel assembly is out of round and/or out of balance.

This would be obvious to someone looking at it.

Of course I may be wrong but checking the obvious causes should be done if you have not already.

 

[Mike S]

Welcome to VAF!!!!

I'm a newbee (have my RV7A tail and was told yesterday that my QB fuselage is in and ready to ship!)

Mark, welcome aboard VAF.

Good to have another builder join up.

I haven't had a opportunity to much spend time under an RVxA cowl so at the risk of showing my ignorance, is there not room to engineer a front strut arrangement similar to the new SR22 nose gear?

Looking at the photo, I doubt there is room to put in a Cirrus style setup, due to the forward leaning oleo.

I have been saying for 5 years or so that the RV 10 style nose gear could probably be adapted without a lot of difficulty, and there is a guy in Oz who is actually in the testing phase of a homebrewed oleo setup.

 

[shiney]

Camera shot

Hi Jeff,

Here is a couple of video clips I took just a couple of months ago. I put together a short movie of takeoff and landings.

can you post a picture of how you mounted the under wing camera, the footage is excellent.

Thanks


Martin

 

[MTBengel]

Mark, the RV-10 has a nose gear very similar to the Cirrus.....hinged at the firewall and dampened by rubber doughnuts, with little flexing of the rather stiff gear leg.

snip...not insurmountable problems but it seems difficult to justify since the vast majority of nosegears haven't folded.

Pierre - Thank you for your reply... unfortunately it only takes looking at a few of the heartbreaking "exceptions" of RV7's on their back to make one wish it had more forgiving front gear. I looked at the RV10 gear drawings (thank you) and it seems Van has a very elegant solution at hand (similar to the SR20) that might solve the "perception" issue with the RVxA two seater nose gear. It would be wonderful if Van would consider a "soft field" upgrade option. I'd pull out my checkbook in a heartbeat for the peace of mind.

Mark
RV7A in progress

 

[Martin Sutter]

In regards to nose wheel shimmy I have been able to totally eliminate it by installing the Matco axle (installing the Beringer nose wheel would be even better), shaving the rubber seal on the bearings to reduce drag and balancing the wheel assembly. Using a precision balancer I was surprised that it took 2 1/4 oz. of balance weight. I did this after installing a new McCreary 8ply tire and tube from Desser. I run my tire pressure at 34 psi and set the nose fork break out force at 28 lbs. While the wheel does not keep on spinning when you turn it by hand, it has very little drag.

I consistently keep the nose wheel up and have noticed no vibration at any speed. On take off I start the roll with stick full aft, then relax back pressure as the nose rises to the horizon to keep it there and let the plane fly itself off. On landing (final at 70 kts in smooth air on final) I touch down on the mains again with the nose raised to the horizon and increase back pressure on the stick to keep it there until the stick is full aft. Once I feel the elevator loose authority and the nose begins to drop I gently lower it to the runway. Upon touching down on the mains I retract the flaps to place more weight on the mains and reduce the pitch-down moment they induce.

Lightly loaded I use half flaps as full flaps force the nose down too fast. With baggage or a heavy passenger full flaps work well. My 7A is quite nose heavy with an IO-360 and Hartzell prop but using these techniques I can keep the nose wheel off the ground above 30kts, taking off or landing.

Martin Sutter
Building and flying RV's since 1988
EAA Technical Counselor