Anatomy of a flip: N131RV

This is the narrative I wrote down shortly after the event. I'm sure it will be entertaining to some and informative to others. I'm sure it will cause a bit of controversy, so be it. We can all learn from my misfortune. I did have the old nose gear fork, but I do not believe it was a factor.

Anatomy of a flip. N131RV

Dec 21, 2007. Depart EYQ at 15:30 (approx) for 1 hour flight to 28TE.

Over Calaveras lake, reduce speed and enter extended left base for 17 at 28TE. On base 10 degrees flaps. Turn final and reduce speed to 75 KIAS, flaps to 25 degrees. Keep reducing power and cross the fence at 65 - 70 KIAS. Hold the aircraft, let speed bleed off and sink down to runway.

Reduce power completely and touch down on mains. Nose wants to drop, so a lot of back pressure to keep it up, Not full back, just enough to keep the nose off, then more until the nose drops gently.

The strip is 2600 feet, with a slight downhill slope from North to South. The upper half is harder and smoother than the lower half, so I always land in the upper half and try to get slowed completely before the lower half.

Rolling out, speed coming down to under 40, then under 30 or so. We are about 1/2 way down the runway.

Nose pops up. Keep stick back. Nose comes down fast. Feel a bit of "shudder" and then the nose starts to go further and further down.

As we come almost to a stop, the ground rises up to meet the cockpit, almost in slow motion.

Panic. "Fire!" is the first thing I think of. No smoke, no heat. Good. It's dark.
Can't see much. Don't smell any fuel. Wiggle feet. Good.

Eyesight fading in, I see a flashing red light. It's the ELT. For some reason, I don't want fire & rescue, so I try to turn it off. Push the wrong button about 10 times until I realize I am upside down and hitting the wrong side. Hear a whirring sound. It's the fuel pump. Hunt around for the master switch. Keep reaching to the wrong area. Finally mentally picture the location and find it and turn it off.

What now?

Unthinking, I unlatch the seatbelt and fall down onto the canopy. Something is jamming into my back. Can see better now. Try to wriggle and turn over. With my legs above me it's not easy. Finally get turned over.

Try to punch canopy with my fist. Ouch. It's tough and just "gives".

OK, what now?

Phone! I have a phone in the cockpit. Where is it? It was plugged in and charging. Spy the cord and start pulling it. It has flown forward under the panel and the cord is tangled in the rudder pedals.

Won't come free. Wriggle, stretch, finally get my head "over" the bottom of the panel and free the phone. Dial my brother (he lives next to the strip) and ask him where he is. He says he is at home (lucky me). I tell him to grab an ax and come get me out of this *#&@#&* plane. He says "what?". I tell him I am upside down on the runway. He says he'll be right there.

Hang up.

Now I'm p*ssed. I want out. I wriggle around some more and finally get a leg free to kick at the canopy. Shatters on first kick and foot goes through. Pull it back and kick some more to make the hole bigger. Looks good! Can't turn around, so stick legs through and wriggle out feet first, on my back, just as my brother comes screaming down the runway.

Post mortem:

The plane is resting upside down. I backtrack the landing gear tracks to try and see what happened.

About 70' feet back up the runway, the nose gear track ends at a small "gopher pile". It appears the nose wheel passed over the side of the pile (about 3 inches of soft dirt) and lifted off the runway. Pace off 12 steps and the nose track resumes, just the other side of a similar pile. About 6 feet from there, the track starts getting wider and deeper. In 10 paces, it's about 6 inches deep and there is a 1 foot deep gouge where the prop hit the ground.

The nose gear strut is folded back and the wheel pant is almost perpendicular. There is a deep crease in in the forward floor skin where the wheel pant contacted the fuselage. It appears the wheel pant kept the gear from folding all the way back (which might have allowed the plane to come to rest upright).

The forward part of the nose wheel pant is intact. I had just rebuilt it a couple of days ago from a taxi incident that happened at EYQ. I had taxied into a small "dip" in the grass taxiway and it crunched the nose wheel pant. This time I built it back "really strong" with 3 layers of bid inside and two on the outside. It's about 3/16ths of an inch thick.

The wheel turns freely. It is not packed with dirt and the castle nut is still covered by the wheel pant.

Well, what were the first words your brother said to you?

Sounds like it was an accident Joe. Glad you are okay, and even more "glad" you shared the experience with us. We can all learn from each others misfortunes, and successes.

Joe, thanks for the report.

I totally agree with your analysis below.

N131RV said:

My analysis:
[*] It is very bad design in that the failure GUARANTEES the aircraft will flip. The gear becomes displaced rearward at a 45 degree angle. With the nose low, this becomes a lever in back of the CG. Then when you slow down to almost stopped, it springs forward and throws the aircraft onto it's back.

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I have been saying the same thing for some time now. This fork/spring is not limited in what direction it can "load up", and when it loads the wrong way----look out.

As I see it, the -10 nose gear is a giant step forward in design. It is also more complicated, expensive, heavy, and uses up more room under the cowl.

BUT, it is not prone to the type of displacement that the "A" style gear is.

IMHO, a nose gear design similar to the 10, would go a long way to mitigating the flip over issues.

Would be interesting to see if these can be down scale engineered (is that a real term??) to work on the 6, 7, 8, and 9 airframe.

Questions

What was the runway condition as far as recent rains? It sounds like it dug in because the ground was soft. Add to that the original perturbing "hole" or whatever that popped the front tire up with the ensuing uncontrolled drop.

I don't know if I agree with your point #5. The wheel pant may in fact be the best protection from allowing the bottom of the gear/nut to hit the dirt and act as a pole vault.

My view is just stay off of turf/dirt (in an -A model) unless you know that it is smooth and hard. I have perhaps 1300 hours in my -6A and landed on one grass strip before I knew about the tipovers and one on a dirt/gravel strip (Monument Valley). This self-imposed restriction may keep me out of a few nice strips but no one can suggest that I don't get to a lot of neat places.

Ground was dry.

Ron Lee said:

What was the runway condition as far as recent rains? It sounds like it dug in because the ground was soft. Add to that the original perturbing "hole" or whatever that popped the front tire up with the ensuing uncontrolled drop.

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The runway was dry. The soil is sandy loam with turf. it was bone dry.

Is it possible the front gear "folded" & the plane "nosed up" when it hit the pile? There was no dirt on the big nut indicating it did not dig in.

Was the other "incident" violent / strong enough to have weakend the gear?

Keep guessing.

Geico266 said:

Is it possible the front gear "folded" & the plane "nosed up" when it hit the pile? There was no dirt on the big nut indicating it did not dig in.

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No. It did not "hit" the pile. It crossed one side of the pile, and there was a clear print of the nose wheel in the loose dirt.

N131RV said:

No. It did not "hit" the pile. It crossed one side of the pile, and there was a clear print of the nose wheel in the loose dirt.

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Did the wheel pant "plow" into the dirt in the pile with enough force to buckle the gear?

Man, I'm glad you are okay. That must have been quite a ride. I remember you asking for help.

You are to be commended for writing this up in the hopes it helps other nose draggers.

Keep Guessing?

Joe, if you took pictures of the two points on the ground where the nose wheel went up and then later hit...plus the nose wheel assembly, it would help.

Of the flips I have heard about, all should have provided better post accident information to help identify causal factors.

So far yours is the only one that I have seen that begins to help.

Pictures, and my last post.

Pictures are at http://new.baron.com/flip

I will not be commenting further on this thread.

Wow, those pics are certainly sobering. Im dont think I could have mustered up the courage to post all this if it had happened to me. You have done a great service for us all. May you have a speedy rebuild.

erich

JMHO, I think the gear buckled when you hit the pile, pushing the nose up, slid along on the nose of the wheel pant, until the prop hit and dug in. Look at the dirt stuck to the prop tip. This accounts for the shutter, the lifting of the nose, and the lowering of the nose. The prop was your pivit point.

The added strength of the fiberglass you added MAY have contributed to the rollover. By not shattering, the wheel pant passed the energy into the gearleg.

Also, I must be honest, IMHO, that field is way to rough to fly off of with the size of the wheels on an RV.

Joe, I'm NOT being critical of you, or your flying. You are to be commended for letting us see this pictures, and your account of what happened. Lord knows I have no room to throw rocks, I have banged up my unfair share of aircraft. I feel for you. I'm just giving my honest opinion, and I look forward to more of your comments, and other analysis.

I live on a grass strip and have flown into quite a few, but I agree with Geico, that is a very rough and soft looking field. From what can I see, I would have serious reservations about landing a nosewheel RV there, old fork or new.

Thanks for sharing and God's speed in getting everything back in order,

Roberta

I'm not taking sides on the "nosegear" controversy, and this latest accident is really sad, just so thankful there were no personal injuries.

Here in North Alabama, we operate a fairly large fleet of RVs (taildraggers, and both old and new versions of nosedraggers) off of several grass strips nearly every Saturday. Merely as a datapoint, I don't think any of our posse would consider using a strip that looked anything like the one in the photos attached to this thread. I know I would never consider landing my taildragger on a strip that I knew was that rough or shaggy (maybe it is just the angle of the sun when the photos were taken....).

I'm saying this, no doubt at the risk of offending some, just to encourage new RVers to consider any landing on a grass strip that is not smooth to be a high-risk operation.

Joe, really hate to see the results of all your work upside down in the field, I can't imagine the heartbreak you are feeling. I hope this has not permanently dampened your enthusiasm for once again enjoying an RV.

I wrote the following before I saw Geico and Sam's posts

And Roberta's post as well.

Joe, your website is an excellent documentary of this accident and should help determine if changes in the gear leg is required or if operational limitations are adequate.

The first picture that I looked at was the fourth (#220). It shows the nose gear assembly furrow leading up to the spinner plant and subsequent flip. I noticed what appeared to be periodic widening of the furrow but at that time could not explain if it was real or what caused it. Then I looked at several other pictures to see if any revealed anything important.

The second picture (#218) was the point where the nose gear went over/into a hole and became airborne. What I also noticed around the area were other mounds that appear similar to those caused by pocket gophers where I live. As an aside, they caused lots of damage to my yard, killed many trees and were a safety hazard to walking. If you ever saw Caddy Shack, that movie was not unlike the efforts I spent early on to try to get rid of them. I would use gopher gassers and the next day it would be pushed out of the hole. I tried carbon monoxide poisoning. I tried pouring gasoline in and igniting it hoping that it would blow them away. Nothing worked until I found mouse trap like gopher traps which have been very effective.

Back to my analysis. The piles of dirt are the cause of your accident and in my opinion render that runway unsuitable for a RV-xA...possibly any aircraft. A flip was just a matter of time. Whether the loam soil you have is too soft is unknown. In one picture it does appear dry. But if you intend to continue flying off of that strip I strongly encourage you to eradicate the pests causing those mounds and ensure that the surface is smooth and a constant, firm consistency.

What remained unclear is what caused the furrow and why the nose wheel pant is almost perpendicular to the bottom of the fuselage. Picture #234 provides the likely answer. The dirt pattern on the front of the nose wheel pant is parallel to the surface of the dirt runway. After the pitch up from the hole, the force of the impact when the nose wheel touched down bent the nose gear enough to cause the front of the nose wheel pant to start burying into the ground. That may have gotten a bit deeper as the plane went forward until at some point the drag caused the plane to flip. During the flip the nose gear was bent back to the position shown in your pictures.

After reading Geico's post again he may be right about the initial hole causing the gear leg to bend back. In a way it does not matter. That runway is unacceptable for your aircraft. I know that you live there but you need to get rid of whatever is destroying your runway.

I found one picture of a -A that apparently had a hard landing on the nose on asphalt. I compared the angle on it to the one of yours that shows the dirt on the nose wheel pant leading section and they appear roughly equivalent as best I can determine. That may support the position that the bend occurred when the nose wheel hit hard AFTER the hole caused it to go up.



The grass in the lower nose gear fairing probably got there during the flip and bent the nose gear near the cowling.

too rough

Joe, as a fellow -A pilot, I really feel for you. It is very sad to see an RV flip over or get otherwise damaged. Having landed my 8A on many dirt, gravel, and grass strips, I have to agree with Geico, Roberta, and Sam that the field in the photo is simply too rough for the little wheels on our RV's.
Best wishes,
Mark

Joe, I can tell you one thing, I have looked at your pictures for several hours now. Down loaded most of them and blew them up. Looked at them again & again. I can tell you one thing for sure, you are a talented RV builder. I sincerly hope the second one will be even better. Just get rid of the gophers.

thanks for posting the pictures ... glad you didn't get hurt.

redbeardmark said:

Joe, as a fellow -A pilot, I really feel for you. It is very sad to see an RV flip over or get otherwise damaged. Having landed my 8A on many dirt, gravel, and grass strips, I have to agree with Geico, Roberta, and Sam that the field in the photo is simply too rough for the little wheels on our RV's.
Best wishes,
Mark

Click to expand...

I guess the lesson here is don't let pocket gophers take over an airport.

It also confirms that if the NG gets launched for any reason late in the roll out, chances are it will kiss earth hard enough to bend aft and become a boat anchor.

A NG launch after rolling through a pot hole is what did my airplane in on 10/13/03. The front tire was airborne for some 6 feet and when it came down, it was the beginning of the end just like what happened to Joe. I also unhooked the seat belt in haste to leave the airplane, promptly fell on my head in broken glass and then kicked out the rest of the canopy and left belly up, just like Joe. It was not funny then, but seems somewhat so now. We're all human and have a terrific compulsion to survive. The possibility of fire in that situation is a great motivator to leave the area.

As many of you know, I do fly off a sod strip - perhaps 200 launches in the past 3 years. So far so good. But that's not to say what happened to Joe was a fluke. It was caused by the pocket gopher mounds, the NG arrangement was a victim of that situation. Those mounds could have done in a TD also IMHO if either main had hit them just right. It was not a good situation all around. I have a good friend who recently wrecked his Luscome on take off when one wheel fell into some kind of hole, spun the airplane around and ended up wiping out one MG and sitting up on the right wing.

Good luck rebuilding the airplane, Joe. Truth is it was an unfortunate event and you were just along for the ride at the end.

Joe, you are to be commended

Posting those pictures allows an analysis that should be very beneficial for the RVs. You may disagree with my analysis (which I am confident is close to factual). Given your accident and the picture that I posted from another RV, I would like to see an engineering assessment from Vans on the forces required to make the nose gear leg bend as it did in both cases (lower leg area).

Then determine what would be required to prevent it in similar cases. It may or may not be worth it.

I did comply with the nose gear service bulletin by making the mod before it came out. I thought that the bottom of the gear leg and associate nut were the problem but your case shows that on some turf it does not have to fit that scenario. What is unclear to me is the type soil that allows a nose wheel pant to dig in like it dig and ultimately case a flip.

I am guessing that the nose wheel pant in the picture that I posted was destroyed by the asphalt during the roll out.

I'm trying to understand this and build a timeline.

Plane hits mound and nose goes up. The spring energy of the gear should be disipated, maybe nose gear is wobbling from it.

Nose comes down. It looks like in photo 220 there might be a 2nd bounce? I see what looks to be a depression, then either a wheel track or a shadow, then a deeper depression and the beginning of the plow. Spring energy is high, forces gear into ground, being easier to move than the rest of the plane.

Gear catches, bends like a pole vault until pant smacks lower fuselage. Spring energy in leg is probably disipated during the deformation. Easier to bend gear than stop the rest of the plane.

Combination weight / slope / airplane tilt causes more load on the front bowl of the wheelpant, causing it to increasingly dig in. More it digs in, the greater the tilt, the more weight it carries, etc, until prop strike.

Since the prop only has dirt on 1 blade and the large amount of disturbed dirt, I'll guess the strike was the culprit in the flip. Seems strange that it'd stop sliding all of a sudden.

Could any plane survive? Would this just buckle the firewall of a 172/182?

Thanks for posting your account and the photos, and glad you could walk away from it.

Interesting observation on the prop dirt

I did not notice that and you may be right that it ultimately caused the flip. I don't believe that the nose gear bent as far back as you see in the picture until the flip because of the angle of the dirt on the leading portion of the wheel pant. I did not notice any dirt in the area that would suggest that the nose of the wheel pant was aimed down during the furrowing period.

It does appear that the prop blade with dirt is bent aft as you might expect if your scenario is correct.

An observation. The 19th photo shows a considerable area cut out in the part of the nose cone just fwd of the wheel. I suspect this could reduce somewhat the skid plate effect of this part of the nose fairing on contact with the ground?? I could imagine these cut-off edges on the lower sides of the nose cone digging a fair way into dry sandy type soil??

Fin 9A

Anatomy of a Flip

I am a new VAF member, a fairly low time pilot and a new RV builder. I joined this forum for the collective wisdom.

I bought my new fork last week and had the nose gear modified today. I want a safe controllable plane.

I have read several threads on this subject in each case a number of posters comments insinuate poor judgement by the pilots under discussion. In both recent cases, that were fairly well documented in photos, a relatively small hole or gopher mount initated the incident during final rollout. In both cases the pilots had made a successful landing, but during the rollout it seems to have gone terribly wrong.

If Joe's choice of a landing site was poor judgement, then who will ever make an off-field landing without a flip?

There appears to be a failure mode in the RVs that good pilots fall into. As the number of incidents grow, the "poor Pilot" argument appears to me to grow weaker.

Joe thanks for this thread, records like yours are the way these "flips" will be understood.

whd721 said:

As the number of incidents grow, the "poor Pilot" argument appears to me to grow weaker.

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Let's not confuse "poor judgment" with being a "poor pilot". There is a difference. We all have mad "poor judgements" from time to time. There is no cure for being a "poor pilot".

I think using that rough field weakened the leg over time. This can't possible be the first time he hit a mound of dirt. The cumulative effect of over stressing the NG certainly contributed to the failure.

Living next to a grass strip I can tell you that you may think your field is smooth and acceptable, until another pilot looks at it. I was invited to land at a budies new strip a few years ago. I really wanted to take the plane apart and trailer it home rather than fly off it. He said it was smooth as silk. NOT!

Cave-ins due to gophers

I used to trap pocket gophers (at least the MN variety), and can say that their underground tunnel network is extensive. I don't recall seeing yet in this thread any discussion of the ground collapsing due to the nosewheel simply hitting the wrong spot on its second "landing". Those little rotten creatures will dig tunnels as they eat roots. They push the dirt up in little "volcanoes", the lawn mowers spread it out, and then they push more up. Eventually, the ground gets quite porous. Joe's nosewheel may have simply come back down right aligned with a run.

I don't think the piles of dirt themselves bent the nose gear back, I would guess it caved in the ground and tracked along a gopher run just below the surface. I didn't see any big windrows of dirt along the rut caused by the nose wheel, which further hints that the ground was hollow under it. But, the long grass makes it a little difficult to be sure. It also seems to me that the force needed to dig a trough like that in solid, dry ground would be enormous, and would immediately cause a flip. At the very least, it would break the nose wheel fairing it seems.

If one takes a small rod and pokes around near gopher mounds, it can be amazing how many runs are nearby.

They don't call MN the "Gopher State" for no reason... I got in trouble on this or another list a while back for mentioning that I popped a gopher at a grass strip here just after landing...

AlexPeterson said:

I don't think the piles of dirt themselves bent the nose gear back, I would guess it caved in the ground and tracked along a gopher run just below the surface. I didn't see any big windrows of dirt along the rut caused by the nose wheel, which further hints that the ground was hollow under it. But, the long grass makes it a little difficult to be sure. It also seems to me that the force needed to dig a trough like that in solid, dry ground would be enormous, and would immediately cause a flip. At the very least, it would break the nose wheel fairing it seems.

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Possible ground collapse, but take a look at the prop. It has dirt caked on it 7-8" up the tip, and it is severely bent. The prop was the pivot point.

Some of the dirt "furrows" would have been scattered all over and not laid on the edges of the trough. There is one picture where the dirt furrows are very clear. Tall grass hides the dirt and the true height of the mounds.

It appears Joe is moving to the taildragger camp after this incident:

Joe's Signature said:

N131RV - RV-7A, IO360A1B6, CS
Now being rebuilt as TD

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Assume your A will flip in emergency off-field landings

My 8A is about 85% done. My kit shipped with the "new" gear leg. I don't plan on landing on dirt or grass strips that were as rough as this one. I do expect, that in the event of an emergency off field landing where I can't reach pavement or a golf course that my plane will flip. I will build into my checklist the actions I would want to take (e.g. fuel pump off, fuel selector to off, etc.) before landing and the flip occurs. That's one of the reasons I will carry a chute on long x-c's over the Great Basin. Not sure I want to be upside down where the nearest human is an hour away. If I think the RV taildraggers has some probability of flipping in a similar situation - just not as great. What's on your checklist?

Here are a couple images of another bent NG. The strut did sustain the entire weight of the airplane as neither wing touched the ground. The bend does seem consistent with other such events.

The first is of the airplane right side in the field during the recovery. The second about 5 days later after it was released by the insurance company and the FAA. It took about 6 months to rebuild.

glider4 said:

My 8A is about 85% done. My kit shipped with the "new" gear leg. I don't plan on landing on dirt or grass strips that were as rough as this one. I do expect, that in the event of an emergency off field landing where I can't reach pavement or a golf course that my plane will flip. I will build into my checklist the actions I would want to take (e.g. fuel pump off, fuel selector to off, etc.) before landing and the flip occurs. That's one of the reasons I will carry a chute on long x-c's over the Great Basin. Not sure I want to be upside down where the nearest human is an hour away. If I think the RV taildraggers has some probability of flipping in a similar situation - just not as great. What's on your checklist?

Click to expand...

Perhaps not as great, but it still happens. Here are four NTSB reports of RV aircraft accidents that happened in my state and neighboring Idaho. I was familiar with three, and happened to notice the fourth while getting info.

L.Adamson

------------------------------------------------------

Aircraft: Coltrin RV-6, registration: N566JH
Injuries: 1 Uninjured.

The pilot said he had entered downwind for landing and had pulled the throttle back to idle
prior to turning base. While on base, he pushed the throttle forward to clear the engine; the
engine did not respond. The pilot changed fuel tanks, checked boost pump, and manipulated the
throttle with no engine response. He performed a forced landing to a potato field and the
aircraft flipped inverted immediately after touchdown. The left horizontal stabilizer and the
vertical stabilizer were bent and wrinkled. The pilot said that the engine's carburetor had been
worked on within the year and he believes the power loss was due to the malfunctioning of the
carburetor.
_______________________________________________________________

Accident occurred Thursday, July 08, 2004 in Cascade, ID
Probable Cause Approval Date: 9/29/2004
Aircraft: Ammeter RV-6, registration: N16JA
Injuries: 2 Minor.

The pilot reported that the airplane touched down "slightly" left of centerline and bounced.
Subsequent to the bounced landing, the airplane drifted to the left and exited the runway edge.
In an effort to steer the airplane back onto the runway the pilot applied right rudder and
power, however, during the maneuver the airplane encountered rough/uneven terrain and nosed
over.

_______________________________________________________________


Aircraft: Ross/Stonecipher VANS RV-6, registration: N345JE
Injuries: 1 Minor.

After initiating a go-around at 100 feet above ground level, the aircraft struck a bird on the
pilot's side of the aircraft canopy. The bird penetrated the canopy and struck the pilot's face.
The pilot retarded power and cleared his vision, and decided he would not be able to land
without overrunning the runway into fences and deep ditches. He attempted to continue the
go-around, but then noted an increase in aircraft vibration. He therefore elected to land the
aircraft in a hay field just beyond the departure end of the runway. The grass was approximately
2 feet high in the forced landing field. The airplane flipped over during the forced landing.

________________________________________________________________

Aircraft: Burdette RV-3, registration: N455DB
Injuries: 1 Serious.

During an attempted full-stop three-point landing in the tailwheel-equipped aircraft, the
aircraft bounced back into the air after the initial touchdown. While it was in the air it
started to drift toward the side of the runway. When the aircraft touched down a second time, it
started to "fishtail." During the pilot's attempt to keep the aircraft tracking straight, it
departed the left side of the runway, encountered a nearby earthen berm, and flipped over onto
its back. There was no evidence that there had been any problem with the rudder or tailwheel
steering systems. On the NTSB Form 6120.1/2, Pilot/Operator Aircraft Accident Report, the pilot
stated that he needed "more takeoff and landing practice."