COZY: Kanab Fly-In; Minor Incident - Part 2


Del Schier
 

Marc and all,

 

Sorry about your incident.  I am commenting as I had my nose gear shimmy, the other day, for the first time since I have had the Cozy.  I have always had a slight shudder when braking hard and slow, < 40 k, but that seemed to be the main gear as looking at the nose wheel it was steady.

 

First thing is; “If it ain’t broke don’t fix it”.  I recently put a bolt through NG3 as I had had NG3 fail years ago. NG3 seemed tight but I put the bolt in anyway.  Also, on Terry Shubert’s recommendation, I put some flox between the metal of NG15.  NG15 seemed very secure as the paint wasn’t cracked anywhere.

 

After the work I flew to see some other canard guys at Sanford, FL and the landing was normal. Coming back to narrow airpark runway I had touched down and was starting to get on the brakes and had obvious severe shimmy. I got off the brakes and it got better and could see it through the window.  I used the brakes lightly and rolled over the car road into the paved overrun.

 

Getting back everything looked good on inspection and I measured just over 4 pounds of friction on the shimmy damper.  I don’t know what caused it but perhaps, since I have a momentary contact gear switch I may not have had it all the way down.  I do remember looking to see it was down but don’t remember if I checked the green light, however my gear warning should have been flashing and beeping if I wasn’t full down.

 

I flew it since with two landings, the first on a long wide runway, and it was completely normal on both landings.  I am not sure what to do or if it even can be fixed.  Maybe just the gear is resonating differently and some bump set it oscillating.  I am sure it wouldn’t hurt to put more caster in it, I have the minimum but that goes away when I hit the brakes hard and CG forward.

Del Schier

Cozy IV N197DL

Cannon Creek Airpark 15FL

 

 

 

From: cozy_builders@... <cozy_builders@...> On Behalf Of Marc J. Zeitlin
Sent: Monday, September 6, 2021 7:08 PM
To: Canard Aviators <canard-aviators@canardzone.groups.io>; COZY Builders <cozy_builders@...>
Subject: COZY: Kanab Fly-In; Minor Incident - Part 2

 

Folks:

 

Continued from Part 1:

 

We taxied to the end of runway 19 to take off to the south with a 2 kt. tailwind, downhill. KKNB's runway is 6200 ft. long, so with temps around 60F and us well below MGW, even a 6000 ft. DA didn't concern me with a tailwind. Maybe that was a stupid decision, in retrospect, given the required GS...

 

Anyway, after the runup, we pulled out onto the runway and accelerated. Everything felt nominal, but I wanted to get a bit more IAS prior to rotation just due to the DA, so I held the nose down as we passed through 72 KIAS. Just around 74 KIAS, we had a severe shimmy on the nose gear and as I relaxed forward pressure, the nose came off the ground, the shimmy stopped, and we rotated and flew off. As we started the climb, I made a quick decision that since the engine and aircraft were working and flying just fine, it would be better to have a problem back at home in Tehachapi than to have it in Kanab where there are essentially no resources, so I decided to continue the flight. When we retracted the nose gear, we could see (through the window) that the casting and tire were still in place - nothing had come off - so I put off a decision on what to do for landing until we got closer to KTSP.

 

Coincidentally, or maybe not, the #1 Dynon ADAHRS decided that even when the wings were pretty obviously level and we were NOT slipping, we were in a 10 degree bank to the right. After reaching cruising altitude (10.5K ft) and contacting LA Center for FF, I started experimenting by switching the primary ADAHRS between #1 and #2. #2 was nominal - perfectly happy to show us what the real world was doing. A reboot of Screen #1 didn't change anything - moving back to ADAHRS #1 showed that it was still drunk. So we flew the rest of the CAVU flight back on ADAHRS #2, and obviously Dynon will be contacted about this anomaly. But it didn't affect the flight in any way (also given that I've got a backup G5 in the panel, so still had two working ADAHRS's).

 

After a couple of hours over the desert in perfect conditions, I started thinking about the landing plan - should I chance a landing with the gear down, without knowing what had caused the shimmy (loose NG6A? loose MKNG15A? Loose steering pivot axis? flat nose tire? broken something? who knows...) or land gear up. Gear up guarantees some damage to the nose, but it's relatively minor and easily fixable, while gear down MAY end up being a nothingburger, but also may end up with the same end result as Part 2 of:

 

 

and the subsequent 4 days. I eventually decided to land gear up and take the small repair hit that I knew would be coming. I explained to Deanie what was going to happen and why, and that we'd be perfectly fine but the plane would need some TLC afterwards.

 

After getting to KTSP, we entered the pattern (which was completely empty - no one anywhere near KTSP) and on downwind, I turned off electrical bus #1, which is the bus that the landing gear system is on. In this way I prevented the "auto-extend" system from putting the nose gear down when I didn't want it to. David Orr was right - the "disable" switch for the auto-extend system is a good idea, and while it's in the schematic I've made available for the system, I had not implemented it, thinking "when would I ever want to disable the nose gear extension". Idiot.

 

So, the 2nd best method was to fly on 1/2 the plane in the landing pattern - I lost the left EFIS, one EI, the transponder, and a number of other completely non-safety critical components on a VFR landing. But I will probably install a "disable" switch in some out of the way location just in case...

 

Anyway, we touched down at about 65 KIAS and I held the nose off the ground as long as I could as we decelerated, but at about 55 KIAS the nose came down hard. It's surprising how strong the smell of burning hockey puck is in the cockpit as the nose bumper disappears. After a few hundred feet of skidding, we came to a safe stop on the runway - I tried to extend the gear, but the bolts holding the clamping plate (NG-5) at the top of the strut had been worn away, so no go.

 

A handy bike rider who was on the parallel taxiway right when we landed helped us drag the plane to the hangar - took about 15 minutes - and a quick inspection showed surprisingly little damage - I'm thinking that 2 or three days of part time work will get the plane flying again. I still have to figure out why the shimmy occurred, so I'll be going over the whole nose gear system with a fine tooth comb.

 

Since every cloud has to have a silver lining (not being an optimist, I don't really buy into that, but gotta say it, right?) I will FINALLY take this third opportunity to install a slightly modified version of Wayne Hicks' Nose Bumper:

 

 

I will be installing the AL plate and the UHMW plate, but I will also install a small rubber puck in the center, as it has far more friction on the ground than the UHMW plate. I also plan to install some sort of sacrificial crush material under the rubber bumper. While I've had two nose gear up landings before (see the link above, as well as one more at KPVC after letting myself get distracted by my son and his friends yakking while we were landing) I had forgotten just how hard the jolt is when the completely non-resilient components on the nose hit the ground.

 

I'm going to try to find some replaceable crushable material, maybe 1/2" - 3/4" thick to put under the rubber bumper - this way, if/when it ever hits again, just that 1/2" of motion during the impact will substantially reduce the loads on the fuselage bottom and sides, minimizing damage.

 

Never a dull moment...

 

--

Marc J. Zeitlin                      marc_zeitlin@...

                                            http://www.cozybuilders.org/

Copyright © 2021                     Burnside Aerospace

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Izzy
 

I've only experienced nosewheel shimmy in three situations:
  • Change in angle of the nosewheel, caused by either excessive weight, lower tire pressure or improperly underextended gear - Lots of things can change the angle of the nosewheel. Colder weather can make the fork stiffer so when it gets hot, maybe it sags a bit more? 
  • Loose castle nut on top - Failed to preflight for 4 lbs of drag....my fault.
  • Broken Fork  - Nothing I could do on this one.
In the most common condition, adding some tire pressure and lightening the front load can help.

In all cases, I'll try to keep the nosewheel off the ground and stay off the brakes until necessary. Hopefully the plane will be doing 40-50 instead of 70 when I actually have to use the brakes and put the nose down.  This means you'll have to accept a long rollout rather than trying to "make the turnoff at Charlie or Make Bravo". 

In my Aeronca, when my son and I would get in the plane and the tire pressure was low with full fuel tanks, I would sometimes get a wicked shimmy on landing. This was alleviated by pushing the stick forward (thus changing the angle temporarily) until the plane slowed down. One time we found the locknut on the top of the shaft was loose. Obvious cause of the shimmy there.

Not sure about the logic of intentionally doing a gear up landing. But if I ran my own shop and wanted to do the Wayne Hicks nose bumper anyway...what the hell. 

Izzy
(603)410-7277


On Tuesday, September 7, 2021, 09:39:45 AM EDT, cozypilot@... <cozypilot@...> wrote:


Marc and all,

 

Sorry about your incident.  I am commenting as I had my nose gear shimmy, the other day, for the first time since I have had the Cozy.  I have always had a slight shudder when braking hard and slow, < 40 k, but that seemed to be the main gear as looking at the nose wheel it was steady.

 

First thing is; “If it ain’t broke don’t fix it”.  I recently put a bolt through NG3 as I had had NG3 fail years ago. NG3 seemed tight but I put the bolt in anyway.  Also, on Terry Shubert’s recommendation, I put some flox between the metal of NG15.  NG15 seemed very secure as the paint wasn’t cracked anywhere.

 

After the work I flew to see some other canard guys at Sanford, FL and the landing was normal. Coming back to narrow airpark runway I had touched down and was starting to get on the brakes and had obvious severe shimmy. I got off the brakes and it got better and could see it through the window.  I used the brakes lightly and rolled over the car road into the paved overrun.

 

Getting back everything looked good on inspection and I measured just over 4 pounds of friction on the shimmy damper.  I don’t know what caused it but perhaps, since I have a momentary contact gear switch I may not have had it all the way down.  I do remember looking to see it was down but don’t remember if I checked the green light, however my gear warning should have been flashing and beeping if I wasn’t full down.

 

I flew it since with two landings, the first on a long wide runway, and it was completely normal on both landings.  I am not sure what to do or if it even can be fixed.  Maybe just the gear is resonating differently and some bump set it oscillating.  I am sure it wouldn’t hurt to put more caster in it, I have the minimum but that goes away when I hit the brakes hard and CG forward.

Del Schier

Cozy IV N197DL

Cannon Creek Airpark 15FL

 

 

 

From: cozy_builders@... <cozy_builders@...> On Behalf Of Marc J. Zeitlin
Sent: Monday, September 6, 2021 7:08 PM
To: Canard Aviators <canard-aviators@canardzone.groups.io>; COZY Builders <cozy_builders@...>
Subject: COZY: Kanab Fly-In; Minor Incident - Part 2

 

Folks:

 

Continued from Part 1:

 

We taxied to the end of runway 19 to take off to the south with a 2 kt. tailwind, downhill. KKNB's runway is 6200 ft. long, so with temps around 60F and us well below MGW, even a 6000 ft. DA didn't concern me with a tailwind. Maybe that was a stupid decision, in retrospect, given the required GS...

 

Anyway, after the runup, we pulled out onto the runway and accelerated. Everything felt nominal, but I wanted to get a bit more IAS prior to rotation just due to the DA, so I held the nose down as we passed through 72 KIAS. Just around 74 KIAS, we had a severe shimmy on the nose gear and as I relaxed forward pressure, the nose came off the ground, the shimmy stopped, and we rotated and flew off. As we started the climb, I made a quick decision that since the engine and aircraft were working and flying just fine, it would be better to have a problem back at home in Tehachapi than to have it in Kanab where there are essentially no resources, so I decided to continue the flight. When we retracted the nose gear, we could see (through the window) that the casting and tire were still in place - nothing had come off - so I put off a decision on what to do for landing until we got closer to KTSP.

 

Coincidentally, or maybe not, the #1 Dynon ADAHRS decided that even when the wings were pretty obviously level and we were NOT slipping, we were in a 10 degree bank to the right. After reaching cruising altitude (10.5K ft) and contacting LA Center for FF, I started experimenting by switching the primary ADAHRS between #1 and #2. #2 was nominal - perfectly happy to show us what the real world was doing. A reboot of Screen #1 didn't change anything - moving back to ADAHRS #1 showed that it was still drunk. So we flew the rest of the CAVU flight back on ADAHRS #2, and obviously Dynon will be contacted about this anomaly. But it didn't affect the flight in any way (also given that I've got a backup G5 in the panel, so still had two working ADAHRS's).

 

After a couple of hours over the desert in perfect conditions, I started thinking about the landing plan - should I chance a landing with the gear down, without knowing what had caused the shimmy (loose NG6A? loose MKNG15A? Loose steering pivot axis? flat nose tire? broken something? who knows...) or land gear up. Gear up guarantees some damage to the nose, but it's relatively minor and easily fixable, while gear down MAY end up being a nothingburger, but also may end up with the same end result as Part 2 of:

 

 

and the subsequent 4 days. I eventually decided to land gear up and take the small repair hit that I knew would be coming. I explained to Deanie what was going to happen and why, and that we'd be perfectly fine but the plane would need some TLC afterwards.

 

After getting to KTSP, we entered the pattern (which was completely empty - no one anywhere near KTSP) and on downwind, I turned off electrical bus #1, which is the bus that the landing gear system is on. In this way I prevented the "auto-extend" system from putting the nose gear down when I didn't want it to. David Orr was right - the "disable" switch for the auto-extend system is a good idea, and while it's in the schematic I've made available for the system, I had not implemented it, thinking "when would I ever want to disable the nose gear extension". Idiot.

 

So, the 2nd best method was to fly on 1/2 the plane in the landing pattern - I lost the left EFIS, one EI, the transponder, and a number of other completely non-safety critical components on a VFR landing. But I will probably install a "disable" switch in some out of the way location just in case...

 

Anyway, we touched down at about 65 KIAS and I held the nose off the ground as long as I could as we decelerated, but at about 55 KIAS the nose came down hard. It's surprising how strong the smell of burning hockey puck is in the cockpit as the nose bumper disappears. After a few hundred feet of skidding, we came to a safe stop on the runway - I tried to extend the gear, but the bolts holding the clamping plate (NG-5) at the top of the strut had been worn away, so no go.

 

A handy bike rider who was on the parallel taxiway right when we landed helped us drag the plane to the hangar - took about 15 minutes - and a quick inspection showed surprisingly little damage - I'm thinking that 2 or three days of part time work will get the plane flying again. I still have to figure out why the shimmy occurred, so I'll be going over the whole nose gear system with a fine tooth comb.

 

Since every cloud has to have a silver lining (not being an optimist, I don't really buy into that, but gotta say it, right?) I will FINALLY take this third opportunity to install a slightly modified version of Wayne Hicks' Nose Bumper:

 

 

I will be installing the AL plate and the UHMW plate, but I will also install a small rubber puck in the center, as it has far more friction on the ground than the UHMW plate. I also plan to install some sort of sacrificial crush material under the rubber bumper. While I've had two nose gear up landings before (see the link above, as well as one more at KPVC after letting myself get distracted by my son and his friends yakking while we were landing) I had forgotten just how hard the jolt is when the completely non-resilient components on the nose hit the ground.

 

I'm going to try to find some replaceable crushable material, maybe 1/2" - 3/4" thick to put under the rubber bumper - this way, if/when it ever hits again, just that 1/2" of motion during the impact will substantially reduce the loads on the fuselage bottom and sides, minimizing damage.

 

Never a dull moment...

 

--

Marc J. Zeitlin                      marc_zeitlin@...

                                            http://www.cozybuilders.org/

Copyright © 2021                     Burnside Aerospace

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Marc J. Zeitlin
 

Izzy Briggs wrote:

Not sure about the logic of intentionally doing a gear up landing.

The logic was a cost/benefit analysis.

I could take a 100% chance of needing to perform 10 - 15 hours worth of repairs, or a completely unknown chance of either:
  • No damage whatsoever in a normal landing, or a non-damage landing with a little bit of shimmy, along with no injury
  • Needing to perform major repairs after the nose gear violently shimmies and rips the whole nose gear box out of the fuselage, as happened to me back in 2004, not to mention the possibility of injury in the case of severe aircraft damage
I chose the 100% choice, since I had zero data on the unknown.

--
Marc J. Zeitlin                      marc_zeitlin@...
                                            http://www.cozybuilders.org/
Copyright © 2021                     Burnside Aerospace


Del Schier
 

My shimmy a couple of landings ago was probably getting on the brakes at the time I hit a bump in our airparks somewhat bumpy runway dipping the nose down and taking out the caster.  I will try and hold the stick back when I get on the brakes, that may help.

 

Hope it doesn’t happen again.

 

Del Schier

Cozy IV N197DL

Cannon Creek Airpark 15FL

 

 

 

From: Izzy Briggs <inbriggs@...>
Sent: Tuesday, September 7, 2021 2:09 PM
To: 'Marc J. Zeitlin' <marc_zeitlin@...>; 'Canard Aviators' <canard-aviators@canardzone.groups.io>; 'COZY Builders' <cozy_builders@...>; cozypilot@...
Subject: Re: COZY: Kanab Fly-In; Minor Incident - Part 2

 

I've only experienced nosewheel shimmy in three situations:

  • Change in angle of the nosewheel, caused by either excessive weight, lower tire pressure or improperly underextended gear - Lots of things can change the angle of the nosewheel. Colder weather can make the fork stiffer so when it gets hot, maybe it sags a bit more? 
  • Loose castle nut on top - Failed to preflight for 4 lbs of drag....my fault.
  • Broken Fork  - Nothing I could do on this one.

In the most common condition, adding some tire pressure and lightening the front load can help.

 

In all cases, I'll try to keep the nosewheel off the ground and stay off the brakes until necessary. Hopefully the plane will be doing 40-50 instead of 70 when I actually have to use the brakes and put the nose down.  This means you'll have to accept a long rollout rather than trying to "make the turnoff at Charlie or Make Bravo". 

 

In my Aeronca, when my son and I would get in the plane and the tire pressure was low with full fuel tanks, I would sometimes get a wicked shimmy on landing. This was alleviated by pushing the stick forward (thus changing the angle temporarily) until the plane slowed down. One time we found the locknut on the top of the shaft was loose. Obvious cause of the shimmy there.

 

Not sure about the logic of intentionally doing a gear up landing. But if I ran my own shop and wanted to do the Wayne Hicks nose bumper anyway...what the hell. 


Izzy
(603)410-7277

 

 

On Tuesday, September 7, 2021, 09:39:45 AM EDT, cozypilot@... <cozypilot@...> wrote:

 

 

Marc and all,

 

Sorry about your incident.  I am commenting as I had my nose gear shimmy, the other day, for the first time since I have had the Cozy.  I have always had a slight shudder when braking hard and slow, < 40 k, but that seemed to be the main gear as looking at the nose wheel it was steady.

 

First thing is; “If it ain’t broke don’t fix it”.  I recently put a bolt through NG3 as I had had NG3 fail years ago. NG3 seemed tight but I put the bolt in anyway.  Also, on Terry Shubert’s recommendation, I put some flox between the metal of NG15.  NG15 seemed very secure as the paint wasn’t cracked anywhere.

 

After the work I flew to see some other canard guys at Sanford, FL and the landing was normal. Coming back to narrow airpark runway I had touched down and was starting to get on the brakes and had obvious severe shimmy. I got off the brakes and it got better and could see it through the window.  I used the brakes lightly and rolled over the car road into the paved overrun.

 

Getting back everything looked good on inspection and I measured just over 4 pounds of friction on the shimmy damper.  I don’t know what caused it but perhaps, since I have a momentary contact gear switch I may not have had it all the way down.  I do remember looking to see it was down but don’t remember if I checked the green light, however my gear warning should have been flashing and beeping if I wasn’t full down.

 

I flew it since with two landings, the first on a long wide runway, and it was completely normal on both landings.  I am not sure what to do or if it even can be fixed.  Maybe just the gear is resonating differently and some bump set it oscillating.  I am sure it wouldn’t hurt to put more caster in it, I have the minimum but that goes away when I hit the brakes hard and CG forward.

Del Schier

Cozy IV N197DL

Cannon Creek Airpark 15FL

 

 

 

From: cozy_builders@... <cozy_builders@...> On Behalf Of Marc J. Zeitlin
Sent: Monday, September 6, 2021 7:08 PM
To: Canard Aviators <canard-aviators@canardzone.groups.io>; COZY Builders <cozy_builders@...>
Subject: COZY: Kanab Fly-In; Minor Incident - Part 2

 

Folks:

 

Continued from Part 1:

 

We taxied to the end of runway 19 to take off to the south with a 2 kt. tailwind, downhill. KKNB's runway is 6200 ft. long, so with temps around 60F and us well below MGW, even a 6000 ft. DA didn't concern me with a tailwind. Maybe that was a stupid decision, in retrospect, given the required GS...

 

Anyway, after the runup, we pulled out onto the runway and accelerated. Everything felt nominal, but I wanted to get a bit more IAS prior to rotation just due to the DA, so I held the nose down as we passed through 72 KIAS. Just around 74 KIAS, we had a severe shimmy on the nose gear and as I relaxed forward pressure, the nose came off the ground, the shimmy stopped, and we rotated and flew off. As we started the climb, I made a quick decision that since the engine and aircraft were working and flying just fine, it would be better to have a problem back at home in Tehachapi than to have it in Kanab where there are essentially no resources, so I decided to continue the flight. When we retracted the nose gear, we could see (through the window) that the casting and tire were still in place - nothing had come off - so I put off a decision on what to do for landing until we got closer to KTSP.

 

Coincidentally, or maybe not, the #1 Dynon ADAHRS decided that even when the wings were pretty obviously level and we were NOT slipping, we were in a 10 degree bank to the right. After reaching cruising altitude (10.5K ft) and contacting LA Center for FF, I started experimenting by switching the primary ADAHRS between #1 and #2. #2 was nominal - perfectly happy to show us what the real world was doing. A reboot of Screen #1 didn't change anything - moving back to ADAHRS #1 showed that it was still drunk. So we flew the rest of the CAVU flight back on ADAHRS #2, and obviously Dynon will be contacted about this anomaly. But it didn't affect the flight in any way (also given that I've got a backup G5 in the panel, so still had two working ADAHRS's).

 

After a couple of hours over the desert in perfect conditions, I started thinking about the landing plan - should I chance a landing with the gear down, without knowing what had caused the shimmy (loose NG6A? loose MKNG15A? Loose steering pivot axis? flat nose tire? broken something? who knows...) or land gear up. Gear up guarantees some damage to the nose, but it's relatively minor and easily fixable, while gear down MAY end up being a nothingburger, but also may end up with the same end result as Part 2 of:

 

 

and the subsequent 4 days. I eventually decided to land gear up and take the small repair hit that I knew would be coming. I explained to Deanie what was going to happen and why, and that we'd be perfectly fine but the plane would need some TLC afterwards.

 

After getting to KTSP, we entered the pattern (which was completely empty - no one anywhere near KTSP) and on downwind, I turned off electrical bus #1, which is the bus that the landing gear system is on. In this way I prevented the "auto-extend" system from putting the nose gear down when I didn't want it to. David Orr was right - the "disable" switch for the auto-extend system is a good idea, and while it's in the schematic I've made available for the system, I had not implemented it, thinking "when would I ever want to disable the nose gear extension". Idiot.

 

So, the 2nd best method was to fly on 1/2 the plane in the landing pattern - I lost the left EFIS, one EI, the transponder, and a number of other completely non-safety critical components on a VFR landing. But I will probably install a "disable" switch in some out of the way location just in case...

 

Anyway, we touched down at about 65 KIAS and I held the nose off the ground as long as I could as we decelerated, but at about 55 KIAS the nose came down hard. It's surprising how strong the smell of burning hockey puck is in the cockpit as the nose bumper disappears. After a few hundred feet of skidding, we came to a safe stop on the runway - I tried to extend the gear, but the bolts holding the clamping plate (NG-5) at the top of the strut had been worn away, so no go.

 

A handy bike rider who was on the parallel taxiway right when we landed helped us drag the plane to the hangar - took about 15 minutes - and a quick inspection showed surprisingly little damage - I'm thinking that 2 or three days of part time work will get the plane flying again. I still have to figure out why the shimmy occurred, so I'll be going over the whole nose gear system with a fine tooth comb.

 

Since every cloud has to have a silver lining (not being an optimist, I don't really buy into that, but gotta say it, right?) I will FINALLY take this third opportunity to install a slightly modified version of Wayne Hicks' Nose Bumper:

 

 

I will be installing the AL plate and the UHMW plate, but I will also install a small rubber puck in the center, as it has far more friction on the ground than the UHMW plate. I also plan to install some sort of sacrificial crush material under the rubber bumper. While I've had two nose gear up landings before (see the link above, as well as one more at KPVC after letting myself get distracted by my son and his friends yakking while we were landing) I had forgotten just how hard the jolt is when the completely non-resilient components on the nose hit the ground.

 

I'm going to try to find some replaceable crushable material, maybe 1/2" - 3/4" thick to put under the rubber bumper - this way, if/when it ever hits again, just that 1/2" of motion during the impact will substantially reduce the loads on the fuselage bottom and sides, minimizing damage.

 

Never a dull moment...

 

--

Marc J. Zeitlin                      marc_zeitlin@...

                                            http://www.cozybuilders.org/

Copyright © 2021                     Burnside Aerospace

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Izzy
 

I definitely want to know what you find for root cause! Sounds like it was a really nasty milk shake. 



Izzy
(603)410-7277

On Sep 7, 2021, at 17:23, Marc J. Zeitlin <marc.j.zeitlin@...> wrote:


Izzy Briggs wrote:

Not sure about the logic of intentionally doing a gear up landing.

The logic was a cost/benefit analysis.

I could take a 100% chance of needing to perform 10 - 15 hours worth of repairs, or a completely unknown chance of either:
  • No damage whatsoever in a normal landing, or a non-damage landing with a little bit of shimmy, along with no injury
  • Needing to perform major repairs after the nose gear violently shimmies and rips the whole nose gear box out of the fuselage, as happened to me back in 2004, not to mention the possibility of injury in the case of severe aircraft damage
I chose the 100% choice, since I had zero data on the unknown.

--
Marc J. Zeitlin                      marc_zeitlin@...
                                            http://www.cozybuilders.org/
Copyright © 2021                     Burnside Aerospace

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Tim Andres
 

We recently discussed the Wilhelmsom NL mount bolts coming loose, this was the cause of my nose wobble incident a few years ago.  
The plane never showed the slightest inclination to wobble before that incident, and then did violently on landing at my home airport. 
I checked all the usual suspects and found nothing amiss, then by chance saw the loose bolt. 
I know Marc is on top of this issue and Im not suggesting his is loose, but it should be one of the first things to check IMO. 
Probably anything that can allow lateral play in the system could be a cause of wobble.
Tim Andres



On Sep 8, 2021, at 6:25 AM, Izzy via groups.io <inbriggs@...> wrote:

I definitely want to know what you find for root cause! Sounds like it was a really nasty milk shake. 



Izzy
(603)410-7277

On Sep 7, 2021, at 17:23, Marc J. Zeitlin <marc.j.zeitlin@...> wrote:


Izzy Briggs wrote:

Not sure about the logic of intentionally doing a gear up landing.

The logic was a cost/benefit analysis.

I could take a 100% chance of needing to perform 10 - 15 hours worth of repairs, or a completely unknown chance of either:
  • No damage whatsoever in a normal landing, or a non-damage landing with a little bit of shimmy, along with no injury
  • Needing to perform major repairs after the nose gear violently shimmies and rips the whole nose gear box out of the fuselage, as happened to me back in 2004, not to mention the possibility of injury in the case of severe aircraft damage
I chose the 100% choice, since I had zero data on the unknown.

--
Marc J. Zeitlin                      marc_zeitlin@...
                                            http://www.cozybuilders.org/
Copyright © 2021                     Burnside Aerospace

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Terry Schubert
 

Hi Del,
 
If you put more castor on the nose wheel be sure you are going the right way.
 
The nose fork pivot shaft should be tilted AFT at the top.  If it is tilted forward at the top divergent flutter can occur.
 
Even if you built your nose fork so it is tilted aft at the top you can still occasionally get divergent flutter if you have heavy nose weight and/or you are on the brakes hard or on a rough surface or if the nose strut isn't fully extended.  Those conditions can cause the shock strut spring to compress which positions the fork pivot to tip forward and start that shimmy.
 
Your landing at the airpark could have contained: hard braking, rough surface & strut not fully extended.
 
Terry Schubert
Central States Association Newsletter Editor Emeritus.


---------- Original Message ----------
From: "Del Schier" <cozypilot@...>
To: "'Marc J. Zeitlin'" <marc_zeitlin@...>, "'Canard Aviators'" <canard-aviators@canardzone.groups.io>, "'COZY Builders'" <cozy_builders@...>
Subject: Re: [c-a] COZY: Kanab Fly-In; Minor Incident - Part 2
Date: Tue, 7 Sep 2021 09:39:21 -0400

Marc and all,

 

Sorry about your incident.  I am commenting as I had my nose gear shimmy, the other day, for the first time since I have had the Cozy.  I have always had a slight shudder when braking hard and slow, < 40 k, but that seemed to be the main gear as looking at the nose wheel it was steady.

 

First thing is; “If it ain’t broke don’t fix it”.  I recently put a bolt through NG3 as I had had NG3 fail years ago. NG3 seemed tight but I put the bolt in anyway.  Also, on Terry Shubert’s recommendation, I put some flox between the metal of NG15.  NG15 seemed very secure as the paint wasn’t cracked anywhere.

 

After the work I flew to see some other canard guys at Sanford, FL and the landing was normal. Coming back to narrow airpark runway I had touched down and was starting to get on the brakes and had obvious severe shimmy. I got off the brakes and it got better and could see it through the window.  I used the brakes lightly and rolled over the car road into the paved overrun.

 

Getting back everything looked good on inspection and I measured just over 4 pounds of friction on the shimmy damper.  I don’t know what caused it but perhaps, since I have a momentary contact gear switch I may not have had it all the way down.  I do remember looking to see it was down but don’t remember if I checked the green light, however my gear warning should have been flashing and beeping if I wasn’t full down.

 

I flew it since with two landings, the first on a long wide runway, and it was completely normal on both landings.  I am not sure what to do or if it even can be fixed.  Maybe just the gear is resonating differently and some bump set it oscillating.  I am sure it wouldn’t hurt to put more caster in it, I have the minimum but that goes away when I hit the brakes hard and CG forward.

Del Schier

Cozy IV N197DL

Cannon Creek Airpark 15FL

 

 

 

From: cozy_builders@... <cozy_builders@...> On Behalf Of Marc J. Zeitlin
Sent: Monday, September 6, 2021 7:08 PM
To: Canard Aviators <canard-aviators@canardzone.groups.io>; COZY Builders <cozy_builders@...>
Subject: COZY: Kanab Fly-In; Minor Incident - Part 2

 

Folks:

 

Continued from Part 1:

 

We taxied to the end of runway 19 to take off to the south with a 2 kt. tailwind, downhill. KKNB's runway is 6200 ft. long, so with temps around 60F and us well below MGW, even a 6000 ft. DA didn't concern me with a tailwind. Maybe that was a stupid decision, in retrospect, given the required GS...

 

Anyway, after the runup, we pulled out onto the runway and accelerated. Everything felt nominal, but I wanted to get a bit more IAS prior to rotation just due to the DA, so I held the nose down as we passed through 72 KIAS. Just around 74 KIAS, we had a severe shimmy on the nose gear and as I relaxed forward pressure, the nose came off the ground, the shimmy stopped, and we rotated and flew off. As we started the climb, I made a quick decision that since the engine and aircraft were working and flying just fine, it would be better to have a problem back at home in Tehachapi than to have it in Kanab where there are essentially no resources, so I decided to continue the flight. When we retracted the nose gear, we could see (through the window) that the casting and tire were still in place - nothing had come off - so I put off a decision on what to do for landing until we got closer to KTSP.

 

Coincidentally, or maybe not, the #1 Dynon ADAHRS decided that even when the wings were pretty obviously level and we were NOT slipping, we were in a 10 degree bank to the right. After reaching cruising altitude (10.5K ft) and contacting LA Center for FF, I started experimenting by switching the primary ADAHRS between #1 and #2. #2 was nominal - perfectly happy to show us what the real world was doing. A reboot of Screen #1 didn't change anything - moving back to ADAHRS #1 showed that it was still drunk. So we flew the rest of the CAVU flight back on ADAHRS #2, and obviously Dynon will be contacted about this anomaly. But it didn't affect the flight in any way (also given that I've got a backup G5 in the panel, so still had two working ADAHRS's).

 

After a couple of hours over the desert in perfect conditions, I started thinking about the landing plan - should I chance a landing with the gear down, without knowing what had caused the shimmy (loose NG6A? loose MKNG15A? Loose steering pivot axis? flat nose tire? broken something? who knows...) or land gear up. Gear up guarantees some damage to the nose, but it's relatively minor and easily fixable, while gear down MAY end up being a nothingburger, but also may end up with the same end result as Part 2 of:

 

 

and the subsequent 4 days. I eventually decided to land gear up and take the small repair hit that I knew would be coming. I explained to Deanie what was going to happen and why, and that we'd be perfectly fine but the plane would need some TLC afterwards.

 

After getting to KTSP, we entered the pattern (which was completely empty - no one anywhere near KTSP) and on downwind, I turned off electrical bus #1, which is the bus that the landing gear system is on. In this way I prevented the "auto-extend" system from putting the nose gear down when I didn't want it to. David Orr was right - the "disable" switch for the auto-extend system is a good idea, and while it's in the schematic I've made available for the system, I had not implemented it, thinking "when would I ever want to disable the nose gear extension". Idiot.

 

So, the 2nd best method was to fly on 1/2 the plane in the landing pattern - I lost the left EFIS, one EI, the transponder, and a number of other completely non-safety critical components on a VFR landing. But I will probably install a "disable" switch in some out of the way location just in case...

 

Anyway, we touched down at about 65 KIAS and I held the nose off the ground as long as I could as we decelerated, but at about 55 KIAS the nose came down hard. It's surprising how strong the smell of burning hockey puck is in the cockpit as the nose bumper disappears. After a few hundred feet of skidding, we came to a safe stop on the runway - I tried to extend the gear, but the bolts holding the clamping plate (NG-5) at the top of the strut had been worn away, so no go.

 

A handy bike rider who was on the parallel taxiway right when we landed helped us drag the plane to the hangar - took about 15 minutes - and a quick inspection showed surprisingly little damage - I'm thinking that 2 or three days of part time work will get the plane flying again. I still have to figure out why the shimmy occurred, so I'll be going over the whole nose gear system with a fine tooth comb.

 

Since every cloud has to have a silver lining (not being an optimist, I don't really buy into that, but gotta say it, right?) I will FINALLY take this third opportunity to install a slightly modified version of Wayne Hicks' Nose Bumper:

 

 

I will be installing the AL plate and the UHMW plate, but I will also install a small rubber puck in the center, as it has far more friction on the ground than the UHMW plate. I also plan to install some sort of sacrificial crush material under the rubber bumper. While I've had two nose gear up landings before (see the link above, as well as one more at KPVC after letting myself get distracted by my son and his friends yakking while we were landing) I had forgotten just how hard the jolt is when the completely non-resilient components on the nose hit the ground.

 

I'm going to try to find some replaceable crushable material, maybe 1/2" - 3/4" thick to put under the rubber bumper - this way, if/when it ever hits again, just that 1/2" of motion during the impact will substantially reduce the loads on the fuselage bottom and sides, minimizing damage.

 

Never a dull moment...

 

--

Marc J. Zeitlin                      marc_zeitlin@...

                                            http://www.cozybuilders.org/

Copyright © 2021                     Burnside Aerospace

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Terry Schubert
 

You might also consider a stiffer spring 
 
 
Terry Schubert
Central States Association Newsletter Editor


---------- Original Message ----------
From: "Del Schier" <cozypilot@...>
To: "'Izzy Briggs'" <INBRIGGS@...>, "'Marc J. Zeitlin'" <marc_zeitlin@...>, "'Canard Aviators'" <canard-aviators@canardzone.groups.io>, "'COZY Builders'" <cozy_builders@...>
Subject: Re: [c-a] COZY: Kanab Fly-In; Minor Incident - Part 2
Date: Tue, 7 Sep 2021 19:02:38 -0400

My shimmy a couple of landings ago was probably getting on the brakes at the time I hit a bump in our airparks somewhat bumpy runway dipping the nose down and taking out the caster.  I will try and hold the stick back when I get on the brakes, that may help.

 

Hope it doesn’t happen again.

 

Del Schier

Cozy IV N197DL

Cannon Creek Airpark 15FL

 

 

 

From: Izzy Briggs <inbriggs@...>
Sent: Tuesday, September 7, 2021 2:09 PM
To: 'Marc J. Zeitlin' <marc_zeitlin@...>; 'Canard Aviators' <canard-aviators@canardzone.groups.io>; 'COZY Builders' <cozy_builders@...>; cozypilot@...
Subject: Re: COZY: Kanab Fly-In; Minor Incident - Part 2

 

I've only experienced nosewheel shimmy in three situations:

  • Change in angle of the nosewheel, caused by either excessive weight, lower tire pressure or improperly underextended gear - Lots of things can change the angle of the nosewheel. Colder weather can make the fork stiffer so when it gets hot, maybe it sags a bit more? 
  • Loose castle nut on top - Failed to preflight for 4 lbs of drag....my fault.
  • Broken Fork  - Nothing I could do on this one.

In the most common condition, adding some tire pressure and lightening the front load can help.

 

In all cases, I'll try to keep the nosewheel off the ground and stay off the brakes until necessary. Hopefully the plane will be doing 40-50 instead of 70 when I actually have to use the brakes and put the nose down.  This means you'll have to accept a long rollout rather than trying to "make the turnoff at Charlie or Make Bravo". 

 

In my Aeronca, when my son and I would get in the plane and the tire pressure was low with full fuel tanks, I would sometimes get a wicked shimmy on landing. This was alleviated by pushing the stick forward (thus changing the angle temporarily) until the plane slowed down. One time we found the locknut on the top of the shaft was loose. Obvious cause of the shimmy there.

 

Not sure about the logic of intentionally doing a gear up landing. But if I ran my own shop and wanted to do the Wayne Hicks nose bumper anyway...what the hell. 


Izzy
(603)410-7277

 

 

On Tuesday, September 7, 2021, 09:39:45 AM EDT, cozypilot@... <cozypilot@...> wrote:

 

 

Marc and all,

 

Sorry about your incident.  I am commenting as I had my nose gear shimmy, the other day, for the first time since I have had the Cozy.  I have always had a slight shudder when braking hard and slow, < 40 k, but that seemed to be the main gear as looking at the nose wheel it was steady.

 

First thing is; “If it ain’t broke don’t fix it”.  I recently put a bolt through NG3 as I had had NG3 fail years ago. NG3 seemed tight but I put the bolt in anyway.  Also, on Terry Shubert’s recommendation, I put some flox between the metal of NG15.  NG15 seemed very secure as the paint wasn’t cracked anywhere.

 

After the work I flew to see some other canard guys at Sanford, FL and the landing was normal. Coming back to narrow airpark runway I had touched down and was starting to get on the brakes and had obvious severe shimmy. I got off the brakes and it got better and could see it through the window.  I used the brakes lightly and rolled over the car road into the paved overrun.

 

Getting back everything looked good on inspection and I measured just over 4 pounds of friction on the shimmy damper.  I don’t know what caused it but perhaps, since I have a momentary contact gear switch I may not have had it all the way down.  I do remember looking to see it was down but don’t remember if I checked the green light, however my gear warning should have been flashing and beeping if I wasn’t full down.

 

I flew it since with two landings, the first on a long wide runway, and it was completely normal on both landings.  I am not sure what to do or if it even can be fixed.  Maybe just the gear is resonating differently and some bump set it oscillating.  I am sure it wouldn’t hurt to put more caster in it, I have the minimum but that goes away when I hit the brakes hard and CG forward.

Del Schier

Cozy IV N197DL

Cannon Creek Airpark 15FL

 

 

 

From: cozy_builders@... <cozy_builders@...> On Behalf Of Marc J. Zeitlin
Sent: Monday, September 6, 2021 7:08 PM
To: Canard Aviators <canard-aviators@canardzone.groups.io>; COZY Builders <cozy_builders@...>
Subject: COZY: Kanab Fly-In; Minor Incident - Part 2

 

Folks:

 

Continued from Part 1:

 

We taxied to the end of runway 19 to take off to the south with a 2 kt. tailwind, downhill. KKNB's runway is 6200 ft. long, so with temps around 60F and us well below MGW, even a 6000 ft. DA didn't concern me with a tailwind. Maybe that was a stupid decision, in retrospect, given the required GS...

 

Anyway, after the runup, we pulled out onto the runway and accelerated. Everything felt nominal, but I wanted to get a bit more IAS prior to rotation just due to the DA, so I held the nose down as we passed through 72 KIAS. Just around 74 KIAS, we had a severe shimmy on the nose gear and as I relaxed forward pressure, the nose came off the ground, the shimmy stopped, and we rotated and flew off. As we started the climb, I made a quick decision that since the engine and aircraft were working and flying just fine, it would be better to have a problem back at home in Tehachapi than to have it in Kanab where there are essentially no resources, so I decided to continue the flight. When we retracted the nose gear, we could see (through the window) that the casting and tire were still in place - nothing had come off - so I put off a decision on what to do for landing until we got closer to KTSP.

 

Coincidentally, or maybe not, the #1 Dynon ADAHRS decided that even when the wings were pretty obviously level and we were NOT slipping, we were in a 10 degree bank to the right. After reaching cruising altitude (10.5K ft) and contacting LA Center for FF, I started experimenting by switching the primary ADAHRS between #1 and #2. #2 was nominal - perfectly happy to show us what the real world was doing. A reboot of Screen #1 didn't change anything - moving back to ADAHRS #1 showed that it was still drunk. So we flew the rest of the CAVU flight back on ADAHRS #2, and obviously Dynon will be contacted about this anomaly. But it didn't affect the flight in any way (also given that I've got a backup G5 in the panel, so still had two working ADAHRS's).

 

After a couple of hours over the desert in perfect conditions, I started thinking about the landing plan - should I chance a landing with the gear down, without knowing what had caused the shimmy (loose NG6A? loose MKNG15A? Loose steering pivot axis? flat nose tire? broken something? who knows...) or land gear up. Gear up guarantees some damage to the nose, but it's relatively minor and easily fixable, while gear down MAY end up being a nothingburger, but also may end up with the same end result as Part 2 of:

 

 

and the subsequent 4 days. I eventually decided to land gear up and take the small repair hit that I knew would be coming. I explained to Deanie what was going to happen and why, and that we'd be perfectly fine but the plane would need some TLC afterwards.

 

After getting to KTSP, we entered the pattern (which was completely empty - no one anywhere near KTSP) and on downwind, I turned off electrical bus #1, which is the bus that the landing gear system is on. In this way I prevented the "auto-extend" system from putting the nose gear down when I didn't want it to. David Orr was right - the "disable" switch for the auto-extend system is a good idea, and while it's in the schematic I've made available for the system, I had not implemented it, thinking "when would I ever want to disable the nose gear extension". Idiot.

 

So, the 2nd best method was to fly on 1/2 the plane in the landing pattern - I lost the left EFIS, one EI, the transponder, and a number of other completely non-safety critical components on a VFR landing. But I will probably install a "disable" switch in some out of the way location just in case...

 

Anyway, we touched down at about 65 KIAS and I held the nose off the ground as long as I could as we decelerated, but at about 55 KIAS the nose came down hard. It's surprising how strong the smell of burning hockey puck is in the cockpit as the nose bumper disappears. After a few hundred feet of skidding, we came to a safe stop on the runway - I tried to extend the gear, but the bolts holding the clamping plate (NG-5) at the top of the strut had been worn away, so no go.

 

A handy bike rider who was on the parallel taxiway right when we landed helped us drag the plane to the hangar - took about 15 minutes - and a quick inspection showed surprisingly little damage - I'm thinking that 2 or three days of part time work will get the plane flying again. I still have to figure out why the shimmy occurred, so I'll be going over the whole nose gear system with a fine tooth comb.

 

Since every cloud has to have a silver lining (not being an optimist, I don't really buy into that, but gotta say it, right?) I will FINALLY take this third opportunity to install a slightly modified version of Wayne Hicks' Nose Bumper:

 

 

I will be installing the AL plate and the UHMW plate, but I will also install a small rubber puck in the center, as it has far more friction on the ground than the UHMW plate. I also plan to install some sort of sacrificial crush material under the rubber bumper. While I've had two nose gear up landings before (see the link above, as well as one more at KPVC after letting myself get distracted by my son and his friends yakking while we were landing) I had forgotten just how hard the jolt is when the completely non-resilient components on the nose hit the ground.

 

I'm going to try to find some replaceable crushable material, maybe 1/2" - 3/4" thick to put under the rubber bumper - this way, if/when it ever hits again, just that 1/2" of motion during the impact will substantially reduce the loads on the fuselage bottom and sides, minimizing damage.

 

Never a dull moment...

 

--

Marc J. Zeitlin                      marc_zeitlin@...

                                            http://www.cozybuilders.org/

Copyright © 2021                     Burnside Aerospace

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Bob Holliston
 

Terry, good point. I flew my first Long EZ for a couple years with no spring at all, just a length of 3/4" round aluminum bar stock in its place. I believe that the nose gear strut flexes quite a bit. 


On Wed, Sep 8, 2021 at 6:01 PM Terry Schubert <jschuber@...> wrote:
You might also consider a stiffer spring 
 
 
Terry Schubert
Central States Association Newsletter Editor

---------- Original Message ----------
From: "Del Schier" <cozypilot@...>
To: "'Izzy Briggs'" <INBRIGGS@...>, "'Marc J. Zeitlin'" <marc_zeitlin@...>, "'Canard Aviators'" <canard-aviators@canardzone.groups.io>, "'COZY Builders'" <cozy_builders@...>
Subject: Re: [c-a] COZY: Kanab Fly-In; Minor Incident - Part 2
Date: Tue, 7 Sep 2021 19:02:38 -0400

My shimmy a couple of landings ago was probably getting on the brakes at the time I hit a bump in our airparks somewhat bumpy runway dipping the nose down and taking out the caster.  I will try and hold the stick back when I get on the brakes, that may help.

 

Hope it doesn’t happen again.

 

Del Schier

Cozy IV N197DL

Cannon Creek Airpark 15FL

 

 

 

From: Izzy Briggs <inbriggs@...>
Sent: Tuesday, September 7, 2021 2:09 PM
To: 'Marc J. Zeitlin' <marc_zeitlin@...>; 'Canard Aviators' <canard-aviators@canardzone.groups.io>; 'COZY Builders' <cozy_builders@...>; cozypilot@...
Subject: Re: COZY: Kanab Fly-In; Minor Incident - Part 2

 

I've only experienced nosewheel shimmy in three situations:

  • Change in angle of the nosewheel, caused by either excessive weight, lower tire pressure or improperly underextended gear - Lots of things can change the angle of the nosewheel. Colder weather can make the fork stiffer so when it gets hot, maybe it sags a bit more? 
  • Loose castle nut on top - Failed to preflight for 4 lbs of drag....my fault.
  • Broken Fork  - Nothing I could do on this one.

In the most common condition, adding some tire pressure and lightening the front load can help.

 

In all cases, I'll try to keep the nosewheel off the ground and stay off the brakes until necessary. Hopefully the plane will be doing 40-50 instead of 70 when I actually have to use the brakes and put the nose down.  This means you'll have to accept a long rollout rather than trying to "make the turnoff at Charlie or Make Bravo". 

 

In my Aeronca, when my son and I would get in the plane and the tire pressure was low with full fuel tanks, I would sometimes get a wicked shimmy on landing. This was alleviated by pushing the stick forward (thus changing the angle temporarily) until the plane slowed down. One time we found the locknut on the top of the shaft was loose. Obvious cause of the shimmy there.

 

Not sure about the logic of intentionally doing a gear up landing. But if I ran my own shop and wanted to do the Wayne Hicks nose bumper anyway...what the hell. 


Izzy
(603)410-7277

 

 

On Tuesday, September 7, 2021, 09:39:45 AM EDT, cozypilot@... <cozypilot@...> wrote:

 

 

Marc and all,

 

Sorry about your incident.  I am commenting as I had my nose gear shimmy, the other day, for the first time since I have had the Cozy.  I have always had a slight shudder when braking hard and slow, < 40 k, but that seemed to be the main gear as looking at the nose wheel it was steady.

 

First thing is; “If it ain’t broke don’t fix it”.  I recently put a bolt through NG3 as I had had NG3 fail years ago. NG3 seemed tight but I put the bolt in anyway.  Also, on Terry Shubert’s recommendation, I put some flox between the metal of NG15.  NG15 seemed very secure as the paint wasn’t cracked anywhere.

 

After the work I flew to see some other canard guys at Sanford, FL and the landing was normal. Coming back to narrow airpark runway I had touched down and was starting to get on the brakes and had obvious severe shimmy. I got off the brakes and it got better and could see it through the window.  I used the brakes lightly and rolled over the car road into the paved overrun.

 

Getting back everything looked good on inspection and I measured just over 4 pounds of friction on the shimmy damper.  I don’t know what caused it but perhaps, since I have a momentary contact gear switch I may not have had it all the way down.  I do remember looking to see it was down but don’t remember if I checked the green light, however my gear warning should have been flashing and beeping if I wasn’t full down.

 

I flew it since with two landings, the first on a long wide runway, and it was completely normal on both landings.  I am not sure what to do or if it even can be fixed.  Maybe just the gear is resonating differently and some bump set it oscillating.  I am sure it wouldn’t hurt to put more caster in it, I have the minimum but that goes away when I hit the brakes hard and CG forward.

Del Schier

Cozy IV N197DL

Cannon Creek Airpark 15FL

 

 

 

From: cozy_builders@... <cozy_builders@...> On Behalf Of Marc J. Zeitlin
Sent: Monday, September 6, 2021 7:08 PM
To: Canard Aviators <canard-aviators@canardzone.groups.io>; COZY Builders <cozy_builders@...>
Subject: COZY: Kanab Fly-In; Minor Incident - Part 2

 

Folks:

 

Continued from Part 1:

 

We taxied to the end of runway 19 to take off to the south with a 2 kt. tailwind, downhill. KKNB's runway is 6200 ft. long, so with temps around 60F and us well below MGW, even a 6000 ft. DA didn't concern me with a tailwind. Maybe that was a stupid decision, in retrospect, given the required GS...

 

Anyway, after the runup, we pulled out onto the runway and accelerated. Everything felt nominal, but I wanted to get a bit more IAS prior to rotation just due to the DA, so I held the nose down as we passed through 72 KIAS. Just around 74 KIAS, we had a severe shimmy on the nose gear and as I relaxed forward pressure, the nose came off the ground, the shimmy stopped, and we rotated and flew off. As we started the climb, I made a quick decision that since the engine and aircraft were working and flying just fine, it would be better to have a problem back at home in Tehachapi than to have it in Kanab where there are essentially no resources, so I decided to continue the flight. When we retracted the nose gear, we could see (through the window) that the casting and tire were still in place - nothing had come off - so I put off a decision on what to do for landing until we got closer to KTSP.

 

Coincidentally, or maybe not, the #1 Dynon ADAHRS decided that even when the wings were pretty obviously level and we were NOT slipping, we were in a 10 degree bank to the right. After reaching cruising altitude (10.5K ft) and contacting LA Center for FF, I started experimenting by switching the primary ADAHRS between #1 and #2. #2 was nominal - perfectly happy to show us what the real world was doing. A reboot of Screen #1 didn't change anything - moving back to ADAHRS #1 showed that it was still drunk. So we flew the rest of the CAVU flight back on ADAHRS #2, and obviously Dynon will be contacted about this anomaly. But it didn't affect the flight in any way (also given that I've got a backup G5 in the panel, so still had two working ADAHRS's).

 

After a couple of hours over the desert in perfect conditions, I started thinking about the landing plan - should I chance a landing with the gear down, without knowing what had caused the shimmy (loose NG6A? loose MKNG15A? Loose steering pivot axis? flat nose tire? broken something? who knows...) or land gear up. Gear up guarantees some damage to the nose, but it's relatively minor and easily fixable, while gear down MAY end up being a nothingburger, but also may end up with the same end result as Part 2 of:

 

 

and the subsequent 4 days. I eventually decided to land gear up and take the small repair hit that I knew would be coming. I explained to Deanie what was going to happen and why, and that we'd be perfectly fine but the plane would need some TLC afterwards.

 

After getting to KTSP, we entered the pattern (which was completely empty - no one anywhere near KTSP) and on downwind, I turned off electrical bus #1, which is the bus that the landing gear system is on. In this way I prevented the "auto-extend" system from putting the nose gear down when I didn't want it to. David Orr was right - the "disable" switch for the auto-extend system is a good idea, and while it's in the schematic I've made available for the system, I had not implemented it, thinking "when would I ever want to disable the nose gear extension". Idiot.

 

So, the 2nd best method was to fly on 1/2 the plane in the landing pattern - I lost the left EFIS, one EI, the transponder, and a number of other completely non-safety critical components on a VFR landing. But I will probably install a "disable" switch in some out of the way location just in case...

 

Anyway, we touched down at about 65 KIAS and I held the nose off the ground as long as I could as we decelerated, but at about 55 KIAS the nose came down hard. It's surprising how strong the smell of burning hockey puck is in the cockpit as the nose bumper disappears. After a few hundred feet of skidding, we came to a safe stop on the runway - I tried to extend the gear, but the bolts holding the clamping plate (NG-5) at the top of the strut had been worn away, so no go.

 

A handy bike rider who was on the parallel taxiway right when we landed helped us drag the plane to the hangar - took about 15 minutes - and a quick inspection showed surprisingly little damage - I'm thinking that 2 or three days of part time work will get the plane flying again. I still have to figure out why the shimmy occurred, so I'll be going over the whole nose gear system with a fine tooth comb.

 

Since every cloud has to have a silver lining (not being an optimist, I don't really buy into that, but gotta say it, right?) I will FINALLY take this third opportunity to install a slightly modified version of Wayne Hicks' Nose Bumper:

 

 

I will be installing the AL plate and the UHMW plate, but I will also install a small rubber puck in the center, as it has far more friction on the ground than the UHMW plate. I also plan to install some sort of sacrificial crush material under the rubber bumper. While I've had two nose gear up landings before (see the link above, as well as one more at KPVC after letting myself get distracted by my son and his friends yakking while we were landing) I had forgotten just how hard the jolt is when the completely non-resilient components on the nose hit the ground.

 

I'm going to try to find some replaceable crushable material, maybe 1/2" - 3/4" thick to put under the rubber bumper - this way, if/when it ever hits again, just that 1/2" of motion during the impact will substantially reduce the loads on the fuselage bottom and sides, minimizing damage.

 

Never a dull moment...

 

--

Marc J. Zeitlin                      marc_zeitlin@...

                                            http://www.cozybuilders.org/

Copyright © 2021                     Burnside Aerospace

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