Kanab Fly-In; Minor Incident - Part 2


Marc J. Zeitlin
 

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


David A Froble
 

On 9/6/2021 7:08 PM, Marc J. Zeitlin wrote:
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.
Did you consider that the shimmy might have been caused by the higher speed?

Not going to second guess, any landing you walk away from is a good landing, if the aircraft is usable, that's a bonus ...

--
David Froble Tel: 724-529-0450
Dave Froble Enterprises, Inc. E-Mail: davef@tsoft-inc.com
DFE Ultralights, Inc.
170 Grimplin Road
Vanderbilt, PA 15486


Marc J. Zeitlin
 

David A Froble wrote:

Marc Zeitlin wrote:
>... 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.
 
Did you consider that the shimmy might have been caused by the higher speed?

I did, which is why I said:

"Maybe that was a stupid decision, in retrospect, given the required GS..."

Not going to second guess, any landing you walk away from is a good landing, if the aircraft is usable, that's a bonus ...

The problem was that while that MAY have been the reason (or a contributor) to the shimmy, I couldn't know exactly what was going on with the gear, and in this case, discretion, and a guaranteed small repair and safe landing, was the better part of valor.

Also, under the conditions listed, 74 KIAS is about 81 KTAS, and with a 2 kt tailwind, my GS would have been about 83 kts. Which is not any higher than I've taken off many times before, particularly when at high DA's and high GW's. So my though process was that it probably wasn't JUST the higher GS as the cause.

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


skovbjerg
 

Marc,
I have had the opportunity to consider a sacrifical material for future “where the nose meet the road” events. Choice fell on hard maple which should do the job without creating any additional dangers.
Good luck
Jay

On Sep 6, 2021, at 16:10, Marc J. Zeitlin <marc.j.zeitlin@...> wrote:


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


Rick Hall
 



On 9/6/2021 5:08 PM, Marc J. Zeitlin wrote:
Folks:
...   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

You probably had at least one take off before touch down, and subsequent take off, at KKNB. I offer the following for your enjoyment.

Had a fella here at LMO experience shimmy on landing after a condition inspection. He removed the nose wheel, all looked good, so he re-greased and reinstalled the nose wheel. Same issue. Asked me for an opinion, I said maybe the spacer is a tad too long and needs a slight shave. I skimmed .001"-.002" off one face and he reinstalled. Another test flight, and it still shimmied.

I said "let me remove the wheel", and I did. Retired to my hangar and I removed the spacers. In a nut shell, it was grease... lots of grease. Enough grease that the spacers never contacted each other, the sleeve over the spacers is so tightly machined that the grease did not smoosh out when tightening the axle bolt. Clears as mud? I thought so.

Point being, grease the bearings only, not everything inside the wheel.

Good to see you and Deanie :)

Rick


Marc J. Zeitlin
 

Jay Skovbjerg wrote:

I have had the opportunity to consider a sacrifical material for future “where the nose meet the road” events. Choice fell on hard maple which should do the job without creating any additional dangers.

Yep - that's what SS1 used, as well (SS2 went with some sort of laminated composite wood product - don't remember exactly what it was).

However, the issue with our planes (or at least the MKIV's) isn't necessarily finding something that can withstand the scraping - Aluminum, maple, some hard plastics, even some rubbers, seem to work pretty well at protecting the nose from scrapes.

For those of us with pre-molded nose bowls (maybe these are only available for the MKIV's - I'm not sure) which are very thin and basically almost cosmetic only, there's little support forward of F-5 to absorb the impact loads when the nose drops 2.5 ft with two folks in the front and with the canard also pushing down hard from the negative AOA.

So I'm not only looking for something that can withstand the scraping, but something to be akin to a "shock absorber" to give even just 1/2" of deflection during the impact, to substantially lessen the maximum "G" loads imparted into the rest of the structure. My rubber bumper crushed the bottom of the nose bowl, as well as the rib inside, upwards about 1/2". This absorbed the impact loads, protecting the rest of the nose structure (nothing aft of F-5 was damaged in any way, nor was anything above the bottom of the nose bowl and rib), but it still caused enough damage to need a few days to repair.

If there's some easily replaceable crush material that can go above the <maple, whatever>, then a nose gear up landing would merely involve replacing the <whatever> and the crush material - maybe 30 minutes of work - and be back in business - no damage to anything else. I've had a few folks suggest some crush materials, such as AL honeycomb - hopefully I'll be able to come up with something...

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


 

Marc-
With a been there done that:
Visualizing in my mind I saw an aluminum 'L' (or two? one on each side), the 'long' leg aft against the strut (gear retracted) or NG5 backing plate, with the short leg holding the crush material with a bit of space. So the scenario is nose drops, the short leg has a bit of 'aft' lean due to nose down attitude, which makes contact and bends aft and up, compressing the crush material.
The destructive plastic bending of the aluminum spreads the contact load over a few milliseconds, as it bends back and up, which is finally absorbed by the 'crush' material. The skid sacrificial material can be mounted between the two sacrificial L's (0.25"?). I could see this integrated as a mod into Wayne Hicks' beautiful version.
FWIW.
-Christian
 
--        www.BrilliantDesignOnline.com
Solidworks Design & CNC Plasma Cutting

         -a division of-
www.AlpineWorldwide.com
       "We build ideas.."


On Tue, Sep 7, 2021 at 11:10 PM Marc J. Zeitlin <marc.j.zeitlin@...> wrote:
Jay Skovbjerg wrote:

I have had the opportunity to consider a sacrifical material for future “where the nose meet the road” events. Choice fell on hard maple which should do the job without creating any additional dangers.

Yep - that's what SS1 used, as well (SS2 went with some sort of laminated composite wood product - don't remember exactly what it was).

However, the issue with our planes (or at least the MKIV's) isn't necessarily finding something that can withstand the scraping - Aluminum, maple, some hard plastics, even some rubbers, seem to work pretty well at protecting the nose from scrapes.

For those of us with pre-molded nose bowls (maybe these are only available for the MKIV's - I'm not sure) which are very thin and basically almost cosmetic only, there's little support forward of F-5 to absorb the impact loads when the nose drops 2.5 ft with two folks in the front and with the canard also pushing down hard from the negative AOA.

So I'm not only looking for something that can withstand the scraping, but something to be akin to a "shock absorber" to give even just 1/2" of deflection during the impact, to substantially lessen the maximum "G" loads imparted into the rest of the structure. My rubber bumper crushed the bottom of the nose bowl, as well as the rib inside, upwards about 1/2". This absorbed the impact loads, protecting the rest of the nose structure (nothing aft of F-5 was damaged in any way, nor was anything above the bottom of the nose bowl and rib), but it still caused enough damage to need a few days to repair.

If there's some easily replaceable crush material that can go above the <maple, whatever>, then a nose gear up landing would merely involve replacing the <whatever> and the crush material - maybe 30 minutes of work - and be back in business - no damage to anything else. I've had a few folks suggest some crush materials, such as AL honeycomb - hopefully I'll be able to come up with something...

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