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Clive J
Joined: 03 Nov 2007
Posts: 340
Location: UK
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 Posted: Fri Jun 01, 2012 12:58 am Post subject: Landing gear shimmy |
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Gerd, I think it's a very relevant point.
I did find it difficult to get the angle from the brake discs as they are on wuss. With any toe in or out the wheels will try and get away from each other or get closer to each other, that is until the grip from the tyres gives way and then they will re-just. Just what you need to set up some stability.
The other thing I wondered about was the bolting of the legs into the central beam. I have two bolts, one as high as I could get it and one as low as I could get it. Along with splay from the toe in or out we have twist in the gear leg. The bolting can only help this. What is the standard for the bolting? Two bolts what size? What sort of fit is the leg in the socket? Anything else?
Regards, Clive
P.S. I don’t have the shimmy thankfully though I don't know why, Esqual from 2003 with Arion legs from 2009
--
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geather
Joined: 06 Feb 2008
Posts: 23
Location: Mt Hutton Australia
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| Posted: Fri Jun 01, 2012 1:21 am Post subject: Landing gear shimmy |
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Gerd,
That's an awfully complex way to adjust wheel alignment.
Jason from Arion has a much simpler method (no chalk, plumbs, rulers, lasers or calculators!!). He showed me this when I was there last year in the builder assist program.
I did speak with Mark some time ago and he was hoping to include this method in the next Newsletter.
It goes something like this:
The wheel axels are hollow and perfectly perpendicular to the direction of travel. Sooo.......
Simply insert a tight fitting dowel into each axel such that the dowels meet in the centre of the plane under the fuselage (I removed the inside locating bolt of the axel to allow the dowel to fit further in the axel to be sure it was a perfect "extension" of the axel)
It is then easy to get a perfect zero toe just by eyeballing the dowels while twisting the gear legs.
To be more accurate - mount a string line across the plane on the wheel pant mounting brackets and align the dowels parallel to the string line.
To easy?
If you wanted toe in or toe out then that would be a fairly simple calculation along the line you have mentioned.
Mine is set to zero toe and I have not noticed any shimmy (but I've only done 5 hours)
Cheers
Geoff Eather (Kit 127) Australia
On 01/06/2012, at 6:29 PM, Gerd Nowack wrote:
[quote]
Dave
One important, maybe crucial detail I find in your list missing: the toe in.
Former statements in this group have mentioned it, and IMHO it plays a major role, too.
I have adjusted my toe in to 1/2 deg, measured with a laser gun sight pointer from the brake disks back to a dedicate plank that I put under the tail and centered with a plumb. I made markings for 0deg toe in by measuring from center of fuse (plumb again) to the point of the brake disk where I later put the laser pointer. This mark is toe in 0, you can easily calculate the distance from 0 to 1 or 1/2 deg with a scientific calculator or the internet( http://www.rapidtables.com/calc/math/Tan_Calculator.htm or an old slide rule by multiplying the tangent of your desired toe in angle with the distance from brake disk to measuring plank. Then make another pencil mark there - outboard of the 0-mark, when you want toe in, of course. Which is where your laser pointer should point.
This way you don`t have to make chalk lines all over the place and you can check unwanted airplane movement that would spoil your measurement by just leaving the plumb in place. And you can keep the plank for later measurements.
Coming to think of it : I made my adjustment without the wings on and of course no load , and should measure the toe in again with wings and fuel.
Please excuse if i sound teaching.I write all this because I hope we all might get some data basis. Then we can compare toe in of the shakers and the non-shakers and maybe get a hint.
Gerd
> Datum: Thu, 31 May 2012 06:58:21 -0500
> Von: "Dave Mccorquodale" <corky(at)hbci.com>
> An: lightning-list(at)matronics.com
> Betreff: Re: Re: Landing gear shimmy
> Earl
> This is certainly not a new subject. I built my Esqual in 05 and it has
> 810 hrs on it. Let me tell u what I have tried.
> 1. clamping "broom handles" to the legs-this worked the
> best
> 2. epoxy aluminum rods to the legs
> 3. epoxy fiberglass rods to the legs
> 4. wrapping legs with fiberglass
> 5. balance wheel pants- still have weights inside pants
> 6. remachined new struts a couple thousands thicker
> this helped but did not cure it
> 7. balanced my tires in water, with a shaft in wheel, buble
> balancer, spinning tires on aircraft
> 8. had video taken in 05 found it to be in mains not nose
> wheel after I built a springed nose gear, this worked well
> but did not fix problem
> 9. bought the best tires
> 10. replace all rims and brakes
>
> I only am trying to save u guys a lot of work, the only thing that worked
> for me was finding a spin balancer that would fit the small rims. Now I
> have no shimmy
> Flat spots on the tires cause it to shimmy also
>
> good luck
>
> Dave McCorquodale
> 167DM
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> ---
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ge |
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wb2ssj(at)rochester.rr.co
Guest
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| Posted: Fri Jun 01, 2012 3:04 am Post subject: Landing gear shimmy |
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Gerd, great idea. I did very same when I built mine 4 years ago. I will
measure again and send in the results. I have very little shimmey at about
20 miles an hour and only rarely. But its still bothers me when it dose
happen. But getting everyones alignment figures might help find the cure.
Tex
---
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n45bm(at)yahoo.com
Guest
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| Posted: Fri Jun 01, 2012 10:00 am Post subject: Landing gear shimmy |
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I used 1 1/2 degrees of toe in, even though the builder's manual calls for only one degree. So, we shall see how this works out. But my method of putting in the toe-in is slightly different from Gerd's
I purchased two 4 foot lengths of 1/2" diameter aluminum rod. I then inserted them into the main gear axles so that they met in the middle. Of course, I had to remove the 1/4" bolt that holds the axle to the gear leg and had the plane on the gear and in a level attitude.
Then, by using trigonometry, I can determine the lengths and angles of a triangle and know how much to twist the wheel to match the short side of the triangle (1 1/2 degrees) in the middle, under the fuselage. I then drilled the gear socket on that gear, matched the other gear's twist so the rod ends matched, and drilled the other gear socket. Schmart them Chinese, huh? Hope this helps you guys.
Bernardo Melendez, kit #110
--- On Fri, 6/1/12, Gerd Nowack <nowacklinden(at)gmx.de> wrote:
From: Gerd Nowack <nowacklinden(at)gmx.de>
Subject: Re: Re: Landing gear shimmy
To: lightning-list(at)matronics.com
Date: Friday, June 1, 2012, 3:29 AM
Dave
One important, maybe crucial detail I find in your list missing: the toe in
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nowacklinden(at)gmx.de
Guest
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| Posted: Fri Jun 01, 2012 11:50 am Post subject: Landing gear shimmy |
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Geoff,
Yes, you`re right, that sounds a lot simpler!
I guess this is another example of our friends at Arion finding a way to do something a little better or easier but forgetting to tell us homebuilders about it....
My initial problem was to do the gear alignment in my Aerospace ( 20 by
14ft). I thought I found a neat solution here.
But, hey, since its so simple to do the toe in measuring, I hope we all can get some data collected for one more step to a shakefree Lightning for all. Maybe somebody even feels a responsibility to do the (anonymized?) collecting of data.... - Yes, another row of dots here!
Oh, another thought: have you all noticed a change in shimmy or shimmy frequency with a heavier vs lighter aircraft?
Gerd
-------- Original-Nachricht --------
| Quote: | Datum: Fri, 1 Jun 2012 19:21:24 +1000
Von: Geoff Eather <geather(at)bigpond.net.au>
An: lightning-list(at)matronics.com
Betreff: Re: Re: Landing gear shimmy
|
[quote]
<geather(at)bigpond.net.au>
Gerd,
That's an awfully complex way to adjust wheel alignment.
Jason from Arion has a much simpler method (no chalk, plumbs, rulers,
lasers or calculators!!). He showed me this when I was there last year in the
builder assist program.
I did speak with Mark some time ago and he was hoping to include this
method in the next Newsletter.
It goes something like this:
The wheel axels are hollow and perfectly perpendicular to the direction of
travel. Sooo.......
Simply insert a tight fitting dowel into each axel such that the dowels
meet in the centre of the plane under the fuselage (I removed the inside
locating bolt of the axel to allow the dowel to fit further in the axel to be
sure it was a perfect "extension" of the axel)
It is then easy to get a perfect zero toe just by eyeballing the dowels
while twisting the gear legs.
To be more accurate - mount a string line across the plane on the wheel
pant mounting brackets and align the dowels parallel to the string line.
To easy?
If you wanted toe in or toe out then that would be a fairly simple
calculation along the line you have mentioned.
Mine is set to zero toe and I have not noticed any shimmy (but I've only
done 5 hours)
Cheers
Geoff Eather (Kit 127) Australia
On 01/06/2012, at 6:29 PM, Gerd Nowack wrote:
>
<nowacklinden(at)gmx.de>
>
> Dave
>
> One important, maybe crucial detail I find in your list missing: the toe
in.
> Former statements in this group have mentioned it, and IMHO it plays a
major role, too.
> I have adjusted my toe in to 1/2 deg, measured with a laser gun sight
pointer from the brake disks back to a dedicate plank that I put under the
tail and centered with a plumb. I made markings for 0deg toe in by measuring
from center of fuse (plumb again) to the point of the brake disk where I
later put the laser pointer. This mark is toe in 0, you can easily calculate
the distance from 0 to 1 or 1/2 deg with a scientific calculator or the
internet( http://www.rapidtables.com/calc/math/Tan_Calculator.htm or an old
slide rule by multiplying the tangent of your desired toe in angle with the
distance from brake disk to measuring plank. Then make another pencil mark
there - outboard of the 0-mark, when you want toe in, of course. Which is
where your laser pointer should point.
> This way you don`t have to make chalk lines all over the place and you
can check unwanted airplane movement that would spoil your measurement by
just leaving the plumb in place. And you can keep the plank for later
measurements.
> Coming to think of it : I made my adjustment without the wings on and of
course no load , and should measure the toe in again with wings and fuel.
>
> Please excuse if i sound teaching.I write all this because I hope we all
might get some data basis. Then we can compare toe in of the shakers and
the non-shakers and maybe get a hint.
>
> Gerd
>
>
>
>
>> Datum: Thu, 31 May 2012 06:58:21 -0500
>> Von: "Dave Mccorquodale" <corky(at)hbci.com>
>> An: lightning-list(at)matronics.com
>> Betreff: Re: Re: Landing gear shimmy
>
>> Earl
>> This is certainly not a new subject. I built my Esqual in 05 and it
has
>> 810 hrs on it. Let me tell u what I have tried.
>> 1. clamping "broom handles" to the legs-this worked the
>> best
>> 2. epoxy aluminum rods to the legs
>> 3. epoxy fiberglass rods to the legs
>> 4. wrapping legs with fiberglass
>> 5. balance wheel pants- still have weights inside pants
>> 6. remachined new struts a couple thousands thicker
>> this helped but did not cure it
>> 7. balanced my tires in water, with a shaft in wheel, buble
>> balancer, spinning tires on aircraft
>> 8. had video taken in 05 found it to be in mains not nose
>> wheel after I built a springed nose gear, this worked well
>> but did not fix problem
>> 9. bought the best tires
>> 10. replace all rims and brakes
>>
>> I only am trying to save u guys a lot of work, the only thing that
worked
>> for me was finding a spin balancer that would fit the small rims. Now
I
>> have no shimmy
>> Flat spots on the tires cause it to shimmy also
>>
>> good luck
>>
>> Dave McCorquodale
>> 167DM
>>
>>
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>> ---
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Jaythree
Joined: 01 Jun 2012
Posts: 3
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| Posted: Fri Jun 01, 2012 9:13 pm Post subject: Re: Landing gear shimmy |
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|
This forum is a gold mine! I'll start by confessing that with only six hours and twelve landings on my new Esqual (with Lightning upgrades) I managed to bend the nosegear leg on a soft turf runway. I bought the Esqual from the builder, who did a magnificent job and I feel worse about dinging his craftsmanship than anything else right now.
But to the point...shimmy. I did experience it on all landings at 35-45 mph rollout. Although the consensus on this forum is that mains gearlegs and/or alignment seem to be the gremlin, I'm wondering if a significant factor may b the angled nosegear trailing fork. Angling the fork aft-down creates a geometry in which the weight on the swivel wants to rotate the forks forward. It's like a ball on a ramp. I have never seen castoring trailing fork nosegear where the fork was not parallel to the ground, eg., Grumman. I don't understand the purpose of the unstable geometry on the Esqual/Lightning. At 35-45 mph, the balancing forces of weight, fairing weathervaning and flywheel momentum of the nosewheel would tend to create a perfect scenario for shimmy. Shimmy up front of course would translate to the mains. Any comments, positive or negative, appreciated.
| Bill Strahan wrote: | Hey, I've talked about this before, haven't I? I've had 3 big changes I wanted to make for a long time: 1) Fix fuel distribution issue. 2) Make some short wingtips. 3) Eliminate the landing gear shimmy.
I installed the flow straightener tube and vanes that Nick sent me about a year ago. That did an amazing job. Perfect? No. Good enough that I'm not considering installing fuel injection? Yep. So #1 is adressed.
I still need to make short wingtips, but my passenger yesterday asked "Why does it shake like that after you land?" GRRRRR.
So I bought an axe handle and started chatting with neighbors here on the airport about cutting and shaping it. I figured I'd buy a 1.125" ball cutter and put a radius in it. Kept putting that off because it didn't sound like fun.
Then it hit me: I really just need it stiffer in fore/aft flexing. And whatever stiffener I make needs to glue to the gear leg so it needs to be a very good fit. Nothing fits better than fiberglass built in-place!
I decided I would tape off the gear and lay up 3 laminations of 7oz cloth directly onto the back of the gear leg. I did that tonight, and it's curing. Tomorrow I'll sand the back of that and use some flock and 5 minute epoxy to attach a 1/8" thick piece of balsa wood that extends about 1.5" behind the gear. Once that's cured I'll lay up about 6 layers of cloth on both sides of the balsa, overlapping onto the section that's on the gear. So the gear shouldn't end up much stiffer since it only has 1/8" thickness between the 6 layer lamination, but it should be SUPER stiff across the 1.5" section.
So I should get that done tomorrow, and let it cure overnight. Then I'll pop it off the gear, trim it, and glue it onto the landing gear leg.
Any thoughts? Nick, any suggestions on the best adhesive to attach to the gear? Should I remove the paint or glue to the paint?
When I glue it I'll put a couple of zip ties around it to hold it while it cures, and leave them on just in case it ever comes loose.
Fingers crossed, I can report in a few days that I have eliminated the dang shimmy once and for all. |
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n45bm(at)yahoo.com
Guest
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| Posted: Sat Jun 02, 2012 5:36 am Post subject: Landing gear shimmy |
|
|
The old Cessna 150 I used to fly as a student also had nose wheel shimmy. It even had a gas strut to help solve that issue, with little help. So, what's new?
Bernardo
--- On Sat, 6/2/12, Jaythree <donaldberk(at)hotmail.com> wrote:
| Quote: |
From: Jaythree <donaldberk(at)hotmail.com>
Subject: Re: Landing gear shimmy
To: lightning-list(at)matronics.com
Date: Saturday, June 2, 2012, 12:13 AM
--> Lightning-List message posted by: "Jaythree" <[url=/mc/compose?to=donaldberk(at)hotmail.com]donaldberk(at)hotmail.com[/url]>
This forum is a gold mine! I'll start by confessing that with only six hours and twelve landings on my new Esqual (with Lightning upgrades) I managed to bend the nosegear leg on a soft turf runway. I bought the Esqual from the builder, who did a magnificent job and I feel worse about dinging his craftsmanship than anything else right now.
But to the point...shimmy. I did experience it on all landings at 35-45 mph rollout. Although the consensus on this forum is that mains gearlegs and/or alignment seem to be the gremlin, I'm wondering if a significant factor may b the angled nosegear trailing fork. Angling the fork aft-down creates a geometry in which the weight on the swivel wants to rotate the forks forward. It's like a ball on a ramp. I have never seen castoring trailing fork nosegear where the fork was not parallel to the ground, eg., Grumman. I don't understand the purpose of the unstable geometry on the Esqual/Lightning. At 35-45 mph, the balancing forces of weight, fairing weathervaning and flywheel momentum of the nosewheel would tend to create a perfect scenario for shimmy. Shimmy up front of course would translate to the mains. Any comments, positive or negative, appreciated.
Bill Strahan wrote:
| Quote: | Hey, I've talked about this before, haven't I? I've had 3 big changes I wanted to make for a long time: 1) Fix fuel distribution issue. 2) Make some short wingtips. 3) Eliminate the landing gear shimmy.
I installed the flow straightener tube and vanes that Nick sent me about a year ago. That did an amazing job. Perfect? No. Good enough that I'm not considering installing fuel injection? Yep. So #1 is adressed.
I still need to make short wingtips, but my passenger yesterday asked "Why does it shake like that after you land?" GRRRRR.
So I bought an axe handle and started chatting with neighbors here on the airport about cutting and shaping it. I figured I'd buy a 1.125" ball cutter and put a radius in it. Kept putting that off because it didn't sound like fun.
Then it hit me: I really just need it stiffer in fore/aft flexing. And whatever stiffener I make needs to glue to the gear leg so it needs to be a very good fit. Nothing fits better than fiberglass built in-place!
I decided I would tape off the gear and lay up 3 laminations of 7oz cloth directly onto the back of the gear leg. I did that tonight, and it's curing. Tomorrow I'll sand the back of that and use some flock and 5 minute epoxy to attach a 1/8" thick piece of balsa wood that extends about 1.5" behind the gear. Once that's cured I'll lay up about 6 layers of cloth on both sides of the balsa, overlapping onto the section that's on the gear. So the gear shouldn't end up much stiffer since it only has 1/8" thickness between the 6 layer lamination, but it should be SUPER stiff across the 1.5" section.
So I should get that done tomorrow, and let it cure overnight. Then I'll pop it off the gear, trim it, and glue it onto the landing gear leg.
Any thoughts? Nick, any suggestions on the best adhesive to attach to the gear? Should I remove the paint or glue to the paint?
When I glue it I'll put a couple of zip ties around it to hold it while it cures, and leave them on just in case it ever comes loose.
Fingers crossed, I can report in a few days that I have eliminated the dang shimmy once and for all.
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Jaythree
Joined: 01 Jun 2012
Posts: 3
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| Posted: Sat Jun 02, 2012 7:13 am Post subject: Re: Landing gear shimmy |
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Well, the geometry and physics can be different for every shimmy, which is a mass oscillation. . I was just talking about theEsqual/Lightning.
[quote="n45bm(at)yahoo.com"]The old Cessna 150 I used to fly as a student also had nose wheel shimmy. It even had a gas strut to help solve that issue, with little help. So, what's new?
Bernardo
--- On Sat, 6/2/12, Jaythree <donaldberk> wrote:
| Quote: |
From: Jaythree <donaldberk>
Subject: Re: Landing gear shimmy
To: lightning-list(at)matronics.com
Date: Saturday, June 2, 2012, 12:13 AM
--> Lightning-List message posted by: "Jaythree" <url>
This forum is a gold mine! I'll start by confessing that with only six hours and twelve landings on my new Esqual (with Lightning upgrades) I managed to bend the nosegear leg on a soft turf runway. I bought the Esqual from the builder, who did a magnificent job and I feel worse about dinging his craftsmanship than anything else right now.
But to the point...shimmy. I did experience it on all landings at 35-45 mph rollout. Although the consensus on this forum is that mains gearlegs and/or alignment seem to be the gremlin, I'm wondering if a significant factor may b the angled nosegear trailing fork. Angling the fork aft-down creates a geometry in which the weight on the swivel wants to rotate the forks forward. It's like a ball on a ramp. I have never seen castoring trailing fork nosegear where the fork was not parallel to the ground, eg., Grumman. I don't understand the purpose of the unstable geometry on the Esqual/Lightning. At 35-45 mph, the balancing forces of weight, fairing weathervaning and flywheel momentum of the nosewheel would tend to create a perfect scenario for shimmy. Shimmy up front of course would translate to the mains. Any comments, positive or negative, appreciated.
Bill Strahan wrote:
| Quote: | Hey, I've talked about this before, haven't I? I've had 3 big changes I wanted to make for a long time: 1) Fix fuel distribution issue. 2) Make some short wingtips. 3) Eliminate the landing gear shimmy.
I installed the flow straightener tube and vanes that Nick sent me about a year ago. That did an amazing job. Perfect? No. Good enough that I'm not considering installing fuel injection? Yep. So #1 is adressed.
I still need to make short wingtips, but my passenger yesterday asked "Why does it shake like that after you land?" GRRRRR.
So I bought an axe handle and started chatting with neighbors here on the airport about cutting and shaping it. I figured I'd buy a 1.125" ball cutter and put a radius in it. Kept putting that off because it didn't sound like fun.
Then it hit me: I really just need it stiffer in fore/aft flexing. And whatever stiffener I make needs to glue to the gear leg so it needs to be a very good fit. Nothing fits better than fiberglass built in-place!
I decided I would tape off the gear and lay up 3 laminations of 7oz cloth directly onto the back of the gear leg. I did that tonight, and it's curing. Tomorrow I'll sand the back of that and use some flock and 5 minute epoxy to attach a 1/8" thick piece of balsa wood that extends about 1.5" behind the gear. Once that's cured I'll lay up about 6 layers of cloth on both sides of the balsa, overlapping onto the section that's on the gear. So the gear shouldn't end up much stiffer since it only has 1/8" thickness between the 6 layer lamination, but it should be SUPER stiff across the 1.5" section.
So I should get that done tomorrow, and let it cure overnight. Then I'll pop it off the gear, trim it, and glue it onto the landing gear leg.
Any thoughts? Nick, any suggestions on the best adhesive to attach to the gear? Should I remove the paint or glue to the paint?
When I glue it I'll put a couple of zip ties around it to hold it while it cures, and leave them on just in case it ever comes loose.
Fingers crossed, I can report in a few days that I have eliminated the dang shimmy once and for all.
|
Read this topic online here:
http://forums.matronics.com/viewtosp; --> http://www.matronics.com/Navigator?Lightning-Lis --> http://www.matronics.c===================
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Clive J
Joined: 03 Nov 2007
Posts: 340
Location: UK
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| Posted: Sat Jun 02, 2012 7:24 am Post subject: Landing gear shimmy |
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I had the angled leg on the Esqual for the first 30 hours, no shimmy but did make the steering a little twitchy. I have the lightning one on now thankfully.
Pulling the plane around the hangar it was off like a supermarket trolley.
Regarding the shimmy, does it promote tyre wear?
From: owner-lightning-list-server(at)matronics.com [mailto:owner-lightning-list-server(at)matronics.com] On Behalf Of Bernard Melendez, Jr.
Sent: 02 June 2012 14:36
To: lightning-list(at)matronics.com
Subject: Re: Re: Landing gear shimmy
The old Cessna 150 I used to fly as a student also had nose wheel shimmy. It even had a gas strut to help solve that issue, with little help. So, what's new?
Bernardo
--- On Sat, 6/2/12, Jaythree <donaldberk(at)hotmail.com (donaldberk(at)hotmail.com)> wrote:
From: Jaythree <donaldberk(at)hotmail.com (donaldberk(at)hotmail.com)>
Subject: Re: Landing gear shimmy
To: lightning-list(at)matronics.com (lightning-list(at)matronics.com)
Date: Saturday, June 2, 2012, 12:13 AM
--> Lightning-List message posted by: "Jaythree" <[url=/mc/compose?to=donaldberk(at)hotmail.com]donaldberk(at)hotmail.com[/url]>
This forum is a gold mine! I'll start by confessing that with only six hours and twelve landings on my new Esqual (with Lightning upgrades) I managed to bend the nosegear leg on a soft turf runway. I bought the Esqual from the builder, who did a magnificent job and I feel worse about dinging his craftsmanship than anything else right now.
But to the point...shimmy. I did experience it on all landings at 35-45 mph rollout. Although the consensus on this forum is that mains gearlegs and/or alignment seem to be the gremlin, I'm wondering if a significant factor may b the angled nosegear trailing fork. Angling the fork aft-down creates a geometry in which the weight on the swivel wants to rotate the forks forward. It's like a ball on a ramp. I have never seen castoring trailing fork nosegear where the fork was not parallel to the ground, eg., Grumman. I don't understand the purpose of the unstable geometry on the Esqual/Lightning. At 35-45 mph, the balancing forces of weight, fairing weathervaning and flywheel momentum of the nosewheel would tend to create a perfect scenario for shimmy. Shimmy up front of course would translate to the mains. Any comments, positive or negative, appreciated.
Bill Strahan wrote:
| Quote: | Hey, I've talked about this before, haven't I? I've had 3 big changes I wanted to make for a long time: 1) Fix fuel distribution issue. 2) Make some short wingtips. 3) Eliminate the landing gear shimmy.
I installed the flow straightener tube and vanes that Nick sent me about a year ago. That did an amazing job. Perfect? No. Good enough that I'm not considering installing fuel injection? Yep. So #1 is adressed.
I still need to make short wingtips, but my passenger yesterday asked "Why does it shake like that after you land?" GRRRRR.
So I bought an axe handle and started chatting with neighbors here on the airport about cutting and shaping it. I figured I'd buy a 1.125" ball cutter and put a radius in it. Kept putting that off because it didn't sound like fun.
Then it hit me: I really just need it stiffer in fore/aft flexing. And whatever stiffener I make needs to glue to the gear leg so it needs to be a very good fit. Nothing fits better than fiberglass built in-place!
I decided I would tape off the gear and lay up 3 laminations of 7oz cloth directly onto the back of the gear leg. I did that tonight, and it's curing. Tomorrow I'll sand the back of that and use some flock and 5 minute epoxy to attach a 1/8" thick piece of balsa wood that extends about 1.5" behind the gear. Once that's cured I'll lay up about 6 layers of cloth on both sides of the balsa, overlapping onto the section that's on the gear. So the gear shouldn't end up much stiffer since it only has 1/8" thickness between the 6 layer lamination, but it should be SUPER stiff across the 1.5" section.
So I should get that done tomorrow, and let it cure overnight. Then I'll pop it off the gear, trim it, and glue it onto the landing gear leg.
Any thoughts? Nick, any suggestions on the best adhesive to attach to the gear? Should I remove the paint or glue to the paint?
When I glue it I'll put a couple of zip ties around it to hold it while it cures, and leave them on just in case it ever comes loose.
Fingers crossed, I can report in a few days that I have eliminated the dang shimmy once and for all.
|
Read this topic online here:
http://forums.matronics.com/viewtosp; --> http://www.matronics.com/Navigator?Lightning-Lis --> http://www.matronics.c===================
| Quote: | | http://www.matronics.com/Navigator?Lightning-List |
01234567
[quote][b]
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Jaythree
Joined: 01 Jun 2012
Posts: 3
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| Posted: Sat Jun 02, 2012 9:03 pm Post subject: Re: Landing gear shimmy |
|
|
Well, the geometry and physics can be different for every shimmy, which is a mass oscillation. . I was just talking about theEsqual/Lightning.
[quote="n45bm(at)yahoo.com"]The old Cessna 150 I used to fly as a student also had nose wheel shimmy. It even had a gas strut to help solve that issue, with little help. So, what's new?
Bernardo
--- On Sat, 6/2/12, Jaythree <donaldberk> wrote:
| Quote: |
From: Jaythree <donaldberk>
Subject: Re: Landing gear shimmy
To: lightning-list(at)matronics.com
Date: Saturday, June 2, 2012, 12:13 AM
--> Lightning-List message posted by: "Jaythree" <url>
This forum is a gold mine! I'll start by confessing that with only six hours and twelve landings on my new Esqual (with Lightning upgrades) I managed to bend the nosegear leg on a soft turf runway. I bought the Esqual from the builder, who did a magnificent job and I feel worse about dinging his craftsmanship than anything else right now.
But to the point...shimmy. I did experience it on all landings at 35-45 mph rollout. Although the consensus on this forum is that mains gearlegs and/or alignment seem to be the gremlin, I'm wondering if a significant factor may b the angled nosegear trailing fork. Angling the fork aft-down creates a geometry in which the weight on the swivel wants to rotate the forks forward. It's like a ball on a ramp. I have never seen castoring trailing fork nosegear where the fork was not parallel to the ground, eg., Grumman. I don't understand the purpose of the unstable geometry on the Esqual/Lightning. At 35-45 mph, the balancing forces of weight, fairing weathervaning and flywheel momentum of the nosewheel would tend to create a perfect scenario for shimmy. Shimmy up front of course would translate to the mains. Any comments, positive or negative, appreciated.
Bill Strahan wrote:
| Quote: | Hey, I've talked about this before, haven't I? I've had 3 big changes I wanted to make for a long time: 1) Fix fuel distribution issue. 2) Make some short wingtips. 3) Eliminate the landing gear shimmy.
I installed the flow straightener tube and vanes that Nick sent me about a year ago. That did an amazing job. Perfect? No. Good enough that I'm not considering installing fuel injection? Yep. So #1 is adressed.
I still need to make short wingtips, but my passenger yesterday asked "Why does it shake like that after you land?" GRRRRR.
So I bought an axe handle and started chatting with neighbors here on the airport about cutting and shaping it. I figured I'd buy a 1.125" ball cutter and put a radius in it. Kept putting that off because it didn't sound like fun.
Then it hit me: I really just need it stiffer in fore/aft flexing. And whatever stiffener I make needs to glue to the gear leg so it needs to be a very good fit. Nothing fits better than fiberglass built in-place!
I decided I would tape off the gear and lay up 3 laminations of 7oz cloth directly onto the back of the gear leg. I did that tonight, and it's curing. Tomorrow I'll sand the back of that and use some flock and 5 minute epoxy to attach a 1/8" thick piece of balsa wood that extends about 1.5" behind the gear. Once that's cured I'll lay up about 6 layers of cloth on both sides of the balsa, overlapping onto the section that's on the gear. So the gear shouldn't end up much stiffer since it only has 1/8" thickness between the 6 layer lamination, but it should be SUPER stiff across the 1.5" section.
So I should get that done tomorrow, and let it cure overnight. Then I'll pop it off the gear, trim it, and glue it onto the landing gear leg.
Any thoughts? Nick, any suggestions on the best adhesive to attach to the gear? Should I remove the paint or glue to the paint?
When I glue it I'll put a couple of zip ties around it to hold it while it cures, and leave them on just in case it ever comes loose.
Fingers crossed, I can report in a few days that I have eliminated the dang shimmy once and for all.
|
Read this topic online here:
http://forums.matronics.com/viewtosp; --> http://www.matronics.com/Navigator?Lightning-Lis --> http://www.matronics.c===================
|
| | - The Matronics Lightning-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Lightning-List |
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