The Murphy Builders Site

Wow! Tough one. Jesse, is that your normal spring shape? It looks like a
greater angle than my aronca spring and I thought that's what you had as
well. I know there are many flying for a long time but I still say the TW
hardware on our rebels seems pretty light! Good Luck. Craig


----- Original Message -----
From: "Jesse Jenks" <jessejenks@hotmail.com>
To: "Builders list" <rebel-builders@dcsol.com>
Sent: Monday, June 06, 2011 2:27 PM
Subject: [rebel-builders] Tailwheel leaf springs/shimmey!

Have been struggling with a bad shimmy that I thought I had mostly figured
out...until yesterday. I installed a 2 leaf steel spring in place of the
fiberglass one and had been having good luck for the past 40 hours despite
needing to have it re bent to get a more horizontal castor angle.
Yesterday it shimmied bad enough to bend the clamp assembly (see pics) Now
I'm back to the drawing board and considering all options. I will need to
fix or remake/reinforce the tail strut support angle as well as modify the
leaf springs or replace them with something else. Any ideas? I had a
beautiful weekend of flying before the destructive shimmy, so I have that
to motivate me to get it fixed. Also, I now know that I can successfully
hold the tail up with brakes until slowing to a slow taxi speed. I got it
to the home airport after the bad shimmy happened at a fuel stop.
thanks.
Jesse

Tailwheel leaf springsshimmey!
http://cid-f0168b2944a206d0.skydrive.li ... GXyc8PA%24




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Looking at the third photo, it appears that your tailwheel king post
tilts back, i.e., the top of the post is aft of the bottom of the
post. If it was that way all along, it will almost guarantee serious
shimmy. As you probably know, the king post needs to be vertical or,
at worst, with the top a smidge forward of the bottom. You can see how
I set up a modified Champ spring for a similar wheel at
http://n254mr.com/node/1492 . I had to adjust two of the bends to get
it to A) fit relatively flat in the clamp, and B) get the king post
vertical. Perhaps that will be helpful.

Ron


On Mon, Jun 6, 2011 at 3:27 PM, Jesse Jenks <jessejenks@hotmail.com> wrote:

Have been struggling with a bad shimmy that I thought I had mostly figured out...until yesterday. I installed a 2 leaf steel spring in place of the fiberglass one and had been having good luck for the past 40 hours despite needing to have it re bent to get a more horizontal castor angle. Yesterday it shimmied bad enough to bend the clamp assembly (see pics) Now I'm back to the drawing board and considering all options. I will need to fix or remake/reinforce the tail strut support angle as well as modify the leaf springs or replace them with something else. Any ideas? I had a beautiful weekend of flying before the destructive shimmy, so I have that to motivate me to get it fixed. Also, I now know that I can successfully hold the tail up with brakes until slowing to a slow taxi speed. I got it to the home airport after the bad shimmy happened at a fuel stop.
thanks.
Jesse

Tailwheel leaf springsshimmey!
http://cid-f0168b2944a206d0.skydrive.li ... GXyc8PA%24

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Ron,
The castor angle is definitely excessive and I was planning to rebend it, but I was operating with the understanding, after long discussions with Alaskan bushwheels and web research, that a slight positive angle was desirable and that negative angles are the major contributing factor to shimmy. I had flown it like that for 40 hours without shimmy until recently. It makes the tail want to go sideways easily with the castor angle so steep though for sure.

From: rshannon@cruzcom.com
Date: Mon, 6 Jun 2011 17:11:07 -0700
Subject: Re: [rebel-builders] Tailwheel leaf springs/shimmey!
To: rebel-builders@dcsol.com

Looking at the third photo, it appears that your tailwheel king post
tilts back, i.e., the top of the post is aft of the bottom of the
post. If it was that way all along, it will almost guarantee serious
shimmy. As you probably know, the king post needs to be vertical or,
at worst, with the top a smidge forward of the bottom. You can see how
I set up a modified Champ spring for a similar wheel at
http://n254mr.com/node/1492 . I had to adjust two of the bends to get
it to A) fit relatively flat in the clamp, and B) get the king post
vertical. Perhaps that will be helpful.

Ron


On Mon, Jun 6, 2011 at 3:27 PM, Jesse Jenks <jessejenks@hotmail.com> wrote:

Have been struggling with a bad shimmy that I thought I had mostly figured out...until yesterday. I installed a 2 leaf steel spring in place of the fiberglass one and had been having good luck for the past 40 hours despite needing to have it re bent to get a more horizontal castor angle. Yesterday it shimmied bad enough to bend the clamp assembly (see pics) Now I'm back to the drawing board and considering all options. I will need to fix or remake/reinforce the tail strut support angle as well as modify the leaf springs or replace them with something else. Any ideas? I had a beautiful weekend of flying before the destructive shimmy, so I have that to motivate me to get it fixed. Also, I now know that I can successfully hold the tail up with brakes until slowing to a slow taxi speed. I got it to the home airport after the bad shimmy happened at a fuel stop.
thanks.
Jesse

Tailwheel leaf springsshimmey!
http://cid-f0168b2944a206d0.skydrive.li ... GXyc8PA%24

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Craig, Sorry to hear the sad news. It must be tough.
My spring is from ABW. They said it is one that they make for the Scout. It was originally 3 leafs but I took one off mostly to get the thickness the same as the fiberglass one so I didn't have to remake the saddle and tail struts, but also because I figured the scout is quite a bit heavier than a Rebel. I am going to beef up the bottom angle, probably make it from 1/4" instead of 1/8". Will have to mill down to 1/8 where the struts attach.

From: snowyrvr@mtaonline.net
To: rebel-builders@dcsol.com
Subject: Re: [rebel-builders] Tailwheel leaf springs/shimmey!
Date: Mon, 6 Jun 2011 16:07:22 -0800

Wow! Tough one. Jesse, is that your normal spring shape? It looks like a
greater angle than my aronca spring and I thought that's what you had as
well. I know there are many flying for a long time but I still say the TW
hardware on our rebels seems pretty light! Good Luck. Craig


----- Original Message -----
From: "Jesse Jenks" <jessejenks@hotmail.com>
To: "Builders list" <rebel-builders@dcsol.com>
Sent: Monday, June 06, 2011 2:27 PM
Subject: [rebel-builders] Tailwheel leaf springs/shimmey!

Have been struggling with a bad shimmy that I thought I had mostly figured
out...until yesterday. I installed a 2 leaf steel spring in place of the
fiberglass one and had been having good luck for the past 40 hours despite
needing to have it re bent to get a more horizontal castor angle.
Yesterday it shimmied bad enough to bend the clamp assembly (see pics) Now
I'm back to the drawing board and considering all options. I will need to
fix or remake/reinforce the tail strut support angle as well as modify the
leaf springs or replace them with something else. Any ideas? I had a
beautiful weekend of flying before the destructive shimmy, so I have that
to motivate me to get it fixed. Also, I now know that I can successfully
hold the tail up with brakes until slowing to a slow taxi speed. I got it
to the home airport after the bad shimmy happened at a fuel stop.
thanks.
Jesse

Tailwheel leaf springsshimmey!
http://cid-f0168b2944a206d0.skydrive.li ... GXyc8PA%24




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I just uploaded an article including diagrams of tailwheel geometry written
by a long-term experienced tailwheel pilot who himself had shimmy problems.
The article can be found in "Area 404-General Documentation." If anyone
would like me to email them this PDF file directly please drop me an email
at tedwaltman@gmail.com

Ted

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of Jesse
Jenks
Sent: Monday, June 06, 2011 4:28 PM
To: Builders list
Subject: [rebel-builders] Tailwheel leaf springs/shimmey!


Have been struggling with a bad shimmy that I thought I had mostly figured
out...until yesterday. I installed a 2 leaf steel spring in place of the
fiberglass one and had been having good luck for the past 40 hours despite
needing to have it re bent to get a more horizontal castor angle. Yesterday
it shimmied bad enough to bend the clamp assembly (see pics) Now I'm back to
the drawing board and considering all options. I will need to fix or
remake/reinforce the tail strut support angle as well as modify the leaf
springs or replace them with something else. Any ideas? I had a beautiful
weekend of flying before the destructive shimmy, so I have that to motivate
me to get it fixed. Also, I now know that I can successfully hold the tail
up with brakes until slowing to a slow taxi speed. I got it to the home
airport after the bad shimmy happened at a fuel stop.
thanks.
Jesse

Tailwheel leaf springsshimmey!
http://cid-f0168b2944a206d0.skydrive.li ... se&resid=F
0168B2944A206D0!648&type=5&Bpub=SDX.Photos&Bsrc=Photomail&authkey=wYW1GXyc8P
A%24




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A good article but unfortunately it is not quite as simple as this
explanation. Lack of torsional rigidity of the Rebel leaf spring
contributes mightily to our shimmy issues. Ideally the pivot angle
should not be free to rotate left and right. Flat leaf springs are not
very torsionally rigid although multileaf springs that are clamped
together are better than a thin leaf. Two steel leaves have been hit and
miss for me so I'd recommend 3 leaves. I would not recommend thinning
the aluminum spring vertically. The closer it is to a box cross section
the better IMO.

Similarly on the amphib nosewheels. If the gear leg has too much side to
side play it will enhance the tendency to shimmy.

Ken

On 6/7/2011 3:33 PM, Ted Waltman wrote:

I just uploaded an article including diagrams of tailwheel geometry written
by a long-term experienced tailwheel pilot who himself had shimmy problems.
The article can be found in "Area 404-General Documentation." If anyone
would like me to email them this PDF file directly please drop me an email
at tedwaltman@gmail.com

Ted

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of Jesse
Jenks
Sent: Monday, June 06, 2011 4:28 PM
To: Builders list
Subject: [rebel-builders] Tailwheel leaf springs/shimmey!


Have been struggling with a bad shimmy that I thought I had mostly figured
out...until yesterday. I installed a 2 leaf steel spring in place of the
fiberglass one and had been having good luck for the past 40 hours despite
needing to have it re bent to get a more horizontal castor angle. Yesterday
it shimmied bad enough to bend the clamp assembly (see pics) Now I'm back to
the drawing board and considering all options. I will need to fix or
remake/reinforce the tail strut support angle as well as modify the leaf
springs or replace them with something else. Any ideas? I had a beautiful
weekend of flying before the destructive shimmy, so I have that to motivate
me to get it fixed. Also, I now know that I can successfully hold the tail
up with brakes until slowing to a slow taxi speed. I got it to the home
airport after the bad shimmy happened at a fuel stop.
thanks.
Jesse

Tailwheel leaf springsshimmey!
http://cid-f0168b2944a206d0.skydrive.li ... se&resid=F
0168B2944A206D0!648&type=5&Bpub=SDX.Photos&Bsrc=Photomail&authkey=wYW1GXyc8P
A%24

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Thanks for the insight guys. I had a gut feeling in my case it's more about torsional flexibility than anything, and since the bending damage to the mounting structure is from twisting of the leaf spring, that makes sense. Unfortunately if I want to add another leaf I will have to re design the tail strut attach angle bracket to accommodate the extra thickness. I was thinking about using a piece of steel square section tube like Wayne has done, and notch the top to accept the third leaf. That way I could keep the same strut attach locations and avoid making longer struts.

Date: Tue, 7 Jun 2011 16:28:03 -0400
From: klehman@albedo.net
To: rebel-builders@dcsol.com
Subject: Re: [rebel-builders] Tailwheel leaf springs/shimmey!

A good article but unfortunately it is not quite as simple as this
explanation. Lack of torsional rigidity of the Rebel leaf spring
contributes mightily to our shimmy issues. Ideally the pivot angle
should not be free to rotate left and right. Flat leaf springs are not
very torsionally rigid although multileaf springs that are clamped
together are better than a thin leaf. Two steel leaves have been hit and
miss for me so I'd recommend 3 leaves. I would not recommend thinning
the aluminum spring vertically. The closer it is to a box cross section
the better IMO.

Similarly on the amphib nosewheels. If the gear leg has too much side to
side play it will enhance the tendency to shimmy.

Ken

On 6/7/2011 3:33 PM, Ted Waltman wrote:

I just uploaded an article including diagrams of tailwheel geometry written
by a long-term experienced tailwheel pilot who himself had shimmy problems.
The article can be found in "Area 404-General Documentation." If anyone
would like me to email them this PDF file directly please drop me an email
at tedwaltman@gmail.com

Ted

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of Jesse
Jenks
Sent: Monday, June 06, 2011 4:28 PM
To: Builders list
Subject: [rebel-builders] Tailwheel leaf springs/shimmey!


Have been struggling with a bad shimmy that I thought I had mostly figured
out...until yesterday. I installed a 2 leaf steel spring in place of the
fiberglass one and had been having good luck for the past 40 hours despite
needing to have it re bent to get a more horizontal castor angle. Yesterday
it shimmied bad enough to bend the clamp assembly (see pics) Now I'm back to
the drawing board and considering all options. I will need to fix or
remake/reinforce the tail strut support angle as well as modify the leaf
springs or replace them with something else. Any ideas? I had a beautiful
weekend of flying before the destructive shimmy, so I have that to motivate
me to get it fixed. Also, I now know that I can successfully hold the tail
up with brakes until slowing to a slow taxi speed. I got it to the home
airport after the bad shimmy happened at a fuel stop.
thanks.
Jesse

Tailwheel leaf springsshimmey!
http://cid-f0168b2944a206d0.skydrive.li ... se&resid=F
0168B2944A206D0!648&type=5&Bpub=SDX.Photos&Bsrc=Photomail&authkey=wYW1GXyc8P
A%24

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I feel the pain, Jesse. I made a first set of struts (aligning stab
angles and incidence, of course) for the original MAM tailspring --
one of the first jobs I ever did on the inherited project. They
weren't good enough (sub-par rivets) so I made another pair. Then I
did the FUS-30 doubler (ugh!) and changed to pneumatic wheel with the
different thickness Champ spring (in some order or other) and before
it was done, ended up making a new TS-3 and at least four different
pairs of stab struts as I recall.

FWIW, I used two of the original three spring leafs and have seen no
evidence of torsional rigidity problems in the first 94 hrs., which
have included some firm landings and rough strips.

BTW, if that's the worst that's happened during your 40 hrs "test
flight period" you're still definitely due for some rousing congrats.
;-)

Ron


On Tue, Jun 7, 2011 at 3:35 PM, Jesse Jenks <jessejenks@hotmail.com> wrote:

Thanks for the insight guys. I had a gut feeling in my case it's more about torsional flexibility than anything, and since the bending damage to the mounting structure is from twisting of the leaf spring, that makes sense. Unfortunately if I want to add another leaf I will have to re design the tail strut attach angle bracket to accommodate the extra thickness. I was thinking about using a piece of steel square section tube like Wayne has done, and notch the top to accept the third leaf. That way I could keep the same strut attach locations and avoid making longer struts.

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Thanks Ron, I wouldn't mind remaking parts so much but I'm away from my workshop for the summer and will have to borrow tools to do whatever repairs are necessary. Kind of a crazy idea I guess....taking a brand new homebuilt on a 1,000 mile trip. I did get lucky with that last bad shimmey landing though; the tailwheel went hard over and it almost took me off the runway. I was quick enough on the brake to correct it.

From: rshannon@cruzcom.com
Date: Tue, 7 Jun 2011 17:05:59 -0700
Subject: Re: [rebel-builders] Tailwheel leaf springs/shimmey!
To: rebel-builders@dcsol.com

I feel the pain, Jesse. I made a first set of struts (aligning stab
angles and incidence, of course) for the original MAM tailspring --
one of the first jobs I ever did on the inherited project. They
weren't good enough (sub-par rivets) so I made another pair. Then I
did the FUS-30 doubler (ugh!) and changed to pneumatic wheel with the
different thickness Champ spring (in some order or other) and before
it was done, ended up making a new TS-3 and at least four different
pairs of stab struts as I recall.

FWIW, I used two of the original three spring leafs and have seen no
evidence of torsional rigidity problems in the first 94 hrs., which
have included some firm landings and rough strips.

BTW, if that's the worst that's happened during your 40 hrs "test
flight period" you're still definitely due for some rousing congrats.
;-)

Ron


On Tue, Jun 7, 2011 at 3:35 PM, Jesse Jenks <jessejenks@hotmail.com> wrote:

Thanks for the insight guys. I had a gut feeling in my case it's more about torsional flexibility than anything, and since the bending damage to the mounting structure is from twisting of the leaf spring, that makes sense. Unfortunately if I want to add another leaf I will have to re design the tail strut attach angle bracket to accommodate the extra thickness. I was thinking about using a piece of steel square section tube like Wayne has done, and notch the top to accept the third leaf. That way I could keep the same strut attach locations and avoid making longer struts.

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