---------------------------------------------------------- Lightning-List Digest Archive --- Total Messages Posted Tue 05/08/12: 11 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 05:09 AM - Thinking of buying (N129JG) 2. 05:56 AM - Re: Thinking of buying (Charles Dewey) 3. 08:42 AM - Re: Thinking of buying (N129JG) 4. 02:37 PM - Re: Landing gear shimmy (Bill Strahan) 5. 03:18 PM - Re: Re: Landing gear shimmy (Mefford, Walt) 6. 03:32 PM - Re: Re: Landing gear shimmy (Mark Stauffer) 7. 03:46 PM - Re: Re: Landing gear shimmy (Jim Logajan) 8. 05:09 PM - Re: Re: Landing gear shimmy (Tex Mantell) 9. 05:29 PM - Re: Re: Landing gear shimmy (Nick Otterback) 10. 08:19 PM - Re: Re: Landing gear shimmy (GARY BARNETT) 11. 09:01 PM - Re: Landing gear shimmy (Bill Strahan) ________________________________ Message 1 _____________________________________ Time: 05:09:44 AM PST US Subject: Lightning-List: Thinking of buying From: "N129JG" No.. not a Lightning. As much as I would love one it is just not in the budget. But I have been looking at an Esqual. In fact I believe it may have been the last of the Factory built Demo planes, N622EA. I know Buzz has made many modifications to his Esqual and I have read it flies like a cat with it's tail on fire. I am planning to go inspect and take a demo flight this Friday. I have an A&P IA traveling with me. Anything in particular we need to be looking for? Thanks, Gene Read this topic online here: http://forums.matronics.com/viewtopic.php?p=372616#372616 ________________________________ Message 2 _____________________________________ Time: 05:56:58 AM PST US From: Charles Dewey Subject: Re: Lightning-List: Thinking of buying Gene- There is a Lightning for sale in Shelbyville for $64K. It is on barnstormers now. --- On Tue, 5/8/12, N129JG wrote: > From: N129JG > Subject: Lightning-List: Thinking of buying > To: lightning-list@matronics.com > Date: Tuesday, May 8, 2012, 8:09 AM > --> Lightning-List message posted > by: "N129JG" > > No.. not a Lightning. As much as I would love one it > is just not in the > budget. But I have been looking at an Esqual. In > fact I believe it may > have been the last of the Factory built Demo planes, > N622EA. I know > Buzz has made many modifications to his Esqual and I have > read it flies > like a cat with it's tail on fire.I am > planning to go inspect and take a > demo flight this Friday. I have an A&P IA > traveling with me. Anything > in particular we need to be looking for? > > Thanks, > > Gene > > > > > Read this topic online here: > > http://forums.matronics.com/viewtopic.php?p=372616#372616 > > > > > > > > Email Forum - > - MATRONICS WEB FORUMS - > List Contribution Web Site - > -Matt > Dralle, List Admin. > > > > ________________________________ Message 3 _____________________________________ Time: 08:42:14 AM PST US Subject: Lightning-List: Re: Thinking of buying From: "N129JG" Thanks for the tip. I saw the ad on Barnstormers and I do not believe it is LSA qualified. That is a key for me. I am limited to about $50K budget right now as we are also building a house. Gene Read this topic online here: http://forums.matronics.com/viewtopic.php?p=372631#372631 ________________________________ Message 4 _____________________________________ Time: 02:37:18 PM PST US Subject: Lightning-List: Re: Landing gear shimmy From: "Bill Strahan" Okay, no egg on my face I suppose. Finally got a video camera to check things out. It's clearly the main gear. It should be on youtube here: http://youtu.be/rzb_eeyhLJU in a few minutes. This clip makes it pretty visible starting at 0:28 on the landing roll. I don't use the brakes much to try to discount that influence, and I let the nose drop the moment I land so I can see if it's the nose or mains. On taxiing back, I decided to accelerate and test it again, and the second shimmy can be seen at 1:28. It may not look like much on a video camera, but that's a serious bit of wiggling in the cockpit. I'm astounded that the stiffeners don't make an impact on it. I can't flex them by hand at all in that direction. This is a big deal for me because I fly into some pretty busy places and it occurs right at the speed I'd be doing on a long runway to hurry up and make a turnoff. That, and I don't like passengers looking a little freaked out and asking what the heck that was. And it can't be good for the whole plane to violently shake like that. For the record, I've balanced tires, changed to 6 ply tires, balanced those, and now the fiberglass stiffeners. No relief yet. Not sure what comes next. Read this topic online here: http://forums.matronics.com/viewtopic.php?p=372654#372654 ________________________________ Message 5 _____________________________________ Time: 03:18:37 PM PST US From: "Mefford, Walt" Subject: RE: Lightning-List: Re: Landing gear shimmy Bill, I have been plagued with similar problems. I tried most of what you have done, except for stiffeners, with little or no effect. I did notice an improvement when I remove the landing gear fairings. I did a lot of research on the subject at one time. There are number of papers on the subject on the NASA web site. These papers go back to the 1940's up to the 80's and 90's. There are just to many variables for a simple fix. Things like tire pressure, runway surface material, the kind of rubber used on the tire, flexing of the airframe, shape of the gear, weight on the tire, toe in and toe out and the list keeps going on. Even modern transports have problems at times and I been on some where the shimmy was very noticeable. A FULL-SCALE INVESTIGATION OF THE EFFECT OF SEVERAL FACTORS On THE SHIMMY OF CASTING WHEELS April 1940, Langley Aeronautical Laboratory. TECHNICAL NOTE 3632 CORRELATION, EVALUATION, AND EXTENSION OF LINEARIZED THEORIES FOR TIRE MOTION AND WHEEL SHIMMY Langley Aeronautical Laboratory, Langley Field, Va. Washington June 1956 TECHNICAL NOTE 4001 SOME CONSIDERATIONS OF HYSTERESIS EFFECTS ON TIRE MOTION AND WHEEL SHIMMY Langley Aeronautical Laboratory, Langley Field, Va. Washington June 1957 REPORT No. 686 STABILITY OF CASTERING WHEELS FOR AIRCRAFT LANDING GEARS REPORT 1299 CORRELATION, EVALUATION, AND EXTENSION OF LINEARIZED THEORIES FOR TIRE MOTION AND WHEEL SHIMMY NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS TECHNICAL MEMORANDUM 1378 DETERMINATION QF THE ELASTICC CONSTANTS OF AIRPLANE TIRES Washington November 1954 NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS TECHNICAL MEMORANDUM 1337 Analytical Study of Shimmy of Airplane Wheels Washington September 1952 NASA/TM- 1999-209143 ARL-TR- 1976 An Overview of Landing Gear Dynamics Langley Research Center, Hampton, Virginia May 1999 Shimmy of Aircraft Main Landing Gears September 2000 ISBN 90-9014104-9 Copyright 2000 by I.J.M. Besselink -----Original Message----- From: owner-lightning-list-server@matronics.com [mailto:owner-lightning-list-server@matronics.com] On Behalf Of Bill Strahan Sent: Tuesday, May 08, 2012 2:37 PM Subject: Lightning-List: Re: Landing gear shimmy Okay, no egg on my face I suppose. Finally got a video camera to check things out. It's clearly the main gear. It should be on youtube here: http://youtu.be/rzb_eeyhLJU in a few minutes. This clip makes it pretty visible starting at 0:28 on the landing roll. I don't use the brakes much to try to discount that influence, and I let the nose drop the moment I land so I can see if it's the nose or mains. On taxiing back, I decided to accelerate and test it again, and the second shimmy can be seen at 1:28. It may not look like much on a video camera, but that's a serious bit of wiggling in the cockpit. I'm astounded that the stiffeners don't make an impact on it. I can't flex them by hand at all in that direction. This is a big deal for me because I fly into some pretty busy places and it occurs right at the speed I'd be doing on a long runway to hurry up and make a turnoff. That, and I don't like passengers looking a little freaked out and asking what the heck that was. And it can't be good for the whole plane to violently shake like that. For the record, I've balanced tires, changed to 6 ply tires, balanced those, and now the fiberglass stiffeners. No relief yet. Not sure what comes next. Read this topic online here: http://forums.matronics.com/viewtopic.php?p=372654#372654 ________________________________ This e-mail and any attachments may contain confidential material for the sole use of the intended recipient. If you are not the intended recipient, please be aware that any disclosure, copying, distribution or use of this e-mail or any attachment is prohibited. If you have received this e-mail in error, please contact the sender and delete all copies. Thank you for your cooperation. ________________________________ Message 6 _____________________________________ Time: 03:32:45 PM PST US From: "Mark Stauffer" Subject: RE: Lightning-List: Re: Landing gear shimmy Hi Bill, I'm sure you've already looked at this but what is your tire pressure? We've also just experienced a case where the gear shimmied with no pants on and then the shimmy was almost next to nothing with the wheel pants back on. Go figure. Also, I don't remember what setting we used when we set the toe in for your gear. Double check that as well. Best regards, Mark -----Original Message----- From: owner-lightning-list-server@matronics.com [mailto:owner-lightning-list-server@matronics.com] On Behalf Of Bill Strahan Sent: Tuesday, May 08, 2012 4:37 PM Subject: Lightning-List: Re: Landing gear shimmy Okay, no egg on my face I suppose. Finally got a video camera to check things out. It's clearly the main gear. It should be on youtube here: http://youtu.be/rzb_eeyhLJU in a few minutes. This clip makes it pretty visible starting at 0:28 on the landing roll. I don't use the brakes much to try to discount that influence, and I let the nose drop the moment I land so I can see if it's the nose or mains. On taxiing back, I decided to accelerate and test it again, and the second shimmy can be seen at 1:28. It may not look like much on a video camera, but that's a serious bit of wiggling in the cockpit. I'm astounded that the stiffeners don't make an impact on it. I can't flex them by hand at all in that direction. This is a big deal for me because I fly into some pretty busy places and it occurs right at the speed I'd be doing on a long runway to hurry up and make a turnoff. That, and I don't like passengers looking a little freaked out and asking what the heck that was. And it can't be good for the whole plane to violently shake like that. For the record, I've balanced tires, changed to 6 ply tires, balanced those, and now the fiberglass stiffeners. No relief yet. Not sure what comes next. Read this topic online here: http://forums.matronics.com/viewtopic.php?p=372654#372654 ________________________________ Message 7 _____________________________________ Time: 03:46:05 PM PST US From: Jim Logajan Subject: Re: Lightning-List: Re: Landing gear shimmy On 5/8/2012 2:36 PM, Bill Strahan wrote: > It should be on youtube here: http://youtu.be/rzb_eeyhLJU in a few minutes. Looks like a bit of resonance kicking in. Not sure, but it looks like maybe each leg alternates in vibration; that is as one vibrates forward the other is going backward. I'm not a mechanical engineer and don't play one on TV, but my uninformed guess is that when one of the legs flexes, the leg geometry may be such that it can't help but cause the wheel to change its toe-in or toe-out angle. In this case as one of the legs starts to bend it may be causing a toe-out condition in the wheel, which causes even more bending and more toe-out. This would likely cause the plane to pull to one side, causing the other wheel to experience a relative toe-out condition, setting up the same thing there. Energy starts swapping sides. Swept-back gear legs _might_ have an inherent geometry problem due to how they rotate the axis of the wheels when they flex due to loads. So the toe-angle would also change with changes in how much you load the airplane. Perhaps gear legs straight out (right angle to the average direction of motion) would flex mostly only up or down, changing the camber angle of the wheels but not the toe-angle. But as I said, I am not an engineer and the above might not be valid observations. ________________________________ Message 8 _____________________________________ Time: 05:09:14 PM PST US From: "Tex Mantell" Subject: Re: Lightning-List: Re: Landing gear shimmy Bill, great video, thank you for your effort. Tex ----- Original Message ----- From: "Bill Strahan" Sent: Tuesday, May 08, 2012 5:36 PM Subject: Lightning-List: Re: Landing gear shimmy > > Okay, no egg on my face I suppose. Finally got a video camera to check > things out. It's clearly the main gear. > > It should be on youtube here: http://youtu.be/rzb_eeyhLJU in a few > minutes. > > This clip makes it pretty visible starting at 0:28 on the landing roll. I > don't use the brakes much to try to discount that influence, and I let the > nose drop the moment I land so I can see if it's the nose or mains. > > On taxiing back, I decided to accelerate and test it again, and the second > shimmy can be seen at 1:28. > > It may not look like much on a video camera, but that's a serious bit of > wiggling in the cockpit. > > I'm astounded that the stiffeners don't make an impact on it. I can't > flex them by hand at all in that direction. > > This is a big deal for me because I fly into some pretty busy places and > it occurs right at the speed I'd be doing on a long runway to hurry up and > make a turnoff. That, and I don't like passengers looking a little > freaked out and asking what the heck that was. And it can't be good for > the whole plane to violently shake like that. > > For the record, I've balanced tires, changed to 6 ply tires, balanced > those, and now the fiberglass stiffeners. No relief yet. Not sure what > comes next. > > > Read this topic online here: > > http://forums.matronics.com/viewtopic.php?p=372654#372654 > > > ________________________________ Message 9 _____________________________________ Time: 05:29:21 PM PST US From: Nick Otterback Subject: Re: Lightning-List: Re: Landing gear shimmy What about a different materal for the leg all together? We dont have the problem on the lsa gear that often if at all. But the overlay angle or sweep of the gear is not as pronounced. Have thought about the use of titanium gear legs. That material is said to be "dead" material due to make up. It does flex but does not spring back with as much pep. Sonex uses this for their main legs, it is a bit more expensive but may be a solution. Let me look into it. Nick Sent from my pocket On May 8, 2012, at 7:06 PM, "Tex Mantell" wrote: > > Bill, great video, thank you for your effort. Tex > > > > > > > > ----- Original Message ----- From: "Bill Strahan" > To: > Sent: Tuesday, May 08, 2012 5:36 PM > Subject: Lightning-List: Re: Landing gear shimmy > > >> >> Okay, no egg on my face I suppose. Finally got a video camera to check things out. It's clearly the main gear. >> >> It should be on youtube here: http://youtu.be/rzb_eeyhLJU in a few minutes. >> >> This clip makes it pretty visible starting at 0:28 on the landing roll. I don't use the brakes much to try to discount that influence, and I let the nose drop the moment I land so I can see if it's the nose or mains. >> >> On taxiing back, I decided to accelerate and test it again, and the second shimmy can be seen at 1:28. >> >> It may not look like much on a video camera, but that's a serious bit of wiggling in the cockpit. >> >> I'm astounded that the stiffeners don't make an impact on it. I can't flex them by hand at all in that direction. >> >> This is a big deal for me because I fly into some pretty busy places and it occurs right at the speed I'd be doing on a long runway to hurry up and make a turnoff. That, and I don't like passengers looking a little freaked out and asking what the heck that was. And it can't be good for the whole plane to violently shake like that. >> >> For the record, I've balanced tires, changed to 6 ply tires, balanced those, and now the fiberglass stiffeners. No relief yet. Not sure what comes next. >> >> >> >> >> Read this topic online here: >> >> http://forums.matronics.com/viewtopic.php?p=372654#372654 >> >> >> >> >> >> >> >> >> >> > > > > > ________________________________ Message 10 ____________________________________ Time: 08:19:28 PM PST US From: GARY BARNETT Subject: RE: Lightning-List: Re: Landing gear shimmy BillThere is a natural resonance in my landing gear around 8 to 10 miles pe r hour. If you are slower or faster there is no vibration but when you hit that speed the wheels bounce pretty good. By adding or subtracting weight (Wheel pants etc.) you just change the resonant frequency. With a resonan ce problem in your landing gear the wheels can be perfectly balanced but th e slightest excitement from a bump in the runway or an out of balance tire =2C at the right speed=2C will get it going Try this=2C jack a wheel off t he ground and using an air gun with a lot of pressure=2C in the area of the tread spin the wheel up to see if you have a balance problem or out of rou nd tire. Make sure you warm up the tire first by a few landings and then b efore it cools off jack it up and let it sit for an hour to stabilize (reac h it's natural shape). Then test it. You may need to put a padded support under the area of the fuselage so the gear can flex freely during the test . If the tires are allowed to cool after a flight while the plane is sitti ng on them they will develope a flat spot that will lead to wheel bounce no matter what you do. Gary Barnett N335AL Sn 133.> Subject: Lightning-List: Re: Landing gear shi mmy > From: bill@gdsx.com > Date: Tue=2C 8 May 2012 14:36:50 -0700 > To: lightning-list@matronics.com > > > Okay=2C no egg on my face I suppose. Finally got a video camera to check things out. It's clearly the main gear. > > It should be on youtube here: http://youtu.be/rzb_eeyhLJU in a few minu tes. > > This clip makes it pretty visible starting at 0:28 on the landing roll. I don't use the brakes much to try to discount that influence=2C and I let the nose drop the moment I land so I can see if it's the nose or mains. > > On taxiing back=2C I decided to accelerate and test it again=2C and the s econd shimmy can be seen at 1:28. > > It may not look like much on a video camera=2C but that's a serious bit o f wiggling in the cockpit. > > I'm astounded that the stiffeners don't make an impact on it. I can't fl ex them by hand at all in that direction. > > This is a big deal for me because I fly into some pretty busy places and it occurs right at the speed I'd be doing on a long runway to hurry up and make a turnoff. That=2C and I don't like passengers looking a little freak ed out and asking what the heck that was. And it can't be good for the who le plane to violently shake like that. > > For the record=2C I've balanced tires=2C changed to 6 ply tires=2C balanc ed those=2C and now the fiberglass stiffeners. No relief yet. Not sure wh at comes next. > > > > > Read this topic online here: > > http://forums.matronics.com/viewtopic.php?p=372654#372654 > > > > > > > =========== =========== =========== =========== > > > ________________________________ Message 11 ____________________________________ Time: 09:01:18 PM PST US Subject: Lightning-List: Re: Landing gear shimmy From: "Bill Strahan" Yes! Titanium for the win! Okay, it just sounds cool. I'd be interested. To cover a few points first: 1) I know the wheels/tires are balanced. I bought a balancer just for that purpose. I'm satisfied they're spot on. 2) I've tried everything from 22 to 38 PSI. No detectable change. 3) It's WORSE with wheelpants. Much worse. 4) I saw no difference with the heavier ply tires, so switched back. The shape was different with the heavier ply and I didn't want to mess with any wheelpant mods to get them to fit. Since they made no difference, I switched back. 5) Braking during the onset of shimmy appears to shorten duration, but I don't know if it's a direct effect, or if it just causes a faster transition out of the resonant frequency. I absolutely love flying 7RW...I just don't enjoy touch and goes or landings very much. I have a 3000 mile trip planned for July, and I would sure like to get this off my list before I go. I've been using the trip to get the last few things I want ironed out (like the ADS-B weather finally!) and this is the last one. Trying to plug away at it. Tomorrow I'll add 6 layers of fiberglass to the stiffeners. If that doesn't do it then the stiffeners are not the solution. And I'll await Nick's info on titanium. I may fly up and see if Nick will try a few high speed runs to see what he thinks. Read this topic online here: http://forums.matronics.com/viewtopic.php?p=372675#372675 ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message lightning-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/Lightning-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/lightning-list Browse Digests http://www.matronics.com/digest/lightning-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.