---------------------------------------------------------- Lightning-List Digest Archive --- Total Messages Posted Thu 01/03/08: 5 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 05:37 PM - Gear leg shimmy experiments (N1BZRich@aol.com) 2. 06:32 PM - Re: Gear leg shimmy experiments (Colin J. Kennedy) 3. 07:58 PM - Re: Gear leg shimmy experiments (Jim Langley) 4. 08:34 PM - Re: Gear leg shimmy experiments (N1BZRich@AOL.COM) 5. 08:35 PM - Re: Gear leg shimmy experiments (N1BZRich@AOL.COM) ________________________________ Message 1 _____________________________________ Time: 05:37:56 PM PST US From: N1BZRich@aol.com Subject: Lightning-List: Gear leg shimmy experiments Hello all Lightning and Esqual listers, Just before Christmas I send out what I called a "two year report for N31BZ" which was some thoughts on the Jabiru 3300 and my highly modified Esqual LS (meaning lots of Lightning Stuff) after flying for two years and some 400+ hours. One thing I mentioned was that I planned to do some experimenting on the gear leg shimmy that we sometimes see (for me it is almost always when landing or taxiing on a hard surface and occurs only when at about 22 mph). Following is that paragraph about the shimmy and below that will be some preliminary results of the shimmy experiments. I have had no real airframe issues during the past two years. The only thing I plan to change, when I get the time, will be to do some experiments on the main gear legs to try to get rid of the sometime gear leg shimmy. I may go the "broom stick" mod that the RV guys do, but before doing that I want to try an easier fix by using a small "V" angle aluminum strip (say 1/8" thick by 1/2" on the angles, by what ever length the gear leg is) that will be clamped to the trailing edge of the gear leg. All I need is the time. I already have the parts. This shimmy occurs on landing roll out on hard surface as you are slowing down through about 22 mph. It does not happen on grass. Tire pressure definitely has an effect, with lower pressure being better. I normally air my mains up to 25 PSI and then re-air them when they look low. That low look seems to be about 15 to 18 PSI. I will let you all know the results when I get the time to do the experiments. As I mentioned above, I have now done some preliminary experiments to find an easy fix to the main gear leg shimmy problem. Actually, I should say that Joe and Linda Mathias and I have done some experiments since we used their Lightning (N59JL) for the experiments. They had their gear leg fairings off during the week after Christmas, so it just seemed like a good idea to try my idea on their airplane. We actually tried two different size aluminum stips clamped to the trailing edge of the gear legs. The first piece of aluminum "V" angle was 1/16" thick by 1/2 wide and 13 inches long. We used three hose clamps on each gear leg to hold these 1/16" V strips in place on each main gear leg. We tried the thinner material first thinking that if it worked it would weigh less. Results were not that noticeable on the taxi test - maybe some improvement, but not near the reduction in shimmy that we wanted. Next we put the 13" long strips of 1/8" thick by 3/4" wide and used the same hose clamps to securely attach the strips to each gear leg trailing edge. Results were very promising on the taxi test and one flight that Linda made that day. Her exact words were "no gear leg shimmy on that landing". Obviously more test flights will be made to confirm that this is a good fix, but we did want to get the word out in case others want to add to our efforts and try it out on your airplane. The aluminum V angle seems to be available at all Lowes, Home Depot and Ace Hardware stores that I have visited, and it is 1/8" thick by 3/4" wide and I think 42" inches long . Only one piece of the aluminum strip is required (about $8.00) and you will cut the length to fit each of your gear legs. We used two 13" pieces on N59JL. The hose clamps are standard hose clamps like we all have laying around the hangar or readily available at the hardware stores. The long term fix will probably be to weld the aluminum V strips to the aluminum gear legs, but the clamps allow you to get them on quickly for the testing. What this fix is doing is adding stiffness to the gear legs, just like the RV guys do by fiber-glassing a grooved broom stick to the trailing edge of the gear legs. I think out fix is less work. Let us all know if you have any questions and if you try this and what results you have. I should have had some photos to send out with this, but alas, I did not think to take photos. I am sure Linda will let us know when she has made a few more landings with this gear leg mod in place. Blue Skies and Happy New Year, Buz **************Start the year off right. Easy ways to stay in shape. http://body.aol.com/fitness/winter-exercise?NCID=aolcmp00300000002489 ________________________________ Message 2 _____________________________________ Time: 06:32:39 PM PST US From: "Colin J. Kennedy" Subject: RE: Lightning-List: Gear leg shimmy experiments Buz, What about using epoxy to attach the aluminum angles? Do you think there is a risk of failure and subsequent damage from flying metal? While a good weld is very strong, could the heat be enough to change the properties of the gear leg material? Colin K. OK -----Original Message----- From: owner-lightning-list-server@matronics.com [mailto:owner-lightning-list-server@matronics.com] On Behalf Of N1BZRich@aol.com Sent: Thursday, January 03, 2008 7:37 PM Subject: Lightning-List: Gear leg shimmy experiments Hello all Lightning and Esqual listers, Just before Christmas I send out what I called a "two year report for N31BZ" which was some thoughts on the Jabiru 3300 and my highly modified Esqual LS (meaning lots of Lightning Stuff) after flying for two years and some 400+ hours. One thing I mentioned was that I planned to do some experimenting on the gear leg shimmy that we sometimes see (for me it is almost always when landing or taxiing on a hard surface and occurs only when at about 22 mph). Following is that paragraph about the shimmy and below that will be some preliminary results of the shimmy experiments. I have had no real airframe issues during the past two years. The only thing I plan to change, when I get the time, will be to do some experiments on the main gear legs to try to get rid of the sometime gear leg shimmy. I may go the "broom stick" mod that the RV guys do, but before doing that I want to try an easier fix by using a small "V" angle aluminum strip (say 1/8" thick by 1/2" on the angles, by what ever length the gear leg is) that will be clamped to the trailing edge of the gear leg. All I need is the time. I already have the parts. This shimmy occurs on landing roll out on hard surface as you are slowing down through about 22 mph. It does not happen on grass. Tire pressure definitely has an effect, with lower pressure being better. I normally air my mains up to 25 PSI and then re-air them when they look low. That low look seems to be about 15 to 18 PSI. I will let you all know the results when I get the time to do the experiments. As I mentioned above, I have now done some preliminary experiments to find an easy fix to the main gear leg shimmy problem. Actually, I should say that Joe and Linda Mathias and I have done some experiments since we used their Lightning (N59JL) for the experiments. They had their gear leg fairings off during the week after Christmas, so it just seemed like a good idea to try my idea on their airplane. We actually tried two different size aluminum stips clamped to the trailing edge of the gear legs. The first piece of aluminum "V" angle was 1/16" thick by 1/2 wide and 13 inches long. We used three hose clamps on each gear leg to hold these 1/16" V strips in place on each main gear leg. We tried the thinner material first thinking that if it worked it would weigh less. Results were not that noticeable on the taxi test - maybe some improvement, but not near the reduction in shimmy that we wanted. Next we put the 13" long strips of 1/8" thick by 3/4" wide and used the same hose clamps to securely attach the strips to each gear leg trailing edge. Results were very promising on the taxi test and one flight that Linda made that day. Her exact words were "no gear leg shimmy on that landing". Obviously more test flights will be made to confirm that this is a good fix, but we did want to get the word out in case others want to add to our efforts and try it out on your airplane. The aluminum V angle seems to be available at all Lowes, Home Depot and Ace Hardware stores that I have visited, and it is 1/8" thick by 3/4" wide and I think 42" inches long . Only one piece of the aluminum strip is required (about $8.00) and you will cut the length to fit each of your gear legs. We used two 13" pieces on N59JL. The hose clamps are standard hose clamps like we all have laying around the hangar or readily available at the hardware stores. The long term fix will probably be to weld the aluminum V strips to the aluminum gear legs, but the clamps allow you to get them on quickly for the testing. What this fix is doing is adding stiffness to the gear legs, just like the RV guys do by fiber-glassing a grooved broom stick to the trailing edge of the gear legs. I think out fix is less work. Let us all know if you have any questions and if you try this and what results you have. I should have had some photos to send out with this, but alas, I did not think to take photos. I am sure Linda will let us know when she has made a few more landings with this gear leg mod in place. Blue Skies and Happy New Year, Buz _____ Start the year off right. Easy ways to stay in shape in the new year. ________________________________ Message 3 _____________________________________ Time: 07:58:04 PM PST US From: "Jim Langley" Subject: RE: Lightning-List: Gear leg shimmy experiments I wonder how the RV guys attach theirs? _____ From: owner-lightning-list-server@matronics.com [mailto:owner-lightning-list-server@matronics.com] On Behalf Of Colin J. Kennedy Sent: Thursday, January 03, 2008 9:31 PM Subject: RE: Lightning-List: Gear leg shimmy experiments Buz, What about using epoxy to attach the aluminum angles? Do you think there is a risk of failure and subsequent damage from flying metal? While a good weld is very strong, could the heat be enough to change the properties of the gear leg material? Colin K. OK ________________________________ Message 4 _____________________________________ Time: 08:34:37 PM PST US From: N1BZRich@AOL.COM Subject: Re: Lightning-List: Gear leg shimmy experiments In a message dated 1/3/2008 9:33:55 P.M. Eastern Standard Time, cjk129@cox.net writes: What about using epoxy to attach the aluminum angles? Do you think there is a risk of failure and subsequent damage from flying metal? While a good weld is very strong, could the heat be enough to change the properties of the gear leg material? Hi Colin, I guess we need to do some sort of study on the strength of epoxy when used on aluminum. Probably the best way would be to epoxy it in place then wrap it with one or two fibergass cloth wraps. That is what the RV guys do - they fiberglass the wood to the gear leg. I really don't think that an epoxy failure would be a major problem, but you certainly would get the shimmy back. The un-epoxyed aluminum part should stay inside the gear leg fairing (certainly with the fiberglass). Probably my only concern would be to immediately check your brake line down that gear leg. As to welding aluminum, I don't have the answer as to whether the heat would alter the temper of the gear leg We need to ask Nick that. I seem to remember seeing some aluminum welding rods at Oshkosh that had a working temperature of around 700 dgrees and could be used with a propane flame. Other than that method, I guess TIG would be the way to go. I only weld steel (4130) with oxygen accelyne. Blue Skies, Buz **************Start the year off right. Easy ways to stay in shape. http://body.aol.com/fitness/winter-exercise?NCID=aolcmp00300000002489 ________________________________ Message 5 _____________________________________ Time: 08:35:17 PM PST US From: N1BZRich@AOL.COM Subject: Re: Lightning-List: Gear leg shimmy experiments In a message dated 1/3/2008 10:59:52 P.M. Eastern Standard Time, pequeajim@gmail.com writes: I wonder how the RV guys attach theirs? They fiberglass the wood dowel to the gear leg. Blue Skies, Buz **************Start the year off right. 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