Walt
Well Known Member
Given the recently reported nose gear leg bolt failure, a few of us “VAFers” have concluded that the time has come to summarize “Nose Gear Lessons Learned” at least from our personal perspectives and in the interest of safety for our fellow VAF RV-A builders and fliers. We are talking about improvement, prevention, and safety; not any inherent flaw in the RV-A nose gear design.
Post Contributors (in alphabetical order): Walt Aronow (“Walt” on VAF, RV-7A), Bruce Hill (bruceh, 9A), Bill Palmer (same, 8A in-work), Bill Pendergrass (rzbill, 7A), and Alex Peterson (AlexPeterson, 6A).
(I want everyone to know that even though I am the one posting this, these other guys did most of the work putting this document together!)
Applicability: RV-6A, 7A, 8A, & 9A
Disclaimer: These “Nose Gear Lessons Learned” are opinion-based, consensus recommendations based on the personal perspectives and experiences of those individuals contributing to this post. These lessons are deduced from our own experiences and the experiences of others as reported on VAF and are not as the result of definitive engineering studies, testing, or similar professional analyses. These lessons learned do not represent the recommendations of Van’s Aircraft except as noted in Van’s published Service information (bulletins, letters and notices, and revisions and changes . . . see the included links). In other words, as an RV-A builder or flier, it is entirely your personal decision whether to acknowledge these lessons learned or ignore them.
Link to Van's SB page:
http://www.vansaircraft.com/public/service.htm
LESSONS LEARNED (RECOMMENDATIONS):
1. Installation
Make sure that all nose gear components are installed correctly.
For example, the stop collar (flange) can easily be installed backward which severely limits nose wheel castering and can create high shear loads on the nose gear leg retainer bolt. If you can visually check the stop collar easily, we recommend referencing Van’s installation drawing for proper stop collar orientation = stop tabs (arms) forward.
Sheared leg retainer bolt from incorrectly installed stop collar:
We highly recommend performing Van’s new Service Bulletin to check the stop collar orientation before further flight:
http://www.vansaircraft.com/pdf/sb14-12-22.pdf
All of the nose gear system components are subjected to high loads, so pay extra attention to correct installation. We recommend carefully checking the entire nose gear system for proper installation, operation, and adjustment. High-quality workmanship is important!
2. Nose Gear Fork
If you still have the older-style nose gear fork, Perform Van’s Mandatory Service Bulletin 07-11-09 (Nose Gear Leg and Fork Upgrade)
http://www.vansaircraft.com/pdf/sb07-11-9.pdf
http://www.vansaircraft.com/pdf/Nosegear_sb_faq.pdf
Read these Van’s Service Letters:
http://www.vansaircraft.com/pdf/Nose_gear_service_letter.pdf
http://www.vansaircraft.com/pdf/letters/nosegear.pdf
3. Nose Wheel
Replace the Van’s-supplied Matco nose wheel with an improved Grove, Berringer, or Modified Matco (Anti-Splat Wheel and Bearing Modification) wheel. Reasons: Lower rolling resistance; reduced nose wheel shimmy. Periodically (at least annually) balance the wheel/tire assembly and check the tire for roundness. Replace/rebalance the tire as necessary.
Matco Wheel Alternative: Carefully and frequently check the Matco Nose Wheel Axle Torque per Van’s Service Letter:
http://www.vansaircraft.com/pdf/Nose_W_T.pdf
Goal: Reduce/Eliminate Wheel Binding and Shimmy.
Comment: The reason that we are recommending changing or modifying the Matco wheel is that many RVers have had difficulty properly installing, lubricating (packing), and adjusting (torquing) the combination of the nose gear fork, 3/8-inch axle bolt, and Matco wheel system (wheel, roller bearings, and cones/mushrooms). Without a perfect installation and frequent, proper adjustment and lubrication, this fork and nose wheel system is prone to perhaps exhibiting bearing binding or even lockup. Proper alignment and stacking of the Matco wheel system to the nose gear fork is not easy, the roller bearing preload is set by the axle torque, and the axle is relatively flexible. We highly recommend installing a nose wheel system which completely separates the bearing preload from the axle torque. A more rigid axle is recommended as well.
Note: Earlier model 6A’s had a more rigid design axle from Vans as shown:
4. Nose Gear Leg Retaining Bolt
Periodically (every annual or more often if operating off rough fields), carefully inspect the nose gear leg and engine mount connection.
(1) Per Van’s drawing, check to make sure that a washer is NOT installed under the head of the retaining bolt. If a washer is installed under the bolt’s head, the bolt’s grip length does not fully contact the engine mount at the bottom. If you insist on installing a washer under the bolt head, the next longer bolt will be required; probably with two washers at the base to avoid showing too many threads beyond the lock nut.
(2) Lift the nose wheel off the ground and check the nose gear leg for play (gear leg movement at the engine mount socket). If some play is observed then remove the AN5-20A nose gear leg attachment bolt and inspect the bolt and bolt hole for wear.
Note: AN5 bolts can have a diameter as low as 0.309. If you have a “slightly loose” nose gear leg either upon initial fabrication or at a periodic check, you might try installing a close-tolerance AN175-20A or NAS6605-26 bolt instead. Note: The NAS6605-26 is specified, because its overall length is the same as the AN5-20A. The -25 (same grip length as the -20A) is too short.
If the engine mount’s bolt hole has been enlarged such that the AN5 (or AN175/NAS6605) bolt is no longer a “close fit,” enlarge the hole slightly (ream) and install an oversize NAS 6605-26X (+.0156 inch) or NAS6605-26Y (+.0312 inch) bolt. The appropriate reamers from Genuine Aircraft Hardware are, respectively, the straight-shank PPR-.3261 (for -X) or PPR-.3417 (for -Y). Both reamers have an approximate 2-1/4-inch flute length with a standard 0.309-inch diameter, 9/16-inch long pilot. Threaded shank versions are PPRT-.3261 and PPRT-.3417. Optional reamers are the PPRL-.3261 or PPRL-.3417 with a 3-inch flute length; same pilot.
Note that oversized NAS6605 bolts still have standard 5/16-24 threads, so standard AN960-516 washers and AN363-516 (MS21045-5) all-metal locknuts fit the oversized bolts.
Note that Van’s Aircraft has not approved the installation of an oversized NAS bolt, but flying with a loose nose gear leg is definitely not recommended!
Technically, the only approved Van’s Aircraft solution for fixing a loose nose gear leg would be to repair (weld and drill) or replace the engine mount and continue to use an AN5-20A bolt as specified. This assumes, of course, that the hole in the nose gear leg itself is not enlarged. If this hole is also enlarged or damaged, the nose gear leg would need to be replaced to remain within what is currently published by Van’s Aircraft (the original plans and drawings).
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Post Contributors (in alphabetical order): Walt Aronow (“Walt” on VAF, RV-7A), Bruce Hill (bruceh, 9A), Bill Palmer (same, 8A in-work), Bill Pendergrass (rzbill, 7A), and Alex Peterson (AlexPeterson, 6A).
(I want everyone to know that even though I am the one posting this, these other guys did most of the work putting this document together!)
Applicability: RV-6A, 7A, 8A, & 9A
Disclaimer: These “Nose Gear Lessons Learned” are opinion-based, consensus recommendations based on the personal perspectives and experiences of those individuals contributing to this post. These lessons are deduced from our own experiences and the experiences of others as reported on VAF and are not as the result of definitive engineering studies, testing, or similar professional analyses. These lessons learned do not represent the recommendations of Van’s Aircraft except as noted in Van’s published Service information (bulletins, letters and notices, and revisions and changes . . . see the included links). In other words, as an RV-A builder or flier, it is entirely your personal decision whether to acknowledge these lessons learned or ignore them.
Link to Van's SB page:
http://www.vansaircraft.com/public/service.htm
LESSONS LEARNED (RECOMMENDATIONS):
1. Installation
Make sure that all nose gear components are installed correctly.
For example, the stop collar (flange) can easily be installed backward which severely limits nose wheel castering and can create high shear loads on the nose gear leg retainer bolt. If you can visually check the stop collar easily, we recommend referencing Van’s installation drawing for proper stop collar orientation = stop tabs (arms) forward.
Sheared leg retainer bolt from incorrectly installed stop collar:
We highly recommend performing Van’s new Service Bulletin to check the stop collar orientation before further flight:
http://www.vansaircraft.com/pdf/sb14-12-22.pdf
All of the nose gear system components are subjected to high loads, so pay extra attention to correct installation. We recommend carefully checking the entire nose gear system for proper installation, operation, and adjustment. High-quality workmanship is important!
2. Nose Gear Fork
If you still have the older-style nose gear fork, Perform Van’s Mandatory Service Bulletin 07-11-09 (Nose Gear Leg and Fork Upgrade)
http://www.vansaircraft.com/pdf/sb07-11-9.pdf
http://www.vansaircraft.com/pdf/Nosegear_sb_faq.pdf
Read these Van’s Service Letters:
http://www.vansaircraft.com/pdf/Nose_gear_service_letter.pdf
http://www.vansaircraft.com/pdf/letters/nosegear.pdf
3. Nose Wheel
Replace the Van’s-supplied Matco nose wheel with an improved Grove, Berringer, or Modified Matco (Anti-Splat Wheel and Bearing Modification) wheel. Reasons: Lower rolling resistance; reduced nose wheel shimmy. Periodically (at least annually) balance the wheel/tire assembly and check the tire for roundness. Replace/rebalance the tire as necessary.
Matco Wheel Alternative: Carefully and frequently check the Matco Nose Wheel Axle Torque per Van’s Service Letter:
http://www.vansaircraft.com/pdf/Nose_W_T.pdf
Goal: Reduce/Eliminate Wheel Binding and Shimmy.
Comment: The reason that we are recommending changing or modifying the Matco wheel is that many RVers have had difficulty properly installing, lubricating (packing), and adjusting (torquing) the combination of the nose gear fork, 3/8-inch axle bolt, and Matco wheel system (wheel, roller bearings, and cones/mushrooms). Without a perfect installation and frequent, proper adjustment and lubrication, this fork and nose wheel system is prone to perhaps exhibiting bearing binding or even lockup. Proper alignment and stacking of the Matco wheel system to the nose gear fork is not easy, the roller bearing preload is set by the axle torque, and the axle is relatively flexible. We highly recommend installing a nose wheel system which completely separates the bearing preload from the axle torque. A more rigid axle is recommended as well.
Note: Earlier model 6A’s had a more rigid design axle from Vans as shown:
4. Nose Gear Leg Retaining Bolt
Periodically (every annual or more often if operating off rough fields), carefully inspect the nose gear leg and engine mount connection.
(1) Per Van’s drawing, check to make sure that a washer is NOT installed under the head of the retaining bolt. If a washer is installed under the bolt’s head, the bolt’s grip length does not fully contact the engine mount at the bottom. If you insist on installing a washer under the bolt head, the next longer bolt will be required; probably with two washers at the base to avoid showing too many threads beyond the lock nut.
(2) Lift the nose wheel off the ground and check the nose gear leg for play (gear leg movement at the engine mount socket). If some play is observed then remove the AN5-20A nose gear leg attachment bolt and inspect the bolt and bolt hole for wear.
Note: AN5 bolts can have a diameter as low as 0.309. If you have a “slightly loose” nose gear leg either upon initial fabrication or at a periodic check, you might try installing a close-tolerance AN175-20A or NAS6605-26 bolt instead. Note: The NAS6605-26 is specified, because its overall length is the same as the AN5-20A. The -25 (same grip length as the -20A) is too short.
If the engine mount’s bolt hole has been enlarged such that the AN5 (or AN175/NAS6605) bolt is no longer a “close fit,” enlarge the hole slightly (ream) and install an oversize NAS 6605-26X (+.0156 inch) or NAS6605-26Y (+.0312 inch) bolt. The appropriate reamers from Genuine Aircraft Hardware are, respectively, the straight-shank PPR-.3261 (for -X) or PPR-.3417 (for -Y). Both reamers have an approximate 2-1/4-inch flute length with a standard 0.309-inch diameter, 9/16-inch long pilot. Threaded shank versions are PPRT-.3261 and PPRT-.3417. Optional reamers are the PPRL-.3261 or PPRL-.3417 with a 3-inch flute length; same pilot.
Note that oversized NAS6605 bolts still have standard 5/16-24 threads, so standard AN960-516 washers and AN363-516 (MS21045-5) all-metal locknuts fit the oversized bolts.
Note that Van’s Aircraft has not approved the installation of an oversized NAS bolt, but flying with a loose nose gear leg is definitely not recommended!
Technically, the only approved Van’s Aircraft solution for fixing a loose nose gear leg would be to repair (weld and drill) or replace the engine mount and continue to use an AN5-20A bolt as specified. This assumes, of course, that the hole in the nose gear leg itself is not enlarged. If this hole is also enlarged or damaged, the nose gear leg would need to be replaced to remain within what is currently published by Van’s Aircraft (the original plans and drawings).
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