rdv Posted June 20, 2010 Report Posted June 20, 2010 Hello all, I recently had a pre-sale inspection performed on a '67 F. One of the items on the snag list was insufficient preload on nose and r/h gear. Can anyone explain exactly what this means? The aircraft has a current certificate of airworthiness. Thanks, Ryan
Kwixdraw Posted June 20, 2010 Report Posted June 20, 2010 The preload is what keeps the linkage braced to keep the landing gear from folding up under a load. Think of it as locking out your elbow to keep someone from putting an arm lock on you and you will have the concept. You need special tools and a good understanding of the landing gear to get this set properly. Doing it wrong or not checking it is a major reason for landing gear related incidents. Find someone at an MSC or at least Mooney experienced who will get it right before you have an incident.
KSMooniac Posted June 21, 2010 Report Posted June 21, 2010 That plane is at-risk for a gear collapse, and the gear rigging should be adjusted by a Mooney-savvy mechanic using the maintenance manual procedures and Mooney-specific gear tools to get it back in spec. These days with hull values depressed, a gear-up landing or gear collapse can total an older plane since a new prop and engine tear-down will be needed. It should be fixed before further flight...
carusoam Posted June 21, 2010 Report Posted June 21, 2010 Something to look for while performing the pre-purchase inspection regarding landing gear pre-tension. Somewhere in the history of the plane there was an AD to change the main landing gear donuts. Make sure the AD was complied with in full. The donuts are the outwardly visible change. The support structure they are mounted on should be changed at the same time. If the structural pieces were not changed, the ability to adjust pre-load may be effected. An MSC will notice this immediately. Someone else may not. If the hardware is in proper working order, adjusting the pre-load is something the A&P can take care of. There are plenty of threads related to donuts on this forum.... As stated above, you want the preload to be proper to minimize collapse. Side loads increase with speed while turning on the ground. Could be hazardous if pre-tension is not properly set. Best regards, -a-
danb35 Posted June 21, 2010 Report Posted June 21, 2010 There is no AD on a '67 F requiring replacement of the gear donuts. There's a factory SB, but no AD. There is an AD (73-21-1) which required replacing the retracting links, but that should have been done in 1972. Compliance with that AD does reduce the required preload amount (see Mooney SB M20-155). Do you have any idea what the measured preload amounts were?
rdv Posted June 21, 2010 Author Report Posted June 21, 2010 R/H is 20-40 inch-pounds low Nose gear insufficient .040, .010. Does this info make sense?
danb35 Posted June 22, 2010 Report Posted June 22, 2010 The info for the main makes sense, the nose not so much. But my question is what was the actual measurement on the main. Some versions of the service manual call for a much higher preload than the current information (published in SB M20-155), which calls for 250-280 in-lb. The nose gear should be measured in the same units, and the spec calls for 100-130 in-lb.
N201MKTurbo Posted June 22, 2010 Report Posted June 22, 2010 If I recall the later Mooneys specify an amount of spring compression for the nose gear instead of preload torque, but the 67F specifies preload torque (I owned and maintained one for 19 years). I think your mechanic is using the wrong service information for your plane. It looks like your gear needs a thorough re-rigging. Takes about three hours if you know what you are doing - weeks if you don't.
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