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Update on my J4A - The local GADO office has been cooperative but it turns out there is a nasty AD on the Hanlon Wilson mufflers that I was planning to use. AD calls for 25 hr inspections for cracks - and no one is permitted to fix them. I decided to bite the bullet & now installing a C120/140/150 muffler system. Trouble is the nose bowl has some interferences so it is chop time to my cowl. But the muffler system is a much better package & I don't regret having to do it. The IA said that OK City FAA engineering would be very leary of any engine swap schemes that used that old muffler scheme.
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Dawley Aviation rebuilt a Hanlon Wilson system for me. It was on a 7AC. They had some trouble though finding the seals that surround the stack on its way into the heat muff. Been a couple of years so they may not do that any more.
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That sounds like a different muffler configuration than my old H-W mufflers. The H-Ws I have are one welded piece of stainless from the exhaust flange thru to the tail pipe. A second stainless stamped pair uses a number of #10 screws to hold and form the heat muff outside. The whole assembly resonates laterally on the engine with very low damping. One side was ~66 Hz and the other at ~105 Hz. I figured it would only be a short time until something fatigue cracked.
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interesting topic, here's in excerpt from the 8900, and why your wings were denied possibly?
"A. Previously Approved Data for an Alteration to a Specific Aircraft. Data that isapproved by the FAA to substantiate an alteration for one aircraft is applicable only to thataircraft described in block 1 of FAA Form 337. Such data developed for the altered product isconsidered acceptable data and may be applied as a basis for developing approved dataapplicable to alterations on another aircraft involving equipment of the same make and model.The make and model of the aircraft may be different if the installation is similar."
Also, there's a nice flow chart in the chapter. Field Approval vs STC is based on is it a Major Alteration (based on CFR43 App A) or a Design Change (based on CFR 21.93). That seems to be where the discussion lies between what can get a field approval vs what needs STC.
