Trim Tabs

Barnaby Wainfan’s recent article about trim tabs [“Wind Tunnel,” September 2016] advised having enough stiffness in the trim tab system to preclude tab flutter. What about mass balancing the tab like a control surface is balanced?

–Steve Grossman

Barnaby Wainfan responds: Mass balancing of tabs has been used to alleviate tab-induced flutter in the past. Several airplanes, including the Avro Lancaster, ARV Super 2, Short SD3-60, and DeHavilland Sea Venom used mass balanced tabs. For more technical detail see: “The Effect of Tab Mass-Balance on Flutter,” Reports and Memoranda No. 2418.

Replacing Lost Documents

I just read Mel Asberry’s column in the August 2016 issue, and as a Designated Airworthiness Representative, I have to disagree with one point.

The question was whether an Amateur-Built aircraft would need to be placed back into Phase I flight testing in the event of a lost airworthiness certificate. Mel’s answer was “No,” and that a replacement certificate could be issued with no other requirements. I agree. However, Mel went on to say that if the operating limitations were also lost, the owner would be required to request amended operating limitations and will be issued the most current version of the limitations.

I disagree that issuance of amended operating limitations is required. The owner may request that an amended special airworthiness certificate and operating limitations be issued to introduce the most current version of the limitations, but he may also simply request a replacement special airworthiness certificate and operating limitations, both of which would replicate those that were originally issued.

–Brian Ingraham

Mel Asberry responds: Thanks for your comments, Brian. What I should have said is that the new owner should request amended operating limitations. Unless the aircraft was bought locally, the Phase I flight test area would need to be changed, in case he ever wanted to do a major change. Otherwise he would have to request a new flight test area at that time.

Grass Strips

I enjoyed the article [“Getting High Off Grass,” October 2016], but think one item should be clarified. The author states that “You can’t just mow off a piece of pasture and start landing there,” claiming that FAR Part 157 mandates notification 90 days prior to starting work. However, if operations are VFR only, and the intent is for use no more than three days per week with no more than 10 operations per day, you are exempt from reporting. I would think this applies to most pastures. We have many like this in my neighborhood.

–Mark Varvayanis

Reader Varvayanis is correct. However, FAR (157.1c) also specifies that the site is to be “used or intended to be used for less than one year.” Proving intent, of course, is always tricky. It is also important to check your local laws and regulations to see if they have additional requirements before starting operations.—Ed.


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