This rock was placed in forward part of an empty C-5 Cargo Bay to avoid the shifting of FRED’s CG to its aft limit

This rock was placed in the Forward Part of an empty C-5 Cargo Bay to avoid the Shifting of FRED’s CG to its Aft Limit

By Dario Leone
Nov 9 2019
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‘On several occasions, C-5 local training missions were delayed because the “pet rocks,” as we called them, had to be loaded,’ Jay Lacklen, former C-5 Pilot.

Jay Lacklen is a former C-5 pilot with 12,500 flying hours and the author of two books, Flying the Line: An Air Force Pilot’s Journey and Flying the Line: An Air Force Pilot’s Journey Volume Two: Military Airlift Command. The following story comes the last book of the trilogy, in progress: “Flying the Line, an Air Force Pilot’s Journey,” book three, “Air Mobility Command, 1993-2004,” in progress.”

Pet Rocks.

In the 1980s, the empty C-5 carrying no cargo could not gracefully complete local training missions for center of gravity (CG) considerations. Without cargo and with low fuel loads, the plane’s CG shifted perilously close to its aft limit. This could create control problems, to include possible loss of control, if not corrected.

The method used to correct the imbalance placed two 15,000-lb. concrete blocks in the forward most part of the cargo compartment to shift the center of gravity forward. On several occasions, locals were delayed because the “pet rocks,” as we called them, had to be loaded.

The name came from an inane Christmas novelty item of a fist-sized painted rock sent as a Christmas “pet” present. No, I could not make that up—the crazy 1980s!

The pet rock requirement arose from a cost-saving measure regarding aircraft wings. To stay within contract funding limits, the Air Force cut the weight and structure support for the aircraft wings. This resulted in a profoundly uneconomic result.

The weakened wings “flapped” at cruise, the wing tips moving up and down in flight. The two primary effects of this blunder to save money required re-winging all the aircraft with the original, stronger wings, and demanded pet rocks for local flights. Pet rocks remedied this problem until the new wings were installed.

This rock was placed in forward part of C-5 Cargo Bay to avoid the shifting of FRED’s CG to its aft limit
This print is available in multiple sizes from – CLICK HERE TO GET YOURS. C-5M Super Galaxy 60th Air Mobility Wing, 349th Air Mobility Wing, 22nd Airlift Squadron, 07-0042 – Travis AFB, CA

Artwork courtesy of

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Dario Leone

Dario Leone

Dario Leone is an aviation, defense and military writer. He is the Founder and Editor of “The Aviation Geek Club” one of the world’s most read military aviation blogs. His writing has appeared in The National Interest and other news media. He has reported from Europe and flown Super Puma and Cougar helicopters with the Swiss Air Force.

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  1. Bundle317 says:

    “Pet Rocks” were part of many of the strategic airlifters of the day. We carried them on the C-141B and C-17’s early on as the C/G flight limits were explored and expanded. The C-141B’s would carry multiple pet rocks in excess of 40,000 total weight for training at Heavy Weight Aerial Refueling on local training flights.

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