Rigging for a Secure Runup

Pilots routinely conduct a run-up prior to launch, but do so at some partial power setting. To test at full power, we must secure the airplane.

It’s a common mistake to chock the main gear. The distance R from the pivot point to the thrust line is large, which makes it easy to tip the airplane on its nose. Even if it’s possible to keep the tail down with elevator application, brakes slip and tires can skid. All it takes is one short moment of inattention for things to get expensive. Why take the chance?

In a perfect world, we would create a direct connection with an anchor point aligned with the thrust line. Doing so is usually impractical, but we can substitute a reasonable proxy by securing to an anchor not far aft of the tailwheel.

The typical steel-tube fuselage incorporates sufficient support structure to allow the application of full static thrust to the tailwheel spring. However, many aluminum or composite airplanes, and almost all tricycle-gear airplanes, do not contain tail structure designed for a thrust load. Bulkheads and tie-down points were intended to handle vertical loads, not a horizontal pull, and they can tear out.

The best answer is to rig a yoke to the top of the main gear legs, as high as possible. The tipping pivot becomes the yoke attach point, so dimension R is minimized. More important, the main gear structure will easily withstand the thrust load.

Sometimes a ground anchor isn’t conveniently available. The universal substitute at most U.S. airports is the trailer hitch ball on a full-size pickup truck. If using the tailwheel spring as the attach point, note there is usually a small upward vector lifting the tail. It can be reduced by lengthening the rope or strap between the tailwheel and the truck.

If the aircraft is without appropriate structure in the tail, use a yoke to the highest possible point on the gear legs. For most nosewheel aircraft, it’s the best approach, as a tie-down ring is rarely as stout as a tailwheel mount.

The best gear leg yoke is a long woven tow strap with an eye at each end. Pass the stem through the eye to form a noose, lay it on the ground, roll the airplane into the noose, slide it up the leg and cinch it tight. A second strap or rope will connect the V of the yoke to the anchor or truck.

Do not use chocks with any of these methods. Doing so just inserts a pivot point where it is unwanted.