Just How Far We Gonna Take This????

by Sam Swift

In a recent Swift checkout, I had my budding Swift pilot perform the various emergency procedures that we've all come to expect. The emergency gear extensions (remember, we just talked about those recently?), hydraulic problems, and the simulated engine-out scenarios were all done with great precision by our soon-to-be Swift soloist. It came time to do the engine-out work, so we climbed up to get some distance between our Alclad and terra firma. We recorded the results so our Swifter would have reference for these later. How long has it been since you took your bird up and did simulated engine-outs? I hear birds chirping....

As we all know deep down, our Swift wasn't blessed with the glide characteristics common to Grob, Discus, Schweizer, or other wonderful sailplanes (sidenote: there IS a sailplane called a Swift, and it's pretty, too). These anvil-esque glide characteristics are but one component of why we treasure flying our Swifts. With the benefit of power, said anvil is quite a performer with the grace of a gazelle. Without spark, it's back to the anvil. So how far will your Swift take you in the event of a catastrophic engine failure?

I consider this example to be a most-likely worst-case scenario. His Swift is a heavy (1400# empty weight) but not atypical of most Super Swifts. It is a 210hp Continental-powered machine with Merlyn aux tanks, original stock wingtips and quite a bit in the panel. Plus it had our two 200+ pound keisters inside and full fuel in the main tanks (aux tanks empty). All-in-all, we were right at the 1970# gross weight AND it was July in Houston (100 ° in the shade, but hey it's a wet heat). This all conspired to give us the poorest glide ratio possible. The power was reduced to idle at around 6000' MSL and the descent was allowed to stabilize for the given configuration down to about 2000' MSL and the resulting VSI indications recorded for the six configurations. These were then repeated for accuracy:

Glide IAS 90 mph CLEAN Gear Down Gear & Flaps Down
Prop High RPM (Fwd) 1,100 fpm 1,250 fpm 1,700 fpm
Prop Low RPM (Aft) 800 fpm 1,050 fpm 1,400 fpm

As you can see, for those of you with a constant-speed prop, pulling the prop back DOES help out your glide. The descent rate for the completely clean configuration is nearly twice as good as the fully-dirty configuration. Using basic math, calculating the least amount of descent rate (800 fpm @ 90mph-CLEAN) gives you 1.875 statute miles per 1,000' AGL. Using the worst of the examples (1,700 fpm @ 90mph, fully dirty) gives you .88 statute miles per 1,000' AGL Go out on a smooth day and try your Swift out and come up with your own numbers. Run some scenarios to see how far you can glide for a given altitude. Remember your glide ratio (or lack thereof) next time you do one of those "bomber" patterns!

Rudder, Rudder, Sam Swift