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Light Sport Flying With In Flight USA - July 2011

Strange Plane?

By Ed Downs

No, the title does not mean to imply that the airplane you are about to fly is “strange,” but that you are strange to the airplane.  In other words, that slick little S-LSA in which you are about to take a demo at AirVenture is just fine, but you may not be.

Many of those reading this month’s column will do so while at EAA AirVenture 2011.  A subset of that “many” will be touring the wide selection of S-LSAs on display, with some of you signed up to take a “fly-to-buy” demo.  The question is, are you really ready to fly that LSA for the first time and give it a fair evaluation?  How are your skills when it comes to jumping into an airplane that is quite different than anything you have flown before?

Even the FAA is asking that question, as our federal friends note an increase in accidents as pilots move from familiar flying machines into those that may be a tad different than what they have flown before.  New FAA Advisory Circular 90-109 (Airman Transitioning to Experimental or Unfamiliar Aircraft) has been issued to cover just that kind of question, as accidents involving transition to strange airplanes continue to mount.  Don’t let the word “Experimental” in the AC title make you think it addresses only the “do-it-yourself” clan.  This AC defines seven “sets” of aircraft which offer significantly different piloting challenges, and S-LSA’s are specifically covered.  Of course, you might think, what can be so different about an S-LSA.  Most of them look somewhat contemporary and they are just simple “low and slow” recreational airplanes, right?  Perhaps you are one of the lucky ones who has been flying something really spiffy and high performance, like a Cirrus SR-22, and think “shucks, if I can handle that hot dog, an S-LSA should be a snap.”  Let’s take a look at that “low and slow” little S-LSA and see if some common sense, numbers and fundamental physics can turn on the master caution light in your brain.

First, are you truly ready to take a demo flight in the AirVenture traffic pattern?  This is a bit like taking your first driving lesson on the Los Angeles freeways.  Are you current and qualified to safely fly both a strange airframe and strange engine, probably your first Rotax 912?  It is entirely possible that your AirVenture demo flight will be little more than a “ride” as your demo pilot simply tries to survive!  Consider doing all the looking and tire kicking at the show, but travel to a local dealer for that demo.  In many cases, the dealer will even cover some of your travel expense if the dealership is not located close by.  In short, make sure your demo environment is such that you are guaranteed a successful experience, even if the plane you are flying does not turn out as you had hoped.  But let’s go back to our original point, just how “strange” can the typical S-LSA be?

AC 90-109 classifies S-LSA’s  as “low inertia/high drag” airplanes.  The Cirrus SR-22 (we will stick with the remarkable Cirrus as our stereotypical high performance airplane) is classified as a “high inertia/low drag” airplane.  While one might argue that many S-LSA’s are “low drag,” when compared to the SR-22, they are a bit on the draggy side.  Interestingly enough, if one simply looks at the FAA’s definition of these two “sets” of aircraft, it would seem clear that we have a classic example of low performance versus high performance.  Or do we?  Let’s take a look at what a typical “high performance” pilot might encounter as he/she jumps from our spirited SR-22 to the typical S-LSA.

  1. Acceleration – Acceleration to take-off speed, either from a dead stop or T&G, depends primarily upon power loading.  Power loading is defined as how many pounds of airplane must each horsepower pull.  Most high performance singles have a power loading of something between 11 and 14 pounds of airplane (at gross weight) per pony.  Our SR-22 sports 310 hp and comes in with a power loading of about 11lbs/hp.  A 100 hp S-LSA (very common) shows up with a power loading of just over 13 lbs/hp, well within our high performance standard.  By comparison, the old Cubs, Champs and T-Crafts come in with a power loading of about 19lbs/hp.  The relatively heavy SR-22 must be accelerated to about 70 to 75 kts prior to rotation, whereas most S-LSAs will jump off the ground at about 50 kts.  And, remember how Newton’s mass acceleration formula works, given similar power loadings, the lighter mass will accelerate faster.  This means that in the time it takes to fully advance the throttle and wiggle your hind end into the seat of a SR-22, the average S-LSA will be airborne.  It is common for the typical S-LSA to become airborne when performing a T&G before it is possible to get full power in.  Be ready!  A number of S-LSAs are now showing up with 115 hp (power loading of 11.5 lbs/hp) and one S-LSA manufacturer has crammed a legal 180 hp engine into an LSA airframe for an impressive power loading of 7.3 lbs/hp.  Perhaps you should add an extra pair of undergarments to your flight kit?
  2. Climb – This is where both power loading and wing loading come in.  We have already decided that both the Cirrus and typical S-LSA have good power loadings, but how hard are we working the wings?  In other words, how much weight must each square foot of wing support?  Low wing loads tend towards good climb, but slower cruise speeds.  High wing loadings need a higher speed to perform, but have less drag.  The wing loading on our SR-22 is just over 23 pounds of weight supported by every square foot of wing.  The typical S-LSA comes in at about 11 lbs/ft², some significantly lower.  The bottom line is that even with low horsepower, most S-LSAs will climb between 900 to 1,200 fpm, similar to the SR-22.  But, the S-LSA may be climbing at speeds of 75/80kts, while the higher wing loading of the Cirrus will need 100/110 kts.  If staying in the typical GA traffic pattern, your Cirrus will be climbing on the upwind, crosswind and, probably, downwind legs.  Your typical S-LSA may reach pattern altitude before turning crosswind. Be ready to level off and keep a sharp eye out for those hot shots who think that mid-field and cross-wind pattern entries are a good idea.
  3. Handling – How a plane “handles” should not be confused with performance.  This writer has flown many airplanes that may perform well, but are unpleasant to fly due to issues of stability of flight control loads.  The High performance SR-22 will strike one as smooth and solid.  The heavier weight of the airframe, wings and tail feathers add a degree of dampening that inhibit over-controlling.  You simply “feel” the mass and resulting inertia of the plane.  The light weight and low mass of the typical S-LSA means it takes little effort to move controls and response is rapid.  While the words “light and agile” are true, many first time LSA pilots find it easy to over-control these “low inertia” airplanes.  Most S-LSA designs favor a stick type control, meaning you may be encountering a flight control system that is familiar to us old guys, but a bit strange to those who learned in the typical Cessna/Piper trainer.  Be prepared to use fingertips, not arm movements, when flying your first S-LSA.
  4. Goodies and Gadgets – Now that you are airborne, the trick is to find the airspeed indicator and figure out how to read it.  To be sure, our trusty Cirrus pilot may feel right at home, but those stepping into their first S-LSA from the world of “steam gauges” may find a bewildering array of advanced technology.  So there you are, in the middle of the AirVenture traffic flow, with your head down looking for airspeed and altitude, wondering why the RPM display shows over 5,500 rpm!  Take the time to learn where the basic indicators are located BEFORE you take the demo flight, and do not let your demo pilot become distracted by trying to impress you with the multi-function, auto flight operation.  Look outside and fly the plane!
  5. Landing – This is where the low inertia aspect of an S-LSA comes in strong.  If using the FAA accepted 1.3 of Vso for our speed on short final, you will find the SR-22 at about 80 kts.  If landing heavy, our Cirrus will have over 270,000 lbs of kinetic energy, which is inertia, to be used for the landing.  This energy is what you use to control the plane during the final landing maneuvering and flare.  Our S-LSA may be on short final at just over 50 kts, carrying about 70,000 lbs of kinetic energy.  This basically means that, when coupled with the higher drag characteristics of an S-LSA, our little plane will transition through the final landing maneuvers, (alignment and flare) over three times faster than the Cirrus.  S-LSAs do not so much land, as they simply approach the ground and stop.  With practice, one may be tempted to land at the take-out window of your favorite fast food eatery, but give it a second thought.  From the demo flight standpoint, be aware that the light and responsive controls, coupled with a very short flare program, can lead to a maneuver that looks more like leaf fluttering to the ground than a plane landing.  Adding to the realities of low inertia is a view over a closely cowled Rotax engine that is very different than that of a Continental or Lycoming powered airplane.  The Rotax is very compact, which results in a “pointy” nose that can give misleading runway alignment cues.

None of these characteristics of an S-LSA are difficult to deal with.  Perhaps very anecdotal, but this writer once accomplished some 35 demo flights in a well known S-LSA over a two day period and noticed an interesting trend.  Low time pilots, even students, had little trouble adapting to the fun offered by the sporty S-LSA we were flying.  The high time guys, especially three old time flight instructors, tended to “fight” the differences, resulting in less than successful experiences.  The moral is, don’t lock into an “it should fly just like the last plane I flew”  attitude that prevents you from having a great time and learning to love low inertia flying.  Don’t be a “stranger” to S-LSA flying.


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