THE LIGHT SPORT AIRCRAFT DILEMMA

The purpose of the Sport Pilot/Light Sport Aircraft rules is to make flying more affordable and thereby arrest the precipitous downhill slide in the U. S. pilot population. Apparently, a lot of people do want to become Sport Pilots, but the stumbling block is a lack of AFFORDABLE Light Sport Aircraft.

Spoto/Mendieta Rose Parrakeet

The new $100,000 plus LSAs obviously do not fit that definition, so what we have left are LSA eligible homebuilts and the relatively few 65 and 75 horsepower lightplanes from the late 1940s that are still around today. Homebuilders are a hardy, resourceful breed and will take care of themselves, but what about those who can spring for no more than $20,000 to $30,000 and are finding that the 65 and 75 h.p. airplanes are going fast? Read on.

Although I think the Sport Pilot/Light Sport Aircraft rules rank right up there with the Amateur-Built rules as the best things the FAA has ever done, I often wonder why gross weight was selected as one of the parameters that define a Light Sport Aircraft (LSA). It certainly has resulted in a lot of illogical exclusions of existing certified aircraft . . . exclusions that are keeping the Sport Pilot community smaller than it could be.

Just so we are all on the same page, a LSA has to fit within the following limitations:


The primary function of the FAA is to do the best it can to ensure aviation safety - and the LSA limitations are intended to keep Sport Pilots in safe, easy-to-fly machines, especially new student pilots who do not have to undergo as many training hours to earn a Sport Pilot certificate as one does for a Private certificate.

Let’s consider, then, the LSA limitations that most directly bear on safety. Certainly, the most significant limitation is the max stall speed. The lower the stall speed, the slower the aircraft can be landed. In case of a forced landing, one’s chances of avoiding serious injury are better the slower the aircraft is moving when it lands in rough terrain or even in trees.

I really don’t see the need for a max speed limitation. The safest part of any flight is when an aircraft is cruising along straight and level. What difference does it make how fast a structurally adequate aircraft is as long as it lands at a low, safe speed? Limiting top speed just penalizes the designer who is clever enough to come up with an aircraft with a low stall speed and a high top speed. This is particularly true in homebuilts, which are generally smaller and lighter than production aircraft.

Then there is gross weight. Why 1,320 pounds . . . or any specific number, for that matter? Aside from weight and balance considerations, gross weight figures into the real world safety equation mainly as it relates to wing loading (gross weight divided by wing area equals wing loading - in pounds per square foot ). From a piloting standpoint, it is wing loading that largely determines whether an airplane floats like a butterfly or has a sink rate like a lead balloon. Presumably the FAA wants LSAs to have light wing loadings
. . . so it would seem that aviation would have been better served if wing loading had been used rather than gross weight as a limiting factor for LSAs.

Take an Aeronca 11AC Chief and an 11CC Super Chief, for example. The LSA eligible 65 h.p. 11AC has a gross weight of 1,300 pounds, a wing area of 175 square feet, a wing loading of 7.4 pounds per square foot and a stall/landing speed of 40 mph. The non-eligible 85 h.p. 11CC has a gross weight of 1,350 pounds, the same 175 square feet of wing area, a 7.7 pound wing loading and a stall/landing speed of 43 mph. The 11AC and the 11CC are the same airplane except for the engines and there’s hardly a gnat’s whisker between the two as far as handling and performance are concerned. Yet, again, the 11AC qualifies as an LSA and the 11CC does not. The 11CC has a gross weight that is only 30 pounds over the 1,320 pound limit. Does that really make any difference? Is the 11AC significantly safer than the 11CC because its wing loading is three tenths of a pound lower and its stall/landing speed is three miles per hour slower?

Now, let’s jump over to an example of the new, mostly European Light Sport Aircraft, many of which are currently priced at around a hundred thousand dollars, give or take a few grand. All the articles I’ve read lately claim that the Rotax 912S powered Flight Design CT is today’s top selling LSA. According to a recent Kitplanes directory, the CTSW model has a gross weight of 1,320 pounds and a max speed of 138 mph - both the exact LSA limitations (those German designers are GOOD!). The wing area is 107 square feet and the wing loading is 12.3 pounds per square foot. The stall/landing speed is 45 mph. The aircraft, of course, also complies with the rest of the LSA requirements.

A 12.3 pound per square foot wing loading, eh? Let’s compare that with some of the U. S. certified lightplanes that meet all the LSA criteria, except for the fact that they have gross weights over 1,320 pounds.

AERONCA 7EC
Wing area - 170.2 sq. ft.
Gross wt. - 1,450 lbs.
Wing loading - 8.52 lbs/sq/ft
Stall/land spd. - 45 mph
Cont. C-90-12F

CESSNA 120/140
Wing area - 159.3 sq. ft.
Gross wt. - 1,450 lbs.
Wing loading - 9.1 lbs/sq/ft
Stall/land spd. - 42/40 mph
Cont. C-85-12

CESSNA 150 to 150M
(Typical numbers)
Wing area - 159 sq. ft.
Gross wt. - 1,600 lbs.
Wing loading - 10.3 lbs/sq/ft
Stall/land spd. - 48 mph
Cont. O-200-A

ERCOUPE 415H
Wing area - 142 sq. ft.
Gross wt. - 1,360 lbs.
Wing loading - 9.5 lbs/sq/ft
Stall/land spd. - 45 mph
Cont. C-75-12

ERCOUPE 415E/G
Wing area - 142.6 sq. ft.
Gross wt. - 1,400 lbs.
Wing loading - 9.8 lbs/sq/ft
Stall/land spd. - 48 mph
Cont. C-85-12

FUNK B (All models)
Wing area - 169 sq. ft.
Gross wt. - 1,350 lbs.
Wing loading - 7.98 lbs/sq/ft
Stall/land spd. - 40 mph
63 to 85 h.p.

PIPER J-4E
Wing area - 183 sq. ft.
Gross wt. - 1,400 lbs.
Wing loading - 7.65 lbs/sq/ft
Stall/land spd. - 40 mph
Cont. A-75-9

LUSCOMBE 8E/F
Wing area - 140 sq. ft.
Gross wt. - 1,400 lbs.
Wing loading - 10 lbs/sq/ft
Stall/land spd. - 48/40 mph
Cont. C-85/C-90

All these aircraft (and there are others) fit well within the LSA limitations, except for those darn gross weights. Note, however, that all of them have wing loadings lower than the LSA approved Flight Design CTSW. Most of them were designed before or just after World War II when typical general aviation airports were short and unpaved. They needed a low stall/landing speed to safely operate out of such airports and the cheapest way to accomplish that was to put large wings on them. They also needed to have a decent rate of climb on low horsepower, so ditto the large wings. Most started out with 50 to 65 h.p., then later had 75 and 85 h.p. engines installed in the same lightweight airframes. That allowed the gross weights to be increased - unfortunately for us today - to over 1,320 pounds. Again, however, the wing loadings and stall/landing speeds increased only slightly - those large wings again. Would anyone claim that an LSA eligible Luscombe 8A is significantly safer than a non-eligible 8E . . . or that an LSA eligible Ercoupe 415C is significantly safer than a non-eligible 415G?

Does anyone think a Rotax powered Flight Design CT is significantly safer than a Continental powered Cessna 150?

In my opinion, all the 1,320 pound gross weight limitation is doing is depriving folks of average means of the opportunity to operate nearly 20,000 additional existing U. S. certificated lightplanes as LSAs. According to the FAA web site, there are 13,845 Cessna 150s alone, plus 3,826 Cessna 120s and 140s. The Aeroncas, Ercoupes, Luscombes, etc., make up the rest. When they are advertised for sale in Trade-A-Plane, most are currently priced in the $20,000 range. All could be affordable LSAs if wing loading were substituted for gross weight . . . and if a limit at least as high as the Flight Design CT’s were allowed.

Or, more simply, if gross weight was just arbitrarily dropped as an LSA limitation . . . much as, apparently, 1,320 pounds was arbitrarily chosen as a limitation.

A probably unintended (at least I hope so) consequence of the 1,320 gross weight limitation is that almost all the U. S. certified two-place lightplanes that do qualify as LSAs have no electrical systems - which means no starters or transponders. Not good for owners based at airports that frown on hand propping . . . and not good for those who want to show up on big airplane’s collision avoidance equipment. It would be nice if those folks had the choice of, say, an Aeronca 7EC instead of a non-electrical 7AC.

In short, nothing but good would come from the simple substitution of wing loading for gross weight - at the CT’s 12.3 pounds per square foot.

But, wait! The LSA approved Sportsplanes Skylark has a 13 pound per square foot wing loading. That’s more than the 12.6 pound wing loading of a 145 h.p., four-place Cessna 170. Geez!

 

Jack Cox, Spring 2007