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European Invasion – AOPA Article

Have you all seen the Dave Hirschman AOPA pilot articled about the European Invasion of LSA aircraft? If you haven’t, have a read here (its short and sweet) https://www.aopa.org/news-and-media/...opean-invasion

I wanted to take a minute and address some really common questions related to this topic about the ICON A5 and how the current S-LSA regulations really boxed in the A5’s design (among a lot of other USA made aircraft).

I want to preface this in saying that the Light Sport Aircraft regulations are almost 20 years old and were a huge win for the industry. The industry also didn't squander this by going hog wild and proved they could self regulate and this shows up in low accident numbers or similar accident numbers when compared to Part 23 Type Certificated aircraft. But there comes a time that the FAA needs to say the experiment is over and release the grip a bit allowing industry to develop more interesting and in some cases safer aircraft (low powered aircraft can be less safe than high powered aircraft)

What is an S-LSA and how are they regulated in the USA?
To understand this better you need to understand that the S-LSA or Special Light Sport Aircraft category is, well, complicated from a regulatory standpoint. The certification requirements are several fold; Mostly there is ASTM F37 Light Sport Aircraft Consensus Standards. These are the “Part 23” style requirements if you will that cover a lot of areas such as Design, Quality, Continued Operation Safety, Maintenance, and POH development, etc of a manufactured Light Sport Aircraft. The operating limitations of Special Light Sport Aircraft are covered in 14 CFR Part 91.327. A keen eye could look into the ASTM F2245 Design Standard and note a couple of really interesting things such as there isn’t listed or even touch upon limits for things like Gross Weight, Power, Stall Speed, Number of seats, etc. Funny enough Inflight propeller control is actually allowed! ASTM are international standards and try hard to remain agnostic to country regulation. The committee is made up of Industry (Manufacturers), Regulatory Agencies, and Users (yes you could be on the committee if you wanted to be). In the USA we are regulated by the FAA, as such and because this isn’t a Type Certificated aircraft it falls under 14 CFR Part 21.190 for certification under the Special Airworthiness Certificate for purposes of operating a Light Sport Aircraft. The FAA needed to “Define” what a Light Sport Aircraft was and if you look in 14 CFR Part 1 “Definitions” listed there is a the definition of a light sport aircraft (copied below) I have taken the liberty of highlighting the items applicable to the A5’s design:

Light-sport aircraft means an aircraft, other than a helicopter or powered-lift that, since its original certification, has continued to meet the following:
(1) A maximum takeoff weight of not more than -
(i) 1,320 pounds (600 kilograms) for aircraft not intended for operation on water; or
(ii) 1,430 pounds (650 kilograms) for an aircraft intended for operation on water.
(2) A maximum airspeed in level flight with maximum continuous power (V_H) of not more than 120 knots CAS under standard atmospheric conditions at sea level.
(3) A maximum never-exceed speed (V_NE) of not more than 120 knots CAS for a glider.
(4) A maximum stalling speed or minimum steady flight speed without the use of lift-enhancing devices (V_S1) of not more than 45 knots CAS at the aircraft's maximum certificated takeoff weight and most critical center of gravity.
(5) A maximum seating capacity of no more than two persons, including the pilot.
(6) A single, reciprocating engine, if powered.
(7) A fixed or ground-adjustable propeller if a powered aircraft other than a powered glider.
(8) A fixed or feathering propeller system if a powered glider.
(9) A fixed-pitch, semi-rigid, teetering, two-blade rotor system, if a gyroplane.
(10) A nonpressurized cabin, if equipped with a cabin.
(11) Fixed landing gear, except for an aircraft intended for operation on water or a glider.
(12) Fixed or retractable landing gear, or a hull, for an aircraft intended for operation on water.
(13) Fixed or retractable landing gear for a glider.

European and other countries have different definition and that where the dichotomy of the situation occurs. For instance the Europeans allow for faster speeds, and inflight adjustable propellers.

So anyway lets break down these areas with respect to the FAA definition:

(1) A maximum takeoff weight of not more than -
(ii) 1,430 pounds (650 kilograms) for an aircraft intended for operation on water.
As many of you are aware the ICON A5 has a maximum takeoff weight of 1,510 lb. Which is greater than the Light Sport Aircraft limits for Amphibians. ICON applied and was granted an exemption to this definition to sign a statement of compliance for a Light Sport Aircraft up to 1680 lb with several caveats (AoA, Spin Resistant, Parachute requirements) which are listed. A copy of this exemption must be on board the aircraft when in operation and is included in the back of the POH. Side note, this exemption must renewed every 5 years by the company and it was last renewed in 2018 (its due again in June 30, 2023). The FAA has also granted exemptions to Terrafugia (flying car) for both weight 1800 lb and stall speed 52 kts and to New Zealand Manufacture - Vickers Aircraft for gross weight (1,850 lb).

Common Question – “Why is the A5’s gross weight 1,510 lb and not 1,680lb, the FAA approved ICON for 1,680.”

Answer: Well, that’s complicated and involves one of the other definitions of a light sport aircraft the V_s1 stall speed. The FAA requires a light sport aircraft to have “(4) A maximum stalling speed or minimum steady flight speed without the use of lift-enhancing devices (V_S1) of not more than 45 knots CAS at the aircraft's maximum certificated takeoff weight and most critical center of gravity.”

Stall speed is direct function of weight, wing area, and CL max of the airfoil. There is also air density and load factor in there too but that’s not a design knob we can turn and ASTM says 1g level stall at 1 kt/sec so those aren’t knobs we can turn. So lets break these terms down:

Wing Area – Obviously if we increase the wing area the stall speed goes down, simply put more lift slower stall speed, however everything is a compromise, more wing area more wetted area more drag, slower plane (there are structures involved too but I’m keeping this simple)

C_L Max – Maximum Coefficient of Lift. This the largest amount of lift the airfoil section can make. When flight testing its just the combined C_L Max of the aircraft (there could be other lifting surfaces in the A5’s case the Seawings. So you’d have to change the airfoil which really you can’t get appreciably more out of the airfoil than the one that ICON developed. The other than thing you can do to increase CLmax is use lift enhancing devices such as flaps. This is why the A5’s stall speed at full flaps is 39 kts not 45 with them retracted.

Weight: The maximum weight the A5 can be is 1510 lb with a 135 sqft wing and a C_LMax of 1.63 to achieve a stall speed of 45 KCAS at Forward CG (critical case). If you increased the weight of the A5 to 1,680 lb the stall speed would be 47.5 KCAS. This doesn’t sound like a big increase in speed (its not) but it’s not 45 KCAS and the FAA demands 45 knots calibrated airspeed (CAS) without aid of Lift Enhancing devices (an area I hope they address in the MOSAIC rules)

Question: Can the A5 be moved into Experimental Light Sport Aircraft (E-LSA)?
Answer: In my opinion I don’t think so because it needs an exemption to be light sport and retain the 1,510 lb gross weight. The problem I see is unless the FAA determines the exemption carries over to E-LSA the aircraft would need to be limited to 1,430 lb takeoff weight. The empty weight of the production A5 is about 1,080 lb. This would leave a number of the aircraft with only 350 lb useful load which is pretty small. I’m not aware of anyone trying to move the aircraft in to E-LSA, this could be an interesting exercise in FSDO/DAR shopping though.

(2) A maximum airspeed in level flight with maximum continuous power (V_H) of not more than 120 knots CAS under standard atmospheric conditions at sea level.

This is not an issue with an A5 its so draggy its difficult to get it to 120 knots in a dive and impossible to get it to 120 in level flight. The A5’s maximum level flight speed is 96 knots calibrated.

(5) A maximum seating capacity of no more than two persons, including the pilot.
This is what regulates the LSA category to two persons.

(6) A single, reciprocating engine, if powered.
This is what regulates the LSA category to single engine.

(7) A fixed or ground-adjustable propeller if a powered aircraft other than a powered glider.
This is what regulates the LSA category to a fixed or ground adjustable propeller. Europeans allow inflight adjustable propellers and ASTM F2245 does as well!

Interestingly this rule really effects the turbo normalized aircraft performance such as the 915iS. A turbo normalized engine is where the turbo charger via a waste gate regulates the intake pressure so that the engine makes the same rated horsepower up to a critical altitude. In the case of the 915iS this is 141 hp from sea level to 15k ft density altitude. If you install a fixed pitch propeller on the turbo normalized engine and pitch the prop to use all the power at sea level it will overspeed dramatically at the critical altitude. This is because the density of the air is changing from a propeller aerodynamics. Typically an engine and propeller degrade in performance similarly as altitude increases and density decreases. But in a turbo normalized engine the engine performance isn’t degrading becuase the turbo is boosting it. The propeller however is and thus the pitch of the prop at altitude will need to be much higher not to over speed. ASTM F2245 says the propeller must be pitched so it shall not allow the engine to exceed safe operating limits established by the engine manufacturer, and that Max RPM shall not be exceed with full throttle in takeoff, climb or flight at 0.9Vh.

So with that if installing a turbo normalized engine it makes much more sense to install constant speed propeller so you can take advantage of the full engine and propeller performance throughout the flight envelope. If you don’t to meet ASTM requirements you will need to pitch the propeller to not overspeed at altitude by sacrificing low altitude performance. Its quite possible if you do that as the aircraft climbs the climb rate will increase which is a rather unusual behavior. (I hope MOSAIC addresses this as well)

(11) Fixed landing gear, except for an aircraft intended for operation on water or a glider.
This is the regulation that allows for retractable landing gear in amphibious aircraft

(12) Fixed or retractable landing gear, or a hull, for an aircraft intended for operation on water.
This is the regulation that allows for retractable landing gear in amphibious aircraft

Interesting restrictions by ASTM:

Night Flight
Some may recall a time where S-LSA’s were not allowed to fly at night. This was before the ASTM standards had incorporated standards for night flight equipment. They were eventually incorporated and now quite a number of S-LSA’s have the equipment for a rated pilot (private pilot or higher) to operate the aircraft at night. This isn't a restriction anymore but sets up the next topic.

Instrument Meteorological Conditions (IMC)
Believe it or not the FAA doesn’t restrict an S-LSA aircraft from operating in IMC, however there are no standards in place that would allow an S-LSA to be manufactured with approval in the POH to do so. There have been numerous requests to the F37 committee to take this up and there has been some work on the subject but as of this writing there is no standards in place for manufactures. There is nothing that would restrict a user from flying their aircraft on a IFR flight plan if properly equipped just as long as they don’t fly into IMC. Same thing for instrument training, as long as they stay in VMC.


Wouldn’t it be great if the ICON could come out with a 915iS equipped aircraft?

Yes, that would be great right! more power!! However here comes the cold wet blanket – As discussed earlier the A5 design is already at a wall for gross weight because of the stall speed. The 915iS weighs 45lb more than the 912iS not to mention all the packaging issues with the need to find a home for a turbo and the intercooler. Installing 45lb more into the airframe could be to some a worthy sacrifice but here comes some more interesting requirements from ASTM.

ASTM F2245-3.1.4 maximum empty weight requirement.

Maximum Empty Weight = Gross weight – Minimum useful load.

Minimum Useful Load is defined as the sum of two 190 lb occupants + weight of all consumable fluids for flight at 1 hour at maximum level flight speed.

The A5 burns 7 gallons per hour at maximum level flight speed which is at Sea level. 7 gallons of fuel weighs 42 lb. So… 190 lb + 190 lb + 42 lb = 422 lb.

The Maximum Empty Weight is = 1510 lb - 422 lb = 1088 lb.

So if you just installed an extra 45 lb with an approximate empty weight of 1080 you would be way out of compliance with the ASTM F2245-3.1.4. On the other hand you could just increase the gross weight but but then the stall speed bites you. This is a ridiculous box the FAA has put the industry in.

This might sound draconian but its really to force the designer to make sure they don’t end up with a plane that doesn’t have a reasonable useful load, forcing or rather encouraging users to constantly fly over gross weight (not safe) or for a user to get an airplane that is fairly useless (protecting the user from designer).

Summary:
So there is a lot to digest there and I hope everyone understands why there is a such a need to revamp the LSA definitions. They are limiting the design of otherwise provable safe aircraft. This is where MOSAIC comes in to play. I won’t go into specifics here because you can read speculation elsewhere, really, we don’t know what the rules are going to look like. Rumor mills say increased gross weight, speed, and seating, but until the NPRM comes out we just don’t know. They are legally mandated by congress to come up with a new rule by January 1, 2023. It could be just what saves the USA light sport manufacturers from the European Invasion and allows innovative aircraft to be designed and the public to gain access to new safe and more useful aircraft. I hope the FAA does their job.

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thank you Bret - this was a very good read. Can you address the possibility/impossibility of a "big-bore" option for the 912? IMHO it seems like a good option for the A5 - but honestly don't know the "ins and outs" of an engine mod like this on an A5.

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I have heard that Rotax might offer a 912 "big bore" engine or "kit" I don't think it has any traction at Rotax as a whole. The 912iS (experimental and ASTM) and 912iSc (certified) are closely tied together from a configuration standpoint and splitting that up is not something I think Rotax is interested in doing. More horsepower would certainly help the A5, but I wouldn't hold your breath for a ASTM consensus standard meeting more powerful 912 engine anytime soon or ever. For what its worth although you can get a "big bore" kit from aftermarket world you cannot do that big bore mod (legally) in an A5 without turning it experimental