Flight Design "Safety Box" & possible LSA Implications

[3Dreaming]

That much weight can get burned off on warmup and taxi.

The big variable is not the avionics, or BRS. It's PEOPLE. My wife and I together weigh 270. So we could fly for 8 hours with a full 32 in the tanks, but the most I can last is 4 hours anyway so we don't take that much gas.

Maybe you should get your engine checked out, I can taxi around for over an hour and a half on 10 pounds of fuel.

[MovingOn]

.......

[MrMorden]

That much weight can get burned off on warmup and taxi.

The big variable is not the avionics, or BRS. It's PEOPLE. My wife and I together weigh 270. So we could fly for 8 hours with a full 32 in the tanks, but the most I can last is 4 hours anyway so we don't take that much gas.

You burn 3.5gph in cruise, and about the same in taxi I guess? Unless your warm up and taxi is like an hour. 10lb is 1.66 gallons. I don't think the CT needs to be THAT warm before takeoff.

[MrMorden]

This is the dilemma of most LSAs, because of the arbitrary 1320lb weight limit, even though, in Europe, the planes fly at higher, more 'useful' weights.

Howard, though this gets kicked around quite frequently on these forums, I must continue to emphasize that the US LSA weight limit is anything but arbitrary. It (along with the 45 KCAS stall speed limit) sets the kinetic energy to be dissipated in a landing or takeoff accident to around 100 kJoules, minimizing injury to occupants. That is about how much we humans can stand without sustaining fatal injuries. It was established as a safety limit, not an arbitrary limit. It's not about the airframe's structural integrity, so much as it is about your structural integrity.

Well, it is *kinda* arbitrary. If 1320lb is low energy, then 1300lb, 1200lb, 1000lb, or 500lb must be even less and thus better, right? There is nothing "magical" about the 1320lb number, other than that is the number the EAA could convince the FAA to agree too. Original draft LSA specs were much lower, I think 1050lb, then 1200lb, finally 1320lb based on lobbying primarily by EAA.

If lower energy is a huge safety benefit in a crash, then why are not 777s and A380s weight limited? There is inconsistency here that is hard to justify a low weight = safety argument since it only exists for this one category. Well, and ultralights. We've already dispelled the myths that those flying LSA are less skilled or medically dangerous in other threads.

[MrMorden]

None of you or your airplanes or your piloting skills can measure up to CTLSi. He is superior in all things. Just ask him.

This started with Ince mis-characterizing the CTLSi. Feeling defensive much?

[drseti]

Well, it is *kinda* arbitrary. If 1320lb is low energy, then 1300lb, 1200lb, 1000lb, or 500lb must be even less and thus better, right?

Well, yes, but exceeding that 100 kJ KE figure is where fatalities occur. It appears EAA convinced FAA to set a limit that would minimize fatalities. If the goal had been to prevent serious injury, the limit would have been more stringent. And, if the goal had been to prevent all injuries, they simply would have grounded everybody. So, I'm glad they chose to draw the line where they did, whether you consider saving lives to be arbitrary, or merely consistent with the FAA's mandate.

[3Dreaming]

And I always thought the 1320 came about because of the 600kg limit in other parts of the world converted to a nice round USA number.

[drseti]

Maybe it did, Tom, but then, where did the 600 kg come from? ASTM is international; they know how to calculate kinetic energy in both metric and imperial units.

[3Dreaming]

Maybe it did, Tom, but then, where did the 600 kg come from? ASTM is international; they know how to calculate kinetic energy in both metric and imperial units.

I am not disputing the energy thing, just where the number came from. I think the 600kg number was out there before the ASTM committee for LSA was formed.

[zaitcev]

I just assume if I ever "roll over" my Sky Arrow I'm toast. Karen in the back has some pretty good structure around her - me not so much.

That really depends on circumstances, I think.

When I rolled Carlson, there was nothing between my head and the runway's pavement except a sheet of aluminum, so I smacked my head a bit. Fortunately, I was wearing my K-10 helmet and I was buckled tight and low enough, so my skull did not get cracked and the weight of my body did not come to crush my neck.

The key consideration in your case is probably how strong the nose of your Sky Arrow is. If it's beefy enough, and if you can lower your seat enough so the line from the nose to the top of your wing goes above your head a bit, then you have good chances, depending on the speed at which you roll it and if you start wearing a helmet.

[IFlyRC]

The Sting has always had a the cockpit enclosed by a roll cage.

Didn't know that. Good info. I've read that the Tecnam Eaglet also has a roll cage. Thus far we have the Flight Design aircraft, the Sting, and the Eaglet on the list. Are there any more?

[Merlinspop]

...if you can lower your seat enough so the line from the nose to the top of your wing goes above your head a bit, then you have good chances, depending on the speed at which you roll it and if you start wearing a helmet.

... and if you do that seat belt mod so you have a lap belt snugging you into the seat pan.

[Jack Tyler]

Paul, you deserve a pat on the back (OK, two pats!) for being one of the few posters on forums (fora?) like this one for pointing out that physics and its relevance to aviation exists even after we leave high school.

"Howard, though this gets kicked around quite frequently on these forums, I must continue to emphasize that the US LSA weight limit is anything but arbitrary.... It was established as a safety limit, not an arbitrary limit. It's not about the airframe's structural integrity, so much as it is about your structural integrity. " .

Still...the 1320# limit still seems, if not 'arbitrary', then certainly discretionary. I say that because other aviation authorities have concluded that higher weight limits still provide adequate safety, and because I really don't think the FAA considers pilots in higher weight category a/c to be 'unsafe' or more expendable. So within the microcosm of Sport Aviation a/c, yes there can be a kinetic energy rationale to support 1320#. (And I believe this applies to LSA seaplanes, too. Must they not comply with the 45 kt stall speed?) But within the broader context of recreational aviation, I think it strikes many of us as just one (USA authored) line drawn on a continuum full of compromises. (And to be sure, I realize you understand all this perhaps more than most of us).

But the dirty little underbelly of the 1320# limit is the degradation in safety that is invited when folks exceed a LSA a/c's MTOW because it lacks a practical useful load. As e.g. when those a/c are employed in longer distance flying where fuel endurance is more important, and where flights may need to be extended because they are VMC restricted and weather conditions force a Plan B. (This is certainly not the sole domain of the LSA owner; we see it at all levels of recreational aviation and even among some of smaller commercial a/c accidents.) And let's also not forget about the 'E' in PAVE, when we are tempted to stretch things (in the duration of a flight or the load out of the a/c) because we are being influenced by external factors.

As you point out, exceeding weight limits doesn't have to be about the airframe necessarily failing structurally; it's about stall speed going up. And what is at the top of the hit parade in recreational aviation fatalities? Loss of control in maneuvering flight, down low when on approach - https://www.faasafety.gov/gslac/ALC/cou ... px?cID=214 So it may be fair to say that the 1320# limit provides some additional level of safety over higher weight class a/c while introducing some potential additional level of risk, as well. At least in the 'real world' that Howard was describing earlier.

[designrs]

... and if you do that seat belt mod so you have a lap belt snugging you into the seat pan.

Good fitting seat belts is so critical. It's readily available safety on any plane. Yet I've seen more planes where you just can't get a good seat belt fit because of the condition, type, difficulty of adjustment, or limits of adjustability. One of the great benefits of plane ownership is the ability to have perfectly fitting seat belts setup just for you (with the occasional tug for re-tensioning).

The added safety of a good roll cage is great, but if the seat belts don't fit and the occupants slam into that roll cage it's not going to be pretty.

[MrMorden]

I read a fairly technical article a while back about aircraft crash fatality rates. The upshot of the article was that speed kills. Basically the rate of fatalities goes up logarithmically with the speed. 40 knots or below is very rarely fatal, up to 60 knots is sometimes fatal, and above 80 knots is almost universally fatal. These numbers held up in the analysis regardless of airplane type or weight. I think the main problem is that even if the airplane stays completely intact, you can't avoid the physics of decelerating a human body very rapidly from higher speed, and internal injuries often kill without any external trauma.

I'd say that I don't really believe that the LSA weight limit is nearly as helpful in reducing the crash danger as the stall speed limitation. The 45 knot clean stall speed LSA limit really does help with keeping the fatal rates down, but the 1320lb weight limit does very little, in fact it ensures that the aircraft structure will be as light as possible, and may sacrifice some structural strength. Two seats and 45kt stall speed practically limits the size of the aircraft anyway, and if it gets out of hand you could just say LSAs cannot require a type rating, and then the size is already limited to 12,500lb.